JPH09218686A - Active silencer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a response characteristic simplifying constitution of hardware and software by generating an electrically equivalent noise to an exhaust noise generated from an engine adapting to an operation state of the engine. SOLUTION: Errors of a phase and a level of main components of a equivalent noise generated by an equivalent noise generation means 13 under an operation state of an engine are compensated for each component, and an electric signal is generated. That is, an error to be given to an equivalent noise processing means 14 to highly maintain extent of suppression made by synthesizing with a silencing wave radiated from a secondary sound source 12 is surely given following frequency of sampling without performing integration for main components of an exhaust noise individually. Therefore, a response characteristic of this device is largely improved comparing with a conventional device in which errors of a phase and a level of a silencing wave is obtained under application of integration operation such as Fourier transform and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active silencer for acoustically synthesizing engine exhaust noise with noise of opposite phase to suppress the emission level of the exhaust noise.

[0002]

2. Description of the Related Art An active silencer is designed to actively combine an acoustic signal generated by a secondary sound source with exhaust noise to reduce the exhaust noise, thereby making the acoustic impedance short-circuit surface to the exhaust noise passive. Since it can be formed over a wider band than a type silencer, it is applied to various vehicles.

FIG. 7 is a diagram showing a configuration example of a conventional active silencer. In the figure, the exhaust port of the engine 70 is extended to the opening of the exhaust pipe via the exhaust pipe 71 ₁ , the front silencer 72 and the exhaust pipe 71 ₂ which are connected in series, and the periphery of the opening is An acoustic tube 73 whose one end has an open surface is provided around the circumference of the acoustic tube 73. A speaker 74 is provided at the other end of the acoustic pipe 73, and is discharged from the exhaust pipe in the vicinity of the opening of the exhaust pipe 71 ₂ and the opening surface of the acoustic pipe 73 while being acoustically tightly coupled to both. The microphone 75 is arranged via a mechanism for shielding the exhaust gas. The output of an engine controller (not shown) that controls the operating condition of the engine 70 is connected to the control input of the equivalent noise generator 76, and the output of the equivalent noise generator is connected to the input of the phase amplitude adjuster 77. . The output of the phase amplitude adjuster 77 is the transfer characteristic identifier 7
8 and the speaker 74, and the output of the transfer characteristic identifier 78 is connected to the input of the inverting amplifier 79 and one input of the error calculator 80. The output of the inverting amplifier 79 is connected to one input of the adder 81, and the output of the microphone 75 is connected to the other input of the adder 81. The output of the adder 81 is connected to the other input of the error calculator 80, and the plurality of outputs of the error calculator are connected to the corresponding inputs of the phase amplitude adjuster 77.

In the conventional example having such a configuration, the engine 7
Exhaust gas and exhaust noise emitted by the exhaust pipe
_It is guided to the front silencer 72 via ₁ , and the front silencer mainly has a high frequency (for example, 500 Hz) in the exhaust noise component.
Component having the above frequency) is suppressed. Further, exhaust noise (hereinafter referred to as “noise wave”) S ₁ that has passed through the front silencer 72 together with the above-described exhaust gas is radiated from the opening of the exhaust pipe 71 ₂ .

On the other hand, the equivalent noise generator 76 generates an electric signal equivalent to the exhaust noise emitted by the engine 70 in accordance with the operating condition given by the engine controller. The phase / amplitude adjuster 77 generates a drive signal by subjecting such an electric signal to a process of correcting an error amount between the phase and the amplitude given from the error calculation unit 80 for each frequency component as described later. The speaker 74 electro-acoustically converts the drive signal, and the resulting acoustic signal is radiated as the sound wave S ₂ via the acoustic tube 73.

