JPH0672121A - Vehicle suspension - Google Patents

Abstract

(57) [Summary] [Object] To provide a vehicle suspension device capable of improving the riding comfort of a vehicle by eliminating a phase delay of a control signal with respect to a vibration frequency exceeding a sprung resonance frequency. [Structure] A shock absorber b interposed between a vehicle body side and each wheel side and capable of changing a damping coefficient by a damping coefficient changing means a, and a sprung vertical acceleration near a position where each shock absorber b is provided are detected. The sprung vertical acceleration detecting means c, the sprung vertical speed detecting means d for detecting the sprung vertical speed in the vicinity of the position where each shock absorber b is provided, and the damping coefficient of each shock absorber b.
Damping coefficient control means e for controlling based on a control signal obtained by adding a correction value obtained from the sprung vertical acceleration to the sprung vertical speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle suspension system for optimally controlling a damping coefficient of a shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a vehicle suspension system for controlling a damping coefficient of a shock absorber, for example, Japanese Patent Laid-Open No. 61-
The one described in Japanese Patent No. 163011 is known.

In this conventional vehicle suspension system, when the direction signs of the sprung vertical velocity signal and the sprung / unsprung relative velocity signal obtained by processing the signals of the sprung vertical acceleration sensor are the same, the damping coefficient is obtained. Is set to be hard and the damping coefficient is controlled to be soft when the signs are different, and the four wheels are independently controlled.

[0004]

However, in the above-mentioned conventional apparatus, since the damping coefficient control is performed based on the sprung vertical velocity signal, there are the following problems.

Namely, a high-pass filter cut-off frequency 1.0 H _Z as the phase characteristic diagram (bandpass filter sprung mass vertical velocity signals for the vibration frequency of FIG. 20,
As shown in (Characteristic diagram when using a 1.5H _Z low-pass filter), the phase characteristic of the sprung vertical velocity signal shows the ideal velocity phase (-90%) as the vibration frequency rises beyond the sprung resonance frequency range. Since the phase delay with respect to drg) becomes large, in the damping coefficient control based on the sprung vertical velocity signal, the control response is reduced by the phase delay and the damping force is delayed. As shown by the characteristics of the vibration transmissibility on the spring with respect to the vibration frequency of (solid line), the vibration transmissibility on the spring becomes high in the region slightly above the sprung resonance frequency, which has a great influence on the riding comfort, and therefore, The ride comfort of the vehicle cannot be improved.

The present invention has been made by paying attention to the above-mentioned conventional problems, and it is possible to improve the riding comfort of the vehicle by eliminating the phase delay of the control signal with respect to the vibration frequency exceeding the sprung resonance frequency. It is intended to provide a vehicle suspension system.

[0007]

Therefore, in the present invention, a control signal obtained by adding a correction value obtained from the sprung vertical acceleration to the sprung vertical velocity is obtained, and the damping coefficient is controlled based on this control signal. I tried to achieve the purpose.

That is, the vehicle suspension system according to claim 1 of the present invention is interposed between the vehicle body side and each wheel side, and the damping coefficient is changed by the damping coefficient changing means a, as shown in the claim correspondence diagram of FIG. A possible shock absorber b, a sprung vertical acceleration detecting means c for detecting sprung vertical acceleration near the position where each shock absorber b is provided, and a sprung vertical direction near the position where each shock absorber b is provided. A sprung vertical velocity detecting means d for detecting the velocity and a damping coefficient control means e for controlling the damping coefficient of each shock absorber b on the basis of a control signal obtained by adding a correction value obtained from the sprung vertical acceleration to the sprung vertical velocity. It has and.

The vehicle suspension system according to a second aspect of the invention is provided with a shock absorber b interposed between the vehicle body side and each wheel side, the damping coefficient of which can be changed by the damping coefficient changing means a, and each shock absorber b. Sprung vertical acceleration detecting means c for detecting sprung vertical acceleration near the position, sprung vertical speed detecting means d for detecting sprung vertical speed near the position where each shock absorber is provided, and each shock absorber sprung near the position where b is provided
Relative speed detection means f for detecting the relative speed between unsprung parts, and damping coefficient of each shock absorber b, a control signal obtained by adding a correction value obtained from the sprung vertical acceleration to the sprung vertical speed is obtained. When the relative speed between the sprung part and the unsprung part has the same sign, the damping coefficient is increased, and when the sign has a different sign, the damping coefficient control means e for controlling the damping coefficient to the minimum is provided.

