JPH06130972A - Active noise reducing device - Google Patents

Abstract

PURPOSE:To provide the active noise reducing device which can be compactly constituted without being affected by the speciality of frequency characteristics from an acoustic wave output device to a residual sound detector. CONSTITUTION:This device is provided with a reference signal detector ND for detecting a reference signal based on a noise source NS, residual sound detector MC for detecting residual sounds in a prescribed area CA, and control means AF for driving and controlling an acoustic wave output device SE so as to minimize the output signal of the residual sound detector MC under the control of adaptive algorithm corresponding to the output of the residual sound detector MC based on the output signal of the reference signal detector ND, and noise discharged from the noise source NS to the prescribed area CA is canceled by outputting the acoustic wave of an inverse phase. Further, the output side of the control means AF and the input side from the residual sound detector MC to the control means AF are connected through a filter means FL for transmitting the frequency component of a prescribed frequency band to the input side in a prescribed state.

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, a peculiar frequency component is generated depending on the frequency characteristic from the control sound source (sound wave output device) to the residual noise detecting means (residual sound detector). A large amount of energy may be required for silencing, which makes it difficult to realize a noise reduction device.

For example, as shown in FIG. 8, when the sound pressure level lowers near a certain frequency, it is necessary to increase the output of the sound wave output device near that frequency in order to compensate for this. However, in some cases, a huge amount of energy is required. In the example of FIG. 8, assuming that the sound wave output device needs 10 W of electric power to cancel the sound wave of 100 Hz, 1 kW is obtained for the sound wave of 300 Hz.
Power is required. Therefore, a large-sized sound wave output device must be used, and the device as a whole becomes large in size, not only becomes heavy but also costly.

Therefore, an object of the present invention is to provide an active noise reduction device which can be constructed in a small size without being affected by the peculiarity in the frequency characteristics from the sound wave output device to the residual sound detector.

[0008]

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 transmitted through the filter means FL for transmitting the frequency component of the predetermined frequency band to the input side in a predetermined state. It is connected.

[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, even if the frequency characteristic from the sound wave output device SE to the residual sound detector MC has peculiarity,
The frequency component of the frequency band showing the peculiarity is corrected in a predetermined state by the filter means FL, for example, or is directly fed back from the output side of the control means AF to the input side. The sound wave output device SE is reliably driven and controlled so that the output signal of the residual sound detector MC is minimized without being affected by the above.

[0010]

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.

Near the outlet of the exhaust pipe 3, a residual sound detector 6 that outputs a signal corresponding to the residual sound is provided. 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 is also supplied to the filter 17, via which the frequency component of a predetermined frequency band is transmitted to the anti-aliasing filter 12 in a predetermined state. The filter 17 is composed of, for example, a bandpass filter having the characteristics shown in FIG. 4, but may be of an analog type or a digital type.

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 by 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 filter 17 may be a digital type, which may also be incorporated in the digital signal processor 10p.

The digital filter 20f is different from the adaptive digital filter 10 in the so-called filtered-XL.
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.

In the present embodiment, the filter 17 having the characteristics shown in FIG. 4 is provided, and when the output of the adaptive digital filter 10 contains the frequency component of the predetermined frequency band showing the peculiarity. Is configured to be corrected through the D / A converter 14 and the smoothing filter 15 through the filter 17 and to be superimposed on the input from the input amplifier 11 to the anti-aliasing filter 12 in the opposite phase. It is possible to eliminate the influence on the adaptive digital filter 10 by treating the frequency component shown as being almost disappeared.

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 the manner 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 includes a frequency component in a predetermined frequency band, it is input through the anti-aliasing filter 12 in the opposite phase after being corrected through the filter 17, and thus the frequency component showing the peculiarity. Almost disappears. Thus, in the present embodiment, a good silencing effect can be obtained by the adaptive digital filter 10 without being affected by the frequency component indicating the peculiarity.

FIG. 6 shows another embodiment of the present invention.
The filter 17 is connected to the output side of the D / A converter 14 and the A / D
It is connected between the input side of the converter 13 and is substantially the same as the above-mentioned embodiment. Also in this embodiment, the filter 17 can be configured by hardware when the capability of the digital signal processor 10p 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 filter 18 composed of a digital type filter is interposed between the input side of the D converter 13 and the input side. This filter 18 has the characteristics as shown in FIG. 5, for example, and the frequency components of the predetermined frequency band are fed back in the opposite phase as they are. Therefore, like the above-mentioned embodiment, the frequency components exhibiting the peculiarity are not affected. A good muffling effect can be obtained. Moreover, according to the present embodiment, the filter 18 can be configured only by changing the software for the digital signal processor 10p, which is easy. The filter 17 may be used in place of the filter 18, or a filter having a characteristic intermediate between the two may be used. Furthermore, in each of the above-described embodiments, the filter 18 of this embodiment may be used instead of the filter 17, or a filter having an intermediate characteristic between the two may be used.

As described above, the present invention relates to the noise reducing device, but 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, therefore, stable damping operation can be ensured without being affected by the frequency component exhibiting the peculiarity by interposing the above-mentioned filter means FL (filters 17 and 18).

[0025]

Since the present invention is configured as described above, it has the following effects. That is, according to the active noise reduction device 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 generate a frequency component in a predetermined frequency band with respect to the input side. Since they are connected via the filter means that transmits in a predetermined state, noise can be surely reduced without being affected by the frequency component indicating the peculiarity.

[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 filter according to the present invention.

FIG. 5 is a characteristic diagram of another embodiment of the filter according to 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.

FIG. 8 is a characteristic diagram showing frequency characteristics from a sound wave output device to a residual sound detector in a conventional active noise reduction device.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. An active noise reduction device for controlling a noise emitted from a noise source to a predetermined region 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 connected via a filter means for transmitting a frequency component of a predetermined frequency band to the input side in a predetermined state. An active noise reduction device characterized in that