JPH0911727A - Suspension device - Google Patents

Abstract

PURPOSE: To make riding comfort better even if a spring constant is made higher by driving a valve element according to the pressure of working fluid applied to a cylinder and the difference between the pressure of a restrictor and that of an accumulator. CONSTITUTION: A cylinder 11 is communicated to an accumulator 3 via a first restrictor 26 and a valve element 20 is driven according to the pressure of working fluid applied to the cylinder 11 and the difference between the pressure of the first restrictor 26 and that of the accumulator 3. Let the spring constant of a spring 6 be K, the spring constant of the accumulator 3 be Ka, and the time constant of primary delay according to the first restrictor 26 be T, the spring constant of the whole suspension device becomes K+Ka/(1+Ts). Therefore, the spring constant for the steady relative displacement of a car body side member and a wheel side member becomes K+Ka to restrict the rolling and the pitching movements of the car body. Since the spring constant for the transient relative displacement thereof becomes K+Ka/(1+Ts), the vibration transmissibility from an upper resonance frequency of the spring to a lower resonance frequency of the spring can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements and improvements in hydropneumatic suspensions used in vehicles and the like.

[0002]

2. Description of the Related Art As a conventional suspension device, for example, Japanese Unexamined Patent Publication No. 6-206419 is known, and a controller is adapted to detect a motion state of a vehicle body.
The spring constant of the gas spring of the hydropneumatic suspension is changed by driving the actuator to obtain an arbitrary spring constant.

[0003]

However, in such a conventional suspension device, the spring constant of the gas spring is set in accordance with the command value of the controller in order to suppress the posture change of the vehicle. In the state where the spring constant is set high, there is a problem that vibration input from the road surface is transmitted to the vehicle body via the gas spring whose spring constant is set high, and the riding comfort deteriorates.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a suspension device capable of ensuring riding comfort even when the spring constant is set high.

[0005]

SUMMARY OF THE INVENTION A first aspect of the present invention is to provide a spring interposed between a vehicle body side member and each wheel side member and an intermediary member between the vehicle body side member and each wheel side member. A cylinder that generates a damping force according to the relative displacement of the vehicle body side member and the wheel side member, a pressure accumulator that communicates with the cylinder to form a gas spring, and supplies and discharges the working fluid to and from the cylinder and the pressure accumulator. In a suspension device including valve means, the valve means includes a pressure adjusting port that communicates with the cylinder and the pressure accumulator, and a valve body that selectively communicates the pressure adjusting port with a tank or a pressurized fluid supply source. A first throttle provided between the pressure accumulator and the pressure adjusting port, and a pressure difference between the pressure of the working fluid applied to the cylinder and the first throttle and the pressure accumulator, Depending on this pressure difference, And a differential pressure responsive means for driving the body.

According to a second aspect of the present invention, in the first aspect of the present invention, the first aperture is composed of a variable aperture, and a control means for driving the first aperture according to a motion state of the vehicle. Equipped with.

A third invention is the first or second invention.
In the invention described above, a second variable throttle is provided between the pressure adjusting port and the cylinder, and a control means for driving the second variable throttle according to the motion state of the vehicle is provided.

[0008]

Therefore, according to the first aspect of the invention, the cylinder communicates with the pressure accumulator through the first throttle, and the valve body has a difference in pressure between the working fluid applied to the cylinder and the pressure between the first throttle and the pressure accumulator. The spring constant of the spring is K,
The gas spring constant of the pressure accumulator communicating with the cylinder is Ka, the first
Assuming that the time constant of the first-order lag due to the diaphragm is T, the overall spring constant of the suspension device is K + Ka / (1 + Ts)
Therefore, the overall spring constant is K + Ka for steady relative displacement between the vehicle body side member and the wheel side member, suppressing the roll or pitch motion of the vehicle body, while the spring is for transient relative displacement. Since the constant is K + Ka / (1 + Ts), it is possible to reduce the vibration transmissibility between the sprung (vehicle body side) resonance frequency and the unsprung (wheel side) resonance frequency, which is high with respect to changes in the posture of the vehicle body. The spring constant is a low spring constant against transient vibration input from the road surface.

In the second aspect of the invention, the time constant T can be changed according to the motion state by using the first diaphragm as a variable diaphragm controlled according to the motion state of the vehicle. It is possible to suppress a change in the posture of the vehicle body while the vehicle is in a transient state in which the vehicle shifts from a steady state to another steady state.

