JPH0314712A - Hydraulic suspension - Google Patents

Abstract

PURPOSE:To restrict the temperature rise in working oil by employing bypass means for selectively connecting a working oil passage to a discharge passage and controlling that the bypass means is connected when the working oil temperature exceeds a specified value. CONSTITUTION:A high pressure flow passage 18 connected to the delivery side of a pump 6 for drawing up working oil in a reservoir 4 is connected to actuators 1FR - 1RL respectively disposed at respective wheels via high pressure flow passages 18F, 18R respectively for the front and rear wheels and via pressure control valves 32, 34, 36, 38, etc. Respective actuators 1FR - 1RL may be connected to the reservoir 4 via low pressure flow passages 48F, 48R. The high pressure flow passage 18R and the low pressure flow passage 48R are connected to each other via a passage 188 having a throttle 184 and a solenoid open-close valve of normally open type in the middle thereof and via a passage 194 having a pilot operation type open-close valve 192 in the middle thereof. When the working oil temperature detected with a temperature sensor 195 exceeds a specified value, the solenoid open-close valve 186 is controlled to be opened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to suspensions for vehicles such as automobiles, and more particularly to hydraulic suspensions.

Conventional technologyAs one of the hydraulic suspensions for vehicles such as automobiles,
For example, as described in Japanese Utility Model Application Publication No. 63-184111, there is a reservoir for storing hydraulic oil, a hydraulic oil supply passage and a hydraulic oil discharge passage communicating with the reservoir, and high-pressure hydraulic oil is supplied from the reservoir to the supply passage. a pump for detecting the temperature of the hydraulic oil, a hydraulic actuator disposed between the wheels and the vehicle body, a pressure adjusting means for adjusting the hydraulic pressure in the actuator, and a pressure: A! ! the control means controls the drive current supplied to the pressure regulating means according to the temperature of the hydraulic oil, thereby preventing malfunctions caused by the viscosity of the hydraulic oil varying depending on the temperature. Hydraulic suspensions designed to avoid this are already known.

Problems to be Solved by the Invention Even in such a suspension, normal operation continues even if the temperature of the hydraulic oil rises, so when the temperature of the hydraulic oil rises, the temperature of the oil seals, packings, etc. also rises, causing damage to these parts. As a result, problems such as seal failure and hydraulic oil leakage may occur.

In view of the above-mentioned problems in conventional hydraulic suspensions, it is an object of the present invention to provide a hydraulic suspension configured to reduce the risk of problems such as seal failure due to temperature rises in hydraulic oil. The purpose is

Means for Solving the Problems According to the present invention, the above-mentioned object is to provide a reservoir for storing an operating tune, a hydraulic oil supply passage and a hydraulic oil discharge passage communicating with the reservoir, and a hydraulic oil supply passage and a hydraulic oil discharge passage communicating with the reservoir, and a hydraulic oil supply passage and a hydraulic oil discharge passage communicating with the reservoir. A bomb for supplying high-pressure hydraulic oil, means for detecting the temperature of the hydraulic oil, a hydraulic actuator disposed between the wheels and the vehicle body, and selectively connecting the supply passageway or the discharge passageway to the actuator. a pressure adjustment means that communicates with the actuator and adjusts the hydraulic pressure in the actuator; a bypass means that selectively communicates and connects the supply passage and the discharge passage; and a control means that controls the pressure adjustment means and the bypass means. The control means is achieved by a hydraulic suspension configured to bring the bypass means into communication when the temperature of the hydraulic oil exceeds a predetermined value.

Effect of the Invention According to the above-described configuration, when the temperature of the hydraulic oil rises above a predetermined value, the bypass means is brought into communication and the supply passage and the discharge passage are connected to each other. Therefore, the pressure in the supply passage is reduced, which lowers the temperature of the hydraulic oil, and when the hydraulic oil is circulated through the supply and discharge passages, heat is dissipated through these pipes, etc. cooled down.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be explained in detail below by way of example embodiments with reference to the accompanying figures.

Embodiment FIG. 1 is a schematic diagram showing a fluid circuit of one embodiment of a hydraulic suspension according to the present invention.

The illustrated suspension fluid circuit includes actuators IPR, I, which are provided corresponding to the front right wheel, front left wheel, rear right wheel, and rear left wheel of the vehicle, which are not shown in the figure, respectively.
These actuators have oil chambers 2PR and 2PL, respectively.
, 2Rl? ,21? It has L.

