WO2006103014A1

WO2006103014A1 - Device and method for influencing the damping characteristics of a vehicle suspension

Info

Publication number: WO2006103014A1
Application number: PCT/EP2006/002616
Authority: WO
Inventors: Eberhard Kutscher; Johannnes Mayer
Original assignee: Daimlerchrysler Ag
Priority date: 2005-03-30
Filing date: 2006-03-22
Publication date: 2006-10-05
Also published as: DE102005014237A1

Abstract

The invention relates to a device for influencing the damping characteristics of a vehicle suspension. Said device comprises a shock-absorbing unit (11i), which is situated between the vehicle body (12) and a wheel carrier (13i) of said vehicle (10). The damping force of the shock-absorbing unit (11i) can be modified by the control of an actuator (14i). In addition, the device is equipped with a control unit (20), which determines a vertical speed variable (vi) that represents a vertical speed occurring in the vehicle body (12). According to the invention, the control unit (20) increases the damping force of the shock-absorbing unit (11i) by means of the actuator control (14i) if the amount of the determined vertical speed variable (vi) is greater than a predefined minimum value (v i,min ). According to the invention, the control unit (20) specifies the minimum value (v i,min ) in accordance with a road condition variable (νi) that represents the road condition, said control unit (20) calculating the road condition variable (νi) by forming an amount and carrying out the subsequent low-pass filtration of a determined vertical speed variable (a i ) that represents a vertical speed occurring in the vehicle body (12).

Description

Device and method for influencing the damping force characteristic of a chassis suspension of a motor vehicle

The invention relates to a device and a method for influencing the damping force characteristic of a chassis suspension of a motor vehicle. The device comprises a damping device, which is arranged between a vehicle body and a wheel carrier of the motor vehicle, wherein the damping force of the damping device is variable by driving an adjusting device. Furthermore, a control unit is provided which determines a vertical speed variable representing a vertical speed occurring at the vehicle body, wherein the control unit increases the damping force of the damping device by driving the adjusting device, if the determined vertical speed variable is greater in magnitude than a predetermined minimum value.

Such a device for influencing the damping force characteristic of a chassis suspension of a motor vehicle is apparent from the document DE 44 32 585 Al. The device comprises a vibration damper, which is arranged between a vehicle body and a wheel carrier of the motor vehicle, wherein the damping force of the vibration damper can be changed by driving an electric actuator. Furthermore, the device has a control unit which determines a vertical speed signal, which occurs at the vehicle body Vertical speed reproduces, wherein the control unit increases the damping force of the vibration damper by controlling the electric actuator, if it appears that the current, ie last detected peak value of the detected vertical speed signal is greater in magnitude than a predetermined threshold, which defines a constructive condition insensitivity of the vibration damper used.

The increase of the damping force itself takes place on the basis of a comparison carried out by the control unit between the current peak value of the ascertained vertical speed signal and an average value continuously calculated from temporally preceding peak values. In this case, the control unit sets the higher damping force by activation of the electric adjusting device, the greater the current peak value of the determined vertical speed signal compared to the calculated average value, i. the greater the excitation of vertical vehicle body movements caused while driving due to the particular road condition. The continuous calculation of the average value is comparatively complicated, so that accordingly high demands are placed on the control unit.

It is an object of the present invention, a device or a method of the type mentioned in such a way that this or this makes it possible to perform with relatively little computational effort dependent on the particular road condition influencing the damping force characteristic of the suspension of the motor vehicle.

This object is achieved according to the features of patent claim 1 and patent claim 12. The device for influencing the damping force characteristic of a chassis suspension of a motor vehicle comprises a damping device, which is arranged between a vehicle body and a wheel carrier of the motor vehicle, wherein the damping force of the damping device is variable by driving an adjusting device. The damping device is used in a known manner for damping undesired vehicle body movements, which occur relative to the wheel carrier or the vehicle tire located thereon.

Furthermore, a control unit is provided which determines a vertical speed variable representing a vertical speed occurring at the vehicle body, wherein the control unit increases the damping force of the damping device by controlling the adjusting device when the determined vertical speed variable is greater in magnitude than a predetermined minimum value.

