Wheel loader

The motor cooling system circulates cooling oil for cooling a motor. A transmission is configured to change a rotation speed ratio of an output shaft with respect to an input shaft by changing a rotation speed of the motor. A transmission case has an output shaft case for housing the output shaft. The output shaft case is positioned forward of the motor and protrudes to a position below the motor. The motor cooling system has a cooling oil tank for storing the cooling oil and a cooling oil pipe which connects a cooling oil tank and the motor. The cooling oil tank is positioned behind the output shaft case and under the motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2014/068938, filed on Jul. 16, 2014. This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2013-165005, filed in Japan on Aug. 8, 2013, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

The present invention relates to a hybrid-type wheel loader.

Background Information

Recently, a hybrid-type wheel loader has been proposed that travels using driving power from an engine and driving power from a motor. A hydraulic-mechanical transmission (HMT) or an electric-mechanical transmission (EMT) are disclosed as transmissions for a hybrid-type wheel loader as in, for example, Japanese Patent Laid-open No. 2006-329244.

The HMT has a planetary gear mechanism, and at least two hydraulic motors connected to rotating elements of the planetary gear mechanism. The hydraulic motor functions as either a motor or a pump in response to the travel state of the wheel loader. The HMT is configured to enable stepless changing of the rotation speed of the output shaft by changing the rotation speed of the hydraulic motor.

An electric motor may be used in an EMT in place of the hydraulic motor in the HMT. The electric motor functions as either a motor or a generator in response to the travel state of the wheel loader. Similar to the HMT, the EMT is configured to enable stepless changing of the rotation speed of the output shaft by changing the rotation speed of the electric motor.

SUMMARY

The temperature of the motor in the transmission of the above-mentioned hybrid-type wheel loader increases and therefore cooling of the motor becomes necessary. However, there is a concern that the size of the vehicle body increases when a cooling system for the motor is added.

An object of the present invention is to enable cooling of the motor while suppressing an increase in the size of the vehicle body in the hybrid-type wheel loader.

A wheel loader according to a first aspect of the present invention is provided with an engine, a travel device, and a transmission. The travel device is driven by the engine. The transmission transmits driving power from the engine to the travel device. The transmission has an input shaft, an output shaft, a gear mechanism, a transmission case, a motor, and a motor cooling system. The gear mechanism includes a planetary gear mechanism and transmits the rotation of the input shaft to the output shaft. The transmission case houses the input shaft, the gear mechanism, and the output shaft. The motor is connected to a rotating element of the planetary gear mechanism and is attached to the transmission case. The motor cooling system circulates cooling oil for cooling the motor. The transmission is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speed of the motor. The transmission case has an output shaft case for housing the output shaft. The output shaft case is positioned forward the motor and protrudes to a position below the motor. The motor cooling system has a cooling oil tank for storing the cooling oil and a cooling oil pipe which connects the cooling oil tank and the motor. The cooling oil tank is positioned behind the output shaft case and under the motor.

The cooling oil tank in the wheel loader according to the present embodiment is positioned behind the output shaft case and under the motor. That is, by arranging the cooling oil tank by using a space behind the output shaft case and under the motor, the transmission case and the cooling oil tank can be arranged in a compact manner.

Moreover, by positioning the cooling oil tank under the motor, the cooling oil can be recovered from the motor to the cooling oil tank due to gravity. As a result, the cooling oil can be circulated efficiently.

The travel device preferably further has an axle shaft that extends in the vehicle width direction and an axle housing for housing the axle shaft. The axle housing is positioned further to the rear of the motor. The cooling oil tank is positioned in front of the axle housing.

In this case, by arranging the cooling oil tank by using a space positioned behind the output shaft case, under the motor, and in front of the axle housing, the transmission case, the cooling oil tank, and the axle housing can be arranged in a compact manner.

The bottom surface of the cooling oil tank preferably has a first sloped surface that slopes to the rear and upward. In this case, air flowing under the wheel loader can be guided toward the axle housing due to the bottom surface of the cooling oil tank. As a result, the axle housing can be cooled.

A virtual extension line of the sloped surface as seen in a side view of the vehicle preferably overlaps the axle housing. In this case, the axle housing can be cooled more effectively.

A vehicle body frame for supporting the transmission is preferably provided. The travel device further has a transmission shaft that transmits driving power from the transmission to the axle shaft. The cooling oil tank is arranged between the side surface of the vehicle body frame and the transmission shaft in the vehicle width direction. In this case, the cooling oil tank can be accessed easily from the side of the wheel loader. As a result, maintenance performance of the cooling oil tank can be improved.

The front surface of the cooling oil tank preferably has a second sloped surface that slopes to the front and downward. The cooling oil pipe is connected to the second sloped surface. In this case, the cooling oil pipe can be connected easily to the second sloped surface.

The motor and the cooling oil tank are preferably arranged on the same side with regard to the center axis of the transmission that extends in the vehicle front-back direction. In this case, the cooling oil pipe can be installed easily.

The wheel loader is preferably further provided with a transmission lubrication system. The transmission lubrication system circulates lubricating oil for lubricating the transmission. The motor cooling system is separate from the transmission lubrication system.

A conventional transmission without a motor is provided with a lubrication system for circulating lubricating oil for lubricating mechanisms, such as gears inside the transmission. The lubricating oil is circulated through the inside of the transmission whereby lubrication and cooling of the mechanisms inside the transmission are carried out.

When the motor is cooled using the transmission lubrication system as in the conventional transmission, there is a concern that the performance of the transmission or of the motor could deteriorate. For example, lubricating oil that has passed through the transmission includes metallic powder produced in the transmission. As a result, there is a possibility that the rotation of the parts inside the motor could be hindered due to the metallic powder if the motor is cooled using the transmission lubrication system.

Moreover, the temperature conditions of the oil suited to the transmission are different from the temperature conditions of the oil suited to the motor. However, it is difficult to control the temperature of the lubricating oil for the transmission and the temperature of the cooling oil for the motor to a temperature suited for each when the motor is cooled using the transmission lubrication system as in the conventional transmission.

Accordingly, the motor cooling system in the wheel loader according to the present exemplary embodiment is separate from the transmission lubrication system and therefore the motor can be cooled while suppressing a deterioration in the performance of the transmission or the motor in comparison to when the motor cooling system is the same system as the transmission lubrication system.

