JP3093238B2 - Vehicle suspension device - Google Patents

Description

The present invention relates to a suspension device for a vehicle, and more particularly, to a suspension device for a vehicle.
The present invention relates to an improvement of a device having a shock absorber having a variable damping force characteristic between a sprung portion and a unsprung portion.

(Prior Art) Generally, a vehicle suspension device is provided with a shock absorber between a sprung portion (body side) and an unsprung portion (wheel side) to attenuate the vertical movement of the vehicle. This shock absorber has a damping force characteristic variable type (a characteristic with a different damping coefficient).
There are various types such as a type in which the damping force can be changed in two steps and a type in which the damping force can be changed in multiple steps or steplessly continuously.

Such a method of controlling a shock absorber having a variable damping force characteristic basically reduces the damping force of the shock absorber when the damping force generated by the shock absorber acts in the vibration direction with respect to the vertical vibration of the vehicle body. Change the damping force of the shock absorber to a high damping side (that is, the hard side) when the damping force is applied in the damping direction. The purpose is to increase the damping energy and thereby improve both the riding comfort and the steering stability of the vehicle.

Various methods have been proposed for determining whether the damping force of the shock absorber acts in the vibration direction or the vibration damping direction of the sprung vertical vibration. For example,
Japanese Patent Laid-Open No. 60-248419 examines whether the sign of the relative displacement between the sprung portion and the unsprung portion and the sign of the relative speed between the sprung portion and the unsprung portion, which is a derivative thereof, match. A method is disclosed in which, when they match, the vibration direction is determined, and when they do not match, the vibration is determined to be the vibration damping direction. A method is disclosed in which it is determined whether or not the sign of the relative speed between the upper part and the unsprung part matches, and if they match, it is determined to be the vibration suppression direction, and if they do not match, it is determined to be the vibration direction.

(Problems to be Solved by the Invention) However, in a vehicle equipped with a shock absorber in which the damping force characteristic can be changed in multiple stages, when the damping force characteristic is changed and controlled so as to generate an ideal damping force, the damping force characteristic is significantly reduced. However, there is a problem that a very loud sound or vibration is generated when changing to the above.

The present invention has been made in view of such a point, and an object of the present invention is to provide a shock absorber in which damping force characteristics can be changed in multiple stages, while fully exhibiting its damping performance, and having a large damping force characteristic. It is intended to prevent generation of sound and vibration due to the change.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a shock absorber which is disposed between a sprung portion and a unsprung portion and whose damping force characteristic can be changed to at least three or more characteristics. Traveling state detecting means for detecting a vibration frequency on a spring of a vehicle, and damping force characteristic limitation for selecting two damping force characteristics from among three or more characteristics of the shock absorber in accordance with the detection result of the detecting means. Means, and damping force characteristic changing means for changing the damping force characteristic of the shock absorber based on a predetermined control law only between the two damping force characteristics selected by the damping force characteristic limiting means. The difference between the damping coefficients of the two damping force characteristics selected when the vibration frequency is in a high-frequency vibration region where the vibration frequency is higher than a predetermined frequency is a low frequency characteristic where the vibration frequency is smaller than the predetermined frequency. The two damping force characteristics are selected so as to be smaller than the difference between the damping coefficients of the two damping force characteristics selected in the wave vibration region.

(Operation) According to the present invention, the traveling state detecting means detects the traveling state of the vehicle (oscillation frequency range on the spring) according to the present invention, and according to the traveling state of the vehicle, three or more characteristics of the shock absorber. From among the two, two damping force characteristics are selected by the damping force characteristic limiting means. At this time, the difference between the damping coefficients of the two damping force characteristics selected when the vibration frequency is higher than a predetermined frequency is selected when the vibration frequency is lower than the predetermined frequency. The two damping force characteristics are selected so as to be smaller than the difference between the two damping force characteristics. The damping force characteristic of the shock absorber is determined by the damping force characteristic changing means based on a predetermined control law.
It only changes between the two damping characteristics.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a component layout of a suspension device according to a first embodiment of the present invention.

