JP2751685B2 - 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 device which suppresses noise by causing noise from a noise source to interfere with a noise suppression sound generated by a control sound source, and more particularly to an active noise control device for accelerating and decelerating a vehicle or the like. The present invention relates to an active noise control device that improves the effect of suppressing indoor noise in a vehicle.

[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 providing the residual noise detection signal and the reference signal to a processor / storage unit. Thus, a drive signal for the loudspeaker is formed. Here, in the adaptive filter processing, the i-th filter coefficient W _mi (n + 1) is set to minimize the evaluation function J set as the mean square sum of the detection signals V _ek of the plurality of microphones according to the LMS algorithm. Then, updating is performed sequentially according to the following equation (1).

[0003] Here, W _mi (n) is the filter coefficient of the previous or n-th sample, μ is the convergence coefficient, V _ek is the k-th microphone output, x is a reference signal correlated with the noise source, and C _km ′ is m
It is a base filter coefficient corresponding to a model space transfer function that models a real space transfer function between the ith speaker and the kth microphone.

[0004]

However, in the above-mentioned conventional active noise control device, a speaker as a control sound source provided in the vehicle compartment is fixed,
When the filter coefficient is updated, the speed at which the adaptive filter in equation (1) converges optimally and the convergence coefficient μ related to stability at that time are fixed values. In the vicinity of the ear, a phase shift occurs between the noise that should be canceled out and the control sound, and a frequency range in which the noise reduction effect is small occurs. That is, as shown in FIG. 9, the effect of reducing the noise in the vehicle cabin causes a plurality of peaks in the noise level depending on the engine speed. For this reason, there is an unsolved problem that when the engine speed crosses the speed at which the noise level peaks during acceleration / deceleration, the noise level suddenly increases and the occupant feels uncomfortable.

In order to solve this problem, it is conceivable to set the convergence coefficient μ in the filter coefficient update equation to a large value to speed up the convergence against a sudden change in the noise level. When the silencing limit near the minimum point of the function is reached, divergence is likely to occur, and a new problem that the frequency of occurrence of abnormal noise increases occurs, which is not a good solution.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and provides a comfortable acoustic space that does not give uncomfortable sound to the occupant regardless of a change in the engine speed. It is an object of the present invention to provide an active noise control device that can be formed.

[0007]

In order to achieve the above object, an active noise control apparatus according to the present invention, as shown in FIG. 1, generates a reference signal for generating a reference signal corresponding to a noise generation state of a noise source. A signal generator, a control sound source to which a reference signal of the reference signal generator is filtered by an adaptive filter and input, a residual noise detector for detecting residual noise at an observation position, and a reference for the reference signal generator. An active noise control device comprising: a filter coefficient updating means for updating a filter coefficient of the adaptive filter processing by a steepest descent method using a convergence coefficient based on a signal and a residual noise detection value of the residual noise detection means, Frequency characteristic detecting means for detecting the frequency characteristic of the noise source, and target value calculation for calculating a target value of the residual noise level based on the frequency characteristic detected value of the frequency characteristic detecting means And a sound pressure error detecting means for calculating a sound pressure error between the target value calculated by the target value calculating means and the residual noise level detected by the residual noise detecting means, and at least the sound pressure error is reduced from zero. A convergence coefficient setting means for increasing the convergence coefficient in accordance with an increase in the sound pressure error until the set value is reached.

[0008]

According to the present invention, the target value of the indoor noise level in a vehicle or the like is represented by a frequency characteristic of a noise source such as an engine, for example, as a function of the rotational speed, and the sound level between the target value and the residual noise level at the current rotational speed is obtained. The control sound output from the control sound source is controlled by obtaining the pressure error, determining the convergence coefficient based on the sound pressure error, and updating the filter coefficient of the adaptive digital filter processing by the steepest descent method using the convergence coefficient. . Therefore, when the sound pressure error between the residual noise level and the target value is small, the convergence coefficient is small, so that the divergence state can be prevented. Conversely, when the sound pressure error is large, the convergence coefficient is set large. That means
When the noise level suddenly increases from the target value due to a change in the engine speed, the increase is effectively suppressed, and a stable noise attenuation effect is exhibited without generating a peak regardless of the engine speed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic configuration diagram showing one embodiment when the present invention is applied to a vehicle equipped with a four-cylinder engine. 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, a front seat 4F and a rear seat 4R are provided, and for example, a lower portion of the dashboard and a rear seat 4R.
The loudspeakers 5a and 5b, which also serve as control sound sources for outputting audio signals as control sound sources, are disposed behind the microphones, and microphones 6a, 6b and 6c as residual noise detecting means are respectively provided at the front, center and rear of the ceiling. Are arranged.

