Title of Invention	THERMOSTAT ATTACHMENT STRUCTURE FOR A WATER-COOLED INTERNAL COMBUSTION ENGINE
Abstract	A thermostat attachment structure, for a water-cooled internal combustion engine having a radiator (41) attached to an upper part of the internal combustion engine (30), characterized in that a thermostat (82) is provided inside a cooling water circulating path, which projects into a tank of the radiator and the said thermostat is attached to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator.

Title of Invention

THERMOSTAT ATTACHMENT STRUCTURE FOR A WATER-COOLED INTERNAL COMBUSTION ENGINE

Abstract

A thermostat attachment structure, for a water-cooled internal combustion engine having a radiator (41) attached to an upper part of the internal combustion engine (30), characterized in that a thermostat (82) is provided inside a cooling water circulating path, which projects into a tank of the radiator and the said thermostat is attached to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator.

Full Text	FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "THERMOSTAT ATTACHMENT STRUCTURE FOR A WATER-COOLED INTERNAL COMBUSTION 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 :- ORIGINAL 581/MUMNP/2000 GRANTED 19-4-2005 [Detailed Description Of The Invention] [Technical Field] The present invention relates to a thermostat attachment structure for a water-cooled internal combustion engine, and particularly to a thermostat attachment structure for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine which enables the attachment structure to be simple, improves ease of assembly and reduces cost. [Related Art] Conventionally, in a water-cooled internal combustion engine having a radiator attached to an upper part, when a thermostat is provided in a circulatory path of the cooling water, a cooling fan is disposed between the internal combustion engine and the radiator, the thermostat is interposed between a cooling water outlet opening of the internal combustion engine and an end of a thermostat cover conduit, with the other end of the conduit being connected to a cooling water inlet of the radiator through a hose (Japanese Patent Laid Open No. Hei.5-78642). [Problems To Be Solved By The Invention] However, in the thermostat attachment structure of the related art, a special cover conduit for retaining and covering the thermostat was required, and a hose for connecting this cover conduit to the radiator was also required, which meant that the number of parts was increased, causing, an increase in cost. Also, there are operations of attaching the thermostat cover conduit to the internal combustion engine, and inserting the hose, which makes assembly extremely complicated. The present invention is intended to solve the above described problems with a thermostat attachment structure for a water-cooled internal combustion engine of the related art, and provides a thermostat attachment structure for a water-cooled internal combustion engine that simplifies the attachment structure, improves the ease of assembly and reduces costs, and also improves cooling responsiveness and cooling stability of cooling water by the radiator. [Means Of Solving The Problems] The present invention relates to a thermostat attachment structure for a water-cooled internal combustion engine that solves the above described problems, and the invention disclosed in claim 1 is a thermostat attachment structure, for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine, having a thermostat provided inside a cooling water circulating path, so as to project into a tank of the radiator. The invention disclosed is constructed as described above, and a thermostat is provided inside a circulating path of cooling water, so as to project into a radiator tank, which means that there is no longer any need for the dedicated cover conduit for retaining and covering the thermostat or the hose for connecting the cover conduit to the radiator, as is required in the related art, making it possible to reduce the number of components and the cost. The attachment of these components required in the related art and insertion operations etc. are also not required, making it possible to improve ease of assembly. Also,, since the thermostat cover conduit and the hose are not required, it becomes possible to connect a cooling water entrance of the internal combustion engine to a cooling water entrance of the radiator without connecting piping, the internal combustion engine and the radiator become arranged close together and the thermostat can appropriately control the cooling water circulation by rapidly sensing the effects of the temperature of cooling water-cooled in the radiator (when the thermostat is provided in a cooling water inlet section of the internal combustion engine) or the temperature of cooling water heated by the internal combustion engine (when the thermostat is provided in a cooling water outlet of the internal combustion engine) and it is possible to improve the cooling responsiveness of the radiator cooling water. Also, since the thermostat is affected less by the external air temperature it is possible to appropriately control the cooling water circulation path to cool the internal combustion engine by accurately sensing the temperature of cooling water whose temperature has risen, and it is possible to improve the cooling responsiveness of the cooling water by the radiator. Also, as disclosed in claim 2, with the structure of the invention of claim 1, the thermostat is attached interposed between a cooling water entrance of the internal combustion engine and a cooling water combustion entrance of the radiator. As a result, it is possible to fix the thermostat in the cooling water circulation path using extremely simple means, and it is possible to mount the thermostat so that it projects into a radiator tank. [Embodiments Of The Invention] Embodiments of the present invention disclosed in claim 1 and claim 2 and shown in Fig. 1 to Fig. 8 will now be described. Accordingly there is provided a thermostat attachment structure, for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine, wherein a thermostat is provided inside a cooling water circulating path, so as to project into a tank of the radiator and the said thermostat is attached so as to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator. [Brief Description Of The Drawing] Fig. 1 is a side elevation of as motorcycle mounted with a water-cooled internal combustion engine to which a thermostat attachment structure of an embodiment of the . present invention as disclosed in claim 1 and claim 2 is applied. Fig. 2 is a cross sectional diagram along arrows II - II in Fig. 1, and is a schematic cross sectional drawing of a power unit including a water-cooled internal combustion engine, -taken through a surface including an axial line of a cylinder, orthogonal to a crankshaft. Fig. 3 is a cross sectional diagram along arrows III - III in Fig. 2. Fig. 4 is a cross sectional diagram along arrows IV - IV in Fig. 2, and shows a perspective side view of a radiator section. Fig. 5 is a cross sectional diagram along arrows V - V in Fig. 2. Fig. 6 is an enlarged view of essential portions of Fig. 2. Fig. 7 is a plan view of a radiator. , Fig. 8 is front elevation of a shroud. Fig. 1 is a side elevation of a motorcycle mounted with a water-cooled internal combustion engine to which a thermostat attachment structure of an embodiment of the present invention as disclosed in.claim 1 and claim 2 is applied, Fig. 2 is a cross sectional diagram along arrows II - II in Fig. 1, and is a schematic cross sectional drawing of a power unit including a water-cooled internal combustion engine, taken through a surface including an axial line of a cylinder, orthogonal to a crankshaft, Fig. 3 is a cross sectional diagram along arrows III - III in Fig. 2, Fig. 4 is a cross sectional diagram along arrows IV - IV in Fig. 2, and shows a perspective side view of a radiator section, Fig. 5 is a cross sectional diagram along arrows V - V in Fig. 2, Fig. 6 is an enlarged view of essential portions of Fig. 2, Fig. 7 is a plan view of a radiator, and Fig. 8 is front elevation of a shroud. In the following, "front, rear, left and right" are viewed in the direction of travel of the vehicle, and indicate the front, rear, left and .right of the vehicle. Also, "vehicle center" means a vertical plane running centrally through the wheels fitted to the motorcycle, when viewed from above. As shown in Fig. 1, a motorcycle 2 to which a structure for mounting a radiator to a power unit 7 of this embodiment is applied has a main frame comprising a front frame 3 and a rear frame 4 linked together by bolts 2. A front suspension mechanism from which a front wheel is suspended and a steering mechanism for steering a front wheel 5 are provided on a front section of the front frame 3, while a power unit 7 for driving a rear wheel is provided in front of the rear frame 4, a rear suspension mechanism from which a rear wheel 6 is suspended is provided at a rear section of the rear frame 4 and a seat 8 is provided in front of and above the rear frame 4. A front frame 9, a front cover 10, a floor step 11, a frame body cover 12 and a rear fender 13 are also attached to the motorcycle 1 in that order from the front to the rear, and a pair of side covers 14 are provided on left and right sides of the floor step 11. A storage box 15 for storing a helmet etc. is provided inside the frame body cover 12 underneath the seat 8. The front suspension mechanism is positioned to the right side of the front . wheel 5, and comprises a swingarm 16 supported on a support shaft at a front lower end section of the front frame 3 so as to be capable of swinging up and down, and a shock absorber 17 having one end pivoting at the swingarm 16 and the other end pivoting at the front frame 3. An axle holder 19 is attached to a front end section of the swingarm 16 via a kingpin 18 so as to be capable of swinging in the lateral direction, and the front wheel 5 is rotatably supported on an axle 20 attached to the axle holder 19. The steering mechanism comprises a handle stem 22 rotatably supported on a headpipe 21 attached to a front upper end of the front frame 3, a steering arm 23 supported on a support shaft at a lower end of the handle stem 22 so as to be capable of swinging up and down, and a link 24 having one end pivoted at the steering arm 23 and the other end pivoted at an arm 19a of the axle holder 19. In this way, the steering mechanism and the front suspension mechanism are made mutually independent mechanisms, which improves steerability. The front of the power unit 7 is not shown in detail, but is fixed to a rear frame 4 so as to be capable of swinging by a pair of hangar bolts respectively inserted into hangar holes 26 in brackets 25 respectively attached to a pair of left and right rear frames 4, and pipe bushes 46 (refer to Fig. 2 and Fig. 3) respectively provided at a front end section of a lower crankcase 421 and a front end section of a cylinder head of the internal combustion engine 30 that will be described later. On the other hand, the rear of the power unit 7 is attached to the rear of a left hand rear frame 4 via a shock absorber 27. As a result, the power unit 7 can swing up and down in response to bumps on the road surface when travelling. Also, axes of the two tube bushes 46 are positioned slightly above a horizontal plane including an axis C1 of the crankshaft 31 of the internal combustion engine 30. The two axes are thus positioned beneath an upper surface of the step floor 11, and the power unit 7.except for the radiator 41 is positioned such that its upper surface is substantially flush with the upper surface of the step floor 11, which gives the vehicle a low center of gravity. The power unit 7 comprises the internal combustion engine 30m and a transmission system 90 made up of a transmission 91 and a final reduction gear 110. The internal combustion engine 30 is a spark ignition type 4-cycle single cylinder water-cooled internal combustion engine, and an air introduction pipe 33 extending from an air cleaner 32 arranged underneath the frame body cover 12 is connected