In FIG. 1, reference numerals 1 to 4 denote four shock absorbers respectively provided for left and right front wheels 5L (only the left front wheel is shown) and rear wheels 6L (only the left rear wheel is shown). It attenuates the vertical movement of each wheel.
Each of the shock absorbers 1 to 4 has three or more damping force characteristics (five in the embodiment described later) having different damping force characteristics due to the built-in actuator 25 (see FIGS. 2 and 3). Changeover is possible,
A vehicle height sensor (not shown) for detecting a relative displacement between the vehicle body (spring up) and the axle (unsprung) is built in. Reference numeral 7 denotes a coil spring disposed on the outer periphery of the upper part of each of the shock absorbers 1 to 4, and 8 denotes a coil spring provided in each of the shock absorbers 1 to 4.
And a control unit that outputs a control signal to the actuator in the shock absorber 4 to change and control the damping force characteristic thereof. A detection signal is output from the vehicle height sensor in each of the shock absorbers 1 to 4 to the control unit 8. Is done.

Also, 11 to 14 are four acceleration sensors for detecting acceleration in a vertical direction (Z direction) on a spring for each wheel, 15 is a vehicle speed sensor provided in a meter of an instrument panel, and 16 is a vehicle speed sensor. A steering angle sensor that detects the steering angle of the front wheels from the rotation of the steering shaft, 17 is an accelerator opening sensor that detects the accelerator opening, and 18 is whether or not the brake is operating based on the brake fluid pressure (that is, whether or not braking is being performed). 19) is a brake pressure switch that detects whether the driver is HARD, SOFT, CONTRO
This is a mode selection switch for switching to any of the modes L. The detection signals of these sensors 11 to 17 and the switches 18 and 19 are both output to the control unit 8.

FIG. 2 shows the structure of the shock absorbers 1-4. However, in this figure, the vehicle height sensors built in the shock absorbers 1 to 4 are omitted.

In FIG. 2, reference numeral 21 denotes a cylinder.
In the piston 21, a piston unit 22 formed by integrally molding a piston and a piston rod is slidably fitted.
The cylinder 21 and the piston unit 22 are connected to an axle (unsprung) or a vehicle body (upspring) via separately provided connecting structures.

The piston unit 22 has two orifices 23, 24
Is provided. One of the orifices 23 is always open. The other orifice 24 is provided so that its throttle (passage area) can be changed in five stages by an actuator 25. As shown in FIG. 3, the actuator 25 includes a shaft 27 rotatably provided in a piston unit 22 via a sleeve 26, and a shaft 27.
And a step motor 28 for rotating the shaft at predetermined angles, and a first motor having four circular holes 29, 29,... Provided at the lower end of the shaft 27 so as to rotate integrally therewith and formed at predetermined intervals in the circumferential direction. And a second orifice plate 32 disposed in the orifice 24 and having an arc-shaped elongated hole 31 corresponding to the circular holes 29, 29,... Of the orifice plate 30. Then, the step motor 28 operates and the first orifice plate 30 rotates, so that the circular hole 29 of the orifice plate 30 does not face the elongated hole 31 of the second orifice plate 32 or not. Also, the number of the circular holes 29 facing each other is sequentially changed from zero to four.

The upper chamber 33 and the lower chamber 34 in the cylinder 21 and the cavity in the piston unit 22 communicating with the two chambers 33 and 34 are filled with a fluid having an appropriate viscosity. This fluid passes through one of the orifices 23 and 24 and the upper chamber 33 and the lower chamber 34.
You can move between.

