Patent Description:
There are some work vehicles including a transmission case that contains therein a gear transmission and a differential mechanism. The gear transmission varies power from a power source and outputs the power. The differential mechanism includes a ring gear rotatable around a rotation axis along a horizontal direction, and transmits the power inputted from the gear transmission to a traveling device.

The differential mechanism stirs a lubricating oil during operation in the transmission case. During that time, the differential mechanism is lubricated with the lubricating oil, and receives resistance from the lubricating oil by stirring the lubricating oil. There are cases where a large amount of the lubricating oil stays in the transmission case and the differential mechanism enters deeply in the lubricating oil in the transmission case. The differential mechanism stirs the lubricating oil at a low-speed rotation during low-speed traveling, and therefore, the differential mechanism is not subjected to high resistance due to the stirring of the lubricating oil. An advantage that the differential mechanism is lubricated by entering deeply in the lubricating oil is greater than a disadvantage that the differential mechanism is subjected to the resistance. Accordingly, the differential mechanism preferably enters deeply in the lubricating oil in the transmission case during low-speed traveling. In contrast, if the differential mechanism enters deeply in the lubricating oil during high-speed traveling, the differential mechanism stirs the lubricating oil at high-speed rotation, resistance exerted on the differential mechanism due to the stirring of the lubricating oil grows stronger, causing large loss of driving force. Hence, the differential mechanism preferably enters shallowly in the lubricating oil during the high-speed traveling.

A lubrication device of powertrain discussed in <CIT> includes an oil pump to supply an oil to a differential chamber, a pipe to connect an oil pan of a gear case and a lower portion of the differential chamber, and a valve disposed in the pipe. With the valve closed, the oil supplied to the differential chamber remains in the lower portion of the differential chamber. With the valve opened, it is configured so that the oil remaining in the lower portion of the differential chamber can flow out to the oil pan. An oil surface of the differential chamber when a vehicle speed is high is kept lower than that when the vehicle speed is low by opening and closing the valve.

US Patent Application Publications <CIT> and <CIT> disclose alternative lubrication systems for vehicle drivetrains.

The lubrication device tends to have a complicated structure because a conventional lubrication technology needs the oil pump and the valve.

The present invention provides a work vehicle in which the differential mechanism can enter deeply in the lubricating oil during the low-speed traveling, and the differential mechanism can enter shallowly in the lubricating oil during the high-speed traveling even by a lubrication device having a simple structure.

A work vehicle according to the present invention includes a gear transmission, a differential mechanism, a transmission case, a first space zone, a second space zone, a partition wall, an upper space and a flow-out path. The gear transmission is configured to vary power from a power source and output the power. The differential mechanism includes a ring gear rotatable around a rotation axis along a horizontal direction, and is configured to transmit the power inputted from the gear transmission to a traveling device. The transmission case contains the gear transmission and the differential mechanism. There are the first space zone as part of an internal space of the transmission case in which first space zone the differential mechanism is located, and the second space zone as part of the internal space which second space zone is adjacent to the first space zone. The partition wall separates the first space zone and the second space zone from each other. The upper space is disposed above the partition wall and configured to allow lubricating oil scooped up from the first space zone by rotation of the ring gear to flow in the second space zone. The flow-out path is disposed below the upper space and configured to allow the lubricating oil staying in the second space zone to flow out to the first space zone.

The ring gear rotates at lower speeds during the low-speed traveling than during the high-speed traveling, thereby decreasing the amount of the lubricating oil which is scooped up by the ring gear from the first space zone and flows through the upper space into the second space zone. The ring gear rotates at higher speeds during the high-speed traveling than during the low-speed traveling, thereby increasing the amount of the lubricating oil which is scooped up by the ring gear from the first space zone and flows through the upper space into the second space zone. In this embodiment, a circulation area of the flow-out path is preset so that the amount of the lubricating oil flowing out of the second space zone through the flow-out path to the first space zone can reach an appropriate amount. Thereby, the amount of the lubricating oil staying in the second space zone during the low-speed traveling becomes smaller than that during the high-speed traveling. This makes it possible to increase the position of the oil surface of the lubricating oil in the first space zone. In contrast, the amount of the lubricating oil staying in the second space zone during the high-speed traveling becomes larger than during the low-speed traveling. This makes it possible to decrease the position of the oil surface of the lubricating oil in the first space zone. That is, the differential mechanism can enter deeply in the lubricating oil during the low-speed traveling, and the differential mechanism can enter shallowly in the lubricating oil during the high-speed traveling. Additionally, the ring gear is usable as a pump that transfers the lubricating oil in the first space zone to the second space zone, and the lubricating oil can flow out of the second space zone to the first space zone by a head difference of the lubricating oil, thus leading to a simple structure of the lubrication device.

The work vehicle of the present invention further includes an area adjustment part configured to adjust a circulation area of the flow-out path.

With this configuration, the circulation area of the flow-out path is adjusted so that the amount of the lubricating oil flowing out of the second space zone through the flow-out path to the first space zone can reach the appropriate amount. With this configuration, the amount of the lubricating oil staying in the second space zone during the low-speed traveling becomes smaller than that during the high-speed traveling. This makes it possible to increase the position of the oil surface of the lubricating oil in the first space zone. In contrast, the amount of the lubricating oil staying in the second space zone during the high-speed traveling becomes larger than that during the low-speed traveling. This makes it possible to decrease the position of the oil surface of the lubricating oil in the first space zone. Even if viscosity of the lubricating oil changes due to, for example, a temperature change of the lubricating oil and a change of the lubrication oil to be used, the circulation area of the flow-out path can be adjusted by the area adjustment part. Consequently, the amount of the lubricating oil flowing out of the second space zone through the flow-out path to the first space zone can be adjusted to an appropriate amount. That is, the differential mechanism can enter deeply in the lubricating oil during the low-speed traveling, and the differential mechanism can enter shallowly in the lubricating oil during the high-speed traveling. Additionally, the ring gear is usable as a pump that transfers the lubricating oil in the first space zone to the second space zone, and the lubricating oil can flow out of the second space zone to the first space zone by a head difference of the lubricating oil, thus leading to a simple structure of the lubrication device.

The work vehicle of the present invention further includes a wall adjustment part configured to adjust lifting and lowering of an upper portion of the partition wall.

