Hydrostatic transmission and power train for vehicle

A hydrostatic transmission for vehicle interposed in a drive-power transmission path between a driving power source and a driving axle for non-stepwisely changing the speed of the vehicle includes an HST housing; a hydraulic pump unit having a pump shaft with first and second ends extending in a fore-aft direction of the vehicle away from each other; a hydraulic motor unit having a motor shaft for outputting the drive power from the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit; a PTO unit having a PTO shaft extending in the fore-aft direction of the vehicle, the PTO shaft being operatively connected to the pump shaft; a charge pump unit for replenishing pressurized hydraulic fluid to a hydraulic circuit, the hydraulic circuit hydraulically connecting the hydraulic pump unit with the hydraulic motor unit, the charge pump unit including a charge pump body, and a charge pump case connected to the HST housing through its wall closer to the driving axle for supporting the charge pump body; the PTO shaft having an one end closer to the driving axle, the one end extending outwardly through the HST housing to have an outer extension positioned outside of the HST housing; and the charge pump case being designed so as to bearing-support the outer extension of the PTO shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a hydrostatic transmission (hereinafter referred to as HST) for vehicle that is interposed in a drive-power transmission path between a drive power source and a driving axle, and a power train for vehicle between the drive power source and the driving axle.

It is known that the HST interposed in the drive-power transmission path between the drive power source and the driving axle is provided with a PTO unit for driving a working device.FIG. 9(a) is a model view illustrating a drive-power transmission in the arrangement that a conventional HST with a PTO unit is applied to a vehicle that has a front axle serving as a driving axle and is provided on the front side of the, vehicle with a mower or any other working device.

As illustrated inFIG. 9(a), the HST with the PTO unit includes a hydraulic pump unit with a pump shaft operatively connected to the drive power source, a hydraulic motor unit with a motor shaft for outputting the drive power through the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit, a PTO unit with a PTO shaft operatively connected to the pump shaft, and an HST housing accommodating the hydraulic pump unit, the hydraulic motor unit and the PTO unit, in which the PTO shaft has a front end extending forwardly through the HST housing.

In some cases, a demand exists for a wide range of speed change of the driving axle and reduced load applied to the HST serving as a main speed change device. In that case, a mechanical transmission serving as an auxiliary speed change device is additionally interposed between the HST as the main speed change device and the driving axle.FIG. 9(b) is a model view illustrating a drive-power transmission path between the drive power source and the driving axle (front axle) in which the HST with the PTO unit and the mechanical transmission are interposed.

Here, comparing the distance between the front end of the PTO shaft and the front axle (hereinafter referred to distance L) in the arrangement ofFIG. 9(a) with the distance L of the arrangement ofFIG. 9(b), the former arrangement is: L=L1, and the latter arrangement is: L=L1+L2, in which L2represents the length of the mechanical transmission with respect to a fore-aft direction of the vehicle.

The front end of the PTO shaft is connected to the mower or any other working device via transmission parts such as a connecting rod with a universal joint. Accordingly, the variation of the distance L necessitates the modification of the transmission parts, the working device and any other associated parts.

Taking for example the vehicle that is provided with the mower as the working device having an elevation function, the variation of the distance L invites not only variation of the length of the connecting rod but also variation of the elevation height of the mower.

That is, since the front end of the PTO shaft serves as a fulcrum for the mower during the upward or downward movement, a simply elongated the elongation of the transmission shaft by L2simply causes the mower to have a different elevation height. Therefore, in order to equalize the elevational height of the mower between the vehicles ofFIGS. 9(a) and9(b), there arises a necessity to modify a hydraulic piston for elevation of the mower or any other parts.

There thus exist the arrangements with only the main speed change device interposed in the drive-power transmission path, and both the main and auxiliary speed change devices interposed therein. In either arrangement, a demand exists for non-variation of the distance between the front end of the PTO shaft and the driving axle. In other words, a demand exists for the arrangement holding the distance between the front end of the PTO shaft and the driving axle constant regardless of the distance between the driving axle and the main speed change device.

The auxiliary speed change device is an optional member that is provided according to a specification of the vehicle. Therefore, regarding parts constituting the power train between the drive power source and the driving axle excepting the auxiliary speed change device, it is preferable to render those parts commonly usable as many as possible for both arrangements with and without the auxiliary speed change device.

The present invention has been conceived in consideration of the above prior arts. It is an object of the present invention to provide an HST that is capable of effectively limiting the variation in distance between an end of the PTO shaft and the driving axle, even if the distance between the driving axle and the HST is varied.

It is another object of the present invention to provide a power train for vehicle that is capable of being adapted to or matching arrangements with or without the auxiliary speed change device or modifications of the same, or meeting any other demands.

SUMMARY OF THE INVENTION

To achieve the above objects, there is provided a hydrostatic transmission for vehicle interposed in a drive-power transmission path between a driving power source and a driving axle for non-stepwisely changing the speed of the vehicle. The hydrostatic transmission includes an HST housing; a hydraulic pump unit disposed within the HST housing and having a pump shaft with first and second ends extending in a fore-aft direction of the vehicle away from each other, in which the first end is positioned closer to the driving axle, and the second end is positioned away from the driving axle and operatively connected to the driving power source; a hydraulic motor unit disposed within the HST housing and having a motor shaft for outputting the drive power from the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit; a PTO unit disposed within the HST housing and having a PTO shaft extending in the fore-aft direction of the vehicle, the PTO shaft being operatively connected to the pump shaft; a charge pump unit for replenishing pressurized hydraulic fluid to a hydraulic circuit, the hydraulic circuit hydraulically connecting the hydraulic pump unit with the hydraulic motor unit, the charge pump unit including a charge pump body that is driven through the first end of the pump shaft, and a charge pump case connected to the HST housing through its wall closer to the driving axle for supporting the charge pump body; the PTO shaft having an one end closer to the driving axle, the one end extending outwardly through the HST housing to have an outer extension positioned outside of the HST housing; and the charge pump case being designed so as to bearing-support the outer extension of the PTO shaft.

According to the HST having the above arrangement, the outer extension of the PTO shaft is bearing-supported by the charge pump case that is connected to the HST housing. Therefore, the variation in distance between the second end of the PTO shaft and the driving axle can be effectively limited, even if the distance between the driving axle and the HST is varied. As a result, the common working device that is driven through the PTO shaft and the common drive power transmission mechanism for transmitting the drive power to the working device can be used for both the arrangements where the HST only is interposed in the drive-power transmission path and where the HST, and the mechanical transmission and/or the PTO device are interposed therein.

In the hydrostatic transmission having the above arrangement, the PTO unit preferably includes a hydraulic clutch device for on/off of the driver power transmission from the pump shaft to the PTO shaft. The charge pump unit also preferably includes a flow divider for dividing the pressurized fluid from the charge pump body to the one for replenishment to the hydraulic circuit and the other for actuation of the hydraulic clutch device, in which the flow divider is disposed within the charge pump case.

The first end of the pump shaft preferably extends outwardly through the charge pump case. The hydrostatic transmission also preferably includes an auxiliary pump unit detachably connected to the pump case for receiving the driving power through the first end of the pump shaft.

According to another aspect of the present invention, there is provided a power train for vehicle between a driving power source and a driving axle. The power train includes a transfer device disposed between a main speed change device that is operatively connected to the driving power source and a differential gear device that transmits the drive power to the driving axle. The transfer device includes a driving shaft and an output shaft. The driving shaft is disposed along a main drive-power transmission axis and operatively connected to a main output shaft of the main speed change device. The main transmission axis is coaxial with the main output shaft, and the output shaft is disposed along the main drive-power transmission axis for outputting the drive power to the differential gear device. With this arrangement, the speed can be stepwisely changed between the driving shaft and the output shaft.

With the power train of the above arrangement, the speed change range available in the drive-power transmission path can easily be widened. Also, by replacing the transfer device with a different one, the specification of the power train can easily be modified. That is, merely mounting or dismounting the transfer device, or modifying the same achieves matching to various specifications of the vehicle.

According to another aspect of the present invention, there is provided a power train for vehicle between a driving power source and a driving axle. The power train includes a transfer device disposed between a main speed change device that is operatively connected to the driving power source and a differential gear device that transmits the drive power to the driving axle. The transfer device includes a driving shaft and an output shaft. The driving shaft is disposed along a main drive-power transmission axis and operatively connected to a main output shaft of the main speed change device, in which the main transmission axis is coaxial with the main output shaft. The output shaft is disposed along the main drive-power transmission axis for outputting the drive power to the differential gear device, in which the drive power is transmitted between the driving shaft and the output shaft. The transfer device also includes an extension extending past the main speed change device in the direction orthogonal to the main drive-power transmission axis, a PTO shaft supported on the extension in such a manner as to be substantially parallel to the main drive-power transmission axis, and a drive-power transmission mechanism for transmitting the drive power synchronized with the output shaft to the PTO shaft.

With the power train having the above arrangement, the PTO shaft that takes off the drive power synchronized with the driving axle can be effectively prevented from interfering with the main speed change device. Thus, the drive-power transmission mechanism disposed on the downstream side of the PTO shaft can be relatively flexibly designed.

In the power train having the above arrangement, the drive-power transmission mechanism preferably includes a driven shaft that is disposed between the main drive-power transmission axis and the PTO shaft in parallel thereto, a first gear train for transmitting the drive power from the driving shaft to the driven shaft at a predetermined speed reducing ratio, a second gear train for transmitting the drive power from the driven shaft to the output shaft at the same speed reducing ratio as the predetermined speed reducing ratio, and a third gear train for transmitting the drive power from the driven shaft to the PTO shaft at the same speed reducing ratio as the predetermined speed reducing ratio.

With the power train having the above arrangement, the PTO shaft can effectively be rotated in synchronization with the output shaft, while sharing in part the common parts between the drive-power transmission line for the PTO system and the drive-power transmission line for the vehicle run. Thus, the transfer device can be manufactured compact as compared with the arrangement that the PTO drive power is taken off through the output shaft of the transfer device.

The power train preferably has the first gear train including an idle gear that is relatively rotatably supported on the driving shaft, and a first driven gear that is relatively non-rotatably supported on the driven shaft to be meshed with the idle gear; the second gear train including a second driven gear that is relatively non-rotatably supported on the driven shaft, and an output gear that is relatively non-rotatably supported on the output shaft to be meshed with the second driven gear; the third gear train including a PTO gear that is meshed with either one of the first and second driven gears to transmit the drive power to the PTO shaft. In this arrangement, the speed reducing ratio of the first driven gear with respect to the idle gear, the speed reducing ratio of the output gear with respect to the second driven gear, and the speed reducing ratio of the PTO gear with respect to the first or second driven gear are the same.

The transfer device preferably includes a clutch member that is relatively non-rotatably and axially slidably supported on the driving shaft. The clutch member is adapted to selectively take a position enabling connection between the driving shaft and the idle gear, a position enabling connection between the driving shaft and the output shaft, and a neutral position between both the positions, enabling shutdown of the drive-power transmission from the driving shaft to the output shaft.

With the arrangement above, through shifting operation of the clutch member, the output shaft and the PTO shaft can be brought into non-outputting state, or the output shaft and the PTO shaft can have speeds changeable in synchronization with each other.

The transfer device preferably includes a counter shaft that is disposed coaxially with the PTO shaft and a slider that is relatively non-rotatably and axially slidably on the PTO shaft and the counter shaft. The PTO gear is supported on the counter shaft via a one-way clutch. The slider is adapted to selectively take a non-outputting position enabling disconnection between the counter shaft and the PTO shaft, a forced outputting position enabling connection between the counter shaft and the PTO shaft while being in meshing engagement with the PTO gear, and a middle position between the non-outputting position and the forced outputting position, enabling connection between the counter shaft and the PTO shaft while being out of the meshing engagement with the PTO gear.

With the arrangement above, it is possible to easily change the outputting state of the PTO shaft. Specifically, through shifting operation of the slider, it is possible to easily change the mode of the PTO shaft between a mode enabling forced synchronization of the PTO shaft with the output shaft, a mode enabling shutdown of the drive power transmission from the output shaft to the PTO shaft when the PTO shaft rotates at a higher speed than the output shaft, and a mode enabling shutdown of the drive power transmission to the PTO shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the HST for the vehicle according to the present invention will be hereinafter described with reference to the accompanying drawings. This embodiment will be described by taking for example the case that the vehicle, to which the HST is applied, has a front axle serving as a main driving axle, and is provided on the front side of the vehicle body with a working device in the form of a mower with an elevation function

FIGS. 1 and 2are respectively the power train model view and the hydraulic circuit diagram of the vehicle to which the HST is applied.FIG. 3is the transverse plan view of the HST andFIG. 4is the cross-section taken along lines IV—IV inFIG. 3.

