JPH10212926A - Noise control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attempt the effect of a noise reduction by improving the installation place of a microphone. SOLUTION: The control error which is the result of a sound wave interference of an exhaust noise radiated from an exhaust pipe 1 with the control sound with a reverse phase and same amplitude for the exhaust noise radiated from a speaker 2 is detected by a microphone 3 and a controller 4 produces the control sound and drives the speaker 2 based on this control error and the engine speed signal. The installation position of the microphone 3 is a place not approached to the exhaust pipe 1 and the speaker 2 extremely and is hardly received the bad influence by a heat and exhaust gas by positioning around the center part of a vehicular rear surface (near the upper/lower center line in view of a vehicular rear side) and the noise control is stabilized and control accuracy is improved as a position with a low sound pressure of the road surface friction sound of the tyre of an own vehicle unrelated to the control or the noise from the other vehicle.

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 mounted on an internal combustion engine and, more particularly, to a noise control device which emits a sound wave of an opposite phase to exhaust sound from an exhaust pipe and suppresses the sound by interference of the sound wave. The present invention relates to an arrangement and a structure of a microphone that collects a control error sound.

[0002]

2. Description of the Related Art FIG. 18 is a block diagram showing a conventional noise control device. In the figure, 1 is an exhaust pipe, 29 is an exhaust pipe 1
, 31 is a control sound having the opposite phase and the same amplitude as the exhaust noise 29 radiated from the exhaust pipe 1, 2 is an anti-phase and the same amplitude as the exhaust noise 29 radiated from the exhaust pipe 1 The speaker 3 radiates the control noise 31 of the control noise 31 which is a result of the sound interference of the control noise 31 having the opposite phase and the same amplitude with respect to the exhaust noise 29 radiated from the exhaust pipe 1 and the exhaust noise 29 radiated from the speaker 2. This is a microphone that detects sound.

Reference numeral 9 denotes a control error signal, which is an output signal of the microphone 3, 5 denotes an engine, 7 denotes an engine rotation signal synchronized with the engine rotation from the engine 5, 4 denotes an engine rotation signal 7, and a control error signal 9 are input. Thus, ANC (Active Noise Control) control for generating and adjusting the control signal 8 having the opposite phase and the same amplitude with respect to the exhaust noise 29 output to the speaker 2 so that the control error signal 9 is minimized is performed. It is a controller.

FIG. 19 shows an example of the internal configuration of the controller 4. In the figure, 4 is a controller, 7 is an engine rotation signal, 8 is a control signal, 9 is a control error signal, 32 is an anti-aliasing low-pass filter, and 33 is a digital signal of the control error signal 9 passed through the anti-aliasing low-pass filter 32. A / D converter for converting to 34
Is a control error signal converted to a digital signal by the A / D converter 33, and 35 is an engine rotation signal 7 and a control error signal 34 converted to a digital signal. To minimize
A digital signal processor (DSP) for performing ANC control for generating and adjusting the control signal 8.

Reference numeral 36 denotes a digital signal format control signal generated by the DSP 35, 37 denotes a D / A converter for converting the digital signal format control signal 36 generated by the DSP 35 into an analog signal 8, 38 denotes a smoothing low-pass filter, and 39 denotes This is an amplifier that converts the signal into an analog signal by the D / A converter 37 and amplifies the control signal 8 that has passed through the smoothing low-pass filter 38.

FIG. 20 shows a digital signal processor (D
3 is an example of the configuration of digital signal processing of SP) 35. In the figure, 7 is an engine rotation signal, 34 is a control error signal in digital signal format, 35 is a DSP, 36 is a control signal in digital signal format, and 40 is a control signal in digital signal format by inputting the engine rotation signal 7. An FIR adaptive filter that generates the FIR adaptive filter 40; a delay element 42 that constitutes the FIR adaptive filter 40; a coefficient 43 of the FIR adaptive filter that determines characteristics of the FIR adaptive filter 40;
An adder 44 constitutes the FIR adaptive filter 40.

Reference numeral 41 denotes a filter coefficient updating algorithm for inputting the engine rotation signal 7 and the control error signal 34 based on a digital signal and updating the coefficient 43 of the FIR adaptive filter so that the control error signal 34 based on the digital signal is minimized. is there.

