Power transmission device for a four-wheel drive vehicle

[Technical problem] To provide a power transmission mechanism for a four-wheel drive vehicle in which a prime mover is disposed at a low position to lower the center of gravity of the vehicle while a driving path from a transmission to a front wheel differential mechanism is also shortened. [Solutions] In a power transmission mechanism for a four-wheel drive vehicle, the power of a prime mover is transmitted to a front wheel differential mechanism which is disposed in front of the prime mover, and to a rear wheel differential mechanism which is disposed behind a transmission, through the transmission which is disposed behind the prime mover. The transmission comprises a front and rear wheel drive shaft that extends along the longitudinal direction of the vehicle body. The transmission is arranged separately from the prime mover and a rear axle drive device. The rear end portion of the front and rear wheel drive shaft is connected to an input shaft of the rear wheel differential mechanism. The front end portion of the front and rear wheel drive shaft is connected to an input shaft of the front wheel differential mechanism via a front wheel power transmission shaft that extends along the longitudinal direction of the vehicle body and passes through the space beneath the prime mover. The front wheel differential mechanism, the prime mover, the transmission, and the rear wheel differential mechanism are arranged along the longitudinal direction of the vehicle body at the center of the vehicle width of the vehicle.

TECHNICAL FIELD

The present invention relates to a power transmission device for a four-wheel drive vehicle.

BACKGROUND

Such multi-purpose four-wheel drive vehicles as ATV (All Terrain Vehicle), UTV (Utility Task Vehicle), and ROV (Recreational Off highway Vehicle) suitable for rough terrain driving, the engine power is transmitted via the transmission which is arranged in the rear of the engine to the front wheel differential mechanism disposed in front of the engine and to the rear wheel differential mechanism disposed in the rear of the transmission (see, for example, Patent Documents 1 and 2).

Patent Document 1 discloses a power unit in which an engine and a transmission are integrated. Patent Document 2 discloses a configuration in which a front wheel drive shaft is provided so as to project outward from one side surface of a transmission integrated with a rear axle, and a propeller shaft is provided to detour around the engine.

PRIOR ART DOCUMENTS

Patent Literature

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the power transmission mechanism of Patent Document 2, the front wheel power transmission shaft (propeller shaft) that transmits power to the front wheel differential mechanism is provided to detour around the engine in a plan view, giving rise to the problem that the universal joint connected to both ends of the front wheel power transmission shaft was greatly inclined to increase noise with also reduced transmission efficiency. Moreover, the multi-purpose four-wheel drive vehicle disclosed in Patent Document 2 uses a power unit where an engine and a transmission are integrated, which constitutes a dedicated product with poor versatility and increased manufacturing costs.

The present invention addresses the technical problem by providing a power transmission device for a four-wheel drive vehicle which aims to improve the above-described present situations.

Means for Solving the Problems

A power transmission mechanism for a four-wheel drive vehicle comprising; a prime mover; a transmission disposed in the rear of the prime mover; a front wheel differential mechanism disposed in front of the prime mover; and a rear wheel differential mechanism disposed in the rear of the transmission; wherein, the power of the prime mover is transmitted via the transmission to the front wheel differential mechanism and the rear wheel differential mechanism; wherein, the transmission which is provided with a front and rear wheel drive shaft extending in the longitudinal direction of a vehicle body is provided separated from the prime mover and the rear wheel differential mechanism; wherein, a rear end of the front and rear wheel drive shaft is connected to the input portion of the rear wheel differential mechanism, wherein, a front end of the front and rear wheel drive shaft is connected to the input portion of the front wheel differential mechanism via a front wheel power transmission shaft extending in the longitudinal direction of the vehicle body and passing through the space beneath the prime mover; and wherein, the front wheel differential mechanism, the prime mover, the transmission and the rear wheel differential mechanism are provided in the longitudinal direction of the vehicle body and at the center of the vehicle width.

According to the present invention, since the prime mover and the transmission are arranged separated from each other so that a general-purpose prime mover can be used, and the prime mover can be arranged at a low position to lower the center of gravity of the vehicle and stability is improved. Furthermore, since the front wheel power transmission shaft is passed through the space beneath the prime mover along the longitudinal direction of the vehicle body at the center of the vehicle width, the drive path from the transmission to the front wheel differential mechanism can be shortened, so that not only the front wheel drive layout can be simplified, reduced noise and improved transmission efficiency can also be realized.

