JPH0999722A - Vehicle suspension device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in comfortableness to ride in and maneu vering stability of a vehicle even to a fuel quantity change in a fuel tank by providing a fuel detecting means to detect a quantity of fuel in the fuel tank and a control gain variable means to vary a control gain according to a detected fuel quantity. SOLUTION: In a damping force characteristic control means (d), damping force characteristic control of respective shock absorbers (b) is performed on the basis of a vehicle behavior signal of respective wheel positions detected by a vehicle behavior detecting means (c) and a control signal obtained by a prescribed control gain. On the other hand, in a control gain variable means (f), variable control of the control gain is performed according to a fuel quantity in a fuel tank detected by a fuel detecting means (e). Therefore, the occurrence of an overs and shorts condition of control force by an increase-decrease change in a fuel quantity in the fuel tank is prevented by variable control of a damping force characteristic. Therefore, the deterioration of comfortableness to ride in and maneuvering stability of a vehicle can be prevented from damage.

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 ensuring ride comfort and steering stability of a vehicle by optimally controlling a damping force characteristic of each shock absorber.

[0002]

2. Description of the Related Art Conventionally, as a vehicle suspension system for controlling a damping force characteristic of a shock absorber, for example, Japanese Patent Publication No.
The one described in Japanese Patent No. 500490 is known.

This conventional vehicle suspension system detects a dynamic vehicle traveling state by a sensor and forms a control signal for controlling a semi-active shock absorber provided on each wheel of the vehicle, and the control signal and the damping signal are generated. The vehicle body was controlled according to the actual value of the force.

[0004]

However, the conventional device has the following problems because no consideration is given to changes in vehicle weight.

That is, in this conventional apparatus, the control gain is set for controlling the damping force characteristic of the shock absorber in each wheel in consideration of a constant vehicle weight and the wheel load balance between the wheels. However, when the fuel tank is full of fuel and when it is almost empty, the weight of the vehicle changes significantly and the wheel load balance between the wheels changes depending on the position of the fuel tank. If it is fixed to the control gain of, the control gain with respect to the running state of the vehicle will not be appropriate.

That is, when the control tuning of the damping force characteristic in the vehicle is performed with a certain reference fuel amount, when the vehicle travels with a larger amount than the reference fuel amount, the inertial force on the spring is increased. As a result, the control force becomes insufficient and the feeling of fluffiness increases, and conversely, when the vehicle travels with an amount smaller than the reference fuel amount, the inertial force on the spring decreases, resulting in excessive control force. Therefore, there is a possibility that optimum ride comfort and steering stability may not be obtained.

The present invention has been made by paying attention to the above-mentioned conventional problems, and can prevent deterioration of the riding comfort and steering stability of the vehicle even when the amount of fuel in the fuel tank changes. It is intended to provide a vehicle suspension system.

[0008]

In order to achieve the above-mentioned object, a vehicle suspension system according to claim 1 of the present invention is provided between a vehicle body side and each wheel side as shown in the claim correspondence diagram of FIG. A shock absorber b intervening in the vehicle and capable of changing the damping force characteristic by the damping force characteristic changing means a, a vehicle behavior detecting means c for detecting the vehicle behavior at each wheel position, and the vehicle behavior detecting means c. A vehicle suspension system including damping force characteristic control means d for performing damping force characteristic control of each shock absorber b based on a vehicle behavior signal at each wheel position and a control signal obtained from a predetermined control gain. The fuel amount detecting means e for detecting the amount of fuel and the control gain varying means f for variably controlling the control gain according to the fuel amount detected by the fuel amount detecting means e are provided.