Here, as an example, an LMS (Least Mean Square) algorithm is used as the filter coefficient updating algorithm 41. The operation of the filter coefficient updating LMS algorithm 41 is as shown in Expression 1. h (n + 1) = h (n) + 2με (n) χ (n) Equation 1

In equation (1), h (n) is the current filter coefficient, μ is a coefficient representing the update rate of the filter coefficient, and ε (n)
Represents a control error signal 34 by a digital signal, χ (n) represents an engine rotation signal 7, and h (n + 1) represents a new filter coefficient generated by calculation. According to the above equation, FIG.
Is updated by updating all the filter coefficients 43 of the FIR adaptive filter 40 of FIG.
4 is controlled to be the minimum.

FIG. 2 shows the operation of the conventional noise control device.
The description will be made with reference to FIG. In the figure, 7 is an engine rotation signal synchronized with the engine rotation, 30 is an exhaust noise signal which is an output signal of the microphone 3 in which only the exhaust noise 29 is detected by the microphone 3, 8 is a control signal, and 9 is a control error signal. .

In FIG. 1, an exhaust noise signal 30 is a signal having a characteristic synchronized with the cycle of the engine rotation signal 7.
Generates a control signal 8 having a waveform opposite in phase and the same amplitude to the exhaust noise signal 30. It can be seen that the noise control reduces the exhaust noise signal 30 to the control error signal 9 as a result of the noise control.

With the above operation, the frequency component of the exhaust noise 29 corresponding to the engine rotation signal 7 at the position of the microphone 3 can be reduced to the background noise level.

FIG. 22 shows a spectrum characteristic of the exhaust noise 29 to be subjected to the noise control, which is an output signal of the microphone 3 in a state where the noise control by the conventional noise control device is stopped. In the figure, reference numeral 45 denotes a spectrum of a noise component which can be controlled by a conventional noise control device and is synchronized with engine rotation, and reference numeral 46 denotes a background noise level in a power spectrum characteristic of exhaust noise 29 to be subjected to noise control.

FIG. 23 shows a spectrum characteristic of the control error signal 9 which is an output signal of the microphone 3 in a state where the noise control by the conventional noise control device is operated. In the figure, reference numeral 46 denotes a background noise level in the spectrum characteristic of the exhaust noise 29 to be subjected to noise control, and reference numeral 47 denotes a result of noise control performed by the conventional noise control device.
It is a spectrum of a noise component synchronized with the engine rotation.

By comparing FIG. 22 with FIG. 23,
In a control error signal 9, which is an output signal of the microphone 3 when noise control is performed by a conventional noise control device, a spectrum 4 of a noise component synchronized with the engine rotation.
5 can be confirmed to be reduced to the background noise level 46.

[0016]

In the conventional noise control apparatus as described above, since the distance between the exhaust pipe 1 and the microphone 3 is extremely short, heat generated from the exhaust pipe 1 at about 200 ° C. However, there is a problem that the microphone 3 which is normally operated at a temperature of about 80 ° C. is damaged. Further, there is a problem that the microphone 3 is damaged by exhaust gas discharged from the exhaust pipe 1.

The sixth embodiment of Japanese Utility Model Laid-Open No. 7-5198 has been made to solve the above problem. In the conventional example, the effect of the exhaust gas from the exhaust pipe 1 is avoided by providing the microphone 3 at a position shifted horizontally from the vertical upper part or the lower part (directly above or below) of the exhaust pipe 1. However, the microphone 3 has other factors besides the above-described problems in the exhaust pipe. For example, there is a frictional noise between the tire and the road surface generated from the tire of the own vehicle, and noise from another vehicle that passes or runs alongside the own vehicle.

In the conventional example, since the noise control device performs control to reduce the frequency component of the exhaust noise 29 corresponding to the rotation speed of the engine 5 to the background noise level, the microphone 3 controls the noise other than the exhaust noise. When installed in a place where the sound pressure is high, the sound pressure of the exhaust noise becomes relatively low, and the S / N of the control error sound detected by the microphone 3
Gets worse. Therefore, the effect of noise control is reduced.

Also, noise generated from another vehicle or
Even if the microphone 3 is installed in a region where the sound pressure of noise other than the exhaust noise such as the friction noise between the tire of the vehicle and the road surface is low, if the exhaust noise 29 cannot be effectively detected,
Similarly, the effect of noise control is reduced.

The present invention has been made to solve such a problem, and has been made to improve the installation environment of the microphone 3 which adversely affects the performance of the microphone 3, such as heat and exhaust gas emitted from the exhaust pipe 1. Also, even when the microphone 3 is separated from the exhaust pipe 1 and the speaker 2, the exhaust noise 29 can be effectively detected, and the noise other than the exhaust noise such as the noise generated from another vehicle or the friction noise between the tire of the own vehicle and the road surface. It is an object of the present invention to obtain an installation position of the microphone 3 where the sound pressure of the noise is low, the control effect of the noise control device is large, and stable control can be performed.

