Patent Description:
The present application relates also to a work vehicle configured such that change of a traveling speed is possible by a transmission engaging/disengaging operation of a multiple plate type clutch.

As a work vehicle having the above-described configuration, Patent Document <NUM> discloses a technique in which driving power of an engine is speed-changed firstly by a hydrostatic stepless speed changer device and speed-changed subsequently by a planetary gear speed changer device and then further speed-changed by an auxiliary speed changer device.

The planetary gear speed changer device described in this Patent Document <NUM> includes three planetary gear speed changing sections (referred to as "planetary transmission mechanisms" in the document) which are disposed in series along a common axis and includes also two clutch mechanisms which are configured to take off driving power from two of the three planetary gear speed changing sections individually. In particular, in this planetary gear speed changer device, the two clutch mechanisms too are disposed in series along the same axis as the three planetary gear speed changing sections.

Further, the auxiliary speed changer device described in Patent Document <NUM> is comprised of combination of two clutch mechanisms and two sets of gears so as to be able to change the driving power transmitted from the planetary gear speed changer device in two high and low speed stages.

As a work vehicle having the above-described configuration, according to the disclosure of Patent Document <NUM>, there is provided a hydraulic speed changer device having a high-speed side first hydraulic clutch and a low-speed side second hydraulic clutch in order to speed-change driving power from a traveling propelling shaft in two high and low stages and a corotation preventing arrangement having a brake member which comes into contact with a transmitting body of the hydraulic speed changer device when both the first hydraulic clutch and the second hydraulic clutch are under transmission disengaging states.

In this Patent Document <NUM>, a second gear to which the driving power from the second hydraulic clutch is transmitted is used as the transmitting body, a piston is accommodated in an oil chamber formed inside a transmission case and the brake member is provided at the leading end of this piston.

In this Patent Document <NUM>, there is also provided a switching valve for feeding work oil selectively to one of the first hydraulic clutch and the second hydraulic clutch. In operation, when the switching valve is under a state of not feeding the work oil to either the first hydraulic clutch or the second hydraulic clutch, the work oil is fed to the piston to cause the brake member to protrude, thereby applying a braking force to the transmitting body.

GB <NUM><NUM> A (which forms the basis for the preamble of claim <NUM>) describes a power transmission mechanism in which changes of transmission ratio are facilitated.

The present invention is defined by the independent claim. Further aspects are defined in the dependent claims.

A problem corresponding to [Related Art <NUM>] is as follows.

With the speed changing arrangement described in Patent Document <NUM>, stepless speed changing operations are possible with the stepless speed changer device and speed changing operations in two stages are possible with the planetary gear speed changer device and further speed changing operations in two additional stages are possible with the auxiliary speed changer device. As a result, this speed changing arrangement realizes speed changing operations in multiple stages.

Further, in the speed changing arrangement described in Patent Document <NUM>, the planetary gear speed changer device allows speed reduction at large speed reduction ratios, so the arrangement allows use of a stepless speed changer device having a small capacity.

However, in the planetary gear speed changer device described in Patent Document <NUM>, since three planetary gear speed changing sections are arranged in series and also two clutch mechanisms are arranged in series, the arrangement is not only complicated, but also invites enlargement thereof in the front/rear direction. Especially, since the speed changing arrangement described in Patent Document <NUM> invites complexity also in the transmission arrangement for taking off speed-changed driving power, so there remains room for improvement.

For the reasons mentioned above, there is a need for a work vehicle that allows suppression of disadvantageous enlargement of the speed changing arrangement and also allows simplification of this speed changing arrangement, without compromising the advantage of using a hydrostatic stepless speed changer device and a planetary gear speed changer device.

The corotation preventing arrangement described in Patent Document <NUM> suppresses occurrence of a phenomenon that when the first hydraulic clutch and the second hydraulic clutch are under the transmission disengaging states, in association with rotation of the propelling shaft, a part of the hydraulic speed changer device will rotate with this propelling shaft, so that the driving power of the propelling shaft is transmitted to wheels, resulting in movement of the wheel at an extremely low speed.

However, the arrangement of Patent Document <NUM>, for prevention of such corotation, the arrangement would require an oil chamber in the transmission case and require also a piston and a brake member. The arrangement further requires a switching valve and an oil passage which feed work oil to the oil chamber when the two hydraulic clutches of the hydraulic speed changer device are under the transmission disengaging states. Thus, the arrangement is complicated, inviting increase in the number of components, leading to cost increase.

For the reasons mentioned above, there is a need for a work vehicle which can suppress the inconvenience of the vehicle body being moved at a low speed when the hydraulic cutch is under the transmission disengaging state, without inviting disadvantageous complication in the arrangement for suppressing corotation.

Solution corresponding to [Problem <NUM>] is as follows.

According to a preferred feature of a work vehicle relating to the present invention, the work vehicle comprises:.

With this feature, the driving power of the engine is speed-changed steplessly by the stepless speed changer device and the driving power thus speed-changed can be speed-reduced largely in each one of the plurality of planetary gear speed changer devices. Therefore, as the stepless speed changer device, one having a small capacity can be employed. Further, the driving powers speed-changed by the plurality of planetary gear speed changer devices will be taken off individually by the clutch mechanisms corresponding thereto, and can be transmitted as such to the traveling speed changing section. In particular, since the plurality of planetary gear speed changer devices are arranged in juxtaposition relationship with each other, reduction in the dimension in the front/rear direction of the space accommodating the planetary gear speed changer devices is possible, in comparison with an arrangement of the plurality of planetary gear speed changer devices being arranged in series.

Therefore, there is realized a work vehicle that allows suppression of disadvantageous enlargement of the speed changing arrangement and also allows simplification of this speed changing arrangement, without compromising the advantage of using a hydrostatic stepless speed changer device and a planetary gear speed changer device.

According to a further preferred feature:.

With the above-described arrangement, the driving shaft transmitting the driving power of the engine penetrates the stepless speed changer device in the front/rear direction and as the driving power available from the penetrating part thereof is transmitted to the input shafts of the plurality of planetary gear speed changer devices via the drive gear mechanism, speed changing operations in the stepless speed changer device are made possible. Further, as the driving power from the output shaft of the stepless speed changer device is transmitted via the branching gear mechanism to the plurality of planetary gear speed changer devices, speed changing operations in the plurality of planetary gear speed changer devices are made possible.

