Vehicle height adjustment system

Abstract

To provide a vehicle height adjustment system which can achieve shortening of a time required for adjustment of a vehicle height.SOLUTION: A vehicle height adjustment system 100 adjusts a height position of a vehicle body with respect to a wheel, and comprises: hydraulic cylinders 1FL and 1FR which are provided between front wheel holding members 51FL and 51FR and the vehicle body, and are telescopically moved by hydraulic oil; a hydraulic oil supply / discharge device 2F which supplies / discharges the hydraulic oil to the hydraulic cylinders 1FL and 1FR; hydraulic cylinders 1RL and 1RR which are provided between rear wheel holding members 51RL and 51RR and the vehicle body, and are telescopically moved by the hydraulic oil; and a hydraulic oil supply / discharge device 2R which are provided separately from the hydraulic oil supply / discharge device 2F, and supplies / discharges the hydraulic oil to the hydraulic cylinders 1RL and 1RR.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vehicle height adjustment system.

Background Art

[0002] Conventionally, a vehicle height adjustment system for adjusting the height position of a vehicle body with respect to wheels has been known (see, for example, Patent Document 1).

[0003] The vehicle height adjustment system of Patent Document 1 includes four actuators and a fluid supply / discharge device that supplies and discharges fluid to and from the four actuators. The four actuators are expandable and contractible by the fluid from the fluid supply / discharge device, and are provided between each holding member that holds each of the four front, rear, left, and right wheels and the vehicle body. In this vehicle height adjustment system, the control of the two actuators on the front wheel side and the control of the two actuators on the rear wheel side are alternately performed, so that the vehicle height is alternately adjusted on the front wheel side and the rear wheel side.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in the vehicle height adjustment system as described above, there is room for improvement in shortening the time required for adjusting the vehicle height.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a vehicle height adjustment system capable of shortening the time required for adjusting the vehicle height.

Means for Solving the Problems

[0007] The vehicle height adjustment system according to the present invention adjusts the height position of the vehicle body with respect to the wheels, and is provided between the front wheel holding member and the vehicle body. Working oil A front wheel side actuator that expands and contracts by Working oil A front wheel side fluid supply and discharge device that supplies and discharges A front-wheel-side hydraulic circuit provided between the front-wheel-side actuator and the front-wheel-side fluid supply / discharge device and having a front-wheel-side vehicle height adjustment valve, is provided between the rear wheel holding member and the vehicle body. Working oil A rear wheel side actuator that expands and contracts by Working oil A rear wheel side fluid supply and discharge device that supplies and discharges A rear-wheel-side hydraulic circuit provided between the rear-wheel-side actuator and the rear-wheel-side fluid supply / discharge device and having a rear-wheel-side vehicle height adjustment valve is provided. Also, The front-wheel-side fluid supply and discharge device includes a front-wheel-side reservoir tank in which hydraulic oil is stored, a front-wheel-side oil pump that pumps up the hydraulic oil in the front-wheel-side reservoir tank and supplies it to the front-wheel-side hydraulic circuit, a front-wheel-side check valve that allows the flow of hydraulic oil from the front-wheel-side oil pump toward the front-wheel-side hydraulic circuit while blocking the flow of hydraulic oil from the front-wheel-side hydraulic circuit toward the front-wheel-side oil pump, and a front-wheel-side return valve that is arranged in parallel with the front-wheel-side check valve on the discharge port side of the front-wheel-side oil pump and can be switched between a front-wheel-side first state in which the discharge port side of the front-wheel-side oil pump and the front-wheel-side hydraulic circuit are blocked and the front-wheel-side hydraulic circuit is communicated with the front-wheel-side reservoir tank side, and a front-wheel-side second state in which the front-wheel-side reservoir tank side and the front-wheel-side hydraulic circuit are blocked and the front-wheel-side hydraulic circuit is communicated with the discharge port side of the front-wheel-side oil pump. Further, the rear-wheel-side fluid supply and discharge device includes a rear-wheel-side reservoir tank in which hydraulic oil is stored, a rear-wheel-side oil pump that pumps up the hydraulic oil in the rear-wheel-side reservoir tank and supplies it to the rear-wheel-side hydraulic circuit, a rear-wheel-side check valve that allows the flow of hydraulic oil from the rear-wheel-side oil pump toward the rear-wheel-side hydraulic circuit while blocking the flow of hydraulic oil from the rear-wheel-side hydraulic circuit toward the rear-wheel-side oil pump, and a rear-wheel-side return valve that is arranged in parallel with the rear-wheel-side check valve on the discharge port side of the rear-wheel-side oil pump and can be switched between a rear-wheel-side first state in which the discharge port side of the rear-wheel-side oil pump and the rear-wheel-side hydraulic circuit are blocked and the rear-wheel-side hydraulic circuit is communicated with the rear-wheel-side reservoir tank side, and a rear-wheel-side second state in which the rear-wheel-side reservoir tank side and the rear-wheel-side hydraulic circuit are blocked and the rear-wheel-side hydraulic circuit is communicated with the discharge port side of the rear-wheel-side oil pump. Also, a front-wheel-side hydraulic sensor is provided for detecting the hydraulic pressure between the front-wheel-side vehicle height adjustment valve and the front-wheel-side return valve in the front-wheel-side hydraulic circuit, and a rear-wheel-side hydraulic sensor is provided for detecting the hydraulic pressure between the rear-wheel-side vehicle height adjustment valve and the rear-wheel-side return valve in the rear-wheel-side hydraulic circuit. And the front-wheel-side return valve is configured to be in the front-wheel-side first state when the front-wheel-side oil pump is stopped and in the front-wheel-side second state when the front-wheel-side oil pump is operating, and the rear-wheel-side return valve is configured to be in the rear-wheel-side first state when the rear-wheel-side oil pump is stopped and in the rear-wheel-side second state when the rear-wheel-side oil pump is operating.

[0008] By configuring in this way, the control of the front wheel side actuator by the front wheel side fluid supply and discharge device and the control of the rear wheel side actuator by the rear wheel side fluid supply and discharge device are performed simultaneously, so that the time required for vehicle height adjustment can be shortened.

Advantages of the Invention

[0009] According to the vehicle height adjustment system of the present invention, the time required for vehicle height adjustment can be shortened.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described.

[0012] First, with reference to FIG. 1, a vehicle height adjustment system 100 according to an embodiment of the present invention will be described.

[0013] The vehicle height adjustment system 100 is configured to adjust the height position of the vehicle body (not shown) relative to the wheels in a vehicle. As shown in FIG. 1, the wheels include a left front wheel 50FL, a right front wheel 50FR, a left rear wheel 50RL, and a right rear wheel 50RR. The front wheel 50FL is rotatably held by a front wheel holding member 51FL, the front wheel 50FR is rotatably held by a front wheel holding member 51FR, the rear wheel 50RL is rotatably held by a rear wheel holding member 51RL, and the rear wheel 50RR is rotatably held by a rear wheel holding member 51RR.

[0014] The vehicle height adjustment system 100 includes hydraulic cylinders 1FL, 1FR, 1RL, and 1RR, hydraulic fluid supply and discharge devices 2F and 2R, hydraulic circuits 3F and 3R, and ECUs 4F and 4R. Note that the hydraulic cylinders 1FL and 1FR are an example of the "front wheel side actuator" of the present invention, and the hydraulic cylinders 1RL and 1RR are an example of the "rear wheel side actuator" of the present invention. The hydraulic fluid supply and discharge device 2F is an example of the "front wheel side fluid supply and discharge device" of the present invention, and the hydraulic fluid supply and discharge device 2R is an example of the "rear wheel side fluid supply and discharge device" of the present invention.

[0015] The hydraulic cylinders 1FL and 1FR are configured to be controlled by the hydraulic fluid supply and discharge device 2F, the hydraulic circuit 3F, and the ECU 4F. The hydraulic cylinders 1RL and 1RR are configured to be controlled by the hydraulic fluid supply and discharge device 2R, the hydraulic circuit 3R, and the ECU 4R. That is, the control system for controlling the hydraulic cylinders 1FL and 1FR on the front wheel side and the control system for controlling the hydraulic cylinders 1RL and 1RR on the rear wheel side are separated and independent.

