Engine harmonic cancellation system afterglow mitigation

1. A method for operating an active noise reduction system for a motor vehicle, where there is an active noise reduction system input signal that is related to the vehicle engine operation, and where the active noise reduction system comprises one or more adaptive filters that use a filter coefficient to modify the amplitude and/or phase of a noise cancellation reference signal and output noise reduction signals that are used to drive one or more transducers with their outputs directed to reduce engine noise, where the value of the coefficient is related to an adaptive filter leakage factor, the method comprising:

monitoring changes in the engine speed based on the input signal that is related to the vehicle engine operation; and

in response to changes in the engine speed, modifying the adaptive filter leakage factor;

wherein the adaptive filter leakage factor is reduced to zero in response to a decrease in the engine speed.

2. The method of claim 1 wherein the adaptive filter leakage factor is reduced only after the decrease in the engine speed exceeds a threshold decrease in engine speed over a given period of time.

3. The method of claim 1 wherein the adaptive filter leakage factor is reduced at least until an output is below an estimated level of engine noise.

4. The method of claim 3 wherein the level of engine noise is estimated from the engine load.

5. The method of claim 3 wherein the level of engine noise is estimated from the engine torque.

6. The method of claim 3 wherein the level of engine noise is estimated based on a comparison of the engine operation to previously measured noise levels at different engine operations.

7. The method of claim 1 wherein the adaptive filter leakage factor is modified for an amount of time.

8. The method of claim 7 wherein the amount of time is variable.

9. The method of claim 8 wherein the amount of time is dependent on the change in engine operation.

10. The method of claim 1 further comprising monitoring changes in the engine load, and wherein the adaptive filter leakage factor is modified based on changes to one or both of the engine speed and the engine load.

11. The method of claim 1 where the value of the adaptive filter coefficient is further related to an adaptive filter adaptation rate, and where in response to changes in engine speed, the adaptation rate is modified.

12. The method of claim 11 wherein the modification of the adaptation rate occurs temporarily.

13. The method of claim 11 wherein, in response to changes in engine speed, one or both of the adaptation rate and the leakage factor are modified, where one or both of the amount of such modification and the duration of such modification are dependent on whether the engine speed increases or decreases, the extent of such increase or decrease, and/or the duration of such increase or decrease.

14. A method for operating an active noise reduction system for a motor vehicle, where there is an active noise reduction system input signal that is related to the vehicle engine operation, and where the active noise reduction system comprises one or more adaptive filters that use a filter coefficient to modify the amplitude and/or phase of a noise cancellation reference signal and output noise reduction signals that are used to drive one or more transducers with their outputs directed to reduce engine noise, where the value of the coefficient is related to an adaptive filter leakage factor, the method comprising:

monitoring changes in the engine speed based on the input signal that is related to the vehicle engine operation; and

in response to changes in the engine speed, decreasing the adaptive filter leakage factor, wherein the adaptive filter leakage factor is decreased only after the change in the engine speed exceeds a threshold change in engine speed over a given period of time, wherein the adaptive filter leakage factor is reduced to zero in response to a decrease in the engine speed, and wherein the adaptive filter leakage factor is reduced at least until an output is below an estimated level of engine noise and wherein the level of engine noise is estimated from the engine load.

15. The method of claim 14 where the value of the adaptive filter coefficient is further related to an adaptive filter adaptation rate, and where in response to changes in engine speed, the adaptation rate is temporarily modified.

16. The method of claim 15 wherein, in response to changes in engine speed, one or both of the adaptation rate and the leakage factor are modified, where one or both of the amount of such modification and the duration of such modification are dependent on whether the engine speed increases or decreases, the extent of such increase or decrease, and/or the duration of such increase or decrease.

17. A device configured to control the operation of an active noise reduction system for a motor vehicle, where there is an active noise reduction system input signal that is related to the vehicle engine operation, and where the active noise reduction system comprises one or more adaptive filters that use a filter coefficient to modify the amplitude and/or phase of a noise cancellation reference signal and output noise reduction signals that are used to drive one or more transducers with their outputs directed to reduce engine noise, where the value of the coefficient is related to an adaptive filter leakage factor, the device comprising:

a processor that is configured to:

monitor changes in the engine speed based on the input signal that is related to the vehicle engine operation; and

in response to changes in the engine speed, modify the adaptive filter leakage factor, wherein the adaptive filter leakage factor is reduced to zero in response to a decrease in the engine speed.