JP2734319B2 - Noise reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction apparatus for canceling a periodic noise synchronized with an engine, such as an indoor noise or a muffler noise, equipped with an internal combustion engine by an adaptive filter.

[0002]

2. Description of the Related Art In recent years, adaptive control apparatuses have been attracting attention as highly flexible controls for controlling machines and the like while adapting to changes in the environment. This has the advantage that the configuration is simplified.

Hereinafter, an example of a conventional noise reduction device will be described with reference to the drawings. FIG. 3 shows a configuration of a conventional noise reduction device.

[0004] In FIG. 3, reference numeral 20 denotes a noise source closely correlated with the engine speed, such as a muffler sound in a vehicle interior or exhaust sound of a muffler; 21, an engine rotation angle sensor;
Is a pulse generator, 23 is an adaptive filter that produces a sound having the same sound pressure and the opposite phase to noise at the position to be silenced, 24 is an amplifier, 25 is a speaker, and 26 is an error arranged near the position to be silenced. 27 is an amplifier, 28 is an FIR filter having a transfer function between the speaker 25 and the error detection sensor 26 as a coefficient, and 29 is a coefficient updater for updating the coefficient of the adaptive filter 23. It is.

Next, the above conventional example will be described. In FIG. 3, a pulse generator 22 generates a pulse train from an engine rotation angle sensor 21 such as an ignition pulse or a crank angle pulse having a strong correlation with a noise source 20 such as an engine noise. Here, as shown in Corona Corp. “CAI Digital Signal Processing”, Hidefumi Obata, pp. 134-136, the pulse generator 22 converts the period of the periodic noise into an adaptive filter 23.
Is generated by multiplying the number of pulses by m or dividing it by k in a cycle divided by the number of taps. (M and k are integers) Adaptive filter 2
Reference numeral 3 denotes a filter that sequentially outputs the values of the taps of the adaptive filter using the pulse generated by the pulse generator 22 as a trigger, and returns to the first tap of the filter again to output to the speaker 25 when the filter has been output to the end. The error detection sensor 26 detects the difference between the output of the speaker 25 and the noise from the noise source 20 and inputs the difference to the coefficient updater 29. Further, the signal of the pulse generator 20 is a FI which has a transfer function between the speaker 25 and the error detection sensor 26 as a coefficient.
It passes through an R filter 28 and becomes one input of a coefficient updater 29. The coefficient updater 29 updates the coefficient of the adaptive filter 23 so that the signal of the error detection sensor 26 is minimized. As described above, the output of the adaptive filter 23 is added to the periodic noise, the added error is multiplied by the weight coefficient by the coefficient updater 29, and the value of the corresponding tap Wi of the adaptive filter 23 is calculated by the following equation (1). Update.

W _{n + 1} (i) = W _n (i) + μ × e × y (1) i = (n) _mod N where W _n : time n μ: step size parameter (to gain) E): Addition error when the output of the adaptive filter is added to the periodic noise y: Output of the FIR filter (Nth order) modN: Integer value modulating N In this way, even in the conventional noise reduction device, Noise can be reduced.

[0007]

However, in the above-described conventional noise reduction apparatus, when the periodic noise is mixed with the aperiodic noise, the SN ratio is small, so that the periodic noise cannot be sufficiently eliminated. There was a problem.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide an excellent noise reduction device which can mitigate periodic noise even from non-periodic noise. Things.

[0009]

According to the present invention, there is provided a periodic signal separator for separating only a periodicity error from an error detection sensor signal which is a difference between input noise and an output of an adaptive filter. It is provided with a gain correction means for determining the output gain of the signal separator, a gain multiplier, and a coefficient updater for setting the coefficient of the adaptive filter from the periodicity error separated by the periodic signal separator.