Further, in the vehicle suspension system according to a second aspect of the invention, the vehicle behavior detecting means c is composed of a sprung vertical speed detecting means g for detecting a sprung vertical speed, and the damping force characteristic of the shock absorber b is changed. When the means a variably controls the damping force characteristic on one stroke side of the extension stroke side and the compression stroke side to the hard characteristic side, the damping force characteristic on the other stroke side is fixed to the soft characteristic. When the damping force characteristic control means d is formed and the direction discrimination code of the sprung vertical velocity detected by the sprung vertical velocity detecting means g is upward positive, the damping force characteristic on the extension side of the shock absorber b is formed. Is a means configured to variably control the damping force characteristic on the pressure stroke side in accordance with the control signal when the downward force is negative.

[0010]

In the vehicle suspension system according to the first aspect of the present invention, as described above, the damping force characteristic control means d uses the vehicle behavior signal of each wheel position detected by the vehicle behavior detection means c and a predetermined control gain. While the damping force characteristic control of each shock absorber b is performed based on the obtained control signal,
In the control gain varying means f, the control gain is variably controlled according to the amount of fuel in the fuel tank detected by the fuel amount detecting means e. Therefore, it is possible to prevent the control force from being excessively or deficiently caused by the increase / decrease in the amount of fuel in the fuel tank by the variable control of the damping force characteristic, thereby preventing deterioration of the riding comfort and the steering stability of the vehicle. it can.

Further, in the vehicle suspension system according to claim 2,
In the damping force characteristic control means d, when the direction discrimination sign of the sprung vertical velocity detected by the sprung vertical velocity detecting means g is upward positive, the damping force characteristic on the extension side of the shock absorber b is negative downward. Is, the damping force characteristic on the pressure stroke side is variably controlled according to the control signal, while the damping force characteristic on the reverse stroke side is in a state of being fixedly controlled by software. In the damping range where the direction discrimination codes of the sprung vertical velocity and the sprung-unsprung relative velocity match, the damping force characteristic on the stroke side of the shock absorber b at that time is variably controlled by the hardware characteristic side. The damping force characteristic of the vehicle is weakened by increasing the damping force characteristic of the shock absorber b at that time in the vibration range where the direction discrimination codes of the two do not match. Such so that the switching control of the basic damping force characteristic based on skyhook control theory is carried out.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a configuration explanatory view of a vehicle suspension system showing an embodiment of the present invention, in which four shock absorbers SA _FL , S are interposed between a vehicle body and four wheels.
A _FR , SA _RL , SA _RR (Note that in describing the shock absorber, when these four are collectively referred to, and when describing their common configuration, they are simply indicated as SA. Indicates the wheel position.
_FL indicates front wheel left, _FR indicates front wheel right, _RL indicates rear wheel left, and _RR indicates rear wheel right. ) Is provided. A vertical acceleration sensor (hereinafter referred to as a vertical acceleration sensor) for detecting a vertical acceleration G is provided on the vehicle body at a position (tower position) near the front wheel left and right shock absorbers SA _FL and SA _FR and the rear wheel left and right shock absorbers SA _RL and SA _RR. , Up and down G sensor) 1
_FL , 1 _FR , 1 _RL , 1 _RR are provided, and although not shown, a fuel amount detecting means 2 for detecting the fuel amount M in the fuel tank is provided, and further, in the vicinity of the driver's seat, A control unit 4 for inputting signals from the upper and lower G sensors 1 (1 _FL , 1 _FR , 1 _RL , 1 _RR ) and the fuel amount detection means 2 and outputting a drive control signal to the pulse motor 3 of each shock absorber SA. Is provided.

The above configuration is shown in the system block diagram of FIG. 3, 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 each of the vertical G sensors 1 _FL. , 1 _FR , 1 _RL , 1 _RR sprung vertical acceleration G _FL ,
The G _FR , G _RL and G _RR signals and the fuel amount M signal from the fuel amount detecting means 2 are input. Then, as shown in FIG. 14, the interface circuit 4a uses the sprung vertical accelerations G _FL , G _FR , G _RL , and G _RR signals to determine the sprung vertical velocities Δx _FL , Δx _FR , and Δx _{RL at} the respective tower positions. Δx _RR and relative speed between sprung and unsprung (Δx−Δx ₀ ) _FL , (Δx−Δx
₀ ) _FR , (Δx-Δx ₀ ) _RL , and (Δx-Δx ₀ ) _RR are provided for the signal processing circuit. The details of this signal processing circuit will be described later.