By arranging the cooling oil tank by using the space behind the output shaft case and under the motor, the transmission case and the cooling oil tank can be arranged in a compact manner in the wheel loader according to the first aspect of the present invention. Moreover, by arranging the cooling oil tank under the motor, the cooling oil can be recovered from the motor to the cooling oil tank due to gravity. As a result, the cooling oil can be circulated efficiently.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will be explained in detail with reference to the figures.FIG. 1is a side view of a wheel loader1according to an exemplary embodiment of the present invention. The wheel loader1includes a vehicle body frame2, a work implement3, traveling wheels4and5, and an operating cabin6as illustrated inFIG. 1. The wheel loader1travels due to the traveling wheels4and5being driven in a rotating manner. The wheel loader1is able to carry out work, such as excavation, by using the work implement3.

The work implement3and the traveling wheels4are attached to the vehicle body frame2. The work implement3is driven by hydraulic fluid from a work implement pump23(seeFIG. 2). The work implement3has a boom11and a bucket12. The boom11is mounted on the vehicle body frame2. The work implement3includes a lift cylinder13and a bucket cylinder14. The lift cylinder13and the bucket cylinder14are hydraulic cylinders. One end of the lift cylinder13is attached to the vehicle body frame2. The other end of the lift cylinder13is attached to the boom11. The boom11swings up and down due to the extension and contraction of the lift cylinder13due to hydraulic fluid from the work implement pump23. The bucket12is attached to the tip of the boom11. One end of the bucket cylinder14is attached to the vehicle body frame2. The other end of the bucket cylinder14is attached to the bucket12via a bell crank15. The bucket12swings up and down due to the extension and contraction of the bucket cylinder14due to hydraulic fluid from the work implement pump23.

The operating cabin6and the traveling wheels5are attached to the vehicle body frame2. The operating cabin6is mounted on the vehicle body frame2. A seat for the operator and a below-mentioned operating device are disposed in the operating cabin6. The vehicle body frame2has a front frame16and a rear frame17. The front frame16and the rear frame17are attached to each other in a manner that allows swinging in the left-right direction.

The work implement3is attached to the front frame16. The operating cabin6is mounted on the rear frame17. Devices, such as a below-mentioned engine21, a transmission24, and a cooling device26, are also mounted on the rear frame17. The transmission24is positioned in front of the engine21. The cooling device26is positioned behind the engine21. The cooling device26has a radiator for cooling liquid coolant for the engine21.

The wheel loader1has a steering cylinder18. The steering cylinder18is attached to the front frame16and the rear frame17. The steering cylinder18is a hydraulic cylinder. The wheel loader1is able to change the advancing direction to the right and left with the extension and contraction of the steering cylinder18due to hydraulic fluid from a below-mentioned steering pump30.

FIG. 2is a schematic view of a configuration of the wheel loader1. As illustrated inFIG. 2, the wheel loader1is provided with the engine21, the work implement pump23, a transmission pump29, the steering pump30, the transmission24, and a travel device25.

The engine21is, for example, a diesel engine. The engine21generates driving power for driving the travel device25, the work implement pump23, the transmission pump29, the steering pump30, and the like.

The work implement pump23, the transmission pump29, and the steering pump30are hydraulic pumps. The work implement pump23, the transmission pump29, and the steering pump30are driven by driving power from the engine21.

The work implement pump23is a variable displacement hydraulic pump. Hydraulic fluid discharged from the work implement pump23is supplied to the lift cylinder13and the bucket cylinder14through a work implement control valve41.

The transmission pump29is a fixed displacement hydraulic pump. Hydraulic fluid discharged from the transmission pump29is supplied to various below-mentioned clutches of the transmission24via a clutch control valve32.

The steering pump30is a variable displacement hydraulic pump. Hydraulic fluid discharged from the steering pump30is supplied to the above-mentioned steering cylinder18through a steering control valve43.

The transmission24transmits driving power from the engine21to the travel device25. The transmission24changes the speed and outputs the driving power from the engine21. A configuration of the transmission24is discussed in detail below.

The travel device25is driven by the engine21. The travel device25has a transmission shaft46, an axle shaft45, and the above-mentioned traveling wheels5. The transmission shaft46transmits driving power from the transmission24to the axle shaft45. The axle shaft45extends in the vehicle width direction and is connected to the traveling wheels5. The axle shaft45transmits driving power from the transmission24to the traveling wheels5. As a result, the traveling wheels5rotate.

A configuration of the transmission24is discussed in detail next. The transmission24is provided with an input shaft61, a first power take-off mechanism22(referred to below as “first PTO22”), a second power take-off mechanism27(referred to below as “second PTO27”), a gear mechanism62, an output shaft63, a first motor MG1, a second motor MG2, and a third motor MG3.

The rotation from the engine21is inputted to the input shaft61. The gear mechanism62transmits the rotation of the input shaft61to the output shaft63. The output shaft63is connected to the above-mentioned travel device25, and transmits the rotation from the gear mechanism62to the travel device25.

The first PTO22is connected to the input shaft61and transmits a portion of the driving power from the engine21to the work implement pump23and the transmission pump29. The second PTO27is connected to the input shaft61parallel to the first PTO22and transmits a portion of the driving power from the engine21to the steering pump30.

The gear mechanism62is a mechanism for transmitting driving power from the engine21. The gear mechanism62is configured so that the rotation speed ratio of the output shaft63with respect to the input shaft61is changed in response to changes in the rotation speeds of the motors MG1, MG2, and MG3. The gear mechanism62has a FR switch mechanism65and a speed change mechanism66.

The FR switch mechanism65has a forward movement clutch CF, a reverse movement clutch CR, and various types of gears. The forward movement clutch CF and the reverse movement clutch CR are hydraulic clutches. The direction of the rotation outputted from the FR switch mechanism65is switched due to the switching between connected and disconnected states of the forward movement clutch CF and connected and disconnected states of the reverse movement clutch CR.

The speed change mechanism66has a middle shaft67, a first planetary gear mechanism68, a second planetary gear mechanism69, a Hi/Lo switch mechanism70, and an output gear71. The middle shaft67is coupled to the FR switch mechanism65. The first planetary gear mechanism68and the second planetary gear mechanism69are disposed on the same axis as the middle shaft67.

The first planetary gear mechanism68has a first sun gear S1, a plurality of first planet gears P1, a first carrier C1that supports the plurality of first planet gears P1, and a first ring gear R1. The first sun gear S1is coupled to the middle shaft67. The plurality of first planet gears P1mesh with the first sun gear S1and are supported in a rotatable manner by the first carrier C1. A first carrier gear Gc1is provided on an outer peripheral part of the first carrier C1. The first ring gear R1meshes with the plurality of first planet gears P1and is able to rotate. A first ring outer periphery gear Gr1is provided on the outer periphery of the first ring gear R1.

