JPH0612088A - Active noise reduction device - Google Patents

Abstract

PURPOSE:To provide the active noise reduction device which prevents overload to an acoustic wave output device and reduces noise in a stable state. CONSTITUTION:This device is provided with a reference signal detector ND to detect a reference signal based on a noise source NS, residual sound detector MC to detect residual sounds in a prescribed area CA, and control means AF to perform control with adaptive algorithm corresponding to the output signal of the residual sound detector MC based on the output signal of the reference signal detector ND and to control the driving of an acoustic wave output device SE so that the output signal of the residual sound detector MC can be minimized, and noise emitted from the noise source NS to the prescribed area CA is canceled by outputting the acoustic waves of a reverse phase. Further, the overload to the acoustic wave output device SE is prevented by providing a gain control means GC to output signals to an input side from the residual sound detector MC to the control means AF and to increase an output signal level corresponding to the increase of an input signal level when the input signal level from the output side of the control means AF exceeds a prescribed level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise reduction device, and more particularly to an active noise reduction device equipped with an adaptive digital filter and suitable as an exhaust noise reduction device for an internal combustion engine.

[0002]

2. Description of the Related Art Adaptive control that uses a digital filter to detect information that affects a control system and automatically changes its own control characteristics in response to changes in the information to achieve an optimum state regardless of changes in load. Can be realized, which is an adaptive digital filter (adaptive digital filter, A
DF), and its use for various controls is being studied.
Especially, in the field of acoustics, in order to eliminate the echo generated through the acoustic path between the speaker and the microphone, attention has been paid to its use in an acoustic echo canceller that generates and identifies a pseudo echo signal that is substantially equal to this echo. However, its use as an active noise reduction device has also been proposed in the field of automobiles and the like.

For example, as in the active cancellation muffler disclosed in Japanese Utility Model Laid-Open No. 63-118321, a speaker tube is provided at the outlet of the exhaust pipe, which is a noise outflow pipe, with respect to the internal combustion engine of the noise source, and the cancel speaker is provided in this speaker pipe. A device is proposed in which noise is emitted from the internal combustion engine, that is, a sound wave having a phase opposite to that of the exhaust sound is output from the cancel speaker in response to a predetermined control signal from the control means, and the sound is silenced by the canceling action of both pressure waves. ing.

Further, as described in, for example, Japanese Patent Laid-Open No. 3-203792, the secondary sound generated from the loudspeaker and the primary sound transmitted from the noise source are caused to interfere with each other to reduce the sound pressure level in the closed space. Active noise attenuators designed to be minimized are also known. In this publication, noise generation states of a plurality of noise sources are detected by noise generation state detection means, and the detected values are used as reference signals, and the number of control sound sources is individually provided for each reference signal. Each of the adaptive filters is input to be subjected to filtering processing, and the outputs of the plurality of adaptive filters are added by the control sound source driving means for each control sound source and supplied to the control sound source, and the control sound based on the drive command is generated from the control sound source. An apparatus has been proposed that updates the filter coefficient of the adaptive filter so that the noise at the observation position is minimized based on the detection value of the residual noise at the observation position by the residual noise detection unit and the detection value of the noise generation state detection unit. .

[0005]

However, in the device described in the above publication, the control sound source (speaker), that is, the sound wave output device outputs sufficient energy to cancel the noise, but the noise level is When the output energy of the sound wave output device that cancels out becomes larger than the allowable level, excessive energy is required for the sound wave output device, which may cause damage due to overload.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an active noise reduction device capable of preventing overload on a sound wave output device and reducing noise in a stable state.

[0007]

In order to achieve the above object, the present invention provides a sound wave having a phase opposite to that of a noise emitted from a noise source NS to a predetermined area CA as shown in FIG. In an active noise reduction device that outputs a sound wave output device SE and controls so as to cancel each other, a reference signal detector ND that detects a reference signal based on a noise source NS, and a predetermined region C
Connected to the residual sound detector MC that detects the residual sound in A, the residual sound detector MC and the reference signal detector ND, and according to the output signal of the residual sound detector MC based on the output signal of the reference signal detector ND Controlled by the adaptive algorithm, and the sound wave output device S is designed to minimize the output signal of the residual sound detector MC.
A control means AF for driving and controlling E is provided, and the control means A
The output side of F to the sound wave output device SE and the input side of the residual sound detector MC to the control means AF are output to the input side when the input signal level from the output side exceeds a predetermined level, and It is connected through gain control means GC in which the output signal level increases in accordance with the increase in the input signal level.

