Sensor of angle of a shaft with a base separating the shaft...

Details Sensor of angle of a shaft with a base separating the shaft... Sensor of angle of a shaft with a base separating the shaft...

1999-06-08

2001-11-13

Metjahic, Safet (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207250

Reexamination Certificate

active

06316935

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a shaft angle sensor suitable for use in an automotive environment, and more particularly, to a shaft angle sensor employing magneto-resistive material for reduced sensitivity to spacing between rotary and stationary elements of the sensor.
In the use of electrical and electromechanical systems in an automobile, it is often necessary to employ an angle sensor to provide an indication of an angle of rotation of a rotatable component relative to a fixed component in the automobile. By way of examples, electrical circuitry is employed: (1) in the operation of a throttle body and/or carburetor with respect to the positioning of a butterfly valve, (2) in conjunction with the positioning of a throttle pedal for feeding fuel to an engine, (3) in conjunction with measurement of rotational angle of shaft used in rotary chassis height sensor equipment, (4) in an electronic throttle body sensor for regulating fuel to an engine, as well as in (5) operation of brake, clutch and positioning of a gear selection, by way of example. It is desirable to have such sensing of rotational angle to be accomplished precisely for optimum operation of the foregoing components of the automobile. However, the automobile represents a hostile environment to the employment of such sensors because of vibration, dirt, and temperature variations, as well as to mechanical concerns of tolerance, spacing, displacement, shaft and bearing wear. A further difficulty arises in the fabrication of the sensor for the automotive environment wherein there is need for excessive precision in the assembly of the sensor.
SUMMARY OF THE INVENTION
The aforementioned problems are overcome and other advantages are provided by a shaft-angle sensor which, in accordance with the invention, comprises a rotatable magnet shaft placed adjacent a bridge circuit having a magnetoresistive (MR) sensing element which determines an angle of the flux of the magnetic shaft. Preferably, a double bridge circuit with a pair of the MR sensing elements is employed, wherein the two bridge circuits are rotated 45 degrees relative to each other to provide the equivalent of sine and cosine components of a measure of the magnetic field produced by a magnet in the end of the magnet shaft. A characteristic of the MR sensor is its ability to measure magnetic field angle while being tolerant to displacement between the rotary and the fixed portions of the sensor. This tolerance to displacement is attained by a fabrication of the sensor with a base of plastic material which is essentially transparent to the magnetic field, wherein the base provides a support for the bridge circuits, and also forms a cavity for receiving a magnetized end of the magnet shaft. Use of the plastic base permits the sensor to be fabricated of circuit components which are later assembled and, wherein, a slight displacement from optimum placement of the components has no more than a negligible error in the measurement due to the tolerance of the MR sensing element to displacement between the rotary and the fixed parts of the sensor. In addition, the plastic material is resistant to moisture and is temperature stable.


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