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. Defining the base 34 and the 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.

Next, FIG. 5 is an enlarged sectional view showing a portion of the piston 31. As shown in FIG. 5, the piston 31 is formed with through holes 31a and 31b, and each through hole is formed. A compression side damping valve 20 and an expansion side damping valve 12 that open and close 31a and 31b respectively are provided. Further, a stud 38 penetrating 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 a flow path (an expansion-side second flow path E, an expansion-side third flow path F, a bypass flow path G, and a compression-side second flow path J described later) that connects the upper chamber A and the lower chamber B with each other. A hole 39 is formed and this communication hole 3
An adjuster 40 for changing the flow passage cross-sectional area of the flow passage is rotatably provided inside the passage 9. Also, the 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. It should be noted that this adjuster 40 corresponds to the pulse motor 3
Is rotated through the control rod 70 (see FIG. 4). Also, the stud 38 has
A first port 21, a second port 13, a third port 18, a fourth port 14, and a fifth port 16 are formed in this order from the top.

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, a through hole 31 is provided between the upper chamber A and the lower chamber B as a flow passage through which a 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
To the extension side first flow path D, the second port 13, the vertical groove 23,
Via 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 fourth port 14, the second port 13, the vertical groove 23, and the fifth port 16. Then, the extension side check valve 17 is opened to reach the lower chamber B by way of the third side flow passage F extending to the lower chamber B and the third port 18, the second lateral hole 25, and the hollow portion 19. There are four channels, channel G. Further, as a flow path through which the 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 is used.
Flow path 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 constructed so that the damping force characteristic can be changed in multiple stages on both the extension side and the compression side by the characteristic as shown in FIG. 6 by rotating the adjuster 40. That is, as shown in FIG.
The state in which both pressure sides are soft (hereinafter, soft area SS
When the adjuster 40 is rotated counterclockwise from
When the damping force characteristic can be changed in multiple stages only on the extension side and the compression side is a region fixed to the low damping force characteristic (hereinafter referred to as the extension side hard region HS). Conversely, when the adjuster 40 is rotated clockwise, Only the compression side has a structure in which the damping force characteristic can be changed in multiple stages, and the extension side is a region fixed to the low damping force characteristic (hereinafter referred to as a compression side hard region SH).

Incidentally, in FIG. 7, when the adjuster 40 is arranged in the position of, the KK section, the LL section and the MM section, the NN section in FIG. 8, FIG. 9, and FIG. 10, and the damping force characteristics at each position are shown in FIGS.

Next, in the control operation of the control unit 4, the configuration of the signal processing circuit for obtaining the sprung vertical velocity Δx and the sprung-unsprung relative velocity (Δx-Δx ₀ ) is shown in the block diagram of FIG. It will be described with reference to the drawings.

First, in B1, the phase delay compensation formula is used,
Each vertical G sensors _{1 (1 FL, 1 FR,} 1 RL, 1 RR) on each spring is detected by the vertical acceleration _{G (G FL, G FR,} G RL, G RR)
Is converted into a sprung vertical speed signal at each tower position.

The general equation for phase delay compensation can be expressed by the following transfer function equation (1).

G _(S) = (AS + 1) / (BS + 1) (1) (A <B) Then, a frequency band (0.5 Hz to 3) necessary for damping force characteristic control is obtained.
Hz), has the same phase and gain characteristics as the case of integration (1 / S), and as a phase lag compensation equation for lowering the gain on the low frequency side (up to 0.05 Hz), the following transfer function equation (2 ) Is used.

