Hydraulic actuating mechanism and hydraulic system

Abstract

The utility model relates to a hydraulic actuating mechanism and a hydraulic system. The hydraulic actuating mechanism comprises a two-way oil pump, a first one-way valve and an energy accumulator. The two-way oil pump is configured to pump hydraulic oil between the first end and the second end in the mode that the pumping direction can be switched. Wherein the first end is communicated with a clutch oil cylinder port through a pipeline, the second end is communicated with a cooling and lubricating port through a pipeline, and the first end and the second end are both communicated with an oil inlet port through pipelines. The first one-way valve is configured to allow the hydraulic oil to flow from the first end to a port of the clutch oil cylinder in a one-way mode. And the energy accumulator is arranged between the first one-way valve and the port of the clutch oil cylinder. According to the hydraulic actuating mechanism, when the clutch is in a joint state, the pressure in the oil cylinder of the clutch is more stable, and the energy consumption of a system is lower.

Description

Technical Field

[0001] This utility model relates to the field of hybrid power transmission technology. Specifically, this utility model relates to a hydraulic actuator and a hydraulic system. Background Technology

[0002] In the hydraulic system of a hybrid transmission, when the clutch is engaged, the bidirectional oil pump needs to supply oil to the clutch cylinder. A check valve is installed between the bidirectional oil pump and the clutch cylinder to maintain the pressure in the clutch cylinder. When the oil pressure in the clutch cylinder is within the pressure threshold range, the bidirectional oil pump reverses, causing the bidirectional oil pump to pump oil to other components in the hydraulic system for cooling and lubrication.

[0003] In current designs, the components of the hydraulic system have high rigidity, and the high-pressure chamber is very small. Even minor leaks in the hydraulic system can cause a drop in oil pressure within the clutch cylinder. To maintain a constant oil pressure inside the clutch cylinder, when the oil pressure falls below a pressure threshold, the bidirectional pump needs to reverse again to supply oil to the clutch cylinder until the oil pressure returns to the threshold range. In traditional hydraulic systems, because minor leaks are difficult to avoid, the bidirectional pump needs to frequently reverse, leading to increased system energy consumption. Therefore, an improved hydraulic actuator and hydraulic system are needed to maintain stable oil pressure within the clutch cylinder and reduce system energy consumption. Utility Model Content

[0004] To solve the above technical problems, this utility model provides a hydraulic actuator and a hydraulic system.

[0005] In a first aspect, embodiments of the present invention provide a hydraulic actuator, comprising: a bidirectional oil pump, a first one-way valve, and an accumulator. The bidirectional oil pump is configured to pump hydraulic oil in a switchable direction between a first end and a second end; wherein the first end is connected to a clutch cylinder port via a pipeline, the second end is connected to a cooling / lubrication port via a pipeline, and both the first end and the second end are connected to an oil inlet port via pipelines. The first one-way valve is configured to allow the hydraulic oil to flow unidirectionally from the first end to the clutch cylinder port. The accumulator is disposed between the first one-way valve and the clutch cylinder port. Through the hydraulic actuator of the present invention, the pressure within the clutch cylinder is more stable and the system energy consumption is lower when the clutch is engaged.

[0006] According to some embodiments of the present invention, the pipeline between the first one-way valve and the clutch cylinder port is connected to the oil unloading port.

[0007] According to some embodiments of the present invention, the hydraulic actuator further includes: a first directional valve, a second directional valve, and a pressure sensor. The first directional valve is disposed between the bidirectional oil pump and the first check valve, and is configured to switch between a connected state and a disconnected state; the second directional valve is disposed between the clutch cylinder port and the unloading port, and is configured to switch between a connected state and a disconnected state; the pressure sensor is disposed between the first check valve and the clutch cylinder port to sense the pressure at the clutch cylinder port.

[0008] According to some embodiments of the present invention, the hydraulic actuator further includes: a hydraulic unit controller; wherein the pressure sensor feeds back a pressure signal to the hydraulic unit controller, and the hydraulic unit controller is configured to control the pumping direction of the bidirectional oil pump, control the connection and disconnection of the first directional valve, and control the connection and disconnection of the second directional valve based on the pressure signal.

