Patent Description:
<CIT>, for example, discloses a conventional work vehicle including a body, left and right front wheels ("front wheels (<NUM>)") provided for the body, and left and right rear crawler units ("crawler units (<NUM>)") provided for the body. The rear crawler units each include a drive wheel ("drive sprocket (<NUM>)") provided for a rear axle ("drive shaft (<NUM>)") of the work vehicle, a front idler wheel ("front-side idler wheel (<NUM>)") forward of the drive wheel, a rear idler wheel ("rear-side idler wheel (<NUM>)") backward of the drive wheel, a plurality of roller wheels ("roller wheels (<NUM>)") between the front idler wheel and the rear idler wheel, a crawler belt ("crawler belt (<NUM>)") wound around the drive wheel, the front idler wheel, the rear idler wheel, and the plurality of roller wheels, and a track frame ("track frame (<NUM>)") swingable about a swing shaft ("shaft (<NUM>)") that extends in the left-right direction of the body and holding the front idler wheel, the rear idler wheel, and the plurality of roller wheels. The work vehicle is configured such that the rear crawler units are each swingable about the swing shaft during travel.

The work vehicle disclosed in <CIT> has room for improvement in terms of the position of the swing shaft in the front-back direction of the body to improve the traction, turn ability, and performance in running through paddy fields.

The above circumstances have led to a demand for a work vehicle having improved traction, turn ability, and performance in running through paddy fields. <CIT> deals with a traction assembly.

The present invention is a work vehicle as defined in claim <NUM>, which includes:.

The above characteristic configuration allows the position change mechanism to move the swing shaft in the front-back direction of the body. This allows the swing shaft to be moved in the front-back direction of the body to a position suitable for traction, turn, or running through a paddy field. The above characteristic configuration therefore allows production of a work vehicle having improved traction, turnability, and performance in running through paddy fields.

The present invention may preferably be further arranged such that the position change mechanism is configured to move the swing shaft in the front-back direction of the body between a front position, at which a center of the swing shaft is forward of a center of the rear axle, and a back position, at which the center of the swing shaft is backward of the center of the rear axle.

The above characteristic configuration allows the swing shaft to be moved to the back position to increase the distance between the respective centers of the front wheels and the swing shaft in the front-back direction of the body. This in turn allows the rear crawler units to be each in close contact with the ground over the entire bottom face for increased traction. The above characteristic configuration also allows the swing shaft to be moved to the front position to reduce the distance between the respective centers of the front wheels and the swing shaft in the front-back direction of the body. This reduces the minimum turn radius to improve the turnability, and also reduces the pressure of ground contact of the front wheels to prevent the front wheels from easily damaging a paddy field while the work vehicle runs through it.

In the work vehicle as defined in claim <NUM>, the position change mechanism includes an actuator to move the swing shaft.

The above characteristic configuration uses an actuator to move the swing shaft, facilitating the movement of the swing shaft.

The present invention may preferably be further arranged such that the swing shaft is below the rear axle, and the actuator is between the rear axle and the swing shaft in a side view.

The above characteristic configuration allows the actuator to be in a space between the drive shaft and the swing shaft.

The present invention may preferably be further arranged such that the actuator includes a hydraulic cylinder configured to extend and contract in the front-back direction of the body.

With the above characteristic configuration, extending and contracting the hydraulic cylinder easily moves the swing shaft in the front-back direction of the body.

In an aspect of the present disclosure that is not claimed per se, a work vehicle includes:.

The above characteristic configuration uses an actuator to move the swing shaft in the front-back direction of the body. This allows the swing shaft to be moved in the front-back direction of the body to a position suitable for traction, turn, or running through a paddy field. The above characteristic configuration therefore allows production of a work vehicle having improved traction, turnability, and performance in running through paddy fields. Further, the above characteristic configuration uses an actuator to move the swing shaft, facilitating the movement of the swing shaft.

In the above aspect of the present disclosure, the control device may cause the actuator to move the swing shaft in the front-back direction of the body between a front position, at which a center of the swing shaft is forward of a center of the rear axle, and a back position, at which the center of the swing shaft is backward of the center of the rear axle.

The above characteristic configuration allows the swing shaft to be moved to the back position to increase the distance between the respective centers of the front wheels and the swing shaft in the front-back direction of the body. This in turn allows the rear crawler units to be each in close contact with the ground over the entire bottom face for increased traction. The above characteristic configuration also allows the swing shaft to be moved to the front position to reduce the distance between the respective centers of the front wheels and the swing shaft in the front-back direction of the body. This reduces the minimum rotation radius to improve the turnability, and also reduces the pressure of ground contact of the front wheels to prevent the front wheels from easily damaging a paddy field while the work vehicle runs through it.