G _(S) = (0.001 S + 1) / (10 S + 1) × γ (2) Note that γ is a signal and gain characteristic when the speed is converted by integration (1 / S). Is a gain for matching, and in this embodiment, γ = 10 is set. as a result,
The gain characteristic of the solid line in (a) of FIG. 15 and FIG.
As shown in the solid line phase characteristic in (b) of 5, the state where only the low frequency side gain is reduced without deteriorating the phase characteristic in the frequency band (0.5 Hz to 3 Hz) required for damping force characteristic control. Becomes The dotted lines (a) and (b) in FIG. 15 indicate the gain characteristic and phase characteristic of the sprung vertical velocity signal whose velocity is converted by integration (1 / S).

At B2, a bandpass filter process for cutting off components other than the target frequency band to be controlled is performed. That is, this bandpass filter BPF is composed of a secondary high-pass filter HPF (0.3 Hz) and a secondary low-pass filter LPF (4 Hz), and has a sprung vertical velocity targeting the sprung resonance frequency band of the vehicle. Δx (Δx _FL ,
Δx _FR , Δx _RL , Δx _RR ) signals are obtained.

On the other hand, at B3, as shown in the following equation (3),
The vertical acceleration G (G _FL , G _FR , G _RL , G _{RR )} detected by each vertical G sensor 1 using the transfer function Gu _(S) from each sprung vertical acceleration to the relative speed between the sprung and unsprung _portions. ) Signal, the relative speed (Δx
−Δx ₀ ) [(Δx−Δx ₀ ) _FL , (Δx−Δx
₀ ) _FR , (Δx−Δx ₀ ) _RL , (Δx−Δx ₀ ) _RR ] signals are obtained. Gu _(S) = -ms / (cs + k) (3) where m is the sprung mass, c is the damping coefficient of the suspension, k is the spring constant of the suspension, and s is the Laplace operator. is there.

Next, the content of the damping force characteristic control operation of the shock absorber SA in the control unit 4 will be described with reference to the flowchart of FIG. In addition,
This basic control is performed by each shock absorber SA _FL , SA _FR ,
This is performed for each SA _RL and SA _RR .

In step 101, the sprung vertical velocity Δx
Is determined to be a positive value. If YES, the flow proceeds to step 102 to control each shock absorber SA to the extension-side hard region HS. If NO, the flow proceeds to step 103.

In step 103, the sprung vertical velocity Δx
Is determined to be a negative value. If YES, the routine proceeds to step 104, where each shock absorber SA is controlled to the pressure-side hard area SH, and if NO, the routine proceeds to step 105.

Step 105 is a processing step when it is judged NO in steps 101 and 103, that is, when the value of the sprung vertical velocity Δx is 0.
At this time, each shock absorber SA is
To control.

Next, the operation of damping force characteristic control will be described with reference to the time chart of FIG. The sprung vertical velocity Δx is
When changing as shown in this figure, as shown in the figure, when the value of the sprung vertical velocity Δx is 0, the shock absorber SA is controlled to the soft region SS.

Further, when the value of the sprung vertical velocity Δx becomes a positive value, the compression side damping force characteristic is controlled to the soft side by controlling to the extension side hard region HS, and the extension side damping force characteristic (target The damping force characteristic position P _T ) is changed in proportion to the sprung vertical velocity Δx based on the following equation (4). P _T = α · M (Δx / Δx−Δx ₀ ) ... (4) where α is a constant on the extension side, M is a fuel amount, The product (α · M) of both forms the (variable) control gain in the claims.

When the value of the sprung vertical velocity Δx becomes a negative value, the compression side hard region SH is controlled to fix the extension side damping force characteristic to the soft characteristic, while the compression side damping force characteristic (target damping force The characteristic position P _C ) is calculated based on the following equation (5).
It changes in proportion to the sprung vertical speed Δx. P _C = β · M (Δx / Δx−Δx ₀ ) ... (5) β is a constant on the pressure side. Further, the product (α · M) of this constant and the fuel amount constitutes the (variable) control gain in the claims.

