Title of Invention

A SIDE VALVE TYPE FOUR STROKE ENGINE

Abstract

A side valve type four stroke engine in which an intake valve (58) and an exhaust valve (59) biased in the valve closing direction and opened/closed in the direction parallel to an axial line of a cylinder bore (31) formed in an engine main body (29) are disposed in said engine main body (29) at positions offset sideways from said cylinder bore (31), and an intake side rocker arm (65) to be brought into contact with the intake valve (58) and an exhaust side rocker arm (66) to be brought into contact with said exhaust valve (59) are rockably supported by said engine main body (29) said engine being characterised in that a rocking fulcrum (PI) of said intake side rocker arm (65), which is supported by said engine main body (29) in such a manner as to be rockable along with the action of a cam (64) common to said intake valve (58) and said exhaust valve (59) , is disposed opposite to an opening/closing axial line (CI) of said intake valve (58) with respect to an opening/closing axial line (CE) of said exhaust valve (59) ; and a rocking fulcrum (CI) of said exhaust side rocker arm (66), which is supported by said engine main body (29) in such a manner as to be rockable along with the action of said cam (64) , is disposed opposite to said opening/closing axial line (CE) of said exhaust valve (59) with respect to said opening/closing axial line of said intake valve (58).

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] PROVISIONAL/COMPLETE SPECIFICATION [See Section 10 and Rule 13; A SIDE VALVE TYPE FOUR STROKE ENGINE HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, having a place of business at.1-1, Minamiaoyama 2-chome, Minato-ku, Tokyo, Japan The following specification particularly describes the nature of the invention and the manner in which it is to be performed : GRANTED 6-5-2005 ORIGINAL 222/MUMNP/2000 The present invention relates to a side valve type four stroke engine. The present invention relates to a side valve type four-cycle engine in whi.ch an intake valve and an exhaust valve biased in the valve closing direction and opened/closed in the direction parallel to an axial line of a cylinder bore formed in an engine main body are disposed in the engine main body at positions offset sideways from the cylinder bore, and an intake side rocker arm to be brought into contact with the intake valve and an exhaust side rocker arm to be brought into contact with the exhaust valve are rockably supported by the engine main body. Such an engine has been known, for example, from Japanese Patent Publication No. Hei 4-21047. [0003] [Problem to be Solved by the Invention] The above-described prior art engine is configured such that intake side and exhaust side rocker arms are rocked while being guided along cam grooves provided in an end surface of a crank web of a crank shaft. The above cam groove is formed into a complicated shape that allows each rocker arm to be returned to the original position for two revolutions of the crank shaft. The formation of such cam grooves in the end surface of the crank web by machining is not easy, and thereby the machining cost is raised. Further, since both the rocker arms are rockably supported by a common supporting shaft fixed to an engine main body and the supporting shaft is disposed at a central portion between opening/closing axial lines of the intake and exhaust valves, a wide gap must be given between the intake and exhaust valves for disposing the supporting shaft. Accordingly, since the gap between the intake and exhaust valves cannot be made narrow, a combustion chamber is required to be made relatively large. [0004] In view of the foregoing, the present invention has been made, and an object of the present invention is to provide a side valve type four-cycle engine, which is capable of making a combustion chamber compact while avoiding an increase in machining cost. [0005] [Means for Solving the Problem] To achieve the above object, according to the present invention, there is provided a side valve type four-cycle engine in which an intake valve and an exhaust valve biased in the valve closing direction and opened/closed in the direction parallel to an axial line of a cylinder bore formed in an engine main body are disposed in the engine main body at positions offset sideways from the cylinder bore, and an intake side rocker arm to be brought into contact with the intake valve and an exhaust side rocker arm to be brought into contact with the exhaust valve are rockably supported by the engine main body, the engine being characterized in that a rocking fulcrum of the intake side rocker arm, which is supported by the engine main body in such a manner as to be rockable along with the action of a cam common to the intake valve and the