JPH0693825A - Active muffler - Google Patents

Abstract

PURPOSE:To ensure a satisfactory sound suppressing function for an active muffler, by stabilizing the sound transmitting characteristic between an sound wave output device and a residual sound detector. CONSTITUTION:An active d muffler comprises a sound wave output device 5 located around the output of an exhaust pipe 3 from an internal combustion engine, housings (a first casing 40 and a second casing 45) surrounding around the outlet of the exhaust pipe 3 and at least the sound wave outlet side of a sound wave outlet device 5 and having an opening separated away from the sound wave outlet device 5 by a specified distance, a residual sound detector 5 located around the opening so as to be exposed to the insides of the housings 40, 45. At least parts of the housings 40, 45 which extend from the sound outlet device 5 to the residual sound detector 6 (the second casing 45) is made of sound absorbable materials. Thus, exhaust sound from the exhaust pipe 3 interferes with sound waves having a reverse phase and issued from the sound wave outlet device 5 so as to be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active silencer mounted on an internal combustion engine, and in particular, it is provided with a sound wave output device for outputting a sound wave having a phase opposite to the exhaust sound from an exhaust pipe, and the sound deadening is performed by the interference effect of the sound waves. The present invention relates to an active silencer for performing.

[0002]

2. Description of the Related Art Recently, attention has been paid to an active silencer that actively silences sound by interfering sound waves with the exhaust sound of an internal combustion engine. For example, as described in Japanese Utility Model Application Laid-Open No. 63-118321, a speaker is provided in an exhaust pipe which is a noise outflow pipe for an internal combustion engine which is a noise source, and noise from the internal combustion engine is generated according to a predetermined control signal from the control means. That is, it is known that a compression pressure wave having a phase opposite to that of the exhaust sound, that is, a sound wave is output from a speaker, and the sound is canceled by the canceling action of both sound waves.

Further, Japanese Utility Model Laid-Open No. 4-15387 discloses an active cancel speaker in which a ring-shaped vibrating member is arranged between the outer circumference of an exhaust pipe and the inner circumference of an outer case.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Saikai 63-11
In the device disclosed in Japanese Patent No. 8321, the output sound wave of the speaker is reflected by the curved wall surface of the pipe, and becomes a reflected sound of various characteristics and is transmitted to the microphone near the outlet of the exhaust pipe. 6 and 7 show the speaker S for the exhaust pipe EX.
Although general arrangement examples of P are shown, in these arrangement examples, a part of the sound wave output from the speaker SP is directly input to the microphone MC, and a part thereof is housed in the housing H.
It is configured to be input to the microphone MC after being reflected by 1 and H2.

That is, in FIG. 6, a housing H1 is provided so as to surround the outlet of the exhaust pipe EX, and a speaker SP is arranged so as to output a sound wave in a direction orthogonal to the axis of the exhaust pipe EX. There is. And the housing H1
Inside, an enclosure E1 is formed behind the speaker SP, and a mixer (mixing portion) M1 including the front of the speaker SP and the outlet of the exhaust pipe EX is formed. Further, in FIG. 7, a speaker SP is arranged so as to output a sound wave in a direction parallel to the axis of the exhaust pipe EX. A speaker SP is provided in the housing H2 provided in the exhaust pipe EX.
Enclosure E2 is enclosed behind the speaker SP
A mixer M2 including the front part of the exhaust pipe EX and the outlet of the exhaust pipe EX is defined. The opening of the mixer M2 has a diameter slightly larger than that of the exhaust pipe EX, but has a smaller diameter than the main body of the housing H2 and has a throttle shape from the main body to the opening.
A wall surface is erected in front of the speaker SP.

In these devices, the main component of the sound wave in the directional direction of the speaker SP is input to the microphone MC after being reflected by the wall surfaces of the housings H1 and H2, but this reflected sound is time-delayed and phase-shifted with respect to the direct sound. However, these values are not constant. Furthermore, from the speaker SP to the microphone M
Since the transmission path to C becomes long, the housings H1 and H2
The acoustic transfer characteristics are likely to fluctuate due to changes in temperature inside. From this, it is extremely difficult to control the muffling at the position of the microphone MC, and the desired muffling performance cannot be obtained.