With this configuration, by adjusting the upper portion of the partition wall to a lifting side by the wall adjustment part, the position of the upper portion of the partition wall can be increased to obtain a large volume of space where the lubricating oil can stay in the second space zone. By adjusting the upper portion of the partition wall to a lowering side by the wall adjustment part, the position of the upper portion of the partition wall can be lowered so that the lubricating oil scooped up by the ring gear can easily climb over the partition wall. Even if the amount of the lubricating oil scooped up by the ring gear during the high-speed traveling in which the ring gear has a higher rotation speed is larger than that during the low-speed traveling, an appropriate amount of the lubricating oil can flow in the second space zone so as to appropriately maintain the height of the oil surface of the lubricating oil in the first space zone by adjusting the upper portion of the partition wall to the lifting side. In contrast, even if the height of scooping up of the lubricating oil scooped up by the ring gear during the low-speed traveling in which the ring gear has a low rotation speed is lower than that during the high-speed traveling, by adjusting the upper portion of the partition wall to the lowering side, the lubricating oil scooped up can easily flow in the second space zone so as to stay in the second space zone, thereby lowering the height of the oil surface of the lubricating oil in the first space zone.

The present invention preferably includes a first guide part, which is disposed in a vertically-directed attitude between the ring gear and the partition wall, and is configured to guide the lubricating oil stirred by the ring gear toward above the partition wall.

With this configuration, the lubricating oil scooped up by the ring gear is guided so as to flow toward the above the partition wall by the first guide part. Therefore, the lubricating oil scooped up by the ring gear can easily flow in the second space zone.

The present invention preferably includes a second guide part, which is disposed below the ring gear in a state of extending in a rotation direction of the ring gear, and is configured to guide the lubricating oil stirred by the ring gear toward the first guide part. An end portion of the second guide part which end portion is located in a downstream side in the rotation direction of the ring gear is preferably connected to a lower end portion of the first guide part.

With this configuration, the lubricating oil stirred below the ring gear is guided so as to flow toward the first guide part by the second guide part, and the lubricating oil flowing toward the first guide part does not leak from between the second guide part and the first guide part. Hence, the lubricating oil stirred below the ring gear can easily flow in the second space zone.

The present invention preferably includes a third guide part disposed, in a state in which the third guide part extends in the rotation direction of the ring gear, at a position opposed to one of two lateral portions in a lower portion of the ring gear which lateral portion is located on a side on which a tooth part of the ring gear is located. The third guide part is preferably configured to guide the lubricating oil stirred by the ring gear toward the first guide part. An end portion of the third guide part which end portion is located toward the second guide part is preferably connected to a lateral end portion of the second guide part which lateral end portion is located toward the third guide part. An end portion of the third guide part which is located on a downstream side of the rotation direction of the ring gear is preferably connected to a lateral end portion of the first guide part which lateral end portion is located toward the third guide part.

With this configuration, the lubricating oil stirred below the ring gear can be guided so as to flow toward the first guide part by the second guide part and the third guide part without leaking from between the second guide part and the third guide part, and the lubricating oil flowing toward the first guide part does not leak from between the second guide part and the first guide part and between the third guide part and the first guide part. Hence, the lubricating oil stirred below the ring gear can easily flow in the second space zone.

The partition wall is preferably disposed in an inclined attitude to guide the lubricating oil stirred by the ring gear toward the second space zone in the present invention.

With this configuration, the partition wall has a guide function to cause the lubricating oil to flow toward the second space zone. Therefore, the partition wall is usable as a guide member to facilitate the flow of the lubricating oil into the second space zone.

The present invention preferably includes an oil feeding part disposed separately from a tooth part in the ring gear and configured to feed the lubricating oil staying in the first space zone toward the second space zone.

With this configuration, the lubricating oil tends to flow in the second space zone because the lubricating oil staying in the first space zone is also fed to the second space zone by the oil feeding part in addition to the tooth part of the ring gear.

The present invention preferably includes a clutch disposed in an upper portion of the second space zone and configured to switch between an on state in which the power from the power source is transmitted to a power take-off shaft, and an off state in which the power transmission from the power source to the power take-off shaft is discontinued.

With this configuration, the clutch is cooled by the lubricating oil, and the lubricating oil dripping from the clutch enters the second space zone and flows out of the second space zone via the flow-out path to the first space zone. It is therefore possible to lubricate the differential mechanism without any special lubrication circuit for the differential mechanism.

The present invention preferably includes a gear interlock mechanism disposed in the second space zone and configured to interlock the clutch and the power take-off shaft.

With this configuration, the lubricating oil is fed by the ring gear, and the gear interlock mechanism is located in the second space zone to which the lubricating oil is supplied from the clutch. It is therefore possible to supply the lubricating oil to the gear interlock mechanism without any special lubrication circuit for the gear interlock mechanism.

An embodiment of the present invention is described with reference to the drawings.

The following description relates to a traveling vehicle body of a tractor (an example of "work vehicles"). In <FIG>, <FIG> and <FIG>, and the like, a direction of an arrow F is "front vehicle body," a direction of an arrow B is "rear vehicle body," a direction of an arrow U is "above vehicle body," a direction of an arrow D is "below vehicle body," a direction of an arrow L is "left vehicle body" and a direction of an arrow R is "right vehicle body.

As illustrated in <FIG>, the traveling vehicle body of the tractor includes an engine <NUM>, a transmission case <NUM>, a vehicle body frame <NUM>, a pair of left and right front wheels <NUM> and a pair of left and right rear wheels <NUM>. A front portion of the transmission case <NUM> is connected to a flywheel housing <NUM> disposed in a rear portion of the engine <NUM>. The vehicle body frame <NUM> is configured by, for example, a front frame <NUM> connected to a lower portion of the engine <NUM>. The front wheels <NUM> are traveling devices disposed at a front portion of the vehicle body frame <NUM> so as to be steerably and drivably. The rear wheels <NUM> are traveling device disposed drivably at a rear portion of the vehicle body frame <NUM>. The tractor includes a driving section <NUM>, which includes the engine <NUM>, which is disposed at a front portion of the traveling vehicle body. The tractor includes an operation section <NUM> at a rear portion of the traveling vehicle body. The operation section <NUM> includes an operation seat <NUM>, a steering wheel <NUM> to perform steering operation of the front wheels <NUM>, and a cabin <NUM> to cover a boarding space. The tractor includes a link mechanism <NUM> and a power take-off shaft <NUM>. The link mechanism <NUM> connects various types of working devices, such as a rotary tiller (not illustrated), to a rear portion of the vehicle body frame <NUM> so that they can be subjected to a lifting operation. The power take-off shaft <NUM> transmits power from the engine <NUM> to the working devices being connected.