Further, as an active noise reduction device, an actuator for outputting a sound wave near an output port of an exhaust sound path including an exhaust pipe of an internal combustion engine, and an actuator arranged near the output port of the exhaust sound path to detect a residual sound. A residual sound detector, a rotation signal detector that outputs a signal synchronized with the rotation of the internal combustion engine, and an adaptive digital filter, and the output signal of the residual sound detector based on the output signal of the rotation signal detector. A control means is provided for updating the coefficient of the transfer function of the adaptive digital filter by a corresponding adaptive algorithm to drive and control the sound wave output device so that the output signal of the residual sound detector is minimized, and the sound wave of the control means is provided. The output side to the output device and the input side to the control means of the residual sound detector are output to the input side when the input signal level from the output side exceeds a predetermined level. Said output signal level is configured to be connected via a gain controller that increases according to the input signal level increases, can be subjected to an active cancellation muffler while.

[0009]

In the above active noise reduction device, when noise is emitted from the noise source NS shown in FIG. 1 into the predetermined area CA, the reference signal detector ND causes a reference signal based on the noise source NS, for example, an internal combustion engine. A rotation signal synchronized with the rotation of the engine is detected and output to the control means AF, and the residual sound detector MC detects the residual sound in the predetermined area CA and outputs it to the control means AF. The control means AF is controlled by an adaptive algorithm corresponding to the output signal of the residual sound detector MC based on the reference signal, and the sound wave output device SE is drive-controlled accordingly so that the output signal of the residual sound detector MC is minimized. It Thus, a sound wave having a phase opposite to that of the noise is output to cancel the noise. At this time, when the output of the control means AF for driving and controlling the sound wave output device SE exceeds the predetermined level set in the gain control means GC, the output signal level of the gain control means GC increases. That is, the control means AF is in phase opposite to the output signal of the residual sound detector MC via the gain control means GC.
The signal level fed back to is increased. In the control means AF, the input signal from the residual sound detector MC is controlled to be the minimum, so the sound wave output device SE
As a result, the sound wave output device SE is reliably driven and controlled without being overloaded.

In the active noise reduction system according to the second aspect of the present invention, when the internal combustion engine is started and rotated, the explosion sound generated according to the explosion in each cylinder is transmitted through the exhaust sound path including the exhaust pipe. The exhaust sound is formed. Then, a signal synchronized with the rotation of the internal combustion engine is output from the rotation signal detector to the control means. Further, a signal corresponding to the exhaust sound output from the exhaust sound path is detected by the residual sound detector and output to the control means.

In the control means, the transfer function of the adaptive digital filter is identified as the transfer function of the exhaust sound path by the adaptive algorithm corresponding to the output signal of the residual sound detector based on the output signal of the rotation signal detector, that is, The coefficient is updated to minimize the output signal of the residual sound detector,
In response to this, a drive signal is output to the actuator. In response to this drive signal, a sound wave is output from the actuator to the output port of the exhaust sound path and is canceled by the exhaust sound output from the exhaust sound path. In this case, when the output of the control means for driving and controlling the actuator exceeds the predetermined level set in the gain controller, the signal fed back to the control means via the gain controller in the opposite phase to the output signal of the residual sound detector. Level increases. Thus, since the control means controls the input signal from the residual sound detector MC to be the minimum, the output signal to the actuator becomes small and there is no overload.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an active noise reduction device according to the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment in which the present invention is applied to an active cancellation muffler, and an exhaust pipe 3 is connected to an exhaust manifold 2 of an internal combustion engine 1. Therefore, the exhaust sound path is constituted by the exhaust manifold 2 and the exhaust pipe 3 with respect to the internal combustion engine 1 which is a noise source. In the vicinity of the outlet of the exhaust pipe 3, an expansion pipe 4 is mounted coaxially with the exhaust pipe 3 so as to surround the outlet,
An actuator 5 is housed in this expansion tube 4.
The actuator 5 constitutes the sound wave output device according to the present invention, and is composed of an electromagnetic or electrodynamic speaker,
Sound waves are output. The actuator 5 may be one or more, and is not limited to an electromagnetic speaker or the like, and the diaphragm may be hydraulically driven by an electromagnetic valve in order to secure high output.

A residual sound detector 6 for outputting a signal according to the residual sound is provided near the outlet of the exhaust pipe 3. The residual sound detector 6 may be in any form as long as it is a means for converting a pressure signal into an electric signal, such as a microphone.

Further, a rotation signal detector 7 for outputting a rotation signal synchronized with the rotation of the internal combustion engine 1 is provided. The rotation signal detector 7 constitutes a reference signal detector for the internal combustion engine 1 which is a noise source, and includes, for example, an ignition signal of the internal combustion engine 1, an output signal of a crank angle sensor (not shown) provided on the crankshaft, It detects a rotation signal synchronized with the rotation of the internal combustion engine 1, such as a signal corresponding to the pressure in the cylinder or the pressure at the outlet of the exhaust valve. As a specific example, a strain gauge (not shown) is attached to a bolt (not shown) that fastens the cylinder block, and the strain gauge detects the strain of the bolt due to the pressure fluctuation in the cylinder. It can be configured to output a signal according to the internal pressure. The output signal of the rotation signal detector 7 is the digital filter 10f described later.
And the digital filter 20f.

The output signal of the residual sound detector 6 is the input amplifier 1
1 is amplified through the antialiasing filter 12
After the aliasing noise, that is, aliasing noise, is blocked at, the signal is converted into a digital signal by the A / D converter 13 and input to the adaptive digital filter 10. The output digital signal of the adaptive digital filter 10 is converted into an analog signal by the D / A converter 14, smoothed by the smoothing filter 15, amplified by the power amplifier 16, and supplied to the actuator 5 as a drive signal. Is configured to.

The output signal of the smoothing filter 15 having a predetermined frequency or more is also supplied to the anti-aliasing filter 12 via the gain controller 17. The gain controller 17 is a gain control means having the characteristics shown in FIG. 4, and may be either an analog type or a digital type. Alternatively, as the gain controller of this embodiment, a logarithmic amplifier (called a log amp) that outputs logarithmic conversion of the input as shown in FIG. 6 may be used.

The adaptive digital filter 10 has a digital filter 10f, and an adaptive algorithm 10a for sequentially controlling the coefficients of the multipliers forming the digital filter 10f is constructed. The transfer function of the digital filter 10f is the exhaust manifold 2 and the exhaust gas. Each coefficient is set via the adaptive algorithm 10a to identify with respect to the transfer function of the exhaust sound path of the pipe 3.

The adaptive digital filter 10 can be realized by forming an integrated circuit using a multiplier, an adder, etc., but in this embodiment, as shown in FIG. 3, a digital signal processor (DSP) 10p, a memory 10m, A
This is realized by the / D converter 13 and the D / A converter 14, and the filter function can be easily changed by changing the program. The memory 10m may be built in the digital signal processor 10p. Further, the gain controller 17 may be a digital type, which may also be built in the digital signal processor 10p.

The digital filter 20f is a so-called filtered-XL for the adaptive digital filter 10.
It constitutes an MS algorithm (Filtered-X LMS Algorithm), and includes a D / A converter 14, a smoothing filter 15, a power amplifier 16, an actuator 5,
The residual sound detector 6, the input amplifier 11, the anti-aliasing filter 12, and the A / D converter 13 are set to have characteristics equivalent to the transfer function.

Next, the operation of the active noise reduction system of this embodiment will be described. When the internal combustion engine 1 starts and rotates, the explosion sound generated in response to the explosion in each cylinder produces an exhaust manifold 2
And transmitted through the exhaust sound path of the exhaust pipe 3 to form exhaust sound. Therefore, the exhaust sound is mainly composed of the sound of the order component of the explosion. Further, a rotation signal synchronized with the rotation of the internal combustion engine 1 is input from the rotation signal detector 7 to the digital signal processor 10p shown in FIG.

The digital signal processor 10p processes the rotation signal in a manner to be described later, and outputs a digital signal. The output digital signal is converted into an analog signal through the D / A converter 14, smoothed by the smoothing filter 15, amplified by the power amplifier 16, and the actuator 5 is driven. As a result, sound waves are output from the actuator 5 into the expansion pipe 4 so as to surround the exhaust sound, and the sound waves are canceled by the exhaust sound. Then, the residual sound is detected by the residual sound detector 6, amplified through the input amplifier 11, and input to the digital signal processor 10p through the anti-aliasing filter 12 and the A / D converter 13.

In the digital signal processor 10p, the coefficient of the transfer function of the digital filter 10f is updated by the adaptive algorithm 10a according to the output signal of the residual sound detector 6 based on the output of the digital filter 20f shown in FIG. The output signal of the sound detector 6 is controlled to be the minimum. At this time, if the output of the smoothing filter 15 is a signal exceeding a predetermined level, the signal is input to the anti-aliasing filter 12 via the gain controller 17 in the opposite phase. Therefore, the output signal of the residual sound detector 6 is gradually reduced and the output of the adaptive digital filter 10 is suppressed to a predetermined level.