In the above configuration, the shock absorbers 1 to 4
It has five damping force characteristics with different damping coefficients. That is, when none of the four circular holes 29, 29,... Of the orifice plate 30 are opposed to the elongated holes 31 of the orifice plate 32, the orifice 24 is completely closed, and the fluid passage is defined by the orifice 23. Only, and the damping force characteristics of the shock absorbers 1 to 4 are HARD characteristics having a considerably high damping coefficient. Also, one circular hole 29 of the orifice plate 30
When only the hole 31 faces the elongated hole 31, the passage of the fluid is the two orifices 23 and 24, but since the orifice 24 has a considerably large throttle, the damping force characteristics of the shock absorbers 1 to 4 have a slightly higher damping coefficient. MEDIUM-HARD characteristics. Furthermore, the two circular holes 29, 29 of the orifice plate 30 are elongated holes 3
When it is in the state facing 1, shock absorbers 1-4
The damping force characteristic is a NORMAL characteristic with a moderate damping coefficient,
Three circular holes 29, 29, 29 in the orifice plate 30 are elongated holes 31
, The damping force characteristics of the shock absorbers 1 to 4 are MEDIUM-SOFT characteristics having a slightly lower damping coefficient, and all the four circular holes 29, 29,. In this state, the damping force characteristics of the shock absorbers 1 to 4 are SOFT characteristics having a low damping coefficient.

FIG. 4 shows a vibration model of the suspension device, and m
s is the sprung mass, mu is the unsprung mass, zs is the sprung displacement,
zu is the unsprung displacement, ks is the spring constant of the coil spring 7, kt is the spring constant of the tire, and v (t) is the damping coefficient of the shock absorber.

FIG. 5 shows a block configuration of a control unit of the suspension device. In FIG. 5, a first vehicle height sensor 41, an acceleration sensor
11 and the actuator 25a are on the left front wheel 5L of the vehicle body, the second vehicle height sensor 42, the acceleration sensor 12 and the actuator 25b are on the right front wheel of the vehicle body, and the third vehicle height sensor 43, the acceleration sensor 13 and the actuator 25c are on the left side of the vehicle body. Rear wheel 6
In L, the fourth vehicle height sensor 44, the acceleration sensor 14, and the actuator 25d respectively correspond to the rear wheels on the right side of the vehicle body. The actuators 25a to 25d are the same as the actuators 25 in FIG.
Are built in the shock absorbers 1-4.

Also, r _{1 to} r ₄ are first to fourth vehicle height sensors 41 to
This is a sprung-unsprung relative displacement signal output from the control unit 44 to the control unit 8, and these signals take continuous values. This signal is output from shock absorber 1
4 is positive when it expands and negative when it shrinks. Note that the relative displacement when the vehicle is stationary (that is, the difference zs-zu between the sprung displacement zs and the unsprung displacement zu shown in FIG. 4) is set to zero, and the magnitude of the relative displacement is determined by the deviation from this. Express.

_G1 to _G4 are first to fourth acceleration sensors 11 to 14, respectively.
Are the sprung absolute acceleration signals in the vertical direction (Z direction) outputted from the control unit 8 to the control unit 8, and these signals take continuous values. This signal is positive when the sprung body receives an upward acceleration and negative when it receives a downward acceleration.

In addition, a vehicle speed signal VS is output from the vehicle speed sensor 15, a steering angle signal θH is output from the steering angle sensor 16, and an accelerator opening signal TVO is output from the accelerator opening sensor 17 to the control unit 8. Take a continuous value. The vehicle speed signal VS is positive when the vehicle moves forward and negative when the vehicle moves backward. The steering angle signal θH is positive when the steering wheel rotates counterclockwise (that is, when turning left) and negative when clockwise (that is, when turning right), as viewed from the driver's side. I do.

Further, a brake pressure signal is output from the brake pressure switch 18.
BP is output to the control unit 8,
This signal takes two values, ON and OFF. ON means that the brake is being operated, and OFF means that it is not.

v1~v4 is an actuator control signal is output to the actuator 25a~25d respectively from the control unit 8, these signals take two values of "I _S", "I _H". "I _S " indicates the damping force characteristics of the shock absorbers 1 to 4 on the SOFT side, and "I _H " indicates the shock absorbers 1 to 4.
This means that the characteristics of the hard side are taken as the damping force characteristics of No. 4 and both the SOFT side and HARD side characteristics are the SOFT characteristics of the characteristic “1” and the MEDIUM-SOFT characteristics of the characteristic “2” as described later.
Characteristic, NORMAL characteristic of characteristic "3", MEDIUM- of characteristic "4"
It is set by selecting from the HARD characteristic and the HARD characteristic of characteristic "5".