With the above-described arrangement, by selectively operating the first clutch mechanism and the second clutch mechanism, it is possible to take off the driving power speed-changed by the first planetary gear speed changer device and the driving power speed-changed by the second planetary gear speed changer device and to further speed-change these driving powers to be transmitted to the traveling mechanism.

According to a still further preferred feature:.

With the above-described arrangement, as the hydraulic pump and the hydraulic motor are disposed on the side of the rear face of the port block, it becomes readily possible to form e.g. an arrangement of causing the input shaft of the hydraulic pump to protrude rearwards and causing the output shaft of the hydraulic motor to protrude rearwards.

According to a feature of a work vehicle relating to the present invention, the work vehicle comprises:.

With the above-described arrangement, in case the first clutch mechanism is set to its power-transmission disengaging state, a drag torque acting on a friction plate of the first clutch mechanism is transmitted to a traveling driving system. Similarly, in case the second clutch mechanism is set to its power-transmission disengaging state, a drag torque acting on a friction plate of the second clutch mechanism is transmitted to the traveling driving system.

On the other hand, according to the claimed arrangement, the rotational power of the intermediate rotational member which is rotated by the drag torque associated with rotation of the first transmission shaft is transmitted to the output portion of the second clutch mechanism via the coupling portion. With this, it becomes possible to e.g. increase the speed difference between the rotational speed of the output portion of the second clutch and the rotational speed transmitted from the coupling portion. Further, by setting the rotational directions of the driving powers transmitted from the coupling portion opposite to each other, it becomes also possible to generate a torque which suppresses relative rotations, thus offsetting the driving power to be transmitted to the traveling driving system. That is, through effective utilization of drag torques which are generated in the two clutch mechanisms under their transmission disengaging states, the arrangement, though not having any actuator, still allows for reduction and offset of the rotational power to be transmitted to the traveling transmission system.

Consequently, there has been realized a work vehicle which can suppress the inconvenience of the vehicle body being moved at a low speed when the hydraulic cutch is under the transmission disengaging state, without inviting disadvantageous complication in the arrangement for suppressing corotation.

According to the invention:
the work vehicle further comprises:.

With the above-described arrangement, traveling driving power is transmitted from the first planetary gear speed changer device via the first shaft to the first clutch mechanism. The first clutch mechanism, under its transmission engaging state, transmits the driving power of the first shaft to the traveling mechanism as forward traveling driving power. Further, the traveling driving power is transmitted from the second planetary gear speed changer device via the second shaft to the second clutch mechanism. The forward traveling clutch section of the second clutch mechanism transmits, under its transmission engaging state, the diving power of the second shaft to the traveling mechanism as forward traveling driving power. The reverse traveling clutch section of the second clutch mechanism transmits, under its transmission engaging state, the driving power of the second shaft to the traveling mechanism as reverse traveling driving power.

According to an additional arrangement to the above-described arrangement:
the coupling portion comprises a gear portion which is rotated by a rotational power of the intermediate rotational member, the gear portion being meshed with the reverse traveling transmission gear.

With the above-described arrangement, when the first clutch mechanism and the second clutch mechanism are under their transmission disengaging states, in association with rotation of the first shaft, a drag torque will be applied in the forward traveling direction from the first clutch mechanism to the traveling mechanism; and in association with rotation of the second shaft, a drag torque will be applied in the forward traveling direction from the forward traveling clutch section of the second clutch to the traveling mechanism and a drag torque will be applied in the reverse traveling direction from the reverse traveling clutch section of the second clutch to the traveling mechanism.

Here, when a comparison arrangement not having the intermediate rotational member is considered, with this comparison arrangement, drag torques will be applied in the forward traveling direction from the two clutch mechanisms and a drag torque will be applied in the reverse traveling direction from one clutch mechanism. Thus, in comparison with a drag torque applied in the reverse traveling direction, the drag torque in the forward traveling direction is greater, thus inviting inconvenience of the vehicle body traveling forwardly at a low speed. On the other hand, by meshing the gear portion rotated by the rotational power of the rotational member rotated by the drag torque of the first shaft with the reverse traveling transmission gear, thereby to increase the drag torque in the reverse traveling direction applied to the traveling mechanism in the above-described comparison arrangement, it becomes also possible to offset the drag torque in the forward traveling direction and the drag torque in the reverse traveling direction with each other.

According to an additional arrangement to the above-described arrangement:
the gear portion is formed in an outer circumference of the intermediate rotational member.

With the above-described arrangement, as it becomes possible to transmit the rotational power of the intermediate rotational member directly from the gear portion to the reverse traveling transmission gear, it becomes also possible to simplify the transmission arrangement.

According to an additional arrangement to the above-described arrangement:.

With the above-described arrangement, by setting the first clutch to the transmission engaging state, traveling at a predetermined speed is made possible. By setting the forward traveling clutch section of the second clutch mechanism to the transmission engaging state, traveling at a speed lower than the above-described predetermined speed is made possible. Further, since a friction plate rotatable together with the intermediate rotational member is disposed adjacent a friction member which is rotatable with a clutch housing of the first clutch mechanism, if the clutch housing of the first clutch mechanism is rotated by a drag torque associated with rotation of the first shaft, it becomes possible to transmit this rotation to the intermediate rotational member.

According to an additional arrangement to the above-described arrangement:
the work vehicle further comprises:
an auxiliary speed changer device configured to speed-change the driving powers from the first clutch mechanism and the second clutch mechanism.

With this arrangement, it becomes possible for the auxiliary speed changer device to speed-change the traveling driving power from the first clutch mechanism and the traveling driving power from the second clutch mechanism and then to transmit the resultant powers to the traveling mechanism.

According to an additional arrangement to the above-described arrangement:
the work vehicle further comprises:.

With the above-described arrangement, it becomes possible for the hydrostatic stepless speed changer device to steplessly speed-change the driving power of the engine and to transmit the resultant power to the first planetary gear speed changer device and the second planetary gear speed changer device. And, as the first planetary gear speed changer device and the second planetary gear speed changer device are accommodated in a transmission case in a juxtaposition relationship with each other, the front/rear length of the transmission case can be reduced.

