Internal combustion engine for vehicle

In an internal combustion engine for a vehicle wherein a crankshaft is supported for rotation on a crankcase and a speed change gear shaft which extends in parallel to the crankshaft and forms part of a transmission for changing the speed of rotational power from the crankshaft is supported for rotation on the crankcase such that it is disposed on one side of the crankshaft with a plurality of oil filters being mounted from the same direction to enhance the maintenance. A cover is coupled to a crankcase on one end side of a crankshaft in an axial direction, and a plurality of oil filters are attached to an outer side wall of the cover on the opposite side to a transmission with respect to the crankshaft and are disposed in an upwardly and downwardly juxtaposed relationship with each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2014-198126 filed Sep. 29, 2014 the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine for a vehicle wherein a crankshaft is supported for rotation on a crankcase which forms part of an engine main body. A speed change gear shaft extends in parallel to the crankshaft and forms part of a transmission for changing the speed of rotational power from the crankshaft is supported for rotation on the crankcase such that it is disposed on one side of the crankshaft.

2. Description of Background Art

An internal combustion engine for a vehicle is known. See, for example, Japanese Patent Laid-Open No. 2011-47352.

A lubrication system of an internal combustion engine and a hydraulic supply system of a hydraulic clutch provided between a crankshaft and a transmission sometimes include oil filters that are separate from each other. In the internal combustion engine for a vehicle disclosed in Japanese Patent Laid-Open No. 2011-47352, the oil filter of the lubrication system is attached to a front face of an engine main body mounted on the vehicle. In addition, the oil filter of the hydraulic supply system is attached to a side face of the engine main body in a state wherein it is mounted on the vehicle. The oil filters are preferably configured such that, upon maintenance of the oil filters, the oil filters can be accessed in the same direction.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention has been made in view of such a situation as described above. It is an object of an embodiment of the present invention to provide an internal combustion engine for a vehicle wherein a plurality of oil filters can be accessed from the same direction to enhance the maintenance.

In order to achieve the object described above, according to an embodiment of the present invention, an internal combustion engine for a vehicle wherein a crankshaft is supported for rotation on a crankcase which forms part of an engine main body and a speed change gear shaft extending in parallel to the crankshaft and forming part of a transmission for changing the speed of rotational power from the crankshaft is supported for rotation on the crankcase so as to be disposed on one side of the crankshaft. A cover is coupled to the crankcase on one end side of the crankshaft in an axial direction, and a plurality of oil filters are attached to an outer side wall of the cover on the opposite side to the transmission with respect to the crankshaft and disposed in an upwardly and downwardly juxtaposed relationship with each other.

According to an embodiment of the present invention, the cover which cooperates with a partition wall is coupled to the crankcase through the partition wall so as to form therebetween an oil reservoir for temporarily reserving oil. A lower half portion of the outer side wall of the cover is formed as an inclined wall portion inclined so as to be spaced away from the transmission toward the upper side. The oil filter of a large size is attached to an upper portion of the inclined wall portion. In addition, the oil filter of a small size is attached to an intermediate portion of the inclined wall portion in an upward and downward direction.

According to an embodiment of the present invention, at least part of an oil pump which discharges oil purified by the oil filter of the large size is disposed in the cover with the oil filter of the large size being disposed adjacent the oil pump in a direction along the axial line of the crankshaft.

According to an embodiment of the present invention, oil pumps, disposed on one side of the partition wall so as to discharge oil purified by the oil filters in a pair, and a different oil pump, disposed on the other side of the partition wall, are disposed in a juxtaposed relationship in a direction parallel to the axial line of the crankshaft.

According to an embodiment of the present invention, an oil suction passage common to pump chambers provided in a plurality of oil pumps which suck in oil from the oil reservoir is provided in the partition wall so as to communicate with the oil reservoir.

According to an embodiment of the present invention, an overflow passage for allowing oil to overflow from the oil reservoir into the crankcase is provided at an upper portion of the partition wall. The overflow passage and the oil suction passage are disposed at a central location of the engine main body in the leftward and rightward direction such that the overflow passage overlaps with part of the oil suction passage as viewed in a plan view in a state wherein the engine main body is mounted on the vehicle.

According to an embodiment of the present invention, a clutch cover is coupled to the partition wall on one end side of the crankshaft in the axial direction so as to cover a hydraulic clutch interposed between the crankshaft and the transmission. The cover is disposed adjacent the clutch cover and has a recessed portion which accommodates part of the clutch cover therein. An oil passage for supplying oil from the oil filter, attached to a lower portion of the cover to the hydraulic clutch side, is formed in the cover, partition wall and clutch cover.

It is to be noted that a spacer plate55in the embodiment corresponds to the partition wall in the present invention. An oil reservoir tank57in the embodiment corresponds to the cover in the present invention. A first main shaft69, a second main shaft70and a countershaft71in the embodiment correspond to the speed change gear shafts in the present invention. In addition, a first oil feed pump127, a second oil feed pump128and a scavenge pump129in the embodiment correspond to the oil pumps in the present invention.

According to an embodiment of the present invention, the plurality of oil filters are attached to the outer side wall of the cover on the opposite side to the transmission with respect to the crankshaft from among the outer side walls of the cover coupled to the crankcase on the one end side of the crankshaft in the axial direction and are disposed in an upwardly and downwardly juxtaposed relationship with each other. Therefore, the oil filters can be accessed from the same direction, and consequently, the maintenance can be enhanced.

According to an embodiment of the present invention, the cover is coupled to the crankcase through the partition wall and cooperates with the partition wall, which is coupled to the crankcase, to form therebetween the oil reservoir. Further, the inclined wall portion inclined so as to be spaced away from the transmission toward the upper side is provided at the lower half portion of the outer side wall of the cover. Further, the oil filter of the large size is attached to the upper portion of the inclined wall portion and the oil filter of the small size is attached to the intermediate portion of the inclined wall portion in the upward and downward direction. Therefore, by forming the oil filter disposed in the proximity of the road surface in the state in which the engine main body is mounted on the vehicle as a small size filter, both an assurance of the capacity of the oil reservoir through suppression of swelling from the lower portion of the cover and an assurance of the protection performance by decrease of the area of the element positioned in the proximity of the road surface can be achieved. As a result, the mounting property of the internal combustion engine on the vehicle can be enhanced.

According to an embodiment of the present invention, at least part of the oil pump which discharges oil purified by the oil filter of the large size is disposed in the cover, and the oil filter of the large size is disposed adjacent the oil pump in the direction along the axial line of the crankshaft. Therefore, the oil passage from the oil pump to the oil filter of the large size can be formed in a reduced length.

According to an embodiment of the present invention, the oil pumps in pair corresponding to the oil filters in pair and the different oil pump are disposed in a juxtaposed relationship with each other in the direction parallel to the axial line of the crankshaft on the opposite sides of the partition wall. Therefore, the oil passages from the oil pumps in a pair to the oil filters can be formed in a reduced length.