Further, a mode selection signal is output from the mode selection switch 19 to the control unit 8, and this signal is a plurality of parallel signals. In this embodiment, HARD, SOF
It takes three values, T and CONTROL. HARD means that the driver has selected the HARD mode, SOFT means that the SOFT mode has been selected, and CONTROL means that the CONTROL mode has been selected. Then, as described later, the damping force characteristics of all the shock absorbers 1 to 4 are fixed to the HARD characteristics in the case of HARD, the damping force characteristics of all the shock absorbers 1 to 4 are fixed to the SOFT characteristics in the case of SOFT, and in the case of CONTROL. The damping force characteristics of each of the shock absorbers 1 to 4 are HARD or SO depending on the vehicle motion state and road surface condition, respectively.
Automatically and independently switched to FT characteristics.

FIG. 6 shows a control flow of the control unit 8. This control operation is executed by a control program installed in the control unit 8. This control program is repeatedly started at a fixed period (1 to 10 ms) by a separately provided start program. Hereinafter, this control operation will be described along the flow.

First, in step S1, it is determined whether the mode selection signal is HARD. If the determination is HARD of YES, “I _H ” is set to all of the actuator control signals v1 to v4 in step S17, and the control signals v1 to v4 are set in step S16.
Is output. As a result, all shock absorbers 1
The damping force characteristics of Nos. To 4 are the characteristics of the HARD side currently set. At this time, the operation is completed.

When the value of the mode selection signal is not HARD,
At step S2, it is determined whether or not the value of the mode selection signal is SOFT.
In set to "I _S" to all the actuator control signals v1 to v4, and outputs the control signal v1 to v4 at step S16.
As a result, the damping force characteristics of all the shock absorbers 1 to 4 become the SOFT side characteristics set at the present time. At this time, the operation is completed.

When the determinations in both steps S1 and S2 are NO, that is, when the value of the mode selection signal is CONTROL, step S
After inputting the sprung unsprung relative displacement signals r1 to r4 in step 3,
In step S4, these r1 to r4 are differentiated by a numerical differentiation method or the like to obtain sprung unsprung relative velocities 1 to 4.

Subsequently, in step S5, the sprung absolute acceleration signals _G1 to
After inputting the _G4 , in a step S6, the _G1 to _G4 are integrated by a numerical integration method or the like, and the vertical vehicle body absolute speed _G1 to
_Ask for _G4 . _G1 to _G4 are acceleration sensors 11 to 14.
, The absolute speed in the vertical direction at the position of step S7 is converted into the absolute speeds _S1 to _S4 of the vertical direction at the positions of the shock absorbers 1 to 4 in step S7.
_{Since S1} to _S4 are required if three of _G1 to _G4 are known, hereinafter, _G1 to _G3 will be used,
_G4 is a reserve value. Here, as shown in FIG.
When the origin is properly set in the horizontal plane and the xy coordinates are taken,
The coordinates of the acceleration sensor _{11~13 (x G1, y G1)} ~ (x G3,
y _G3 ), the coordinates of shock absorbers 1-4 are (x _S1 , y _S1 )
When ( _xS4 , _yS4 ), _S1 to _S4 are obtained by the following equations.

However, the two coefficient matrices and their product are obtained in advance and given as constants.