With the above-described arrangement, by setting an oil amount of the work oil fed to the hydraulic motor from the variable displacement type hydraulic pump driven by the driving power of the engine, a driving speed of the hydraulic motor can be adjusted. Further, since the input shaft of the hydraulic pump and the output shaft of the hydraulic pump protrude rearwards from the stepless speed changer device, it becomes possible to transmit the driving power of the penetrating portion of the drive shaft penetrating the stepless speed changer device from the driving gear mechanism to the input shaft and from the branching gear mechanism to the first planetary speed changer device and the second planetary speed changer device.

Next, an embodiment of the present invention will be explained with reference to the accompanying drawings.

As shown in <FIG>, a traveling vehicle body A includes a pair of left and right front wheels <NUM> and a pair of left and right rear wheels <NUM>. An engine <NUM> is provided inside an engine hood <NUM> disposed at a front portion of the traveling vehicle body A. At a rear portion of the traveling vehicle body A, there is disposed a driving section B having a cabin <NUM>. With these, there is constituted a tractor as a "work vehicle". In this tractor, the left and right front wheels <NUM> and the left and right rear wheels <NUM> function as "traveling mechanism(s)".

As shown in <FIG> and <FIG>, a sign F in the drawings denotes the "forward direction" and a sign B denotes the rear direction, a sign U denotes "upper direction", a sign D denotes the "lower direction", a sign R denotes "right direction" and a sign L denotes "left direction", respectively.

Inside the cabin <NUM>, there are provided a driver's seat <NUM> disposed at a mid position between left and right rear wheel fenders <NUM> and a steering wheel <NUM> disposed forwardly thereof. Further, adjacent the driver's seat <NUM>, there are provided operational levers, switches, etc..

As shown in <FIG>, in this tractor, on the rear side of the engine <NUM>, a main clutch housing <NUM>, a stepless speed changer housing <NUM> and a transmission case <NUM> are connected in this mentioned order. The transmission case <NUM> accommodates a traveling speed changer device <NUM> (an example of a "traveling speed changing section") for transmitting driving power to the left and right front wheels <NUM> and rear wheels <NUM>.

At rear portions of the transmission case <NUM>, there are provided a pair of left and right lift arms <NUM> which are pivotally lifted up/down by driving power of a hydraulic cylinder <NUM> and a pair of left and right lower links <NUM>, pivotal ends of the lift arms <NUM> and the lower links <NUM> being connected under a suspended state via lift rods <NUM>. In a rear face of the transmission case <NUM>, there is provided a PTO shaft <NUM> that allows takeoff of driving power to the outside.

With this tractor, a utility implement such as a rotary cultivator, a plow, etc. will be connected to rear ends of the left and right lower links <NUM>, so that the implement can be lifted up/down by elevating/lowering operations of the left and right lift arms <NUM>. Further, in case a rotary cultivator is used as an (utility) implement, a drive shaft will be provided between the PTO shaft <NUM> and the rotary cultivator for transmitting driving power thereto.

In this tractor, as shown in <FIG>, the main clutch housing <NUM> accommodates therein a main clutch mechanism <NUM> and the stepless speed changer housing <NUM> accommodates therein a hydrostatic stepless speed changer device <NUM>. Further, the transmission case <NUM> accommodates therein a first planetary gear speed changer device Q1 on the high speed side having a small speed changing ratio, a second planetary gear speed changer mechanism Q2 on the low speed side having a large speed changing ratio, a first clutch mechanism C1 and a second clutch mechanism C2, a traveling speed changer device <NUM>, and an implement speed changer device <NUM>.

As shown in <FIG>, with this speed changing arrangement, the stepless speed changer device <NUM>, the first planetary gear speed changer device Q1, the second planetary gear speed changer device Q2, the first clutch mechanism C1, the second clutch mechanism C2 and transmission gears operably coupled therewith together constitute a main speed changer device 50A. Further, a first speed changing section <NUM>, a second speed changing section <NUM> and transmission gears operably coupled therewith together constitute an auxiliary speed changer device 50B.

Moreover, there are provided a traveling transmission arrangement for transmitting the driving power from the traveling speed changer device <NUM> via a rear wheel drive shaft <NUM> to a rear wheel differential gear <NUM> and further to the rear wheels <NUM> and a traveling transmission arrangement for transmitting the driving power from the rear wheel drive shaft <NUM> to a front wheel differential gear <NUM> and further to the front wheels <NUM>.

Also, the traveling transmission arrangement for transmitting the driving power to the front wheels <NUM> is configured such that the driving power is transmitted from the rear wheel drive shaft <NUM> via the front wheel transmission gear <NUM> to a front wheel transmission shaft <NUM> and then via this front wheel transmission shaft <NUM> to the front wheel drive shaft <NUM> via a front wheel speed changer device <NUM> and further to a front wheel differential gear <NUM>.

In particular, in this arrangement, the first planetary gear speed changer device Q1 and the second planetary gear speed changer device Q2 are specific examples of "a plurality of planetary gear speed reduction devices"; and the first clutch mechanism C1 and the second clutch mechanism C2 are specific examples of clutch mechanisms for engaging/disengaging transmission of the driving power from the planetary gear speed reduction mechanisms.

The main clutch mechanism <NUM> is configured to be settable to a state of transmitting driving power of the engine <NUM> and a state of not transmitting the power, in response to a worker's operation. The stepless speed changer device <NUM>, in response to a speed changing operation by a worker, speed-change a traveling speed steplessly and enables also stopping of the traveling vehicle body A by creating a state of not outputting any driving power.

As shown in <FIG> and <FIG>, the stepless speed changer device <NUM> has a configuration that a variable displacement type hydraulic pump P to which the driving power of the engine <NUM> is transmitted via an input shaft <NUM>, a hydraulic motor M configured to transmit a speed-changed driving power to the first planetary gear speed changer device Q1 and the second planetary gear speed changer device Q2 via an output shaft <NUM>, and a port block <NUM> defining a pair of oil passages for feeding/discharging work oil between the hydraulic pump P and the hydraulic motor M are all accommodated within a stepless speed changer housing <NUM>. Further, the input shaft <NUM> and the output shaft <NUM> are provided under a parallel posture, with protruding ends thereof being oriented rearwards.