to an upstream end of a throttle body 34 arranged on the right side of the vehicle. An intake pipe 35 connected to an intake port of the cylinder head 43 is connected to a downstream end of the throttle body 34, and a fuel injection valve 36 is attached to the intake pipe 35. Fuel is supplied from a fuel tank arranged below the step floor 11 to this fuel injection valve 36. An exhaust muffler 39 connected to an exhaust pipe 38 connected to an exhaust port of the cylinder head 43 is also arranged on the right side of the vehicle. A radiator 41 receiving cooling air blown from a cooling fan 58 arranged in front of the internal combustion engine 30 is arranged above the internal combustion engine 30. The transmission system 90 is provided with a planetary gear type transmission 91, and output of the transmission system is transmitted to the rear wheel 6 by a shaft drive mechanism provided with a drive shaft of the final reduction gear 110 to drive the rear wheel 6. Next, the power unit 7 will be described in more detail. As shown in Fig. 2 and Fig. 3, the internal combustion engine 30 is comprised of a crankcase 42, a cylinder head 43 and a cylinder head cover 44 stacked on top of each other in that order. The crankcase 42 is divided into upper and lower crankcases 42u and 421 by a dividing surface A including the axis of the crank shaft 31 and sloping with respect to a horizontal plane, with a dividing surface for the lower crankcase 421 facing the upper left of the vehicle body. A cylinder 45 having an axis sloping diagonally upwards to the right with respect to the vehicle center is integrally formed with an upper part of the lower crankcase 42u, and the cylinder head 43 is attached to an fitting surface B of the cylinder facing up and to the right of the vehicle. This fitting surface B is sloped relative to the horizontal plane and to the dividing surface A, and a plane including the dividing surface A and a plane including the fitting surface B intersect beyond the lower right of the upper and lower crankcases 42u and 421 (the bottom right in Fig. 2). The upper and lower crankcases 42u and 421 also serve as part of a transmission case 92 for covering the front of the transmission, being a structural element of the transmission system 90 for transmitting drive power of the crankshaft 31 to the rear wheel 6. A tube bush 46 into which a hangar bolt, for supporting the power unit 7 on a bracket 25 of the rear frame 4, is provided on an outer surface of a front left end of the lower crankcase 421. This tube bush 46 is comprised of a cylindrical section 46a integrally formed with the lower crankcase 421, a flexible tube 46b made of a rubber cylinder or the like having an outer surface fixed to an inner surface of cylindrical section 46a, and a metal insertion tube 46c having an outer surface fixed to an inner surface of the flexible tube 46b and a hanger bolt inserted inside. A tube bush 46 having the same structure is also provided on an outer surface of a front right end of the cylinder head 43. The crankshaft 31 arranged in the so called transverse manner, oriented in the longitudinal direction of the vehicle, is rotatably supported in the crankcase 42 by a pair of ball bearings 49 and 50. Each of the ball bearings 49 and 50 is held in a concave groove having a semicircular section respectively formed in the dividing surfaces A of the upper and lower crankcases 42u and 421, and the axis CI of the crankshaft 31 is positioned on the dividing surface A. The crankshaft 31 is driven to rotate by the reciprocating piston 47 via a connecting rod 48 having a little end pivoted at a piston pin of the piston 47 fitted into the cylinder bore of the cylinder 45 so as to be capable of sliding, and a big end pivoted on a crank pin of the crankshaft 31. Also, a balance weight 31a is provided on the crankshaft 31 on the opposite side to the piston pin, to suppress vibrations caused by reciprocation of the piston 47 and the connecting rod 48. The relationship between the dividing surface A, the fitting surface B and the axis of the cylinder 45 will now be described in greater detail. At a reference plane orthogonal to the axis C1 of the crankshaft 31 and including the axis C2 of the cylinder 45, an angle formed by a line intersecting the dividing surface A and the reference surface and a reference vertical line, being a vertical half-line extending upwards from the axis C1 of the crankshaft 31, is an acute angle. An angle formed by the axis of the cylinder 45 and the reference vertical line is also an acute angle, and the two angles a and are substantially the same. An angle y which is a corresponding angle to angle a, formed by a line extended from a line crossing the fitting surface B and the reference plane, and the reference vertical line, is smaller than the angle a . Accordingly, in the reference plane, the dividing surface A, the fitting surface B and the axis of the cylinder 45 also respectively form angle a , angle and angle y with respect to the center CO of the vehicle. The values of these angles , and y are suitably defined taking into account the size of a bank angle to be set. An intake port connecting to the intake pipe 35, an exhaust port connecting to the exhaust pipe 38 and a supercharging port connecting to a discharged air suction pipe connected to a supercharger 52 are respectively formed in the cylinder head 43, and communicate with a combustion chamber formed in an underside of the cylinder head 43. A mixture of fuel injected towards the intake port from the fuel injection valve 36 fitted in the intake pipe 35 and air is supplied to the fuel chamber. A spark plug 51 for igniting this mixture is fitted in the cylinder head 43 projecting into the fuel chamber. A supercharging cylinder 52a forming a housing for the supercharger 52 is engaged in a hole formed in a rear end of the cylinder head 43. A cam shaft 53 oriented in the longitudinal direction of the vehicle is rotatably supported in the cylinder head 43 via a pair of bearings 54 and 55. Each of the bearings 54 and 55 is respectively supported in concave grooves having a semicircular section formed in the lower crankcase 42u and the fitting surface B of the cylinder head 43, and an axis C3 of the cam shaft 53 is positioned on the fitting surface B. With this arrangement of the cam shaft 53, it is possible to keep the height of the cylinder 45 in an axial direction low compared to an internal combustion engine having the cam shaft 53 supported only by the cylinder head 43. As shown in Fig. 3, an alternator 56 is provided on a front end of the crankshaft 31 positioned further forward than a front side ball bearing 49, and a rotor 56a of this alternator 56 is fixed to the crankshaft 31 by passing a bolt thread section of a front end . of the crankshaft 31 through the rotor and screwing on a nut 57. A cooling fan 58 for sending cooling air to the radiator 41 is fixed to the rotor 56a of the alternator 56 using a bolt 59. The periphery of the cooling fan 58 is. covered by a shroud 40 (a fan cover). An air intake 40a is formed in a front section of the shroud 40. On the other hand, a first drive gear 60 and a second drive gear 61 are respectively attached, in that order going to the rear, to a rear side of the crankshaft 31 further back than the ball bearing 50 so as to rotate together with the crankshaft 31. An engagement hole coaxial with the axis C1 of the crankshaft 31 is formed in a rear end surface of the crankshaft 31 a hollow oil pump drive shaft 62a is fitted into the engagement hole, so as to rotate together with the crankshaft 31. . An oil pump 62 is a trochoid type pump, and a rotor 62b is driven to rotate by the oil pump drive shaft 62a inside an inner space of a casing formed using joining surfaces of the upper and lower crankcases 42u and 421 and the transmission case 92. Oil that has accumulated in the bottom of the lower crankcase 421 is sucked through an intake passageway 63 formed in the transmission case 92 by the oil pump 62, and discharged oil is supplied to the cam shaft 53, center shaft 93 of the transmission, and respective bearing sections through oilways provided in the crankcase 42 and the transmission case 92 and an oil pipe. Oil is also supplied to the two ball bearings 49 and 50 or the crankshaft 31 and to sliding sections of the crank pin and the big end of the connecting rod 48 through the inside of the oil pump drive shaft 62a. . The first drive gear 60 meshes with a large gear 65 fitted so as to rotate together with an idler shaft 64. This idler shaft 64 also serves as a balancer shaft, which will be described later. The number of teeth of the large gear 65 is therefore the same as the number of teeth of the first drive gear 60 so that the idler shaft 64 rotates the same number of times as the crankshaft 31. In order to rotate the cam shaft 53, a small gear 66 meshing with a cam gear 67 provided so as to rotate together with the cam shaft 53 is provided integrally with the large gear 65. With this gear train, the cam shaft 53 rotates once for every two rotations of the crankshaft 31. A rotating plate is fitted to a front end of the cam shaft 53, and detection of the engine stroke necessary for fuel injection timing control is carried out by detecting the rotational position of this rotational plate using a rotational position sensor 76. The cam gear 67 is spline fitted to a supercharging crankshaft 52c that causes a supercharging piston 52b of a double-acting supercharger 52 to reciprocate. A hollow section constituting an oilway for supplying oil to sliding sections of respective cams and rocker arms that will be described later is formed in the cam shaft 53, and an elongated section of the supercharging crankshaft 52c is forced into a supercharger side end of this hollow section. In this way, the cam shaft 53 rotates together with the supercharging crankshaft 52c. An intake cam, an exhaust cam and a supercharging cam for respectively driving the an intake valve 68, exhaust valve (not shown) and a supercharging valve 69 to open are provided on the cam shaft 53. Of these three valves, the intake valve 68 is driven to open by a second rocker arm 71 rocked by a rod 72 lowered by a first rocker arm 70 rocked by contact with the intake cam. The exhaust valve is not shown in the drawings, but has a similar structure and is driven to open at a different timing. On the other hand, the supercharging valve 69 is driven to open by a second rocker arm 74 rocked by a rod 75 pushed up by a first rocker arm 73 rocked by contact with the supercharging cam. The idler shaft 64 is arranged oriented in the longitudinal direction of the vehicle arid formed in a stepped cylindrical shape, and is provided with a large cylindrical section 64a and a small cylindrical section 64b. The large cylindrical section 64a and the small cylindrical section 64b are respectively supported so as to be capable of rotation by bearings 77 and 78 held by the upper and lower crank cases 42u and 421. Each of these bearings 77 and 78 is held in a concave groove having a semicircular cross section respectively formed in the dividing surfaces A of the upper and lower crankcases 42u and 42k similarly to the ball bearings 49 and 50 for the crankshaft 31, and the axis of the idler shaft 64 is positioned on the dividing surface A. Also, because the dividing surface A is sloping at an angle a with respect to the vehicle center CO, the axis C4 of the idler shaft 64 is positioned lower down than the axis CI of the crankshaft 31 and on the right side (the left side in the drawing) with respect to the vehicle center. -£0046-] A housing 79a for a cooling water pump 79 (a chamber for a magneto type cooling water pump 79) is housed inside the large cylindrical section 64a of the idler shaft 64, keeping an radial clearance from the inner surface of the large cylindrical section 64a. A cover 79b for the cooling water pump 79 is fitted into this housing 79a, in a fluid-tight manner, and piping (a conduit) 80 from an outlet side tank of the radiator is connected to the cover 79b. Although not shown in detail, a discharge hole 81 communicating with a discharge section of the cooling water pump 79 and communicating with a cooling