The second planetary gear mechanism69has a second sun gear S2, a plurality of second planet gears P2, a second carrier C2that supports the plurality of second planet gears P2, and a second ring gear R2. The second sun gear S2is coupled to the first carrier C1. The plurality of second planet gears P2mesh with the second sun gear S2and are supported in a rotatable manner by the second carrier C2. The second ring gear R2meshes with the plurality of second planet gears P2and is able to rotate. A second ring outer periphery gear Gr2is provided on the outer periphery of the second ring gear R2. The second ring outer periphery gear Gr2meshes with the output gear71, and the rotation of the second ring gear R2is outputted to the output shaft63via the output gear71.

The Hi/Lo switch mechanism70is a mechanism for switching the driving power transmission path of the transmission24between a high-speed mode (Hi mode) in which the vehicle speed is high and a low-speed mode (Lo mode) in which the vehicle speed is low. The Hi/Lo switch mechanism70has a Hi-clutch CH that is ON during the Hi mode and a Lo-clutch CL that is ON during the Lo mode. The Hi-clutch CH connects or disconnects the first ring gear R1and the second carrier C2. The Lo-clutch CL connects or disconnects the second carrier C2and a fixed end72to prohibit or allow the rotation of the second carrier C2.

The clutches CH and CL are hydraulic clutches, and hydraulic fluid from the transmission pump29is supplied to each of the clutches CH and CL. The hydraulic fluid for the clutches CH and CL is controlled by the clutch control valve32.

The first motor MG1, the second motor MG2, and the third motor MG3function as drive motors that generate driving power using electrical energy. The first motor MG1, the second motor MG2, and the third motor MG3also function as generators that use inputted driving power to generate electrical energy.

The first motor gear Gm1is fixed to a rotating shaft Sm1of the first motor MG1. The first motor gear Gm1meshes with the first carrier gear Gc1. A second motor gear Gm2is fixed to a rotating shaft Sm2of the second motor MG2. The second motor gear Gm2meshes with the first ring outer periphery gear Gr1.

The third motor MG3assists the first motor MG1and the second motor MG2. The speed change mechanism66has a motor switching mechanism73, and the motor switching mechanism73selectively switches the target of the assistance from the third motor MG3to the first motor MG1or the second motor MG2.

Specifically, the motor switching mechanism73has a first motor clutch Cm1, a second motor clutch Cm2, a first connecting gear Ga1, and a second connecting gear Ga2. A third motor gear Gm3is connected to a rotating shaft Sm3of the third motor MG3, and the third motor gear Gm3meshes with the first connecting gear Ga1. The first motor clutch Cm1switches between connecting and disconnecting the first connecting gear Ga1and the rotating shaft Sm1of the first motor MG1. The first connecting gear Ga1meshes with the second connecting gear Ga2. The second motor clutch Cm2switches between connecting and disconnecting the second connecting gear Ga2and the rotating shaft Sm2of the second motor MG2.

The first motor clutch Cm1and the second motor clutch Cm2are hydraulic clutches. Hydraulic fluid from the transmission pump29is supplied to each of the motor clutches Cm1and Cm2. The hydraulic fluid for the motor clutches Cm1and Cm2is controlled by the clutch control valve32.

While the first motor clutch Cm1is connected and the second motor clutch Cm2is disconnected, the third motor gear Gm3assists the first motor MG1. While the second motor clutch Cm2is connected and the first motor clutch Cm1is disconnected, the third motor gear Gm3assists the second motor MG2.

The first motor MG1is connected to a capacitor64via a first inverter I1. The second motor MG2is connected to the capacitor64via a second inverter I2. The third motor MG3is connected to the capacitor64via a third inverter I3.

The capacitor64functions as an energy reservoir unit for storing energy generated by the motors MG1, MG2, and MG3. That is, the capacitor64stores electrical power generated by the motors MG1, MG2, and MG3when the total electrical power generation amount of the motors MG1, MG2, and MG3is high. The capacitor64releases electrical power when the total electrical power consumption amount of the motors MG1, MG2, and MG3is high. That is, the motors MG1, MG2and MG3are driven by electrical power stored in the capacitor64. A battery may be used as another electrical power storage means in place of the capacitor.

The wheel loader1is provided with a control unit31. The control unit31applies command signals for indicating the command torques for the motors MG1, MG2, and MG3to the inverters I1, I2, and I3. The control unit31applies command signals for controlling the clutch hydraulic pressure of the clutches CF, CR, CH, CL, Cm1, and Cm2to the clutch control valve32. The clutch control valve32includes a plurality of valves for controlling the clutches CF, CR, CH, CL, Cm1, and Cm2.

The motors MG1, MG2, and MG3and the clutches CF, CR, CH, CL, Cm1, and Cm2are controlled with command signals from the control unit31, whereby the speed change ratio and the output torque of the transmission24are controlled. The operations of the transmission24are discussed below.

An outline of operations of the transmission24when the vehicle speed increases from zero in the forward movement side while the rotation speed of the engine21remains fixed, will be explained with reference toFIGS. 3 and 4.FIG. 3illustrates functions of the motors MG1, MG2, and MG3and states of the clutches in the modes. The Lo mode has an L1mode and an L2mode. The Hi mode has an H1mode and an H2mode. InFIG. 3, “M” signifies the fact that the motors MG1, MG2, and MG3are functioning as driving motors. “G” signifies the fact that the motors MG1, MG2, and MG3are functioning as generators. “O” signifies the fact that the clutch is in the connected state. “X” signifies the fact that the clutch is in the disconnected state.

FIG. 4illustrates rotation speeds of the motors MG1, MG2, and MG3with respect to the vehicle speed. When the rotation speed of the engine21is fixed, the vehicle speed changes in response to the rotation speed ratio of the transmission24. The rotation speed ratio is the ratio of the rotation speed of the output shaft63with respect to the rotation speed of the input shaft61. Therefore, the variation in the vehicle speed inFIG. 4matches the variation of the rotation speed ratio of the transmission24. That is,FIG. 4illustrates the relationships between the rotation speeds of the motors MG1, MG2, and MG3and the rotation speed ratio of the transmission24. The solid line inFIG. 4represents the rotation speed of the first motor MG1, the dashed line represents the rotation speed of the second motor MG2, and the long dashed short dashed line represents the rotation speed of the third motor MG3.

