JPH0424111A - Suspension device for vehicle - Google Patents

Abstract

PURPOSE:To keep off the occurrence of noise and vibration due to the sudden change of a damping force characteristic by changing the damping force characteristic stepwise at each interval between adjacent characteristics when the damping force characteristic selected on the basis of a specified control law is apart from the current one of a shock absorber. CONSTITUTION:Each of four shock absorbers 1-4, installed each in response to symmetrical front wheels 5L and rear wheels 6L, is made selectable to more than three damping force characteristics. Each detection signal out of respective level-control sensors in each of these shock absorbers 1-4 is outputted to a control unit 8 which outputs a control signal to each actuator in these shock absorbers 1-4 and controls these damping force characteristics for alteration. In this case, the control unit 8 selects the damping force characteristics of these shock absorbers 1-4 on the basis of a specified control law. When the damping force characteristics are changed to the selected characteristic, this alternation is performed stepwise at each interval between adjacent characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a suspension system for a vehicle, and particularly relates to an improvement in a suspension system that includes a shock absorber with variable damping force characteristics between a sprung portion and an unsprung portion.

(Prior Art) Generally, in a vehicle suspension system, a shock absorber is provided between a sprung mass (on the vehicle body side) and an unsprung mass (on the wheel side) for damping vertical motion of the wheel. These shock absorbers include those with variable damping force characteristics, such as those whose damping force characteristics (characteristics with different damping coefficients) can be changed in two stages, high and low, and those whose damping force can be changed in multiple stages or continuously. There are many things that are equal.

This control method for a shock absorber with variable damping force characteristics basically reduces the damping force of the shock absorber when the damping force generated by the shock absorber acts in the excitation direction against vertical vibration of the vehicle body. When the damping force acts in the damping direction, the damping force of the shock absorber is changed to the high damping side (hard side) to reduce the vibration energy transmitted to the spring. The damping energy is increased, thereby improving both ride comfort and handling stability of the vehicle.

Various methods have been proposed for determining whether the damping force of the shock absorber acts in either the excitation direction or the damping direction of the sprung ball under-ball vibration. For example, JP-A-6
Publication No. 0-248419 describes a method of checking whether the sign of the relative displacement amount between the sprung mass and the unsprung mass coincides with the sign of the relative velocity between the sprung mass and the sprung mass, which is its differential value. , a method is disclosed in which when they match, it is determined to be the vibration excitation direction, and when they do not match, it is determined to be the vibration damping direction.
Publication No. 163011 states that it is checked whether the sign of the absolute speed of the spring 1 and the sign of the relative speed between the sprung mass and the unsprung mass match, and if they match, it is determined that the vibration is in the damping direction, and if they do not match, it is determined that the damping direction is applied. A method for determining that the direction is the vibration direction is disclosed.

(Problem to be solved by the invention [1]) However, in a vehicle equipped with a shock absorber whose damping force characteristics can be changed in multiple stages, when changing and controlling the damping force characteristics to generate a damping force close to the ideal, it is difficult to change the damping force characteristics of the shock absorber. There is a problem in that very loud noises and vibrations are generated when the damping force characteristics change significantly and rapidly.

The present invention has been made in view of the above, and an object of the present invention is to provide a shock absorber whose damping force characteristics can be changed in multiple stages, while effectively exhibiting its damping performance. This is to prevent noise and vibration from occurring due to such changes.

(Means for solving problem a) In order to achieve the above object, the invention described in claim (1):
As a suspension device for a vehicle, there is a shock absorber that is arranged between a sprung mass and a sprung mass, and whose damping force characteristics can be changed to three or more characteristics, and a damping force characteristic of the shock absorber based on a predetermined control law. a damping force characteristic selection means for selecting a damping force characteristic; and a damping force characteristic changing means for changing the damping force characteristic of the shock absorber stepwise for each adjacent characteristic when changing the damping force characteristic to the characteristic selected by the selection means. This is a configuration that includes the following.

The inventions described in claims (2) to (6) are all
1) According to the invention described above, the change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is changed according to the running state of the vehicle.

