The present invention relates to a method of improving the control behavior of an anti-lock control system, wherein a vehicle reference speed that is used as a reference quantity to determine the wheel slip of the individual wheels is derived from the rotating behavior of the vehicle wheels, and criteria are obtained for identifying a cornering situation and the curve direction, wherein for identifying cornering the wheel slip values are filtered by way of a low-pass filter and the filtered values are compared.
It is already known in the art to extend the functions of an anti-lock control system by employing the system for improving the driving stability or deceleration stability in the curve. For this purpose, during cornering or during a partial deceleration, i.e., in a deceleration process in which the threshold of response to the anti-lock control system is not achieved, a stabilizing moment about the vertical axis of the vehicle is created by specifically delaying the brake pressure build-up on the wheels at the inner side of the curve compared to the brake pressure on the wheels on the outer side of the curve (`Bremsanlage und Schlupf-Regelsystem der neuen 7-er Reihe von BMW` (Brake System and Slip Control System of the new BMW No. 7 series); ATZ 97 (1995), pp. 8-15, and `Bremsanlage und Schlupf-Regelsysteme der neuen Baureihe 5 von BMW` (Brake System and Slip Control Systems of the new BMW No. 5 series); ATZ 98 (1996), pp. 188-194. The information on the actual steering angle is derived--if no steering angle sensor is used--from the transverse acceleration which, in turn, is calculated from the wheel sensor signals.
DE 34 13 738 C2 discloses an anti-lock control system (ABS) provided with a system for identifying a cornering situation based on wheel slip measurement. To identify a cornering situation, the sum of slip values on the wheels at one vehicle side are summed up and compared to the slip values on the wheels at the other vehicle side, generating a cornering identification signal as soon as the difference of the summed-up slip values exceeds a predetermined limit value. Upon identification of a cornering situation, selective criteria, such as `select-low` or `select high` according to which the pressure variation in the individual brake pressure control channels of the said brake system is controlled, and limit values for rendering the said selective criteria effective, are varied. In this way, the control will be adjusted to the varying conditions during straight-forward driving and during cornering.
DE 21 19 590 A1 which has an older filing date teaches generating a cornering identification signal with the aid of a transverse acceleration meter, such as a mercury switch.
The calculation of the filtered wheel slip and the evaluation of this quantity to determine criteria for cornering are described in the patent application DE 195 22 634 A1 which is not prior published. The filtered wheel slip values are compared and evaluated for cornering identification according to the above publications. Cornering is identified when simultaneously the values of the filtered wheel slip on both front wheels exceed a predetermined maximum slip value and the filtered wheel slip of a rear wheel is in excess of an equally predetermined maximum slip value and the filtered wheel slip of the second rear wheel is below a determined minimum slip value.
When cornering is identified, switch-over to a special, i.e., cornering, control mode is effected according to patent application DE 195 22 632 A1 which is also not prior published.
An object of the present invention is to improve, in a method of the type referred to hereinabove, the ability of evaluating the measuring signals and, more particularly, the reliable identification of a cornering situation compared to straight travel.