Title of Invention	A FRAME STRUCTURE FOR A MOTORCYCLE AND A METHOD OF MANUFACTURING THE SAME.
Abstract	To provide a frame for a motorcycle including an engine with a large displacement by integrally joining metal plates formed by press-working to each other. [Solving Means] A frame structure for a motorcycle is formed by preparing pair of metal plates formed into recessed shapes by press-working and integrally joining the metal plates to each other. The above pair of metal plates are composed of an upper member 31 having a recessed sectional shape opened downwardly and a lower member 32 having a recessed sectional shape opened upwardly. The upper member 31 has flanges 31c projecting outwardly from both side ends of the upper member 31, and the lower member 32 has flanges 32c projecting outwardly from both side ends of the lower member 32. The upper member 31 is overlapped from above to the lower member 32 such that the flanges 31c of the upper member 31are butted to the flanges 32c of the lower member 32 in the vertical direction, and is joined to the lower member 32 by welding the flanges 31c and 32c thus butted to each other, to form a main frame 30 having an approximately flat upper surface and being provided with a head pipe 22 joined to a front end of the main frame 30. the frame 30 extends substantially over the entire length of a motorcycle, and it has front and rear portions which are different in terms of width in the lateral direction of the vehicular body.

Title of Invention

A FRAME STRUCTURE FOR A MOTORCYCLE AND A METHOD OF MANUFACTURING THE SAME.

Abstract

To provide a frame for a motorcycle including an engine with a large displacement by integrally joining metal plates formed by press-working to each other. [Solving Means] A frame structure for a motorcycle is formed by preparing pair of metal plates formed into recessed shapes by press-working and integrally joining the metal plates to each other. The above pair of metal plates are composed of an upper member 31 having a recessed sectional shape opened downwardly and a lower member 32 having a recessed sectional shape opened upwardly. The upper member 31 has flanges 31c projecting outwardly from both side ends of the upper member 31, and the lower member 32 has flanges 32c projecting outwardly from both side ends of the lower member 32. The upper member 31 is overlapped from above to the lower member 32 such that the flanges 31c of the upper member 31are butted to the flanges 32c of the lower member 32 in the vertical direction, and is joined to the lower member 32 by welding the flanges 31c and 32c thus butted to each other, to form a main frame 30 having an approximately flat upper surface and being provided with a head pipe 22 joined to a front end of the main frame 30. the frame 30 extends substantially over the entire length of a motorcycle, and it has front and rear portions which are different in terms of width in the lateral direction of the vehicular body.

