JPH09132017A - Damping force control device in suspension system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhibit damping force characteristics the same as specified by its target by adjusting the damping force of a damping force variable shock absorber by the use of a signal comparatively easy to be detected such as relative speeds and relative displacements above and below a spring. SOLUTION: A damping force target value operating means 3 which sets a damping constant target value for a damping force variable shock absorber by using relative speeds and relative displacements above and below a spring as an input, is equipped with a target value setting means 15 for setting a specified constant, that is, a basic damping constant target value, and with a correction value operating means operating a clamping constant correction value out of an ideal clamping force operated based on relative speeds and relative displacements. And it is so constituted that the sum of the basic damping constant target value and the damping constant correction value shall be outputted as the damping constant target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for optimally controlling a damping force in a suspension system in which a shock absorber capable of variably controlling a damping force and a spring are combined, in accordance with a vibration state which changes from moment to moment.

[0002]

2. Description of the Related Art In a suspension system using a shock absorber having a variable damping force, a damping coefficient is changed according to a vibration state to increase, for example, a damping rate of vibration from above a spring and isolation of vibration from below a spring. Proposals for improving the effect are made by the following references and the like.

Reference 1 ... D. Karnopp et
al. : Vibration Control Usi
ng Semi-Active Force Gene
rats, J. et al. E. FIG. I. ASME, May, 619
/ 626 (1974), Reference 2 ... Takehiko Fujioka, Koji Kido; Study on control method of variable damper (Vehicle vibration control viewed from VSS theory), Preprint 862 197/200 (1989) of the Society of Automotive Engineers of Japan , Reference 3 ... A
n Introduction to Sliding
mode Variable Structure
control, A .; S. I. Zinober, Var
iable Structure and Lyapu
nov control, 1/20, Springer
(1994).

These control methods use the sliding mode control or the like to switch the damping coefficient of the shock absorber moment by moment according to the speed of the shock absorber on the spring relative to the absolute coordinate or the position relative to the absolute coordinate. The optimum damping characteristic is obtained according to the vibration state.

[0005]

However, it is often impossible to directly detect the velocity and displacement with respect to the absolute coordinates used for these controls,
Since these signals must be substituted by indirect or approximate values, the damping force characteristics may not reach the target value.

The present invention has been proposed in order to solve such a problem, and uses a damping force variable shock by using signals that are relatively easy to detect, such as relative speed and relative displacement of sprung and unsprung springs. By adjusting the damping force of the absorber,
An object of the present invention is to provide a damping force control device capable of exhibiting a desired damping force characteristic.

[0007]

According to a first aspect of the present invention, sprung and unsprung relative velocity detecting means, sprung and unsprung relative displacement detecting means, and the detected relative velocity and relative displacement are input. In a suspension system including a damping force target value calculating means for setting a damping constant target value of the damping force variable shock absorber as described above, and a damping force variable shock absorber for inputting the damping constant target value to adjust the damping constant, The damping force target value calculating means is a target value setting means for setting a basic damping constant target value which is a predetermined constant, and a damping constant correction value obtained by correcting the ideal damping force calculated based on the relative speed and the relative displacement. A correction value calculating means for calculating is provided, and is configured to output a damping constant target value including the basic damping constant target value and the damping constant correction value.

According to a second aspect of the present invention, in the first aspect of the present invention, a switching input computing means for computing a switching input based on a predetermined gain, a relative speed, a relative displacement and a state quantity of the filter, and a predetermined gain, a relative speed and a relative speed. A linear input calculation means for calculating a linear input from the displacement and the state quantity of the filter; an adder for adding the switching input and the linear input; and a filter for outputting an ideal damping force with the ideal input that is the output of the adder as an input. Based on this ideal damping force, the correction value calculation means calculates the damping constant correction value.

In a third aspect based on the second aspect, the filter is a low pass filter having a predetermined cutoff frequency.

[0010]

Therefore, in the present invention, the damping constant target value input to the damping force variable shock absorber is based on the basic damping constant target value which is a predetermined constant and the relative speed and relative displacement of the sprung and unsprung springs. It is calculated as a value obtained by adding the calculated ideal damping force and the damping constant correction value, and the damping force characteristic is controlled based on this value.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

First, in FIG. 1, 1 is a relative displacement detecting means for detecting the relative displacement of the damping force variable shock absorber 4 between the sprung and unsprung portions, and 2 is also the relative velocity between the sprung and unsprung portions. The relative velocity detecting means 3 calculates a target value of the damping force based on the relative displacement and the relative velocity, inputs the result to the damping force variable shock absorber 4, and controls so as to generate the target damping force. It is a damping constant target value calculation means for.