Subsequently, in step S8, the sprung absolute speed _S (or the sprung absolute displacement Zs, which is an integral value thereof) is continuously measured to calculate the sprung vibration frequency f. Then, step S9
It is determined whether or not the frequency f is smaller than the predetermined value f _{L. If} the determination is YES, “1” is set to “I _S ” and “5” to “I _H ” in step S11. set. On the other hand, when the determination in step S9 is NO, further frequency f is determined whether greater or not than a predetermined value _{f H (f H> f L} ) at step S10, when the determination is YES, the step S12 In "I _S "
Is set to “1” and “I _H ” is set to “2”. If the determination is NO, “1” is set to “I _S ” in step S13,
" _IH " is set to "4". Step S8 above
~ S10 and the acceleration sensors 11 ~ 14 constitute a traveling state detecting means 51 for detecting the vibration frequency on the spring as the traveling state of the vehicle, and the control flow of steps S9 ~ S13 allows Accordingly, damping force characteristic limiting means 52 for limiting and selecting two damping force characteristics from the five characteristics of the shock absorbers 1 to 4 is provided.

After limitingly selecting two damping force characteristics in any of the above steps S11 to S13, in step S14, the determination function h is calculated by the following equation.
Ask for i.

hi = i · si (i = 1, 2, 3, 4) In other words, the determination function hi is a value of the product of the sprung unsprung relative speed i and the sprung absolute speed si of each wheel.

Subsequently, in step S15, if the judgment function hi is zero or a positive value (hi ≧ 0), vi = I _H is set. If the judgment function hi is a negative value (hi <0), vi = I _{H S.} After this setting, actuator control signals v1 to v4 are output in step S16, and the routine returns. By the above steps S14 to S16, a judgment function hi which is the product of the sprung unsprung relative speed i and the sprung absolute speed si is calculated, and according to whether the judgment function hi is zero or more, Damping force characteristic changing means for changing the damping force characteristics of each of the shock absorbers 1 to 4 between the two damping force characteristics limitedly selected by the damping force characteristic limiting means 52
53 are configured.

Therefore, according to such control, the driver can
When the ROL mode is selected, two damping force characteristics are selected from the five damping force characteristics of each of the shock absorbers 1 to 4, and the relative speed i between the sprung and unsprung portions is selected between the two damping force characteristics. (= Si-ui) and sprung absolute speed
When the judgment function hi, which is the product i · si with si, is zero or more (hi ≧ 0) (that is, when the sprung mass moves upward and the shock absorbers 1 to 4 extend and the damping force acts downward, And when the sprung mass moves downward and the shock absorbers 1-4 shrink and their damping force acts upward),
When it is determined that the damping force generated by the shock absorbers 1 to 4 acts in the vibration damping direction with respect to the vertical vibration on the spring, the damping force characteristics of the shock absorbers 1 to 4 are changed to the characteristics on the HARD side. When the function hi is less than or equal to zero (hi <0)
(In the case opposite to the above), it is determined that the damping force generated by the shock absorbers 1 to 4 acts in the vibration direction with respect to the vertical vibration on the spring, and the damping force characteristics of the shock absorbers 1 to 4 are changed. Changed to SOFT side characteristics. For this reason, for example, the control law becomes very simple as compared with the case where the damping force characteristic is changed based on a predetermined control law among the five damping force characteristics, so that the cost can be reduced and the control or operation reliability can be reduced. Improvement can be achieved.

Moreover, the two damping force characteristics selected from the five damping force characteristics of the shock absorbers 1 to 4 are not fixed, but are changed according to the difference in the vibration frequency on the spring as the running state of the vehicle. Is done. That is, the SOFT characteristic and the HARD characteristic are in the low frequency vibration region (f <f _L ), and the SOFT characteristic and the MEDIUM-HARD characteristic are in the medium frequency vibration region (f _L <f <f _H ). _{In H} <f), SOFT characteristics and MEDIUM-
Since each of the SOFT characteristics is selected, improvement of steering stability in the low-frequency vibration region and improvement of riding comfort in the high-frequency vibration region can be achieved at a high level.

Further, as a unique effect of the present invention, particularly in the high frequency vibration region, the damping force characteristics of the shock absorbers 1 to 4 are as follows:
Since the selection is changed only between characteristics close to each other (SOFT characteristics and MEDIUM-SOFT characteristics) with little difference in damping coefficient, it is possible to prevent the occurrence of sound or vibration due to a large change in damping force characteristics. Therefore, the ride comfort can be further improved.

