JP2748734B2 - 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 actively reducing noise in a passenger compartment of an automobile, a passenger compartment of an aircraft, and the like.

[0002]

2. Description of the Related Art Conventionally, as an active noise control device of this type, there is, for example, one shown in FIG. 7 of British Patent Publication No. 2149614.

This conventional apparatus is applied to a cabin of an aircraft or a closed space similar to the cabin. The closed apparatus 101 includes loudspeakers 103a, 103b, 103c and microphones 105a, 105b, 105c, 105d. Control sounds that cause noise to interfere are generated by the speakers 103a, 103b, and 103c, and residual signals (residual noise) are measured by the microphones 105a, 105b, 105c, and 105d. These loudspeakers 103a, 103b, 103c and microphones 105a, 105b, 105c, 105d are connected to a signal processor 107. The signal processor 107 is connected to the microphone 105a, 105b and the fundamental frequency of the noise source measured by the fundamental frequency measuring means. , 105c, 105
d and receives the input signal from the loudspeakers 103a, 1 so that the sound pressure level in the closed space 101 is minimized.
A drive signal is output to the terminals 03b and 103c.

Here, in the closed space 101, three loudspeakers 103a, 103b, 103c and four microphones 105a, 105b, 105c, 105d are provided, respectively. 10
3a and 105a are provided one by one.
Assume that the transfer function from the noise source to the microphone 105a is H, and the loudspeaker 103a is connected to the microphone 10a.
The transfer function to 5a is C, the sound source information signal noise source produces a X _p, the noise signal E as a residual noise which is observed by the microphone 105a is a _{E = X p · H + X} p · G · C Become. Here, G is a transfer function required for silencing. When the noise is completely canceled at the point to be silenced (the position of the microphone 105a), E = 0.
At this time, G becomes: G = −H / C. Then, G that minimizes the microphone detection signal E is obtained, and the filter coefficient in the signal processor 107 is adaptively updated based on this G. As a method of obtaining a filter coefficient so as to minimize the microphone detection signal E, an LMS algorithm (Le
as a mean square).

When a plurality of microphones are installed as shown in FIG.
Control is performed so that the sum of the signals detected in 5b, 105c, and 105d is minimized.

[0006]

As described above, the conventional active noise control apparatus aims at minimizing the noise level detected by the microphone. However, in a car or the like, it may not be sufficient to simply keep the cabin quiet. For example, depending on the occupant, if the engine sound or the acceleration sound during idling does not cause any discomfort, the occupant may have a feeling that the driver can drive without feeling tired by hearing the sound. Also, depending on the type of vehicle, such as a sporty vehicle, not only quietness in the vehicle compartment is required but also a comfortable engine sound may be required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an active noise control device capable of reducing a signal of a target frequency to a target level and reducing other frequencies.

[0008]

A control sound source for generating a control sound that interferes with noise to reduce noise at an evaluation point, a means for detecting residual noise at a predetermined position after the interference, and a noise source for generating noise Means for detecting a signal relating to a state, means for extracting a signal of a target frequency from an output signal of the noise generation state detection means, and inputting an output signal of the noise generation state detection means and performing filter processing with a predetermined filter coefficient. A main adaptive filter that outputs a drive signal of the control sound source, a sub-adaptive filter that receives the signal of the extracted target frequency, performs filter processing with a predetermined filter coefficient, and outputs a drive signal of the control sound source, and the residual noise detection. Means for separating an output signal of the means into a signal of a target frequency and other signals, and a filter of the main adaptive filter so that the other signals are minimized. Characterized by comprising an auxiliary adaptive controller main adaptive controller and the target frequency signal obtained by the separation and updates the number to update the filter coefficients of the secondary adaptive filter such that the target level.

[0009]

The main adaptive filter receives the output signal of the noise generation state detection means, filters the signal with a predetermined filter coefficient, and outputs a drive signal for the control sound source. As a result, the control sound source generates a control sound having a phase opposite to that of the noise. At this time,
The main adaptive filter updates the filter coefficients of the main adaptive filter such that the other signals separated by the signal separating means are minimized. Therefore, the noise at the evaluation point can be reduced by such control.

At the same time, the sub-adaptive filter receives the signal of the target frequency extracted by the signal extracting means, performs a filtering process using a predetermined filter coefficient, and outputs a drive signal of the control sound source. Then, the sub-adaptive controller inputs the signal of the target frequency separated by the signal separating means, and updates the filter coefficient of the sub-adaptive filter so that the signal has the target level. Therefore, the noise at the target frequency can be kept at the target level.

[0011]

Embodiments of the present invention will be described below.

The description will be made by taking the interior space of the vehicle as an example.

