JP3410499B2 - Active noise reduction device - Google Patents

Description

Description: 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 having an adaptive digital filter and suitable as an exhaust noise reduction device for an internal combustion engine. According to. 2. Description of the Related Art Generally, an adaptive filter detects information affecting a control system and automatically changes its own control characteristic in accordance with the change, so that an optimum filter is optimal regardless of a change in load. It is capable of realizing adaptive control for setting a state. In particular, utilization of an adaptive digital filter (adaptive digital filter, ADF) for various controls is under study.
Particularly, in the acoustic field, in order to cancel an echo generated through an acoustic path between a speaker and a microphone, its use in an acoustic echo canceller for generating and identifying a pseudo echo signal substantially equal to the echo has attracted attention. 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 an active cancel muffler described in Japanese Utility Model Application Laid-Open No. 63-118321, a speaker tube is provided at an outlet of an exhaust pipe as a noise discharge pipe for a noise source internal combustion engine, and a cancel speaker is provided in the speaker pipe. A device is proposed in which, in response to a predetermined control signal from the control means, a noise from the internal combustion engine, that is, a sound wave having an opposite phase to the exhaust sound is output from the cancel speaker, and the sound is canceled by the action of canceling both pressure waves. ing. Further, as described in, for example, JP-A-3-203792, a secondary sound generated from a loudspeaker interferes with a primary sound transmitted from a noise source to reduce the sound pressure level in a closed space. Active noise attenuators designed to be minimized are also known. In this publication, the noise generation state of a plurality of noise sources is detected by a noise generation state detection unit, and each of the detected values is used as a reference signal, and each reference signal is individually provided by the number of control sound sources. Each is input to the adaptive filter and subjected to a filtering process, the outputs of the plurality of adaptive filters are added for each control sound source by the control sound source driving means and supplied to the control sound source, and the control sound source generates a control sound based on a drive command. An apparatus has been proposed which updates a filter coefficient of an adaptive filter based on a detection value of a residual noise at an observation position by a residual noise detection unit and a detection value of a noise generation state detection unit so as to minimize noise at the observation position. . However, in the apparatus and the like described in the above publication, since the control sound source, that is, the sound wave output device itself has frequency characteristics, a frequency signal which is difficult to reproduce is supplied. Then, a predetermined sound wave is not output, and in this case, the adaptive filter naturally does not converge properly.
Alternatively, the adaptive filter does not converge even when a sound wave in a frequency band that resonates between the sound wave output device and the residual noise detector is output. Thus, in these cases, the noise reduction performance is significantly reduced. SUMMARY OF THE INVENTION It is an object of the present invention to provide an active noise reduction device capable of ensuring stable noise reduction performance without being affected by the frequency characteristics of a sound output device. [0007] In order to achieve the above object, the present invention, as shown in FIG. In the active noise reduction device, which outputs a sound wave from the sound wave output device SE so as to cancel each other, a reference signal detector ND for detecting a reference signal based on the noise source NS, and a predetermined region C
A residual sound detector MC for detecting the residual sound in A, connected to 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 The sound wave output device S is controlled by an adaptive algorithm so that the output signal of the residual sound detector MC is minimized.
E, a first filter means FL1 for driving and controlling the reference signal detector N, and an adaptive algorithm according to an output signal of the first filter means FL1 to the sound output device SE.
And a second filter means FL2 for controlling the first filter means FL1 based on the output signal of the D, and the second filter means FL2, the frequency characteristic of the acoustic output device SE
The filter is set to have a canceling characteristic, and the sound is supplied to the first filter means FL1.
Output signal in a frequency band that is difficult to reproduce
It is not to be paid . In the above active noise reduction apparatus, when noise is emitted from the noise source NS shown in FIG. 1 into the predetermined area CA, the reference signal detector ND uses the reference signal based on the noise source NS. For example, a rotation signal synchronized with the rotation of the internal combustion engine is detected and output to the first filter means FL1, and a residual sound in a predetermined area CA is detected by the residual sound detector MC and output to the first filter means FL1. You. The first filter means FL1 is controlled by an adaptive algorithm according to the output signal of the residual sound detector MC based on the reference signal, and the sound wave output device SE is controlled so that the output signal of the residual sound detector MC is minimized accordingly. Drive controlled. Thus, a sound wave having a phase opposite to that of the noise is output, and the noise is canceled. At this time, even when an output signal that is difficult to reproduce due to, for example, the output characteristics of the sound wave output device SE is supplied from the first filter means FL1, the output of the first filter means FL1 is the frequency of the sound wave output device SE. Since the signal is fed back to the first filter means FL1 via the second filter means FL2 having the characteristic of canceling the characteristic, the supply of the output signal in the frequency band which is difficult to reproduce by the sound wave output device SE is suppressed, and the residual sound detection is performed. The sound wave output device SE is reliably driven and controlled such that the output signal of the device MC is minimized. Preferred embodiments 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 cancel muffler. An exhaust pipe 3 is connected to an exhaust manifold 2 of an internal combustion engine 1, and a catalytic converter 9 is interposed in the exhaust pipe 3. Accordingly, an exhaust sound path is constituted by the exhaust manifold 2, the catalytic converter 9, and the exhaust pipe 3 for the internal combustion engine 1 as a noise source. Near 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, and an actuator 5 is accommodated in the expansion pipe 4. The actuator 5 constitutes a sound wave output device according to the present invention, and is composed of an electromagnetic or electrodynamic speaker, and outputs sound waves. The number of the actuators 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 corresponding 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 converts the 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 as a noise source. For example, an ignition signal of the internal combustion engine 1, an output signal of a crank angle sensor (not shown) provided on a 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) for fastening the cylinder block, and the strain gauge detects the distortion of the bolt caused by the fluctuation in the pressure in the cylinder. It can be configured to output a signal corresponding to the internal pressure. An output signal of the rotation signal detector 7 is supplied to a first digital filter 1 described later.
