JP2501715B2 - Noise control 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 control device for eliminating noise from a muffler of an automobile and outputting a signal having an anti-phase equal sound pressure from a speaker. Particularly, the present invention relates to a noise reduction effect in a space. The purpose is to prevent variations in quantity.

[0002]

2. Description of the Related Art Conventionally, a passive muffler such as a muffler has been used to reduce noise generated from an internal combustion engine, etc., but improvements have been made in terms of size, muffling characteristics and the like. On the other hand, the noise generated from the sound source
An active noise control device has been proposed which outputs a compensation sound of equal sound pressure from a speaker to cancel noise. By the way, the frequency characteristics or the stability of the active noise control device itself are not sufficient, and its practical use has been delayed. However, as a result of the recent development of signal processing technology using digital circuits and expansion of the frequency range to be handled, many practical noise control devices have been proposed (for example, Japanese Patent Laid-Open No. 63-311396).

This is because a noise source microphone installed upstream of the duct detects the noise, and a signal processing circuit outputs a signal of opposite phase and equal sound pressure to the noise from the speaker installed downstream of the duct, and the mute result is output. It is a so-called two-microphone / one-speaker type active noise control device in which a feedback system for detecting and feeding back by a microphone for a sound deadening point is combined with a feed-forward system.

[0004]

By the way, in the conventional noise control device, since it is preferable that the noise is silenced at the place where the speaker is installed, the microphone for detecting the silenced result is provided in the vicinity of the speaker. It was being done.
However, since it is provided only in the vicinity, information on the residual noise output from the microphone cannot be obtained at a location away from the muffler, so the amount of silencing is not always uniform, and the silencing effect is not effective in a part of the space. There was a problem that there was a bias.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device in which the effect of silencing is less locally biased.

[0006]

In order to solve the above-mentioned problems, the present invention is arranged near the exit of a tail pipe that emits noise at the end pipe of a muffler that suppresses the detoning noise of the exhaust gas of an automobile. An actuator, a plurality of microphones, and a synthesizing circuit are provided in a noise control device that eliminates the noise of.

The actuator outputs an erasing sound having a sound pressure opposite in phase to the noise of the tail pipe. The plurality of microphones are respectively installed at least in the vicinity of the actuator, at a certain distance from the actuator, and at a position on the back side of the actuator where leaked noise exists.
The residual noise from which noise has been eliminated as an error signal.
It

[0008] The combining circuit of the plurality of microphones
This is used to weight the error signals and combine them to eliminate noise.
Feed back the weighted composite signal.

[0009]

According to the noise control device of the present invention, the actuator outputs the erasing sound having an equal phase antiphase with the noise of the tail pipe. The microphones are installed at least at positions in the vicinity of the actuator, at a certain distance from the actuator, and at the position on the back side of the actuator where leaked noise exists, and the residual sound in each part of the automobile is measured. The outputs are combined by the combining circuit based on the silencing contributions of the plurality of microphones, and the adaptive filter forms a compensation signal based on the combined signal. That is, by averaging the sensor inputs of the erasing points by synthesizing and synthesizing multiple points, the muffling effect can be obtained not only in the vicinity of the tail pipe but also in a distant place, and the unevenness of the muffling effect in the entire vehicle can be prevented and uniform. You can get a good muffling effect.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a noise control device which is a premise of an embodiment of the present invention. The noise control device shown in this figure includes an actuator 20 that eliminates noise emitted from a tail pipe 2 that is a terminal pipe of a muffler 1 that eliminates the explosion noise of an automobile exhaust, a noise from the tail pipe 2, the noise and the actuator. Three microphones 5-1 and 5- arranged to supplement residual noise with the elimination sound of the anti-phase equal sound pressure emitted from 20 as an error signal and to be described later.
2 and 5-3 and a signal to the actuator 20 are converted from a digital signal to an analog signal or amplified, and an analog signal from the microphones 5-1, 5-2 and 5-2 is converted to a digital signal. FIR (Finite) that inputs and reproduces a reproduced noise signal, which will be described later, as a controlled signal and forms and outputs a compensating sound that eliminates noise through the interface 6.
Impulse Response), and a coefficient updating means for inputting a combined signal of error signals from the microphones 5-1, 5-2 and 5-3 to update the FIR filter coefficient of the adaptive filter 7. 8 and the output of the adaptive filter 7 to normalize the filter coefficient of the coefficient updating means 8 and the interface 6, actuator 20, microphone 5
1, 5-2 and 5-3, the first transfer characteristic simulating means 9 simulating the transfer characteristics up to the coefficient updating means 8 and the compensation signal of the adaptive filter 7 are inputted, and the transfer characteristic simulating means 9 is inputted.
Second transfer characteristic simulating means 10 having the same transfer characteristic simulating means 8 as described above, and the second transfer characteristic simulating means 1
0 output signal and microphones 5-1, 5-2 and 5-
A difference signal calculating means 11 for calculating a difference signal between the output signal of No. 3 and the combined signal and forming this difference signal as a reproduced noise signal to the adaptive filter 7 and the first transfer characteristic simulating means 9.
And The adaptive filter 7, the coefficient updating means 8, the first transfer characteristic simulating means 9, the second transfer characteristic simulating means 10 and the difference signal calculating means 11 are constituted by a digital signal processor (DSP).