As illustrated in those Figures, HST1is interposed in the drive-power transmission path between drive power source300and the driving axle (i.e., front axle310in this embodiment). That is, the HST1functions as one component of the power train for vehicle between power source300and the driving axle. The HST1includes hydraulic pump unit10, hydraulic motor unit20, PTO unit30and HST housing40. The hydraulic pump unit10has pump shaft11extending in the fore-aft direction of the vehicle with an end away from the driving axle (rear end11bin this embodiment) operatively connected to the drive power source300. The hydraulic motor unit20has motor shaft21extending in the fore-aft direction of the vehicle and is designed to output the drive power through the motor shaft21whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit10. The PTO unit30has PTO shaft31extending in the fore-aft direction of the vehicle and operatively connected to the pump shaft11. The HST housing40accommodates the hydraulic pump unit10, hydraulic motor unit20and PTO unit30.

The HST housing40has center section41adapted to support thereon the hydraulic pump unit10and the hydraulic motor unit20and forming therein a hydraulic circuit for hydraulic connection between both units10,20, and housing body42connected to the center section41so as to enclose the hydraulic pump unit10, the hydraulic motor unit20and the PTO unit30. In this embodiment, a pair of hydraulic lines101are employed as the hydraulic circuit formed in the center section41.

In this embodiment as illustrated inFIG. 3, the center section41forms a part of the wall (front wall) of the HST housing40closer to the driving axle. This center section41may also be designed to form a wall (rear wall) away from the driving axle.

At least one of the hydraulic pump unit10and the hydraulic motor unit20is designed to be of a variable displacement type enabling the variation of the inflow/outflow amounts of hydraulic fluid. In this embodiment, the hydraulic pump unit10is of the variable displacement type, while the hydraulic motor unit20is of a fixed displacement type. In this respect, it is a matter of course to employ the arrangement with the hydraulic pump unit of the fixed displacement type and the hydraulic motor unit of the variable displacement type, or with both the units of the variable displacement type.

The hydraulic pump unit10includes pump shaft11, piston unit12, cylinder block13, output adjusting member14, and control shaft15(seeFIG. 8and the other Figures). The pump shaft11has rear end11bextending rearwards through the housing body42to be operatively connected with the power source300and front end11aextending forwards through the center section41. The piston unit12rotates around the axis of the pump shaft11as a result of the rotation of the pump shaft11and reciprocates in association with this rotation. The cylinder block13reciprocably supports the piston unit12while being supported by the center section41in such a manner as to be in communication with the pair of hydraulic lines101. The output adjusting member14is designed to vary the amount of inflow/outflow by the piston unit12through limiting the stroke length of the piston unit12based upon its tilting position. The control shaft15is designed to adjust the tilting position of the output adjusting member14.

Since this embodiment employs an axial piston type pump unit as the hydraulic pump unit10, a movable swash plate is employed to function as the output adjusting member14. Accordingly, where a radial piston type hydraulic pump unit is employed, a cam ring is employed as the output adjusting member.

The hydraulic motor unit20of the fixed displacement type includes cylinder block23that is supported on the center section41in such a manner as to be in communication with the pair of hydraulic lines101, piston unit22that is slidably supported within the cylinder block23, and reciprocable and rotatable by pressurized hydraulic fluid from the pair of hydraulic lines101, and motor shaft21that is rotatable around the axis as a result of the rotation of the piston unit22, thereby enabling the rotational output adjusted according to the output adjusting member14to be outputted through the motor shaft21.

As illustrated inFIG. 1, the vehicle of this embodiment is provided with a mechanical transmission320as a transfer device for providing a wide range of speed change of the driving axle, in which the mechanical transmission320transfers the drive power between the HST1serving as the main speed change device and differential device350with front axle310serving as the main driving axle mounted therein. Because of this, the motor shaft21forwardly extends through the center section41to have forward end21aconnected to the mechanical transmission320.

The mechanical transmission320may include for example driving shaft321that is connected to the motor shaft21in such a manner as to be relatively non-rotatable around the axis, clutch member322that is relatively non-rotatably and axially slidably supported on the driving shaft321, idle gear323that is relatively rotatably supported on the driving shaft321and adapted to be selectively engaged with and disengaged from the clutch member322according to the axial slide of the clutch member322, driven shaft324that is disposed parallel with the driving shaft321, first driven gear325that is relatively non-rotatably supported on the driven shaft324to be meshed with the idle gear323, second driven gear326that is relatively non-rotatably supported on the driven shaft324, output shaft327that is disposed coaxially with the motor shaft21and operatively connected to the front axle310via the differential gear device350, output gear328that is relatively non-rotatably supported on the output shaft327to be meshed with the second driven gear326and adapted to be selectively engaged with and disengaged from the clutch member322according to the axial slide of the clutch member322, and casing340for accommodating these members.

According to the mechanical transmission320having the above arrangement, the clutch member322is selectively engaged with the output gear328or the driving gear323, thereby providing two different rotational speed stages to the output shaft327.

The mechanical transmission320is preferably provided with second PTO unit330, as illustrated inFIG. 1.

The second PTO unit330may include for example counter shaft331disposed parallel with the driven shaft324, PTO gear332that is relatively rotatably supported on the counter shaft331to be meshed with the first driven gear325, second PTO clutch member333that is selectively engaged with and disengaged from the PTO gear332, and second PTO shaft334that relatively non-rotatably supports the second PTO clutch member333and has a rear end extending rearwards.

The second PTO unit330provided can easily take off the drive-power synchronized with the front axle310serving as the main driving axle. Therefore, in the cases such as that a rear axle (not shown) besides the front axle310is to be driven, it is possible to constantly rotate these axles synchronously to each other without necessity of a complicated transmission mechanism.

The mechanical transmission serving as a transfer device between the HST and the differential device will be hereinafter described in more detail.FIG. 10is a perspective view of an area extending from the HST1to the front axle310as viewed obliquely from behind.

As illustrated inFIG. 10, the mechanical transmission320is provided on an upper portion thereof with range shift arm341afor shifting the clutch member322of the mechanical transmission320, and shifting arm341bfor the shifting the second PTO clutch member333. The range shift arm341aand the shifting arm341bare coupled respectively to manipulating members mounted on a driver's stand such as mechanical transmission manipulating lever La and second PTO unit manipulating lever Lb.

A reference code43inFIG. 10represents speed change arm43for tilting and rotating the output adjusting member of HST1. The speed change arm43has a first end connected to speed change pedal P or any other manipulation member on the driver's stand via a wire or the like and a second end connected to the output adjusting member14. Accordingly, the speed change arm is rotated in response to the operator's manipulation of the manipulation member, thereby tilting and rotating the output adjusting member.

FIGS. 11 and 12illustrate cross sectional plan views of the mechanical transmission320. Specifically,FIGS. 11 and 12are cross-section taken along the drive-power transmission path of the mechanical transmission320, and cross-section including a moving part of the range shift arm341a.FIG. 13is a longitudinal cross-section of the mechanical transmission320with its stepped cross-section as viewed from behind.