That is, in the case of the invention set forth in claim (2), the change interval time is set to become gradually shorter as the vehicle speed increases, and in the case of the invention set forth in claim (3), the change interval time is set to become shorter as the vehicle speed increases. It is set to become gradually shorter as the steering angular speed increases. Furthermore, in the case of the invention described in claim (4), the change interval time is set to become gradually shorter as the deceleration of the vehicle increases, and
5) In the case of the invention described above, the change interval time is set to become gradually longer as the friction coefficient of the road surface becomes smaller.

Furthermore, in the case of the invention set forth in claim (6), the change interval time is set to become gradually shorter as the stroke speed of the shock absorber increases.

(Function) With the above configuration, in the present invention, when the damping force characteristic selected by the damping force selection means based on a predetermined control law is different from the current damping force characteristic of the shock absorber, the damping force characteristic is changed. The damping force characteristics are changed by the means stepwise between adjacent characteristics, and the damping force characteristics do not change abruptly.

(Example) Embodiments of the present invention will be described below based on the drawings.

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

In FIG. 1, 1 to 4 are four shock absorbers provided corresponding to the left and right front wheels 5L (only the left front wheel is shown) and the rear wheel 6L (only the left rear wheel is shown), This dampens the vertical movement of each wheel.

Each of the shock absorbers 1 to 4 has three or more (in the embodiment, five) damping force characteristics with different damping coefficients by a built-in actuator 25 (see FIGS. 2 and 3). It is changeable and has a built-in vehicle height sensor (not shown) that detects relative displacement between the vehicle body (sprung) and the axle (sprung). 7 is a coil spring disposed on the upper outer periphery of each of the above-mentioned shock absorbers 1 to 4; 8 is a coil spring disposed on the upper outer periphery of each of the above-mentioned shock absorbers 1 to 4;
This is a control unit that outputs control signals to the actuators in the above-mentioned shock absorbers 1 to 4 to change and control their damping force characteristics, and outputs detection signals from the vehicle height sensors in each of the above-mentioned stock absorbers 1 to 4 to the control unit 8. is output.

Further, 11 to 14 are four acceleration sensors that detect the acceleration in the vertical direction (Z direction) on the springs of each wheel, 15 is a vehicle speed sensor installed in the meter of the instrument panel that detects the vehicle speed, and 16 is a vehicle speed sensor that detects the vehicle speed. A steering angle sensor 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 a sensor that detects whether the brake is in operation (that is, whether or not it is braking) based on the brake fluid pressure. ), and 19 is a brake pressure switch that detects the damping force characteristics of shock absorbers 1 to 4.
This is a mode selection switch that switches to either mode D, 5OFT, or C0NTR0L, and these sensors 11
17 and switches 18 and 19 are all outputted to the control unit 8.

FIG. 2 shows the structure of the shock absorbers 1 to 4 mentioned above.

However, in this figure, vehicle height sensors built into the shock absorbers 1 to 4 are omitted.

In FIG. 2, 21 is a cylinder, and a piston unit 22 formed by integrally molding a piston and a piston rod is slidably inserted into the cylinder 21. The cylinder 21 and piston unit 22 are
They are connected to the axle (unsprung) or the vehicle body (sprung) via separate connection structures.

The piston unit 22 has two orifices 23.
24 are provided. Orifice 2 of one of them
3 is always open. Moreover, the other orifice 24 is
The aperture (passage area) is provided to be changeable in five stages by an actuator 25. The actuator 25
As shown in FIG. 3, the shaft 2 is rotatably provided within the piston unit 22 via a sleeve 26.
7, a step motor 28 that rotates the shaft 27 at predetermined angles, and four circular holes 29, which are rotatably provided at the lower end of the shaft 27 and formed at predetermined intervals in the circumferential direction. 29. a first orifice plate 30 having a circular hole 29 in said orifice plate 30 disposed within the orifice 24; 29. ...
A second orifice plate 32 having an arc-shaped elongated hole 31 corresponding to the second orifice plate 32 is provided. Then, as the step motor 28 operates and the first orifice plate 30 rotates, the circular hole 29 of the orifice plate 30 is rotated.
may or may not be opposed to the long hole 31 of the second orifice plate 32, and the number of opposing circular holes 29 may also be changed sequentially from zero to four.