<FIG> is a diagram illustrates a power transmission device <NUM>. The power transmission device <NUM> transmits the power of the engine <NUM> to the front wheels <NUM>, the rear wheels <NUM>, and the power take-off shaft <NUM>. As illustrated in <FIG> and <FIG>, the power transmission device <NUM> includes the transmission case <NUM> whose front portion is connected to the flywheel housing <NUM> disposed in the rear portion of the engine <NUM>. The transmission case <NUM> is disposed in the traveling vehicle body in a state in which a front-hack direction of the transmission case <NUM> coincides with a front-back direction of the traveling vehicle body as illustrated in <FIG>. The transmission case <NUM> is configured so as to be divisible into a front case part 3a, an intermediate case part 3b, and a rear case part 3c. A front portion of the front case part 3a is connected to the flywheel housing <NUM>. The intermediate case part 3b is connected to a rear portion of the front case part 3a. A front portion of the rear case part 3c is connected to a rear portion of the intermediate case part 3b.

As illustrated in <FIG>, the transmission case <NUM> contains therein a gear transmission <NUM>, to which the power from the engine <NUM>, which is a power source, is inputted, which varies the power, and from which the varied power varied is outputted to the front wheels <NUM> and the rear wheels <NUM>; a rear wheel differential mechanism <NUM> (corresponding to the differential mechanism); and an operation power transmission device <NUM>, which transmits the power from the engine <NUM> to the power take-off shaft <NUM>.

The gear transmission <NUM> includes an input shaft <NUM>, a major transmission section <NUM>, a staged transmission section <NUM>, a forward-reverse switching device <NUM>, a first gear interlock mechanism <NUM>, and a front wheel transmission device <NUM> as illustrated in <FIG>. Power of an output shaft 1a of the engine <NUM> is transmitted via a major clutch <NUM> to the input shaft <NUM>, and the input shaft <NUM> inputs the transmitted power to the transmission case <NUM>. The major transmission section <NUM> is connected to the input shaft <NUM>. Output of the major transmission section <NUM> is inputted to the staged transmission section <NUM>. Output of the staged transmission section <NUM> is inputted to the forward-reverse switching device <NUM>. The first gear interlock mechanism <NUM> transmits output of the forward-reverse switching device <NUM> to the rear wheel differential mechanism <NUM>. The output of the forward-reverse switching device <NUM> is transmitted via the first gear interlock mechanism <NUM> to the front wheel transmission device <NUM>.

The major transmission section <NUM> includes a planetary gear device 18A and a continuously variable transmission device 18B as illustrated in <FIG>.

The planetary gear device 18A includes two planetary gear device sections disposed side by side in the front-back direction of the transmission case <NUM>. Hereinafter, a description is given where one of these two planetary gear device sections which is disposed on a front side is referred to as a first planetary gear device section <NUM>, and one of these two planetary gear device sections which is disposed on a rear side is referred to as a second planetary gear device section <NUM>.

The first planetary gear device section <NUM> includes a planetary gear <NUM>, a transmission gear (not illustrated) that meshes with the planetary gear <NUM>. The second planetary gear device section <NUM> includes a planetary gear <NUM>. A coupling member (not illustrated) that interlockingly couples the transmission gear and the planetary gear <NUM> is disposed across the first planetary gear device section <NUM> and the second planetary gear device section <NUM>. A carrier <NUM> of the first planetary gear device section <NUM> and a carrier <NUM> of the second planetary gear device section <NUM> are integrally rotatably coupled to each other. With this configuration, the planetary gear device 18A is configured as a complex planetary gear device.

The continuously variable transmission device 18B is configured by a hydrostatic continuously variable transmission device and includes a variable displacement hydraulic pump P and a hydraulic motor M.

Power of the input shaft <NUM> is inputted via a front rotating shaft <NUM> and a second gear interlock mechanism <NUM> to the hydraulic pump P in the major transmission section <NUM>. By performing a gear shift operation to change a swash plate angle of the hydraulic pump P in the continuously variable transmission device 18B, the inputted power is shifted to forward rotation power and reverse rotation power, and the forward rotation power and the reverse rotation power are shifted steplessly. The shifted power is outputted from the hydraulic motor M. Output of the continuously variable transmission device 18B is inputted via a third gear interlock mechanism <NUM> to a sun gear <NUM> of the first planetary gear device section <NUM>. Power of the input shaft <NUM> is inputted via a fourth gear interlock mechanism <NUM> to an internal gear <NUM> of the first planetary gear device section <NUM>. Power transmitted from the engine <NUM> via the continuously variable transmission device 18B, and power transmitted from the engine <NUM> not via the continuously variable transmission device 18B are synthesized by the first planetary gear device section <NUM> and the second planetary gear device section <NUM> in the planetary gear device 18A. Synthetic power is outputted from a first output shaft 37a, a second output shaft 37b, and a third output shaft 37c included in the second planetary gear device section <NUM>.

The staged transmission section <NUM> includes four staged clutches to which the synthetic power from the planetary gear device 18A, and an output shaft <NUM> as illustrated in <FIG>. These four staged clutches are a first clutch CL1, a second clutch CL2, a third clutch CL3, and a fourth clutch CL4 illustrated in <FIG>, which are disposed on the output shaft <NUM>.

The synthetic power from the planetary gear device 18A is staged in four speed ranges and then outputted from the output shaft <NUM> by appropriate operations of the continuously variable transmission device 18B and the four staged clutches (the first clutch CL1, the second clutch CL2, the third clutch CL3 and the fourth clutch CL4) in the staged transmission section <NUM>.

