WO2006125626A1

WO2006125626A1 - Device and method for influencing the damping characteristics of the chassis suspension of a motor vehicle

Info

Publication number: WO2006125626A1
Application number: PCT/EP2006/004960
Authority: WO
Inventors: Eberhard Kutscher; Johann Mayer
Original assignee: Daimlerchrysler Ag
Priority date: 2005-05-27
Filing date: 2006-05-24
Publication date: 2006-11-30
Also published as: DE102005024487A1

Abstract

The invention relates to a device and a method for influencing the damping characteristics of the chassis suspension of a motor vehicle. Said device comprises a damping mechanism (11i) provided for damping undesired body movements between an automotive body (12) and a wheel carrier (13i) of the motor vehicle (10), the damping force of said damping mechanism being variable by actuating an adjusting element (14i). A control mechanism (20) increases the damping force of the damping mechanism (11i) by actuating the adjusting element (14i) when a defined trigger criterion is met. The invention is characterized in that the damping force is increased independent of the direction of the body movement only for the pressure stage of the damping mechanism (11i) or alternatively only for the tensile stage of the damping mechanism (11i).

Description

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

The invention relates to an apparatus and a method for influencing the damping force characteristic of a chassis suspension of a motor vehicle, comprising a damping device which is arranged for damping unwanted vehicle body movements 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 device is provided which reduces the damping force of the damping device by controlling the adjusting device when a predetermined triggering criterion is met.

Such a device for controlling the damping force characteristic of a suspension suspension is shown in the document DE 198 15 859 Al. The device comprises a vibration damper, which is arranged between a vehicle body and a vehicle wheel, wherein the damping force characteristic of the vibration damper is variable by driving an adjusting device. The control of the adjusting device by means of a central control unit, the damping force characteristic of the vibration damper when fulfilling respective trigger criteria according to different operating modes.

In a mode of operation commensurate with the "Sky Hook" theory, the center control unit sets a hard damping force characteristic for the rebound of the damper, and a soft damping force characteristic for the compression stage of the damper, as a result of a vertical velocity occurring at the vehicle body, such that an upward vehicle body movement Conversely, the central control unit sets a hard damping force characteristic for the compression stage of the vibration damper, and a soft damping force characteristic for the rebound damping damper, when a vertical vehicle-body movement occurs due to the vertical speed occurring at the vehicle body.

Further, a special mode is provided, which is set by the central control unit upon detection of highly dynamic steering maneuvers and in which a hard damping force characteristic is provided both for the rebound and for the compression stage of the vibration damper.

Object of the present invention is to develop a device or a method of the type mentioned in such a way that an additional mode is created, the damping force over the entire cycle of the vehicle body movement, ie over a complete up and down movement of the vehicle body on average between that of the sky-hook mode and that of the special mode of the known device.

This object is achieved according to the features of patent claim 1 and patent claim 9, respectively. The device for influencing the damping force characteristic of a chassis suspension of a motor vehicle comprises a damping device, which is arranged for damping unwanted vehicle body movements 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 device is provided which reduces the damping force of the damping device by controlling the adjusting device when a predetermined triggering criterion is met.

According to the invention, the reduction of the damping force is independent of the direction of the vehicle body movement exclusively for the compression stage of the damping device.

The damping force characteristic of the damping device is in the following two-stage for the sake of simplicity, namely according to the two stages "soft" and "hard" adjustable, although also a finer or even continuous gradation can be provided.

Accordingly, when the predetermined release criterion for the rebound rebound of the damping device is met, the control device sets a hard damping force characteristic for the compression stage of the damping device and determines a soft damping force characteristic for the compression section of the damping device if it is ascertained that there is an upward vehicle body movement. If, on the other hand, it results that the vehicle body movement is directed downwards, the control device sets a hard damping force characteristic both for the rebound stage and for the compression stage of the damping device. A reduction in the damping force of the rebound, as it would be provided according to the sky-hook theory in the latter case, thus omitted. In this way, seen over the entire cycle of movement of the vehicle body movement on average, a damping force which is between those of the "Sky Hook" mode and those of the special mode of the known device and which allows a nuanced adjustment of the damping force characteristic and thus the damping properties According to an alternative embodiment of the device according to the invention, the reduction of the damping force takes place independently of the direction of the vehicle body movement exclusively for the rebound stage of the damping device.