A cavity within the piston unit 22 communicating with the upper chamber 33 and lower chamber 34 within the cylinder 21 and the double chambers 33, 34 is filled with a fluid having an appropriate viscosity. This fluid can move between the upper chamber 33 and the lower chamber 34 through any of the orifices 23, 24 mentioned above.

In the above configuration, the shock absorbers 1 to 4 have five damping force characteristics with different damping coefficients. That is, the four circular holes 29 in the orifice plate 30. 29
．． ... are the long holes 3 of the orifice plate 32.
1, the orifice 24 is completely closed and the only fluid passage is the orifice 23, and the damping force characteristics of the shock absorbers 1 to 4 become HARD characteristics with a considerably high damping coefficient. Further, when only one circular hole 29 of the orifice plate 30 faces the elongated hole 31, the fluid passage is through both orifices 23.2.
4, but since the orifice 24 has a considerably large aperture, the damping force characteristics of the shock absorbers 1 to 4 become MEDIUM-HARD characteristics with a slightly high damping coefficient. moreover,
When the two circular holes 29 and 29 of the orifice plate 30 face the elongated hole 31, the shock absorber 1
The damping force characteristic of ~4 is a NORMAL characteristic with a medium damping coefficient, and the three circular holes 29 of the orifice plate 30
, 29. 29 face the elongated hole 31, the damping force characteristics of the shock absorbers 1 to 4 become MEDIUM-5OFT characteristics with a slightly lower damping coefficient, and the four circular holes 29. 29. When all of the shock absorbers 1 to 4 face the elongated hole 31, the damping force characteristics of the shock absorbers 1 to 4 become 5OFT characteristics with a low damping coefficient.

Figure 4 shows the vibration model of the suspension device, with ms
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 the control section of the suspension device. In FIG. 5, the first vehicle height sensor 41, acceleration sensor 11, and actuator 25a are connected to the front wheel 5L on the left side of the vehicle body.
The second vehicle height sensor 42, acceleration sensor 12 and actuator 25b are connected to the front wheel on the right side of the vehicle body, and the third vehicle height sensor 43, acceleration sensor 13 and actuator 25b are connected to the front wheel on the right side of the vehicle body.
c corresponds to the rear wheel 6L on the left side of the vehicle body, and the fourth vehicle height sensor 44, acceleration sensor 14, and actuator 25d correspond to the rear wheel on the right side of the vehicle body. The actuators 25a to 25d are the actuator 25 in FIG.
The vehicle height sensors 41 to 44 are built into the shock absorbers 1 to 4.

Further, r1 to r4 are sprung upper and lower relative displacement signals outputted from the first to j@4 vehicle height sensors 41 to 44 to the control unit 8, respectively, and these signals are all continuous. Takes a value. This signal is positive when the shock absorbers 1 to 4 extend, and negative when they contract. Note that the relative displacement when the vehicle is stationary (that is, the difference ZS between the sprung displacement ZS and the unsprung displacement ZU shown in Fig. 4)
-ZU) is set to zero, and the deviation from this represents the magnitude of relative displacement.

2C, 1 to 2C, and 4 are absolute sprung acceleration signals in the vertical direction (Z direction) outputted from the first to fourth acceleration sensors 11 to 14 toward the control unit 8, respectively, and all of these signals are Takes continuous values. This signal is
It is positive when the sprung mass receives upward acceleration, and negative when it receives downward acceleration.

In addition, the vehicle speed signal ■S is sent from the vehicle speed sensor 15, the steering angle signal θH is sent from the steering angle sensor 16, and the accelerator opening sensor 1
7 outputs an accelerator opening signal TVO to the control unit 8, and all of these signals take continuous values.

The vehicle speed signal vS is positive when the vehicle is moving forward, and negative when the vehicle is moving backward. As seen from the driver's side, the steering angle signal θH is positive when the steering wheel rotates counterclockwise (that is, when turning left), and negative when it rotates clockwise (that is, when turning right). do.

Furthermore, a brake pressure signal BP is outputted from the brake pressure switch 18 toward the control unit 8, and this signal has two values: ON and 0FF (7). ON means that the brake is being operated, and OFF means that it is not.