The mechanical transmission320is detachably interconnected between the HST1and the differential device350. Specifically, the casing340of the mechanical transmission320is designed to be detachably interconnected to the HST housing40of the HST1and differential housing351of the differential device350, respectively.

In the arrangement with the mechanical transmission320removed, it is possible to couple the motor shaft21of the HST1to the differential device350. That is, the output shaft327of the mechanical transmission320is disposed coaxially with the motor shaft21of the HST1(hereinafter referred to main drive-power transmission axis (ML)), so that the motor shaft21can be directly connected to the differential device350in the arrangement with the mechanical transmission removed.

Specifically, when mounting the mechanical transmission320, four elongated bolts G are screwed into the front side of the differential housing351of the differential device350, passing the HST housing40and the casing340of the mechanical transmission340, so that they are interconnected (seeFIG. 10). In this manner of use, the driving shaft321of the mechanical transmission320is connected to the motor shaft21of the HST1in such a manner as to be relatively non-rotatable with respect to the axis, while the output shaft327of the mechanical transmission320is connected to power input part352of the differential device350via bevel gear327a.

On the other hand, when the mechanical transmission320is out of use, the HST1can be connected directly to the differential device350of the HST1. In this manner of use, the motor shaft21of the HST1is connected to the power input part352of the differential device via bevel gear327a′ having the same arrangement as the bevel gear327a(seeFIG. 14).

The casing340includes body340athat supports the driving shaft321, the output shaft327and the driven shaft324, and extension340bthat extends from the body340aand past the HST1in the direction perpendicular to the main drive-power transmission axis ML. The second PTO shaft334is supported on this extension340b. This arrangement can simplify the power train between the second PTO shaft334and the subsequent members.

The shifting operation of the mechanical transmission320will be hereinafter described in more detail.

As illustrated inFIG. 11, the driving shaft321is disposed coaxially with the motor shaft21and connected thereto in such a manner as to be relatively non-rotatable with respect to the axis. An end of the driving shaft321is relatively rotatably positioned in the rear side of the output shaft327. That is, the output shaft327is disposed coaxially with the driving shaft321, and loosely supported for the relative rotation with respect to the axis.

The clutch member322is relatively non-rotatably and axially slidably supported on the driving shaft321between the idle gear323relatively rotatably supported on the driving shaft321and the output gear328relatively non-rotatably supported on the output shaft327.

More specifically, the clutch member322includes spline hub322athat is relatively non-rotatably fitted around the driving shaft321, and sleeve322bthat is relatively non-rotatably and axially slidably fitted around the spline hub322a.

The idle gear323and the output gear328respectively have engaging elements323aand328aon portions adjacent to the spline hub322awith the same pitch as that of a spline formed on the outer circumference of the spline hub322a.

Accordingly, through the axial sliding motion of the sleeve322b, it can take a position enabling engagement with the spline hub322aonly (hereinafter referred to neutral position), a position enabling engagement with both the spline hub322aand the engaging element323a(hereinafter referred to low speed position), and a position enabling engagement with the spline hub322aand the engaging element328a(hereinafter referred to high speed position).

More specifically, the idle gear323and the first driven gear325each have a particular number of teeth (pitch circle diameter) set so that the rotational speed of the driving shaft321is reduced at predetermined speed reducing ratio R and transmitted to the driven shaft324. Also, the second driven gear326and the output gear328each have a particular number of teeth set so that the rotational speed of the driven shaft324is reduced at predetermined speed reducing ratio R and transmitted to the output shaft327.

That is, the number of teeth of each gear is set so that the speed reducing ratio of the first driven gear325with respect to the idle gear323and that of the output gear328with respect to the second driven gear326are: R.

With the sleeve322bat the low speed position, the drive power of the driving shaft321is transmitted to the output shaft327via the idle gear323, first driven gear325, driven shaft324, second driven gear326and output gear328. Therefore, when the rotational speed of the driving shaft321is: V, the output shaft327is rotated at a rotational speed of V/R2.

On the other hand, with the sleeve322bat the high speed position, the driving shaft321is directly connected to the output shaft327with the sleeve322b. Therefore, when the rotational speed of the driving shaft321is: V, the output shaft327is also rotated at a rotational speed of V.

The description of the operation mechanism of the sleeve322bwill be hereinafter made with reference mainly toFIGS. 12 and 13.

As illustrated inFIG. 12, supporting shaft342parallel with the main drive power transmission axis ML is supported on the casing340, on which selector fork343is axially slidably supported. The selector fork343includes driving part343aand passive part343bthat extend away from each other in the radial direction from the connected portion with the supporting shaft342. The driving part343ahas an end engaged with the sleeve322b. The driving part343aforms therein a hollowed portion with a closed end. The hollowed portion with the closed end opens to a through-hole, through which the supporting shaft342extends, and extends in the direction orthogonal to the through-hole. The hollowed portion is provided therein with ball345and helical compression spring344that biases the ball345towards the supporting shaft342. The supporting shaft342forms thereon dished recesses342L,342N,342H along a direction from the idle gear323to the output gear328respectively for receiving the ball345. The ball345engages with either recess to prevent unexpected movement of the selector fork343, and retreats to the inside of the hollowed portion against the biasing force of the spring344when the selector fork343is forced to slide on the supporting shaft342. The ball345is then positioned on a different recess of those recesses with the biasing force of the spring344to prevent the unexpected movement of the selector fork343.

The range shift arm341aabove the casing340has a rotational shaft extending into the casing340. A driving arm346is connected to an extended portion of the rotational shaft inside of the casing. The driving arm346extends in the direction orthogonal to the rotational shaft and has an end engaging with the passive part343b.

More specifically, the passive part343bhas a U-shape with an open end, and is connected to the driving arm346via an engaging pin347positioned between the legs of the U-shaped passive part343b. With this arrangement, the rotational shaft is rotated around the axis thereof by the rotation of the range shift arm341aaround the rotational shaft, so that the driving arm346is rotated around the rotational shaft. This rotation of the driving arm346allows the passive part343b(selector form343) to slide along the supporting shaft342.

Thus, the sliding movement of the selector fork343along the supporting shaft342causes the movement of the sleeve322bengaged with the selector fork343, which enables the sleeve to take the neutral position, low speed position or high speed position. More specifically, when the ball345engages with each of the recesses342L,342N,342H of the supporting shaft342, the sleeve322bcorrespondingly takes the low speed position enabling the engagement with both the spline hub322aand the engaging element323a, neutral position enabling the engagement with the spline hub322aonly, and high speed position enabling the engagement with both the spline hub322aand the engaging element328a.

