Patent Description:
<CIT> discloses supplying operating oil from a hydraulic pump, a control valve, or the like through a supply oil passage in a power transmission shaft to a hydraulically operable section, and specifically discloses how the operating oil is supplied into the supply oil passage (see Fig. <NUM>, the portion indicated with reference numeral "<NUM>" and its surroundings). <CIT> and <CIT> disclose other examples of work vehicles with oil supply systems.

<CIT> discloses rotating the power transmission shaft to rotate an inlet port relative to a supply port of a shaft holder, meaning a repeated switch between a state where the inlet port coincides with and faces the supply port and a state where the inlet port is apart from the supply port.

Operating oil, when exiting the supply port and entering the inlet port, tends to have a pressure loss that is relatively large with the inlet port slightly past the supply port and that is relatively small with the inlet port farthest apart from the supply port.

This means a repeated switch between a state where the operating oil has a high pressure (with a small pressure loss) and a state where the operating oil has a low pressure (with a large pressure loss) through the rotation of the power transmission shaft. This pulsation of the pressure of operating oil may cause the hydraulically operable section, which receives the operating oil, to malfunction.

The present invention has an object of providing a work vehicle that is configured to supply operating oil to a hydraulically operable section through a supply oil passage in a power transmission shaft drivable to rotate and that prevents the hydraulically operable section from malfunctioning.

A work vehicle according to the present invention includes:.

The work vehicle is configured as follows: Operating oil supplied to the first supply port of the shaft holder flows through the first supply port into the outer flow path. The operating oil then flows from the outer flow path through the second supply port into the shaft groove of the power transmission shaft. The operating oil then flows from the shaft groove through the inlet port and the supply oil passage to be supplied to the hydraulically operable section.

The work vehicle has an outer oil passage in the shaft holder between the first supply port of the shaft holder and the shaft groove of the power transmission shaft along the flow of operating oil. The outer flow path of the shaft holder is in the shape of a ring around the shaft groove of the power transmission shaft. The outer flow path is thus relatively long along the circumference, and has a relatively large capacity. The outer oil passage of the shaft holder, which is configured as above, reduces the pressure loss of operating oil and prevents an abrupt change in the pressure of operating oil.

Thus, while a switch is repeated between a state where the operating oil has a high pressure (with a small pressure loss) and a state where the operating oil has a low pressure (with a large pressure loss), the outer oil passage, when the operating oil transitions from the state where the operating oil has a low pressure to the state where the operating oil has a high pressure, prevents an abrupt increase in the pressure of the operating oil and thereby prevents the pressure from becoming excessively high.

Similarly, the outer oil passage, when the operating oil transitions from the state where the operating oil has a high pressure to the state where the operating oil has a low pressure, prevents an abrupt decrease in the pressure of the operating oil and thereby prevents the pressure from becoming excessively low.

The work vehicle prevents the pressure of operating oil from becoming excessively high or excessively low, and thereby has only a small difference between the state where the operating oil has a high pressure and the state where the operating oil has a low pressure. This reduces the pulsation of the pressure of operating oil and prevents the hydraulically operable section from malfunctioning.

The work vehicle may preferably be further configured such that the at least one second supply port includes a plurality of second supply ports spaced from each other along a circumference of the inner circumferential portion of the shaft holder.

The above work vehicle is configured such that the shaft holder includes a plurality of second supply ports. This allows the inlet port of the power transmission shaft to coincide with and face a second supply port of the shaft holder two or more times through a single rotation of the power transmission shaft.

With the above configuration, when the inlet port of the power transmission shaft has moved past a second supply port of the shaft holder such that the operating oil transitions from the state where the operating oil has a high pressure (with a small pressure loss) to the state where the operating oil has a low pressure (with a large pressure loss), the inlet port faces another second supply port before the pressure of the operating oil becomes excessively low, so that the operating oil is in the state where the operating oil has a high pressure.

The work vehicle prevents an excessive decrease in the pressure of operating oil in the state where the operating oil has a high pressure, and thereby has only a small difference between the state where the operating oil has a high pressure and the state where the operating oil has a low pressure. This advantageously reduces the pulsation of the pressure of operating oil and prevents the hydraulically operable section from malfunctioning.