[0006] transfer characteristic identifier 78 consists of a FIR filter or the like have equivalent electrical transfer characteristics inherent transmission characteristic of the acoustic tube 73, equivalent electrical signal to vanishing wave S ₂ described above (hereinafter , "Silenced electrical signal s ₂ ") is generated. In addition, the microphone 75 captures an acoustic signal given by the vector sum of the noise wave S ₁ radiated from the opening of the exhaust pipe 71 ₂ and the sound wave S ₂ radiated from the opening of the acoustic pipe 73, and the sound- An electrical signal that is electrically converted and corresponds to the sum of the noise wave and the sound wave (hereinafter referred to as "detection signal")
(= S ₁ + s ₂ ) is output. The adder 81 outputs an error signal s ₁ ′ that is substantially equal to the noise wave S ₁ described above by taking the sum of such a detection signal and the electric signal given in reverse phase via the inverting amplifier 79.

The error calculating section 80 takes in the error signal s ₁ ′ and the above-mentioned silenced electric signal s ₂ , individually and in parallel, performs a fast Fourier transform (FFT), and calculates the exhaust noise S ₁ described above. The power difference and the phase difference are calculated for each of the main frequencies in the frequency spectrum, and an error signal indicating these differences is output. The phase amplitude adjuster 77 adds the difference between the phase indicated by such an error signal and π radian to the electric signal generated by the equivalent noise generator 76, and the difference between the electric powers similarly indicated by the error signal. A compression signal is sequentially applied to generate a drive signal.

That is, between the sound wave S ₂ emitted from the speaker 74 via the acoustic pipe 73 and the noise wave S ₁ emitted from the opening of the exhaust pipe 71 ₂ , the main frequency of the exhaust noise is generated. Since the energy level is substantially the same for each component and the phase is maintained substantially opposite to each other, the acoustic impedance short-circuit surface for exhaust noise is in a wide band in a physically wide area from the vicinity of the exhaust pipe 71 _2. Is formed over the entire area, and the effective emission level of exhaust noise is reliably suppressed.

[0009]

However, in the above-mentioned conventional example, the response to the change in the distribution of the frequency spectrum of the exhaust noise depends on the time required for sampling the error signal s ₁ ′ and the silencing electric signal s _2. , The time required by the phase amplitude adjuster 77 to vary the amplitude and the phase according to the calculation time required for the fast Fourier transform, which is started by the error calculation unit 80 when the sampling is completed, and the error signal obtained as a result of the calculation. Delay for a time equal to the sum of. Therefore, when the rotation speed of the engine 70 sharply increases or decreases, the primary component of the exhaust noise also sharply increases (for example, as shown in FIG. 8, the rotation speed of a 6-cylinder engine is 2 seconds). When the speed suddenly changed from 800 rpm to 7000 rpm, it changed from 32.5 Hz to 350 Hz), and in the band where the phase amplitude adjuster 77 could not follow (FIG. 8), the silencing characteristic was significantly deteriorated.

Further, although it is possible to optimize the operation time required for the fast Fourier transform and the configuration of the phase amplitude adjuster 77 described above, the time required for sampling to be performed prior to the fast Fourier transform is as follows: Generally, a value equal to at least the reciprocal of the frequency at which the muffling characteristics should be obtained is required, so it is not possible to flexibly follow sudden changes in engine operating conditions, and regulations concerning exhaust noise levels are prioritized. If it is required, there is a high possibility that restrictions will be imposed on the form related to the operation of the engine.

It is an object of the present invention to provide an active silencer which improves the responsiveness while simplifying the hardware and software configurations.

[0012]

FIG. 1 is a block diagram showing the principle of the invention described in claims 1 to 4.