According to an embodiment of the present invention, the oil suction passage common to the pump chambers of the plurality of oil pumps which suck in oil from the oil reservoir is provided in the partition wall so as to suck in oil from the oil reservoir. Therefore, a reduction in the size by common use of the oil suction passage can be achieved.

According to an embodiment of the present invention, the overflow passage provided at the upper portion of the partition wall for allowing oil to overflow from the oil reservoir into the crankcase and the oil suction passage are disposed at the central location of the engine main body in the leftward and rightward direction such that the overflow passage overlaps with part of the oil suction passage as viewed in a plan view in the state in which the engine main body is mounted on the vehicle. Therefore, the left-right difference by fluidity of the oil in the oil reservoir in terms the oil sucking performance of the oil pumps and the oil discharging performance from the oil reservoir can be equalized. Thus, the dispersion by leftward and rightward tilting of the vehicle body can be reduced.

According to an embodiment of the present invention, the clutch cover is coupled to the partition wall so as to cover the hydraulic clutch, and the cover having the recessed portion which accommodates part of the clutch cover therein is disposed adjacent the clutch cover. Therefore, the distance of the outer side wall positioned on the opposite side to the transmission with respect to the crankshaft from among the outer side walls of the cover can be made short thereby to prevent upsizing of the engine main body. Further, the oil passage for supplying oil from the oil filter at the lower portion of the cover to the hydraulic clutches side is formed in the cover, partition wall and clutch cover. Therefore, a reduction in the length of the oil passage can be anticipated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is described with reference to the accompanying drawings. It is to be noted that the terms of front, rear, left, right, up, and down are used to represent directions as viewed from an occupant on a four-wheel drive vehicle.

Referring toFIGS. 1 to 3, a pair of left and right front wheels WF are suspended at a front portion of a vehicle body frame F of a four-wheel drive vehicle for off road operation in the form of a four-wheeled vehicle. A pair of left and right rear wheels WR are suspended at a rear portion of the vehicle body frame F.

The vehicle body frame F includes a pair of left and right lower frames11, a pair of left and right center upright frames12, a pair of left and right front side frames13, a pair of left and right rear side frames14, a center cross member15, a front cross member16, an upper rear cross member17, and a lower rear cross member18. The lower frames11extend in the forward and rearward direction, and the center upright frames12extend upwardly from an intermediate portion of the lower frames11in the forward and rearward direction. The front side frames13extend forwardly from an upper end of the center upright frames12and extend forwardly downwardly from a middle portion thereof until they are connected to a front portion of the lower frames11. The rear side frames14extend rearwardly from an upper end of the center upright frames12and extend downwardly from a middle portion thereof until they are connected to a rear end of the lower frames11. The center cross member15connects upper end portions of the pair of left and right center upright frames12to each other, and the front cross member16connects intermediate bent portions of the pair of left and right front side frames13to each other. The upper rear cross member17connects intermediate bent portions of the pair of left and right rear side frames14, and the lower rear cross member18connects lower portions of the pair of left and right rear side frames14to each other.

It is to be noted that the pair of left and right center upright frames12and the pair of left and right front side frames13configure an outer shell of a front boarding space FS for a driver and a front passenger. A front floor19is supported at a front portion of the vehicle body frame F and is disposed in front of the center upright frames12so as to allow the driver and the front passenger to position themselves on the vehicle. Further, the pair of left and right center upright frames12and the pair of left and right rear side frames14form an outer shell for a rear boarding space RS for fellow passengers. A rear floor20is supported at a rear portion of the vehicle body frame F and is disposed behind the center upright frames12so as to allow the fellow passengers to position themselves on the vehicle.

In the front boarding space FS for a driver and a front passenger, a driver's seat21and a front passenger seat22are disposed in a spaced relationship from each other in the vehicle widthwise direction. The driver's seat21is disposed behind a steering wheel25for steering the pair of left and right front wheels WF. The front passenger seat22is disposed on one side in the leftward and rightward direction (in the present embodiment, on the right side) of the driver's seat21.

Each of the driver's seat21and the front passenger seat22includes a seat portion21aor22a, and a backrest portion21bor22bwhich extends upwardly from a rear portion of the seat portion21aor22a. Further, a second front passenger seat23is provided between the driver's seat21and the front passenger seat22and has a backrest portion23band a seat portion23a. The backrest portion23bis displaced forwardly with respect to the backrest portions21band22bof the driver's seat21and the front passenger seat22, and the seat portion23ais disposed between the seat portions21aand22aof the driver's seat21and the front passenger seat22. Meanwhile, a pair of left and right rear passenger seats24are provided in the rear boarding space RS for fellow passengers.

In addition, a front portion of the vehicle body frame F is covered with a front cover27, and a front side cover28, a pair of left and right center side covers29and a pair of left and right rear side covers30are attached to the vehicle body frame F. The front side cover28covers a rear side lower portion of the front boarding space FS from the sides, and the center side covers30cover a front side lower portion of the rear boarding space RS from the sides. The rear side covers30cover a rear side lower portion of the rear boarding space RS from the sides. Further, a pair of left and right front doors33are supported for pivotal motion at left and right rear portions of the front cover27by a pair of upper and lower hinge portions35. The front doors33are capable of opening and closing front doorways31formed between the front side cover28and the front cover27. A rear door34is supported for pivotal motion at a front portion of each rear side cover30by a pair of upper and lower hinge portions36. The rear door34is capable of opening and closing a rear doorway32formed between the center side cover29and the rear side cover30.

A two-cylinder internal combustion engine E is mounted on the vehicle body frame F such that it is disposed substantially centrally in the forward and rearward direction of the vehicle as viewed in plan. The internal combustion engine E exerts power for driving the pair of left and right front wheels WF and the pair of left and right rear wheels WR to rotate. An engine main body38of the internal combustion engine E is postured such that it is laid in an upright position in which an axial line of a crankshaft39extends along the forward and rearward direction and a cylinder axial line C is inclined to the front passenger seat22side in the vehicle widthwise direction. The engine main body38is disposed below the driver's seat21and the front passenger seat22at a central location in the vehicle widthwise direction.

An intake system40in the internal combustion engine E includes a throttle body41, an air cleaner42, a pair of connecting tubes43and a single intake duct44. The throttle body41is connected for each cylinder to a cylinder head54of the engine main body38. The air cleaner42is disposed between the driver's seat21and the front passenger seat22as viewed in plan. The connecting tubes43connect the throttle body41and the air cleaner42to each other. The intake duct44introduces air into the air cleaner42.

In addition, the backrest portion23bof the second front passenger seat23provided between the driver's seat21and the front passenger seat22is integrally continuous to the backrest portions21band22bof the driver's seat21and the front passenger seat22and is displaced forwardly with respect to the backrest portions21band22b. The backrest portions21b,22band23bof the driver's seat21, front passenger seat22and second front passenger seat23form a recessed portion45which is recess to the front side as viewed in a plan view. The air cleaner42described hereinabove is disposed in the recessed portion45.

The intake duct44is connected at the downstream end thereof to a right side portion of the air cleaner42and extends to a right side portion of the vehicle body behind the seat portion22bof the front passenger seat22. A plurality of resonators46,47and48are connected to different locations of the intake duct44.