water jacket 84 formed around the cylinder bore is formed in the upper crankcase 42u (refer to Fig. 2 and Fig. 5). Fig. 5 shows part of an enclosure 128 surrounding the periphery of the alternator 56 looking from the outside. This enclosure 128 is formed protruding from an outer front surface of the upper crankcase 42u. A rotating shaft 79c having one end supported by a roof section of the cover 79b and the other end supported by a bottom of the housing 79a,so as to be capable of rotation, is provided inside a pump chamber formed by the housing 79a and the cover 79b, extending in an axial direction inside a pump chamber. The cooling water pump 79 has three blades, and is provided with an impeller 79d integrally attached to the rotating shaft 79c, with a permanent magnet 79e being attached in a circumferential direction of a shaft section of the impeller 79d. In the clearance between the inner surface of the large cylindrical section 64a of the idler shaft 64 and the housing 79a, the permanent magnet 79f is fitted in the circumferential direction with a microscopic clearance maintained at the inner surface of the large cylindrical section 64a from the housing 79a, and forms a magnetic coupling to a permanent magnet 79e on a shaft section of the impeller 79d. Accordingly, when the idler shaft rotates, the impeller 79d rotates through this magnetic coupling and cooling water flowing into the pump chamber through the conduit 80 is subjected to a rise in pressure by the cooling water pump and is forced into the cooling water jacket 84 through the discharge section of the cooling water pump 79 and the discharge hole in the upper crankcase 42u. As shown in Fig. 2, the radiator 41 is arranged so that it is suspended in the V-shape formed by the lower crankcase 42u and the cylinder head 43, and the left and right ends of the radiator are respectively fixed to an upper left end of the lower crankcase 42u and an upper right end of the cylinder head 43 via a stay (attachment plate) 120 using bolts. Cooling water that has been used to cool high temperature sections of the cylinder 45 and the cylinder head 43 flows from an cooling water outlet of the cylinder head 43 through the thermostat 82 to an inlet side tank 122 ( refer to Fig. 7) of the radiator 41, as shown in Fig. 2. The cooling water outlet of the cylinder head 43 is formed in a projecting tube shape, as shown in Fig. 2 and Fig. 6, and a flow path is established between the cooling water outlet of the cylinder head 43 and the inlet side tank 122 of the radiator 41 by engaging the projecting tube section in a housing chamber 41a formed integrally with the inlet side tank 122 of the radiator 41 through a chamber wall of the housing chamber 41a. The thermostat 82 is arranged and fixed in a cooling water circulation path at a position where the projecting tube section 43a passes through a wall of the housing chamber 41a. The housing chamber 41a is integrally formed with a side section of the inlet side tank 122 of the radiator 41, and comprises part of the inlet side tank 122. The chamber is provided so as to come into contact with a right rear end half of the core section of the radiator 41. The attachment structure of the thermostat 82 will now be described in greater detail with reference to Fig. 2, Fig. 6 and Fig. 7. A concave inlet pipe section 130 receiving the projecting tube section 43a is formed in the chamber wall (bottom wall) of the housing chamber 41a at the section where the projecting tube section 43a passes through the chamber wall of the housing chamber 41a, and a front half section of the projecting tube section 43a is fitted into this concave inlet pipe section 130. An inner end of the concave inlet pipe section 130 is bent inwards to form an annular step section 130a. The concave inlet pipe section 130 constitutes a cooling water inlet of the radiator 41. An annular flange section 82a formed projecting from an outer surface of the body of the thermostat 82 is fitted between an end surface of the projecting tube section . 43a and an inner surface of the step section 130a of the concave inlet pipe section 130 via seal means, thus fitting the thermostat 82 between a cooling water outlet of the cylinder head 43 corresponding to the cooling water outlet of the internal combustion engine 30 and a cooling water inlet of the radiator 41. A valve body section 82b of the thermostat 82 is inserted very deeply into the housing chamber 41a and the thermostat 82 is fitted so as to project deeply into the housing chamber 41a. A wax part of the thermostat 82 is arranged at a cooling water outlet side of the cylinder head 43. Engaging of the projecting tube section 43a with the concave inlet pipe section 130, and the gripping of the thermostat 82 by the inner surface of the projecting tube section 43a and the inner surface of the step section 130a of the concave inlet pipe section 130, are carried out at the same time as arranging and fixing the radiator so that it is suspended in the V-shaped space formed by the lower crankcase 42u and the cylinder head 43, as described previously. Since the radiator 41 is arranged utilizing the space in the V-shape formed by the lower erankcase 42u and the cylinder head 43 in this way, it is possible to reduce the space required by the radiator attachment structure and the power unit 7 can be made compact. This also makes it possible to enlarge the storage space below the seat 8. There is also no longer any need to connect between the cooling water outlet of the cylinder head 43 and the inlet side tank 122 of the radiator 41 using piping such as a hose etc., and there is no need for a dedicated thermostat or troublesome piping, and it is possible to increase the degree of freedom of the piping for peripheral components. In addition,. connecting between cooling water passageways is simplified and cooling performance can be made much more stable by taking the cooling water passageway between the cylinder head 43 and the radiator 41 through the thermostat 82 to make it as short as possible. The structure of the radiator 41 will now be described in greater detail. As shown in Fig. 2, Fig. 4 and Fig. 7, the radiator 41 comprises the inlet side tank 122 and the outlet side tank 123, with these two tanks 122 and 123 being joined by a heat exchanger tube 124 having a number of fins. When viewed from the front, the radiator 41 has an overall shape where a central section that is elongated and swells out more at the top than at the bottom (refer to Fig. 2), and is arranged so as to bridge across the V-shaped space formed by the lower erankcase 42u and the cylinder head 43 and fixed. In plan view, the overall shape of the radiator is rectangular, with only one end section of the inlet side tank for receiving cooling water flowing out from the housing chamber 41a into which the projecting tube section 43a of the cylinder head 43 is fitted formed projecting in a lengthwise direction (refer to Fig. 7). The size and shape of the radiator 41 are suitably determined taking into consideration the weight of cooling water required and the layout of surrounding components etc. Cooling water flows from the inlet side tank 122 into the inside of the heat exchanger tube 124 having a number of fins and is cooled by cooling air blown out from the cooling fan 58. Cooling water that has been cooled inside the firmed heat exchanger tube then flows inside the outlet side tank 123 and is fed from the cooling water outlet 125 provided in one end of the tank 123 to an inlet section of the cooling water pump 79 through the conduit 80. After the cooling air is discharged from the cooling fan 58 it flows into a cooling air duct D while being induced by an elongated cooling air section 40b (refer to Fig. 4 and Fig. 8), formed so that part of an outer wall of the shroud 40 swells out in a radial direction and is elongated in an axial direction, and a shroud wall 126, not shown in the drawings, having a U-shape projecting from an upper surface of the lower crankcase 42u, and flows from the bottom of a space in the V-shape formed by the lower crankcase 42u and the cylinder head 43 to the core section of the radiator 41. Cooling air flowing to the core section of the radiator 41 spreads around the top and both left and right sides of the core and flows out. At this time, the air comes into uniform contact with the heat exchanger tube having a plurality of fins and effective heat exchange is carried out between the cooling water flowing inside the core. A cooling water supply section 127 is provided in an upper part of the inlet side tank 122 of the radiator 41. Although not shown in the drawings, this cooling water supply section 127 is integrally provided with a relief mechanism. A cylindrical weight 83 provided with a partial opening is fitted to an outer surface of the large cylindrical section 64a of the idler shaft 64, so as to provide a balancer for suppressing oscillations caused by rotation of the crankshaft 31 provided with the balance weight 31a and oscillations caused by reciprocation of the piston 47 and the connecting rod 48. As a result, the idler shaft 64 functions as a drive shaft for driving the water pump 79 as well as a balancer shaft. In this way, by having the idler shaft 64 provided with a drive mechanism for driving the cam shaft 53 functioning as a drive shaft for the water pump 79 and as a balancer shaft, it becomes possible to make the internal transmission case 92. The center shaft 93 is supported so that rotation is impossible using a detent section for covering a shaft end fitted to the final reduction gear case 114. The axis C5 of the center shaft 93 is arranged on the dividing surface A of the upper and lower . crankcases 42u and 421. Since, as described above, the front end of the center shaft 93 is supported by the front ends of the upper and lower crankcases 42u and 421 and arranged further to the front of the vehicle than the rear end of the crankshaft 31, it is possible to arranged the crankshaft 31 and the center shaft 93 on top of one another in the longitudinal direction, the length of the power unit 7 in the longitudinal direction can be reduced and a compact power unit 7 is made possible. A second drive gear 61 of the crankshaft 31 meshes with an input gear 94 fitted to a flange provided on a middle section in an axial direction of a flanged boss 101 rotatably engaged with the center shaft 93 of the transmission 91. A rear section of the flanged boss 101 is coupled to a clutch inner 95a of the starting clutch 95 so as to rotate integrally with it, and a starting driven gear 105 meshing with a small gear 104 of the idler shaft forming a reduction mechanism of a starter motor is attached to a front section of the flanged boss 101 via a unidirectional clutch 106. Reference numeral 102 represents a drive gear directly connected to a rotating shaft of the starter motor, and reference numeral 103 represents a large gear of the idler shaft meshing with the drive gear 102. The starting clutch 95 has a clutch inner 95a, a clutch outer 95b and a centrifugal weight, and the starting clutch 95 is put into a completely connected state by connecting the clutch inner 95a and the clutch outer 95b and rotating them together using the operation of the centrifugal weight 95c when the rotational speed of the clutch inner 95a reaches a specified rate. The respective changing clutches 96 - 98 have a planetary gear mechanism and a clutch mechanism. combustion engine 30 compact, and to arrange the plurality of rotating shafts compactly, even in a narrow space. The cam shaft 53 and the idler shaft 64 are arranged at a side where the horizontal plane including the dividing surface A and the horizontal plane including the fitting surface B cross, namely a side where the two planes approach each other, with respect to the axis of the cylinder 45. With this arrangement of the cam shaft 53 and the idler shaft 64, the idler shaft 64 supported in the dividing surface A and the cam shaft 53 supported on the fitting surface B can be arranged close together, and it is possible for the cam shaft 53 and the idler shaft 64 to be joined together directly by a small gear 66 and a cam gear 67, without interposing