JP3182020B2 - Vehicle suspension system - Google Patents

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 characteristic of a shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a vehicle suspension device for controlling damping characteristics of a shock absorber, for example, Japanese Unexamined Patent Publication No.
What is described in 163011 is known.

In this conventional vehicle suspension system, the direction of a sprung vertical speed determined by filtering from a sprung vertical acceleration detected by a sprung vertical acceleration sensor and a relative direction of a sprung and unsprung speed detected by a load sensor are described. When the discriminating codes are the same, the damping characteristics are hardened, and when the discriminating codes are different, the damping characteristics are controlled independently based on the Skyhook theory such that the damping characteristics are softened. .

[0004]

However, in the above-described conventional apparatus, as described above, the sprung vertical speed signal is obtained by filtering the sprung vertical acceleration signal detected by the sprung vertical acceleration sensor. Therefore, if the phase of the sprung vertical speed signal is matched to the vicinity of the sprung resonance frequency by band-pass filter processing, high-frequency input signals can be cut during low-speed running of the vehicle, so that the riding comfort of the vehicle is ensured. On the other hand, at the time of high-speed running, components near the sprung resonance frequency and low-frequency components become high, and both the phase and the gain are insufficient in the above-described band-pass filter processing. There is a problem that the vibration cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is directed to a vehicle suspension device capable of ensuring both the riding comfort of a vehicle at low speeds and the steering stability at high speeds. It is intended to provide.

[0006]

In order to achieve the above-mentioned object, a vehicle suspension system according to the present invention is interposed between a vehicle body side and each wheel side as shown in a conceptual view of a claim in FIG. A shock absorber b whose damping characteristic can be changed by the damping characteristic changing means a, a sprung vertical speed detecting means c for detecting a sprung vertical speed, and an output circuit of the sprung vertical speed detecting means c are provided in parallel. At least sprung resonance frequency
A plurality of filters d and d including different numbers and different pass frequency bands, a vehicle speed sensor e for detecting a vehicle speed, and a signal of a filter having a narrower pass frequency band including a sprung resonance frequency as the vehicle speed decreases. A signal synthesizing processing means f in which a signal synthesizing ratio of a filter having a wide pass frequency band including a sprung resonance frequency increases as the synthesizing ratio increases and, conversely, as the speed increases, the attenuation characteristics of each shock absorber b are at least determined by the signal synthesizing. And damping characteristic control means g for performing optimal control based on the vehicle behavior detection value including the sprung vertical speed signal synthesized by the processing means f.

[0007]

Since the vehicle suspension system of the present invention is configured as described above, when the vehicle is running at a low speed, for example, the sprung vertical speed signal having a narrow frequency band including the sprung resonance frequency is mainly used. This makes it possible to perform the damping characteristic control based on the synthesized signal, whereby the damping characteristic control on the high damping characteristic side due to the high-frequency vibration input is cancelled.

Accordingly, high-frequency vibration input from the road surface during low-speed running can be absorbed with low damping characteristics and transmission to the sprung can be suppressed. Can be secured.

When the vehicle is running at high speed, damping characteristic control is performed based on a composite signal mainly composed of a sprung vertical speed signal having a wider frequency band. Since the speed approaches the actual sprung speed and the gain increases, effective damping characteristic control is performed.

Therefore, it is possible to improve the vibration damping property to the low frequency vibration input and the responsiveness to the high frequency input at the time of high-speed running, so that the steering stability of the vehicle can be secured.

[0011]

An embodiment of the present invention will be described with reference to the drawings. (First Embodiment) First, the configuration will be described.

FIG. 2 is an explanatory view showing the structure of the vehicle suspension system according to the first embodiment. The vehicle suspension device is interposed between the vehicle body and four wheels, and is provided with four shock absorbers SA ₁ , SA ₂ and SA.
₃ , SA ₄ (when describing these shock absorbers collectively and when describing their common configuration, they are simply indicated as SA). Then, a vertical acceleration sensor (hereinafter, referred to as a vertical G sensor) 1 ₁ , which detects a sprung vertical acceleration, is provided on the vehicle body near each shock absorber SA.
1 ₂ , 1 ₃ , 1 ₄ (in the description of the upper and lower G sensors, when these four are collectively referred to, and when describing their common configuration, they are simply indicated as 1), At a position near the driver's seat, there is provided a control unit 4 that receives signals from the upper and lower G sensors 1 and the vehicle speed sensor 5 and outputs a drive control signal to the pulse motor 3 of each shock absorber SA. .