In the region in which the vehicle speed is zero or greater to less than V1, the Lo-clutch CL is connected, the Hi-clutch CH is disconnected, the first motor clutch Cm1is connected, and the second motor clutch Cm2is disconnected (L1mode). Because the Hi-clutch CH is disconnected, the second carrier C2and the first ring gear R1are disconnected. Because the Lo-clutch CL is connected, the second carrier C2is fixed. Moreover, the first connecting gear Ga1is connected to the rotating shaft Sm1of the first motor MG1and the second connecting gear Ga2is disconnected from the rotating shaft Sm2of the second motor MG2. As a result, the third motor MG3is connected to the first motor MG1via the third motor gear Gm3, the first connecting gear Ga1, and the first motor clutch Cm1. The third motor MG3is disconnected from the second motor MG2because the second motor clutch Cm2is disconnected.

The driving power from the engine21in the L1mode is inputted to the first sun gear S1via the middle shaft67, and the driving power is outputted from the first carrier C1to the second sun gear S2. Conversely, the driving power inputted to the first sun gear S1is transmitted from the first planet gears P1to the first ring gear R1and outputted through the first ring outer periphery gear Gr1and the second motor gear Gm2to the second motor MG2. The second motor MG2functions mainly as a generator in the L1mode, and a portion of the electrical power generated by the second motor MG2is stored in the capacitor64.

The first motor MG1and the third motor MG3function mainly as electric motors in the L1mode. The driving power of the first motor MG1and the third motor MG3is outputted to the second sun gear S2along a path from the first motor gear Gm1to the first carrier gear Gc1to the first carrier C1. The driving power outputted to the second sun gear S2as described above is transmitted to the output shaft63along a path from the second planet gears P2to the second ring gear R2to the second ring outer periphery gear Gr2to the output gear71.

In the region in which the vehicle speed is V1or greater to less than V2, the Lo-clutch CL is connected, the Hi-clutch CH is disconnected, the first motor clutch Cm1is disconnected, and the second motor clutch Cm2is connected (L2mode). Therefore, the second connecting gear Ga2is connected to the rotating shaft Sm2of the second motor MG2and the first connecting gear Ga1is disconnected from the rotating shaft Sm1of the first motor MG1. As a result, the third motor MG3is connected to the second motor MG2via the third motor gear Gm3, the first connecting gear Ga1, the second connecting gear Ga2, and the second motor clutch Cm2. The third motor MG3is disconnected from the first motor MG1because the first motor clutch Cm1is disconnected.

The driving power from the engine21in the L2mode is inputted to the first sun gear S1via the middle shaft67, and the driving power is outputted from the first carrier C1to the second sun gear S2. Conversely, the driving power inputted to the first sun gear S1is transmitted from the first planet gears P1to the first ring gear R1and outputted through the first ring outer periphery gear Gr1and the second motor gear Gm2to the second motor MG2. Moreover, the driving power is outputted from the second motor gear Gm2to the third motor MG3via the second motor clutch Cm2, the second connecting gear Ga2, the first connecting gear Ga1, and the third motor gear Gm3. The second motor MG2and the third motor MG3function mainly as generators in the L2mode, and a portion of the electrical power generated by the second motor MG2and the third motor MG3is stored in the capacitor64.

The first motor MG1functions mainly as an electric motor in the L2mode. The driving power of the first motor MG1is outputted to the second sun gear S2along a path from the first motor gear Gm1to the first carrier gear Gc1to the first carrier C1. The driving power outputted to the second sun gear S2as described above is transmitted to the output shaft63along a path from the second planet gears P2to the second ring gear R2to the second ring outer periphery gear Gr2to the output gear71.

In the region in which the vehicle speed is V2or greater to less than V3, the Lo-clutch CL is disconnected, the Hi-clutch CH is connected, the first motor clutch Cm1is disconnected, and the second motor clutch Cm2is connected (H1mode). Because the Hi-clutch CH is connected in the H1mode, the second carrier C2and the first ring gear R1are connected. Because the Lo-clutch CL is disconnected, the second carrier C2is released. Therefore, the rotation speeds of the first ring gear R1and the second carrier C2match. Moreover, the second connecting gear Ga2is connected to the rotating shaft Sm2of the second motor MG2and the first connecting gear Ga1is disconnected from the rotating shaft Sm1of the first motor MG1. As a result, the third motor MG3is connected to the second motor MG2via the third motor gear Gm3, the first connecting gear Ga1, the second connecting gear Ga2, and the second motor clutch Cm2. The third motor MG3is disconnected from the first motor MG1because the first motor clutch Cm1is disconnected.

The driving power from the engine21in the H1mode is inputted to the first sun gear S1and the driving power is outputted from the first carrier C1to the second sun gear S2. The driving power inputted to the first sun gear S1is outputted from the first carrier C1through the first carrier gear Gc1and the first motor gear Gm1to the first motor MG1. The first motor MG1functions mainly as a generator in the H1mode, and thus a portion of the electrical power generated by the first motor MG1is stored in the capacitor64.

The second motor MG2and the third motor MG3function mainly as electric motors in the H1mode. The driving power of the third motor MG3is transmitted to the rotating shaft Sm2of the second motor MG2via the third motor gear Gm3, the first connecting gear Ga1, the second connecting gear Ga2, and the second motor clutch Cm2. The driving power of the second motor MG2and the driving power of the third motor MG3is outputted to the second carrier C2along a path from the second motor gear Gm2to the first ring outer periphery gear Gr1to the first ring gear R1to the Hi-clutch CH. The driving power outputted to the second sun gear S2as described above is outputted through the second planet gears P2to the second ring gear R2, and the driving power outputted to the second carrier C2is outputted through the second planet gears P2to the second ring gear R2. The driving power combined by the second ring gear R2in this way is transmitted through the second ring outer periphery gear Gr2and the output gear71to the output shaft63.

In the region in which the vehicle speed is V3or greater to less than V4, the Lo-clutch CL is disconnected, the Hi-clutch CH is connected, the first motor clutch Cm1is connected, and the second motor clutch Cm2is disconnected (H2mode). In the H2mode, the first connecting gear Ga1is connected to the rotating shaft Sm1of the first motor MG1and the second connecting gear Ga2is disconnected from the rotating shaft Sm2of the second motor MG2. As a result, the third motor MG3is connected to the first motor MG1via the third motor gear Gm3, the first connecting gear Ga1, and the first motor clutch Cm1. The third motor MG3is disconnected from the second motor MG2because the second motor clutch Cm2is disconnected.

The driving power from the engine21in the H2mode is inputted to the first sun gear S1and the driving power is outputted from the first carrier C1to the second sun gear S2. The driving power inputted to the first sun gear S1is outputted from the first carrier C1through the first carrier gear Gc1and the first motor gear Gm1to the first motor MG1and the third motor MG3. The first motor MG1and the third motor MG3function mainly as generators in the H2mode, and thus a portion of the electrical power generated by the first motor MG1and the third motor MG3is stored in the capacitor64.