Full Text	The present invention relates to a frame structure for a motorcycle and a method of manufacturing the same. The present invention relates to an improved frame structure for a motorcycle manufactured by joining metal plates shaped by press-working to each other into one body, and a method of manufacturing a frame for a motorcycle by joining metal plates shaped by press- working to each other into one-body. [0002] [Prior Art] Techniques of manufacturing a frame for a motorcycle by press-working raw steel plates into a pair of members and welding the members to each other into one-body have been disclosed as follows: One technique has been disclosed in Japanese Utility Model Laid-open No. Sho 61-133486 and Japanese Patent Laid-open No. Sho 58-49582, in which a pair of right and left members are each formed into an approximately V-shape in a side view and a recessed shape in cross-section by press-working in such a manner that each member has flanges projecting upwardly and downwardly from upper and lower edges of the member, whereby a frame is obtained by overlapping and butting the flanges of the right and left members to each other in the horizontal direction and welding the flanges to each other into one-body. Another technique has been disclosed in Japanese Utility Model Publication No. Sho 61-22072, in which a pair of right and left members are each formed into an approximately T-shape in a side view and a recessed shape in cross - section in such a manner that each member has flanges projecting upwardly and downwardly from upper and lower edges of the member, whereby a frame is obtained by overlapping the flanges of the right and left members to each other and welding the flanges to each other into one-body. [0003] Each of the above-described prior art frame structures is of a type used for a very small-sized and lightweight motorcycle mounting an engine with a very small displacement. Specifically, the frame for a motorcycle disclosed in the former documents, that is, in Japanese Utility Model Laid-open No. Sho 61-133486 and Japanese Patent Laid-open No. Sho 58-49582 is of a type in which a head pipe is disposed at a front end of an upper portion of the V-shaped frame and a sheet is disposed at a rear end of the upper portion of the frame, and a power unit including an engine integrated with a transmission case is swingably mounted in a V-shaped valley portion of the frame. On the other hand, the frame disclosed in Japanese Utility Model Publication No. Sho 61-22072 is of a type used for a very small-sized, lightweight motorcycle mounting an engine with a small displacement like the above frame, wherein the frame is formed into a simple T- shape in a side view. [0004] [Problem to be Solved by the Invention] A frame used for a motorcycle mounting an engine with a somewhat large displacement or a large-sized motorcycle is often formed by assembling a plurality of pipe members by welding or the like. In manufacturing such a frame, there is a tendency to raise the manufacturing cost of the frame and increase the weight of the frame because the number of components of the frame is very large, the work of bending the pipe members is complicated, the number of portions to be welded is large, and the frame structure is complicated. In order to simplify the prior art frame structure for a motorcycle mounting an engine with a somewhat large or a very large displacement, facilitate the manufacturing method for the frame, reduce the weight of the frame, and lower the manufacturing cost of the frame, it may be considered to adopt the above-described prior art frame structure formed by joining metal plates to each other into one-body as a backborn type frame extending approximately in the horizontal direction substantially over the entire length of the motorcycle; however, such an attempt has the following problems: [0005] Since the prior art frame structure is configured such that each of right and left members shaped by press -working has flanges projecting upwardly and downwardly from upper and lower edges of the member and the flanges of the right and left members are butted and welded to each other in the horizontal direction, the flanges project upwardly and downwardly from the frame thus obtained. In particular, since the flanges project upwardly from the upper surface of the frame at a widthwise central portion throughout the overall length of the frame, there are limitations in arranging, on the upper surface of the frame, accessaries of the motorcycle and components whose arrangement is important in terms of appearance such as a fuel tank and a sheet. That is to say, it is difficult to directly arrange the fuel tank, the sheet and the like on the frame, and to mount these parts on the frame, it is required to provide mounting stays and brackets for mounting these parts. This is disadvantageous in that the frame structure is complicated, and the number of components of the frame is increased and thereby the number of portions to be welded is increased, resulting in the raised manufacturing cost. The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a simple frame structure with a high rigidity and a high strength, particularly effective as a frame including a main frame usable for a motorcycle mounting an engine with a large displacement, by welding metal plates shaped by press-working to each other into one-body, which frame structure is further effective to facilitate the manufacturing process, reduce the number of parts, lower the manufacturing cost, and reduce the weight of the frame. Another object of the present invention is to provide a method of simply manufacturing a frame for a motorcycle at a low cost. According to the present invention there is provided a frame structure for a motorcycle, which is formed by preparing a pair of metal plates formed into recessed shapes by press-working and integrally joining said metal plates to each other, characterized in that said pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly; said upper member has flanges projecting outwardly from both side ends of said upper member, and said lower member has flanges projecting outwardly from both side ends of said lower member; and said upper member is overlapped from above to said lower member such that said flanges of said upper member are butted to said flanges of said lower member in the vertical direction, and is joined to said lower member by welding said flanges thus butted to each other, to form a main frame having an flat upper surface and being provided with a head pipe joined to a front end of said main frame. According to the present invention there is also provided a method of manufacturing a frame for a motorcycle, comprising the steps of: preparing a pair of metal plates formed into recessed shapes by press-working; and integrally joining said metal plates to each other. the improvement comprising the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends of said lower member, and welding a sub-frame member to side walls of said lower member in such a manner as to suspend said sub-frame member from said lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of said upper member, and overlapping said upper member on said lower member and welding said overlapped flanges to each other, to form a main frame. With this configuration, a main frame having the backborn structure for a motorcycle, which ensures a desirable rigidity and a desirable strength, can be simply formed by press-working metal plates at a low cost. The main frame has an approximately flat upper surface, and accordingly, components such as accessories, a fuel tank, and a sheet can be mounted on the upper surface directly or via simple stays or brackets. Also the main frame is formed by joining the upper and lower members, each of which is formed by press-working, to each other in the vertical direction, in the vertical direction, and accordingly, the weight of the main frame can be reduced, and the width of each of the front and rear portions of the main frame can be freely set such that a head pipe or an engine hanger is allowed to be joined to the front or rear portion, and accessaries, a fuel tank or a sheet is allowed to be mounted on the front or rear portion. [0009] According to an invention described in claim 2, in addition to the configuration of the invention described in claim 1, a sub-frame member formed by press-working is joined to the lower member of the main frame in such a manner as to be suspended therefrom. With this configuration, since a sub-frame member other than the members constituting the main frame of a vehicular body of a motorcycle is formed by press-working and is welded to the lower member of the main frame, it is possible to facilitate the configuration and manufacture of the components of the vehicular body, to reduce the weight of the vehicular body, and to manufacture the vehicular body at a low cost. [0010] According to an invention described in claim 3, in addition to the configuration of the invention described in claim 1, outer ends of the flanges of one of the upper member and the lower member of the main frame are bent, and leading ends of the flanges of the other of the upper member and the lower member are covered with the bent portions. With this configuration, it is possible to enhance the rigidity and strength of the flanges by providing the bent portions at the outer ends of the flanges. In other words, it is possible to simply increase the rigidity and strength of the flanges only by adding the work of bending the leading ends of the flanges to the work of press-forming the flanges. [0011] According to an invention described in claim 4, in addition to the configuration of the invention described in claim 1, a cross member constituting a mounting portion for mounting rear cushion units is provided at a location of the main frame in such a manner as to be interposed between the upper member and the lower member in the width direction of the same main frame. Since the cross member for mounting the rear cushion units is provided at a location of the main frame, composed of the upper member and the lower member joined to each other, in such a manner as to be interposed between the upper member and the lower member in the width direction of the main frame, it is possible to simplify the structure for mounting the cross member, and to enhance the rigidity and strength of the portion of the main frame at which the cross member for mounting the rear cushion units is provided. [0012] According to an invention described in claim 5, in addition to the configuration of the invention described in claim 1, a mounting portion for mounting a fuel tank and a sheet is integrally formed at a location on the upper surface of the main frame by press -working. With this configuration, since the mounting portion for mounting a fuel tank and a sheet is formed on the upper surface of the main frame without provision of any special member, it is possible to simplify the frame structure, reduce the number of components of the frame, reduce the manufacturing steps, for example, eliminate the welding step, and lower the manufacturing cost. [0013] According to an invention described in claim 6, there is provided a method of manufacturing a frame for a motorcycle, including the steps of: preparing a pair of metal plates formed into recessed shapes by press- working; and integrally joining the metal plates to each other, characterized in that the method includes the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends of the lower member, and welding a sub-frame member to side walls of the lower member in such a manner as to suspend the sub-frame member from the lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of the upper member, and overlapping the upper member on the lower member and welding the overlapped flanges to each other, to form a main frame. [0014] With this configuration, a sub-frame member is previously integrally joined to the upwardly recessed lower member of the main frame by welding the sub-frame member to the side walls of the lower member and then the downwardly recessed upper member is integrally joined to the lower member by overlapping and welding the flanges of the upper member to the flanges of the lower member. For example, the lightweight and easy-to-handle lower member is held by a jig or the like, and in such a state, the lightweight sub-frame member formed by press-working is butted from below to the lower member and is welded thereto, and then the upper member is overlapped and welded to the lower member. As a result, the welding works for the frame is improved by facilitating the handling and setting of the members of the frame and simplifying the welding procedure. This makes it possible to simply manufacture the frame and hence to reduce the manufacturing cost of the frame for a motorcycle. Also since the sub-frame member is previously welded to the lower member in such a manner as to be suspended from the lower member, it is possible to enhance the degree of freedom in welding between the lower member and the sub-frame member and in arrangement thereof. [Brief Description of the Drawings] [Fig. 1] Fig. 1 is a side view showing an appearance of one example of a motorcycle to which a frame structure of the present invention is applied. [Fig. 2] Fig. 2 is a plan view of Fig. 1. [Fig. 3] Fig. 3 is a side view showing an appearance of a frame of the present invention. [Fig. 4] Fig. 4 is a plan view of Fig. 3. [Fig. 5] Fig. 5 is an exploded perspective view of composing members of the frame. [Fig. 6] Fig. 6 is an enlarged sectional view taken on line 6-6 of Fig. 3. [Fig. 7] Fig. 7 is an enlarged sectional view taken on line 7-7 of Fig. 3. [Fig. 8] Fig. 8 is an enlarged sectional view taken on line 8-8 of Fig. 3. [Fig. 9] Fig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 3. [Fig. 10] Fig. 10 is an enlarged view seen in the direction shown by an arrow 10 of Fig. 3. [Fig. 11] Fig. 11 is an enlarged sectional view taken on line 11-11 of Fig. 3. [Fig. 12] Fig. 12 is an enlarged sectional view taken on line 12-12 of Fig. 3. [Fig. 13] Fig. 13 is a view seen in the direction shown by an arrow 13 of Fig. 3. [Fig. 14] Fig. 14 is a view seen along the direction shown by an arrow 14 of Fig. 3. [Figs. 15 (a) to 15 (e)] Figs. 15(a) to 15(e) are views showing sequential steps of manufacturing the frame, wherein Fig. 15(a) shows a state before a sub-frame member is assembled to a lower member; Fig. 15(b) shows a state in which the sub-frame member is assembled to the lower member and welded thereto; Fig. 15(c) shows a state before an upper member is assembled to the lower member; Fig. 15(d) shows a state in which the upper member is welded to the lower member; and Fig. 15(e) shows a state after the upper member is welded to the lower member. [Fig. 16] Fig. 16 is a vertical sectional side view of an essential portion of a main frame showing a state in which a containing space is provided in the main frame. [Fig. 17] Fig. 17 is a vertical sectional view of an essential portion of a main frame according to an alternative embodiment showing a state in which a containing space is provided in the main frame. [0015] [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the drawings should be viewed in the direction of symbols. Fig. 1 is a side view showing an appearance of one example of a motorcycle to which a frame structure of the present invention is applied, and Fig. 2 is a plan view of Fig. 1. First, the outline of a motorcycle used in this embodiment will be described with reference to Figs. 1 and 2. A motorcycle 1 includes a frame 21 to be described in detail later. A front wheel 2 is steerably supported by a front fork 3 passing through a head pipe 22 provided at the front end of the frame 21. Swing arms 4 extend rearwardly from right and left lower intermediate portions of the frame 21, and a rear wheel 5 is supported by the swing arms 4. Right and left rear cushion units 6 for suspending the rear wheel 5 are interposed between right and left rear portions of the swing arms 4 and right and left rear portions of the frame 21, respectively. [0016] A fuel tank 7 is disposed on a front portion of the frame 21, and a passenger"s sheet 8 is disposed on the frame 21 so as to be positioned behind the fuel tank 7. An engine 9 is mounted on the frame 21 so as to be positioned under the fuel tank 7. A drive sprocket lOa is disposed on one side of a mission case 10 positioned on a rear lower portion of the engine 9, and is connected to a driven sprocket 5a provided on the same side of the rear wheel 5 via a chain 10 for driving the rear wheel 5. A headlamp 12 is disposed on the upper side of a front portion of the front fork 3, and a handlebar 13 is disposed on a top bridge provided on an upper end portion of the front fork 3 so as to be positioned directly behind the headlamp 12. A meter unit 14 is disposed in front of the handlebar 13. [0017] Side cowls 15 are provided to cover right and left sides of a lower front portion of the sheet 7, and rear cowls 16 are provided to cover right and left sides of a section extending from an intermediate portion to a rear portion of the sheet 7 in the longitudinal direction. A rear fender 17 is provided on rear portions of the rear cowls 16 in such a manner as to be tilted rearwardly, downwardly therefrom. An upper half of the front wheel 2 is covered with a front fender 2a. The sheet 8 is of a tandem type extending longer in the longitudinal direction. A rear grip 18 used to be grasped by a passenger during running or grasped by a driver upon standing a main stand of the motorcycle is disposed on the sheet 8 so as to extend on the right and left sides of a lower rear portion of the sheet 8. The rear grip 18 is, as shown in Fig. 2, formed into an approximately U-shape in a plan view. A carburetor 19 disposed behind a cylinder of the engine 9 is connected to an air cleaner (not shown) disposed in a rear space hidden by the side cowls 15. In Fig. 2, reference numeral 20 designates a muffler extending rearwardly, outwardly from one side of the rear portion of the motorcycle 1. [0018] Fig. 3 is a side view showing an appearance of the frame of the present invention. The frame 21 includes a main frame 30, a front member 40, a middle member 50, and a rear member 70. The main frame 30 extends longer in the longitudinal direction substantially throughout the overall length of the motorcycle. Right and left portions of the front member 40 are welded to both sides of a section extending from the front end to an intermediate position of a front portion of the main frame 30 in such a manner as to be tilted rearwardly, downwardly therefrom. The middle member 50 is suspended from an intermediate portion of the main frame 30 in such a manner as to be tilted slightly rearwardly, downwardly therefrom. The rear member 70 is disposed to connect a rear portion of the main frame 30 to a lower portion of the middle member 50. The rear member 70, the middle member 50 positioned on the front side, and the main frame 30 positioned on the upper side form an approximately triangular space 23, and the air cleaner (not shown) is disposed in the space 23. The head pipe 22 is provided at the front end of the main frame 30 in such a manner as to be slightly forwardly, downwardly therefrom. An upper surface of the main frame 30 is curved to be tilted slightly downwardly in the direction from the front portion to the intermediate portion of the main frame 30 and to be tilted slightly upwardly from the intermediate portion to the rear portion of the main frame 30. The upper surface of the main frame 30, however, substantially flattened and extends in the longitudinal direction in an approximately horizontal state. Two stays 81 for mounting and supporting a rear portion of the sheet 8 are suspended downwardly from the rear portion of the main frame 30. [0019] Fig. 4 is a plan view of Fig. 3. As shown in Fig. 4, the main frame 30 is formed such that a front portion 30a has a narrow width Wl; a rear portion 30c has a wide width W2; and an intermediate portion 30b connecting the front portion 30a to the rear portion 30c has a width gradually increased in a region from a rear end of the front portion 30a to a front end of the rear portion 30c. [0020] Fig. 5 is an exploded perspective view of composing members of the frame 21. The main frame 30 is composed of an upper member 31 formed into a recessed shape opened downwardly in cross-section and a lower member 32 formed into a recessed shape opened upwardly in cross - section, which members 31 and 32 are paired in the vertical direction. A front end of each of the upper and lower members 31 and 32 has an arcuate recess in which a rear half of the upper portion of the head pipe 22 is inserted. It should be noted that the recess 3la of the upper member 31 is shown in Fig. 5 but the recess of the lower member 32 is omitted in Fig. 5 for the sake of simplicity. These upper and lower members 31 and 32 are formed, for example, by press-working raw steel plates. Flanges 31c are integrally provided on ends of right and left side walls 31b of the upper member 31 in such a manner as to be outwardly projectingly bent therefrom, and flanges 32c are integrally provided on ends of right and left side walls 32b of the lower member 32 in such a manner as to be outwardly projectingly bent therefrom. The flanges 31c and 32c are opposed to each other. [0021] An upper surface 31d of the upper member 31 is substantially flattened. Electrical equipment mounting bosses 31e and 31f, spaced in the longitudinal direction, are integrally formed by press-working on the upper surface 31d at positions located both at an intermediate portion of the front side of the upper surface 31d in the longitudinal direction and at an intermediate portion in the width direction of the upper surface 31d. An electrical equipment mounting stay 33 formed into a recessed shape in cross - section is located directly behind the rear side mounting boss 31f of the upper surface 31d, and is welded thereto in such a manner that the stay 33 stands on the upper surface 31d while crossing the entire width of the upper surface 31d. [0022] A mounting stay 34 for mounting the fuel tank 7 and the sheet 8 is provided on the upper surface 31d of the upper member 31 at a position located both at an intermediate portion in the longitudinal direction and at an intermediate portion in the width direction. The mounting stay 34 is formed by swelling a portion of the upper surface 31d upwardly, and cutting out a rear portion of the swelled portion to form a cutout 34b. A rear portion of the fuel tank 7 is mounted on the mounting stay 34 by fixing a mounting piece (not shown) provided on the back surface of the rear portion of the fuel tank 7 on the mounting stay 34 using a screw which passes through a mounting hole 34a of the mounting stay 34. A front portion of the sheet 8 is supported on the upper surface 31d of the upper member 31 of the main frame 30 by inserting a tongue-like mounting piece (not shown) provided on the back surface of the front portion of the sheet 8 in the cutout 34b. Since the mounting stay 34 is formed by swelling upwardly a portion of the upper surface 31d of the upper member 31 by means of press-working, it can be provided without necessity of provision of any member different from the composing members of the main frame and also it can be provided simultaneously with formation of the upper