Further, in the figure, 4 indicates a reserve tank for storing hydraulic oil, and the reserve tank 4 is connected to the suction side of the pump 6 through a suction flow path 10 in which a filter 8 for removing foreign matter is provided in the middle. ing. A drain passage 12 is connected to the pump 6 for collecting hydraulic oil leaking inside the pump 6 into the reserve tank 4. Pump 6 is. Engine 14
The engine 14
The rotation speed is detected by the rotation speed sensor 16.

A high pressure flow path 18 is connected to the discharge side of the pump 6.

A check valve 20 is provided in the middle of the high-pressure flow path 18 to allow only the flow of the hydraulic fluid from the bomb toward each actuator, and between the bomb 6 and the check valve 20, the hydraulic fluid discharged from the bomb An attenuator 22 is provided to absorb pressure pulsations and reduce pressure changes. High pressure channel 1
8 has a high pressure flow path 18F for the front wheels and a high pressure flow path 18R for the rear wheels.
are connected at one end, and accumulators 24 and 26 are connected to these high pressure channels, respectively. Each of these accumulators has high-pressure gas sealed therein so as to absorb pressure pulsations of the hydraulic oil and to perform a pressure accumulating function. In addition, the high pressure channels 18F and 18H include high pressure channel 18FR for the right front wheel and high pressure channel 1 for the left front wheel, respectively.
8F'L and high pressure flow path 18RR for right rear wheel, high pressure flow path 181 for left rear wheel? One end of L is connected. High pressure channel 1
In the middle of 8FR, 18PL, 1 8RR, 1 8RL are filters 2 8PR, 2 8PL, 2, respectively.
8RR, 28RL are provided, and the other ends of these high pressure channels are respectively pressure control valves 32, 34, 36,
38 pilot-operated 3-port switching control valves 40,
It is connected to P boats 42, 44, and 46.

The pressure control valve 32 is connected to the switching control valve 40 and the high pressure flow path 18F.
Low pressure flow path 48Pl for R and right front wheel? It consists of a flow path 50 that serially connects the flow path, and a fixed throttle 52 and a variable throttle 54 provided in the middle of the flow path.

A low pressure passage 48PR is connected to the R boat of the switching control valve 40, and a connection passage 56 is connected to the A boat. The switching control valve 40 has a fixed throttle 52 and a variable throttle 54.
This is a Subur valve that takes in the pressure Pp in the flow path 50 between the When the pressures Pp and Pa are equal to each other, the switching position 40a is switched to the switching position 40b where communication of all ports is cut off, and the pressure Pp is switched to the switching position 40b.
When the pressure is lower than the pressure Pa, the switch is switched to a switching position 40c that connects the boat R and the port A in communication. Further, the variable throttle 54 changes the effective passage cross-sectional area of the throttle by controlling the current applied to the solenoid 58, thereby changing the pressure Pp in cooperation with the fixed throttle 52.

Similarly, pressure control valves 34 to 38 are each pressure control valve 32
pilot-operated three-boat switching control valves 42 , 44 , 46 corresponding to the switching control well 40 , flow passages 60 , 62 , 64 corresponding to the flow passage 50 , and fixed throttles 66 , 68 corresponding to the fixed throttle 52 . , 70, and variable apertures 72, 74, and 76 corresponding to the variable aperture 54, and the variable apertures 72 to 76 have solenoids 78, 80, and 82, respectively.

Moreover, the switching control valves 42, 44, 46 are connected to the switching control well 40.
The R boat has a low pressure flow path 4 8 FL for the left rear wheel, and a low pressure flow path 4 8 FL for the right rear wheel.
8RR, one end of the low pressure flow path 48RL for the left rear wheel is connected to the A boat, and connection flow paths 84, 86, and 8 are connected to the A boat, respectively.
One end of 8 is connected. In addition, the switching control valves 42 to 4
6 is the pressure Pp in the flow passages 60 to 64 between the corresponding fixed throttle and variable throttle, and the corresponding connection flow passages 84 to 8.
It is a Subur valve that takes in the pressure Pa in 8 as a pilot pressure, and when the pressure pp is higher than the pressure Pa, the switching position 42a, 4 connects the boat P and the boat A for communication.
4a and 46a, and switch to switching positions 42b, 44b, and 46b which cut off communication between all ports when pressures Pp and Pa are equal to each other, and connect boat R and boat A when pressure Pp is lower than pressure Pa. It is designed to switch to switching positions 42c, 44c, and 46c for connection.

As schematically shown in FIG. 1, each actuator I FR, I FL. IRR and IRL are cylinders 106PR, 106PL, and 10 that define oil chambers 2PR, 2PL, 2RR, and 2RL, respectively.
6RR, 1 0 6RL and pistons 1 0 g PR, 1 0 8 that fit into the respective corresponding cylinders.
FL, 108RR, and 108RL, each connected to the vehicle body (not shown in the diagram) through a cylinder, and connected to a suspension arm (not shown in the diagram) at the tip of the piston rod. has been done.

Although not shown in the drawings, a suspension spring is elastically mounted between an upper seat fixed to the rod portion of the piston and a lower seat fixed to the cylinder.

Also, the cylinder 106FR, 106 of each actuator
FL, 1 0 61? I? , 106RL are connected to one ends of drain channels 110, 112, 114, and 116. Drain channels 110, 112, 114, 11
The other end of 6 is connected to a drain passage 118, which is connected to the reserve tank 4 via a filter 120, so that the working fluid leaked from the oil chamber is returned to the reserve tank. It has become.

Accumulators 132, 134, 136, and 138 are connected to the oil chambers 2PR, 2PL, 2RR, and 2RL via throttles 124, 126, 128, and 130, respectively. Also piston 108PR. 1 0 8FL
, 1 0 8 RR. 108RL has flow paths 140PR, 140FL, 140RR, respectively.
, 140RL are provided.

These flow paths correspond to flow paths 5, 6, and 84 to 8, respectively.
8 and the oil chambers 2PR, 2PL, 2RR, 2RL, and filters 142PR, 142 are installed in the middle, respectively.
It has FL, 1 4 2 RR, and 1 4 2 RL. Another actuator! PR, l PL, I
In the vicinity of RR, I RL, there are vehicle heights XPR, XFL, XRR, corresponding to each wheel, respectively.
Vehicle height sensor 144FR, 144FL, which detects XRL,
144RR and 144RL are provided.

Pilot-operated shutoff valves 150, 152, 154, 156 are provided in the middle of the connecting channels 56, 84-88, respectively, and these shutoff valves are connected to the corresponding pressure control valves 40, 42, 44, 46, respectively. High pressure flow path 1 on the more upstream side
When the differential pressure between the pressure in 8FR, 18PL, 18RR, and 18RL and the pressure in drain flow path 110, 112, 114, and 116 is below a predetermined value, a closed state is maintained. In addition, the portions between the corresponding pressure control valves and cutoff valves of the connection channels 56, 84 to 88 are respectively connected to the flow channels 15
8, 160, 162, and 164 communicate with the portions of the flow paths 50, 60, 62, and 64 of the corresponding pressure control valves downstream of the variable throttle. Relief valves 166, 168, 170, and 17 are provided in the middle of the flow paths 158 to 164, respectively.
2 are provided, and these relief valves each take in the pressure of the upstream portion of the corresponding flow path 158, 160, 162, 164, that is, the corresponding connection flow path side, as a pilot pressure, and the pilot pressure is When a predetermined value is exceeded, the valve is opened to guide a portion of the hydraulic oil in the corresponding connection flow path to the flow paths 50, 60 to 64.

In addition, the shutoff valves 150 to 156 are connected to the high pressure flow path 18FR, respectively.
1 8PL, 1 8RR. The valve may be configured to maintain the valve closed state when the pressure difference between the pressure in the 18RL and the atmospheric pressure is less than or equal to a predetermined value.

The other ends of the low pressure passages 48PR and 48FL are connected to one end of the low pressure passage 48F for the front wheels, and the other ends of the low pressure passages 48RR and RL are connected to one end of the low pressure passage 481 for the rear wheels. is connected to one end of the The other ends of the low pressure channels 48F and 48R are connected to one end of the low pressure channel 48 in communication. The low pressure flow path 48 has an oil cooler 174 in the middle and a filter 17 at the other end.
It is connected to the reserve tank 4 via 6. A portion of the high-pressure flow path 18 between the check valve 20 and the attenuator 22 is connected to the low-pressure flow path 48 through a flow path 178 . A relief valve 180 is provided in the middle of the flow path 178 and is set to a predetermined pressure in advance.

