A bulldozer includes a steering clutch, a steering brake, a hydraulic pump that discharges a lubricating oil, a first lubricating oil supply path, a second lubricating oil supply path, a third lubricating oil supply path, and a flow amount switching valve disposed on the second lubricating oil supply path. The first lubricating oil supply path supplies a portion of the lubricating oil discharged by the hydraulic pump to the steering clutch The second lubricating oil supply path supplies a portion of the lubricating oil discharged by the hydraulic pump to the steering brake. The third lubricating oil supply path supplies, to the steering brake, a portion of the lubricating oil that has passed through the steering clutch. The flow amount switching valve switches an amount of the lubricating oil supplied to the steering brake.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2016/079475, filed on Oct. 4, 2016. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2015-200840, filed in Japan on Oct. 9, 2015, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

The present invention relates to a bulldozer.

Description of the Related Art

Conventionally, power from an engine is transmitted through a transmission to left and right drive wheels, and left and right crawlers are driven by the drive wheels in a bulldozer. This type of bulldozer is provided with a steering clutch and a steering brake in correspondence with the respective left and right drive wheels. Turning of the bulldozer is conducted by controlling the left and right steering clutches and steering brakes with hydraulic pressure (see, for example, Japanese Laid-open Patent No. 2010-143259).

In Japanese Laid-open Patent No. 2010-143259, lubricating oil is supplied from a hydraulic pump to the steering clutch through a clutch lubricating oil supply path, and lubricating oil is supplied from the hydraulic pump to the steering brake through a brake lubricating oil supply path. The lubricating oil that has passed through the steering clutch and the lubricating oil that has passed through the steering brake is recovered in a lubricating oil tank.

SUMMARY

There is a demand to increase the amount of the lubricating oil supplied to the steering clutch and the steering brake, and increase the respective capacities of the steering clutch and the steering brake. Moreover, there may be a demand to reduce the amount of the lubricating oil supplied to the steering clutch and the steering brake, and reduce the capacity of the hydraulic pump. Accordingly, the effective use of the lubricating oil discharged from the hydraulic pump is desired.

An object of the present invention is to provide a bulldozer that is able to effectively use lubricating oil in consideration of the above problem.

A bulldozer according to a first aspect is provided with a steering clutch, a steering brake, a hydraulic pump, a first lubricating oil supply path, a second lubricating oil supply path, a third lubricating oil supply path, and a flow amount switching valve. The steering clutch transmits or cuts off the rotational force of an input shaft to an output shaft. The steering brake brakes the output shaft. The hydraulic pump discharges a lubricating oil. The first lubricating oil supply path supplies a portion of the lubricating oil discharged by the hydraulic pump to the steering clutch. The second lubricating oil supply path supplies a portion of the lubricating oil discharged by the hydraulic pump to the steering brake. The third lubricating oil supply path supplies a portion of the lubricating oil that has passed through the steering clutch to the steering brake. The flow amount switching valve is disposed on the second lubricating oil supply path and switches the amount of the lubricating oil supplied to the steering brake.

According to the bulldozer as in the first aspect, a portion of the lubricating oil that has been discharged by the hydraulic pump and that has passed through the steering clutch is supplied to the steering brake through the third lubricating oil supply path. Therefore, the lubricating oil discharged by the hydraulic pump can be used effectively because a portion of the lubricating oil supplied to the steering clutch can be reused in the steering brake.

A bulldozer according to a second aspect is related to the first aspect, and the steering clutch has a clutch housing coupled to the output shaft, a plurality of first clutch disks fixed to the clutch housing, and a plurality of second clutch disks that rotate with the input shaft. The steering brake has a brake housing, a plurality of fixed plates that are fixed to the brake housing, and a plurality of brake disks that rotate with the output shaft. The plurality of fixed plates and the plurality of brake disks are spaced further away from the input shaft than the plurality of first clutch disks and the plurality of second clutch disks in the radial direction perpendicular to the input shaft.

According to the bulldozer as in the second aspect, a first lubricating oil recovery path can be provided so as not to interfere with the steering brake.

A bulldozer according to a third aspect is related to the first aspect, and the steering clutch has a clutch housing coupled to the output shaft, a plurality of first clutch disks fixed to the clutch housing, and a plurality of second clutch disks that rotate with the input shaft. The steering brake has a brake housing, a plurality of fixed plates that are fixed to the brake housing, and a plurality of brake disks that rotate with the output shaft. The brake housing is spaced away from a center line in the axial direction of the plurality of first clutch disks and the plurality of second clutch disks in the axial direction parallel to the input shaft.