0f, the second digital filter 20f, and the third digital filter 30f. The output signal of the residual sound detector 6 is supplied to the input amplifier 1
1 through the anti-aliasing filter 12
After the aliasing noise, ie, aliasing noise, is blocked by the A / D converter 13, the signal is converted into a digital signal by the A / D converter 13 and is input to the first digital filter 10f. Then, the first digital filter 10
The output digital signal of f is converted into an analog signal by a D / A converter 14, smoothed by a smoothing filter 15 and then amplified via a power amplifier 16.
The actuator 5 is configured to be supplied as a drive signal. A first adaptive algorithm 10a for sequentially controlling the coefficients of a multiplier constituting the first digital filter 10f is set, and the transfer function of the first digital filter 10f is changed to the exhaust manifold 2 and the exhaust pipe 3. Each coefficient is set via the first adaptive algorithm 10a so as to identify the transfer function of the exhaust sound path of the first embodiment. Thus, the first digital filter 10f and the like constitute the first filter means FL1 according to the present invention. The second digital filter 20f is a so-called filtered filter with respect to the first digital filter 10f.
X LMS algorithm (Filtered-X LMS Algorithm)
And transmission from the D / A converter 14 to the smoothing filter 15, the power amplifier 16, the actuator 5, the residual sound detector 6, the input amplifier 11, the anti-aliasing filter 12, and the A / D converter 13. It is set to have characteristics equivalent to the function. Further, in the present embodiment, a third digital filter 30f constituting the second filter means FL2 according to the present invention and having the characteristics shown in FIG. 4 is provided. The third digital filter 30f applies the output of the first digital filter 10f, that is, the drive signal of the actuator 5 to the second adaptive algorithm 30a and outputs the first digital filter 10f in accordance with the output signal of the rotation signal detector 7.
It is configured to update the coefficient of f. FIG. 4 shows the third
FIG. 6 shows an example of the characteristics of the digital filter 30f.
The frequency characteristic of the actuator 5 is the characteristic of the third digital filter 30f that is set when the reproduction frequency is flat at, for example, 70 Hz to 500 Hz. Thus, the characteristics of the third digital filter 30f are set so as to cancel the frequency characteristics of the actuator 5.
Thus, the output of the first digital filter 10f functions to suppress signals in a frequency band in which reproduction by the actuator 5 is difficult. The first digital filter 10f to the third digital filter 30f can be realized by forming an integrated circuit using a multiplier, an adder, and the like. In this embodiment, as shown in FIG. 3, a digital signal processor (DSP) is used. ) 10p, memory 10m, A / D converter 1
3 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. Next, the operation of the active noise reduction device of this embodiment will be described. When the internal combustion engine 1 starts and rotates, an explosion sound generated in response to an explosion in each cylinder is generated by an exhaust manifold 2.
The exhaust sound is transmitted through the exhaust sound path of the exhaust pipe 3 to form an exhaust sound. Therefore, the exhaust sound is mainly constituted by the sound of the exponent order component. 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 performs predetermined processing according to the rotation signal, and outputs a digital signal. The output digital signal is D
Is converted into an analog signal via the / A converter 14,
After being smoothed by the smoothing filter 15, it is amplified by the power amplifier 16 and the actuator 5 is driven.
As a result, a sound wave is output from the actuator 5 so as to surround the exhaust sound in the expansion pipe 4, and is canceled out. 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 via the anti-aliasing filter 12 and the A / D converter 13. In the digital signal processor 10p, based on the output of the residual sound detector 6 based on the output of the second digital filter 20f shown in FIG.
The coefficient of the transfer function of 0f is updated, and the output signal of the residual sound detector 6 is controlled to be minimized. At this time, the frequency characteristic of the actuator 5 is, for example, 70H as described above.
When the reproduction is difficult at z to 500 Hz, the supply of the output signal in this frequency band is controlled through the third digital filter 30f, so that the frequency components that are difficult to reproduce by the actuator 5 are substantially. It will disappear. Thus, in the present embodiment, a good silencing effect can be obtained by the first digital filter 10f to the third digital filter 30f without being affected by the frequency characteristics of the actuator 5. As described above, the present invention relates to a noise reduction device, but can be applied to a vibration damping device almost as it is. That is, for example, a vibration damping device for an internal combustion engine can be configured by providing a vibration device and a vibration detector on an engine mount that supports the internal combustion engine and replacing them with the above-described sound output device and residual sound detector, respectively. . In this case, too, by interposing the above-mentioned second filter means FL2 (the third digital filter 30f or the like), the actuator 5 can be stabilized without being affected by frequency components which are difficult to reproduce in the actuator 5. Damping operation can be ensured. Since the present invention is configured as described above, the following effects can be obtained. That is, in the active noise reduction device of the present invention, the sound wave output device is driven and controlled by the first filter means so that the output signal of the residual sound detector is minimized, and the sound wave output from the first filter means is controlled. based on the output signal supplied to the apparatus, the first filtering unit is configured to be controlled by the second filter means having a characteristic corresponding to the frequency characteristic of the acoustic output device, the frequency of the sound wave output device Stable noise reduction performance can be secured without being affected by characteristics, and noise can be reliably reduced.

