Data processing: measuring – calibrating – or testing – Testing system – For transfer function determination
Patent
1996-12-20
1999-01-26
Shah, Kamini
Data processing: measuring, calibrating, or testing
Testing system
For transfer function determination
702 97, 731173, G01D 1800
Patent
active
058647759
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of and apparatus for calibrating rotary position transducers. Such a method and apparatus may be used within an internal combustion engine so as to compensate for systematic errors in measurements of the engine position.
U.S. Pat. No. 5,117,681 describes measuring the positions of teeth on a position sensor for an internal combustion engine by running the engine up to a high speed and then cutting the fuel to the engine. It is assumed that the engine will undergo smooth deceleration. The average velocity of the engine is measured over one or more complete revolutions. Further measurements of velocity are made between consecutive teeth and these measurements are compared with the average measurement. Discrepancies in the velocity measurements are attributed to non-uniformities in the positions of the teeth.
It has been found that even though the measurements are taken under fuel cut conditions, a cyclic variation in the engine speed is still present due to cylinder compressions and piston inertial effects. This causes inaccuracies when comparing intertooth velocities with averaged velocities measured over one or more cycles of the engine.
According to a first aspect of the present invention there is provided a method of calibrating an apparatus for measuring rotational movement, the apparatus comprising a plurality of markers arranged to move past a sensor in response to rotary motion of a first element whose position is to be measured, the method comprising measuring a first rotational speed of the first element between first and second positions separated by less than one revolution and corresponding to a first number of markers passing the sensor, measuring a second rotational speed of the first element between third and fourth positions corresponding to a second number of markers passing the sensor, the third and fourth positions lying between the first and second positions, and correcting an estimate of the distance between the third and fourth positions by comparing the first rotational speed measurement with the second rotational speed measurement.
It is thus possible to determine errors in the positioning of the markers and to use the estimation of the errors to correct subsequent measurements of rotary position and/or speed.
The first element may be a shaft of an internal combustion engine, such as a crankshaft or a cam shaft. Advantageously the first element carries a toothed wheel thereon, the wheel being arranged to rotate with the shaft and the teeth being arranged to pass a sensor.
Preferably the first and second positions are separated by no more than (720/N) degrees where N is the number of cylinders of the internal combustion engine. Advantageously the third and fourth positions are one intertooth separation apart.
Preferably the third and fourth positions are substantially symmetrically disposed about a midpoint between the first and second positions. Advantageously the speed of the engine is monitored so as to ensure that measurements are only taken during periods when the rate of change of acceleration is less than a predetermined threshold.
Advantageously the times, during a single revolution or rotation slightly in excess of a single revolution, at which each one of the teeth passes the sensor are recorded. The measurements of the time may be analysed in conjunction with engine position data so as to determine the relative position of each tooth with respect to a reference tooth and/or the position of each tooth with respect to its neighbours.
Preferably the engine position data is provided by counting the passage of the teeth past the sensor.
According to a second aspect of the present invention there is provided an apparatus for calibrating an apparatus for measuring rotational movement, the apparatus for measuring rotational movement comprising a plurality of markers arranged to move past a sensor in response to rotary motion of a first element whose position is to be measured, the apparatus for calibrating position errors comprising speed m
REFERENCES:
patent: 5117681 (1992-06-01), Dosdall et al.
patent: 5170365 (1992-12-01), Collopy et al.
patent: 5237504 (1993-08-01), Holmes et al.
Bradshaw Benjamin James
Wakeman Anthony Claude
Lucas Industries Public Limited Company
Shah Kamini
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