■1 to v4 are actuator control signals output from the control unit 8 to the actuators 25a to 25d, respectively, and these signals are the UP signal and the D
Takes the binary value of the OWN signal.

The UP signal is a switching signal that changes the damping force characteristics of shock absorbers 1 to 4 to a HARD side characteristic with a damping coefficient that is one step higher than the current characteristic, and the DOWN signal changes the damping force characteristics of shock absorbers 1 to 4. , is a switching signal for changing the characteristics to the 5OFT side, which has a damping coefficient one step lower than the current characteristics.

Furthermore, a mode selection signal is outputted from the mode selection switch 19 toward the control unit 8, and this signal is a plurality of parallel signals, and in the case of this embodiment, a HARD
, 5OFT, C0NTR0L. HARD indicates that the driver has selected HARD mode.
T indicates that 5OFT mode is selected, C0NTR
0L means that the C0NTR0L mode is selected. When HARD is set, the damping force characteristics of all shock absorbers 1 to 4 are fixed to HARD characteristics, and 5O
When FT is set, the damping force characteristics of all shock absorbers 1 to 4 are fixed to 5OFT characteristics, and when C0NTR0L, the damping force characteristics of each shock absorber 1 to 4 are set to HARD or 5OFT depending on the vehicle motion state, road surface condition, etc. characteristics can be switched automatically and independently.

6 and 7 show the control flow of the control unit 8 when the C0NTR0L mode is selected (specifically, the damping force characteristic selection control flow and the damping force characteristic change control flow). These control operations are all executed by a control program installed in the control unit 8. This control program is sequentially and repeatedly activated at a fixed period (1 to 10 m5) by a separately provided activation program.

In the damping force characteristic selection control flow shown in Fig. 6,
First, in step S1, the relative displacement signal r1 for sprung and unsprung
After inputting ~r4, in step S2, this rl-r4 is differentiated by numerical differential method or the like to obtain the relative speeds 11 to t4 between the sprung and unsprung parts. Next, in step S3, the vertical spring 1 absolute acceleration signals 2e+ to 2G4 are input, and in step S4, these 2c+ to 2G4 are integrated by numerical integration, etc., to obtain the vertical spring mass absolute speeds 2G1 to Z.
Find G4. Since this ic+~2c< is the sprung mass absolute velocity at the position of the acceleration sensors 11-14, in step S5 it is converted to the sprung mass absolute velocity at the position of each shock absorber 1-4 S1-i5. Convert to Scarcity
1~is< can be calculated if three of G1-2c and 4 are known, so below, 2G1~2(,3 will be used, and 2G4 is a preliminary value.Here, As shown in Figure 1, take the origin appropriately within the horizontal plane, and
When taking the coordinates, the coordinates of the acceleration sensors 11 to 13 are (XG+, yG+) ~ (xcg, yax),
The coordinates of shock absorbers 1 to 4 are (xs+, ys+
) ~(xs4.ys4), is+~tsa
is calculated using the following formula.

However, the two coefficient matrices and their product are calculated in advance,
It is given as a constant.

Subsequently, in step S6, the determination function h1 is determined using the following equation.

hl -fi -2sj (i-1,・2,3.
4) In other words, this determination function h1 is the value of the product of the sprung mass relative speed t1 and the sprung mass absolute speed si of each wheel.

After determining the determination function hi, it is determined in steps 87 to S10 which of the five regions the determination function h1 belongs to. These five regions are each gain value g,
~The product of g4 and the square of the sprung-spring relative velocity H (g-
ri2), and each gain value g1~
g4 has the following magnitude relationship.

gl<gz<g3<g4 Then, when the determination function hi is in a region smaller than gl・ri2 (hl≦g1・g12), step Sl
Set "1" to Nt (lower than the target damping force characteristic C for switching shock absorbers 1 to 4 at l, referred to as target damping force characteristic), and determine if the judgment function is hl is greater than gl ・i12 and gl ・ri2 Small area (g+ ・?i
2<hi≦g2・ri2), step S12
Set the target damping force retention Nt to "2". In addition, the judgment function is that hi is larger than gl ・ri2 and g3 ・7
Area smaller than i2 (gz ・gl 2<hi≦g,
・ri2), the target damping force characteristic Nt is set to "3" in step 519, and the determination function is set in the region where hi is larger than g, ・g4 ・smaller than ri2
3・ri 2<hi 6g4・t12), the target damping force retention Nt is set to “4” in step S14, and further, the determination function hl), the target damping force retention Nt is set to "5" in step 515.