member 31. This makes it possible to reduce the number of parts because it is not required to mount any separate member, to easily form the mounting stay 34 because it is not required to weld any separate member, and to reduce the weight of the upper member 31 because it is not required to mount any separate member. The same is true for the above-described electrical equipment mounting bosses 31e and 31f. [0023] At a rear end of the intermediate portion of the upper member 31, the right and left side walls 31b including the flanges 31c projecting outwardly therefrom have arcuate recesses 31g opened downwardly, and at a rear end, corresponding to the above rear end on the upper member 31 side, of the intermediate portion of the lower member 32, the right and left side walls 32b including the flanges 32c projecting outwardly therefrom have arcuate recesses 32g opened upwardly. The recesses 31g and 32g are symmetric in the vertical direction. When the upper member 31 is overlapped from above to the lower member 32 and the flanges 31c are butted and welded to the flanges 32c, a shaft-like cross member 35 for mounting and supporting at its both ends upper ends of the rear cushion units 6 is interposed between the recesses 31g and 32g and is welded thereto, to be thus integrated with the main frame 30. Since the cross member 35 for mounting and supporting the rear cushion units 6 is interposed between the recesses 31g and 32g formed at the rear end of the intermediate portion of the main frame 30 in the width direction, it is possible to enhance the rigidity and strength of the rear end of the intermediate portion of the main frame 30. [0024] A rear cowl mounting stay 36 formed in a recessed shape in a front view is disposed on the upper surface 31d, and lower ends of right and left side walls 36a of the mounting stay 36 are welded to the upper halves of portions near both ends of the cross member 35, and front and rear projecting pieces 36b are welded on the upper surface 31d of the upper member 31. In this case, an upwardly swelled mounting base is integrally formed on the upper surface 31d of the upper member 31 by press-working and the front and rear projecting pieces 36b are welded on the upper surface of the mounting base. [0025] A plurality of recessed ribs 37 each extending longer in the longitudinal direction are formed by press-working in the rear portion of the upper surface 31d of the upper member 31 for enhancing the rigidity of the upper member 31. The rear portion of the upper surface 31d has two right and left rear grip mounting holes 39 on its front side and one rear grip mounting hole 39 on its rear side. On the other hand, front and rear mounting pieces 38a of a mounting stay 38 for mounting accessaries of the engine are welded to one side of the intermediate portion of the lower member 32. [0026] As shown in Fig. 3, the front members 40 is adapted to connect a rear half of the head pipe 22, the front end of the front half of the main frame 30, and an upper edge of the front half of the main frame 30 to each other. The front member 40, which is equivalent to an upper half of the so-called down tube, is composed of right and left members 41. The member 41 is obtained by press-working a raw steel plate into an approximately V-shape in a side view. Each member 41 includes a plate-like portion 41a formed into a recessed shape in cross-section by inwardly bending upper and lower edges of the plate-like portion 41a. The inwardly bent lower edge of the plate-like portion 41a, which is taken as a lower wall piece 41b, is provided with an inwardly projecting piece 41c. The inwardly bent upper edge of the plate-like portion 41a is provided with an upper wall piece 41f which projects while being bent in a Z-shape inwardly from the upper edge . Right and left symmetric swelled circular portions 42 are formed on end portions of the right and left plate-like portions 41a in such a manner as to be swelled outwardly. Each swelled circular portion 42 has a mounting holes 42a allowing a pipe-like mounting stay 43 for mounting the front portion of the fuel tank 7 to pass therethrough. [0027] An intermediate portion of each plate-like portion 41a has an approximately triangular window 44 for reducing the weight of the plate-like portion 41a. The window 44 has an edge portion 44a bent inwardly from the peripheral edge of the window 44 for enhancing the rigidity of the window 44 portion. The right and left plate-like portions 41a include right and left lower extending portions 41d tilted downwardly, rearwardly. The right and left lower extending portions 41d are also formed into symmetric recessed shapes in cross - section. In addition, the above-described lower wall piece 41b extends to the lower end of the lower extending portion 41d. A rear edge portion of the V-shape in a side view of each plate-like portion 41a has a rear wall piece 41e formed into an inwardly, rearwardly bent Z-shape. A lower portion of each lower extending portion 41d has two mounting holes 45 spaced from each other in the vertical direction. Two cross members 46 formed of pipe members are put between both the lower extending portions 41d in such a manner that holes of the cross members 46 are aligned with the mounting holes 45. [0028] As shown in Fig. 3, the middle member 50 is suspended downwardly from the intermediate portion of the main frame 30. The middle member 50 is composed of a main member 51 and a sub-member 61, each of which is obtained by press-working raw steel plates. The main member 51 has a recessed shape becoming deeper toward the rear side in a plan view, and it extends longer in the vertical direction in a side view. The main member 51 includes right and left side walls 51b, and a rear wall 51a whose upper portion is cutout to form two forked portions 51c. The forked portions 51c extend slightly longer in the longitudinal direction for increasing the welding area when the forked portions 51c are welded to the lower member 32. A lower portion 51d of each side wall 51b is swelled forwardly in an approximately inverse L-shape for ensuring a certain height of the lower portion 51d in the vertical direction. [0029] A reinforcing gusset 52 formed into a recessed shape in cross - section is put in a recessed space in cross - section formed between portions, positioned on the upper sides of the lower portions 51d, of the side walls 51b of the main member 51 and is integrally welded to the portions, positioned on the upper sides of the lower portions 51d, of the side walls 51b. The portions, to which the gusset 52 is welded, of the side walls 51b have mounting holes 53 allowing a supporting pipe 54 for turnably supporting a pivot at front ends of the swing arms 4 to pass therethrough. The lower portions 51d of the right and left side walls 51b of the main member 51 have on the front upper sides right and left symmetric mounting holes 55 for mounting the engine 9, and also have on the rear sides right and left symmetric mounting holes 56 for allowing a cross member 57 for mounting a stand to pass therethrough. The right and left side walls 51b include forwardly projecting portions 51e over the mounting holes 55, and the projecting portions 51e have right and left symmetric mounting holes 58 for mounting the engine 9. [0030] The sub-member 61 has a length in the height direction which is equivalent to a length from upper portions of the mounting holes 53 to the forked portions 51c of the main member 51, and is formed into a recessed shape shallower than the recessed shape of the main member 51. The sub-member 61 has a rear wall 61a and side walls 61b bent slightly, forwardly from both sides of the rear wall 61a. The projecting amount of the side wall 61b is small. The sub-member 61 also has an upper portion 61c bent forwardly from the rear wall 61a. The upper portion 61c forms a ceiling portion which is butted to the back side of a bottom surface 32d of the lower member 32 when the middle member 50 is mounted to the lower member 32. A lower end portion of the rear wall 61a has a recess 61d opened downwardly at its central portion in the width direction. The above sub-member 61 is inserted from the front into the main member 51 and is welded thereto. [0031] As shown in Fig. 3, the rear member 70 is adapted to connect the rear portion of the main frame 30 to the lower portion of the middle member 50. The rear member 70 is composed of a main member 71 and a sub-member 74, each of which is formed by press- working raw steel plates. The main member 71 has an arch shape in a side view and has a deeply recessed shape in cross - section. The main member 71 includes a rear wall 71a, and right and left side walls 71b. Mounting bosses 72 for mounting the right and left side cowls 15 are integrally provided on intermediate portions of both the side walls 71b. Each of the mounting bosses 72 has a mounting hole 72a. Both side walls 71b also have side cowl mounting holes 72b under the mounting holes 72a. [0032] The side walls 71b of the main member 71 have lower portions 71c projecting forwardly therefrom, and the lower portions 71c have right and left symmetric forked portions 73 each of which is opened forwardly in a recessed shape. The forked portions 73 are welded to the side walls 51b of the main member 51 of the middle member 50 in such a manner as to hold both side projecting portions of the supporting pipe 54 of the middle member 50. The sub-member 74 having a recessed shape in cross-section includes a rear wall 74a, and right and left side walls 74b bent forwardly from both sides of the rear wall 74a. The depth of the recessed shape of the sub-member 74 is shallower than that of the main member 71, and as shown in Fig. 3, the sub-member 74 has a length in the height direction which is equivalent to a length from a portion over the forked portion 73 to the side cowl mounting portion 72 of the main member 71. The sub-member 74 is inserted from the upper sides of the forked portions 73 of the main member 71 into the side cowl mounting bosses 72 of the side walls 71b of the main member 71, and is integrated with the main member 71 by welding the side walls 74b of the sub-member 74 to the side walls 71b of the main member 71. Since the portion of the rear member 70, in which the sub-member 74 is welded to the main member 71, has a closed structure in cross - section, it is reinforced in terms of rigidity and strength. [0033] The joining structure between the main frame 30 and each of the front member 40, middle member 50, and rear member 70 will be described below with reference to Figs. 6 and 9. Fig. 6 is an enlarged sectional view taken on line 6-6 of Fig. 3. The upper member 31 is welded to the lower member 32 to form the hollow main frame 30 having a closed structure in cross-section. Specifically, the flanges 31c of the upper member 31 are overlapped from above to the opposed flanges 32c of the lower member 32, and are integrally joined thereto by welding specific portions of the flanges 31c to the corresponding portions of the flanges 32c, for example, by spot-welding. In Fig. 6, symbol "a" designate a weld portion of the spot-welding. The front member 40 is joined to the main frame 30 by butting the upper wall pieces 41f provided at the upper edges of the plate-like portions 41a of the right and left members 41 to outer surfaces of the right and left side walls 32b of the lower member 32 of the main frame 30, and joining them to each other, for example, by spot-welding. [0034] The pipe-like mounting stay 43 is integrally mounted to the members 41 by allowing the mounting stay 43 to pass through the mounting holes 42a provided in the swelled circular portions 42 and joining the stay 43 to peripheral edges of the mounting holes 42a, for example, by MIG welding. In Fig. 6, symbol "b" designates a weld portion of the MIG welding. The front ends of the plate-like portions 41a are joined to an outer peripheral portion of the head pipe 22, for example, by MIG welding. The opposed ends of the lower walls 41b of the plate-like portions 41a are butted to each other, and a gusset 47 is mounted to back surfaces of the lower walls 41b and is joined to outer ends of the lower walls 41b, for example, by MIG welding. In Fig 6, symbol "c" designates a weld portion of the MIG welding. A front end of the gusset 47 is joined to a rear half of a lower portion of the head pipe 22, for example, by MIG welding. [0035] The projecting amounts of the flanges 31c outwardly from both the sides of the upper member 31 are set to be larger than those of the flanges 32c outwardly from both the sides of the lower member 32. The projecting end of each of the flanges 31c is downwardly bent to form a bent portion 31h having an approximately inverse L-shape in cross-section. In this embodiment, the flanges 31c, positioned under the fuel tank, of the upper member 31 of the main frame 30 are bent downwardly. With this configuration, it is possible to hidden outer ends of the flanges 32c of the lower member 32, and to enhance the rigidity of the flanges 31 by provision of the bent portions 31h and hence to enhance the rigidity and strength of the upper member 31, and thereby, enhance the rigidity and strength of the entire main frame 30 including the upper member 31 and the lower member 32 integrated with the upper member 31. [0036] Fig. 7 is an enlarged sectional view taken on line 7-7 of Fig. 3. After the upper member 31 is joined to the lower member 32 by welding the flanges 31c and 32c to each other as described above, the mounting stay 38 for mounting accessaries of the engine is joined to one of the side walls 32b of the lower member 32, for example, by spot-welding. In Fig. 7, symbol "d" designates a weld portion of the spot-welding. The mounting stay 38 including the front and rear mounting pieces 38a positioned on the upper side and a main body 38b positioned on the lower side is formed into an approximately Z-shape in cross - section. The mounting pieces 38a positioned on the upper side are welded on one of the side walls 32b of the lower member 32, and the main body 38b on the lower side is provided with a weld nut 38c for mounting accessaries of the engine. [0037] Fig. 8 is an enlarged sectional view taken on line 8-8 of Fig. 3. The mounting portion for mounting the shaft-like cross member 35 as the member for supporting the rear cushion units is shown in Fig. 8. The rear end of the intermediate portion, constituting the above mounting portion, of the main frame 30 is wider than the front portion of the main frame 30 as described above. At the rear end of the intermediate portion, constituting the above mounting portion, of the main frame 30, the side walls 31b including the flanges 31c of the upper member 31 are cutout to form the arcuate recesses 31g and similarly the side walls 32b including the flanges 32c of the lower member 32 are cutout to form the arcuate recesses 32g. The arcuate recesses 31g and 32g are symmetric in the vertical direction. Portions near both the ends of the cross member 35 are put between the recesses 31g and 32g, and are welded to peripheral edges of end portions of the recesses 31g and 32g, for example, by MIG welding. In Fig. 8, symbol "e" designates a weld portion of the MIG welding. In this way, at the rear end of the intermediate portion of the main frame 30, the cross member 35 is interposed integrally between the upper and lower members 31 and 32 in the width direction, and accordingly it is possible to enhance the rigidity and strength of the rear end of the intermediate portion of the main frame 30. Both the ends, designated by reference numeral 35a, of the cross member 35 are small in diameter than a main body of the cross member 35, and mounting bosses 6a provided at upper ends of the right and left rear cushion units 6 are mounted to and supported by both the ends 35a of the cross member 35. [0038] The rear portion of the main member 71 of the rear member 70 is joined to the back side of the lower member 32 in a range from the rear end of the intermediate portion, to which the cross member 35 is mounted, to the rear portion of the lower member 32. Concretely, the rear portion of the main member 71 of the rear member 70 is integrally joined to the main frame 30 by locating the rear wall 71a of the main member 71 under the bottom surface 32d of the lower member 32 with a slight gap put therebetween, overlapping the right and left side walls 71b of the main member 71 to outer surfaces of the side walls 32b of the lower member 32, and joining the side walls 71b to the side walls 32b, for example, by spot-welding. In Fig. 8, symbol "f" designates a weld portion of the spot-welding. [0039] Pig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 3. At the portion of the upper member 31 of the main frame 30 shown in Fig. 9, the upper surface 31d has the right and left recessed ribs 37 extending in the longitudinal direction as described above. The above-described sheet mounting stays 81 are welded to outer surfaces of the right and left side walls 32b on the rear side of the lower member 32. The right and left sheet mounting stays 81 form a sheet mounting stay unit having a right/left division structure, and are formed by press-working raw steel plates. Each of the stays 81 is formed into an approximately Z-shape in cross - section, but the right and left stays 81, particularly designated by reference numerals 81A and 81B, are different in length in the vertical direction. Upper portions 81a of the stays 81 are butted to the outer surfaces of the right and left side walls 32b on the rear side of the lower member 32 and joined thereto, for example, by spot-welding. In Fig. 9, symbol "g" designates a weld portion of the spot-welding. [0040] Fig. 10 is an enlarged view seen in the direction shown by an arrow 10 of Fig. 3. The gusset 47 is formed into a shape shown in Fig. 10 in a front view. The mounting stay 43 for mounting the front portion of the fuel tank is allowed to pass, from right to left, through the mounting holes 42a formed in the swelled circular portions 42 provided on the right and left members 41 of the front member 40, and is joined to the peripheral edges of the mounting holes 42a, for example, by MIG welding. In Fig. 10, the portion welded by the above MIG welding is, as described above, designated by symbol "b". The right and left ends 43a of the stay 43 project rightwardly and leftwardly from the front member 40. In Fig. 10, the weld portion at the rear end of the gusset 47 is, as described above, designated by symbol "c". [0041] Opposed ends of lower halves of the lower wall pieces 41b of the right and left members 41 are butted and joined to each other, for example, by MIG welding. In Fig. 10, symbol "h" designates a weld portion of the MIG welding. Since the front wheel 2 is positioned in front of the above weld portion, the welding is performed in such a manner as not to produce a forwardly projecting weld portion in consideration of vertical movement of the front wheel 2 resulting from cushion movement thereof, to thereby ensure a sufficient cushion stroke of the front wheel 2. The projecting pieces 41c provided on the upper portions of the lower wall pieces 41b are vertically overlapped and joined to each other, for example, by spot-welding. In Fig 10, symbol "i" designates a weld portion of the spot-welding. In this case, the weld portion does not project forwardly, so that it is possible to ensure a sufficient cushion stroke of the front wheel 2 like the above case. [0042] Fig. 11 is an enlarged sectional view taken on line 11-11 of Fig. 3. The lower portion of the front member 40 is shown in Fig. 11. The lower wall pieces 41b of the right and left members 41, on the front side of the front member 40, are, as shown in Fig. 11, overlapped to each other in the vertical direction, and the outer overlapped edge of the lower wall piece 41b located on the outer side is welded to the other lower wall piece 41b located on the inner side as shown by symbol "h". The rear wall pieces 41e formed into flange-like shapes, on the rear side of the front member 40, are overlapped to each other in the lateral direction and are joined to each other, for example, by spot-welding. In Fig. 11, symbol "k" designates a joining portion. At the rear wall pieces 41e, as described above, the upper and lower pipe-like cross members 46 are allowed to pass, from right to left, through the mounting holes and are joined to peripheral edges of the mounting holes, for example, by MIG welding. In Fig. 11, symbol "j" designates a joining portion. [0043] A front portion of an engine hanger 82 shown by a chain line in Fig. 3 is connected to the cross members 46 with bolts 83 passing through the cross members 46, and a rear portion of the engine hanger 82 is bolted on a front portion of the crank case of the engine 9. In this way, the engine 9 is mounted and supported by the front member 40. The front member 40, which is formed by welding the right and left plates formed into recessed shapes by press-working, has a high rigidity closed structure in cross - section as a whole, so that it can strongly and certainly support the front portion of the heavy engine. Also, since the front member 40 has a simple structure obtained by butting and welding the right and left members 41 to each other and welding the cross members 46 put therebetween to the members 41, it can be easily manufactured. [0044] Fig. 12 is an enlarged sectional view taken on line 12-12 of Fig. 3. The main member 51 of the middle member 50 includes the rear wall 51a and the right and left side walls 51b, and is formed by press-working raw steel plates as described above. The main member 51 is, as shown in Fig. 12, formed into a deep recessed shape. The sub-member 61 to be disposed inside the main member 51 similarly includes the rear wall 61a and the right and left side walls 61b, and is similarly formed by press-working raw steel plates. The sub-member 61 is formed into a shallow recessed shape. The sub-member 61 is inserted inside the main member 51 with a space in the longitudinal direction put between the rear wall 61a of the sub-member 61 and the rear wall 51a of the main member 51, and the side walls 61b and 51b overlapped to each other in the lateral direction, that is, from inside to outside and are joined to each other, for example, by spot-welding. In Fig. 12, symbol "m" designates a weld portion of the spot-welding. [0045] The middle member 50 has a high rigidity closed sectional structure in which the auxiliary recessed structure is inserted in the main recessed structure and the right and left sides of the auxiliary recessed structure are welded to those of the main recessed structure, and accordingly, it can exhibit sufficient rigidity and strength necessary for supporting the rear hanger of the engine 9 and the swing arms 4. An upper portion lOb of the mission case 10 at the rear portion of the engine 9 is held between the projecting portions 51e formed on the side walls 51b of the main member 51 of the middle member 50 and is mounted and supported by the projecting portions 51e with a bolt 64 passing through the mounting holes 58 formed in the projecting portions 51e. [0046] Fig. 13 is an enlarged view seen in the direction shown by an arrow 13 of Fig. 3. The right and left forked portions 73 of the main member 71 of the rear member 70 are inserted, from the rear side, around the right and left supporting pipe mounting portions of the main member 51 of the middle member 