In the power transmission mechanism for a four-wheel drive vehicle according to the present invention, the input portion of the rear wheel differential mechanism is positioned higher from where is the bottom surface of the prime mover, and the front and rear wheel drive shaft is supported to the transmission in a front-lowered orientation.

According to this embodiment, by supporting the front and rear wheel drive shaft in a front-lowered manner, the input shaft of the rear wheel differential mechanism is supported in a front-lowered manner while securing the rear wheel differential mechanism to be located at a higher position, the input shaft of the input portion of the rear wheel differential mechanism could be provided on the same axis as the front and rear wheel drive shaft. Moreover, the rear end portion of the front and rear wheel drive shaft and the input shaft of the rear wheel differential mechanism are connected by a cylindrical shaft coupling such as a coupling, whereby the efficiency of power transmission from the front and rear wheel drive shaft to the rear wheel differential mechanism can be improved and noise can be suppressed.

Further, in the power transmission mechanism for a four-wheel drive vehicle of the present invention, the input portion of the rear wheel differential mechanism is positioned at substantially the same height as a connection portion between the front and rear wheel drive shaft and the front wheel power transmission shaft; wherein the front and rear wheel drive shaft is supported to the transmission in a substantially horizontal orientation.

According to this embodiment, the input shaft of the input portion of the rear wheel differential mechanism can be supported to orientate substantially horizontally and provided on the same axis as the front and rear wheel drive shaft, and the rear end portion of the front and rear wheel drive shaft and the input shaft of the rear wheel differential mechanism are connected by a cylindrical shaft coupling such as a coupling, so that the efficiency of power transmission from the front and rear wheel drive shaft to the rear wheel differential mechanism can be improved and noise can be suppressed. Furthermore, even if the interval in the longitudinal direction between the transmission and the rear wheel differential mechanism is changed, without significantly changing the structure of the transmission and the rear wheel differential mechanism, the rear end potion of the front and rear wheel drive shaft can be connected to an input shaft as an input portion of the rear wheel differential mechanism, and the versatility of the power transmission mechanism is hence improved.

In such an embodiment, by using a hypoid gear mechanism and a biaxial parallel shaft gear mechanism as the input gear mechanism of the rear wheel differential mechanism, the rear wheel differential mechanism is secured at a higher position, while the input shaft of the rear wheel differential mechanism can be supported to orient substantially horizontally and to the lower part of the rear wheel differential mechanism. Furthermore, the front wheel power transmission shaft is disposed in a substantially horizontal orientation and provided on the same axis as the front and rear wheel drive shaft, so that the front end of the front and rear wheel drive shaft and the rear end of the first front wheel power transmission shaft can be connected to each other by a cylindrical shaft coupling, so that the efficiency of power transmission from the front and rear wheel drive shaft to the first front wheel power transmission shaft can be improved and noise can be suppressed.

In the power transmission mechanism for a four-wheel drive vehicle of the present invention, the prime mover is provided with a power output shaft extending in the horizontal direction of the vehicle body, and the transmission is provided with a power input shaft extending in the horizontal direction of the vehicle body, with the transmission being configured to locate separated from and behind the prime mover, wherein the power output shaft and the power input shaft are connected with each other by an endless body.

According to this embodiment, a general-purpose prime mover can be used, and the output of the prime mover can be input to the transmission via an endless body which is provided on the side of the prime mover and the transmission. For example, an endless body of a continuously variable transmission (CVT), an endless body of a chain transmission mechanism without a speed change function, or an endless body of a belt transmission mechanism can be used as such an endless body.

Effects of the Invention

According to the power transmission mechanism for a four-wheel drive vehicle of the present invention, the prime mover is disposed at a low position to lower the center of gravity of the vehicle while the driving path from the front wheel differential mechanism to the transmission is also shortened.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. As shown inFIG.1andFIG.2, in the power transmission mechanism200for the four-wheel drive vehicle100of the present embodiment, the power of the engine1as a prime mover is transmitted to the front wheel differential mechanism72in the front axle drive device7which is disposed in front of the engine1, and to the rear wheel differential mechanism52in the rear axle drive device5which is disposed behind the gear transmission3, through the gear transmission3which is used as a transmission and is disposed behind the engine1. As shown inFIG.3, the gear transmission3includes a front and rear wheel drive shaft34that extends along the longitudinal direction of the vehicle body on the lower side inside the gear transmission housing36. The gear transmission3is arranged separately from the engine1and the rear axle drive device5.