It is another object of the present invention to prevent the sensitivity from being lowered due to adhesion of dust or rainwater to the microphone.

[0022]

[Means for Solving the Problems]

(1) A noise control device according to the present invention includes: a speaker that emits a control sound that reduces engine exhaust noise emitted from a rear end portion of an exhaust pipe of an automobile vehicle by sound wave interference; A microphone for detecting a synthesized sound, and a controller for generating a control sound signal output from the speaker based on an output signal of the microphone, wherein the microphone is installed at a rear portion of the vehicle and when the vehicle is viewed from behind. It is arranged near the vertical center line of the vehicle.

(2) A speaker which emits a control sound for reducing engine exhaust noise radiated from the rear end portion of an exhaust pipe of an automobile by sound wave interference, and detects a synthesized sound of the engine exhaust noise and the control sound. Microphone
A controller for generating a control sound signal output from the speaker based on the output signal of the microphone, wherein the distance between the microphone and the speaker is determined by the distance between the microphone and the rear end of the engine exhaust pipe when viewed from the rear of the vehicle. It is arranged to be equal to or more than.

(3) A speaker that emits a control sound for reducing engine exhaust noise emitted from a rear end portion of an exhaust pipe of an automobile by sound wave interference, and detects a synthesized sound of the engine exhaust noise and the control sound. Microphone
A controller for generating a control sound signal output from the speaker based on the output signal of the microphone; and arranging the microphone at a rear portion of the vehicle and near a vertical center line of the vehicle when the vehicle is viewed from behind. In addition, when viewed from the rear of the vehicle, the distance between the microphone and the speaker is arranged to be equal to or longer than the distance between the microphone and the rear end of the engine exhaust pipe.

(4) The microphone is installed on a flat portion on the rear surface of the vehicle.

(5) The microphone is installed at the rear end of the vehicle.

(6) The microphone is installed on a flat portion outside the rear shock absorber of the vehicle.

(7) A speaker that emits a control sound for reducing engine exhaust noise emitted from the rear end of an exhaust pipe of an automobile by sound wave interference, and a synthesized sound of the engine exhaust noise and the control sound is detected. Microphone
The microphone includes a controller that generates a control sound signal output from the speaker based on an output signal of the microphone, and a waterproof cover that covers a surface of a sound collection unit of the microphone.

(8) A speaker that emits a control sound for reducing engine exhaust noise emitted from the rear end portion of the exhaust pipe of an automobile by sound wave interference, and a synthesized sound of the engine exhaust noise and the control sound is detected. Microphone
The microphone includes a controller that generates a control sound signal output from a speaker based on the output signal of the microphone, and a waterproof and dustproof case that seals the microphone.

(9) The controller is a controller that generates a control sound signal output from the speaker based on the output signal of the microphone and a signal synchronized with the rotation of the engine.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 shows a noise control device according to an embodiment of the present invention.
Is a speaker, 3 is a microphone, 5 is an engine, 7 is an engine rotation signal from the engine 5, 8 is a control signal, 9 is a control error signal which is an output signal of the microphone 3, 4 is an engine rotation signal 7 and a control error signal 9. This is a controller that generates a control signal 8.

Reference numeral 6 denotes a vehicle on which the exhaust pipe 1, the speaker 2, the microphone 3, the controller 4, and the engine 5 are mounted. In this case, the microphone 3 is located near the center of the rear surface of the vehicle shown in FIG.
It is located at 0. Since this installation location is separated from other vehicles passing on both sides and also away from the rear tires of the own vehicle, noise other than the exhaust pipe noise can be prevented from entering the microphone 3 as much as possible.

The operation of the noise control device configured as described above is the same as that of the conventional example, and the description is omitted.

The arrangement of the microphone 3 will be described with reference to FIG. In the figure, reference numeral 6 denotes a host vehicle, 11a and 11b.
Represents noise from other vehicles, 12 represents noise from other vehicles 11a and 11b, 1
Reference numeral 3 denotes a road surface friction sound of tires of the own vehicle 6, and reference numeral 14 denotes a region where sound pressure of noise other than exhaust noise is low, such as the noise 12 from the other vehicles 11 a and 11 b and the road surface friction sound 13 of the tires of the own vehicle 6.

As shown in FIG. 3, when the microphone 3 is installed on the rear surface of the vehicle, the microphone 3 is installed in the area 14 in FIG. This is a position where the sound pressure of the road surface friction noise 13 of the tire or the noise 12 from the other vehicles 11a and 11b is low. That is, the area 10 around the center of the rear surface of the vehicle in FIG. 2 is an area 14 where the sound pressure of noise other than the exhaust noise is low. The area 14 is a portion near the vertical center line of the vehicle when the vehicle is viewed from behind.