A third aspect of the present invention uses a second throttle provided between the pressure adjusting port and the cylinder as a variable throttle controlled according to a vehicle motion state, so that the damping constant of the cylinder moves. It can be changed according to the state, and it is possible to suppress the posture change of the vehicle body during the transitional state in which the motion of the vehicle transits from the steady state to another steady state.

[0011]

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

1 and 2 show an embodiment in which the present invention is applied to a four-wheeled vehicle, in which a load of the vehicle body is placed between the vehicle body side member 7 and each wheel side member (not shown). A coil spring 6 for supporting and a cylinder 1 for generating a damping force are arranged in parallel, and a pressure accumulator 3 forming a gas spring is communicated with each cylinder 1, so that the cylinder 1 and the pressure accumulator 3 are valves. A working fluid is supplied from a pump 4 as a source of pressurized fluid via a spool valve 2 as means.

Upper and lower oil chambers 11 and 1 inside the cylinder 1
A piston 10 coupled to the vehicle body side member 7 via a rod 14 is slidably accommodated and defines an oil passage 1 that connects upper and lower oil chambers 11 and 12 to each other.
3 is formed, and a damping force is generated by the relative movement of the piston 10 and the cylinder 1.

The piston 10 is relatively displaced inside the cylinder 1 in accordance with the relative movement of the vehicle body side member 7 and the wheel side member,
The volume in the cylinder 1 changes according to the volume of the rod 14 penetrating into the cylinder 1 according to this displacement amount.

The oil chamber 11 of the cylinder 1 is provided with a pressure accumulator 3 and a spool valve 2 which are arranged for each wheel through an oil passage 40 formed inside the piston 10 and the rod 14.
Communicate with

The pressure accumulator 3 is, as shown in FIG.
A gas chamber 32 accommodating a predetermined gas through 0 and an oil chamber 31 communicating with the cylinder 1 through the spool valve 2 are defined, and the gas chamber 32 is the pressure of the working fluid supplied to the oil chamber 31. A gas spring that generates a reaction force according to

A spool 20 as a valve body for adjusting the supply pressure according to the axial displacement is slidably accommodated in the spool valve 2, and the pump 4 faces the spool 20.
A pump port 21 that communicates with the tank, a tank port 22 that communicates with the reservoir tank 5, and a pressure adjusting port 23 that selectively increases or decreases the pressure to the cylinder 1 and the pressure accumulator 3 are opened. The pressure adjusting port 23 communicates with the pump port 21 or the tank port 22 according to the displacement of the spool 20.

The pressure adjusting port 23 communicates with the oil passage 40 via a throttle 26 as a first throttle, and also communicates with an oil passage 41 via a throttle 27 as a second throttle.
Further, the pressure adjusting port 23 communicates with a pilot passage 24 that drives the spool 20 rightward in the drawing.

A pilot passage 25 for guiding the pressure of the oil chamber 31 to the spool 20 is formed from the oil passage 41 between the throttle 27 and the pressure accumulator 3, and the spool 20 is provided in the oil chamber 31 of the pressure accumulator 3. It is driven leftward in the figure according to the pressure.

The spool 20 has pilot passages 24, 2
The pilot passage 24 is displaced in the axial direction according to the differential pressure of 5
When the pressure in the pilot passage 25 is higher than that in the pilot passage 25, the pressure adjusting port 23 communicates with the tank port 22.
To communicate with the pump port 21, and the pilot passages 24 and 25 constitute differential pressure responsive means.

With the above construction, the operation will be described below.

When the pressure in the cylinder 1 changes according to the displacement of the wheel side member, this pressure change is caused by the throttle 26 of the oil passage 40.
It acts on the pilot passage 24 via the
6 through the throttle 27 of the oil passage 41 to the oil chamber 31 of the pressure accumulator 3
And the pilot passage 25 of the spool 20 respectively.

Here, the pressure in the cylinder 1 is P, the flow rate of fluid flowing in and out of the cylinder 1 is Q, and the resistance of the throttle 26 is R.
a, the resistance of the throttle 27 is Rb, and the spring constant of the gas stored in the pressure accumulator 3 is Ka, the throttle 26 is connected to the spool 20.
The pressure Pa acting on is expressed by the following equation (1).