a separate idler shaft between them. This makes it possible to keep the height of the cylinder 45 in the axial direction low, and to reduce the number of components. Further, this arrangement of the cam shaft 53 and the idler shaft 64 is realized using a narrow space between surfaces of the horizontal plane including the dividing surface A and the horizontal plane including the fitting surface B at a side where they are close to each other is effectively utilized. It is therefore possible to form a wide space at a side surface of the cylinder 45 opposite to the narrow space shutting out the cylinder 45, and the radiator 41, being one the peripheral components described previously, can be arranged in this space. The planetary gear type transmission 91, being a structural element of the transmission system 90 of the power unit 7, is comprised of a center shaft 93, an input gear 94, a starting clutch 95, 2-speed, 3-speed and 4-speed changing clutches 96 - 98, and an output shaft 99. The center shaft 93 oriented in the longitudinal direction of the vehicle is a central shaft of the transmission 91, and a front end of the center shaft 93 is fitted into semicircular grooves formed in inner front surfaces of the upper and lower crankcases 42u and 421, on the dividing surface A of the upper and lower crankcases 42u and 421, while a rear end of the center shaft 93 is inserted into and supported by a support hole of a gear case 114 of the final reduction gear 110 fitted to a rear end surface of the The output gear 107 is fitted to the output gear 99 of the planetary gear type transmission 91 so as to rotate integrally with it, and the outfput gear 107 meshes with a gear 112 fixed to a drive shaft 11 of the final reduction gear 110. A bevel gear, not shown, is formed on a rear end of the drive shaft 111 oriented in the longitudinal direction of the vehicle, and this bevel gear meshes with a driven bevel gear attached to an axle of the rear wheel 6. In this way, rotation of the output shaft 111 is reduced and transmitted to the rear wheel 6 to drive the rear wheel 6. Reference numeral 113 represents a rotational speed sensor. The structure for attaching the radiator 41 to the power unit 7 of this embodiment is constructed as described above, and brings about the following effects. When the radiator 41 is attached to an upper section of the power unit 7, the crankshaft 31 of the power unit 7 is arranged transversely in a longitudinal direction of the vehicle, the cylinder 45 of the power unit 7 is arranged sloping upwards with respect to a right side direction of the vehicle, and the transmission system of the power unit 7 is arranged sloping upwards with respect to a left side direction of the vehicle, and the radiator 41 is arranged suspended in a V-shape formed at an upper part of the power unit 7 by these two sloping sections. As a result of this, it becomes possible to attach the radiator by suspending it utilizing the valley of the V-shape at the upper part of the power unit 7 formed by the two sloping section that would normally be dead space, and it is possible to reduce the space taken up by the attachment structure for the radiator 41. This in turn makes it possible to obtain a wide storage space below the seat 8 above the radiator 41. Since, it is possible to attach the radiator 41 to an upper part of the power unit 7 above the axis of the cylinder 45 arranged sloping upwards in the left side direction of the vehicle looking in the longitudinal of the vehicle, it becomes possible to attach the radiator 41 to a front section of the power unit 7, and the position of the radiator is close to a hinged section pivotally supporting the power unit 7 so that it can be swung by hangar bolts. This in tum means that when the power unit 7 is swinging, shaking of the radiator 41 is slight, displacement of the upper part of the radiator 41 (a cap etc. provided with a cooling water supply section 127) becomes small and there is no need to fix the radiator 41 in a particularly stable manner to the power unit 7 with respect to swinging displacement. This means that the attachment strength of the radiator can be reduced, and that alone simplifies the structure for attaching the radiator to the power unit 7. Further, since the cooling fan 58 is attached to one end of the crankshaft 31, the cooling fan 58 is covered by the shroud 40 and cooling air blown from the cooling fan 58 is led to the radiator 41, it is possible to attach the cooling fan 58 close to the radiator 41 making it possible to improve the cooling performance of the radiator 41. It is also possible to reduce the size of the shroud 40. In this embodiment, the radiator 41 is suspended between V-shaped upper sections of the power unit 7, but it can be expected that such a V-shape will not always be possible, depending, on the structure of the water-cooled internal combustion engine 30 or the power unit 7. In such cases, it is possible to make the bottom of the radiator 41 into a suitably concave shape and form a space corresponding to the V-shape to either enable this space to act as a cooling duct or provide a fan in the space. The attachment structure for the thermostat 92 of this embodiment has the above described structure and enables the following effects. Since the thermostat 82 is provided in a circulation path of the cooling water so as to project into a housing chamber 41a constituting part of an inlet side tank 122 of the radiator 41, there is no longer any need for a cover conduit specifically for holding and covering the thermostat 82 or a hose for connecting this conduit to the radiator 41, as in the related art, which makes it possible to reduce the number of components and to reduce the cost. Also, attachment components that were required in the related art and insertion operations etc. are also no longer necessary which means that it is possible to improve the ease of assembly of the radiator 41 and the thermostat 82. Also, since there is no need for a conduit for the thermostat cover or the hose, the cooling water outlet of the internal combustion engine 30 and the cooling water inlet of the radiator 41 can be connected together without connecting piping, the internal combustion engine 30 and the radiator 41 are arranged close together, the thermostat 82 can appropriately control circulation of cooling water by rapidly detecting effects of the temperature of cooling water that has been heated by the internal combustion engine 30 and it is possible to improve the cooling responsiveness of the radiator cooling water. Also, since the thermostat 82 is affected less by external temperature it is possible to appropriately control the circulation path of cooling water by accurately sensing the temperature of cooling water that has been heated up by cooling the internal combustion engine 30, and it is possible to improve the cooling stability of the cooling water used in the radiator 41. Since the thermostat 82 is attached in between the projecting tube section 43a of the cylinder head 43 forming a cooling water outlet of the internal combustion engine 30 and a concave inlet pipe section 130 of the housing chamber 41a forming a cooling water inlet of the radiator 41, it is possible to fix the thermostat 82 in the circulating path of the cooling water using simple means, and it is possible to provide the thermostat 82 so that it projects into a tank (housing chamber 41a) of the radiator 41. In this embodiment, the projecting tube section 43a part of the cylinder head 43 is made a cooling water outlet of the internal combustion engine 30 and the housing chamber 41a formed integrally with a side section of the inlet side tank 122 of the radiator 41 is made a cooling water inlet of the radiator 41, but this is not limiting, and it is also possible to reverse the circulating direction of the cooling water and make the housing chamber 41a the cooling water outlet of the radiator 41 and make the projecting tube section 43a part the cooling water inlet of the internal combustion engine 30. In this case also it is possible for the thermostat 82 to suitable control circulation of the cooling water by rapidly detecting temperature effects of the cooling water in the radiator 41 and it is possible to improve the cooling responsiveness of cooling water used in the radiator. Since the thermostat 82 is affected less by external temperature, it is possible to improve the cooling stability of cooling water used in the radiator 41. In this case, it is also possible to reverse the orientation of the thermostat 82 and arrange a wax section 131 of the thermostat 82 on the housing chamber 41a side. Also, positions where the cooling water outlet of the internal combustion engine 30 and the cooling water inlet of the radiator 41 are connected without a hose can be provided on the cylinder 45 side. In this case, the projecting cylinder section is fitted into the concave inlet pipe section 130 of the housing chamber 41a of the radiator 41 by forming a projecting cylinder section (corresponding to the projecting tube section 43a of the cylinder head 43) communicating with the cooling water jacket 84 in the cylinder 45 and suitably reducing the size of the radiator 41 etc. The thermostat 82 is then arranged in engagement sections of the projecting tube section and the concave inlet pipe section 130. The projecting tube section 43a part of the cylinder head 43 is made a cooling water inlet and this cooling water inlet communicates with a discharge section of the water pump 79. In this way also, the same effects as described above can be obtained. It is also possible to use a reverse cooling water circulating direction in the piping connection structure between the internal combustion engine 30, the radiator 41 and the water pump 79. In this embodiment, the water-cooled internal combustion engine 30 is integral with the transmission system 90 and constitutes part of the power unit 7, but this is not limiting and it is also possible to have a water-cooled internal combustion engine that is not integral with the transmission system 90, or to have a water-cooled internal combustion engine with a single cylinder or a plurality of cylinders arranged at an upper part so that a radiator can be attached, and the attachment structure for the thermostat 82 of this embodiment.can also, be applied to this ty.pe of water-.cooled combustion engine. [Description Of The Numerals] 31 crankshaft 31a balance weight 32 air cleaner 33 air introduction pipe 34 throttle body 35 intake pipe 36 fuel injection valve 37 fuel tank 38 exhaust pipe 39 exhaust muffler 40 shroud (fan cover) 40a air intake 40b elongated baffle section 41 radiator 41a housing chamber 42 crankcase 42u, 421 upper and lower crankcases 43 cylinder head 43a projecting tube section 44 cylinder.head cover 45 cylinder 46 pipe bush 46a cylinder section 46b . flexible pipe 46c metal insertion tube 47 piston 48 connecting rod 49, 50 ball bearing 51 spark plug 52 piston type supercharger 52c supercharging crankshaft 53 cam shaft 54,55 bearing 56 alternator 56a rotor 57 stator 58 cooling fan 59 bolt 60 first drive gear 61 second drive gear 62 oil pump 62a oil pump drive shaft 62 b rotor 63 intake passageway 64 idler shaft 64a large cylindrical section 64b small cylindrical section 65 large gear 66 small gear 67 cam gear 68 intake valve 69 supercharging valve 70 first rocker arm 71 second rocker arm 72 rod .. 73 first rocker arm 74 second rocker arm 75 rod 76 rotation position sensor 77,78 bearing 79 cooling water pump 79a housing 79b cover 79c rotating shaft 79d impeller We Claim: 1. A thermostat attachment structure, for a water-cooled internal combustion engine having a radiator (41) attached to an upper part of the internal combustion engine (30), characterized in that a thermostat (82) is provided inside a cooling water circulating path, which projects into a tank of the radiator and the said thermostat is attached to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator. 2. A thermostat attachment structure for a water-cooled internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings. Dated this 23rd day of June, 2000. (JAYANTA PAL) OF REMFRY & SAGAR ATTORNEY FOR THF APPLICANTS

