JPH10184763A - Car height adjusting device and car height adjusting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the overall length in the axial direction, simplify structure, and reduce the number of parts used even if a required lifting stroke can be attained. SOLUTION: This device is provided with an inner cylinder 106 fitted on the car body 103 side, a piston block 112 movably-inserted in the inner cylinder 106, the first oil chambers 119, 120 partitioned by the piston block 112 in the inner cylinder 106, and the second oil chamber 131 which is movably-fitted on the outer periphery side of the inner cylinder 106 and partitioned between the inner cylinder 106 and the piston block 112. The first oil chambers 119, 120 and the second oil chamber 131 are connected to one side of a pump for hydraulic oil supply and a tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle height adjusting device and a vehicle height adjusting system used for adjusting the height of a vehicle in three stages of high, medium and low.

[0002]

2. Description of the Related Art As a conventional vehicle height adjusting device and a vehicle height adjusting system, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 62-231810. FIG. 7 is a sectional view showing such a conventional vehicle height adjusting device. FIG. 1 shows an upper piston 2 sliding in an upper cylinder 1, a lower cylinder 10 having a cylindrical upper end connected to a lower end of the upper piston 2, and a cylinder bore formed in a lower portion of the lower cylinder 10. And a lower piston 13 sliding on the cover 2
0, the upper cylinder 1 and the upper piston 2 constitute an upper jack, and the lower cylinder 10 and the lower piston 1
Reference numeral 3 denotes a lower jack. By the way, 26,
Reference numeral 27 denotes an oil chamber for supplying hydraulic oil provided above the upper piston 2 and the lower piston 13.

FIG. 8 shows a conventional vehicle height adjusting system, which has a vehicle height adjusting device as shown in FIG. 2
Hydraulic oil is supplied / discharged to solenoid valves 6 and 27 via solenoid valves 31 and 32, and hydraulic oil in oil chambers 26 and 27 is returned to tank 34 via solenoid valve 33. .

A pump 35 is driven by a motor 36 and is capable of supplying hydraulic oil to the oil chambers 26 and 27 via the solenoid valves 31 and 32, respectively.
Reference numeral 37 denotes a selection switch for adjusting the vehicle height. Reference numeral 38 denotes a motor 36 and each solenoid valve 3 based on the detection output of a pressure detection switch 39 of a pump 35 and a vehicle speed sensor 40.
This is a control device that controls the operations of 1, 32, and 33.

In this vehicle height adjusting system, when the vehicle height is switched from low to medium, the solenoid valve 31 is turned on at the same time as the operation of the pump 35 by the motor 36, and the oil chamber 26 is connected to the oil chamber 26 via the solenoid valve 31. The operating oil is supplied from the pump 35 to increase the vehicle height.

On the other hand, when lowering the vehicle height from middle to low,
When both the solenoid valve 31 and the solenoid valve 33 are turned on, the hydraulic oil in the oil chamber 26 is discharged to the tank 34 via these solenoids 31 and 33, so that the vehicle height can be reduced. .

Further, when the vehicle height is changed from medium to high, the pump 35 is operated and the solenoid valve 32 is turned on in the middle position of the vehicle height.
The pump 3 is connected to the oil chamber 27 through the solenoid valve 32.
The hydraulic oil from 5 is supplied to raise the vehicle height to a high position.

On the other hand, when the vehicle height is changed from high to medium, the solenoid valves 32 and 33 are turned on at the same time, whereby the hydraulic oil in the oil chamber 27 is released from these solenoid valves 3 and 3.
The vehicle is discharged to the tank 34 via the wheels 2 and 33, and the vehicle height falls to the middle position.

[0009]

However, in such a conventional vehicle height adjusting device and the conventional vehicle height adjusting system, the upper jack and the lower jack have a two-stage configuration in series. Parts, and therefore the overall axial length is increased, which increases the bending moment acting on the jack bearings, and requires a sufficiently long bearing and a strong connection between each jack. As a result, the length in the axial direction is further increased, and there is a problem that the arrangement in the vehicle may become difficult.

Further, in order to switch the vehicle height between low, middle and high levels, independent upper and lower jacks are used, respectively, to connect them or to attach them to a vehicle. There is a problem that it is configured in a unique and complicated shape, and it is necessary to use two components, such as a sealing member and a stopper, two by two.

