JP2527280B2 - Noise reduction device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention actively cancels noise and the like generated by the propagation of mechanical vibrations with the same amplitude and opposite phase sound.
The present invention relates to a noise reduction device that reduces noise, and more particularly to a noise reduction device that is suitable for avoiding an increase in noise when a situation in which a silencing effect cannot be obtained occurs.

[0002]

2. Description of the Related Art When a mechanical vibration source is near, noise is generated by propagating mechanical vibration. An automobile or a ship has an engine as a periodic mechanical vibration source, and in an aircraft or the like, vibration of a wing becomes a periodic mechanical vibration source. Since this noise depends on the mechanical vibration frequency, the frequency can be known. However, it is often difficult to know where the ceiling, floor, walls, windows, etc. of the vehicle interior or passenger compartment resonate due to the transmitted mechanical vibration and become the actual noise generation source. Therefore,
Noise that cancels noise by obtaining secondary sound that has the same amplitude and opposite phase to noise from the frequency of mechanical vibration and the spatial acoustic transfer function of the vehicle interior, and radiates this secondary sound into the vehicle interior. Reduction devices have been developed.

FIG. 6 is a schematic configuration diagram of a conventional noise reduction device. The noise reduction device is a controller that includes a microphone 4 that detects sound pressure at a plurality of locations in a noise space such as a passenger compartment, a plurality of speakers 5 that radiate a secondary sound into the noise space, and a microprocessor 2 as a calculation unit. It consists of three. When mechanical vibration propagates from the engine 1 to the vehicle interior or the like, noise is generated in the vehicle interior due to the mechanical vibration.
Therefore, the microprocessor 2 considers the spatial acoustic transfer function of the noise space, calculates a secondary sound that actively cancels this noise from the mechanical vibration frequency, and outputs this secondary sound to the speaker 5.
Radiates from inside the vehicle to reduce noise inside the vehicle. At this time, the microprocessor 2 uses, for example, a least mean square algorithm (hereinafter, referred to as an LMS algorithm), which is a kind of steepest descent method, so that each speaker 5 is minimized so that the residual sound in the vehicle compartment detected by the microphone 4 becomes minimum. The secondary sound radiated from is calculated.

Incidentally, as a related art, there is British Patent Publication No. 2149614A.

[0005]

The conventional noise reduction device described above is used in such a manner that the power supply is kept in the ON state and the noise reduction control function is always activated during the period when the noise is suppressed by the secondary sound radiation. To do. However, during the period in which the noise reduction device is functioning, if an event that the spatial acoustic transfer function between the microphone and the speaker changes significantly, for example, an event such as a sudden change in temperature, the muffling effect disappears. It has been found that the noise may increase due to the secondary sound radiation. It is troublesome for an occupant or the like to turn off the switch of the noise reduction device one by one when the noise increases, and it is too late to turn off the switch after the noise increases, which makes the installation of the noise reduction device meaningless. To popularize the noise reduction device,
There is a need to solve this problem.

It is an object of the present invention to provide a noise reduction device that does not increase noise due to secondary sound radiation due to a significant change in the spatial acoustic transfer function of the noise space.

[0007]

The object is to detect a noise generated by the propagation of mechanical vibration, and a computing means for calculating a secondary sound having the same amplitude and opposite phase with respect to the noise. In a noise reduction device including a secondary sound generation unit that generates a secondary sound calculated by the calculation unit and reduces the noise, a divergence prediction unit that predicts whether noise and residual sound of the secondary sound diverge. And a function interruption means for automatically interrupting the function of the control means when the divergence prediction means predicts the divergence of the residual sound.

[0008]

When the noise is predicted to increase due to the secondary sound radiation, the function interruption means automatically interrupts the noise reduction control, so that it is not necessary to manually turn the noise reduction device on and off. In addition, this function interruption means does not turn off the noise reduction control after the noise actually increases, but predicts and interrupts it before the noise actually increases, which causes annoyance due to the noise increase. There is no.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In machines equipped with power sources such as internal combustion engines,
Usually, the piston, connecting rod, etc. in the power source reciprocate at the same frequency as the combustion cycle of the power source to rotate the power source drive shaft. The reciprocating motion of the piston or the like is an unbalanced force and propagates to other parts of the machine as mechanical vibration of the power source, and noise is generated at the propagation destination. The frequency of this noise is the same as the combustion cycle of the power source, and is twice the frequency of the rotation of the drive shaft. In the case of machines equipped with recent high-performance engines, the engine's normal rotation speed range is 600 rpm to 750
Since it is 0 rpm, the noise frequency is 20 Hz to 250
It becomes Hz. When the mechanical vibration described above propagates to a place where resonance occurs in this frequency range, noise becomes particularly severe.