A crank angle sensor 7 is attached to the engine 3. The crank angle detection signal X, which is a one-cycle sine wave signal every time the crankshaft rotates by 180 degrees, and a crankshaft detection signal X, for example, Is 15
Engine speed detecting signal consisting of a single sine-wave signal each time the time rotation E _N is output. The residual noise detection signals e _{1 to} e ₃ output from the microphones 6a to 6c
There is input to a controller 15, a crank angle detection signal X of the crank angle sensor 7, the switch signal of the engine speed detection signal E _N and the ignition switch 10 is also input to the controller 15.

As shown in FIG. 3, the controller 15
An A / D conversion circuit 21 which receives a crank angle detection signal X, A / D converts the signal, and outputs the signal, and a microphone 6a
An amplifier 22a~22c for amplifying the residual noise detecting signals e ₁ to e ₃ of ~6c, 23a~ A / D conversion circuit for the amplified output is A / D converted outputs of these amplifiers 22a~22c
23c and, a waveform shaping circuit 24 to the engine rotational speed detection signal E _N and waveform shaping the pulse signal outputted from the crank angle sensor 7, the A / D converter circuit 21,23a~2
The microcomputer 26 receives the converted output of 3c, the waveform shaped output of the waveform shaping circuit 24, and the switch signal of the ignition switch 10, and the drive signals y ₁ and y of the loudspeakers 5a and 5b output from the microcomputer 26. D / a conversion circuit 27a that outputs ₂ converts D / a, and 27b, these D / a converter 27
a and 27b are input, and analog switches 28a and 28b for controlling these with a control signal CA from the microcomputer 26;
amplifiers 29a and 29b that amplify analog signals output from a and 28b and supply the amplified signals to loudspeakers 5a and 5b
And

[0012] Here, the microcomputer 26 is always sequentially updated by the filter coefficient W _mi loudspeaker performs convolution operation of the engine rotational speed detection signal X as a reference signal on the basis of 5a, the drive signal to 5b y
₁ and y ₂ , and a filter with a filter coefficient corresponding to the model space transfer function modeled in accordance with the number of combinations of the space transfer function between the microphone and the speaker based on the engine speed detection signal X. Digital filter processing for generating a processed reference signal r _km (see the equation (5) described later), and adaptive digital filter processing based on the filtered reference signal r _km and the residual noise detection signals e _{1 to} e _3. performing the filter coefficient updating process for updating the filter coefficient W _mi using the LMS (Least Mean Square) algorithm in.

Here, the control principle of the microcomputer 26 will be described using a general formula. Now, the residual noise detection signals detected by the k-th microphones 6a to 6c are set to e _k
(n), k-th microphones 6a to 6c when there is no control sound (secondary sound) from loudspeakers 5a and 5b
Table transfer function H _miles in FIR (finite impulse response) function between but the residual noise detecting signals detected e _pt (n), and m-th loudspeaker 5a and 5b and the k-th microphone 6a~6c J (j = 0, 1,
2, ──I _c -1) is the filter coefficient corresponding to the term
_kmj ', the engine speed detection signal X (n), the engine speed detection signal X (n), and the i-th (i = 0) of the adaptive digital filter for driving the m-th loudspeakers 5a and 5b. , 1,2, when the coefficients of ─I _F -1) and W _mi, the following equation (2) 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 filter coefficient W _mi represented in the adaptive digital filter (filter order).