50 in such a manner as to hold the supporting pipe 54 therebetween. At the above supporting pipe mounting portions of the main member 51, upper and lower portions 73a of the right and left forked portions 73 overlapped to the side walls 51b of the main member 51 are joined thereto, for example, by spot-welding. In Fig. 3, symbol "n" designates a weld portion of the spot-welding. Both ends 54a of the supporting pipe 54, which project outwardly from the forked portions 73 overlapped to the side walls 51d, are adapted to turnably support the front ends of the swing arms 4 . [0047] At the portion, on which the supporting pipe 54 is disposed, of the main member 51, the reinforcing gusset 52 having a recessed shape in cross - section is overlapped and welded to the rear wall 51a and the right and left side walls 51b of the main member 51 in order to reinforce the swing arm supporting portion. An extending piece 71d, which is provided at the lower end of the rear wall 71a of the main member 71 of the rear member 70, is joined to a lower portion of the rear wall 51a of the main member 51, for example, by spot-welding. In Fig. 13, symbol "p" designates a weld portion of the spot-welding. The above-described stand mounting cross member 57 is allowed to pass, from right to left, through the lower portion 51d of the main member 51 via the mounting holes 56 and is joined to the lower portion 51d, for example, by MIG welding. In Fig. 13, symbol "q" designates a weld portion of the MIG welding. The supporting pipe 54 and the stand mounting cross member 57, which are provided at the lower portion of the main member 51 while crossing the main member 51, function as reinforcing beams for enhancing the rigidity and strength of the lower portion of the main member 51 at which the sub-member 61 is not disposed. [0048] Fig. 14 is an enlarged view seen in the direction shown by an arrow 14 of Fig. 3. Right and left lower ends of the recessed cutout 61d of the sub-member 61 of the middle member 50 are butted to an upper surface of the supporting pipe 54 and is joined thereto, for example, by MIG welding. In Fig. 14, symbol "r" designates a weld portion of the MIG welding. [0049] Figs. 15 (a) to 15(e) are views illustrating sequential steps of manufacturing a frame for a motorcycle according to the present invention. Fig. 15(a) shows a state before the main member 51 of the middle member 50 as a sub-frame member is assembled to the lower member 32. The lower recessed portion of the lower member 32, formed by the bottom surface 32d and the right and left side walls 32b, is inserted between the forked portions 51c provided on the upper portion of the main member 51. [0050] Fig. 15 (b) shows a state in which the main member 51 is assembled to the lower member 32 and is then welded thereto. The right and left side walls 32b are overlapped to the inner surfaces of the forked portions 51c in the lateral direction. Two electrodes G of a spot-welder are respectively pushed on the inner surface of one side wall 32b and the outer surface of the associated forked portion 51c, being pressed and energized, to spot-weld the side wall 32b to the forked portion 51c. In Fig. 15(b), symbol "s" designates a weld portion of the spot-welding. While only the welding on the right side is shown in Fig. 15(b), the welding on the left side is similarly performed. In this way, the main member 51 is integrally joined to the lower member 32 by welding in such a manner as to be suspended downwardly from the lower member 32. The state in which the welding has been performed on the right and left sides is shown in Fig. 15 (c) . [0051] Fig. 15 (c) shows a state in which the upper member 31 is prepared in the state that the main member 51 of the middle member 50 as a sub-frame member is suspended from the lower member 32. The upper member 31 is overlapped on the lower member 32 in the direction shown by an arrow. Fig. 15(d) shows a state in which the upper member 31 has been overlapped on the lower member 32. In this state, the flanges 31c of the upper member 31 are overlapped on the flanges 32c of the lower member 32. Then, the electrodes G of the spot-welder, arranged in the vertical direction, are set to hold one flange 31c and the associated flange 32c, being pressed and energized, to spot-weld the flange 31c to the flange 32c. While the welding on the right side is shown in Fig. 15(d) , the welding on the left side is similarly performed. In Fig. 15 (d) , symbol "a" designates a weld portion of the spot-welding. [0052] In this way, as shown in Fig. 15 (e) , the main member 51 is previously welded to the lower member 32 so as to be suspended therefrom, and the upper member 31 is overlapped on the lower member 32 and is joined thereto, for example, by spot-welding the flanges 31c and 32c to each other, to obtain the main frame 30 from which the main member 51 is integrally suspended. The main frame 30 is shown in Fig. 15 (e) . The bent portions 31h are formed at the leading ends of the flanges 31c of the upper member 31 for enhancing the rigidity of the flanges 31c and hiding the ends of the flanges 32c of the lower member 32. [0053] In the method of manufacturing the frame according to the present invention, a sub-frame member is previously suspended downwardly from the lower member before the upper member is joined to the lower member by overlapping and welding the flanges provided on both the ends of the upper member to the flanges provided on both the ends of the lower member so as to form the main frame having a closed sectional structure, and accordingly, the lightweight and easy-to-handle single sub-frame member can be easily assembled to the lightweight and easy-to-handle single lower member by welding using a simple jig. At the step of overlapping the upper member on the lower member after welding of the sub-frame member to the lower member, the lightweight and easy-to-handle single upper member can be easily set on the lower member and can be easily joined thereto only by welding the flanges to each other. In this regard, the frame can be easily manufactured in accordance with the present invention. Since the frame can be manufactured by a simple process, it is possible to reduce the manufacturing cost of the frame for a motorcycle. Further, since the sub-frame member is previously welded to the lower member in such a manner as to be suspended downwardly therefrom, it is possible to increase the degree of freedom in welding between the lower member and the sub-frame member and in arrangement thereof. [0054] Fig. 16 is a vertical sectional side view of an essential portion of the main frame showing a state in which a containing box is provided in the main frame. The main frame 30 is a joining structure in which the upper and lower members 31 and 32 each having a recessed sectional shape are joined to each other via the flanges 31c and 32c. The rear portion of the main frame 30 is, as described above, wider than the front portion thereof, and accordingly, a space 90 having a certain height in the vertical direction can be provided in the rear portion of the main frame 30. The space 90 can be used as a containing box for containing a thin article such as a tool. An opening portion 91 with a rack is provided in the rear portion of the upper surface 31d of the upper member 31, and a lid 92 openable/closable with a hinge 93 provided at the end of the opening portion 91 is provided to cover the opening portion 91. [0055] Fig. 17 is a vertical sectional side view of an essential portion of the main frame showing a state in which an alternative example of a containing box is provided in the main frame. As described above, the upper member 31 is formed by press-working. Upon press-working of the upper member 31, an upwardly swelled portion 131d is simultaneously formed at a suitable location of the rear portion of the upper member 31 by press-working. With this configuration, a space 90 having a height larger than that of the above -described space 90 can be obtained. Like the above embodiment, an opening portion 91 with a rack is provided in an upper surface of the swelled portion 131d, and a lid 92 openable/closable with a hinge 93 provided at the end of the opening portion 91 is provided to cover the opening portion 91. According to this embodiment, the space 90 can be used as a containing box for containing a thick article. [0056] The welding process is not limited to spot-welding and MIG welding used in the above embodiments. For example, an arbitrary resistance welding process such as seam welding or laser welding can be used for joining the frame. Although the composing member of the frame is formed by press-working a raw steel plate in the above embodiments, it may be formed by press-working an aluminum plate. That is to say, the composing member of the frame can be formed by press-working a metal plate insofar as such a metal plate is weldable and has a high rigidity. [0057] [Effect of the Invention] The present invention having the above configuration exhibits the following effects: According to the invention described in claim 1, there is provided a frame structure for a motorcycle, which is formed by preparing a pair of metal plates formed into recessed shapes by press-working and integrally joining the metal plates to each other, characterized in that the pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly; the upper member has flanges projecting outwardly from both side ends of the upper member, and the lower member has flanges projecting outwardly from both side ends of the lower member; and the upper member is overlapped from above to the lower member such that the flanges of the upper member are butted to the flanges of the lower member in the vertical direction, and is joined to the lower member by welding the flanges thus butted to each other, to form a main frame having an approximately flat upper surface and being provided with a head pipe joined to a front end of the main frame. Accordingly, a lightweight main frame having the backborn structure, which ensures a desirable rigidity and a desirable strength, can be simply formed by integrally joining metal plates, each of which is formed by press-working, to each other at a low cost. [0058] In particular, according to the present invention, the main frame having the backborn structure is obtained by integrally joining the upper member and the lower member, each of which is formed by press-working, to each other by welding the flanges of the upper member to the flanges of the lower member in the vertical direction, and accordingly, it is possible to freely set the width of the frame in the lateral direction of a vehicular body of a motorcycle while keeping constant the length of the frame in the longitudinal direction of the vehicular body unlike an aluminum pipe structure having a closed cross-section obtained, for example, by drawing an aluminum based material. That is to say, it is possible to easily form the main frame having a necessary shape at a low cost. Since the main frame has an approximately flat upper surface, mounting portions for mounting components such as accessaries, a fuel tank, and a sheet can be directly formed on the upper member without provision of any special members or without necessity of welding of the special members, it is possible to simplify the structure and manufacture of the main frame, reduce the number of parts, reduce the weight of the main frame, and lower the manufacturing cost of the main frame. Since the upper surface of the main frame is flattened, it is possible to use simple stays and brackets for mounting and supporting accessaries and other parts, and to simplify the structure for mounting and supporting the stays and brackets to the upper member and the lower member. [0059] Since the main frame is obtained by joining the upper and lower plates, each of which is formed by press-working, to each other in the vertical direction, the width of each of the front portion and rear portion of the main frame can be freely set such that a head pipe or an engine hanger is allowed to be joined to the front or rear portion, and accessaries, a fuel tank or a sheet is allowed to be mounted on the front or rear portion. Accordingly, it is possible to simplify the structure of these frame members to be mounted to the main frame and facilitate the welding procedure for welding the frame members to the main frame. Since the main frame having the front and rear portion different in terms of width in the lateral direction can be easily obtained, the entire frame having the front and rear portion different in terms of width in the lateral direction can be easily obtained. In this way, it is possible to simplify the structure of the entire frame, facilitate the manufacture of the entire frame, and reduce the manufacturing cost of the entire frame. Also since the main frame having a hollow structure of a closed cross - section is obtained by joining the upper and lower members to each other by welding the right and left projecting flanges of the upper member to the right and left projecting flanges of the lower member, it is possible to ensure a high rigidity and a high strength enough to be used as a main frame for a motorcycle having an engine with a large displacement. [0060] According to the invention described in claim 2, in addition to the configuration of the invention described in claim 1, a sub-frame member formed by press-working is joined to the lower member of the main frame in such a manner as to be suspended therefrom. Accordingly, in addition to the effect of the invention described in claim 1, since a sub-frame member other than the members constituting the main frame of the vehicular body is formed by press-working and is welded to the lower member of the main frame, it is possible to simplify the configuration of the components of the vehicular body and also simplify the frame structure. Since each of the main frame and the sub-frame member is obtained by integrally joining plates formed by press-working to each other by welding or the like, it is possible to facilitate the manufacture of the frame and hence to manufacture a lightweight vehicular body of a motorcycle having a high rigidity and a high strength at a low cost. [0061] According to the invention described in claim 3, in addition to the configuration of the invention described in claim 1, outer ends of the flanges of one of the upper member and the lower member of the main frame are bent, and leading ends of the flanges of the other of the upper member and the lower member are covered with the bent portions. Accordingly, in addition to the effect of the invention described in claim 1, since the outer ends of the flanges of one of the upper member and lower member are hidden by the bent portions provided at the outer ends of the other of the upper member and the lower member, it is possible to improve the appearance characteristic of the main frame part of which is possibly is exposed, and also since the edges of the main frame are hidden upon assembly of the entire motorcycle, it is possible to improve the assembling characteristic of the motorcycle. In particular, according to the present invention, it is possible to further enhance the rigidity and strength of the flanges by provision of the bent portions. That is to say, it is possible to simply increase the rigidity and strength of the flanges by providing the bent portions at the outer ends of the flanges. Such an effect can be realized only by adding the work of bending the leading ends of the flanges to the work of press-forming the flanges. [0062] According to the invention described in claim 4, in addition to the configuration of the invention described in claim 1, a cross member constituting a mounting portion for mounting rear cushion units is provided at a location of the main frame in such a manner as to be interposed between the upper member and the lower member in the width direction of the same main frame. That is to say, the cross member for mounting the rear cushion units is provided at a location of the main frame, which is of a joining structure having the upper member and the lower member each of which extends substantially over the entire length of the motorcycle, in such a manner as to be interposed between the upper member and the lower member. Accordingly, in addition to the effect of the invention described in claim 1, it is possible to enhance the rigidity and strength of the main frame extending substantially over the entire length of the motorcycle by provision of the cross member for mounting the rear cushion units at a location of the main frame, and hence to enhance the rigidity and strength of the main frame without necessity of provision of any additional member for improving the rigidity and strength. The cross member for mounting the rear cushion units can be simply mounted on the main frame by inserting the cross member between the upper member and the lower member and welding it thereto. The welding of the cross member to the upper and lower members can be simultaneously performed along with the welding of the upper member to the lower members. This is advantageous in terms of manufacture of the main frame. Further, since the cross member is integrated with the upper and lower members by welding or the like, it is possible to enhance the rigidity and strength of the portion of the main frame at which the cross member for mounting the rear cushion units is provided. [0063] According to the invention described in claim 5, in addition to the configuration of the invention described in claim 1, a mounting portion for mounting a fuel tank and a sheet is integrally formed at a location on the upper surface of the main frame by press-working. Accordingly, in addition to the effect of the invention described in claim I, the mounting portion for mounting a fuel tank and a sheet can be formed on the upper surface of. the main frame without use of any special member. As a result, it is possible to simplify the structure of the main frame, reduce the components of the main frame, and reduce the number of manufacturing steps, for example, eliminate the welding steps, and since the number of the parts is reduced, it is possible to reduce the weight of the entire frame of the motorcycle and to reduce the manufacturing cost of the frame. [0064] According to the invention described in claim 6, there is provided a method of manufacturing a frame for a motorcycle, including the steps of: preparing a pair of metal plates formed into recessed shapes by press-working; and integrally joining the metal plates to each other, characterized in that the method includes the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends of the lower member, and welding a sub-frame member to side walls of the lower member in such a manner as to suspend the sub-frame member from the lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of the upper member, and overlapping the upper member on the lower member and welding the overlapped flanges to each other, to form a main frame. With this configuration, the sub-frame member is previously suspended downwardly from the lower member before the upper member is joined to the lower member by overlapping and welding the flanges provided on both the ends of the upper member to the flanges provided on both the ends of the lower member so as to form the main frame having a closed sectional structure, and accordingly, the lightweight and easy-to-handle single sub-frame member can be easily assembled to the lightweight and easy-to-handle single lower member by welding using a simple jig. [0065] At the step of overlapping the upper member on the lower member after welding of the sub-frame member to the lower member, the lightweight and easy-to-handle single upper member can be easily set on the lower member and can be easily joined thereto only by welding the flanges provided on the upper member to the flanges provided on the lower member to each other. In this regard, the frame can be easily manufactured in accordance with the present invention. Since the frame can be manufactured by a simple process, it is possible to reduce the manufacturing cost of the frame for a motorcycle. Further, since the sub-frame member is previously welded to the lower member in such a manner as to be suspended downwardly therefrom, it is possible to increase the degree of freedom in welding between the lower member and the sub-frame member and in arrangement thereof. [Explanation of Symbols] 1: motorcycle, 30: main frame, 22: head pipe, 31: upper member, 32: lower member, 31b, 32b: flange, 31c: bent portion at outer edge of flange, 34: mounting portion for mounting fuel tank and sheet, 35: cross member for mounting rear cushion unit, 40, 50, 70: sub-frame member WE CLAIM: 1. A frame structure for a motorcycle, which is formed by preparing a pair of metal plates formed into recessed shapes by press-working and integrally joining said metal plates to each other, characterized in that said pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly; said upper member has flanges projecting outwardly from both side ends of said upper member, and said lower member has flanges projecting outwardly from both side ends of said lower member; and said upper member is overlapped from above to said lower member such that said flanges of said upper member are butted to said flanges of said lower member in the vertical direction, and is joined to said lower member by welding said flanges thus butted to each other, to form a main frame having an flat upper surface and being provided with a head pipe joined to a front end of said main frame. 2. A frame structure for a motorcycle as claimed in claim 1, wherein a sub-frame member formed by press-working is joined to said lower member of said main frame. 3. A frame structure for a motorcycle as claimed in claim 1, wherein outer ends of said flanges of one of said upper member and said lower member of said main frame are bent, and leading ends of said flanges of the other of said upper member and said lower member are covered with said bent portions. 4. A frame structure for a motorcycle as claimed in claim 1, wherein a cross member constituting a mounting portion for mounting rear cushion units is interposed between said upper member and said lower member in the width direction of the same main frame. 5. A frame structure for a motorcycle as claimed in claim 1, wherein a mounting portion for mounting a fuel tank and a sheet is integrally formed at a location on the upper surface of said main frame by press- working. 6. In a method of manufacturing a frame for a motorcycle, as claimed in claim 1, comprising the steps of: preparing a pair of metal plates formed into recessed shapes by press-working; and integrally joining said metal plates to each other, the improvement comprising the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends-of said lower member, and welding a sub-frame member to side walls of said lower member in such a manner as to suspend said sub-frame member from said lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of said upper member, and overlapping said upper member on said lower member and welding said overlapped flanges to each other, to form a main frame. 7. A frame structure for a motorcycle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 8. In a method of manufacturing a frame for a motorcycle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Full Text