In the hydraulic pump P, a pump body 24a rotatable with the input shaft <NUM> is provided with a plurality of plungers which can be expanded and contracted. And, this hydraulic pump P includes a movable swash plate 24b which is operable to set expansion/contraction amounts of the plungers at the time of driven rotation of the pump body 24a. And, a servo piston (not shown) for controlling the posture of this movable swash plate 24b is supported to the stepless speed changer housing <NUM>.

In the hydraulic motor M, a motor body 26a rotatable with the output shaft <NUM> is provided with a plurality of plungers which can be expanded and contracted. And, there is provided a fixed swash plate 26b which converts an expanding/contracting movement of the plunger into a rotary motion.

With the above-described configuration, under a state of the movable swash plate 24b being set to a predetermined angle (angle relative to the pump axis), if the pump body 24a is rotatably driven, in association with this rotation, end portions of the plurality of plungers of the hydraulic pump P will come into contact with the movable swash plate 24b and contracted one after another thereby. In the course of this, the work oil is fed to one of the pair of oil passages of the port block <NUM> and under the pressure of this work oil, the plurality of plungers of the hydraulic motor M will be expanded one after another, and in the course of these expansions, the motor body 26a is rotated by a reaction force from the fixed swash plate 26b. Incidentally, in association with the rotation of the hydraulic motor M, the plunger of the hydraulic motor M is contracted, and in association with this contraction, the work oil is returned via the other flow passage to the hydraulic pump P.

With this stepless speed changer device <NUM>, by adjusting an angle of the movable swash plate 24b through an operation of the servo piston, a discharge amount of the work oil is controlled, whereby the rotational speed of the hydraulic motor M can be set as desired. Further, by setting the angle of the movable swash plate 24b orthogonal relative to the input axis, feeding and discharging of the work oil between the hydraulic pump P and the hydraulic motor M are stopped, whereby the hydraulic motor M can be stopped also.

As shown in <FIG> and <FIG>, a main drive shaft <NUM> to which the driving power of the engine <NUM> is transmitted via the main clutch mechanism <NUM> is disposed to penetrate the stepless speed changer device <NUM> in the front/rear direction; and there is provided a driving gear mechanism <NUM> for transmitting driving power from this main drive shaft <NUM> to the input shaft <NUM> of the stepless speed changer device <NUM>.

Further, a branching gear mechanism <NUM> is provided for transmitting driving power from the output shaft <NUM> of the stepless speed changer device <NUM> to the first planetary gear speed changer device Q1 and the second planetary gear speed changer device Q2 in distribution.

As shown in <FIG>, the first planetary gear speed changer device Q1 and the second planetary gear speed changer device Q2 are accommodated and disposed in a juxtaposition positional relationship along the left/right direction inside the transmission case <NUM>. In order to engage or disengage transmission of the driving power from a first output shaft 46a of the first planetary gear speed changer device Q1, the first clutch mechanism C1 is disposed on the same axis as that of the first output shaft 46a. Similarly, in order to engage or disengage transmission of the driving power from a second output shaft 46b of the second planetary gear speed changer device Q2, the second clutch mechanism C2 is disposed on the same axis as that of the second output shaft 46b.

More particularly, in the first planetary gear speed changer device Q1, a first input shaft 41a includes a first sun gear 42a. Between a first ring gear 43a disposed to be rotatable coaxially with the first input shaft 41a and the first sun gear 42a, there are provided a plurality of first planetary gears 44a. And, a gear portion formed in a first carrier 45a which supports the plurality of first planetary gears 44a is meshed with a coupling gear portion <NUM> provided in the main drive shaft <NUM>.

Also, this first planetary gear speed changer device Q1 includes a first output shaft 46a which is rotatable in unison with the first ring gear 43a.

In the second planetary gear speed changer device Q2, a second input shaft 41b includes a second sun gear 42b. Between a second ring gear 43b disposed to be rotatable coaxially with the second input shaft 41b and the second sun gear 42b, there are provided a plurality of second planetary gears 44b. And, a gear portion formed in a second carrier 45b which supports the plurality of second planetary gears 44b is meshed with the coupling gear portion <NUM> provided in the main drive shaft <NUM>.

This second planetary gear speed changer device Q2 includes a second output shaft 46b which is rotatable in unison with the second carrier 45b.

As shown in <FIG>, the first clutch mechanism C1 is configured as a wet multiple plate type which can be selectively switched to a power-transmission engaging state of transmitting driving power and a power transmission disengaging state of not transmitting the driving power, with feeding/discharging of the work oil. The second clutch mechanism C2 is comprised of two wet multiple plate type clutch sections each of which can be selectively switched to a power transmission engaging state of engaging driving power transmission and a power transmission disengaging state of disengaging driving power transmission, with feeding/discharging of the work oil.

There is provided a tubular intermediate shaft <NUM> coaxial and rotatable relative to the main drive shaft <NUM>. When the first clutch mechanism C1 is set to the transmission engaging state, high-speed driving power from the first output shaft 46a of the first planetary gear speed changer device Q1 can be transmitted to the intermediate shaft <NUM> via a first transmission gear <NUM>.

One of the two clutch sections (the right side in <FIG>) of the second clutch mechanism C2 is designed as forward traveling transmission, so that by setting this clutch section to the power-transmission engaging state, low-speed driving power from the second output shaft 46b of the second planetary gear speed changer device Q2 can be transmitted to the intermediate shaft <NUM> via a second transmission gear <NUM>.

The other of the two clutch sections (the left side in <FIG>) of the second clutch mechanism C2 is designed as reverse traveling transmission, so that by setting this clutch section to the power-transmission engaging state, low-speed driving power from the second output shaft 46b of the second planetary gear speed changer device Q2 can be transmitted to a first counter shaft <NUM> via a third transmission gear <NUM>.