Pa = P-Ra × Q (1) When the flow rate passing through the pressure adjusting port 23 is Qp, the flow rate Qb passing through the throttle 27 becomes Qb = Q-Qp, and the pressure Pb acting on the pilot passage 25 is obtained. Is Pb = Pa−Rb × Qb (2), and the pressure Pb in the pilot passage 25 is equal to the pressure in the oil chamber 31 of the pressure accumulator 3.

The pressure of the oil chamber 31 of the pressure accumulator 3 is balanced with the spring reaction force of the gas chamber 32 whose volume is changed by the fluid flowing in and out of the pressure accumulator 3. The volume of the fluid flowing in and out of the pressure accumulator 3 is Qb / s, which is the integrated value of the flow rate, where s is the Laplace operator.

The pressure receiving area of the piston 30 of the pressure accumulator 3 is Aa
Then, the stroke of the gas spring of the pressure accumulator 3 is (Qb
/ S) / Aa, the reaction force of the gas spring is (Qb / s) / Aa ×
ka, the pressure of the working fluid according to the reaction force of the gas spring is (Qb
/ S) / Aa × ka / Aa, and the pressure Pb is Pb = (Qb / s) / Aa × ka / Aa (3)

Therefore, the flow rate Q of the pilot passage 25
b becomes Qb = sPb × Aa ² / ka (4)

[0028] When this equation (4) is substituted into equation (2) above, Pb = Pa-Rb × sPb × Aa 2 / ka Pb {1+ (Rb × Aa 2 / ka) s} = Pa Pb (1 + Ts) = Pa (5) However, T = Rb × Aa ² / ka.

The spool 20 is displaced according to the pressure difference ΔP applied to both ends according to the above equation (5), and this pressure difference ΔP is ΔP = Pa−Pb = Pa {1-1 / (1 + Ts)} = Pa {Ts / (1 + Ts)} (6)

When the pressure in the cylinder 1 rises, the spool 20 moves to connect the pressure adjusting port 23 to the tank port 22 to reduce the pressure in the cylinder 1, while the pressure in the cylinder 1 decreases. In this case, the spool 20 is displaced in the opposite direction to communicate the pressure adjusting port 23 with the pump port 21 and the pressure rises. As a result,
The working fluid corresponding to the pressure difference ΔP in the expression (6) is supplied and discharged from the pressure adjustment port 23.

That is, of the flow rate Q of the working fluid flowing in and out of the cylinder 1, the flow rate Qp passes through the pressure adjusting port 23 by an amount corresponding to the above equation (6), and the flow rate Qp is Qp = Ts / (1 + Ts) × Q ... (7) Therefore, Qb = Q−Qp = 1 / (1 + Ts) × Q ... (8) and the volume Qb / s of the working fluid flowing in and out of the pressure accumulator 3 is obtained.
Is Qb / s = 1 / (1 + Ts) × Q / s (9)

The above equation (3) represents the reaction force of the gas spring of the pressure accumulator 3, and from this equation, Pb = (Qb / s) / Aa × ka / Aa = (Qb / s) / Aa ² × ka / (1 + Ts) (10)

Assuming that the pressure receiving area of the piston 10 of the cylinder 1 is As and the stroke of the cylinder 1 is Xs,
The volume Q / s of fluid flowing into and out of the cylinder 1 with respect to the stroke of the cylinder 1 is Q / s = As × Xs (11), and the force F due to the pressure P in the cylinder 1 is F = P × As ... (12).

By multiplying both sides of the above equation (1) by the pressure receiving area As and using the equations (5) and (8), the pressure difference of the equation (6) becomes 0 and Pa = Pb. ) And further using the relationship of (11), the above (12)
Organizing the formulas, F = P × As = (Pa + Q × Ra) × As = {Pb + Q × Ra} × As) = {(Q / s) Aa ² × ka / (1 + Ts) + Q × Ra} × As = { ^{aa 2 × ka / (1 +} Ts)} (Q / s) × As + Ra × Q × As = {aa 2 × ka / (1 + Ts)} × As 2 × Xs + Ra × As 2 × sXs = Ka / (1 + Ts) × Xs + C × sXs (13) where Ka = Aa ² × ka × As ² ; gas spring constant of pressure accumulator 3 C = Ra × As ² ; damping constant of cylinder 1.

That is, the stroke X of the suspension
For s, the spring constant of the gas spring of the pressure accumulator 3 is Ka / (1
+ Ts).