7 and 8 show modified examples of the control flow of the control unit as second and third embodiments of the present invention, respectively. All of these control flows are different from the first embodiment only in the method of selecting the determination factor as the running state of the vehicle and the method of selecting the damping force characteristic of the shock absorber.

That is, in the case of the control flow shown in FIG.
After calculating the sprung unsprung relative speeds 1 to 4 and the sprung absolute speeds _S1 to _S4 in S23 to S27, the change state of the sprung absolute speeds _S1 to _S4 or the change of the sprung unsprung relative speed is determined in step S28. It is determined from the state or the like whether or not the road surface is a bad road. Then, if the determination is a bad road of YES, step S29
In "2" to "I _S" is set respectively to "5" to "I _H", if the determination is not a bad road NO, the "1" to "I _S" in step S30, "I _H Is set to "3". The running state detecting means 61 for detecting the road surface state as the running state of the vehicle is constituted by the above step S28 and the vehicle height sensors 41 to 44 or the acceleration sensors 11 to 14, and the like, and according to the control flow of steps S28 to S30, A damping force characteristic limiting means 62 for limiting and selecting two damping force characteristics from among the five characteristics of the shock absorbers 1 to 4 according to the road surface condition is provided. Each of the shock absorbers 1 between the two damping force characteristics limited and selected by the damping force characteristic limiting means 62 is used.
The control law in the damping force characteristic changing means 63 for changing the damping force characteristics of Nos. To 4 is the same as that of the first embodiment, and is the product of the sprung unsprung relative speed i and the sprung absolute speed si. A judgment function hi is calculated (step S31), and this judgment function h
The damping force characteristic is changed to the HARD side or the SOFT side according to whether or not i is equal to or greater than zero (step S32).

In such a control, when the road surface is not a rough road, the SOFT characteristic and the NORMAL characteristic are selected from the five damping force characteristics of the shock absorbers 1 to 5, but when the road surface is a rough road, the MEDIUM -Since the SOFT characteristic and the HARD characteristic are selected, and both of the selected characteristics are changed to the HARD side, it is possible to effectively increase the ground contact of the wheel on a rough road by changing the damping force characteristic. Also, the two selection characteristics are:
Regardless of whether the road is bad or not, the damping force characteristics are always relatively close to each other, so that it is possible to prevent the occurrence of sound or vibration due to a large change in the damping force characteristic.

In the case of the control flow shown in FIG. 8, step S48
After inputting the vehicle speed signal VS and the steering angle signal θH with,
In S49, it is determined whether the vehicle speed VS is greater than a predetermined value V0, and in step S50 or S51, the steering angle θH is set to a predetermined value θ0.
It is determined whether it is greater than or equal to. If both the determinations in steps S49 and S50 or S49 and S51 are NO, in step S52, “1” is set to “I _S ” and “3” is set to “I _H ”. Is YES and the other is NO
When the, "2" to "I _S" in step S53, "I _H" "4" were set respectively, when both the determination is YES together, "3 to" I _S "in step S54 ”Is set to“ 5 ”for“ I _H ”. Steps S48 and S49 above,
The vehicle speed sensor 15 and the steering angle sensor 16 constitute a running state detecting means 71 for detecting the vehicle speed and the steering angle as the running state of the vehicle, and according to the control flow of steps S49 to S54, according to the vehicle speed and the steering angle. A damping force characteristic limiting means 72 for limiting and selecting two damping force characteristics from the five characteristics of the shock absorbers 1 to 4 is provided. The control law in the damping force characteristic changing means 73 for changing the damping force characteristics of each of the shock absorbers 1-4 between the two damping force characteristics limited and selected by the damping force characteristic limiting means 72 is the case of the first embodiment. A determination function hi, which is the product of the sprung unsprung relative speed i and the sprung absolute speed si, is calculated (step S55), and depending on whether the determination function hi is equal to or greater than zero, Change damping force characteristics to HARD side or SOFT side (step
S56).