Accordingly, when the predetermined triggering criterion for the compression stage of the damping device is met, the control device sets a hard and for the rebound damping unit a soft damping force characteristic, if it is determined that there is a downward vehicle body movement. If, on the other hand, it results that the vehicle body movement is directed upwards, then the control device sets a hard damping force characteristic both for the compression stage and for the rebound damping stage.

Which of the two alternative embodiments is used is ultimately at the discretion of the person skilled in the art.

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

So that a reliable statement can be made as to whether a change or adaptation of the damping force characteristic due to the current dynamic driving situation on the motor vehicle is required or not, it is advantageous if in the triggering criterion a vertical speed variable describing a vertical speed occurring at the vehicle body, a roll angular velocity quantity describing a temporal change of a roll angle occurring at the vehicle body, a pitch angle speed magnitude , which describes a change over time of a pitch occurring at the vehicle body, or a Hubgeschwindigkeitsgröße, which describes a change with time of a occurring relative to the vehicle center of gravity on the vehicle body vertical stroke is received. In this case, a separate trigger criterion is specified for each of the aforementioned variables.

Advantageously, the vertical velocity magnitude, roll angular velocity magnitude, pitch angular velocity magnitude, and stroke velocity magnitude are calculated by the controller based on a determined vertical acceleration magnitude describing a vertical acceleration occurring at the vehicle body such that a common sensor device may be used to provide the former.

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

In order to be able to take into account a possible impairment of the surface condition of the traveled road, as it is caused due to roadway waves, potholes and the like, whether a change or adaptation of the Dampfungskraftcharakteristik is necessary or not, there is also the possibility that the control device that Tripping criterion in response to a road condition size, which reflects the current surface condition of the busy road, adapts.

The same applies to a possible consideration of the longitudinal dynamics of the motor vehicle, for which purpose the control device adapts the triggering criterion additionally or alternatively to the road condition variable as a function of a determined longitudinal speed variable which reproduces the instantaneous longitudinal speed of the motor vehicle. In this case, it is in principle conceivable, in addition to the longitudinal dynamics of the motor vehicle, to also take into account its transverse dynamics in the form of corresponding variables.

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 which 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 characteristic) than when the bypass valve is open (soft damping characteristic).

In order to enable an independent for the compression direction and the pulling direction of the damping device influencing the damping force characteristic, the adjusting device for the pressure stage and the rebound separate bypass valves, wherein the switchable for the pressure stage of the damping device bypass valve is permeable only in the printing direction and that for the rebound of the Damping device switchable bypass valve is permeable only in the pulling direction. By appropriate control of the bypass valves of the adjusting device can then be

- Set first damping mode, in which regardless of the direction of the vehicle body movement both for the rebound and for the compression stage of the damping device, a soft damping force characteristic is provided (basic mode), a

- Setting the second operating mode, in which for an upward vehicle body movement for the rebound of the damping device a hard and for the compression stage of the damping device, a soft damping force characteristic, and vice versa for a downward vehicle body movement for the compression stage of the damping device a hard and for the rebound of the Damping a soft damping force characteristic is provided ("Sky Hook" mode), a

- Set the third damping mode, in which for a nachbenden vehicle body movement for the rebound of the damping device is a hard and for the compression stage of the damping device is provided a soft damping force characteristic, and in which for a downward vehicle body movement for both the rebound and for the compression stage of the damping device is provided with a hard damping force characteristic (intermediate mode)

- set alternative third damping mode, in which for a downward vehicle body movement for the compression stage of the damping device a hard and for the rebound of the damping device a soft damping force characteristic is provided, and in which a hard damping force characteristic is provided for an upward vehicle body movement both for the compression stage and for the rebound of the damping device (alternative intermediate mode), and a

- Set fourth damping mode in which regardless of the direction of the vehicle body movement both for the compression stage and for the rebound damping of the damping device a hard damping force characteristic is provided (special mode).