According to the first aspect of the invention, the exhaust noise radiated from the opening is arranged so as to face the opening of the exhaust pipe forming the exhaust passage for the exhaust noise generated from the engine, and the exhaust noise is converted into acoustic-electricity. And an acoustic-electrical conversion means 11 for outputting a detection signal, and an acoustic emission port at a position which can be regarded as a point sound source in common with the opening, and the input electrical signal is acoustically converted to be emitted from the emission port. A secondary sound source 12 that emits a sound wave,
The equivalent noise generating means 13 for generating an electrical equivalent noise having the same frequency spectrum as the exhaust noise while adapting to the operating condition of the engine, and the equivalent noise generated by the equivalent noise generating means 13 under the operating condition. Equivalent noise processing means 14 for correcting an error instructed in terms of phase and level for each main component to generate an electric signal, and transfer characteristics of the secondary sound source 12 to the electric signal generated by the equivalent noise processing means 14. An equivalent filtering process is applied to generate a silence signal,
A first filtering means 15 for extracting a component individually corresponding to a main component from the muffling signal, and an acoustic-electrical converting means 11
A second filtering means 16 for taking a difference between the detection signal output by the first filtering means 15 and the muffling signal generated by the first filtering means 15, and extracting a component individually corresponding to a main component from the difference. Filtering means 15 and second filtering means 16
With respect to the components extracted by and, 2 at a predetermined frequency and a certain time Δt apart are performed in parallel.
Sampling means 17 for sampling two instantaneous values a and b, and a phase of a sine wave showing the components of each of the main components when the two instantaneous values a and b are sampled by the sampling means 17. A storage means 18 for previously storing a correspondence relationship between a phase θ given as an average of one or both of them and a quasi-gradient h ′ given by the equation of h ′ = ((b / a) −1) / Δt; Of the components extracted by the one filtering unit 15 and the second filtering unit 16, the components having the same band are given by the equations for the instantaneous values a and b sampled by the sampling unit 17. The quasi-gradient h ′ is calculated, and the phases θ ₁ and θ ₂ are obtained by referring to the storage means 18 based on the quasi-gradient, and the difference between these phases and π radians and the ratio of sine to each phase. And the error as an equivalent noise processing means 14
And an error detecting means 19 for instructing to.

According to a second aspect of the present invention, in the active silencer according to the first aspect, the first filtering means 15 and the second filtering means 16 operate depending on the operating condition of the engine. It is characterized by including means for varying a pass band in a band in which a main component of exhaust noise adapted to a situation is distributed.

According to a third aspect of the invention, in the active silencer according to the first or second aspect, the time Δt is
The sampling means 17 is set to a value that is directly proportional to the center frequency of the component to be sampled, and the storage means 18 is common to all the main components.
The invention described in claim 4 is the active silencer according to any one of claims 1 to 3, wherein the time Δt is
It is characterized in that it is set as a value of a monotone non-increasing function with respect to the center frequency of the component to be sampled by the sampling means 17.

(Operation) In the active silencer according to the invention described in claim 1, the equivalent noise generating means 13 has the same frequency spectrum as the exhaust noise generated from the engine while adapting to the operating condition of the engine. Generates electrical equivalent noise. The secondary sound source 12 has an acoustic emission port at a position that can be regarded as a point sound source common to the opening of the exhaust pipe that forms the exhaust passage of such exhaust noise, and the equivalent noise described above is equivalent to the equivalent noise described later. The sound wave is generated by being taken in through the processing means 14 and converted into sound, and the sound wave is emitted from the emission port. The sound-to-electricity conversion means 11 is arranged so as to face the opening of the exhaust pipe that forms the above-described exhaust noise discharge path, and exhaust noise and sound wave radiated from the opening and the emission port of the secondary sound source. Acoustic-electrically converted to output a detection signal.

The first filtering means 15 responds to the above-mentioned sound deadening by subjecting the electric signal generated by the equivalent noise processing means 14 to the later-described filtering processing equivalent to the transfer characteristic of the secondary sound source 12. A mute signal to be generated is generated, and components corresponding to the above-described main components are individually extracted from the mute signal. Further, the second filtering means 16 takes the difference between the detection signal output by the acoustic-electrical converting means 11 and the silencing signal generated by the first filtering means 15, and the same main component is obtained from the difference. The components individually corresponding to are extracted. The sampling means 17 samples two instantaneous values a and b of the components extracted by these filtering means in parallel with each other at a predetermined frequency with a predetermined time Δt apart.