[0016] The hydraulic cylinder 1FL is provided between the front wheel holding member 51FL and the vehicle body. The hydraulic cylinder 1FL functions as a shock absorber and is configured to be able to adjust the distance between the front wheel holding member 51FL and the vehicle body by expanding and contracting. A suspension spring (not shown) is provided in parallel with the hydraulic cylinder 1FL between the front wheel holding member 51FL and the vehicle body.

[0017] Specifically, the hydraulic cylinder 1FL includes a housing 11, a piston 12, and a piston rod 13. The housing 11 has an internal space, in which the piston 12 is movably accommodated, and the piston rod 13 is connected to the piston 12. The housing 11 is connected to the front wheel holding member 51FL, and the piston rod 13 is connected to the vehicle body. The internal space of the housing 11 is partitioned by the piston 12, and oil chambers 14 and 15 are formed. A communication passage 16 for communicating the oil chambers 14 and 15 is formed in the piston 12, and a throttle is provided in the communication passage 16. Therefore, the hydraulic cylinder 1FL is configured to generate a damping force according to the moving speed of the piston 12 with respect to the housing 11.

[0018] The hydraulic cylinder 1FR is provided between the front wheel holding member 51FR and the vehicle body. The hydraulic cylinder 1RL is provided between the rear wheel holding member 51RL and the vehicle body. The hydraulic cylinder 1RR is provided between the rear wheel holding member 51RR and the vehicle body. The other configurations of the hydraulic cylinders 1FR, 1RL, and 1RR are the same as those of the hydraulic cylinder 1FL described above.

[0019] The hydraulic fluid supply and discharge device 2F is provided for supplying and discharging hydraulic fluid to and from the hydraulic cylinders 1FL and 1FR via a hydraulic circuit 3F. The hydraulic fluid supply and discharge device 2F includes an oil pump 21F, a motor 22F for operating the oil pump 21F, a reservoir tank 23F in which the hydraulic fluid is stored, and a check valve 24F and a return valve 25F arranged in parallel on the discharge port side of the oil pump 21F. Note that the hydraulic fluid is an example of the "fluid" of the present invention.

[0020] The oil pump 21F is provided to pump up the hydraulic oil in the reservoir tank 23F and supply it to a common passage 31F (described later) of the hydraulic circuit 3F. The check valve 24F is configured to allow the flow of the hydraulic oil from the oil pump 21F toward the common passage 31F while blocking the flow of the hydraulic oil from the common passage 31F toward the oil pump 21F. The return valve 25F is provided to switch between the supply of the hydraulic oil from the oil pump 21F to the common passage 31F and the discharge of the hydraulic oil from the common passage 31F to the reservoir tank 23F. Specifically, when the oil pump 21F is stopped, the return valve 25F shuts off the discharge port side of the oil pump 21F and the common passage 31F, connects the common passage 31F to the reservoir tank 23F side, and when the oil pump 21F is operating, shuts off the reservoir tank 23F side and the common passage 31F, and connects the common passage 31F to the discharge port side of the oil pump 21F.

[0021] The hydraulic circuit 3F is provided between the hydraulic cylinders 1FL and 1FR and the hydraulic oil supply and discharge device 2F. The hydraulic circuit 3F includes a common passage 31F, individual passages 32FL and 32FR, vehicle height adjustment valves 33FL and 33FR, and accumulators 34FL and 34FR.

[0022] The common passage 31F is connected to the hydraulic oil supply and discharge device 2F and is provided with a hydraulic pressure sensor 41F. The individual passage 32FL is connected to the common passage 31F via the vehicle height adjustment valve 33FL. The individual passage 32FL is provided with the hydraulic cylinder 1FL and the accumulator 34FL. The individual passage 32FR is connected to the common passage 31F via the vehicle height adjustment valve 33FR. The individual passage 32FR is provided with the hydraulic cylinder 1FR and the accumulator 34FR.