As described above, it is preferable to install the microphone 3 at a position that is hardly affected by heat or exhaust gas from the exhaust pipe 1 and that is least affected by noise other than exhaust noise. In the experiment, 10 around the center of the rear surface of the vehicle in FIG.
By installing the microphone 3, the sound pressure level of noise other than exhaust noise can be lowered by 3 to 6 dB.

When performing ANC (Active Noise Control) control, the component of the exhaust noise 29 to be controlled is reduced to the dark noise level. Level exhaust noise 29
If it is lower, the control accuracy of noise control will be improved.

In particular, when a process for reducing the corresponding frequency component according to the rotation speed of the engine 5 is performed, the influence of the noise of other vehicles which does not depend on the rotation speed of the engine 5 is eliminated, thereby achieving a stable operation. It is possible to perform the reduced processing.

Embodiment 2 FIG. 4 shows an embodiment of the arrangement of the exhaust pipe 1, the speaker 2, and the microphone 3. In the figure, 1 is an exhaust pipe, 2 is a speaker, 3 is a microphone, 15 is a line showing a constant sound pressure part at the position of the microphone 3 in the sound pressure distribution of the control sound 31 (shown in FIG. 18), and 18 is the same. In the sound pressure distribution of the exhaust noise 29 (shown in FIG. 18), a line indicating a constant sound pressure portion at the position of the microphone 3, and 19 is a noise control effect range.

FIG. 5 is a diagram showing iso-sound pressure lines in the distribution of sound pressure of the control sound 31 radiated from the speaker 2 when viewed from above the vehicle.
1 is a sound pressure distribution 15a close to the shape shown in the figure even during traveling.
And behaves as a sound generated from the point sound source 16.

On the other hand, FIG. 6 is a view showing an iso-sound pressure line in the sound pressure distribution of the exhaust noise 29 radiated from the exhaust pipe 1 when viewed from above the vehicle. The generated exhaust noise 29 generates a pulsating sound due to the discharge of an air current having a flow velocity, so that the exhaust noise 29 is not emitted from the point sound source 16 such as the control sound 31 radiated from the speaker 2 but from the exhaust pipe 1 as shown in the figure. Is the linear sound source 17 in the flow velocity direction. Since the line sound source 17 can be considered that the point sound sources 16 (two point sound sources are shown as an example in FIG. 6) exist continuously in the discharge direction of exhaust gas, a sound close to the shape of the drawing is obtained. Pressure distribution 18
a.

As described above, the exhaust noise 29 and the control sound 3
1 have different sound pressure distributions, when the exhaust pipe 1, the speaker 2, and the microphone 3 are arranged side by side in the rear of the vehicle, as shown in FIG.
The exhaust pipe 1 and the microphone 3 are arranged in this order (microphone 3
Better arrangement if the distance between the microphone 3 and the exhaust pipe 1 is the same as the distance between the microphone 3 and the exhaust pipe 1), so that the sound pressure is minimized at the position of the microphone 3. The control sound 31 is emitted from the speaker 2. Therefore, the sound pressure distribution 15 of the control sound 31 is approximately equal to the sound pressure distribution 18 of the exhaust noise 29. Therefore, the effect range 19 of the noise control is widened.

FIG. 7 shows a case where the exhaust pipe 1, the speaker 2, and the microphone 3 are arranged in this order. As shown in the figure, the control sound 31 is radiated from the speaker 2 so that the sound pressure is minimized at the position of the microphone 3. Therefore, the sound pressure distribution 1 of the control sound 31 is different from the sound pressure distribution 18 of the exhaust noise 29.
5 is small. For this reason, the effect range 19 of the noise control becomes narrow.

By arranging the exhaust pipe 1, the speaker 2, and the microphone 3 as described above so that the distance between the microphone 3 and the speaker 2 is equal to or longer than the distance between the microphone 3 and the exhaust pipe 1, noise is reduced. The control effect range 19 can be widened. When the exhaust pipe 1, the speaker 2, and the microphone 3 are arranged side by side at the rear of the vehicle, since the exhaust pipe 1 and the speaker 2 cannot be arranged at the same distance from the microphone 3, the speaker 2, the exhaust pipe 1, and the microphone 3 are not arranged. By arranging them in the order of 3, the effect range 19 of the noise control can be widened.

It should be noted that even if the microphone 3 is positioned diagonally above the exhaust pipe 1, the microphone 3 and the speaker 2
May be arranged to be equal to or longer than the distance between the microphone 3 and the exhaust pipe 1.