Next, of the damping force characteristic control operation of the control unit 4, the switching operation state of the control area of the shock absorber SA will be mainly described with reference to the time chart of FIG.

In the time chart of FIG. 17, area a
Is a state in which the sprung vertical speed Δx is reversed from a negative value (downward) to a positive value (upward). At this time, the relative speed (Δx−Δx ₀ ) is still a negative value (shock absorber SA).
Is a pressure stroke side), and at this time, the shock absorber SA is controlled to the extension side hard region HS based on the direction of the sprung vertical speed Δx,
Therefore, in this area, the shock absorber SA at that time is
The pressure stroke side, which is the stroke of, has soft characteristics.

In the region b, the sprung vertical velocity Δx remains a positive value (upward), and the sprung-sprung relative velocity (Δx-Δx ₀ ) changes from a negative value to a positive value (shock absorber). Since the stroke of SA is the area switched to the extension side), at this time, the shock absorber SA is controlled to the extension side hard area HS based on the direction of the sprung vertical velocity Δx, and the shock absorber SA is also controlled. Is also an extension stroke, and therefore, in this region, the extension side which is the stroke of the shock absorber SA at that time has a hard characteristic proportional to the value of the sprung vertical velocity Δx.

In the region c, the sprung vertical velocity Δx is reversed from a positive value (upward) to a negative value (downward), but at this time, the sprung-unsprung relative velocity (Δx) is still.
-Δx ₀ ) is a positive value area (the stroke of the shock absorber SA is the extension stroke side), and at this time, the shock absorber SA is in the compression side hard area SH based on the direction of the sprung vertical velocity Δx. Is controlled by
In this region, the extension side, which is the stroke of the shock absorber SA at that time, has soft characteristics.

In the region d, the sprung vertical velocity Δx remains a negative value (downward), and the sprung-sprung relative velocity (Δx-Δx ₀ ) changes from a positive value to a negative value (shock absorber). Since the stroke of SA is on the extension side), at this time, the shock absorber SA is controlled to the compression side hard region SH based on the direction of the sprung vertical velocity Δx, and the stroke of the shock absorber is also It is a pressure stroke,
Therefore, in this area, the shock absorber SA at that time is
The pressure stroke side, which is the stroke of, has a hard characteristic proportional to the value of the sprung vertical velocity Δx.

As described above, in this embodiment, the sprung vertical velocity Δx and the sprung-unsprung relative velocity (Δx-Δ
x ₀ ) has the same sign (area b, area d), the stroke side of the shock absorber SA at that time is controlled to a hardware characteristic, and when it has a different sign (area a, area c), it is the shock absorber at that time. The same control as the damping force characteristic control based on the skyhook control theory of controlling the stroke side of SA to the soft characteristic is performed based on only the sprung vertical velocity Δx signal. Further, in this embodiment, when the stroke of the shock absorber SA is changed, that is, when the area a is changed to the area b and the area c is changed to the area d (soft characteristic to hard characteristic), the stroke is changed. The damping force characteristic position on the side is the previous area a,
Since the switching to the hardware characteristic side has already been performed in c, the switching from the soft characteristic to the hardware characteristic can be performed without a time delay, and thus high control response can be obtained and the hardware characteristic to the soft characteristic can be obtained. Switching to the pulse motor 3 is performed without driving the pulse motor 3, which improves the durability of the pulse motor 3 and
Power consumption will be saved.

Next, of the control operation of the control unit 4, the contents of variable control of the damping force characteristics (target damping force characteristic positions P _C , P _T ) based on changes in the fuel amount M in the fuel tank will be described.

