JP2825689B2 - Active noise control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control apparatus for suppressing noise by causing a noise from a noise source to interfere with a noise suppression signal generated by a control sound source.

[0002]

2. Description of the Related Art Conventionally, as an active noise control device of this type, there is one described in, for example, Japanese Patent Application Laid-Open No. 1-501344. This conventional example is an active noise control device that emits a control sound from a loudspeaker to reduce noise transmitted from a noise source into the vehicle interior, and detects residual noise in the vehicle interior using a plurality of microphones. Adaptively filtering the reference signal by generating at least one reference signal including optionally selectable harmonics of the noise source and supplying the residual noise detection signal and the reference signal to a processor / storage unit. Thus, a drive signal for the loudspeaker is formed.

In such an active noise control device, if an abnormality occurs in the control system due to, for example, deterioration of a speaker, deviation of a space transfer function, change in use environment, etc., divergence occurs and noise cannot be suppressed. And the control sound may be noise. For this reason, it is necessary to detect an abnormality in the control system and stop the generation of the control sound when the abnormality occurs. However, in general, when an abnormality is detected by the abnormality detection means, it is not possible to discriminate between a transient abnormality such as mixing of external noise and a control system abnormality due to, for example, deterioration of a speaker. In order to shorten the system stop period due to an abnormality, for example, when the vehicle stops running and the engine speed becomes equal to or lower than the idle speed, the system stop is reset and the abnormality determination is performed again.

[0004]

However, in the case of the abnormality determination method according to the above-mentioned conventional example, when a system abnormality really occurs, such as deterioration of the frequency characteristics of the system, every time the rotational speed falls below the idle speed. Since the system stoppage is reset in a short time, an abnormal sound is generated many times, although only for a short time, and there is an unsolved problem that the occupant feels uncomfortable.

In order to solve this problem, it is conceivable to stop the reset operation at the idling speed or lower and continue the system stop. In this case, even if a temporary abnormality occurs, the system is stopped. There is no opportunity for restart, which hinders effective use of the active noise control device. Therefore,
An object of the present invention is to provide an active noise control device capable of restarting the system while reducing the frequency of occurrence of abnormal noise as much as possible.

[0006]

In order to achieve the above object, an active noise control apparatus according to the present invention, as shown in FIG. 1, applies a drive signal from a control means to noise transmitted from a noise source. In the active noise control device in which the control sound from the control sound source generated by the above is interfered to reduce the residual noise energy of both and reduce the noise, the abnormality of the control means is determined by the magnitude of the residual noise energy. Active noise control, comprising: abnormality detection means for detecting; and control sound stop means for stopping generation of a control sound at least until an ignition switch is turned off when an abnormality is detected by the abnormality detection means. apparatus.

[0007]

According to the present invention, when the residual noise energy is less than the predetermined value, it is determined that the system operates normally and effectively controls and suppresses the noise transmitted from the noise source. When the residual noise energy exceeds a predetermined value, it is determined that an abnormality has occurred in the system, and the system is stopped at least until the ignition switch is turned off.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram of the present invention, and FIG.
1 is a schematic configuration diagram showing one embodiment when the present invention is applied to a vehicle. In FIG. 2, reference numeral 1 denotes a vehicle body, and a four-cylinder engine 3 as a noise source is disposed in front of a vehicle compartment 2. Inside the cabin 2, there are a front seat 4F and a rear seat 4R.
And a loudspeaker 5a also serving as a control sound source for outputting an audio signal as a control sound source, for example, at the lower portion of the dashboard and behind the rear seat 4R.
And 5b, and microphones 6 as residual noise detecting means at the front, center and rear of the ceiling, respectively.
a, 6b and 6c are provided.

The engine 3 has a crank angle sensor.
7 is attached, and the crank angle sensor 7
Generates one pulse every 180 degrees of rotation
The state detection signal x is output. And the microphone
6a to 6c output residual noise detection signals e₁~ E _Three
Is input to the processor unit 15 and the
Detection signal x of ignition angle sensor 7 and ignition switch
12 ON / OFF signals are input to the processor unit 15
Is done.

