JP2997309B2 - 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 a wheel. 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 characteristic can be changed in two stages and a type in which the damping force characteristic can be changed in multiple stages or in a continuously variable manner.

As a method of controlling such a damping force characteristic variable shock absorber, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-163011, the sprung absolute speed and the relative speed between the sprung and the unsprung are disclosed. Is detected by each detection means,
It checks whether the sign of the sprung absolute speed and the sign of the sprung unsprung relative speed match, and when the sign does not match, the damping force generated by the shock absorber excites the vertical vibration of the vehicle body. It is determined that the damping force is acting in the damping direction, and the damping force characteristic of the shock absorber is set to the low damping side (that is, the soft side). Switching the damping force characteristic of to the high damping side (that is, the hard side),
2. Description of the Related Art It is known that vibration damping energy is increased with respect to vibration energy transmitted to a vehicle body to improve both ride comfort and steering stability of the vehicle.

Also, the unsprung absolute speed is detected instead of the sprung absolute speed, and the damping force characteristic of the shock absorber is determined according to whether the sign of the unsprung absolute speed matches the sign of the sprung unsprung relative speed. Are also known.

(Problems to be Solved by the Invention) However, the conventional control method described above has a problem that when the damping force of the shock absorber is switched, if the damping force changes suddenly, a loud switching sound is generated. There is also a demand that the damping force characteristic of the shock absorber should be on the soft side and not change in the high frequency vibration region.

The present invention has been made in view of such a point, and an object of the present invention is to prohibit a change in the damping force characteristic when the damping force greatly changes in accordance with the switching of the damping force characteristic of the shock absorber. It is an object of the present invention to provide a vehicle suspension device capable of changing the damping force characteristic only when the change is very slight, and effectively preventing generation of a loud switching sound.

(Means for solving the problem) In order to achieve the above object, a solution of the present invention is a shock absorber provided between a sprung portion and a unsprung portion and having a variable damping force characteristic, as a vehicle suspension device. And, an absolute speed detecting means for detecting a sprung absolute speed or an unsprung absolute speed, a relative speed detecting means for detecting a relative speed between sprung and unsprung, and receiving signals from both of the detecting means, If the sign of the sprung absolute speed or the unsprung absolute speed and the sprung unsprung relative speed match, the damping force characteristics of the shock absorber will be on the high damping side, and if they do not match, the damping force characteristics of the shock absorber will be on the low damping side. And damping force characteristic control means for performing change control. A relative displacement detecting means for detecting a relative displacement between the sprung and unsprung parts; and a damping force change rate calculating means for calculating a damping force change rate of the shock absorber based on a value obtained by differentiating a signal from the relative displacement detecting means. The damping force characteristic when the absolute value of the damping force change rate calculated by the calculating means is larger than a predetermined value calculated when the damping force does not change or when the sprung unsprung relative speed does not change. Control correction means for correcting the control of the control means so as to stop the change of the damping force characteristic of the shock absorber is provided.

(Operation) With the above configuration, according to the present invention, when the damping force change rate greatly changes with a change in the damping force characteristic of the shock absorber, the control of the damping force characteristic control unit is corrected by the control correction unit, The change of the damping force characteristic of the shock absorber is stopped, whereby the switching sound caused by the rapid change of the damping force can be suppressed.

(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 provided corresponding to left and right front wheels 5L (only the left front wheel is shown) and left and right rear wheels 6L (only the left rear wheel is shown). Thus, the vertical movement of each wheel is attenuated. Each of the shock absorbers 1 to 4 has a built-in actuator 25 (refer to FIG. 2) so that the damping force characteristic can be changed between high and low, and can be switched between a vehicle body (sprung) and an axle (unsprung). A vehicle height sensor (not shown) is incorporated as relative displacement detection means for detecting relative displacement between the two. Reference numeral 7 denotes a coil spring disposed on the outer periphery of each of the shock absorbers 1 to 4, and 8 a control for outputting a control signal to an actuator in each of the shock absorbers 1 to 4 to variably control the damping force characteristics. A detection signal is output from the vehicle height sensor in each of the shock absorbers 1 to 4 to the control unit 8.