Full Text

FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
COMPLETE SPECIFICATION
[See Section 10]
"THERMOSTAT ATTACHMENT STRUCTURE FOR A WATER-COOLED INTERNAL COMBUSTION 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 :-

ORIGINAL
581/MUMNP/2000

GRANTED
19-4-2005

[Detailed Description Of The Invention]
[Technical Field]
The present invention relates to a thermostat attachment structure for a water-cooled internal combustion engine, and particularly to a thermostat attachment structure for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine which enables the attachment structure to be simple, improves ease of assembly and reduces cost.
[Related Art]
Conventionally, in a water-cooled internal combustion engine having a radiator attached to an upper part, when a thermostat is provided in a circulatory path of the cooling water, a cooling fan is disposed between the internal combustion engine and the radiator, the thermostat is interposed between a cooling water outlet opening of the internal combustion engine and an end of a thermostat cover conduit, with the other end of the conduit being connected to a cooling water inlet of the radiator through a hose (Japanese Patent Laid Open No. Hei.5-78642).

[Problems To Be Solved By The Invention]
However, in the thermostat attachment structure of the related art, a special cover conduit for retaining and covering the thermostat was required, and a hose for connecting this cover conduit to the radiator was also required, which meant that the number of parts was increased, causing, an increase in cost. Also, there are operations of attaching the thermostat cover conduit to the internal combustion engine, and inserting the hose, which makes assembly extremely complicated.
The present invention is intended to solve the above described problems with a thermostat attachment structure for a water-cooled internal combustion engine of the related art, and provides a thermostat attachment structure for a water-cooled internal combustion engine that simplifies the attachment structure, improves the ease of assembly and reduces costs, and also improves cooling responsiveness and cooling stability of cooling water by the radiator. [Means Of Solving The Problems]
The present invention relates to a thermostat attachment structure for a water-cooled internal combustion engine that solves the above described problems, and the invention disclosed in claim 1 is a thermostat attachment structure, for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine, having a thermostat provided inside a cooling water circulating path, so as to project into a tank of the radiator.
The invention disclosed is constructed as described above, and a thermostat is provided inside a circulating path of cooling water, so as to project into a radiator tank, which means that there is no longer any need for the dedicated cover conduit for retaining and covering the thermostat or the hose for connecting the cover conduit to the radiator, as is required in the related art, making it possible to reduce the number of components and the cost. The attachment of these components required in the related art and insertion operations etc. are also not required, making it possible to improve ease of
assembly.

Also,, since the thermostat cover conduit and the hose are not required, it becomes possible to connect a cooling water entrance of the internal combustion engine to a cooling water entrance of the radiator without connecting piping, the internal combustion engine and the radiator become arranged close together and the thermostat can appropriately control the cooling water circulation by rapidly sensing the effects of the temperature of cooling water-cooled in the radiator (when the thermostat is provided in a cooling water inlet section of the internal combustion engine) or the temperature of cooling water heated by the internal combustion engine (when the thermostat is provided in a cooling water outlet of the internal combustion engine) and it is possible to improve the cooling responsiveness of the radiator cooling water.
Also, since the thermostat is affected less by the external air temperature it is possible to appropriately control the cooling water circulation path to cool the internal combustion engine by accurately sensing the temperature of cooling water whose temperature has risen, and it is possible to improve the cooling responsiveness of the cooling water by the radiator.
Also, as disclosed in claim 2, with the structure of the invention of claim 1, the thermostat is attached interposed between a cooling water entrance of the internal combustion engine and a cooling water combustion entrance of the radiator.
As a result, it is possible to fix the thermostat in the cooling water circulation path using extremely simple means, and it is possible to mount the thermostat so that it projects into a radiator tank.
[Embodiments Of The Invention]
Embodiments of the present invention disclosed in claim 1 and claim 2 and shown in Fig. 1 to Fig. 8 will now be described.

Accordingly there is provided a thermostat attachment structure, for a water-cooled internal combustion engine having a radiator attached to an upper part of the internal combustion engine, wherein a thermostat is provided inside a cooling water circulating path, so as to project into a tank of the radiator and the said thermostat is attached so as to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator.
[Brief Description Of The Drawing]
Fig. 1 is a side elevation of as motorcycle mounted with a water-cooled internal
combustion engine to which a thermostat attachment structure of an embodiment of the . present invention as disclosed in claim 1 and claim 2 is applied.
Fig. 2 is a cross sectional diagram along arrows II - II in Fig. 1, and is a schematic cross
sectional drawing of a power unit including a water-cooled internal combustion engine, -taken through a surface including an axial line of a cylinder, orthogonal to a crankshaft.
Fig. 3 is a cross sectional diagram along arrows III - III in Fig. 2.
Fig. 4 is a cross sectional diagram along arrows IV - IV in Fig. 2, and shows a
perspective side view of a radiator section.
Fig. 5 is a cross sectional diagram along arrows V - V in Fig. 2.
Fig. 6 is an enlarged view of essential portions of Fig. 2.

Fig. 7 is a plan view of a radiator. ,
Fig. 8 is front elevation of a shroud.

Fig. 1 is a side elevation of a motorcycle mounted with a water-cooled internal combustion engine to which a thermostat attachment structure of an embodiment of the present invention as disclosed in.claim 1 and claim 2 is applied, Fig. 2 is a cross sectional diagram along arrows II - II in Fig. 1, and is a schematic cross sectional drawing of a power unit including a water-cooled internal combustion engine, taken through a surface including an axial line of a cylinder, orthogonal to a crankshaft, Fig. 3 is a cross sectional diagram along arrows III - III in Fig. 2, Fig. 4 is a cross sectional diagram along arrows IV - IV in Fig. 2, and shows a perspective side view of a radiator section, Fig. 5 is a cross sectional diagram along arrows V - V in Fig. 2, Fig. 6 is an enlarged view of essential portions of Fig. 2, Fig. 7 is a plan view of a radiator, and Fig. 8 is front elevation of a shroud.
In the following, "front, rear, left and right" are viewed in the direction of travel of the vehicle, and indicate the front, rear, left and .right of the vehicle. Also, "vehicle center" means a vertical plane running centrally through the wheels fitted to the motorcycle, when viewed from above.
As shown in Fig. 1, a motorcycle 2 to which a structure for mounting a radiator to a power unit 7 of this embodiment is applied has a main frame comprising a front frame 3 and a rear frame 4 linked together by bolts 2.
A front suspension mechanism from which a front wheel is suspended and a steering mechanism for steering a front wheel 5 are provided on a front section of the front frame 3, while a power unit 7 for driving a rear wheel is provided in front of the rear frame 4, a rear suspension mechanism from which a rear wheel 6 is suspended is provided at a rear section of the rear frame 4 and a seat 8 is provided in front of and above the rear frame 4.
A front frame 9, a front cover 10, a floor step 11, a frame body cover 12 and a rear fender 13 are also attached to the motorcycle 1 in that order from the front to the rear, and a pair of side covers 14 are provided on left and right sides of the floor step 11. A storage box 15 for storing a helmet etc. is provided inside the frame body cover 12 underneath the seat 8.
The front suspension mechanism is positioned to the right side of the front . wheel 5, and comprises a swingarm 16 supported on a support shaft at a front lower end

section of the front frame 3 so as to be capable of swinging up and down, and a shock absorber 17 having one end pivoting at the swingarm 16 and the other end pivoting at the front frame 3. An axle holder 19 is attached to a front end section of the swingarm 16 via a kingpin 18 so as to be capable of swinging in the lateral direction, and the front wheel 5 is rotatably supported on an axle 20 attached to the axle holder 19.

The steering mechanism comprises a handle stem 22 rotatably supported on a headpipe 21 attached to a front upper end of the front frame 3, a steering arm 23 supported on a support shaft at a lower end of the handle stem 22 so as to be capable of swinging up and down, and a link 24 having one end pivoted at the steering arm 23 and the other end pivoted at an arm 19a of the axle holder 19.
In this way, the steering mechanism and the front suspension mechanism are made mutually independent mechanisms, which improves steerability.
The front of the power unit 7 is not shown in detail, but is fixed to a rear frame 4 so as to be capable of swinging by a pair of hangar bolts respectively inserted into hangar holes 26 in brackets 25 respectively attached to a pair of left and right rear frames 4, and pipe bushes 46 (refer to Fig. 2 and Fig. 3) respectively provided at a front end section of a lower crankcase 421 and a front end section of a cylinder head of the internal combustion engine 30 that will be described later.
On the other hand, the rear of the power unit 7 is attached to the rear of a left hand rear frame 4 via a shock absorber 27.
As a result, the power unit 7 can swing up and down in response to bumps on the road surface when travelling.
Also, axes of the two tube bushes 46 are positioned slightly above a horizontal plane including an axis C1 of the crankshaft 31 of the internal combustion engine 30. The two axes are thus positioned beneath an upper surface of the step floor 11, and the power unit 7.except for the radiator 41 is positioned such that its upper surface is substantially flush with the upper surface of the step floor 11, which gives the vehicle a low center of gravity.

The power unit 7 comprises the internal combustion engine 30m and a transmission system 90 made up of a transmission 91 and a final reduction gear 110.
The internal combustion engine 30 is a spark ignition type 4-cycle single cylinder water-cooled internal combustion engine, and an air introduction pipe 33 extending from an air cleaner 32 arranged underneath the frame body cover 12 is connected to an upstream end of a throttle body 34 arranged on the right side of the vehicle. An intake pipe 35 connected to an intake port of the cylinder head 43 is connected to a downstream end of the throttle body 34, and a fuel injection valve 36 is attached to the intake pipe 35. Fuel is supplied from a fuel tank arranged below the step floor 11 to this fuel injection valve 36.
An exhaust muffler 39 connected to an exhaust pipe 38 connected to an exhaust port of the cylinder head 43 is also arranged on the right side of the vehicle. A radiator 41 receiving cooling air blown from a cooling fan 58 arranged in front of the internal combustion engine 30 is arranged above the internal combustion engine 30.
The transmission system 90 is provided with a planetary gear type transmission 91, and output of the transmission system is transmitted to the rear wheel 6 by a shaft drive mechanism provided with a drive shaft of the final reduction gear 110 to drive the rear wheel 6.
Next, the power unit 7 will be described in more detail. As shown in Fig. 2 and Fig. 3, the internal combustion engine 30 is comprised of a crankcase 42, a cylinder head 43 and a cylinder head cover 44 stacked on top of each other in that order.
The crankcase 42 is divided into upper and lower crankcases 42u and 421 by a dividing surface A including the axis of the crank shaft 31 and sloping with respect to a horizontal plane, with a dividing surface for the lower crankcase 421 facing the upper left of the vehicle body. A cylinder 45 having an axis sloping diagonally upwards to the right with respect to the vehicle center is integrally formed with an upper part of the lower crankcase 42u, and the cylinder head 43 is attached to an fitting surface B of the cylinder facing up and to the right of the vehicle.