As shown in FIG. 3, the processor unit 15 converts the input reference signal x into an analog-to-digital (A / D) signal and outputs the converted signal. Digital filter 2 input as signal x
4 and the adaptive digital filter 26 and the residual noise correction signals e _{1 to} e ₃ from the microphones 6 a to ₆ c are A / D
A / D converters 30a to 30c for conversion, and these A / D
A microprocessor 34 for inputting the converted signals from the converters 30a to 30c and the output signal r _km of the digital filter 24; D / A converters 36a and 36b for D / A converting the processed signal of the adaptive digital filter 26; A warning oscillator 11 for detecting a sound.

Here, the digital filter 24 receives the reference signal x and is filtered by a filter coefficient corresponding to the modeled space transfer function according to the number of combinations of the space transfer function between the microphone and the speaker. is intended to generate a reference signal r _miles, the adaptive digital filter 26 is functionally has a filter corresponding to the number of output channels to the speakers 5a and 5b individually inputs the reference signal x, set at the time A convolution process is performed based on the set filter coefficients to produce speaker drive signals y _1, y
₂ is output to the loudspeakers 5a and 5b via the analog switches 8a and 8b.

The microprocessor 34 includes a residual noise detection signal e ₁ -e _{3 and a} filtered reference signal r _km.
And the filter coefficient of the adaptive filter 26 is LMS (L
eastMean Square) The algorithm performs noise suppression processing that changes using the algorithm, calculates the residual noise energy of each microphone, for example, the average value of the residual noise detection signal, and compares the minimum value with the set value to detect abnormalities. After the sound is detected and the abnormal sound is detected, the ignition switch 12
There off to alert and reset the control signal CS until completion off analog switch 8a, and 8b speaker drive signal y _1, y ₂ by loudspeakers 5a, stops driving of 5b, is further ignition switch 12 is turned off A warning signal is output for a certain period of time
9b is turned on, the oscillator 11 outputs a warning sound of a frequency that does not cause discomfort to the occupant to the loudspeakers 5a and 5b, and turns on the warning lamp 10.

Here, the general formula of the residual noise detection signal is expressed as follows. Now, the k-th microphone 6a ~
6c the residual noise detecting signal detected is e _k (n), loudspeakers 5a and the control sound from 5b residual noise detection signal k-th microphone 6a~6c detects when (secondary sound) is no e _pt (n), the j-th (j = 0, 1, j) when the transfer function H _km between the m-th loudspeakers 5a and 5b and the k-th microphones 6a to 6c is represented by a FIR (finite impulse response) function. 2, the filter coefficient corresponding to the term of {I _c -1) is C _kmj ′, and the reference signal is x (n).
, The reference signal x (n) and the m-th loudspeaker 5
i and i of the adaptive filter driving i and 5b (i = 0,
1,2, when the coefficients of ─I _F -1) and W _mi, the following equation (1) is satisfied.

[0014] Here, each term with (n) is a sample value at sampling time n, and K is the microphone 6a
6c (three in this embodiment), M is the number of loudspeakers 5a and 5b (two in this embodiment), and I _C is FIR
The number of taps of the filter coefficients C _miles' expressed by the digital filter (filter order), a I _F is the number of taps of the adaptive filter W _m (filter order).

The second term on the right side of the above equation (1) represents the sum of secondary sounds reaching the k-th microphones 6a to 6c. The update equation of the filter coefficient of the adaptive filter using the LMS algorithm which is the steepest descent method is given by the following (2)
It is expressed by an equation. Here, α is a convergence coefficient, which is related to the speed at which the filter converges optimally and the stability at that time.

As described above, the adaptive digital filter 26
The filter coefficients W _mi (n + 1) of the microphones 6a to 6
c based on the residual noise detection signals e ₁ (n) to e ₃ (n) output from the control signal c and the reference signal x (n) from the crank angle sensor 7.
By sequentially updating according to the MS algorithm, drive signals y ₁ (n) and y ₂ (n) that minimize the input residual noise detection signals e ₁ (n) to e ₃ (n) are formed. The control sound supplied to the loudspeakers 5a and 5b and output therefrom cancels out the noise in the passenger compartment 2.

Next, the operation of the above embodiment will be described with reference to the flowchart of FIG. The power of the entire system is turned on when the key switch is turned on, and the microprocessor 34 executes the timer interrupt processing shown in FIG. 4 every predetermined time (for example, 1 msec). That is, in step S0, it is determined whether or not the engine speed N obtained from the reference signal x has exceeded a set value. If the engine speed N is equal to or less than the set value, the noise reduction control is stopped in step S21.
Is reset to stop the generation of the control sound, and then returns to the main program.
Move to.

In step S1, the control signal CS is turned on to enable the noise suppression control. Next, in step S2, the residual noise detection signal e ₁
To e ₃ , the reference signal x, the state signal IGN of the ignition switch 12 and the filtered reference signal r _km output from the digital filter 24, and then the process proceeds to step S3, where the filter coefficient is calculated according to the above equation (2). W _mi (n + 1) is calculated, and then the process proceeds to step S4 to output the calculated filter coefficient W _mi (n + 1) to the adaptive digital filter 26, and then proceeds to step S5.

[0019] calculates the average value of the residual noise detecting signal e _k for each the step S5 each microphone, step S6
Then, the average value of the residual noise calculated in step S5 is compared with a preset value. If any one of the average values is larger than the set value, that is, if divergence or mixing of external noise occurs, the process proceeds to step S7, where the flag 1 is set and the fact that an abnormal sound is detected is stored. Step S
The process proceeds to step S8, and if all the average values are equal to or smaller than the set value, the process directly proceeds to step S8.

In step S8, it is determined whether an abnormality has been detected in the past based on the state of the flag 1. If the flag 1 has been set, an abnormal sound has been detected. By resetting CS, the analog switch 8 is turned off and the loudspeaker 5 is turned off.
Cancels the emission of control sounds from. If the flag 1 is not set, it is normal and the process proceeds to step S9.
By setting the control signal CS, the analog switch 8 is kept on, the control sound is emitted from the loudspeaker 5, and the noise suppression control is continued.

Next, in step S11, it is determined whether or not the ignition switch 12 has been turned off.
If the ignition switch 12 is on, the process returns to the main program via step S20. If the ignition switch 12 is off, the process proceeds to step S12. In step S12, it is determined whether an abnormality has been detected in the past based on the state of the flag 1, and
If the flag 1 is not set, it is normal, and the process returns to the main program via step S20. If the flag 1 is set, an abnormality has been detected, and the process proceeds to step S13 to warn of the abnormality.

In step S13, it is determined whether or not the warning timer has started counting, based on the state of the flag 2. If the flag 2 has not been set, the flow proceeds to step S14 to start the warning timer. 2
Is set to store the start of the warning timer, and the flow proceeds to step S16. If the flag 2 has been set, the process proceeds to step S16.

In step S16, it is determined whether or not the time of the warning timer has expired. If the time has not expired, the flow proceeds to step S17 to continue outputting the warning signal and return to the main program. If the warning timer has expired, the flow proceeds to step S18 to reset the warning signal, and in step S19, resets the flag 1 for abnormality detection determination and returns to the main program.

When the ignition switch 12 is turned on in step S11 and when the flag 1 for abnormality detection determination is not set in step S12, the reset of the warning timer, the flag 2 and the warning signal is continued in step S20. . In the processing of FIG. 4, the processing of steps S5 to S7 corresponds to the abnormality detecting means, and the processing of steps S8 to S10 corresponds to the control sound stopping means.

Thus, now the components of the system, in particular the loudspeakers 5a, 5b and the microphones 6a-
Assuming that there is no deterioration in the frequency characteristic of the control signal 6c, that is, there is no deterioration in the frequency characteristic of the system, and that there is no noise from the outside in a normal state, the residual in the absence of the control sound of the first term on the right side of the equation (1) The noise detection signal and the signal of the sum of the control sounds reaching the microphone in the second term on the right side cancel each other,
Since the average value of the residual noise detection signal detected by the microphone is a small value, the average value is equal to or less than the set value in step S6, and since the flag 1 is not set in step S7, the system control signal is continuously set in step S9. When the analog switches 8a and 8b are turned on, the speaker drive signals y ₁ and y ₂ output from the adaptive digital filter 26 become loudspeakers 5a and 5b.
b, the engine noise is continuously suppressed by the noise suppression control. Then, even after detecting that the ignition switch 12 has been turned off in step S11, since the flag 1 has not been set in step S12, the process directly returns to the main program, and the noise suppression control continues.

From this normal state, the loudspeakers 5a,
5b, the microphones 6a to 6c, and the like cause deterioration in the frequency characteristics of the system, or when noise is mixed in from the outside, the residual noise detection signal when there is no control sound in the first term on the right side of the equation (1) , The signals of the sum of the control sounds reaching the microphone in the second term on the right-hand side cannot cancel each other, and the average value of the residual noise detection signal detected by the microphone increases, and the average value exceeds the set value in step S6. That is, the flag 1 is set in step S7, the control signal CS is reset in step S10, the analog switches 8a and 8b are turned off, and the speaker drive signals y ₁ and y ₂ output from the adaptive digital filter 26 are loud. The noise is not supplied to the speakers 5a and 5b, and the noise suppression control stops.

This system stop state is indicated by flag 1
Since the ignition switch 12 is turned off in step S11, the warning timer started in step S14 after the ignition switch 12 is turned off has timed out in step S16. Is detected, and step S
The process is continued until the flag 1 is reset at 19.

After the ignition switch 12 is turned off, since the abnormality detection flag 1 is set in step 12, the warning timer is started in steps S13 to S15, and the warning timer times out in step S16. Until step S17, the warning signal is continuously output. This warning signal is output from the analog switch 9a,
9b is turned on, a signal from the oscillator 11 having a frequency that does not cause discomfort to the occupant is supplied to the loudspeakers 5a and 5b, and the warning light 10 is turned on to call the occupant's attention. And after the warning timer times out,
In step S18, the warning signal is reset, and in step S1
The flag 1 is reset at 9 so that the noise suppression control after restart can be performed.

In the above-described embodiment, the warning signal is reset by the warning timer. However, the warning signal may be reset by a confirmation operation by an occupant operating a switch or by turning off a key switch. Further, in the above embodiment, the case where the warning sound is output by turning off the ignition switch after detecting the abnormality has been described, but the warning sound is output when the abnormality is continuously detected a predetermined number of times. Is also good.

Further, in the above-described embodiment, the case where the filtered reference signal r _km is obtained by the digital filter 24 has been described. However, the present invention is not limited to this. The digital filter processing may be performed by the microprocessor 34, and the digital filter 24, the adaptive filter 26, and the microprocessor 34 may be configured by one microprocessor. In this case, the analog switch 8a, 8b may be omitted and the drive signals y ₁ and y ₂ may be set to zero in the event of an abnormality.

Further, in the above embodiment, the case where a loudspeaker is applied as a control sound source has been described. However, the present invention is not limited to this, and a vibrator can be applied. Can also apply the acceleration vibration sensor.
Further, the number of loudspeakers and microphones is not limited to the above-described embodiment, and may be any number equal to or more than one.

Furthermore, in the above embodiment, the case where the present invention is applied to a vehicle has been described. However, the present invention is not limited to this, and can be applied to the case of noise reduction control in the cabin of an aircraft.

[0033]

As described above, according to the active noise control device of the present invention, when the residual noise energy becomes large, it is detected as an abnormality of the system, and from the time of detection until the ignition switch is turned off at least. Since the system is stopped, occupants do not hear unpleasant sounds repeatedly while the vehicle is running, and the system can be restarted by turning on the ignition switch again. When an abnormality is detected, a comfortable acoustic space can be obtained again.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a basic configuration of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment.

FIG. 3 is a block diagram of a processor unit of the embodiment.

FIG. 4 is a flowchart of the embodiment.

[Explanation of symbols]

 5 Loudspeaker 6 Microphone 8 Switch 9 Switch 10 Warning light 24 Digital filter 26 Adaptive filter 34 Microprocessor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-315346 (JP, A) JP-A-2-306844 (JP, A) JP-A-56-5239 (JP, A) JP-A-58-58 57193 (JP, A) JP-A-59-9699 (JP, A) JP-A-5-27780 (JP, A) JP-A-5-27779 (JP, A) (58) Fields investigated (Int. ⁶ , DB name) B60R 11/02 F01N 1/00 G10K 11/178

Claims (1)

(57) [Claims] An active device in which a noise transmitted from a noise source is caused to interfere with a control sound from a control sound source generated by a drive signal from a control means to reduce residual noise energy of the two and reduce noise. An abnormality detecting means for detecting an abnormality of the control means based on the magnitude of the residual noise energy; and when the abnormality detecting means detects an abnormality, a control sound is generated at least until an ignition switch is turned off. And a control sound stopping means for stopping the noise.