FIG. 1 is a block diagram of an active noise control apparatus according to one embodiment of the present invention. A loudspeaker 3 as a control sound source and a residual noise detecting means in a vehicle room 1 which is a closed space. A microphone 5 is provided, and the loudspeaker 3 is connected to an adaptive digital filter 9 as an adaptive filter of the controller 7. Further, the microphone 5 is connected to the signal separating means 11. The signal separating means 11, other signals microphone 5 and the signal e ₂ of the target frequency of the sound to be emphasized that output as detected noise signal e a residual noise in the passenger compartment 1, and attempt is made to reduce it is to separate and e _1. The other signal e ₁ is input to the adaptive controller 13 of the controller 7,
The target frequency signal e ₂ is supplied to the adaptive controller 13 and the comparator 15.
To be entered. The comparator 15 is connected to a target level setting unit 17 for setting a target level of a sound to be emphasized. The output of the comparator 15 is input to the adaptive controller 13 of the controller 7.

On the other hand, the noise in the passenger compartment 1 is generated, for example, by a power plant 19, in which the engine, a transmission as a power transmission device, and a differential gear are integrally housed. I have. For example, a crank angle signal sensor 21 is used as a means for detecting a signal relating to the noise generation state of the noise source. In this embodiment, the detected crank angle signal is used as a reference signal _xp as an adaptive digital filter 9 and adaptive control. Input to the container 13.

The reference signal x _p is input to a signal extracting means 23, which outputs the reference signal x _p
, A signal of the target frequency is extracted and input to the adaptive digital filter 9.

In the description of FIG. 1, the controller 7 digitally processes the analog signal and outputs it as an analog signal. Therefore, the controller 7 needs an A / D converter, a D / A converter, and the like. The illustration and description are omitted for those described.

FIG. 2 specifically shows the adaptive digital filter 9, adaptive controller 13, signal separating means 11, signal extracting means 23, comparator 15, and target level setting unit 17 shown in FIG.

The adaptive digital filter 9 comprises a main adaptive digital filter 9a and two sub-adaptive digital filters 9b and 9c.
The output signals of a, 9b, and 9c are output to the loudspeaker 3 via the adder 25 as the drive signal y.

The adaptive controller 13 is a main adaptive controller 13a.
And two sub-adaptive controllers 13b and 13c. As the main adaptive controller 13a other signals e ₁ separated out of the noise signal e output from the microphone 5 is minimized, it is to update the filter coefficients of the main adaptive digital filter 9a. The sub-adaptive controller 13
b and 13c are signals e of the separated target frequency.
The filter coefficients of the sub-adaptive digital filters 9b and 9c are updated so that ₂ (e ₂₁ , e ₂₂ ) becomes the target level.

The signal separator 11 comprises tracking filters 11a, 11b and 11c. The tracking filter 11a outputs, for example,
In a four-cylinder vehicle, a secondary component of engine rotation (corresponding to a primary component of a crank angle detection signal) is passed. The tracking filter 11b passes a fourth-order engine rotation component as a harmonic component of a second-order engine rotation component. The tracking filter 11c has the engine rotation
It prevents the following ingredients and fourth order component, and passes the other signal e _1.

The comparator 15 includes a first comparator 15a and a second comparator 15a.
And a comparator 15b.

The target level setting device 17 comprises a first target level setting device 17a and a second target level setting device 17b.

[0023] Then, the first comparator 15a is a structure in which output from the tracking filter 11a and the engine rotational secondary component e ₂₁ from the first target level setting unit 17a to the target signal e _h1 and the receiving sub adaptive controller 13b ing. The second comparator 15b is configured to be output from the tracking filter 11b and the signal e ₂₂ of the engine 4 primary component from the second target level setting unit 17b to the target signal e _h2 and the receiving sub adaptive controller 13c .

The signal extracting means 23 comprises tracking filters 23a and 23b. The tracking filter 23a passes a secondary component of engine rotation, that is, a primary component x _p1 of the crank angle detection signal x _p from the reference signal x _p. ,
The input is to the sub-adaptive digital filter 9b. It said tracking filter 23b is the engine rotational fourth order component, i.e., second order component of the crank angle detection signal x _p x _p2
And input to the sub-adaptive digital filter 9c.

Next, the operation will be described.

The crank angle signal sensor 21 outputs a pulse detection signal corresponding to the crank angle correlated with the engine noise. The pulse detection signal main adaptive digital filter 9a as a reference signal x _p In this embodiment, the input signal extracting unit 23, and the adaptive controller 13.

In the signal extracting means 23, the primary component x _p1 of the crank angle detection signal passes through the tracking filter 23a, is input to the sub-adaptive digital filter 9b, and the secondary component of the crank angle detection signal passes through the tracking filter 23b. , Are input to the sub-adaptive digital filter 9c.

