Drive system for work machine, and work machine

Abstract

According to the present invention, a motor is disposed between first and second drive wheels. A first planetary gear mechanism is disposed between the first drive wheel and the motor, and a driving force from the motor is input to the first planetary gear mechanism. A first brake is disposed between the first planetary gear mechanism and the first drive wheel. A first clutch is disposed between the first planetary gear mechanism and the first brake. A second planetary gear mechanism is disposed between the second drive wheel and the motor, and a driving force from the motor is input to the second planetary gear mechanism. A second brake is disposed between the second planetary gear mechanism and the second drive wheel. A second clutch is disposed between the second planetary gear mechanism and the second brake.

Description

Driving System for Working Machine and Working Machine

[0001] The present disclosure relates to a driving system for a working machine and a working machine.

[0002] Some driving systems for working machines transmit driving force from a common motor to the left and right final drive assemblies. For example, the driving system in Patent Document 1 includes a motor and left and right final drive assemblies. A planetary gear mechanism and a brake are respectively arranged between the motor and each of the left and right final drive assemblies. The driving force of the motor is transmitted to the left final drive assembly via the left planetary gear mechanism. The driving force of the motor is transmitted to the right final drive assembly via the right planetary gear mechanism.

[0003] U.S. Patent Publication No. 2016 / 0097185

[0004] In the above-described driving system, the rotation of the motor may be decelerated due to the braking force of the brake. For example, when the left and right brakes perform a braking operation to brake the working machine, the rotation of the motor may be decelerated due to the braking force of the left and right brakes. Alternatively, when one of the left and right brakes performs a braking operation for the working machine to turn, the motor may be decelerated by the braking force. An object of the present disclosure is to suppress deceleration of the rotation of the motor during braking by the brake in a driving system for a working machine.

[0005] A drive system for a work machine according to a first aspect of the present disclosure comprises a first drive wheel, a second drive wheel, a motor, a first planetary gear mechanism, a first brake, a first clutch, a second planetary gear mechanism, a second brake, and a second clutch. The motor is positioned between the first drive wheel and the second drive wheel. The first planetary gear mechanism is positioned between the first drive wheel and the motor and receives driving force from the motor. The first brake is positioned between the first planetary gear mechanism and the first drive wheel. The first clutch is positioned between the first planetary gear mechanism and the first brake. The second planetary gear mechanism is positioned between the second drive wheel and the motor and receives driving force from the motor. The second brake is positioned between the second planetary gear mechanism and the second drive wheel. The second clutch is positioned between the second planetary gear mechanism and the second brake.

[0006] A drive system for a work machine according to a second aspect of the present disclosure comprises a first drive wheel, a second drive wheel, a motor, a first gear set, a first brake, a first clutch, a second gear set, a second brake, and a second clutch. The motor is positioned between the first drive wheel and the second drive wheel. The first gear set is positioned between the first drive wheel and the motor and receives driving force from the motor. The first brake is positioned between the first gear set and the first drive wheel. The first clutch is positioned between the first gear set and the first brake. The second gear set is positioned between the second drive wheel and the motor and receives driving force from the motor. The second brake is positioned between the second gear set and the second drive wheel. The second clutch is positioned between the second gear set and the second brake.

[0007] A drive system for a work machine according to a third aspect of this disclosure comprises a first drive wheel, a second drive wheel, a motor, a planetary gear mechanism, a first brake, a first clutch, a second brake, and a second clutch. The motor is positioned between the first drive wheel and the second drive wheel. The planetary gear mechanism receives driving force from the motor. The first brake is positioned between the planetary gear mechanism and the first drive wheel. The first clutch is positioned between the planetary gear mechanism and the first brake. The second brake is positioned between the planetary gear mechanism and the second drive wheel. The second clutch is positioned between the planetary gear mechanism and the second brake.

[0008] Other embodiments of the present disclosure of a work machine include a vehicle body, a running gear, and a drive system according to the first, second, or third embodiment described above. The running gear supports the vehicle body. The drive system drives the running gear.