A pair of exhaust pipes50are connected to a lower portion side wall of the cylinder head54of the engine main body38and are connected to an exhaust muffler51. The exhaust muffler51is supported on the vehicle body frame F and disposed so as to extend in the vehicle widthwise direction along a rear edge of the vehicle body frame F.

Referring also toFIGS. 4 and 5, the engine main body38has a crankcase52, a cylinder block53and the cylinder head54. The crankcase52supports the crankshaft39, which extends in the forward and rearward direction of the vehicle, for rotation thereon. The cylinder block53is coupled to the crankcase52and has the inclined cylinder axial line C described above. The cylinder head54is coupled to an upper portion of the cylinder block53. The crankcase52is configured from a upper case portion52aand a lower case member52bcoupled to each other on a coupling plane along a plane VL1orthogonal to the cylinder axial line C. The upper case portion52aand the cylinder block53are formed integrally with each other. Further, the crankshaft39is supported for rotation between the upper case portion52aand the lower case member52bsuch that an axial line thereof is orthogonal to the cylinder axial line C on the plane VL1.

A spacer plate55is coupled to a rear face of the crankcase52and configures part of the engine main body38. A clutch cover56and an oil reserving tank57are coupled to the crankcase52through the spacer plate55such that they project rearwardly from the crankcase52. Further, an auxiliary transmission case58is coupled to the opposite side of the crankshaft39to the oil reserving tank57with respect to the axial line of the crankshaft39, namely, on the front face side of the crankcase52. An oil pan59is coupled to a lower portion of the crankcase52.

Referring also toFIG. 6, a power transmission apparatus T is provided midway of a power transmission system between the crankshaft39of the internal combustion engine E and the front wheels WF and rear wheels WR which are all driving wheels. The power transmission apparatus T configures a power unit P together with the internal combustion engine E. The power transmission apparatus T includes a transmission60, and first and second hydraulic clutches63and64interposed between the transmission60and the crankshaft39.

Output power from the power unit P is transmitted to the left and right front wheels WF through a front wheel propeller shaft65(refer toFIG. 3) extending in the forward and rearward direction and is transmitted to the left and right rear wheels WR through a rear wheel propeller shaft66(refer toFIG. 3) extending in the forward and rearward direction. The front wheel propeller shaft65and the rear wheel propeller shaft66are disposed such that they pass on the right side of the crankcase52.

The transmission60includes a main transmission61accommodated in the crankcase52, and an auxiliary transmission62accommodated in the auxiliary transmission case58. The auxiliary transmission case58is configured from a first case member67coupled to the front face of the crankcase52and a second case member68cooperating with the crankcase52to sandwich the first case member67therebetween.

The main transmission61includes a first main shaft69, a second main shaft70, a countershaft71, first, third and fifth speed gear trains G1, G3and G5, and second, fourth and sixth speed gear trains G2, G4and G6. The first main shaft69and the second main shaft70are input power shafts from the crankshaft39to the transmission60. The first, third and fifth speed gear trains G1, G3and G5are provided for selective establishment between the first main shaft69and the countershaft71. Meanwhile, the second, fourth and sixth speed gear trains G2, G4and G6are provided for selective establishment between the second main shaft70and the countershaft71.

The first and second main shafts69and70are supported for relative rotation on the upper case portion52aof the crankcase52such that the second main shaft70coaxially surrounds part of the first main shaft69. The first and second main shafts69and70are disposed on the right side with respect to the crankshaft39so as to have axial lines parallel to the crankshaft39. Meanwhile, the countershaft71is supported for rotation on the upper case portion52aof the crankcase52such that it has an axial line parallel to the first and second main shafts69and70.

Selective establishment of the first to sixth speed gear trains G1to G6is changed over by operation of a speed changing electric motor72. The speed changing electric motor72is attached to a sideward projection55aprovided on the spacer plate55in such a manner so as to project to the right side from the clutch cover56as clearly depicted inFIG. 4.

A power transmission cylindrical shaft73is supported for relative rotation but against relative movement in an axial direction at a position of the first main shaft69adjacent the second main shaft70on the rear side in the axial direction. The power transmission cylindrical shaft73coaxially surrounds the first main shaft69. The first hydraulic clutch63is provided on the first main shaft69such that it can carry out changeover between connection and disconnection of power between the power transmission cylindrical shaft73and the first main shaft69. The second hydraulic clutch64is provided on the power transmission cylindrical shaft73and the second main shaft70such that it can carry out changeover between connection and disconnection of power between the power transmission cylindrical shaft73and the second main shaft70.

To the power transmission cylindrical shaft73, rotational power from the crankshaft39is transmitted through a primary reduction apparatus74and a damper spring75. The primary reduction apparatus74is configured from a primary driving gear wheel76which rotates together with the crankshaft39and a primary driven gear wheel77disposed coaxially with the first and second main shafts69and70and held in meshing engagement with the primary driving gear wheel76. The primary driven gear wheel77is connected to the power transmission cylindrical shaft73through the damper spring75.

The first hydraulic clutch63has a first hydraulic chamber78and is disposed on the outer side in the axial direction with respect to the primary reduction apparatus74. In a state in which hydraulic pressure does not act upon the first hydraulic chamber78, the first hydraulic clutch63is in a clutch-off state in which power transmission is cut off. However, when hydraulic pressure acts upon the first hydraulic chamber78, the first hydraulic clutch63is in a clutch-on state in which rotational power transmitted thereto from the crankshaft39through the primary reduction apparatus74, damper spring75and power transmission cylindrical shaft73is transmitted to the first main shaft69.

The second hydraulic clutch64has a second hydraulic chamber79and is disposed on the inner side in the axial direction with respect to the first hydraulic clutch63in such a manner as to cooperate with the first hydraulic clutch63to sandwich the primary reduction apparatus74therebetween. In a state in which hydraulic pressure does not act upon the second hydraulic chamber79, the second hydraulic clutch64is in a clutch-off state in which power transmission is cut off. However, when hydraulic pressure acts upon the second hydraulic chamber79, the second hydraulic clutch64is in a clutch-on state in which rotational power transmitted thereto from the crankshaft39through the primary reduction apparatus74, damper spring75and power transmission cylindrical shaft73is transmitted to the second main shaft70.

First and second axial oil paths80and81are provided in the first main shaft69such that they extend in parallel to each other in an axial direction and are closed at the inner end thereof. The first axial oil path80is communicated with the first hydraulic chamber78while the second axial oil path81is communicated with the second hydraulic chamber79. In addition, a first oil path82communicating with the first axial oil path80and a second oil path83communicating with the second axial oil path81are formed in the clutch cover56.

The auxiliary transmission62includes a speed change drive shaft85, an idle shaft86and a driving force output power shaft87. The speed change drive shaft85is provided coaxially with the countershaft71of the main transmission61and extends in the forward and rearward direction. The speed change drive shaft85is supported for rotation on the first and second case members67and68of the auxiliary transmission case58. In addition, the speed change drive shaft85has a rear end portion penetrating for rotation through the first case member67and projecting to the crankcase52side. The countershaft71penetrates for rotation through the crankcase52and is coaxially connected to a rear end portion of the speed change drive shaft85through a damper mechanism88. In particular, rotational power of the countershaft71is transmitted to the speed change drive shaft85through the damper mechanism88.