According to the bulldozer as in the third aspect, the lubricating oil that has passed through the steering clutch can be supplied effectively to the steering brake by using centrifugal force.

EFFECT OF THE INVENTION

According to the present invention, a bulldozer can be provided that uses lubricating oil effectively.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(Overall Configuration of a Bulldozer1)

FIG. 1is a system configuration of a bulldozer1according to an embodiment. The bulldozer1is provided with an engine2, a power transmission mechanism3, a pair of travel devices4a,4b,a lubricating oil supply unit6, a control unit7, and a power take-off device8.

Power from the engine2is transmitted to the power take-off device8. The power take-off device8distributes the power from the engine2to the lubricating oil supply unit6, the power transmission mechanism3, and an unillustrated operating fluid pump. The operating fluid pump supplies operating fluid to a hydraulic cylinder for driving a work implement (a blade or a ripper and the like).

The lubricating oil supply unit6has a hydraulic pump30, a lubricating oil tank19, and a flow amount switching valve43. In the present embodiment, the hydraulic pump30is a fixed displacement pump driven by power from the engine2. The hydraulic pump30is driven by the engine2. The hydraulic pump30sucks in lubricating oil stored in the lubricating oil tank19and discharges the lubricating oil to a discharge path30a.The discharge path30ais joined to a first lubricating oil supply path31and a second lubricating oil supply path33. The lubricating oil discharged by the hydraulic pump30to the discharge path30ais distributed to the first lubricating oil supply path31and the second lubricating oil supply path33in predetermined proportions. The predetermined proportions can be adjusted as appropriate with the respective opening diameters of the first lubricating oil supply path31and the second lubricating oil supply path33.

The flow amount switching valve43is disposed on the second lubricating oil supply path33. The flow amount switching valve43is an electromagnetic control valve controlled with control signals from the control unit7. The flow amount switching valve43switches between an open state and a closed state in response to the presence or absence of an excitation current. The flow amount switching valve43enters the open state when a pair of below mentioned steering brakes5a,5benter a braking state, and the flow amount switching valve43enters the closed state when the pair of steering brakes5a,5benter a non-braking state. The lubricating oil that is discharged by the hydraulic pump30and flows into the second lubricating oil supply path33flows toward the pair of steering brakes5a,5bwhen the flow amount switching valve43is in the open state, and flows toward the recovery tank19when the flow amount switching valve43is in the closed state.

The power transmission mechanism3transmits the power from the engine2transmitted via the power take-off device8, to the pair of travel devices4a,4b.The power transmission mechanism3has a torque converter9, a transmission10, a bevel gear11, an input shaft12, a pair of steering clutches13a,13b,a pair of output shafts14a,14b,and the pair of steering brakes5a,5b.

The torque converter9is coupled to the power take-off device8and the transmission10. The torque converter9transmits the power from the power take-off device8to the transmission10through a fluid. The transmission10changes the speed of the rotation motion transmitted from the torque converter9. The transmission10is able to switch between forward travel and reverse travel. The transmission10is coupled to the bevel gear11. The power output from the transmission10is transmitted through the bevel gear11to the input shaft12. The input shaft12is coupled to the pair of steering clutches13a,13b.

The pair of steering clutches13a,13bare wet multiplate clutches that can be switched between an engaged state and a released state with hydraulic pressure. The pair of steering clutches13a,13bare coupled to the pair of output shafts14a,14b.When the steering clutch13ais in the engaged state, the power from the input shaft12is transmitted to the output shaft14a.When the steering clutch13bis in the engaged state, the power from the input shaft12is transmitted to the output shaft14b.A configuration of the pair of steering clutches13a,13bis discussed below.

The first lubricating oil supply path31communicates with the pair of steering clutches13a,13band the discharge path30a.The first lubricating oil supply path31supplies a portion of the lubricating oil discharged by the hydraulic pump30to the pair of steering clutches13a,13b.A first lubricating oil recovery path32communicates with the pair of steering clutches13a,13band the lubricating oil tank19. The first lubricating oil recovery path32returns the lubricating oil that has passed through the pair of steering clutches13a,13bto the lubricating oil tank19.