This fitting surface B is sloped relative to the horizontal plane and to the dividing surface A, and a plane including the dividing surface A and a plane including the fitting surface B intersect beyond the lower right of the upper and lower crankcases 42u and 421 (the bottom right in Fig. 2).
The upper and lower crankcases 42u and 421 also serve as part of a transmission case 92 for covering the front of the transmission, being a structural element of the transmission system 90 for transmitting drive power of the crankshaft 31 to the rear wheel 6.
A tube bush 46 into which a hangar bolt, for supporting the power unit 7 on a bracket 25 of the rear frame 4, is provided on an outer surface of a front left end of the lower crankcase 421. This tube bush 46 is comprised of a cylindrical section 46a integrally formed with the lower crankcase 421, a flexible tube 46b made of a rubber cylinder or the like having an outer surface fixed to an inner surface of cylindrical section 46a, and a metal insertion tube 46c having an outer surface fixed to an inner surface of the flexible tube 46b and a hanger bolt inserted inside. A tube bush 46 having the same structure is also provided on an outer surface of a front right end of the cylinder head 43.
The crankshaft 31 arranged in the so called transverse manner, oriented in the longitudinal direction of the vehicle, is rotatably supported in the crankcase 42 by a pair of ball bearings 49 and 50. Each of the ball bearings 49 and 50 is held in a concave groove having a semicircular section respectively formed in the dividing surfaces A of the upper and lower crankcases 42u and 421, and the axis CI of the crankshaft 31 is positioned on the dividing surface A.
The crankshaft 31 is driven to rotate by the reciprocating piston 47 via a connecting rod 48 having a little end pivoted at a piston pin of the piston 47 fitted into the cylinder bore of the cylinder 45 so as to be capable of sliding, and a big end pivoted on a crank pin of the crankshaft 31. Also, a balance weight 31a is provided on the crankshaft 31 on the opposite side to the piston pin, to suppress vibrations caused by reciprocation of the piston 47 and the connecting rod 48.

The relationship between the dividing surface A, the fitting surface B and the axis of the cylinder 45 will now be described in greater detail.
At a reference plane orthogonal to the axis C1 of the crankshaft 31 and including the axis C2 of the cylinder 45, an angle formed by a line intersecting the dividing surface A and the reference surface and a reference vertical line, being a vertical half-line extending upwards from the axis C1 of the crankshaft 31, is an acute angle. An angle formed by the axis of the cylinder 45 and the reference vertical line is also an acute angle, and the two angles a and are substantially the same.
An angle y which is a corresponding angle to angle a, formed by a line extended from a line crossing the fitting surface B and the reference plane, and the reference vertical line, is smaller than the angle a . Accordingly, in the reference plane, the dividing surface A, the fitting surface B and the axis of the cylinder 45 also respectively form angle a , angle and angle y with respect to the center CO of the vehicle. The values of these angles , and y are suitably defined taking into
account the size of a bank angle to be set.
An intake port connecting to the intake pipe 35, an exhaust port connecting to the exhaust pipe 38 and a supercharging port connecting to a discharged air suction pipe connected to a supercharger 52 are respectively formed in the cylinder head 43, and communicate with a combustion chamber formed in an underside of the cylinder head 43.
A mixture of fuel injected towards the intake port from the fuel injection valve 36 fitted in the intake pipe 35 and air is supplied to the fuel chamber. A spark plug 51 for igniting this mixture is fitted in the cylinder head 43 projecting into the fuel chamber. A supercharging cylinder 52a forming a housing for the supercharger 52 is engaged in a hole formed in a rear end of the cylinder head 43.
A cam shaft 53 oriented in the longitudinal direction of the vehicle is rotatably supported in the cylinder head 43 via a pair of bearings 54 and 55. Each of the bearings 54 and 55 is respectively supported in concave grooves having a semicircular section

formed in the lower crankcase 42u and the fitting surface B of the cylinder head 43, and an axis C3 of the cam shaft 53 is positioned on the fitting surface B. With this arrangement of the cam shaft 53, it is possible to keep the height of the cylinder 45 in an axial direction low compared to an internal combustion engine having the cam shaft 53 supported only by the cylinder head 43.
As shown in Fig. 3, an alternator 56 is provided on a front end of the crankshaft 31 positioned further forward than a front side ball bearing 49, and a rotor 56a of this alternator 56 is fixed to the crankshaft 31 by passing a bolt thread section of a front end . of the crankshaft 31 through the rotor and screwing on a nut 57. A cooling fan 58 for sending cooling air to the radiator 41 is fixed to the rotor 56a of the alternator 56 using a bolt 59. The periphery of the cooling fan 58 is. covered by a shroud 40 (a fan cover). An air intake 40a is formed in a front section of the shroud 40.
On the other hand, a first drive gear 60 and a second drive gear 61 are respectively attached, in that order going to the rear, to a rear side of the crankshaft 31 further back than the ball bearing 50 so as to rotate together with the crankshaft 31. An engagement hole coaxial with the axis C1 of the crankshaft 31 is formed in a rear end surface of the crankshaft 31 a hollow oil pump drive shaft 62a is fitted into the engagement hole, so as to rotate together with the crankshaft 31.
. An oil pump 62 is a trochoid type pump, and a rotor 62b is driven to rotate by the oil pump drive shaft 62a inside an inner space of a casing formed using joining surfaces of the upper and lower crankcases 42u and 421 and the transmission case 92.

Oil that has accumulated in the bottom of the lower crankcase 421 is sucked through an intake passageway 63 formed in the transmission case 92 by the oil pump 62, and discharged oil is supplied to the cam shaft 53, center shaft 93 of the transmission, and respective bearing sections through oilways provided in the crankcase 42 and the transmission case 92 and an oil pipe. Oil is also supplied to the two ball bearings 49 and 50 or the crankshaft 31 and to sliding sections of the crank pin and the big end of the connecting rod 48 through the inside of the oil pump drive shaft 62a.

. The first drive gear 60 meshes with a large gear 65 fitted so as to rotate together with an idler shaft 64. This idler shaft 64 also serves as a balancer shaft, which will be described later. The number of teeth of the large gear 65 is therefore the same as the number of teeth of the first drive gear 60 so that the idler shaft 64 rotates the same number of times as the crankshaft 31.
In order to rotate the cam shaft 53, a small gear 66 meshing with a cam gear 67 provided so as to rotate together with the cam shaft 53 is provided integrally with the large gear 65. With this gear train, the cam shaft 53 rotates once for every two rotations of the crankshaft 31. A rotating plate is fitted to a front end of the cam shaft 53, and detection of the engine stroke necessary for fuel injection timing control is carried out by detecting the rotational position of this rotational plate using a rotational position sensor 76.
The cam gear 67 is spline fitted to a supercharging crankshaft 52c that causes a supercharging piston 52b of a double-acting supercharger 52 to reciprocate. A hollow section constituting an oilway for supplying oil to sliding sections of respective cams and rocker arms that will be described later is formed in the cam shaft 53, and an elongated section of the supercharging crankshaft 52c is forced into a supercharger side end of this hollow section. In this way, the cam shaft 53 rotates together with the supercharging crankshaft 52c.
An intake cam, an exhaust cam and a supercharging cam for respectively driving the an intake valve 68, exhaust valve (not shown) and a supercharging valve 69 to open are provided on the cam shaft 53. Of these three valves, the intake valve 68 is driven to open by a second rocker arm 71 rocked by a rod 72 lowered by a first rocker arm 70 rocked by contact with the intake cam. The exhaust valve is not shown in the drawings, but has a similar structure and is driven to open at a different timing. On the other hand, the supercharging valve 69 is driven to open by a second rocker arm 74 rocked by a rod 75 pushed up by a first rocker arm 73 rocked by contact with the supercharging cam.
The idler shaft 64 is arranged oriented in the longitudinal direction of the

vehicle arid formed in a stepped cylindrical shape, and is provided with a large cylindrical section 64a and a small cylindrical section 64b. The large cylindrical section 64a and the small cylindrical section 64b are respectively supported so as to be capable of rotation by bearings 77 and 78 held by the upper and lower crank cases 42u and 421.
Each of these bearings 77 and 78 is held in a concave groove having a semicircular cross section respectively formed in the dividing surfaces A of the upper and lower crankcases 42u and 42k similarly to the ball bearings 49 and 50 for the crankshaft 31, and the axis of the idler shaft 64 is positioned on the dividing surface A. Also, because the dividing surface A is sloping at an angle a with respect to the vehicle center CO, the axis C4 of the idler shaft 64 is positioned lower down than the axis CI of the crankshaft 31 and on the right side (the left side in the drawing) with respect to the vehicle center. -£0046-]
A housing 79a for a cooling water pump 79 (a chamber for a magneto type cooling water pump 79) is housed inside the large cylindrical section 64a of the idler shaft 64, keeping an radial clearance from the inner surface of the large cylindrical section 64a. A cover 79b for the cooling water pump 79 is fitted into this housing 79a, in a fluid-tight manner, and piping (a conduit) 80 from an outlet side tank of the radiator is connected to the cover 79b.
Although not shown in detail, a discharge hole 81 communicating with a discharge section of the cooling water pump 79 and communicating with a cooling water jacket 84 formed around the cylinder bore is formed in the upper crankcase 42u (refer to Fig. 2 and Fig. 5). Fig. 5 shows part of an enclosure 128 surrounding the periphery of the alternator 56 looking from the outside. This enclosure 128 is formed protruding from an outer front surface of the upper crankcase 42u.
A rotating shaft 79c having one end supported by a roof section of the cover 79b and the other end supported by a bottom of the housing 79a,so as to be capable of rotation, is provided inside a pump chamber formed by the housing 79a and the cover 79b, extending in an axial direction inside a pump chamber. The cooling water pump 79 has three blades, and is provided with an impeller 79d integrally attached to the rotating

shaft 79c, with a permanent magnet 79e being attached in a circumferential direction of a shaft section of the impeller 79d.
In the clearance between the inner surface of the large cylindrical section 64a of the idler shaft 64 and the housing 79a, the permanent magnet 79f is fitted in the circumferential direction with a microscopic clearance maintained at the inner surface of the large cylindrical section 64a from the housing 79a, and forms a magnetic coupling to a permanent magnet 79e on a shaft section of the impeller 79d.

