Speed sensor instability detection
A speed sensor instability detection and correction system for use with a vehicle includes a speed sensor output variation extractor monitoring and recording change in output of a speed sensor over time. A speed sensor output variation comparison module detects speed sensor instability based on a comparison between the speed sensor output variation and a predetermined threshold. An output speed determination module selectively determines output speed in alternative ways based on whether speed sensor instability is detected.
1. A method for detecting wheel slippage based on output speed of a wheeled vehicle, comprising:
determining whether output speed instability is detected;
generating a median filtered output speed when output speed instability is detected; and
determining whether wheel slippage is present based on the median filtered output speed when output speed instability is detected.
2. The method of claim 1 wherein said determining whether output speed instability is detected includes monitoring change in a pulley speed sensor output signal over time.
3. The method of claim 2 wherein said determining whether output speed instability is detected further includes making a comparison between change in pulley speed over time and a predetermined threshold.
4. The method of claim 3 wherein said determining whether output speed instability is detected further includes detecting instability based on results of the comparison over time.
5. The method of claim 1 wherein said generating a median filtered output speed further includes filtering an output signal of a pulley speed sensor with a median filter.
6. The method of claim 1 wherein said determining whether wheel slippage is present includes calculating speed ratio based on the median filtered output speed.
7. The method of claim 6 wherein said determining whether wheel slippage is present further includes calculating wheel axle torque based on the speed ratio.
8. The method of claim 7 wherein said determining whether wheel slippage is present further includes:
calculating an output derivative based on the median filtered output speed; and
calculating an expected derivative based on the wheel axle torque.
9. The method of claim 8 wherein said determining whether wheel slippage is present further includes comparing the output derivative to the expected derivative.
10. The method of claim 1 further comprising:
generating a Kalman filtered output speed when output speed instability is not detected; and
determining whether wheel slippage is present based on the Kalman filtered output speed when output speed instability is not detected.