JPH09166988A - Active noise eliminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically improve a responsibility to the change of revolving speed of an engine than hereto fore in an active noise eliminator for synthesizing an acoustic signal having a reverse phase witch an exhaust noise generated from the engine and reducing the radiation level of the exhaust noise. SOLUTION: The phase and level obtained by an exhaust noise extracting means 51 and the revolving speed of an engine 43 are inputted to an adjusting means 53, the phase and level corresponding to the revolving speed are called in from the preset transmission characteristic data of a noise eliminating pipe system 47, a phase adjusting value with which the called-in phase is adjusted to 180 or 360deg and a level adjusting value with which the called-in level is adjusted to zero are obtained and the phase and level obtained by the means 51 are corrected by these adjusting values.

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 reducing an emission noise level of exhaust noise by synthesizing an antiphase acoustic signal with exhaust noise generated from an engine.

[0002]

2. Description of the Related Art Generally, an active muffler positively combines an acoustic signal generated by a secondary sound source with exhaust noise to reduce the exhaust noise, thereby reducing the acoustic impedance to the exhaust noise. Since the short-circuit surface can be formed over a wider band than the passive silencer,
It is being adopted in various vehicles.

Of the conventional active silencers, for example, the one disclosed in Japanese Patent Laid-Open No. 4-272417 is shown in FIG.
As shown in FIG. 3, a sounding body 32 provided at a pipe end 31 which is an end portion of the exhaust pipe 30 so as not to be directly exposed to exhaust gas exhausted from the exhaust pipe 30, and a microphone provided at the end of the exhaust pipe 30. 33, a band pass filter (BPF) 34, an equalizer 35, and a power amplifier 36 that are connected in series between the microphone and the sounding body 32.

In the active silencer having such a structure, the microphone 33 converts the exhaust noise reaching the exhaust port from the engine into an electric signal, and the band pass filter 34 includes the component of the electric signal of the engine. Higher-order frequency components are extracted according to the rotational speed and other operating conditions. Equalizer 35
Between the sounding body 32 and the microphone 33 along the exhaust pipe 30, on the basis of the distribution of the frequency spectrum of the exhaust noise previously acquired according to the operating condition of the engine for the frequency component extracted in this way. The amount of phase shift and the amount of attenuation of the resonance system formed at are adjusted.

The power amplifier 36 power-amplifies the electric signal composed of the frequency components thus adjusted, converts the electric signal into an acoustic signal through the sounding body 32, and radiates the electric signal toward the exhaust port. Therefore, with respect to the main frequency component of the exhaust noise described above, the sounding body 3 is passed through the microphone 33, the bandpass filter 34, the equalizer 35, and the power amplifier 36.
By setting the gain and the phase amount up to 2 to constant values in advance, the exhaust noise radiated from the exhaust pipe 30 is combined with the acoustic signal radiated from the sounding body 32 in the opposite phase and reduced.

However, in such an active silencer, since the exhaust noise and the sound absorbing sound from the sounding body 32 are input to the microphone 33, the microphone 33 detects the phase and level of the exhaust noise independently. Therefore, the equalizer 35 is set so that the output from the microphone 33 becomes zero.
There is no method other than the converging operation, and there is a problem that the converging time is required to surely muffle the exhaust noise.

The present applicant has previously developed an active silencer capable of effectively solving such a problem, and filed an application as Japanese Patent Application No. 7-125396. As shown in FIG. 6, in this active silencer, the exhaust pipe 11 for discharging exhaust noise generated from the engine to the outside has an opening and an opening portion substantially coincide with each other, and one end is closed by the outer circumference. And a conversion body (corresponding to reference numeral 12 in the figure) provided in or near the opening of the exhaust pipe 11 for acoustic-electric conversion of exhaust noise, and closing of the cylinder. A secondary sound source (corresponding to reference numeral 15 in the drawing) which is arranged in the vicinity of the end portion and which electrically-acoustically converts an electric signal which gives an operation amount for acoustically canceling the exhaust noise, and sends the electric signal to the acoustic pipe 14. , Adjusting means for adjusting the operation amount (reference numeral 1 in the figure
9 and 20) and the operation amount from the adjusting means 19 and 20, and based on the transfer characteristics of the secondary sound source 15 and the acoustic tube 14 set in advance, the sound wave from the secondary sound source 15 is eliminated. Identification means (corresponding to 21 in the figure) for identifying the phase and level at the position of the conversion means 12, and the conversion of the exhaust noise based on the signal from the conversion means 12 and the signal from the identification means 21. Based on the exhaust noise extraction means (corresponding to reference numerals 22 and 16 in the figure) for obtaining the phase and level at the position of the means 12, the signal from the identification means 21 and the signals from the exhaust noise extraction means 22 and 16, A correction means (corresponding to reference numeral 17 in the drawing) for obtaining a correction amount for the fluctuation of the phase difference and the level difference and outputting the correction amount to the adjusting means 19, 20 is configured.