The first counter shaft <NUM> is provided under posture parallel with the intermediate shaft <NUM>, and a second counter shaft <NUM> is provided under a posture parallel with these and a rear wheel drive shaft <NUM> is provided on the same axis as the first counter shaft <NUM>.

The auxiliary speed changer device 50B is constituted of a first speed changing section <NUM> provided between the first counter shaft <NUM> and the rear wheel drive shaft <NUM>, a second speed changing section <NUM> provided on the same axis as the second counter shaft <NUM>, and a transmission gear operably coupled therewith. This auxiliary speed changer device 50b realizes speed changes in three stages of: high speed, intermediate speed and low speed and realizes also a reverse traveling transmission state.

The first speed changing section <NUM> and the second speed changing section <NUM> respectively is configured as a manually operable meshing type clutch.

This auxiliary speed changer device 50B includes, between the intermediate shaft <NUM> and the first speed changing section <NUM>, a high speed transmission gear <NUM> and an intermediate speed transmission gear <NUM>, includes, between the first counter shaft <NUM> and the second counter shaft <NUM>, a first low speed transmission gear <NUM>, and further includes, between the second speed changing section <NUM> and the rear wheel drive shaft <NUM>, a second low speed transmission gear <NUM>.

With the above-described configuration of the traveling speed changer device <NUM>, the driving power of the engine <NUM> is speed-changed steplessly in the stepless speed changer device <NUM>. When the first clutch mechanism C1 is set to the power-transmission engaging state, high-speed driving power speed-changed by the first planetary gear speed changer device Q1 is transmitted via the first transmission gear <NUM> to the intermediate shaft <NUM>. Further, when one clutch section of the second clutch mechanism C2 is set to the power-transmission engaging state, low-speed driving power is transmitted via the second transmission gear <NUM> to the intermediate shaft <NUM>. Further, when the other clutch section of the second clutch mechanism Q2 is set to the power-transmission engaging state, driving power for reverse traveling is transmitted to the first counter shaft <NUM>.

In this main speed changer device 50A, a control mode is set such that the first clutch mechanism C1 and the second clutch mechanism C2 will not be set to the power-transmission engaging states simultaneously. Similarly, an operation mode is set so that the first speed changing section <NUM> and the second speed changing section <NUM> will not be set to the power-transmission engaging states simultaneously.

In the auxiliary speed changer device 50B, under the state of the driving power of either one of the first clutch mechanism C1 and the second clutch mechanism C2 being transmitted to the intermediate shaft <NUM>, the first speed changing section <NUM> transmits the driving power from the high speed transmission gear <NUM> to the rear wheel drive shaft <NUM>, whereby high speed rotational driving powers will be transmitted to the rear wheels <NUM> and to the front wheels <NUM>.

Similarly to the above, under the state of the driving power of either one of the first clutch mechanism C1 and the second clutch mechanism C2 being transmitted to the intermediate shaft <NUM>, when the first speed changing section <NUM> transmits the driving power from the intermediate speed transmission gear <NUM> to the rear wheel drive shaft <NUM>, whereby intermediate speed rotational driving powers will be transmitted to the rear wheels <NUM> and to the front wheels <NUM>.

Moreover, under the state of the driving power of either one of the first clutch mechanism C1 and the second clutch mechanism C2 being transmitted to the intermediate shaft <NUM>, when the first speed changing section <NUM> effects no transmission, the first counter shaft <NUM> will be rotated by the driving force transmitted via the high speed transmission gear <NUM>. Therefore, under this state, if the second speed changing section <NUM> is set to the power-transmission engaging state, low speed driving power speed-reduced via the first low speed transmission gear <NUM> and the second low speed transmission gear <NUM> will be transmitted to the rear wheel drive shaft <NUM> and low speed driving powers will be transmitted to the rear wheels <NUM> and the front wheels <NUM>.

Further, by setting the other one of the two clutch sections of the second clutch mechanism to the power-transmission engaging state, under a state of the driving power being transmitted from the third transmission gear <NUM> to the first counter shaft <NUM>, if the first speed changing section <NUM> is operated to transmit the driving power of the first counter shaft <NUM> to the rear wheel drive shaft <NUM>, reverse driving powers will be transmitted to the rear wheels <NUM> and the front wheels <NUM>. Incidentally, the operational position for transmitting the driving power from the first counter shaft <NUM> to the rear wheel drive shaft <NUM> in the second clutch mechanism C2 is the same position as the position for transmitting the driving power from the high speed transmission gear <NUM> to the rear wheel drive shaft <NUM>.

A front wheel speed changer device <NUM> is disposed between the front wheel drive shaft <NUM> and the front wheel transmission shaft <NUM> and includes a constant speed transmission gear 65a, an acceleration transmission gear 65b and a switching clutch mechanism 65c. This switching clutch mechanism 65c is configured as a hydraulic multiple plate type which is operated under a state of selectively transmitting the driving power with feeding/discharging of the work oil and a state of blocking, i.e. not transmitting the driving power.

With the above-described arrangement, when the traveling vehicle body A is to travel straight, the constant speed transmission gear 65a is set to the transmission engaging state under control by the switching clutch mechanism 65c, the peripheral speed of the front wheels <NUM> and the peripheral speed of the rear wheels <NUM> are set equal to each other. Also, in case the steering wheel <NUM> has been operated by an amount exceeding a set amount, the acceleration transmission gear 65b is set to the transmission engaging state under the control of the switching clutch mechanism 65c, the peripheral speed of the front wheels <NUM> is set higher than the peripheral speed of the rear wheels <NUM>, thereby to reduce the turning radius. Further, in the case of traveling under a state of no driving power being transmitted to the front wheels <NUM> (two-wheel state), by the switching clutch mechanism 65c, it is possible to set to the state of disengaging driving power transmission.

At a position rearwardly of the intermediate shaft <NUM>, there is provided an arrangement for transmitting the driving power from the main drive shaft <NUM> via a pump drive gear <NUM> to an implement pump <NUM>.

The implement speed changer device <NUM> includes a hydraulic multiple plate type implement clutch <NUM> for engaging/disengaging transmission of the driving power from the main drive shaft <NUM>, an implement speed changing section <NUM>, an implement speed changer shaft <NUM> to which driving power from the implement speed changing section <NUM> is transmitted, and an output gear <NUM> for transmitting the driving power from the implement speed changer shaft <NUM> to the PTO shaft <NUM>.