According to the invention, the control unit predetermines the minimum value as a function of a road condition variable representing the road condition, wherein the control unit calculates the road condition variable by magnitude formation and subsequent low-pass filtering of a determined vertical acceleration variable representing a vertical acceleration occurring at the vehicle body, in particular due to road bumps occurring during the journey , Potholes and the like is caused. The calculated enztraßenzustandsgröße thus represents a direct measure of the respective surface condition of the busy road.

Since an increase in the damping force is inevitably accompanied by a deterioration of driving comfort, it can be ensured by appropriate specification of the minimum value that the damping force of the damping device is increased only if the particular road condition actually requires. The specific procedure for calculating the road condition variable-it is merely the amount of the determined vertical acceleration variable and then carrying out a low-pass filtering-makes it possible to carry out a modulation of the damping force characteristic that is dependent on the road condition with comparatively little computational effort. The calculation of the road condition variables can take place here in real time, so that the specification of the minimum value always takes place in accordance with the currently present road condition and an inappropriate influencing of the damping force characteristic can largely be avoided.

To calculate the road condition variable, the control unit has, for example, an analog computer or a correspondingly programmed digital signal processor (DSP).

Advantageous embodiments of the device according to the invention will become apparent from the dependent claims.

Advantageously, the determination of the vertical speed variable takes place on the basis of the determined vertical acceleration quantity, for example by carrying out a numerical integration, so that no separate sensor is necessary to provide the vertical speed variable.

The vertical acceleration variable can be determined in a simple manner by using a linear acceleration sensor assigned to the vehicle body, whose measuring axis is oriented in the direction of the perpendicular to the earth's surface.

In order to be able to make a reliable statement as to whether influencing the damping force characteristic due to the driving dynamics of the motor vehicle is necessary or not, it is advantageous if the configuration control unit in the specification of the minimum value in addition to the caused due to the particular road conditions and reproduced by the calculated road condition variable vertical dynamics of the motor vehicle at the same time its horizontal dynamics, ie its longitudinal dynamics and / or transverse dynamics considered. This can take place, for example, in the form of a determined longitudinal speed variable which describes the longitudinal speed of the motor vehicle and / or a determined transverse acceleration variable which describes a lateral acceleration acting on the motor vehicle.

In order to make the influencing of the damping force characteristic as simple as possible in dependence on the respective road condition, it is also advantageous if the control unit determines a road condition coefficient based on the calculated road condition variable, which is multiplied by a fixed base minimum value to specify the minimum value of the vertical speed variable ,

The same applies in the case of an additional consideration of the horizontal dynamics of the motor vehicle, for which purpose the control unit determines associated correction factors on the basis of the determined longitudinal speed variable and / or the determined lateral acceleration quantity, which are likewise multiplied by the fixed minimum value for setting the minimum value.

The determination of the road condition coefficient - and optionally the correction factors - can be done by using a stored in the control unit functional relationship, which can be achieved depending on the chosen course of the functional relationship sporty or comfort-emphasized damping force characteristic of the chassis suspension. Advantageously, the damping force for the rebound stage and the compression stage of the damping device can be changed separately by controlling the adjusting device, so that it is possible to influence the damping force characteristic of the suspension for an upward vehicle body movement independently of a downward vehicle body movement.

In this case, the control unit increases the damping force of the rebound damping relative to the damping force of the compression stage of the damping device if it is ascertained on the basis of the determined vertical speed that, when the predetermined minimum value is exceeded, there is an upward vehicle movement. Conversely, the control unit increases the damping force of the compression stage relative to the damping force of the rebound of the damping device when it is determined on the basis of the determined vertical speed size that when the predetermined minimum value is exceeded, there is a downward vehicle body movement.

By influencing the damping force characteristic corresponding to the sky-hook theory, a further increase in driving comfort can be achieved without impairing the effectiveness with regard to the damping of the vehicle body movements that occur.

The damping device may in particular be a common telescopic damper, which comprises a hydraulically or pneumatically damped main damper piston. To change the damping force, the adjusting device preferably has a bypass valve that can be switched on by the damping device, which allows the hydraulic or pneumatic volume flow flowing through the telescopic damper to be bridged, so that a higher damping force is established when the bypass valve is closed ("hard" damping force channel). characteristic) than when the bypass valve is open ("soft" damping force characteristic).