(A) Traveling with the fuel fully filled When traveling with the fuel fully filled in the fuel tank, the target damping force characteristic positions P _C and P _T are calculated by the above equation (4). Since the value of the fuel amount M in (5) is maximized, the target damping force characteristic positions P _C and P _T are set to be higher in proportion to the maximum value. It is possible to prevent the occurrence of a control force shortage state due to an increase in inertial force, by the damping force characteristic that is variably set to be higher.

Therefore, even when the amount of fuel in the fuel tank is full, the optimum damping force characteristic control based on the skyhook control theory is performed, and the riding comfort and steering stability of the vehicle are secured. be able to.

(B) When traveling with the amount of fuel close to empty When traveling with the amount of fuel in the fuel tank close to empty,
The above formula for obtaining the target damping force characteristic positions P _C , P _T
Since the values of the fuel amount M in (4) and (5) are minimized, the target damping force characteristic positions P _C and P _T are set to be lower in proportion to the values, which results in the vehicle weight. It is possible to prevent the occurrence of an excessive control force state due to a decrease in (spring sprung inertia force) with a damping force characteristic that is variably set to be low.

Therefore, even when the amount of fuel in the fuel tank becomes almost empty, the optimum damping force characteristic control based on the skyhook control theory is performed, and the riding comfort and steering stability of the vehicle are improved. And can be secured.

As described above, the vehicle suspension system of this embodiment has the following effects. Even if the fuel amount M in the fuel tank changes, it is possible to prevent deterioration of the riding comfort and steering stability of the vehicle.

As a means for converting the sprung vertical acceleration to the sprung vertical velocity, a phase delay compensation formula is used to prevent signal drift due to an extra low frequency signal input, such as during braking. As a result, it becomes possible to prevent the controllability of the damping force characteristic of the shock absorber SA from deteriorating and ensure the riding comfort of the vehicle.

Since switching from the soft characteristic to the hard characteristic is performed without a time delay, a high control response is obtained, and the switching from the hard characteristic to the soft characteristic is performed without driving the actuator. This makes it possible to improve the durability of the actuator and save power consumption.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to this embodiment, and the present invention is applicable even if there are design changes and the like within the scope not departing from the gist of the present invention. include.

For example, in the embodiment, the case where the sprung vertical speed signal and the sprung unsprung relative speed signal are used as the vehicle behavior signal detected by the vehicle behavior detecting means has been described, but only one of them is used. Alternatively or additionally, a sprung vertical acceleration signal, a sprung unsprung relative acceleration, or the like may be used.

Further, in the embodiment, the variable setting of the damping force characteristic depending on the fuel amount is performed for all the shock absorbers on the front wheel side and the rear wheel side. However, depending on the position of the fuel tank, the front wheel side or the rear wheel side may be changed. Only one of the wheel sides may be used, or even when both are performed, the values may be set to different variable characteristics on the front wheel side and the rear wheel side.

In the embodiment, the soft area SS is controlled only when the sprung vertical speed signal is 0. However, a predetermined dead zone centered at 0 is provided and the sprung vertical range is set within this dead zone. Control hunting can be prevented by maintaining the damping force characteristic in the soft region SS while the speed changes.

In the embodiment, when the damping force characteristic changing means of the shock absorber variably controls the damping force characteristic on one stroke side of the extension stroke side and the compression stroke side to the hard characteristic side, the other An example using a structure in which the damping force characteristic on the stroke side of is fixed to the soft characteristic was shown.
It goes without saying that the present invention can be applied to a system using a structure in which the damping force characteristics in both the compression and compression strokes change simultaneously.

[0053]

As described above, the present invention claims 1.
In the vehicle suspension system described above, as described above, the fuel amount detecting means for detecting the amount of fuel in the fuel tank, and the control for variably controlling the control gain according to the fuel amount detected by the fuel amount detecting means. By providing the gain varying means, it is possible to prevent deterioration of the riding comfort and steering stability of the vehicle even when the amount of fuel in the fuel tank changes.