The implement speed changing section <NUM> includes two implement speed changer clutches 74a disposed coaxially with the implement speed changer shaft <NUM>, an implement counter shaft 74b rotatably fitted on the rear wheel drive shaft <NUM>, a first implement gear 74c for transmitting driving power from the implement clutch <NUM> to the implement counter shaft 74b, and three second implement gears 74d configured to transmit the driving power from the implement counter shaft 74b to a corresponding one of the two implement speed changer clutches 74a. Incidentally, each of the two implement speed changer clutches 74a is configured as a manually operable meshing type clutch.

With this implement speed changing section <NUM> in operation, in a situation of the implement clutch <NUM> being set to the transmission engaging state, by selective operation of the two implement speed changer clutches 74a, it is possible to set the driving power transmitted from the main drive shaft <NUM> to one of a reduced speed transmission state, an intermediate speed transmission state, a high speed transmission state and a reverse transmission state, to transmit the power to the implement speed changer shaft <NUM>. Further, the implement pump <NUM> is configured to feed lubricant oil reserved in the transmission case <NUM> as the work oil.

Incidentally, the work oil of the implement pump <NUM> is fed via a control valve (not shown) to the first clutch mechanism C1, the second clutch mechanism C2, the switching clutch mechanism 65c and to the implement clutch <NUM>.

The driving power of the engine <NUM> is speed-changed steplessly by the stepless speed changer device <NUM> and then the resultant speed-changed driving power can be largely reduced in speed by the two planetary gear speed changer devices, namely, the first planetary gear speed changer device Q1, the second planetary gear speed changer device Q2. Therefore, the stepless speed changer device <NUM> to be employed can be one having a small capacity. Further, the driving powers speed-changed respectively by the first planetary gear speed changer device Q <NUM> and the second planetary gear speed changer device Q2 can be taken off via the first clutch mechanism C1 and the second clutch mechanism C2 corresponding respectively thereto and then transmitted to the traveling speed changer device <NUM>.

In particular, since the first planetary gear speed changer device Q <NUM> and the second planetary gear speed changer device Q2 are disposed in the juxtaposition relationship with each other, compared with an arrangement of disposing a plurality of planetary gear speed changer devices in series, the space accommodating the planetary gear speed changer devices can be formed compact in the front/rear direction. Consequently, there has been realized a work vehicle that allows suppression of disadvantageous enlargement of the speed changing arrangement and also allows simplification of this speed changing arrangement, without compromising the advantage of using a hydrostatic stepless speed changer device and a planetary gear speed changer device.

The present invention may alternatively be configured as follows, in addition to the foregoing embodiment (in the following, elements having same or substantially same functions as the foregoing embodiment will be denoted with same or like numerals, marks provided in the foregoing embodiment).

In the configuration of this Further Embodiment (a), when the engine <NUM> is to be started or the traveling vehicle body A is to be stopped, control will be set for stopping flow of work oil by setting the angle of the movable swash plate 24b of the stepless speed changer device <NUM> to a posture orthogonal to the pump axis or setting the first clutch mechanism C1 and the second clutch mechanism C2 to the power transmission disengaging states, simultaneously.

In this way, in the Further Embodiment (a), as components for constituting the main clutch housing <NUM> and the main clutch mechanism <NUM> described in the foregoing embodiment are no longer needed, the reduction in the number of components of the work vehicle is made possible and the size of the vehicle body in the front/rear direction is reduced to allow compactization of the work vehicle as well as weight reduction of the vehicle body.

(b) As shown in <FIG>, like Further Embodiment (a) described above, a transmission case <NUM> of a tractor (an example of "work vehicle") is configured with omission of the main clutch housing <NUM> and the main clutch mechanism <NUM> described in the foregoing embodiment. More particularly, there is provided an arrangement for suppressing occurrence of inconvenience of the traveling vehicle body A being moved at a low speed due to drag torques applied respectively from the first output shaft 46a (an example of "first shaft") and the second output shaft 46b (an example of "second shaft") in the case of both the wet type first clutch mechanism C <NUM> and the wet type second clutch mechanism C2 being under the power transmission disengaging states.

As shown in <FIG> and <FIG>, the first clutch mechanism C1, under its transmission engaging state, transmits the driving power of the first output shaft 46a (an example of "first shaft") as forward traveling driving power via the first forward traveling output gear 36a to the first forward traveling input gear 36b of the intermediate shaft <NUM>.

Further, the second clutch mechanism C2 includes a forward traveling clutch section C2f and a reverse traveling clutch section C2r. The forward traveling clutch section C2f, under its power-transmission engaging state, transmits the driving power of the second output shaft 46b (an example of "second shaft") as forward traveling driving power via a second forward traveling output gear 37a to a second forward traveling input gear 37b of the intermediate shaft <NUM>. The reverse traveling clutch section C2r, under its power-transmission engaging state, transmits the driving power of the second output shaft 46b (an example of "second shaft") as reverse traveling driving power via a second reverse traveling output gear 38a (an example of "reverse traveling output gear") to a second reverse traveling input gear 38b (an outputting section, an example of "reverse traveling transmission gear") of the first counter shaft <NUM>.

Incidentally, in this transmission case <NUM>, there is set an arrangement such that the driving speed transmitted to the front wheels <NUM> and the rear wheels <NUM> when the first clutch mechanism C <NUM> is set to the transmission engaging state may be higher than the driving speed transmitted to the front wheels <NUM> and the rear wheel <NUM> when the forward traveling clutch section C2f of the second clutch mechanism C2 is set to the transmission engaging state.

In this Further Embodiment (b), as shown in <FIG>, there is provided an intermediate rotational member <NUM> to which a drag torque is applied in association with rotation of the first output shaft 46a, and an arrangement is provided such that by transmitting rotational power of this intermediate rotational member <NUM> to the second reverse traveling output gear 38a (an example of "reverse traveling transmission gear"), the phenomenon of traveling driving power being transmitted to the left and right front wheels <NUM> and the left and right rear wheels <NUM> as the traveling mechanism may be suppressed.

