The present invention relates to a method of improving the control behavior of an anti-lock and/or traction-slip controlled brake system, wherein the rotational behavior of the individual wheels is measured and evaluated for determining a vehicle reference speed, the wheel slip, the deceleration and acceleration of the individual wheels and, if required, other control quantities, and wherein threshold values of the wheel slip are predefined for the commencement of the control.
Brake systems with electronic anti-lock control (ABS) are nowadays included in the standard equipment of a great number of automotive vehicles. Also, extension of the ABS to traction slip control is no rare occurrence. In systems of this type the rotational behavior of the individual wheels is measured by means of wheel sensors and evaluated by electronic circuits to generate the control quantities and braking pressure control signals. Among these control quantities which result from the wheel rotational behavior are mainly wheel slip, wheel speed, wheel deceleration and wheel acceleration and a so-called vehicle reference speed which is defined by logical combining of the individual wheel speeds.
Identifying the actual control situation from the data provided by the individual wheel sensors and the consistent controlling of the braking pressure for anti-lock control or traction slip control is always difficult when the interpretation of the rotational behavior of the wheels does not permit a definite indication of the instantaneous road situation and the vehicle behavior. Further, it is known that disturbances on the road surface or road surface irregularities of any type may cause misinformation of the controller or the evaluating circuit and undesirable control operations or variations in the control which have adverse effects on the control. This is because deceleration and acceleration actions or slip signals occur on the individual vehicle wheels due to the road disturbances which are interpreted by the controller as instabilities of the wheel run.
Road surface disturbances or irregularities of the abovementioned type impair the ABS function. The ABS may even respond when the brake is not applied as soon as the ABS identification thresholds, which are slip or deceleration thresholds, are exceeded. When the brake is applied subsequently in the current ABS control, relatively great yaw torques may be caused which impair the driving stability of the vehicle. Also, the vehicle deceleration which is achievable in the given situation in an optimal braking operation will not be reached. Similar difficulties or discrepancies from the optimal behavior occur during traction slip control operations.
Therefore, an object of the present invention is to suppress the effects of various types of road irregularities on the control function of an ABS or TCS system and to thereby improve the control behavior of the ABS or TCS system. The objective is to achieve this improvement without disadvantages for the control sensitivity and control quality in other situations.