The work vehicle may preferably be further configured such that the first supply port is positioned differently from the plurality of second supply ports along the circumference of the inner circumferential portion of the shaft holder.

The above work vehicle is configured such that the first supply port of the shaft holder is positioned differently from the second supply ports. This prevents operating oil having flown through the first supply port into the outer oil passage from immediately flowing from the outer oil passage into a second supply port.

The above configuration allows operating oil having flown through the first supply port into the outer oil passage to tend to remain in the outer oil passage, and facilitates preventing an abrupt change in the pressure of operating oil in the outer oil passage. This advantageously reduces the pulsation of the pressure of operating oil and prevents the hydraulically operable section from malfunctioning.

The work vehicle may preferably be further configured such that the outer flow path has a first cross-sectional area on a plane orthogonal to the circumference of the inner circumferential portion of the shaft holder, whereas the shaft groove has a second cross-sectional area on a plane orthogonal to a circumference of the power transmission shaft, the first cross-sectional area being larger than the second cross-sectional area.

The above work vehicle is configured such that the outer oil passage of the shaft holder has a cross-sectional area larger than that of the shaft groove of the power transmission shaft, meaning that the outer flow path has a large capacity.

The above configuration allows facilitates preventing an abrupt change in the pressure of operating oil in the outer oil passage of the shaft holder. This advantageously reduces the pulsation of the pressure of operating oil and prevents the hydraulically operable section from malfunctioning.

The work vehicle may preferably further include: a cylinder attached to the inner circumferential portion of the shaft holder and holding the power transmission shaft in such a manner that the power transmission shaft is rotatable to allow the shaft holder to hold the power transmission shaft in such a manner that the power transmission shaft is rotatable, wherein the cylinder includes an outer groove extending entirely around an outer circumferential portion of the cylinder along a circumference of the inner circumferential portion of the shaft holder and defining the outer flow path together with the inner circumferential portion of the shaft holder, and the at least one second supply port is provided for the cylinder and extends from the outer groove to an inner circumferential portion of the cylinder.

The above work vehicle is configured such that the shaft holder has a first supply port, and includes a cylinder as a member separate from the shaft holder, the cylinder having an outer groove and a second supply port.

Attaching the cylinder to the inner circumferential portion of the shaft holder causes the inner circumferential portion and the outer groove to define an outer flow path of the shaft holder. The second supply port is provided for the shaft holder.

It is relatively easy to provide the outer groove and the second supply port for the cylinder, meaning that it is relatively easy to provide the first and second supply ports and the outer oil passage for the shaft holder. This reduces the production cost.

<FIG> illustrate a tractor as an example work vehicle. <FIG> shows "F" to indicate the forward direction, "B" to indicate the backward direction, "U" to indicate the upward direction, and "D" to indicate the downward direction.

As illustrated in <FIG>, the tractor includes a body <NUM>, left and right front wheels <NUM>, and left and right rear wheels <NUM>, the front and rear wheels <NUM> and <NUM> supporting the body <NUM>. The tractor also includes a hood <NUM> at a front portion of the body <NUM> and a driver section <NUM> at a back portion of the body <NUM>.

The body <NUM> is provided with components such as an engine <NUM>, a flywheel housing <NUM> coupled to a back portion of the engine <NUM>, a transmission case <NUM> coupled to a back portion of the flywheel housing <NUM>, and a front frame <NUM> coupled to a front portion of the engine <NUM>.

The front wheels <NUM> are held by the front frame <NUM>, whereas the rear wheels <NUM> are held by a back portion of the transmission case <NUM>. The hood <NUM> covers the engine <NUM>. The driver section <NUM> is covered by a cabin <NUM>, and includes a driver's seat <NUM> and a steering wheel <NUM> for turning the front wheels <NUM>.

The tractor also includes a link mechanism <NUM> and a PTO shaft <NUM>. The link mechanism <NUM> is disposed at a back portion of the body <NUM> and linkable with any of various work devices (not illustrated in the drawings). The PTO shaft <NUM> is disposed at a back portion of the transmission case <NUM> and configured to transmit motive power to the work device.

