Active noise control system and active vibration control system

Abstract

An active noise control system includes a filter coefficient updating unit including an imaginary term estimator. The imaginary term estimator estimates an imaginary term Ie from a real term Re of an error signal e supplied from a microphone. The filter coefficient updating unit updates a filter coefficient W of an adaptive filter based on the imaginary term Ie, the real term Re, and a corrective signal supplied from a reference signal corrector. The filter coefficient updating unit updates the filter coefficient W successively in respective sampling periods.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an active noise control system (ANC) as a basis of the present invention;

FIG. 2A is a diagram showing time-dependent changes of an error signal which occur when the active noise control system shown in FIG. 1 operates;

FIG. 2B is a diagram showing time-dependent changes of an updating quantity for a filter coefficient which occur when the active noise control system shown in FIG. 1 operates;

FIG. 3 is a block diagram of an active noise control system according to an embodiment of the present invention;

FIG. 4A is a diagram showing time-dependent changes of an error signal which occur when the active noise control system shown in FIG. 3 operates;

FIG. 4B is a diagram showing time-dependent changes of an updating quantity for a filter coefficient which occur when the active noise control system shown in FIG. 3 operates;

FIG. 5 is a block diagram of an imaginary term estimator shown in FIG. 3 which comprises a differentiator and a first filter;

FIG. 6 is a block diagram of an imaginary term estimator shown in FIG. 3 which comprises a differentiator and a second filter;

FIG. 7 is a block diagram of an imaginary term estimator shown in FIG. 3 which comprises a differentiator, a third filter, and a reference signal corrector;

FIG. 8 is a block diagram of a modified active noise control system which is similar to the active noise control system shown in FIG. 5 except that it includes a reference signal generating means;

FIG. 9 is a block diagram of an imaginary term estimator shown in FIG. 3 which comprises an integrator and a first filter; and

FIG. 10 is a block diagram of an active vibration control system according to an embodiment of the present invention.

Claims

1. An active noise control system comprising: an adaptive filter for being supplied with a reference signal that is correlated to first noise generated by a noise source on a vehicle, and generating a control signal based on the reference signal;noise output means for outputting third noise based on said control signal in order to cancel out second noise generated in the vehicle based on said first noise;noise detecting means for generating an error signal based on canceling error noise between said second noise and said third noise;reference signal correcting means for correcting said reference signal based on sound transfer characteristics from said noise output means to said noise detecting means, and outputting the corrected reference signal as a corrective signal; andfilter coefficient updating means, having an imaginary term estimator for estimating an imaginary term of said error signal based on the error signal which comprises a real term, for updating a filter coefficient of said adaptive filter in order to minimize said error signal, based on said imaginary term estimated by said imaginary term estimator, said real term, and said corrective signal.

2. An active noise control system according to claim 1, wherein said imaginary term estimator has a real term differentiator for calculating a time differential value of said real term, and estimates said imaginary term based on the time differential value calculated by said real term differentiator.

3. An active noise control system according to claim 1, wherein said imaginary term estimator has a real term integrator for calculating a time integral value of said real term, and estimates said imaginary term based on the time integral value calculated by said real term integrator.

4. An active noise control system according to claim 2, wherein said imaginary term estimator further has a first filter for dividing the time differential value calculated by said real term differentiator by an angular frequency corresponding to the frequency of said error signal and multiplying the time differential value by −1.

5. An active noise control system according to claim 2, wherein said imaginary term estimator further has a first filter having characteristics represented by the reciprocal, multiplied by −1, of an angular frequency corresponding to the frequency of said error signal, for passing therethrough said time differential value calculated by said real term differentiator.

6. An active noise control system according to claim 3, wherein said imaginary term estimator further has a first filter for multiplying the time integral value calculated by said real term integrator by an angular frequency corresponding to the frequency of said error signal.

7. An active noise control system according to claim 3, wherein said imaginary term estimator further has a first filter having characteristics represented by an angular frequency corresponding to the frequency of said error signal, for passing therethrough the time integral value calculated by said real term integrator.

8. An active noise control system according to claim 1, wherein said imaginary term estimator has a second filter for dividing said corrective signal by an angular frequency corresponding to the frequency of said error signal and multiplying said corrective signal by −1.

9. An active noise control system according to claim 1, wherein said imaginary term estimator has a second filter having characteristics represented by the reciprocal, multiplied by −1, of an angular frequency corresponding to the frequency of said error signal, for passing said corrective signal therethrough.