The first clutch mechanism C1 includes, inside a first clutch housing CH1, a first sleeve <NUM> which is rotated with the first forward traveling output gear 36a and includes also a plurality of driving side friction plates <NUM> engageable with a plurality of first slits 80a defined in the outer circumference of the first clutch housing CH1, a plurality of driven side friction plates <NUM> engaged on the first sleeve <NUM> for transmitting torque thereto, and a first piston <NUM> operable to place the driving side friction plates <NUM> and the driven side friction plates <NUM> under pressed contact each other by feeding the pressure oil.

In this first clutch mechanism C1, the first clutch housing CH1 is rotatable together with the first output shaft 46a, and the driving side friction plates <NUM> and the driven side friction plates <NUM> are disposed in alternation. And, oil passages for feeding/discharging work oil to/from the first piston <NUM> are formed inside the first output shaft 46a.

And, when the work oil is fed to the first piston <NUM> by feeding of the work oil, there is realized a power-transmission engaging state in which the plurality of driving side friction plates <NUM> and the plurality of driven side friction plates <NUM> are placed under pressed contact with each other, whereby the driving power of the first output shaft 46a will be transmitted to the first forward traveling output gear 36a. With discharging of the work oil, the pressure from the piston is released, whereby the plurality of driving side friction plates <NUM> and the plurality of driven side friction plates <NUM> will be detached from each other, thus realizing a transmission disengaging state of not transmitting the driving power.

In the second clutch mechanism C2, inside a second clutch housing CH2, a forward traveling clutch section C2f and a reverse traveling clutch section C2r are accommodated. And, the forward traveling clutch section C2f and the reverse traveling clutch section C2r have basically same arrangements as those of the first clutch mechanism C1. The forward traveling clutch section C2f includes a forward traveling piston C2fp for pressing the friction plates for contact and the reverse traveling clutch section C2r includes a reverse traveling piston C2rp for pressing the friction plates for contact.

With the above-described arrangement in operation, with feeding of the work oil to the forward traveling piston C2fp, there is realized a power-transmission engaging state for transmitting the driving power of the second output shaft 46b to the second forward traveling output gear 37a. With discharging of the work oil, there is realized the power-transmission disengaging state of not transmitting the driving power thereto. Further, with feeding of the work oil to the reverse traveling piston C2rp, there is realized a power-transmission engaging state for transmitting the driving power of the second output shaft 46b to the second reverse traveling output gear 38a. With discharging of the work oil, there is realized a power-transmission disengaging state of not transmitting the driving power thereto.

The first clutch mechanism C <NUM> and the second clutch mechanism C2 respectively is configured to allow introduction thereto of the lubricant oil reserved in the transmission case <NUM>. Due to this configuration, in the case of the first clutch mechanism C1 being under the power-transmission disengaging state, even when the driving side friction plates <NUM> and the driven side friction plates <NUM> are spaced apart from each other in their positional relationship, due to the viscosity of the lubricant oil, these discs will be rotated together, so that a drag torque will be transmitted via the first forward traveling output gear 36a to the front wheels <NUM> and the rear wheels <NUM>.

Further, in case the forward traveling clutch section C2f and the reverse traveling clutch section C2r of the second clutch mechanism C2 are under the transmission disengaging state, like the first clutch mechanism C1, the discs therein will be rotated together, so that a drag torque will be transmitted to the front wheels <NUM> and the rear wheels <NUM>.

In this Further Embodiment (b), the intermediate rotational member <NUM> is provided as a tubular member fitted on the first output shaft 46a to be freely rotatable relative thereto, and for this intermediate rotational member <NUM>, a gear portion <NUM> as a "coupling portion" is formed integrally on the outer circumference side of this intermediate rotational member <NUM>, with this gear portion <NUM> being meshed with the second reverse traveling input gear 38b.

As shown in <FIG>, the intermediate rotational member <NUM> is disposed, inside the first clutch housing CH1, on the side opposite the first sleeve <NUM> in the direction along the axis of the first output shaft 46a. In the first clutch housing CH1, on the side opposite to first slits 80a in the direction along the axis of the first output shaft 48a, there are formed a plurality of second slits 80b.

Further, there are provided a plurality of plate-like friction plates <NUM> (an example of "friction members") engageable with the second slits 80b of the first clutch housing CH1 and a plurality of plate-like friction rings <NUM> (an example of "friction plates") fitted on the outer circumference of the intermediate rotational member <NUM> for transmitting torque thereto. Although the plurality of friction plates <NUM> and the plurality of friction rings <NUM> are similar in the configuration to those of the first clutch mechanism C1, the former differs from the latter in that there is provided no piston for causing the plurality of friction plates <NUM> and the plurality of friction rings <NUM> to come into contact with each other.

Since the first clutch housing CH1 is rotated in unison with the first output shaft 46a as described above, even when the first clutch mechanism C1 is set under the transmission disengaging state, the first clutch housing CH1 will still be rotated and in association with this rotation, the friction plates <NUM> will be rotated, so that the friction rings <NUM> adjacent thereto will be rotated due to the influence of resultant drag torque. As a result of this, rotational power will be transmitted to the intermediate rotational member <NUM> and this rotational power will be transmitted via the second reverse traveling input gear 38b to the first counter shaft <NUM>. In this way, a drag torque transmitted from the intermediate rotational member <NUM> to the first counter shaft <NUM> will be applied in the direction of causing the traveling vehicle body A to travel in reverse.

In the case of the configuration of the transmission case <NUM> shown in <FIG>, in case the first clutch mechanism C1 is under the transmission disengaging state and the forward traveling clutch section C2f and the reverse traveling clutch section C2r of the second clutch mechanism C2 are under the transmission disengaging states, from the first clutch mechanism C <NUM> and the forward traveling clutch section C2f, drag torques will be applied in the forward traveling direction to the front wheels <NUM> and the rear wheels <NUM> and, from the reverse traveling clutch section C2r, drag torques will be applied in the reverse traveling direction to the front wheels <NUM> and the rear wheels <NUM>.