On the other hand, in the storage means 18, for each of the similar main components, the 2
The phase θ corresponding to the average of one or both of the phases of the sine wave representing the component at each instant when the two instantaneous values a and b are sampled, and h ′ = ((b / a) -1) / Δt The corresponding relationship with the quasi-gradient h'given by the formula is shown. The error detection means 19
Among the components extracted by the first filtering unit 15 and the second filtering unit 16, for each of the components having the same band, the instantaneous values a and b sampled by the sampling unit 17 are expressed by the above equation. A given quasi-gradient h'is calculated, and the storage means 18 is referenced based on the quasi-gradient to obtain the phases θ ₁ , θ _2.
And the difference between these phases and π radians, and the ratio of the sine to each phase are taken as the error. The equivalent noise processing means 14 determines, for each main component of the equivalent noise generated by the equivalent noise generating means 13 under the operating condition of the engine,
The above-mentioned errors in phase and level are corrected to generate the electric signal described above.

That is, for each of the main components of the exhaust noise, the error to be given to the equivalent noise processing means 14 in order to maintain a high degree of suppression by the combination with the sound wave emitted from the secondary sound source 12, Since the sampling frequency is surely given without performing integration, the responsiveness is greatly improved as compared with the conventional example to which the Fourier transform is applied.

In the active silencer according to the second aspect of the invention, in the active silencer according to the first aspect, the first filtering means 15 and the second filtering means 16 depend on the operating condition of the engine. Accordingly, the passband is varied in the band in which the main components of exhaust noise are distributed according to the operating conditions. Therefore, the phase and level of the muffling sound waves emitted from the secondary sound source 12 are accurately set in accordance with the operating condition of the engine, and the muffling characteristic is maintained high even when the operating condition changes.

In the active silencer according to the third aspect of the invention, the time Δt is set to a value which is directly proportional to the center frequency of the component to be sampled by the sampling means 17, so that the sampling means The values of the two instantaneous values a and b sampled by 17 have the same value with respect to the phase θ regardless of their center frequencies, and the relationship between the quasi-gradient and the phase to be stored in the storage means 18 beforehand is also the same. There will be one way.

Therefore, the storage area of the storage means 18 to be referred to by the error detection means 19 is made common regardless of the above-mentioned center frequency, the size of software is reduced, and the processing procedure is simplified to respond. The nature is enhanced. In the active silencer according to the fourth aspect of the present invention, the time Δt is set as the value of the monotone non-increasing function of the center frequency of the component to be sampled by the sampling means 17.

That is, since the time Δt is set to a smaller value as the center frequency is higher, the two time values a and b are smaller as the center frequency is lower because the time Δt is constant. The accuracy of the quasi-gradient is reduced, and the noise suppression characteristics are suppressed from being deteriorated due to the noise being superposed in the analog region in the preceding stage of the sampling means 17 and the SN ratio being lowered.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a diagram showing an embodiment corresponding to the invention described in claims 1 to 4. In the figure, those having the same functions and configurations as those shown in FIG.
The same reference numerals are given and the description is omitted here. The difference between the present embodiment and the configuration of the conventional example shown in FIG. 7 is that an error calculating section 20 is provided instead of the error calculating section 80.

In the error calculator 20, the output of the adder 81 is connected to the inputs of the filters 21 _{1 to} 21 _N , and the output of the transfer characteristic identifier 78 is connected to the inputs of the filters 22 _{1 to} 22 _N. The outputs of the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N are connected to the corresponding inputs of the processor 23, and the outputs of the processors are connected to the corresponding inputs of the phase amplitude adjuster 77.

Regarding the correspondence relationship between this embodiment and the block diagram shown in FIG. 1, the microphone 75 corresponds to the sound-electricity converting means 11, the sound tube 73 and the speaker 74 correspond to the secondary sound source 12, and The equivalent noise generator 76 corresponds to the equivalent noise generator 13, the phase amplitude adjuster 77 corresponds to the equivalent noise processor 14, and the transfer characteristic identifier 78 and the filters 22 _{1 to} 22 _N correspond to the first filter 15. Correspondingly, the inverting amplifier 79, the filters 21 _{1 to} 21 _N and the adder 81 correspond to the second filtering means 16, and the processor 23 corresponds to the sampling means 17, the storage means 18 and the error detection means 19.