In the above expression (2), “｛ΣW _mi · X (nj
-i)｝ ”(= y _m ) is the engine speed detection signal X
Represents the output when adaptive digital filter processing is performed, and
The term “{C _kmj ｛ΣW _mi ＸX (nji) は] indicates that the signal energy input to the m-th loudspeakers 5a and 5b is output as acoustic energy from these loudspeakers 5a and 5b, and the space transfer function in the vehicle compartment The signal at the time of reaching the k-th microphones 6a to 6c after C _km is shown. Further, the entire second term on the right side of “{C _kmj ｛ΣW _mi · X (nji)}” is the k-th microphone 6a Since the signals reaching to 6c are added for all speakers,
Represents the sum of secondary sounds reaching the k-th microphones 6a to 6c.

Next, an evaluation function J is placed as shown in the following equation (3). In this embodiment, the LMS algorithm is adopted,
A filter coefficient W _mi that minimizes the evaluation function J is obtained, and each filter coefficient W _mi of the adaptive digital filter processing is updated. The LMS algorithm that is the steepest descent method is described in (4) below.
As shown in equation, using the n-th value W _mi (n) as the filter coefficients of the adaptive digital filter processing to calculate the gradient ∂J / ∂W _mi of mean square error, which was α multiplied (n +
1) A value W _mi (n + 1) is obtained, and an operation is performed to reduce the value of the evaluation function J.

[0017] However, Here, α is a convergence coefficient, and is a coefficient related to the speed at which the filter converges optimally and the stability at that time.If this value is small, the update width of the filter coefficient becomes small, and the noise suppression control Stability is increased, but noise reduction performance is attenuated. Also, as this value is larger, the noise reduction performance of attenuating the noise is higher, but if it is too large, the noise suppression control becomes unstable and may diverge.

Therefore, in the present embodiment, in order to set the convergence coefficient α, the ROM of the storage device built in the microcomputer 26 stores in advance the relationship between the engine speed and the target value of the residual noise level in FIG. And a convergence coefficient storage table shown in FIG. 7 representing the relationship between the sound pressure error ε between the target value and the actual noise level and the convergence coefficient α. The convergence coefficient α is determined with reference to the table. Here, as shown in FIG. 6, the target value storage table stores the target value T of the residual noise level in order to make the occupant sense an increase in the engine speed.
Is set to increase gradually and linearly with an increase in the engine speed N. Also, as shown in FIG. 7, the convergence coefficient storage table shows that the convergence coefficient α increases exponentially until the sound pressure error ε reaches a predetermined value ε ₁ from zero, and thereafter, the sound pressure error ε increases. Convergence coefficient α regardless of
Is set to be a constant value.

That is, the target value of the residual noise level is set within the noise reduction limit of the system, and the noise reduction performance is controlled by reducing the convergence coefficient α before the residual noise in the vehicle interior reaches the noise reduction limit. As a result, the noise in the vehicle cabin can have a flat characteristic with no peak with respect to the engine speed. In Expression (4), β is a divergence suppression coefficient, which is a coefficient calculated as a negative term that determines the output of the control sound, and is an element that suppresses divergence. By increasing this value, the filter coefficient W _mi in the adaptive digital filter processing is reduced, and the loudspeaker 5
a, the drive signals y _1, loud and the value of y ₂ is decreased speakers 5a for 5b, the sound pressure of the control sound output from 5b decreases.

As described above, the filter coefficient W _mi (n + 1) in the adaptive digital filter processing is determined by the microphone 6
a to 6c output residual noise detection signals e ₁ (n) to e
_An LMS algorithm based on ₃ (n), an engine speed detection signal X (n) from the crank angle sensor 7 and an output y _m (n) when the engine speed detection signal X (n) is subjected to adaptive digital filtering. , The 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, and these are loudspeakers. The noise in the passenger compartment 2 is offset by the control sounds supplied to and output from 5a and 5b.

Next, the operation of the above embodiment will be described with reference to the flowcharts of FIGS. When the key switch is turned on, the entire system is turned on, and the microcomputer 26 executes a timer interrupt process shown in FIG. 4 every predetermined time (for example, 1 msec). The control signal CA is set to "1" by the initialization processing by the main program when the power supply is turned on, thereby the analog switch 28a, the drive signal y ₁ outputted from the microcomputer 26 by _28b, y ₂ is a loudspeaker 5a ,
5b, the β update counter N is cleared, the reset timer T is reset, the convergence coefficient α is set to the initial value, and the divergence suppression coefficient β is set to “1”.