On the other hand, according to the apparatus disclosed in Japanese Utility Model Laid-Open No. 4-15387, the compression and compression pressure waves, that is, the sound waves are uniformly output around the exhaust pipe by the vibrating plate, and uniform characteristics are obtained on the outer circumference of the exhaust pipe. Therefore, the silencing action can be effectively performed. However, this publication does not describe the above-mentioned problems associated with the microphone and the outer case (housing) for detecting the residual sound.

Therefore, the present invention is an active silencer that includes a sound wave output device and a residual sound detector, and cancels sound by interfering sound waves of an opposite phase with the exhaust sound from the exhaust pipe. The purpose is to stabilize the acoustic transfer characteristics between the sound detector and the sound detector, and to secure good silencing performance.

[0009]

In order to achieve the above object, the present invention provides a sound wave output device disposed near the outlet of an exhaust pipe of an internal combustion engine, and an outlet of the exhaust pipe and at least the sound wave output device. A housing having an opening at a predetermined distance from the sound wave output device while surrounding the sound wave output side of
A residual sound detector disposed in the vicinity of the opening so as to be exposed in the housing, and muffles the exhaust sound from the exhaust pipe by interfering a sound wave of an opposite phase output from the sound wave output device. In the active silencer for performing the above, at least a portion of the housing from the sound wave output device to the residual sound detector is made of a sound absorbing material.

[0010]

In the active silencer having the above structure, when the internal combustion engine is started and rotated, the explosion sound generated in response to the explosion in each cylinder is transmitted through the exhaust sound path including the exhaust pipe and exhaust sound. And is discharged from the exhaust pipe. On the other hand, the sound wave output device operates in response to the detection signal of the residual sound detector, and a sound wave having an opposite phase is output in the housing, and the exhaust sound is canceled. In this case, since at least the portion from the sound wave output device to the residual sound detector of the housing is formed of the sound absorbing material, the component of the sound wave output from the sound wave output device that is reflected in the housing is formed of the sound absorbing material. It will be attenuated at the part where In other words, the ratio of the component in which the output sound wave is directly transmitted to the residual sound detector becomes large. Furthermore,
When the output sound wave is configured to interfere coaxially with the exhaust sound emitted from the outlet end of the exhaust pipe, the output sound wave with small output fluctuation and phase alignment over the wide frequency band is It will certainly interfere.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an active silencer according to the present invention will be described below with reference to the drawings. 1 and 2 relate to an embodiment of the present invention. First, referring to FIG. 2 showing the overall configuration, 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. It is equipped. Therefore, the exhaust manifold 2, the catalytic converter 9, and the exhaust pipe 3 constitute an exhaust sound path for the internal combustion engine 1 which is an exhaust sound source. An active silencer 4 is attached near the outlet 3a of the exhaust pipe 3. The active silencer 4 is provided with a sound wave output device 5 that outputs a sound wave, and a residual sound detector 6 that detects a residual sound near the outlet 3 a of the exhaust pipe 3. Further, a rotation signal detector 7 that outputs a signal synchronized with the rotation of the internal combustion engine 1 is provided, and is connected to the adaptive controller 10 together with the residual sound detector 6. This adaptive controller 10 has an adaptive digital filter and updates the coefficient of the transfer function of the adaptive digital filter by an adaptive algorithm according to the output signal of the residual sound detector 6 based on the output signal of the rotation signal detector 7 to obtain the residual sound. The sound wave output device 5 is driven and controlled so that the output signal of the detector 6 is minimized.

The active silencer 4 includes a sound output device 5 in a first case 40 having a bottomed cylindrical shape as shown in an enlarged view in FIG.
And a cylindrical second case 45 is joined to the first case 40, and an enclosure 40b is formed inside the first case 40 on the drive device 5a side of the sound wave output device 5. At the same time, the mixer 45b (mixing section) is defined in the second case 45 in which the diaphragm 5b of the sound wave output device 5 is oriented.

The second case 45 is made of a sound absorbing material and is joined to the first case 40 and at the same time the opening end 4 is formed.
It is opened to the outside through 5c. The inner diameter of the open end portion 45c is formed larger than the outer diameter of the exhaust pipe 3, but smaller than the outer diameter of the enclosure 45b portion, and has a throttle shape. As shown in FIG. 1, the exhaust pipe 3 is bent and formed in a substantially crank shape, penetrates the side wall 45a in an oblique direction with respect to the second case 45, and the outlet end 3b is in the second case 4.
5 is attached so as to be located on the axis connecting the open end portion 45c of 5 and the sound wave output device 5.