FIG. 1 is a block diagram of a noise reduction device according to an embodiment of the present invention. The basic configuration is the same as that shown in FIG. 6, a plurality of speakers 5 as actuators that generate secondary sounds, a microphone 4 that detects residual sounds in a noise space, and a microprocessor that serves as a computing unit. It comprises a controller 3 comprising 2. Further, the microprocessor 2 is provided with a D / A converter 6 for converting a digital signal as an arithmetic signal into an analog signal, and a power amplifier 7 for amplifying the analog signal. The microprocessor 2 performs various calculations based on the engine rotation frequency fetched from the engine 1 and the residual sound in the noise space fetched from the microphone 4, and calculates the phase and amplitude control means 9 for calculating the phase and amplitude of the secondary sound. The divergence prediction means 8 that constantly determines whether the secondary sound signal is in a normal state or is moving to an abnormal state, and the secondary sound signal calculated by the phase amplitude control means 9 when the divergence is predicted is D / A. Converter 6
And the control stop means 10 for preventing the transmission of

FIG. 2 is a detailed block diagram of the controller 3. D / A converter 6 and power amplifier 7 shown in FIG.
Are omitted in FIG. In order to explain the divergence prediction algorithm to be described later, it is assumed that the noise reduced by the secondary sound has a single frequency caused by the engine speed, and this will be described below as a “noise frequency”.
In the present embodiment, the phase amplitude control means 9 of the microprocessor 2 described with reference to FIG. 1 is composed of software sine wave generation means, LMS algorithm and phase amplitude control filter, and the divergence prediction means 8 is also software divergence prediction. The control stop means 10 is also configured by software. Of course, each of these means 8, 9, 1
It goes without saying that 0 can be configured by hardware.

When the crank angle pulse synchronized with the rotation of the engine is input to the controller 3 as a reference signal, the crank angle pulse is converted into a sine wave having the same frequency as the noise frequency by the sine wave generating means. Further, the noise signal in the noise space detected by the microphone 4 (the main component of this signal is the above noise frequency) and the reference sine wave signal output from the sine wave generating means are supplied to the LMS algorithm. To be done. The LMS algorithm controls the coefficient of the phase amplitude control filter so as to minimize the sum of squares of the noise signal. Then, the reference sine wave signal output from the sine wave generating means is filtered by this phase amplitude control filter, and the filtered signal (secondary sound signal) is output from the speaker 5. The phase / amplitude control filter is an adaptive digital filter (W filter) that controls the phase and amplitude of a single frequency, and is controlled by two coefficient values (W1, W2).

In the control by the LMS algorithm, for example, when a plurality of microphones are arranged in the noise space as the noise detecting means, the coefficient of the adaptive digital filter is set so that the sum of squares of the sound pressure detected by each microphone becomes the minimum. It is determined. Here, it is assumed that the value of the spatial acoustic transfer function of the noise space suddenly changes due to a sudden temperature change or the like. In this case, the document “A Multiple Error LMS Algorithm and It's Application to
The Active Control of Sound and Vibration (A Multiple Error LMS Algorit
hm and Its Application to the Active Control of So
und and Vibration) "(IEEE Transactions on Acoust
ics, Speach, and Signal Processing, Vol. ASSP-35,
No. 10, October, 1987),
The signal controlled by the LMS algorithm deviates from the relationship of the same amplitude and the opposite phase at the position where the microphone is arranged, does not converge so as to minimize the square sum of the sound pressure, and diverges on the contrary. Therefore, if the secondary sound signal generated in this state is radiated from the speaker to the noise space, not only the ideal silencing effect cannot be obtained, but also the noise is increased.

FIG. 3 is an explanatory diagram showing the behavior of the adaptive digital filter when the noise reduction control is normally performed and when the noise reduction control is diverged. As can be seen from this figure, the coefficient values W1 and W2 of the adaptive digital filter are within a certain range while the noise reduction control is normally performed, but when they diverge, the values deviate from this range. Becomes In this embodiment, the coefficient values W1 and W2 are monitored, noise is predicted to increase due to the secondary sound radiation when the coefficient values W1 and W2 deviate from the set range, and the secondary sound radiation is interrupted. Coefficient value W
If the secondary sound emission is interrupted at the first stage where 1 and W2 deviate from the set range, the noise will not actually increase. The reason is that the coefficient of the adaptive digital filter is updated at a speed twice or more the frequency of the noise to be reduced. That is, in general, the coefficient is updated at a speed of 500 Hz or higher for a noise frequency of 250 Hz. Therefore, by monitoring whether the values of the coefficient values W1 and W2 of the adaptive digital filter become abnormal, it is possible to predict whether or not the noise will be increased (diverged) by the secondary sound radiation. . Then, when the divergence is predicted, the control stop means cuts off the output of the secondary sound signal to the speaker side, so that the emission of the secondary sound from the speaker is blocked before the occupant or the like is discomforted. It will be possible.