The damping modes here have, in the order of their numbering, a mean increasing damping force over the entire movement cycle of the vehicle body movement, so that a nuanced, i. finely graded adaptation of the damping force characteristic and thus the damping properties of the suspension suspension is possible according to the respective driving dynamic situation of the motor vehicle.

In order to facilitate compression of the wheel spring means in the case of road bumps and the like occurring during running, the damping devices are usually designed such that a lower damping force is provided with respect to the respectively set damping force characteristic (soft or hard) for a downward vehicle body movement in the case of an upward vehicle body movement.

Thus, the third damping mode has a lower damping force acting on average over the entire movement cycle of the vehicle body movement than the corresponding alternative damping mode, which ultimately results in a further damping action. Fung in the adjustment of the damping force characteristic allowed.

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 an embodiment of the device according to the invention for a motor vehicle,

FIG. 2 a) shows a diagram representing an exemplary functional relationship v ° _ref (V ₁ ), FIG.

FIG. 2 b) is a diagram representing an exemplary functional relationship φ ° _ef (V ₁ ), and FIG

Fig. 2 c) is a diagram representing an exemplary functional relationship K ₁ (μ _L ).

Fig. 1 shows an embodiment of the invention

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

The device according to the invention arranged in the motor vehicle 10 comprises a damping device Hi, which is arranged to damp undesired vehicle body movements between a vehicle body 12 and a wheel carrier 13i of the motor vehicle 10, wherein the damping force of the damping device Hi can be changed by controlling an associated setting device 14i. The damping device Hi and the adjusting device 14i are in this case - 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 device 20 which controls the damping force of the damping device Hi by activating it. tion of the adjusting device 14i reduced when a predetermined triggering criterion AKRIT is met.

The increase of the damping force takes place here, regardless of the direction of the vehicle body movement exclusively for the compression stage of the damping device Hi.

The damping force characteristic of the damping device Hi in the following two-stage, namely according to the two stages "soft" and "hard" adjustable.

Accordingly, the control device 20 sets a hard damping force characteristic for the rebound damping stage Hi when the predetermined triggering criterion AKRIT is satisfied, and a soft damping force characteristic for the compression stage of the damping device Hi if it is determined that there is a vehicle body movement directed upwards. If, on the other hand, it is found that the vehicle body movement is directed downwards, the control device 20 sets a hard damping force characteristic both for the rebound stage and for the compression stage of the damping device Hi. The direction of the current vehicle body movement results from the evaluation of a vertical speed occurring on the vehicle body 12 in the region of the damping device Hi.

According to an alternative embodiment of the device according to the invention, the increase of the damping force is independent of the direction of the vehicle body movement exclusively for the rebound of the damping device Hi.

Accordingly, the control device 20 sets a hard damping force for the compression stage of the damping device Hi when the predetermined triggering criterion AKRIT is satisfied, and a soft damping force for the rebound damping stage Hi. Characteristic when it is determined that there is a downward vehicle body movement. If, on the other hand, it is found that the vehicle body movement is directed upwards, the control device 20 sets a hard damping force characteristic both for the compression stage and for the rebound damping stage Hi.

For the sake of clarity, reference will be made below to the first of the two possible alternative embodiments.

A vertical speed variable V ₁ , which describes a vertical speed occurring at the vehicle body 12 in the area of the damping device Hi, a roll angular velocity variable φ which describes a temporal change of a rolling angle occurring at the vehicle body 12, a pitch angular velocity variable ή, which changes over time describes a pitch occurring at the vehicle body 12, or a Hubgeschwindigkeitsgröße z, which describes a temporal change occurring in relation to the vehicle center of gravity SP on the vehicle body 12 vertical stroke, a. Here, a separate triggering criterion AKRIT is specified for each of the above variables, so that the control of the adjusting devices 14a to 14d and thus the influence of the damping force characteristic can be made individually different depending on the underlying triggering criterion AKRIT. The exact form of the trigger criteria AKRIT will be discussed in detail later.