exhaust valve, is disposed opposite to an opening/closing axial line of the intake valve with respect to an opening/closing axial line of the exhaust valve; and a rocking fulcrum of the exhaust side rocker arm, which is supported by the engine main body in such a manner as to be rockable along with the action of the cam, is disposed opposite to the opening/closing axial line of the exhaust valve with respect to the opening/closing axial line of the intake valve. [0006] With this configuration, since the intake side and exhaust side rocker arms are rocked along with the action of the single cam, it is possible to reduce the machining cost as compared with the prior art configuration in which cam grooves are formed in an end surface of the crank web. Further, since the rocking fulcrum of the intake side rocker arm is disposed opposite to the opening/closing axial line of the intake valve with respect to the opening/closing axial line of the exhaust valve and the rocking fulcrum of the exhaust side rocker arm is disposed opposite to the opening/closing axial line of the exhaust valve with respect to the opening/closing axial line of the intake valve, it is possible to make a gap between the intake and exhaust valves narrow while ensuring the rocked amounts of the intake side and exhaust side rocker arms in accordance with the lift amounts of the intake and exhaust valves, and hence to make the combustion chamber compact. Accordingly, the present invention relates to a side valve type four stroke engine in which an intake valve and an exhaust valve biased in the valve closing direction and opened/closed in the direction parallel to an axial line of a cylinder bore formed in an engine main body are disposed in said engine main body at positions offset sideways from said cylinder bore, and an intake side rocker arm to be brought into contact with the intake valve and an exhaust side rocker arm to be brought into contact with said exhaust valve are rockably supported by said engine main body said engine being characterised in that a rocking fulcrum of said intake side rocker arm, which is supported by said engine main body in such a manner as to be rockable along with the action of a cam common to said intake valve and said exhaust valve, is disposed opposite to an opening/closing axial line of said intake valve with respect to an opening/closing axial line of said exhaust valve; and a rocking fulcrum of said exhaust side rocker arm, which is supported by said engine main body in such a manner as to be rockable along with the action of said cam, is disposed opposite to said opening/closing axial line of said exhaust valve with respect to said opening/closing axial line of said intake valve. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS [Fig. l] A side view of a bicycle with an auxiliary engine. [Fig. 2] A vertical sectional view of the engine, which is equivalent to a sectional view taken on line 2-2 of Fig. 3 . (Fig. 3] A sectional view taken on line 3-3 of Fig. 2. [Fig. 4] A sectional view taken on line 4-4 of Fig. 2. [Fig. 5] An enlarged sectional view taken on line 5-5 of Fig. 4 . [Fig. 6] A sectional view taken on line 6-6 of Fig. 5 showing the engine from which a timing driven gear is omitted. [0007] [Mode for Carrying Out the Invention] Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. [0008] Figs. 1 to 6 show one embodiment of the present invention, wherein Fig. 1 is a side view of a bicycle with an auxiliary engine; Fig. 2 is a vertical sectional view of the engine, which is equivalent to a sectional view taken on line 2-2 of Fig. 3; Fig. 3 is a sectional view taken on line 3-3 of Fig. 2; Fig. 4 is a sectional view taken on line 4-4 of Fig. 2; Fig. 5 is an enlarged sectional view taken on line 5-5 of Fig. 4; and Fig. 6 is a sectional view taken on line 6-6 of Fig. 5 showing the engine from which a timing driven gear is omitted. [0009] Referring first to Fig. 1, a body frame 10 of a bicycle with an auxiliary engine includes a head pipe 11 at the front end of the body frame 10; a down frame 12 extending rearward from the head pipe 11; and a seat post 13 provided in parallel to the head pipe 11, the seat post 13 extending upward from the top of the rear end portion of the down frame 12. The head pipe 11, down frame 12, and seat post 13 are integrally formed from an aluminum alloy or the like by casting. [0010] A front fork 14 is steerably supported by the head pipe 11. A front wheel Wp is rotatably supported by the branched lower ends of the front fork 14, and a steering handlebar 15 is provided at the upper end of the front fork 14. A pair of right and left rear fork portions 16 extend rearward from the rear end of the down frame 12. A rear wheel WR as a drive wheel is rotatably supported between the rear ends of the rear fork portions 16. A pair