FIG. 3 is a system block diagram showing the above configuration. The control unit 4 includes an interface circuit 4a, a CPU 4b, and a drive circuit 4c. , And the vehicle speed signal from the vehicle speed sensor 5 are input. As shown in FIG. 14, a set of five filter circuits is provided in the interface circuit 4a. That is, the LPF 1 is a low-pass filter for removing high-frequency (30 Hz or more) noise from the sprung vertical acceleration signal. The LPF 2 is a low-pass filter circuit for integrating the sprung vertical acceleration and converting it into a sprung vertical speed signal. HPF1 is a high-pass filter having a cut-off frequency of 1.0 Hz, and LPF3 is a low-pass filter having a cut-off frequency of 1.5 Hz. Both filters have a narrow frequency band including a sprung resonance frequency (1.0H).
The band-pass filter BPF1 obtains a sprung vertical speed signal Va of z to 1.5 Hz). HPF2 is provided in parallel with both filters HPF1 and LPF3,
A high-pass filter having a cutoff frequency of 0.1 Hz constitutes a band-pass filter BPF2 for obtaining a sprung vertical velocity signal Vb in a wide frequency band (0.1 Hz to ΔHz).

Next, FIG. 4 is a sectional view showing the structure of the shock absorber SA.
A is a cylinder 30, a piston 31 that defines the cylinder 30 in an upper chamber A and a lower chamber B, an outer cylinder 33 in which a reservoir chamber 32 is formed on the outer periphery of the cylinder 30, a lower chamber B and a reservoir chamber 32. Base 34 and piston 31
A guide member 35 for guiding the sliding of the piston rod 7 connected to the outer cylinder 33, a suspension spring 36 interposed between the outer cylinder 33 and the vehicle body, and a bump rubber 37.

FIG. 5 is an enlarged sectional view showing a part of the piston 31. As shown in FIG. 5, the piston 31 has through holes 31a and 31b formed therein, and An expansion damping valve 12 and a compression damping valve 20 for opening and closing 31a and 31b, respectively, are provided. A stud 38 that penetrates the piston 31 is screwed and fixed to the bound stopper 41 screwed to the tip of the piston rod 7, and the stud 38 bypasses the through holes 31a and 31b. Communication for forming flow paths (extension-side second flow paths E, expansion-side third flow paths F, bypass flow paths G, and compression-side second flow paths J to be described later) that communicate the upper chamber A and the lower chamber B. A hole 39 is formed.
An adjuster 40 for changing the flow path cross-sectional area of the flow path is rotatably provided in 9. Also, stud 38
The communication hole 3 is formed on the outer periphery of the communication hole 3 in accordance with the direction of fluid flow.
An expansion-side check valve 17 and a compression-side check valve 22 that allow and shut off the flow on the flow path side formed by 9 are provided. The adjuster 40 is rotated by the pulse motor 3 via a control rod 70 (see FIG. 4). The first port 21, the second port 13, the third port 18, the fourth port 14, and the fifth port 16 are formed on the stud 38 in order from the top.

On the other hand, the adjuster 40 has a hollow portion 19, a first horizontal hole 24 and a second horizontal hole 25 communicating between the inside and the outside, and a vertical groove 23 formed in the outer peripheral portion. I have.

Therefore, between the upper chamber A and the lower chamber B, a through-hole 31 is formed as a flow path through which fluid can flow in the extension stroke.
b, the inside of the extension side damping valve 12 is opened to open the lower chamber B
, The second port 13, the vertical groove 23,
Via the second port 13, the vertical groove 23, and the fifth port 16 via the fourth port 14, the outer peripheral side of the extension side damping valve 12 is opened to open the outer peripheral side of the extension side damping valve 12 to reach the lower chamber B, Then, the extension side check valve 17 is opened to open the extension side third flow path F to the lower chamber B, and the bypass to the lower chamber B via the third port 18, the second horizontal hole 25, and the hollow portion 19. There are four flow paths G. In addition, as a flow path through which fluid can flow in the pressure stroke, the pressure side first valve that opens the pressure side damping valve 20 through the through hole 31a.
Channel H, hollow portion 19, first lateral hole 24, first port 21
, The pressure-side second flow path J that opens the pressure-side check valve 22 to reach the upper chamber A through the air passage, and the bypass flow that reaches the upper chamber A through the hollow portion 19, the second horizontal hole 25, and the third port 18. Road G
And three flow paths.