According to the example, the vehicle body 12 in the region of the damping devices Ha to Hc is assigned a total of three linear acceleration sensors 21a to 21c, the measuring axes of which are oriented in the direction of the perpendicular to the earth's surface. in the control device 20, by evaluating the acceleration signals provided by the linear acceleration sensors 21a to 21c, a vertical acceleration variable a _ir describing a vertical acceleration occurring on the vehicle body 12 in the region of the damping devices Hi is determined. On the basis of this, the control device 20 then calculates the vertical speed variable V ₁ by performing a numerical integration.

The calculation of the roll angular velocity magnitude φ, the pitch angular velocity magnitude ή and the stroke velocity magnitude z is performed from the calculated vertical velocity magnitude V ₁ , for which transformation equations of the shape

CpSCp (V ₁ , s), (1.1)

ή≡ή ( _Vl , 1), (1.2)

z≡z (V ₁ , ItI ₁ ), (1.3)

in which V ₁ denotes the vertical speed variable, In ₁ the proportion of the total mass of the motor vehicle 10 which is effectively loaded on the damping device Hi, s the track width of the motor vehicle 10, and 1 the base distance between the front axle and the rear axle of the motor vehicle 10. The variables s and 1 are vehicle-specific constants which are stored in a data memory associated with the control device 20. The large In ₁ results, for example, from a wheel contact force f _x occurring at the wheel carrier 13 i and the vertical acceleration variable a _x ITi ₁ = -. (1, 4)

For the solutions of the transformation equations (1.1) to (1.3) follows then on the basis of simple geometric considerations

"" LüZl "., ₍₁ .6;

"'a ^v a *" a * a. - _.

Z ». (1 • /) m _a + ... + m _d

Furthermore, the triggering criterion AKRIT is adapted by the control device 20 as a function of a road condition variable μ ₁ which represents the current surface state of the road being traveled in the area of the damping device Hi, and / or a determined longitudinal speed variable V ₁ , which represents the instantaneous longitudinal speed of the motor vehicle 10 ,

The determination of the road condition variable μ _x takes place, for example, by analyzing the frequency and / or amplitude spectrum of the determined vertical _{acceleration variable} a _lf, whereas the wheel speed _signals provided by wheel speed sensors 22 are used to determine the longitudinal speed variable V ₁ .

As already mentioned, a separate triggering criterion AKRIT is specified for each of the variables V ₁ , φ, ή and z. For the ex- The form of these trigger criteria will be discussed in more detail below.

A first triggering criterion AKRIT _{1, V} is fulfilled when the vertical velocity variable V ₁ is greater than an associated threshold value v _{1> ref} ,

V ₁ > v _{1 (re £} , (2.1)

wherein the controller 20 _sets the threshold v _ljref according to an equation of shape

V _lf rβ _f = V °, _ref (V ₁ ) - _Kl (2.2)

calculates, in the v ° _ref, a base threshold dependent on the slow speed V ₁ and K ₁ one of the road condition magnitude μ _^. dependent correction factor.

A second trigger criterion AKRIT _φ is satisfied if the roll angular velocity gro is larger than an associated threshold φ _ref ,

wherein the control means 20 the threshold value φ _ref according to an equation of the shape

Φref = Φref ( ^V l) - ^K ^ (2.4 calculated in the φ ° _ef the designated over i = a ... d averaged correction factor K _{1 is} a dependent on the longitudinal velocity value V ₁ base threshold value and Ic. ₁

A third trigger criterion AKRIT _n is fulfilled if the pitch angular velocity variable ή is greater than an associated threshold value ή _ref ,

wherein the control means 20 the threshold value ή _ref according to an equation of the shape

in which ή ° _ef denotes a base threshold dependent on the longitudinal velocity variable V ₁ .

A fourth triggering criterion AKRIT ₂ is fulfilled if the stroke speed variable z is greater than an associated threshold value z _ref ,

Z ₁ > z _ref , (2.7)

wherein the controller 20 sets the threshold value z _ref according to an equation of shape

in which z ° _ef denotes a base threshold dependent on the longitudinal velocity variable V ₁ . Since in the trigger criteria AKRIT _{1 (V} or AKRIT ,, ^ _, - enter into very different aspects of the vehicle body movement and there is no direct relationship between them, it is in principle conceivable, any selection or combination of the above triggering criteria AKRIT _{1 / V} or AKRIT _{φ # ηfZ} for the purpose of adapting the driving force to the damping force characteristic.