Further, the upper piston 2 and the lower piston 1
3 needs to be provided with a surface treatment layer such as hard chrome plating from the viewpoint of environmental resistance because it is exposed to the outside.
There has been a problem that the product cost increases as a whole.

In addition, since the two jacks operate independently, the hydraulic circuits must also be independent.
For this reason, in order to prevent the hydraulic oil from spilling between the front and rear and left and right jacks due to fluctuations in the weight of the running vehicle, and to eliminate the inclination of the vehicle body, it is not possible to stop the jack to be operated in the middle, In order to suppress the abnormal increase in the pressure of the jack part due to the expansion of the hydraulic oil due to the temperature rise, it is necessary to use each oil passage connecting the oil chambers 26 and 27. In addition, there is a problem that a relief valve for compensating the circuit pressure is required one by one.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem. Although the required vertical stroke can be obtained, the overall axial length can be shortened. It is an object of the present invention to provide a low-cost vehicle height adjustment device and a vehicle height adjustment system that can reduce the number of parts used and prevent the sliding members and the like from being exposed to the outside, thereby improving environmental resistance.

[0014]

According to a first aspect of the present invention, there is provided a vehicle height adjusting apparatus including: an inner cylinder mounted on a vehicle body; and an movably inserted inside the inner cylinder. Piston block,
A first oil chamber partitioned by a piston block in the inner cylinder, and an outer cylinder movably provided on the outer peripheral side of the inner cylinder to partition the second oil chamber between the piston block, The first oil chamber and the second oil chamber are respectively connected to one of a pump and a tank for supplying hydraulic pressure.

According to a second aspect of the present invention, in the vehicle height adjusting apparatus, the first oil chamber is connected to a pump and a tank for supplying hydraulic pressure through an oil passage provided in a piston rod of the shock absorber. It is.

A vehicle height adjustment system according to a third aspect of the present invention is a vehicle height adjustment system comprising: a first electromagnetic valve that is switched to supply hydraulic oil from a pump to a first oil chamber via a check valve; A second solenoid valve that is switched to supply hydraulic oil from the pump to the oil chamber via a check valve, and a first electromagnetic valve and a hydraulic oil for the first oil chamber and the second oil chamber, respectively. A third solenoid valve which is switched to return to the tank via the second solenoid valve, and which is connected between the second oil chamber and the tank so that the operating pressure is lower than the pressure of the first oil chamber; An operating check valve and a relief valve that are higher than the pressure of the oil chamber are provided, and one of the first solenoid valve, the second solenoid valve, and the third solenoid valve is operated by operating the vehicle height selection switch in the control device. The operation is controlled according to the detected oil pressure of the first oil chamber and the second oil chamber. The vehicle body of the vehicle height by high, medium, is obtained so as to adjust to any of the low three-phase.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a vehicle height adjusting device according to the present invention, in which 101 is not shown. A spring 103 is interposed between the axle and the upper spring seat 102.
Reference numeral 4 denotes a head cover attached to the vehicle body 103, the center of which is squeezed to form a hole 105.

The upper end of the inner cylinder 106 is fixed around the hole 105 by welding or the like.
The O-ring 108 is provided on the outer periphery of the closing plate 107 to ensure a sealing property with the inner periphery of the inner cylinder 106.

An oil hole 109 is formed in the center of the closing plate 107 so as to penetrate therethrough.
The oil hole 111 of the connecting member 110 connected to the outside surface (upper surface) of the oil passage 111 communicates with the oil hole 111, and the oil hole 111 and the oil hole 109 can be connected to a circuit A described later.

Reference numeral 112 denotes the inner cylinder 106.
A piston block having a piston 113 movably inserted in the piston block 112,
Piston 11 in sliding contact with the inner periphery of inner cylinder 106
The piston 113 has a recess 114 having a predetermined pressure receiving surface at the upper center, and an oil hole 115 connecting the recess 114 and the outer periphery of the piston block 112.
Is provided.