FIG. 2 shows a concrete configuration of the damping constant target value calculating means 3. As shown in the drawing, the relative speed x _{1 of} the sprung and unsprung portions (hereinafter, simply referred to as the relative speed), and the sprung and the springs. A switching input calculation means 11 for calculating a switching input based on a lower relative displacement x ₂ (hereinafter, simply referred to as a relative displacement) and a state quantity x _{c of} a filter Wc (s) 13 described later, and a relative speed, a relative displacement, Based on the linear input calculation means 12 that calculates a linear input based on the filter state quantity x _c , the adder 16 that adds the switching input and the linear input, and the ideal input that is the output of the adder 16. The filter Wc (s) 13 that outputs an ideal damping force, and the filter Wc
(S) The correction value calculating means 15 for calculating the correction value of the damping force constant from the ideal damping force output from 13, the target value setting means 14 for setting the basic damping constant target value, and these outputs are added. And an adder 17 that outputs the damping constant target value.

Explaining these in more detail, the switching input computing means 11 calculates the switching input u _sw from the relative velocity, the relative displacement, the state quantity x _{c of the} filter and the predetermined gains N, M, ρ and the constant δ as follows. calculate.

The linear input calculation means 12 calculates the linear input u _ln from the predetermined gain L as follows.

The filter W _c (s) 13 has an ideal input u
_ideal = u _sw + u _ln , the ideal damping force f
_ideal is calculated as follows. Here, A _c , B _c , and C _c are constant matrices of appropriate dimensions that represent the attenuation characteristics of the filter W _c (s) 13. For example, the filter is a low-pass filter with a cutoff frequency of 10 Hz.

The damping force target value calculation means 3 is Outputs the damping force target value c ^* . Here, c ₀ is a predetermined constant determined from the vibration damping characteristics in the high frequency band. Note that, in relation to the description of the claims, c ₀ is the damping constant target value,

The damping force variable shock absorber 4 inputs c ^* , and the generated damping force c It is assumed that

How to derive each control gain will be described below.

Consider the suspension system of FIG. The equation of motion for this system can be written as m ₁ is unsprung mass, k ₁ is unsprung rigidity, m ₂ is sprung mass, k ₂ is spring rigidity, and c ₂ is Is the acceleration relative to the absolute coordinates of, z ₀ is the disturbance displacement, z ₁ is the unsprung displacement, and z ₂ is the sprung displacement. This is a model that simplifies the suspension of an automobile. For example, m ₁
The following argument holds even if → 0 and k ₁ → ∞.
The purpose of the suspension system is to damp the motion on the spring in the presence of the disturbance z ₀ .

[0021] Is obtained. Equation (8) is rewritten as follows. However c _u is the damping coefficient variable allowance of the damping force variable shock absorber 4. c ₀ is determined in consideration of the vibration characteristics in the high frequency band, as will be described later, regardless of the actual variable amount of the shock absorber.

U is passed through the filter W _c (s) Generate like. In this way, for example, W
_{If c} (s) is used as a low-pass filter, the high frequency component of u (s) will be attenuated, and in the high frequency band Becomes This effect will be explained later

Now, when u is generated as in equation (10),
The suspension system and the expansion system of the filter can be expressed as follows. Becomes

The control gain will be derived based on the sliding mode control theory.

[0025] Can be rewritten.

When u _ideal is generated as in equation (19), S is reached within a sufficiently short time for practical use from the start of control.
Switching the switching mode of the liding mode; Can be generated. That is, the expanded state is constrained to the plane of σ = 0 [see reference 3]. At this time, the movement of the expansion system Can be expressed as

To satisfy the control purpose, it suffices to constrain the state to the desired switching surface. In other words, the expression (17) may be expressed as a preferable vibration characteristic. this is This is equivalent to the problem of damping the system represented by the following with the state feedback v = −Fy ₁ . The following publicly known method may be used to design such a feedback gain F (switching surface).

When the state is restricted to the switching surface σ = 0, the following evaluation function The switching surface that minimizes σ _∞ = 0, σ _∞ = F _∞ y ₁ + y ₂ is set by the H _∞ optimization from equation (16). Assuming that is white noise, Sliding Mode
When the next evaluation function The switching surface σ ₂ = 0 and σ ₂ = F ₂ y ₁ + y ₂ that minimizes can be designed by H ₂ optimization [see Reference 3].

[0029] I wish I could It is.

The ideal damping force u _ideal for realizing the Sliding Mode is It is an appropriate matrix and is calculated as follows. Σ, Θ,
Define Φ as follows: Here p ₂ is a positive definite symmetric solution of the following Lyapunov equation: Φ _* and p are design parameters, respectively, Sliding
A stability matrix that determines the speed of convergence to Mode, and a positive constant that determines the magnitude of u _sw . Also δ ≧ 0 is a design parameter and is a positive constant that prevents chattering. Response of damping constant is fast enough and relative displacement,
When the relative speed can be detected sufficiently fast, even if δ = 0, u _sw becomes a discontinuous switching input and the state can be surely restricted to the switching surface.

From u _{ideal the} ideal damping force is defined as Is generated. With the ideal damping force, the force f _abs that can be generated by the shock absorber is If the filter W _c (s) and the switching surface σ = 0 are set appropriately, a sufficient control effect can be expected in the practical region. From this, the target value c ^* of the damping constant of the damping force variable shock absorber is as shown in equation (5) in consideration of the fixed component c ₀ of the damping force. And it is sufficient.