The determination of the basic threshold values v ° _ref , φ ° _ef , ή ° _ef and z ° _{e £} is made by using functional relationships stored in the control device 20. These are reproduced by way of example for the basic threshold values v ° _ref and φ ° _ef as a function of the slow speed variable V ₁ , and for the correction factor K ₁ as a function of the road condition variable μ _x through the diagrams a) to c) of FIG.

The following numerical example is intended to illustrate the calculation of the threshold _values v _liref and φ _ref , where the values given for the longitudinal speed V ₁ and the road condition magnitude μ _{λ represent} a drafty trip on a typical medium-surface-condition highway:

V ₁ = 100 km / h, μ _x = 0.4. (2.9)

Starting from Fig. 2 then results by simply reading

v ° _ref = 0.1 m / s, φ ° _ef = 0.022 rad / s, K ₁ = 1.5, (3.0)

and by inserting into equation (2.2) or equation (2.4), in the latter case, for the sake of simplicity, assuming ^" K ₁ = 1.5, ^v i, r _e f = 0.15 m / s, φ _ref = 0.033 rad / s. (3.1)

By way of example, the damping device Hi is a common telescopic damper which comprises a hydraulically or pneumatically damped main damping piston. To change the damping force, the actuator 14i has a damping valve Hi switchable bypass valve 23i or 24i, which allows to bypass the flowing through the telescopic damper hydraulic or pneumatic flow, so that when the bypass valve 23i or 24i a higher damping force adjusts ( hard damping force characteristic) than when the by-pass valve 23i or 24i is open (soft damping force characteristic).

In order to allow an independent for the compression direction and the pulling direction of the damping device Hi influencing the damping force characteristic, the actuator 14i for the pressure stage and the rebound separate Bypassventi- Ie 23i and 24i, wherein the switchable for the compression stage of the damping device Hi bypass valve 24i is permeable exclusively in the pressure direction and the switchable for the rebound of the damping device Hi bypass valve 23i is permeable only in the pulling direction.

By appropriate control of the bypass valves 23i and 24i of the adjusting device 14i can then be

- Set first damping mode, in which regardless of the direction of the vehicle body movement for both the rebound and for the compression stage of the damping device Hi a soft damping force characteristic is provided (basic mode), a - Setting the second damping mode, in which for a nachbenden vehicle body movement for the rebound damping Hi a hard and damping force for the compression damping device Hi a soft damping force characteristic, and vice versa for a downward vehicle body movement for the compression stage of the damping device Hi a hard and for the rebound of the damper Hi, a soft damping force characteristic is provided ("sky-hook" mode)

- Set the third damping mode, in which for a nachbenden vehicle body movement for the rebound of the damping device Hi a hard and for the compression stage of the damping Hi a soft damping force characteristic is provided, and in which for a downward vehicle body movement both for the rebound as also for the compression stage of the damping device Hi a soft damping force characteristic is provided (intermediate mode), a

- Set alternative third damping mode, in which for a downward vehicle body movement for the compression stage of the damping device Hi a hard damping force and for the rebound of the damping Hi a soft damping force is provided, and in which for an upward vehicle body movement both for the compression as well as for the rebound of the damping device Hi a soft damping force characteristic is provided (alternative intermediate mode), and a

- set the fourth damping mode, in which, regardless of the direction of the vehicle body movement, both for the compression and for the rebound damping Hi a hard damping force characteristic: is provided (special mode).

In this case, the damping modes have, in the order of their numbering, a mean increasing damping force over the entire movement cycle of the vehicle body movement. The respective direction of the vehicle body movement 12 recognizes the control device 20 by evaluating the sign of the determined vertical speed variable V ₁ .

The actuation of the bypass valves 23i and 24i takes place by means of a driver 30i, for example a demultiplexer, which is connected to the control device 20 via an electrical or optoelectronic control line 31i.