In the shock absorber, the expansion side has a variable damping coefficient and the compression side has a low damping coefficient fixed to the expansion side hard area, and the compression side has a variable damping coefficient and the expansion side has a low compression coefficient hard area to the expansion side. Both the side and the pressure side are formed in a structure having three regions, a soft region having a low damping coefficient, and the damping coefficient control means sets the shock absorber to the expansion hard region when the control signal is equal to or more than a positive threshold value. The shock absorber is controlled in the pressure side hard area when the control signal is below the negative threshold value, and the shock absorber is controlled in the soft area when the control signal is between the positive and negative threshold values. You may.

Further, in obtaining the control signal,
For the sprung vertical velocity and sprung vertical acceleration, a signal that has passed through a bandpass filter including the sprung resonance frequencies of the front and rear wheels may be used.

[0012]

[Function] Each sprung vertical velocity detecting means and sprung vertical acceleration detecting means move up and down on the spring (bouncing).
When is detected, the damping coefficient control means obtains a control signal based on the sprung vertical velocity and the correction value obtained from the sprung vertical acceleration, and controls the damping coefficient of the shock absorber according to this control signal.

In this control, the sprung vertical acceleration signal is always in phase with respect to the sprung vertical velocity signal, and the acceleration value increases as the vibration frequency increases. By performing the damping coefficient control based on the control signal obtained by adding the correction value obtained from the acceleration signal to the sprung vertical velocity signal, the control response to the high frequency input is improved.

Therefore, the phase delay of the control signal with respect to the vibration frequency exceeding the sprung resonance frequency is eliminated and the control response is improved, whereby the ride comfort of the vehicle can be improved.

Further, in the apparatus according to the second aspect, the damping coefficient control means increases the damping coefficient when the control signal and the sprung / unsprung relative speed have the same sign, while the both have different signs. Then the damping coefficient is minimized. Also in this case, the phase delay of the control signal with respect to the vibration frequency exceeding the sprung resonance frequency is eliminated, and the control response is improved, whereby the riding comfort of the vehicle can be improved.

[0016]

Embodiments of the present invention will be described with reference to the drawings. (First Embodiment) First, the structure will be described. Figure 2
It is a structure explanatory view showing the vehicle suspension system of the 1st example which is an example of the invention of Claims 1, 3, 4, and is a vehicle body and 4
The four shock absorbers SA ₁ , SA ₂ , SA ₃ , SA ₄ are interposed between the four wheels (when describing these four shock absorbers collectively, and when these four shock absorbers are commonly referred to, Is simply displayed as SA). And, in the vehicle body in the vicinity of each shock absorber SA,
Vertical acceleration sensor that detects sprung vertical acceleration (hereinafter,
A vertical G sensor) 1 is provided. In addition, the signal from each sensor 1 is input to the position near the driver's seat,
A control unit 4 that outputs a drive control signal to the pulse motor 3 of each shock absorber SA is provided.

FIG. 3 is a system block diagram showing the above configuration, in which the control unit 4 comprises an interface circuit 4a, a CPU 4b and a drive circuit 4c, and the interface circuit 4a is provided with signals from the above-mentioned respective sensors 1. Is entered. In the interface circuit 4a, a set of three filter circuits shown in FIG. 14 is provided for each upper and lower G sensor 1. That is, LPF1
Is a low-pass filter circuit for removing noise in the high frequency range (30 Hz or higher) from the signals sent from the upper and lower G sensors 1. BPF is passed through a frequency range including the sprung resonance frequency of the sprung mass vertical acceleration bouncing component signal _{a (a 1, a 2,} a 3, a 4 Incidentally, _{1,2, 3,4} figures each shock corresponds to the position of the absorber SA. the same applies is less.) is a band-pass filter circuit forming the, in this embodiment, a high-pass filter cut-off frequency 1.0 H _Z, a low-pass filter of 1.5 H _Z It is made up of. LPF2 is a bandpass filter circuit B
Bounce component signal a of sprung vertical acceleration that has passed PF
And bounce component signal v (v
_{1, v 2, v 3,} v 4 Numerals _{1, 2, 3 and 4} correspond to the position of the shock absorbers SA. The same applies to the following. ) Is a low-pass filter circuit for converting to. Note that FIG. 19 shows the gain characteristic with respect to the vibration frequency of the signal processed by the BPF.