Within the auxiliary transmission case58, a high speed driving gear wheel89, a low speed driving gear wheel90and a reverse driving gear wheel91are supported for relative rotation on the speed change drive shaft85and are disposed in this order from the front side. A high speed switching shifter92is supported for sliding movement on the speed change drive shaft85between the second case member68and the high speed driving gear wheel89against relative rotation to the speed change drive shaft85. In particular, the high speed switching shifter92is supported such that it can be changed over between a position at which it is engaged with the high speed driving gear wheel89and a neutral position at which it is disengaged from the high speed driving gear wheel89. Further, a forward-backward switching shifter93is supported for sliding movement on the speed change drive shaft85between the low speed driving gear wheel90and the reverse driving gear wheel91against relative rotation to the speed change drive shaft85. In particular, the forward-backward switching shifter93is supported such that it can be changed over among a position at which it is engaged with the low speed driving gear wheel90, another position at which it is engaged with the reverse driving gear wheel91and a neutral position at which it is not engaged with any of the low speed driving gear wheel90and the reverse driving gear wheel91.

The idle shaft86is formed as a cylindrical member which surrounds a support shaft94which is supported for relative rotation on the first and second case members67and68of the auxiliary transmission case58, and is supported for rotation on the support shaft94. A small diameter idle gear wheel95and a large diameter idle gear wheel96are provided integrally at a front portion and a rear portion of the idle shaft86within the auxiliary transmission case58, respectively. The large diameter idle gear wheel96is held in meshing engagement with the reverse driving gear wheel91.

A boss97is fixed to the driving force output power shaft87such that it is disposed at a position corresponding to the small diameter idle gear wheel95and the high speed driving gear wheel89and low speed driving gear wheel90of the speed change drive shaft85. The boss97is in a cylindrical shape. To the boss97, a small diameter driven gear wheel99is connected through a damper spring98and a large diameter driven gear wheel101is connected through a damper spring100. The high speed driving gear wheel89meshes with the small diameter driven gear wheel99, and the low speed driving gear wheel90and the small diameter idle gear wheel95mesh with the large diameter driven gear wheel101.

The high speed switching shifter92is retained for rotation by a first shift fork102and the forward-backward switching shifter93is retained for rotation by a second shift fork103. The first shift fork102and the second shift fork103are supported for sliding movement on a shift fork shaft104supported on the first and second case members67and68of the auxiliary transmission case58having an axial line parallel to the speed change drive shaft85. Further, a shift drum105is supported for rotation on the first and second case members67and68such that it has an axial line parallel to the shift fork shaft104. Guide grooves106and107are provided on an outer periphery of the shift drum105and are engaged by the first and second shift forks102and103, respectively.

When the shift drum105rotates, the first and shift forks102and103are moved along the shift fork shaft104to selectively connect the high speed driving gear wheel89, low speed driving gear wheel90and reverse driving gear wheel91against relative rotation to the speed change drive shaft85.

Referring also toFIGS. 7 and 8, the auxiliary transmission case58is adjacent from the front side and is coupled to the front face of the crankcase52which supports the first and second main shafts69and70, which are input power shafts to the transmission60, for rotation thereon. The auxiliary transmission case58has an output power shaft supporting portion110formed thereon such that it projects to the outer side from the crankcase52. The driving force output power shaft87is supported for rotation on the output power shaft supporting portion110and is offset in an axial direction from the first and second main shafts69and70. A rear end of the driving force output power shaft87extends for rotation through the output power shaft supporting portion110and projects rearwardly. Between the first case member67and the output power shaft supporting portion110, a ball bearing111and an oil seal112disposed on the outer side of the ball bearing111are interposed. The rear wheel propeller shaft66is connected to a rear end portion of the output power shaft supporting portion110and passes along the right side of the crankcase52. Meanwhile, a front portion of the driving force output power shaft87extends for rotation through the output power shaft supporting portion110and projects forwardly. Between the second case member67and the output power shaft supporting portion110, a ball bearing113and an oil seal114, disposed on the outer side of the ball bearing113, are interposed. The front wheel propeller shaft65is connected to a front end portion of the output power shaft supporting portion110and passes along the right side of the crankcase52.

In the auxiliary transmission case58, the first case member67coupled to the crankcase52of the engine main body38and the second case member68are coupled to each other with a gasket121interposed therebetween such that the first case member67and second case member68can be decoupled from each other in the axial direction of the driving force output power shaft87. A breather chamber115is formed between the first case member67and the second case member68such that it is disposed above a projection from the output power shaft supporting portion110at one end portion of the driving force output power shaft87, in the present embodiment, above a projection from the output power shaft supporting portion110at a rear end portion of the driving force output power shaft87.

In addition, the first case member67has a side wall67aand a projection67b. The side wall67afaces in a projection direction of the output power shaft supporting portion110from the crankcase52, namely, in the rightward direction. The projection67bis provided integrally so as to project integrally to a side from the side wall67a. The projection67bcooperates with the second case member68to configure the output power shaft supporting portion110.

A swollen portion116is provided integrally at a location of the first case member67corresponding to an upper portion of the output power shaft supporting portion110such that it is swollen to the opposite side to the second case member68, namely, to the rear side. The swollen portion116has a breather chamber forming wall portion116aprovided at an upper portion of the swollen portion116such that it forms a recessed portion117open to the second case member68side. The breather chamber forming wall portion116ais coupled to a breather chamber forming wall portion68aprovided at a position of an upper portion of the second case member68corresponding to the output power shaft supporting portion110so as to form a recessed portion118which is open to the first case member67side. The breather chamber115is formed from the recessed portions117and118which are communicated with each other. In addition, the swollen portion116is formed so as to integrally connect to the side wall67aof the first case member67.

On the second case member68of the auxiliary transmission case58, a cylindrical portion68bis formed integrally such that it extends forwardly along the axial direction of the driving force output power shaft87so as to cover the driving force output power shaft87from a side.

Referring toFIGS. 9 and 10, in order to form a flow path in the breather chamber115as a labyrinth flow path, a plurality of partition walls119are formed integrally in a projecting manner on the first case member67and a plurality of partition walls120are integrally formed in a projecting manner on the second case member68.

In addition, the breather chamber115is formed such that it exhibits a higher position toward the engine main body38in a state in which the power unit P is mounted on the vehicle body frame F. An inlet port122is provided in the breather chamber forming wall portion116asuch that it is communicated with a lowermost portion of the breather chamber115. Gas introduced into the inlet port122flows in a zigzag fashion as indicated by arrow marks inFIGS. 9 and 10, whereupon it is separated into vapor and liquid. Then, the gas circulates upwardly in the breather chamber115and then is derived from an outlet pipe123. The outlet pipe123is provided in the breather chamber forming wall portion116asuch that it is communicated with an uppermost portion of the breather chamber115.