That is, in step S1, a switch signal of the ignition switch 10 is read, and it is determined whether or not the switch signal is on. This determination is for determining whether or not the engine 3 is rotating. When the ignition switch 10 is in the off state, it is determined that the engine is being stopped, and the timer interrupt processing is terminated as it is. When 10 is in the ON state, the process proceeds to step S2.

[0023] In step S2, the residual noise detecting signals e ₁ to e ₃ and the reference signal X (n) reads, then the process proceeds to step S3, the engine speed detection signal E _N from the crank angle sensor 7 The engine speed is calculated by reading and measuring the pulse interval or counting the number of pulses per unit time. Next, the process proceeds to step S4 to calculate the target value T of the noise level in the vehicle compartment with reference to the target value storage table of FIG. 6 based on the current engine speed.

Next, the process proceeds to step S5, where
According to the equation (6), the residual noise level E is obtained by calculating the sum of the squares of the sound pressure of the residual noise which is the output of the microphones 6a to 6c in the vehicle compartment. E = e ₁ ² + e ₂ ² + e ₂ ² (6) Next, in step S6, the target value T calculated in step S4 and the residual noise level E calculated in step S5.
After calculating the sound pressure error ε (= TE) from
Move to 7.

In this step S7, the convergence coefficient α is determined by referring to the convergence coefficient storage table in FIG. 7 based on the sound pressure error ε obtained in step S6. Next, in step S8, digital filter processing corresponding to the equation (5) is performed to calculate a filtered reference signal r _km , and then the process proceeds to step S9, where the filter processing performed in step S8 is performed. The reference signal r _km and the residual noise detection signal e ₁ to
The filter coefficient W _mi (n + 1) is calculated by performing the calculation of the above equation (4) based on e _3, and then the process proceeds to step S10, where the adaptive digital signal is calculated based on the calculated filter coefficient W _mi (n + 1). The loudspeakers 5a, 5
drive signals y ₁ and y ₂ for b. Then, the process proceeds to step S11, where the calculated drive signals y ₁ and y ₂
Output to the A conversion circuits 27a and 27b, and then to step S
The process proceeds to step S12, where the divergence suppression process is executed, the timer interrupt process ends, and the process returns to the predetermined main program.

The divergence suppression processing, as shown in FIG. 5, first, in step S20, each loudspeaker 5a, is W power W _P representing the stability of the output of the drive signal y _1, y ₂ which drives the 5b divergent It is determined whether or not the threshold value is equal to or greater than the prevention threshold value A. If W _P <A, it is determined that the system is stable, and the process returns to the processing in FIG. 4 as it is. If W _P ≧ A, the system is unstable. Is determined to be approaching
Move to step S21.

Here, the derivation of the W power W _P will be described. The general expression of the output for each loudspeaker is expressed as follows. Here, W _m0 and W _m1 are filter coefficients of an adaptive digital filter for controlling the amplitude and phase of the m-th speaker output signal, and y _m is an output of the adaptive digital filter and is a filter coefficient of the adaptive digital filter. And the reference signal X (n).

When the equation (7) is Z-transformed, the following equation (8) is obtained. Y _m (Z) = W _m0 · X (Z) + W _m1 · X (Z) · Z ^-1 = (W _m0 + W _m1 · Z ^-1 ) X (Z) ……………… (8) so,

[0029]

(Equation 1)

Here, ω = 2πf: input signal angular frequency T = 1 / f _sample : sample period f _sample : sample frequency If power on both sides is obtained by the equation (9), the following equation (10) is obtained.

[0031]

(Equation 2)

In the equation (10), since the input power _XP is generated by a program, the amount used to actually check the output instability is calculated from the filter coefficient of the adaptive digital filter as follows: Equation (11) is used, and this is called W power W _P. W _P = W _m0 ² + W _m1 ² + 2 · W _m0 · W _m1 cos (2πf / f _sample ) (11) In step S21, the β update counter N is incremented and the process proceeds to step S22. I do. Here, the β update counter N is a counter that accumulates the number of times that the W power has exceeded the divergence prevention threshold A during the noise suppression control.
If the number of times exceeds, the system is considered to be unstable, and β is updated.

