JP2514219B2 - Fluid suspension system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fluid suspension device capable of changing a spring constant by changing a volume of a fluid.

[Prior Art] Examples of conventional fluid suspension devices include, for example, JP-A-58-218410 (first prior art) and "GALANT.ET".
ERNA Σ New model vehicle manual ”, published by Mitsubishi Motors Corporation in August 1983 (second conventional example), is known.

In the first conventional example, suspension devices including air chambers are provided at front, rear, left, and right four wheel positions of the vehicle, and the air chambers of the left and right suspension devices are connected via an opening / closing valve, and the opening / closing valve is closed during vehicle height adjustment. Together with this, it is configured to open when the vehicle body is not rolled.

In the second conventional example, a suspension device including a main air chamber and a sub air chamber is provided at front, rear, left and right four wheel positions of the vehicle, and the main air chamber and the sub air chamber of each suspension device are communicated with each other at a low vehicle speed, It is configured to switch the spring constant between two types, soft and hard, by cutting off at high vehicle speed.

[Problems to be Solved by the Invention]

However, in the above-mentioned first conventional example, since the air chambers of the left and right suspension devices are connected or shut off by the on-off valve, the switching of the spring constant of the suspension device is limited to two steps and the minimum. There is an unsolved problem that the spring constant cannot be set low and the riding comfort cannot be improved.

Further, in the second conventional example, the suspension device provided at each wheel position is provided with the main air chamber and the sub air chamber, and at the time of low vehicle speed, the main air chamber and the sub air chamber are made to communicate with each other so as to have a low spring constant. At high vehicle speeds, the main air chamber and the sub air chamber are shut off so as to have a high spring constant, but in this case as well, the switching of the spring constant is only in two stages, and the low spring constant is the same as that of the sub air chamber. Since the volume of the sub air chamber is determined by the volume and cannot be set large in a normal vehicle, there is an unsolved problem that there is a certain limit in reducing the low spring constant.

Therefore, in order to switch the spring constant in three steps,
Considering the first conventional example and the second conventional example, as shown in FIG. 6, the main air connected to the suspension device S provided at each wheel position by the pipe P ₁ with the opening / closing valve V ₁ interposed. It is conceivable to include the chamber A _M and the sub air chamber A _S and connect the main air chambers A _M of the left and right suspension devices S with the pipe P ₂ having the open / close valve V ₂ interposed therebetween. In order to ensure the stability of the vehicle at high vehicle speeds, when the spring constant is maximized, the on-off valve V ₁ inside the suspension device and the three on-off valves V ₂ outside must be closed. External open / close valve
V ₂ needs to be closed during anti-roll control and at high vehicle speeds, and the frequency of opening and closing increases, causing a failure.
A new problem arises that cannot withstand long-term use and cannot secure reliability.

Therefore, the present invention has been made by paying attention to the problems of the above-described conventional example, and the spring constant can be switched in three stages, and the switching frequency of the on-off valve can be reduced by switching the spring constant to improve reliability. An object of the present invention is to provide a fluid suspension device capable of performing the above.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a main fluid chamber interposed between each wheel of a vehicle and a vehicle body, and a sub-fluid connected to each main fluid chamber via a first on-off valve. A first suspension valve and a first suspension valve for connecting or shutting off the main fluid chamber and the sub fluid chamber to change the spring constant. It is characterized in that a control device is provided for controlling the second on-off valves to be opened in a low vehicle speed range and closed in a high vehicle speed range while being connected via a valve.

[Action]

In the present invention, the lowest spring constant can be set by opening the first and second on-off valves, and the medium spring constant can be set by closing only the second on-off valve. The highest spring constant can be set by closing the first and second on-off valves, and three different spring constants can be set. Therefore, in a relatively low-speed normal traveling state, by opening the first and second opening / closing valves, the vibration input having a phase difference between the left and right as the lowest spring constant is effectively absorbed to improve the riding comfort.
Further, when the vehicle rolls, the first on-off valve is closed to exert the anti-roll effect as the maximum spring constant, and when the vehicle speed is high, the second on-off valve is closed and the medium spring constant is set, so that the vehicle travels. Ensure stability.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

 FIG. 1 is a system diagram showing an embodiment of the present invention.