[0009] According to some embodiments of the present invention, the hydraulic unit controller controls the pumping direction of the bidirectional oil pump via a motor.

[0010] According to some embodiments of the present invention, the hydraulic actuator further includes a suction filter, which is disposed between the bidirectional oil pump and the oil inlet port, and configured to suction and filter the hydraulic oil.

[0011] According to some embodiments of the present invention, a second check valve is provided between the first end of the bidirectional oil pump and the oil inlet port; a third check valve is provided between the second end of the bidirectional oil pump and the oil inlet port; and a fourth check valve is provided between the second end of the bidirectional oil pump and the cooling and lubrication port.

[0012] According to some embodiments of this utility model, the energy accumulator is a spring-type energy accumulator or an air-filled energy accumulator.

[0013] In a second aspect, embodiments of the present invention also provide a hydraulic system, comprising: a hydraulic actuator as described in any of the above embodiments, an oil tank, and a clutch cylinder. The oil tank supplies hydraulic oil to the hydraulic actuator via the oil inlet port, and the hydraulic actuator discharges the hydraulic oil back to the oil tank via the oil outlet port. The clutch cylinder is connected to the hydraulic actuator via the clutch cylinder port.

[0014] According to some embodiments of the present invention, the hydraulic actuator further includes: a first directional valve disposed between the bidirectional oil pump and the first one-way valve, a second directional valve disposed between the clutch cylinder port and the unloading port, a pressure sensor disposed between the first one-way valve and the clutch cylinder port, and a hydraulic unit controller; wherein, the hydraulic unit controller is configured as follows:

[0015] When the clutch cylinder switches to the engaged state, and the pressure of the clutch cylinder sensed by the pressure sensor is less than the pressure threshold, the bidirectional oil pump is controlled to pump the hydraulic oil from the second end to the first end, the first directional valve is controlled to be in the connected state, and the second directional valve is controlled to be in the disconnected state.

[0016] When the clutch cylinder is engaged and the pressure of the clutch cylinder sensed by the pressure sensor is within the pressure threshold range, the bidirectional oil pump is controlled to pump the hydraulic oil from the first end to the second end.

[0017] When the clutch cylinder switches to the disengaged state, the first directional valve is controlled to be in the open state, and the second directional valve is controlled to be in the connected state.

[0018] In the hydraulic actuator and hydraulic system of this invention, an accumulator is installed to store hydraulic oil, increasing the oil storage capacity of the hydraulic system. When the clutch is engaged, if a minor leak occurs in the hydraulic system causing a drop in the oil pressure of the clutch cylinder, the accumulator can release a certain amount of hydraulic oil, keeping the oil pressure in the clutch cylinder within the pressure threshold range. Therefore, installing an accumulator helps maintain stable oil pressure in the clutch cylinder and eliminates the need for the bidirectional oil pump, which is already pumping oil towards the second end, to frequently switch its pumping direction to replenish oil to the clutch cylinder. Thus, energy consumption is lower compared to traditional hydraulic systems. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of a hydraulic system according to an embodiment of the present invention is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the described embodiments of this utility model are within the protection scope of this utility model.

[0022] This invention relates to a hydraulic system in a hybrid transmission, applicable to applications such as vehicles. The clutch in a hybrid transmission switches between engaged and disengaged states via a hydraulic system. In the engaged state, oil is supplied to the clutch cylinder in the hydraulic system, and the pressure needs to be maintained within a pressure threshold range; in the disengaged state, the hydraulic oil in the clutch cylinder needs to be discharged. This invention designs a hydraulic actuator and hydraulic system that enables more stable pressure within the clutch cylinder and lower system energy consumption in the engaged state.

[0023] Figure 1 A schematic diagram of a hydraulic system according to an embodiment of the present invention is shown. Figure 1 As shown, the hydraulic system includes a hydraulic actuator 1, an oil tank 2, and a clutch cylinder 3. When the clutch is engaged, the hydraulic actuator 1 draws hydraulic oil from the oil tank 2 and supplies oil to the clutch cylinder 3 until the pressure in the clutch cylinder 3 is within the pressure threshold range. When the pressure in the clutch cylinder 3 is stable within the pressure threshold range, the hydraulic actuator 1 can also supply oil to other mechanisms for cooling and lubrication. When the clutch is disengaged, the hydraulic actuator 1 discharges the hydraulic oil from the clutch cylinder 3 into the oil tank 2.