of right and left stays 17 are provided between the rear ends of the rear fork portions 16 and an intermediate portion of the seat post 13 in the vertical direction. [0011] The seat post 13 is formed into a cylindrical shape. A supporting pipe 18 is inserted from above in the seat post 13 and is fixed thereto. Before the supporting pipe 18 is fixed to the seat post 13, the vertical position of the supporting pipe 18 inserted in the seat post 13 is adjustable. A driver's saddle 20 is mounted on the upper end of the supporting pipe 18. [0012] A front half of the down frame 12 is formed into an approximately U-shape in transverse cross-section with its lower side opened. A fuel tank 21 is contained in the front half of the down frame 12. A cap 22 provided at the upper end of the fuel tank 21 projects upward from the down frame 12. [0013] A pedal shaft 23 is rotatably supported by a rear portion of the down frame 12. Two pedals 24 to be depressed by the driver sitting on the saddle 20 are fixed at both ends of the pedal shaft 23 in such a manner as to be disposed on both sides of the down frame 12. A drive sprocket 25 is disposed on the right side of the down frame 12 (as seen along the running direction of the bicycle with an auxiliary engine) in such a manner as to be coaxial with the pedal shaft 23. An endless chain 27 is wound between a driven sprocket 26 provided coaxially with the rear wheel WR and the drive sprocket 25. [0014] A side valve type four-cycle engine 28, which generates a power for assisting a depressed force of the pedals 24 depressed by the driver, is mounted on a lower portion of the down frame 12 of the body frame 10. In addition, part of the down frame 12 is configured as part of an engine main body 29. [0015] Referring particularly to Figs. 2 to 4, the engine main body 29 of the engine 28 is composed of a cylinder block 30, a cylinder head 32 disposed in front of the cylinder block 30, and a crank case 33 disposed behind the cylinder block 30. The cylinder block 30 is disposed with an axial line of a cylinder bore 31 formed in the cylinder block 30 directed substantially horizontally along the longitudinal direction of the bicycle, and the cylinder head 32 and the crank case 33 are connected to the cylinder block 30. [0016] A piston 34 is slidably fitted in the cylinder bore 31 formed in the cylinder block 30. A crank shaft 36 having the axial line extending along the width direction of the bicycle is connected to the piston 34 via a connecting rod 35. The crank case 33, in which the crank shaft 36 is contained, is composed of a lower case 37 connected to the cylinder block 30, and an upper case 38 formed by the rear portion of the down frame 12. The upper case 3 8 formed by the rear portion of the down frame 12, which is not directly connected to the cylinder block 30, is connected to the lower case 37. A parting plane 39 between the lower case 37 and the upper case 38 is set to be in parallel to the axial line of the cylinder bore 31 and the axial line of the crank shaft 36. [0017] The crank shaft 36 is contained in the lower case 37 of the crank case 33 that is composed of the lower and upper cases 37 and 38. Two portions, positioned on both sides of a crank pin 36a, of the crank shaft 36 are rotatably supported on the lower case 37 side. To be more specific, the crank shaft 36 in this embodiment integrally includes the crank pin 36a to which a connecting rod 35 is connected, crank webs 36b and 36c located on both sides of the crank pin 36a, and crank journals 36d and 36e projecting outwardly from the crank webs 36b and 36c, respectively, and the crank journals 36d and 36e are rotatably supported by holders 40 and 41 fixed in the lower case 37 via ball bearings 42 and 43, respectively. [0018] The holders 40 and 41 are held between the cylinder block 30 and the lower case 37. The cylinder head 32, cylinder block 30, holders 40 and 41, and lower case 37 are co-fastened by means of four stud bolts 44 arranged around the cylinder bore 31 and screwed in the lower case 37 and nuts 45 screwed with the stud bolts 44. To be more specific, the stud bolts 44 with their one-ends planted in the lower case 37 by screwing are inserted in the holders 40 and 41, cylinder block 30 and cylinder head 32, and the nuts 45 are screwed with the other ends, projecting from the cylinder head 32, of the stud bolts 44. The cylinder head 32 is also fastened to the cylinder block 30 by means of one or a plurality of bolts 46 located apart from the arrangement positions of the nuts 45 screwed with the stud bolts 44. [0019] A generator 48 is disposed outside one of the holders 40 and 41, which is located on the left side with respect to the bicycle's posture directed forward in the longitudinal direction of the bicycle, that is, outside the left holder 40. A rotor 