Now, the description of the second PTO unit330will be made in more detail with reference mainly toFIGS. 11 and 12.

As illustrated inFIG. 11, the counter shaft331and the second PTO shaft334are disposed coaxially with each other in such a manner as to be relatively rotatable with each other around the axis.

The PTO gear332includes cylindrical body332asupported on the counter shaft331via one-way clutch365. The cylindrical body332ais provided thereon with external gear portion332bthat is meshed with the first driven gear325and internal gear portion332c.

The second PTO clutch member333includes cylindrical slider333athat is relatively non-rotatably and axially slidably supported on the counter shaft331and the second PTO shaft334. Specifically, the slider333ahas an internal gear portion that is meshed with a spline provided on the each-other-facing portions of the counter shaft331and the second PTO shaft334, so that it can take a position enabling the engagement with both the counter shaft331and the second PTO shaft334, and a position enabling the disengagement from the counter shaft331.

The slider333aalso has external gear portion333bthat is engaged with the internal gear portion332cof the cylindrical body332a, and annular groove333cfor axial sliding of the slider in the axial direction.

The shifting arm341bhas a rotational shaft extending into the casing340. A driving arm361is connected to an extended portion of the rotational shaft inside of the casing. The driving arm361extends in the direction orthogonal to the rotational shaft and has an end engaging with the annular groove333cof the slider333a.

Accordingly, the rotation of the shifting arm341baround the rotational shaft causes the rotation of the rotational shaft around the axis, and hence the rotation of the driving arm361around the rotational shaft. Thus, the slider333aslides along the counter shaft333aand the second PTO shaft334in response to the rotation of the driving arm361.

Now, the description of the shifting action of the second PTO unit330will be described in more detail.

Firstly, with the slider333aat position A illustrated inFIG. 11, the drive power is transmitted from the first driven gear325to the second PTO shaft334via the second PTO gear332and the slider333a. That is, with the slider333aat the position illustrated inFIG. 11, the second PTO unit330is drawn into a forcible output mode.

Secondly, with the slider333aat position B illustrated inFIG. 11, the second PTO gear332is released from engaging relationship with the slider333a, while the counter shaft331is brought into connection with the second PTO shaft334via the slider333ain such a manner to be relatively non-rotatable around the axis. As described above, the second PTO gear332is supported on the counter shaft331via the one-way clutch365. Accordingly, with the slider333aat the position B, semi-output mode becomes effective, enabling the interruption of the transmission of the drive power from the second PTO gear332to the counter shaft331in the case where the rotation number of the second PTO shaft334exceeds that of the second PTO gear332.

Lastly, with the slider333aat position C illustrated inFIG. 11, the slider333ais disengaged from the counter shaft331. Accordingly, non-output mode becomes effective, enabling non-output of the drive power through the second PTO shaft334.

When the drive power for the rear wheels is to be taken off through the second PTO shaft334, the second PTO shaft334is preferably rotated in synchronization with the output shaft327. For this purpose, the following arrangement is employed in this embodiment. That is, the transmission ratio from the driven shaft324to the counter shaft331or the second PTO shaft334is set to be the same as the transmission ratio from the driven shaft324to the output shaft327.

Specifically, the second PTO gear332is designed so that the speed reducing ratio of the second PTO gear332with respect to the first driven gear325can be the same as the speed reducing ratio R of the output gear328with respect to the second driven gear326. Thereby, the second PTO shaft334is rotated in synchronization with the output shaft327regardless of the shifting state of the mechanical transmission320.

That is, with the mechanical transmission320in a low speed state or with the sleeve322bat the low speed position, the driven shaft324is rotated at a speed of V/R via the idle gear323and the first driven gear325when the driving gear321is rotated at a rotational speed of V. The output shaft327is also rotated at a speed of V/R2via the second driven gear326and the output gear328. At this moment, the second PTO gear332has a gear ratio of R with respect to the first driven gear325, so that the second PTO gear332is rotated at a speed of V/R2likewise the output shaft327.

With the mechanical transmission320in a high speed state or with the sleeve322bat the high speed position, the output shaft327is rotated at a speed of V that is the same as the rotational speed of the driving shaft321. The driven shaft324is also rotated at a speed of R×V via the output gear328and the second driven gear326. At this moment, the second PTO gear332has a gear ratio of R with respect to the first driven gear325, so that the second PTO gear332is rotated at a speed of V likewise the output shaft327.

In this embodiment, the second PTO shaft334is thus rotated in synchronization with the output shaft327regardless of the shifting state of the mechanical transmission.

The second PTO gear332is meshed with the first driven gear325in this embodiment. However, the present invention is not necessarily limited to this embodiment. Rather, various embodiments can be employed as far as the speed change ratio from the driven shaft324to the counter shaft331or the second PTO shaft334is the same as the speed change ratio from the driven shaft324to the output shaft327. For example, it is possible to employ an arrangement that enables the second PTO gear332to be meshed with the second driven gear326.

In the above description, the mechanical transmission320that is capable of selectively performing speed-change-and-power-transmission/power-shutdown between the HST1and the differential device is employed as the transfer device between the HST1and the differential device. However, the present invention is not necessarily limited to this embodiment.

For example, where the speed change between the HST and the differential device is not needed, a constant speed transmission device may be employed as the transfer device, as illustrated inFIG. 15. In the following description on the constant speed transmission device illustrated inFIG. 15, same or identical parts to those of the mechanical transmission320have been given the same reference characters to omit a detailed description thereof.

As illustrated inFIG. 15, in the constant speed transmission device, the driving shaft321and the output shaft327are coupled to each other via cylindrical coupling member322′ in such a manner as to be constantly non-rotatable with respect to each other around the axis.

The drive power to the second PTO gear is transmitted from the driving shaft321via the idle gear323and the first driven gear325. Each gear is set so that the second PTO shaft is rotated in synchronization with the output shaft.

Specifically, it is possible to employ the arrangement with the idle gear323, the first driven gear325and the second PTO gear332all having the same number of teeth, or the arrangement with the first driven gear325designed to increase or decrease the speed at a predetermined speed change ratio with respect to the idle gear and the second PTO gear332designed to increase or decrease the speed at the same speed change ratio as the predetermined speed change ratio with respect to the first driven gear325.

Now, the description of the PTO unit30will be made. The PTO unit30includes PTO shaft31that is disposed in the fore-aft direction of the vehicle and has front end31aextending forwardly through the front wall of the HST housing40, and hydraulic clutch device32that is designed for on/off of the drive power transmission from the pump shaft11to the PTO shaft31.

