Fluid-pressure and analogous brake systems – Speed-controlled – Split coefficient of friction
Patent
1997-08-13
1999-02-02
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Split coefficient of friction
303148, B60T 832, B60T 860, B60T 884, B60T 800
Patent
active
058655140
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a circuit arrangement which is provided for an automotive vehicle brake system with electronic anti-lock control to enhance the driving stability in critical driving situations and includes circuits for the individual control of the braking pressure in the wheel brakes of the front wheels in response to the rotational behavior of the wheels and for the limitation of yawing torques which occur due to braking maneuvers on road surfaces having a different friction coefficient on the right/left sides. The circuit may include a hard wired circuit, a programmed circuit, or mixed forms thereof.
BACKGROUND OF THE INVENTION
German patent application No. 39 25 828 discloses a circuit arrangement of this type. An anti-lock control system with individual control of the braking pressure on both wheels of an axle is described. The braking pressure difference on the two wheels of an axle is restricted to limit the yawing torque on split road surfaces, and the allowable braking pressure difference is determined as a function of the difference in friction coefficients and the magnitude of the lower coefficient of friction. In the event of exceeding of the allowable braking pressure difference, in consideration of the motional condition of the LM-wheel, that is the wheel on the lower coefficient side, the braking pressure on the HM-wheel, i.e. the other wheel of the same axle, is reduced. To determine the allowable pressure difference in this known anti-lock control system, the pressure introduced by the driver is measured on the right and the left wheel, and the nominal pressure is compared to the actual pressure in each case. The coefficient of friction is assessed on the basis of the braking pressure.
Further, German patent application No. 41 14 734 discloses a circuit arrangement for anti-lock control with an individual braking pressure control and yawing torque limitation which is based on the fact that a value, representative of the pressure difference on the two wheels of an axle, is constantly determined from the pressure reduction signals and, under .mu.-split conditions, the medium pressure increase gradient on the HM-wheel is varied as a function of the pressure difference and the vehicle deceleration and that the braking pressure on the HM-wheel is reduced by a value, which is responsive to the vehicle deceleration and the pressure difference, at the time of the occurrence of the so-called yawing torque peak.
The above mentioned, known provisions do not permit preventing the generation of yawing torques of a dangerous amount in defined, especially critical situations. For example, different wheel lock pressure levels in the individual wheel brakes occur on road surfaces having varying coefficients of friction, so-called .mu.-patch road surfaces, due to a changing dynamic axle load distribution and the related variation of the wheel vertical forces. When these variations occur on the right and the left road surface side, they cause yawing torques which may jeopardize the driving stability. Especially in vehicles having a short wheelbase and front-wheel drive, the rear axle alone cannot ensure that driving stability is maintained.
In principle, the previous solutions involve slowing down the occurrence of yawing torques during braking on .mu.-split road surfaces by a decelerated braking pressure rise on the front HM wheel to give the driver time for a reaction, i.e., for countersteering. However, when the coefficient of friction changes, in particular from a high value to a low value, the described effects will be encountered.
OBJECT OF THE INVENTION
An object of the present invention is to prevent the occurrence of dangerous yawing torques even in defined, especially critical driving situations, above all when passing from a high, homogeneous coefficient of friction to a .mu.-split road surface or during braking maneuvers on .mu.-patch road surfaces, and to virtually enhance the driving stability also in such driving situations.
SUMMARY OF THE INVEN
REFERENCES:
patent: 4489382 (1984-12-01), Jonner et al.
patent: 5315518 (1994-05-01), Lin
German Report of the German Patent Office relating to Parent German Patent Application No. 44 41 624.5.
English trnaslation of the International Preliminary Examination Report of Application No. PCT/EP95/03738 filed Sep. 22, 1995.
Ehmer Norbert
Lehmer Ronald
Striegel Thomas
Woywod Jurgen
Butler Douglas C.
ITT Manufacturing Enterprises Inc.
Lewis J. Gordon
Twomey Thomas N.
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