METHOD FOR OPERATING A CHASSIS OF A MOTOR VEHICLE, AND MOTOR VEHICLE

Abstract

A method for operating a chassis of a motor vehicle according to the principle of a skyhook control, the chassis having at least one adjustable damper according to which body movements of the motor vehicle body resulting from road bumps are damped using the skyhook damping value (d.sub.sky). When driving over a road bump, a classification is made as to whether a critical body movement of the motor vehicle body is to be expected, and that in case of a classification as a critical body movement, the critical classified body movement is compensated for using a stored critical skyhook damping value (d.sub.sky-crit) which is greater than the skyhook damping value (d.sub.sky).

Claims

1. A method for operating a chassis of a motor vehicle according to the principle of a skyhook control, the chassis having at least one adjustable damper according to which body movements of the motor vehicle body resulting from road bumps are damped using the skyhook damping value (d.sub.sky), the method comprising: when driving over a road bump, a classification is made as to whether a critical body movement of the motor vehicle body is to be expected, wherein, in the event of a classification as a critical body movement, the body movement classified as critical is compensated for by using a stored critical skyhook damping value (d.sub.sky-crit) which is greater than the skyhook damping value (d.sub.sky).

2. The method according to claim 1, wherein the following applies to the stored critical skyhook damping value (d.sub.sky-crit): critical skyhook damping value (d.sub.sky-crit)≥4000 Ns/m.

3. The method according to claim 1, wherein the classification is carried out by measuring spring deflections that occur and determining the resulting spring speeds from the measured spring deflections and filtering the determined spring speeds in a low-pass filter, the absolute value of the filtered spring speeds being determined in each case and the absolute value of the filtered spring speeds being compared with a stored lower limit speed, wherein if the absolute value of a filtered spring speed is greater than the stored lower limit speed, the body movement to be expected is classified as a critical body movement of the motor vehicle body, and a control signal for reducing the critical body movement is generated.

4. The method according to claim 3, wherein the absolute value of the filtered spring speeds is also compared with a stored upper limit speed, wherein if the absolute value of the filtered spring speed is ≥the stored upper limit speed, the control signal is set to the value of 1; if the absolute value of the filtered spring speed is ≤the stored lower limit speed, the control signal is set to the value of 0; and if the stored lower speed limit is <the absolute value of the filtered spring speed<the stored upper limit speed, the value of the control signal is determined by interpolation.

5. The method according to claim 4, wherein the control signal for reducing the critical body movement is maintained for a stored period of time.

6. A motor vehicle, comprising a chassis according to which the wheels of the motor vehicle are each mounted on the motor vehicle body via a wheel suspension having an adjustable damper, and a regulation/control unit regulating/controlling the adjustable dampers, wherein the adjustable dampers are operated such that when driving over a road bump, a classification is made as to whether a critical body movement of the motor vehicle body is to be expected, wherein, in the event of a classification as a critical body movement, the body movement classified as critical is compensated for by using a stored critical skyhook damping value (d.sub.sky-crit) which is greater than the skyhook damping value (d.sub.sky).

7. The motor vehicle according to claim 6, wherein the regulation/control unit is set up to carry out the classification.

8. The motor vehicle according to claim 6, wherein the following applies to the stored critical skyhook damping value (d.sub.sky-crit): critical skyhook damping value (d.sub.sky-crit)≥4000 Ns/m.

9. The motor vehicle according to claim 6, wherein the classification is carried out by measuring spring deflections that occur and determining the resulting spring speeds from the measured spring deflections and filtering the determined spring speeds in a low-pass filter, the absolute value of the filtered spring speeds being determined in each case and the absolute value of the filtered spring speeds being compared with a stored lower limit speed, wherein if the absolute value of a filtered spring speed is greater than the stored lower limit speed, the body movement to be expected is classified as a critical body movement of the motor vehicle body (10), and a control signal for reducing the critical body movement is generated.

10. The motor vehicle according to claim 9, wherein the absolute value of the filtered spring speeds is also compared with a stored upper limit speed, wherein if the absolute value of the filtered spring speed is ≥the stored upper limit speed, the control signal is set to the value of 1; if the absolute value of the filtered spring speed is ≤the stored lower limit speed, the control signal is set to the value of 0; and if the stored lower speed limit is <the absolute value of the filtered spring speed<the stored upper limit speed, the value of the control signal is determined by interpolation.

11. The motor vehicle according to claim 10, wherein the control signal for reducing the critical body movement is maintained for a stored period of time.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] Further advantages and possible applications of the invention result from the following description in connection with the figures.

[0031] FIG. 1 shows a schematic representation of the skyhook principle;

[0032] FIG. 2 shows a graphical representation of the effect of the skyhook damping value on body acceleration;

[0033] FIG. 3 shows a schematic flowchart of the method;

[0034] FIG. 4a shows the determined spring speeds plotted against time;

[0035] FIG. 4b shows the filtered spring speeds from FIG. 4a as absolute values plotted against time, and

[0036] FIG. 4c shows the resulting control signal.