The hydraulic clutch device32includes first gear32athat is relatively non-rotatably supported on the pump shaft11, driving gear member32bthat is relatively rotatably supported on the PTO shaft31to be meshed with the first gear32a, driving-side clutch plate32cthat is relatively non-rotatably and axially non-slidably supported on the driving gear member32b, driven-side clutch plate32dthat is disposed opposite to the driving-side clutch plate32c, pressing member32ethat is relatively non-rotatably and axially slidably supported on the PTO shaft31in such a manner as to relatively non-rotatably support the driven-side clutch plate32dand bring the same into engagement with the driving-side clutch plate32cby the effect of hydraulic pressure, and biasing member32fthat biases the pressing member32ein such a manner as to move the driven-side clutch plate32daway from the driving-side clutch plate32c. According to this arrangement, the PTO shaft31is rotated in synchronization with the pump shaft11upon receiving the effect of the hydraulic pressure.

Brake device33is preferably provided to apply braking power on the PTO shaft31in association with power shutdown action of the hydraulic clutch device32to the PTO shaft31. The brake device33provided can effectively prevent the PTO shaft31from rotating with the moment of inertia effected by the working device connected to the PTO shaft31when shutting down the drive power transmission to the PTO shaft31.

The HST1according to this embodiment additionally includes charge pump unit50for feeding pressurized hydraulic fluid to the pair of hydraulic lines101.

The charge pump unit50includes charge pump body51of a trochoid gear type that is supported on front extension11aof the pump shaft11, and charge pump case52that is connected to a wall of the HST housing40closer to the driving axle, enclosing the charge pump body51. In this embodiment, the center section41corresponds to this wall.

The charge pump case52includes center portion52athat forms therein a hereinafter described hydraulic line communicated with an inlet port and an outlet port of the charge pump body51, and projection52bthat projects from the center portion52aand extends in the vehicle width direction towards the outside. The projection52bis designed to provide bearing support for the front end31aof the PTO shaft31.

By providing the bearing support for the front end31aof the PTO shaft31through the charge pump case52, the following effects can be provided.

In comparison with distance D (i.e., the distance between the front wall of the HST housing and the driving axle) in the arrangement with the mechanical transmission interposed between the HST and the driving axle (FIG. 1) and the distance D in the arrangement without the mechanical transmission (FIG. 9a), the former is longer than the latter by L2of the length of the mechanical transmission320with respect to the fore-aft direction of the vehicle.

Therefore, in order to have the distance between the driving axle and the front end of the PTO shaft constant in the respective arrangements, it is necessary to have the front end of the PTO shaft further extending towards the front side of the vehicle from the HST housing. However, simply extending the front end of the PTO shaft may result in rotational deflection of the PTO shaft or the like.

On the contrary, in this embodiment, since the front end31aof the PTO shaft31is bearing-supported by the charge pump case52, the rotational deflection can effectively be prevented even in the arrangement with the front end31aof the PTO shaft31further extending from the HST housing40.

In this embodiment, the HST is designed so that the front end31aof the PTO shaft31can be supported by the HST only. Specifically, the front end31aof the PTO shaft31is supported by the charge pump case52that is a constituent member of the HST1, so that improved assembling efficiency is obtainable as compared with the arrangement with the front end of the PTO shaft supported by a separate member such as a vehicle body other than the HST.

The HST1having the above arrangement preferably includes auxiliary pump unit60of an external gear type that is detachably mounted thereon.FIG. 5is a view as viewed along lines V—V inFIG. 3.

As illustrated inFIGS. 3 and 5, the auxiliary pump unit60may include first pump gear61that is relatively non-rotatably supported on a portion of the front end11aof the pump shaft11, which portion forwardly extends from the charge pump case52, second pump gear62that is meshed with the first pump gear61, idle shaft63that supports thereon the second pump gear62, and auxiliary pump case64that is connected to the charge pump case52, enclosing the first and second pump gears61,62.

By providing the auxiliary pump unit60, it is possible to provide a sufficient amount of pressurized hydraulic fluid according to the specification of each vehicle without applying an excessive load on the charge pump unit50. Specifically, where the vehicle is designed to enable the mower to elevate, and/or where a power steering device is provided for the steering wheels, the auxiliary pump unit60provided can make the charge pump unit50available for feeding the pressurized hydraulic fluid to the pair of hydraulic lines101and the hydraulic clutch device32in the PTO unit30, and make the auxiliary pump unit60available for feeding the pressurized hydraulic fluid to the mower elevation device and/or the power steering device, thereby preventing excessive load to the charge pump unit50, while providing a sufficient amount of the pressurized hydraulic fluid.

The description will be hereinafter made for the hydraulic circuit of the HST1.

As illustrated inFIGS. 2 and 6, the charge pump case52is provided with inlet line102having a first end opening to the outside and a second end connected to inlet port51aof the charge pump body51, and pressurized fluid line104having a first end connected to outlet port51bof the charge pump body51and a second end branched to first pressurized fluid line105and second pressurized fluid line106via flow divider103and then opening to the outside. The first end of the inlet line102is in communication with hydraulic fluid tank400via pipe fitting140(seeFIGS. 2,5and6).

As illustrated inFIGS. 2 and 7, the center section41to be connected to the charge pump case52is provided with the pair of hydraulic lines101, first bypass line110for communication between the pair of hydraulic lines101, charge line111having a first end communicated with the first pressurized fluid line105and a second end connected to the first bypass line110, charge relief valve112interposed in the charge line111, and pair of high pressure relief valves113and pair of charge check valves114, which pairs are interposed in the first bypass line110between its connection point to the charge line111and its connection point to the pair of hydraulic lines101.

The center section41is preferably and additionally provided with second bypass line115for communication between the pair of hydraulic lines101, drain line116having a first end communicated with the second bypass line115and a second end communicated with the hydraulic fluid tank, and pair of suction valves117interposed in the second bypass line115between its connection point to the drain line116and its connection point to the pair of hydraulic lines101. By providing the pair of suction valves117, it is possible to prevent the generation of negative pressure in the pair of hydraulic lines101in the case where a vehicle stops on a slope with its engine stopped, and hence prevent the vehicle from rolling down on the slope (freewheeling).

As illustrated inFIGS. 2 and 4, the center section41is also provided with pressurized fluid feeding line120having a first end communicated with the second pressurized fluid line106and a second end opening to the inside of the HST housing40.

The second end of the pressurized fluid feeding line120is communicated with PTO hydraulic line122formed in the rear wall of the HST housing42via conduit121disposed within the HST housing121.

