Measuring and testing – Test stand – For engine
Reexamination Certificate
2002-07-12
2004-11-30
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Test stand
For engine
C324S207130, C324S207240
Reexamination Certificate
active
06823725
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to actuators, and more particularly relates to a linear distance sensor.
BACKGROUND OF THE INVENTION
It is known in the art to determine the position and angular speed of e.g. vehicle wheels by means of arrangements comprised of magnetically coded discs or rings and magnetic field sensors. For this purpose, permanent-magnetic material is fitted to the coded discs or rings (so-called encoders). A variation of the magnetic field on the encoder is required to have the position determined by the sensors. This is done either by alternating the north-south magnetization of the magnetic material along a circle arc on the encoder, or by a periodically reduced distance of the magnetic material from the sensor. The magnetic field is now scanned along the circle arc by a magnetic field sensor, which may e.g. be a Hall sensor or a magneto-resistive resistor, in order to determine the wheel position and the angular speed e.g. by counting the signal edges of the sensor signal. The signal produced by the sensor can be amplified and triggered by an electronic circuit fitted in the area of the sensor or integrated in the sensor (active magnetic field sensor).
A comparable arrangement is described in WO 95/17680, but also in WO 97/42508 for determining the wheel condition in a motor vehicle.
U.S. Pat. No. 4,712,083 discloses a magnetic distance sensor of high resolution which likewise uses the principle of the rotating permanent-magnetic encoder. The encoder is formed of evenly spaced hard magnets, and the magnetic field of all individual magnets is aligned towards the moving direction. The arrangement described is also provided exclusively to determine the position of rotating bodies.
To determine the slide controller position in a linear potentiometer, a slidable permanent magnet whose position is detected by means of a stationary gyromagnetic field sensor is used in DE 196 12 422. This type of sensor reacts especially sensitively to angular variations of the magnetic field.
A distance sensor to determine the position of a throttle valve in a motor vehicle is described in U.S. Pat. No. 5,929,631. In this arrangement, a Hall element is used as a magnetic field sensor or, what is preferred, a resistor element which makes use of the giant magneto-resistive effect (GMR). The said publication further mentions that the arrangement for position determination can be used for radial movements and for linear movements. The proposed solution resides in arranging a large number of magnetic sensors along the passage at a regular distance. In one embodiment, an arrangement is illustrated wherein eight GMR-sensors are arranged spherically on a rotating cylinder and, during the rotation, pass by a rod-shaped permanent magnet that is fixed to the inside of the cylinder jacket. This method of position determination is disadvantageous because a chain or matrix of individual sensors must be connected to an electronic evaluating circuit. Determining the position in this way is technically complicated and cost-intensive.
An increase in the resolution of magnetic distance sensors can be achieved according to DE 43 27 047 by anti-parallel aligning the hard magnets arranged on the encoder, on the one hand, and by employing two magnetic field sensors, on the other hand, which are arranged so as to be slightly offset laterally in the direction of the moving direction. The effect of outside disturbances can be further reduced by connecting several magneto-resistive deposit-film resistors to provide Wheatstone bridges. The arrangement described permits being generally used for measuring circular or linear changes in position of two objects that are movable in relation to each other. The above publication, however, does not provide any hints how a distance sensing unit must be constructed under practically relevant conditions as they prevail e.g. in motor vehicles.
BRIEF SUMMARY OF THE INVENTION
In view of the above, an object of the present invention it to propose a linear distance sensor for motor vehicles which offers a maximum of reliability and a high distance resolution under conditions relevant in practice such as corrosion, wear, dirt, extreme heat, and extreme cold.
According to the present invention, this object is achieved by a linear distance sensor which is described in the following:
A linear distance sensor with an integrated magnetically effective component for e.g. mechanical actuation devices of brake units is described according to the present invention. Among others, the present invention is based on the idea of utilizing the mechanics of the actuation device additionally as the mechanics of non-contact linear distance indicators, the purpose of which is to depict the driver's request for actuation either weighted distance-proportionally or distance-responsively.
The magnetic field of the encoder is measured or sensed by one or more magnetic field sensors. The magnetic field is sensed by the magnetic field sensor either completely or only partially, while it is to be understood by partial sensing of the magnetic field under the present invention that of the measurement quantity entirely describing the magnetic field, such as field strength and direction of the field vector, not all the quantities are sensed by the sensor module(s), but e.g. only the field strength and two direction coordinates of the field vector in the x-y plane of an appropriately chosen system of coordinates.
The sensor module according to the present invention comprises at least one magnetic-field-sensitive sensor and, if necessary, an electronic circuit for further processing the sensor signal. The present invention may be implemented by magnetic-field-sensitive sensors that operate according to the XMR principle, preferably, the AMR (Anisotropic Magneto-Resistive) principle, the GMR (Giant Magneto-Resistive) principle, or the Hall principle.
AMR principle means that the sensor utilizes the anisotropic magneto-resistive effect. Corresponding sensors are e.g. disclosed in S. Mengel, ‘Technologieanalyse Magnetismus Band 2: XMR-Technologien’, section 2.2, pages 18 to 20, VDI Technologiezentrum Physikalische Technologien, Düsseldorf, 1997. GMR principle implies that the sensor element utilizes the ‘Giant Magneto-Resistive Effect’. The Hall principle implies that the sensor utilizes the Hall effect. Preferably, exclusively sensors are employed which operate according to the AMR principle.
In a favorable aspect, the linear distance sensor according to the present invention is characterized in that the sensor module comprises a bridge circuit made of magnetic field sensors whose main plane is aligned in parallel to the surface normal and to the longitudinal axis of the displaceable element.
Under the present invention, the surface normal of the displaceable element means a directional vector that is vertical to the surface of the displaceable element.
If e.g. the displaceable element assumes the shape of a rod with a circular cross-section, the surface normal corresponds to the radius vector of the rod.
In a second favorable embodiment, the main plane of at least one sensor module with bridge circuit is aligned vertically to the surface normal of the displaceable element.
It is especially advantageous when both above-mentioned sensor variations are realized in the linear distance sensor of the present invention. In this function principle, different magnetic field components of a magnetic encoder track are used, and the field strength pattern of the encoder track is converted into different signals.
The output signal or the output signals of the magnetic sensors that contain data about the movement are preferably provided in an electrical form at the output. This signal can be conditioned by one or more sensor circuits and e.g. made available in a digitalized fashion at the output of the sensor circuit.
The means for producing the permanent course of lines of magnetic flux is also referred to as encoder in literature. It comprises, for example, either a permanent-magnetic mate
Continental Teves AG & Co. oHG
Honigman Miller Schwartz & Cohn LLP
Jenkins Jermaine
Lefkowitz Edward
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