METHOD FOR DETERMINING AN ACTUAL LEVEL OF A VEHICLE

Abstract

A method for determining an actual level of a vehicle, includes determining an actual level of the vehicle as a function of a distance between at least one wheel of the vehicle and a superstructure of the vehicle, wherein the distance is determined by means of a signal detected by at least one chassis sensor, wherein the signal includes at least signal portions that correspond to an own movement of the vehicle and signal portions that correspond to an excitation by a road on which the vehicle actually drives; filtering the signal portions corresponding to the own movement of the vehicle out of the signal detected by the at least one chassis sensor by means of a filter function; calculating the actual level of the vehicle from a difference between the filtered signal without the signal portions that correspond to the own movement of the vehicle and the signal detected by the at least one chassis sensor.

Claims

1. A method for determining an actual level of a vehicle, comprising: determining an actual level of the vehicle as a function of a distance between at least one wheel of the vehicle and a superstructure of the vehicle wherein the distance is determined by means of a signal detected by at least one chassis sensor, said signal including at least signal portions that correspond to an own movement of the vehicle and signal portions that correspond to an excitation by a road on which the vehicle actually drives; filtering the signal portions corresponding to the own movement of the vehicle out of the signal detected by the at least one chassis sensor by means of a filter function; calculating the actual level of the vehicle from a difference between the filtered signal without the signal portions that correspond to the own movement of the vehicle and the signal detected by the at least one chassis sensor.

2. The method of claim 1, wherein the at least one filter function is selected in dependence on a frequency range of a movement of at least one component of the vehicle.

3. The method of claim 1, wherein the filter function is selected so that additionally signal portions that correspond to extended unevennesses on the road on which the vehicle actually drives are filtered out of the signal detected by the at least one chassis sensor.

4. The method of claim 1, wherein the signal portions filtered out of the signal detected by the at least one chassis sensor frequency portions are selected so that a respectively filtered signal is calculated without using an averaging function.

5. The method of claim 1, further comprising smoothing the difference formed between the filtered signal and the signal detected by the at least one chassis sensor by a smoothening function to take a system inertia of a chassis system of the chassis into account.

6. The method of claim 1, further comprising adjusting the at least one filter function by an adjustment factor so that the difference between the filtered signal and the signal detected by the at least one chassis sensor optimally approximates an ideal signal, said adjustment factor depending on respective filter coefficients of the at least one filter function.

7. The method of claim 1, wherein the at least one filter function s is selected from the group consisting of Butterworth filter, Chebyshev filter, adaptive filter, Wiener filter, Kalman filter, bandpass filter, low pass filter, high-pass filter with low cutoff frequency and high-pass filter.

8. A vehicle, comprising: a control device configured to determine an actual level of the vehicle via a distance between at least one wheel of the vehicle and a superstructure of the vehicle and to determine the distance by means of a signal detected by at least one chassis sensor, said signal including at least signal portions which correspond to an own movement of the vehicle and signal portions that correspond to an excitation by a road on which the vehicle actually drives; said control device being further configured to filter the signal portions of the own movement of the vehicle out of the signal detected by the at least one chassis sensor by means of at least one filter function and to determine the actual level of the vehicle from a difference between the filtered signal without the signal portions that correspond to the own movement of the vehicle and the signal detected by the at least one chassis sensor and to provide the actual level of the vehicle to a control function of at least one component of the vehicle.

9. The vehicle of claim 8, wherein the control device is further configured to provide the actual level of the vehicle to a level regulation device for adjusting to a predetermined set point value, in order to correspondingly select at least one lift or lowering speed of the level regulation to be adjusted.