Next, FIG. 4 is a sectional view showing the structure of the shock absorber SA.
A is a cylinder 30, a piston 31 defining the cylinder 30 into an upper chamber A and a lower chamber B, an outer cylinder 33 having a reservoir chamber 32 formed on the outer periphery of the cylinder 30, a lower chamber B and a reservoir chamber 32. Which defines the base 34 and the piston 32
A guide member 35 that guides the sliding of the piston rod 7 that is connected to the vehicle, a suspension spring 36 that is interposed between the outer cylinder 33 and the vehicle body, and a bumper bar 37.

Next, FIG. 5 is an enlarged sectional view showing a portion of the piston 31. As shown in FIG. 5, the piston 31 has through holes 31a and 31b formed therein, and each through hole is formed. An expansion side damping valve 12 and a compression side damping valve 20 that open and close 31a and 31b respectively are provided. In addition, the stud 38 that is fixed to the tip of the piston rod 7 and penetrates the piston 31 has an upper chamber A
Is formed with a communication hole 39 for communicating the lower chamber B with the lower chamber B. Further, an adjuster 40 for changing the flow passage cross-sectional area of the communication hole 39 and a fluid communication hole 39 depending on the direction of fluid flow are formed.
An expansion-side check valve 17 and a pressure-side check valve 22 that allow and block the flow of the air are provided. The adjuster 40 is rotated by the pulse motor 3 (see FIG. 4). In addition, the stud 38 has a first port 21, a second port 13, and a third port in order from the top.
A port 18, a fourth port 14 and a fifth port 16 are formed.

On the other hand, in the adjuster 40, a hollow portion 19 is formed, a first lateral hole 24 and a second lateral hole 25 which communicate the inside and the outside are formed, and a vertical groove 23 is formed in the outer peripheral portion. There is.

Therefore, between the upper chamber A and the lower chamber B, the inside of the extension side damping valve 12 is opened by passing through the through hole 31b as a flow passage through which the fluid can flow in the extension stroke. First side flow path D extending to B, second port 13, vertical groove 2
The expansion side second flow path E which opens the outer peripheral side of the expansion side damping valve 12 to the lower chamber B via the third and fourth ports 14, and the second
The extension side check valve 17 is opened via the port 13, the vertical groove 23, and the fifth port 16 to reach the lower chamber B.
Channel F, third port 18, second lateral hole 25, hollow portion 19
There are four flow paths, a bypass flow path G, which leads to the lower chamber B via. Also, as a flow path through which the fluid can flow in the pressure stroke,
The pressure-side first flow path H that opens the pressure-side damping valve 20 through the through hole 31a and the pressure-side check valve 22 through the hollow portion 19, the first lateral hole 24, and the first port 21 to open the upper chamber A. Pressure side second flow path J leading to the hollow part 19, the second lateral hole 2
5, There are three flow paths, a bypass flow path G reaching the upper chamber A via the third port 18.

That is, the shock absorber SA is constructed so that the damping coefficient can be changed in multiple steps by rotating the adjuster 40 with the characteristics shown in FIG. 6 on both the expansion side and the compression side. That is, as shown in FIG. 7, both the extension side and the compression side are in the soft state (hereinafter, the soft region S
When the adjuster 40 is rotated counterclockwise from (S), the damping coefficient can be changed in multiple steps only on the expansion side, and the compression side becomes a region where the damping coefficient is fixed to a low damping coefficient (hereinafter referred to as the expansion side hard region HS). On the contrary, when the adjuster 40 is rotated clockwise, the damping coefficient can be changed in multiple steps only on the compression side, and the extension side becomes a region where the low damping coefficient is fixed (hereinafter referred to as the compression side hard region SH). There is.

By the way, in FIG. 7, the KK cross section, the MM cross section, and the NN cross section in FIG. 10 and the damping force characteristics at each position are shown in FIGS.

Next, the operation of the control unit 4 for controlling the drive of the pulse motor 3 will be described with reference to the flowchart of FIG. Note that this control is separately performed for each shock absorber SA.

In step 101, the upper and lower G sensors 1,
The vertical acceleration obtained from 1, 1, 1 is applied to each filter circuit L.
This is a step of performing processing by PF1, BPF, and LPF2 to obtain a sprung vertical acceleration signal a and a sprung vertical velocity signal v as bounce components.