Reference numerals 11 to 14 denote four acceleration sensors for detecting acceleration in a vertical direction (Z direction) on a spring of each wheel, reference numeral 15 denotes a vehicle speed sensor provided in a meter of an instrument panel, and reference numeral 16 denotes a vehicle speed sensor. Is 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). or not)
19 is a brake pressure switch that detects the HARD, SOFT, CONT
This is a mode selection switch for switching to any one of the ROL modes. The detection signals of these sensors 11 to 17 and the switches 18 and 19 are all output to the control unit 8.

FIG. 2 shows the structure of the shock absorbers 1-4, and FIG. 2A shows the damping force characteristics of the shock absorbers 1-4.
FIG. 2B shows a case where the damping force characteristics of the shock absorbers 1 to 4 are SOFT characteristics (characteristics having a low damping coefficient). 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 (spring) 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 as to be opened and closed by an actuator 25. The actuator 25 includes a solenoid 26, a control rod 27, and two springs 28a and 28b. The control rod 27 is connected to the solenoid 2
The orifice 24 is opened and closed by moving up and down in the piston unit 22 by the magnetic force received from 6 and the biasing force received from both springs 28a and 28b.

The upper chamber 29 and the lower chamber 30 in the cylinder 21 and the cavity in the piston unit 22 communicating with the two chambers 29 and 30 are filled with a fluid having an appropriate viscosity. This fluid passes through one of the orifices 23, 24 and the upper chamber 29 and the lower chamber 30.
You can move between.

In the above configuration, the shock absorbers 1 to 4 perform the following operations.

That is, when the solenoid 26 is not energized, the force of the spring 28a for urging the control rod 27 downward is set stronger than the force of the spring 28b for urging the control rod 27 upward. 27 is pressed downward, closing orifice 24 (see FIG. 2A). Therefore, the passage of the fluid is only the orifice 23, and the damping force characteristics of the shock absorbers 1 to 4 are HARD (high damping) characteristics.

When the solenoid 26 is energized, the solenoid 26
The control rod 27 is pulled up by the magnetic force of 26, and the orifice 24 is opened (see FIG. 2B). For this reason, both orifices 23 and 24 are fluid passages, and the damping force characteristics of the shock absorbers 1 to 4 are SOFT (low damping) characteristics.

As described above, the damping force characteristics of the shock absorbers 1 to 4 become HARD characteristics when the solenoid 26 is not energized. Therefore, even if the control unit 7 fails, the shock absorbers 1 to 4 maintain the HARD characteristics. It is possible to keep the steering stability.

FIG. 3 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, ks is the spring constant of the tire, and v (t) is the damping coefficient of the shock absorber.

FIG. 4 shows a block configuration of a control unit of the suspension device. In FIG. 4, a first vehicle height sensor 41, a first acceleration sensor 11, and a first actuator 25a are mounted on a left front wheel 5L of a vehicle body, a second vehicle height sensor 42, a second acceleration sensor 12a.
And the second actuator 25b is attached to the front right wheel of the vehicle body,
Third vehicle height sensor 43, third acceleration sensor 13 and third
The actuator 25c corresponds to the rear wheel 6L on the left side of the vehicle body, and the fourth vehicle height sensor 44, the fourth acceleration sensor 14, and the fourth actuator 25d correspond to the rear wheel 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, r1 to r4 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 sprung displacement zs and the unsprung displacement zs-zu shown in FIG. 3) is set to zero, and the deviation from this represents the magnitude of the relative displacement.

