Fluid-pressure and analogous brake systems – Speed-controlled – Variable target slip values
Patent
1994-11-08
1996-06-18
Ballato, Josie
Fluid-pressure and analogous brake systems
Speed-controlled
Variable target slip values
303158, F02F 310, B22D 1908, B05D 714
Patent
active
055271022
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for controlling brake pressure in a motor vehicle wherein wheel speed signals are used to generate slip signals and wheel acceleration signals, which in turn are used to generate brake pressure control signals.
The quality of the braking retardation of an ABS-controlled vehicle and the pedal reactions depend on the rapidity with which the required optimum pressure level is reached, the amplitude of the pressure modulation having to be very small. The amplitude of the pressure modulation is substantially dependent in this case on the magnitude of the preceding pressure reduction or on how long the period of activation of the discharge valve is.
As an example, a method is known for dimensioning the discharge valve activation time which uses a constant magnitude to correct a value determined from the "prehistory" of the control, and can vary this time as a function of the current wheel behavior.
Also known is a method which uses just such a time value from the prehistory, but calculates it with the aid of a correction value dependent on the wheel acceleration of the previous control cycle, the correction value being inversely proportional to the wheel acceleration.
The disadvantage of these known solutions is that owing to the ever present system delay times the pressure reduction does not match the physical wheel behavior, or that because of roadway defects which are present the ABS control reacts with control fluctuations, for example in the case of small wheel reaccelerations, so that overall the aim of a small pressure modulation is not achieved.
SUMMARY OF THE INVENTION
These disadvantages are removed by the proposed brake system by determining the wheel acceleration (or the wheel reacceleration) and the slip in the unstable region of the wheel and relating them to prescribed magnitudes, from which the calculation of the reduction time of the new control cycle is performed in such a way that the wheel reacceleration following the pressure reduction corresponds to a precalculated magnitude.
In this case, the invention proceeds from a brake system, in general an antilock system, for the wheels of a vehicle, consisting of sensors for determining the behavior of the Wheel motion, an evaluation circuit for processing the sensor signals and for generating brake pressure control signals, and a brake pressure control unit which is fed the brake pressure control signals for the purpose of pressure variation. It is possible in this way to form slip signals and acceleration signals of at least one wheel or a wheel group. The invention is distinguished in that the brake pressure control signals are determined in such a way that the acceleration of at least one wheel is limited to values which depend on the maximum slip value within a prescribable time interval. The maximum slip value can be determined for this purpose within the prescribable time interval from the slip signals. The brake pressure control signals are then determined in such a way that the acceleration of at least one wheel is limited to values which depend on the maximum slip value.
It is particularly advantageous that brake pressure control signals whose duration is determined as a function of the maximum slip value determined are generated for the purpose of pressure variation.
Furthermore, it can be provided in an advantageous embodiment of the invention that a basic duration and a correcting quantity for correcting the basic duration are determined in order to determine the duration of the brake pressure control signals, the correcting quantity being determined as a function of the maximum slip value determined.
The prescribed time interval can correspond to a control cycle. The abovementioned correcting quantity is then used to correct the basic duration of the pressure variation in the following control cycle.
Furthermore, it is advantageous that the maximum acceleration value is determined within the prescribable time interval from the acceleration signals of at least one wheel
REFERENCES:
patent: 4923255 (1990-05-01), Braschel et al.
patent: 4985839 (1991-01-01), Dominke
patent: 5080448 (1992-01-01), Mori et al.
patent: 5249852 (1993-10-01), Beyer et al.
patent: 5251970 (1993-10-01), Braschel et al.
Grossardt Bernd
Sonntag Eberhard
Ballato Josie
Robert & Bosch GmbH
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