[0024] The hydraulic actuator 1 provided by this utility model is described in detail below. In some embodiments, see Figure 1 As shown, the hydraulic actuator 1 includes: a bidirectional oil pump 11, a first check valve CV1, and an accumulator 12.

[0025] Specifically, the bidirectional oil pump 11 is configured to pump hydraulic oil in a switchable direction between a first end 11a and a second end 11b; wherein the first end 11a is connected to the clutch cylinder port 1a via a pipeline, the second end 11b is connected to the cooling and lubrication port 1b via a pipeline, and both the first end 11a and the second end 11b are connected to the oil inlet port 1c via pipelines; wherein the clutch cylinder port 1a is connected to the clutch cylinder 3, the cooling and lubrication port 1b is connected to other mechanisms in the hybrid transmission that require cooling and lubrication, and the oil inlet port 1c is connected to the cylinder 2. Thus, when the bidirectional oil pump 11 switches to pump oil from the second end 11b to the first end 11a, the hydraulic oil is pumped to the clutch cylinder port 1a. At this time, the hydraulic actuator 1 is used to supply oil to the clutch cylinder 3 to provide hydraulic energy. When the bidirectional oil pump 11 switches to pump oil from the first end 11a to the second end 11b, the bidirectional oil pump 11 stops supplying oil to the clutch cylinder port 1a and instead supplies oil to the cooling and lubrication port 1b to cool and lubricate other mechanisms in the hybrid transmission.

[0026] The first check valve CV1 is configured to allow hydraulic oil to flow unidirectionally from the first end 11a to the clutch cylinder port 1a. In other words, the first check valve CV1 can prevent the hydraulic oil in the clutch cylinder 3 from flowing back, thereby maintaining the stability of the oil pressure in the clutch cylinder 3 when the clutch is engaged.

[0027] Accumulator 12 is located between the first one-way valve CV1 and the clutch cylinder port 1a. Accumulator 12 is an energy storage device in the hydraulic system. Accumulator 12 can store hydraulic oil, increasing the oil storage capacity of the hydraulic system. When the bidirectional oil pump supplies oil to the clutch cylinder port 1a, accumulator 12 can convert oil pressure into compressive energy or potential energy and store it. When the clutch is engaged, if a small leak occurs in the hydraulic system and causes a drop in oil pressure in the clutch cylinder 3, accumulator 12 can release a certain amount of hydraulic oil, converting the stored compressive energy or potential energy into hydraulic energy and releasing it to supply the hydraulic system. This keeps the oil pressure in the clutch cylinder 3 within the pressure threshold range. Therefore, setting up accumulator 12 helps to maintain the stability of oil pressure in the clutch cylinder 3 without requiring the bidirectional oil pump 11, which is already pumping oil to the second end 11b, to frequently switch the pumping direction to supply oil to the clutch cylinder 3. Therefore, it consumes less energy compared to traditional hydraulic systems. Of course, when the pressure of the hydraulic system increases instantaneously, the accumulator 12 can also absorb some energy to ensure that the pressure of the entire system is normal.

[0028] The accumulator 12 can be a spring-type accumulator or an air-filled accumulator, and this utility model does not limit it in this regard.

[0029] It should be understood that the accumulator 12 is an automatic pressure regulating device. When a minor leak occurs in the hydraulic system, causing a drop in the oil pressure of the clutch cylinder 3, and the hydraulic energy replenished by the accumulator 12 to the clutch cylinder 3 is insufficient to compensate for the lost hydraulic energy, the bidirectional oil pump 11 will still switch the pumping direction, supplying oil from the second end 11b to the first end 11a to replenish the lost hydraulic energy to the clutch cylinder 3. The accumulator 12 significantly reduces the number of times the bidirectional oil pump 11 needs to perform this hydraulic energy replenishment switching.

[0030] Further, see Figure 1 As shown, the pipeline between the first check valve CV1 and the clutch cylinder port 1a is connected to the oil discharge port 1d. The oil discharge port 1d is connected to the oil tank 2. When the clutch switches from the engaged state to the disengaged state, the hydraulic energy in the clutch cylinder 3 needs to be discharged. The hydraulic oil in the clutch cylinder 3 is discharged into the oil tank 2 through the oil discharge port 1d, while the first check valve CV1 prevents the hydraulic oil from flowing back to the bidirectional oil pump 11 side.