_G1 to _G4 are first to fourth acceleration sensors 11 to
These are sprung absolute acceleration signals in the vertical direction (Z direction) output from the control unit 14 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, respectively. 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 to v4 are actuator control signals output from the control unit 8 to the actuators 25a to 25d, respectively, and these signals take two values of "1" and "0". When "1", the solenoid 26 (see FIG. 2) of the actuator 25 is not energized, and the damping force characteristics of the shock absorbers 1 to 4 become HARD characteristics. When it is “0”, the solenoid 26 of the actuator 25 is energized,
The damping force characteristics of the shock absorbers 1 to 4 are SOFT characteristics.

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, in the case of HARD, the damping force characteristics of all the shock absorbers 1 to 4 are fixed to the HARD characteristics, in the case of SOFT, the damping force characteristics of all the shock absorbers 1 to 4 are fixed to the SOFT characteristics, 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. 5 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, all of the actuator control signals v1 to v4 are set to "1" in step S15, and the control signals v1 to v4 are set in step S13.
Is output. As a result, all shock absorbers 1
The damping force characteristics of ~ 4 are HARD characteristics. At this time, the operation is completed.

When the value of the mode selection signal is not HARD,
In step S2, it is determined whether or not the value of the mode selection signal is SOFT.
Sets "0" to all of the actuator control signals v1 to v4, and outputs these control signals v1 to v4 in step S13.
As a result, the damping force characteristics of all the shock absorbers 1 to 4 become SOFT characteristics. 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. By the above steps S3 and S4 and the vehicle height sensors 41 to 44, the relative speeds 1 to 4 between the sprung and unsprung (that is, the difference between the sprung absolute speed and the unsprung absolute speed ( _S1 - _u1 ) to ( _S4 −
_u4 )) is constituted by a relative speed detecting means 51 for detecting ( ₄ )).

Here, the vehicle height sensors 41 to 44 (see FIG. 4)
The detection accuracy is about 1.4mm from the capability of the D converter,
Since the sampling is performed at regular intervals (1 to 10 ms), the values of the sprung-unsprung relative displacement signals r1 to r4 from the sensors 41 to 41 are, as shown in FIG. Along with the digitalization. For this reason, in the low frequency vibration region where the vibration waveform gradually changes, the relative speeds 1 to 4 between the sprung and unsprung portions often become zero.

Subsequently, in step S5, the sprung absolute acceleration signals _G1 to
After inputting _G4 , in step S6, these _G1 to _G4 are integrated by numerical integration or the like, and the vertical sprung absolute speed _{G1
Find G4} . _G1 to _G4 are the acceleration sensors 11 to
Since the absolute speed in the vertical direction at the position 14 is the sprung absolute speed in the step S7, it is converted into the absolute speeds _S1 to _S4 in the vertical direction at the positions of the shock absorbers 1 to 4 in step S7. _{Since S1} to _S4 can be obtained if three of _G1 to _G4 are known, _G1 to _G3 will be used hereinafter, and _G4 will be a spare value. Here, as shown in FIG. 1, take the appropriate origin in the horizontal plane, when taking the xy coordinates, the coordinates of the acceleration sensor _{11~13 (x G1, y G1)} ~ (x G3, y
_G3 ), the coordinates of the shock absorbers 1-4 are ( _xS1 , _yS1 )
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. The above-mentioned steps S5 to S7 and the acceleration sensors 11 to 14 constitute a sprung absolute speed detecting means 52 for detecting the sprung absolute speeds _S1 to _S4 in the vertical direction at the positions of the shock absorbers 1 to ₄ .

Thereafter, in step S8, a judgment function hi is obtained by the following equation.

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 S9, the judgment function hi is set to zero or a positive value (hi ≧ 0) and vi = 0.

Thereafter, in step S10, each of the shock absorbers 1 to
4 is determined by the following equation.

fsi (k) =-(vi (k) + bs) .i (k) where vi (k) is a variable attenuation constant at time k, zero for SOFT, and a positive predetermined value for HARD. vm. Also, bs is a fixed attenuation constant, which is an attenuation constant at the time of SOFT. i (k) is the relative speed between the sprung and unsprung parts at the time k previously obtained in step S4.