[0023] The vehicle height adjustment valve 33FL is, for example, a normally closed electromagnetic on-off valve provided to connect or disconnect the individual passage 32FL to / from the common passage 31F. The vehicle height adjustment valve 33FL is configured to open when the hydraulic oil of the hydraulic cylinder 1FL is supplied or discharged. The accumulator 34FL has a gas chamber and an oil chamber formed by partitioning the internal space of the housing with a partition member. The gas chamber is filled with gas, and the oil chamber is connected to the individual passage 32FL. The accumulator 34FL is configured such that the volumes of the gas chamber and the oil chamber change according to the hydraulic pressure in the individual passage 32FL, and functions as a gas spring that generates an elastic force for the telescopic movement of the hydraulic cylinder 1FL.

[0024] The vehicle height adjustment valve 33FR is, for example, a normally closed electromagnetic on-off valve provided to connect or disconnect the individual passage 32FR to / from the common passage 31F. The vehicle height adjustment valve 33FR is configured to open when the hydraulic oil of the hydraulic cylinder 1FR is supplied or discharged. The accumulator 34FR has a gas chamber and an oil chamber formed by partitioning the internal space of the housing with a partition member. The gas chamber is filled with gas, and the oil chamber is connected to the individual passage 32FR. The accumulator 34FR is configured such that the volumes of the gas chamber and the oil chamber change according to the hydraulic pressure in the individual passage 32FR, and functions as a gas spring that generates an elastic force for the telescopic movement of the hydraulic cylinder 1FR.

[0025] The ECU 4F is configured to adjust the vehicle height on the front wheel 50FL and 50FR sides. An operation switch (not shown), a vehicle height sensor (not shown), a hydraulic pressure sensor 41F, a motor 22F, vehicle height adjustment valves 33FL and 33FR, etc. are connected to the ECU 4F. The operation switch is provided to receive a vehicle height adjustment instruction from the user. The vehicle height sensor is provided to detect the distance between the front wheel holding member 51FL and the vehicle body and to detect the distance between the front wheel holding member 51FR and the vehicle body. The hydraulic pressure sensor 41F is provided to detect the hydraulic pressure of the hydraulic cylinders 1FL and 1FR. The ECU 4F is configured to control the motor 22F, the vehicle height adjustment valves 33FL and 33FR based on inputs from the operation switch, the vehicle height sensor, the hydraulic pressure sensor 41F, etc.

[0026] The hydraulic oil supply / discharge device 2R is provided to supply and discharge hydraulic oil to and from the hydraulic cylinders 1RL and 1RR via the hydraulic circuit 3R. That is, the hydraulic oil supply / discharge device 2R is provided separately from the hydraulic oil supply / discharge device 2F. The hydraulic oil supply / discharge device 2R includes an oil pump 21R, a motor 22R that operates the oil pump 21R, a reservoir tank 23R in which the hydraulic oil is stored, and a check valve 24R and a return valve 25R that are arranged in parallel on the discharge port side of the oil pump 21R.

[0027] The oil pump 21R is provided to pump up the hydraulic oil in the reservoir tank 23R and supply it to a common passage 31R (described later) of the hydraulic circuit 3R. The check valve 24R is configured to allow the flow of hydraulic oil from the oil pump 21R toward the common passage 31R while blocking the flow of hydraulic oil from the common passage 31R toward the oil pump 21R. The return valve 25R is provided to switch between the supply of hydraulic oil from the oil pump 21R to the common passage 31R and the discharge of hydraulic oil from the common passage 31R to the reservoir tank 23R. Specifically, when the oil pump 21R is stopped, the return valve 25R blocks the discharge port side of the oil pump 21R and the common passage 31R, connects the common passage 31R to the reservoir tank 23R side, and when the oil pump 21R is operating, blocks the reservoir tank 23R side and the common passage 31R, and connects the common passage 31R to the discharge port side of the oil pump 21R.