[0031] In some embodiments, such as Figure 1 As shown, the hydraulic actuator 1 may also include a first directional valve V1, a second directional valve V2, and a pressure sensor P.

[0032] Specifically, the first directional valve V1 is located between the bidirectional oil pump 11 and the first check valve CV1, and is configured to switch between an on and off state. Optionally, the first directional valve V1 can be a two-position two-way solenoid valve. When the clutch switches from an engaged state to an engaged state, and when the clutch remains engaged, the first directional valve V1 switches to the on state. While the bidirectional oil pump 11 typically no longer needs to supply oil to the clutch cylinder 3 when the clutch remains engaged, it still needs to supply oil to the clutch cylinder 3 in cases of minor hydraulic system leakage as mentioned above, where the accumulator 12 is insufficient to compensate for the hydraulic energy lost by the clutch cylinder 3. Therefore, the first directional valve V1 also needs to remain on state when the clutch remains engaged. When the clutch switches from an engaged state to an disengaged state, and when the clutch remains disengaged, the first directional valve V1 switches to the off state.

[0033] The second directional valve V2 is located between the clutch cylinder port 1a and the unloading port 1d, and is configured to switch between an engaged state and an unengaged state. Optionally, the second directional valve V2 can be a two-position two-way solenoid valve. When the clutch switches from the disengaged state to the engaged state, and when the clutch remains in the engaged state, the second directional valve V2 switches to the unengaged state, so that the hydraulic oil on the clutch cylinder 3 side is not unloaded. When the clutch switches from the engaged state to the disengaged state, and when the clutch remains in the disengaged state, the second directional valve V2 switches to the engaged state to unload the hydraulic oil on the clutch cylinder 3 side into the oil tank 2.

[0034] The pressure sensor P is set between the first one-way valve CV1 and the clutch cylinder port 1a to sense the pressure at the clutch cylinder port 1a. That is, the pressure sensor P can detect the oil pressure of the clutch cylinder 3 in real time, so as to determine whether the clutch cylinder 3 is within the pressure threshold range when the clutch is switched to and engaged, and then determine whether the bidirectional oil pump 11 needs to be operated to turn and replenish oil.

[0035] Further, see Figure 1 As shown, the hydraulic actuator 1 also includes a hydraulic unit controller 13. The pressure sensor P can feed back the pressure signal from one side of the clutch cylinder 3 to the hydraulic unit controller 13. The hydraulic unit controller 13 is configured to control the pumping direction of the bidirectional oil pump 11, control the connection and disconnection of the first directional valve V1, and control the connection and disconnection of the second directional valve V2 based on the pressure signal.

[0036] When the clutch switches from the disengaged state to the engaged state, and when the clutch remains in the engaged state, the hydraulic unit controller 13 controls the first directional valve V1 to switch to the connected state and controls the second directional valve V2 to switch to the disengaged state. When the clutch switches from the engaged state to the disengaged state, and when the clutch remains in the disengaged state, the hydraulic unit controller 13 controls the first directional valve V1 to switch to the disengaged state and controls the second directional valve V2 to switch to the connected state.

[0037] Furthermore, the pressure sensor P can feed back the pressure signal from one side of the clutch cylinder 3 to the hydraulic unit controller 13 in real time. It can be understood that since the accumulator 12 is an automatically regulating and stabilizing device, when the clutch is engaged, if a minor leak occurs in the hydraulic system but the accumulator 12 is sufficient to compensate for the hydraulic energy lost by the clutch cylinder 3, the oil pressure of the clutch cylinder 3 detected by the pressure sensor P will still remain within the pressure threshold range. At this time, the bidirectional oil pump 11 can still supply oil to the cooling and lubrication port 1b without needing to change the pumping direction. If a minor leak occurs in the hydraulic system and the accumulator 12 is insufficient to compensate for the hydraulic energy lost by the clutch cylinder 3, the oil pressure detected by the pressure sensor P will remain within the pressure threshold range. When the oil pressure in clutch cylinder 3 is less than the pressure threshold, the pressure signal is fed back to the hydraulic unit controller 13. At this time, the hydraulic unit controller 13 controls the bidirectional oil pump 11 to switch the pumping direction, switching to supply oil to clutch cylinder 3 from the second end 11b to the first end 11a to replenish hydraulic energy, until the pressure sensor P detects that the oil pressure on one side of clutch cylinder 3 has reached the pressure threshold range. Then, the hydraulic unit controller 13 controls the bidirectional oil pump 11 to switch the pumping direction again, switching to supply oil to the cooling lubrication port 1b from the first end 11a to the second end 11b.