In the case of the above-described configuration in which drag torques are applied in the forward traveling direction from two clutches and a drag torque is applied in the reverse traveling direction from one clutch, the drag torques in the forward traveling direction are greater than the drag torque in the reverse traveling direction, thus tending to invite the inconvenience of low-speed forward traveling of the vehicle body.

On the other hand, as shown in <FIG>, since the gear portion <NUM> of the intermediate rotational member <NUM> is meshed with the second reverse traveling input gear 38b, it becomes possible to cause the rotational power of the intermediate rotational member <NUM> to be effective in the reverse traveling direction. With this, by increasing the drag torque in the reverse traveling direction so as to offset the drag torque in the forward traveling direction with the drag torque in the reverse traveling direction, the inconvenience of low speed movement of the traveling vehicle body A is resolved. In particular, since the above-described configuration does not include any actuator for suppressing the inconvenience of low speed movement of the traveling vehicle body A, no complexity of the configuration or increase in the number of components thereof will be invited, either.

(c) As the coupling member for transmitting the rotational power of the intermediate rotational member <NUM> to the second reverse traveling input gear 38b (outputting section) of the second clutch mechanism C2, a timing belt or a plurality of gears will be used.

As a variation of this Further Embodiment (c), the second reverse traveling output gear 38a of the second clutch mechanism C2 will be used as an "outputting section" and in order to transmit the rotational power of the intermediate rotational member <NUM> to this second reverse traveling output gear 38a, the coupling portion may be constituted of a gear portion <NUM> formed in the outer circumference of the intermediate rotational member <NUM> in combination with an idle gear meshing with this gear portion <NUM>. In the case of this arrangement, as the idle gear meshes with the second reverse traveling output gear 38a, a rotational power in the opposite direction to the rotational direction of the intermediate rotational member <NUM> will be transmitted to the second reverse traveling output gear 38a.

(d) As an arrangement for causing the intermediate rotational member <NUM> to apply a drag torque in association with rotation of the first output shaft 46a (first shaft), an arrangement of simply fitting the intermediate rotational member <NUM> loosely on the first output shaft 46a or a coupling arrangement for generating a drag torque to the first output shaft 46a with utilization of a fluid may be employed. Further alternatively, an arrangement of supporting the intermediate rotational member <NUM> and the coupling portion (e.g. the gear portion <NUM>, etc.) to different shaft members may be employed.

The Further Embodiment (d) involves a technical concept that the intermediate rotational member <NUM> and the coupling portion (e.g. the gear portion <NUM>, etc.) need not necessarily be disposed on a common axis. Therefore, it is conceivable to support the gear portion <NUM> as the coupling portion to a shaft body located at a different location from that of the first output shaft 46a and to transmit the drag torque from the intermediate rotational member <NUM> to the gear portion <NUM> by a timing belt, an endless chain, a gear (or gears), etc..

As an arrangement similar to the above, it is also conceivable to provide a shaft body rotated by the driving power of the first output shaft 46a at a location different from the location of the first output shaft 46a and to fit the intermediate rotational member <NUM> on this shaft body for transmitting the drag torque associated with rotation of the shaft body to the intermediate rotational member <NUM> and further transmitting it from this intermediate rotational member <NUM> to the gear portion <NUM>.

(e) The stepless speed changer housing <NUM> and the main clutch housing <NUM> of the stepless speed changer device <NUM> may be formed integral with each other. Or, the stepless speed changer device <NUM> and the transmission case <NUM> may be formed integral with each other. With these arrangements, in comparison with an arrangement wherein these members are manufactured separately and then connected to each other with using bolts or the like, improvement in the strength will be made possible and reduction in the weight of the entire transmission system too will be made possible.

(f) The traveling speed changer device <NUM> maybe constituted by using three or more planetary gear speed changer mechanisms. By using three or more planetary gear speed changer devices as above, speed change operations in multiple stages can be made easily.

(g) The input shaft <NUM> and the output shaft <NUM> of the stepless speed changer device <NUM> may be caused to protrude forwardly. With this, it becomes possible to transmit the driving power of the engine <NUM> directly to the input shaft <NUM>.

The present invention is applicable to a work vehicle configured such that driving power of an engine is speed-changed by a stepless speed changer device and a planetary gear speed changer device.

Claim 1:
A work vehicle comprising:
a first clutch mechanism (C1) of a wet type configured to engage/disengage transmission of a traveling driving power transmitted from a first shaft (46a) to a traveling mechanism (<NUM>,<NUM>);
a second clutch mechanism (C2) of a wet type configured to engage/disengage transmission of a traveling driving power transmitted from a second shaft (46b) to the traveling mechanism (<NUM>,<NUM>);
an intermediate rotational member (<NUM>) rotatable relative to the first shaft (46a) due to a drag torque associated with rotation of the first shaft (46a); and
a coupling portion (<NUM>) configured to transmit a rotational power of the intermediate rotational member (<NUM>) to an output portion of the second clutch mechanism (C2),
characterized in that
the work vehicle further comprises:
a first planetary gear speed changer device (Q1) for speed-changing traveling driving power and transmitting the resultant power to the first shaft (46a);
a second planetary gear speed changer device (Q2) for speed-changing traveling driving power and transmitting the resultant power to the second shaft (46b);
the first clutch mechanism (C <NUM>) being configured to transmit, under its transmission engaging state, the driving power of the first shaft (46a) to the traveling mechanism (<NUM>,<NUM>) as a forward traveling driving power;
the second clutch mechanism (C2) including a forward traveling clutch section (C2f) configured to transmit, under its transmission engaging state, the driving power of the second shaft (46b) to the traveling mechanism (<NUM>,<NUM>) as a forward traveling driving power and a reverse traveling clutch section (C2r) configured to transmit, under its transmission engaging state, the driving power of the second shaft (46b) to the traveling mechanism (<NUM>,<NUM>) as a reverse traveling driving power; and
the second clutch mechanism (C2) further including a reverse traveling output gear (38a) configured to output the reverse traveling driving power from the reverse traveling clutch section (C2r), so that with meshing of the reverse traveling output gear (38a) with a reverse traveling transmission gear (38b), the reverse traveling driving power is transmitted to the traveling mechanism (<NUM>,<NUM>).