The sound wave output device 5 of this embodiment is of a cone speaker type and comprises a diaphragm 5b and a drive device 5a for driving the same. The drive device 5a is supported by the housing 40, and the vibration plate 5b is in the axial direction. It is arranged so as to vibrate and output a sound wave in the mixer 40b. The drive device 5b is, for example, an electrodynamic type device that converts an electric signal into mechanical vibration of the diaphragm 5b, and the diaphragm 5b vibrates when an AC voltage drive signal is supplied to a movable coil (not shown). A compressional pressure wave or sound wave is output.

Further, the opening end portion 45c of the second case 45 is formed.
Is provided with a residual sound detector 6 substantially in the directional direction of the diaphragm 5b, and the residual sound detector 6 detects the residual sound of the interference effect of the output sound wave of the sound wave output device 5 on the exhaust sound, A signal corresponding to this is output. Note that the residual sound detector 6 may take any form, such as a microphone and a pressure sensor, as long as it is a means for converting a pressure signal into an electric signal.

Next, the operation of the active silencer of this embodiment will be described. When the internal combustion engine 1 is started and rotated, the explosion sound generated in response to the explosion in each cylinder is transmitted through the exhaust sound path of the exhaust manifold 2, the catalytic converter 9 and the exhaust pipe 3 to form exhaust sound. Then, a rotation signal synchronized with the rotation of the internal combustion engine 1 is output to the adaptive controller 10. Further, the residual sound at the opening end portion 45 c is detected by the residual sound detector 6 and output to the adaptive controller 10.

In the adaptive controller 10, the transfer function of the adaptive digital filter is identified as the transfer function of the exhaust sound path by an adaptive algorithm corresponding to the output signal of the residual sound detector 6 based on the output signal of the rotation signal detector 7. That is, the coefficient is updated so that the output signal of the residual sound detector 6 is minimized, and the drive signal is output to the sound wave output device 5 accordingly. When a drive signal is input to the drive device 5a of the sound wave output device 5, the diaphragm 5b is driven in response to the drive signal and vibrates at a predetermined frequency, and a sound wave having a phase opposite to the exhaust sound is generated in the second case 45. Output, exhaust pipe 3
Will interfere with the exhaust sound emitted from the outlet 3a. That is, the exhaust sound is canceled in the opening cross section of the opening end portion 45c of the second case 45 including the residual sound detector 6 by the interference action of the sound wave of the opposite phase to the exhaust sound. Therefore,
An appropriate sound deadening region is formed in the opening cross section of the opening end 45c including the residual sound detector 6.

In this case, since the second case 45 is made of a sound absorbing material, the component of the output sound wave of the sound wave output device 5 reflected on the inner surface of the second case 45 is attenuated, and the residual sound detector is detected. 6, the level of the sound wave input as the indirect sound is reduced, and the component directly transmitted, that is, the ratio to the direct sound is reduced. In other words, the proportion of direct sound is high.

By the way, the adaptive controller 10
Is an input signal of the output signal of the rotation signal detector 7 and a detection signal of the residual sound detector 6, that is, an error signal, and remains in a muffling area (installation position of the residual sound detector 6) in which the output sound wave and the exhaust sound are canceled. The sound wave output device 5 outputs sound waves having opposite phases so that the sound becomes minimum.
However, the signal output from the adaptive controller 10 at that time is affected by acoustic transmission from the sound wave output device 5 to the sound deadening region, unlike the signal representing the output sound wave that actually reaches the sound deadening region. Therefore, the adaptive controller 10 needs to correct the acoustic transfer characteristics from the sound wave output device 5 to the sound deadening region.

There are two methods for this correction. One is to use a constant value as the correction value, assuming that the transfer characteristic from the sound wave output device 5 to the residual sound detector 6 is constant. The other one is a method in which the correction value itself is sequentially identified and updated while performing active cancellation. The latter correction method requires a system for measuring the transfer characteristics from the sound wave output device 5 to the residual sound detector 6, and also increases the amount of calculation, which causes a change in a wide frequency band such as vehicle exhaust noise. If the target is a loud sound,
High-speed calculation is required for the noise reduction, and the cost becomes very expensive. Therefore, it is realistic to use the former correction method.