[0010]

Therefore, according to the present invention, since only the periodic error can be eliminated from the periodic and aperiodic errors, the periodic error can be eliminated without being affected by the aperiodic error. Can be deleted.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the noise reduction device of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a noise reduction device according to the present invention. In FIG. 1, reference numeral 1 denotes a noise source having a close correlation with the engine speed, such as a muffler sound in a vehicle interior and a muffler exhaust sound. 2 is an engine rotation angle sensor, 3
Is a pulse generator. Reference numeral 4 denotes an adaptive filter for producing a sound having the same sound pressure and the opposite phase to the noise at the position to be silenced. The output of the adaptive filter 4 is amplified by the amplifier 5 and is output from the speaker 6 in the opposite phase to the noise and the same sound pressure. A sound is produced. Reference numeral 7 denotes an error detection sensor that is arranged near the position where noise is to be silenced and detects an error signal obtained by adding the input noise as noise and the output of the speaker 6, such as a microphone and a vibration pickup. An amplifier 8 amplifies the output of the error detection sensor 7. Reference numeral 9 denotes a periodic signal separator, which separates the output of the error detection sensor 7 into a periodic error and an aperiodic error. 1
0 is a gain correction means, which calculates the gain so as to minimize the square value of the difference between the error detection sensor 7 and the output of the periodic signal separator 9 over one cycle. Reference numeral 11 denotes a gain multiplier, which outputs a gain correction means 1 to the output of the periodic signal separator 9.
It multiplies the calculation result of 0. 12 is a speaker 6
With the transfer function between the sensor and the error detection sensor 7 as a coefficient
An R filter 13 is a coefficient updater that updates the coefficients of the adaptive filter 4 based on the outputs of the gain multiplier 11 and the FIR filter 12.

Next, the operation of the above embodiment will be described. In FIG. 1, when noise synchronized with the engine speed such as engine noise is generated from the noise source 1, an error signal obtained by adding the input noise as the noise and the output of the speaker 6 is detected by the error detection sensor 7. Is done.
The error output of the error detection sensor 7 is separated into a periodic error and an aperiodic error by the periodic signal separator 9, and only the periodic error is input to the gain multiplier 11. The periodic signal separator 9 can be realized by a tracking filter using a synchronous filter using a pulse obtained by the pulse generator 3 or a switched capacitor filter.

An example of the periodic signal separator 9 shown in FIG. 2 will be described. In FIG. 2, the adaptive filter 14 is updated by multiplying a weight coefficient by a coefficient updating unit 16 so that an error obtained by adding the output of the adaptive filter 14 to the input noise through the delay element 15 becomes zero. For example, an FIR filter is used for the adaptive filter 14, and a general LMS algorithm is used for the update algorithm. As a result,
The periodic noise is obtained as an output of the adaptive filter 14.

The gain correction means 10 includes an error detection sensor 7
The gain is calculated so as to minimize the sum of squares of the difference over one cycle between the output of the periodic signal separator 9 and the output of the periodic signal separator 9, and the result is output to the gain multiplier 11. The gain multiplier 11 is based on the result of the gain correction means 10 and is used as the periodic signal separator 9.
Is multiplied by its gain. Thereby, the convergence of the periodic signal separator 9 is accelerated.

The pulse generator 3 generates a pulse at a period obtained by dividing the longest period among the periodic noises to be silenced by the number of taps of the adaptive filter 4. The period of this noise is closely correlated with the engine speed, and is obtained from the engine rotation angle sensor 2 which indicates the engine speed such as the engine ignition timing and the crank signal. If the number of pulses of the engine rotation angle sensor 2 is sufficiently larger than the period of the periodic noise, the pulse generator 3 may divide the frequency, and the number of pulses of the engine rotation angle sensor 2 is smaller than the number of taps of the adaptive filter 4. In this case, the frequency may be multiplied by PLL control or the like. According to this method, since the periodic noise has a deep correlation with the output of the engine rotation angle sensor 2, it can sufficiently cope with the periodic fluctuation of the noise. The adaptive filter 4 is a filter that sequentially outputs the tap values of the adaptive filter 4 using the pulse generated by the pulse generator 4 as a trigger, and returns to the first tap when the final tap is output, and outputs the same.