The present invention relates to a frame structure for a motorcycle and a method of manufacturing the same.
The present invention relates to an improved frame structure for a motorcycle manufactured by joining metal plates shaped by press-working to each other into one body, and a method of manufacturing a frame for a motorcycle by joining metal plates shaped by press-
working to each other into one-body. [0002]
[Prior Art]
Techniques of manufacturing a frame for a motorcycle by press-working raw steel plates into a pair of members and welding the members to each other into
one-body have been disclosed as follows:
One technique has been disclosed in Japanese
Utility Model Laid-open No. Sho 61-133486 and Japanese
Patent Laid-open No. Sho 58-49582, in which a pair of right and left members are each formed into an approximately V-shape in a side view and a recessed shape in cross-section by press-working in such a manner that each member has flanges projecting upwardly and downwardly from upper and lower edges of the member, whereby a frame is obtained by overlapping and butting the flanges of the right and left members to each other
in the horizontal direction and welding the flanges to
each other into one-body.
Another technique has been disclosed in Japanese
Utility Model Publication No. Sho 61-22072, in which a
pair of right and left members are each formed into an approximately T-shape in a side view and a recessed shape in cross - section in such a manner that each member has
flanges projecting upwardly and downwardly from upper and lower edges of the member, whereby a frame is obtained by overlapping the flanges of the right and left members to each other and welding the flanges to each other into one-body. [0003]
Each of the above-described prior art frame structures is of a type used for a very small-sized and lightweight motorcycle mounting an engine with a very small displacement. Specifically, the frame for a
motorcycle disclosed in the former documents, that is, in
Japanese Utility Model Laid-open No. Sho 61-133486 and
Japanese Patent Laid-open No. Sho 58-49582 is of a type
in which a head pipe is disposed at a front end of an
upper portion of the V-shaped frame and a sheet is
disposed at a rear end of the upper portion of the frame,
and a power unit including an engine integrated with a
transmission case is swingably mounted in a V-shaped
valley portion of the frame.
On the other hand, the frame disclosed in Japanese Utility Model Publication No. Sho 61-22072 is of a type used for a very small-sized, lightweight motorcycle mounting an engine with a small displacement like the above frame, wherein the frame is formed into a simple T-
shape in a side view. [0004]
[Problem to be Solved by the Invention]
A frame used for a motorcycle mounting an engine with a somewhat large displacement or a large-sized motorcycle is often formed by assembling a plurality of pipe members by welding or the like. In manufacturing such a frame, there is a tendency to raise the manufacturing cost of the frame and increase the weight of the frame because the number of components of the frame is very large, the work of bending the pipe members is complicated, the number of portions to be welded is large, and the frame structure is complicated.
In order to simplify the prior art frame structure for a motorcycle mounting an engine with a somewhat large or a very large displacement, facilitate the manufacturing method for the frame, reduce the weight of the frame, and lower the manufacturing cost of the frame, it may be considered to adopt the above-described prior art frame structure formed by joining metal plates to each other into one-body as a backborn type frame extending approximately in the horizontal direction substantially over the entire length of the motorcycle; however, such an attempt has the following problems:
[0005]
Since the prior art frame structure is configured such that each of right and left members shaped by press -working has flanges projecting upwardly and downwardly from upper and lower edges of the member and the flanges of the right and left members are butted and welded to each other in the horizontal direction, the flanges project upwardly and downwardly from the frame thus obtained.
In particular, since the flanges project upwardly from the upper surface of the frame at a widthwise central portion throughout the overall length of the frame, there are limitations in arranging, on the upper surface of the frame, accessaries of the motorcycle and components whose arrangement is important in terms of appearance such as a fuel tank and a sheet. That is to say, it is difficult to directly arrange the fuel tank, the sheet and the like on the frame, and to mount these parts on the frame, it is required to provide mounting stays and brackets for mounting these parts. This is disadvantageous in that the frame structure is complicated, and the number of components of the frame is increased and thereby the number of portions to be welded is increased, resulting in the raised manufacturing cost.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a simple frame structure with a high rigidity and a high strength, particularly effective as a frame including a main frame usable for a motorcycle mounting an engine with a large displacement, by welding metal plates shaped by press-working to each other into one-body, which frame structure is further effective to facilitate the manufacturing process, reduce the number of parts, lower the manufacturing cost, and reduce the weight of the frame.
Another object of the present invention is to provide a method of simply manufacturing a frame for a motorcycle at a low cost.
According to the present invention there is provided a frame structure for a motorcycle, which is formed by preparing a pair of metal plates formed into recessed shapes by press-working and integrally joining said metal plates to each other,
characterized in that
said pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly;
said upper member has flanges projecting outwardly from both side ends of said upper member, and said lower member has flanges projecting outwardly from both side ends of said lower member; and
said upper member is overlapped from above to said lower member such that said flanges of said upper member are butted to said flanges of said lower member in the vertical direction, and is joined to said lower member by welding said flanges thus butted to each other, to form a main frame having an flat upper surface and being provided with a head pipe joined to a front end of said main frame.
According to the present invention there is also provided a method of manufacturing a frame for a motorcycle, comprising the steps of:
preparing a pair of metal plates formed into recessed shapes by press-working; and
integrally joining said metal plates to each other.
the improvement comprising the steps of:
preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends of said lower member, and welding a sub-frame member to side walls of said lower member in such a manner as to suspend said sub-frame member from said lower member; and
preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of said upper member, and overlapping said upper member on said lower member and welding said overlapped flanges to each other, to form a main frame.
With this configuration, a main frame having the backborn structure for a motorcycle, which ensures a desirable rigidity and a desirable strength, can be simply formed by press-working metal plates at a low cost. The main frame has an approximately flat upper surface, and accordingly, components such as accessories, a fuel tank, and a sheet can be mounted on the upper surface directly or via simple stays or brackets. Also the main frame is formed by joining the upper and lower members, each of which is formed by press-working, to each other in the vertical direction,
in the vertical direction, and accordingly, the weight of the main frame can be reduced, and the width of each of the front and rear portions of the main frame can be freely set such that a head pipe or an engine hanger is allowed to be joined to the front or rear portion, and accessaries, a fuel tank or a sheet is allowed to be mounted on the front or rear portion. [0009]
According to an invention described in claim 2, in addition to the configuration of the invention described in claim 1, a sub-frame member formed by press-working is joined to the lower member of the main frame in such a manner as to be suspended therefrom.
With this configuration, since a sub-frame member other than the members constituting the main frame of a vehicular body of a motorcycle is formed by press-working and is welded to the lower member of the main frame, it is possible to facilitate the configuration and manufacture of the components of the vehicular body, to reduce the weight of the vehicular body, and to manufacture the vehicular body at a low cost. [0010]
According to an invention described in claim 3, in addition to the configuration of the invention described
in claim 1, outer ends of the flanges of one of the upper member and the lower member of the main frame are bent, and leading ends of the flanges of the other of the upper member and the lower member are covered with the bent portions.
With this configuration, it is possible to enhance the rigidity and strength of the flanges by providing the bent portions at the outer ends of the flanges. In other words, it is possible to simply increase the rigidity and strength of the flanges only by adding the work of bending the leading ends of the flanges to the work of press-forming the flanges. [0011]
According to an invention described in claim 4, in addition to the configuration of the invention described in claim 1, a cross member constituting a mounting portion for mounting rear cushion units is provided at a location of the main frame in such a manner as to be interposed between the upper member and the lower member in the width direction of the same main frame.
Since the cross member for mounting the rear cushion units is provided at a location of the main frame, composed of the upper member and the lower member joined to each other, in such a manner as to be interposed
between the upper member and the lower member in the width direction of the main frame, it is possible to simplify the structure for mounting the cross member, and to enhance the rigidity and strength of the portion of the main frame at which the cross member for mounting the rear cushion units is provided. [0012]
According to an invention described in claim 5, in addition to the configuration of the invention described in claim 1, a mounting portion for mounting a fuel tank and a sheet is integrally formed at a location on the upper surface of the main frame by press -working.
With this configuration, since the mounting portion for mounting a fuel tank and a sheet is formed on the upper surface of the main frame without provision of any special member, it is possible to simplify the frame structure, reduce the number of components of the frame, reduce the manufacturing steps, for example, eliminate the welding step, and lower the manufacturing cost. [0013]
According to an invention described in claim 6, there is provided a method of manufacturing a frame for a motorcycle, including the steps of: preparing a pair of metal plates formed into recessed shapes by press-
working; and integrally joining the metal plates to each other, characterized in that the method includes the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends of the lower member, and welding a sub-frame member to side walls of the lower member in such a manner as to suspend the sub-frame member from the lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of the upper member, and overlapping the upper member on the lower member and welding the overlapped flanges to each other, to form a main frame. [0014]
With this configuration, a sub-frame member is previously integrally joined to the upwardly recessed lower member of the main frame by welding the sub-frame member to the side walls of the lower member and then the downwardly recessed upper member is integrally joined to the lower member by overlapping and welding the flanges of the upper member to the flanges of the lower member. For example, the lightweight and easy-to-handle lower member is held by a jig or the like, and in such a state, the lightweight sub-frame member formed by press-working
is butted from below to the lower member and is welded thereto, and then the upper member is overlapped and welded to the lower member. As a result, the welding works for the frame is improved by facilitating the handling and setting of the members of the frame and simplifying the welding procedure. This makes it possible to simply manufacture the frame and hence to reduce the manufacturing cost of the frame for a motorcycle. Also since the sub-frame member is previously welded to the lower member in such a manner as to be suspended from the lower member, it is possible to enhance the degree of freedom in welding between the lower member and the sub-frame member and in arrangement thereof.
[Brief Description of the Drawings] [Fig. 1]
Fig. 1 is a side view showing an appearance of one example of a motorcycle to which a frame structure of the present invention is applied. [Fig. 2]
Fig. 2 is a plan view of Fig. 1. [Fig. 3]
Fig. 3 is a side view showing an appearance of a frame of the present invention. [Fig. 4]
Fig. 4 is a plan view of Fig. 3. [Fig. 5]
Fig. 5 is an exploded perspective view of composing members of the frame. [Fig. 6]
Fig. 6 is an enlarged sectional view taken on line 6-6 of Fig. 3. [Fig. 7]
Fig. 7 is an enlarged sectional view taken on line 7-7 of Fig. 3. [Fig. 8]
Fig. 8 is an enlarged sectional view taken on line 8-8 of Fig. 3. [Fig. 9]
Fig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 3. [Fig. 10]
Fig. 10 is an enlarged view seen in the direction shown by an arrow 10 of Fig. 3. [Fig. 11]
Fig. 11 is an enlarged sectional view taken on line 11-11 of Fig. 3. [Fig. 12]
Fig. 12 is an enlarged sectional view taken on line
12-12 of Fig. 3. [Fig. 13]
Fig. 13 is a view seen in the direction shown by an arrow 13 of Fig. 3. [Fig. 14]
Fig. 14 is a view seen along the direction shown by an arrow 14 of Fig. 3. [Figs. 15 (a) to 15 (e)]
Figs. 15(a) to 15(e) are views showing sequential steps of manufacturing the frame, wherein Fig. 15(a) shows a state before a sub-frame member is assembled to a lower member; Fig. 15(b) shows a state in which the sub-frame member is assembled to the lower member and welded thereto; Fig. 15(c) shows a state before an upper member is assembled to the lower member; Fig. 15(d) shows a state in which the upper member is welded to the lower member; and Fig. 15(e) shows a state after the upper member is welded to the lower member. [Fig. 16]
Fig. 16 is a vertical sectional side view of an essential portion of a main frame showing a state in which a containing space is provided in the main frame. [Fig. 17]
Fig. 17 is a vertical sectional view of an
essential portion of a main frame according to an alternative embodiment showing a state in which a containing space is provided in the main frame.
[0015]
[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the drawings should be viewed in the direction of symbols.
Fig. 1 is a side view showing an appearance of one example of a motorcycle to which a frame structure of the present invention is applied, and Fig. 2 is a plan view of Fig. 1.
First, the outline of a motorcycle used in this
embodiment will be described with reference to Figs. 1 and 2. A motorcycle 1 includes a frame 21 to be described in detail later. A front wheel 2 is steerably supported by a front fork 3 passing through a head pipe 22 provided at the front end of the frame 21. Swing arms 4 extend rearwardly from right and left lower intermediate portions of the frame 21, and a rear wheel 5 is supported by the swing arms 4. Right and left rear cushion units 6 for suspending the rear wheel 5 are interposed between right and left rear portions of the swing arms 4 and right and left rear portions of the frame 21, respectively. [0016]
A fuel tank 7 is disposed on a front portion of the frame 21, and a passenger"s sheet 8 is disposed on the frame 21 so as to be positioned behind the fuel tank 7. An engine 9 is mounted on the frame 21 so as to be positioned under the fuel tank 7. A drive sprocket lOa is disposed on one side of a mission case 10 positioned on a rear lower portion of the engine 9, and is connected to a driven sprocket 5a provided on the same side of the rear wheel 5 via a chain 10 for driving the rear wheel 5.
A headlamp 12 is disposed on the upper side of a front portion of the front fork 3, and a handlebar 13 is
disposed on a top bridge provided on an upper end portion of the front fork 3 so as to be positioned directly behind the headlamp 12. A meter unit 14 is disposed in front of the handlebar 13. [0017]
Side cowls 15 are provided to cover right and left sides of a lower front portion of the sheet 7, and rear cowls 16 are provided to cover right and left sides of a section extending from an intermediate portion to a rear portion of the sheet 7 in the longitudinal direction. A rear fender 17 is provided on rear portions of the rear cowls 16 in such a manner as to be tilted rearwardly, downwardly therefrom. An upper half of the front wheel 2 is covered with a front fender 2a.
The sheet 8 is of a tandem type extending longer in the longitudinal direction. A rear grip 18 used to be grasped by a passenger during running or grasped by a driver upon standing a main stand of the motorcycle is disposed on the sheet 8 so as to extend on the right and left sides of a lower rear portion of the sheet 8. The rear grip 18 is, as shown in Fig. 2, formed into an approximately U-shape in a plan view.
A carburetor 19 disposed behind a cylinder of the engine 9 is connected to an air cleaner (not shown)
disposed in a rear space hidden by the side cowls 15. In Fig. 2, reference numeral 20 designates a muffler extending rearwardly, outwardly from one side of the rear portion of the motorcycle 1. [0018]
Fig. 3 is a side view showing an appearance of the frame of the present invention.
The frame 21 includes a main frame 30, a front member 40, a middle member 50, and a rear member 70. The main frame 30 extends longer in the longitudinal direction substantially throughout the overall length of the motorcycle. Right and left portions of the front member 40 are welded to both sides of a section extending from the front end to an intermediate position of a front portion of the main frame 30 in such a manner as to be tilted rearwardly, downwardly therefrom. The middle member 50 is suspended from an intermediate portion of the main frame 30 in such a manner as to be tilted slightly rearwardly, downwardly therefrom. The rear member 70 is disposed to connect a rear portion of the main frame 30 to a lower portion of the middle member 50. The rear member 70, the middle member 50 positioned on the front side, and the main frame 30 positioned on the upper side form an approximately triangular space 23, and
the air cleaner (not shown) is disposed in the space 23.
The head pipe 22 is provided at the front end of the main frame 30 in such a manner as to be slightly forwardly, downwardly therefrom.
An upper surface of the main frame 30 is curved to be tilted slightly downwardly in the direction from the front portion to the intermediate portion of the main frame 30 and to be tilted slightly upwardly from the intermediate portion to the rear portion of the main frame 30. The upper surface of the main frame 30, however, substantially flattened and extends in the longitudinal direction in an approximately horizontal state.
Two stays 81 for mounting and supporting a rear portion of the sheet 8 are suspended downwardly from the rear portion of the main frame 30. [0019]
Fig. 4 is a plan view of Fig. 3.
As shown in Fig. 4, the main frame 30 is formed such that a front portion 30a has a narrow width Wl; a rear portion 30c has a wide width W2; and an intermediate portion 30b connecting the front portion 30a to the rear portion 30c has a width gradually increased in a region from a rear end of the front portion 30a to a front end of the rear portion 30c.
[0020]
Fig. 5 is an exploded perspective view of composing members of the frame 21.
The main frame 30 is composed of an upper member 31 formed into a recessed shape opened downwardly in cross-section and a lower member 32 formed into a recessed shape opened upwardly in cross - section, which members 31 and 32 are paired in the vertical direction. A front end of each of the upper and lower members 31 and 32 has an arcuate recess in which a rear half of the upper portion of the head pipe 22 is inserted. It should be noted that the recess 3la of the upper member 31 is shown in Fig. 5 but the recess of the lower member 32 is omitted in Fig. 5 for the sake of simplicity. These upper and lower members 31 and 32 are formed, for example, by press-working raw steel plates.
Flanges 31c are integrally provided on ends of right and left side walls 31b of the upper member 31 in such a manner as to be outwardly projectingly bent therefrom, and flanges 32c are integrally provided on ends of right and left side walls 32b of the lower member 32 in such a manner as to be outwardly projectingly bent therefrom. The flanges 31c and 32c are opposed to each other.
[0021]
An upper surface 31d of the upper member 31 is substantially flattened. Electrical equipment mounting bosses 31e and 31f, spaced in the longitudinal direction, are integrally formed by press-working on the upper surface 31d at positions located both at an intermediate portion of the front side of the upper surface 31d in the longitudinal direction and at an intermediate portion in the width direction of the upper surface 31d. An electrical equipment mounting stay 33 formed into a recessed shape in cross - section is located directly behind the rear side mounting boss 31f of the upper surface 31d, and is welded thereto in such a manner that the stay 33 stands on the upper surface 31d while crossing the entire width of the upper surface 31d.
[0022]
A mounting stay 34 for mounting the fuel tank 7 and the sheet 8 is provided on the upper surface 31d of the upper member 31 at a position located both at an intermediate portion in the longitudinal direction and at an intermediate portion in the width direction. The mounting stay 34 is formed by swelling a portion of the upper surface 31d upwardly, and cutting out a rear portion of the swelled portion to form a cutout 34b. A