<FIG> is an explanatory drawing illustrating a relationship among a speed change state of the continuously variable transmission device 18B, a speed range and a rotational velocity V of the output shaft <NUM> of the staged transmission section <NUM>. An ordinate in <FIG> represents the rotational velocity V of the output shaft <NUM>. An abscissa in <FIG> represents the speed change state of the continuously variable transmission device 18B, in which "N" represents a neutral state, "-MAX" represents a speed change state at a maximum speed in a reverse rotation direction, and "+MAX" represents a speed change state at a maximum speed in a forward rotation direction.

If the first clutch CL1 of the four staged clutches is brought into an engaged state and the continuously variable transmission device 18B is subjected to a gear shift operation, the power of the first output shaft 37a is varied by a first speed gear interlock mechanism 39a and the first clutch CL1, and the varied power is outputted from the output shaft <NUM>. As illustrated in <FIG>, the rotational velocity V of the output shaft <NUM> reaches a rotational velocity of a first speed range, and the rotational velocity V of the output shaft <NUM> increases steplessly from a velocity "<NUM>" to the maximum velocity "V1" of the first speed range along with a shift from "-MAX" to "+MAX" in the continuously variable transmission device 18B.

If the second clutch CL2 of the four staged clutches is brought into an engaged state and the continuously variable transmission device 18B is subjected to a gear shift operation, the power of the third output shaft 37c is varied by a second speed gear interlock mechanism 39b and the second clutch CL2, and the varied power is outputted from the output shaft <NUM>. As illustrated in <FIG>, the rotational velocity V of the output shaft <NUM> reaches a higher rotational velocity of a second speed range than the first speed range, and the rotational velocity V of the output shaft <NUM> increases steplessly from a minimum velocity "V1" of the second speed range to the maximum velocity "V2" of the second speed range along with a shift from "+MAX" to "-MAX" in the continuously variable transmission device 18B.

If the third clutch CL3 of the four staged clutches is brought into an engaged state and the continuously variable transmission device 18B is subjected to a gear shift operation, the power of the second output shaft 37b is varied by a third speed gear interlock mechanism 39c and the third clutch CL3, and the varied power is outputted from the output shaft <NUM>. As illustrated in <FIG>, the rotational velocity V of the output shaft <NUM> reaches a higher-side rotational velocity of a third speed range than the second speed range, and the rotational velocity V of the output shaft <NUM> increases steplessly from a minimum velocity "V2" of the third speed range to the maximum velocity "V3" of the third speed range along with a shift from "-MAX" to "+MAX" in the continuously variable transmission device 18B.

If the fourth clutch CL4 of the four staged clutches is brought into an engaged state and the continuously variable transmission device 18B is subjected to a gear shift operation, the power of the third output shaft 37c is varied by the fourth speed gear interlocking mechanism 39d and the fourth clutch CL4, and the varied power is outputted from the output shaft <NUM>. As illustrated in <FIG>, the rotational velocity V of the output shaft <NUM> reaches a higher-side rotational velocity of a fourth speed range than the third speed range, and the rotational velocity V of the output shaft <NUM> increases steplessly from a minimum velocity "V3" of the fourth speed range to the maximum velocity "V4" of the fourth speed range along with a shift from "+MAX" to "-MAX" in the continuously variable transmission device 18B.

As illustrated in <FIG>, the forward-reverse switching device <NUM> includes an input shaft <NUM>, which is connected to the output shaft <NUM> of the staged transmission section <NUM>; a forward clutch CLF and a reverse clutch CLR, which are disposed on the input shaft <NUM>; and an output shaft <NUM>. The output shaft <NUM> is connected via a forward gear mechanism 41f to the forward clutch CLF, and is connected via a reverse gear mechanism 41r to the reverse clutch CLR. As illustrated in <FIG>, the reverse gear mechanism 41r includes a reverse gear <NUM> configured to mesh with a tooth part of an output rotary member of the reverse clutch CLR. The reverse gear <NUM> is relatively rotatably supported on an input shaft 22a of the rear wheel differential mechanism <NUM>.

In the forward-reverse switching device <NUM>, if the forward clutch CLF is brought into an engaged state, power transmitted from the staged transmission section <NUM> to the input shaft <NUM> is converted to forward movement power by the forward clutch CLF and the forward gear mechanism 41f, and the forward movement power is outputted from the output shaft <NUM>. If the reverse clutch CLR is brought into an engaged state, power transmitted from the staged transmission section <NUM> to the input shaft <NUM> is converted to reverse movement power by the reverse clutch CLR and the reverse gear mechanism 41r, and the reverse movement power is outputted from the output shaft <NUM>. The forward movement power and the reverse movement power outputted from the output shaft <NUM> are transmitted to the first gear interlock mechanism <NUM> and are then transmitted to the input shaft 22a of the rear wheel differential mechanism <NUM> by the first gear interlock mechanism <NUM>.

The forward movement power and the reverse movement power outputted from the forward reverse switching device <NUM> are inputted via the first gear interlock mechanism <NUM> to the input shaft 22a, and the rear wheel differential mechanism <NUM> outputs the inputted powers to the left and right rear wheels <NUM>. Output of the rear wheel differential mechanism <NUM> is transmitted via a reduction device <NUM> to the rear wheels <NUM>. The reduction device <NUM> is configured by a planetary gear device. A steering brake <NUM> is disposed on a transmission system from the rear wheel differential mechanism <NUM> to the rear wheels <NUM>.

The front wheel transmission device <NUM> includes an input shaft <NUM>, a constant velocity clutch CLT and a speed-up clutch CLH, which are disposed on the input shaft <NUM>, and an output shaft <NUM> as illustrated in <FIG>. The forward movement power and the reverse movement power from the forward reverse switching device <NUM> are transmitted via the first gear interlock mechanism <NUM> to the input shaft <NUM>. The output shaft <NUM> is connected via a constant velocity gear mechanism 44a to the constant velocity clutch CLT, and is connected via a speed-up gear mechanism 44b to the speed-up clutch CLH. A parking brake <NUM> is connected to the input shaft <NUM>.