Step 102 uses the following equation 1
A control signal V (V
₁ , V ₂ , V ₃ , V ₄ ) is the step of calculating.

<Equation 1> Front wheel right V ₁ = v ₁ + A _f · a ₁ Front wheel left V ₂ = v ₂ + A _f · a ₂ Rear wheel right V ₃ = v ₃ + A _r · a ₃ Rear wheel left V ₄ = _{v 4 + a r · a 4} ( correction value) Note, a _f is the front wheels of the proportional constant a _r, the rear wheel proportionality constant a _1: on front right spring vertical acceleration signal a _2: on the front wheel left the spring vertical Acceleration signal a ₃ : Rear-spring right sprung vertical acceleration signal a ₄ : Rear-wheel left sprung vertical acceleration signal v ₁ : Front-right right sprung vertical velocity signal v ₂ : Front-wheel left sprung vertical velocity signal v ₃ : Spiral vertical speed signal on the right of the rear wheel v ₄ : Spiral vertical speed signal on the left of the rear wheel.

In each equation, A _f · a ₁ and A _r ·
The portion a ₁ is the correction value. Note that FIG. 18 shows the sprung vertical velocity signal v ₁ , the control signal V _1, and the correction value A _f · a _1.
FIG. 19 is a time chart showing the change characteristics of FIG.
Is low frequency (1.0 _Hz ) input, (b) in Fig. 18 is high frequency (2.
0 _Hz ) It shows the characteristic at the time of input. That is, as shown in this figure, at the time of low frequency (1.0 _Hz ) input, since the fluctuation range of the correction value A _f · a ₁ is small, the phase of the control signal V ₁ with respect to the sprung vertical velocity signal v ₁ is small. Amount of advance s
_{While 1} is small, when the high frequency (2.0 _Hz ) is input, the fluctuation range of the correction value A _f · a ₁ becomes large, so the phase of the control signal V ₁ advances with respect to the sprung vertical velocity signal v ₁ . Since the amount s ₂ becomes large, it is possible to cancel the phase delay of the control signal V ₁ with respect to the vibration frequency in the high frequency range.

Thus, the sprung vertical velocity and the correction value are obtained from the signals from the vertical G sensor 1, and the portions of the vertical G sensor 1 and the control unit 4 that obtain these are the springs within the scope of the claims. The upper / lower vertical velocity detecting means and the sprung vertical acceleration detecting means are constituted.

Step 103 is a step of determining whether or not the control signal V is equal to or larger than a predetermined threshold value δ _T , and if YES, the process proceeds to step 104, and if NO, the step 1
Go to 05.

Step 104 is a shock absorber S
This is a step of controlling A to the extension side hard area HS.

Step 105 is a step of judging whether or not the control signal V is a value between a predetermined threshold value δ _T and a threshold value −δ _{C. If} YES, then the routine proceeds to step 106, and if NO. Go to step 107.

Step 106 is a shock absorber S
This is a step of controlling A in the soft area SS.

Step 107 is a step which is displayed for the sake of convenience. If NO is determined in steps 103 and 105, the control signal V is below a predetermined threshold value -δ _C , and in this case, Go to step 108.

Step 108 is a shock absorber S
This is a step of controlling A to the pressure side hard area SH.

Next, the operation of the embodiment apparatus will be described with reference to the time chart of FIG.

When the control signal V changes as shown in this figure, when the control signal V is a value between the predetermined thresholds δ _T and -δ _C , the shock absorber SA is controlled to the soft region SS. To do.

When the control signal V becomes equal to or higher than the threshold value δ _T , the expansion side hard region HS is controlled to fix the compression side to a low damping coefficient, while the expansion side damping coefficient is made proportional to the control signal V. To change. At this time, the damping coefficient C is C = kV
Control so that. In addition, k shows a proportional constant.

When the control signal V becomes equal to or lower than the threshold value -δ _{C, the} compression side hard area SH is controlled to fix the extension side to a low damping coefficient, while the compression side damping coefficient is made proportional to the control signal V. To change. Also at this time, the damping coefficient C is C = k
・ V is controlled to be V.