[0009] According to this disclosure, the transmission of driving force from the motor to each drive wheel and the braking of each drive wheel can be controlled independently. Therefore, a single motor can be used to rotate the work machine.

[0010] This is a perspective view of a work machine according to an embodiment. This is a skeleton diagram of the drive system according to an embodiment. This is a skeleton diagram of the drive system showing the power transmission system during straight-line travel. This is a skeleton diagram of the drive system showing the power transmission system during braking. This is a skeleton diagram of the drive system showing the power transmission system during right turns. This is a skeleton diagram of the drive system showing the power transmission system during left turns. This is a skeleton diagram of the drive system according to another embodiment.

[0011] The following description of the working machine according to the embodiment will be made with reference to the drawings. Figure 1 is a perspective view of the working machine 1 according to the embodiment. The working machine 1 according to this embodiment is a bulldozer. As shown in Figure 1, the working machine 1 comprises a body 2, a working machine 3, and left and right traveling devices 4. Note that the right traveling device is not shown in Figure 1. The body 2 includes a driver's cab 6 and a power room 7. The power room 7 is located in front of the driver's cab 6. The working machine 3 is operably supported on the body 2. The working machine 3 includes a blade 8. The traveling device 4 supports the body 2.

[0012] The left-side running gear 4 includes a track 11 and a track frame 12. The track frame 12 supports the track 11 via several road wheels (not shown) and idlers. Although not shown, the right-side running gear also includes a track and a track frame, similar to the left-side running gear 4.

[0013] The work machine 1 includes a drive system 10. The drive system 10 is supported by the vehicle body 2 and the left and right running gears 4. The drive system 10 includes a left drive wheel 21 and a right drive wheel 31 (see Figure 2). The track 11 of the left running gear 4 is wrapped around the left drive wheel 21. The track of the right running gear is wrapped around the right drive wheel 31. The left drive wheel 21 and the right drive wheel 31 are sprockets. The axes of the left drive wheel 21 and the right drive wheel 31 extend in the left-right direction of the work machine 1. In the following description, the direction parallel to the axes of the left drive wheel 21 and the right drive wheel 31 is defined as the axial direction. Furthermore, the direction away from the centerline of the vehicle body of the work machine 1 in the axial direction is defined as the outward direction in the axial direction, and the opposite direction is defined as the inward direction in the axial direction.

[0014] Figure 2 is a skeleton diagram of the drive system 10. As shown in Figure 2, the drive system 10 comprises a motor 20, the left drive wheel 21 described above, a first planetary gear mechanism 22, a first clutch 23, a first intermediate shaft 24, a first brake 25, a first final drive assembly 26, the right drive wheel 31 described above, a second planetary gear mechanism 32, a second clutch 33, a second intermediate shaft 34, a second brake 35, and a second final drive assembly 36.

[0015] Motor 20 is positioned between the left drive wheel 21 and the right drive wheel 31 in the axial direction. Motor 20 is an electric motor. Motor 20 includes a first rotating shaft 28 and a second rotating shaft 38. Motor 20 is positioned such that the rotating shafts 28 and 38 are parallel to the axial direction. The first rotating shaft 28 extends to the left from motor 20. The second rotating shaft 38 extends to the right from motor 20. The left drive wheel 21 and the right drive wheel 31 are rotated by a common driving force from motor 20. The track 11 of the left running gear 4 is wrapped around the left drive wheel 21. The track of the right running gear is wrapped around the right drive wheel 31.

[0016] The first planetary gear mechanism 22 is a reduction gear. The first planetary gear mechanism 22 has the first clutch 23, the first intermediate shaft 24, the first brake 25, and the first final drive assembly 26 arranged in the axial direction.

[0017] The first planetary gear mechanism 22 is located to the left of the motor 20 in the axial direction. The first planetary gear mechanism 22 is located between the motor 20 and the first clutch 23 in the axial direction. The first planetary gear mechanism 22 is located coaxially with the motor 20. The first planetary gear mechanism 22 includes a first sun gear 41, a first planetary gear 42, a first carrier 43, and a first ring gear 44.