If the constant velocity clutch CLT is brought into an engaged state in the front wheel transmission device <NUM>, power transmitted from the forward reverse switching device <NUM> to the input shaft <NUM> is transmitted via the constant velocity clutch CLT and the constant velocity gear mechanism 44a to the output shaft <NUM>, and the power is transmitted from the output shaft <NUM> via a rotating shaft <NUM> to the front wheel differential mechanism <NUM>. This leads to a situation where the pair of left and right front wheels <NUM> and the pair of left and right rear wheels <NUM> are driven in a state in which an average peripheral speed of the pair of left and right front wheels <NUM> is approximately equal to an average peripheral speed of the pair of left and right rear wheels <NUM>, namely, a so-called four-wheel drive state at an equal velocity of the front and rear wheels. If the speed-up clutch CLH is brought into an engaged state, power transmitted from the forward reverse switching device <NUM> to the input shaft <NUM> is transmitted via the speed-up clutch CLH and the speed-up gear mechanism 44b to the output shaft <NUM>, and the power is transmitted from the output shaft <NUM> to the front wheel differential mechanism <NUM>. This leads to a situation where the pair of left and right front wheels <NUM> and the pair of left and right rear wheels <NUM> are driven in a state in which the average peripheral speed of the pair of left and right front wheels <NUM> is higher than the average peripheral speed of the pair of left and right rear wheels <NUM>, specifically, a so-called four-wheel drive state in which the front wheels have a higher speed.

The operation power transmission device <NUM> is connected via the front rotating shaft <NUM> and a rear rotating shaft <NUM> to the input shaft <NUM> as illustrated in <FIG>. The operation power transmission device <NUM> includes an operation clutch <NUM> (corresponding to a clutch) to which power from the engine <NUM> is inputted, and an operation power transmission mechanism <NUM> (corresponding to a gear interlock mechanism) that varies the output of the operation clutch <NUM> and transmits the output to the power take-off shaft <NUM>. The front rotating shaft <NUM> is disposed behind the input shaft <NUM> so as to be located on the same straight line as the input shaft <NUM>. The rear rotating shaft <NUM> is disposed behind the front rotating shaft <NUM> so as to be located on the same straight line as the front rotating shaft <NUM>.

The operation clutch <NUM> in the operation power transmission device <NUM> performs switching between a state in which the power from the engine <NUM> is transmitted to the power take-off shaft <NUM> and a state in which a power transmission from the engine <NUM> to the power take-off shaft <NUM> is discontinued. That is, if the operation clutch <NUM> is switched to an engaged state, the rear rotating shaft <NUM> and the operation power transmission mechanism <NUM> are interlockingly connected to each other by the operation clutch <NUM>, so that the power from the input shaft <NUM> is transmitted to the power take-off shaft <NUM>. If the operation clutch <NUM> is switched to a disengaged state, the interlocking connection between the rear rotating shaft <NUM> and the operation power transmission mechanism <NUM> is disconnected by the operation clutch <NUM>, so that the power transmission from the input shaft <NUM> to the power take-off shaft <NUM> is disconnected.

As illustrated in <FIG>, the rear wheel differential mechanism <NUM> is contained in a rear portion of the transmission case <NUM>. As illustrated in <FIG>, <FIG>, <FIG> and <FIG>, the rear wheel differential mechanism <NUM> includes an input shaft 22a located at a front portion of the rear wheel differential mechanism <NUM>, and a ring gear 22b engaged with an input gear 22c included in the input shaft 22a. Power of the input shaft 22a is transmitted via the input gear 22c to the ring gear 22b, and the ring gear 22b is rotationally driven around a rotation axis Y along a horizontal direction. In the present embodiment, the ring gear 22b is rotationally driven around the rotation axis Y along a vehicle body lateral width direction. A differential case 22d is connected to the ring gear 22b. Left and right output shafts 22e are extended from the differential case 22d. The differential case 22d includes therein a differential pinion 22f and a side gear <NUM> that transmit power of the ring gear 22b to the left and right output shafts 22e.

As illustrated in <FIG> and <FIG>, a partition wall <NUM> is disposed at a portion of an inner side of the transmission case <NUM> which is displaced in a direction orthogonal to the rotation axis Y and in a direction along the horizontal direction with respect to the ring gear 22b. In the present embodiment, the partition wall <NUM> is disposed at a portion behind the ring gear 22b in the inner portion of the transmission case <NUM>. As illustrated in <FIG>, the partition wall <NUM> is connected to a left sidewall portion <NUM>, a right sidewall portion 3d and a bottom wall portion 3e in the transmission case <NUM>. As illustrated in <FIG>, a first space zone A1 as part of an internal space of the transmission case <NUM> in which first space zone A1 the rear wheel differential mechanism <NUM> is located, and a second space zone A2 as part of the internal space which second space zone A2 is adjacent to the first space zone A1 are partitioned by the partition wall <NUM>. In the present embodiment, as illustrated in <FIG>, the partition wall <NUM> includes a basal portion 75b, which is formed integrally with the transmission case <NUM> and includes a notched portion 75a; and an upper portion forming member 75c, which is supported on the basal portion 75b and configured to close the notched portion 75a and form an upper portion 75t of the partition wall <NUM>. Although the partition wall <NUM> may be formed totally integrally with the transmission case <NUM>, the partition wall <NUM> may be attached to the transmission case <NUM>.

As illustrated in <FIG> and <FIG>, an upper space <NUM> to establish communication between the first space zone A1 and the second space zone A2 is disposed above the partition wall <NUM>. When the rear wheel differential mechanism <NUM> outputs a forward movement power, the ring gear 22b is driven in a rotation direction indicated by an arrow Z in <FIG>, and is configured so that the lubricating oil located in the first space zone A1 can flow through the upper space <NUM> into the second space zone A2 by being scooped up by a tooth part of the ring gear 22b. Specifically, the lubricating oil scooped up by rotation of the ring gear 22b flows in the second space zone A2 through a portion located below the operation clutch <NUM> in the upper space <NUM> and portions located on two lateral sides of the operation clutch <NUM> in the upper space <NUM>.

As illustrated in <FIG> and <FIG>, the flow-out path <NUM> to establish communication between the second space zone A2 and the first space zone A1 is disposed at a portion located below the upper space <NUM>. In the present embodiment, the flow-out path <NUM> is configured by a through hole disposed in the partition wall <NUM>. If a position of an oil surface of the lubricating oil staying in the second space zone A2 is higher than a position of an oil surface of the lubricating oil staying in the first space zone A1, the lubricating oil located in the second space zone A2 can flow out through the flow-out path <NUM> into the first space zone A1 by a head difference between the lubricating oil located in the second space zone A2 and the lubricating oil located in the first space zone A1.