Embodiment 3 FIG. 8 shows an embodiment in the case where the microphone 3 is attached to the flat portion 20 around the central portion 10 of the rear surface of the vehicle in the first or third embodiment. Thereby, the microphone 3 can effectively detect only the direct noise of the exhaust noise 29 and the control sound 31. Thereby, the control operation for reducing the exhaust noise 29 can be stabilized.

Here, the flat portion 20 is a portion having a flat surface substantially perpendicular to the discharge direction of the exhaust gas from the exhaust pipe 1, and the non-flat portion is the other portion.

FIG. 10 shows the frequency / gain characteristics of the transfer function of the control transmission system when the microphone 3 is installed on the non-flat portion 21 on the rear surface of the vehicle in FIG. In the figure, reference numeral 22 denotes a peak of the frequency / gain characteristic in the transfer function of the control transmission system, and reference numeral 23 denotes a dip of the frequency / gain characteristic in the transfer function of the control transmission system. From the figure,
When the microphone 3 is installed on the non-flat portion 21 on the rear surface of the vehicle, there are many peaks 22 and dips 23 and the level is large.

When there is a large peak 22 in the frequency / gain characteristic in the transfer function of the control transfer system, the peak 2
At a certain frequency, the control sound 31 radiated from the speaker 2 in the control transmission system has a larger control sound 31 than the region without the peak 22 in the control error sound detected by the microphone 3. The level is detected, and the LM in the controller 4 shown in FIG.
The S (Least Mean Square) algorithm 41 has the control sound 31
The coefficient 43 of the FIR adaptive filter is updated so as to reduce the amplitude of. Therefore, the coefficient 43 of the FIR adaptive filter is
Has a small value, and the amplitude of the generated control sound 31 is small. For this reason, the effect of noise control is reduced.

When a large dip 23 exists in the frequency / gain characteristics of the transfer function of the control transfer system,
At a certain frequency where the dip 23 is present, in the control transmission system, although the control sound 31 is emitted from the loudspeaker 2, the control error sound detected by the microphone 3 is smaller than the region where the dip 23 is not present. Since the level of the small control sound 31 is detected and the LMS algorithm 41 in the controller 4 updates the coefficient 43 of the FIR adaptive filter to increase the amplitude of the control sound 31, the coefficient 43 of the FIR adaptive filter is The value becomes large, and the amplitude of the generated control sound 31 increases.

For this reason, an excessive level of sound is output from the speaker 2, and the effect of noise control is reduced. In addition, the value of the coefficient 43 of the FIR adaptive filter causes a failure due to overflow in digital calculation.

As described above, the peak 22 and the dip 23 of the frequency / gain characteristic in the transfer function of the control transmission system
Affects the output amplitude of the control signal 8 in the controller 4, and when the peak 22 or the dip 23 is large, the control operation becomes unstable, the control effect is reduced, or the control is broken. Occur.

As a result, the peak 22 of the frequency / gain characteristic in the transfer function of the control transfer system and the dip 23
, The control calculation can be stabilized, and the noise control effect can be improved.

FIG. 9 shows the frequency / gain characteristics of the transfer function of the control transmission system when the microphone 3 is installed on the flat portion 20 on the rear surface of the vehicle in FIG. As shown in the figure, when the microphone 3 is installed on the flat portion 20 on the rear surface of the vehicle, the peak 22 and the dip 2
3 is small.

As a result of comparing the frequency / gain characteristics of the transfer function of the control transfer system of FIGS. 9 and 10, the characteristic when the microphone 3 is installed on the flat portion 20 of FIG. 9 is better than the non-flat portion of FIG. The peak 22 and the dip 23 are smaller than the characteristics when the microphone 3 is installed in the microphone 21.

As a result, the peak 22 and the dip 23 in the frequency / gain characteristics of the transfer function of the control transmission system can be reduced by installing the microphone 3 on the flat portion 20 on the rear surface of the vehicle. The control calculation can be stabilized, and the noise control effect can be improved.

Embodiment 4 FIG. FIG. 11 shows an embodiment in which the microphone 3 is attached to a shock absorber (bumper) 24 at the rear of the vehicle as the flat portion 20 on the rear surface of the vehicle according to the first or third embodiment. Thus, similarly to the third embodiment, the peak 22 in the transfer function of the control transfer system is obtained.
And dip 23 decreases, stabilizes control calculation,
The noise control effect can be improved.