The pair of output shafts14a,14bare coupled to the pair of travel devices4a,4b.The travel device4ahas a sprocket17aand a crawler belt18a.The sprocket17ais coupled to the output shaft14a.The crawler belt18ais wound onto the sprocket17a.The sprocket17ais rotated and driven by the output shaft14aand the crawler belt18ais driven as a result thereof. The travel device4bhas a sprocket17band a crawler belt18b.The sprocket17bis coupled to the output shaft14b.The crawler belt18bis wound onto the sprocket17b.The sprocket17bis rotated and driven by the output shaft14band the crawler belt18bis driven as a result thereof.

The pair of steering brakes5a,5bare disposed between the pair of steering clutches13a,13band the pair of travel devices4a,4b.The pair of steering brakes5a,5bare both wet multiplate negative brakes that can be switched between a braking state and a non-braking state with hydraulic pressure. The steering brake5abrakes the rotation of the output shaft14ain the braking state and does not brake the rotation of the output shaft14ain the non-braking state. A configuration of the pair of steering brakes5a,5bis discussed below.

The second lubricating oil supply path33communicates with the pair of steering brakes5a,5band the discharge path30a.The second lubricating oil supply path33supplies a portion of the lubricating oil discharged by the flow amount switching valve43to the pair of steering brakes5a,5b.A second lubricating oil recovery path34communicates with the pair of steering brakes5a,5band the lubricating oil tank19. The second lubricating oil recovery path34returns the lubricating oil that has passed through the pair of steering brakes5a,5bto the lubricating oil tank19.

A third lubricating oil supply path35communicates with the pair of steering clutches13a,13band pair of steering brakes5a,5b.The third lubricating oil supply path35supplies a portion of the lubricating oil that has passed through the pair of steering clutches13a,13bto the pair of steering brakes5a,5b.Therefore, when the flow amount switching valve43is in the open state, lubricating oil is supplied from the second lubricating oil supply path33and the third lubricating oil supply path35respectively to the pair of steering brakes5a,5b.When the flow amount switching valve43is in the closed state, lubricating oil is supplied from the third lubricating oil supply path35to the pair of steering brakes5a,5b.In this way, lubricating oil is normally supplied from the third lubricating oil supply path35to the pair of steering brakes5a,5b.

The control unit7receives operation signals from a throttle operating unit71, a speed change operating unit72, a steering operating unit73, and a brake operating unit74. The throttle operating unit71outputs operation signals indicating the rotation speed of the engine2. The speed change operating unit72outputs operation signals indicating the velocity stages of the transmission10. The steering operating unit73outputs operation signals indicating switching between forward motion, reverse motion, and the turning direction of the bulldozer1. The braking operating unit74outputs operation signals indicating the acceleration and deceleration of the bulldozer1.

The control unit7sets the pair of steering brakes5a,5bto the braking state and sets the flow amount switching valve43to the closed state when operation signals are received from the brake operating unit74. The control unit7sets the pair of steering brakes5a,5bto the non-braking state and sets the flow amount switching valve43to the closed state when no operation signals are received from the brake operating unit74. The control unit7sets the pair of steering brakes5a,5bto the non-braking state and sets the flow amount switching valve43to the closed state when operation signals are not received from the brake operating unit74.

The control unit7sets the steering brake5aor the steering brake5bto the braking state and sets the flow amount switching valve43to the open state when operation signals are received from the steering operating unit73. The control unit7sets the pair of steering brakes5a,5bto the non-braking state and sets the flow amount switching valve43to the closed state when no operation signals are received from the steering operating unit73.

(Configuration in the Vicinity of the Steering Clutch13aand the Steering Brake5a)

The following is an explanation of a configuration in the vicinity of the steering clutch13aand the steering brake5awith reference to the drawings. The configuration in the vicinity of the steering clutch13aand the steering brake5ais the same as the configuration in the vicinity of the steering clutch13band the steering brake5b. Consequently, only the configuration in the vicinity of the steering clutch13aand the steering brake5awill be discussed below.

FIG. 2is a cross-sectional view of the configuration in the vicinity of the steering clutch13aand the steering brake5a.The steering clutch13ahas a rotating member40, a clutch housing41, a plurality of first clutch disks42, a plurality of second clutch disks43, and a clutch piston44.