[0018] The first sun gear 41 is connected to the first rotating shaft 28 of the motor 20. The first sun gear 41 rotates integrally with the first rotating shaft 28. The first planetary gear 42 meshes with the first sun gear 41. The first carrier 43 is fixed so that it cannot revolve around the first sun gear 41. Therefore, the first planetary gear 42 is supported by the first carrier 43 so that it cannot revolve around the first sun gear 41. The first planetary gear 42 is capable of rotation. The first ring gear 44 meshes with the first planetary gear 42. The first ring gear 44 rotates due to the rotation of the first planetary gear 42.

[0019] The first intermediate shaft 24 is arranged coaxially with the motor 20. In the axial direction, the first intermediate shaft 24 is positioned between the first planetary gear mechanism 22 and the first final drive assembly 26. The first clutch 23 is arranged coaxially with the motor 20. In the axial direction, the first clutch 23 is positioned to the left of the first planetary gear mechanism 22. In the axial direction, the first clutch 23 is positioned between the first planetary gear mechanism 22 and the first brake 25. The first clutch 23 is connected to the first ring gear 44 and the first intermediate shaft 24. When the first clutch 23 is engaged, it connects the first ring gear 44 and the first intermediate shaft 24 to each other. When the first clutch 23 is disengaged, it disengages the first ring gear 44 and the first intermediate shaft 24 to each other.

[0020] The first brake 25 is positioned coaxially with the motor 20. The first brake 25 is positioned to the left of the first clutch 23 in the axial direction. The first brake 25 is positioned between the first clutch 23 and the first final drive assembly 26 in the axial direction. In the braking state, the first brake 25 engages with the first intermediate shaft 24, thereby braking the first intermediate shaft 24. In the non-braking state, the first brake 25 releases the first intermediate shaft 24.

[0021] The axis of the first final drive assembly 26 is positioned eccentrically from the axis of the motor 20. The first final drive assembly 26 is positioned to the left of the first intermediate shaft 24. In the axial direction, the first final drive assembly 26 is positioned between the left drive wheel 21 and the first intermediate shaft 24. The first final drive assembly 26 includes a pair of parallel shaft gears 28A and 28B and a planetary gear mechanism 29.

[0022] The pair of parallel-axis gears 28A and 28B constitute a reduction gear. The pair of parallel-axis gears 28A and 28B includes a first parallel-axis gear 28A and a second parallel-axis gear 28B. The axes of the first parallel-axis gear 28A and the second parallel-axis gear 28B are parallel to each other. The first parallel-axis gear 28A is connected to a first intermediate shaft 24. The first parallel-axis gear 28A rotates integrally with the first intermediate shaft 24. The second parallel-axis gear 28B meshes with the first parallel-axis gear 28A.

[0023] The planetary gear mechanism 29 is a reduction gear. The planetary gear mechanism 29 is located to the left of a pair of parallel shaft gears 28A and 28B. The axis of the planetary gear mechanism 29 is eccentrically positioned from the axis of the motor 20. The planetary gear mechanism 29 includes a sun gear 45, a planetary gear 46, a carrier 47, and a ring gear 48. The sun gear 45 is connected to the second parallel shaft gear 28B. The sun gear 45 rotates integrally with the second parallel shaft gear 28B. The planetary gear 46 meshes with the sun gear 45. The planetary gear 46 is capable of orbiting the sun gear 45. The planetary gear 46 is supported by the carrier 47 so that it can orbit the sun gear 45. The ring gear 48 meshes with the planetary gear 46. The ring gear 48 is fixed so as not to rotate. The carrier 47 rotates due to the orbit of the planetary gear 46. The left drive wheel 21 is connected to the carrier 47. The left drive wheel 21 rotates as the carrier 47 rotates.