However, since the former correction method is premised on the condition that "the transfer characteristic from the sound wave output device 5 to the residual sound detector 6 is always constant", the frequency range is wide and the change is drastic, and the environment is large. It is not easy to apply it to exhaust noise that has a sharp temperature change. According to this embodiment, since the second case 45 is made of the sound absorbing material as described above, the sound wave output from the sound wave output device 5 is generated by the second case 45.
Therefore, the component directly transmitted to the residual sound detector 6, that is, the ratio of the direct sound becomes large, and since the residual sound detector 6 is located in the sound wave output direction of the sound wave output device 5, It is possible to stabilize the acoustic transfer characteristics from the output device 5 to the residual sound detector 6, and it is possible to maintain high characteristics with a small output fluctuation in a wide frequency band and obtain characteristics with uniform phases.

FIG. 3 shows another embodiment of the active silencer of the present invention. The active silencer 4x of this embodiment has a first case 41 and a second case 42, The sound wave output device 5x is supported by the first case 41 to form a sound wave output unit. The first case 41 has a large-diameter outer cylinder portion 41.
a and an inner cylindrical portion 41b having a small diameter which is coaxially arranged with the outer cylindrical portion 41a, and the wall portion 41 is provided between the axial end portions of the both.
The shape is closed by c. The other axial end of the outer tubular portion 41a is open and a step portion 41d is formed.
In this embodiment, the outer cylinder portion 41a, the inner cylinder portion 41b, and the wall portion 41c are integrally formed of the same metal material as that of the exhaust pipe 3, for example. In the first case 41, the exhaust pipe 3 is fitted to the inner cylinder portion 41b, and is fixed to the stay 43 joined to the exhaust pipe 3 with bolts and nuts 44.

The second case 42 is a cylindrical body made of a sound absorbing material, which is composed of a large diameter portion 42a, a small diameter portion 42b and an inclined portion 42c between them. The step portion 41d of the first case 41 is fitted into the opening of the large-diameter portion 42a of the second case 42 to form a mixer surrounding the outlet 3a of the exhaust pipe 3. Then, the small diameter portion 42b of the second case 42
Is provided with a residual sound detector 6 similar to that of the above-described embodiment.

The sound wave output device 5x of this embodiment comprises an annular vibration plate 51 and a driving device 50 for driving the vibration plate 51. The driving device 50 is supported by the inner cylindrical portion 41b of the first case 41 and vibrates. The plate 51 is arranged so as to vibrate in the axial direction of the inner cylindrical portion 41b. Thus, the drive device 50 side of the sound wave output device 5x is surrounded by the first case 41 to form an enclosure. Although the diaphragm 51 of this embodiment has an annular shape, it may have a conical shape having a hole at the center.

The driving device 50 is an electrodynamic device for converting an electric signal into mechanical vibration of the diaphragm 51, and a winding is wound around a bobbin 52 fixed to the central portion of the diaphragm 51 so that a movable coil 53 is formed. The movable coil 53 is arranged between the core 54 fitted into the inner cylindrical portion 41b of the first case 41 and the permanent magnet 55 joined to the core 54 and arranged outside with a predetermined gap. ing. Further, an elastic member 56 having a wavy cross section is joined to the outer peripheral surface of the bobbin 52 and the inner peripheral surface of the outer tubular portion 41a. When an AC voltage drive signal is supplied to the movable coil 53, the vibrating plate 51 vibrates and a compressional pressure wave, that is, a sound wave is output.

The drive device 50 is not limited to the above, but a coil is wound around a core connected to a permanent magnet, and a drive signal is supplied to this coil to generate a vibration plate 51.
It is also possible to configure an electromagnetic type device that vibrates. Besides this, electrostatic type used in the field of speakers,
Various configurations such as electrostrictive type and magnetostrictive type can be adopted,
Further, the diaphragm 51 may be hydraulically driven to ensure high output.