Further, 116 is an inner cylinder 10
6, an O-ring 117 and a metal ring 118 are respectively attached to surfaces facing the outer peripheral side of the piston block 112 and the inner peripheral side of an outer cylinder described later, respectively.
The O-ring 117 is slidable on the piston block 112, and the metal ring 118 is slid on the inner periphery of the outer cylinder via a minute gap (not shown) formed by a matching gap of the metal ring 118. I have.

The piston block 112 defines two oil chambers 119 and 120 which communicate with each other in the inner cylinder 106 through oil holes 115.
9 and 120 form a first oil chamber.

On the other hand, 121 is an inner cylinder 106
The outer cylinder 121 is provided with a seal member 124 and a backup ring 133 slidably contacting the outer periphery of the inner cylinder 106 in an oil-tight manner. Installed. In addition, 123 is a bearing member of the inner cylinder 106.

At the lower end of the opening of the outer cylinder 121, a closing plate 125 for closing the lower end is fixed by welding or the like. 12
Reference numeral 6 denotes a cushioning material joined to the lower surface of the closing plate 125 by bolts 127.

The upper spring seat 102 supports the spring 101 via a holding member 128 between the spring 101 and an axle (not shown).

129 is an inner cylinder 106
Is connected to a circuit B, which will be described later. The oil hole 130 has one end communicating with a gap 122 between the inner cylinder 106 and the outer cylinder 121. ing.

Reference numeral 131 denotes a second oil chamber as an oil chamber partitioned by the outer cylinder 121, the piston block 112, and the closing plate 125.
18 and the oil hole 130
Is in communication with

FIG. 2 is a hydraulic circuit diagram showing a vehicle height adjusting system constituted by connecting a hydraulic circuit to a vehicle height adjusting device.
In the figure, reference numeral 151 denotes a pump driven by a motor 152. The pump 151 supplies hydraulic oil in a tank 153 to a vehicle height adjusting device through a circuit A via a check valve 154 and a first solenoid valve 155. Oil hole 111, 1
09 and the oil chamber 119, and through the check valve 154 and the second solenoid valve 156 to the oil hole 130, the gap 122, and the oil chamber 131 of the vehicle height adjusting device through the circuit B.

Reference numeral 157 denotes an oil passage 159 connecting the check valve 154 and each of the solenoid valves 155 and 156, and the tank 15
3 is a third solenoid valve connected via a throttle 158 to the third solenoid valve.

Further, reference numeral 161 denotes a circuit B and a tank 156.
Operating check valve connected between the
Is a circuit A connecting the first solenoid valve 155 and the oil hole 109.
And a relief valve connected between the tank 153.

Reference numerals 162 and 163 denote pressure detection switches for detecting two types of high and low oil pressures in the oil passage 159, respectively, and reference numeral 164 denotes a vehicle height L (low), N (medium), and H (high). The high selection signal, the vehicle speed signal from the vehicle speed sensor, and the detected pressure signals from the pressure detection switches 162 and 163 are input signals, respectively, and the motor 152 and the first solenoid valve 155
This is a control device that controls operations of the second solenoid valve 156 and the third solenoid valve 157.

The vehicle height adjusting device S as shown in FIG.
Are provided on the left and right front wheels and the rear wheels of the vehicle, and are connected as shown in FIG.

Next, the operation will be described. In the present invention, the vehicle height L (low), N
The vehicle height is raised and lowered and held by selection input of (medium) and H (high).

(A) Adjusting the vehicle height from L to N First, the motor 152 and the first solenoid valve 155 are energized under the control of the control device 164. Thereby, the pump 15
1 is operated, and the pump oil pressure (hydraulic oil) is sent to the oil chamber 119 and the oil chamber 120 in the inner cylinder 106 constituting the vehicle height adjusting device S via the circuit A.

As a result, a pressure corresponding to the weight of the vehicle body is generated in the oil chamber 119, and the piston block 112 is pushed down from the state shown in FIG. ), The outer cylinder 121 is lowered, and the head cover 104, that is, the vehicle body is relatively lifted. By this lifting, the piston 113 stops at a position where it hits the stopper 135.

Further, by stopping the piston 113, the pressure in the oil chamber 119 further increases, and this pressure becomes
The pressure is detected by the pressure switch 162 for detecting the high pressure.
The energization to 52 and the first solenoid valve 155 is stopped.

For this reason, the two solenoid valves 155, 156
Are turned off, and the vehicle height is held at the N position by the checking operation.