The actuator 20 includes two speakers 3 and 4, an enclosure 21 that seals the rear portions of the two speakers 3 and 4, and a muffled sound emitted from the front surfaces of the two speakers 3 and 4 of the tail pipe 2. It consists of an erasing sound guide section 22 leading to the exit. FIG. 2 is a diagram showing the arrangement of the microphones of FIG. As shown in FIGS. 3A and 3B, in the rear partial view of the automobile as viewed from above or from the front, the first microphone 5-1 is installed at the outlet of the tail pipe 2 and is similar to a conventional installation place. . The second microphone 5-2 is installed at a position of about 1 m in the opposite lateral direction from the first microphone 5-1. Furthermore the third
The microphone 5-3 is installed between the actuator 20 and the muffler 1 due to noise that leaks from the space generated between the tail pipe 2 and the erase sound guide portion 22 and turns around. The above microphones 5-1, 5-2 and 5-3
The above arrangement is an example, and it may be provided in various places.

FIG. 3 is a diagram showing a circuit for synthesizing microphone outputs. The synthesizing circuit 6-10 shown in this figure includes an adding circuit 6-11 for adding signals from the microphones 5-1, 5-2 and 5-3, and an inverting circuit 6 for inverting the output of the adding circuit 6-11. -12 and the adder circuit 6-11
Adjust the resistors R1, R2 and R3 of the microphone 5
And a multiplexer <br/> forming adjusting means 6-13 for weighting synthesis of the output of -1,5-2 and 5-3. The synthesis adjusting means 6-13
Is adjusted at the beginning, and the microphones 5-1, 5-2 and 5 are
-3 resistance R of the adder circuit according to the contribution to muffling the noise
The resistance values of 1, R2 and R3 are changed. The signals Sm1, Sm2 from the microphones 5-1, 5-2 and 5-3,
Sm3 is weighted and combined and output as Sm.

The transfer characteristic Hd1 of the first transfer characteristic simulating means 9 and the second transfer characteristic simulating means 10 is determined as follows. Stop the noise emission from the tail pipe 2,
Instead of the adaptive filter 7, white noise is output from that position, and the actuator 20, the interface 6,
Via the microphones 5-1, 5-2 and 5-3 and the interface 6, the transfer characteristic Hd1 of the second transfer characteristic simulating means 10 is set so that the output signal of the difference signal calculating means 11 becomes zero.
To determine Hd1 thus obtained as the first
Transfer characteristic simulating means 9 and second transfer characteristic simulating means 10
Set to.

In the coefficient updating means 8, the FIR filter coefficient (Ck (n); k: number of stages) of the adaptive filter 7 is obtained from the following equation by the least square method. Ck (n) = Ck (n-1) + (Sm (n) .alpha.) / Te (n + k-1) (1) where α is the convergence coefficient and Sm (n) is the microphone 5-
The combined signal of 1, 5-2 and 5-3, Te (n + k-1) is the first
Is a normalized signal from the transfer characteristic simulating means 9, and n is an ordinal number of the digital signal.