When the spring constant of the coil spring 6 installed in parallel with the cylinder 1 is K, the spring constant of the suspension device is K + Ka / (1 + Ts).

The transmission rate at which the input from the road surface is transmitted to the vehicle body by this spring characteristic is as shown in FIG. 3, and the spring characteristic of the suspension as in the above-mentioned conventional example (spring constant = K).
+ Ka), the spring constant decreases as the input frequency increases, and thus the resonance frequency on the spring decreases.

Therefore, when the posture of the vehicle body changes due to a constant inertial force, the spring constant becomes high, and the change in the posture of the vehicle body is suppressed, while the spring constant becomes low when inputting from a transient road surface. As a result, it is possible to suppress the transmission of vibration from the unsprung portion to the sprung portion and to secure a good riding comfort.

Now, as shown in FIG. 4, when the vehicle is turning, an outward inertial force on the side opposite to the turning center acts on the center of gravity of the vehicle body. A roll moment acts on the vehicle body by this inertial force, and a force acts on the suspension outside the vehicle body in the contracting direction of the cylinder 1 and on the suspension inside the vehicle body in the extending direction of the cylinder 1. When the turning is in a steady state, the roll angle of the vehicle body is the roll angle φ in which the roll rigidity of the suspension and the roll moment due to the inertial force are balanced.

In FIG. 4, the vehicle is turning with the left side in the figure as the turning center, and an inertial force to the right in the figure acts on the center of gravity of the vehicle body. This inertial force is the centripetal acceleration of the turning α, When the mass is W, α × W, and when the height from the tire contact surface to the center of gravity is H, the roll moment acting on the vehicle body is α × W × H.

Here, when the roll angle of the vehicle body is φ and the roll rigidity of the suspension is Kr, the vehicle body rolls to the point where the roll moment and the reaction force of the roll rigidity of the suspension due to the roll of the vehicle body are balanced, and this roll angle is Kr × φ = α × W × H φ = α × W × H / Kr (14)

The roll rigidity Kr of the suspension is the roll rigidity Kr _ST by a stabilizer (not shown) and the roll rigidity Kr _SP by the spring constant K _SP of the suspension Kr _SP = K _SP ×
It is the sum of t.

Kr = Kr _ST + Kr _SP = Kr _ST + K _SP × t (15) where t is the distance in the left-right direction of the tire contact surface.

Substituting the equation (15) into the equation (14), φ = α × W × H / Kr = α × W × H / (Kr _ST + K _SP × t) (16) The vehicle body rolls up to the roll angle φ represented by the equation (16). Spring constant K of this suspension
_{Since SP} is K + Ka / (1 + Ts), the spring constant during steady turn is K + Ka, and it is possible to suppress the roll of the vehicle body and maintain stable traveling.

In this state, if the projection or the like is crossed over, the spring characteristic of the suspension shifts to a transient state and the spring constant becomes K + Ka / (1 + Ts), as shown in FIG. 3, and the spring constant decreases from the road surface. The transmission of vibrations to the vehicle body is suppressed, and good riding comfort can be maintained.

FIG. 5 is a model showing the pitch direction of the vehicle.
5 shows a pitch movement when the vehicle is braking. When the vehicle is being braked, a force in the direction of contraction of the cylinder 1 acts on the suspension in front of the center of gravity of the vehicle body, and a force in the direction of extension of the cylinder 1 acts on the suspension behind the center of gravity of the vehicle. Pitch motion occurs (acceleration results in reverse pitch motion).

When the acceleration or deceleration is in a steady state, the pitch angle ψ of the vehicle body becomes a pitch angle in which the spring constant and the inertial force are balanced, and the pitch rigidity Kp against the pitch moment due to this inertial force is Kp = K _SP × d (17)

If the longitudinal acceleration is β, the pitch moment due to inertial force is β × W × H, so the pitch angle ψ of the vehicle body is ψ = β × W × H / (K _SP × d) ( 18). However, d is the distance between the tire contact surfaces of the front and rear wheels.

The spring constant K _SP of this suspension is K
Since it is + Ka / (1 + Ts), the spring constant during steady turn becomes K + Ka, and the pitch of the vehicle body can be suppressed to maintain stable running.