The second motor MG2functions mainly as an electric motor in the H2mode. The driving power of the second motor MG2is outputted to the second carrier C2along a path from the second motor gear Gm2to the first ring outer periphery gear Gr1to the first ring gear R1to the Hi-clutch CH. The driving power outputted to the second sun gear S2as described above is outputted through the second planet gears P2to the second ring gear R2, and the driving power outputted to the second carrier C2is outputted through the second planet gears P2to the second ring gear R2. The driving power combined by the second ring gear R2in this way is transmitted through the second ring outer periphery gear Gr2and the output gear71to the output shaft63.

While forward movement driving has been discussed above, the operations of reverse movement driving are the same.

Next, a configuration of the transmission24will be discussed.FIG. 5is a perspective view of a transmission24.FIG. 6is a left surface side view of the transmission24.FIG. 7is a rear surface view of the transmission24.

The transmission24has a transmission case33. The transmission case33houses the input shaft61, the gear mechanism62, and the output shaft63. Specifically, the transmission case33has an input shaft case331, a middle shaft case332, and an output shaft case333. The input shaft case331houses the input shaft61. The input shaft61extends in the front-back direction of the vehicle. As illustrated inFIG. 7, a lower part of the input shaft case331includes a curved surface part334. The curved surface part334is curved to protrude downwards. Specifically, the input shaft case331has a shape that is approximately cylindrical. The center axis of the input shaft case331extends in the vehicle front-back direction. The center axis of the input shaft case331matches a center axis Ax1of the input shaft61.

The transmission case33has a first PTO case335and a second PTO case336. The first PTO case335houses the first PTO22(seeFIG. 2). The second PTO case336houses the second PTO27(seeFIG. 2). The first PTO case335and the second PTO case336are positioned over the input shaft case331. The first PTO case335and the second PTO case336are connected to the input shaft case331. The first PTO case335and the second PTO case336are arranged in a row in the vehicle width direction.

The middle shaft case332houses the above-mentioned first planetary gear mechanism68and the second planetary gear mechanism69. Furthermore, the middle shaft case332houses the middle shaft67. The middle shaft67extends in the vehicle front-back direction and is positioned under the input shaft61. The middle shaft case332is arranged in line with the input shaft case331in the vehicle front-back direction. Specifically, the middle shaft case332is positioned in front of the input shaft case331. The middle shaft case332is positioned forward the first PTO case335and the second PTO case336. A bottom part of the middle shaft case332is positioned below a bottom part of the input shaft case331. The above-mentioned clutch control valve32is attached to the front surface of the middle shaft case332.

As illustrated inFIG. 7, the transmission case33further has a protruding part337that protrudes downward from the bottom part of the input shaft case331. The protruding part337extends in the vehicle front-back direction and is connected to the middle shaft case332. A portion of the middle shaft67positioned further to the rear of the middle shaft case332is arranged inside the protruding part337.

The output shaft case333houses the output shaft63. The output shaft case333is positioned under the middle shaft case332. The output shaft case333is positioned forward the input shaft case331. A bottom part of the output shaft case333is positioned the furthest below the transmission case33. The output shaft63protrudes from the output shaft case333. The output shaft63extends in the vehicle front-back direction and is coupled to the transmission shaft46.

The first motor MG1, the second motor MG2, and the third motor MG3are attached to the transmission case33. Specifically, the first motor MG1, the second motor MG2, and the third motor MG3are attached to the middle shaft case332.

The first motor MG1and the second motor MG2are arranged below the input shaft61. The first motor MG1and the second motor MG2overlap the traveling wheels5as seen from the side of the vehicle (seeFIG. 1). Portions of the first motor MG1and the second motor MG2overlap the curved surface part334as seen in a projection view in the up-down direction. That is, the first motor MG1and the second motor MG2overlap the input shaft case331as seen in a projection view in the up-down direction (seeFIG. 15). Portions of the first motor MG1and the second motor MG2overlap the middle shaft case332as seen in the vehicle front-back direction. The first PTO case335and the second PTO case336are arranged over the first motor MG1and the second motor MG2. The output shaft case333is positioned forward the first motor MG1and the second motor MG2and protrudes to a position below the first motor MG1.

As illustrated inFIG. 7, the first motor MG1and the second motor MG2are arranged symmetrically relative to a vertical plane PL1that passes through the center axis Ax1of the input shaft61. The input shaft61, the middle shaft67, and the output shaft63are arranged in a row in the up-down direction as seen in the shaft direction of the input shaft61.

A rotational axis Ax2of the first motor MG1is positioned below the bottom part of the input shaft case331. A rotational axis Ax3of the second motor MG2is positioned below the bottom part of the input shaft case331. The bottom part of the first motor MG1is positioned below the bottom part of the input shaft case331. The bottom part of the second motor MG2is positioned below the bottom part of the input shaft case331. The uppermost part of the first motor MG1is positioned above the bottom part of the input shaft case331. The uppermost part of the second motor MG2is positioned above the bottom part of the input shaft case331. The first motor MG1and the second motor MG2are arranged with an interval therebetween in the vehicle width direction. The protruding part337is arranged between the first motor MG1and the second motor MG2in the vehicle width direction. That is, the middle shaft67is arranged between the first motor MG1and the second motor MG2in the vehicle width direction. The first motor MG1and the second motor MG2are arranged obliquely upward the output shaft63.

The third motor MG3is arranged beside of the transmission case33. The third motor MG3is arranged on the same side as the first motor MG1with respect to the vertical plane PL1that passes through the center of the transmission case33. In the present embodiment, the first motor MG1and the third motor MG3are arranged to the left of the vertical plane PL1. The second motor MG2is arranged to the right of the vertical plane PL1that passes through the center of the transmission case33. The third motor MG3is arranged by being shifted in the vehicle front-back direction with respect to the first motor MG1and the second motor MG2. Specifically, the third motor MG3is positioned forward the first motor MG1and the second motor MG2. The third motor MG3is arranged to the side of the middle shaft case332. The third motor MG3is positioned above the output shaft case333.