A series of operations of the above noise control device will be described. The average transfer characteristic Hd from the output of the adaptive filter 7 to the microphone 5 and the average transfer characteristic Hm from the microphones 5-1, 5-2 and 5-3 to the filter coefficient updating means 8 are set from the tail pipe 2 as a noise source. Let Hnoise be the average transfer characteristic up to the microphones 5-1, 5-2 and 5-3. The average transfer characteristics Hd, Hm,
Hnoise is for each microphone 5-1, 5-2 and 5-
The transfer characteristics Hd, Hm, and Hnoise of No. 3 may be obtained by weighting the contribution of silencing the noises of the microphones 5-1, 5-2, and 5-3. Further, the noise signal from the tail pipe 2 is Sn, the output signals from the microphones 5-1, 5-2 and 5-3 are Sm1, Sm2 and Sm3, the compensation signal from the adaptive filter 7 is Sc, and the microphone 5 Let the input signal Sm of the coefficient updating means 8 which is the combined output from -1, 5-2 and 5-3 and the difference signal that is the output of the difference signal calculating means 11 be Se . Here, the difference signal Se will be
Used as a noise reproduction signal. Further, the transfer characteristic Hd1 simulated by the first transfer characteristic simulating means 9 and the second transfer characteristic simulating means 10 is Hd1 = Hd.Hm (2), and the microphones 5-1, 5-2 and 5-3 are provided. The signal Sm0 detected at is as follows.

Sm0 = Sn.Hnoise + Sc.Hd (3) The noise reproduction signal which is the input signal of the adaptive filter 7 and the like, and the difference signal Se which is the calculation result in the difference signal calculating means 125 is From the above equations (2) and (3), it is obtained as follows. Se = Sm0.Hm-SC.Hd1 = (Sn.Hnoise + Sc.Hd) .Hm-SC.Hd.Hm = (Sn.Hnoise + Sc.Hd-SC.Hd) .Hm = Sn.Hnoise.Hm (4) ) Is formed as.

The input signal Sm of the coefficient updating means 8 becomes Sm = Hm.Sm0 (5), and the other input signal Te becomes the noise reproduction signal Se.
Then, the transfer characteristic Hd1 is calculated by the first transfer characteristic simulating means 9.
Required. In adaptive filter 7, coefficient updating
Since the filter coefficient is changed by the means 8 so that this input signal Sm becomes zero, the compensation signal Sc which is the output signal of the adaptive filter 7 has Sm = 0, that is, Sm0 = 0.
Is determined from the above equation (2) as follows.

Sc ≈−Sn · Hnoise / Hd (5)

[0019]

As described above, according to the present invention, a plurality of microphones are respectively installed at a position near the actuator, a position separated from the actuator by a certain distance, a position on the back side of the actuator where leaked noise exists, and the like. Then, the residual sound in each part of the automobile is measured, and the output is combined based on the muffling contribution of each microphone to form a compensating signal to muffle the noise. The sound deadening effect can be obtained even in a place, the bias of the sound deadening effect in the entire vehicle can be prevented, and a uniform sound deadening effect can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a noise control device which is a premise of an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of the microphones in FIG.

FIG. 3 is a diagram showing a circuit for synthesizing microphone outputs.

[Explanation of symbols]

 1 ... Muffler 2 ... Tail pipe 3, 4 ... Speakers 5-1, 5-2, 5-35 ... Microphone 6 ... Interface 6-1 ... Synthesis circuit 7 ... Adaptive filter 20 ... Actuator

Front page continuation (72) Inventor Masahiro Babasaki 1-228 Goshodori, Hyogo-ku, Kobe, Hyogo Prefecture, within Fujitsu Ten Ltd. (56) Reference JP-A-4-127697 (JP, A) 4-15387 (JP, U) Actual flat 5-38310 (JP, U)

Claims (1)

(57) [Claims] 1. A muffler (1) for extinguishing the noise of automobile exhaust
A noise control device arranged near the exit of a tail pipe (2) that emits noise at the end pipe of the tail pipe (2) and cancels noise from the tail pipe (2). An actuator (20) that outputs the erasing sound, and at least a position near the actuator (20), a position apart from the actuator (20) by a certain distance, and a position on the back side of the actuator (20) where leaked noise exists. Once installed , the residual noise from which noise has been eliminated is
A plurality of microphones for detecting as No. (5-1,5-
And 2,5-3), said plurality of microphones (5-1, 5-2, and 5-3)
This is used to weight the error signals and combine them to eliminate noise.
A synthesis circuit for feeding back the weighted synthesis signal (6-
10) The noise control device comprising: