Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-07-10
1993-09-14
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 96, B60T 832
Patent
active
052442586
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an anti-skid brake control system for a motor vehicle of the type comprising a speed sensor associated with a vehicle wheel for producing a signal representative of the wheel speed V.sub.R ; an evaluation circuit responsive to the wheel speed signal for determining the wheel acceleration V.sub.R, the approximate vehicle speed V.sub.Ref, and the longitudinal wheel slippage .lambda., and for producing brake pressure control signals in response thereto; and brake pressure control means, responsive to the aforesaid control signals, for controlling the brake pressure applied to the vehicle wheel(s). The evaluation circuit and the brake pressure control device are operative to reduce the brake pressure, to maintain the brake pressure at a substantially constant level, and to increase the brake pressure in pulsed increments so as to provide the driver-selected braking force while limiting the longitudinal wheel slippage.
PRIOR ART
The German Patent No. 20 63 944 discloses an anti-skid brake control system having these features. It determines deceleration and acceleration signals (-b, +b) that are generated in addition to slippage signals and are combined in AND and OR-gates so as to form brake pressure control signals.
SUMMARY OF THE INVENTION
It is an object of the invention to further improve such systems and, in particular, to achieve high pressure build-up frequencies, in case the distance of the pressure from the locking pressure is large, and small pressure build-up frequencies in case the distance is small.
It is an object of this invention to adjust the wheel brake cylinder pressure of a vehicle such that, on the one hand, a highest-possible adhesion coefficient .mu..sub.B is available in the longitudinal direction of the tires and, on the other hand, a high adhesion coefficient .mu..sub.S is available in the transverse direction of the tires.
This is the case when brake slippage values are obtained which are close to the maximum of the .mu.-slippage curve but do not exceed this maximum.
The slope of the .mu.-slippage curve has small positive values in this range and the dynamic behavior of the slippage is asymptotically stable. The German patent publication No. 36 18 691 discloses a process which determines the slope of the slippage curve and adjusts the slippage such that the slope of the slippage curve assumes small positive values.
The invention predominantly uses the wheel circumferential speed V.sub.R of the controlled wheels as a measuring value. An embodiment to be described hereinafter also measures the vehicle deceleration in case a supported vehicle reference speed V.sub.Ref is to be used.
The brake pressure is adjusted by means of hydraulic valves, the actuating logic of which can assume, for example, the following operational conditions: duration build-up, pulsed build-up with prescribed length of pulse, pressure maintenance, duration reduction.
The wheel speed is sensed and evaluated to digital signals at intervals of 3 ms, for example. The control is carried out in limiting cycles which include an event-controlled pulsed pressure build-up, a pressure reduction, and a maintenance phase leading into the stable range of the slippage curve.
During the pressure maintenance phase following a build-up pulse the following stability criterion is individually monitored for each controlled wheel: ##EQU1## In this relationship: .alpha., .beta., b.sub.1, .DELTA..lambda..sub.1 are constants, maintenance phase, manner to be described hereinafter.
For values P.sub.y =0 the wheel is definitely stable, therefore a build-up pulse can be formed.
From values 0<P.sub.y <e.g. 0.5 it can be concluded that the wheel is in a dynamic transition; hence, the pressure is maintained. P.sub.y >0.5 suggests instability or limited stability; hence, the wheel brake pressure is reduced. In case the wheel behavior is undisturbed, the above stability criterion can be illustrated in a phase plane of the parameters V and .DELTA..lambda. (FIG. 1).
The whe
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Patent Abstrs. of Japan, vol. 9, No. 249--Oct. 5, 1985.
Bosch Technische Berichte (Feb. 1982) "Antiskid System (ABS) for Passenger Cars", H. Leiber et al. pp. 65-70.
Kost Friedrich
Ruf Wolf D.
van Zanten Anton
Graham Matthew C.
Robert & Bosch GmbH
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