That is, the shock absorber SA is configured so that the damping characteristic can be changed in multiple steps by rotating the adjuster 40 with the characteristics shown in FIG. 6 on both the extension side and the compression side. That is, as shown in FIG. 7, when the adjuster 40 is rotated counterclockwise from a state where both the extension side and the compression side are soft (hereinafter, referred to as a soft area SS), the attenuation characteristic of the extension side only is multi-stepped. It is possible to change the compression side to a region where the compression side is fixed to the low attenuation characteristic (hereinafter referred to as the extension side hard region HS). Conversely, when the adjuster 40 is rotated clockwise, the attenuation characteristic of only the compression side can be changed in multiple stages. The extension side has a structure fixed to a low attenuation characteristic (hereinafter referred to as a compression side hard area SH).

FIG. 7 shows the KK section, LL section, MM section, and NN section in FIG. 8, 9 and 10 and the damping force characteristics at each position are shown in FIGS.

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

First, in step 101, a sprung vertical acceleration signal obtained from each of the vertical G sensors 1 is processed by a set of five filter circuits shown in FIG. Processing for obtaining the speed signals Va and Vb is performed. The signals Va and Vb are given positive values when the sprung vertical acceleration is in the upward direction, and are given negative values when the sprung vertical acceleration is in the downward direction.

In step 102, a combined sprung vertical speed signal Vs obtained by combining the sprung vertical speed signals Va and Vb is obtained based on the following equation.

Vs = θa · m · Va + θb (1−m) · Vb where θa and θb are proportional constants and m is a coefficient. The coefficient m is a function of the vehicle speed as shown in the map of FIG. The function is such that the coefficient is 1 when the vehicle speed is 0 and the coefficient value decreases as the vehicle speed increases. Therefore, at low speed, a synthesized signal Vs is obtained in which the sprung vertical speed signal Va having a narrow frequency band (1.0 Hz to 1.5 Hz) is mainly used.
Further, at high speed, a synthesized signal Vs is obtained in which the sprung vertical speed signal Vb having a wide frequency band (0.1 Hz to ΔHz) is mainly used.

In step 103, proportional constants α (α _f , α _r ) and β (β _f , β _r ) as functions of the vehicle speed obtained by the vehicle speed sensor 5 are set based on the map shown in FIG.

[0025] Step 104, using the following equation, the sprung mass vertical velocity synthesized signal _{Vs (Vs 1, Vs 2,} Vs 3, V
s ₄ ) and the control signals V (V _FR , V _FL , V _RR , V _RL ) of the position of each wheel are calculated based on the proportional constants α, β, γ.

[0026] The front wheel right _{V FR = α f · Vs 1} + β f (Vs 1 -Vs 3) + γ f (Vs 1
−Vs ₂ ) front wheel left V _FL = α _f · Vs ₂ + β _f (Vs ₂ −Vs ₄ ) + γ _f (Vs ₂
−Vs ₁ ) right rear wheel V _RR = α _r · Vs ₃ + β _r (Vs ₃ −Vs ₁ ) + γ _r (Vs ₃
−Vs ₄ ) Rear wheel left V _RL = α _r · Vs ₄ + β _r (Vs ₄ −Vs ₂ ) + γ _r (Vs ₄
−Vs ₃ ) Note that α _f , β _f , and γ _f are the respective proportional constants of the front wheels α _r , β _r , and γ _r are the respective proportional constants of the rear wheels.

In each equation, the part bounded by the first α _f and α _r is the bounce rate, and β _f and β _r
The portion between the two is the pitch rate, γ _f , γ _r
The rolled part is the roll rate.

[0028] Step 105, the control signal V is a step equal to or larger than a predetermined threshold value [delta] _T, controls the shock absorber SA to the extension side hard region HS proceeds to step 106 is YES Then, the process proceeds to step 107 if NO.

[0029] Step 107, the control signal V is determining whether a value between a predetermined threshold value [delta] _T and the threshold - [delta _C, shock absorber proceeds to step 108 is YES The SA is controlled to the soft area SS, and the process proceeds to step 109 if NO.

Step 109 is a step displayed for the sake of convenience.
When it is determined that O is the control signal V is less than a predetermined threshold value - [delta _C, in this case, the process proceeds to step 110,
The shock absorber SA is controlled to the pressure side hard area SH.

Next, the control operation of the control unit 4 will be described with reference to the time chart of FIG.