[0038] The hydraulic unit controller 13 can control the pumping direction of the bidirectional oil pump 11 via the motor M.

[0039] In some embodiments, the hydraulic actuator 1 further includes a suction filter 14. For example... Figure 1 As shown, the suction filter 14 is located between the bidirectional oil pump 11 and the oil inlet port 1c, and is configured to suction and filter the hydraulic oil supplied from the oil tank 2 to filter out impurities in the hydraulic oil.

[0040] In some embodiments, such as Figure 1 As shown, a second check valve CV2 is provided between the first end 11a of the bidirectional oil pump 11 and the oil inlet port 1c; a third check valve CV3 is provided between the second end 11b of the bidirectional oil pump 11 and the oil inlet port 1c; the second check valve CV2 and the third check valve CV3 are connected in parallel on both sides of the bidirectional oil pump 11 so that the hydraulic oil flows unidirectionally between the oil tank 2 and the bidirectional oil pump 11, preventing the backflow of hydraulic oil.

[0041] Optionally, a fourth check valve CV4 may be provided between the second end 11b of the bidirectional oil pump 11 and the cooling and lubrication port 1b to allow hydraulic oil to flow unidirectionally between the other mechanisms of the hybrid transmission that require cooling and lubrication and the bidirectional oil pump 11, preventing backflow of hydraulic oil.

[0042] This utility model also provides a hydraulic system, such as Figure 1As shown, the hydraulic system includes a hydraulic actuator 1, an oil tank 2, and a clutch cylinder 3 as described in any of the above embodiments. The oil tank 2 supplies hydraulic oil to the hydraulic actuator 1 via an inlet port 1c, and the hydraulic actuator 1 discharges hydraulic oil to the oil tank 2 via an outlet port 1d. The clutch cylinder 3 is connected to the hydraulic actuator 1 via a clutch cylinder port 1a.

[0043] In some embodiments, the hydraulic actuator 1 further includes a first directional valve V1, a second directional valve V2, a pressure sensor P, and a hydraulic unit controller 13. The arrangement of these components is as described in the previous embodiments and will not be repeated here. The hydraulic unit controller 13 is configured as follows:

[0044] When the clutch cylinder 3 switches to the engaged state, and the pressure of the clutch cylinder 3 sensed by the pressure sensor P is less than the pressure threshold, the bidirectional oil pump 11 is controlled to pump hydraulic oil from the second end 11b to the first end 11a, the first directional valve V1 is controlled to be in the connected state, and the second directional valve V2 is controlled to be in the disconnected state.

[0045] When the clutch cylinder 3 is engaged, and the pressure of the clutch cylinder 3 sensed by the pressure sensor P is within the pressure threshold range, the bidirectional oil pump 11 is controlled to pump hydraulic oil from the first end 11a to the second end 11b.

[0046] When the clutch cylinder 3 switches to the disengaged state, the first directional valve V1 is controlled to be in the open state, and the second directional valve V2 is controlled to be in the connected state.

[0047] While possible embodiments have been described exemplarily in the foregoing description, it should be understood that numerous variations of the embodiments exist through combinations of all known and readily conceived technical features and implementation methods. Furthermore, it should be understood that the exemplary embodiments are merely examples and do not in any way limit the scope, application, or construction of this invention. The foregoing description is more intended to provide those skilled in the art with technical guidance for transforming at least one exemplary embodiment, wherein various changes, particularly regarding the function and structure of the components, can be made without departing from the scope of the claims.