Referring toFIG. 11, the first and second hydraulic clutches63and64are changed over between engagement and disengagement by a clutch actuator125, which is disposed on the clutch cover56. In addition, an oil reservoir126for temporarily reserving oil is formed between the spacer plate55and the oil reserving tank57. Oil from a first oil feed pump127which sucks up oil from the oil reservoir126is supplied to the clutch actuator125through a first oil filter130. The clutch actuator125operates to carry out changeover between action and release of hydraulic pressure upon and from the first oil path82and the first axial oil path80communicating with the first hydraulic chamber78of the first hydraulic clutch63and further carry out changeover between action and release of hydraulic pressure upon and from the second oil path83and the second axial oil path81communicating with the second hydraulic chamber79of the second hydraulic clutch64. The first and second hydraulic clutches63and64are changed over between engagement and disengagement by the changeover by the clutch actuator125. Surplus oil from the first oil feed pump127is returned to the oil reservoir126through a first relief valve133.

A second oil feed pump128is connected to the oil reservoir126commonly with a first oil feed pump127. Oil from the second oil feed pump128is supplied to a plurality of lubricated portions132of the power unit P through a second oil filter131, and surplus oil from the second oil feed pump128is returned to the oil reservoir126through a second relief valve134.

The discharge capacity of the second oil feed pump128is set higher than that of the first oil feed pump127. Accordingly, the second oil filter131is configured in a greater size than that of the first oil filter130.

Oil in the oil pan59is sucked up by a scavenge pump129through a strainer135. Oil discharged from the scavenge pump129is supplied to the oil reservoir126through an oil cooler136.

Referring also toFIGS. 12 to 14, the first oil feed pump127, second oil feed pump128and scavenge pump129are disposed on the spacer plate55so as to cooperate with each other to configure a pump unit138.

Paying attention particularly toFIG. 14, the first oil feed pump127has a pump chamber141formed between the spacer plate55and a partition plate140fastened to one face of the spacer plate55on the oil reserving tank57side. The first oil feed pump127further has an inner rotor143and an outer rotor144accommodated in the pump chamber141. The inner rotor143is fixed to an oil pump shaft142having an axial line parallel to the crankshaft39, and the outer rotor144meshes with the inner rotor143.

Further, the second oil feed pump128has a pump chamber147formed between a partition plate145and a pump cover146, which cooperates with the spacer plate55to sandwich the partition plate145therebetween. The second oil feed pump128further has an inner rotor148and an outer rotor149accommodated in the pump chamber147. The inner rotor148is fixed to the oil pump shaft142, and the outer rotor149meshes with the inner rotor148.

The partition plate145and the pump cover146are fastened to the spacer plate55by fastening by a plurality of bolts150.

The scavenge pump129has a pump chamber153formed between the spacer plate55and a pump cover152fastened to the other face of the spacer plate55on the crankcase52by a plurality of bolts151. The scavenge pump129further has an inner rotor154and an outer rotor155accommodated in the pump chamber153. The inner rotor154is fixed to the oil pump shaft142, and the outer rotor155meshes with the inner rotor154.

The scavenge pump129extends through and is supported for rotation on the spacer plate55, partition plate145and pump covers146and152. A balancer shaft156is connected coaxially against relative rotation on the oil pump shaft142and rotates in an interlocking relationship with the crankshaft39.

By such a disposition of the pump unit138on the spacer plate55, the first oil feed pump127, second oil feed pump128and scavenge pump129are disposed in a juxtaposed relationship in a direction parallel to the axial line of the crankshaft39.

The first oil feed pump127which discharges oil purified by the first oil filter130and the second oil feed pump128which discharges oil purified by the second oil filter131are disposed on one side of the spacer plate55(in the present embodiment, on the oil reserving tank57side). The scavenge pump129which is the other oil pump is disposed on the other side of the spacer plate55(in the present embodiment, on the crankcase52side). In the oil reserving tank57, at least part of the second oil feed pump128which is an oil pump which discharges oil purified by the second oil filter131which is a large-size oil filter is disposed.

In addition, the pump unit138including the second oil feed pump128is disposed on the spacer plate55positioned closely to the oil reserving tank57to which the first and second oil filters130and131are attached in a direction along the axial line of the crankshaft39. Therefore, the second oil filter131is disposed in the proximity of the second oil feed pump128.

The first oil feed pump127and the second oil feed pump128suck in oil from the oil reservoir126. An oil suction passage158is provided in the spacer plate55such that it is communicated commonly with the pump chamber141of the first oil feed pump127and the pump chamber147of the second oil feed pump128.

The oil suction passage158is formed in a tubular portion157provided on the spacer plate55and extends in the upward and downward direction. A communication hole159is provided at a lower portion of the tubular portion157. The communication hole159communicates the oil reservoir126with the oil suction passage158.

An overflow passage160is provided at an upper portion of the spacer plate55and allows oil in the crankcase52to overflow from the oil reservoir126. The overflow passage160and the oil suction passage158are disposed at a central location of the engine main body38in the leftward and rightward direction in such a manner that the overflow passage160overlaps with part of the oil suction passage158as viewed in a plan view in a state in which engine main body38is mounted on the vehicle. In particular, relative positions of the overflow passage160and the oil suction passage158are determined such that, on a projection view on a plane perpendicular to the axial line of the crankshaft39, part of the oil suction passage158is disposed within a width W between a pair of vertical lines which pass the opposite ends of the overflow passage160in the leftward and rightward direction.

Referring also toFIG. 15, the oil reserving tank57is positioned adjacent the clutch cover56and has a recessed portion161which accommodates part of the clutch cover56therein. Further, the first oil filter130and the second oil filter131are attached in an upwardly and downwardly juxtaposed relationship with each other on an outer side wall57aof the oil reserving tank57on the opposite side to the transmission60with respect to the crankshaft39, namely, on the opposite side to the clutch cover56.

A lower half of the outer side wall57aof the oil reserving tank57is formed as an inclined wall portion57aainclined so as to be spaced away from the transmission60toward the upper side. The second oil filter131which is a large size oil filter is attached to an upper portion of the inclined wall portion57aawhile the first oil filter130which is a small size oil filter is attached to an intermediate portion of the inclined wall portion57aain the upward and downward direction.

Oil discharged from the first oil feed pump127is introduced into a first passage162(refer toFIGS. 12 and 13) provided in the spacer plate55. With the first passage162, a second passage163provided in the oil reserving tank57is communicated when the oil reserving tank57is coupled to the spacer plate55. A bottomed first filter mounting hole167for attaching the first oil filter130is provided at an intermediate portion in the upward and downward direction of the inclined wall portion57aaof the outer side wall57aof the oil reserving tank57. The second passage163is formed in the oil reserving tank57such that it communicates with the first filter mounting hole167.