As illustrated in <FIG> and <FIG>, the partition wall <NUM> includes an area adjustment part <NUM>, which is capable of adjusting a circulation area of the flow-out path <NUM>; and a wall adjustment part <NUM>, which is capable of adjusting lifting and lowering of the upper portion 75t of the partition wall <NUM>.

Specifically, as illustrated in <FIG>, the area adjustment part <NUM> includes an area adjustment member <NUM> and an area adjustment motor <NUM> as an actuator connected to the area adjustment member <NUM>. The area adjustment motor <NUM> is configured by an electric motor. The area adjustment member <NUM> is slidably supported on a first guide rail <NUM> included in the basal portion 75b in the partition wall <NUM>. The area adjustment member <NUM> and the area adjustment motor <NUM> are connected to each other by engaging a screw shaft <NUM> drivably disposed in the area adjustment motor <NUM> and a screw hole (not illustrated) included in the operation section <NUM> in the area adjustment member <NUM>. A portion of the screw shaft <NUM> which is located on a side opposite to the area adjustment motor <NUM> with respect to the operation section <NUM> is rotatably and slidably supported on a support part <NUM> in the area adjustment member <NUM>.

The screw shaft <NUM> is driven by the area adjustment motor <NUM>, and the operation section <NUM> is subjected to a movement operation by the screw shaft being rotated in the area adjustment part <NUM>. If the operation section <NUM> is subjected to the movement operation in a direction away from the area adjustment motor <NUM>, the area adjustment member <NUM> is guided on the first guide rail <NUM> and is subjected to a slide operation in a direction to enter the flow-out path <NUM>, and an area (circulation area) where the lubricating oil can be circulated in the flow-out path <NUM> is adjusted to a narrow side by the area adjustment member <NUM>. If the operation section <NUM> is subjected to a movement operation in a direction toward the area adjustment motor <NUM>, the area adjustment member <NUM> is guided on the first guide rail <NUM> and is subjected to a slide operation in a direction away from the flow-out path <NUM>, and the area (circulation area) where the lubricating oil can be circulated in the flow-out path <NUM> is adjusted to a wide side by the area adjustment member <NUM>.

Specifically, as illustrated in <FIG>, the wall adjustment part <NUM> includes the upper portion forming member 75c to form the upper portion 75t of the partition wall <NUM>, and an upper portion adjustment motor <NUM> as an actuator connected to the upper portion forming member 75c. The upper portion adjustment motor <NUM> is configured by an electric motor. The upper portion forming member 75c is slidably supported on the second guide rail <NUM> disposed at portions on two lateral sides of the notched portion 75a of the basal portion 75b on the partition wall <NUM>. The upper portion forming member 75c and the upper portion adjustment motor <NUM> are connected to each other by engaging a screw shaft <NUM> drivably disposed in the upper portion adjustment motor <NUM> and a screw hole (not illustrated) included in the operation section <NUM> disposed in the upper portion forming ember 75c. A portion of the screw shaft <NUM> which is located on a side opposite to the upper portion adjustment motor <NUM> with respect to the operation section <NUM> is rotatably and slidably supported on a support part <NUM> in the upper portion forming member 75c.

In the wall adjustment part <NUM>, the screw shaft <NUM> is driven by the upper portion adjustment motor <NUM>, and the operation section <NUM> is subjected to a movement operation by the screw shaft <NUM> being rotated. If the operation section <NUM> is subjected to a movement operation in a direction away from the upper portion adjustment motor <NUM>, the upper portion forming member 75c is subjected to a lifting operation by being guided by the second guide rail <NUM>, and a height position of the upper portion 75t in the partition wall <NUM> is adjusted to a high side by the upper portion forming member 75c. If the operation section <NUM> is subjected to a movement operation in a direction toward the upper portion adjustment motor <NUM>, the upper portion forming member 75c is subjected to a lowering operation by being guided by the second guide rail <NUM>, and the height position of the upper portion 75t in the partition wall <NUM> is adjusted to a low side by the upper portion forming member 75c.

As illustrated in <FIG>, a lubrication control device <NUM> is linked to the area adjustment motor <NUM> of the area adjustment part <NUM> and the upper portion adjustment motor <NUM> of the wall adjustment part <NUM>. An oil temperature sensor <NUM> to detect a temperature of the lubricating oil located inside the transmission case <NUM>, and a vehicle speed sensor to detect a traveling speed of a vehicle body are linked to the lubrication control device <NUM>.

The lubrication control device <NUM> is configured using a microcomputer. The lubrication control device <NUM> includes a first area setting section <NUM>, a second area setting section <NUM>, a first height setting section <NUM>, and a second height setting section <NUM>. The first area setting section <NUM> stores a predetermined relationship between a lubricating oil temperature and a circulation area scale as a set circulation area. The second area setting section <NUM> stores a predetermined relationship between a vehicle velocity and the circulation area scale as a set circulation area. The third height setting section <NUM> stores a predetermined relationship between the lubricating oil temperature and the high position of the upper portion 75t as a set height position. The second height setting section <NUM> stores a predetermined relationship between the vehicle velocity and the height position of the upper portion 75t as a set height position.

The lubrication control device <NUM> obtains a circulation area corresponding to a detected oil temperature detected by the oil temperature sensor <NUM> from the set circulation area stored in the first area setting section <NUM>, and outputs an operation command to adjust circulation area to the obtained circulation area to the area adjustment part <NUM> so as to activate the area adjustment part <NUM>. The lubrication control device <NUM> obtains a height position of the upper portion 75t in the partition wall <NUM> which corresponds to the detected oil temperature detected by the oil temperature sensor <NUM>, from the set height position stored in the first height setting section <NUM>, and outputs an operation command to adjust the height position of the upper portion 75t in the partition wall <NUM> to the obtained height position , to the wall adjustment part <NUM> so as to activate the wall adjustment part <NUM>.