rear portion of the fuel tank 7 is mounted on the mounting stay 34 by fixing a mounting piece (not shown) provided on the back surface of the rear portion of the fuel tank 7 on the mounting stay 34 using a screw which passes through a mounting hole 34a of the mounting stay 34. A front portion of the sheet 8 is supported on the upper surface 31d of the upper member 31 of the main frame 30 by inserting a tongue-like mounting piece (not shown) provided on the back surface of the front portion of the sheet 8 in the cutout 34b.
Since the mounting stay 34 is formed by swelling upwardly a portion of the upper surface 31d of the upper member 31 by means of press-working, it can be provided without necessity of provision of any member different from the composing members of the main frame and also it can be provided simultaneously with formation of the upper member 31. This makes it possible to reduce the number of parts because it is not required to mount any separate member, to easily form the mounting stay 34 because it is not required to weld any separate member, and to reduce the weight of the upper member 31 because it is not required to mount any separate member.
The same is true for the above-described electrical equipment mounting bosses 31e and 31f.
[0023]
At a rear end of the intermediate portion of the upper member 31, the right and left side walls 31b including the flanges 31c projecting outwardly therefrom have arcuate recesses 31g opened downwardly, and at a rear end, corresponding to the above rear end on the upper member 31 side, of the intermediate portion of the lower member 32, the right and left side walls 32b including the flanges 32c projecting outwardly therefrom have arcuate recesses 32g opened upwardly. The recesses 31g and 32g are symmetric in the vertical direction.
When the upper member 31 is overlapped from above to the lower member 32 and the flanges 31c are butted and welded to the flanges 32c, a shaft-like cross member 35 for mounting and supporting at its both ends upper ends of the rear cushion units 6 is interposed between the recesses 31g and 32g and is welded thereto, to be thus integrated with the main frame 30.
Since the cross member 35 for mounting and
supporting the rear cushion units 6 is interposed between the recesses 31g and 32g formed at the rear end of the intermediate portion of the main frame 30 in the width direction, it is possible to enhance the rigidity and strength of the rear end of the intermediate portion of
the main frame 30. [0024]
A rear cowl mounting stay 36 formed in a recessed shape in a front view is disposed on the upper surface 31d, and lower ends of right and left side walls 36a of the mounting stay 36 are welded to the upper halves of portions near both ends of the cross member 35, and front and rear projecting pieces 36b are welded on the upper surface 31d of the upper member 31.
In this case, an upwardly swelled mounting base is integrally formed on the upper surface 31d of the upper member 31 by press-working and the front and rear projecting pieces 36b are welded on the upper surface of the mounting base. [0025]
A plurality of recessed ribs 37 each extending longer in the longitudinal direction are formed by press-working in the rear portion of the upper surface 31d of the upper member 31 for enhancing the rigidity of the upper member 31. The rear portion of the upper surface 31d has two right and left rear grip mounting holes 39 on its front side and one rear grip mounting hole 39 on its rear side.
On the other hand, front and rear mounting pieces
38a of a mounting stay 38 for mounting accessaries of the engine are welded to one side of the intermediate portion of the lower member 32. [0026]
As shown in Fig. 3, the front members 40 is adapted to connect a rear half of the head pipe 22, the front end of the front half of the main frame 30, and an upper edge of the front half of the main frame 30 to each other.
The front member 40, which is equivalent to an upper half of the so-called down tube, is composed of right and left members 41. The member 41 is obtained by press-working a raw steel plate into an approximately V-shape in a side view.
Each member 41 includes a plate-like portion 41a formed into a recessed shape in cross-section by inwardly bending upper and lower edges of the plate-like portion 41a. The inwardly bent lower edge of the plate-like portion 41a, which is taken as a lower wall piece 41b, is provided with an inwardly projecting piece 41c. The inwardly bent upper edge of the plate-like portion 41a is provided with an upper wall piece 41f which projects while being bent in a Z-shape inwardly from the upper edge .
Right and left symmetric swelled circular portions
42 are formed on end portions of the right and left plate-like portions 41a in such a manner as to be swelled outwardly. Each swelled circular portion 42 has a mounting holes 42a allowing a pipe-like mounting stay 43 for mounting the front portion of the fuel tank 7 to pass therethrough. [0027]
An intermediate portion of each plate-like portion 41a has an approximately triangular window 44 for reducing the weight of the plate-like portion 41a. The window 44 has an edge portion 44a bent inwardly from the peripheral edge of the window 44 for enhancing the rigidity of the window 44 portion.
The right and left plate-like portions 41a include right and left lower extending portions 41d tilted downwardly, rearwardly. The right and left lower extending portions 41d are also formed into symmetric recessed shapes in cross - section. In addition, the above-described lower wall piece 41b extends to the lower end of the lower extending portion 41d.
A rear edge portion of the V-shape in a side view of each plate-like portion 41a has a rear wall piece 41e formed into an inwardly, rearwardly bent Z-shape.
A lower portion of each lower extending portion 41d
has two mounting holes 45 spaced from each other in the vertical direction. Two cross members 46 formed of pipe members are put between both the lower extending portions 41d in such a manner that holes of the cross members 46 are aligned with the mounting holes 45. [0028]
As shown in Fig. 3, the middle member 50 is suspended downwardly from the intermediate portion of the main frame 30.
The middle member 50 is composed of a main member 51 and a sub-member 61, each of which is obtained by press-working raw steel plates.
The main member 51 has a recessed shape becoming deeper toward the rear side in a plan view, and it extends longer in the vertical direction in a side view. The main member 51 includes right and left side walls 51b, and a rear wall 51a whose upper portion is cutout to form two forked portions 51c. The forked portions 51c extend slightly longer in the longitudinal direction for increasing the welding area when the forked portions 51c are welded to the lower member 32. A lower portion 51d of each side wall 51b is swelled forwardly in an approximately inverse L-shape for ensuring a certain height of the lower portion 51d in the vertical direction.
[0029]
A reinforcing gusset 52 formed into a recessed shape in cross - section is put in a recessed space in cross - section formed between portions, positioned on the upper sides of the lower portions 51d, of the side walls 51b of the main member 51 and is integrally welded to the portions, positioned on the upper sides of the lower portions 51d, of the side walls 51b. The portions, to which the gusset 52 is welded, of the side walls 51b have mounting holes 53 allowing a supporting pipe 54 for turnably supporting a pivot at front ends of the swing arms 4 to pass therethrough.
The lower portions 51d of the right and left side walls 51b of the main member 51 have on the front upper sides right and left symmetric mounting holes 55 for mounting the engine 9, and also have on the rear sides right and left symmetric mounting holes 56 for allowing a cross member 57 for mounting a stand to pass therethrough.
The right and left side walls 51b include forwardly projecting portions 51e over the mounting holes 55, and the projecting portions 51e have right and left symmetric mounting holes 58 for mounting the engine 9. [0030]
The sub-member 61 has a length in the height
direction which is equivalent to a length from upper portions of the mounting holes 53 to the forked portions 51c of the main member 51, and is formed into a recessed shape shallower than the recessed shape of the main member 51.
The sub-member 61 has a rear wall 61a and side walls 61b bent slightly, forwardly from both sides of the rear wall 61a. The projecting amount of the side wall 61b is small. The sub-member 61 also has an upper portion 61c bent forwardly from the rear wall 61a. The upper portion 61c forms a ceiling portion which is butted to the back side of a bottom surface 32d of the lower member 32 when the middle member 50 is mounted to the lower member 32. A lower end portion of the rear wall 61a has a recess 61d opened downwardly at its central portion in the width direction.
The above sub-member 61 is inserted from the front into the main member 51 and is welded thereto. [0031]
As shown in Fig. 3, the rear member 70 is adapted to connect the rear portion of the main frame 30 to the lower portion of the middle member 50.
The rear member 70 is composed of a main member 71 and a sub-member 74, each of which is formed by press-
working raw steel plates.
The main member 71 has an arch shape in a side view and has a deeply recessed shape in cross - section. The main member 71 includes a rear wall 71a, and right and left side walls 71b. Mounting bosses 72 for mounting the right and left side cowls 15 are integrally provided on intermediate portions of both the side walls 71b. Each of the mounting bosses 72 has a mounting hole 72a. Both side walls 71b also have side cowl mounting holes 72b under the mounting holes 72a. [0032]
The side walls 71b of the main member 71 have lower portions 71c projecting forwardly therefrom, and the lower portions 71c have right and left symmetric forked portions 73 each of which is opened forwardly in a recessed shape. The forked portions 73 are welded to the side walls 51b of the main member 51 of the middle member 50 in such a manner as to hold both side projecting portions of the supporting pipe 54 of the middle member 50.
The sub-member 74 having a recessed shape in cross-section includes a rear wall 74a, and right and left side walls 74b bent forwardly from both sides of the rear wall 74a. The depth of the recessed shape of the sub-member 74
is shallower than that of the main member 71, and as shown in Fig. 3, the sub-member 74 has a length in the height direction which is equivalent to a length from a portion over the forked portion 73 to the side cowl mounting portion 72 of the main member 71.
The sub-member 74 is inserted from the upper sides of the forked portions 73 of the main member 71 into the side cowl mounting bosses 72 of the side walls 71b of the main member 71, and is integrated with the main member 71 by welding the side walls 74b of the sub-member 74 to the side walls 71b of the main member 71. Since the portion of the rear member 70, in which the sub-member 74 is welded to the main member 71, has a closed structure in cross - section, it is reinforced in terms of rigidity and strength. [0033]
The joining structure between the main frame 30 and each of the front member 40, middle member 50, and rear member 70 will be described below with reference to Figs. 6 and 9.
Fig. 6 is an enlarged sectional view taken on line 6-6 of Fig. 3.
The upper member 31 is welded to the lower member 32 to form the hollow main frame 30 having a closed
structure in cross-section. Specifically, the flanges 31c of the upper member 31 are overlapped from above to the opposed flanges 32c of the lower member 32, and are integrally joined thereto by welding specific portions of the flanges 31c to the corresponding portions of the flanges 32c, for example, by spot-welding. In Fig. 6, symbol "a" designate a weld portion of the spot-welding.
The front member 40 is joined to the main frame 30 by butting the upper wall pieces 41f provided at the upper edges of the plate-like portions 41a of the right and left members 41 to outer surfaces of the right and left side walls 32b of the lower member 32 of the main frame 30, and joining them to each other, for example, by spot-welding. [0034]
The pipe-like mounting stay 43 is integrally mounted to the members 41 by allowing the mounting stay 43 to pass through the mounting holes 42a provided in the swelled circular portions 42 and joining the stay 43 to peripheral edges of the mounting holes 42a, for example, by MIG welding. In Fig. 6, symbol "b" designates a weld portion of the MIG welding.
The front ends of the plate-like portions 41a are joined to an outer peripheral portion of the head pipe 22,
for example, by MIG welding. The opposed ends of the lower walls 41b of the plate-like portions 41a are butted to each other, and a gusset 47 is mounted to back surfaces of the lower walls 41b and is joined to outer ends of the lower walls 41b, for example, by MIG welding. In Fig 6, symbol "c" designates a weld portion of the MIG welding. A front end of the gusset 47 is joined to a rear half of a lower portion of the head pipe 22, for example, by MIG welding. [0035]
The projecting amounts of the flanges 31c outwardly from both the sides of the upper member 31 are set to be larger than those of the flanges 32c outwardly from both the sides of the lower member 32. The projecting end of each of the flanges 31c is downwardly bent to form a bent portion 31h having an approximately inverse L-shape in cross-section. In this embodiment, the flanges 31c, positioned under the fuel tank, of the upper member 31 of the main frame 30 are bent downwardly.
With this configuration, it is possible to hidden outer ends of the flanges 32c of the lower member 32, and to enhance the rigidity of the flanges 31 by provision of the bent portions 31h and hence to enhance the rigidity and strength of the upper member 31, and thereby, enhance
the rigidity and strength of the entire main frame 30 including the upper member 31 and the lower member 32 integrated with the upper member 31. [0036]
Fig. 7 is an enlarged sectional view taken on line 7-7 of Fig. 3.
After the upper member 31 is joined to the lower member 32 by welding the flanges 31c and 32c to each other as described above, the mounting stay 38 for mounting accessaries of the engine is joined to one of the side walls 32b of the lower member 32, for example, by spot-welding. In Fig. 7, symbol "d" designates a weld portion of the spot-welding.
The mounting stay 38 including the front and rear mounting pieces 38a positioned on the upper side and a main body 38b positioned on the lower side is formed into an approximately Z-shape in cross - section. The mounting pieces 38a positioned on the upper side are welded on one of the side walls 32b of the lower member 32, and the main body 38b on the lower side is provided with a weld nut 38c for mounting accessaries of the engine. [0037]
Fig. 8 is an enlarged sectional view taken on line 8-8 of Fig. 3.
The mounting portion for mounting the shaft-like cross member 35 as the member for supporting the rear cushion units is shown in Fig. 8. The rear end of the intermediate portion, constituting the above mounting portion, of the main frame 30 is wider than the front portion of the main frame 30 as described above. At the rear end of the intermediate portion, constituting the above mounting portion, of the main frame 30, the side walls 31b including the flanges 31c of the upper member 31 are cutout to form the arcuate recesses 31g and similarly the side walls 32b including the flanges 32c of the lower member 32 are cutout to form the arcuate recesses 32g. The arcuate recesses 31g and 32g are symmetric in the vertical direction. Portions near both the ends of the cross member 35 are put between the recesses 31g and 32g, and are welded to peripheral edges of end portions of the recesses 31g and 32g, for example, by MIG welding. In Fig. 8, symbol "e" designates a weld portion of the MIG welding.
In this way, at the rear end of the intermediate portion of the main frame 30, the cross member 35 is interposed integrally between the upper and lower members 31 and 32 in the width direction, and accordingly it is possible to enhance the rigidity and strength of the rear
end of the intermediate portion of the main frame 30.
Both the ends, designated by reference numeral 35a, of the cross member 35 are small in diameter than a main body of the cross member 35, and mounting bosses 6a provided at upper ends of the right and left rear cushion units 6 are mounted to and supported by both the ends 35a of the cross member 35. [0038]
The rear portion of the main member 71 of the rear member 70 is joined to the back side of the lower member 32 in a range from the rear end of the intermediate portion, to which the cross member 35 is mounted, to the rear portion of the lower member 32.
Concretely, the rear portion of the main member 71 of the rear member 70 is integrally joined to the main frame 30 by locating the rear wall 71a of the main member 71 under the bottom surface 32d of the lower member 32 with a slight gap put therebetween, overlapping the right and left side walls 71b of the main member 71 to outer surfaces of the side walls 32b of the lower member 32, and joining the side walls 71b to the side walls 32b, for example, by spot-welding. In Fig. 8, symbol "f" designates a weld portion of the spot-welding. [0039]
Pig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 3.
At the portion of the upper member 31 of the main frame 30 shown in Fig. 9, the upper surface 31d has the right and left recessed ribs 37 extending in the longitudinal direction as described above.
The above-described sheet mounting stays 81 are welded to outer surfaces of the right and left side walls 32b on the rear side of the lower member 32. The right and left sheet mounting stays 81 form a sheet mounting stay unit having a right/left division structure, and are formed by press-working raw steel plates.
Each of the stays 81 is formed into an
approximately Z-shape in cross - section, but the right and left stays 81, particularly designated by reference numerals 81A and 81B, are different in length in the vertical direction. Upper portions 81a of the stays 81 are butted to the outer surfaces of the right and left side walls 32b on the rear side of the lower member 32 and joined thereto, for example, by spot-welding. In Fig. 9, symbol "g" designates a weld portion of the spot-welding. [0040]
Fig. 10 is an enlarged view seen in the direction
shown by an arrow 10 of Fig. 3.
The gusset 47 is formed into a shape shown in Fig. 10 in a front view. The mounting stay 43 for mounting the front portion of the fuel tank is allowed to pass, from right to left, through the mounting holes 42a formed in the swelled circular portions 42 provided on the right and left members 41 of the front member 40, and is joined to the peripheral edges of the mounting holes 42a, for example, by MIG welding. In Fig. 10, the portion welded by the above MIG welding is, as described above, designated by symbol "b". The right and left ends 43a of the stay 43 project rightwardly and leftwardly from the front member 40. In Fig. 10, the weld portion at the rear end of the gusset 47 is, as described above, designated by symbol "c". [0041]
Opposed ends of lower halves of the lower wall pieces 41b of the right and left members 41 are butted and joined to each other, for example, by MIG welding. In Fig. 10, symbol "h" designates a weld portion of the MIG welding.
Since the front wheel 2 is positioned in front of the above weld portion, the welding is performed in such a manner as not to produce a forwardly projecting weld
portion in consideration of vertical movement of the front wheel 2 resulting from cushion movement thereof, to thereby ensure a sufficient cushion stroke of the front wheel 2.
The projecting pieces 41c provided on the upper portions of the lower wall pieces 41b are vertically overlapped and joined to each other, for example, by spot-welding. In Fig 10, symbol "i" designates a weld portion of the spot-welding. In this case, the weld portion does not project forwardly, so that it is possible to ensure a sufficient cushion stroke of the front wheel 2 like the above case. [0042]
Fig. 11 is an enlarged sectional view taken on line 11-11 of Fig. 3.
The lower portion of the front member 40 is shown in Fig. 11. The lower wall pieces 41b of the right and left members 41, on the front side of the front member 40, are, as shown in Fig. 11, overlapped to each other in the vertical direction, and the outer overlapped edge of the lower wall piece 41b located on the outer side is welded to the other lower wall piece 41b located on the inner side as shown by symbol "h".
The rear wall pieces 41e formed into flange-like
shapes, on the rear side of the front member 40, are overlapped to each other in the lateral direction and are joined to each other, for example, by spot-welding. In Fig. 11, symbol "k" designates a joining portion.
At the rear wall pieces 41e, as described above, the upper and lower pipe-like cross members 46 are allowed to pass, from right to left, through the mounting holes and are joined to peripheral edges of the mounting holes, for example, by MIG welding. In Fig. 11, symbol "j" designates a joining portion. [0043]
A front portion of an engine hanger 82 shown by a chain line in Fig. 3 is connected to the cross members 46 with bolts 83 passing through the cross members 46, and a rear portion of the engine hanger 82 is bolted on a front portion of the crank case of the engine 9. In this way, the engine 9 is mounted and supported by the front member 40.
The front member 40, which is formed by welding the right and left plates formed into recessed shapes by press-working, has a high rigidity closed structure in cross - section as a whole, so that it can strongly and certainly support the front portion of the heavy engine. Also, since the front member 40 has a simple structure
obtained by butting and welding the right and left members 41 to each other and welding the cross members 46 put therebetween to the members 41, it can be easily manufactured. [0044]
Fig. 12 is an enlarged sectional view taken on line 12-12 of Fig. 3.