Next, the effect of c ₀ will be described. The equation of motion (7) of the suspension system can be rewritten as follows. It can be seen that each input gain is set. Therefore, the value of c ₂ should be reduced. It will be good.

However, in the control method described above, for example, if W _c (s) is a low-pass filter and c ₀ is a sufficiently small value, at high frequencies as described in equation (11). The effect of de control appears and the damping of the suspension system can be improved.

The present invention is also applicable to automobile suspensions. In automobiles, if the damping constant of the shock absorber becomes extremely small in the high frequency band, the ground contact of the tire may be affected. Therefore, in the present invention, by designing the minimum c ₀ as a design parameter in advance, it is possible to design the suspension characteristics in consideration of the grounding property.

FIG. 4 shows the result of computer simulation of a typical suspension system. Figure 4 shows the suspension system z
The power spectrum density of the displacement and acceleration on the spring when white noise is added is shown as ₁ . It can be seen that, according to the control method described here, the damping effect is improved at almost all frequencies as compared with the case where the damping force of the shock absorber is fixed.

[0036]

As described above, according to the present invention, it is possible to obtain a sufficient damping effect by using the signals of relative speed and relative displacement between sprung and unsprung that are relatively easy to detect. Further, when applied to the suspension of an automobile, it becomes possible to design a suspension control system in consideration of the disturbance blocking characteristic in the high frequency band and the grounding property of the tire.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a damping force target value calculating means.

FIG. 3 is a model diagram of a suspension system.

FIG. 4 is an explanatory diagram showing a vibration damping effect of the present invention.

[Explanation of symbols]

 1 Relative Displacement Detection Means 2 Relative Velocity Detection Means 3 Damping Force Target Value Calculation Means 4 Damping Force Variable Shock Absorbers 11 Switching Input Calculation Means 12 Linear Input Calculation Means 13 Filters Wc (s) 14 Correction Value Calculation Means 15 Target Value Setting Means

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[Procedure amendment]

[Submission date] March 26, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

FIG. 2 shows a concrete configuration of the damping constant target value calculating means 3. As shown in the drawing, the relative speed x ₂ of the sprung and unsprung parts (hereinafter simply referred to as the relative speed), the sprung part and the spring. A switching input calculation means 11 for calculating a switching input based on a lower relative displacement x ₁ (hereinafter, simply referred to as a relative displacement) and a state quantity x _{c of} a filter Wc (s) 13, which will be described later, and a relative speed, a relative displacement, Based on the linear input calculation means 12 that calculates a linear input based on the filter state quantity x _c , the adder 16 that adds the switching input and the linear input, and the ideal input that is the output of the adder 16. The filter Wc (s) 13 that outputs an ideal damping force, and the filter Wc
(S) Correction value calculation means 14 for calculating the correction value of the damping force constant from the ideal damping force output from 13, the target value setting means 15 for setting the basic damping constant target value, and these outputs are added. And an adder 17 that outputs the damping constant target value.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

The filter W _c (s) 13 has an ideal input U
_ideal = U _sw = U _ln to ideal damping force f
_ideal is calculated as follows. Here, A _c , B _c , and C _c are constant matrices of appropriate dimensions that represent the attenuation characteristics of the filter W _c (s) 13. For example, the filter is a low-pass with a cutoff frequency of 10 [Hz] In that case, A _c = B _c = −2π × 10 C _c = 1.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

When U _ideal is generated as shown in the equation (9), Sl is reached within a sufficiently short time for practical use from the start of control.
The iding Mode can be generated on the switching surface; σ = 0, σ = Fy ₁ + y ₂ (15). That is, the expanded state quantity is constrained to the plane of σ = 0 [see reference 3]. At this time, the movement of the expansion system Ie Can be expressed as

Claims (3)

[Claims] 1. A relative speed detecting means on the sprung and the unsprung,
Sprung and unsprung relative displacement detection means, damping force target value calculation means for setting the damping constant target value of the damping force variable shock absorber using these detected relative velocity and relative displacement as input, and this damping constant target value In a suspension system including a damping force variable shock absorber that adjusts the damping constant by inputting, the damping force target value calculating means is a target value setting means for setting a basic damping constant target value that is a predetermined constant. A correction value calculating means for calculating a damping constant correction value that corrects the ideal damping force calculated based on the relative velocity and the relative displacement, and a damping constant target including these basic damping constant target value and damping constant correction value A suspension damping force control device characterized in that it is configured to output a value. 2. A switching input calculation means for calculating a switching input from a predetermined gain, a relative speed, a relative displacement and a state quantity of a filter, and a linear input from a predetermined gain, a relative speed, a relative displacement and a state quantity of the filter. And a filter for outputting an ideal damping force with the ideal input, which is the output of the adder, as an input, based on this ideal damping force. The damping force control device for a suspension system according to claim 1, wherein said correction value calculation means calculates a damping constant correction value. 3. The damping force control device for a suspension system according to claim 2, wherein the filter is a low-pass filter having a predetermined cutoff frequency.