It is necessary to replenish the oil chamber 131 with hydraulic oil during the lowering operation of the outer cylinder 121. The operating check valve 161 detects such a pressure drop in the oil chamber 131 and opens to detect the pressure drop. Thus, supply of hydraulic oil into the oil chamber 131 is realized through the operation check valve 161.

(B) Adjusting the vehicle height from N to L In this case, when both the first solenoid valve 155 and the third solenoid valve 157 are energized, the hydraulic oil in the oil chamber 119 becomes oily. The fluid is returned to the tank 153 through the holes 109 and 111, the circuit A, the first solenoid valve 155, the throttle 158, and the third solenoid valve 157, respectively.

Thus, when the piston 113 and the lower surface of the closing plate 107 come into contact with each other, the pressure in the oil chamber 119 disappears. At this time, the pressure is reduced by the pressure switch 1 for detecting low pressure.
63, and based on the detection output, the control device 164 simultaneously stops energizing the respective solenoid valves 155, 157.

Accordingly, the vehicle height stops at the position L as shown in FIG.

In the process of raising the piston block 112 in which the piston 113 comes into contact with the lower surface of the closing plate 107, the volume of the oil chamber 131 is reduced.
It is necessary to escape the hydraulic oil in 1 to the outside.

At this time, the operating check valve 161 is open because the pressure at the time of lowering the vehicle body is acting on the operating check valve 161.
The operating oil in the oil chamber 131 is supplied to the gap 122, the oil hole 130,
It functions to return to the tank 153 through the circuit B.

(C) Adjusting the vehicle height from N to H In this case, the motor 15
Both the second and second solenoid valves 156 are energized.

As a result, the hydraulic pressure from the pump 151 is sent into the oil chamber 131 through the oil hole 130, the gap 122, and the opening of the metal ring 118 of the vehicle height adjusting device via the circuit B to further lift the vehicle body. Can be.

Here, since the pressure receiving area of the first piston 113 in the oil chamber 119 is smaller than the pressure receiving area of the closing plate 125, the pressure of the oil chamber 119 when the vehicle body is lifted is equal to the oil chamber 131 described above. Higher than the pressure.

Therefore, by setting the operating pressure of the operating check valve 160 to an intermediate needle of the operating pressure of the under-built cylinder 106 and the piston block 112,
During the adjustment from the vehicle height N to H, the operation check valve 160 can be prevented from being opened.

Accordingly, the discharge pressure of the hydraulic oil of the pump 151 passes through the operation check valve 160 and is stored in the tank 153.
As shown in Fig. 3 (c) without leaving the vehicle,
Can be lifted further.

When the vehicle height is increased from N to H, the stopper 13 provided on the outer cylinder 121 is used.
6 comes into contact with the upper edge of the support member 116, so that the oil chamber 1
31 and the pressure in the circuit B increase, this is detected by the pressure detection switch 162, and based on this detection output, the control device 164 causes the motor 152 and the second solenoid valve 15 to operate.
The power supply to 6 is stopped.

Therefore, the vehicle height is maintained at the H position by the check operation of the second solenoid valve 156.

(D) Adjusting the vehicle height from H to N In this case, the second solenoid valve 156 and the third solenoid valve 157 are energized. , Oil hole 130, tank B through circuit B
Returned to 3. At this time, the rapid upward movement of the outer cylinder 121 is restricted by the throttle 158 to avoid instability of the vehicle body.

Thus, the upper end of the closing plate 125 is
As shown in (b), when the oil chamber 131 comes into contact with the lower surface of the piston block 122, the pressure in the oil chamber 131 disappears.
, The current supply to the second solenoid valve 156 and the third solenoid valve 157 is stopped.

At this time, the oil chamber 119 holds the first solenoid valve 1
The pressure is maintained by the checking operation of 55.

Therefore, the piston block 112 does not rise in the inner cylinder 106, so that the vehicle height does not drop below N, and the first solenoid valve 155 and the second solenoid valve 156 The vehicle height is stably maintained at the N position by the both check operations.

(E) Adjusting the vehicle height from L to H In this case, the vehicle height is changed from L to N according to the procedure described above.
And then from N to H. At this time, the vehicle height can be raised from L to H at once by energizing the motor 152 and the first solenoid valve 155.