In such an active silencer, the identification means 2
The phase and level identified by 1 become substantially equal to the phase and level at the position of the actual sound deadening conversion means 12, and the exhaust noise extraction means 22, 16 extract based on this identified phase and level. The phase and level at the position of the exhaust noise converting means 12 are also substantially equal to the phase and level at the actual position of the exhaust noise converting means 12.

Therefore, the correction amount obtained on the basis of the signal from the identifying means 21 and the signals from the exhaust noise extracting means 22 and 16 is intended for the actual exhaust noise and sound deadening at the position of the converting means 12. Therefore, it is possible to eliminate the convergence time for surely suppressing the exhaust noise.

[0010]

However, in such an active silencer, it takes a relatively long time to measure the phase difference and the level difference in the correction means 17, and the engine is depressed due to depression of the accelerator or the like. If the number of revolutions changes abruptly, it becomes difficult to follow up, and as shown in FIG. 7, there is a problem that the silencing performance deteriorates.

In FIG. 7, the engine speed is 40 Hz.
Is the muffling characteristic when the secondary sound source 15 is turned on, and the curve (b) shows the muffling characteristic when the secondary sound source 15 is turned off. The characteristics are shown, and in particular, it can be seen that the silencing performance is extremely deteriorated around 70 Hz. The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide an active silencer capable of significantly improving the followability to changes in the engine speed.

[0012]

In the active silencer of the present invention, the opening of the exhaust pipe, which exhausts exhaust noise generated from the engine to the outside, substantially coincides with the opening of the exhaust pipe. A muffling pipe system to be arranged, a conversion means provided in or near the opening of the exhaust pipe for acoustic-electric conversion of exhaust noise, and arranged on the opposite side to the opening of the muffling pipe system. A secondary sound source that electro-acoustically converts an electric signal that gives an operation amount that acoustically cancels exhaust noise and sends it to the muffling pipe system, an adjusting unit that adjusts the operation amount, and the operation from the adjusting unit. Inputting the amount, the identification means for identifying the phase and the level at the position of the converting means of the sound deadening from the secondary sound source based on the preset transfer characteristic of the muffling conduit system, and the converting means from the converting means. From the signal and the identification means An exhaust noise extracting means for obtaining a phase and a level of the exhaust noise at the position of the converting means based on a signal, and the adjusting means inputs the phase and the level obtained by the exhaust noise extracting means. , Inputting the rotational frequency of the engine, and invoking a phase and level corresponding to the rotational frequency from preset transfer characteristic data of the muffling pipe system, and a phase such that the invoked phase becomes 180 deg or 360 deg. It is characterized in that an adjustment amount and a level adjustment amount such that the called level becomes zero are obtained, and the phase and the level obtained by the exhaust noise extracting means are corrected by these values.

(Operation) In the active silencer of the present invention, the identifying means determines the phase and level at the position of the transforming means of the muffling sound from the secondary sound source based on the preset transfer characteristic of the muffling conduit system. To be identified. The phase and level identified in this way are approximately equal to the phase and level at the position of the actual sound wave converting means.

Therefore, the phase and level at the position of the exhaust noise converting means extracted by the exhaust noise extracting means based on the identified phase and level are also the phase and level at the actual position of the exhaust noise converting means. Are almost equal. Then, according to the present invention, the phase and level of the exhaust noise extracted by the exhaust noise extracting means at the position of the converting means are used as the sound source noise and adjusted by the adjusting means.

In the adjusting means, the phase and level corresponding to the present rotation frequency are called from the preset transfer characteristic data of the muffling pipe system, and the called phase is 180.
The amount of phase adjustment that obtains deg or 360 ° is obtained, and the amount of level adjustment that obtains the called level becomes zero. The amount of phase adjustment and the amount of level adjustment obtained in this way take into consideration the transfer characteristics of the muffling pipe system, and the phase and level obtained by the exhaust noise extraction means are corrected by these values. , Is output as the operation amount to the secondary sound source.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. In the figure, reference numeral 41 indicates an exhaust pipe connected to the engine 43. This exhaust pipe 4
A microphone 45 is arranged outside the first opening 41 a.