In step S22, it is determined whether or not the flag 1 set when the reset timer T is started is set. If the flag 1 is set, the flow directly proceeds to step S25, and the flag 1 is set. If not, the process proceeds to step S23 and the reset timer T
Is started, the flag 1 is set in step S24, and the process proceeds to step S25. Here, the reset timer T indicates that the W power does not diverge during the noise suppression control.
A time (for example, 180 seconds) for accumulating the number of times described above is set.

Next, in step S25, it is determined whether or not the reset timer T has timed out. When the time has expired, the flow proceeds to step S26 to clear the β update counter N, and then to step S27 to reset the flag 1 After the reset, the process returns to the process in FIG. 4, and if the time is not up, the process proceeds to step S29. In this step S29, it is determined whether or not the count number of the β update counter N has become C or more, and if it is less than C, the process returns to the processing of FIG.
29, the value of the divergence suppression coefficient β is updated to twice,
Next, the processing shifts to step S30 to clear the β update counter N, and then shifts to step S31 where the divergence suppression coefficient β
Is determined to be equal to or greater than the set value D, and the set value D
If the value is less than the set value D, the process returns to the process of FIG. 4. If the value is equal to or more than the set value D, the process proceeds to step S32, where the control signal CA having the logical value "1" is output to the analog switches 28a and 28b. Of the loudspeakers 5a and 5b to stop the system by stopping the emission of the control sounds from the loudspeakers 5a and 5b.

Here, the processing in step S3 in FIG. 4 and the crank angle sensor 7 correspond to the frequency characteristic detecting means, the processing in step S4 corresponds to the target value calculating means, and
Steps S5 and S6 correspond to sound pressure error detection means, and step S7 corresponds to convergence coefficient setting means. Therefore, assuming that the key switch is off and the vehicle is parked, the power supply of the controller 15 is shut off, and the execution of the noise suppression control process is stopped.

When the key switch is turned on from this state, energization of the controller 15 is started, and the controller 15 executes the processing shown in FIGS. At this time, when the ignition switch 10 is maintained in the off state, the engine 3 is stopped and no noise is generated, so that when the timer interrupt processing of FIG. Since the noise reduction processing is ended, the noise suppression control processing is not executed.

In this state, when the ignition switch 10 is turned on and the engine is started, the execution of the noise suppression control processing is started when the timer interruption processing of FIG. 4 is executed. This noise suppression control process, through steps S1, a reference signal reads the X (n), then step from the residual noise detecting signals e ₁ to e ₃ and the crank angle sensor 7, which is the output of the microphone 6a~6c in step S2 S
In step 3, the engine speed is read from the crank angle sensor 7 to calculate the engine speed. Then, the target value T of the calculated residual noise level at the current engine speed is calculated with reference to the target value storage table of FIG. This target value T is set within the silencing limit of the system. Next, the sum of the sound pressure squares of the residual noise is calculated to obtain a residual noise level E, a sound pressure error ε which is a difference between the residual noise level E and the target value T is calculated, and then, based on the sound pressure error ε. The convergence coefficient α is set with reference to the convergence coefficient storage table of FIG.

At this time, in a constant speed running state in which the engine speed is substantially constant, the filter coefficient _Wmi in the adaptive filter processing converges within a substantially target range,
Since the sound pressure error ε becomes small, the convergence coefficient α also becomes a small value, and it is possible to prevent the noise suppression control from becoming a stable region and becoming divergent. From this state, as the acceleration / deceleration running state, the engine speed fluctuates,
When the residual noise level E sharply increases from the target value T, the sound pressure error ε
When the sound pressure error ε suddenly increases, the convergence coefficient α is referred to by referring to the convergence coefficient storage table in FIG.
Is set, the convergence coefficient α becomes an exponentially large value. Therefore, the convergence speed of the filter coefficient in the filter coefficient update processing for searching for the filter coefficient so as to minimize the evaluation function J in step S9 is reduced. It is possible to reduce the exponential increase of the sound pressure error ε, and then decrease exponentially when approaching the convergence area, so that the noise attenuation effect can be exhibited in a short time without divergence. Can be. As a result, as shown in FIG. 8, a flat control characteristic can be obtained without a peak in the residual noise level depending on the engine speed, and a comfortable acoustic space can be formed. In addition, since the noise level gradually increases with an increase in the engine speed, the occupant can be made aware of the acceleration / deceleration state of the vehicle.

Then, using the convergence coefficient value α thus set, the filter coefficient W _mi in the adaptive digital filter processing is sequentially updated in accordance with the LMS algorithm, and the evaluation function represented by the above equation (3) is obtained. Drive signal y for loudspeakers 5a and 5b so that J is minimized.
₁ and y ₂ are calculated, and are calculated by the D / A conversion circuits 27a and 27a.
7b and the analog switches 28a and 28b, and are supplied to the loudspeakers 5a and 5b. For this reason, control sounds corresponding to the drive signals y ₁ and y ₂ are emitted from the loudspeakers 5 a and 5 b and interfere with the noise, so that the evaluation function J, that is, the residual noise detection signals e ₁ to e of the microphones 6 a to 6 c are output. the sum of the square sum and the square sum of the drive signals y _1, y ₂ of e ₃ is silenced controlled to be minimized.

Subsequent to the noise suppression processing described above, the divergence suppression processing is executed in step S12 of FIG. In this divergence suppression processing, first, as shown in FIG.
Each loudspeaker 5a, W power representing the stability of the output of the drive signal y _1, y ₂ which drives the 5b in is equal to or divergent prevention threshold A or more. Here, the divergence prevention threshold A means that when the W power is less than the divergence prevention threshold A, the system is operating stably, and when the W power is a value equal to or greater than the divergence prevention threshold A, the system does not operate. This is a threshold for determining that the vehicle is approaching stable.

Therefore, assuming that the noise suppression control is normally performed, the W power is less than the divergence prevention threshold A, so that it is determined that the vehicle is in a stable state, and the process returns to the processing of FIG. However, if the noise suppression control is approaching an unstable state, the W power becomes equal to or greater than the divergence prevention threshold A, so the flow shifts to step S21 to increment the β update counter N, and then resets the reset timer in steps S22 to S24. If T is not counting, the timer starts. Then, in a step S25, it is determined whether or not the time of the reset timer T has expired. In this way, the reset timer T is provided for accumulating the β update counter N in order to prevent erroneous determination of divergence when W power becomes large due to other than divergence, for example, due to mixing of external noise. In order to separate.

Therefore, if the time of the reset timer T has expired, the β update counter N is cleared in step S26, and the flag 1 in which the reset timer T is being set is reset in step S27, and the process returns. On the other hand, if the reset timer T has not expired, it is determined in step S28 whether the β update counter N has counted the number of times that the W power has become equal to or greater than the divergence prevention threshold A C times. That is, it is considered that the system has become unstable when C or more times are counted. Therefore, if it is less than C times, the system is not yet unstable, and the process returns to the processing of FIG. 4 as it is. If it is more than C times, the system is in an unstable state. Update to twice the value (β = β × 2),
The outputs of the loudspeakers 5a and 5b are reduced. Next, in step S30, the β update counter N is cleared, and in step S31, it is determined whether the value of the divergence suppression coefficient β has become equal to or greater than the set value D. If the value of the divergence suppression coefficient β is smaller than the set value D, the process returns. If the value of the divergence suppression coefficient β is equal to or larger than the set value D, the divergence state is determined, and the process proceeds to step S32 to immediately stop the sound emission from the loudspeakers 5a and 5b and stop the noise suppression control.

As described above, in the divergence suppressing process, the reset timer T and the β update counter N are provided, and the β update counter N
Is cleared within a certain period of time after the start, the divergence suppression coefficient β is not updated by an increase in the filter output in the adaptive digital filter processing that occurs sporadically over a long period of time. ,
Further, when the divergence must be suppressed in a case where the filter output in the adaptive digital filter processing frequently increases, the divergence suppression coefficient β can be updated effectively.

In the above embodiment, the case where the noise level target value T increases with an increase in the engine speed has been described. However, the present invention is not limited to this.
The noise level target value may be a constant value regardless of the engine speed, or may be decreased as the engine speed increases. In the above embodiment,
The convergence factor α with respect to sounds pressure error until a predetermined set value epsilon ₁ is increased exponentially, there has been described a case where a constant value when exceeding the predetermined set value epsilon _1, is not limited to this, a predetermined set value until epsilon ₁ increases along a relatively steep linear, may be increased along a gentle straight when exceeds a predetermined value epsilon _1, in extreme cases, the convergence factor α as two large and small values, which may be switched before and after a predetermined set value epsilon _1.

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. A microphone can also apply an acceleration vibration sensor. Furthermore, the number of loudspeakers and microphones to be installed is not limited to the above embodiment, but may be any number equal to or more than one.

In the above embodiment, the case where the engine noise is suppressed has been described. However, the present invention is not limited to this. The road noise can be suppressed by detecting the vibration input from the road surface to the wheel, or the window glass can be suppressed. Vibration can be detected to suppress wind noise, and these complex sounds can also be suppressed. Further, in the above-described embodiment, the case where the microcomputer 26 performs the adaptive digital filter processing and the digital filter processing of the filter coefficient according to the model space transfer function has been described. Can also be applied.

Further, in the above-described 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 reducing noise in an aircraft cabin.

[0048]

As described above, according to the active noise control device of the present invention, the target value of the noise level in the vehicle compartment is represented by a function of the rotation speed of the rotary noise source, and the target value at the current rotation speed is obtained. Find the sound pressure error between the value and the residual noise level,
Based on this sound pressure error, the convergence coefficient is set to a value that increases with an increase in the sound pressure error at least until the sound pressure error reaches a predetermined set value, and the steepest descent method is used using this convergence coefficient. The filter coefficient of the digital filter is calculated and the noise reduction effect of the control sound generated by the control sound source is automatically controlled, so that it is possible to quickly converge to the target value while preventing the divergence of the adaptive filter coefficient. Thus, the peak of the noise level caused by the number of rotations is suppressed, flat noise attenuation characteristics can be exhibited regardless of the number of rotations, and an effect that a comfortable acoustic space can be formed can be obtained.

[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 controller according to the embodiment.

FIG. 4 is a flowchart of the embodiment.

FIG. 5 is a flowchart of the embodiment.

FIG. 6 is a characteristic diagram showing a relationship between an engine speed and a target value of a residual noise level.

FIG. 7 is a characteristic diagram showing a relationship between a sound pressure error and a convergence coefficient α.

FIG. 8 is a characteristic diagram illustrating a relationship between an engine speed and a noise level according to the embodiment.

FIG. 9 is a characteristic diagram showing a relationship between an engine speed and a noise level in a conventional example.

[Explanation of symbols]

 2 Cab 3 Engine 5a, 5b Loudspeaker 6a-6c Microphone 7 Crank angle sensor 10 Ignition switch 15 Controller 26 Microcomputer 28a, 28b Analog switch

Claims (1)

(57) [Claims] 1. A reference signal generating means for generating a reference signal according to a noise generation state of a noise source, a control sound source to which a reference signal of the reference signal generating means is filtered by an adaptive filter means and inputted, and A residual noise detecting means for detecting residual noise at a position, and a filter for the adaptive filter processing by a steepest descent method using a convergence coefficient based on a reference signal of the reference signal generating means and a residual noise detection value of the residual noise detecting means. An active noise control device comprising: a filter coefficient updating unit that updates a coefficient; a frequency characteristic detecting unit that detects a frequency characteristic of the noise source; and a residual noise level based on a frequency characteristic detection value of the frequency characteristic detecting unit. Target value calculation means for calculating a target value of the target noise, and a sound between the target value calculated by the target value calculation means and the residual noise level detected by the residual noise detection means. Sound pressure error detecting means for calculating a pressure error; and convergence coefficient setting means for increasing the convergence coefficient in accordance with an increase in the sound pressure error at least until the sound pressure error reaches a set value from zero. An active noise control device characterized by the following.