[0024] The second planetary gear mechanism 32, the second clutch 33, the second intermediate shaft 34, the second brake 35, and the second final drive assembly 36 have a structure that is symmetrical to the first planetary gear mechanism 22, the first clutch 23, the first intermediate shaft 24, the first brake 25, and the first final drive assembly 26, respectively. The second planetary gear mechanism 32, the second clutch 33, the second intermediate shaft 34, the second brake 35, and the second final drive assembly 36 are arranged in line along the axial direction.

[0025] The second planetary gear mechanism 32 is a reduction gear. The second planetary gear mechanism 32 is located to the right of the motor 20 in the axial direction. The second planetary gear mechanism 32 is located between the motor 20 and the second clutch 33 in the axial direction. The second planetary gear mechanism 32 is located coaxially with the motor 20. The second planetary gear mechanism 32 includes a second sun gear 51, a second planetary gear 52, a second carrier 53, and a second ring gear 54.

[0026] The second sun gear 51 is connected to the second rotating shaft 38 of the motor 20. The second sun gear 51 rotates integrally with the second rotating shaft 38. The second planetary gear 52 meshes with the second sun gear 51. The second carrier 53 is fixed so that it cannot revolve around the second sun gear 51. Therefore, the second planetary gear 52 is supported by the second carrier 53 so that it cannot revolve around the second sun gear 51. The second planetary gear 52 is capable of rotation. The second ring gear 54 meshes with the second planetary gear 52. The second ring gear 54 rotates due to the rotation of the second planetary gear 52.

[0027] The second intermediate shaft 34 is arranged coaxially with the motor 20. In the axial direction, the second intermediate shaft 34 is positioned between the second planetary gear mechanism 32 and the second final drive assembly 36. The second clutch 33 is arranged coaxially with the motor 20. In the axial direction, the second clutch 33 is positioned to the right of the second planetary gear mechanism 32. In the axial direction, the second clutch 33 is positioned between the second planetary gear mechanism 32 and the second brake 35. The second clutch 33 is connected to the second ring gear 54 and the second intermediate shaft 34. When the second clutch 33 is engaged, it connects the second ring gear 54 and the second intermediate shaft 34 to each other. When the second clutch 33 is disengaged, it disengages the second ring gear 54 and the second intermediate shaft 34 to each other.

[0028] The second brake 35 is positioned coaxially with the motor 20. The second brake 35 is positioned to the right of the second clutch 33 in the axial direction. The second brake 35 is positioned between the second clutch 33 and the second final drive assembly 36 in the axial direction. In the braking state, the second brake 35 engages with the second intermediate shaft 34. This brakes the second intermediate shaft 34. In the non-braking state, the second brake 35 releases the second intermediate shaft 34.

[0029] The axis of the second final drive assembly 36 is positioned eccentrically from the axis of the motor 20. The second final drive assembly 36 is positioned to the right of the second intermediate shaft 34. In the axial direction, the second final drive assembly 36 is positioned between the right drive wheel 31 and the second intermediate shaft 34. The second final drive assembly 36 includes a pair of parallel shaft gears 38A and 38B and a planetary gear mechanism 39.

[0030] The pair of parallel-axis gears 38A and 38B constitute a reduction gear. The pair of parallel-axis gears 38A and 38B includes a first parallel-axis gear 38A and a second parallel-axis gear 38B. The axes of the first parallel-axis gear 38A and the second parallel-axis gear 38B are parallel to each other. The first parallel-axis gear 38A is connected to a second intermediate shaft 34. The first parallel-axis gear 38A rotates integrally with the second intermediate shaft 34. The second parallel-axis gear 38B meshes with the first parallel-axis gear 38A.