[0028] The hydraulic circuit 3R is provided between the hydraulic cylinders 1RL and 1RR and the hydraulic oil supply / discharge device 2R. The hydraulic circuit 3R includes a common passage 31R, individual passages 32RL and 32RR, vehicle height adjustment valves 33RL and 33RR, and accumulators 34RL and 34RR.

[0029] The common passage 31R is connected to the hydraulic oil supply / discharge device 2R and is provided with a hydraulic pressure sensor 41R. The individual passage 32RL is connected to the common passage 31R via the vehicle height adjustment valve 33RL. The individual passage 32RL is provided with the hydraulic cylinder 1RL and the accumulator 34RL. The individual passage 32RR is connected to the common passage 31R via the vehicle height adjustment valve 33RR. The individual passage 32RR is provided with the hydraulic cylinder 1RR and the accumulator 34RR.

[0030] The vehicle height adjustment valve 33RL is, for example, a normally closed electromagnetic on-off valve, and is provided to connect or disconnect the individual passage 32RL to or from the common passage 31R. The vehicle height adjustment valve 33RL is configured to open when the hydraulic oil of the hydraulic cylinder 1RL is supplied or discharged. The accumulator 34RL has a gas chamber and an oil chamber formed by partitioning the internal space of the housing with a partition member. The gas chamber is filled with gas, and the oil chamber is connected to the individual passage 32RL. The accumulator 34RL is configured such that the volumes of the gas chamber and the oil chamber change according to the hydraulic pressure in the individual passage 32RL, and functions as a gas spring that generates an elastic force for the telescopic movement of the hydraulic cylinder 1RL.

[0031] The vehicle height adjustment valve 33RR is, for example, a normally closed electromagnetic on-off valve, and is provided to connect or disconnect the individual passage 32RR to or from the common passage 31R. The vehicle height adjustment valve 33RR is configured to open when the hydraulic oil of the hydraulic cylinder 1RR is supplied or discharged. The accumulator 34RR has a gas chamber and an oil chamber formed by partitioning the internal space of the housing with a partition member. The gas chamber is filled with gas, and the oil chamber is connected to the individual passage 32RR. The accumulator 34RR is configured such that the volumes of the gas chamber and the oil chamber change according to the hydraulic pressure in the individual passage 32RR, and functions as a gas spring that generates an elastic force for the telescopic movement of the hydraulic cylinder 1RR.

[0032] The ECU 4R is configured to adjust the vehicle height on the rear wheel 50RL and 50RR sides. An operation switch, a vehicle height sensor (not shown), a hydraulic pressure sensor 41R, a motor 22R, the vehicle height adjustment valves 33RL and 33RR, etc. are connected to the ECU 4R. The vehicle height sensor is provided to detect the distance between the rear wheel holding member 51RL and the vehicle body, and to detect the distance between the rear wheel holding member 51RR and the vehicle body. The hydraulic pressure sensor 41R is provided to detect the hydraulic pressure of the hydraulic cylinders 1RL and 1RR. The ECU 4R is configured to control the motor 22R, the vehicle height adjustment valves 33RL and 33RR based on inputs from the operation switch, the vehicle height sensor, the hydraulic pressure sensor 41R, etc. Further, the ECU 4R is configured to be communicable with the ECU 4F.

[0033] In such a vehicle height adjustment system 100, during vehicle height increase control for increasing the vehicle height, the ECU 4F drives the motor 22F to operate the oil pump 21F, and at the same time, the vehicle height adjustment valves 33FL and 33FR are opened. For this reason, the hydraulic oil discharged from the oil pump 21F is supplied to the hydraulic cylinders 1FL and 1FR via the hydraulic circuit 3F. Also, the ECU 4R drives the motor 22R to operate the oil pump 21R, and at the same time, the vehicle height adjustment valves 33RL and 33RR are opened. For this reason, the hydraulic oil discharged from the oil pump 21R is supplied to the hydraulic cylinders 1RL and 1RR via the hydraulic circuit 3R. As a result, the hydraulic cylinders 1FL, 1FR, 1RL, and 1RR extend and the vehicle height increases. After that, when the vehicle height reaches the target value, the ECU 4F closes the vehicle height adjustment valves 33FL and 33FR, and stops the operation of the oil pump 21F. Also, the ECU 4R closes the vehicle height adjustment valves 33RL and 33RR, and stops the operation of the oil pump 21R.