Referring toFIG. 16, oil purified by the first oil filter130is introduced into a third passage164. The third passage164is provided in the oil reserving tank57such that it is open at one end portion thereof coaxially to an inner end portion of the first filter mounting hole167and open at the other end portion thereof to a coupling face of the oil reserving tank57to the spacer plate55. Meanwhile, an elongated hole is provided in the spacer plate55and has one end communicated with the other end portion of the third passage164. A lid plate168is fastened to the spacer plate55for closing the opposite side of the elongated hole to the oil reserving tank57thereby to form a fourth passage165, which has one end communicated with the other end of the third passage164, in the spacer plate55.

A clutch cover attachment seat169is formed on the spacer plate55and continues in an endless fashion to the spacer plate55for fastening the clutch cover56. The fourth passage165is open at the other end thereof to the clutch cover attachment seat169. A fifth passage166is provided in the clutch cover56and connects to the clutch actuator125such that it is communicated with the other end of the fourth passage165.

The third to fifth passages164to166configure an oil passage170which supplies oil from the first oil filter130attached to the inclined wall portion57aaat a lower portion of the oil reserving tank57to the first and second hydraulic clutches63and64side through the clutch actuator125. The oil passage170is formed in the oil reserving tank57, spacer plate55and clutch cover56.

Oil discharged from the second oil feed pump128is introduced to a sixth passage171(refer toFIGS. 12 and 13) provided in the pump cover146. With the sixth passage171, a seventh passage172provided in the oil reserving tank57is in communication when the oil reserving tank57is coupled to the spacer plate55. A bottomed second filter mounting hole175for attaching the second oil filter131is provided at an upper portion of the inclined wall portion57aaof the outer side wall57aof the oil reserving tank57. The seventh passage172is formed in the oil reserving tank57in a communicating relationship with the second filter mounting hole175.

Oil purified by the second oil filter131is introduced into an eighth passage173provided in the oil reserving tank57. The oil reserving tank57is coaxially open at one end portion thereof to an inner end portion of the second filter mounting hole175and is open at the other end portion thereof to the spacer plate55side. Meanwhile, a ninth passage174is provided in the spacer plate55so as to communicate at one end thereof with the other end of the eighth passage173. The ninth passage174is in communication with an oil path (not depicted) provided in the crankcase52. The oil path is in communication with the lubricated portions132when the spacer plate55is coupled to the crankcase52.

A suction hole176is provided in the pump cover152provided in the scavenge pump129so as to suck up oil from within the oil pan59. A tenth passage177is provided in the spacer plate55such that it is communicated at one end thereof with the pump chamber153so that it introduces oil discharged from the scavenge pump129. A passage forming recessed portion178is provided in the spacer plate55and is open to the oil reserving tank57side. The passage forming recessed portion178extends in the upward and downward direction with an intermediate portion thereof in the upward and downward direction curved and is closed up at the opposite upper and lower end portions. The tenth passage177is open at the other end thereof to a lower portion of the passage forming recessed portion178. Meanwhile, a passage forming recessed portion179is provided in the oil reserving tank57in such a manner so as to have a shape corresponding to the passage forming recessed portion178and cooperates with the passage forming recessed portion178to configure an eleventh passage180.

The eleventh passage180has an upper end portion open to an outer peripheral portion of an oil cooler attachment seat181in order to attach the oil cooler136disposed above the second oil filter131thereto. The oil cooler attachment seat181is formed on an outer face of an upper portion of the oil reserving tank57which faces rearwardly of the vehicle. A twelfth passage182is provided in the oil reserving tank57and is open at one end portion thereof to a central portion of the oil cooler attachment seat181and open at the other end portion thereof to an upper portion of the oil reservoir126formed between the oil reserving tank57and the spacer plate55. In particular, oil discharged from the scavenge pump129is introduced into the oil cooler136through the tenth passage177and the eleventh passage180, and the oil cooled by the oil cooler136is supplied to the oil reservoir126through the twelfth passage182.

In addition, in a state in which the power unit P is mounted on the vehicle, the first and second oil filters130and131attached to the left side outer side wall57aof the oil reserving tank57are disposed at positions corresponding to the left side rear side cover30. Thus, as depicted inFIG. 17, in a state in which the left side rear side cover30is removed, the first and second oil filters130and131can be visually observed from the outside, and maintenance work of the first and second oil filters130and131is facilitated.

Referring toFIG. 18, the crankshaft39and the balancer shaft156, which is disposed coaxially with the oil pump shaft142of the pump unit138on the left side with respect to the crankshaft39, are supported for rotation on the crankcase52of the engine main body38. Between the crankshaft39and the balancer shaft156, which has balance weights184and185for each cylinder of the two-cylinder internal combustion engine E and has an axial line parallel to the crankshaft39, a gear transmission mechanism188is provided. The gear transmission mechanism188includes a driving gear wheel186fixed to the crankshaft39and a driven gear wheel187fixed to the balancer shaft156.

An outer rotor208is fixed to a projecting end portion of the crankshaft39which projects forwardly from the crankcase52. An inner stay209is fixed to the second case member68, which forms part of the auxiliary transmission case58, and cooperates with the outer rotor208to configure a generator210. A starting driven gear wheel211is connected to the outer rotor208through a one-way clutch212, and rotational power is inputted to the starting driven gear wheel211from a starter motor not depicted. The gear transmission mechanism188is provided between the crankshaft39and the balancer shaft156so as to be disposed between the crankcase52and the starting driven gear wheel211.

Referring also toFIG. 19, the balancer shaft156is formed so as to have a pair bearing portions156aand156band a gear wheel supporting portion156c. The bearing portions156aand156bare supported for rotation on the crankcase52through ball bearings190and191, respectively. The gear wheel supporting portion156cis connected to one156aof the bearing portions156aand156band disposed on the outer side of the crankcase52. The gear wheel supporting portion156cis formed in a tapering relationship such that the diameter thereof decreases away from the bearing portion156a.

A tubular boss portion187ais provided integrally on the driven gear wheel187and has an tapering attachment hole191in which the gear wheel supporting portion156cis fitted. A fitting recessed portion193is provided on the boss portion187aon the large diameter end side of the attachment hole191such that it has an axial line along a radial direction of the balancer shaft156. A pin192is fitted at a half portion on one end side thereof with a large diameter end of the gear wheel supporting portion156cand is fitted at a half portion on the other end side thereof with the fitting recessed portion193.

A sub gear wheel194for cooperating with the driven gear wheel187to absorb a backlash is mounted on the boss portion187aon the small diameter end side of the attachment hole191with a spring195as a biasing member interposed between the sub gear wheel194and the driven gear wheel187.

Referring toFIG. 20, the balance weights184and185are provided on the balancer shaft156in such a manner so that they are concentrated upon one portion of a plane VL2including the axial line of the balancer shaft156. The fitting position of the pin192with the gear wheel supporting portion156cis determined such that the pin192is directed upwardly in a phase of rotation of the balance weights184and185determined by the self-weight of the balance weights184and185in a natural state in which the axial line of the balancer shaft156extends horizontally.

A bolt197is screwed in the gear wheel supporting portion156csuch that it cooperates with an end portion of the boss portion187aon the opposite side to the crankcase52to sandwich a pressing plate196therebetween. By the provision of the bolt197, an end portion of the boss portion187ais pressed in a direction in which the gear wheel supporting portion156cis fitted into the attachment hole191. Thus, the driven gear wheel187is fixed to the gear wheel supporting portion156cby the pin192and the bolt197.