In the illustrated embodiment, the high pressure channel 18R and the low pressure channel 4
81? is a flow path 18 that has a filter 182, a throttle 184, and a normally open electromagnetic on-off valve 186 that can adjust the flow rate.
8 are connected to each other. The electromagnetic on-off valve 186 is configured to open by energizing a solenoid 190 and changing its excitation current, and to adjust the flow rate of hydraulic oil passing through the valve. Also, high pressure flow path 18R
and the low pressure flow 7848R are connected to each other by a flow path 194 having a pilot-operated on-off valve 192 in the middle. The on-off valve 192 takes in the pressure on both sides of the throttle 184 as a pilot pressure, and maintains the closed position 192a when there is no differential pressure on both sides of the throttle 184, and when the pressure on the high pressure flow path 18H side with respect to the throttle 184 is high. The valve is switched to the open position 192b. Thus aperture 1
84, the electromagnetic on-off valve 186 and the on-off valve 192 cooperate with each other to selectively communicate and connect the high-pressure flow path 18R and the low-pressure flow path 48R, and therefore the high-pressure flow path 18 and the low-pressure flow path 48, so that the pressure is lower than that of the high-pressure flow path. A bypass valve 196 is configured to control the flow rate of the actuation tune flowing into the flow path.

Furthermore, in the illustrated embodiment, the high pressure flow path 18R and the low pressure flow path 481? are provided with pressure sensors 197 and 198, respectively, and these pressure sensors detect the pressure Ps of the hydraulic oil in the high-pressure flow path and the pressure Pd of the hydraulic oil in the low-pressure flow path, respectively. . In addition, pressure sensors 199 are provided in the connection channels 56, 84, 86, and 88, respectively.
FR, 199PL, 199RR, 199R
These pressure sensors detect the pressures in the chambers 2PR, 2FL, 2RR, and 2RL, respectively. Furthermore, each of the reserve tanks 4 is provided with a temperature sensor 195 that detects the temperature T of the hydraulic oil stored in the tank.

The electromagnetic on-off valve 186 and the pressure control valves 32-38 are controlled by an electric control device 200 shown in FIG. Electrical control device 200 includes a microcomputer 202 .

The microcomputer 202 may have a general configuration as shown in FIG. 2, and includes a central processing unit (CPU) 204 and a read-only memory (ROM) 2.
06, random access memory (RAM) 208,
It has an input port device 210 and an output port device 212, which are connected to each other by a bidirectional common bus 214.

The input boat device 210 includes a signal indicating the rotation speed N of the engine 14 from the rotation speed sensor 16, a signal indicating the temperature T of the hydraulic oil from the temperature sensor 195, and pressure sensors 197 and 198.
Signals indicating the pressure Ps in the high-pressure flow path and the pressure Pd in the low-pressure flow path, respectively, pressure sensors 199PL and 199PR.
, 199RL, 199RI? Oil chamber 2PL, respectively.
Pressure P1 (1-1
, 2, 3, 4), the ignition switch (
IGSW) 216, a signal indicating whether the ignition switch is in the on state, vehicle height sensor 144PL, 1
From 44PR, 144RL, and 144RR, the left front wheel and right front wheel, respectively? Vehicle height X1 of the part corresponding to the rear wheel and right rear wheel (
1-1, 2, 3, 4) are respectively input.

The input boat device 210 also includes a signal indicating the vehicle speed V from the vehicle speed sensor 234, a signal indicating the longitudinal acceleration Ga from the longitudinal G (acceleration) sensor 236, and a signal indicating the longitudinal acceleration Ga from the longitudinal G (acceleration) sensor 238.
More lateral acceleration G! A signal indicating the steering angle θ from the steering angle sensor 240, a signal ID indicating the throttle opening sensor θa detected by the throttle opening sensor 242
A signal indicating whether SW244 is in the on state, BKS
A signal indicating whether the W246 is on or not, and a signal indicating whether the vehicle height control mode set by the vehicle height setting switch 248 is high mode or low mode are now manually input. There is.

The input boat device 210 appropriately processes the signals input thereto, and processes them based on the program stored in the ROM 206 (according to instructions from the CPU 204).
■It is designed to output the processed signal to. R.O.
The M206 stores the control flows shown in FIGS. 3 and 6 and the maps shown in FIGS. 4 and 5, and the CPU
is designed to process signals based on each control flow.