DETAILED DESCRIPTION

[0037] FIG. 1 shows a schematic representation of a motor vehicle body 10 which rolls over a road 14 via a wheel 12. Between motor vehicle body 10 and wheel 12, a chassis 16 is arranged in a known manner, which comprises an adjustable damper 16-2 in addition to a suspension spring 16-1.

[0038] The spring/damper properties of the wheel 12 when rolling on the road 14 are taken into account by the tire spring designated with the reference numeral 12-1 and the tire damper designated with the reference numeral 12-2.

[0039] As is known, the skyhook principle or the skyhook approach is based on the theoretical consideration that the motor vehicle body 10, which rolls over the road 14 via the wheel 12, can remain at rest if the motor vehicle body 10 is connected to an inertial reference system 20, e. g. sky, via a so-called skyhook damper 18. Since the imaginary arrangement of the skyhook damper 18 above the vehicle body 10 is impossible to implement, the adjustable damper 16-2 is controlled accordingly in such a way that body movements of the motor vehicle body 10 resulting from bumps in the road are damped, i.e. the “skyhook” effect is simulated.

[0040] The crucial influencing parameter is the so-called skyhook damping value d.sub.sky, since this values indicates how strongly the body movement of the motor vehicle body 10 is to be damped.

[0041] The influence of the skyhook damping value d.sub.sky on the accelerations of the motor vehicle body 10 resulting from driving over bumps in the road can be seen in FIG. 2, in which the amplitude of the body acceleration against frequency is shown. The natural frequency of the motor vehicle body 10 at approximately 1.3 Hz and the natural frequency of the wheel 12 at approximately 11 Hz can be clearly seen.

[0042] Reference numeral 30 designates the unregulated curve, i.e. skyhook damping value d.sub.sky=0 Ns/m, reference numeral 40 designates the curve with a skyhook damping value d.sub.sky=1500 Ns/m, and reference numeral 50 designates the curve with a skyhook damping value d.sub.sky=5000 Ns/m.

[0043] Here, as can be seen from FIG. 2, the unregulated curve 30 shows clear vibration amplitudes in the range of the natural frequency of the motor vehicle body 10. These vibration amplitudes can be greatly reduced if the skyhook damping value d.sub.sky is increased, cf. curve 40 with d.sub.sky=1500 Ns/m and curve 50 with d.sub.sky=5000 Ns/m. It can also be seen that with high skyhook damping, cf. curve 50 with d.sub.sky=5000 Ns/m, the amplitudes in the isolation area also increase, approximately 3 Hz to 8 Hz, which in turn means a deterioration in driving comfort.

[0044] As can be seen from FIG. 3, it is provided according to the invention that in a first step 100 the occurring spring deflections are measured via spring deflection sensors installed in the motor vehicle. The spring speeds are determined in step 200 by taking the derivative of the measured spring deflections.

[0045] Here, the determined spring speeds comprise in particular signal components resulting from the movement of the motor vehicle body 10 and the movement of the wheel 12, cf. FIG. 4a, signals shown in a narrow line.

[0046] Since only an excitation in the range of the natural frequency of the motor vehicle body 10 can lead to a large and thus relevant body movement, in step 300 the signal components of the body frequency are extracted from the spring speeds via a low-pass filter, cf., FIG. 4a, signals shown in bold line. Since the direction of the excitation is not important, in step 400 the filtered spring speeds are considered as absolute values, cf. FIG. 4b.

[0047] Since several spring deflection sensors are generally installed in the motor vehicle, the maximum value is selected in step 500. If said maximum value exceeds a fixed lower limit speed, cf. FIG. 4b, dash-dotted line, the classification is classified as critical, which is to be damped accordingly with the critical skyhook damping value d.sub.sky-crit.

[0048] For a smooth transition between the “normal” skyhook damping with the “normal” skyhook damping value d.sub.sky and the related increased skyhook damping with the critical skyhook damping value d.sub.sky-crit, there is an interpolation in step 600 between the lower speed limit and a fixed upper limit speed, cf. FIG. 4b, dashed line, i.e. the signal for increasing the skyhook damping is 0 if the unfiltered, absolute spring speed is equal to or below the lower limit speed and 1 if the filtered, absolute spring speed is equal to or above the upper limit speed, cf. FIG. 4c.

[0049] Since, when the lower speed limit is exceeded, it can be assumed that the motor vehicle body 10 is experiencing an excitation that leads to significant body vibration and the skyhook damping is already increased when the lower speed limit is exceeded, cf. step 800, the body movement is already damped before it is fully developed.

[0050] In order to damp the entire oscillation period of the motor vehicle body 10, the increased skyhook damping is maintained for a time to be set, cf. FIG. 4c, dashed line. This is implemented in step 700 by means of a corresponding holding element.