Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-12-21
2001-11-13
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240, C074SDIG007, C074S473100
Reexamination Certificate
active
06316936
ABSTRACT:
TECHNICAL FIELD
The invention relates to a displacement measuring system for obtaining a linear displacement signal for a movable control element.
BACKGROUND ART
Multiple-ratio automatic transmissions for automotive vehicle drivelines have multiple-ratio gearing and fluid pressure-activated clutches and brakes that are engaged and released under the control of a hydraulic valve circuit. The circuit includes a manual valve that can be shifted linearly to each of several drive ranges for the multiple-ratio transmission. The clutches and brakes establish and disestablish each of several torque flow paths through the gearing. The circuit is supplied with fluid pressure developed by an engine-driven pump.
The control circuit includes a pressure regulator that regulates line pressure made available by the pump. Regulated line pressure is distributed to selected valve members to establish the various forward driving ratio ranges and a reverse driving ratio. The selection of the drive ranges and reverse is under the control of a manual valve. A driver-operated mechanical linkage is used to adjust the position of the manual valve.
In order to obtain an accurate indication of the actual position of the manual valve, a mechanical position sensor is located on the exterior of the transmission housing, which contains the control valve system and the multiple-ratio gearing.
The position sensor comprises a mechanical lever connected directly to the manual valve. The position of the mechanical lever is detected by a sliding electrical contact array, which forms a part of an electric sensor circuit that detects the various manual valve positions.
A position sensor of this kind has inherent disadvantages because it is susceptible to malfunction if the sliding contacts of the contact array become contaminated and establish an open circuit in the position sensor. The sensor also creates driveline packaging difficulties because of the space that must be dedicated to the sensor.
DISCLOSURE OF INVENTION
The invention comprises a position sensor for detecting the position of the manual valve in an automatic transmission for an automotive vehicle which does not rely upon sliding contacts of a contact array and which can be located within the transmission housing, thereby avoiding packaging difficulties associated with known manual valve position sensors for automatic transmissions. The sensor comprises a magnet system mounted adjacent to and driven by the manual valve within the transmission housing. A magnetic field created by the magnet system is configured so that it produces maximum intensity at desired reference points relative to manual valve position.
An array of giant magneto-resistive elements (GMR elements) is positioned adjacent to a moving manual valve to measure the field strength of the magnet system. The GMR elements all have the same base resistance, but the resistance values of the individual elements in the array change as the magnet system is moved relative to the array. The resistance of the GMR elements closest to the maximum field reference points has a lower resistance than those farther from the same reference points.
A commercial source for GMR elements is Nonvolatile Electronics, Inc.
The sensor of the invention uses digital and analog electronics to convert the change of GMR element resistance into usable position information for the manual valve. A scanning logic makes it possible to generate a voltage waveform based on the combined resistances of a set number of selected GMR elements. The scanning logic waveform will change as the manual valve shifts and the resistance of the GMR elements changes. One waveform cycle is produced by one scan through all of the GMR elements in a successive pattern.
The voltage across a load resistor is measured during each clock interval of an electronic shift register, which forms a part of the scanning logic. The scanning pattern continues indefinitely, thus causing a changing stepped voltage to be produced across the load resistor. The voltage across the load resistor will be highest when the GMR elements positioned in the strongest part of the magnetic field are selected. It is lowest when the elements in the weakest field are selected.
Analog filtering optimizes the voltage signal. The position information is contained in the analog voltage signal. The output signal obtained in this fashion is distributed to a processing unit and decoded to produce a pulse-width modulated output signal (PWM) with a duty cycle proportional to the displacement of the manual valve.
The magnet system is carried by a magnet carrier, which is mounted on a housing and adapted to slide relative to the housing in a direction transverse to the direction of movement of the manual valve. A slider post is positioned in a linear slot in the housing and extends into an angled slot guide track in the magnet carrier. The slider post is directly contacted by the manual valve. The guide track and the slider post translate linear movement of the manual valve into a transverse motion of the magnet carrier. In this way, the magnet carrier is adjusted relative to the GMR array. This configuration minimizes space, thereby optimizing packaging geometry.
REFERENCES:
patent: 4592249 (1986-06-01), Lehmann et al.
patent: 4652821 (1987-03-01), Kreft
patent: 4698996 (1987-10-01), Kreft et al.
patent: 5570015 (1996-10-01), Takaishi et al.
patent: 5589769 (1996-12-01), Krahn
patent: 5812330 (1998-09-01), Akada
patent: 5861747 (1999-01-01), Kubinski
patent: 5929631 (1999-07-01), Striker et al.
Butler Susan A.
Gietzen Diane M.
Siciak Raymond Carl
Striker David Lee
Patidar Jay
Shelton Larry I.
Visteon Global Technologies Inc.
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