According to instructions from the CPU 204, the output boat device 212 outputs a control signal to the electromagnetic on-off valve 186 via a drive circuit 220, and outputs a control signal to the pressure control valves 32-3 via drive circuits 222-228.
8. In detail, variable apertures 54, 72, 74, 76 respectively
A control signal is output to the solenoids 58, 78, 80, and 82, and a control signal is output to the display 232 via the drive circuit 230.

The operation of the illustrated embodiment will now be described with reference to the flowchart shown in FIG.

Note that the control flow shown in FIG. 3 is started when the ignition switch 216 is closed. In addition, in the flowchart shown in FIG. 3, the flag Fc indicates whether the pressure PS of the hydraulic oil in the high-pressure flow path has ever exceeded the threshold pressure PC for completely opening the shutoff valves 150 to 156. 1 is related to whether the pressure Ps is the pressure Pc
The flag Fs indicates that the standby pressure pbt(1-
Standby pressure current 1bi corresponding to 1, 2, 3, 4)
This relates to whether or not (1-1, 2, 3, 4) is set, and 1 indicates that the standby pressure current is set.

First, in step 10, a main relay (not shown in the figure) is turned on, and then in step 2
Go to 0.

In step 20, the contents stored in the RAM 208 are cleared and all flags are reset to O, and the process then proceeds to step 30.

In step 30, a signal indicating the rotation speed N of the engine 14 detected by the rotation speed sensor 16, a signal indicating the rotation speed N of the engine 14 detected by the rotation speed sensor 16,
A signal indicating the temperature T of the hydraulic oil detected by the pressure sensor 195, a signal indicating the pressure Ps in the high pressure channel detected by the pressure sensor 197, a signal indicating the pressure Pd in the low pressure channel detected by the pressure sensor 198, Pressure sensor 1 9 9PL,
．． Oil chambers 2PL, 21'R, 2RL, 2RR detected by 199PR, 199RL, 199RR
Signal indicating internal pressure Pi, ignition switch 21
A signal indicating whether or not 6 is in the on state, vehicle height sensor 14
A signal indicating vehicle height X1 detected by 4PL, 144PR, 144RL, and 144RR, a signal indicating vehicle speed V detected by vehicle speed sensor 234, a signal indicating longitudinal acceleration Ga detected by longitudinal G sensor 236, and lateral G sensor 2
38, a signal indicating the steering angle θ detected by the steering angle sensor 240, and a signal IDSW 244 indicating the throttle opening sensor θa detected by the throttle opening sensor 242 are in the ON state. A signal indicating whether the BKSW 246 is on or not, a signal indicating whether the mode set by the vehicle height setting switch 248 is high mode or low mode are read, Then step 40
Proceed to.

Step 40. At step 200, it is determined whether the ignition switch is in the OFF state, and when it is determined that the ignition switch is in the OFF state, the process proceeds to step 200, where it is determined that the ignition switch is in the ON state. When this has been carried out, the process advances to step 50.

In step 50, it is determined whether or not the engine is being operated by determining whether the engine rotation speed N detected by the rotation speed sensor 16 and read in step 30 exceeds a predetermined value. is carried out, and when it is determined that the engine is not being operated, the process proceeds to step 90, and when it is determined that the engine is being operated, the process proceeds to step 60.

Note that whether or not the engine is being operated may be determined by determining whether or not the generated voltage of a generator (not shown in the drawings) driven by the engine is equal to or higher than a predetermined value.

In step 60, from the time when engine operation is started, in step 150, which will be described later, the pressure control valves 32 to 3 are
A timer is started for a time Ts until the standby pressure Pbl of 8 is set, after which the process proceeds to step 70. In this case, if the timer Ts has already been activated, the timer continues counting.

In step 70, the solenoid 1 of the bypass valve 196 [current IbIJ energized to the solenoid 190 of the valve 186]
Based on the map stored in the ROM 206 and corresponding to the graph shown in FIG.

In step 80, the current 1b calculated in step 70 is applied to the solenoid 190 of the electromagnetic on-off valve 186, thereby driving the bypass valve 196 in the closing direction, and then the process proceeds to step 90.