In the above aspect of the present disclosure, the control device may have, as a control mode for controlling how the actuator is driven, an automatic control mode, in which the control device controls how the actuator is driven in accordance with a turn of the body.

The above characteristic configuration allows the swing shaft to be moved in accordance with a turn of the body. This eliminates the need for the driver to move the swing shaft when the driver causes the body to make a turn.

In the above aspect of the present disclosure, the work vehicle may further include: an operation switch for use to drive the actuator, wherein the control device has, as the control mode, a manual control mode, in which the control device controls how the actuator is driven in response to a manual operation of the operation switch.

The above characteristic configuration allows the swing shaft to be moved in response to a manual operation of the operation switch. This allows the driver to move the swing shaft on the basis of the driver's appropriate determination.

In the above aspect of the present disclosure, the actuator may include a hydraulic cylinder configured to extend and contract in the front-back direction of the body.

The description below deals with an embodiment of the present invention with reference to drawings. In the description below, arrow F indicates the forward direction of the body, arrow B indicates the backward direction of the body, arrow L indicates the leftward direction of the body, and arrow R indicates the rightward direction of the body.

<FIG> illustrates a tractor as an example of the "work vehicle" of the present invention. The tractor includes a body <NUM>, a motor section <NUM>, a driver section <NUM>, a transmission section <NUM>, and a work device (not shown in the drawings). The body <NUM> includes a travel device <NUM> and a body frame <NUM> supported by the travel device <NUM>.

The travel device <NUM> includes left and right front wheels <NUM> and left and right rear crawler units <NUM>. The front wheels <NUM> are steerable and drivable. The rear crawler units <NUM> are unsteerable and drivable. The tractor (body <NUM>) is switchable between a two-wheel drive state, in which only the rear crawler units <NUM> are driven, and a four-wheel drive state, in which both the front wheels <NUM> and the rear crawler units <NUM> are driven.

The motor section <NUM> is on a front portion of the body frame <NUM>. The motor section <NUM> includes an engine E and a hood <NUM> covering the engine E. The driver section <NUM> is on a back portion of the body frame <NUM>. The driver section <NUM> includes a driver's seat <NUM> for a driver to sit on, a steering wheel <NUM> for use to steer the body <NUM>, and a cabin <NUM> defining a space for the driver. The work device (such as a rotary tiller device) is held by a link mechanism M at a back portion of the body frame <NUM> in such a manner as to be capable of being lifted and lowered.

The transmission section <NUM> is under the driver section <NUM>. The transmission section <NUM> is configured to vary power from the engine E and transmit the resulting power to the front wheels <NUM>, the rear crawler units <NUM>, and the work device. The transmission section <NUM> includes a transmission case <NUM>. The transmission case <NUM> doubles as a back portion of the body frame <NUM>. The transmission case <NUM> is connected to two rear axle cases <NUM> on the left and right sides, respectively. The rear axle cases <NUM> contain a rear axle <NUM> extending in the left-right direction of the body and configured to drive the rear crawler units <NUM>.

As illustrated in <FIG> and <FIG>, the rear crawler units <NUM> each include a drive wheel <NUM>, a front idler wheel <NUM>, a rear idler wheel <NUM>, a plurality of (four for the present embodiment) roller wheels <NUM>, a crawler belt <NUM>, a track frame <NUM>, and a position change mechanism <NUM>. The two rear crawler units <NUM> are identical in configuration to each other. The description below deals with the left rear crawler unit <NUM> as an example.

The drive wheel <NUM> is provided for the rear axle <NUM> in such a manner as to be rotatable integrally with the rear axle <NUM>. The front idler wheel <NUM> is forward of the drive wheel <NUM>. The front idler wheel <NUM> is held by a front end portion of the track frame <NUM> by means of a tension adjustment mechanism <NUM> in such a manner as to be capable of adjusting the tension of the crawler belt <NUM>. The front idler wheel <NUM>, in other words, serves as a tension wheel. The rear idler wheel <NUM> is backward of the drive wheel <NUM>. The rear idler wheel <NUM> is held by a back end portion of the track frame <NUM>.

The plurality of roller wheels <NUM> are between the front idler wheel <NUM> and the rear idler wheel <NUM>. The two front-side roller wheels <NUM> are held by a front-side roller wheel frame <NUM> at a front portion of the track frame <NUM>. The front-side roller wheel frame <NUM> is provided with a front-side crawler guide <NUM> attached thereto and configured to guide the crawler belt <NUM>.