(F) Adjusting the vehicle height from H to L In this case, the vehicle height may be reduced from H to N and from N to L in the above-described procedure.
By energizing the respective solenoid valves 155, 156, 157 simultaneously, it is possible to lower the vehicle height to L at once.

The relief valve 160 not only protects the motor 152 when the pressure detection switches 162 and 163 fail, but also increases the pressure in the hydraulic circuit abnormally due to the temperature rise in each vehicle height holding state. That is, the relief valve 160 defines the upper limit of the circuit pressure.

In this embodiment, since the oil holes 111 and 130 connected to the circuits A and B are arranged at the upper part of the apparatus, the piping work for these is facilitated.

FIG. 4 shows the motor 152, the solenoid valves 155, 156, 15 in the vehicle height adjusting system shown in FIG.
7. Operate check valve 161, pressure detection switch 1
It is explanatory drawing which shows the vehicle height adjustment operation | movement according to each operation state of 62,163.

FIG. 5 shows another embodiment of the present invention. This is basically different from the vehicle height adjusting device shown in FIG. 1 in that a vehicle height adjusting device is formed above a shock absorber 170. In particular, a center hole 172 as an oil passage formed in a piston rod 171 of the shock absorber 170 is provided with an oil chamber 119 constituting a first oil chamber.
And the circuit A.

Therefore, one end (lower end) of the center hole 172 is
The piston rod 171 is opened near its center at the outer periphery thereof, communicates with the oil chamber 119, and has the other end (upper end) of the center hole 172.
Are in communication with the circuit A.

The inner cylinder 106 in this embodiment
A has a partition 173 integrally in the center, and this partition 17
3, a piston rod 171 penetrates through the centers of the piston block 112 and the closing plate 125, and seal members 174, 175, 17 are provided between the partition plate 173, the piston block 112 and the closing plate 125 and the piston rod 171.
6,177 are interposed respectively.

The rubber bush 179 is provided on the upper portion of the partition 173 via a collar 178 which wraps the outer periphery of the piston rod 171 and determines the mounting dimensions of the rubber bush described later.
Is provided, and a rubber bush 180 is further mounted on the rubber bush 179 via the head cover 104.

The rubber bush 180 is provided with a nut member 181 screwed around the upper end of the piston rod 171.
Accordingly, the upper end of the piston rod 171 can be elastically supported so as to be swingable with respect to the head cover 104.

Reference numeral 126A denotes a piston rod 171.
The cushioning material is attached to the upper end to prevent the closing plate 125 from hitting the upper end of the shock absorber 170.
182 is a dustproof cover that covers a part of the cushion material 126A and the piston rod 171. The dustproof cover 182 is formed of the upper spring seat 102 and the closing plate 12.
5, a perforated cup-shaped holding member 183 fixed to the lower end of
Is held at the lower end.

In this embodiment, when the vehicle height is adjusted from L to N or from N to L, the hydraulic oil from the pump 151 is supplied from the first solenoid valve 155, the circuit A and the piston rod 171. The hydraulic oil in the oil chamber 119 is introduced into the oil chamber 119 through the central hole
2, circuit A, first solenoid valve 155 and third solenoid valve 1
The tank is discharged through each of them.

The other components of the vehicle height adjusting device are as follows.
It is the same as the case described with reference to FIG.
The adjustment between H is as shown in FIG. This embodiment is characterized in that the center hole 172 provided in the piston rod 171 is a passage connecting the circuit A and the oil chamber 119.

[0068]

As described above, according to the present invention, an inner cylinder mounted on a vehicle body side, a piston block movably inserted into the inner cylinder,
A first oil chamber defined by a piston block in the inner cylinder, an outer cylinder movably provided on an outer peripheral side of the inner cylinder and defining a second oil chamber between the piston block, and a first oil chamber. A first solenoid valve that is switched to supply hydraulic oil from the pump to the oil chamber via a check valve, and a switch to supply hydraulic oil from the pump to the second oil chamber through a check valve. A second solenoid valve, and a third solenoid valve that is switched to return the hydraulic oil in the first oil chamber and the second oil chamber to the tank via the first solenoid valve and the second solenoid valve, respectively. An operating check valve and a relief valve connected between the second oil chamber and the tank, the operating pressure of which is lower than the pressure of the first oil chamber and higher than the pressure of the second oil chamber,
By operating the vehicle height selection switch, one of the first solenoid valve, the second solenoid valve and the third solenoid valve is operated and controlled according to the detected oil pressure of the first oil chamber and the second oil chamber, and the vehicle body Since the height is adjusted to one of three levels of high, medium and low, the piston block can be stored in the inner cylinder and this inner cylinder can be stored in the outer cylinder. This makes it possible to shorten the overall axial length, despite the sufficient lifting stroke required for adjusting the vehicle height, thereby simplifying the configuration and reducing the number of components used. ,
Further, the effect of preventing the sliding members and the like from being exposed to the outside and improving the environmental resistance can be obtained. Further, since the supply port for the hydraulic oil can be arranged at the upper part of the system, the pipes connected to these are provided. Has an effect that the laying is easy.

Further, according to the present invention, the first oil chamber is connected to the pump and the tank for supplying hydraulic pressure through the oil passage provided in the piston rod of the shock absorber. The high adjusting device can be arranged in series, and at this time, an effect is obtained that the piston rod can be effectively used as a supply oil passage for hydraulic oil to the oil chamber.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a vehicle height adjusting device according to an embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram showing a vehicle height adjustment system according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a change state of an operation of the vehicle height adjusting device in FIG. 1;

FIG. 4 is an explanatory diagram showing an operation state according to a vehicle height level of each section of the vehicle height adjustment system in FIG. 2;

FIG. 5 is a sectional view showing a vehicle height adjusting device according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a change state of the operation of the vehicle height adjusting device shown in FIG. 4;

FIG. 7 is a sectional view showing a conventional vehicle height adjusting device.

FIG. 8 is a hydraulic circuit diagram showing a conventional vehicle height adjustment system.

[Explanation of symbols]

 103 body 106 inner cylinder 112 piston block 113 piston 119 oil chamber (first oil chamber) 120 oil chamber (first oil chamber) 121 outer cylinder 131 second oil chamber 151 pump 153 tank 154 check valve 155 first Solenoid valve 156 Second solenoid valve 157 Third solenoid valve 160 Relief valve 161 Operate check valve 164 Control device 170 Shock absorber 171 Piston rod 172 Center hole (oil passage)

Claims (3)

[Claims] An inner cylinder mounted on a vehicle body side, a piston block movably inserted into the inner cylinder, a first oil chamber partitioned by the piston block in the inner cylinder, An outer cylinder movably provided on the outer peripheral side and defining a second oil chamber between the outer cylinder and the piston block, wherein the first oil chamber and the second oil chamber are respectively provided with a pump and a tank for supplying hydraulic pressure. A vehicle height adjustment device connected to each one. 2. The vehicle height adjusting device according to claim 1, wherein the first oil chamber is connected to a pump and a tank for supplying hydraulic pressure through an oil passage provided in a piston rod of the shock absorber. . 3. An inner cylinder mounted on the vehicle body side, a piston block movably inserted into the inner cylinder, a first oil chamber defined by the piston block in the inner cylinder, and an inner cylinder. An outer cylinder movably provided on the outer peripheral side and defining a second oil chamber between the outer cylinder and a piston block, and switching to supply hydraulic oil from a pump to the first oil chamber via a check valve. A first solenoid valve, a second solenoid valve that is switched to supply hydraulic oil from a pump to the second oil chamber via a check valve, and operation of the first oil chamber and the second oil chamber. A third solenoid valve that is switched to return oil to the tank via the first solenoid valve and the second solenoid valve, respectively, and a first solenoid valve and a second solenoid valve that are operated by operating a vehicle height selection switch A control device for controlling the operation of one of the third and third solenoid valves in accordance with the detected oil pressures of the first oil chamber and the second oil chamber to adjust the vehicle height of the vehicle body to one of three levels; A relief valve connected between the chamber and the tank, and an operating pressure connected to an oil passage connecting the second oil chamber and the tank, the operating pressure of which is lower than the pressure of the first oil chamber and higher than the pressure of the second oil chamber. A vehicle height adjustment system comprising a high operated check valve.