In this state, when the vehicle overruns the protrusions, the spring characteristic of the suspension shifts to a transient state as shown in FIG. 3 and the spring constant becomes K + Ka / (1 + Ts), which decreases from the road surface. The transmission of vibrations to the vehicle body is reduced, and good riding comfort can be maintained.

FIG. 6 shows a second embodiment, in which the diaphragm 27 of the first embodiment is a variable diaphragm 27A which is driven according to a command value from the controller 8, and the other configurations are the same as those of the first embodiment. It is similar to the embodiment.

The controller 8 calculates a command value according to the detection value of the motion state detecting means 9. The motion state detecting means 9 is composed of, for example, a lateral acceleration sensor or a longitudinal acceleration sensor.

In the controller 8 having such a configuration, a command value for suppressing the movement of the vehicle body in the roll direction is calculated in accordance with the detected value of the lateral acceleration sensor, and the controller 8 is operated in accordance with the detected value of the longitudinal acceleration sensor. A command value is calculated so as to suppress the movement of the vehicle body in the pitch direction. Alternatively, the command value may be obtained after calculating the roll moment applied to the vehicle body from the steering angle sensor and the vehicle speed in place of the lateral acceleration sensor, and in the longitudinal direction by an accelerator switch or a brake switch instead of the longitudinal acceleration sensor. The command value may be calculated after detecting the acceleration.

The variable throttle 27A changes the flow passage cross-sectional area according to the command value. The spring constant of the suspension of the first embodiment is K + Ka / (1 + Ts), but the time constant T of the first-order lag is As shown in the equation (5), T =
Since Rb × Aa ² / ka, the resistance Rb changes by changing the flow passage cross-sectional area of the variable throttle 27A, and the time constant T
Is set to an arbitrary value by the controller 8.

For example, as shown in FIG. 4, when the vehicle makes a transition from a straight traveling state to a turning state, a roll occurs on the vehicle body, but this roll is transient until the turning state converges to a steady state. It becomes an exercise.

With respect to such a transient movement, the spring constant of the suspension is K + Ka / (1 + Ts). Therefore, if the time constant T is large, the effect of suppressing the rolling of the vehicle body by the spring is small. Therefore, the posture of the car body is unstable.

In such a transient state, the time constant T is increased by increasing the flow passage cross-sectional area of the variable throttle 27A.
Becomes smaller, the effect of suppressing the movement of the vehicle body by the spring becomes greater, and the stability of the vehicle can be improved.

On the other hand, after the vehicle is in the steady state, the time constant T is set large by reducing the flow passage cross-sectional area of the variable throttle 27A, and the spring constant for the transient input from the road surface is set. As a result, the ride comfort can be ensured, and the stability of the vehicle and the ride comfort can both be secured.

FIG. 7 shows a third embodiment, in which the diaphragm 26 of the first embodiment is replaced by a controller 8 similar to that of the second embodiment.
The variable throttle 26A is driven in accordance with the command value from, the flow passage cross-sectional area of the oil passage 40 is variable, and other configurations are the same as in the first embodiment.

Also in this case, the spring constant with respect to the stroke of the suspension is K + Ka / (1 + Ts) as in the above embodiment, but the flow passage cross-sectional area of the variable throttle 26A changes according to a command from the controller 8. Therefore, the flow path resistance Ra of the variable throttle 26A changes, and C of the second term on the right side of the above equation (13), that is, the damping constant of the suspension changes according to a command from the controller 8.

The command value from the controller 8 is the second value
Similar to the embodiment, it is set according to the detection value of the motion state detecting means 9, and the above-mentioned Japanese Patent Application Nos. 7-51487 and 514 are used.
No. 88, 51489 drives the variable aperture 26A so that the damping constant C corresponds to the motion state of the vehicle.

For example, as shown in FIG. 4, when the vehicle makes a transition from a straight traveling state to a turning state, a roll occurs on the vehicle body, but this roll makes a transient motion until the turning state converges to a steady state. Becomes

With respect to such a transient movement, the spring constant of the suspension is K + Ka / (1 + Ts). Therefore, if the time constant T is large, the effect of suppressing the rolling of the vehicle body by the spring is small. Therefore, the posture of the car body is unstable.

In such a transient state, the time constant T is reduced by reducing the flow passage cross-sectional area of the variable throttle 26A.
Becomes smaller, the effect of suppressing the movement of the vehicle body by the spring becomes greater, and the stability of the vehicle can be improved.

On the other hand, after the vehicle is in the steady state, the time constant T is set large by reducing the flow passage cross-sectional area of the variable throttle 26A, and the spring constant for the transient input from the road surface is set. As a result, the ride comfort can be ensured, and the stability of the vehicle and the ride comfort can both be secured.

[0066]

As described above, according to the first aspect of the present invention, the cylinder communicates with the pressure accumulator through the first throttle, and the valve body has the pressure of the working fluid applied to the cylinder and the first throttle and the pressure accumulator. Since the suspension device is driven according to the pressure difference between the two, the overall spring constant of the suspension device is K + Ka / (1 + Ts), and the overall spring constant for steady relative displacement between the vehicle body side member and the wheel side member. Becomes K + Ka, which suppresses the roll or pitch motion of the vehicle body, while the spring constant is K + Ka / (1 + Ts) for transient relative displacement, so that the sprung (vehicle body side) resonance frequency to the unsprung ( Wheel side)
It is possible to reduce the vibration transmissibility between resonance frequencies,
It has a high spring constant against changes in the vehicle body posture and a low spring constant against transient vibration input from the road surface, suppressing the transmission of transient vibration input from the road surface to the vehicle body and providing a comfortable ride. It is possible to secure the stability of the vehicle body in a steady state while ensuring the above.

In the second aspect of the invention, the time constant T can be changed according to the motion state by using the first diaphragm as a variable diaphragm controlled according to the motion state of the vehicle. It is possible to suppress changes in the posture of the vehicle body during a transitional state in which the vehicle makes a transition from a steady state to another steady state, and to suppress the transfer of transient vibration input from the road surface to the vehicle body to ensure riding comfort. However, it becomes possible to secure the stability of the vehicle body in the steady state.

In the third aspect of the invention, the damping constant of the cylinder is changed by changing the second throttle interposed between the pressure adjusting port and the cylinder to a variable throttle controlled according to the vehicle motion state. It can be changed according to the state, and it is possible to suppress the posture change of the vehicle body during the transitional state in which the vehicle motion transits from a steady state to another steady state, and to stabilize the vehicle body while ensuring riding comfort. It is possible to improve the property.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a suspension device showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing one wheel of the suspension device.

FIG. 3 is a graph showing a relationship between an input frequency and a vibration transmissibility, wherein a solid line shows a steady state and a broken line shows a transient state.

FIG. 4 is a vehicle model in the roll direction.

FIG. 5 is a vehicle model in the pitch direction.

FIG. 6 is a schematic configuration diagram of a spool valve showing a second embodiment.

FIG. 7 is a schematic configuration diagram of a spool valve showing a third embodiment.

[Explanation of symbols]

 1 Cylinder 2 Spool Valve 3 Accumulator 4 Pump 5 Reservoir Tank 6 Coil Spring 7 Car Body Side Member 8 Controller 9 Motion State Detection Means 10 Piston 20 Spool 21 Pump Port 22 Tank Port 23 Pressure Adjustment Port 24, 25 Pilot Passage 26, 27 Throttle 30 piston 31 oil chamber 32 gas chamber

Claims (3)

[Claims] 1. A spring interposed between a vehicle body side member and each wheel side member, and a spring interposed between the vehicle body side member and each wheel side member, of the vehicle body side member and the wheel side member, respectively. In a suspension device including a cylinder that generates a damping force according to relative displacement, a pressure accumulator that communicates with the cylinder to form a gas spring, and valve means that supplies and discharges a working fluid to the cylinder and the pressure accumulator. The valve means includes a pressure adjusting port that communicates with the cylinder and the pressure accumulator, a valve body that selectively communicates the pressure adjusting port with a tank or a pressurized fluid supply source, and the pressure accumulator and the pressure adjusting port. A pressure difference between the pressure of the working fluid applied to the cylinder and the pressure of the first throttle interposed between the first throttle and the pressure accumulator is detected, and the valve element is operated according to the pressure difference. The differential pressure responsive means to drive Suspension device characterized by having. 2. The first diaphragm is constituted by a variable diaphragm, and a control means for driving the first diaphragm according to a motion state of a vehicle is provided. Suspension device. 3. A second variable throttle is provided between the pressure adjusting port and the cylinder, and a control means for driving the second variable throttle according to a motion state of the vehicle is provided. The suspension device according to claim 1 or 2, which is characterized in that.