The rotating member40is fixed to the input shaft12and rotates around a shaft center12S of the input shaft12. The clutch housing41surrounds the outside of the plurality of first clutch disks42and the plurality of second clutch disks43. The plurality of first clutch disks42are fixed to the rotating member40. The plurality of second clutch disks43are fixed to the clutch housing41. The plurality of first clutch disks42and the plurality of second clutch disks43are disposed alternately in the axial direction parallel to the shaft center12S of the input shaft12.

The clutch housing41is coupled to the output shaft14a.The clutch housing41is supported by a first shaft bearing45ain a manner that allows relative rotation with respect to the rotating member40. The clutch housing41is supported by a second shaft bearing45band a third shaft bearing45cin a manner that allows relative rotation with respect to a below mentioned brake housing46. When the steering clutch13ais in an engaged state, the clutch housing41rotates around a shaft center14S with the output shaft14a.In the present embodiment, the shaft center14S of the output shaft14amatches the shaft center12S of the input shaft12.

When operating fluid is supplied to the clutch piston44, the clutch piston44presses the plurality of first clutch disks42and the plurality of second clutch disks43. Consequently, the steering clutch13aenters the engaged state and the clutch housing41rotates around the shaft center12S with the rotating member40.

The steering brake5ahas the brake housing46, a plurality of fixed plates47, a plurality of brake disks48, and a brake piston49.

The brake housing46surrounds the outside of the plurality of fixed plates47and the plurality of brake disks48. The brake housing46is spaced away from a center line CL in the axial direction of the plurality of first clutch disks42and the plurality of second clutch disks43, in the axial direction parallel to the shaft center14S of the output shaft14a. The brake housing46does not overlap the center line CL of the plurality of first clutch disks42and the plurality of second clutch disks43, in the radial direction perpendicular to the shaft center14S of the output shaft14a.While the brake housing46overlaps a portion of the plurality of first clutch disks42and the plurality of second clutch disks43in the radial direction in the present embodiment, the brake housing46may not overlap a portion of the plurality of first clutch disks42and the plurality of second clutch disks43.

The plurality of fixed plates47are fixed to the brake housing46. The plurality of plurality of brake disks48are fixed to the clutch housing41. The plurality of plurality of fixed plates47and the plurality of brake disks48are disposed alternately in the axial direction parallel to the shaft center14S of the output shaft14a.The plurality of plurality of fixed plates47and the plurality of brake disks48are pressed by a disk spring which is not illustrated.

The plurality of fixed plates47and the plurality of brake disks48are spaced further away from the output shaft14athan the plurality of first clutch disks42and the plurality of second clutch disks43in the radial direction perpendicular to the shaft center14S of the output shaft14a.The plurality of fixed plates47and the plurality of brake disks48are disposed further to the outside in the radial direction than the plurality of first clutch disks42and the plurality of second clutch disks43. However, a portion of the plurality of fixed plates47and the plurality of brake disks48may overlap a portion of the plurality of first clutch disks42and the plurality of second clutch disks43in the radial direction.

When operating fluid is supplied to the brake piston49, the brake piston49separates the plurality of fixed plates47and the plurality of brake disks48from each other. Consequently, the steering brake5aenters the non-braking state.

The flow of the lubricating oil supplied to the steering clutch13aand to the steering brake5awill be explained below.

The lubricating oil discharged by the hydraulic pump30(seeFIG. 1) is supplied to the steering clutch13athrough the first lubricating oil supply path31. The lubricating oil that has passed through the steering clutch13ais distributed in predetermined proportions to the first lubricating oil recovery path32and the third lubricating oil supply path35(see arrows inFIG. 2). The predetermined proportions can be adjusted as appropriate with the respective opening diameters of the first lubricating oil recovery path32and the third lubricating oil supply path35. While four first lubricating oil recovery paths32and eight third lubricating oil supply paths35are provided in approximately equal intervals in the circumferential direction centered on the shaft center12S of the input shaft12in the present embodiment, the numbers and positions of the first lubricating oil recovery path32and the third lubricating oil supply path35may be changed as appropriate.

