Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Patent
1996-08-26
1999-12-07
Strecker, Gerard
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
32420721, G01P 3487
Patent
active
059989890
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for detecting rotary or angular movements.
BACKGROUND OF THE INVENTION
Devices of this type are often required on automobiles to monitor the rotational behavior of the individual vehicle wheels. Wheel speed is of critical importance as an input variable for control systems, such as anti-lock systems, traction slip control systems and driving stability control systems.
Sensor devices to determine the rotational speed of wheels are known in a great number of applications. Normally, the measuring data emitter in such sensor devices is an incremental encoder which is coupled mechanically to the component or wheel the rotation of which is to be measured. Further, there is a transducer or sensor which scans the encoder. Ferromagnetic toothed wheels, toothed rings, ferromagnetic hole discs, etc., are used as encoders. When sensors are used in wheel bearings, it is also customary to employ magnetized structures as a measuring data emitter, for example, annular or circular arrangements of successive north/south poles, embedded in a mechanic carrier member.
It is also common to use so-called "passive" sensors according to the reluctance principle. These sensors use a copper coil with a permanent magnet as a transducer. The transducer is coupled magnetically to the toothed disc serving as measuring data emitter, or to any other encoder. The encoder modulates the magnetic coupling reluctance synchronously with movement, and an alternating voltage representative of the movement is induced in the copper coil. The frequency of the alternating voltage permits being evaluated as a measured quantity to determine the rotational wheel speed. The magnitude of the induced signal voltage is a function of the rotational speed and the air slot between the measuring data emitter and the transducer or between the tooth system and the sensor.
"Active" sensors, which also cover the subject matter of the present invention, are well known in the art. In principle, they are combined of a magneto-statically sensitive element and a permanent magnet which is magnetically coupled to the encoder. The encoder modulates, synchronously to movement, the magnetic coupling reluctance or the field direction, and the sensor element responds to the variation of the flux density or the movement of a field vector. Examples in the art of such magneto-statically responsive elements are Hall probes and magneto-resistive structures on the basis of permalloys. The magnitude of the signal voltage on the sensor element is responsive to the air slot, but independent of the rotational speed or the frequency.
The publication entitled "Magneto-resistive rotational speed sensor--reliable and inexpensive" (Graeger, Petersen, Elektronik 24/1992, pages 48 to 52) describes an active rotational speed sensor of such a type which interacts with a toothed disc made of ferromagnetic material that is the measuring data emitter. The actual sensor element includes a permanent magnet on the side remote from the toothed disc. The magnetic field of this magnet serves to bias the magneto-resistive sensor element and to produce the magnetic coupling reluctance with the co-rotating toothed wheel. Therefore, a permanent magnet with a relatively large volume is required to permit an air slot that is sufficient in practical operations.
An object of the present invention is to provide a device of the previously mentioned type including an active sensor element which, compared to known devices of this type, necessitates a minimum possible structural volume to permit accommodation of the device in a wheel bearing of an automotive vehicle, for example, and which also permits a largest possible air slot or distance between the measuring data emitter and the transducer.
A special feature of the device of the present invention is that the measuring data emitter has successive permanent magnet areas of alternating polarity in the direction of rotation, and that the sensor element is arranged and the bias magnet is magnetized such th
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patent: 4646088 (1987-02-01), Inoue
patent: 4865468 (1989-09-01), Kato et al.
Derwent's Abstract, Nr92-322587/39, Woche 923, Abstract of SU, 1689859 (As Belo Solid Body Phys Inst Viteb), Nov. 7, 1991.
ITT Automotive Europe GmbH
Strecker Gerard
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