The main member 51 of the middle member 50 includes the rear wall 51a and the right and left side walls 51b, and is formed by press-working raw steel plates as described above. The main member 51 is, as shown in Fig. 12, formed into a deep recessed shape. The sub-member 61 to be disposed inside the main member 51 similarly includes the rear wall 61a and the right and left side walls 61b, and is similarly formed by press-working raw steel plates. The sub-member 61 is formed into a shallow recessed shape.
The sub-member 61 is inserted inside the main member 51 with a space in the longitudinal direction put between the rear wall 61a of the sub-member 61 and the rear wall 51a of the main member 51, and the side walls 61b and 51b overlapped to each other in the lateral direction, that is, from inside to outside and are joined to each other, for example, by spot-welding. In Fig. 12,
symbol "m" designates a weld portion of the spot-welding. [0045]
The middle member 50 has a high rigidity closed sectional structure in which the auxiliary recessed structure is inserted in the main recessed structure and the right and left sides of the auxiliary recessed structure are welded to those of the main recessed structure, and accordingly, it can exhibit sufficient rigidity and strength necessary for supporting the rear hanger of the engine 9 and the swing arms 4.
An upper portion lOb of the mission case 10 at the rear portion of the engine 9 is held between the projecting portions 51e formed on the side walls 51b of the main member 51 of the middle member 50 and is mounted and supported by the projecting portions 51e with a bolt 64 passing through the mounting holes 58 formed in the projecting portions 51e. [0046]
Fig. 13 is an enlarged view seen in the direction shown by an arrow 13 of Fig. 3.
The right and left forked portions 73 of the main member 71 of the rear member 70 are inserted, from the rear side, around the right and left supporting pipe mounting portions of the main member 51 of the middle
member 50 in such a manner as to hold the supporting pipe 54 therebetween. At the above supporting pipe mounting portions of the main member 51, upper and lower portions 73a of the right and left forked portions 73 overlapped to the side walls 51b of the main member 51 are joined thereto, for example, by spot-welding. In Fig. 3, symbol "n" designates a weld portion of the spot-welding.
Both ends 54a of the supporting pipe 54, which project outwardly from the forked portions 73 overlapped to the side walls 51d, are adapted to turnably support the front ends of the swing arms 4 . [0047]
At the portion, on which the supporting pipe 54 is disposed, of the main member 51, the reinforcing gusset 52 having a recessed shape in cross - section is overlapped and welded to the rear wall 51a and the right and left side walls 51b of the main member 51 in order to reinforce the swing arm supporting portion.
An extending piece 71d, which is provided at the lower end of the rear wall 71a of the main member 71 of the rear member 70, is joined to a lower portion of the rear wall 51a of the main member 51, for example, by spot-welding. In Fig. 13, symbol "p" designates a weld portion of the spot-welding.
The above-described stand mounting cross member 57 is allowed to pass, from right to left, through the lower portion 51d of the main member 51 via the mounting holes 56 and is joined to the lower portion 51d, for example, by MIG welding. In Fig. 13, symbol "q" designates a weld portion of the MIG welding.
The supporting pipe 54 and the stand mounting cross member 57, which are provided at the lower portion of the main member 51 while crossing the main member 51, function as reinforcing beams for enhancing the rigidity and strength of the lower portion of the main member 51 at which the sub-member 61 is not disposed. [0048]
Fig. 14 is an enlarged view seen in the direction shown by an arrow 14 of Fig. 3.
Right and left lower ends of the recessed cutout 61d of the sub-member 61 of the middle member 50 are butted to an upper surface of the supporting pipe 54 and is joined thereto, for example, by MIG welding. In Fig. 14, symbol "r" designates a weld portion of the MIG welding. [0049]
Figs. 15 (a) to 15(e) are views illustrating sequential steps of manufacturing a frame for a
motorcycle according to the present invention.
Fig. 15(a) shows a state before the main member 51 of the middle member 50 as a sub-frame member is assembled to the lower member 32.
The lower recessed portion of the lower member 32, formed by the bottom surface 32d and the right and left side walls 32b, is inserted between the forked portions 51c provided on the upper portion of the main member 51. [0050]
Fig. 15 (b) shows a state in which the main member 51 is assembled to the lower member 32 and is then welded thereto. The right and left side walls 32b are overlapped to the inner surfaces of the forked portions 51c in the lateral direction. Two electrodes G of a spot-welder are respectively pushed on the inner surface of one side wall 32b and the outer surface of the associated forked portion 51c, being pressed and energized, to spot-weld the side wall 32b to the forked portion 51c. In Fig. 15(b), symbol "s" designates a weld portion of the spot-welding.
While only the welding on the right side is shown in Fig. 15(b), the welding on the left side is similarly performed. In this way, the main member 51 is integrally joined to the lower member 32 by welding in such a manner
as to be suspended downwardly from the lower member 32.
The state in which the welding has been performed on the right and left sides is shown in Fig. 15 (c) . [0051]
Fig. 15 (c) shows a state in which the upper member 31 is prepared in the state that the main member 51 of the middle member 50 as a sub-frame member is suspended from the lower member 32. The upper member 31 is overlapped on the lower member 32 in the direction shown by an arrow.
Fig. 15(d) shows a state in which the upper member 31 has been overlapped on the lower member 32. In this state, the flanges 31c of the upper member 31 are overlapped on the flanges 32c of the lower member 32.
Then, the electrodes G of the spot-welder, arranged in the vertical direction, are set to hold one flange 31c and the associated flange 32c, being pressed and energized, to spot-weld the flange 31c to the flange 32c. While the welding on the right side is shown in Fig. 15(d) , the welding on the left side is similarly performed. In Fig. 15 (d) , symbol "a" designates a weld portion of the spot-welding. [0052]
In this way, as shown in Fig. 15 (e) , the main
member 51 is previously welded to the lower member 32 so as to be suspended therefrom, and the upper member 31 is overlapped on the lower member 32 and is joined thereto, for example, by spot-welding the flanges 31c and 32c to each other, to obtain the main frame 30 from which the main member 51 is integrally suspended.
The main frame 30 is shown in Fig. 15 (e) .
The bent portions 31h are formed at the leading ends of the flanges 31c of the upper member 31 for enhancing the rigidity of the flanges 31c and hiding the ends of the flanges 32c of the lower member 32. [0053]
In the method of manufacturing the frame according to the present invention, a sub-frame member is previously suspended downwardly from the lower member before the upper member is joined to the lower member by overlapping and welding the flanges provided on both the ends of the upper member to the flanges provided on both the ends of the lower member so as to form the main frame having a closed sectional structure, and accordingly, the lightweight and easy-to-handle single sub-frame member can be easily assembled to the lightweight and easy-to-handle single lower member by welding using a simple jig.
At the step of overlapping the upper member on the
lower member after welding of the sub-frame member to the lower member, the lightweight and easy-to-handle single upper member can be easily set on the lower member and can be easily joined thereto only by welding the flanges to each other. In this regard, the frame can be easily manufactured in accordance with the present invention.
Since the frame can be manufactured by a simple process, it is possible to reduce the manufacturing cost of the frame for a motorcycle. Further, since the sub-frame member is previously welded to the lower member in such a manner as to be suspended downwardly therefrom, it is possible to increase the degree of freedom in welding between the lower member and the sub-frame member and in arrangement thereof. [0054]
Fig. 16 is a vertical sectional side view of an essential portion of the main frame showing a state in which a containing box is provided in the main frame.
The main frame 30 is a joining structure in which the upper and lower members 31 and 32 each having a recessed sectional shape are joined to each other via the flanges 31c and 32c. The rear portion of the main frame 30 is, as described above, wider than the front portion thereof, and accordingly, a space 90 having a certain
height in the vertical direction can be provided in the rear portion of the main frame 30.
The space 90 can be used as a containing box for containing a thin article such as a tool. An opening portion 91 with a rack is provided in the rear portion of the upper surface 31d of the upper member 31, and a lid 92 openable/closable with a hinge 93 provided at the end of the opening portion 91 is provided to cover the opening portion 91. [0055]
Fig. 17 is a vertical sectional side view of an essential portion of the main frame showing a state in which an alternative example of a containing box is provided in the main frame.
As described above, the upper member 31 is formed by press-working. Upon press-working of the upper member 31, an upwardly swelled portion 131d is simultaneously formed at a suitable location of the rear portion of the upper member 31 by press-working. With this configuration, a space 90 having a height larger than that of the above -described space 90 can be obtained. Like the above embodiment, an opening portion 91 with a rack is provided in an upper surface of the swelled portion 131d, and a lid 92 openable/closable with a hinge 93 provided at the
end of the opening portion 91 is provided to cover the opening portion 91.
According to this embodiment, the space 90 can be used as a containing box for containing a thick article. [0056]
The welding process is not limited to spot-welding and MIG welding used in the above embodiments. For example, an arbitrary resistance welding process such as seam welding or laser welding can be used for joining the frame.
Although the composing member of the frame is formed by press-working a raw steel plate in the above embodiments, it may be formed by press-working an aluminum plate. That is to say, the composing member of the frame can be formed by press-working a metal plate insofar as such a metal plate is weldable and has a high rigidity. [0057]
[Effect of the Invention]
The present invention having the above configuration exhibits the following effects:
According to the invention described in claim 1, there is provided a frame structure for a motorcycle, which is formed by preparing a pair of metal plates
formed into recessed shapes by press-working and integrally joining the metal plates to each other, characterized in that the pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly; the upper member has flanges projecting outwardly from both side ends of the upper member, and the lower member has flanges projecting outwardly from both side ends of the lower member; and the upper member is overlapped from above to the lower member such that the flanges of the upper member are butted to the flanges of the lower member in the vertical direction, and is joined to the lower member by welding the flanges thus butted to each other, to form a main frame having an approximately flat upper surface and being provided with a head pipe joined to a front end of the main frame. Accordingly, a lightweight main frame having the backborn structure, which ensures a desirable rigidity and a desirable strength, can be simply formed by integrally joining metal plates, each of which is formed by press-working, to each other at a low cost. [0058]
In particular, according to the present invention,
the main frame having the backborn structure is obtained by integrally joining the upper member and the lower member, each of which is formed by press-working, to each other by welding the flanges of the upper member to the flanges of the lower member in the vertical direction, and accordingly, it is possible to freely set the width of the frame in the lateral direction of a vehicular body of a motorcycle while keeping constant the length of the frame in the longitudinal direction of the vehicular body unlike an aluminum pipe structure having a closed cross-section obtained, for example, by drawing an aluminum based material. That is to say, it is possible to easily form the main frame having a necessary shape at a low cost.
Since the main frame has an approximately flat upper surface, mounting portions for mounting components such as accessaries, a fuel tank, and a sheet can be directly formed on the upper member without provision of any special members or without necessity of welding of the special members, it is possible to simplify the structure and manufacture of the main frame, reduce the number of parts, reduce the weight of the main frame, and lower the manufacturing cost of the main frame.
Since the upper surface of the main frame is
flattened, it is possible to use simple stays and brackets for mounting and supporting accessaries and other parts, and to simplify the structure for mounting and supporting the stays and brackets to the upper member and the lower member. [0059]
Since the main frame is obtained by joining the upper and lower plates, each of which is formed by press-working, to each other in the vertical direction, the width of each of the front portion and rear portion of the main frame can be freely set such that a head pipe or an engine hanger is allowed to be joined to the front or rear portion, and accessaries, a fuel tank or a sheet is allowed to be mounted on the front or rear portion. Accordingly, it is possible to simplify the structure of these frame members to be mounted to the main frame and facilitate the welding procedure for welding the frame members to the main frame. Since the main frame having the front and rear portion different in terms of width in the lateral direction can be easily obtained, the entire frame having the front and rear portion different in terms of width in the lateral direction can be easily obtained. In this way, it is possible to simplify the structure of the entire frame, facilitate the manufacture
of the entire frame, and reduce the manufacturing cost of the entire frame. Also since the main frame having a hollow structure of a closed cross - section is obtained by joining the upper and lower members to each other by welding the right and left projecting flanges of the upper member to the right and left projecting flanges of the lower member, it is possible to ensure a high rigidity and a high strength enough to be used as a main frame for a motorcycle having an engine with a large displacement. [0060]
According to the invention described in claim 2, in addition to the configuration of the invention described in claim 1, a sub-frame member formed by press-working is joined to the lower member of the main frame in such a manner as to be suspended therefrom. Accordingly, in addition to the effect of the invention described in claim 1, since a sub-frame member other than the members constituting the main frame of the vehicular body is formed by press-working and is welded to the lower member of the main frame, it is possible to simplify the configuration of the components of the vehicular body and also simplify the frame structure.
Since each of the main frame and the sub-frame
member is obtained by integrally joining plates formed by press-working to each other by welding or the like, it is possible to facilitate the manufacture of the frame and hence to manufacture a lightweight vehicular body of a motorcycle having a high rigidity and a high strength at a low cost. [0061]
According to the invention described in claim 3, in addition to the configuration of the invention described in claim 1, outer ends of the flanges of one of the upper member and the lower member of the main frame are bent, and leading ends of the flanges of the other of the upper member and the lower member are covered with the bent portions. Accordingly, in addition to the effect of the invention described in claim 1, since the outer ends of the flanges of one of the upper member and lower member are hidden by the bent portions provided at the outer ends of the other of the upper member and the lower member, it is possible to improve the appearance characteristic of the main frame part of which is possibly is exposed, and also since the edges of the main frame are hidden upon assembly of the entire motorcycle, it is possible to improve the assembling characteristic of the motorcycle.
In particular, according to the present invention, it is possible to further enhance the rigidity and strength of the flanges by provision of the bent portions. That is to say, it is possible to simply increase the rigidity and strength of the flanges by providing the bent portions at the outer ends of the flanges. Such an effect can be realized only by adding the work of bending the leading ends of the flanges to the work of press-forming the flanges. [0062]
According to the invention described in claim 4, in addition to the configuration of the invention described in claim 1, a cross member constituting a mounting portion for mounting rear cushion units is provided at a location of the main frame in such a manner as to be interposed between the upper member and the lower member in the width direction of the same main frame. That is to say, the cross member for mounting the rear cushion units is provided at a location of the main frame, which is of a joining structure having the upper member and the lower member each of which extends substantially over the entire length of the motorcycle, in such a manner as to be interposed between the upper member and the lower member. Accordingly, in addition to the effect of the
invention described in claim 1, it is possible to enhance the rigidity and strength of the main frame extending substantially over the entire length of the motorcycle by provision of the cross member for mounting the rear cushion units at a location of the main frame, and hence to enhance the rigidity and strength of the main frame without necessity of provision of any additional member for improving the rigidity and strength.
The cross member for mounting the rear cushion units can be simply mounted on the main frame by inserting the cross member between the upper member and the lower member and welding it thereto. The welding of the cross member to the upper and lower members can be simultaneously performed along with the welding of the upper member to the lower members. This is advantageous in terms of manufacture of the main frame. Further, since the cross member is integrated with the upper and lower members by welding or the like, it is possible to enhance the rigidity and strength of the portion of the main frame at which the cross member for mounting the rear cushion units is provided. [0063]
According to the invention described in claim 5, in addition to the configuration of the invention described
in claim 1, a mounting portion for mounting a fuel tank and a sheet is integrally formed at a location on the upper surface of the main frame by press-working. Accordingly, in addition to the effect of the invention described in claim I, the mounting portion for mounting a fuel tank and a sheet can be formed on the upper surface of. the main frame without use of any special member.
As a result, it is possible to simplify the structure of the main frame, reduce the components of the main frame, and reduce the number of manufacturing steps, for example, eliminate the welding steps, and since the number of the parts is reduced, it is possible to reduce the weight of the entire frame of the motorcycle and to reduce the manufacturing cost of the frame. [0064]
According to the invention described in claim 6, there is provided a method of manufacturing a frame for a motorcycle, including the steps of: preparing a pair of metal plates formed into recessed shapes by press-working; and integrally joining the metal plates to each other, characterized in that the method includes the steps of: preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side
ends of the lower member, and welding a sub-frame member to side walls of the lower member in such a manner as to suspend the sub-frame member from the lower member; and preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of the upper member, and overlapping the upper member on the lower member and welding the overlapped flanges to each other, to form a main frame. With this configuration, the sub-frame member is previously suspended downwardly from the lower member before the upper member is joined to the lower member by overlapping and welding the flanges provided on both the ends of the upper member to the flanges provided on both the ends of the lower member so as to form the main frame having a closed sectional structure, and accordingly, the lightweight and easy-to-handle single sub-frame member can be easily assembled to the lightweight and easy-to-handle single lower member by welding using a simple jig. [0065]
At the step of overlapping the upper member on the lower member after welding of the sub-frame member to the lower member, the lightweight and easy-to-handle single upper member can be easily set on the lower member and can be easily joined thereto only by welding the flanges
provided on the upper member to the flanges provided on the lower member to each other. In this regard, the frame can be easily manufactured in accordance with the present invention.
Since the frame can be manufactured by a simple process, it is possible to reduce the manufacturing cost of the frame for a motorcycle. Further, since the sub-frame member is previously welded to the lower member in such a manner as to be suspended downwardly therefrom, it is possible to increase the degree of freedom in welding between the lower member and the sub-frame member and in
arrangement thereof.
[Explanation of Symbols]
1: motorcycle, 30: main frame, 22: head pipe, 31: upper member, 32: lower member, 31b, 32b: flange, 31c: bent portion at outer edge of flange, 34: mounting portion for mounting fuel tank and sheet, 35: cross member for mounting rear cushion unit, 40, 50, 70: sub-frame member