Suspension devices 2a to 2d are interposed between the vehicle body 1 and the front left wheel, the front right wheel, the rear left wheel, and the rear right wheel (all are not shown). These suspension devices 2a to 2d are, for example, suspension links 3a to 3d. And shack absorbers 4a to 4d, main air chambers 5a to 5d, and sub air chambers 6a to 6d. The main air chambers 5a to 5d are the vehicle body 1 and the shock absorber.
4a to 4d are formed by elastic bodies 7a to 7d made of, for example, rubber that surround the space between the cylinder tubes in the vertical direction, and the sub air chambers 6a to 6d are air chambers of fixed volume. . And the main air chambers 5a to 5d and the sub air chambers 6a to 6d
Are connected via electromagnetic opening / closing valves 8a to 8d as first opening / closing valves.

Further, the sub air chambers 6a, 6b of the left and right suspension devices 2a, 2b on the front wheel side are connected via a normally closed electromagnetic on-off valve 9f as a second on-off valve, and the left and right suspension devices on the rear wheel side are connected. Similarly between the 2c and 2d sub air chambers 6c and 6d, a normally closed solenoid on-off valve 9r is also used as a second on-off valve.
Connected through.

Further, the main air chambers 5a to 5d are connected to the air supply / discharge device 12 via electromagnetic opening / closing valves 11a to 11d for vehicle height adjustment, respectively. The air supply / exhaust device 12 includes a compressor 14 rotatably driven by a DC drive motor 13, a dryer 15 connected to the compressed air discharge port, and a reservoir connected to the outlet of the dryer 15 via a check valve 16. A tank 17, an electromagnetic on-off valve 18 interposed between the outlet side of the reservoir tank 17 and the outlet side of the drier 15, and an exhaust electromagnetic on-off valve 19 connected to a pipe between the compressor 14 and the dryer 15. The outlet of the dryer 15 is connected to the vehicle height adjusting electromagnetic on-off valves 11a to 11d via piping.

On the other hand, vehicle height sensors 20a to 20d configured by, for example, potentiometers for detecting relative displacement between wheels and the vehicle body are provided between the vehicle body 1 and the suspension arms 3a to 3d at positions of the respective suspension devices 2a to 2d. Air supply and exhaust device 12
A pressure switch 21 is arranged between the check valve 16 and the reservoir tank 17, and a vehicle speed sensor 22 for detecting a vehicle speed and a lateral acceleration sensor 23 for detecting a lateral acceleration of the vehicle.

Then, each solenoid valve 8a-8d, 9f, 9r, 11a-11d, 18,
The controller 19 controls the motor 19 and the drive motor 13.

The controller 29 is a microcomputer 30, a driving circuit 31; 32; 33a to 33d; 34, 35 for driving the electromagnetic on-off valves 8a to 8d; 9f, 9r; 11a to 11d; 18, 19 and a battery 36 and driving. A drive circuit 36 for driving a relay 37 interposed between the motor 13 and the motor 13.
And a multiplexer 38 that selects a detection signal from each of the vehicle height sensors 20a to 20d, and an A / D converter 39 that converts an analog amount signal of the vehicle height sensors 20a to 20d selected by the multiplexer 38 into a digital signal. It is configured to include and.

The microcomputer 30 is configured to include at least an interface circuit 40, an arithmetic processing device 41, and a storage device 42 such as RAM or ROM. The interface circuit 40 has an A / D converter 39 and a pressure switch 21 on its input side. The vehicle speed sensor 22 and the lateral acceleration sensor 23 are connected, and the multiplexer 38 and the drive circuits 31 to 36 are connected to the output side.

The arithmetic processing unit 41 receives an A / A signal via the interface circuit 40.
The signals of the D converter 39, the pressure switch 21, the vehicle speed sensor 22, and the lateral acceleration sensor 23 are read, and each electromagnetic control valve 8a-8d, 9f, 9r, 11a-11d, 18, 19 is controlled based on these signals. It executes processing such as vehicle speed response control, anti-roll control, and vehicle height control.

Further, the storage device 42 stores a predetermined program necessary for executing the processing in the arithmetic processing device 41, and
The processing results and the like of the arithmetic processing unit 41 are sequentially stored.

 Next, the operation of the above embodiment will be described.

When the ignition switch is turned on, the controller 29 is powered on, and the vehicle height sensors 20a to 20d are sequentially selected by sequentially switching the multiplexer 38 by a control signal from the interface circuit 40, and the selected vehicle height sensor 20a is selected. The detection signal of ~ 20d is converted into a digital signal by the A / D converter 39, and the microcomputer 30
Of the pressure switch 21, the vehicle speed sensor 22, and the lateral acceleration sensor 23 are further supplied to the interface circuit 40.

In this state, the microcomputer 30 executes the arithmetic processing shown in FIG.

That is, in step, the vehicle speed detection value V of the vehicle speed sensor 22 is read, and the electromagnetic opening / closing valves 9f, 9r are determined according to whether the detection value V is within a predetermined vehicle speed setting range having hysteresis.
Vehicle speed response processing for controlling the opening and closing of the vehicle is executed.

Then, the process shifts to a step to determine whether the vehicle is in a roll state. This determination is based on the lateral acceleration sensor 23
The lateral acceleration detection value is read, and it is determined whether or not it is equal to or greater than a predetermined set value.If it is less than the predetermined set value, it is determined that the roll is not in a roll state, and the process proceeds to step. When it is determined that the state is the state, the process proceeds to the step, the roll suppression process is executed, and then the process returns to the step.

In the step, the vehicle height detection values of the vehicle height sensors 20a to 20d are read, and the electromagnetic opening / closing valves 11a to 11d are read according to these vehicle height detection values.
After the vehicle height adjustment processing for controlling the opening / closing of d, 18, and 19 is executed, the process returns to the step.

The vehicle speed response process is, as shown in FIG. 3, a flag F indicating whether or not the vehicle speed is less than a predetermined set vehicle speed V _{A1 in} step.
It is determined whether ₁ is “0”. Here, when the flag F ₁ is “0”, the routine proceeds to step, where it is judged whether or not the vehicle speed detection value V is equal to or higher than a predetermined set vehicle speed V _A1 , and the judgment result is V ≧ V _A1 . At times, the process proceeds to step, and it is determined whether or not the flag F ₂ indicating whether or not the vehicle speed exceeds the predetermined set vehicle speed V _A2 (V _A2 > V _A1 ) is “0”. When the judgment result is flag F ₂ is "0", the processing proceeds to step determines whether the vehicle speed detection value V exceeds the predetermined vehicle speed V _A2, when a V ≦ V _A2 is proceeds to step Then, the solenoid on-off valves 9f and 9r are opened, for example, a control signal CS ₁ having a logical value “1” is output to the drive circuit 32,
Next, the process proceeds to step, the flag F ₁ is set to "1", and then the vehicle speed response process is ended.

If the result of the determination in step is that the flag F ₁ is set to "1", the process proceeds to step and it is determined whether or not the vehicle speed detection value V is less than a predetermined set vehicle speed V _B1 (V _B1 <V _A1 ). If V ≧ V _B1 , the process shifts to the step, and if V <V _B1 , the process shifts to the step to open the electromagnetic on-off valves 9f and 9r, for example, a logical value “0”. The control signal CS _{1 of} "is output to the drive circuit 32, then the process proceeds to step, the flag F ₁ is reset to" 0 ", and then the vehicle speed response process ends.

Further, when the step determination result is V <V _A1 , the step proceeds to the step, and when the step determination result is that the flag F ₂ is "1", the step proceeds.
In this step, the vehicle speed detection value V is the predetermined vehicle speed set value V
It is determined whether or not it is less than _B2 (V _A1 <V _B2 <V _A2 ) and V <V
_If it is _B2 , move to step 9
A control signal CS ₁ having a logical value “1” for opening f and 9r is output to the drive circuit 32, and then the flag F ₂ is reset to “0” in step, and then the vehicle speed response process is ended.

Furthermore, when the step determination result is V ≧ V _A2 and when the step determination result is V> V _B2 , the logical value “0” is entered to move to the step and close the electromagnetic on-off valves 9f and 9r. The control signal CS ₁ of is output to the drive circuit 32,
Then, the process proceeds to step, the flag F ₂ is set to "1", and the vehicle speed response process is ended.