In addition, when the gear transmission mechanism188is to be assembled by placing the driving gear wheel186of the crankshaft39into meshing engagement with the driven gear wheel187and the sub gear wheel194in a state in which the coupling face of the lower case member52bto the upper case portion52aand lies horizontally so as to face upwardly in a state in which the balancer shaft156in a state in which the driven gear wheel187and the sub gear wheel194are assembled thereto is sub-assembled to the lower case member52bof the crankcase52, the assembly is carried out such that alignment marks provided on a side face of the sub gear wheel194and the driving gear wheel186are aligned with each other.

Referring toFIG. 19, the bolt197of the balancer shaft156on which the balance weights184and185are provided has an engaging portion197aprovided thereon for engagement against relative rotation with a water pump shaft199as a rotary shaft provided on a water pump198which is a first auxiliary apparatus.

The water pump198includes an impeller202fixed to the water pump shaft199and accommodated in a pump chamber201. The pump chamber201is formed between the second case member68which configures part of the auxiliary transmission case58and a pump cover200fastened to the second case member68.

The engaging portion197aof the bolt197extends along a diametrical line of the bolt197and projects to the water pump shaft199side. The engaging portion197ais engaged with a locking recessed portion203provided at an end portion of the water pump shaft199on the bolt197side to connect the bolt197fixed to the balancer shaft156coaxially against relative rotation to the water pump shaft199.

The oil pump shaft142of the pump unit138which is a second auxiliary apparatus is connected coaxially against relative rotation to an end portion of the balancer shaft156on the opposite side to the gear wheel supporting portion156c. In particular, at an end portion of the balancer shaft156on the opposite side to the gear wheel supporting portion156c, a locking recessed portion204is formed such that it extends along a diametrical line of the balancer shaft156. An engaging portion142ais provided in a projecting manner at an end portion of the oil pump shaft142on the balancer shaft156side and is engaged with the locking recessed portion204.

Now, an operation of the present embodiment is described. The crankshaft39and the balancer shaft156which is disposed on the left side with respect to the crankshaft39are supported for rotation on the crankcase52of the engine main body38. The balancer shaft156having the balance weights184and185provided thereon for each cylinder and having an axial line parallel to the crankshaft39is formed such that it has the pair of bearing portions156aand156bsupported for rotation on the crankcase52and the gear wheel supporting portion156cdisposed on the outer side of the crankcase52continuously to one156aof the bearing portions156aand156band formed in such a tapering relationship so that the diameter thereof decreases away from the bearing portion156a. On the driven gear wheel187which configures part of the gear transmission mechanism188provided between the crankshaft39and the balancer shaft156, the tubular boss portion187ahaving the tapering attachment hole191in which the gear wheel supporting portion156cis fitted is provided integrally. The fitting recessed portion193in which the pin192which has an axial line along a radial direction of the balancer shaft156and is fitted at a half portion thereof on one end side with a large diameter end of the gear wheel supporting portion156cis fitted at a half portion thereof on the opposite end side is provided on the boss portion187aon the large diameter end side of the attachment hole191.

Accordingly, relative positions of the balancer shaft156and the driven gear wheel187around the axial line are determined by a structure which does not include a keyway. Thus, while the continuity of the tapering faces of the outer circumference of the gear wheel supporting portion156cand the inner circumference of the attachment hole191is achieved, the productivity is improved. Further, positioning of the driven gear wheel187around the axial line of the boss portion187aand the gear wheel supporting portion156ccan be firmly achieved. Consequently, an increase of the transmission torque can be anticipated while upsizing of the balancer shaft156is prevented.

Further, the sub gear wheel194which cooperates with the driven gear wheel187to absorb a backlash is mounted on the boss portion187aon the small diameter end side of the attachment hole191with the spring195interposed between the sub gear wheel194and the driven gear wheel187. Therefore, there is no possibility of interference of the sub gear wheel194with the portion which plays a role for positioning the driven gear wheel187and the balancer shaft156c. Consequently, a degree of freedom in the shape of the sub gear wheel194can be assured and the assembling property can be enhanced.

Further, the balance weights184and185are provided on the balancer shaft156in a concentrated manner at a portion of the plane VL2including the axial line of the balancer shaft156. Further, the fitting position of the pin192with the gear wheel supporting portion156cis determined such that the pin192is directed upwardly in a phase of rotation which depends upon the self-weight of the balance weights184and185in a natural state in which the axial line of the balancer shaft156extends horizontally. Therefore, when the boss portion187aof the driven gear wheel187is assembled to the gear wheel supporting portion156cof a tapering shape, even if the pin192is provided at a position on the rear face side of the driven gear wheel187, phase adjustment of the balancer shaft156to the driven gear wheel187, and hence, phase adjustment of the balancer shaft156to the crankshaft39, is facilitated, and the assembling property is improved.

Further, the engaging portion197afor engaging against relative rotation with the water pump shaft199provided on the water pump198is provided on the bolt197which is screwed in the gear wheel supporting portion156cin such a manner so as to press the end face of the boss portion187aon the side on which the gear wheel supporting portion156cis fitted in the attachment hole191. Therefore, a reduction in the size of the balancer shaft156can be maintained even against an increase of the load which is to act upon the balancer shaft156from the water pump198.

Further, since the pump unit138is connected coaxially against relative rotation at an end portion of the balancer shaft156on the opposite side to the gear wheel supporting portion156c, even if the load to act upon the balancer shaft156increases, a reduction in the size of the balancer shaft156can be maintained.

Further, the first main shaft69, second main shaft70and countershaft71which extend in parallel to the crankshaft39and configure part of the transmission60for changing the speed of the rotational power from the crankshaft39are disposed on the right side with respect to the crankshaft39. Further, the oil reserving tank57is coupled to the crankcase52on one end side of the crankshaft39in the axial direction, and the first and second oil filters130and131are attached to the outer side wall57aof the oil reserving tank57on the opposite side to the transmission60with respect to the crankshaft39such that they are disposed in an upwardly and downwardly juxtaposed relationship with each other. Therefore, the first and second oil filters130and131can be accessed from the same direction (in the embodiment, from the left side of the vehicle), and consequently, the maintenance property can be enhanced.

Further, the oil reserving tank57which cooperates with the spacer plate55coupled to the crankcase52to form therebetween the oil reservoir126for temporarily reserving oil therein is coupled to the crankcase52with the spacer plate55interposed therebetween. A lower half portion of the outer side wall57aof the oil reserving tank57is formed as the inclined wall portion57aawhich is inclined such that the space from the transmission60increases toward the upper side, and the second oil filter131of a large size is attached to an upper portion of the inclined wall portion57aawhile the first oil filter130of a small size is attached to an intermediate portion of the inclined wall portion57aain the upward and downward direction. Therefore, by forming the first oil filter130disposed in the proximity of the road surface in a state in which the engine main body38is mounted on the vehicle as a small size filter, both an assurance of the capacity of the oil reservoir126through suppression of swelling from a lower portion of the oil reserving tank57and an assurance of the protection performance by decrease of the area of the element positioned in the proximity of the road surface can be achieved. As a result, the mounting property of the internal combustion engine E on the vehicle can be enhanced.