In step 90, it is determined whether or not the pressure Ps in the high-pressure flow path is equal to or higher than the threshold value Pc. When it is determined that Ps is not 2Pc, the process proceeds to step 120, where P5'&Pc is determined. When it is determined that there is, the process advances to step 100.

In step 100, flag Fc is set to 1, and then the process proceeds to step 105.

In step 105, the oil temperature sensor 195i:
: Based on the detected hydraulic oil temperature T, oil temperature determination control, which will be described later with reference to FIG. 6, is performed, and then the process proceeds to step 110.

In step 110, active calculations are performed based on the various signals read in step 30 in order to control the ride comfort of the vehicle and the attitude of the vehicle body.
The current 1ui to be applied to the solenoids 58, 78, 80, 82 of the variable throttles 54, 72-76 of each pressure control valve is calculated, and then the process proceeds to step 170.

Note that the active calculation performed in this step does not form the gist of the present invention, and a detailed explanation thereof will be omitted. It may be carried out as described in Japanese Patent No. 63-331042.

In step 120, it is determined whether the flag Fc is 1 or not, and it is determined that it is Fc -1, that is, the pressure Ps of the hydraulic oil in the high pressure flow path has exceeded the threshold pressure Pc. If it is determined that the value has become lower than this, the process proceeds to step 105, and it is determined that the pressure is not Fc-1, that is, it is determined that the pressure Ps has never exceeded the threshold pressure pc. If the process has been performed, the process advances to step 130.

In step 130, it is determined whether the flag Fs is 1 or not, and when it is determined that it is Fs-1, the process advances to step 170, and when it is determined that it is not Fsml, the process proceeds to step 170. Proceed to step 140.

In step 140, it is determined whether or not the time Ts has elapsed, and when it is determined that the time Ts has not elapsed, the process proceeds to step 170, where it is determined that the time Ts has elapsed. When this has been performed, the process advances to step 150.

In step 150, the operation of the TS timer is stopped, and the pressure P1 read in step 30 is stored in the RAM 208 as the standby pressure Pbl, and the pressure shown in FIG. Based on the map corresponding to the graph shown in FIG. Oil chamber 2PL, 2PR, 2RL,
Variable throttles 72, 54 of pressure control valves 34, 32, 38, 36 to provide a pressure substantially equal to the pressure pt in 2RR.
, 76, 74, the current 1bl (1-1, 2, 3, 4) to be applied to the solenoids 78, 58, 82, 80 is calculated, and then the process proceeds to step 160.

In step 160, the flag Fs is set to 1, and the process then proceeds to step 170.

In step 170, it is determined whether the current 1b calculated in step 70 is greater than or equal to the reference value 1bo, and when it is determined that Ib≧Ibo is not satisfied, the process proceeds to step 30. Returning, if it is determined that Ib≧1 bo, the process proceeds to step 180.

In step 180, the pressure Ps of the working fluid in the high pressure flow path read in step 30 is determined to be the reference value Pso (<
A determination is made as to whether Ps≧Pso
If it is determined that it is not PsmPso, the process returns to step 30, and if it is determined that it is PsmPso, the process proceeds to step 190.

In step 190, the current Ibi calculated in step 150 or the current 1ul calculated in step 110 is applied to the variable throttle solenoid 58 of each pressure control valve.
, 78 to 82, each pressure control valve is driven to control its control pressure, and then step 3
0, and steps 30-190 described above are repeated.

In step 200, the bypass valve 1 is stopped by stopping the power supply to the solenoid 190 of the electromagnetic on-off valve 186.
96 is opened, and the process then proceeds to step 210.

In step 210, the main relay is turned off, thereby ending the control flow shown in FIG. 3 and stopping power supply to the electric control device 200 shown in FIG. Ru.

Claims (1)

[Claims] A reservoir for storing hydraulic oil, a hydraulic oil supply passage and a hydraulic oil discharge passage communicating with the reservoir, a pump for supplying high-pressure hydraulic oil from the reservoir to the supply passage, and means for detecting the temperature of the hydraulic oil. , a hydraulic actuator disposed between a wheel and a vehicle body, a pressure adjusting means for selectively communicating and connecting the supply passage or the discharge passage with the actuator and adjusting the hydraulic pressure in the actuator; a bypass means for selectively connecting the passage and the discharge passage; and a control means for controlling the pressure regulating means and the bypass means; A hydraulic suspension configured to communicate the bypass means.