[0034] Also, in the vehicle height adjustment system 100, during vehicle height decrease control for decreasing the vehicle height, the ECU 4F opens the vehicle height adjustment valves 33FL and 33FR while keeping the oil pump 21F stopped. For this reason, the hydraulic oil in the hydraulic cylinders 1FL and 1FR is returned to the reservoir tank 23F via the hydraulic circuit 3F and the return valve 25F. Also, the ECU 4R opens the vehicle height adjustment valves 33RL and 33RR while keeping the oil pump 21R stopped. For this reason, the hydraulic oil in the hydraulic cylinders 1RL and 1RR is returned to the reservoir tank 23R via the hydraulic circuit 3R and the return valve 25R. As a result, the hydraulic cylinders 1FL, 1FR, 1RL, and 1RR contract and the vehicle height decreases. After that, when the vehicle height reaches the target value, the ECU 4F closes the vehicle height adjustment valves 33FL and 33FR, and the ECU 4R closes the vehicle height adjustment valves 33RL and 33RR.

[0035] -Effect- In this embodiment, as described above, by separately providing the hydraulic fluid supply and discharge device 2F that supplies and discharges hydraulic fluid to the hydraulic cylinders 1FL and 1FR, and the hydraulic fluid supply and discharge device 2R that supplies and discharges hydraulic fluid to the hydraulic cylinders 1RL and 1RR, the control of the hydraulic cylinders 1FL and 1FR by the hydraulic fluid supply and discharge device 2F and the control of the hydraulic cylinders 1RL and 1RR by the hydraulic fluid supply and discharge device 2R are performed simultaneously, thereby shortening the time required for vehicle height adjustment. Also, the load on the oil pumps 21F and motors 22F is reduced, and the load on the oil pumps 21R and motors 22R is reduced, thereby improving durability.

[0036] -Other Embodiments- Note that the embodiments disclosed this time are illustrative in all respects and are not a basis for limiting interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Also, the technical scope of the present invention includes all modifications within the meaning and scope equivalent to the claims.

[0039] Also, in the above embodiment, an example was shown in which the ECU 4F that controls the motor 22F, the vehicle height adjustment valves 33FL and 33FR, and the ECU 4R that controls the motor 22R, the vehicle height adjustment valves 33RL and 33RR are separately provided. However, the present invention is not limited to this, and the motor and vehicle height adjustment valve on the front wheel side and the motor and vehicle height adjustment valve on the rear wheel side may be controlled by one ECU.

[0040] Also, in the above embodiment, a pressure accumulator tank (not shown) that accumulates the hydraulic pressure pressurized by the oil pump 21F may be provided in the common passage 31F, or a pressure accumulator tank (not shown) that accumulates the hydraulic pressure pressurized by the oil pump 21R may be provided in the common passage 31R.

[0041] Further, in the above embodiment, a sub-accumulator (not shown) connectable in parallel with the accumulator 34FL may be provided, a sub-accumulator (not shown) connectable in parallel with the accumulator 34FR may be provided, a sub-accumulator (not shown) connectable in parallel with the accumulator 34RL may be provided, or a sub-accumulator (not shown) connectable in parallel with the accumulator 34RR may be provided.

Industrial Applicability

[0042] The present invention can be used in a vehicle height adjustment system that adjusts the height position of the vehicle body with respect to the wheels.