Here, the characteristic Nt-rlJ is the 5OFT characteristic, "2" is the MEDIUM-3OFT characteristic, and "3" is the NORMAL characteristic.
"4" is the MEDIUM-HARD characteristic, "5" is the MEDIUM-HARD characteristic.
” respectively mean HARD characteristics.

After selecting the target damping force characteristic Nt in any of steps Sll to SI5, the process returns. Through the above flow, the relative velocity N between the sprung upper and lower spring and the velocity 2si between the spring main gun and
Damping force characteristic selection means 51 is configured to select and set the target damping force retention Nt from among the five damping force characteristics of each shock absorber 1 to 4 according to the magnitude of the judgment function hi, which is the product of . .

In the damping force characteristic change control flow shown in Fig. 7,
First, in step S21 it is determined whether the flag F is "1", and in step S22 it is determined whether the flag F is "2". Here, the flag F-1 means that the switching timing for changing the damping force characteristic to the HARD side is being determined, and the flag F-2 means that the timing for changing the damping force characteristic to the 5OFT side is being determined. This means that the current switching timing is being determined.

Both steps S21. All judgments in S22 are N.
When the flag is O (that is, when the flag is F-0), the currently selected damping force characteristic (hereinafter referred to as the current damping force characteristic) N of the shock absorbers 1 to 4 is recognized in step S24. At the same time as inputting the vehicle speed V (vehicle speed signal VS) at step S25, the steering angle (studder angle signal) is inputted at step S25.
Input θH. Then, in step 82B, the steering angle θH is differentiated by a numerical differential method or the like to calculate the steering angular velocity θH,
In step S27, the vehicle speed V is differentiated by numerical differentiation or the like to calculate the deceleration a.

Next, in step 52B, the coefficient of friction μ of the road surface is input, and in step S29, the shock absorbers 1 to 4 are input.
Input the stroke speed, i.e., the relative speed i between the sprung and unsprung parts. Specifically, the input of the road surface friction coefficient μ is based on the ABS (anti-skid brake system) installed on the vehicle.
and a method of inputting the μ estimation signal from the traction device,
Alternatively, a simple method of inputting the wiper switch ON/OFF signal, etc. is used.

Subsequently, in steps 530 to S34, the waiting time TV,
Calculate Tθl, Ta, Tp, “rr, and step S35
Then, the total waiting time T is calculated from these waiting times based on the following formula.

T-TV-TθH-Ta+TB-Tr ・fx) Calculation of each of the above waiting times TV, TθH, Ta, Tμ, Tt is as follows:
Both are performed using maps stored in advance. The waiting time TV corresponds to the vehicle speed V, and is set to be constant in the low vehicle speed range, but to gradually decrease as the vehicle speed V increases in the middle and high vehicle speed ranges. Waiting time TθH
corresponds to the steering angular velocity θH, and is set to increase linearly as the steering angular velocity θH increases outside the dead zone region. The waiting time Ta corresponds to the deceleration of the vehicle, and is set to increase linearly as the deceleration a increases outside the dead zone region. The waiting time Tμ corresponds to the friction coefficient μ of the road surface, and increases as the friction coefficient μ approaches zero, and is set to zero on a normal road surface (a road surface where μ is close to 1). The waiting time Tt corresponds to the sprung/unsprung relative speed t1, and outside the dead zone area, the relative speed t1
It is set to increase linearly as .

The above-mentioned total waiting time T has the significance of the change interval time when the damping force characteristics of the shock absorbers 1 to 4 are changed step by step between adjacent characteristics by the damping force characteristic changing means 53 described later, Steps 830 to S35 constitute a change interval time setting means 52 that sets the total waiting time T as this change interval time. The total waiting time T set by the change interval time setting means 52 has the following characteristics, considering the sign of each term in the above equation (1).