When the control signal V based on the sprung vertical velocity changes as shown in FIG. 3, when the control signal V is a value between the predetermined threshold values δ _T and −δ _C , the shock absorber SA is turned off. Control to the soft area SS.

When the control signal V becomes equal to or greater than the threshold value δ _{T, the} compression side is controlled to the expansion side hard region HS so that the compression side is fixed to the low attenuation characteristic, while the expansion side attenuation characteristic is made proportional to the control signal V. Change. At this time, the attenuation characteristic C is C = k ₁ · V
Is controlled so that Incidentally, k ₁ is a proportionality constant of the expansion side.

When the control signal V becomes equal to or less than the threshold value -δ _{C, the} compression side is controlled to the compression side hard area SH to fix the extension side to the low attenuation characteristic, while making the compression side attenuation characteristic proportional to the control signal V. Change. Also at this time, the attenuation characteristic C is C = k ₂
・ V is controlled to be V. Note that k ₂ is a proportional constant on the pressure side.

In the time chart of FIG.
The area a is a state in which the control signal V based on the sprung vertical speed is reversed from a negative value (downward) to a positive value (upward), but at this time, the relative speed is still a negative value (the shock absorber SA has a negative value). Since the stroke is a pressure stroke side), at this time, the shock absorber SA is controlled to the extension side hard region HS based on the direction of the control signal V.
Therefore, in this area a, the shock absorber S at that time is
The pressure stroke side, which is the stroke of A, has soft characteristics.

In the region b, the control signal V based on the sprung vertical speed remains a positive value (upward), and the relative speed changes from a negative value to a positive value (the stroke of the shock absorber SA is on the extension stroke side). At this time, the shock absorber SA is controlled to the extension-side hard area HS based on the direction of the control signal V, and the stroke of the shock absorber is also the extension stroke. In this region b, the extension stroke side, which is the stroke of the shock absorber SA at that time, has a hard characteristic proportional to the value of the control signal V.

The area c is a state in which the control signal V based on the sprung vertical velocity is reversed from a positive value (upward) to a negative value (downward). At this time, the relative velocity is still a positive value. (The stroke of the shock absorber SA is on the extension stroke side.) At this time, the shock absorber SA is controlled to the compression-side hard region SH based on the direction of the control signal V. In c, the softening characteristic is on the extension stroke side which is the stroke of the shock absorber SA at that time.

In the area d, the control signal V based on the sprung vertical speed remains a negative value (downward), and the relative speed changes from a positive value to a negative value (the stroke of the shock absorber SA is on the extension stroke side). At this time, the shock absorber SA is controlled to the compression-side hard region SH based on the direction of the control signal V, and the stroke of the shock absorber is also the compression stroke. Then, the pressure stroke side, which is the stroke of the shock absorber SA at that time, has a hard characteristic proportional to the value of the control signal V.

As described above, in this embodiment, when the sprung vertical speed and the relative speed between the sprung and unsprung have the same sign (region b, region d), the shock absorber S at that time is used.
A damping characteristic control based on the skyhook theory, in which the stroke side of A is controlled to a hard characteristic, and when the sign is different (regions a and c), the stroke side of the shock absorber SA at that time is controlled to a soft characteristic. The same control will be performed without detecting the relative speed between sprung and unsprung. Further, in this embodiment, when shifting from the area a to the area b and from the area c to the area d, the switching of the damping characteristic is performed without driving the pulse motor 3.

Next, a control operation based on a change in the traveling speed of the vehicle will be described. (A) Low-speed running When the vehicle is running at low speed, the damping based on the composite signal Vs in which the sprung vertical speed signal Va having a narrow frequency band including the sprung resonance frequency (1.0 Hz to 1.5 Hz) is mainly used. Characteristic control is performed, and thereby, a state is obtained in which the damping characteristic control on the high damping characteristic side due to the high-frequency vibration input is cancelled.

[0041] Therefore, the Oite at the time of low-speed running low frequency Der
Characteristics of the sprung resonance frequency due to the sprung vertical speed signal
Control is performed, and the damping characteristics of the shock absorber SA
It will be controlled to the low damping characteristic side,
During both low-speed running, high-frequency vibration input from unsprung
Since it is possible to suppress the transmission to the sprung portion by absorbing the low damping characteristic of the shock absorber SA, it is possible to eliminate the rugged feeling due to the high-frequency vibration input and to secure the riding comfort of the vehicle.