As described above, in the vehicle suspension system according to the first embodiment, the correction value A _f · a ₁ obtained from the sprung acceleration signal a _{1 corresponds} to the sprung vertical velocity signal v ₁ . Of the control signal V ₁ obtained by adding the correction value A _f · a ₁ to the sprung vertical velocity signal v ₁ because the phase always advances and the amount of advance increases as the vibration frequency increases. By performing the damping coefficient control based on, the phase delay of the control signal V ₁ with respect to the vibration frequency exceeding the sprung resonance frequency is eliminated, and the control response is improved. As a result, as shown by the dotted line in FIG. It has a feature that it is possible to improve the riding comfort of the vehicle by reducing the transmissibility to the sprung in the sprung resonance frequency range.

Next, other embodiments will be described, but in describing these embodiments, only the differences from the first embodiment will be described. Also, the first reference numeral
The same reference numerals as those in the embodiment denote the same objects.

(Second Embodiment) In the second embodiment, as the shock absorber SA of the damping coefficient variable type, when the pulse motor 3 is driven, as shown in FIG. , With a well-known structure that changes from high damping to low damping (for example, see Japanese Utility Model Publication No. 63-112914).
This is an example of using the public relations).

In the second embodiment, as shown in FIG. 22, in addition to the sprung G sensor 1, a load sensor (a sprung / unsprung relative speed detecting means) 6, 6, 6, as an input means.
6 is provided. The load sensor 6 is provided at the mounting portion of the shock absorber SA to the vehicle body, and detects the damping force (corresponding to the relative speed) F generated in the shock absorber SA as a load. .

Control unit 304 of the second embodiment
23 will be described with reference to the flowchart of FIG. 23, the step 301 is to determine the damping force F detected by the load sensor 6.
Is a step of reading, and after this processing, steps 101 and 102 similar to those in the first embodiment are performed, and then the process proceeds to step 302.

In step 302, the damping force F and the control signal V
YES in the step of determining whether and are the same sign
Then, the process proceeds to step 303, and if NO (different sign), the process proceeds to step 304.

In step 303, the damping force F is F = k
-Change the damping coefficient so that it becomes V.

In step 304, the damping coefficient of the shock absorber SA is controlled so that both the extension and the compression have the minimum damping coefficient.

Although the embodiment has been described above, the specific configuration is not limited to this embodiment, and the present invention includes a design change and the like within a range not departing from the gist of the invention.

[0049]

As described above, in the vehicle suspension system of the present invention, the control signal obtained by adding the correction value obtained from the sprung vertical acceleration to the sprung vertical speed is obtained, and the damping coefficient control means uses this control signal. By controlling the damping coefficient of the shock absorber based on the above, the phase response of the sprung vertical velocity with respect to the vibration frequency exceeding the sprung resonance frequency is eliminated by the phase advance of the sprung vertical acceleration to control the response. As a result, it is possible to improve the ride quality of the vehicle by reducing the transmissibility to the sprung in the vibration frequency region exceeding the sprung resonance frequency.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a claim showing a vehicle suspension device of the present invention.

FIG. 2 is a structural explanatory view showing a vehicle suspension device of the first embodiment of the present invention.

FIG. 3 is a system block diagram showing a vehicle suspension system of the first embodiment.

FIG. 4 is a sectional view showing a shock absorber applied to the device of the first embodiment.

FIG. 5 is an enlarged cross-sectional view showing a main part of the shock absorber.

FIG. 6 is a damping force characteristic diagram corresponding to the piston speed of the shock absorber.

FIG. 7 is an attenuation coefficient characteristic diagram corresponding to the step position of the pulse motor of the shock absorber.

FIG. 8 is a K of FIG. 5 showing a main part of the shock absorber.
FIG.

FIG. 9 is an M of FIG. 5 showing a main part of the shock absorber.
FIG.

FIG. 10 is a sectional view taken along line NN of FIG. 5, showing a main part of the shock absorber.

FIG. 11 is a damping force characteristic diagram of the shock absorber when the extension side is hard.

FIG. 12 is a damping force characteristic diagram of the shock absorber in a soft state on the extension side and the compression side.

FIG. 13 is a damping force characteristic diagram of the shock absorber in a compression side hard state.

FIG. 14 is a block diagram showing a main part of a control unit of the first embodiment.

FIG. 15 is a flowchart showing the control operation of the control unit of the first embodiment device.

FIG. 16 is a time chart showing the operation of the first embodiment device.