- The total waiting time T is set to gradually become shorter as the vehicle speed increases, based on changes in the TV.

(2) The total waiting time T is set to gradually become shorter as the steering angular velocity increases, based on the change in -TθH.

■ The total waiting time T is based on the change in -Ta,
It is set to become gradually shorter as the deceleration of the vehicle increases.

(2) The total waiting time T is set to gradually increase as the road surface friction coefficient decreases based on changes in Tμ.

■ The total waiting time T is based on the change in -T.
It is set to become gradually shorter as the sprung/spring lower relative speed (stroke speed of the shock absorber) increases.

The total waiting time T is a very short time, and the following magnitude relationship is established between the maximum values of each waiting time so that the total waiting time T is always a positive value. is set to .

TV MAX > (TθHMAx+TaMAXxTt
MAX) After calculating the total waiting time T in step S35, waiting for the switching timing in step S37, and then, in step 838, calculating the target damping force retention previously found in the damping force characteristic selection control flow shown in FIG. Recognize Nt. Subsequently, in step S39, the target damping characteristic Nt
It is determined whether the difference between the current damping force characteristic N and the current damping force characteristic N is a positive value, that is, whether or not the current damping force characteristic is to be changed to a HARD side characteristic.

If the determination in step S39 is YES, step S40 sets the damping force characteristics of the shock absorbers 1 to 4 to a characteristic (N+
Change to 1). This change applies to control unit 8
Shock absorber actuator 25 corresponding to
This is done by outputting UP signals v1 to v4 towards a to 25d (see FIG. 4). Next, in step S41, it is determined whether the target damping force characteristic Nt matches the changed damping force characteristic (N+1), and when the determination is YES, rOJ is set in the flag F in step S42. , returns, while if the determination is NO, that is, they do not match, it is determined in step S43 whether or not the total waiting time T has elapsed. If this determination is NO, the flag F is set to "1" in step S44, and then the process returns. After waiting for the total waiting time T to elapse between step 543 and S21, the damping force characteristic is further changed to a characteristic (N+1) on the HARD side in step s40.

On the other hand, when the determination in step S39 is NO, in step S45 the damping force characteristics of the shock absorbers 1 to 4 are changed to a characteristic (N-1) which is one stage 5 OFT side from the current characteristic N. This change can be made from the control unit 8 to the corresponding shock absorber actuators 25a to 25.
This is done by outputting DOWN signals v1 to V4 toward the terminals d (see FIG. 4). Next, in step S46, it is determined whether the target damping force characteristic Nt matches the changed damping force characteristic (N-1), and when the determination is YES, the process moves to step S42, while the determination is If NO, it is determined whether or not the total waiting time T has elapsed in step S47. When this determination is No, after setting flag F to "2" in step 848,
Return. After waiting for the total waiting time T to elapse between steps S47 and S22, step S4
5 further improves the damping force characteristics by 5 OFT side characteristics (N-1)
Change to

Through the change control flow as described above, when changing the damping force characteristics of the shock absorbers 1 to 4 to the target damping force retention Nt selected by the damping force characteristic selection means 51, the change is performed in stages between adjacent characteristics. A damping force characteristic changing means 53 is configured.

Therefore, in such damping force characteristic change control, the target damping force characteristic N selected by the damping force selection means 53
t is the current damping force N of shock absorbers 1 to 4
For example, when the current damping force characteristic N is different from the 5OFT characteristic (N-1) and the target damping force characteristic Nt is the HARD characteristic (N
t-5), the damping force characteristics of shock absorbers 1 to 4 are sequentially MEDIUM-SO from 5OFT characteristics.
FT characteristics (N-2), NORMAL characteristics (N-3),
HARD via MEDIUM-HARD characteristics (N-4)
Since the damping force characteristic is changed to (N-5), it is possible to prevent the generation of loud noises and vibrations due to sudden changes in the damping force characteristic.

In addition, the time required to change the damping force characteristics in stages is extremely short, and characteristic delays do not become a problem. It is possible to improve damping performance by changing the characteristics to appropriate ones.