In order to enable the damping force characteristic to be influenced independently of the direction of pull and the direction of compression of the damping device, the adjusting device for the rebound and the pressure stage has separate bypass valves, the bypass valve which can be engaged for the rebound of the damping device being permeable exclusively in the direction of pull, and for the pressure stage of the damping device switchable bypass valve is permeable only in the pressure direction.

The device according to the invention or the method according to the invention will be explained in more detail below with reference to the accompanying drawings. Showing:

1 shows a schematically illustrated embodiment of the device according to the invention,

FIG. 2 a) shows a measurement curve a _A (t) which is an exemplary one

Waveform of the determined vertical acceleration quantity a _± as a function of time t,

FIG. 2 b) shows a measurement curve a _{i / filt} (t) which _reproduces the signal course from FIG. 2 a) after carrying out a high-pass filtering with a cutoff frequency of f _g = 5 Hz, FIG.

2 c) a measurement curve | a _{i / filt} (t) | showing the waveform of Fig. 2 (b) after the magnitude is formed, Fig. 2 d) a trace μi (t), the waveform of

FIG. 2 c) after execution of a low-pass filtering with a time constant of τ = 5 s,

Fig. 3 a) a diagram showing a functional relationship between the road condition size \ i _± and the

Shows road condition coefficients K ₁ ,

3 b) is a diagram showing a functional relationship between the longitudinal velocity variable V ₁ and the associated correction factor λ _vl ,

Fig. 3 c) is a diagram showing a functional relationship between the lateral acceleration quantity a _q and the

corresponding correction factor λ _aq reproduces.

1 shows an exemplary embodiment of the device according to the invention for influencing the damping force characteristic of a chassis suspension of a motor vehicle.

The arranged in the motor vehicle 10 device comprises a damping device Hi, which is arranged between a vehicle body 12 and a wheel carrier 13i of the motor vehicle 10, wherein the damping force of the damping device Hi by controlling an adjusting device 14i is variable. The damping device Hi and the adjusting device 14i are here - as well as a not shown for reasons of clarity Radfedereinrichtung - common part of the suspension 15i. By way of example, it is a four-wheeled motor vehicle 10, so that in the present case i = a ... d applies.

Furthermore, there is a control unit 20 which determines a vertical speed variable V ₁ which has a rich of the damping device Hi on the vehicle body 12 occurring vertical speed, the control unit 20 increases the damping force of the damping device Hi by controlling the actuator 14i when the determined vertical speed variable V _{1 is} greater than a predetermined minimum value v _ijinin .

The control unit 20 specifies the minimum value v _{i / min} as a function of a road condition representing road condition variable μ _ά , wherein the control unit 20 calculates the road condition variable μi by magnitude and subsequent low pass filtering a determined vertical acceleration ai, the one in the range of the damping device Hi on the vehicle body 12 reproduces vertical acceleration.

In addition, the control unit 20 while taking account of the horizontal dynamics, ie the longitudinal dynamics and / or lateral dynamics when specifying the minimum value of v _{i / min} in addition to the induced due to the respective road condition and μ through the calculated road state variable _A reproduced vertical dynamics of the motor vehicle 10. This takes place in the form of a determined longitudinal velocity variable V ₁ , which describes the longitudinal velocity of the motor vehicle 10, and / or a determined lateral acceleration variable a _q , which describes a lateral acceleration acting on the motor vehicle 10.

The determination of these two variables takes place by using wheel speed sensors 22 and a vehicle body 12 associated lateral acceleration sensor 23 whose measuring axis is oriented in the transverse direction of the motor vehicle 10, wherein the control unit 20, the longitudinal speed V ₁ by evaluating the wheel speed provided by the Raddrehzahlsensoren 22 Raddrehzahlsignale and the lateral acceleration a _q determined by evaluation of the provided by the lateral acceleration sensor 23 acceleration signal. alternative For reasons of simplicity, the lateral acceleration quantity a _q can also be derived from a sensor-determined steering angle variable which describes a steering angle set on a steering device of the motor vehicle 10.

To calculate the road condition variable μ _i7, which takes place in real time in the present case, the control unit 20 has an analog computer or a correspondingly programmed digital signal processor (DSP).

According to the example, the vehicle body 12 in the region of the damping devices IIa to 11c is assigned a total of three linear acceleration sensors 23a to 23c whose measuring axes are oriented in the direction of the perpendicular to the earth's surface, wherein the control unit 20 evaluates the vertical acceleration magnitude by evaluating the acceleration signals provided by the linear acceleration sensors 23a to 23c ai and on the basis of which, by performing a numerical integration, the vertical velocity variable v _{A is} determined.

The measured curves a) to d) shown in FIG. 2 illustrate the procedure for calculating the road condition variable μ _A in the following.

FIG. 2 a) shows a measurement curve a i (t) which represents an exemplary signal variation of the determined vertical acceleration quantity a _A as a function of the time t. The arrow hereby marks a transition occurring during the journey between a road section with a good surface condition, in the present case a smooth asphalt, and an adjoining road section with a comparatively poor surface condition, in particular due to unevenness, potholes and the like. Since it is possible for the vehicle body 12 to be excited during travel on the basis of elongated road shafts to produce low-frequency vertical oscillations which would lead to a distortion of the road condition variable μ _A , the control unit 20 limits the determined vertical acceleration variable a _t to high frequencies. The cutoff frequency f _{g of} this high-pass filtering is typically in the range between 2 and 10 Hz.

FIG. 2 b) shows a measurement curve a _{i / filt} (t) which _reproduces the signal curve of FIG. 2 a) after carrying out a high-pass filtering with a cutoff frequency of f _g = 5 Hz.

The thus determined vertical _{acceleration quantity} a _{i / flop} then forms the basis for the actual calculation of the road state variable μ i, ie the amount formation carried out by the control unit 20 and subsequent low-pass filtering, the latter according to a recursive equation of the shape

μ _x Ck) = A ₁ • | a _{1 / falls} (kl) | + B _1. | A _irfilt (kl) | , (1.1)

A ₁ = le ^{"τ / τ} , B ₁ = e ^{~ T / t} , (1.2)

where k is the current sampling time, k-1 is the previous sampling time, T is the sampling time, and τ is the time constant of the low-pass filtering. The sampling time T is typically on the order of 10 to 100 ms.

Fig. 2 c) shows a measurement curve | a _{i / filt} (t) | which reproduces the waveform of Fig. 2 b) after formation of the amount. Furthermore, FIG. 2 d) shows a measurement curve μ _± (t), which reproduces the signal curve of FIG. 2 c) after subsequent low-pass filtering with a time constant of τ = 5 s. As can be seen, the calculated road condition quantity μ _{± represents} a direct measure of the respective surface condition of the vehicle This is the greater, the worse the surface condition of the busy road is.

The control unit 20 determines on the basis of the calculated road condition quantity] i _± a road condition coefficient K ₁ , which is multiplied by a fixed base minimum value v ° _{min in} order to specify the minimum value v _{i / min} . The basic minimum value v ° _in , for example, is between 0.15 and 0.25 m / s and may be different for the damping devices Hi of the front axle and the rear axle of the motor vehicle 10, so that the structurally determined mass distribution of the motor vehicle 10 in the specification of the Minimum value v _{i; min} . In addition, it is conceivable to adapt the damping force characteristic of the suspension 15i to the driving behavior of the respective driver by modifying the predetermined basic minimum value v ° _min . The basic minimum value v? _min can be in this case via a valve disposed in the motor vehicle 10 operating element 24 modify the driver's side, with an even tougher and harder damping force characteristic is achieved or chassis vote, the smaller the minimum base

V °, _n , i _n is.

Furthermore, the control unit 20 determines on the basis of the determined longitudinal speed variable V ₁ and / or the determined lateral acceleration variable a _q respectively associated correction factors λ _vl and λ _aq , which are also multiplied to take into account the horizontal dynamics of the motor vehicle 10 with the fixed predetermined base minimum value v ° _min , All in all, therefore, there is an equation of form for the minimum value v _ijmin

Vi, _min = (Ki -λ _{v: L} -λ _aq ) -v ° _ _min . (1.3)

The determination of the road condition coefficient K ₁ and of the two correction factors λ _vl and λ _aq takes place here by using functionalities stored in the control unit 20. nal contexts. These are exemplified by the diagrams a) to c) of Fig. 3 reproduced.