WE CLAIM:
1. A frame structure for a motorcycle, which is formed by preparing a pair of metal plates formed into recessed shapes by press-working and integrally joining said metal plates to each other,
characterized in that
said pair of metal plates are composed of an upper member having a recessed sectional shape opened downwardly and a lower member having a recessed sectional shape opened upwardly;
said upper member has flanges projecting outwardly from both side ends of said upper member, and said lower member has flanges projecting outwardly from both side ends of said lower member; and
said upper member is overlapped from above to said lower member such that said flanges of said upper member are butted to said flanges of said lower member in the vertical direction, and is joined to said lower member by welding said flanges thus butted to each other, to form a main frame having an flat upper surface and being provided with a head pipe joined to a front end of said main frame.
2. A frame structure for a motorcycle as claimed in claim 1, wherein a sub-frame member formed by press-working is joined to said lower member of said main frame.
3. A frame structure for a motorcycle as claimed in claim 1, wherein
outer ends of said flanges of one of said upper member and said lower
member of said main frame are bent, and leading ends of said flanges of
the other of said upper member and said lower member are covered with
said bent portions.
4. A frame structure for a motorcycle as claimed in claim 1, wherein a
cross member constituting a mounting portion for mounting rear
cushion units is interposed between said upper member and said lower
member in the width direction of the same main frame.
5. A frame structure for a motorcycle as claimed in claim 1, wherein a
mounting portion for mounting a fuel tank and a sheet is integrally
formed at a location on the upper surface of said main frame by press-
working.
6. In a method of manufacturing a frame for a motorcycle, as claimed
in claim 1, comprising the steps of:
preparing a pair of metal plates formed into recessed shapes by press-working; and
integrally joining said metal plates to each other,
the improvement comprising the steps of:
preparing a lower member having a recessed sectional shape extending longer in the longitudinal direction and including flanges projecting from both side ends-of said lower member, and welding a sub-frame member to side walls of said lower member in such a manner as to suspend said sub-frame member from said lower member; and
preparing an upper member having a recessed sectional shape opened downwardly and including flanges projecting from both side ends of said upper member, and overlapping said upper member on said lower member and welding said overlapped flanges to each other, to form a main frame.
7. A frame structure for a motorcycle substantially as hereinbefore
described with reference to and as illustrated in the accompanying
drawings.
8. In a method of manufacturing a frame for a motorcycle
substantially as hereinbefore described with reference to and as
illustrated in the accompanying drawings.

Documents:

980-del-1999-abstract.pdf

980-del-1999-claims.pdf

980-del-1999-complete specification (granted).pdf

980-del-1999-correspondence-others.pdf

980-del-1999-correspondence-po.pdf

980-del-1999-description (complete).pdf

980-del-1999-drawings.pdf

980-del-1999-form-1.pdf

980-del-1999-form-19.pdf

980-del-1999-form-2.pdf

980-del-1999-form-3.pdf

980-del-1999-form-5.pdf

980-del-1999-gpa.pdf

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Patent Number

208809

Indian Patent Application Number

0980/DEL/1999

PG Journal Number

35/2007

Publication Date

31-Aug-2007

Grant Date

10-Aug-2007

Date of Filing

16-Jul-1999

Name of Patentee

HONDA GIKEN KOGYO KABUSHIKI KAISHA

Applicant Address

1-1, MINAMIAOYAMA 2-CHOME, MINATO-KU, TOKYO,JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	KIYOTAKA FUJIHARA	4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA, JAPAN
2	KAZUHARU WAKUSAKA,	4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA, JAPAN

PCT International Classification Number

B62J17/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	HEI-10-272350	1998-09-25	Japan