49 of the generator 48 is fixed to one end, projecting from the holder 40, of the crank shaft 36. A stator 50 of the generator 48 is fixed to a supporting cylinder 40a that integrally projects from the holder 40 in such a manner as to coaxially surround the one end of the crank shaft 36. [0020] A combustion chamber 54 facing to part of the top of the piston 34 is formed between the cylinder block 30 and the cylinder head 32 in such a manner as to direct forward in the longitudinal direction of the bicycle with its center offset rightward from the axial line of the cylinder bore 31. An ignition plug 57 with its inner end facing to the combustion chamber 54 is mounted in the cylinder head 32. [0021] An intake port 55 communicated to the combustion chamber 54 is provided in an upper portion of the cylinder block 30, and an exhaust port 56 communicated to the combustion chamber 54 is provided in a lower portion of the cylinder block 30. [0022] An intake valve 58 for permitting/forbidding the communication between the intake port 55 and the combustion chamber 54, and an exhaust valve 59 for permitting/forbidding the communication between the exhaust port 56 and the combustion chamber 54 are located over the cylinder bore 31 provided in the cylinder block 30. Both the valves 58 and 59 are supported by the cylinder block 30 in such a manner as to be openable/closable in the direction parallel to the axial direction of the cylinder bore 31, and are biased in the valve closing direction by springs. [0023] The intake valve 58 and the exhaust valve 59 are opened/closed by a valve system 60. The valve system 60 includes a timing drive gear 61 fixed to the crank shaft 36; a timing driven gear 63 rotatably supported by a supporting shaft 62 fixed to the cylinder block 30 and meshed with the timing drive gear 61; a cam 64 integrally formed on the timing driven gear 63; an intake side rocker arm 65 supported by the cylinder block 30 in such a manner as to be rocked along with the action of the cam 64 and linked with the intake valve 58; and an exhaust side rocker arm 66 supported by the cylinder block 30 in such a manner as to be rocked along with the action of the cam 64 and linked with the exhaust valve 59. [0024] The timing drive gear 61 is provided the other end, of the crank shaft 36, positioned outside the holder 41 located on the right side with respect to the bicycle's posture directed forward in the longitudinal direction of the bicycle. The timing drive gear 61 reduces the rotational power of the crank shaft 36 to half, and transmits the rotational power thus reduced to the timing driven gear 63 and the cam 64. In other words, the cam 64 is rotated at a rotational speed that is one half the rotational speed of the crank shaft 36. [0025] Referring particularly to Figs. 5 and 6, a base portion of the intake side rocker arm 65 is rockably supported by a collar 68 fastened to the cylinder block 30 with a bolt 67, and a base portion of the exhaust side rocker arm 66 is rockably supported by a collar 70 fastened to the cylinder block 30 with a bolt 69. The outer surfaces of both the collars 68 and 70 are formed in such a manner as to be eccentric from the axial lines of the bolts 67 and 69, respectively. By changing the relative positions in the peripheral direction of the collars 68 and 70 with respect to the bolts 67 and 69, it is.possible to adjust tappet clearances between the intake valve 58 and the exhaust valve 59 and the intake side and exhaust side rocker arms 65 and 66, respectively. [0026] The collar 68, that is, a rocking fulcrum PI at which the intake side rocker arm 65 is rockably supported by the cylinder block 30 is disposed opposite to an opening/closing axial line CI of the intake valve 58 with respect to an opening/closing axial line CE of the exhaust valve 59. The collar 70, that is, a rocking fulcrum PE at which the exhaust side rocker arm 66 is rockably supported by the cylinder block 30 is disposed opposite to the opening/closing axial line CE of the exhaust valve 59 with respect to the opening/closing axial line CI of the intake valve 58. Intermediate portions of both the rocker arms 65 and 66 are overlapped to each other in such a manner as to be relatively slidable, and tips of both the rocker arms 65 and 66 are brought into slide-contact with the cam 64. [0027] The downstream end of an intake pipe 72 communicated to the intake port 55 is connected to an upper portion of the cylinder block 30, and the upstream end of the intake pipe 72 is connected to the downstream end of a carburetor 73. The carburetor 73, positioned behind the fuel tank 21, is disposed such that part thereof is contained in the down frame 12 of the body frame 10. The upstream end of the exhaust pipe 74 communicated to the exhaust port 56 is connected to a lower portion of