[0031] The planetary gear mechanism 39 is a reduction gear. The planetary gear mechanism 39 is located to the right of a pair of parallel shaft gears 38A and 38B. The axis of the planetary gear mechanism 39 is eccentrically positioned from the axis of the motor 20. The planetary gear mechanism 39 includes a sun gear 55, a planetary gear 56, a carrier 57, and a ring gear 58. The sun gear 55 is connected to the second parallel shaft gear 38B. The sun gear 55 rotates integrally with the second parallel shaft gear 38B. The planetary gear 56 meshes with the sun gear 55. The planetary gear 56 is capable of revolving around the sun gear 55. The planetary gear 56 is supported by the carrier 57 so that it can revolve around the sun gear 55. The ring gear 58 meshes with the planetary gear 56. The ring gear 58 is fixed so as not to rotate. The carrier 57 rotates due to the revolving of the planetary gear 56. The right drive wheel 31 is connected to the carrier 57. The right drive wheel 31 rotates as the carrier 57 rotates.

[0032] The work machine 1 includes an engine 14, a generator 15, a PTO 16, a hydraulic pump 17, a control valve 18, and a controller 19. The generator 15 generates electricity when driven by the engine 14. The electricity generated by the generator 15 is supplied to the motor 20 via an inverter / converter (not shown).

[0033] The PTO 16 transmits the driving force from the engine 14 to the hydraulic pump 17. The hydraulic pump 17, driven by the driving force from the engine 14, discharges hydraulic fluid into the hydraulic circuit. The control valve 18 controls the hydraulic fluid supplied from the hydraulic circuit to the first and second clutches 23, 33 and the first and second brakes 25, 35. The controller 19 includes, for example, a processor and memory. The controller 19 controls the first and second clutches 23, 33 and the first and second brakes 25, 35 by electrically controlling the control valve 18.

[0034] For example, when the work machine 1 is traveling in a straight line, the controller 19 engages the first and second clutches 23 and 33, and deactivates the first and second brakes 25 and 35. As a result, as shown by the solid arrows in Figure 3, the driving force of the motor 20 is transmitted to the left drive wheel 21 via the first planetary gear mechanism 22 and the first final drive assembly 26. The driving force of the motor 20 is also transmitted to the right drive wheel 31 via the second planetary gear mechanism 32 and the second final drive assembly 36. As a result, the left and right drive wheels 21 and 31 are driven, causing the work machine 1 to travel in a straight line.

[0035] When the work machine 1 is being braked, the controller 19 disengages the first and second clutches 23 and 33, and applies the first and second brakes 25 and 35. As a result, as shown in Figure 4, the driving force of the motor 20 is not transmitted to the left drive wheel 21 and the right drive wheel 31. In addition, the first brake 25 and the second brake 35 brake the left and right drive wheels 21 and 31, respectively, but as indicated by the dashed arrows, their braking forces are not transmitted to the motor 20. Therefore, the deceleration of the motor 20's rotation is suppressed.

[0036] When the work machine 1 turns to the right, the controller 19 engages the first clutch 23, deactivates the first brake 25, disengages the second clutch 33, and applies the second brake 35. As a result, as shown by the solid arrows in Figure 5, the driving force of the motor 20 is transmitted to the left drive wheel 21 but not to the right drive wheel 31. In addition, the second brake 35 brakes the right drive wheel 31, but as shown by the dashed arrows, this braking force is not transmitted to the motor 20. Therefore, the deceleration of the motor 20's rotation is suppressed.

[0037] When the work machine 1 turns left, the controller 19 engages the second clutch 33, deactivates the second brake 35, disengages the first clutch 23, and applies the first brake 25. As a result, as shown by the solid arrows in Figure 6, the driving force of the motor 20 is transmitted to the right drive wheel 31 but not to the left drive wheel 21. Also, the first brake 25 brakes the left drive wheel 21, but as shown by the dashed arrows, this braking force is not transmitted to the motor 20. Therefore, the deceleration of the motor 20's rotation is suppressed.

[0038] In the drive system 10 according to this embodiment described above, the first clutch 23 is positioned between the first planetary gear mechanism 22 and the first brake 25, and the second clutch 33 is positioned between the second planetary gear mechanism 32 and the second brake 35. Therefore, the transmission of driving force from the motor 20 to each drive wheel 21, 31 and the braking of each drive wheel 21, 31 can be controlled independently. As a result, the work machine 1 can be rotated with a single motor.