Further, at least part of the second oil feed pump128which discharges oil purified by the second oil filter131of a large size is disposed in the oil reserving tank57, and the second oil filter131is disposed adjacent the second oil feed pump128in a direction along the axial line of the crankshaft39. Therefore, the oil passage from the second oil feed pump128to the second oil filter131can be formed in a reduced length.

Further, the first oil feed pump127which discharges oil purified by the first oil filter130and the second oil feed pump128which discharges oil purified by the second oil filter131are disposed on one side of the spacer plate55while the scavenge pump129which is a different oil pump is disposed on the other side of the spacer plate55. Further, the first oil feed pump127, second oil feed pump128and scavenge pump129are disposed in a juxtaposed relationship with each other in a direction parallel to the axial line of the crankshaft39. Therefore, the oil passage from the first oil feed pump127to the first oil filter130and the oil path from the second oil feed pump128to the second oil filter131can be formed in a reduced length.

Further, the oil suction passage158common to the pump chambers141and147provided in the first and second oil feed pumps127and128into which oil is sucked from the oil reservoir126is provided in the spacer plate55in a communicating relationship with the oil reservoir126. Therefore, reduction in size by common use of the oil suction passage158can be achieved.

Further, the overflow passage160which allows oil to overflow from the oil reservoir126into the crankcase52is provided at an upper portion of the spacer plate55. Further, the overflow passage160and the oil suction passage158are disposed at a central portion of the engine main body38in the leftward and rightward direction in such a manner that the overflow passage160overlaps with part of the oil suction passage158as viewed in a plan view in a state in which the engine main body38is mounted on the vehicle. Therefore, the left-right difference by fluidity of the oil in the oil reservoir126in terms the oil sucking performance of the first and second oil feed pumps127and128and the oil discharging performance from the oil reservoir126can be equalized, and the dispersion by leftward and rightward tilting of the vehicle body can be reduced.

Further, the clutch cover56which covers the first and second hydraulic clutches63and64interposed between the crankshaft39and the transmission60is coupled to the spacer plate55on one end portion side of the crankshaft39in the axial direction. Meanwhile, the oil reserving tank57has the recessed portion161for accommodating part of the clutch cover56and is disposed adjacent the clutch cover56. Therefore, the distance of the outer side wall57apositioned on the opposite side to the transmission60with respect to the crankshaft39from among the outer side walls of the oil reserving tank57of the clutch cover56from the crankshaft39can be made short thereby to prevent upsizing of the engine main body38. In addition, the oil passage170for supplying oil from the first oil filter130attached to a lower portion of the oil reserving tank57to the first and second hydraulic clutches63and64side is formed in the oil reserving tank57, spacer plate55and clutch cover56. Therefore, a reduction in the length of the oil passage170can be anticipated.

Further, the transmission60includes the first and second main shafts69and70which have an axial line parallel to the driving force output power shaft87and are disposed at a position offset in the axial direction from the driving force output power shaft87. Further, the crankcase52for supporting the first and second main shafts69and70for rotation and the auxiliary transmission case58having the output power shaft supporting portion110for supporting the driving force output power shaft87for rotation are disposed adjacent each other such that the output power shaft supporting portion110projects to the right side from the crankcase52. Further, the breather chamber115disposed above the projection from the output power shaft supporting portion110at least at one end portion (in the embodiment, at a rear end portion) of the driving force output power shaft87is formed between the first and second case members67and68which cooperate with each other to configure the auxiliary transmission case58. Therefore, the coupling portions of the first and second case members67and68can be reinforced by formation of the breather chamber115, and reduction in weight by function aggregation of the auxiliary transmission case58can be anticipated. In addition, since the breather chamber115is disposed above the projection from the output power shaft supporting portion110at a rear end portion of the driving force output power shaft87, a foreign article dropping from above can be prevented from entering the oil seal112side provided between the rear end portion of the driving force output power shaft87and the output power shaft supporting portion110. Consequently, the protection of the oil seal112can be anticipated.

Further, the first case member67has the side wall67awhich faces in the projection direction of the output power shaft supporting portion110from the crankcase52, namely, in the rightward direction. The first case member67further has the projection67bwhich is provided integrally in a projecting manner so as to project to the right side from the side wall67aand cooperates with the second case member68to configure the output power shaft supporting portion110. Further, the swollen portion116which is swollen to the opposite side to the second case member68so as to form part of the breather chamber115is provided integrally on the projection67bin an integrally continuing relationship to the side wall67a. Therefore, the continuing portion of the projection67bto the side wall67acan be reinforced by the swollen portion116.

Further, the first and second case members67and68are coupled to each other such that they can be separated in the axial line direction of the driving force output power shaft87. Further, the cylindrical portion68bextending in the axial direction of the driving force output power shaft87is formed integrally on the second case member68in such a manner so as to cover the driving force output power shaft87from a side. Further, the first case member67is coupled to the crankcase52of the engine main body38of the internal combustion engine E. Therefore, the portion of the auxiliary transmission case58which projects sidewardly farther than the crankcase52so as to support the driving force output power shaft87is structured independently of the engine main body38thereby to achieve stabilization of the oil face in the output power shaft supporting portion110of the auxiliary transmission case58which supports the driving force output power shaft87. In addition, since the auxiliary transmission case58independent of the engine main body38is reinforced by formation of the breather chamber115, while the auxiliary transmission case58is reinforced, the driving force output power shaft87can be disposed at a position spaced from the engine main body38.

Further, the partition walls119and120for forming the flow path in the breather chamber115as a labyrinth flow path are provided integrally in a projecting manner on the first and second case members67and68, respectively. Therefore, the breather chamber115can be reinforced by the plurality of partition walls119and120thereby to further raise the reinforcing effect by the breather chamber115of the auxiliary transmission case58.

Further, the crankcase52of the power unit P is mounted at a central location in the forward and rearward direction of the four-wheeled vehicle in a posture in which the crankshaft39supported for rotation on the crankcase52is directed in the forward and rearward direction of the vehicle and the driving force output power shaft87is directed in the forward and rearward direction of the vehicle such that it is connected to the propeller shafts65and66which pass along the side of the crankcase52. Therefore, downsizing and disassembly and assembly of the crankcase52are facilitated.

Furthermore, the four-wheeled vehicle is a four-wheel drive vehicle wherein the front wheels WF and the rear wheels WR are driven, and the driving force output power shaft87is connected at the opposite end portions thereof to the front and rear wheel propeller shafts65and66which pass along the side of the crankcase52. Therefore, reactive force acting upon the power unit P from the front and rear wheel propeller shafts65and66can be reduced and vibrations of the power unit P can be reduced.

While the embodiment of the present invention has been described, the present invention is not limited to the embodiment described above, but allows various design changes without departing from the spirit of the present invention described in the claims.