the cylinder block 30. The exhaust pipe 74 extends rearward while passing under the engine 28, and is connected to an exhaust muffler 75 (see Fig. 1} disposed between the engine 28 and the rear wheel WR. [0028] Referring again to Fig. 2, both ends of a main shaft 94 having an axial line parallel to that of the crank shaft 36 are rotatably supported by the lower case 37 of the crank case 33. One end of the pedal shaft 23 having an axial line parallel to that of the main shaft 94 is rotatably supported, via a ball bearing 95, by a left side wall (as seen along the running direction of the bicycle) of the upper case 38 of the crank case 33. The outer end of a rotating cylinder shaft 96, which coaxially surrounds the other end side of the pedal shaft 23, is rotatably supported, via a ball bearing 97, by a right side wall (as seen along the running direction of the bicycle) of the upper case 38. The inner end of the rotating cylinder shaft 96 is relatively rotatably supported by the pedal shaft 23. A roller bearing 98 is interposed between the outer end of the rotating cylinder shaft 96 and the pedal shaft 23. That is to say, the pedal shaft 23 and the rotating cylinder shaft 96, which are coaxial with each other, are relatively rotatably supported by the upper case 38 of the crank case 33. The drive sprocket 25 is fixed to the outer end of the rotating cylinder shaft 96. [0029] A primary drive gear 99 is fixed to the one crank web 36c of the pair of the crank webs 36b and 36c of the crank shaft 36. A primary driven gear 100 meshed with the primary drive gear 99 is relatively rotatably supported by the main shaft 94. [0030] A starting clutch 102 including an input member 103 forbidden in its rotation relative to the main shaft 94 and an output gear 104 permitted in its rotation relative to the main shaft 94 is mounted on the main shaft 94. The primary driven gear 100 is connected to the input member 103 of the starting clutch 102 via a damper 101. When the rotational speed of the input member 103 driven by the crank shaft 36 via the primary drive gear 99, primary driven gear 100, and damper 101 exceeds a setting value, the starting clutch 102 transmits a power from the input member 103 to the output gear 104. [0031] The output gear 104 of the starting clutch 102 is connected to a rotating cylinder shaft 96 via a first planetary gear type speed reducer 105. A carrier 106 of the first planetary gear type speed reducer 105 is mounted to the rotating cylinder shaft 96 in such a manner as to be forbidden in its rotation relative to the rotating cylinder shaft 96. A sun gear 107 is meshed with the output gear 104. A ring gear 108 is engaged with the main shaft 94 in such a manner as to be forbidden in its rotation around the axial line of the rotating cylinder shaft 96. [0032] A second planetary gear type speed reducer 111 is mounted to the pedal shaft 23 in such a manner as to be opposed to the first planetary type speed reducer 105 with a gap put therebetween. A carrier 112 of the second planetary gear type speed reducer 111 is engaged with the upper case 38 in such a manner as to be forbidden in its rotation around the axial line of the pedal shaft 23. A ring gear 113 is supported by the pedal shaft 23 in such a manner as to be rotatable around the axial line of the pedal shaft 23, and a sun gear 114 is supported by the ring gear 113 in such a manner as to be rotatable around the axial line of the ring gear 113. [0033] A shifter 115 coaxial with the pedal shaft 23 is mounted, via a helical gear, on the pedal shaft 23 at a position between the first and second planetary gear type speed reducers 105 and 111. A spring 116, which is forbidden in its rotation around the axial line of the pedal shaft 23 by engagement with the upper case 38, is friction.engaged with the outer periphery of the shifter 115. When the pedal shaft 23 is rotated in the direction of forward movement of the bicycle, the shifter 115 being in the state in which the rotation thereof is forbidden by the friction engagement with the spring 116 is moved onto the first planetary gear type speed reducer 105 side. Meanwhile, when the pedal shaft 23 is rotated in the direction of backward movement of the bicycle, the shifter 115 being in the state in which the rotation thereof is forbidden by the friction engagement with the spring 116 is moved onto the second planetary gear type speed reducer 111 side. The shifter 115 can be ratchet-engaged with the carrier 106 of the first planetary gear type speed reducer 105. With this ratchet.engagement, the power transmission from the shifter 115 to the carrier 106 is permitted but the power transmission from the carrier 106 to the shifter 115 is forbidden. Further, the shifter 115 can be ratchet.engaged with the ring gear 113 of the second planetary gear type speed