Subsequently, in step S11, each of the shock absorbers 1-4
, The damping force fsi (k) at time k and the damping force fsi (k-1) at time k-1
Find the difference between The above steps S10 and S11 constitute a damping force change rate calculating means 53 for calculating the damping force change rate Δfsi (k) of the shock absorbers 1-4.

Thereafter, in step S12, the damping force change rate Δfsi
The absolute value of (k) is greater than zero or a predetermined value close to zero (the value of the damping force change rate calculated when the damping force does not change or the sprung unsprung relative speed does not change as described later). If the determination is NO, the process immediately proceeds to step S13, while if the determination is YES, the process proceeds to step S13.
, The actuator control signal vi is not changed, and the process proceeds to step S13. In step S13, actuator control signals v1 to v4 are output, and the process returns.
By the above steps S8, S9, S13, a judgment function hi which is a product of the sprung unsprung relative speed i and the sprung absolute speed si is calculated, and depending on whether or not the judgment function hi is zero or more. A damping force characteristic control means 54 for controlling the damping force characteristics of each of the shock absorbers 1 to 4 to be changed to the HARD characteristic or the SCFT characteristic is provided. Also, the damping force change rate Δfsi of the shock absorbers 1-4 is determined by steps S12 and S14.
When the absolute value of (k) is larger than the predetermined value calculated when the damping force does not change or when the sprung unsprung relative speed does not change, the shock absorbers 1 to A control correcting means 55 for correcting the change of the damping force characteristic of No. 4 to be stopped is configured.

Therefore, according to such control, the driver can
When the ROL mode is selected, when the judgment function hi, which is the product i of the sprung unsprung relative speed i (= si−ui) and the sprung absolute speed si, is zero or a positive value, (hi ≧
0) (ie, when the sprung mass moves upward and the shock absorbers 1-4 extend and their damping force acts downward,
And the sprung body moves downward and the shock absorber 1
4 is contracted and its damping force acts upward), 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, and the shock absorbers 1 to 4 are determined. The damping force characteristics of No. 4 are changed to HARD characteristics. When the judgment function hi is a negative value (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 exciting direction with respect to the vertical vibration on the spring, and the damping force characteristics of the shock absorbers 1 to 4 are determined. Changed to SOFT characteristics. As a result, the vibration damping energy is increased with respect to the vibration energy transmitted to the sprung portion, and both the riding comfort and the steering stability can be improved.

In addition, such a change in the damping force characteristics of the shock absorbers 1 to 4 is stopped by the control correction means 55 when the absolute value of the damping force change rate Δfsi (k) is equal to or more than a predetermined value close to zero, and is changed to zero or zero. It is performed only when it is equal to or less than a predetermined value close to zero.

Here, the damping force change rate Δfs (k) (= fs (k) −f
s (k-1)) is a variable damping constant vi (k) at time k.
And the variable damping constant v (k-1) at time k-1, there are the following four cases.

(1) When v (k−1) = 0 and v (k) = 0 Δfs (k) = − bs ((k) − (k−1) (2) v when v (k−1) = vm When (k) = vm Δfs (k) = − (vm + bs) ((k) − (k−
1)) (3) When v (k−1) = 0 and v (k) = vm Δfs (k) = − bs ((k) − (k−1)) − v
m (k) (4) When v (k−1) = vm and v (k) = 0 Δfs (k) = − bs ((k) − (k−1)) + v
m (k-1) In the above three cases (3) and (4), in almost all cases, the absolute value of the damping force change rate Δfsi (k) becomes a value larger than zero. The change of the force characteristic is aborted. Also, in the cases of (1) and (2), | (k) − (k−1) |> 0 in the high frequency vibration region, so that the change of the damping force characteristic is stopped. After all, the damping force characteristic is changed only in the cases of (1) and (2) and in the low frequency vibration region, that is, when the stroke acceleration of the shock absorbers 1 to 4 is small and the damping force is small. The switching sound at the time of the change can be suppressed as much as possible.

