Fluid-pressure and analogous brake systems – Speed-controlled – And traction control
Patent
1996-12-20
1999-11-09
Young, Lee W.
Fluid-pressure and analogous brake systems
Speed-controlled
And traction control
303148, B60T 832
Patent
active
059800003
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP95/02290.
BACKGROUND OF THE INVENTION
The present invention relates to a circuit for a brake system with traction slip control by brake management which includes wheel sensors to measure the wheel rotational behavior and electronic circuits to evaluate the sensor signals and to generate braking pressure control signals which are used to introduce braking pressure into the wheel brakes of the overspeeding wheel when a predetermined variable traction slip control threshold is exceeded.
A circuit of this type is disclosed in German patent application No. 40 17 845, for example. The traction slip of each driven wheel is controlled individually. The control threshold, in excess of which traction slip control commences, is variable in this known circuitry. The control threshold includes a predetermined basic value and a portion derived from the wheel slip acceleration. Suitably, a wheel slip value responsive to the vehicle speed is used as a basic value. To improve the starting behavior, the basic threshold founds on a relatively high initial value which decreases linearly with the vehicle speed and reincreases starting from a defined vehicle speed of, for example, 25 km/h.
The purpose of such a variation of the control thresholds, which determine the commencement of traction slip control, is to conform the traction slip control or the introduction of pressure into the wheel brake of the overspeeding wheel, in comparison to known control systems with invariable control thresholds, with a still greater accuracy to different road conditions, with the objective of improving the control quality.
German patent No. 37 41 247 discloses conforming the slip threshold values for a traction slip control system to the tires of an automotive vehicle.
SUMMARY OF THE INVENTION
The general objective of the present invention is also to improve the starting behavior of a vehicle. In particular, the traction or the driving behavior, the driving stability and the steerability (in vehicles with front-wheel drive) is improved on road surfaces having low coefficients of friction and in situations with slight differences in the coefficients of friction between right/left.
It has been found that this objective can be achieved by a circuit of the type previously mentioned having special features which involve circuits which, after overspeeding of a wheel of a driven axle and commencement of traction slip control, determine the traction slip of the second, non-controlled wheel of the driven axle and evaluate this value to produce a correction factor which corrects the traction slip control threshold of the controlled wheel as a function of the instantaneous traction slip of the second, non-controlled wheel.
Thus, the present invention is based on the consideration that it is not, or not only, the control of the overspeeding wheel having the worse road contact which is of importance for improving the traction and steerability of the vehicle. Rather, the stabilization of the second, non-controlled drive wheel having the higher coefficient of friction is most important. In contrast to prior art traction slip control systems with brake management, therefore, the control threshold of the controlled wheel is varied as a function of the traction slip of the non-controlled wheel which is on the side with the high coefficient of friction in the majority of cases. Therefore, the control threshold of the drive wheel on the low friction side is conformed to the coefficient of friction on the high friction side such that a maximum possible engine torque is transmitted to the high friction wheel by way of the low friction side. Ideally, an amount of traction slip as high as required to optimally utilize the coefficient of friction develops on the high friction side where no control is effected. The wheel remains in the stable range of the .mu.-slip curve. Should the friction value change so that now the relatively higher coefficient of friction is o
REFERENCES:
patent: 4984165 (1991-01-01), Muller et al.
patent: 5293315 (1994-03-01), Kolbe et al.
patent: 5322356 (1994-06-01), Kolbe et al.
patent: 5415468 (1995-05-01), Latarnik et al.
patent: 5601347 (1997-02-01), Fischle et al.
Alberg Verena
Kolbe Alexander
ITT Automotive Europe GmbH
Young Lee W.
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