When setting the different damping modes, the control device 20 follows the following control scheme, where SKRIT _{i / V} or SKRIT _{φ> η, z} to trigger the "Sky-Hook"

Operating mode and XKRIT _iiV or XKRIT _φ _ _ηr - on to trigger the

Special operating mode provided trigger criterion. This is optionally met when due to significant deterioration of the surface condition of the busy road vehicle body movements occur that require a relation to the basic mode or the intermediate mode increased damping force required. Each of the triggering criteria AKRIT _{1; V} or AKRIT " _{rr | / Z} is assigned a separate triggering criterion SKRIT _ifV or SKRIT _{φ, η, z} and XKRIT _{i / V} or XKRIT _{φ # riiZ} .

0 = not fulfilled, 1 = fulfilled, X = all the same

The setting of the respective operating mode takes place in the case of the triggering criteria AKRIT _{i, V} , SKRIT _{i, V} and XKRIT _{i (V} each wheel individually, ie with respect to that wheel i of the motor vehicle 10, to the triggering criteria AKRIT _{i <v} , SKRIT _{i / V} and XKRIT _{i; V} respectively refer Alternatively, the adjustment can also take place by axle, that is on that axis, the wheel is at the i, or for all four wheels i = a ... d same as in the rest. in connection with the triggering criteria AKRIT _φ , _n , _z , SKRIT _φ , _η , ₂ and XKRIT _φ , _n , _{2 is} provided.

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), which is arranged for damping unwanted vehicle body movements 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 device (20), which reduces the damping force of the damping device (lli) by driving the adjusting device (14i) when a predetermined triggering criterion is met, characterized in that the reduction the damping force is independent of the direction of the vehicle body movement exclusively for the compression stage of the damping device (lli) or alternatively exclusively for the rebound of the damping device (lli).

2. A device according to claim 1, characterized in that a vertical speed variable (V ₁ ) which describes a vertical speed occurring at the vehicle body (12) is included in the triggering criterion. velocity variable (φ) describing a change in the temporal change of a roll angle occurring at the vehicle body (12), a pitch angular velocity quantity (ή) describing a temporal change of a pitch angle occurring at the vehicle body (12), or a stroke velocity magnitude (z) representing a time change describes a occurring in relation to the vehicle center of gravity on the vehicle body (12) vertical stroke, received.

3. Apparatus according to claim 2, characterized in that the calculation of the vertical speed variable (V ₁ ) and / or the roll angular velocity (φ) and / or the pitch angular velocity (ή) and / or the Hubgeschwindigkeitsgröße (z) on the basis of a vertical acceleration magnitude Ia ₁ ), which describes a vertical acceleration occurring on the vehicle body (12), takes place.

4. The device according to claim 3, characterized in that the determination of the vertical acceleration quantity (ai) by using the vehicle body (12) associated linear acceleration sensor (21a, ..., 21c) takes place, the measuring axis is directed in the direction of the perpendicular to the earth's surface.

5. The device according to claim 1, characterized in that the control device (20) the triggering criterion in response to a determined road condition variable (μi), which reflects the current surface state of the busy road, adapts.

6. The device according to claim 1, characterized in that the control device (20) the triggering criterion in response to a determined longitudinal speed variable (V ₁ ), which reflects the instantaneous longitudinal speed of the motor vehicle (10), adapts.

7. The device according to claim 1, characterized in that the adjusting device (14i) for changing the damping force of the damping device (lli) switchable by-pass valve (23i, 24i).

8. The device according to claim 7, characterized in that the adjusting device (14i) for the compression stage and the rebound of the damping device (lli) separate bypass valves (23i, 24i), wherein the for the pressure stage of the damping device (lli) switchable bypass valve is permeable exclusively in the pressure direction and for the rebound of the damping device (lli) switchable bypass valve (23i, 24i) is permeable only in the pulling direction.

9. A method for influencing the damping force characteristic of a suspension of a motor vehicle, in which a damping device (lli) for damping unwanted vehicle body movements 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 ) can be changed, and in which the damping force of the damping device (lli) is reduced when a predetermined triggering criterion is met, characterized in that the reduction of the damping force is performed independently of the direction of vehicle body movement exclusively for the compression stage of the damping device (lli) or alternatively exclusively for the rebound of the damping device (lli).