[0039] Furthermore, when the first brake 25 is applied, the first clutch 23 is released, so the braking force of the first brake 25 is not transmitted to the motor 20. Similarly, when the second brake 35 is applied, the second clutch 33 is released, so the braking force of the second brake 35 is not transmitted to the motor 20. This suppresses the deceleration of the motor 20's rotation.

[0040] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention.

[0041] The work machine 1 is not limited to a bulldozer, but may also be other machines such as an excavator, wheel loader, grader, or dump truck. The configuration of the running gear 4 is not limited to that of the above embodiment and may be changed. For example, the running gear 4 may include tires instead of tracks. The drive wheels are not limited to sprockets, but may also consist of wheels and tires.

[0042] The structure or arrangement of the drive system 10 is not limited to that of the above embodiment and may be modified. For example, the motor 20 may be a hydraulic motor. The first and second clutches 23 and 33 may be mechanically controlled in conjunction with the operation of other components, independently of commands from the controller 19. The first and second brakes 25 and 35 may be mechanically controlled in conjunction with the operation of other components, independently of commands from the controller 19. The drive system 10 may include other gear sets, such as parallel shaft gears, instead of the first planetary gear mechanism 22 and the second planetary gear mechanism 32.

[0043] The configuration or arrangement of the final drive assemblies 26 and 36 is not limited to that of the above embodiments and may be modified. For example, the final drive assemblies 26 and 36 may include other gear sets, such as parallel shaft gears, instead of the planetary gear mechanisms 29 and 39.

[0044] In the above embodiment, two planetary gear mechanisms, a first planetary gear mechanism 22 and a second planetary gear mechanism 32, are connected to the motor 20, but the number of planetary gear mechanisms connected to the motor 20 may be one. For example, FIG. 7 is a skeleton diagram of a drive system 10 according to another embodiment. As shown in FIG. 7, the drive system 10 includes a planetary gear mechanism 60. The planetary gear mechanism 60 includes a sun gear 61, a planetary gear 62, a carrier 63, and a ring gear 64. The sun gear 61 is connected to a rotating shaft 65 of the motor 20. The sun gear 61 rotates integrally with the rotating shaft 65. The planetary gear 62 meshes with the sun gear 61. The planetary gear 62 is supported by the carrier 63 so as to be able to revolve around the sun gear 61. The planetary gear 62 is capable of rotating on its own axis. The carrier 63 can revolve around the sun gear 61 together with the planetary gear 62. The ring gear 64 meshes with the planetary gear 62. The ring gear 64 is non-rotatably fixed. The first clutch 23 and the second clutch 33 are each connected to the carrier 63 via a connecting shaft 66. The connecting shaft 66 extends through the motor 20 and the rotating shaft 65. The connecting shaft 66 is rotatable relative to the motor 20 and the rotating shaft 65.

[0045] In the drive system 10 according to the present embodiment, the driving force from the motor 20 passes through the first final drive assembly 26 and the second final drive assembly 36 from one planetary gear mechanism 60, and is transmitted to the left drive wheel 21 and the right drive wheel 31 respectively. Therefore, similarly to the above-described embodiment, the working machine 1 can be turned by one motor 20.

[0046] According to the present disclosure, in a drive system for a working machine, a reduction in the rotation speed of the motor during braking by a brake is suppressed.

[0047] 2: Body, 4: Running gear, 10: Drive system, 20: Motor, 21: Left drive wheel, 22: First planetary gear mechanism, 23: First clutch, 25: First brake, 26: First final drive assembly, 31: Right drive wheel, 32: Second planetary gear mechanism, 33: Second clutch, 35: Second brake, 36: Second final drive assembly, 41: First sun gear, 42: First planetary gear, 43: First carrier, 44: First ring gear, 51: Second sun gear, 52: Second planetary gear, 53: Second carrier, 54: Second ring gear, 60: Planetary gear mechanism, 61: Sun gear, 62: Planetary gear, 63: Carrier, 64: Ring gear

Claims

1. A drive system for a work machine, comprising: a first drive wheel; a second drive wheel; a motor disposed between the first drive wheel and the second drive wheel; a first planetary gear mechanism disposed between the first drive wheel and the motor and receiving driving force from the motor; a first brake disposed between the first planetary gear mechanism and the first drive wheel; a first clutch disposed between the first planetary gear mechanism and the first brake; a second planetary gear mechanism disposed between the second drive wheel and the motor and receiving driving force from the motor; a second brake disposed between the second planetary gear mechanism and the second drive wheel; and a second clutch disposed between the second planetary gear mechanism and the second brake.