10. A control device for installation in a vehicle, said control device being configured to determine an actual level of the vehicle via a distance between at least one wheel of the vehicle and a superstructure of the vehicle and to determine the distance by means of a signal detected by at least one chassis sensor, said signal including at least signal portions which correspond to an own movement of the vehicle and signal portions that correspond to an excitation by a road on which the vehicle actually drives; said control device being further configured to filter the signal portions of the own movement of the vehicle out of the signal detected by the at least one chassis sensor by means of at least one filter function and to determine the actual level of the vehicle from a difference between the filtered signal without the signal portions that correspond to the own movement of the vehicle and the signal detected by the at least one chassis sensor and to provide the actual level of the vehicle to a control function of at least one component of the vehicle.

11. The control device of claim 10, wherein the component of the vehicle is at least one member selected from the group consisting of air suspension chassis, roll stabilization and spring mount adjustment.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0034] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

[0035] FIG. 1 shows a schematic overview over a possible embodiment of the presented method.

[0036] FIG. 2 shows a signal detected by a chassis sensor provided according to a possible embodiment of the presented method;

[0037] FIG. 3 shows a signal processing according to a possible embodiment of the presented method.

[0038] FIG. 4 shows different filter functions according to different possible embodiments of the presented method.

[0039] FIG. 5 shows a model based implementation of a filter function according to a possible embodiment of the presented method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

[0041] FIG. 1 shows a vehicle 1. The vehicle 1 is equipped with an active body suspension system, i.e., a so-called active body control. In order to regulate the active body control so that the vehicle 1 remains at a constant vehicle level, i.e., a constant vehicle height h.sub.vcl at which a superstructure of the vehicle 1 substantially remains at a same distance to respective wheel carriers of the vehicle 1, an actual value of the distance between the superstructure and respective wheels, i.e., the vehicle height h.sub.vcl has to be provided to the active vehicle body suspension system so that the active vehicle body suspension system can actively regulate the distance between the superstructure and the wheel carriers.

[0042] This absolute vehicle height h.sub.vcl has an initial state and can be changed by a driver request or a regulating system request. This vehicle level is ideally interpretable as fixed value and is therefore temporally constant as stated in the equation (1).

h.sub.vcl=h.sub.vcl(t)=const. (1)

[0043] The vehicle height h.sub.vcl is interpreted by the active body suspension system as target value and hereby corresponds to an ideal information regarding the actual vehicle height h.sub.vcl.

[0044] When the vehicle 1 drives over an uneven road the road excites a coupled spring-damper-mass system of the active body suspension system to undergo coupled vibrations which causes the actual vehicle height h.sub.vcl or the difference between the wheel carrier edge and the tire profile as externally visible variable of the measured vehicle height to fluctuate. For determining the vehicle height h.sub.vcl spring travel sensors are used which detect a differential movement between the wheel carrier and the superstructure. From the spring travel sensors of the vehicle 1 conclusions can thus be drawn regarding the wheel-own level of the vehicle 1, i.e., a distance between a respective wheel and the vehicle superstructure as indicated by arrows 3 and 5.

[0045] In addition a road profile predetermines a frequency spectrum for respective spring travel sensors as indicated by arrow 7, which frequency spectrum changes in dependence on the speed with which the vehicle 1 moves along the road as indicated by the axis 9 and in dependence on roll movements of the vehicle 1, as indicated by a spatial angle and a horizontal axis 11 or a vertical axis 13.

[0046] FIG. 2 shows a frequency spectrum 15 of a signal detected by a spring travel sensor of the vehicle 1, which signal is shown in a diagram 17 which defines a time axis in [s] on the abscissa 19 and an amplitude axis in [mm] on the ordinate 21. The frequency spectrum 15 represents a signal of the body suspension system of the vehicle 1w high signal is very strongly interfered, with a level change of 20 mm between 15 and 35 seconds as indicated by the regions 23 and 25.