A rotational axis Ax4of the third motor MG3is positioned above the rotational axis Ax2of the first motor MG1and the rotational axis Ax3of the second motor MG2. As illustrated inFIG. 6, an end E1of the rotating shaft Sm1of the first motor MG1and an end of the rotating shaft Sm2of the second motor MG2are oriented in a direction from the first motor MG1and the second motor MG2toward the third motor MG3in the vehicle front-back direction. An end E3of the rotating shaft Sm3of the third motor MG3is oriented in a direction from the third motor MG3toward the first motor MG1and the second motor MG2in the vehicle front-back direction. Specifically, the end E1of the rotating shaft Sm1of the first motor MG1and the end of the rotating shaft Sm2of the second motor MG2face toward the front. The end E3of the rotating shaft Sm3of the third motor MG3faces toward the rear.

FIG. 8is a side surface view of a portion of the rear part of the wheel loader1. A portion of the configuration, such as the traveling wheels5and an exterior cover, are omitted inFIG. 8to facilitate understanding. As illustrated inFIG. 8, the travel device25has an axle housing47. The axle housing47houses the axle shaft45. The axle housing47is supported in a swingable manner on the vehicle body frame2. Specifically, the axle housing47is supported in a swingable manner on the rear frame17. The axle housing47is swingable around the transmission shaft46and consequently end parts on the left and right of the axle shaft45move in the up-down direction.

The first motor MG1and the second motor MG2are arranged by being shifted in the vehicle front-back direction with respect to the axle housing47. Specifically, the axle housing47is positioned further toward the rear than the first motor MG1and the second motor MG2. The bottom part of the first motor MG1is arranged below the uppermost part of the axle housing47. The bottom part of the second motor MG2is arranged below the uppermost part of the axle housing47.

The transmission shaft46is arranged under the transmission24and extends in the vehicle front-back direction. The transmission shaft46is arranged behind the output shaft case333. The transmission shaft46is arranged under the middle shaft case332. The transmission shaft46is arranged on the same axis as the output shaft63. Therefore, the first motor MG1and the second motor MG2are arranged obliquely upward the transmission shaft46as seen in the axial direction of the transmission shaft46.

FIG. 9is a rear surface view of a portion of the rear part of the wheel loader1. A portion of the configuration such as the traveling wheels5and the axle housing47are omitted inFIG. 9to facilitate understanding. As illustrated inFIG. 9, the rear frame17has a left side part171and a right side part172. The transmission24is arranged between the left side part171and the right side part172and is supported by the vehicle body frame2. The first motor MG1and the second motor MG2are arranged between the left side part171and the right side part172.

The rear frame17has a plurality of mount parts48to51(seeFIG. 15) for supporting the operating cabin6. The operating cabin6is attached in a detachable manner to the mount parts48to51. Therefore, the operating cabin6is attached in a detachable manner to the vehicle body frame2. Specifically, the plurality of mount parts48to51include a pair of front mount parts48and51and a pair of rear mount parts49and50. The third motor MG3is positioned under the operating cabin6.

As illustrated inFIG. 8, a side part opening173is provided in the left side part171. The side part opening173is positioned to the side of the transmission24. A portion of the first motor MG1opposes the side part opening173. An exterior cover (not illustrated) is attached in a detachable manner to the left side part171. The side part opening173is covered by the exterior cover while the exterior cover is attached. A portion of the first motor MG1is visible through the side part opening173while the exterior cover is removed. An opening similar to the side part opening173of the left side part171is provided in the right side part172.

FIG. 10is a view seen obliquely from below of a portion of the rear part of the wheel loader1. As illustrated inFIG. 10, a bottom part opening174is provided in the bottom surface of the rear frame17. The bottom part opening174is positioned under the transmission24. As illustrated inFIG. 9, the bottom part opening174is positioned under the output shaft case333and the transmission shaft46. Therefore, the bottom part opening174is positioned under the first motor MG1and the second motor MG2. A bottom plate (not illustrated) is attached to the bottom surface of the rear frame17in a detachable manner to cover the bottom part opening174.

As illustrated inFIG. 8, the vehicle body frame2further has a mount bracket52that supports the axle housing47in a swingable manner. The mount bracket52is positioned in front of the axle housing47. The mount bracket52is a plate-like member which extends in the vehicle width direction and the up-down direction.

As illustrated inFIG. 9, an upper surface of the mount bracket52has a recessed part521. The recessed part521has a shape that is recessed downward from the upper surface of the mount bracket52. The first motor MG1and the second motor MG2are arranged to pass through the recessed part521in the vehicle front-back direction. Specifically, the recessed part521has a first recessed part522and a second recessed part523. The first recessed part522and the second recessed part523are aligned in the vehicle width direction and are joined to each other. The first motor MG1is arranged so as to pass through the first recessed part522in the vehicle front-back direction. The second motor MG2is arranged to pass through the second recessed part523in the vehicle front-back direction. The protruding part337of the transmission case33is arranged between the first recessed part522and the second recessed part523.

The mount bracket52has a through-hole524. The through-hole524passes through the mount bracket52in the vehicle front-back direction. The through-hole524is located under the recessed part521. Specifically, the recessed part521has a ridge part525positioned between the first recessed part522and the second recessed part523. The ridge part525has a shape that rises to a position above the bottom part of the first recessed part522and the bottom part of the second recessed part523. The through-hole524is positioned under the ridge part525. The transmission shaft46passes through the through-hole524.

Next, a transmission lubrication system53and a motor cooling system54included in the transmission24will be discussed.FIG. 11Ais a schematic view illustrating a configuration of the transmission lubrication system53.FIG. 11Bis a schematic view of a configuration of the motor cooling system54. The transmission lubrication system53circulates lubricating oil for lubricating the transmission24.

As illustrated inFIG. 11A, the transmission lubrication system53has a lubricating oil pump531, an oil cooler532, and a lubricating oil pipe533. The lubricating oil pump531and the oil cooler532are connected to the transmission case33via the lubricating oil pipe533. A lubricating oil filter534is provided between the oil cooler532and the transmission case33in the lubricating oil pipe533.

The lubricating oil inside the transmission case33is stored inside the output shaft case333. The lubricating oil pump531feeds the lubricating oil inside the output shaft case333to the oil cooler532. The lubricating oil is cooled in the oil cooler532and supplied to the transmission case33. The lubricating oil lubricates various gears inside the transmission case33. The lubricating oil drips off the various gears and is stored in the output shaft case333.