2. The drive system according to claim 1, wherein the first planetary gear mechanism includes a first sun gear, a first planetary gear meshing with the first sun gear, a first ring gear meshing with the first planetary gear, and a first carrier connected to the first planetary gear, and the first clutch is connected to the first ring gear; and the second planetary gear mechanism includes a second sun gear, a second planetary gear meshing with the second sun gear, a second ring gear meshing with the second planetary gear, and a second carrier connected to the second planetary gear, and the second clutch is connected to the second ring gear.

3. The drive system according to claim 1, comprising: a first final drive assembly that transmits the driving force from the motor to the first drive wheel; and a second final drive assembly that transmits the driving force from the motor to the second drive wheel, wherein the first planetary gear mechanism is disposed between the motor and the first final drive assembly; the second planetary gear mechanism is disposed between the motor and the second final drive assembly; the first brake is disposed between the first planetary gear mechanism and the first final drive assembly; and the second brake is disposed between the second planetary gear mechanism and the second final drive assembly.

4. The drive system according to claim 1, wherein the first clutch is released when the first brake performs a braking operation.

5. The drive system according to claim 1, wherein the second clutch is released when the second brake performs a braking operation.

6. A work machine comprising: a vehicle body; a running device that supports the vehicle body; and a drive system according to claim 1 that drives the running device.

7. A drive system for a work machine, comprising: a first drive wheel; a second drive wheel; a motor disposed between the first drive wheel and the second drive wheel; a first gear set disposed between the first drive wheel and the motor and receiving driving force from the motor; a first brake disposed between the first gear set and the first drive wheel; a first clutch disposed between the first gear set and the first brake; a second gear set disposed between the second drive wheel and the motor and receiving driving force from the motor; a second brake disposed between the second gear set and the second drive wheel; and a second clutch disposed between the second gear set and the second brake.

8. The drive system according to claim 7, comprising: a first final drive assembly that transmits the driving force from the motor to a first drive wheel; and a second final drive assembly that transmits the driving force from the motor to a second drive wheel, wherein the first gear set is disposed between the motor and the first final drive assembly; the second gear set is disposed between the motor and the second final drive assembly; the first brake is disposed between the first gear set and the first final drive assembly; and the second brake is disposed between the second gear set and the second final drive assembly.

9. The drive system according to claim 7, wherein the first clutch is released when the first brake performs a braking operation.

10. The drive system according to claim 8, wherein the second clutch is released when the second brake performs a braking operation.

11. A work machine comprising: a vehicle body; a running device supporting the vehicle body; and a drive system according to claim 7 for driving the running device.

12. A drive system for a work machine, comprising: a first drive wheel; a second drive wheel; a motor disposed between the first drive wheel and the second drive wheel; a planetary gear mechanism that receives driving force from the motor; a first brake disposed between the planetary gear mechanism and the first drive wheel; a first clutch disposed between the planetary gear mechanism and the first brake; a second brake disposed between the planetary gear mechanism and the second drive wheel; and a second clutch disposed between the planetary gear mechanism and the second brake.

13. The drive system according to claim 12, wherein the planetary gear mechanism includes a sun gear, a planetary gear meshing with the sun gear, a ring gear meshing with the planetary gear, and a carrier connected to the planetary gear, and the first clutch and the second clutch are each connected to the carrier.

14. A work machine comprising: a vehicle body; a running device supporting the vehicle body; and a drive system according to claim 12 for driving the running device.

Images