The outer periphery of the exhaust pipe 41 on the side of the opening 41a is covered with an outer cylindrical pipe 47a of a muffling pipe system 47. The opening 47b of the outer tube 47a corresponds to the opening 41a of the exhaust pipe 41.
The position is almost the same as. A communication pipe 47c is connected to the outer cylinder pipe 47a of the muffling pipe system 47.

At the end of the communication pipe 47c, a muffling pipe line system 47 is provided.
There is a speaker 49 acoustically coupled to. The output of the microphone 45 is connected to the input of the adjustment unit 53 via the subtractor 51. The output of the adjusting unit 53 is connected to the speaker 49 and the identifying unit 55. The output of the identification unit 55 is connected to the subtractor 51.

The identifying section 55 has a silencer system identifier 57 in which a variable phase shifter and a variable gain amplifier are arranged in series. The adjustment unit 53 has a phase / amplitude adjuster 59 in which a variable phase shifter and a variable gain amplifier are arranged in series.

The phase / amplitude adjuster 59 has a control CP
The table data 63 is output via U61. The control CPU 61 is provided with an electric signal indicating the rotation speed of the engine 43. The output of the phase / amplitude adjuster 59 is connected to the phase inverter 65. Hereinafter, the operation of the present embodiment will be described.

The microphone 45 converts the exhaust noise reaching the opening 41a of the exhaust pipe 41 from the engine 43 into an electric signal. The adjustment unit 53 outputs an electric signal that gives an operation amount that acoustically cancels exhaust noise to the speaker 49. The acoustic signal output from the speaker 49 propagates in the muffling pipe system 47 and is radiated to the outside from the opening 47b.

The muffling line system identifier 57 of the identifying section 55 is composed of, for example, FIR, IIR, etc., and based on the transfer characteristics of the speaker 49 and the muffling line system 47 set in advance,
The phase and level of the sound wave S1 from the speaker 49 at the position of the microphone 45 are identified. In this way, the phase and level identified by the identifying unit 55 are substantially equal to the phase and level of the actual sound wave elimination S1 at the position of the microphone 12.

Therefore, the phase and level of the exhaust noise S2 at the position of the microphone 45 extracted by the subtracter 51 based on the identified phase and level are also the phase and the level of the actual exhaust noise S2 at the position of the microphone 45. Is almost equal to. Therefore, in this embodiment, the phase and level extracted by the subtractor 51 based on the phase and level identified by the identifying unit 55 are adjusted by the adjusting unit 5.
It is used as a sound source sound in 3 above.

The rotation frequency of the engine 43 is input to the control CPU 61 of the adjusting section 53, and the control CPU 61 transmits from the table data 63 of the silencing pipe line system 47 which is preset corresponding to the rotation frequency of the engine 43. The characteristic data is called and the correction value is output to the phase / amplitude adjuster 59. That is, in the table data 63, the engine 43
The filter constants for the phase / amplitude adjuster 59 are tabulated based on the transfer characteristics of the muffling conduit system 47 at intervals of, for example, about 10 Hz in accordance with the rotation frequency of.

Then, the control CPU 61 calls in a constant corresponding to the rotational frequency of the engine 43 at that time and the phase /
Output to the amplitude adjuster 59. Here, for example, 100Hz
When the transfer characteristic is 30 deg and -3 dB, the phase adjustment amount is a delay of 9.167 mS and the amplitude adjustment amount is +3.
dB. That is, in this embodiment, the transfer characteristics of the muffling pipe system 47 as shown in FIGS. 2 and 3 are made into table data, and as shown by the arrows in these figures, the called phase is A phase adjustment amount is obtained so as to be 360 deg, and a level adjustment amount is obtained so that the called level becomes zero.

Here, for frequencies not included in the table data 63, either one of the preceding and following data is selected by gradient calculation from the preceding and following frequency data.
The phase adjustment amount and the level adjustment amount thus obtained are output to the phase / amplitude adjuster 59, and the set values of the phase / amplitude adjuster 59 are changed. Then, the phase is further inverted by the phase inverter 65.

