Electricity: measuring and testing – Electrical speed measuring
Patent
1989-10-20
1991-08-27
Strecker, Gerard R.
Electricity: measuring and testing
Electrical speed measuring
188181R, 324161, 324163, 324166, 324225, 364565, G01P 348, G01P 346, G01P 356, B60T 832
Patent
active
050436589
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device and a method for measuring the rotational speed of a wheel in an anti-locking-protected vehicle brake system comprising a rotational speed sensor in which electromagnetic signals are induced corresponding to the rotational speed of the wheel and having an amplitude and frequency increasing regularly with the rotational speed.
The functionability of an anti-locking system for brakes (ABS) depends inter alia substantially on whether the rotational speed sensors monitoring the wheel rotation behavior furnish exact measurement values. If the speed sensors furnish inaccurate measurement results the ABS system cannot function.
It has therefore already been provided in the prior art to monitor the rotational speed sensors of the anti-locking-protected braked wheels. Thus, it is known for each speed sensor to provide a synchronizable a stable multivibrator which when the speed sensor is connected and the wheel is stationary oscillates with a natural frequency low compared with the measuring pulse repetition frequency occurring when the wheel rotates and the natural oscillation of which stops in the presence of a short-circuit at the input and/or when the input is open.
It is also known to check the functionability of an anti-locking system rotational speed sensor in that in dependence upon the vehicle velocity time periods are determined in which no measuring pulses are received by the rotational speed sensors.
Finally, to monitor the functionability of rotational speed sensors it has also been proposed to determine during a starling phase the velocity at which the rotational speed sensors associated with the individual wheels each generate a measuring signal having an amplitude above a threshold value. If this velocity is below a predetermined value the wheel whose rotational speed sensor has generated the inadequate signal is removed from the anti-locking system control.
The rotational speed sensors which can be used in anti-locking systems are known to the expert (cf. for example BOSCH TECHNISCHE BERICHTE, volume 7, 1980, No. 2, p. 84). Used at present, and also preferably employed with the present invention, are rotational speed sensors operating by the magnetic induction principle. If a toothed disc associated with the sensor rotates the magnetic flux at the sensor changes and a substantially sinusoidal AC voltage is induced in a coil of the sensor. The frequency of the induced voltage is a measure of the rotational speed of the monitored wheel.
Since the induced voltage depends on the change of the magnetic flux with time, with increasing rotational speed of the wheel not only the frequency of the induced AC voltage increases but also its amplitude. This means that at low rotational speeds the measuring signal becomes weaker.
Among others, axial and radial arrangements of toothed ring and coil are known.
The rotational speed measuring signal obtained in this manner can be subject to disturbances and falsified in a great many ways. In particular, an air gap between the tooth disc and the electrical conductor in which the induction is generated can change in the course of time. The magnetically induced signals can also be falsified by soiling, rust or the like.
It is known from DE-A 3,200,529 in a rotational speed sensor of the type described here to suppress interference oscillations. For this purpose, in dependence upon the time the respective peak value of the amplitude is measured and a reference parameter corrected.
The measurement of the rotational speed of an anti-locking-protected braked wheel can however also be falsified by other influences. Thus, it is possible that due in particular to resonance oscillations of oscillatable parts near the rotational speed sensor, in particular so-called brake squeal, a signal of the rotational speed sensor contains harmonics which are superimposed on the actual measuring signal. By such harmonics the number of zero passages of the electromagnetically induced signal can be increased and this wrongly indicates an increase in the freq
REFERENCES:
patent: 4575677 (1986-03-01), Dennis
patent: 4808920 (1989-02-01), Brauninger et al.
patent: 4837508 (1989-06-01), Garnault
Braschel Volker
Seitz Dieter
Lucas Industries Public Limited Company
Strecker Gerard R.
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