FIG. 3 is a diagram for explaining the operation of this embodiment. FIG. 4 is an operation flowchart of this embodiment. The operation of this embodiment corresponding to the invention described in claim 1 will be described below with reference to FIGS. Filter 21
Each of _{1 to} 21 _N and the filters 22 _{1 to} 22 _N has a desired pass band in a main component band of the exhaust noise component output from the engine 70, which is required to obtain a silencing characteristic.
In the following, for simplification, it is assumed that the filters having the same subscript numbers added to the codes have the same pass band.

Therefore, the filter 21₁~ 21_NOutput
Is the error signal s output by the adder 81.₁′ Of success
Of the minutes, the main components mentioned above are obtained individually and filtered
22 ₁~ 22_NMute electric signal s to output_Two As for
The main components of are obtained. By the way,
Filter 21₁~ 21_N, 22₁~ 22_NAbout
The band is narrow enough to suppress the main component
If the sharpness is high, it will be
The waveform of the electric signal is a sine wave as shown in Fig. 3 (a) and (b).
Can be considered.

Further, such a sine wave gradient (derivative coefficient with respect to time) h is generally given by a function of the phase θ shown by the curve shown in FIG. 5 (a). In addition,
In the following, for the sake of simplicity, it is assumed that the difference in frequency is ignored, the difference in frequency is ignored, and the amplitude of the sine wave is normalized by its maximum amplitude.

Further, of the amplitude values obtained by sampling the above-mentioned sine wave asynchronously at a constant cycle Δt under such conditions, two values adjacent to each other in the order of time series (obtained in advance) The value is referred to as “sample value a”, and the value obtained subsequently is referred to as “sample value b”.) H ′ = (b / a−1) / Δt. Regarding the gradient h ′, generally, the value of the phase θ is 2nπ to (2n + 0.5) π, (2n + 0) with respect to the natural number n in the same manner as the gradient h represented by the formula of h = (ba) / Δt. .5) π ~ (2
n + 1) π, (2n + 1) π ~ (2n + 1.5) π, (2n + 1.5) π ~
Since it is given as a function that monotonically increases or decreases in each section that takes a value of 2nπ and is normalized by the sample value a, it is determined without depending on the above-mentioned amplitude value.

The processor 23, as shown in FIG. 5B, in a specific storage area of its main memory (not shown),
For each of the center frequencies of the pass bands that the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N individually have, the phase table 3 discretely showing the above-mentioned correspondence between the phase θ and the quasi-gradient h ′.
1 in advance. Note that the phase table 31
However, the reason why it is individually provided for each center frequency described above is
This is because when the sampling period described later is constant regardless of the center frequency, the sample values a and b cannot be obtained with the same value even if the phase θ is the same.

Further, the processor 23 has a filter 21 ₁
Error signals s ₁ ′ obtained at the outputs of ˜21 _N , 22 _{1 to} 22 _N
And the silenced electric signal s ₂ are sampled in parallel at a constant period Δt (FIG. 4 (1)).
Further, the processor 23 determines that such an error signal s ₁ ′
And how the mute electric signal s _2, sample values obtained obtained in the order of time-series for each frequency component _{(a 11, b 1 1)} ~ (a
_1N , b _1N ), (a ₂₁ , b ₂₁ )-(a _2N , b _2N ), the forward gradient h ₁₁ ′ -h _1N ′, h ₂₁ ′ -h Calculate _2N '(Fig. 4 (2)),
And phase theta ₁₁ by referring to the phase table 31 corresponding to each frequency component on the basis of these order gradient individually
~ Θ _1N and θ ₂₁ ~ θ _2N are obtained (Fig. 4 (3)). When referring to the phase table 31 as described above, in order to eliminate the uncertainty of π radian shown in FIG. 5A, the processor 23 uses polar coordinates if the preceding sample value a is positive. If the first quadrant and the second quadrant are oppositely negative, the areas of the phase table corresponding to the third quadrant and the fourth quadrant are referred to.