(B) High-speed running When the vehicle is running at high speed, a wide frequency band (0.1H
z to ∞Hz) Damping characteristic control is performed based on the composite signal Vs in which the sprung vertical speed signal Vb is dominant, whereby the phase at a low frequency approaches the actual sprung speed and the gain is increased. Becomes effective, effective damping characteristic control is performed.

Accordingly, the vibration damping property against low-frequency vibration input is improved, and the steering stability of the vehicle during high-speed running can be ensured.

As described above, in this embodiment, the following effects can be obtained. This makes it possible to ensure both the riding comfort of the vehicle at low speed running and the steering stability at high speed running.

Since a sufficient control force can be generated not only for the bounce but also for the pitch and roll due to the moment of inertia, it is possible to provide a vehicle suspension system that is excellent in vehicle ride comfort and steering stability. .

Since the frequency of switching the attenuation characteristic is reduced as compared with the attenuation characteristic control based on the conventional skyhook theory, the control response can be improved and the durability of the pulse motor 3 can be improved.

In obtaining the bounce rate, pitch rate, and roll rate, different coefficients α,
Since β and γ are used, in the vehicle, even if the sprung resonance frequency, the pitch resonance frequency, and the roll resonance frequency are different from each other, each rate can be accurately detected based on the sprung vertical speed.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment only in a part of the control contents of the control unit 4 in the first embodiment, and the other configuration is the same as the first embodiment. Therefore, only the differences will be described. . This embodiment shows an example in which three or more band-pass filters are provided in the filter circuit as shown in FIG.
That is, as shown in FIG. 19, three or more band-pass filters _{BPF 1, BPF 2, ·······,} BPF n, it is provided in parallel. BPF ₁ has a cutoff frequency of 1.0 Hz and HPF ₁ has a cutoff frequency of 1.0 Hz.
It consists of the LPF ₁ and, BPF ₂ includes a HPF ₂ cutoff frequency is 0.8 Hz, consists of a cut-off frequency and LPF ₂ of 1.1 Hz, although not (shown, BPF ₃
Is composed of HPF ₃ having a cut-off frequency of 0.1 Hz and LPF ₃ having a cut-off frequency of 5.0 Hz.
PF _n is turned cutoff frequency comprised of 0.1Hz the HPF _n (cutoff frequency functions of both the LPF _n of ∞Hz), so on, gradually as the frequency band becomes wider configuration ing. And in this example,
In step 102 in FIG. 15, the combined signal Vs of the sprung vertical velocity is obtained by the following equation.

Vs = θ ₁ · m ₁ · V ₁ + θ ₂ · m ₂ · V ₂ + ··· + θ _n · m _n ·
V _n where θ (θ ₁ , θ ₂ ,..., Θ _n ) is a proportionality constant and m (m
_1, m _2, · · · ·, m _n) is a coefficient, the coefficients m
_{Is, m 1 + m 2 + ····} + m n = have been set to 1 and becomes such a value, the coefficient m _1, m _2, · · · ·, m _n is 2
As shown in the map of FIG.
When the coefficient m ₁ is 1, the coefficient m increases as the vehicle speed increases.
_The function is such that the coefficient value increases in the order of the coefficients m ₂ ,..., _Mn while the value of ₁ decreases. In the gain characteristic diagram of FIG. 21 and the phase characteristic diagram of FIG. 22, the dotted line shows the processed signal of BPF ₂ , the chain line shows the processed signal of BPF ₃ , and the solid line shows the processed signal of BPF _n . Thus, the gain and the phase can be changed in the direction of the arrow as the vehicle speed increases.

That is, when the vehicle is running at a low speed, m ₁
Since the side coefficient value increases, the vertical sprung mass velocity signal V ₁ of the vicinity of the sprung resonance frequency is a processing signal of BPF ₁
In this case, the damping characteristic control based on the synthesized signal Vs is mainly performed, whereby the damping characteristic control on the high damping characteristic side due to the high frequency vibration input is cancelled. As in the case of the first embodiment, the rugged feeling due to the high-frequency vibration input can be eliminated and the riding comfort of the vehicle can be ensured.

In the high-speed running state, the coefficient value on the _mn side becomes large. Therefore, the sprung vertical speed signal V _n having a wide wave number band (0.1 Hz to ΔHz), which is a processed signal of the BPF _n , is obtained.
In this case, the damping characteristic control based on the synthesized signal Vs, which is the main component, is performed, and thereby, as in the case of the first embodiment, the damping property to the low frequency vibration input and the response to the high frequency input are improved. As a result, the steering stability of the vehicle during high-speed running can be ensured.