Further, by installing the microphone 3 in the shock absorber 24 at the rear of the vehicle, the microphone 3 is disposed in an area other than the shock absorber 24 at the rear of the vehicle in the area 14 (shown in FIG. 3) where the sound pressure of noise other than exhaust noise is low. As compared with the case where the microphone 3 is installed, the distance to the exhaust pipe 1 and the speaker 2 is relatively short, so that the control error sound can be effectively detected and the calculation accuracy of the noise control calculation is improved.

By installing the microphone 3 in the shock absorber 24 at the rear of the vehicle, the microphone 3 is located at the rearmost end of the vehicle, and the exhaust noise 29 radiated to the rear of the vehicle is detected. In this case, there is no obstruction, so that the occurrence of the peak 22 and the dip 23 of the frequency / gain characteristic in the transfer function of the control transfer system can be suppressed, and the control calculation can be stabilized. Furthermore, since the shock absorber 24 at the rear of the vehicle is generally made of resin,
It is easy to assemble, and it is also possible to embed the microphone unit.

Embodiment 5 FIG. FIG.
Is a diagram illustrating an embodiment in which the microphone unit 25 is a sound wave detector in the microphone 3.
Sound collecting section 26 (diameter of about 10 m)
m), a resin waterproof cover 2 with a thickness of about 0.5 mm
7 is attached so as to be in close contact. With this, 500H
A waterproof and dustproof structure can be provided without lowering the sensitivity of the microphone 3 at z or less.

Further, by making the surface of the resin waterproof cover 27 attached to the sound pickup section 26 a flat surface, it is possible to prevent foreign substances such as wax and dirt from adhering, and the sensitivity characteristic of the microphone 3 is improved. Peaks 22 and dips 23 of the control transmission system that affect noise control, such as changes
Can be prevented. Even if foreign matter such as wax or dirt adheres, the surface of the resin waterproof cover 27 attached to the sound pickup unit 26 is flat, so that wiping and cleaning are easy. Although the thickness is set to 0.5 mm here, the thickness may be determined according to the required frequency band.

Embodiment 6 FIG. In the fifth embodiment, the surface of the microphone unit 25 in the microphone 3 is
The thickness of the resin waterproof cover 27 attached to the sound pickup section 26 so as to be in close contact with the sound pickup section 26 is about 0.5 mm (when the diameter of the sound absorbing section of the microphone is about 10 mm), but the strength is further improved. An embodiment will be described.

FIG. 13 shows an embodiment of the strength improvement in which the shape of the back side of the resin waterproof cover 27 is changed. The thickness of the resin waterproof cover 27 is about 1 mm, which is about twice as thick as that of the fifth embodiment. In order to prevent the sensitivity of the microphone 3 from being lowered, a structure is adopted in which several voids 27a for sound collection are provided on the back side of the resin waterproof cover 27, and thin portions are provided.

FIG. 14 shows the sound-collecting gap portion 27a as viewed from the microphone insertion side, and the hatched portion is the gap portion 27a. Thus, the same effect as in the fifth embodiment can be obtained, and the mechanical strength of the resin waterproof cover 27 can be increased. That is, the required frequency range can be absorbed by the thin part, and
The thick part improves the strength of the waterproof cover.

FIGS. 15 and 16 show other examples of the structure of the sound-collecting gap portion 27a. FIG. 15 shows a thick girder portion 27 in a hatched sound collecting void portion 27a.
b is provided in two places in parallel. Also, FIG.
A thick girder-like portion 27b is provided in the hatched sound-collecting gap portion 27a at two locations in each of the vertical and horizontal directions.

Embodiment 7 In the above fifth and sixth embodiments, as shown in FIGS. 12 and 13, the microphone case 28 and the resin waterproof cover 27 are separate bodies, so that the mounting portion (the threaded portion in the figure) of the resin waterproof cover 27 is different. It is conceivable that the sensitivity characteristic of the microphone 3 changes or the microphone case 28 is flooded due to looseness or the like.

As a countermeasure, as shown in FIG. 17, by integrating the resin waterproof cover 27 and the microphone case 28, the microphone 3 due to the looseness of the resin waterproof cover 27 which exists in the fifth and sixth embodiments. Can completely prevent problems such as a change in the sensitivity characteristic of the device and infiltration from the mounting portion of the resin waterproof cover 27.
Airtightness, waterproofness, and dustproof performance are improved. Also, the number of parts can be reduced. Further, a structure in which the bumper, the waterproof cover, and the microphone case are integrated may be adopted.