Further, the processor 23, with respect to the phases θ _{11 to} θ _1N and θ _{21 to} θ _2N thus obtained, the frequency component i (= 1) of the error signal s ₁ ′ and the silencing electric signal s _2.
By performing the calculation shown to N) each into an expression of _{Δθ i = θ 1i -θ 2i -π} ΔL i = Sinθ 1i / Sinθ 2i, the phase error [Delta] [theta] _i
And the level error ΔL _i are calculated (FIG. 4 (4)), and the phase difference and the relative level are given to the phase amplitude adjuster 77 (FIG. 4 (5)).

The phase amplitude adjuster 77, the speaker 74, the acoustic tube 73, the transfer characteristic identifier 78, the inverting amplifier 79, and the inverting amplifier 79, which are performed according to the phase error Δθ _i and the level error ΔL _i thus provided, The operation of the adder 81 is the same as that of the conventional example, and therefore its explanation is omitted here. As described above, according to the present embodiment, the phase error Δθ _i and the level error ΔL _{i for} each frequency component i of the error signal s ₁ ′ and the silencing electrical signal s ₂ can be reliably performed at each sampling period Δt described above. Since it is found and given to the phase amplitude adjuster 77, these phase error and level error are originally the Fourier transform (FFT) which is an integral operation.
6 in comparison with the conventional example required under DFT).
The response is significantly improved as shown in (a), and (b) in the same figure.
As shown in, the muffling characteristics are uniformly obtained over a wide band.

The present embodiment corresponding to the invention described in claim 2 will be described below with reference to FIG. The characteristic of the configuration of the present embodiment is that, as shown by the dotted line in FIG. 2, the specific outputs of the above-mentioned engine controller (not shown) are individually input to the control inputs of the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N. It is at the connected point.

In such an embodiment, the filter 21 ₁
.. 21 _N and 22 _{1 to} 22 _N store in advance the pass characteristics (consisting of the pass band and the sharpness) that should be individually selected according to the operating conditions of the engine. In addition, the filter 21
_{1 to} 21 _N and 22 _{1 to} 22 _N monitor the operating status of the engine 70 that is sequentially notified from the engine controller, and always select the one of the passage characteristics stored in advance that is adapted to the operating status as described above. select. Therefore, these filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N have the components of the error signal s ₁ ′ and the silencing electric signal s ₂ of the engine 70 of the components of the error signal s ₁ ′ under the pass characteristics thus selected. The main frequency components adapted to the distribution of the frequency components of the exhaust noise according to the operating conditions are individually extracted and given to the processor 23.

The operation of each of the other parts is the same as the operation in the embodiment corresponding to the invention described in claim 1, and therefore the description thereof is omitted here. As described above, according to the present embodiment, the speaker 74 is connected to the acoustic tube 73.
Since the silencing wave S ₂ radiated via the engine can flexibly obtain the main component of the exhaust noise adapted to the operating condition of the engine 70 accurately and flexibly, the silencing sound S ₂ can be compared with the embodiment corresponding to the invention according to claim 1. The characteristics are further enhanced.

The present embodiment corresponding to the invention described in claim 3 will be described below with reference to FIG. In the present embodiment, the processor 23 includes the filters 21 _{1 to} 21 _N and 22.
Center frequencies f _{11 to} f _1N , f _{21 to} f of the pass band of _{1 to} 22 _N
The components of the error signal s ₁ ′ and the silenced electric signal s ₂ obtained at the outputs of these filters are sampled at a cycle individually proportional to _2N .

Therefore, with respect to the values of the sample values a and b obtained under the sampling with such a period, the center frequencies f _{11 to} f _1N of the pass bands of the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N , Regardless of f _{21 to} f _2N (or the above-mentioned pass band), all the above-mentioned components have the same value with respect to the phase θ. Therefore, the phase table 31 that the processor 23 has in its main memory is given the common content for all of the above-mentioned center frequencies, so it is unified, and the phase table 31 is calculated by referring to the phase table. The procedure is standardized and simplified regardless of its center frequency.

Therefore, according to the present embodiment, the scale of the software is reduced, the responsiveness is improved as compared with the embodiments corresponding to the inventions according to claims 1 and 4, and the noise reduction is equivalent to those of these embodiments. The characteristics are surely obtained. Hereinafter, FIG.
The present embodiment corresponding to the invention of claim 4 will be described with reference to FIG.

As shown by the alternate long and short dash line in FIG. 2, a specific output of the engine controller (not shown) is that the filters 21 _{1 to} 21 _N and 22 ₁ to 22 ₁ ...
It is connected to the input port of the processor 23 together with the control input of 22 _N. In the embodiment having such a configuration, the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N are the same as those of the embodiment corresponding to the invention described in claim 2, and the engine 70 provided from the above-mentioned arithmetic controller. The pass band is changed according to the operating status.

Further, the processor 23 takes in the operating statuses in parallel, and the center frequencies f _{11 to} f _{1N of the} pass bands taken by the filters 21 _{1 to} 21 _N and 22 _{1 to} 22 _N according to such operating statuses. , F _{21 to} f _2N , the sampling period is set to a value inversely proportional to f _{21 to} f _2N . Therefore, in the embodiments corresponding to the inventions described in claims 1 and 2, since the sampling frequency is constant, the accuracy of the forward slope which has been changed according to the center frequency is kept constant, and the silencing characteristic is improved. Maintained high.

Although the error signal s ₁ ′ and the silencing electrical signal s ₂ are sampled by the processor 23 in each of the above-described embodiments, the present invention is not limited to such a configuration. Filters 21 _{1 to} 21 _N , 22
_{1 to} 22 _N front stage, transfer characteristic identifier 78 and adder 81
Of the A / D converters, and a configuration in which equivalent processing is performed in the digital region in the subsequent stage of these A / D converters, and each unit other than the speaker 74 and the microphone 75 is equivalent in the digital region. It is also possible to adopt a configuration for performing a calculation.

Further, in each of the above-described embodiments, the phase corresponding to the quasi-gradient is obtained by referring to the phase table 31, but the present invention is not limited to such a configuration, and the operation time is allowable. If it can be suppressed to a possible value,
It is also possible to obtain the phase corresponding to the quasi-gradient by repeatedly performing the arithmetic operation with the quasi-gradient as the target value for the sine function for the sampling period converted into the phase.

Further, in each of the above-described embodiments, the front silencer 73 is interposed between the exhaust pipe 71 ₁ and the exhaust pipe 71 ₂ , but for such a front silencer, for example, It may not be installed if the exhaust noise component to be suppressed is sufficiently low under the operating mode of the engine 70 or is sufficiently suppressed under the application of the present invention.
Further, in each of the above-described embodiments, the speaker 74 constitutes a point sound source that is substantially common to the opening of the exhaust pipe 71 ₂ via the acoustic pipe 73, but the present invention is not limited to such a configuration. For example, when the acoustic emission surface of the speaker 74 can be directly regarded as a similar point sound source, the speaker may be arranged directly around the opening of the exhaust pipe 71 ₂ and the acoustic pipe 73 may not be included. It is possible.

Further, in each of the above-described embodiments, the processor 23 has the phase table 31 and the phase error Δθ.
_i and the level error ΔL _i are calculated to calculate the phase amplitude adjuster 77.
However, the present invention is not limited to such a configuration. For example, instead of the processor, the phase table 3
It is also possible to configure with a memory including a memory corresponding to 1 and an arithmetic unit that performs an equivalent arithmetic operation.

[0047]

As described above, according to the first aspect of the invention, the phase difference and the level difference of the sound wave are calculated under the application of the Fourier transform and other integral operations. Responsiveness is enhanced. According to the second aspect of the invention, the muffling characteristic is maintained high even in a state where the operating condition of the engine that generates exhaust noise changes.

According to the third aspect of the invention, the size of software is reduced and the responsiveness is enhanced. According to the invention described in claim 4, the variation in the silencing characteristics is surely suppressed for each frequency component of the exhaust noise. Therefore, in the equipment to which these inventions are applied, exhaust noise is stably suppressed over a wide band while adapting to the operating condition of the engine, and the restrictions relating to the operating condition are relaxed, and the operating environment is improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the invention described in claims 1 to 4.