As a result, the optimum operation amount is the speaker 49.
The exhaust noise is silenced. In the active silencer configured as described above, the control amount obtained based on the output from the identifying unit 55 and the output from the subtractor 51 determines the actual exhaust noise S2 and the silence S1 at the position of the microphone 45. It becomes a target, and it is possible to eliminate the convergence time for surely suppressing the exhaust noise.

In the above-described active silencer, the phase and level of the exhaust noise extracted by the subtractor 51 at the position of the microphone 45 is used as the silence source sound, and the adjusting unit 53 simply converts this to the silence source sound. Since the amount of operation to the speaker 49 is adjusted by various corrections, the calculation time is shortened,
The followability with respect to changes in the rotation speed of the engine 43 can be significantly improved as compared with the conventional case.

FIG. 4 shows the active silencer described above.
It is a muffling characteristic when the rotation speed of the engine 43 is swept from 40 Hz to 350 Hz for 10 seconds. The curve (a) shows the muffling characteristic when the speaker 49 is turned on, and the curve (b) shows the speaker 49 turned off. The sound deadening characteristics at the time are shown, and it can be seen that the followability is significantly improved as compared with the active silencer shown in FIG.

In the embodiment described above, the adjusting section 53
The phase called by the control CPU 61 at 360 de
Although the example in which the phase adjustment amount is obtained so as to obtain g is described, the present invention is not limited to this embodiment, and for example, the phase adjustment amount is obtained so that the called phase becomes 180 degrees. In this case, since the phase is inverted, the phase inverter is unnecessary.

[0031]

As described above, in the active silencer of the present invention, the phase and level at the position of the exhaust noise converting means extracted by the exhaust noise extracting means are used as the silence source sound, and the adjusting means is used. Since the sound source noise is simply corrected and used as the operation amount for the secondary sound source, the calculation time is shortened, and the followability with respect to changes in the engine speed can be greatly improved as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an active silencer of the present invention.

FIG. 2 is an explanatory diagram showing a transfer characteristic of a muffling pipe system of the active silencer of FIG. 1 with respect to a phase difference.

FIG. 3 is an explanatory diagram showing a transfer characteristic of a muffling pipe system of the active silencer of FIG. 1 with respect to an amplitude ratio.

4 is an explanatory diagram showing a silencing characteristic of the active silencer of FIG. 1. FIG.

FIG. 5 is a circuit diagram showing an example of a conventional active silencer.

FIG. 6 is a circuit diagram showing an example of an active silencer previously filed by the applicant.

7 is an explanatory diagram showing a silencing characteristic of the active silencer of FIG. 6. FIG.

[Explanation of symbols]

 41 Exhaust Pipe 41a Opening 43 Engine 45 Microphone 47 Silence Pipeline System 47b Opening 49 Speaker 51 Subtractor 53 Adjusting Section 55 Identification Section

Claims (1)

[Claims] 1. An opening (47b) on an outer circumference of an exhaust pipe (41) for exhausting exhaust noise generated from an engine (43) to substantially coincide with an opening (41a) of the exhaust pipe (41). A silencer conduit system (47) arranged in such a manner, a conversion means (45) provided at or near the opening (41a) of the exhaust pipe (41) for acoustic-electrically converting exhaust noise, and the silencer. An electric signal, which is arranged on the opposite side of the opening (47b) of the pipe line system (47) and gives an operation amount for acoustically canceling the exhaust noise, is electro-acoustically converted into the muffling pipe line system (47). A secondary sound source (49) to be sent out, an adjusting means (53) for adjusting the operation amount, and an operation amount input from the adjusting means (53) to input a preset muffling pipe system (47). Silence from the secondary sound source (49) based on transfer characteristics Said converting means (4
Identification means (55) for identifying the phase and level at the position 5), the signal from the conversion means (45) and the identification means (5).
5) based on the signal from the exhaust noise, the exhaust noise extracting means (51) for obtaining the phase and level of the exhaust noise at the position of the converting means (45), the adjusting means (53), Extraction means (5
In addition to inputting the phase and level obtained in 1), the rotation frequency of the engine (43) is input, and the rotation frequency is corresponded to from preset transfer characteristic data of the muffling pipe system (47). The phase and level are summoned, and the phase adjustment amount so that the summed phase becomes 180 deg or 360 deg and the summed level adjustment amount so that the summed level becomes zero are obtained. An active silencer characterized by correcting the phase and level obtained by a noise extraction means (51).