The lubricating oil discharged by the hydraulic pump30is supplied to the steering brake5athrough the second lubricating oil supply path33, and a portion of the lubricating oil that has passed through the steering clutch13ais supplied to the steering brake5athrough the third lubricating oil supply path35(see arrows inFIG. 2). The flow amount switching valve43(seeFIG. 1) disposed on the second lubricating oil supply path33enters the open state when the steering brake5ais in the braking state, and enters the closed state when the steering brake5ais in the non-braking state. As a result, when the steering brake5ais in the braking state, the steering brake5ais cooled and lubricated due to the supply of the lubricating oil from the respective second lubricating oil supply path33and the third lubricating oil supply path35. Conversely, when the steering brake5ais in the non-braking state, the lubrication of the steering brake5ais maintained mainly due to the supply of the lubricating oil to the steering brake5afrom the third lubricating oil supply path35. The lubricating oil that has passed through the steering brake5ais returned to the second lubricating oil recovery path34.

(1) The bulldozer1is provided with the first lubricating oil supply path31, the second lubricating oil supply path33, the third lubricating oil supply path35, and the flow amount switching valve43. The first lubricating oil supply path31supplies a portion of the lubricating oil discharged by the hydraulic pump30to the steering clutch13a.The second lubricating oil supply path33supplies a portion of the lubricating oil discharged by the hydraulic pump30to the steering brake5a.The third lubricating oil supply path35supplies a portion of the lubricating oil that has passed through the steering clutch13ato the steering brake5a.The flow amount switching valve43is disposed on the second lubricating oil supply path33and switches the amount of lubricating oil supplied to the steering brake5a.

As indicated inFIG. 3in the conventional lubricating oil supply system, all of the lubricating oil that has been discharged by the hydraulic pump30′ and has passed through the steering clutch13ais returned to the recovery tank19through the first lubricating oil recovery path32. Therefore, the total amount of the lubricating oil required by the steering clutch13aand the lubricating oil required by the steering brake5amust be discharged by the hydraulic pump30. The numbers depicted inFIG. 3indicate examples of amounts of lubricating oil flowing through each of the paths.

However, as indicated inFIG. 4in the lubricating oil supply system according to the present embodiment, a portion of the lubricating oil that has been discharged by the hydraulic pump30and that has passed through the steering clutch13ais supplied to the steering brake5athrough the third lubricating oil supply path35. Therefore, the lubricating oil discharged by the hydraulic pump30can be used effectively because a portion of the lubricating oil supplied to the steering clutch13acan be reused in the steering brake5a.As a result, the capacity of the hydraulic pump30can be reduced because the supply amounts of the lubricating oil to the steering clutch13aand the steering brake5acan be reduced. The numbers depicted inFIG. 4indicate examples of amounts of lubricating oil flowing through each of the paths.

While the amount of lubricating oil is set from the point of view of reducing the capacity of the hydraulic pump30inFIG. 4, the supply amounts of the lubricating oil to the steering clutch13aand the steering brake5acan be increased if the capacity of the hydraulic pump30is maintained at the same level as that of the hydraulic pump30′ inFIG. 3. As a result, the capacities of the steering clutch13aand the steering brake5acan be increased.

(2) The brake housing46is spaced away from the center line CL of the plurality of first clutch disks42and the plurality of second clutch disks43, in the axial direction parallel to the shaft center14S of the output shaft14a.As a result, the first lubricating oil recovery path32can be provided in a manner that does not interfere with the steering brake5a.

(3) The plurality of fixed plates47and the plurality of brake disks48are spaced further away from the input shaft12than the plurality of first clutch disks42and the plurality of second clutch disks43in the radial direction perpendicular to the shaft center14S of the output shaft14a.As a result, the lubricating oil that has passed through the steering clutch13acan be supplied effectively to the steering brake5awith a centrifugal force.

The present invention is not limited to the above embodiment and various changes and modifications may be made without departing from the spirit of the invention.

While the flow amount switching valve43switches between the open state and the closed state in the above embodiment, a small amount of the lubricating oil may be allowed to pass through even in the closed state by providing an orifice, and furthermore, the entire amount of the lubricating oil is not required to pass through even in the open state.

While the brake housing46is spaced away from the center line CL of the plurality of first clutch disks42and the plurality of second clutch disks43in the axial direction in the present embodiment, the brake housing46overlap the center line CL of the plurality of first clutch disks42and the plurality of second clutch disks43.

While the plurality of fixed plates47and the plurality of brake disks48are spaced further away from the output shaft14athan the plurality of first clutch disks42and the plurality of second clutch disks43in the radial direction in the above embodiment, the invention is not limited in this way.

INDUSTRIAL APPLICABILITY

The present invention is useful in the field of construction machinery according to the bulldozer as in the present invention because the lubricating oil can be used effectively.