FIG. 17 is a vibration transmissibility characteristic on the spring with respect to the vibration frequency of the device of the first embodiment.

FIG. 18 is a time chart showing change characteristics of a sprung vertical velocity signal, a control signal, and a correction value in the device of the first embodiment.

FIG. 19 is a gain characteristic with respect to a vibration frequency of a signal processed by the BPF of the first embodiment device.

FIG. 20 is a phase characteristic diagram of the sprung vertical velocity signal with respect to the vibration frequency of the first embodiment device.

FIG. 21 is a damping coefficient characteristic diagram of the shock absorber of the second embodiment device.

FIG. 22 is a system block diagram showing a device of the second embodiment.

FIG. 23 is a flowchart showing the control operation of the control unit of the second embodiment device.

[Explanation of symbols]

 a damping coefficient changing means b shock absorber c sprung vertical acceleration detecting means d sprung vertical speed detecting means e damping coefficient control means f sprung / unsprung relative speed detecting means

[Procedure amendment]

[Submission date] May 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

Next, FIG. 5 is an enlarged sectional view showing a portion of the piston 31. As shown in FIG. 5, the piston 31 has through holes 31a and 31b formed therein, and each through hole is formed. An expansion side damping valve 12 and a compression side damping valve 20 that open and close 31a and 31b respectively are provided. A communication hole 39 that communicates the upper chamber A and the lower chamber B is formed at the tip of the piston rod 7 that penetrates the piston 31, and the flow passage cross-sectional area of the communication hole 39 is changed. There is provided an adjuster 40 for this purpose, and an extension side check valve 17 and a pressure side check valve 22 that allow and block the flow of the fluid through the communication hole 39 depending on the direction of flow of the fluid. The adjuster 40 is rotated by the pulse motor 3 (see FIG. 4).
Further, at the tip of the piston rod 7, the first
A port 21, a second port 13, a third port 18, a fourth port 14 and a fifth port 16 are formed. Also, in the figure

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 4

[Correction method] Change

[Correction content]

[Figure 4]

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

Claims (4)

[Claims] 1. A shock absorber which is interposed between a vehicle body side and each wheel side and whose damping coefficient can be changed by a damping coefficient changing means, and a sprung vertical acceleration near the position where each shock absorber is provided is detected. The sprung vertical acceleration detection means, the sprung vertical speed detection means for detecting the sprung vertical speed in the vicinity of the position where each shock absorber is installed, and the damping coefficient of each shock absorber A vehicle suspension device, comprising: a damping coefficient control unit that controls based on a control signal to which a correction value obtained from acceleration is added. 2. A shock absorber which is interposed between the vehicle body side and each wheel side and whose damping coefficient can be changed by a damping coefficient changing means, and a sprung vertical acceleration in the vicinity of the position where each shock absorber is provided is detected. Sprung up / down acceleration detection means, sprung up / down speed detection means for detecting sprung up / down speed near the position where each shock absorber is installed, and sprung / unsprung position near the position where each shock absorber is installed Relative speed detection means for detecting the relative speed between the two, and the damping coefficient of each shock absorber is calculated by adding a correction value obtained from the sprung vertical acceleration to the sprung vertical speed to obtain a control signal and the sprung / spring. When the relative velocity between the lower parts has the same sign, the damping coefficient is increased, while when the sign has a different sign, the damping coefficient control means for controlling the damping coefficient to a minimum is provided. Vehicle suspension system, characterized in that. 3. The shock absorber includes an expansion side hard region in which the expansion side is variable and the compression side is fixed at a low damping coefficient, and a compression side hard region is in which the compression side is variable and the expansion side is fixed at a low damping coefficient. The damping coefficient control means controls the shock absorber in the extension side hard area when the control signal is equal to or higher than the positive threshold value, by forming the structure having three areas, that is, the soft area having the low damping coefficient on both the side and the compression side. The shock absorber is controlled in the pressure side hard area when the control signal is less than the negative threshold value, and the shock absorber is controlled in the soft area when the control signal is between the positive and negative threshold values. The vehicle suspension system according to claim 1, wherein: 4. The sprung vertical velocity and the sprung vertical acceleration in obtaining the control signal are signals that have passed through a band pass filter including the sprung resonance frequencies of the front and rear wheels, respectively. The vehicle suspension system according to claim 1 or claim 2.