METHOD AND APPARATUS TO MONITOR POSITION OF A ROTATABLE SHAFT

• US 20090115408A1
• Filed: 10/06/2008
• Published: 05/07/2009
• Est. Priority Date: 11/06/2007
• Status: Active Grant

• Current Assignee: Bayerische Motoren Werke AG, Daimler AG (Mercedes-Benz Group AG), Chrysler Group LLC (Stellantis NV)
• Original Assignee: BMW AG (Bayerische Motoren Werke AG), Daimler AG (Mercedes-Benz Group AG), GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust), Chrysler LLC (Stellantis NV)
• Inventors: West, Stephen T., Gleason, Sean E.
• Granted Patent: US 8,179,127 B2
• Time in Patent Office: Days
• US Class Current: 324/207.250
• CPC Class Codes: G01D 18/001 Calibrating encoders
• CPC Class Codes: G01D 5/2046 by a movable ferromagnetic element, e.g. a core
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G01P 3/44 for measuring angular speed G01P3/56 takes precedence
• CPC Class Codes: G01P 3/46 by measuring amplitude of generated current or voltage in general G01R19/00
• CPC Class Codes: G01P 3/481 of pulse signals

Abstract

A rotatable shaft is equipped with a measurement device that generates output signals corresponding to discrete angular positions of the shaft. Rotational angles of the shaft are measured for a complete rotational period. A true angular velocity of the shaft is determined. Angular velocity is calculated between contiguous pairs of the discrete angular positions. A velocity correction is determined, and a rotational angle error term is determined based upon the velocity correction.

Claims

1. Method for monitoring rotational position of a rotatable shaft, comprising:

generating output signals corresponding to a plurality of discrete rotational angles of the shaft;

monitoring the output signals and elapsed times corresponding to the discrete rotational angles of the shaft for a complete rotation during which rotational speed of the shaft is substantially constant;

determining a true angular velocity of the shaft for the complete rotation during which the rotational speed of the shaft is substantially constant;

calculating angular velocities between contiguous pairs of the discrete rotational angles;

determining a velocity correction based upon the calculated angular velocities and the true angular velocity;

determining an error in measurement of the rotational angle of the shaft based upon the velocity correction; and

determining a rotational angle error term combinable with the discrete rotational angles of the shaft.

2. The method of claim 1, wherein angular velocities are calculated between contiguous pairs of the discrete rotational angles for the complete rotation of the shaft, and wherein a velocity correction is determined for each of the contiguous pairs of discrete rotational angles.

3. The method of claim 2, wherein a rotational angle error term is determined for each of the contiguous pairs of discrete angular positions.

4. The method of claim 2, wherein velocity corrections are determined by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between contiguous pairs of the discrete rotational angles for the complete rotation of the shaft.

5. The method of claim 1, further comprising correcting the discrete rotational angles of the shaft based upon the rotational angle error terms.

6. The method of claim 1, further comprising equipping the shaft with a measurement device operative to generate the output signals corresponding to the plurality of discrete rotational angles of the shaft.

7. The method of claim 6, comprising determining the rotational angle error term for the measurement device based upon the velocity correction.

8. Method for measuring a true rotational angle of a rotatable shaft, comprising:

fixedly attaching a resolver rotor to the shaft;

providing a resolver stator to generate a resolver stator signal corresponding to rotational angles at discrete angular positions of the rotor;

rotating the shaft and monitoring the resolver stator signal;

measuring the rotational angles and elapsed times therebetween for a complete rotation of the shaft during which rotational speed of the shaft is substantially constant;

determining a true angular velocity of the shaft for the complete rotation during which the rotational speed of the shaft is substantially constant;

calculating an angular velocity between contiguous pairs of the discrete angular positions for the complete rotation of the shaft;

determining a velocity correction between the calculated angular velocity and the true angular velocity;

determining a rotational angle error term based upon the velocity correction; and

correcting the measured rotational angle with the rotational angle error term.

9. The method of claim 8, wherein a velocity correction is determined for each of the contiguous pairs of discrete rotational angles.

10. The method of claim 9, wherein the rotational angle error term is determined for each of the contiguous pairs of discrete angular positions.

11. The method of claim 8, comprising determining the velocity correction by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between each of the contiguous pairs of the discrete angular positions for the complete rotation.

12. The method of claim 11, further comprising measuring rotational angles of the shaft corresponding to the discrete angular positions for a plurality of complete rotations during which the rotational speed of the shaft is substantially constant.

13. Method to determine an error in measurement of an angular position of a rotatable shaft, comprising:

determining rotational angles corresponding to discrete angular positions of the shaft;

rotating the shaft and measuring the rotational angles corresponding to the discrete angular positions for a complete rotation of the shaft during which rotational speed of the shaft is substantially constant;

determining a true angular velocity of the shaft for the complete rotation during which rotational speed of the shaft is substantially constant;

calculating angular velocities between contiguous pairs of the discrete angular positions for the complete rotation of the shaft;

determining a velocity correction between the calculated angular velocity and the true angular velocity for each of the contiguous pairs of discrete angular positions; and

determining a rotational angle error term based upon the velocity correction for each of the contiguous pairs of discrete angular positions.

14. The method of claim 13, wherein the velocity corrections are determined by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between each of the contiguous pairs of the discrete angular positions for the complete rotation.

15. The method of claim 14, further comprising correcting the measured rotational angles of the shaft based upon the rotational angle error terms.