As illustrated inFIGS. 2 and 4, the HST housing42is provided with the PTO hydraulic line122having a first end connected to the conduit121and a second end connected to the hydraulic clutch device32, relief valve123, electromagnetic switching valve124and accumulator125respectively interposed in the PTO hydraulic line122, and drain line126communicated with the electromagnetic switching valve124.

The auxiliary pump case64is provided as illustrated inFIGS. 2 and 5with third pressurized fluid line130passing through a meshing portion between the first pump gear61and the second pump gear62and having opposite ends opening to the outside.

Of the opposite ends of the third pressurized fluid line130, first end130ais connected via suitable conduit to a housing of the differential device350, which housing also serves as the hydraulic fluid tank400, so that the third pressurized fluid line130supplies the pressurized hydraulic fluid through second end130bto hydraulic circuit200for elevation of the mower and actuation of the power steering device (seeFIG. 2). The return fluid from the circuit200passes the inside of the HST housing40through a hydraulic fluid cooler, and then returns to the hydraulic fluid tank400. Reference code410inFIG. 2represents a common filter.

While the description in this embodiment was made by taking for example the case where the front axle310acts as the main driving axle and the PTO shaft31extends to the front side with respect to the fore-aft direction of the vehicle, the present invention is not necessarily limited to this embodiment. Rather, the present invention is also applicable to the arrangement where the rear axle acts as the main driving axle and the PTO shaft extends to the rear side with respect to the fore-aft direction of the vehicle.

The HST1is preferably provided with neutral return mechanism480for biasing the output adjusting member14to the neutral position in response to the tilting and rotating action of the output adjusting member14in the vehicle advancing direction or vehicle reversing direction. The vehicle advancing direction and vehicle reversing direction respectively mean the tilting or rotating directions that generate the rotational outputs respectively moving the vehicle forward and rearward.

The description will be herein made for the neutral return mechanism480.FIG. 16is a cross-section taken along lines XVI—XVI inFIG. 3.

As illustrated inFIGS. 8 and 16, the control shaft15includes body15athat is relatively rotatably supported on the housing40while being non-rotatable with respect to the output adjusting member14, and outer extension15bthat outwardly extends from the body15ato the outside of the housing40, so that the tilting and rotating position of the output adjusting member14can be changed from the outside of the housing40. That is, the output adjusting member14can be tilted and rotated through the rotation of the outer extension15bof the control shaft15around the axis.

In this embodiment, the speed change arm43is connected to the outer extension15bof the control shaft15, and the free end of the speed change arm43is connected to the speed change pedal P disposed closer to a driver seat via a suitable connection member (not shown), as illustrated inFIGS. 10 and 16.

The control shaft15and the output adjusting member14may be integrally formed with each other, or separately formed while having a mechanism allowing the associated operation with each other.

The housing40preferably forms therein opening40athrough which the output adjusting member (movable swash plate in this embodiment)14can pass. By forming the opening40a, it is possible to have the control shaft15and output adjusting member14connected or formed integrally with each other and mounted within the housing40. In this arrangement, the clearance between the inner circumference of the opening40aand the outer circumference of the control shaft15may be sealed by plate-like lid40bwith a bearing boss.

FIGS. 17 and 18are cross sections taken along lines XVII—XVII inFIG. 8with the output adjusting member14set at the neutral position and the maximum output position in the vehicle advancing direction.

As illustrated in FIGS.8and16–18, the neutral return mechanism480includes torsion spring481that is supported around the outer extension15bof the control shaft15, and detent pin482that lies at reference position N when the output adjusting member14is at the neutral position, and tilts and rotates in the X and Y-directions around the axis of the control shaft15by a displacement amount corresponding to a tilted and rotated position of the output adjusting member14when the output adjusting member14tilts and rotates in the vehicle advancing direction and reversing direction.

In this embodiment, the detent pin482has proximal end482aconnected to the output adjusting member14and distal end482bextending outwardly from circular slot40cformed in the lid40b(see FIGS.8and17–18), while both ends of the torsion spring481lie respectively on the both sides of the distal end482bwith respect to the moving direction thereof (seeFIGS. 17 and 18).

With the above arrangement, the detent pin482presses first end481aand second end481bof the torsion spring481against its biasing force through its pivotal movement in the vehicle advancing direction (X direction) and reversing direction (Y direction).

The neutral return mechanism480includes fixing member483for fixing the second end481band first end481aof the torsion spring481in position during the pivotal movement of the detent pin482in the vehicle advancing direction and reversing direction. Specifically, the fixing member483is adapted to limit the movement of the second end481bof the torsion spring481during the detent pin482presses the first end481aof the torsion spring481, and limit the movement of the first end481aof the torsion spring481during the detent pin482presses the second end481bof the torsion spring481.

In this embodiment, the neutral return mechanism480includes cover member485that is attached on the outer surface of the lid40bto cover over the torsion spring481and the detent pin482, thereby effectively preventing the intrusion of impurities such as dusts into the housing. A fixing pin to be fixed to the cover member485is used as the fixing member483.

The fixing pin483is preferably an eccentric pin having body483ato be interposed between the both ends481aand481bof the torsion spring481, and an eccentric part483boutwardly extending with its axis eccentric to the axis of the body483a. Whereby, the relative position of the body483ato the control shaft15can be varied through the rotation of the eccentric part483baround the axis of the body483aand hence adjustment of the output adjusting member14to the neutral position after assembling of the HST can easily be performed.

The neutral return mechanism480also includes auxiliary device490that biases the detent pin482to the reference position N during the pivotal movement of the detent pin482.

As illustrated inFIGS. 17 and 18, the auxiliary device490includes cylindrical casing491fixed on the cover member485with an outer end positioned outside of the cover member485, push pin492that is axially slidably placed in the cylindrical casing491with a distal end of the push pin492abuttable against the detent pin482by the pivotal movement of the detent pin482, lid member493that seals the outer end of the cylindrical casing491, and biasing spring494that is disposed between a distal end of the push pin492and the lid member493.

The auxiliary device490is disposed so that the axial direction of the push pin492is substantially matched to the pivoting direction of the detent pin482. That is, the auxiliary device490is designed so that the detent pin482presses the push pin492in the axial direction against the biasing force of the biasing spring494during the pivotal movement of the detent pin482from the reference position N in the vehicle advancing direction (X direction) and/or the vehicle reversing direction (Y direction), as illustrated inFIG. 18.

The lid member493is preferably fixed on the cylindrical casing491in such a manner as to be adjustably positioned along the axis of the cylindrical casing491. With this arrangement, the biasing force of the biasing spring494can be suitably adjusted.