Further, in the vehicle suspension system according to claim 2,
The vehicle behavior detecting means is composed of a sprung vertical velocity detecting means for detecting a sprung vertical velocity, and the damping force characteristic changing means of the shock absorber is configured to dampen one of the extension stroke side and the pressure stroke side. When the force characteristic is variably controlled to the hard characteristic side, the damping force characteristic on the other stroke side is formed to be fixed to the soft characteristic, and the damping force characteristic control means detects the sprung vertical velocity detection means. The damping force characteristic on the extension side of the shock absorber is changed when the direction identification code of the sprung vertical velocity is positive in the upward direction, and the damping force characteristic on the pressure stroke side is changed in accordance with the control signal when the downward direction is negative. As a result of the control, the damping force characteristic on the stroke side of the shock absorber at that time is controlled in the damping range where the direction discrimination codes of the sprung vertical velocity and the sprung-unsprung relative velocity match. In addition to increasing the damping force of the vehicle by variably controlling the drive characteristics, the damping force characteristics on the stroke side of the shock absorber at that time should be soft characteristics in the vibration range where the direction identification codes of the two do not match. It becomes possible to perform basic switching control of damping force characteristics based on the skyhook control theory, such as weakening the excitation force of the vehicle.

[Brief description of drawings]

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

FIG. 2 is a configuration explanatory view of a vehicle suspension system showing the embodiment of the invention.

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

FIG. 4 is a sectional view showing a shock absorber applied to the vehicle suspension system showing the embodiment of the invention.

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 a damping force 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 a perspective view of the shock absorber shown in FIG.
It is a -L cross section and a MM cross section.

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 signal processing circuit for obtaining a sprung vertical velocity and a sprung-unsprung relative velocity in the vehicle suspension system showing the embodiment of the invention.

FIG. 15 is a diagram showing a gain characteristic (a) and a phase characteristic (b) of the sprung vertical velocity signal obtained by the signal processing circuit.

FIG. 16 is a flowchart showing the details of the damping force characteristic control operation of the control unit in the vehicle suspension system showing the embodiment of the invention.

FIG. 17 is a time chart showing the details of the damping force characteristic control operation of the control unit in the vehicle suspension system showing the embodiment of the invention.

[Explanation of symbols]

 a damping force property changing means b shock absorber c vehicle behavior detecting means d damping force characteristic control means e fuel amount detecting means f control gain varying means g sprung vertical velocity detecting means (vehicle behavior detecting means)

Claims (2)

[Claims] 1. A shock absorber which is interposed between a vehicle body side and each wheel side and whose damping force characteristic changing means can change the damping force characteristic, and a vehicle behavior detecting means which detects a vehicle behavior at each wheel position. A damping force characteristic control means for performing damping force characteristic control of each shock absorber based on a vehicle behavior signal at each wheel position detected by the vehicle behavior detection means and a control signal obtained from a predetermined control gain. The suspension device includes a fuel amount detecting means for detecting the amount of fuel in the fuel tank, and a control gain varying means for variably controlling the control gain according to the fuel amount detected by the fuel amount detecting means. A vehicle suspension device characterized by the above. 2. The vehicle behavior detecting means is composed of a sprung vertical velocity detecting means for detecting a sprung vertical velocity, and the damping force characteristic changing means of the shock absorber is one of an extension stroke side and a pressure stroke side. When the damping force characteristic of one stroke side is variably controlled to the hard characteristic side, the damping force characteristic of the other stroke side is fixed to the soft characteristic. When the direction discrimination code of the sprung vertical velocity detected by the vertical velocity detecting means is positive in the upward direction, the damping force characteristic on the extension side of the shock absorber is indicated, and when it is negative in the downward direction, the damping force characteristic on the pressure stroke side is indicated. The vehicle suspension system according to claim 1, wherein the vehicle suspension system is configured to be variably controlled according to a control signal.