The motor cooling system54is separate from the transmission lubrication system53and circulates cooling oil for cooling the first to third motors MG1to MG3.FIG. 12is a perspective view of the transmission24including the motor cooling system54. As illustrated inFIG. 11BandFIG. 12, the motor cooling system54has a cooling oil pump541, a motor cooler542, a cooling oil tank543, and a cooling oil pipe544. The cooling oil pump541, the motor cooler542, and the cooling oil tank543are connected to the first to third motors MG1to MG3via the cooling oil pipe544. Specifically, the cooling oil pipe544includes a first cooling oil pipe551, a second cooling oil pipe552, a third cooling oil pipe553, a first supply pipe554, a second supply pipe555, a third supply pipe556, a first drain pipe557, a second drain pipe558, and a third drain pipe559. The first cooling oil pipe551connects the cooling oil tank543and the cooling oil pump541. The second cooling oil pipe552connects the cooling oil pump541and the motor cooler542. The third cooling oil pipe553is connected to the motor cooler542. The motor cooler542cools the cooling oil. The motor cooler542is included in the above-mentioned cooling device26with the oil cooler532. The third cooling oil pipe553is connected to the first supply pipe554, the second supply pipe555, and the third supply pipe556. A cooling oil filter561is provided in the third cooling oil pipe553.

The first supply pipe554is connected to the first motor MG1. A first branch pipe562is connected to the first supply pipe554. Specifically, the first supply pipe554is connected to a cooling oil path inside the rotating shaft Sm1of the first motor MG1. The first branch pipe562is connected to an upper part of the motor case of the first motor MG1. A configuration of the first motor MG1is discussed below.

The second supply pipe555is connected to the second motor MG2. A second branch pipe563is connected to the second supply pipe555. Specifically, the second supply pipe555is connected to a cooling oil path inside the rotating shaft Sm2of the second motor MG2. The second branch pipe563is connected to an upper part of the motor case of the second motor MG2.

The third supply pipe556is connected to the third motor MG3. A third branch pipe564is connected to the third supply pipe556. Specifically, the third supply pipe556is connected to a cooling oil path inside the rotating shaft Sm3of the third motor MG3. The third branch pipe564is connected to an upper part of the motor case of the third motor MG3.

The first drain pipe557connects the first motor MG1and the cooling oil tank543. The second drain pipe558connects the second motor MG2and the cooling oil tank543. The third drain pipe559connects the third motor MG3and the cooling oil tank543.

The cooling oil tank543stores the cooling oil for cooling the first motor MG1, the second motor MG2, and the third motor MG3. The cooling oil pump541sucks in the cooling oil inside the cooling oil tank543via the first cooling oil pipe551and feeds the cooling oil to the motor cooler542via the second cooling oil pipe552. The cooling oil is cooled by the motor cooler542. The cooling oil is branched from the third cooling oil pipe553to the first supply pipe554, the second supply pipe555, and the third supply pipe556.

The cooling oil is supplied from the first supply pipe554and the first branch pipe562to the first motor MG1to cool the first motor MG1. The cooling oil is returned from the first motor MG1to the cooling oil tank543via the first drain pipe557. The cooling oil is supplied from the second supply pipe555and the second branch pipe563to the second motor MG2to cool the second motor MG2. The cooling oil is returned from the second motor MG2to the cooling oil tank543via the second drain pipe558. The cooling oil is supplied from the third supply pipe556and the third branch pipe564to the third motor MG3to cool the third motor MG3. The cooling oil is returned from the third motor MG3to the cooling oil tank543via the third drain pipe559.

FIG. 13is a cross-sectional view of the first motor MG1. As illustrated inFIG. 13, the first motor MG1has a motor case74, the rotating shaft Sm1, a rotor75, and a stator76. The motor case74houses the rotating shaft Sm1, the rotor75, and the stator76. The rotor75is fixed to the rotating shaft Sm1and is provided to rotate with the rotating shaft Sm1. The rotor75has a magnet751. The magnet751is configured, for example, by stacking a plurality of thin plate-like electromagnetic steel sheets. The stator76is arranged to encircle the periphery of the rotor75. The stator76has a coil761.

The rotating shaft Sm1has the liquid coolant path752. The liquid coolant path752is provided along the center axis of the rotating shaft Sm1. The liquid coolant path752communicates with a through-hole753. The through-hole753passes through the rotating shaft Sm1in the axial direction. The cooling oil from the first supply pipe554is supplied to the liquid coolant path752and is supplied to the rotor75via the through-hole753. The cooling oil supplied to the rotor75is scattered inside the motor case74by centrifugal force caused by the rotation of the rotor75.

A cooling oil supply port741is provided in the uppermost part of the motor case74. The cooling oil supply port741communicates with a space inside the motor case74. The above-mentioned first branch pipe562is connected to the cooling oil supply port741. The cooling oil from the first branch pipe562drips down due to gravity via the cooling oil supply port741whereby the cooling oil is supplied to the motor case74.

A cooling oil drain port742is provided in the bottom part of the motor case74. The cooling oil drain port742communicates with a space inside the motor case74. The abovementioned first drain pipe557is connected to the cooling oil drain port742. The cooling oil supplied to the inside of the motor case74is returned due to gravity from the cooling oil drain port742to the cooling oil tank543via the first drain pipe557.

Explanations of the configurations of the second motor MG2and the third motor MG3will be omitted because the configurations thereof are similar to the configuration of the above-mentioned first motor MG1.

As illustrated inFIG. 8, the cooling oil tank543is positioned below the first motor MG1and the second motor MG2. The cooling oil tank543is positioned below the third motor MG3. The cooling oil tank543is positioned behind the output shaft case333and under the first motor MG1. The cooling oil tank543is positioned in front of the axle housing47. The cooling oil tank543overlaps the traveling wheels5as seen in a side view of the vehicle (seeFIG. 1).

FIG. 14is an enlarged view of a configuration of the cooling oil tank543inFIG. 8and the vicinity thereof. As illustrated inFIG. 14, the cooling oil tank543is attached to the mount bracket52via a bracket540. The bottom surface of the cooling oil tank543has a first sloped surface571that slopes to the rear and upward. A virtual extension line ELI of the first sloped surface571as seen in a side view of the vehicle overlaps the axle housing47.

The front surface of the cooling oil tank543has a second sloped surface572that slopes to the front and downward. The cooling oil pipe544is connected to the second sloped surface572. Specifically, the first cooling oil pipe551, the first drain pipe557, the second drain pipe558, and the third drain pipe559are connected to the second sloped surface572. The first drain pipe557is arranged to not have a portion that extends upward from the first motor MG1toward the cooling oil tank543. The second drain pipe558is arranged to not have a portion that extends upward from the second motor MG2toward the cooling oil tank543. The third drain pipe559is arranged to not have a portion that extends upward from the third motor MG3toward the cooling oil tank543.

