Fluid-pressure and analogous brake systems – Pipeless valves
Patent
1992-07-24
1994-07-26
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Pipeless valves
303100, 303103, 188181C, 36442602, B60T 866
Patent
active
053322991
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In a known method, the triggering of ABS control is made more difficult in order to avoid starting control unnecessarily due to disturbance signals.
SUMMARY OF THE INVENTION
An anti-lock control system for brakes of wheels of a motor vehicle, according to one embodiment of the invention, comprises: sensors for determining wheel speeds of the wheels of the motor vehicle and producing respective wheel speed signals; an evaluation circuit for receiving the wheel speed signals, and producing respective brake pressure control signals and wheel slip signals representing slip values for the wheels of the motor vehicle; brake pressure control devices for receiving the brake pressure control signals and varying brake pressure at the respective brakes of the wheels of the motor vehicle; and a component block, within the evaluation circuit, having a slip combination means for receiving the wheel slip signals produced in the evaluation circuit and producing a slip combination signal representing a slip combination value formed from an average value or a sum of at least the slip values for the wheels of one axle, and further having a threshold value means for receiving the slip combination signal and producing an output enable signal which is combined with a predetermined instability criterion, formed in the evaluation circuit from the wheel slip signals and the slip combination signal, to trigger production of the brake pressure control signals, the output enable signal being used to avoid the triggering of control by a disturbance on the signal of a single sensor, e.g. by a blow to the wheel. On the other hand, the control system remains sensitive to the occurrence of an instability at more than one wheel--preferably the two wheels of the front axle. The occurrence of an instability signal at both wheels is an indication that a tendency towards locking has in fact occurred. Whether or not control is then determined by a slip signal alone and/or additionally by a retardation signal or some other instability criterion, into which the slip signal of only one wheel then enters, is immaterial to the invention.
It is possible simply to form the average value or the sum of the slip values or, alternatively, additionally to assign to these slip values weighting factors which, for example, impose a larger weighting factor K.sub.1 on the larger slip value .lambda..sub.1. For these two cases, and assuming average value formation, the criteria for the beginning of control, assuming that the exceeding of a slip threshold determines the pressure reduction, are as follows:
Beginning of control at: ##EQU1##
Here, J.sub.1 and J.sub.2 are limiting values and .lambda..sub.r, .lambda..sub.l, .lambda..sub.1 and .lambda..sub.2 are slip values. It is appropriate if K.sub.1 +K.sub.2 =2. In the case of sum formation, J is of course larger, for example twice as large. After control has been triggered, .lambda..sub.r or .lambda..sub.l is then compared to the slip threshold again.
The invention can also be used with other instability criteria, e.g. with criteria in accordance with German Offenlegungsschrift 3,614,770, in which wheel retardation values and slip values are integrated and then added and the sum then compared to a threshold value for the purpose of control. The invention can also be used with an instability criterion in accordance with the earlier Patent Application P 3841977.7, in which the instability criterion K is given by the following relation: wheel slip, IL is the integral of the wheel slip and a.sub.F2 is the vehicle retardation. If K reaches a threshold, pressure reduction starts. For the beginning of control, L (in IL also) is not the slip of one wheel but the average value or in the case of corresponding other constants b and c, the sum of the slip values of an axle.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a block diagram for an anti-lock control system according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An illustrative embodiment
REFERENCES:
patent: 3754797 (1973-08-01), Rodi et al.
patent: 4964045 (1990-10-01), Iwata et al.
patent: 5005132 (1991-04-01), Yoshino
patent: 5083631 (1992-01-01), Nakayama et al.
Oberleitner Robert J.
Poon Peter M.
Robert & Bosch GmbH
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