The following numerical example is intended to illustrate the calculation of the minimum value v _iιmin , wherein the values given for the road _{condition variable} μ _A and for the longitudinal speed variable V ₁ and / or the lateral acceleration variable a _{q represent} a speedy drive on a country road when driving through an elongated curve:

μ _d = 0.4, V ₁ = 100 km / h, a _q = 4 m / s ² . (1.4)

Starting from Fig. 3 then arises

Ki = 1, 5, λ _vl = 0, 5, λ _aq = 0, 6 (1.5)

and from this by inserting into equation (1.3) assuming a fixed basic minimum value of v ° _ _min = 0.2 m / s

Vi, _min = (1, 5-0,4-0, 6) -0,2 m / s = 0, 09 m / s. (1.6)

In the case of the above numerical example, the increase in the damping force of the damping device 11 is then carried out when the determined vertical _{velocity variable} V ₁ _exceeds a predetermined minimum value of v _iiTOin = 0.09 m / s.

By way of example, the damping force for the rebound stage and the compression stage of the damping device 11 can be changed separately by actuating the adjusting device 14i, the control of the adjusting device 14i taking place in accordance with the "Sky Hook" theory.

In this case, the control unit 20 increases the damping force of the rebound damping relative to the damping force of the compression stage of the damping device lli, if it is determined on the basis of the determined vertical speed variable V ₁ that in amount exceeding the predetermined minimum value Vi, i _ra _{n is} a present vehicle body upward movement. Conversely, the control unit 20 increases the damping force of the compression stage relative to the damping force of the rebound damping Hi, if it is determined on the basis of the determined vertical speed V ₁ that when the minimum value v _{i / rain is} exceeded, there is a downward vehicle body movement.

The damping device Hi is, for example, a telescopic damper comprising a hydraulically or pneumatically damped main damper piston. In order to change the damping force, the adjusting device 14i has a bypass valve 25i or 26i which can be engaged by the damping device Hi and allows the hydraulic or pneumatic volume flow flowing through the telescopic damper to be bridged so that a higher damping force is achieved when the bypass valve 25i or 26i is closed ( "Hard" damping force characteristic) than when the bypass valve 25i or 26i is open ("soft" damping force characteristic).

In order to allow the damping force characteristic to be influenced independently of the direction of pull and the direction of compression of the damping device Hi, the adjusting device 14i has separate bypass valves 25i and 26i for the rebound and the pressure stage, the bypass valve 25i which can be engaged for the rebound of the damping device Hi is permeable exclusively in the pulling direction and the switchable for the compression stage of the damping device Hi bypass valve 26i is permeable only in the printing direction.

The control of the bypass valves 25i and 26i via a driver 3Oi, for example, a demultiplexer, which is connected to the control unit 20 via an electrical or optoelectronic control line 31i.

In order to control the setting device 14i according to the "sky-hook" theory, the following control scheme can be found: where a positive vertical velocity quantity Vi> 0 denotes an upward vehicle body movement and a negative vertical velocity variable V ₁ <0 denotes a downward vehicle body movement:

n = AND operation, 0 = bypass valve closed, 1 = bypass valve open

Claims

DaimlerChrysler AGPatent claims

1. A device for influencing the damping force characteristic of a chassis suspension of a motor vehicle, with a damping device (lli) disposed between a vehicle body (12) and a wheel carrier (13i) of the motor vehicle (10), wherein the damping force of the damping device (lli) by driving an adjusting device (14i) is variable, and with a control unit (20) which determines a vertical speed (V ₁ ), which reproduces a vertical speed on the vehicle body (12), wherein the control unit (20) the damping force of the damping device (lli ) is increased by triggering the adjusting device (14i) if the determined vertical speed variable (V ₁ ) is greater in magnitude than a predetermined minimum value (v _iιmin ), characterized in that the control unit (20) the minimum value (v _{i / min} ) in Dependence of a road condition representing the road condition e (μ _A ), wherein the control unit (20) calculates the road condition quantity (μ _± ) by magnitude formation and subsequent low-pass filtering of a determined vertical acceleration quantity (aj representing a vertical acceleration (a _x ) occurring at the vehicle body (12).