The two back-side roller wheels <NUM> are held by a back-side roller wheel frame <NUM> at a back portion of the track frame <NUM>. The back-side roller wheel frame <NUM> is provided with a back-side crawler guide <NUM> attached thereto and configured to guide the crawler belt <NUM>.

The crawler belt <NUM> is wound around the drive wheel <NUM>, the front idler wheel <NUM>, the rear idler wheel <NUM>, and the roller wheels <NUM>. The track frame <NUM> holds the front idler wheel <NUM>, the rear idler wheel <NUM>, and the roller wheels <NUM>. The track frame <NUM> is swingable about a swing shaft <NUM> extending in the left-right direction of the body. The swing shaft <NUM> is below the rear axle <NUM>. The swing shaft <NUM> is movable in the front-back direction of the body (detailed later).

As illustrated in <FIG>, the position change mechanism <NUM> is capable of moving the swing shaft <NUM> in the front-back direction of the body, specifically between (i) a front position (see <FIG> and <FIG>), at which the swing shaft <NUM> has a center X1 forward of the center X2 of the rear axle <NUM>, and (ii) a back position (see <FIG>), at which the swing shaft <NUM> has a center X1 backward of the center X2 of the rear axle <NUM>.

The position change mechanism <NUM> includes a fixed frame <NUM>, a movable frame <NUM>, a plurality of (four for the present embodiment) guide rods <NUM>, and a hydraulic cylinder <NUM> (as an example of the "actuator" or "hydraulic cylinder" for the present invention).

The fixed frame <NUM> is connected to the body frame <NUM>. The fixed frame <NUM> is bolted to the bottom face of the corresponding rear axle case <NUM>. The fixed frame <NUM> includes an upper plate <NUM>, a front plate <NUM>, and a back plate <NUM>.

The movable frame <NUM> is connected to the track frame <NUM> (swing shaft <NUM>). The movable frame <NUM> is movable in the front-back direction of the body relative to the fixed frame <NUM>. The movable frame <NUM> includes a front plate <NUM>, a back plate <NUM>, a middle plate <NUM>, left and right side plates <NUM>, and a boss <NUM>.

The boss <NUM> extends from the left side plate <NUM> to the right side plate <NUM>. The boss <NUM> is held by the front plate <NUM> and the back plate <NUM> by means of the middle plate <NUM>. The swing shaft <NUM> is rotatably disposed through the boss <NUM>.

The swing shaft <NUM> has a left end portion protruding from the left end of the boss <NUM> and extends through the left side plate <NUM>. The swing shaft <NUM> has a right end portion protruding from the right end of the boss <NUM> and extends through the right side plate <NUM>. The left and right end portions of the swing shaft <NUM> are each provided with a stay <NUM> attached thereto. The track frame <NUM> is held by the swing shaft <NUM> by means of the stays <NUM> in such a manner as to be swingable about the center X1 of the swing shaft <NUM>.

The guide rods <NUM> are disposed through both the fixed frame <NUM> and the movable frame <NUM>. Specifically, the guide rods <NUM> extend through the front plate <NUM>, the front plate <NUM>, the back plate <NUM>, and the back plate <NUM>. The guide rods <NUM> are each in the form of a round bar. The movable frame <NUM> is guided by the guide rods <NUM> when moved in the front-back direction of the body relative to the fixed frame <NUM>.

The hydraulic cylinder <NUM> serves as an actuator to move the swing shaft <NUM>. The hydraulic cylinder <NUM> is capable of extending and contracting in the front-back direction of the body. The hydraulic cylinder <NUM> is disposed through both the fixed frame <NUM> and the movable frame <NUM>. The hydraulic cylinder <NUM> is below the corresponding rear axle case <NUM>. Specifically, the hydraulic cylinder <NUM> is between the upper plate <NUM> and the boss <NUM>. The hydraulic cylinder <NUM> is, in other words, between the rear axle <NUM> and the swing shaft <NUM> in a side view.

The hydraulic cylinder <NUM> includes a cylinder tube 34A and a piston rod 34B. The cylinder tube 34A includes a base portion held by the front plate <NUM> by means of a stay <NUM>. The front plate <NUM> has an opening 38a to receive the stay <NUM> and the cylinder tube 34A. The piston rod 34B extends through the back plate <NUM>. The piston rod 34B includes a leading end portion connected to the back plate <NUM>.

As illustrated in <FIG>, contracting the hydraulic cylinder <NUM> causes the movable frame <NUM> to move forward together with the swing shaft <NUM> and the track frame <NUM>. This moves the swing shaft <NUM> to the front position.