According to the HST1having the above arrangement, when the driver releases the manipulating member such as the manipulation lever (not shown) operatively connected to the output adjusting member14from the engaged state, the output adjusting member14automatically and promptly returns to the neutral position. Therefore, the braking distance for stopping the vehicle can be shortened by efficiently utilizing a dynamic brake by the HST1.

That is, when the driver tilts or rotates the output adjusting member14in the vehicle advancing direction or reversing direction via the manipulating member and the control shaft15, the detent pin482pivotally moves against the biasing forces effected by two biasing members, namely the torsion spring481supported around the control shaft and the biasing spring494of the auxiliary device490. Accordingly, the driver's releasing action causes the detent pin482to return to the reference position N by the biasing forces of both the torsion spring481and the biasing spring494, so that the output adjusting member14promptly returns to the neutral position.

Where the HST has the movable swash plate as the output adjusting member14and employs a so-called shoe-type arrangement that the movable swash plate and the axial piston unit are connected together via universal joint16(seeFIG. 16), a self-return moment of the movable swash plate for returning to the neutral position is small so that this arrangement is particularly effective for the desirable effect as mentioned above.

Since the auxiliary device490is of a simple arrangement that has only the push pin492and the biasing spring494as main components, it is possible to produce the above desirable effect, while not inviting the large-sizing and complexity of the entire HST.

It is preferable to limit the tilting or rotating range of the output adjusting member14, thereby effectively preventing excessive increase in vehicle speed. In this embodiment, the housing40forms therein the slot40cdefining the pivoting range of the detent pin482, so that the slot40climits the pivoting range of the detent pin482or the tilting range of the output adjusting member14. More preferably, the output adjusting member14has a smaller tilting range in the vehicle reversing direction than in the vehicle advancing direction, so that the maximum speed in the vehicle reversing direction can effectively be limited.

The arrangement for limiting the tilting range of the output adjusting member14may be varied. For example, it is possible to provide in the housing40a pair of stoppers that are abuttable to the output adjusting member14.

The auxiliary device490may be selectively provided on either one or both of a vehicle advancing side and reversing side of the detent pin482for a desirable arrangement. Specifically, openings485afor the attachment of the auxiliary device are respectively formed in the walls on the vehicle advancing side and the vehicle reversing side of the detent pin482in the cover member485, so that the auxiliary device490can be selectively attached in place without needs of separate operations or parts for obtaining a suitable arrangement. Accordingly, if it is desired to prevent the abrupt stop of the vehicle, the auxiliary device490may be provided only on the vehicle advancing side of the detent pin482.

With the arrangement as described above, where the detent pin is pivotally movable around the control shaft in association with the tilting action of the output adjusting member in the variable displacement type unit, and during the tilting of the detent pin from the reference position, the detent pin is biased towards the reference position through the biasing force of the auxiliary device as well as the biasing force by the torsion spring supported on the control shaft, the output adjusting member automatically and promptly returns to the neutral position once the driver releases the output adjusting member from the operational mode. Therefore, the dynamic brake action by the HST can promptly and effectively be produced at the time of stopping the vehicle, and therefore the braking distance of the vehicle can be shortened.

By having the auxiliary device acting only during the vehicle runs in the advance direction, it is possible to effectively prevent sudden stop of the vehicle when the vehicle runs in the reverse direction.

By employing the auxiliary device including the pressing member abuttable against the detent pin and the biasing member biasing the detent pin towards the reference position via the pressing member during the pivotal movement of the detent pin, the above desirable effects can be produced through such a remarkably simple structure.

When the biasing member is a spring having the distal end abutted against the pressing member and the proximal end supported by a biasing-force adjusting member, which can be fixed at a given position along the axis along which the spring is compressed and expanded, it is possible to properly adjust the biasing force effected by the spring to the detent pin. Accordingly, the dynamic brake action by the HST can be properly adjusted according to preference.

In this embodiment, the auxiliary pump unit60is provided in addition to the charge pump unit50, where the charge pump unit50is used for feeding pressurized hydraulic fluid to the pair of hydraulic lines101and the hydraulic clutch device32in the PTO unit30, while the auxiliary pump unit60is used for feeding the pressurized hydraulic fluid to the mower elevation device and/or the power steering device. This arrangement thus enables the feeding of a large amount of pressurized hydraulic fluid, but may invite cost increase due to the increased number of pumps.

To address the above, where a relatively small amount of hydraulic fluid to be fed is acceptable, only a single charge pump unit50′ may be used, thereby achieving the feeding of the pressurized hydraulic fluid to those three devices, while reducing the costs involved.

FIG. 19is a transverse plan view of HST1′ equipped only with the charge pump unit50′.FIGS. 20 and 21are cross-sections taken along lines XX—XX and XXI—XXI inFIG. 19. Further,FIG. 22is a hydraulic circuit diagram of the vehicle to which the HST1′ is applied. In the following description on the embodiment illustrated inFIGS. 19 to 22, same or identical parts to those of this embodiment have been give the same reference characters to omit a detailed description thereof.

As illustrated inFIG. 19, the charge pump unit50′ includes charge pump body51′ that is driven through the front extension11aof the pump shaft11, and charge pump case52′ that is connected to the HST housing40while supporting thereon the charge pump body51′.

The charge pump case52′ includes central part52a′ that forms therein a herein described hydraulic line into which the pressurized hydraulic fluid flows from the charge pump body51′, and extension52b′ that extends from the central part52a′ outwardly with respect to the vehicle width direction, so that the front extension31aof the PTO shaft31can be bearing-supported by the extension52b′ .

The charge pump case52′ is provided with inlet line103′ that receives the pressurized hydraulic fluid from the charge pump body51′ via filter102a′, pressurized fluid charge line105′ and pressurized fluid line109′ for the hydraulic device that are branched from the inlet line103′ via branching part104′, pressure reducing valve107′ that is mounted in the pressurized fluid charge line105′ to set a charging hydraulic pressure, pressurized fluid line106′ for the PTO that receives a surplus fluid discharged through the pressure reducing valve107′, and resistive valve108′ that is mounted in the pressurized fluid line109′ for the hydraulic device.

The pressurized fluid charge line105′ is communicated with the charge line111via the filter102b′ . The pressurized fluid line106′ for the PTO is communicated with the hydraulic line122for the PTO via the hydraulic fluid feeding line120and the conduit121. The pressurized fluid line109′ for the hydraulic device is opened in the rear side of the charge pump case52′ and is communicated with the hydraulic circuit200for the working device via a suitable conduit.

This specification is by no means intended to restrict the present invention to the preferred embodiments set forth therein. Various modifications to the hydrostatic transmission and the power train for vehicle, as described herein, may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.