The rear end portion of the front and rear wheel drive shaft34is connected to an input shaft51as an input portion of the rear wheel differential mechanism52. The front end portion of the front and rear wheel drive shaft34is connected to an input shaft71as an input portion of the front wheel differential mechanism72via a front wheel power transmission shaft92that extends along the longitudinal direction of the vehicle body and passes through the space beneath the engine1. In the power transmission mechanism200, the front wheel differential mechanism72, the engine1, the gear transmission3, and the rear wheel differential mechanism52are arranged along the longitudinal direction of the vehicle body at the center of the vehicle width of the vehicle100.

In the power transmission mechanism200for the four-wheel drive vehicle100of the present embodiment, the engine1and the gear transmission3are separately disposed, so that the general-purpose engine1can be adopted and the engine1is disposed at a low position so that the center of gravity of the vehicle100can be lowered to improve the stability. Furthermore, since the power transmission mechanism200allows the front wheel power transmission shaft92to pass through the space beneath the engine1along the longitudinal direction of the vehicle body at the center of the vehicle width of the vehicle100, the driving path from the front transmission differential mechanism72to the gear transmission3is shortened, the front wheel drive layout can therefore be simplified, and noise reduction and improved transmission efficiency is achieved.

Next, an embodiment of the power transmission mechanism200for the four-wheel drive vehicle100will be described more specifically with reference toFIG.1toFIG.9. As shown inFIG.1andFIG.2, the power transmission mechanism200of the vehicle100includes an engine1as a prime mover, a belt transmission2driven by the engine1, and a gear transmission3as a transmission driven by the belt transmission2. In the back of the gear transmission3is provided a rear axle drive device5for driving a pair of left and right rear wheels4and a rear axle4a. A front axle drive device7that drives a pair of left and right front wheels6and a front axle6ais provided in front of the engine1. The output of the gear transmission3is distributed and transmitted to the rear axle drive device5and the front axle drive device7.

The rear axle drive device5supports an input shaft51extending in the longitudinal direction of the vehicle body and a pair of left and right output shafts53extending in the horizontal direction in a plan view in the rear axle drive housing5aas a housing. The front end portion of the input shaft51protrudes forward from the rear axle drive housing5a, to be connected via the shaft coupling50to the rear wheel drive shaft34which protrudes rearward from a lower left portion of a rear surface of a gear transmission housing36(to be described later) in the gear transmission3.

Respective output shaft53of the rear axle drive device5protrudes left- and right-ward from the rear axle drive housing5aand is interlocked and connected to the rear axle4aof respective left and right rear wheel4via a universal joint and a transmission shaft. A rear wheel differential mechanism52is housed inside the rear axle drive housing5a, and the left and right output shafts53are connected to each other through the rear wheel differential mechanism52to operate differentially. A bevel ring gear52aas an input gear of the rear wheel differential mechanism52meshes with a bevel pinion gear51awhich is fixed to the rear end of the input shaft51.

As shown inFIG.7, the rear wheel differential mechanism52comprises a differential case55that is rotatably supported in the rear axle drive housing5aso as to have the same rotational axis as the output shaft53, a bevel ring gear52awhich is fixed to the differential case55, a pinion shaft56that is arranged orthogonal to the rotation axis of the differential case55and rotates integrally with the differential case55, pinions57,57that are rotatably supported by the pinion shaft56, and differential side gears53a,53athat are fixed to the ends of output shafts53,53and mesh with the pinions57,57, and a differential lock mechanism54that locks the rear wheel differential mechanism52.

The differential lock mechanism54comprises a differential lock slider58provided on the outer periphery of the cylindrical portion of the differential case55opposite to the side where the bevel ring gear52ais fixed, a differential lock slider58which is non-rotatable and axially slidable relative to the differential case55, and an engaging claw59that is fixed to the differential lock slider58with its front end engaging with the left differential side gear53a. The differential lock slider58is linked to the differential lock lever60, through the operation of which, the differential lock slider58slides and the engaging claw59is locked to the left differential side gear53a, and the differential case55and the output shaft53are connected with each other in a relatively non-rotatable manner, the rear wheel differential mechanism52is locked and the left and right output shafts53,53are driven at the same rotational speed.

As shown inFIG.1andFIG.2, the front axle drive device7provides support, in a front axle drive housing7aserving as a housing, to an input shaft71extending in the longitudinal direction of the vehicle body in a plan view, and to a pair of left and right output shafts73extending in the horizontal direction. The input shaft71is supported in a front-raised orientation (with the front portion in the higher position and the rear portion in the lower position), and the rear end portion of the input shaft71protrudes rearward from the front axle drive housing7ato connect to the front end portion of the second front wheel power transmission shaft94via the shaft coupling95. The second front wheel power transmission shaft94extends along the longitudinal direction of the vehicle body at the center of the vehicle width, and is disposed on the same axial center as the input shaft71, in a front-raised orientation (with the front portion in the higher position and rear portion in the lower position).

Respective output shaft73of the front axle drive device7protrudes left- and right-ward from the front axle drive housing7aand is interlocked and connected to the front axle6aof respective left and right front wheel6via a universal joint and a transmission shaft. A front wheel differential mechanism72is housed in the front axle drive housing7a, and the left and right output shafts73are connected to each other through the front wheel differential mechanism72to operate differentially. A bevel ring gear72aas an input gear of the front wheel differential mechanism72meshes with a bevel pinion gear71a which is fixed to the front end of the input shaft71.

As shown inFIG.1andFIG.2, both the left side surface of the main body of the engine1and the left side surface of the gear transmission housing36that is the housing of the gear transmission3are fixed to the right side surface of the belt transmission housing2athat is the housing of the belt transmission device2. A driving pulley12and a driven pulley13are provided side by side in the belt transmission housing2a, and a belt14as an endless body is wound around the driving pulley12and the driven pulley13.

The power output shaft11of the engine1extending in the horizontal direction of the vehicle body and the power input shaft15of the gear transmission3are arranged to extend horizontally in the belt transmission housing2a. The power output shaft11is a rotation center axis (pulley shaft) of the drive pulley12, and the power input shaft15is a rotation center axis (pulley shaft) of the driven pulley13. The belt transmission2is a continuously variable transmission (CVT) configured to change the output/input rotational speed ratio continuously by changing the width of the pulley grooves of the pulleys12and13according to the change in the rotational speed of the engine1.

The gear transmission3will be described with reference toFIG.1toFIG.9. In the gear transmission housing36, a power input shaft15, a transmission shaft16, an idle shaft17(seeFIG.6), and an intermediate shaft18extending in the horizontal direction of the vehicle body are arranged to extend in parallel with each other in the horizontal direction of the vehicle body. A front and rear wheel drive shaft34extending in the longitudinal direction of the vehicle body is supported in the lower part of the gear transmission housing36in a front-lowered orientation (with the front portion in the lower position and rear portion in the higher position).

The gear transmission housing36is configured by joining a left housing37and a right housing38. The left housing37rotatably supports the left end portions of the shafts15,16,17, and18through the respective bearings. The right housing38rotatably supports the right end portions of the shafts15,16,17, and18through the respective bearings. The power input shaft15protrudes left-ward from the left housing37from the left end portion.

The rear end side of the front and rear wheel drive shaft34is rotatably supported by the lower portion of the left housing37via a bearing, and the rear end portion protrudes rearward from the left housing37. The front end side of the front and rear wheel drive shaft34is rotatably supported via a bearing in a clutch housing39which is attached to the left lower portion of the front surface of the left housing37, and the front end portion protrudes forward from the left housing37.

As shown inFIG.2andFIG.5, the left end portion of the power input shaft15protruding leftward from the upper left side of the left housing37is the central axis (pulley axis) for the rotation of the driven pulley13of the belt transmission device2in the belt transmission housing2a. A forward high speed drive gear21and a forward low speed and reverse drive gear22are fixed (or integrally formed) in the order from left to right in the gear transmission housing36onto the power input shaft15.

A forward high-speed driven gear24, a reverse driven gear26, and a forward low-speed driven gear25are mounted on the transmission shaft16in the order from left to right, in such a manner that all of which are rotatable relative to the transmission shaft16. The forward high speed driven gear24meshes with the forward high speed drive gear21. The forward low speed driven gear25meshes with the forward low speed and reverse drive gear22. The reverse driven gear26meshes with an idle gear27(seeFIG.6) which is supported by the idle shaft17, and the idle gear27meshes with the forward low speed and reverse drive gear22.

A first clutch slider28that is provided at a position between the forward high-speed driven gear24and the reverse driven gear26and a second clutch slider29that is provided on the right side of the forward low-speed driven gear25are mounted onto the transmission shaft16in such a manner that the first clutch slider28and the second clutch slider29can slide in the axial direction and cannot rotate relative to the transmission shaft16. The clutch sliders28and29slide by the rotation of a shift drum61(described later) according to the operation of a speed change operation tool (lever, pedal, dial, etc.) provided in the vehicle100. The first clutch slider28can be switched to either one of the three positions including a forward high speed position at which the forward high speed driven gear24is to be meshed with, a reverse position at which the reverse driven gear26is to be meshed with, and a neutral position at which no gear is to be meshed with. The second clutch slider29can be switched between two positions, namely a forward low speed position at which the forward low speed driven gear25is to be meshed with and a neutral position at which no gear is to be meshed with.

Thus, the gear transmission3is configured to switch to either one of the states among which the transmission shaft16is driven at a low speed in the forward rotation direction in a forward low speed state, at a high speed in the forward rotation direction in a forward high speed state, in the reverse rotation direction in a reverse drive state, and a neutral state where the power transmission to the transmission shaft16is interrupted.

In the gear transmission housing36, the intermediate drive gear30that is fixed to the transmission shaft16at a position on the right side of the second clutch slider29is engaged to an intermediate driven gear31at the right end portion of the intermediate shaft18that is supported by the lower portion in the gear transmission housing36. A fixed intermediate driven gear31is engaged. A bevel pinion32that is fixed to the left end portion of the intermediate shaft18meshes with a bevel gear33that is fixed to the middle portion of the front and rear wheel drive shaft34.

As shown inFIG.2toFIG.7, the rear end portion of the front and rear wheel drive shaft34that extends in the longitudinal direction of the vehicle body at the vehicle width center portion and is supported in a front-lowered orientation, is connected to an input shaft51as an input of the rear wheel differential mechanism52, by such as a cylindrical shaft coupling50. The input shaft51extends along the longitudinal direction of the vehicle body at the center of the vehicle width, and is disposed on the same axial center as the front and rear wheel drive shaft34, in a front-lowered orientation (with the front portion in the lower position and rear portion in the higher position).

The connecting portion between the front and rear wheel drive shaft34and the input shaft51is covered with a cylindrical connecting cover41. A front end portion of the connecting cover41is bolted to a lower left portion of the rear surface of the gear transmission3. The rear end portion of the connecting cover41is bolted to the front surface of the rear axle drive housing5a.

As shown inFIG.2,FIG.6andFIG.7, the front end portion of the front and rear wheel drive shaft34protruding forward from the left housing37is accommodated in a clutch housing39. For example, a press-fit torque limiter81is connected to the front end of the front and rear wheel drive shaft34. The torque limiter81consists of a cylindrical member that is fitted to the front end portion of the front and rear wheel drive shaft34, and when a high load is applied to the connection between the front and rear wheel drive shaft34and the torque limiter81when the vehicle body jumps and lands when traveling on rough terrain, the cylindrical member constituting the torque limiter81will slide on the front and rear wheel drive shafts34(the torque limiter81and the front and rear wheel drive shafts34rotate relative to each other), therefore protecting the engine1and the power transmission mechanism200from the sudden load.

Also, in the clutch housing39, a front wheel output shaft83extending in the longitudinal direction is rotatably supported via a bearing in front of the front and rear wheel drive shaft34. The front wheel output shaft83is supported in a front-lowered orientation (with the front portion in the lower position and rear portion in the higher position), and is disposed on the same axis as the front and rear wheel drive shaft34. A clutch82such as a meshing clutch is interposed between the torque limiter81and the rear end of the front wheel output shaft83.

The clutch82comprises a first clutch member82athat is fitted in a relatively non-rotatable manner to the outer periphery of the torque limiter81, and a second clutch member82bthat is fitted in a relatively non-rotatable manner to the outer circumference of the rear end portion of the front wheel output shaft83. The first clutch member82ais slidable in the axial direction on the outer peripheral side of the torque limiter81by the operation of the clutch lever82c. The first clutch member82aand the second clutch member82bare engaged with each other, so that the rotation of the front and rear wheels drive shaft34is transmitted to the front wheel output shaft83via the torque limiter81and the clutch82, and the first clutch member82aand the second clutch member82bare separated from each other, so that power transmission between the front and rear wheels drive shaft34and the front wheel output shaft83is interrupted.

The front end of the front wheel output shaft83protrudes forward from the clutch housing39and is connected to the universal joint91. The front end side of the universal joint91is connected to the rear end of the first front wheel power transmission shaft92that extends in a substantially horizontal orientation along the longitudinal direction of the vehicle body at the center of vehicle width. The first front wheel power transmission shaft92extends forward through the space beneath the engine1.

The engine lower portion1a(for example, an oil pan) of the engine1is provided with a notch-like or groove-like recess extending in the longitudinal direction, and at the position of which a middle portion (near the rear end portion) is arranged. Accordingly, the first front wheel power transmission shaft92is configured to pass through the space beneath the engine1, making it possible for the engine1to be disposed at a lower position, and the center of gravity of the vehicle100can be lowered to achieve improved stability.

The front end portion of the first front wheel power transmission shaft92is disposed in front of the engine1in a plan view, and is connected via the universal joint93, the second front wheel power transmission shaft94and the shaft coupling95to a rear end portion of an input shaft71as an input portion of a front wheel differential mechanism72in the front axle drive device7.

In the gear transmission3, the clutch82is engaged to transmit the output of the gear transmission3to the left and right output shafts73of the front axle drive device7, that is, the left and right front wheels6. The vehicle100travels by driving the left and right rear wheels4and the left and right front wheels6, that is, it travels by four-wheel driving. By disengaging the clutch82, the output of the gear transmission3is not transmitted to the left and right front wheels6, and the vehicle100travels by driving only the left and right rear wheels4, that is, it travels by two-wheel driving.

Next, the drive mechanism of the clutch sliders28,29will be described with reference toFIG.8. A pair of shift forks63,64that engage with a shift drum61that rotates in conjunction with the shift lever62are connected to the clutch sliders28and29that are fitted to the transmission shaft16in such a manner as to be slidable in the axial direction. The shift lever62is connected upward to the right end portion of the shift lever shaft65rotatably supported at the upper front portion of the right side surface of the gear transmission housing36, and rotates around the shift lever shaft65in conjunction with the operation of a shift operation tool (lever, pedal, dial, etc.) not shown in the drawing.

As shown inFIG.9, a drive gear66composed of a fan-shaped gear that is fixed to the left end portion of the shift lever shaft65meshes with a shift gear67that is fixed to the right end portion61aof the shift drum61. As the shift lever62rotates, the shift lever shaft65and the drive gear66rotate, and the shift gear67and the shift drum61rotate in conjunction therewith.

Further, a shift drum positioning mechanism75is connected to the right end portion61aof the shift drum61. The shift drum positioning mechanism75comprises star-shaped plate76that is fixed to the right end of the shift drum61on the left side of the shift gear67, and a stopper member78that is rotatably supported by a supporting column77that is fixed to the right housing38of the gear transmission housing36. The star-shaped plate76has four concave portions on the outer periphery. The stopper member78comprises a stopper arm78athat is rotatably supported by the supporting column77, a stopper roller78bthat is rotatably supported by the front portion of the stopper arm78aand a coil spring78cthat urges the stopper arm78aso as to push the stopper roller78bto slide to the outer peripheral surface of the star-shaped plate76.

When the shift drum61drives to rotate with the rotation of the shift lever62, the star-shaped plate76also rotates together with the shift drum61. Meanwhile, the stopper roller78brides onto the convex portion on the outer periphery of the star-shaped plate76, with the stopper arm78aand the stopper roller78bbeing pushed outward, and the stopper roller78bwill then move into the recess next to the original recess of the star plate76due to the biasing force by the coil spring78c. This way, when the shift drum61is positioned at each of the positions described above, the shift drum positioning mechanism75is configured to apply a rotational resistance to the shift drum61.

Here, the right end portion61aof the shift drum61, the shift lever shaft65, the drive gear66, the shift gear67and the shift drum positioning mechanism75are accommodated in a shift gear chamber38which is provided at the upper front portion of the right side surface of the gear transmission housing36. The shift gear chamber38ais separated by a partition wall38bfrom the internal space of the gear transmission housing36in which the main body of the shift drum61and the gears21,22,24,25,26,27and the like are accommodated. The shift gear chamber38ais covered with a detachable shift gear chamber cover40, and the right end portion of the shift lever shaft65protrudes right-ward from the shift gear chamber cover40.

As described above, the drive gear66and the shift drum positioning mechanism75are provided in the shift gear chamber38athat is separated from the internal space of the gear transmission housing36, where the main body of the shift drum61covered with the detachable shift gear chamber cover40is accommodated. As a result, the number of assembly steps can be reduced and maintainability can be improved.

As shown inFIG.8, the shift forks63,64are slidably supported on a horizontally long shift fork shaft70that is provided in the gear transmission housing36. A first shift pin63athat is provided at one end of the first shift fork63engages with a first cam groove68that is provided in the shift drum61, and a second shift pin64athat is provided at one end of the second shift fork64engages with a second cam groove69that provided in the shift drum61. The shift forks63,64are given with the step feed according to the cam grooves68,69by the intermittent rotation of the shift drum61, and the gear transmission3is set to either one of the forward low speed state, the forward high speed state, the reverse drive state, and the neutral state.

As shown inFIG.1toFIG.8, the power transmission mechanism200for the four-wheel drive vehicle100according to the present embodiment is so configured that the engine1and the gear transmission3are separated from each other, that the general-purpose engine1can be adopted. In addition, the engine1is disposed at a low position so that the center of gravity of the vehicle100is lowered to improve the stability. Furthermore, since the power transmission mechanism200allows the front wheel power transmission shaft92to pass through the space beneath the engine1along the longitudinal direction of the vehicle body at the center of the vehicle width of the vehicle100, the driving path from the front transmission differential mechanism72to the gear transmission3is shortened, the front wheel drive layout can therefore be simplified, and noise reduction and improved transmission efficiency is achieved.

As shown inFIG.1toFIG.7, in the power transmission mechanism200, an input shaft51as an input part of the rear wheel differential mechanism52is positioned above the lower surface of the engine1, and the front and rear wheel drive shaft34is supported by the gear transmission3to in a front-lowered orientation. As a result, the input shaft51of the rear wheel differential mechanism52is supported in a front-lowered manner while securing the rear wheel differential mechanism52to be located at a higher position, the input shaft51of the rear wheel differential mechanism52could be provided on the same axis as the front and rear wheel drive shaft34. Moreover, the rear end portion of the front and rear wheel drive shaft34and the input shaft51of the rear wheel differential mechanism52are connected by a cylindrical shaft coupling50such as a coupling, whereby the efficiency of power transmission from the front and rear wheel drive shaft34to the rear wheel differential mechanism52can be improved and noise can be suppressed.

As shown inFIGS.1toFIG.5, the power transmission mechanism200is provided with a power output shaft11that extends in the horizontal direction of the vehicle body on the engine1and a power input shaft15that extends in the horizontal direction of the vehicle body on the gear transmission3. The gear transmission3is provided separated from and behind the engine1, and the power output shaft11and the power input shaft15are connected by a belt14. This way, the general-purpose engine1can be adopted, and the output of the engine1can be input to the gear transmission3via the belt14provided on the side of the engine1and the gear transmission3.

Next, another embodiment of the power transmission mechanism200will be described with reference toFIGS.10-FIG.13. In the present embodiment, the same components as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

In this embodiment, a hypoid gear mechanism is used for the rear wheel differential mechanism52, where a hypoid gear52bas an input gear of the rear wheel differential mechanism52engages with the hypoid pinion51bthat is fixed to the rear end of the input shaft51. The input shaft51as an input part of the rear wheel differential mechanism52is located at the height substantially the same as the connection location of the front and rear wheel drive shaft34and the first front wheel power transmission shaft92, and is supported to the gear transmission3in such a manner that the front and rear wheel drive shaft34that is provided at the lower part of the gear transmission3is substantially horizontal oriented.

The input shaft51of the rear wheel differential mechanism52is supported substantially horizontally by the rear axle drive housing5a. The two axes of the input shaft51and the output shaft53are positioned so as to be twisted from each other. The rear end portion of the front and rear wheel drive shaft34and the front end portion of the input shaft51of the rear wheel differential mechanism52are connected by a cylindrical shaft coupling50such as a coupling. This way, the efficiency of power transmission from the front and rear wheel drive shaft34to the rear wheel differential mechanism52can be improved, and noise can be suppressed.

Further, even if the interval in the longitudinal direction between the gear transmission3and the rear wheel differential mechanism52is changed, without significantly changing the structure of the gear transmission3and the rear wheel differential mechanism52, the rear end potion of the front and rear wheel drive shaft34can be connected to an input shaft51as an input portion of the rear wheel differential mechanism52, and the versatility of the power transmission mechanism200is hence improved. For example, a change in the interval in the longitudinal direction between the gear transmission3and the rear wheel differential mechanism52can be dealt with by adjusting the length of either or both of the front and rear wheel drive shaft34and the input shaft51. In addition, the length of the connection cover41is also changed along with the change of the interval mentioned above.

Further, in the present embodiment, by using a hypoid gear mechanism as the input gear mechanism of the rear wheel differential mechanism52, the rear wheel differential mechanism52is secured at a higher position (as is the position of the output shaft53), while the input shaft51of the rear wheel differential mechanism52can be supported to orient substantially horizontally and to the lower part of the rear wheel differential mechanism52. That is, by using the hypoid gear, the degree of freedom of the height position of the output shaft53is increased. Further, the front wheel power transmission shaft92is disposed to orient substantially horizontally and provided on the same axis as the front and rear wheel drive shaft34, so that the front end of the front and rear wheel drive shaft34and the rear end of the first front wheel power transmission shaft92can be connected to each other by a cylindrical shaft coupling96, so that the efficiency of power transmission from the front and rear wheel drive shaft34to the first front wheel power transmission shaft92can be improved and noise can be suppressed.

Next, still another embodiment of the power transmission mechanism200will be described with reference toFIG.14. In the present embodiment, the same components as those in the embodiment shown inFIGS.10toFIG.13are denoted by the same reference numerals, and detailed description thereof is omitted.

In this embodiment, a parallel shaft gear mechanism having an input shaft51and a relay shaft51cis used as the input gear mechanism of the rear wheel differential mechanism52. Both the input shaft51and the relay shaft51cextend along the longitudinal direction of the vehicle body and are arranged in parallel with each other and orient substantially horizontally, and the relay shaft51cis disposed above the input shaft51. In the rear wheel differential mechanism52, the input shaft51and the output shaft53are so positioned that their axes are twisted from each other.

The input shaft51is supported on the same axial center as the front and rear wheel drive shaft34that is supported to orient substantially horizontally. The front end portion of the input shaft51is connected to the rear end portion of the front and rear wheel drive shaft34via the shaft coupling50. A drive gear51dthat is fixed to the middle part of the input shaft51is engaged with a driven gear51ethat is fixed to the middle part of the relay shaft51c. A bevel pinion gear51athat is fixed to the rear end of the relay shaft51cmeshes with a bevel ring gear52aas an input gear of the rear wheel differential mechanism52. The rotational power of the front and rear wheel drive shaft34is transmitted to the bevel ring gear52athrough the drive gear51d, the driven gear51eand the bevel pinion gear51a.

Also in this embodiment, since the rear end portion of the front and rear wheel drive shaft34and the front end portion of the input shaft51of the rear wheel differential mechanism52are connected by the shaft coupling50, the efficiency of power transmission from the front and rear wheel drive shaft34to the rear wheel differential mechanism52can be improved and noise can be suppressed. Further, even if the interval in the longitudinal direction between the gear transmission3and the rear wheel differential mechanism52is changed, without significantly changing the structure of the gear transmission3and the rear wheel differential mechanism52, the rear end potion of the front and rear wheel drive shaft34can be connected to an input shaft51as an input portion of the rear wheel differential mechanism52, and the versatility of the power transmission mechanism200is hence improved.

Further, by using a parallel shaft gear mechanism having an input shaft51and a relay shaft51cas an input gear mechanism of the rear wheel differential mechanism52, the rear wheel differential mechanism52is secured at a higher position (as is the position of the output shaft53), while the input shaft51of the rear wheel differential mechanism52can be supported to orient substantially horizontally and to the lower part of the rear wheel differential mechanism52.

In the present embodiment, the gear transmission3is not provided with the torque limiter81, the clutch82, the front wheel output shaft83nor the clutch housing39(seeFIG.1andFIG.10, etc.). The front end side of the front and rear wheel drive shaft34is rotatably supported by the gear transmission housing36, and the front end portion of the front and rear wheel drive shaft34protrudes forward from the gear transmission housing36. The front end portion of the front and rear wheel drive shaft34is connected to the rear end portion of the first front wheel power transmission shaft92which is on the same axis as the front and rear wheel drive shaft34via a cylindrical shaft coupling96. The configuration in which the gear transmission3is not provided with either of the torque limiter81, the clutch82, the front wheel output shaft83and the clutch housing39, or the like, can also be applied to those embodiments as shown inFIGS.1toFIG.9and inFIGS.10toFIG.13.

The embodiments of the present invention have been described above, but the present invention can also be embodied in various ways. For example, it is possible to use an electric motor instead of the engine1as a prime mover. Further, as an alternative variation to the endless body, a chain transmission mechanism having no speed change function or an endless body of the belt transmission mechanism can be used instead of the belt14of the belt transmission device2.

EXPLANATION OF SYMBOLS

1Engine (prime mover)3Gear transmission (transmission)5Rear axle drive device7Front axle drive device11Power output shaft14Belt15Power input shaft34Front and rear wheel drive shaft52Rear wheel differential mechanism72Front wheel differential mechanism92First front wheel power transmission shaft (front wheel power transmission shaft)100Four-wheel drive vehicle200Power transmission mechanism