Claims

1. A hydraulic actuator, characterized by include: A bidirectional oil pump (11) is configured to pump hydraulic oil in a switchable pumping direction between a first end (11a) and a second end (11b); wherein the first end (11a) is connected to the clutch cylinder port (1a) via a pipeline, the second end (11b) is connected to the cooling lubrication port (1b) via a pipeline, and both the first end (11a) and the second end (11b) are connected to the oil inlet port (1c) via pipelines. A first check valve (CV1) is configured to allow unidirectional flow of hydraulic oil from the first end (11a) to the clutch cylinder port (1a); and An accumulator (12) is disposed between the first one-way valve (CV1) and the clutch cylinder port (1a).

2. The hydraulic actuator of claim 1, wherein, The pipeline between the first one-way valve (CV1) and the clutch cylinder port (1a) is connected to the unloading port (1d).

3. The hydraulic actuator of claim 2, wherein, Also includes: The first directional valve (V1) is disposed between the bidirectional oil pump (11) and the first check valve (CV1) and is configured to switch between a connected state and a disconnected state; A second directional valve (V2) is disposed between the clutch cylinder port (1a) and the unloading port (1d) and is configured to switch between a connected state and a disconnected state. as well as A pressure sensor (P) is disposed between the first check valve (CV1) and the clutch cylinder port (1a) to sense the pressure at the clutch cylinder port (1a).

4. The hydraulic actuator of claim 3, wherein Also includes: Hydraulic unit controller (13); The pressure sensor (P) feeds back the pressure signal to the hydraulic unit controller (13), which is configured to control the pumping direction of the bidirectional oil pump (11), control the connection and disconnection of the first directional valve (V1), and control the connection and disconnection of the second directional valve (V2) based on the pressure signal.

5. The hydraulic actuator of claim 4, wherein, The hydraulic unit controller (13) controls the pumping direction of the bidirectional oil pump (11) via a motor (M).

6. The hydraulic actuator of claim 1, wherein, Also includes: A suction filter (14) is disposed between the bidirectional oil pump (11) and the oil inlet port (1c) and is configured to suction and filter the hydraulic oil.

7. The hydraulic actuator of claim 1, wherein A second check valve (CV2) is provided between the first end (11a) of the bidirectional oil pump (11) and the oil inlet port (1c); a third check valve (CV3) is provided between the second end (11b) of the bidirectional oil pump (11) and the oil inlet port (1c); and a fourth check valve (CV4) is provided between the second end (11b) of the bidirectional oil pump (11) and the cooling and lubrication port (1b).

8. The hydraulic actuator of claim 1, wherein, The accumulator (12) is a spring-type accumulator or an air-filled accumulator.

9. A hydraulic system characterized by, include: Hydraulic actuator (1) as described in any one of claims 1-8; An oil tank (2) supplies hydraulic oil to the hydraulic actuator (1) via the oil inlet port (1c), and the hydraulic actuator (1) discharges the hydraulic oil to the oil tank (2) via the oil outlet port (1d); and The clutch cylinder (3) is connected to the hydraulic actuator (1) via the clutch cylinder port (1a).

10. The hydraulic system of claim 9, wherein, The hydraulic actuator (1) further includes: a first directional valve (V1) disposed between the bidirectional oil pump (11) and the first check valve (CV1), a second directional valve (V2) disposed between the clutch cylinder port (1a) and the unloading port (1d), a pressure sensor (P) disposed between the first check valve (CV1) and the clutch cylinder port (1a), and a hydraulic unit controller (13). The hydraulic unit controller (13) is configured as follows: When the clutch cylinder (3) switches to the engaged state, and the pressure of the clutch cylinder (3) sensed by the pressure sensor (P) is less than the pressure threshold, the bidirectional oil pump (11) is controlled to pump the hydraulic oil from the second end (11b) to the first end (11a), the first directional valve (V1) is controlled to be in the connected state, and the second directional valve (V2) is controlled to be in the disconnected state. When the clutch cylinder (3) is engaged, and the pressure of the clutch cylinder (3) sensed by the pressure sensor (P) is within the pressure threshold range, the bidirectional oil pump (11) is controlled to pump the hydraulic oil from the first end (11a) to the second end (11b). When the clutch cylinder (3) switches to the disengaged state, the first reversing valve (V1) is controlled to be in the open state, and the second reversing valve (V2) is controlled to be in the connected state.

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