FIG. 4 is a block diagram of a controller of a noise reduction device according to another embodiment of the present invention. In the embodiment shown in FIG. 2, the divergence is predicted by the filter coefficient value obtained by the LMS algorithm, but the divergence prediction algorithm of the present embodiment is
The control unit is controlled by predicting the divergence from the pressure signal of the noise detected by the microphone.
FIG. 5 is an explanatory diagram of the principle of predicting divergence from a microphone detection signal. The change in the sound pressure S detected by the microphone, that is, the time derivative dS / dt, has little fluctuation as shown in FIG. 5A when the noise reduction control is normally performed. However, when entering the divergent state, as shown in FIG. 5B, dS / dt rapidly changes and becomes unstable. Therefore, the time differential value of the noise detection signal S is monitored, and when the degree of change exceeds the set value, the control stop means cuts off the output of the secondary sound signal to the speaker side, thereby preventing an increase in noise. It becomes possible to do.

In the above-mentioned embodiment, the case of reducing the noise accumulated in the closed space such as the passenger compartment or the passenger compartment has been described.
It goes without saying that the present invention can also be applied to a noise reduction device that reduces noise emitted to the open space outside the vehicle. Also,
It goes without saying that the present invention can be applied not only to noise but also to a vibration reduction device that cancels mechanical vibrations by secondary vibrations having the same amplitude and opposite phase.

[0017]

According to the present invention, in a device for canceling noise or mechanical vibration by secondary sound having the same amplitude and opposite phase, or secondary vibration, noise is generated by the generation of secondary sound or secondary vibration. When the situation becomes worse, the noise is predicted before it becomes worse and the generation of secondary sound and secondary vibration is automatically interrupted, so it is possible to always achieve good noise reduction. Becomes

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a controller shown in FIG.

3 is an explanatory diagram of coefficients of the phase amplitude control filter shown in FIG.

FIG. 4 is a configuration diagram of a controller according to another embodiment of the present invention.

5 is a prediction explanatory diagram of the divergence prediction algorithm shown in FIG. 4. FIG.

FIG. 6 is an explanatory diagram of a conventional noise reduction device.

[Explanation of symbols]

1 ... Engine, 2 ... Microprocessor, 3 ... Controller, 4 ... Microphone, 5 ... Speaker, 6 ... D / A
Converter, 7 ... Power amplifier, 8 ... Divergence prediction means, 9 ... Phase amplitude control means, 10 ... Control stop means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhide Sasaki 2520, Takaba, Katsuta-shi, Ibaraki Hitachi Ltd. Automotive Equipment Division (72) Inventor Toshiyuki Tabata 2 Takara-cho, Kanagawa-ku, Yokohama Kanagawa Prefecture Nissan Automotive Co., Ltd.

Claims (7)

(57) [Claims] 1. A noise detecting means for detecting noise generated by the propagation of mechanical vibration, and a calculating means for calculating a secondary sound having a phase opposite to the noise from the frequency of the mechanical vibration.
In a noise reduction device provided with a secondary sound generation unit that generates the secondary sound calculated by the calculation unit and reduces the noise, the phase relationship between the noise and the secondary sound at the position where the noise detection unit is arranged is reversed. A noise reduction device comprising means for automatically interrupting the generation of a secondary sound when it deviates from the phase relationship or when the amplitude of the secondary sound deviates from the amplitude of the noise. 2. A noise detecting means for detecting noise generated by propagation of mechanical vibration, a calculating means for calculating a secondary sound that actively cancels the noise from the frequency of the mechanical vibration, and a calculating means of the calculating means. In a noise reduction device including a secondary sound generation unit that generates the calculated secondary sound and reduces the noise, when the noise at the position where the noise detection unit is arranged and the residual sound of the secondary sound increases, the secondary sound is generated. A noise reduction device comprising means for automatically interrupting. 3. The noise generated by the propagation of mechanical vibration,
In a noise reduction device having a control means for canceling and reducing the secondary sound calculated from the frequency of the mechanical vibration and generated,
A divergence predicting means for predicting whether or not the residual sound of the noise and the secondary sound diverges, and a function suspending means for automatically suspending the function of the control means when the divergence predicting means predicts the divergence of the residual sound. A noise reduction device comprising: 4. The control means according to claim 3, wherein the control means generates a secondary sound from the output of the adaptive digital filter, and the divergence prediction means monitors the coefficient of the adaptive digital filter to predict whether or not the residual sound diverges. A noise reduction device characterized by: 5. The noise reduction device according to claim 3, wherein the divergence predicting means monitors the sound pressure of the residual sound to predict whether or not the residual sound diverges. 6. The divergence predicting means according to claim 3, wherein the secondary sound signal sent to the secondary sound generating actuator of the control means is monitored to predict whether or not the residual sound diverges. Characteristic noise reduction device. 7. A vibration reducing device having a control means for reducing mechanical vibration propagating from a vibration source by secondary vibration calculated from the frequency of the vibration and generating the generated mechanical vibration, A divergence prediction means for predicting whether or not the synthetic vibration with the secondary vibration diverges, and a function interruption means for automatically interrupting the function of the control means when the divergence prediction means predicts the divergence of the residual vibration. A vibration reduction device comprising: