Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-06-23
2001-01-09
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C341S015000, C123S406580
Reexamination Certificate
active
06172500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetic sensors and specifically to magnetic sensors of the type wherein a magnetic transducer reads a ferromagnetic target configured in a unique pattern to yield information about a mechanical application.
2. Discussion of the Related Art
Many types of magnetic sensors are known in the art. Many of these use Hall effect or magnetoresistive (MR) transducers combined within a magnetic or ferromagnetic target having a pattern of features keyed to details within a mechanical apparatus being monitored by the magnetic sensor. These features may be the magnetic signature of a magnetized target or the presence or absence of ferromagnetic metal in various sizes on a metal target placed near the transducer. Exemplary of one such system is U.S. Pat. No.5,469,054 to Bicking.
When the metal target is circular in shape the sensing system is called a “gear tooth sensor” from the resemblance of the target to a toothed mechanical gear. These gear tooth sensors are often used in the automotive arts wherein the target is linked to crankshaft for use in engine control. Sensor designers continually seek refinement of the target system to improve engine control.
SUMMARY OF THE INVENTION
The present invention provides a scheme of gear tooth sensing wherein the target is optimized to provide a hard edge transition, i.e. a tooth-to-slot or slot-to-tooth transition at least every 30° for use in fuel injection, spark ignition, and misfire control. Three different 30° segment configurations are provided which have features optimally configured to provide a sufficient number of timing signals without providing so many feature transitions that the engine control computer is over loaded. The 30° segments are ordered to provide a unique feature pattern over any 90° segment of the target for correct crank angle detection.
The target is optimized to provide unambiguously readable features, i.e. teeth and slots, which provide consistent magnetic signal signals from the transducer. The features are of only two sizes, wide and narrow. Therefore, according to the present invention, the narrow slots are made sufficiently wide to avoid fringing effects so that a narrow slot will give the same level of transducer output as a wide slot. Also, to be unambiguously readable the size of the large features are approximately three times the size of the small features in degree angles.
While the numbers and sizes of the specific embodiments herein may refer to specific engine types and sensor configurations it will be appreciated that the principles elucidated herein can be applied to a variety of mechanical apparatus and their sensing systems.
REFERENCES:
patent: 5264789 (1993-11-01), Braun et al.
patent: 5469054 (1995-11-01), Bicking
Abeyta Andrew A.
Honeywell International Inc
Norris Roland W
Snow Walter E.
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