Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-06-01
2000-10-24
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303186, 303 971, B60T 834
Patent
active
061355763
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of improving the control behavior of a brake system with anti-lock control, wherein the rotational behavior of the wheels is measured and evaluation and logical combining of the wheel rotational speed data permits producing a vehicle reference speed, wheel slip data and wheel acceleration data and other control parameters which are used to proportion and modulate the braking pressure.
Electronically controlled anti-lock brake systems (ABS) have gained in significance in the past years. Systems of this type are on the market in large numbers and various designs. In the majority of systems known in the art, the data required for anti-lock control are produced by measuring the rotational behavior of the vehicle wheels. A vehicle reference speed is determined by logically combining the signals originating from the individual wheels and can be taken into account as a reference quantity to calculate the wheel slip and other control parameters and, in addition, to set and modulate the braking pressure in the wheel brakes of the individual vehicle wheels.
Difficulties are involved in the identification of the actual control situation by way of the data furnished by the wheel sensors and the adjustment or modulation of the braking pressure in terms of an optimal braking behavior when the interpretation of the sensor signals is no absolute indicator of the instantaneous driving and control situation. Further, per se contradicting demands in terms of wheel stability (by pressure relief) and a short stopping distance (by a maximum possible braking pressure) must be satisfied in pressure modulation which is performed by the ABS controller on the basis of the so-called control philosophy, i.e., the predetermined algorithms, in response to the rotational behavior of the individual wheels.
There is a number of situations which are especially difficult to be identified by the ABS controller and which give rise to misinterpretations if no special measures are taken. For example, bumps and other disturbances in the road surface cause vehicle decelerations which are erroneously interpreted as locking tendency by the controller. Therefore, it is appropriate to analyze the rotational behavior of the wheels pursuant criteria of different types in order to discover contradictions and to protect individual control measures, especially those which are critical in terms of safety, according to different aspects and criteria.
An object of the present invention is to identify control situations where the braking pressure adjusted by the control is too low or is below the per se achievable optimum.
SUMMARY OF THE INVENTION
It has been found that this object can be achieved by a method including that the lowest wheel speed is continuously compared with the highest wheel speed during a braking operation, that in the event of a correlation, at least by approximation, between the lowest and the highest wheel speed and if the correlation lasts longer than a predefined time interval, the pressure in the wheel brakes of the front wheels is permitted to increase, or caused to increase directly or indirectly, after this time interval. For example, the braking pressure in the front wheels is increased by opening of the inlet valves which are inserted in the pressure fluid path from the master cylinder of the brake system to the front-wheel brakes. The same effect can be achieved indirectly by rise of the reference speed which is used as a reference quantity for the proportioning of braking pressure.
In a preferred aspect of the present invention, the predefined time interval is varied as a function of the acceleration (or deceleration) of the non-driven vehicle wheels, and the predefined time interval is set to a small value as long as the acceleration of all non-driven wheels is in excess of a predetermined limit value, and is set to a longer duration when the acceleration is lower (or the deceleration is greater). Instead of the two-step method, it is also possible to ar
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patent: 5415469 (1995-05-01), Poggenburg et al.
patent: 5855419 (1999-01-01), Urai et al.
ITT Manufacturing Enterprises Inc.
Oberleitner Robert J.
Siconolfi Robert A.
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