FIG. 2 is a diagram showing an embodiment corresponding to the first to fourth aspects of the present invention.

FIG. 3 is a diagram for explaining the operation of this embodiment.

FIG. 4 is an operation flowchart of the embodiment.

FIG. 5 is a diagram showing a configuration of a phase table.

FIG. 6 is a diagram showing responsiveness and muffling characteristics of the present embodiment.

FIG. 7 is a diagram showing a configuration example of a conventional active silencer.

FIG. 8 is a diagram showing a silencing characteristic of a conventional example.

[Explanation of symbols]

 11 Acoustic-Electric Conversion Means 12 Secondary Sound Source 13 Equivalent Noise Generation Means 14 Equivalent Noise Processing Means 15 First Filtering Means 16 Second Filtering Means 17 Sampling Means 18 Storage Means 19 Error Detection Means 20, 80 Error Calculator 21 , 22 filter 23 processor 31 phase table 70 engine 71 exhaust pipe 72 front silencer 73 acoustic pipe 74 speaker 75 microphone 76 equivalent noise generator 77 phase amplitude adjuster 78 transfer characteristic identifier 79 inverting amplifier 81 adder

Claims (4)

[Claims] 1. An exhaust noise radiated from the opening, which is arranged so as to face an opening of an exhaust pipe forming an exhaust passage for exhaust noise generated from an engine, and outputs a detection signal. An acoustic-electrical conversion means (11) and an acoustic radiation port at a position which can be regarded as a point sound source common to the opening, acoustically transforms an input electric signal to radiate a sound wave from the radiation port. A secondary sound source (12), an equivalent noise generating means (13) for generating an electrical equivalent noise having the same frequency spectrum as the exhaust noise while adapting to the operating condition of the engine, and Equivalent noise processing means (14) for correcting the error instructed for the phase and level for each main component of the equivalent noise generated by the equivalent noise generating means (13) to generate the electric signal; The equivalent noise processing hand A filtering process equivalent to the transfer characteristic of the secondary sound source (12) is applied to the electrical signal generated by (14) to generate a muffling signal, and a component individually corresponding to the main component is extracted from the muffling signal. First filtering means
(15), and the difference between the detection signal output by the acoustic-electric conversion means (11) and the muffling signal generated by the first filtering means (15), and the main component is obtained from the difference. Second filtering means (16) for individually extracting the corresponding components
And the first filtering means (15) and the second filtering means (16)
With respect to the components extracted by and, 2 at a predetermined frequency and a certain time Δt apart are performed in parallel.
Sampling means (17) for sampling two instantaneous values a and b, and the sampling means (17) for each of the main components
And the phase θ given by the average of one or both of the phases of the sine wave representing the component at the time when the two instantaneous values a and b are sampled, and h ′ = ((b / a) −1) / Storage means (18) for pre-storing the corresponding relationship with the quasi-gradient h'given by the expression of Δt, the first filtering means (15) and the second filtering means (16).
For each of the components having the same band among the components extracted by and, the quasi-gradient h'given by the above equation is calculated for the instantaneous values a and b sampled by the sampling means (17). , Said storage means based on its quasi-gradient
The phases θ ₁ and θ ₂ are obtained with reference to (18), and the difference between these phases and π radians and the ratio of the sine to each phase are used as the error in the equivalent noise processing means (14). An active silencer comprising an error detecting means (19) for indicating. 2. The active silencer according to claim 1, wherein the first filtering means (15) and the second filtering means (16) are adapted to the operating conditions according to the operating conditions of the engine. An active silencer including means for varying a pass band in a band in which main components of the exhaust noise are distributed. 3. The active silencer according to claim 1 or 2, wherein the time Δt is set to a value which is directly proportional to the center frequency of the component to be sampled by the sampling means (17). The storage means (18) is an active silencer characterized in that all the main components are made common. 4. The active silencer according to any one of claims 1 to 3, wherein the time Δt is a monotone with respect to the center frequency of the component to be sampled by the sampling means (17). An active silencer characterized by being set as a value of a non-increasing function.