The lubrication control device <NUM> obtains a circulation area corresponding to the detective vehicle speed detected by the vehicle speed sensor from the set circulation area stored in the second area setting section <NUM>, and outputs an operation command to adjust the circulation area to the obtained circulation area to the area adjustment part <NUM> so as to activate the area adjustment part <NUM>. The lubrication control device <NUM> obtains a height position of the upper portion 75t in the partition wall <NUM> which corresponds to the detected vehicle speed detected by the vehicle speed sensor <NUM>, from the set height position stored in the second height setting section <NUM>, and outputs an operation command to adjust the height position of the upper portion 75t in the partition wall <NUM> to the obtained height position, to the wall adjustment part <NUM> so as to activate the wall adjustment part <NUM>.

A guide member <NUM>, which guides the lubricating oil stirred by the ring gear 22b toward above the partition wall <NUM>, is disposed below the first space zone A1 as illustrated in <FIG> and <FIG>. A front connection arm <NUM> is disposed in a front portion of the guide member <NUM> in the vehicle body front-back direction, and a rear connection arm <NUM> is disposed in a rear portion of the guide member <NUM> in the vehicle body front-back direction as illustrated in <FIG>. In the guide member <NUM>, the front connection arm <NUM> is connected to a support part <NUM> included in the transmission case <NUM> by a connection bolt, and the rear connection arm <NUM> is supported on the transmission case <NUM> by being connected to a support part 3i included in the transmission case <NUM> by a connection bolt as illustrated in <FIG>.

As illustrated in <FIG>, the guide member <NUM> includes a first guide part <NUM> disposed in a vertically-directed attitude at a rear end portion of the guide member <NUM> in the vehicle body front-back direction, a second guide part <NUM> disposed on a bottom portion of the guide member <NUM>, and a third guide part <NUM> disposed in the vertically-directed attitude at an end portion of the guide member <NUM> in a vehicle body lateral direction.

As illustrated in <FIG>, the first guide part <NUM> can be disposed in the vertically-directed attitude between a lower portion of the ring gear 22b and the partition wall <NUM> because the guide member <NUM> is supported on the transmission case <NUM>. The lubricating oil scooped up by the ring gear 22b is guided by the first guide part <NUM> so as to flow toward above the partition wall <NUM>.

As illustrated in <FIG> and <FIG>, because the guide member <NUM> is supported on the transmission case <NUM>, the second guide part <NUM> can be disposed below the ring gear 22b so as to extend in a rotation direction of the ring gear 22b. The lubricating oil stirred by the ring gear 2b is guided by the second guide part <NUM> so as to flow toward the first guide part <NUM>. As illustrated in <FIG> and <FIG>, an end portion 84a of the second guide part <NUM> on a downstream side of the rotation direction of the ring gear 22b is connected to a lower end portion 83a of the first guide part <NUM>, and therefore the lubricating oil flowing toward the first guide part <NUM> does not leak from between the second guide part <NUM> and the first guide part <NUM>.

As illustrated in <FIG> and <FIG>, because the guide member <NUM> is supported on the transmission case <NUM>, the third guide part <NUM> can be disposed at a position opposed to one of two lateral portions in a lower portion of the ring gear 22b at which the tooth part of the ring gear 22b is located, so as to extend in the rotation direction of the ring gear 22b. The lubricating oil stirred by the ring gear 22b is guided by the second guide part <NUM> so as to flow toward the first guide part <NUM>. As illustrated in <FIG> and <FIG>, an end portion 85a of the third guide part <NUM> located toward the second guide part is connected to a lateral end portion 84b of the second guide part <NUM> located toward the third guide part, and an end portion 85b of the third guide part <NUM> which is located on a downstream side of the rotation direction of the ring gear 22b is connected to a lateral end portion 83b of the first guide part <NUM> located toward the third guide part. Therefore, the lubricating oil flowing toward the first guide part <NUM> does not leak from between the third guide part <NUM> and the second guide part <NUM>, and from between the third guide part <NUM> and the first guide part <NUM>.

When the rear wheel differential mechanism <NUM> transmits forward movement power, the lubricating oil is stirred by the ring gear 22b being rotated, and the lubricating oil flows from the first space zone A1 via the upper space <NUM> into the second space zone A2 is guided by being guided by the guide member <NUM>. During high-speed traveling, the rotational velocity of the ring gear 22b is higher than that during low-speed traveling, and the lubricating oil is stirred by the ring gear 22b. In some cases, an amount of the lubricating oil flowing from the first space zone A1 via the upper space <NUM> into the second space zone A2 becomes larger than an amount of the lubricating oil flowing from the second space zone A2 via the flow-out path <NUM> into the first space zone A1.

A rotational velocity of the ring gear 22b during the low-speed traveling is lower than that during the high-speed traveling, and the lubricating oil is stirred by the ring gear 22b. There occurs a decrease in the amount of the lubricating oil flowing from the first space zone A1 via the upper space <NUM> into the second space zone A2 by being guided by the guide member <NUM>. Depending on the rotational velocity of the ring gear 22b, even though the lubricating oil located in the first space zone A1 is stirred by the ring gear 22b, the stirred lubricating oil may not reach the upper space <NUM>, failing to flow into the second space zone A2. Accordingly, the amount of the lubricating oil staying in the second space zone A2 is less likely to become larger the amount of the lubricating oil flowing from the second space zone A2 via the flow-out path <NUM> into the first space zone A1.

The lubricating oil has a lower viscosity with increasing temperature of the lubricating oil, and the lubricating oil stirred by the ring gear 22b tends to flow in the second space zone A2. And, at the same time, the lubricating oil tends to circulate the flow-out path <NUM>. Therefore, if a height position of the upper portion 75t of the partition wall <NUM> and a circulation area of the flow-out path <NUM> are kept constant, a volume of the first space zone A1 and a volume of the second space zone A2 become unstable depending on the temperature of the lubricating oil. However, with the present embodiment, the lubrication control device <NUM> adjusts the circulation area in the flow-out path <NUM> to a circulation area having a size corresponding to the temperature of the lubricating oil by controlling the area adjustment part <NUM> on the basis of the detected oil temperature obtained from the oil temperature sensor <NUM>. At the same time, the lubrication control device <NUM> adjusts the height position of the upper portion 75t of the partition wall <NUM> to a height position corresponding to the temperature of the lubricating oil by controlling the wall adjustment part <NUM> on the basis of the detected oil temperature obtained from the oil temperature sensor <NUM>. Consequently, irrespective of a temperature change in the lubricating oil, it is easy to adjust the amount of lubricating oil staying in the second space zone A2 and the amount of the lubricating oil flowing from the second space zone A2 into the first space zone A1 to an amount suitable for the temperature of the lubricating oil.

