Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1988-09-26
1990-05-01
Kashnikow, Andres
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 61, 303105, 303109, B60T 864, B60T 870
Patent
active
049213148
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an anti-locking brake control system for a motor vehicle. The system is of the type comprising wheel speed sensors for determining the speeds of the individual vehicle wheels, an evaluation circuit which receives the wheel speed signals and generates brake pressure control signals, and a brake pressure control valve responsive to the brake pressure control signals for controlling the brake pressure applied to the wheels.
In anti-locking brake systems in which brake pressure is built up in pulses so as to achieve a flat average rate of pressure increase, it is known to make the initial brake-pressure pulse after an instability greater than the pulses that follow. This can be seen in FIG. 1.
In FIG. 1, the duration T0 of the pressure rise time is dependent on the number of such pulses or on the pressure build-up time which was necessary in the preceding control cycle to cause the wheel to become unstable. The holding time T.sub.H either has a fixedly pre-established length, or else it is the time considered to be optimum, and this time T.sub.H is determined through a learning process.
SUMMARY OF THE INVENTION
It is an object of the invention to further optimize brake control.
This object, as well as further objects of the present invention which will become apparent from the description that follows are achieved, according to the present invention, by providing a brake pressure control unit which operates in such a manner that, after brake pressure decays, the brake pressure is at first increased in a timed build-up with reference to the brake pressure build-up in a preceding control cycle, and thereafter the brake pressure is further increased by a sequence of pulses until an instability is again detected. This timed pressure build-up thus has at least two timed brake pressure build-up phases which have respective durations such that the duration of each one of the timed build-up phases in a given time pressure build-up is longer than the length of the subsequent timed build-up phase in the control cycle, if any. In addition, the duration of the timed build-up is a function of the preceding pressure decay time, this function being such as to reduce the value of longer decay times relative to shorter decay times.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention and to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an example of controlled brake pressure versus time in an anti-locking brake control system of the prior art.
FIG. 2 is a diagram of one example of controlled brake pressure verses time in the anti-locking brake control system according to the principles of the present invention.
FIG. 3 is a diagram of brake pressure verses the period during which the brake pressure relief valve is open.
FIG. 4 is a diagram of brake pressure verses time in an anti-locking brake control system according to the present invention.
FIG. 5 is a block diagram of the basic elements of an anti-locking brake control system, which include wheel sensors, an evaluation (processing) circuit and brake pressure control valves.
FIG. 6 is a block diagram of one possible circuit, according to the present invention, which may be employed in the processing circuit of FIG. 5.
FIG. 7 is a block diagram of another possible circuit, according to the present invention, which may be employed in the processing circuit of FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For this purpose the pressure rise time T0 preceding the set series of pulses is preferably broken down into two pulse rise times T01 and T02, wherein T01 is decidedly longer than T02.
Since T01 and T02 can produce a pressure increase of the desired amount only if it is known whether the pressure level at the beginning of the time period T01 is definitely different from the pressure level in the preceding pressure regulating cycle, allowance is also made for the pressure decay ti
REFERENCES:
patent: 3888550 (1975-06-01), Reinecke et al.
patent: 4054328 (1977-10-01), Leiber et al.
patent: 4183588 (1980-01-01), Snyder
patent: 4225195 (1980-09-01), Weise et al.
patent: 4485445 (1984-11-01), Braschel
patent: 4647115 (1987-03-01), Leiber et al.
patent: 4673226 (1987-06-01), Every et al.
Braschel Volker
Schafer Jochen
Seitz Dieter
Kashnikow Andres
Newholm Timothy
Robert & Bosch GmbH
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