Explanation of Signs

[0043] 1FL Hydraulic cylinder (front wheel side actuator) 1FR Hydraulic cylinder (front wheel side actuator) 1RL Hydraulic cylinder (rear wheel side actuator) 1RR Hydraulic cylinder (rear wheel side actuator) 2F Hydraulic fluid supply / discharge device (front wheel side fluid supply / discharge device) 2R Hydraulic fluid supply / discharge device (rear wheel side fluid supply / discharge device) 51FL Front wheel holding member 51FR Front wheel holding member 51RL Rear wheel holding member 51RR Rear wheel holding member 100 Vehicle height adjustment system

Claims

【Claim 1】 A vehicle height adjustment system for adjusting the height position of a vehicle body with respect to wheels, comprising: a front wheel side actuator provided between a front wheel holding member and the vehicle body and expanding and contracting by hydraulic oil; a front wheel side fluid supply / discharge device for supplying and discharging hydraulic oil to / from the front wheel side actuator; a front wheel side hydraulic circuit provided between the front wheel side actuator and the front wheel side fluid supply / discharge device and including a front wheel side vehicle height adjustment valve; a rear wheel side actuator provided between a rear wheel holding member and the vehicle body and expanding and contracting by hydraulic oil; a rear wheel side fluid supply / discharge device provided separately from the front wheel side fluid supply / discharge device for supplying and discharging hydraulic oil to / from the rear wheel side actuator; and a rear wheel side hydraulic circuit provided between the rear wheel side actuator and the rear wheel side fluid supply / discharge device and including a rear wheel side vehicle height adjustment valve. The front wheel side fluid supply / discharge device includes: a front wheel side reservoir tank in which hydraulic oil is stored; a front wheel side oil pump for pumping up the hydraulic oil in the front wheel side reservoir tank and supplying it to the front wheel side hydraulic circuit; a front wheel side check valve that allows the flow of hydraulic oil from the front wheel side oil pump toward the front wheel side hydraulic circuit while blocking the flow of hydraulic oil from the front wheel side hydraulic circuit toward the front wheel side oil pump; a front wheel side return valve arranged in parallel with the front wheel side check valve on the discharge port side of the front wheel side oil pump, and capable of switching between a front wheel side first state of blocking the discharge port side of the front wheel side oil pump and the front wheel side hydraulic circuit and communicating the front wheel side hydraulic circuit with the front wheel side reservoir tank side, and a front wheel side second state of blocking the front wheel side reservoir tank side and the front wheel side hydraulic circuit and communicating the front wheel side hydraulic circuit with the discharge port side of the front wheel side oil pump; The rear wheel side fluid supply / discharge device includes: a rear wheel side reservoir tank in which hydraulic oil is stored; a rear wheel side oil pump for pumping up the hydraulic oil in the rear wheel side reservoir tank and supplying it to the rear wheel side hydraulic circuit; a rear wheel side check valve that allows the flow of hydraulic oil from the rear wheel side oil pump toward the rear wheel side hydraulic circuit while blocking the flow of hydraulic oil from the rear wheel side hydraulic circuit toward the rear wheel side oil pump; A rear-wheel-side return valve is arranged in parallel with the rear-wheel-side check valve on the discharge port side of the rear-wheel-side oil pump, and shuts off the discharge port side of the rear-wheel-side oil pump and the rear-wheel-side hydraulic circuit to put the rear-wheel-side hydraulic circuit into a first rear-wheel-side state in which it communicates with the rear-wheel-side reservoir tank, and shuts off the rear-wheel-side reservoir tank side and the rear-wheel-side hydraulic circuit to put the rear-wheel-side hydraulic circuit into a second rear-wheel-side state in which it communicates with the discharge port side of the rear-wheel-side oil pump, and is switchable between these states. A front-wheel-side hydraulic sensor is provided for detecting the hydraulic pressure between the front-wheel-side vehicle height adjustment valve and the front-wheel-side return valve in the front-wheel-side hydraulic circuit. A rear-wheel-side hydraulic sensor is provided for detecting the hydraulic pressure between the rear-wheel-side vehicle height adjustment valve and the rear-wheel-side return valve in the rear-wheel-side hydraulic circuit. The front-wheel-side return valve is configured to be in the first front-wheel-side state when the front-wheel-side oil pump is stopped and in the second front-wheel-side state when the front-wheel-side oil pump is operating. The rear-wheel-side return valve is configured to be in the first rear-wheel-side state when the rear-wheel-side oil pump is stopped and in the second rear-wheel-side state when the rear-wheel-side oil pump is operating. A vehicle height adjustment system characterized by this.

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