Thus, in this embodiment, when a drive signal is input to the drive device 50 of the sound wave output device 5, the diaphragm 51 is driven in response to the drive signal and the exhaust pipe 3 is driven at a predetermined frequency.
Vibrates in the axial direction, and a sound wave having a phase opposite to the exhaust sound is output around the outlet 3a of the exhaust pipe 3 in the second case 42 and interferes with the exhaust sound emitted from the exhaust pipe 3. In this case, since the second case 42 of the present embodiment is made of the sound absorbing material, the component reflected by the inner surface of the second case 42 in the output sound wave from the sound wave output device 5x is attenuated. That is, the ratio of the direct sound transmitted to the residual sound detector 6 becomes large, and the acoustic transfer characteristics from the sound wave output device 5 to the residual sound detector 6 can be stabilized as in the above-described embodiment.

FIGS. 4 and 5 show still another embodiment of the active silencer of the present invention, in which the sound wave output device 5 of the embodiment of FIG. 1 transmits sound waves coaxially with the open end 3b of the exhaust pipe 3. 4 is arranged to output sound waves, the sound wave output device 5 is arranged to output sound waves in a direction perpendicular to the axis of the exhaust pipe 3 in the embodiment shown in FIG. A sound wave output device 5 is arranged so as to output a sound wave in parallel with the axis of the exhaust pipe 3. Therefore, the first cases 46, 48 of these embodiments
The shapes of the second cases 47 and 49 are different from those of the embodiment shown in FIG. 1, but the second cases 47 and 49 forming the mixer are made of a sound absorbing material like the second case 45 described above. Since the rest of the configuration is the same as that of the embodiment of FIG. 1, the substantially same parts are designated by the same reference numerals and the description thereof will be omitted. Thus, also in these embodiments, the component reflected by the second cases 47 and 49 of the output sound wave from the sound wave output device 5 is attenuated, and the sound wave output device 5 outputs the residual sound detector 6
It is possible to stabilize the sound transmission characteristics up to.

In each of the above-mentioned embodiments, the second case on the mixer side is made of a sound absorbing material, but the first case on the enclosure side may be made of a sound absorbing material. Thereby, the radiated sound emitted from the sound wave output device through the first case can also be reduced.

[0030]

Since the present invention is configured as described above, it has the following effects. That is, in the active silencer of the present invention, at least the portion of the housing from the sound wave output device to the residual sound detector is formed of a sound absorbing material, and a component of the output sound wave of the sound wave output device that is reflected in the housing. Is attenuated in the portion formed of the sound absorbing material, and therefore the proportion of the component directly transmitted to the residual sound detector is large, so that the acoustic transfer characteristics between the sound wave output device and the residual sound detector are stable. It is possible to secure good noise reduction performance.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an embodiment of an active silencer of the present invention.

FIG. 2 is a configuration diagram showing an overall configuration of an embodiment of an active silencer of the present invention.

FIG. 3 is a sectional view of another embodiment of the active silencer of the present invention.

FIG. 4 is a sectional view of still another embodiment of the active silencer of the present invention.

FIG. 5 is a sectional view of still another embodiment of the active silencer of the present invention.

FIG. 6 is a cross-sectional view showing an example of a general arrangement of speakers with respect to an exhaust pipe and an example of a housing shape.

FIG. 7 is a cross-sectional view showing another general arrangement example of the speakers with respect to the exhaust pipe and another housing shape example.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Exhaust Manifold 3 Exhaust Pipe 4, 4x Active Silencer 5 Sound Wave Output Device 6 Residual Sound Detector 7 Rotation Signal Detector 10 Adaptive Controller 40, 41, 46, 48 First Case 42, 45, 47, 49 Second case

Claims (1)

[Claims] 1. A sound wave output device disposed near an outlet of an exhaust pipe of an internal combustion engine, and an outlet of the exhaust pipe and at least a sound wave output side of the sound wave output device are surrounded by a predetermined distance from the sound wave output device. And a housing having an opening,
A residual sound detector disposed in the vicinity of the opening so as to be exposed in the housing, and muffles the exhaust sound from the exhaust pipe by interfering a sound wave of an opposite phase output from the sound wave output device. In the active silencer for performing the above, at least a portion of the housing from the sound wave output device to the residual sound detector is formed of a sound absorbing material.