BRIEF DESCRIPTION OF THE 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 cancel muffler according to one embodiment of the present invention. FIG. 3 is a block diagram of a configuration for realizing a digital filter in one embodiment of the present invention. FIG. 4 is a characteristic diagram of a third digital filter in one embodiment of the present invention. [Description of Signs] 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 10f 1 digital filter (first filter means) 20f second digital filter 30f third digital filter (second filter means)

Continuation of front page (56) References JP-A-6-35480 (JP, A) JP-A-5-67948 (JP, A) JP-A-4-359297 (JP, A) JP-A-1-314500 (JP) JP-A-6-27975 (JP, A) JP-A-6-4083 (JP, A) JP-A-5-46187 (JP, A) JP-A-3-40598 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G10K 11/178 F01N 1/00 H03H 17/02 601 H03H 21/00

Claims (1)

(57) [Claim 1] An active type which controls so that a sound emitted from a noise source to a predetermined region is canceled out by outputting a sound wave having an opposite phase to the noise from a sound output device. In the noise reduction device, a reference signal detector that detects a reference signal based on the noise source, a residual sound detector that detects a residual sound in the predetermined area, and a connection to the residual sound detector and the reference signal detector Then, based on the output signal of the reference signal detector, control is performed by an adaptive algorithm according to the output signal of the residual sound detector, and drive control of the sound wave output device is performed so that the output signal of the residual sound detector is minimized. First filter means for controlling the first filter means based on an output signal of the reference signal detector by an adaptive algorithm according to an output signal of the first filter means to the sound wave output device. And a second filter means that the filter means of the second, set the characteristic to cancel the frequency characteristic of the sound wave output device, in the sound wave output device to said first filter means
Prevent supply of output signals in frequency bands that are difficult to reproduce
Active noise reducing device, characterized in that the.