The rotational velocity of the ring gear 22b increases with increasing the traveling speed, thereby increasing the amount of the lubricating oil flowing in the second space zone A2 by being scooped up by the ring gear 22b. In other words, the rotational velocity of the ring gear 22b decreases with decreasing the traveling speed, and even though the lubricating oil is scooped up by the ring gear 22b, the lubricating oil is less likely to go up higher and flow in the second space zone A2. Additionally, a change in the amount of the lubricating oil flowing in the second space zone A2 causes a change in the head difference between the lubricating oil in the second space zone A2 and the lubricating oil in the first space zone A1, and the amount of the lubricating oil passing through the flow-out path <NUM> is likely to change. Therefore, if the height position of the upper portion 75t of the partition wall <NUM> and the circulation area of the flow-out path <NUM> are kept constant, the volume of the first space zone A1 and the volume of the second space zone A2 become unstable depending on the traveling speed. However, with the present embodiment, the lubrication control device <NUM> adjusts the circulation area in the flow-out path <NUM> to a circulation area having a size corresponding to the vehicle speed by controlling the area adjustment part <NUM> on the basis of the detected vehicle speed obtained from the vehicle speed sensor <NUM>. At the same time, the lubrication control device <NUM> adjusts the height position of the upper portion 75t of the partition wall <NUM> to a height position corresponding to the vehicle speed by controlling the wall adjustment part <NUM> on the basis of the detected vehicle speed obtained from the vehicle speed sensor <NUM>. Consequently, irrespective of the change in the vehicle speed, it is easy to adjust the amount of lubricating oil staying in the second space zone A2 and the amount of the lubricating oil flowing from the second space zone A2 into the first space zone A1 to an amount suitable for the vehicle speed.

<FIG> is a sectional view illustrating an accumulated state of the lubricating oil during high-speed traveling. <FIG> is a sectional view illustrating an accumulated state of the lubricating oil during low-speed traveling. As illustrated in <FIG> and <FIG>, a position of an oil surface S1 of the lubricating oil in the first space zone A1 during the low-speed traveling is higher than a position of an oil surface S2 of the lubricating oil in the first space zone A1 during the high-speed traveling, and the rear wheel differential mechanism <NUM> during the low-speed traveling enters deeper than during the high-speed traveling. Consequently, the rear wheel differential mechanism <NUM> can be sufficiently lubricated during the low-speed traveling. The position of the oil surface S2 of the lubricating oil in the first space zone A1 during the high-speed traveling is lower than the position of the oil surface S1 in the first space zone A1 during the low-speed traveling, and the rear wheel differential mechanism <NUM> during the high-speed traveling enters the lubricating oil shallowerly than during the low-speed traveling. This reduces resistance received by the rear wheel differential mechanism <NUM> due to stirring of the lubricating oil during the high-speed traveling, thereby reducing loss of driving force.

An actuating clutch <NUM> is disposed in an upper portion of the second space zone A2 as illustrated in <FIG>. The actuating clutch <NUM> is capable of switching between: an engaged state in which the power from the engine <NUM> is transmitted to the power take-off shaft <NUM>; and a disengaged state in which the power transmission from the engine <NUM> to the power take-off shaft <NUM> is discontinued.

The actuating clutch <NUM> is configured by a wet multi-plate friction clutch. A lubrication circuit (not illustrated) including a lubrication pipe (not illustrated) disposed outside the transmission case <NUM> or a lubrication pipe (not illustrated) externally fitted on the rear rotating shaft <NUM> is configured to supply the lubricating oil for cooling purposes to the actuating clutch <NUM>. The lubricating oil supplied to the actuating clutch <NUM> drips from, for example, the notched portion in a clutch case 71a of the actuating clutch <NUM>. The dripped lubricating oil enters the second space zone A2 and flows out of the second space zone A2 and passes through the flow-out path <NUM> into the first space zone A1. The lubricating oil dripped from the actuating clutch <NUM> can be supplied to the rear wheel differential mechanism <NUM> as a lubricating oil.

As illustrated in <FIG>, the second space zone A2 includes the operation power transmission mechanism <NUM> as a gear interlock mechanism for interlocking the actuating clutch <NUM> and the power take-off shaft <NUM>. The operation power transmission mechanism <NUM> is configured by a gear transmission that varies the power from the actuating clutch <NUM> and transmits the varied power to the power take-out shaft <NUM>. The operation power transmission mechanism <NUM> is lubricated by the lubricating oil staying in the second space zone A2.

Claim 1:
A work vehicle comprising:
a gear transmission (<NUM>) configured to vary power from a power source (<NUM>) and output the varied power;
a differential mechanism (<NUM>) including a ring gear (22b) rotatable around a rotation axis (Y) along a horizontal direction, the differential mechanism (<NUM>) being configured to transmit the power inputted from the gear transmission (<NUM>) to a traveling device (<NUM>);
a transmission case (<NUM>) containing the gear transmission (<NUM>) and the differential mechanism (<NUM>);
a first space zone (A1) as part of an internal space of the transmission case (<NUM>) in which first space zone the differential mechanism (<NUM>) is located;
a second space zone (A2) as part of the internal space which second space zone is adjacent to the first space zone;
a partition wall (<NUM>) separating the first space zone (A1) and the second space zone (A2);
an upper space (<NUM>) disposed above the partition wall (<NUM>) and configured to allow lubricating oil scooped up from the first space zone (A1) by rotation of the ring gear (22b) to flow in the second space zone (A2);
a flow-out path (<NUM>) disposed below the upper space (<NUM>) and configured to allow the lubricating oil staying in the second space zone (A2) to flow out to the first space zone (A1); and
an area adjustment part (<NUM>) configured to adjust a circulation area of the flow-out path (<NUM>);
the work vehicle being characterized in that it further comprises a wall adjustment part (<NUM>) configured to adjust, by lifting and lowering, ef an upper portion (75t) of the partition wall (<NUM>).