[0047] In the situation shown in FIG. 2 the vehicle drives on a road with very great profile steps with a speed in the range of 50 km/h appropriate for driving in a city. Hereby a respective wheel fluctuated relative to the superstructure of the vehicle 1 by about 80 millimeters in absolute amplitude. This strong movement is superimposed in the region 25 by a lifting and lowering process of about 20 mm length, which is executed by an air spring of the active body suspension system of the vehicle 1 in the range between 15 and 35 seconds. Because the vibrations of the wheel are superimposed in dependence on the profile steps of the road by the lifting and lowering processes of the air spring of the active body suspension system a determination of the actual vehicle height h.sub.vcl via average value formation is not possible.

[0048] In order to determine the vehicle height h.sub.vcl independent of movements of the air spring of the active body suspension system the presented method provides that an average value free and speed dependent road excitation of the active body suspension system is determined by a high pass filter of low cutoff frequency. For this it is provided that a difference between unfiltered and filtered signals of a respective spring travel sensor of he vehicle 1 is formed which immediately provides an actual and absolute vehicle height h.sub.vcl. It is in particular provided that the high pass filter is selected in dependence on known properties of the active body suspension system so that the movements caused by the movement so the active body suspension system are effectively extracted by the high pass filter and are then used for calculating the difference, which ultimately gives the vehicle height h.sub.vcl.

[0049] For reducing remaining vibration portions by taking into account a maximally permitted signal delay of a downstream signal processing regulation system a smoothing low-pass filtering can optionally be performed as shown in FIG. 3. In this case a signal detected by a spring travel sensor 30 is filtered via a high-pass filter as described above and indicated by diagram 31. In order to smoothen a signal generated by the high-pass filter and to thereby optimize the signal for provision to further components of the vehicle 1 the signal is fed into a low-pass filter as indicated by diagram 33. The low-pass filter then outputs a smoothed signal from which an actual vehicle level h.sub.vcl can be concluded as indicated by arrow 35.

[0050] FIG. 4 shows a result of the signal manipulation or reduction by means of different high pass and low pass filters in a diagram 40, which is formed by an abscissa 41 over a time axis in [s] and on an ordinate 43 over an amplitude in [mm]. Depending on the filter construction of the high pass and low pass portions an overestimation or underestimation of a signal amplitude resulting form a respective signal can be observed. In order to correct a potential overestimation or underestimation an adjustment factor (Gain), which is dependent from the respective filter coefficient, can be provided so that the absolute vehicle height h.sub.vcl can be optimally and directly outputted.

[0051] In FIG. 4 a second degree high-pass filter configuration is used. With this an amplitude damping of low-frequency signal portions with 40 dB per decade can be observed. In a field of development, which takes real-time enabled control devices into account this represents a good compromise between dynamic driving behavior for a fast signal adjustment at manageable processing effort.

[0052] The courses 46, 47 and 48 approximate an ideal course 45 of a vehicle height signal. The course 46 shows a filtering based on a Butterworth filter without amplitude adjustment. The course 47 shows a filtering based on a Butterworth filter with amplitude adjustment and a Gain of 0.9. The course 48 shows a filtering based on a Chebyshev filter with a gain of 0.9.

[0053] A characteristic filter interpretation is shown in FIG. 5. A circuit diagram 50 shows a model based implementation of a filter of 2. Order a filter behavior, i.e., a behavior as high pass or low-pass filter is determined by respective coefficients.

[0054] The second-degree filter implementation has three denominator coefficients and three numerator coefficients of a transfer function. Correspondingly FIG. 5 represents an exemplary implementation of a filter function in which a respective first denominator coefficient is always 1 as is typical for Butterworth, Chebyshev Bessel and other filter configuration methods. Thus b2 and b3 stand for remaining denominator coefficients and a1, a2, a3 for numerator coefficients of an equation (2) of a transfer function.

[00001]$\begin{array}{cc}H\left(s\right)=\frac{a.Math..Math.1+a.Math..Math.2.Math.s+a.Math..Math.3.Math.s^2}{1+b.Math..Math.2.Math.s+b.Math..Math.3.Math.s^2}& \left(2\right)\end{array}$