Embodiment 8 FIG. In the first and second embodiments, as shown in FIG. 2, the exhaust pipe 1 is on the right side (or left side) when viewed from the rear of the vehicle.
Each of the above-described embodiments can be realized even when the is located near the center. Also in this case, the distance between the microphone 3 and the speaker 2 is set to be equal to or longer than the distance between the microphone 3 and the exhaust pipe 1.

[0069]

Since the present invention is configured as described above, it has the following effects.

(1) The microphone is installed at the rear of the vehicle.
In addition, by arranging the vehicle near the vertical center line of the vehicle when viewed from the rear, the sound pressure of noise other than exhaust noise, which is dark noise, is reduced, and the control accuracy of noise control is improved.

(2) By arranging the microphone and the speaker so that the distance between the microphone and the speaker is equal to or longer than the distance between the microphone and the rear end of the engine exhaust pipe when viewed from the rear of the vehicle, the speaker and the exhaust pipe emit radiation. The sound pressure distribution of the sound to be made is substantially the same, and the effect range of the noise control is widened.

(3) By providing the above (1) and (2), the sound pressure of noise other than exhaust noise, which is a dark noise, is reduced, control accuracy of noise control is improved, and a speaker and an exhaust pipe are provided. The sound pressure distribution of the sound radiated from is substantially the same, and the effective range of the noise control is widened.

(4) By arranging the microphone on the flat part of the rear surface of the vehicle, the peak and dip of the frequency / gain characteristics in the transfer function of the control transfer system are reduced, the control calculation is stabilized, and the noise control effect is improved. I do.

(5) By installing the microphone at the rear end of the vehicle, the control error sound is effectively detected, and the control effect is improved.

(6) By installing the microphone on a flat portion outside the rear shock absorber of the vehicle, the control error sound is effectively detected, the control effect is improved, and the assembly is facilitated.

(7) By covering the surface of the sound pickup section of the microphone with the waterproof cover, the sensitivity of the microphone is maintained and the waterproof and dustproof performance is improved.

(8) By sealing the microphone with a waterproof and dustproof case, the sensitivity of the microphone is maintained and the waterproof and dustproof performance is further improved.

(9) By generating a control sound signal output from the speaker based on the microphone output signal and a signal synchronized with the engine rotation, the influence of the noise of another vehicle independent of the engine speed can be obtained. It can be eliminated and noise can be reduced stably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a noise control device according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing the vicinity of the center of the rear surface of the vehicle in the noise control device according to Embodiment 1 of the present invention;

FIG. 3 is a relationship diagram showing a distribution of noise other than engine exhaust noise in the noise control device according to Embodiment 1 of the present invention.

FIG. 4 is a configuration diagram illustrating a control effect area of the noise control device according to the second embodiment of the present invention.

FIG. 5 is a configuration diagram showing distribution characteristics of sound radiated from a speaker according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing distribution characteristics of exhaust noise radiated from an exhaust pipe according to Embodiment 2 of the present invention.

FIG. 7 is a configuration diagram showing a control effect area of the noise control device in the description of the second embodiment of the present invention.

FIG. 8 is a configuration diagram illustrating a microphone mounting surface of the noise control device according to the third embodiment of the present invention.

FIG. 9 is an acoustic transfer characteristic diagram showing control transfer characteristics in a noise control device according to Embodiment 3 of the present invention.

FIG. 10 is an acoustic transfer characteristic diagram showing a relation with a control transfer characteristic in the description of the noise control device according to the third embodiment of the present invention.

FIG. 11 is a layout diagram of a noise control device according to Embodiment 4 of the present invention.

FIG. 12 is a configuration diagram of an error signal detection microphone according to a fifth embodiment of the present invention.

FIG. 13 is a configuration diagram of an error signal detection microphone according to Embodiment 6 of the present invention.

FIG. 14 is a structural diagram of a main part of a resin waterproof cover according to a sixth embodiment of the present invention.

FIG. 15 is a structural view of a main part of a resin waterproof cover according to a sixth embodiment of the present invention.

FIG. 16 is a structural diagram of a main part of a resin waterproof cover according to a sixth embodiment of the present invention.

FIG. 17 is a configuration diagram of an error signal detection microphone according to Embodiment 7 of the present invention.

FIG. 18 is a configuration diagram showing a conventional noise control device.

FIG. 19 is a configuration diagram showing a controller unit of a conventional noise control device.

FIG. 20 is a configuration diagram illustrating an algorithm of a controller unit of a conventional noise control device.

FIG. 21 is a waveform chart showing a relationship among an engine rotation signal, exhaust noise, control sound, and control error sound.

FIG. 22 is a characteristic diagram showing a spectrum characteristic of exhaust noise radiated from an exhaust pipe.