reducer 111. With this ratchet.engagement, the power transmission from the shifter 115 to the ring gear 113 is permitted but the power transmission from the ring gear 113 to the shifter 115 is forbidden. [0034] Accordingly, when the pedal shaft 23 is rotated in the direction of forward movement of the bicycle by depressing the pedals 24, the shifter 115 is moved until it is ratchet-engaged with the carrier 106 of the first planetary gear type speed reducer 105. In such a state, by applying a rotational power over the rotational resistance applied to the shifter 115 by friction engagement with the spring 116 to the pedal shaft 23, the rotational power can be transmitted from the pedal shaft 23 to the rotating cylinder shaft 96 via the shifter 115 and carrier 106. [0035] On the other hand, a helical gear 117 meshed with the outer periphery of the sun gear 114 of the second planetary gear type speed reducer 111 is rotatably supported by the main shaft 94, and a spring 118 forbidden in its rotation around the axial line of the main shaft 94 by engagement with the lower case 37 is friction-engaged with the helical gear 117. A rotating member 119 opposed to the helical gear 117 with a gap put therebetween is mounted on the main shaft 94 in such a manner as to be forbidden in its rotation relative to the main shaft 94. [0036] When the pedal shaft 23 is rotated in the direction of backward movement of the bicycle by depressing the pedals 24, the shifter 115 is moved until it is ratchet-engaged with the ring gear 113 of the second planetary gear type speed reducer 111. In such a state, by applying a rotational power over the rotational resistance applied to the shifter 115 by friction engagement with the spring 116 to the pedal shaft 23, the rotational power is transmitted from the pedal shaft 23 to the helical gear 117 via the shifter 115 and the second planetary gear type speed reducer 111. As a result, the helical gear 117 being in the state in which the rotation thereof is forbidden by friction engagement with the spring 118 is moved to the rotating member 119 side. Further, the helical gear 117 can be ratchet-engaged with the rotating member 119. With this ratchet-engagement, the power transmission from the helical gear 117 to the rotating member 119 is permitted but the power transmission from the rotating member 119 to the helical gear 117 is forbidden. [0037] Accordingly, by rotating the pedal shaft 23 in the direction of backward movement of the bicycle to move the helical gear 117 until the helical gear 117 is ratchet-engaged with the rotating member 119, and applying a rotational power over the rotational resistance applied to the helical gear 117 by friction engagement with the spring 118 to the pedal shaft 23, the rotational power can be transmitted from the pedal shaft 23 to the main shaft 94 via the shifter 115, second planetary gear type speed reducer 111, helical gear 117, and rotating member 119. Further, the rotational power of the main shaft 94 is transmitted to the crank shaft 36 via the clutch plate 86 of the starting clutch 102, damper 101, primary driven gear 100, and primary drive gear 99, with a result that the engine 28 is started. [0038] The function of this embodiment will be described below. The crank case 33 of the engine 28 is formed by connecting the lower and upper cases 37 and 38 dividable along the parting plane 39 extending in parallel to the axial line of the crank shaft 36, and only the lower case 38 is connected to the cylinder block 30. Accordingly, it is possible to simplify the seal structure of the connection plane between the cylinder block 30 and the crank case 33 and hence to improve the sealing performance. [0039] Since the two portions, on both sides of the crank pin 36a, of the crank shaft 36 are rotatably supported by the lower case 37, it is possible to enhance the supporting rigidity of the crank shaft 36 and hence to improve the durability of the crank shaft 36. [0040] Since the parting plane 39 is in parallel to the axial line of the cylinder bore 31 of the cylinder block 30, the lower case 37 can be formed into a bowl-like shape with its upper side opened. This makes it possible to simplify the shape of the lower case 37. [0041] Since the crank shaft 36 is supported by the holders 40 and 41 fixed to the lower case 37 via the ball bearings 42 and 43 respectively, it is possible to accurately support the crank shaft 36 while avoiding the increase number of steps. To be more specific, in the case of adopting a structure in which the crank shaft 36 is supported by bearings mounted in supporting holes formed in a pair of members arranged on both end sides of the crank shaft 36, the supporting accuracy of the crank shaft 36 must be ensured by simultaneously machining the supporting holes of both the members in a