Furthermore, in particular, in the case of this embodiment, when changing the damping force characteristics stepwise between adjacent characteristics, the change interval time (total waiting time) T between the characteristics is appropriately set according to the driving condition. This change makes it possible to achieve both improved damping performance and prevention of noise and vibration at a high level. In other words,
When the vehicle speed v1, the rudder angle θH, and the deceleration a, which are the steering elements, change significantly, the change interval time T becomes shorter, and the responsiveness of the characteristic change is improved, so that the steering stability can be improved satisfactorily. In addition, when the road surface friction coefficient μ, which is an element of the road surface condition, is small, or the stroke speed of the shock absorbers 1 to 4, which is correlated with the unevenness of the road surface (
Even when the relative speed of the sprung vehicle is large, the change interval time T is shortened and the responsiveness of the characteristic change is improved, so stability can be favorably improved depending on the road surface condition.

FIG. 8 shows a modification of the damping force characteristic change control flow.

In the case of this modification, it is determined whether the total waiting time T has elapsed in step S43 or S47, and when this determination is YES, step S40 is immediately performed as in the embodiment.
Or move to S45 and make the damping force characteristics one step HARD.
Instead of changing the characteristics to the side or 5OFT side, the flag F is set to "0" in step S51 or S52, and then the process returns. In this control, the total waiting time T
If the target damping force characteristics change during the period of time, there is an advantage that this can be quickly dealt with.

(Effects of the Invention) As described above, according to the vehicle suspension device of the present invention, the damping force characteristic selected based on the predetermined control law is different from the current damping force characteristic of the shock absorber. Sometimes, the damping force characteristics are changed stepwise between adjacent characteristics, so while ensuring good damping performance by appropriately changing the damping force characteristics in multiple stages, the noise caused by sudden changes in the damping force characteristics can be reduced. It is possible to prevent the occurrence of vibration.

In particular, in the inventions described in claims (2) to (6), the characteristics are adjusted between adjacent characteristics depending on the running state of the vehicle, that is, the vehicle speed, steering angle speed, vehicle deceleration, road surface friction coefficient, or shock absorber stroke speed. Since the interval when changing the damping force characteristics is appropriately changed, it is possible to achieve both improved damping performance and prevention of noise and vibration generation at a high level.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a perspective view showing the layout of parts of a suspension device, FIG. 2 is a longitudinal side view showing the main parts of a shock absorber, and FIG. 3 is a diagram showing the configuration of an actuator. 4 is a schematic diagram showing a vibration model of the suspension device, FIG. 5 is a block configuration diagram of the control section of the suspension device, FIG. 6 is a flowchart showing the selection control flow of damping force characteristics, and FIG. 7 8 is a flowchart showing a damping force characteristic change control flow, and FIG. 8 is a partial diagram of the flowchart showing a modification of the same change control flow. 1 to 4... Shock absorber 51... Damping force characteristic selection means 53... Damping force characteristic changing means porridge 2 Ward 3 Ward

Claims (6)

[Claims] (1) A shock absorber that is arranged between the sprung mass and the unsprung mass and whose damping force characteristics can be changed to three or more characteristics, and the damping force characteristic of the shock absorber is selected based on a predetermined control law. damping force characteristic selection means; and damping force characteristic changing means for changing the damping force characteristic of the shock absorber stepwise for each adjacent characteristic when changing the damping force characteristic of the shock absorber to the characteristic selected by the selection means. A vehicle suspension device characterized by: (2) The vehicle according to claim (1), wherein the change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is set to become gradually shorter as the vehicle speed increases. suspension equipment. (3) The change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is set to become gradually shorter as the steering angular speed increases. Vehicle suspension equipment. (4) Claim (1) wherein the change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is set to become gradually shorter as the deceleration of the vehicle increases. Suspension equipment for the vehicle described. (5) Claim (1) wherein the change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is set to become gradually longer as the coefficient of friction of the road surface becomes smaller. Suspension equipment for the vehicle described. (6) Claim (1) wherein the change interval time when changing the damping force characteristics for each adjacent characteristic in the damping force characteristic changing means is set to become gradually shorter as the stroke speed of the shock absorber increases. ) Suspension equipment for the vehicle described.