2. Apparatus according to claim 1, characterized in that the determination of the vertical velocity variable (V ₁ ) is based on the determined vertical acceleration magnitude (aj).

3. A device according to claim 1, characterized in that the determination of the vertical acceleration quantity (a _± ) by using the vehicle body (12) associated linear acceleration sensor (23a, ..., 23c) takes place, the measuring axis is oriented in the direction of the perpendicular to the earth's surface ,

4. The device according to claim 1, characterized in that the control unit (20) in the specification of the minimum value (v _{i / min} ) in addition to the calculated road condition variable (μi) a determined longitudinal speed (V ₁ ), the longitudinal speed of the motor vehicle ( 10), and / or a determined transverse acceleration variable (a _q ) which describes a lateral acceleration acting on the motor vehicle (10).

5. The device according to claim 1, characterized in that the control unit (20) on the basis of the calculated road condition variable (μi) determines a road condition coefficient (K ₁ ), which is to specify the minimum value

( ^v i, min) with a fixed base minimum value

(v ° _rain ) is multiplied.

6. The device according to claim 4, characterized in that the control unit (20) on the basis of the determined longitudinal speed variable (V ₁ ) and / or the determined lateral acceleration variable (a _q ) respectively associated correction factors (λ _vl , λ _aq ) determines the default of Minimum value (v _{1 / now} ) with a fixed predetermined minimum value (v ° _{l (llιn} ) are multiplied.

7. The device according to at least one of claims 5 or 6, characterized in that the determination of the road condition coefficient (K ₁ ) and / or the determination of the correction factors (λ _vl , λ _aq ) by using a in the control unit (20) stored functional relationship he follows.

8. The device according to claim 1, characterized in that the damping force for the rebound and the compression stage of the damping device (lli) by controlling the adjusting device (14i) is separately variable.

9. The device according to claim 8, characterized in that the control unit (20) the damping force of the rebound relative to the damping force of the compression stage of the damping device (lli) increases when it is determined due to the determined vertical speed variable (V ₁ ) that in amount exceeding the predetermined Conversely, the minimum value (v _{1> now} ) is an upward vehicle body movement and, conversely, that the control unit (20) increases the damping force of the compression stage relative to the damping force of the rebound damping unit (lli), as determined by the determined vertical velocity variable (V ₁ ). that when the predetermined minimum value (v _{1; rain} ) is exceeded _{, there is} a downward vehicle body movement.

10. The device according to claim 1, characterized in that the adjusting device (14i) for changing the Dämp- has one of the damping device (lli) switchable bypass valve (25i, 26i).

11. The device according to claim 10, characterized in that the adjusting device (14i) for the rebound stage and the compression stage of the damping device (lli) has separate bypass valves (25i, 26i), wherein the for the rebound of the damping device (lli) switchable bypass valve (25i) is permeable exclusively in the pulling direction and the bypass valve (26i) which can be engaged for the pressure stage of the damping device (lli) is permeable exclusively in the pressure direction.

12. A method for influencing the damping force characteristic of a chassis suspension of a motor vehicle, wherein a damping device (lli) between a vehicle body (12) and a wheel carrier (13i) of the motor vehicle (10) is arranged, wherein the damping force of the damping device (lli) by controlling a Adjusting means (14i) can be changed, and in which a vertical speed variable (V ₁ ) is determined, which represents a vertical speed occurring at the vehicle body (12), wherein the damping force of the damping device (lli) is increased by driving the adjusting device (14i), if the determined vertical speed _variable (V ₁ ) is greater in magnitude than a predetermined minimum value (v _iimln ), characterized in that the minimum value (v _{i /} _inin ) is predefined as a function of a road condition variable (Pi) representing the road condition, the road condition variable (μj by B etragsbildung and subsequent low-pass filtering of a determined vertical acceleration quantity (aj is calculated, which reproduces a vertical acceleration occurring at the vehicle body (12) Ia ₁ ).