Moreover, the variable damping constant v (k-1) at time k-1
Is equal to the variable damping constant vi (k) at time k,
That is, the damping force characteristic is set to HARD or
Since the damping force characteristic is changed when the command to change to SOFT is issued two or more times in succession, the damping force characteristic is not changed even if the change command is issued spontaneously due to disturbance or the like. Erroneous change switching of the damping force characteristic can be prevented.

The present invention is not limited to the above embodiment,
Other various modifications are included. For example, in the above embodiment, the present invention determines whether the product of the sprung absolute speed s and the sprung unsprung relative speed (= su) is equal to or greater than zero or not. Applied when changing the damping force characteristic to the HARD characteristic or SOFT characteristic. Instead of the sprung absolute speed s, the product of the unsprung absolute speed u and the sprung unsprung relative speed (= su) is Shock absorber 1 or 2 depending on whether it is zero or more
The same applies to the case where the damping force characteristic of No. 4 is changed to the HARD characteristic or the SOFT characteristic.

Further, in the above embodiment, the case where the damping force characteristics of the shock absorbers 1 to 4 can be changed between high and low two stages has been described. However, the present invention provides a multi-stage or stepless continuous damping force characteristic of the shock absorber of three or more stages. It is needless to say that the same can be applied to a case where it can be changed in a practical manner.

(Effect of the Invention) As described above, according to the vehicle suspension system of the present invention, the changeover of the damping force characteristic of the shock absorber based on the predetermined control law is switched only when the damping force of the shock absorber hardly changes. This is executed and is stopped when the damping force of the shock absorber changes greatly as in the high-frequency vibration region, so that it is possible to prevent generation of a loud switching sound. Further, even if the switching command is issued only once due to disturbance or the like, the change switching is not executed, so that erroneous switching can be prevented.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention. FIG. 1 is a perspective view showing a component layout of a suspension device, FIG. 2 is a longitudinal side view showing a main part of a shock absorber, and FIG. FIG. 4 is a block diagram of a control unit of the suspension device, and FIG.
FIG. 6 is a flowchart showing a control flow, and FIG. 6 is an explanatory diagram for explaining digitization of a signal from a vehicle height sensor. 1-4 Shock absorbers 41-44 Vehicle height sensor (relative displacement detecting means) 51 ... Relative speed detecting means 52 ... Spring-absolute speed detecting means 53 ... Damping force change rate calculating means 54 ... Damping Force characteristic control means 55 ... Control correction means

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichiro Yamashita 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Hiroshi Uchida 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda (58) Investigated field (Int. Cl. ⁷ , DB name) B60G 17/015

Claims (1)

(57) [Claims] 1. A shock absorber provided between a sprung portion and a unsprung portion and having a variable damping force characteristic, an absolute speed detecting means for detecting a sprung absolute speed or an unsprung absolute speed, and a sprung portion and a spring. A relative speed detecting means for detecting the relative speed between the lower and the upper and lower sprung absolute speed or the unsprung relative speed and the sign of the relative speed between the unsprung and unsprung, respectively, upon receipt of signals from the two detecting means A damping force characteristic control means for controlling the damping force characteristic of the shock absorber to a high damping side and changing the damping force characteristic of the shock absorber to a low damping side when they do not match, and a relative displacement detection for detecting a relative displacement between a sprung and unsprung portion. Means, a damping force change rate calculating means for calculating a damping force change rate of the shock absorber based on a value obtained by differentiating the signal from the relative displacement detecting means, and a damping force change rate calculated by the calculating means. When the absolute value is larger than a predetermined value calculated when the damping force does not change or when the sprung unsprung relative speed does not change, the control of the damping force characteristic control means changes the damping force characteristic of the shock absorber. A suspension device for a vehicle, comprising: a control correction unit that corrects the suspension.