Accordingly, when the idler shaft rotates, the impeller 79d rotates through this magnetic coupling and cooling water flowing into the pump chamber through the conduit 80 is subjected to a rise in pressure by the cooling water pump and is forced into the cooling water jacket 84 through the discharge section of the cooling water pump 79 and the discharge hole in the upper crankcase 42u.
As shown in Fig. 2, the radiator 41 is arranged so that it is suspended in the V-shape formed by the lower crankcase 42u and the cylinder head 43, and the left and right ends of the radiator are respectively fixed to an upper left end of the lower crankcase 42u and an upper right end of the cylinder head 43 via a stay (attachment plate) 120 using bolts.
Cooling water that has been used to cool high temperature sections of the cylinder 45 and the cylinder head 43 flows from an cooling water outlet of the cylinder head 43 through the thermostat 82 to an inlet side tank 122 ( refer to Fig. 7) of the radiator 41, as shown in Fig. 2.
The cooling water outlet of the cylinder head 43 is formed in a projecting tube shape, as shown in Fig. 2 and Fig. 6, and a flow path is established between the cooling water outlet of the cylinder head 43 and the inlet side tank 122 of the radiator 41 by engaging the projecting tube section in a housing chamber 41a formed integrally with the inlet side tank 122 of the radiator 41 through a chamber wall of the housing chamber 41a. The thermostat 82 is arranged and fixed in a cooling water circulation path at a position where the projecting tube section 43a passes through a wall of the housing

chamber 41a.
The housing chamber 41a is integrally formed with a side section of the inlet side tank 122 of the radiator 41, and comprises part of the inlet side tank 122. The chamber is provided so as to come into contact with a right rear end half of the core section of the radiator 41.
The attachment structure of the thermostat 82 will now be described in greater detail with reference to Fig. 2, Fig. 6 and Fig. 7.
A concave inlet pipe section 130 receiving the projecting tube section 43a is formed in the chamber wall (bottom wall) of the housing chamber 41a at the section where the projecting tube section 43a passes through the chamber wall of the housing chamber 41a, and a front half section of the projecting tube section 43a is fitted into this concave inlet pipe section 130. An inner end of the concave inlet pipe section 130 is bent inwards to form an annular step section 130a. The concave inlet pipe section 130 constitutes a cooling water inlet of the radiator 41.

An annular flange section 82a formed projecting from an outer surface of the body of the thermostat 82 is fitted between an end surface of the projecting tube section . 43a and an inner surface of the step section 130a of the concave inlet pipe section 130 via seal means, thus fitting the thermostat 82 between a cooling water outlet of the cylinder head 43 corresponding to the cooling water outlet of the internal combustion engine 30 and a cooling water inlet of the radiator 41. A valve body section 82b of the thermostat 82 is inserted very deeply into the housing chamber 41a and the thermostat 82 is fitted so as to project deeply into the housing chamber 41a. A wax part of the thermostat 82 is arranged at a cooling water outlet side of the cylinder head 43.
Engaging of the projecting tube section 43a with the concave inlet pipe section 130, and the gripping of the thermostat 82 by the inner surface of the projecting tube section 43a and the inner surface of the step section 130a of the concave inlet pipe section 130, are carried out at the same time as arranging and fixing the radiator so that it is suspended in the V-shaped space formed by the lower crankcase 42u and the cylinder head 43, as described previously.

Since the radiator 41 is arranged utilizing the space in the V-shape formed by the lower erankcase 42u and the cylinder head 43 in this way, it is possible to reduce the space required by the radiator attachment structure and the power unit 7 can be made compact. This also makes it possible to enlarge the storage space below the seat 8.
There is also no longer any need to connect between the cooling water outlet of the cylinder head 43 and the inlet side tank 122 of the radiator 41 using piping such as a hose etc., and there is no need for a dedicated thermostat or troublesome piping, and it is possible to increase the degree of freedom of the piping for peripheral components. In addition,. connecting between cooling water passageways is simplified and cooling performance can be made much more stable by taking the cooling water passageway between the cylinder head 43 and the radiator 41 through the thermostat 82 to make it as short as possible.
The structure of the radiator 41 will now be described in greater detail.
As shown in Fig. 2, Fig. 4 and Fig. 7, the radiator 41 comprises the inlet side tank 122 and the outlet side tank 123, with these two tanks 122 and 123 being joined by a heat exchanger tube 124 having a number of fins.
When viewed from the front, the radiator 41 has an overall shape where a central section that is elongated and swells out more at the top than at the bottom (refer to Fig. 2), and is arranged so as to bridge across the V-shaped space formed by the lower erankcase 42u and the cylinder head 43 and fixed.
In plan view, the overall shape of the radiator is rectangular, with only one end section of the inlet side tank for receiving cooling water flowing out from the housing chamber 41a into which the projecting tube section 43a of the cylinder head 43 is fitted formed projecting in a lengthwise direction (refer to Fig. 7). The size and shape of the radiator 41 are suitably determined taking into consideration the weight of cooling water required and the layout of surrounding components etc.
Cooling water flows from the inlet side tank 122 into the inside of the heat

exchanger tube 124 having a number of fins and is cooled by cooling air blown out from the cooling fan 58. Cooling water that has been cooled inside the firmed heat exchanger tube then flows inside the outlet side tank 123 and is fed from the cooling water outlet 125 provided in one end of the tank 123 to an inlet section of the cooling water pump 79 through the conduit 80.
After the cooling air is discharged from the cooling fan 58 it flows into a cooling air duct D while being induced by an elongated cooling air section 40b (refer to Fig. 4 and Fig. 8), formed so that part of an outer wall of the shroud 40 swells out in a radial direction and is elongated in an axial direction, and a shroud wall 126, not shown in the drawings, having a U-shape projecting from an upper surface of the lower crankcase 42u, and flows from the bottom of a space in the V-shape formed by the lower crankcase 42u and the cylinder head 43 to the core section of the radiator 41.
Cooling air flowing to the core section of the radiator 41 spreads around the top and both left and right sides of the core and flows out. At this time, the air comes into uniform contact with the heat exchanger tube having a plurality of fins and effective heat exchange is carried out between the cooling water flowing inside the core.
A cooling water supply section 127 is provided in an upper part of the inlet side tank 122 of the radiator 41. Although not shown in the drawings, this cooling water supply section 127 is integrally provided with a relief mechanism.
A cylindrical weight 83 provided with a partial opening is fitted to an outer surface of the large cylindrical section 64a of the idler shaft 64, so as to provide a balancer for suppressing oscillations caused by rotation of the crankshaft 31 provided with the balance weight 31a and oscillations caused by reciprocation of the piston 47 and the connecting rod 48.
As a result, the idler shaft 64 functions as a drive shaft for driving the water pump 79 as well as a balancer shaft. In this way, by having the idler shaft 64 provided with a drive mechanism for driving the cam shaft 53 functioning as a drive shaft for the water pump 79 and as a balancer shaft, it becomes possible to make the internal

transmission case 92.
The center shaft 93 is supported so that rotation is impossible using a detent section for covering a shaft end fitted to the final reduction gear case 114. The axis C5 of the center shaft 93 is arranged on the dividing surface A of the upper and lower
. crankcases 42u and 421.

Since, as described above, the front end of the center shaft 93 is supported by the front ends of the upper and lower crankcases 42u and 421 and arranged further to the front of the vehicle than the rear end of the crankshaft 31, it is possible to arranged the crankshaft 31 and the center shaft 93 on top of one another in the longitudinal direction, the length of the power unit 7 in the longitudinal direction can be reduced and a compact power unit 7 is made possible.
A second drive gear 61 of the crankshaft 31 meshes with an input gear 94 fitted to a flange provided on a middle section in an axial direction of a flanged boss 101 rotatably engaged with the center shaft 93 of the transmission 91. A rear section of the flanged boss 101 is coupled to a clutch inner 95a of the starting clutch 95 so as to rotate integrally with it, and a starting driven gear 105 meshing with a small gear 104 of the idler shaft forming a reduction mechanism of a starter motor is attached to a front section of the flanged boss 101 via a unidirectional clutch 106. Reference numeral 102 represents a drive gear directly connected to a rotating shaft of the starter motor, and reference numeral 103 represents a large gear of the idler shaft meshing with the drive gear 102.
The starting clutch 95 has a clutch inner 95a, a clutch outer 95b and a centrifugal weight, and the starting clutch 95 is put into a completely connected state by connecting the clutch inner 95a and the clutch outer 95b and rotating them together using the operation of the centrifugal weight 95c when the rotational speed of the clutch inner 95a reaches a specified rate.
The respective changing clutches 96 - 98 have a planetary gear mechanism and a clutch mechanism.

combustion engine 30 compact, and to arrange the plurality of rotating shafts compactly,
even in a narrow space.

The cam shaft 53 and the idler shaft 64 are arranged at a side where the horizontal plane including the dividing surface A and the horizontal plane including the fitting surface B cross, namely a side where the two planes approach each other, with respect to the axis of the cylinder 45. With this arrangement of the cam shaft 53 and the idler shaft 64, the idler shaft 64 supported in the dividing surface A and the cam shaft 53 supported on the fitting surface B can be arranged close together, and it is possible for the cam shaft 53 and the idler shaft 64 to be joined together directly by a small gear 66 and a cam gear 67, without interposing a separate idler shaft between them. This makes it possible to keep the height of the cylinder 45 in the axial direction low, and to reduce the number of components.
Further, this arrangement of the cam shaft 53 and the idler shaft 64 is realized using a narrow space between surfaces of the horizontal plane including the dividing surface A and the horizontal plane including the fitting surface B at a side where they are close to each other is effectively utilized. It is therefore possible to form a wide space at a side surface of the cylinder 45 opposite to the narrow space shutting out the cylinder 45, and the radiator 41, being one the peripheral components described previously, can be arranged in this space.
The planetary gear type transmission 91, being a structural element of the transmission system 90 of the power unit 7, is comprised of a center shaft 93, an input gear 94, a starting clutch 95, 2-speed, 3-speed and 4-speed changing clutches 96 - 98, and an output shaft 99.
The center shaft 93 oriented in the longitudinal direction of the vehicle is a central shaft of the transmission 91, and a front end of the center shaft 93 is fitted into semicircular grooves formed in inner front surfaces of the upper and lower crankcases 42u and 421, on the dividing surface A of the upper and lower crankcases 42u and 421, while a rear end of the center shaft 93 is inserted into and supported by a support hole of a gear case 114 of the final reduction gear 110 fitted to a rear end surface of the