On the other hand, the coefficient updater 13 extracts the periodicity error extracted by the periodic signal separator 9 and the output gain of which has been adjusted by the gain correcting means 10 and the transfer function between the speaker 6 and the error detection sensor 7 as a coefficient. , The weight coefficient is sequentially updated from the signal of the FIR filter 12 according to the following equation (1). Here, since the adaptive filter 4 basically cancels out only the periodicity error determined by the pulses of the engine rotation angle sensor 2 and the pulse generator 3, mixing of the non-periodicity error is not preferable due to malfunction. However, in this embodiment, since only the periodic error can be extracted by the periodic signal separator 9, malfunction due to the non-periodic error is eliminated.

As described above, according to the above-described embodiment, by providing an adaptive filter that outputs so as to cancel out only periodic noise, malfunction due to mixing of non-periodic noise is eliminated, convergence is fast, and noise reduction error is achieved. Can also be reduced.

[0019]

According to the present invention, as is clear from the above embodiment, only a periodic error is extracted by a periodic signal separator from an error signal which is a difference between noise including periodic noise and an output of an adaptive filter. Since the adaptive filter is operated by the error signal, the periodicity error included in the error signal can be quickly canceled.

Further, according to the present invention, the gain is calculated from the output of the error detection sensor and the output of the periodic signal separator, and the result is multiplied by the output of the periodic signal separator, thereby obtaining the periodic signal separator. Has a faster effect, and the noise can be reduced more quickly.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a noise reduction device according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram of a periodic signal separator of the apparatus.

FIG. 3 is a configuration block diagram of a conventional noise reduction device.

[Description of Signs] 1 Noise source 2 Engine rotation angle sensor 3 Pulse generator 4 Adaptive filter 5 Amplifier 6 Speaker 7 Error detection sensor 8 Amplifier 9 Periodic signal separator 10 Gain correction means 11 Gain multiplier 12 FIR filter 13 Coefficient updater

Claims (6)

(57) [Claims] 1. A rotation angle sensor for detecting an engine speed of an internal combustion engine, a pulse generator for generating a pulse signal from the rotation angle sensor, an error detection sensor installed near a position to be silenced, and a silencer. An adaptive filter that generates a signal having the same phase and the same sound pressure with respect to the noise at the position where the noise is generated ; a speaker that outputs a signal for canceling the noise; and the output of the pulse generator is applied to the speaker and the error detection sensor. And an error based on the output of the pulse generator.
A periodic signal separator for separating a periodic signal from a signal from the detection sensor , and an output of the periodic signal separator and the error detection.
From the output of the output sensor according to the amplitude level of the periodic signal.
And gain correction means for calculating the gain, the gain correction manually
The output of the periodic signal separator is obtained based on the calculation result of the stage.
A gain multiplier and outputting the multiplying in, the gain multiplication
The gain-adjusted periodic signal output from the calculator and the F
At the position where sound is to be silenced from the output signal of the IR filter.
The coefficients of the adaptive filter are sequentially changed so that the noise reduction becomes maximum.
A noise reduction device comprising: a coefficient updater that determines and updates the next . 2. The noise reduction device according to claim 1, wherein the number of pulses per cycle of the rotation angle sensor is equal to or an integer multiple of the number of taps of the adaptive filter. 3. The noise reduction device according to claim 1, wherein the pulse generator has a function of multiplying or dividing the rotation angle sensor signal. 4. The noise reduction device according to claim 1, wherein the periodic signal separator is a tracking filter that separates a periodic signal having a strong correlation with the engine speed. 5. The periodic signal separator comprises a delay element, an adaptive filter, and a weight coefficient multiplier for updating a filter coefficient of the adaptive filter so as to minimize a difference between an output of the delay element and an output of the adaptive filter. The noise reduction device according to claim 1, wherein the noise reduction is performed. 6. The noise reduction device according to claim 1, wherein the gain correction means determines an output gain of the periodic signal separator that minimizes a sum of squares of a difference between an output of the error detection sensor and an output of the periodic signal separator. .