As described above, in this embodiment, since an optimal control signal can be obtained according to the change in the traveling speed of the vehicle, fine control of the damping characteristic adapted to each stage from low speed to high speed can be performed. Will be able to do it.

Although the embodiment has been described above, the specific configuration is not limited to this embodiment, and any change in design or the like without departing from the gist of the present invention is included in the present invention.

For example, in the embodiment, a part of the proportionality constant is changed depending on the vehicle speed. However, it may be set to a constant value.

Further, in the embodiment, the case where the damping characteristic control is performed based only on the sprung vertical speed is described. However, when the control is performed in combination with other vehicle behaviors such as the sprung and unsprung relative speed. The present invention can be applied.

Further, in the embodiment, when the damping characteristic on one of the stroke side on the extension side and the compression side is variably controlled, the shock absorber having a structure in which the reverse stroke side is maintained at a predetermined low damping characteristic is used. Control using a shock absorber having a structure in which the damping characteristics of the pressure side and the compression side simultaneously change can be performed.

[0057]

As described above, the vehicle suspension according to the present invention has a sprung resonance frequency as the vehicle speed decreases.
Narrow signal combination ratio of the filter pass-frequency band including the increases, sprung resonance frequency as becomes faster reversed
With the provision of the signal synthesizing processing means for increasing the signal synthesizing ratio of the filter having a wide pass frequency band including the above, it is possible to secure both the riding comfort of the vehicle at low speed running and the steering stability at high speed running. Is obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual view of a claim showing a vehicle suspension system of the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration of a vehicle suspension device according to an embodiment of the present invention.

FIG. 3 is a system block diagram showing a vehicle suspension device according to the embodiment.

FIG. 4 is a cross-sectional view showing a shock absorber applied to the embodiment device.

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

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

FIG. 7 is a damping characteristic diagram corresponding to a step position of a pulse motor of the shock absorber.

FIG. 8 is a perspective view of the shock absorber shown in FIG.
It is -K sectional drawing.

FIG. 9 is a perspective view of the shock absorber shown in FIG.
It is an L sectional view and MM sectional view.

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 when the shock absorber is on the extension side hard.

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

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

FIG. 14 is a block diagram illustrating a filter circuit.

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

FIG. 16 is a time chart showing the control operation of the control unit.

FIG. 17 is a map showing variable characteristics of a coefficient with respect to a vehicle speed.

FIG. 18 is a map showing a variable characteristic of a proportional constant with respect to a vehicle speed.

FIG. 19 is a block diagram showing a filter circuit in the vehicle suspension system of the second embodiment.

FIG. 20 is a map showing variable characteristics of a coefficient with respect to a vehicle speed in the vehicle suspension system of the second embodiment.

FIG. 21 is a gain characteristic diagram with respect to a vibration frequency of a sprung vertical velocity signal that has passed through each band-pass filter in the device of the second embodiment.

FIG. 22 is a phase characteristic diagram with respect to a vibration frequency of a sprung vertical velocity signal that has passed through each band-pass filter in the device of the second embodiment.

[Explanation of symbols]

 a damping characteristic changing means b shock absorber c sprung vertical speed detecting means d filter e vehicle speed sensor f signal synthesis processing means g damping characteristic control means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-358917 (JP, A) JP-A-61-1520 (JP, A) JP-A-61-163011 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) B60G 17/015

Claims (1)

(57) [Claims] 1. A shock absorber interposed between a vehicle body side and each wheel side and capable of changing a damping characteristic by a damping characteristic changing means, a sprung vertical speed detecting means for detecting a sprung vertical speed, A plurality of filters provided in parallel with the output circuit of the vertical speed detecting means and including at least a sprung resonance frequency and having different pass frequency bands, a vehicle speed sensor for detecting a vehicle speed, and as the vehicle speed decreases, The signal combining ratio of a filter having a narrow pass frequency band including a sprung resonance frequency increases, and conversely, the signal combining ratio of a filter having a wide passing frequency band including a sprung resonant frequency increases as the speed increases. Signal synthesizing processing means, and vehicle behavior detection including at least a sprung vertical velocity signal synthesized by the signal synthesizing processing means with damping characteristics of each shock absorber. Vehicle suspension system, characterized in that it and a damping characteristic control means for optimal control based on.