As illustrated in <FIG>, the transmission case <NUM> contains a first planetary device <NUM>, a second planetary device <NUM>, a continuously variable transmission device <NUM>, a power transmission device <NUM>, a forward/rearward travel switching device <NUM>, a rear-wheel differential gear device <NUM>, a front-wheel transmission device <NUM>, a PTO clutch <NUM>, and a PTO transmission device <NUM>.

The engine <NUM> transmits motive power from its output shaft 1a through a clutch <NUM> to the input shaft <NUM> of the transmission case <NUM>. The motive power is then transmitted from the input shaft <NUM> to a power transmission shaft <NUM> and a power transmission shaft <NUM>. The power transmission shaft <NUM> transmits the motive power to the PTO clutch <NUM>. The motive power is varied by the PTO transmission device <NUM> and transmitted to the PTO shaft <NUM>.

The engine <NUM> transmits its motive power from its output shaft 1a through the clutch <NUM> to the first planetary device <NUM>, the second planetary device <NUM>, the continuously variable transmission device <NUM>, and the power transmission device <NUM>. The motive power is varied and transmitted to an output shaft <NUM> (which corresponds to the "power transmission shaft").

The motive power from the output shaft <NUM> is transmitted from a power transmission shaft <NUM> to the forward/rearward travel switching device <NUM> and from a cylindrical power transmission shaft <NUM>, which is rotatably attached to the power transmission shaft <NUM>, to a power transmission shaft <NUM>, to the rear-wheel differential gear device <NUM>, and to the rear wheels <NUM>.

The motive power from the power transmission shaft <NUM> is transmitted to a power transmission shaft <NUM> and through a power transmission shaft <NUM> to the front-wheel transmission device <NUM>. The motive power from the front-wheel transmission device <NUM> is transmitted from a front-wheel output shaft <NUM> through a power transmission shaft <NUM> to a front-wheel differential gear device <NUM> and to the front wheels <NUM>.

As illustrated in <FIG>, the first planetary device <NUM> includes a sun gear <NUM>, a plurality of planetary gears <NUM>, and a ring gear <NUM>, whereas the second planetary device <NUM> includes a sun gear <NUM>, a plurality of planetary gears <NUM>, and a ring gear <NUM>. The first and second planetary devices <NUM> and <NUM> share a common carrier <NUM>. The planetary gears <NUM> are coupled to the planetary gears <NUM> with a cylindrical power transmission shaft <NUM> attached to the carrier <NUM>, so that the first and second planetary devices <NUM> and <NUM> constitute a compound planetary device.

The motive power from the input shaft <NUM> is transmitted through a power transmission shaft <NUM> to the ring gear <NUM> of the first planetary device <NUM>.

The motive power from the input shaft <NUM> is transmitted from a power transmission gear <NUM> coupling the power transmission shafts <NUM> and <NUM> to each other through a power transmission shaft <NUM> to the continuously variable transmission device <NUM>. The continuously variable transmission device <NUM> is of a hydraulic type, and outputs normal-direction motive power and reverse-direction motive power to be transmitted through a power transmission shaft <NUM> to the sun gear <NUM> of the first planetary device <NUM>.

The first and second planetary devices <NUM> and <NUM> composite (i) the motive power transmitted from the engine <NUM> through the continuously variable transmission device <NUM> to the sun gear <NUM> of the first planetary device <NUM> and (ii) the motive power transmitted from the engine <NUM> not through the continuously variable transmission device <NUM> to the ring gear <NUM> of the first planetary device <NUM>.

The motive power composited by the first and second planetary devices <NUM> and <NUM> is transmitted from the ring gear <NUM> of the second planetary device <NUM> to an output shaft <NUM>, from the carrier <NUM> to an output shaft <NUM>, and from the sun gear <NUM> of the second planetary device <NUM> to an output shaft <NUM>.

As illustrated in <FIG>, the power transmission device <NUM> includes first to fourth clutches CL1 to CL4 (each of which corresponds to the "hydraulically operable section") and an output shaft <NUM>.

The motive power from the output shaft <NUM> is transmitted to the first clutch CL1. The motive power from the output shaft <NUM> is transmitted to the third clutch CL3. The motive power from the output shaft <NUM> is transmitted to the second and fourth clutches CL2 and CL <NUM>.

The first to fourth clutches CL1 to CL4 are of a hydraulic multi-disc type. The first to fourth clutches CL1 to CL4 are each urged to a disengaged state, and become engaged in response to receiving operating oil. The first to fourth clutches CL1 to CL4, in response to becoming engaged, each transmit its motive power to the output shaft <NUM>.

<FIG> illustrates how the continuously variable transmission device <NUM> is related to the first to fourth clutches CL1 to CL4. <FIG> show "V" to indicate the rotation speed of the output shaft <NUM>, "N" to indicate the neutral position of the continuously variable transmission device <NUM>, "+MAX" to indicate the maximum speed by the normal-direction motive power of the continuously variable transmission device <NUM>, and "-MAX" to indicate the maximum speed by the reverse-direction motive power of the continuously variable transmission device <NUM>.

As illustrated in <FIG>, in response to the first clutch CL1 becoming engaged, the motive power composited by the first and second planetary devices <NUM> and <NUM> is transmitted through the ring gear <NUM> of the second planetary device <NUM>, the output shaft <NUM>, and the first clutch CL1 to the output shaft <NUM>.

In this state, varying the continuously variable transmission device <NUM> between -MAX and +MAX changes the rotation speed V of the output shaft <NUM> continuously between zero speed and a speed V1, as shown with "First-gear range" in <FIG>.

As illustrated in <FIG>, in response to the second clutch CL2 becoming engaged, the motive power composited by the first and second planetary devices <NUM> and <NUM> is transmitted through the sun gear <NUM> of the second planetary device <NUM>, the output shaft <NUM>, and the second clutch CL2 to the output shaft <NUM>.

In this state, varying the continuously variable transmission device <NUM> between -MAX and +MAX changes the rotation speed V of the output shaft <NUM> continuously between the speed V1 and a speed V2, as shown with "Second-gear range" in <FIG>.

As illustrated in <FIG>, in response to the third clutch CL3 becoming engaged, the motive power composited by the first and second planetary devices <NUM> and <NUM> is transmitted through the carrier <NUM>, the output shaft <NUM>, and the third clutch CL3 to the output shaft <NUM>.

In this state, varying the continuously variable transmission device <NUM> between -MAX and +MAX changes the rotation speed V of the output shaft <NUM> continuously between the speed V2 and a speed V3, as shown with "Third-gear range" in <FIG>.

As illustrated in <FIG>, in response to the fourth clutch CL4 becoming engaged, the motive power composited by the first and second planetary devices <NUM> and <NUM> is transmitted through the sun gear <NUM> of the second planetary device <NUM>, the output shaft <NUM>, and the fourth clutch CL4 to the output shaft <NUM>.

In this state, varying the continuously variable transmission device <NUM> between -MAX and +MAX changes the rotation speed V of the output shaft <NUM> continuously between the speed V3 and a speed V4, as shown with "Fourth-gear range" in <FIG>.

As illustrated in <FIG>, the forward/rearward travel switching device <NUM> includes a forward-travel clutch CLF, a rearward-travel clutch CLR, power transmission shafts <NUM> and <NUM>, and a relay gear <NUM>. The power transmission shaft <NUM> receives the motive power from the output shaft <NUM>.

The forward/rearward travel switching device <NUM> is configured such that in response to the forward-travel clutch CLF becoming engaged, the motive power from the power transmission shaft <NUM> is transmitted through the forward-travel clutch CLF to the power transmission shaft <NUM> in a forward-travel state and from the power transmission shaft <NUM> through the power transmission shaft <NUM> to the rear-wheel differential gear device <NUM>.

The forward/rearward travel switching device <NUM> is configured such that in response to the rearward-travel clutch CLR becoming engaged, the motive power from the power transmission shaft <NUM> is transmitted through the rearward-travel clutch CLR and the relay gear <NUM> to the power transmission shaft <NUM> in a rearward-travel state and from the power transmission shaft <NUM> through the power transmission shaft <NUM> to the rear-wheel differential gear device <NUM>.

As illustrated in <FIG>, the front-wheel transmission device <NUM> includes a standard clutch CLT, a speed-increasing clutch CLH, a power transmission shaft <NUM>, and a front-wheel output shaft <NUM>.

With each front wheel <NUM> at an angle within a range extending from the straight-travel position to predetermined left and right angles, the standard clutch CLT is in an engaged state.

In this state, the motive power from the power transmission shaft <NUM> is transmitted through the power transmission shafts <NUM> and <NUM> and the standard clutch CLT to the front-wheel output shaft <NUM> and through the power transmission shaft <NUM> and the front-wheel differential gear device <NUM> to the front wheels <NUM>. This drives the front and rear wheels <NUM> and <NUM> at the same speed.

Turning each front wheel <NUM> to the left or right beyond the left or right predetermined angle causes the speed-increasing clutch CLH to become engaged.

In this state, the motive power from the power transmission shaft <NUM> is transmitted through the power transmission shafts <NUM> and <NUM> and the speed-increasing clutch CLH to the front-wheel output shaft <NUM> and through the power transmission shaft <NUM> and the front-wheel differential gear device <NUM> to the front wheels <NUM>. This drives the front wheels <NUM> at a speed higher than the speed at which the rear wheels <NUM> are driven.

As illustrated in <FIG>, <FIG>, and <FIG>, the output shaft <NUM> and the power transmission shaft <NUM> are coupled to each other with a cylindrical coupler <NUM>. The transmission case <NUM> contains a shaft holder <NUM> near an end of the output shaft <NUM>.

The shaft holder <NUM> has a cylindrical space in the longitudinal direction of the output shaft <NUM>. The shaft holder <NUM> also has four supply ports 30a, 30b, 30c, and 30d (which correspond to the "first supply port") on an inner circumferential portion 30e defining the cylindrical space.

The supply ports 30a to 30d are arranged in the longitudinal direction of the inner circumferential portion 30e and evenly spaced from one another. Around the circumference of the inner circumferential portion 30e, the supply ports 30a and 30c are at the same phase, whereas the supply ports 30b and 30d are at the same phase, and the supply ports 30a and 30c are different in phase from the supply ports 30b and 30d.

As illustrated in <FIG> and <FIG>, the transmission case <NUM> contains a cylinder <NUM> attached to the inner circumferential portion 30e defining the cylindrical space in the shaft holder <NUM>. As illustrated in <FIG>, the cylinder <NUM> includes a body <NUM>, a plurality of rings <NUM>, and supply ports <NUM>, <NUM>, <NUM>, and <NUM> (which correspond to the "second supply port").

As illustrated in <FIG>, the body <NUM> is cylindrical. The rings <NUM> are at an outer circumferential portion of the body <NUM> and apart from one another in the longitudinal direction. The outer circumferential portion of the body <NUM> and the side faces of the rings <NUM> define a plurality of outer grooves <NUM>, <NUM>, <NUM>, and <NUM> extending around the entire outer circumferential portion of the cylinder <NUM>.

The outer groove <NUM> has four supply ports <NUM> evenly spaced from one another along the circumference of the body <NUM> and extending from the outer groove <NUM> to an inner circumferential portion 44a of the body <NUM>.

The outer groove <NUM> has four supply ports <NUM>, the outer groove <NUM> has four supply ports <NUM>, and the outer groove <NUM> has four supply ports <NUM>, similarly to the supply ports <NUM>. The supply ports <NUM> to <NUM> are at the same phase along the circumference of the body <NUM>.

Attaching the cylinder <NUM> to the inner circumferential portion 30e of the shaft holder <NUM> as illustrated in <FIG> and <FIG> connects the supply port 30a of the shaft holder <NUM> with the outer groove <NUM> of the cylinder <NUM>. This allows the supply port 30a to be between adjacent supply ports <NUM> of the cylinder <NUM> along its circumference.

The above attachment connects the supply port 30b of the shaft holder <NUM> with the outer groove <NUM> of the cylinder <NUM>. This allows the supply port 30b to be between adjacent supply ports <NUM> of the cylinder <NUM> along its circumference.

The above attachment connects the supply port 30c of the shaft holder <NUM> with the outer groove <NUM> of the cylinder <NUM>. This allows the supply port 30c to be between adjacent supply ports <NUM> of the cylinder <NUM> along its circumference.

The above attachment connects the supply port 30d of the shaft holder <NUM> with the outer groove <NUM> of the cylinder <NUM>. This allows the supply port 30d to be between adjacent supply ports <NUM> of the cylinder <NUM> along its circumference.

As illustrated in <FIG>, the output shaft <NUM> has an end provided with a plurality of rings <NUM> disposed around an outer circumferential portion of the output shaft <NUM> and spaced from one another in the longitudinal direction of the output shaft <NUM>. The rings <NUM> define a plurality of shaft grooves <NUM>, <NUM>, <NUM>, and <NUM> extending entirely around the outer circumferential portion of the output shaft <NUM>.

As illustrated in <FIG>, <FIG>, the output shaft <NUM> has a plurality of inlet ports <NUM>, <NUM>, <NUM>, and <NUM> extending inside the output shaft <NUM> in the radial direction of the output shaft <NUM>. The inlet ports <NUM> to <NUM> connect with the grooves <NUM> to <NUM>, respectively.

As illustrated in <FIG> and <FIG>, the inlet ports <NUM> and <NUM> are apart from each other by a small distance and are at respective phases close to each other around the circumference of the output shaft <NUM>, whereas the inlet ports <NUM> and <NUM> are apart from each other by a small distance and are at respective phases close to each other around the circumference of the output shaft <NUM>. The inlet ports <NUM> and <NUM> are at respective phases exactly opposite to each other around the circumference of the output shaft <NUM>, whereas the inlet ports <NUM> and <NUM> are at respective phases exactly opposite to each other around the circumference of the output shaft <NUM>.

As illustrated in <FIG> and <FIG>, the output shaft <NUM> has an oil passage <NUM> extending inside the output shaft <NUM> in its longitudinal direction and configured to supply lubricating oil to different sections.

The output shaft <NUM> also has a plurality of supply oil passages <NUM>, <NUM>, <NUM>, and <NUM> extending inside the output shaft <NUM> in its longitudinal direction. The supply oil passage <NUM> is connected with the inlet port <NUM> inside the output shaft <NUM> and with the first clutch CL1 (see <FIG>).

The supply oil passage <NUM> is connected with the inlet port <NUM> inside the output shaft <NUM> and with the fourth clutch CL4 (see <FIG>).

The supply oil passage <NUM> is connected with the inlet port <NUM> inside the output shaft <NUM> and with the second clutch CL2 (see <FIG>).

The supply oil passage <NUM> is connected with the inlet port <NUM> inside the output shaft <NUM> and with the third clutch CL3 (see <FIG>).

As illustrated in <FIG>, the cylinder <NUM> has outer grooves <NUM> to <NUM> extending around the entire outer circumferential portion of the cylinder <NUM> along the circumference of the inner circumferential portion 30e of the shaft holder <NUM>.

Attaching the cylinder <NUM> to the inner circumferential portion 30e of the shaft holder <NUM> as illustrated in <FIG> and <FIG> causes the inner circumferential portion 30e and the outer grooves <NUM> to <NUM> to define a plurality of outer flow paths <NUM>, <NUM>, <NUM>, and <NUM>. This allows the shaft holder <NUM> to have outer flow paths <NUM> to <NUM> each in the shape of a ring around the corresponding one of the shaft grooves <NUM> to <NUM> of the output shaft <NUM> (power transmission shaft).

The supply ports 30a to 30d (first supply port) of the shaft holder <NUM> are connected with the outer flow paths <NUM> to <NUM> (outer grooves <NUM> to <NUM> of the cylinder <NUM>), respectively.

The supply ports <NUM> to <NUM> (second supply port) of the cylinder <NUM> extend from the outer flow paths <NUM> to <NUM> (outer grooves <NUM> to <NUM> of the cylinder <NUM>), respectively, to the inner circumferential portion 44a of the cylinder <NUM> (body <NUM>).

Attaching the cylinder <NUM> to the inner circumferential portion 30e of the shaft holder <NUM> allows the inner circumferential portion 44a (see <FIG>) of the cylinder <NUM> (body <NUM>) to serve as the inner circumferential portion 30e of the shaft holder <NUM>.

As a result, the supply ports <NUM> to <NUM> (second supply port) of the cylinder <NUM> extend from the outer flow paths <NUM> to <NUM> (outer grooves <NUM> to <NUM> of the cylinder <NUM>), respectively, to the inner circumferential portion 30e of the shaft holder <NUM> (inner circumferential portion 44a of the cylinder <NUM> (body <NUM>)).

The supply ports <NUM> (second supply port) of the cylinder <NUM> are in communication with the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft). The supply ports <NUM> (second supply port) of the cylinder <NUM> are in communication with the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft).

As illustrated in <FIG>, <FIG>, the cylinder <NUM> has a plurality of supply ports <NUM> to <NUM> (second supply port) spaced from one another along the circumference of the inner circumferential portion 30e of the shaft holder <NUM>.

As illustrated in <FIG>, the supply ports 30a to 30d (first supply port) of the shaft holder <NUM> are between adjacent supply ports <NUM> to <NUM> (second supply port) of the cylinder <NUM> along its circumference. The supply ports 30a to 30d (first supply port) are thus positioned differently from the supply ports <NUM> to <NUM> (second supply port) along the circumference of the inner circumferential portion 30e.

As illustrated in <FIG>, the outer flow paths <NUM> to <NUM> (outer grooves <NUM> to <NUM> of the cylinder <NUM>) each have a first cross-sectional area on a plane orthogonal to the circumference of the inner circumferential portion 30e of the shaft holder <NUM>, whereas the shaft grooves <NUM> to <NUM> of the output shaft <NUM> each have a second cross-sectional area on a plane orthogonal to the circumference of the output shaft <NUM> (power transmission shaft), the first cross-sectional area being larger than the second cross-sectional area.

As illustrated in <FIG> and <FIG>, supplying operating oil to the supply ports 30a to 30d (first supply port) of the shaft holder <NUM> causes the operations below.

The operating oil supplied to the supply port 30a (first supply port) of the shaft holder <NUM> is then supplied from the supply port 30a through the outer flow path <NUM> (outer groove <NUM> of the cylinder <NUM>), the supply ports <NUM> (second supply port) of the cylinder <NUM>, the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft), the inlet port <NUM>, and the supply oil passage <NUM> to the first clutch CL1 (hydraulically operable section) (see <FIG>) to cause the first clutch CL1 to become engaged.

The operating oil supplied to the supply port 30b (first supply port) of the shaft holder <NUM> is then supplied from the supply port 30b through the outer flow path <NUM> (outer groove <NUM> of the cylinder <NUM>), the supply ports <NUM> (second supply port) of the cylinder <NUM>, the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft), the inlet port <NUM>, and the supply oil passage <NUM> to the fourth clutch CL4 (hydraulically operable section) (see <FIG>) to cause the fourth clutch CL4 to become engaged.

The operating oil supplied to the supply port 30c (first supply port) of the shaft holder <NUM> is then supplied from the supply port 30c through the outer flow path <NUM> (outer groove <NUM> of the cylinder <NUM>), the supply ports <NUM> (second supply port) of the cylinder <NUM>, the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft), the inlet port <NUM>, and the supply oil passage <NUM> to the second clutch CL2 (hydraulically operable section) (see <FIG>) to cause the second clutch CL2 to become engaged.

The operating oil supplied to the supply port 30d (first supply port) of the shaft holder <NUM> is then supplied from the supply port 30d through the outer flow path <NUM> (outer groove <NUM> of the cylinder <NUM>), the supply ports <NUM> (second supply port) of the cylinder <NUM>, the shaft groove <NUM> of the output shaft <NUM> (power transmission shaft), the inlet port <NUM>, and the supply oil passage <NUM> to the third clutch CL3 (hydraulically operable section) (see <FIG>) to cause the third clutch CL3 to become engaged.

The cylinder <NUM> may have, for each outer groove <NUM>, <NUM>, <NUM>, <NUM> (outer flow path <NUM>, <NUM>, <NUM>, <NUM>), two or three supply ports <NUM>, <NUM>, <NUM>, <NUM> or five or six supply ports <NUM>, <NUM>, <NUM>, <NUM>.

The cylinder <NUM> may have supply ports <NUM> to <NUM> in different numbers for the respective outer grooves <NUM> to <NUM> (outer flow paths <NUM> to <NUM>).

The cylinder <NUM> may have supply ports <NUM> to <NUM> at different phases along the circumference of the cylinder <NUM> for the respective outer grooves <NUM> to <NUM> (outer flow paths <NUM> to <NUM>).

The cylinder <NUM> may have supply ports <NUM> to <NUM> unevenly spaced from one another along the circumference of the cylinder <NUM>.

The configurations illustrated in <FIG> and the first and second alternative embodiments may be applied to the forward-travel clutch CLF and rearward-travel clutch CLR of the forward/rearward travel switching device <NUM> or the standard clutch CLT and speed-increasing clutch CLH of the front-wheel transmission device <NUM>.

This case includes two hydraulically operable sections. The shaft holder <NUM> thus has two supply ports 30a and 30b. The cylinder <NUM> has two outer grooves <NUM> and <NUM> (outer flow paths <NUM> and <NUM>) and two sets of supply ports <NUM> and <NUM>. The power transmission shafts <NUM> and <NUM> have two shaft grooves <NUM> and <NUM>, two inlet ports <NUM> and <NUM>, and two supply oil passages <NUM> and <NUM>.

The configurations illustrated in <FIG> and the first and second alternative embodiments may be applied to the PTO clutch <NUM>.

This case includes a single hydraulically operable section. The shaft holder <NUM> thus has a single supply port 30a. The cylinder <NUM> has a single outer groove <NUM> (outer flow path <NUM>) and a single set of supply ports <NUM>. The power transmission shaft <NUM> has a single shaft groove <NUM>, a single inlet port <NUM>, and a single supply oil passage <NUM>.

The transmission case <NUM> may not contain a cylinder <NUM>. With this configuration, the shaft holder <NUM> not only has supply ports 30a to 30d, but also directly has outer flow paths <NUM> to <NUM> and supply ports <NUM> to <NUM>.

The operating oil may be supplied, instead of from the supply oil passages <NUM> to <NUM> to the hydraulic clutch, through the supply oil passages <NUM> to <NUM> to a hydraulic operation section (corresponding to the "hydraulically operable section") configured to slide a transmission gear of a gear shift device.

Claim 1:
A work vehicle, comprising:
a power transmission shaft (<NUM>) drivable to rotate;
a shaft holder (<NUM>) holding the power transmission shaft (<NUM>) in such a manner that the power transmission shaft is rotatable; and
a hydraulically operable section (CL1, CL2, CL3, CL4) configured to operate in response to receiving operating oil,
the power transmission shaft (<NUM>) including:
a shaft groove (<NUM>-<NUM>) extending entirely around an outer circumferential portion of the power transmission shaft (<NUM>);
an inlet port (<NUM>-<NUM>) extending inside the power transmission shaft (<NUM>) in a radial direction of the power transmission shaft and connected with the shaft groove (<NUM>-<NUM>) ; and
a supply oil passage (<NUM>-<NUM>) extending inside the power transmission shaft (<NUM>) in a longitudinal direction of the power transmission shaft and connected with the inlet port (<NUM>-<NUM>) inside the power transmission shaft,
the shaft holder (<NUM>) including:
an outer flow path (<NUM>-<NUM>) in a shape of a ring around the shaft groove (<NUM>-<NUM>);
a first supply port (30a-30d) connected with the outer flow path (<NUM>-<NUM>) and configured to receive operating oil; and
at least one second supply port (<NUM>-<NUM>) extending from the outer flow path (<NUM>-<NUM>) to an inner circumferential portion (30e) of the shaft holder (<NUM>) and communicating with the shaft groove (<NUM>-<NUM>), characterised in that
the work vehicle being configured to cause operating oil to be supplied from the first supply port (30a-30d) sequentially through the outer flow path (<NUM>-<NUM>), the at least one second supply port (<NUM>-<NUM>), the shaft groove (<NUM>-<NUM>), the inlet port (<NUM>-<NUM>), and the supply oil passage (<NUM>-<NUM>) to the hydraulically operable section (CL1, CL2, CL3, CL4).