FIG. 15is a bottom surface view of a portion of the rear part of the wheel loader1. As illustrated inFIG. 15, the cooling oil tank543is arranged between the side surface of the vehicle body frame2and the transmission shaft46in the vehicle width direction. In the present exemplary embodiment, the cooling oil tank543is arranged between the left side part171of the vehicle body frame2and the transmission shaft46in the vehicle width direction.

The first motor MG1, the third motor MG3, and the cooling oil tank543are arranged on the same side with regard to the center axis of the transmission24that extends in the vehicle front-back direction. That is, the first motor MG1, the third motor MG3, and the cooling oil tank543are arranged on the same side with regard to the vertical plane PL1that includes the center axis Ax1of the input shaft61. In the present exemplary embodiment, the first motor MG1, the third motor MG3and the cooling oil tank543are arranged to the left of the vertical plane PL1. A portion of the cooling oil tank543overlaps the first motor MG1as seen from the bottom surface.

The wheel loader1according to the present exemplary embodiment has the following characteristics.

The cooling oil tank543is positioned behind the output shaft case333and under the first motor MG1. That is, by arranging the cooling oil tank543by using the space behind the output shaft case333and under the first motor MG1, the transmission case33and the cooling oil tank543can be arranged in a compact manner.

Moreover, by arranging the cooling oil tank543below the first to third motors MG1to MG3, the cooling oil can be recovered from the first to third motors MG1to MG3to the cooling oil tank543due to gravity. As a result, the cooling oil can be circulated efficiently.

Moreover, the motor cooling system54is separate from the transmission lubrication system53and therefore the first to third motors MG1to MG3can be cooled while suppressing a deterioration in the performance of the transmission24or the first to third motors MG1to MG3in comparison to when the motor cooling system54is the same system as the transmission lubrication system53.

The axle housing47is positioned further toward the rear than the first motor MG1. The cooling oil tank543is positioned in front of the axle housing47. As a result, by arranging the cooling oil tank543by using the space positioned behind the output shaft case333, under the first motor MG1, and in front of the axle housing47, the transmission case33, the cooling oil tank543, and the axle housing47can be arranged in a compact manner.

The bottom surface of the cooling oil tank543has the first sloped surface571that slopes to the rear and upward. As a result, air flowing under the wheel loader1can be guided toward the axle housing47due to the bottom surface of the cooling oil tank543. As a result, the axle housing47can be cooled.

The virtual extension line ELI of the sloped surface as seen in a side view of the vehicle overlaps the axle housing47. As a result, the axle housing47can be cooled more effectively due to the air flowing under the wheel loader1.

The cooling oil tank543is arranged between the side surface of the rear frame17and the transmission shaft46in the vehicle width direction. In this case, the cooling oil tank543can be accessed easily from the side of the wheel loader1. As a result, maintenance performance of the cooling oil tank543can be improved.

The front surface of the cooling oil tank543has the second sloped surface572that slopes to the front and downward. Moreover, the first cooling oil pipe551, the first drain pipe557, the second drain pipe558, and the third drain pipe559are connected to the second sloped surface572. As a result, the first cooling oil pipe551, the first drain pipe557, and the second drain pipe558that extend from above the cooling oil tank543can be connected to the second sloped surface572without being bent in a large manner. Consequently, the connections of the first cooling oil pipe551, the first drain pipe557, and the second drain pipe558to the second sloped surface572are facilitated.

The first motor MG1, the third motor MG3, and the cooling oil tank543are arranged on the same side with respect to the center axis of the transmission24that extends in the vehicle front-back direction. As a result, the installation of the first drain pipe557and the second drain pipe558is facilitated.

Although an exemplary embodiment of the present invention has been described so far, the present invention is not limited to the above exemplary embodiments and various modifications may be made within the scope of the invention.

The present invention may be applicable to another type of speed change device, such as a HMT, without being limited to the EMT. In this case, the first motor MG1functions as a hydraulic motor and a hydraulic pump. The second motor MG2functions as a hydraulic motor and a hydraulic pump. The third motor MG3functions as a hydraulic motor and a hydraulic pump. The first motor MG1, the second motor MG2, and the third motor MG3are variable capacitor pump/motors, and the capacities are controlled by the control unit31.

The configuration of the transmission24is not limited to the configuration of the above exemplary embodiment. For example, the coupling and disposition of the elements of the two planetary gear mechanisms68and69are not limited to the coupling and disposition of the above exemplary embodiments. The number of planetary gear mechanisms is not limited to two. For example, the transmission may be provided with one planetary gear mechanism. The number of motors is not limited to three. The number of motors may be one, two, or four or more. For example, the third motor MG3may be omitted.

All of the first motor MG1and the second motor MG2may overlap the input shaft case331as seen in a projection view in the up-down direction. All of the first motor MG1and the second motor MG2may overlap the middle shaft case332as seen in the vehicle front-back direction.

The shape of the input shaft case331is not limited to a cylindrical shape. So long as at least the lower part of the input shaft case331has the curved surface part334that is curved to protrude downward, the upper part of the input shaft case331may have a linear shape.

The locations of the first to third motors MG1to MG3are not limited to the positions of the above exemplary embodiment and may be changed. The shape of the transmission case33is not limited to the position of the above exemplary embodiment and may be changed. For example, the positions of the first to third motors MG1to MG3and/or the shape of the transmission case33may be reverse in the front-back direction to the respective positions and shape in the above exemplary embodiment. Alternatively, the positions of the first to third motors MG1to MG3and/or the shape of the transmission case33may be reverse in the left-right direction to the respective positions and shape in the above exemplary embodiment.

The clutch control valve32may be arranged in a location other than the front surface of the transmission24. For example, the clutch control valve32may be arranged on the rear surface of the transmission24.

The shape of the mount bracket52is not limited to the shape described in the above exemplary embodiment. For example, the shape of the recessed part521in the mount bracket52may be changed. Alternatively, the recessed part521may be omitted.

The shape of the vehicle body frame2is not limited to the shape in the above exemplary embodiment. For example, the bottom part opening174may be omitted. Alternatively, the side part opening173may be omitted.

The position of the cooling oil tank543is not limited to the position of the above exemplary embodiment. For example, the cooling oil tank543may be arranged under the second motor MG2. Alternatively, the cooling oil tank543may be arranged in a location other than under the transmission24. The shape of the cooling oil tank543is not limited to the shape in the above exemplary embodiment. For example, the first sloped surface571may be omitted. Alternatively, the second sloped surface572may be omitted. Alternatively, the cooling oil tank543may have a rectangular solid shape, a cubic shape, or a cylindrical shape.

According to the present invention, cooling of the motor is enabled while an increase in the size of the vehicle body can be suppressed in the hybrid-type wheel loader.