10. An active noise control system according to claim 1, wherein said imaginary term estimator has a third filter for dividing said reference signal by an angular frequency corresponding to the frequency of said error signal and multiplying said reference signal by −1, and a reference signal corrector for correcting the divided and multiplied reference signal based on said sound transfer characteristics.

11. An active noise control system according to claim 1, wherein said imaginary term estimator has a third filter having characteristics represented by the reciprocal, multiplied by −1, of an angular frequency corresponding to the frequency of said error signal, for passing said corrective signal therethrough, and a reference signal corrector for correcting the reference signal having passed through said third filter based on said sound transfer characteristics.

12. An active noise control system according to claim 2, wherein when said control signal and said corrective signal are generated, said third noise is output, said error signal is detected, and said filter coefficient is updated successively in each given sampling period, said real term differentiator calculates said time differential value by dividing, by said sampling period, the difference between the real term of the error signal that is input in a present sampling cycle and the real term of the error signal that is input in a preceding sampling cycle.

13. An active noise control system according to claim 12, wherein if said sampling period is a fixed sampling period, said imaginary term estimator estimates said imaginary term by dividing said difference by said fixed sampling period and the frequency of said error signal and multiplying said difference by −1.

14. An active noise control system according to claim 12, wherein if said sampling period is a fixed sampling period, said imaginary term estimator estimates said imaginary term by dividing said difference by said fixed sampling period and passing the divided difference through a first filter having characteristics represented by the reciprocal, multiplied by −1, of an angular frequency corresponding to the frequency of said error signal.

15. An active noise control system according to claim 12, wherein if said sampling period is a variable sampling period, said imaginary term estimator estimates said imaginary term by multiplying said difference by a number representing the reciprocal of the product of said variable sampling period and the frequency of said error signal and by −1.

16. An active noise control system according to claim 12, wherein if said sampling period is a variable sampling period, said imaginary term estimator estimates said imaginary term by dividing said difference by said variable sampling period and passing the divided difference through a first filter having characteristics represented by the reciprocal, multiplied by −1, of an angular frequency corresponding to the frequency of said error signal.

17. An active noise control system according to claim 3, wherein when said control signal and said corrective signal are generated, said third noise is output, said error signal is detected, and said filter coefficient is updated successively in each given sampling period, said real term integrator calculates said time integral value by multiplying, by said sampling period, the sum of the real term of the error signal that is input in a present sampling cycle and the real term of the error signal that is input in a preceding sampling cycle.

18. An active noise control system according to claim 17, wherein if said sampling period is a fixed sampling period, said imaginary term estimator estimates said imaginary term by multiplying said sum by said fixed sampling period and the frequency of said error signal.

19. An active noise control system according to claim 17, wherein if said sampling period is a fixed sampling period, said imaginary term estimator estimates said imaginary term by multiplying said sum by said fixed sampling period and passing the multiplied sum through a first filter having characteristics represented by an angular frequency corresponding to the frequency of said error signal.

20. An active noise control system according to claim 17, wherein if said sampling period is a variable sampling period, said imaginary term estimator estimates said imaginary term by dividing said sum by a number representing the reciprocal of the product of said variable sampling period and the frequency of said error signal.

21. An active noise control system according to claim 17, wherein if said sampling period is a variable sampling period, said imaginary term estimator estimates said imaginary term by multiplying said sum by said variable sampling period and passing the multiplied sum through a first filter having characteristics represented by an angular frequency corresponding to the frequency of said error signal.

22. An active noise control system according to claim 1, wherein said noise source comprises an engine on said vehicle;said second noise comprises noise produced in a passenger compartment of said vehicle;said noise output means comprises a speaker disposed in said passenger compartment; andsaid noise detecting means comprises a microphone disposed in said passenger compartment.

23. An active vibration control system comprising: an adaptive filter for being supplied with a reference signal that is correlated to first vibration generated by a vibration source on a vehicle, and generating a control signal based on the reference signal;vibration output means for outputting third vibration based on said control signal in order to cancel out second vibration generated in the vehicle based on said first vibration;vibration detecting means for generating an error signal based on canceling error vibration between said second vibration and said third vibration;reference signal correcting means for correcting said reference signal based on vibration transfer characteristics from said vibration output means to said vibration detecting means, and outputting the corrected reference signal as a corrective signal; andfilter coefficient updating means, having an imaginary term estimator for estimating an imaginary term of said error signal based on the error signal which comprises a real term, for updating a filter coefficient of said adaptive filter in order to minimize said error signal, based on said imaginary term estimated by said imaginary term estimator, said real term, and said corrective signal.