state in which the members are assembled. According to the present invention, however, since the ball bearings 42 and 43 are mounted in the holders 40 and 41, it is possible to eliminate the above-described simultaneous machining and hence to accurately support the crank shaft 36 by the holders 40 and 41. [0042] Since the intake side and exhaust side rocker arms 65 and 66 are rocked along with the action of the single cam 64, it is possible to reduce the machining cost as compared with the prior art configuration in which cam grooves are formed in an end surface of the crank web. [0043] Since the rocking fulcrum PI of the intake side rocker arm 65 is disposed opposite to the opening/closing axial line CI of the intake valve 58 with respect to the opening/closing axial line CE of the exhaust valve 59 and the rocking fulcrum PE of the exhaust side rocker arm 66 is disposed opposite to the opening/closing axial line CE of the exhaust valve 59 with respect to the opening/closing axial line CI of the intake valve 58, it is possible to make a gap between the intake and exhaust valves 58 and 59 narrow while ensuring the rocked amounts of the intake side and exhaust side rocker arms 65 and 66 in accordance with the lift amounts of the intake and exhaust valves 58 and 59, and hence to make the combustion chamber 54 compact. [0044] While the embodiment of the present invention has been described in detail, the present invention is not limited thereto, and it is to be understood that various changes in design may be made without departing from the scope of the claim. [0045] [Effect of the Invention] As described above, according to the present invention, it is possible to reduce the machining cost by rocking intake side and exhaust side rocker arms along with the action of a single cam, and also to make a gap between intake and exhaust valves narrow while ensuring the rocked amounts of the intake side and exhaust side rocker arms in accordance with the lift amounts of the intake and exhaust valves, and hence to make the combustion chamber compact. [Explanation of Characters] 28: engine, 29: engine main body, 31: cylinder bore, 58: intake valve, 59: exhaust valve, 64: cam, 65: intake side rocker arm, 66: exhaust side rocker arm, CI: opening/closing axial line of intake valve, CE: opening/closing axial line of exhaust valve, PI: rocking fulcrum of intake side rocker arm, PE: rocking fulcrum of exhaust side rocker arm WE CLAIM 1. A side valve type four stroke engine in which an intake valve (58) and an exhaust valve (59) biased in the valve closing direction and opened/closed in the direction parallel to an axial line of a cylinder bore (31) formed in an engine main body (29) are disposed in said engine main body (29) at positions offset sideways from said cylinder bore (31), and an intake side rocker arm (65) to be brought into contact with the intake valve (58) and an exhaust side rocker arm (66) to be brought into contact with said exhaust valve (59) are rockably supported by said engine main body (29) said engine being characterised in that a rocking fulcrum (PI) of said intake side rocker arm (65), which is supported by said engine main body (29) in such a manner as to be rockable along with the action of a cam (64) common to said intake valve (58) and said exhaust valve (59) , is disposed opposite to an opening/closing axial line (CI) of said intake valve (58) with respect to an opening/closing axial line (CE) of said exhaust valve (59) ; and a rocking fulcrum (CI) of said exhaust side rocker arm (66), which is supported by said engine main body (29) in such a manner as to be rockable along with the action of said cam (64) , is disposed opposite to said opening/closing axial line (CE) of said exhaust valve (59) with respect to said opening/closing axial line of said intake valve (58). 2. A side valve type four stroke engine substantially as hereinbefore described with reference to and illustrated in the accompanying drawings. Dated this 15th day of March, 2000. [JAYANTA PAL] OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

222-mum-2000-cancelled pages(06-05-2005).pdf

222-mum-2000-claims(granted)-(06-05-2005).doc

222-mum-2000-claims(granted)-(06-05-2005).pdf

222-mum-2000-correspondence (28-03-2006).pdf

222-mum-2000-correspondence(ipo)-(15-02-2007).pdf

222-mum-2000-drawings(06-05-2005).pdf

222-mum-2000-form 1(15-03-2000).pdf

222-mum-2000-form 19(15-04-2004).pdf

222-mum-2000-form 2(granted)-(06-05-2005).doc

222-mum-2000-form 2(granted)-(06-05-2005).pdf

222-mum-2000-form 3(106-05-2005).pdf

222-mum-2000-form 3(15-03-2000).pdf

222-mum-2000-form 3(23-02-2001).pdf

222-mum-2000-form 5(15-03-2000).pdf

222-mum-2000-petition under rule 138(06-05-2005).pdf

222-mum-2000-power of authority(06-05-2005).pdf

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