That is, in this embodiment, the gain controller 17 having the characteristics shown in FIG. 4 is provided.
When the output of the adaptive digital filter 10 exceeds a predetermined level, the smoothing filter 15 outputs a signal that increases in accordance with the increase of the output, to the gain controller 17
The output of the adaptive digital filter 10 is suppressed to a predetermined level because it is configured to be input in the opposite phase to the input side of the anti-aliasing filter 12 via.
Thus, in the present embodiment, even if the exhaust noise becomes abnormally large, the output of the adaptive digital filter 10 is suppressed to a predetermined level without abnormally increasing, so that the actuator 5 is not overloaded. .

FIG. 6 shows another embodiment of the present invention.
The gain controller 17 is connected between the output side of the D / A converter 14 and the input side of the A / D converter 13, and is substantially the same as the above-described embodiment. Also in this embodiment, the digital signal processor 10p is used.
The gain controller 17 can be configured by hardware when the capability of is low.

FIG. 7 shows still another embodiment of the present invention, in which the output side of the adaptive digital filter 10 and A /
A gain controller 18 composed of a digital filter is interposed between the input side of the D converter 13 and the input side. According to this embodiment, the gain controller 18 can be configured simply by changing the software for the digital signal processor 10p, which is easy.

As described above, although the present invention relates to the noise reduction device, it can be applied to the vibration damping device as it is. That is, for example, a vibration damping device for an internal combustion engine can be constructed by providing a vibration device and a vibration detector on an engine mount that supports the internal combustion engine and replacing them with the sound wave output device and the residual sound detector, respectively. . Even in this case, by interposing the above-mentioned gain control means GC (gain controller 17), it is possible to ensure stable damping operation without overloading the vibration generator.

[0027]

Since the present invention is configured as described above, it has the following effects. That is, according to the active noise reduction apparatus of the present invention, the output side of the control means to the sound wave output device and the input side of the residual sound detector to the control means are controlled so that the input signal level from the output side is a predetermined level. When the noise exceeds a certain level, the sound wave output device is overloaded because it is connected to the input side through gain control means that increases the output signal level according to the increase of the input signal level. The drive can be appropriately controlled without causing a load, and noise can be reduced in a stable state.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a configuration of an active noise reduction device of the present invention.

FIG. 2 is a block diagram of an active cancellation muffler according to an embodiment of the present invention.

FIG. 3 is a block diagram of a configuration for realizing an adaptive digital filter according to an exemplary embodiment of the present invention.

FIG. 4 is a characteristic diagram of a gain controller according to an embodiment of the present invention.

FIG. 5 is a characteristic diagram of another embodiment of the gain controller in one embodiment of the present invention.

FIG. 6 is a block diagram of an active cancellation muffler according to another embodiment of the present invention.

FIG. 7 is a block diagram of an active cancellation muffler according to still another embodiment of the present invention.

[Explanation of symbols]

 1 Internal Combustion Engine (Noise Source) 2 Exhaust Manifold (Exhaust Sound Path) 3 Exhaust Pipe (Exhaust Sound Path) 4 Expansion Tube 5 Actuator (Sound Wave Output Device) 6 Residual Sound Detector 7 Rotation Signal Detector 10 Adaptive Digital Filter (Control Means) ) 17,18 Gain controller (gain control means)

Claims (2)

[Claims] 1. An active noise reduction device for controlling a noise emitted from a noise source to a predetermined area so that a sound wave having a phase opposite to the noise is output from a sound wave output device to cancel the noise. A reference signal detector for detecting a reference signal based on the residual signal, a residual sound detector for detecting a residual sound in the predetermined region, and a residual sound detector and an output of the reference signal detector connected to the reference signal detector. A control means for controlling the sound wave output device so that the output signal of the residual sound detector is minimized by controlling with an adaptive algorithm according to the output signal of the residual sound detector based on the signal; The output side to the sound wave output device and the input side from the residual sound detector to the control means are output to the input side when the input signal level from the output side exceeds a predetermined level, and the input side is output. An active noise reduction device characterized by being connected via a gain control means for increasing an output signal level according to an increase in a force signal level. 2. An actuator for outputting a sound wave near an output port of an exhaust sound path including an exhaust pipe of an internal combustion engine, a residual sound detector arranged near the output port of the exhaust sound path for detecting a residual sound, and A rotation signal detector that outputs a signal synchronized with the rotation of the internal combustion engine, and an adaptive digital filter, and the adaptive algorithm based on the output signal of the rotation signal detector by the adaptive algorithm according to the output signal of the residual sound detector. A control means for driving and controlling the sound wave output device so that the output signal of the residual sound detector is minimized by updating the coefficient of the transfer function of the digital filter; and an output side of the control means to the sound wave output device. The input side of the residual sound detector to the control means is output to the input side when the input signal level from the output side exceeds a predetermined level, and the input signal level An active noise reduction device characterized by being connected via a gain controller whose output signal level increases in accordance with an increase.