Therefore, in this vehicle speed response process, as shown in FIG. 4, the vehicle is accelerated from the stopped state to set vehicle speed V _A1.
Until it reaches, the solenoid on-off valves 9f and 9r are controlled to be closed, and the sub air chambers 6a, 6b and 6c, 6d of the left and right suspension devices 2a, 2b and 2c, 2d are shut off to set the vehicle speed. V
_{When A1} is exceeded, the solenoid on-off valves 9f and 9r are controlled to open, and the sub air chambers 6 of the left and right suspension devices 2a, 2b and 2c, 2d are controlled.
The communication between a, 6b and 6c, 6d is established, and if the vehicle speed further increases from this state and exceeds the set vehicle speed V _A2 , the solenoid opening / closing valve 9f
And 9r are controlled to the closed state. Therefore, the set vehicle speed V _A1
By selecting V _B1 and V _B1 as vehicle speeds during traffic congestion, for example, 35 km / h and 25 km / h, the electromagnetic on-off valves 9f and 9r will not be controlled to be in the open state during traffic congestion that repeatedly stops and travels, The control frequency of the solenoid on-off valves 9f and 9r can be greatly reduced. When the vehicle speed decelerates after _{exceeding the} set vehicle speed V _A1 (or V _A2 ), the solenoid opening / closing valve 9f is not released until the set vehicle speed becomes less than V _B1 (or V _B2 or less).
9r has a hysteresis characteristic that the closed state (or open state) is controlled to prevent control hunting. Also, since the solenoid on-off valve 9f.9r is a normally closed type, the left and right suspension devices are independent when the vehicle is stopped, and when one of these fails, it does not affect the other. It is possible to prevent sudden changes in vehicle height.

Further, the roll restraining process is performed by each suspension device 2a-
The control signal CS ₂ of logical value “0” is output to the drive circuit 31 to close all the solenoid on-off valves 8a to 8d interposed between the 2d main air chambers 5a to 5d and the sub air chambers 6a to 6d. After that, the roll suppression process ends. When the roll restraining process is executed in this manner, the main air chambers 5a to 5d of the respective suspension devices 2a to 2d are cut off, so that the air spring constant of the suspension devices 2a to 2d is the volume of the main air chambers 5a to 5d. Since it is determined only by the value, it becomes a large value, and the roll of the vehicle body can be suppressed and the anti-roll effect can be exhibited.

Further, in the vehicle height adjustment processing, as shown in FIG. 5, first, in a step, the vehicle height detection values of the vehicle height sensors 20a to 20d are read, and based on these, it is determined whether or not the vehicle height adjustment is performed. This determination is made based on whether or not at least one of the vehicle height detection values of the vehicle height sensors 20a to 20d falls within, for example, a preset target vehicle height area. Control signal of logical value "0" that shifts and stops drive motor 13 of compressor 14
Outputs _CSM to the drive circuit 36 and at the same time solenoid valve for exhaust 1
9 to exit the vehicle height adjustment processing after outputting a control signal CS _E of logic value "0" to the closed state, when not within the target vehicle height region, the step determines that the required height adjustment The control signal CS ₁ having a logical value “0” is output to shift the electromagnetic on-off valves 9f and 9r to the closed state, and then the process proceeds to step to determine whether the vehicle height increase control or the vehicle height decrease control is performed. To do. In this determination, the vehicle height lowering control is determined when the vehicle height detection value H exceeds the allowable upper limit setting value H _H , and the vehicle height increasing control is determined when the vehicle height detection value H is less than the allowable lower limit setting value H _L.

Then, when the determination result of the step is vehicle height increase control, the process proceeds to step, the switch signal of the pressure switch 21 is read, and it is determined whether or not the accumulated pressure of the reservoir tank 17 reaches a predetermined set value, and the predetermined value is determined. When the set value is reached, the process proceeds to step and the control signal CS of the logical value "1" for opening the corresponding solenoid on-off valves 11a to 11d is opened.
_After outputting _{Ha to} CS _Hd to the drive circuits 33a to 33d, the process shifts to the step, and when it does not reach the predetermined set value, the process shifts to the step and the drive motor 13 of the compressor 14 is driven to rotate and the logical value "1" After outputting the control signal CS _M to the drive circuit 36 and the control signals CS _{Ha to} CS _Hd of the logical value “1” for opening the corresponding solenoid on-off valves 11a to 11d to the drive circuits 33a to 33d, Go to step.

In the step, the vehicle height detection values H of the vehicle height sensors 20a to 20d are read again, and it is determined whether or not these are within the allowable lower limit set value H _L and the allowable upper limit set value H _H , and H _L ≦ H ≦ when a H _H terminates the vehicle height adjustment processing determines that the vehicle height adjustment completion, when H <H _L repeats the above vehicle height increasing process returns to step.

If the result of step determination is vehicle height lowering control, the process proceeds to step and the corresponding solenoid valve 11a
Control signal CS _{Ha to} CS _Hd to open 11d to 11h drive circuit 33a
And outputs the ～33D, the control signal CS _E of logic value "1" to control the exhaust solenoid valve 19 to the open state output to drive circuit 35, then the vehicle height sensor 20a~20d proceeds to step
The vehicle height detection values H are read and it is determined whether or not they are within the allowable range. When _HL ≤ H ≤ H _H, it is determined that the vehicle height adjustment is completed and the vehicle height adjustment processing is ended. , H> H _H, the process returns to the step and the vehicle height lowering process is repeated.

When the vehicle is stopped, the vehicle speed sensor 22
Since the vehicle speed detection value of is 0, in the vehicle speed response process of FIG. 3, the control signal CS ₁ having the logical value “0” is output to the drive circuit 32 in this step. The exciting current is not output from the drive circuit 32, the electromagnetic on-off valves 9f and 9r interposed between the suspension devices 2a and 2b and between the suspension devices 2a and 2d maintain the closed state, and the suspension devices 2a to 2d have main air. It is set to a medium spring constant determined by the sum of the volumes of the chambers 5a to 5d and the sub air chambers 6a to 6d.

Since lateral acceleration is not applied to the vehicle in this stopped state,
When the vehicle height value is within the target vehicle height range, the process returns to the step as it is, and when the vehicle height changes due to the passenger getting on and off and the vehicle height value deviates from the target vehicle height range, the vehicle height of the step is changed. The vehicle height adjustment is performed by the adjustment processing so that the vehicle height falls within the target vehicle height region.

Then, when the vehicle is started from the stopped state and reaches a predetermined vehicle speed V _A1 or higher, the electromagnetic opening / closing valve interposed between the suspension devices 2a and 2b and between 2c and 2d by the vehicle speed response process of FIG. 9f and 9r are controlled to be in an open state, whereby the auxiliary air chambers 6a and 6b of the suspension devices 2a and 2b on the front wheel side are communicated with each other, and the suspension device 2a on the rear wheel side is connected.
And the sub air chambers 6c and 6b of 2b communicate with each other. In this state,
For example, when traveling on a rough road and vibration inputs having a phase difference such that one is bound and the other is rebound to the left and right suspension devices, for example, 2a and 2b, the sub air chamber of the bound suspension device 2a is transmitted. Suspension on the rebound side from 6a through solenoid on-off valve 9f
Since the movement of air to the sub air chamber 6b of 2b is allowed, the spring constant for the bound side becomes smaller than the spring constant during stopping and low speed running, and it is possible to absorb the vibration input and provide a comfortable ride. Can be improved.

When the vehicle speed exceeds the predetermined vehicle speed set value V _A2 by further accelerating from this traveling state, the electromagnetic open / close valves 9f, 9r interposed between the sub air chambers 6a, 6b and 6c, 6d are controlled to be in the closed state. Therefore, the air spring constant of each of the suspension devices 2a to 2d is set to the medium spring constant, and the traveling stability of the vehicle can be ensured.

On the other hand, if the vehicle is in a turning state while the vehicle is traveling, a lateral acceleration is generated in the vehicle in response to this, and this is the lateral acceleration sensor 23.
Is detected by When the lateral acceleration detection value of the lateral acceleration sensor 23 becomes equal to or larger than a predetermined set value, the step moves from step of FIG. 2 to step, and the main air chambers 5a to 5d and the sub air chamber 6a of the suspension devices 2a to 2d. Since the electromagnetic on-off valves 8a to 8d interposed between the 6d and 6d are controlled to the closed state,
An anti-roll effect can be exhibited as a high air spring constant. Moreover, since the vehicle height adjustment process is not performed during the roll suppression control, the running stability is not impaired.

In addition, when the vehicle height detection value of the vehicle height sensors 20a to 20d deviates from the target vehicle height region in a traveling state in which the vehicle is not rolling, the vehicle height adjustment described above is performed to ensure that the vehicle height is in an appropriate state. Hold on.

It should be noted that, in the above-mentioned embodiment, the case of controlling the communication between the sub air chambers of the left and right suspension devices by the electromagnetic opening / closing valves 9f, 9r has been described, but the present invention is not limited to this, and each suspension device 2a. All the sub air chambers of up to 2d may be controlled to open / close by electromagnetic opening / closing valves.

Further, in the above embodiment, the case where the electromagnetic on-off valves 9f, 9r are opened only when traveling at medium vehicle speed has been described, but the invention is not limited to this, and basically at low vehicle speed and medium vehicle speed. Alternatively, the electromagnetic on-off valves 9f and 9r may be controlled to open.

Further, the vehicle height sensors 20a to 20d are not limited to potentiometers, and any displacement detector such as an ultrasonic distance measuring device can be applied.

Furthermore, the detector for detecting the roll state of the vehicle is not limited to the lateral acceleration sensor 23, and the roll state of the vehicle can be estimated from the vehicle speed and the steering angle, or the roll angular velocity sensor can be used to detect the roll state. The roll angle can be calculated from the time differential value, or an arbitrary roll state detector can be applied.

Further, although the one using air as the working medium has been illustrated, the present invention is not limited to this, and an appropriate fluid such as gas other than air or oil or other liquid can be used.

Further, the open / close valves 8a to 8d and 9f, 9r are not limited to the solenoid valve open / close valves, and mechanical open / close valves may be applied.

Furthermore, although the one configured by using a microcomputer as the controller is shown, instead of this,
It is also possible to configure a controller by combining electronic circuits such as an addition circuit, a subtraction circuit, a command value setting circuit, a comparison circuit, and a logic circuit.

〔The invention's effect〕

As described above, according to the present invention, the suspension device provided between each wheel of the vehicle and the vehicle body is provided with the main air chamber and the sub air chamber connected to the main air chamber via the first opening / closing valve, and Since the sub air chambers of the left and right suspension devices are arranged so as to be opened in the low vehicle speed range and closed in the high vehicle speed range, the second open / close valve is configured to be interposed. By controlling the opening and closing, it is possible to set the spring constant in three stages, and since the control frequency of the second opening and closing valve can be minimized, it is possible to endure long-term use and improve reliability. In addition, it is possible to improve the riding comfort by effectively absorbing the vibration input having a phase difference between the left and right in the low vehicle speed range and improving the riding comfort in the low vehicle speed range. Control and ride Effect that can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIGS. 2 and 3 are flow charts showing procedures of processing executed by a microcomputer, respectively, and FIG. 4 is a waveform diagram used for explaining vehicle speed response processing. FIG. 5 is a flowchart showing the procedure of processing executed by the microcomputer,
FIG. 6 is a schematic view showing a conventional example. 2a-2d …… Suspension device, 5a-5d …… Main air chamber,
6a ~ 6d ... sub air chamber, 8a ~ 8d ... electromagnetic on-off valve (first on-off valve), 9f, 9r ... electromagnetic on-off valve (second on-off valve), 11a ~
11d …… Electromagnetic on-off valve for vehicle height adjustment, 12 …… Air supply / exhaust device, 1
4 …… Compressor, 17 …… Reservoir tank, 18 …… Supply solenoid on-off valve, 19 …… Exhaust solenoid on-off valve, 20a-20d…
… Vehicle height sensor, 22 …… Vehicle speed sensor, 23 …… Lateral acceleration sensor, 29 …… Controller, 30 …… Microcomputer, 31-36 …… Drive circuit, 40 …… Interface circuit,
41 ... arithmetic processing unit, 42 ... storage unit.

Claims (1)

(57) [Claims] 1. A main fluid chamber provided between each wheel of a vehicle and a vehicle body, and a sub-fluid chamber connected to each main fluid chamber via a first opening / closing valve. In the fluid suspension device in which the spring constant can be changed by connecting or shutting off the main fluid chamber and the sub-fluid chamber with the one on-off valve, the left and right sub-fluid chambers are connected to each other via the second on-off valve. The fluid suspension device is provided with a control device for controlling each second on-off valve to open in a low vehicle speed range and close in a high vehicle speed range.