In the case of such a control, when the vehicle speed and the steering angle are each equal to or less than a predetermined value, the shock absorbers 1 to 4
The SOFT characteristic and the NORMAL characteristic are selected from among the five damping force characteristics described above, and when one of the vehicle speed and the bending angle is equal to or more than a predetermined value, the MEDIUM-SOFT characteristic and the MEDIUM-HARD characteristic are selected, and the vehicle speed and the Since the two damping force characteristics selected with the increase in the steering angle are both changed to the HARD side, the steering stability at high vehicle speed or turning can be effectively improved by changing the damping force characteristics. Further, since the two selected damping force characteristics are always ones having relatively close damping coefficients, it is possible to prevent the occurrence of sound or vibration due to a large change in the damping force characteristics.

The control law of the damping force characteristic changing means for changing the characteristic only between the damping force characteristics limited by the damping force characteristic limiting means includes a sprung unsprung relative speed i and a sprung absolute speed si as in the embodiment. Not only those that change based on
Of course, various other control rules may be used, for example, a control rule that is changed based on the relative displacement between the sprung and unsprung portions and the relative speed between the sprung and unsprung portions.

(Effect of the Invention) As described above, according to the vehicle suspension device of the present invention, two damping forces are selected from among three or more characteristics of the shock absorber in accordance with the running state of the vehicle (the vibration frequency on the spring). A characteristic is selected, and only between the selected damping force characteristics, the damping force characteristic of the shock absorber is changed based on a predetermined control law, so that the change of the damping force characteristic is appropriately changed according to the running state of the vehicle. It is possible to prevent noise and vibration from occurring due to a significant change in the damping force characteristic. In addition, there is an effect that control can be simplified.

In particular, the difference between the damping coefficients of the two damping force characteristics selected when the vibration frequency is higher than a predetermined frequency is selected when the vibration frequency is lower than the predetermined frequency. Since the above two damping force characteristics are selected so as to be smaller than the difference between the damping coefficients of the two damping force characteristics, the steering stability in the low frequency vibration region and the riding comfort in the high frequency vibration region are improved. Can be compatible at a high level.

[Brief description of the drawings]

The drawings show an embodiment of the present invention, and FIGS.
1 shows a first embodiment, FIG. 1 is a perspective view showing a component layout of a suspension device, FIG. 2 is a vertical sectional side view showing a main part of a shock absorber, and FIG. 3 is an exploded perspective view showing a configuration of an actuator. FIG. 4 is a schematic diagram showing a vibration model of the suspension device, FIG. 5 is a block diagram of a control unit of the suspension device, and FIG. 6 is a flowchart showing a control flow. 7 and 8 are views corresponding to FIG. 6 showing the second and third embodiments, respectively. 1-4 Shock absorbers 51, 61, 71 Running state detecting means 52, 62, 72 Damping force characteristic limiting means 53, 63, 73 Damping force characteristic changing means

Continuation of the front page (56) References JP-A 2-56008 (JP, U) JP-A 63-93205 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60G 1 / 00-25/00

Claims (1)

(57) [Claims] 1. A shock absorber disposed between a sprung portion and a unsprung portion and capable of changing a damping force characteristic to at least three or more characteristics, and a running state detecting means for detecting a vibration frequency on a spring of the vehicle. And damping force characteristic limiting means for selecting two damping force characteristics from among three or more characteristics of the shock absorber according to the detection result of the detecting means; and two damping force characteristic selecting means selected by the damping force characteristic limiting means. Damping force characteristic changing means for changing the damping force characteristic of the shock absorber based on a predetermined control law only between the damping force characteristics; The difference between the damping coefficients of the two damping force characteristics selected in the vibration region is the reduction of the two damping force characteristics selected in the low frequency vibration region where the vibration frequency is lower than the predetermined frequency. A suspension device for a vehicle, wherein the two damping force characteristics are selected so as to be smaller than a difference between damping coefficients.