The output gear 107 is fitted to the output gear 99 of the planetary gear type transmission 91 so as to rotate integrally with it, and the outfput gear 107 meshes with a gear 112 fixed to a drive shaft 11 of the final reduction gear 110. A bevel gear, not shown, is formed on a rear end of the drive shaft 111 oriented in the longitudinal direction of the vehicle, and this bevel gear meshes with a driven bevel gear attached to an axle of the rear wheel 6. In this way, rotation of the output shaft 111 is reduced and transmitted to the rear wheel 6 to drive the rear wheel 6. Reference numeral 113 represents a rotational speed sensor.
The structure for attaching the radiator 41 to the power unit 7 of this embodiment is constructed as described above, and brings about the following effects.
When the radiator 41 is attached to an upper section of the power unit 7, the crankshaft 31 of the power unit 7 is arranged transversely in a longitudinal direction of the vehicle, the cylinder 45 of the power unit 7 is arranged sloping upwards with respect to a right side direction of the vehicle, and the transmission system of the power unit 7 is arranged sloping upwards with respect to a left side direction of the vehicle, and the radiator 41 is arranged suspended in a V-shape formed at an upper part of the power unit 7 by these two sloping sections.
As a result of this, it becomes possible to attach the radiator by suspending it utilizing the valley of the V-shape at the upper part of the power unit 7 formed by the two sloping section that would normally be dead space, and it is possible to reduce the space taken up by the attachment structure for the radiator 41. This in turn makes it possible to obtain a wide storage space below the seat 8 above the radiator 41.
Since, it is possible to attach the radiator 41 to an upper part of the power unit 7 above the axis of the cylinder 45 arranged sloping upwards in the left side direction of the vehicle looking in the longitudinal of the vehicle, it becomes possible to attach the radiator 41 to a front section of the power unit 7, and the position of the radiator is close to a hinged section pivotally supporting the power unit 7 so that it can be swung by hangar bolts. This in tum means that when the power unit 7 is swinging, shaking of the radiator 41 is slight, displacement of the upper part of the radiator 41 (a cap etc. provided with a cooling water supply section 127) becomes small and there is no need

to fix the radiator 41 in a particularly stable manner to the power unit 7 with respect to swinging displacement. This means that the attachment strength of the radiator can be reduced, and that alone simplifies the structure for attaching the radiator to the power unit 7.
Further, since the cooling fan 58 is attached to one end of the crankshaft 31, the cooling fan 58 is covered by the shroud 40 and cooling air blown from the cooling fan 58 is led to the radiator 41, it is possible to attach the cooling fan 58 close to the radiator 41 making it possible to improve the cooling performance of the radiator 41. It is also possible to reduce the size of the shroud 40.
In this embodiment, the radiator 41 is suspended between V-shaped upper sections of the power unit 7, but it can be expected that such a V-shape will not always be possible, depending, on the structure of the water-cooled internal combustion engine 30 or the power unit 7. In such cases, it is possible to make the bottom of the radiator 41 into a suitably concave shape and form a space corresponding to the V-shape to either enable this space to act as a cooling duct or provide a fan in the space.
The attachment structure for the thermostat 92 of this embodiment has the above described structure and enables the following effects.
Since the thermostat 82 is provided in a circulation path of the cooling water so
as to project into a housing chamber 41a constituting part of an inlet side tank 122 of the
radiator 41, there is no longer any need for a cover conduit specifically for holding and
covering the thermostat 82 or a hose for connecting this conduit to the radiator 41, as in
the related art, which makes it possible to reduce the number of components and to
reduce the cost. Also, attachment components that were required in the related art and
insertion operations etc. are also no longer necessary which means that it is possible to
improve the ease of assembly of the radiator 41 and the thermostat 82.

Also, since there is no need for a conduit for the thermostat cover or the hose, the cooling water outlet of the internal combustion engine 30 and the cooling water inlet of the radiator 41 can be connected together without connecting piping, the internal combustion engine 30 and the radiator 41 are arranged close together, the thermostat 82

can appropriately control circulation of cooling water by rapidly detecting effects of the temperature of cooling water that has been heated by the internal combustion engine 30 and it is possible to improve the cooling responsiveness of the radiator cooling water.
Also, since the thermostat 82 is affected less by external temperature it is possible to appropriately control the circulation path of cooling water by accurately sensing the temperature of cooling water that has been heated up by cooling the internal combustion engine 30, and it is possible to improve the cooling stability of the cooling water used in the radiator 41.
Since the thermostat 82 is attached in between the projecting tube section 43a of the cylinder head 43 forming a cooling water outlet of the internal combustion engine 30 and a concave inlet pipe section 130 of the housing chamber 41a forming a cooling water inlet of the radiator 41, it is possible to fix the thermostat 82 in the circulating path of the cooling water using simple means, and it is possible to provide the thermostat 82 so that it projects into a tank (housing chamber 41a) of the radiator 41.
In this embodiment, the projecting tube section 43a part of the cylinder head 43 is made a cooling water outlet of the internal combustion engine 30 and the housing chamber 41a formed integrally with a side section of the inlet side tank 122 of the radiator 41 is made a cooling water inlet of the radiator 41, but this is not limiting, and it is also possible to reverse the circulating direction of the cooling water and make the housing chamber 41a the cooling water outlet of the radiator 41 and make the projecting tube section 43a part the cooling water inlet of the internal combustion engine 30. In this case also it is possible for the thermostat 82 to suitable control circulation of the cooling water by rapidly detecting temperature effects of the cooling water in the radiator 41 and it is possible to improve the cooling responsiveness of cooling water used in the radiator. Since the thermostat 82 is affected less by external temperature, it is possible to improve the cooling stability of cooling water used in the radiator 41. In this case, it is also possible to reverse the orientation of the thermostat 82 and arrange a wax section 131 of the thermostat 82 on the housing chamber 41a side.
Also, positions where the cooling water outlet of the internal combustion

engine 30 and the cooling water inlet of the radiator 41 are connected without a hose can be provided on the cylinder 45 side. In this case, the projecting cylinder section is fitted into the concave inlet pipe section 130 of the housing chamber 41a of the radiator 41 by forming a projecting cylinder section (corresponding to the projecting tube section 43a of the cylinder head 43) communicating with the cooling water jacket 84 in the cylinder 45 and suitably reducing the size of the radiator 41 etc. The thermostat 82 is then arranged in engagement sections of the projecting tube section and the concave inlet pipe section 130. The projecting tube section 43a part of the cylinder head 43 is made a cooling water inlet and this cooling water inlet communicates with a discharge section of the water pump 79. In this way also, the same effects as described above can be obtained. It is also possible to use a reverse cooling water circulating direction in the piping connection structure between the internal combustion engine 30, the radiator 41 and the water pump 79.
In this embodiment, the water-cooled internal combustion engine 30 is integral with the transmission system 90 and constitutes part of the power unit 7, but this is not limiting and it is also possible to have a water-cooled internal combustion engine that is not integral with the transmission system 90, or to have a water-cooled internal combustion engine with a single cylinder or a plurality of cylinders arranged at an upper part so that a radiator can be attached, and the attachment structure for the thermostat 82 of this embodiment.can also, be applied to this ty.pe of water-.cooled combustion engine.

[Description Of The Numerals]

31 crankshaft
31a balance weight
32 air cleaner
33 air introduction pipe
34 throttle body
35 intake pipe
36 fuel injection valve
37 fuel tank
38 exhaust pipe
39 exhaust muffler
40 shroud (fan cover)
40a air intake
40b elongated baffle section
41 radiator
41a housing chamber
42 crankcase
42u, 421 upper and lower crankcases
43 cylinder head
43a projecting tube section
44 cylinder.head cover
45 cylinder
46 pipe bush
46a cylinder section
46b . flexible pipe
46c metal insertion tube
47 piston
48 connecting rod
49, 50 ball bearing
51 spark plug
52 piston type supercharger
52c supercharging crankshaft
53 cam shaft

54,55 bearing
56 alternator
56a rotor
57 stator
58 cooling fan
59 bolt
60 first drive gear
61 second drive gear
62 oil pump
62a oil pump drive shaft
62 b rotor
63 intake passageway
64 idler shaft
64a large cylindrical section
64b small cylindrical section
65 large gear
66 small gear
67 cam gear
68 intake valve
69 supercharging valve
70 first rocker arm
71 second rocker arm
72 rod ..
73 first rocker arm
74 second rocker arm
75 rod
76 rotation position sensor
77,78 bearing
79 cooling water pump
79a housing
79b cover
79c rotating shaft
79d impeller

We Claim:
1. A thermostat attachment structure, for a water-cooled internal combustion engine having a radiator (41) attached to an upper part of the internal combustion engine (30), characterized in that a thermostat (82) is provided inside a cooling water circulating path, which projects into a tank of the radiator and the said thermostat is attached to be interposed between a cooling water entrance of the internal combustion engine and a cooling water entrance of the radiator.
2. A thermostat attachment structure for a water-cooled internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.
Dated this 23rd day of June, 2000.

(JAYANTA PAL)
OF REMFRY & SAGAR
ATTORNEY FOR THF APPLICANTS

Documents:

581-mum-2000-cancelled pages(19-04-2005).pdf

581-mum-2000-claims(granted)-(19-04-2005).doc

581-mum-2000-claims(granted)-(19-04-2005).pdf

581-mum-2000-correspondence(19-02-2007).pdf

581-mum-2000-correspondence(ipo)-(17-05-2004).pdf

581-mum-2000-drawing(19-04-2005).pdf

581-mum-2000-form 1(05-05-2005).pdf

581-mum-2000-form 1(23-06-2000).pdf

581-mum-2000-form 2(granted)-(19-04-2005).doc

581-mum-2000-form 2(granted)-(19-04-2005).pdf

581-mum-2000-form 3(16-03-2001).pdf

581-mum-2000-form 3(19-04-2005).pdf

581-mum-2000-form 3(23-06-2000).pdf

581-mum-2000-form 5(23-06-2000).pdf

581-mum-2000-petition under rule 137(19-04-2005).pdf

581-mum-2000-petition under rule 138(19-04-2005).pdf

581-mum-2000-power of attorney(19-04-2005).pdf

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Patent Number

204372

Indian Patent Application Number

581/MUM/2000

PG Journal Number

43/2008

Publication Date

24-Oct-2008

Grant Date

19-Feb-2007

Date of Filing

23-Jun-2000

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	ATSUSHI OGASAWARA	C/O KABUSHIKI KSIDHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA, JAPAN.
2	TAKAFUMI ASAKURA	C/O KABUSHIKI KSIDHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA.

PCT International Classification Number

F 01 P 3/18

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	HEI-11-207168	1999-07-22	Japan