FIG. 23 is a characteristic diagram showing a control effect of a conventional noise control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Exhaust pipe 2 Speaker 3 Microphone 4 Controller 5 Engine 6 Vehicle (own vehicle) 7 Engine rotation signal 8 Control signal 9 Control error signal 10 Around center of rear surface of vehicle 11a Other vehicle on right side of own vehicle 11b Other on left side of own vehicle Vehicle 12 Noise from other vehicles 13 Tire road surface friction noise 14 Region where the sound pressure of noise other than exhaust noise is low 15 Sound pressure distribution of control sound 15a Sound pressure distribution of point sound source 16 point sound source 17 Linear sound source in flow direction 18 Exhaust noise 18a Sound pressure distribution of line sound source 19 Effective range of noise control 20 Flat portion on rear surface of vehicle 21 Non-flat portion on rear surface of vehicle 22 Peak of control transmission system 23 Dip of control transmission system 24 Vehicle rear shock absorber 25 Microphone unit 26 Microphone unit sound collecting part 27 Resin waterproof cover 27a Void part for sound absorption 27b Digit shape Minute 28 microphone case 29 exhaust noise 30 exhaust noise signal 31 control sound 32 anti-aliasing low-pass filter 33 A / D converter 34 control error signal converted into digital signal 35 digital signal processor (DSP) 36 digital signal format control signal 37 D / A converter 38 Smoothing low-pass filter 39 Amplifier 40 FIR adaptive filter 41 Filter coefficient updating algorithm 42 Delay element 43 FIR adaptive filter coefficient 44 Adder 45 Noise component synchronized with engine rotation when noise control is stopped 46 Background noise level 47 Noise component synchronized with engine rotation during noise control operation

Claims (9)

[Claims] 1. A speaker that emits a control sound for reducing engine exhaust noise emitted from a rear end portion of an exhaust pipe of an automobile vehicle by sound wave interference, and a microphone that detects a synthesized sound of the engine exhaust noise and the control sound. A controller that generates a control sound signal output from the speaker based on the output signal of the microphone, and installs the microphone at the rear of the vehicle and near the vertical center line of the vehicle when viewing the vehicle from behind. A noise control device characterized by being arranged. 2. A speaker for radiating a control sound for reducing engine exhaust noise radiated from a rear end portion of an exhaust pipe of an automobile vehicle by sound wave interference, and a microphone for detecting a synthesized sound of the engine exhaust noise and the control sound. A controller that generates a control sound signal output from the speaker based on the output signal of the microphone, and that, when viewed from the rear of the vehicle, sets a distance between the microphone and the speaker between the microphone and the rear end of the engine exhaust pipe. A noise control device, wherein the noise control device is arranged so as to be equal to or longer than the distance. 3. A speaker for radiating a control sound for reducing engine exhaust noise radiated from a rear end portion of an exhaust pipe of an automobile by sound wave interference, and a microphone for detecting a synthesized sound of the engine exhaust noise and the control sound. A controller that generates a control sound signal output from the speaker based on the output signal of the microphone, and installs the microphone at the rear of the vehicle and near the vertical center line of the vehicle when viewing the vehicle from behind. A noise control device, wherein the distance between the microphone and the speaker is equal to or greater than the distance between the microphone and the rear end of the engine exhaust pipe when viewed from behind the vehicle. 4. The noise control device according to claim 1, wherein the microphone is installed on a flat portion on a rear surface of the vehicle. 5. The noise control device according to claim 1, wherein the microphone is provided at a rear end of the vehicle. 6. The noise control device according to claim 1, wherein the microphone is provided on a flat portion outside a rear shock absorber of the vehicle. 7. A speaker for emitting a control sound for reducing engine exhaust noise emitted from a rear end portion of an exhaust pipe of an automobile vehicle by sound wave interference, and a microphone for detecting a combined sound of the engine exhaust noise and the control sound. A noise control device comprising: a controller that generates a control sound signal output from the speaker based on an output signal of the microphone; and a waterproof cover that covers a surface of a sound collection unit of the microphone. 8. A speaker for emitting a control sound for reducing engine exhaust noise emitted from a rear end portion of an exhaust pipe of an automobile vehicle by sound wave interference, and a microphone for detecting a combined sound of the engine exhaust noise and the control sound. A noise control device comprising: a controller that generates a control sound signal output from a speaker based on an output signal of the microphone; and a waterproof and dustproof case that seals the microphone. 9. The controller according to claim 1, wherein the controller generates a control sound signal output from a speaker based on an output signal of the microphone and a signal synchronized with rotation of the engine. 2. The noise control device according to claim 1.