As illustrated in <FIG>, extending the hydraulic cylinder <NUM> causes the movable frame <NUM> to move backward together with the swing shaft <NUM> and the track frame <NUM>. This moves the swing shaft <NUM> to the back position.

<FIG> shows the control system of the tractor, which includes a control device <NUM>, an operation switch <NUM>, a mode switch <NUM>, and a hydraulic pressure control valve <NUM>. The control device <NUM> includes a drive controller <NUM>, a turn determiner <NUM>, and a storage <NUM>.

The drive controller <NUM> is configured to control how the hydraulic cylinder <NUM> is driven. Specifically, the drive controller <NUM> is configured to cause the hydraulic cylinder <NUM> to move the swing shaft <NUM> in the front-back direction of the body between the front position and the back position. The swing shaft <NUM> for the present embodiment is movable between two positions, namely a front position and a back position. The drive controller <NUM> opens and closes the hydraulic pressure control valve <NUM> to extend and contract the hydraulic cylinder <NUM>. The drive controller <NUM> has the following two modes as its mode for controlling how the hydraulic cylinder <NUM> is driven: an autonomous control mode, in which the way the hydraulic cylinder <NUM> is driven is controlled in accordance with a turn of the body <NUM>, and a manual control mode, in which the way the hydraulic cylinder <NUM> is driven is controlled in response to a manual operation of the operation switch <NUM>.

The turn determiner <NUM> is configured to determine whether the body <NUM> is going to make (or making) a turn. In response to a predetermined operation on the tractor, the turn determiner <NUM> determines that the body <NUM> is going to make a turn. Examples of the predetermined operation include the following: the front wheels <NUM> have been turned by a turning angle not smaller than a predetermined angle; the front wheel <NUM> on the outer side of a turn has been driven to rotate at a rate approximately twice as high as that of the rear crawler unit <NUM>; the front wheel <NUM> on the outer side of a turn has been driven to rotate at a rate approximately twice as high as that of the rear crawler unit <NUM> while the other rear crawler unit <NUM> on the inner side has been braked; the tractor has been steered in the two-wheel drive state to make a turn; the steering wheel <NUM> has been turned by a large amount, and the work device has been lifted automatically; and the body <NUM> has been driven to travel backward, and the work device has been lifted automatically.

The storage <NUM> stores programs for sections such as the drive controller <NUM> and the turn determiner <NUM> to perform their various functions, as well as data on settings of the automatic control mode and the manual control mode.

The operation switch <NUM> is for use to drive the hydraulic cylinder <NUM>. The operation switch <NUM> is manually operable to open and close the hydraulic pressure control valve <NUM> to extend and contract the hydraulic cylinder <NUM>. The operation switch <NUM> is configured to generate an instruction to extend the hydraulic cylinder <NUM> (extension instruction) and an instruction to contract the hydraulic cylinder <NUM> (contraction instruction). The mode switch <NUM> is for use to switch the control mode between the automatic control mode and the manual control mode.

In the automatic control mode, the drive controller <NUM> contracts the hydraulic cylinder <NUM> in response to the turn determiner <NUM> determining that the body <NUM> is going to make a turn. This moves the swing shaft <NUM> to the front position. Further, in the automatic control mode, the drive controller <NUM> extends the hydraulic cylinder <NUM> in response to the turn determiner <NUM> determining that the body <NUM> is not going to make a turn (for example, during traction). This moves the swing shaft <NUM> to the back position.

Claim 1:
A work vehicle, comprising:
a body (<NUM>);
left and right front wheels (<NUM>) provided for the body; and
left and right rear crawler units (<NUM>) provided for the body,
the rear crawler units (<NUM>) each including:
a drive wheel (<NUM>) provided for a rear axle (<NUM>) of the work vehicle;
a front idler wheel (<NUM>) forward of the drive wheel (<NUM>);
a rear idler wheel (<NUM>) backward of the drive wheel (<NUM>);
a plurality of roller wheels (<NUM>) between the front idler wheel (<NUM>) and the rear idler wheel (<NUM>);
a crawler belt (<NUM>) wound around the drive wheel (<NUM>), the front idler wheel (<NUM>), the rear idler wheel (<NUM>), and the plurality of roller wheels (<NUM>);
a track frame (<NUM>) swingable about a swing shaft (<NUM>) that extends in a left-right direction of the body (<NUM>) and holding the front idler wheel (<NUM>), the rear idler wheel (<NUM>), and the plurality of roller wheels (<NUM>);
a position change mechanism (<NUM>) configured to move the swing shaft (<NUM>) in a front-back direction of the body (<NUM>); characterized in that:
the position change mechanism (<NUM>) includes an actuator (<NUM>) to move the swing shaft (<NUM>).