Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-07-21
2001-12-18
Metjahic, Safet (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207150
Reexamination Certificate
active
06331772
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a sensor component with a coded magnetic transmitter and associated sensor device, positioned such that they can be moved relative to each other and wherein the magnetic transmitter is arranged inside a diamagnetic or paramagnetic case that is closed relative to the sensor device.
A known sensor component of this type (German Patent 38 44 578 C2) comprises two magnetic transmitters that are axially coupled via a torsion shaft and, as circular rings, are provided with a magnetic coding in a circumferential direction as scale for the torsion angle. The torsion shaft is part of a steering gear for motor vehicles and, together with other steering parts and drive parts, is positioned rotatably inside a bearing housing. In the radial range of the magnetic transmitter, the gear housing is provided with an opening through which a magnetic-field sensitive sensor, belonging to a sensor component that is flanged onto the outside of the gear housing, extends close to the cylindrical shell surfaces of the magnetic transmitter. This kind of configuration protects the magnetic transmitters against outside influences. However, at least one through opening, as well as a seal between the sensor component and the gear housing must be provided at a predetermined location.
SUMMARY OF THE INVENTION
It is an object of the invention to create a sensor component which permits a simplified design in the region of the coupling section between magnetic transmitter and sensor component.
A sensor of the present invention includes a coded magnetic transmitter and an associated sensor device positioned such that they can be moved relative to each other. The magnetic transmitter is arranged inside a diamagnetic or a paramagnetic case or shell closed relative to the sensor device. The sensor component has a case or shell made of an austenitic steel with more than 0.4 weight percentage nitrogen and has a yield strength between 900 MPa and 2500 MPa.
If a sensor element is designed according to the invention, the magnetic transmitter fits inside a shell that is closed at least relative to the sensor component. This shell tightly encloses the magnetic transmitter in adjustment direction and ensures a reliable protection against mechanical interference with the magnetic transmitter. For the most part, the magnetic field lines emanating from the magnetic transmitter penetrate the shell diamagnetically or paramagnetically. It is preferable if a nitrogen-alloyed steel with high nitrogen content and extreme hardness is used for the shell.
The magnetic transmitter can be produced in the manner of a tube or bar from a permanent magnetic material and can be designed with a magnetic coding extending in longitudinal direction. The magnetic transmitter for this embodiment, for example, can be arranged in a hollow piston rod of a hydraulic power steering actuator, wherein the tube-shaped piston rod has a completely closed jacket surface and the magnetic transmitter is positioned in an actuator housing such that it can be displaced in longitudinal direction. The sensor component can be secured so as to be radial to the piston rod where the piston rod exits from the actuator housing or on an adjacent, locally fixed carrier. The sensor device then detects the information from the magnetic transmitter during the longitudinal displacement of the piston rod.
If the magnetic transmitter is designed in the manner of a circular disc or a circular ring, with the magnetic coding extending in circumferential direction, it can also be arranged inside a hollow steering spindle, wherein the sensor component can be locally fixed on a carrier in which the steering spindle is positioned or on a neighboring carrier. The steering spindle is preferably formed from a magnetically transparent material. It is particularly preferable if the steering spindle is made from an austenite steel with extreme hardness and a high nitrogen content of more than 0.3 weight percentages of nitrogen. However, the magnetic transmitter can also be fixed concentrically on the outer jacket surface of the steering spindle and can be protected with its own shell that is attached to the steering spindle.
The magnetic transmitter, secured inside the shell, and the shell or a structural component supporting the magnetic transmitter and the shell are positioned such that they can move relative to each other. In contrast, the sensor component is positioned such that it is locally fixed. The radial distance between the magnetic transmitter, designed as a scale, and the associated sensor device can vary over a wide range that depends on the pole separation, e.g. between 0 and 15 mm, without a significant weakening of the signals occurring at the sensor component. As a result, the assembly of the sensor component involves little adjustment and integration into the respective mechanical component is possible with low additional volume.
The sensor component can also have several magnetic field-sensitive individual sensors, which are respectively assigned to one magnetic transmitter. For reasons of safety, a parallel operation of several magnetic transmitters is also possible. In addition, the individual magnetic transmitters can be formed from several partial magnetic transmitters, arranged parallel to each other, to which respectively at least one individual sensor is assigned and which carry different magnetic coding, so that not only the relative, but also the absolute torsion angle or longitudinal displacement distance can be derived from the pulse signals that are read out at each partial magnetic transmitter from the mechanical displacement movement. Otherwise, the sensor component can include magnetoresistive sensors, Hall sensors and inductive sensors for acquiring the magnetic fields, for which the magnetic polarization changes via the adjustment distance of the magnetic transmitter.
The use of an austenite steel with extreme hardness and a very high nitrogen content is especially preferred as material for the jacket and/or the raw material for the sensor. It is favorable if the steel does not have magnetic components even when processed mechanically and can thus be processed, particularly deformed, ground and/or polished without additional reworking. This is a particular advantage for highly stressed structural elements, for which the translatory motion and the angular motion must be measured, especially for hydraulic actuating mechanisms, dampers, push-pull rods guided inside bushings and linear drives of any kind.
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Horst Flechtner et al., “Entwicklung eines inkrementalen Winkelgebers”, F & M 100 (1992) 4, pp. 137-139.
Reinhard Drews et al., “Entwicklung eines digitalen Lenkwinkelsensors auf Induktivbasis”, F & M 101 (1993) 10, pp. 381-384.
E. Houdremont, Handbuch der Sonderstahlkunde [Handbook for Specialized Steel], vol. 2,3rdEdition, Springer Publishing House, 1956, pp. 1327-1331.
Fischer Roland
Windte Volker
Daimler-Chrysler AG
Kinberg Robert
Metjahic Safet
Spencer George H.
Venable
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