Fluid-pressure and analogous brake systems – Speed-controlled – Wheel generated pulse signal control
Patent
1996-09-20
1998-03-17
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Wheel generated pulse signal control
303172, 303173, 303174, 364426018, B60T 832, G01P 348
Patent
active
057278555
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an anti-locking control system.
In vehicles that are equipped with an anti-locking control system, typically four but in individual cases sometimes only three rpm sensors are used, assigned to the various wheels. The output signals of these rpm sensors generally have a pulse train. From the time interval between individual pulses or pulse edges, the speed of the wheel in rpm is ascertained.
For the anti-locking control system, the reference vehicle speed is also required. This reference vehicle speed is typically ascertained from the four wheel speeds; precisely how the reference vehicle speed is calculated from one or more wheel speeds is known in principle and will therefore not be explained in further detail here.
Since the essential variables from which trigger signals are formed in an anti-locking control system are formed from the aforementioned wheel speed sensors or the associated output signals, reliable monitoring of whether the sensors are functioning properly must be performed. In German patent application P 44 05 801.2, a monitoring system has therefore been proposed which is used in ABS or anti-locking control systems and which makes it possible to detect various malfunctions of the wheel rpm sensors.
In anti-locking control systems, interference signals that approximately correspond to the 50 Hz mains frequency have proved to be problematic. Such interference signals are within a frequency range that proves to be critical in ABS or anti-locking control. Electrical interference from the power supply grid can mean an incorrectly ascertained wheel speed and thus an inadvertent increase in the calculated reference vehicle speed. It is therefore the object of the invention, when such interference signals are present, to detect them and to suppress their effect. The suppression of interference signals should be accomplished without additional components.
SUMMARY OF THE INVENTION
The anti-locking control system according to the invention has the advantage that interference signals that occur at a frequency corresponding to the usual mains frequency are detected and are reliably precluded both in the evaluation of the rpm sensor signals and in the reference vehicle speed formed from these signals.
These advantages are attained in that the reference vehicle speed is determined from the wheel speed signals by a different method at low vehicle speeds than at higher vehicle speeds. At reference vehicle speeds that are below a noncritical threshold, a positive adaptation of the reference vehicle speed is prohibited if signals arrive at at least one wheel rpm sensor in which the time intervals between arriving signal edges are approximately equivalent to the mains frequency. Accordingly, as soon as such time intervals are recorded, a newly ascertained reference vehicle speed is not used if it is higher than the previous value.
Further advantageous features of the invention are attained by means of additional provisions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block circuit diagram showing the variables of an anti-locking control system that are essential to understanding the invention; and FIG. 2 illustrates one possible method for determining the reference vehicle speed.
DESCRIPTION OF PREFERRED EMBODIMENT
In FIG. 1, the rpm sensors assigned to the individual wheels are marked 10, 11, 12, and 13. These rpm sensors scan toothed disks, which each rotate in synchronism with one wheel and have a predetermined number of teeth. The rpm sensors furnish the output signals S1, S2, S3, S4. Typically, these signals are a train of pulses. From the time interval between the pulses, or between the same kinds of pulse edges, the wheel speeds or wheel rpms needed for the ABS or anti-locking control are ascertained in the evaluation arrangement 14, typically a microprocessor. The time intervals to be evaluated are designated as T1-T4, for the individual signals S1-S4.
The evaluation arrangement 14 corresponds to the usual evaluation circuits and
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Dominke Peter
Koch-Ducker Heinz-Jurgen
Pfau Martin
Sager Frank
Butler Douglas C.
Robert & Bosch GmbH
Striker Michael J.
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