In the main adaptive digital filter 9a and the sub adaptive digital filters 9b and 9c, the reference signal x _p and the primary components x _p1 and x _p2 are filtered by filter coefficients adaptively rewritten by a control algorithm described later.

The output signals of the main adaptive digital filter 9a and the sub adaptive digital filters 9b and 9c are added by the adder 25 and output to the loudspeaker 3 as a drive signal y. The loudspeaker 3 outputs a control sound into the passenger compartment 1 in response to the drive signal y, and overlaps with the noise transmitted from the engine into the passenger compartment 1 in an opposite phase. As a result, the remaining sound pressure component is reduced to the microphone 5. And is input to the signal separating means 11 as a noise signal e.

The passed signal separating means 11, the tracking filter 11a is an engine rotational secondary component e _21, the tracking filter 11b is passed through the engine 4 order component e _22, the tracking filter 11c is passing other signals e ₁ .

The main adaptive controller 13a receives the other signals e ₁
And updates the filter coefficients of the main adaptive digital filter 9 so that the sum of the squares of the signal e ₁ is minimized. Sub adaptive controller 13b receives the engine rotational secondary component e ₂₁ separated from the noise signal e to update the filter coefficients of the secondary adaptive digital filter 9b. In this case, the update is not performed so that the sum of squares of the signal e ₂₁ is minimized.
The target level e _h1 set by the first target level setter 17a
Is updated to be equal to the sum of squares of. That is, the noise signal e ₂₁ of the engine rotation secondary component and the target level e _h1 are input to the first comparator 15a, and it is compared whether the secondary component e ₂₁ is larger or smaller than the target level e _h1 . According to the result, the filter coefficient of the sub-adaptive digital filter 9b is increased or decreased by an algorithm described later.

[0032] Also inputs the engine rotation quartic component e ₂₂ separated from the noise signal e in the sub adaptive controller 13c, a target level e _h2 in the second comparator 15b 4
By its magnitude compared with the following components e ₂₂ is to increase or decrease the filter coefficient of the sub adaptive digital filter 9c.

Here, the LMS algorithm as a control algorithm for updating the filter coefficient of the adaptive digital filter 9 will be described using a general formula.

The noise signal detected by the l-th microphone is e _l (n), and the noise signal detected by the l-th microphone when there is no control sound from the loudspeaker is e e (n).
_pl (n), the j-th (j = 0, 1, 2,..., I _c ) transfer function (FIR (finite impulse response) function) between the m-th loudspeaker and the l-th evaluation point, ie, the working position −
The filter coefficient when the term of 1) is represented by a digital filter is C _lmj , and the reference signal, ie, the sound source information signal x
_p (n) and the reference signal x _p (n), and the i-th (i = 0, i) of the adaptive filter for driving the m-th loudspeaker
Let W _mi be the coefficient of 1, 2, 1..., I _K -1)

[0035]

(Equation 1)

The following holds.

Next, the evaluation function (variable to be minimized) J
e

[0038]

(Equation 2)

Here,

Then, in order to find the filter coefficient W _mi that minimizes the evaluation function Je, the LMS algorithm is employed. In other words, the evaluation function Je a value obtained by partially differentiating each filter coefficient Wmi updates the filter coefficient W _mi.

Therefore, from equation (2),

[0042]

(Equation 3)

From the equation (1),

[0044]

(Equation 4)

Therefore, the right side of the equation (4) is represented by r
_{If lm} ( _ni ) is used, the rewriting equation of the filter coefficient can be obtained by the LMS algorithm of the following equation (5).

[0046]

(Equation 5)

As is clear from this form, the stability and convergence of this algorithm are governed by the convergence coefficient α.

In order to reduce noise, a filter coefficient W _mi that minimizes the evaluation function Je is obtained, and the filter coefficient of the adaptive digital filter 9 is updated. In the case of FIG. 2, this corresponds to the case where the main adaptive controller 13a updates the filter coefficient of the main adaptive digital filter 9a.

On the other hand, when emphasizing a specific sound, the target function (square value) is used instead of minimizing the evaluation function Je.
Equation (5) is corrected as follows.

FIG. 3 shows a case where the evaluation function is minimized (e _min
² ) and a case where the target level is set (e _h ² ) is schematically shown, and corresponds to equation (5).
In this example, the coefficients of the adaptive digital filter are two, W ₀ and W ₁ , for easy understanding. The quadratic surface drawn by the solid line in FIG. 3 indicates the square value of the sound pressure taken when the coefficients of the adaptive digital filter are W ₀ and W ₁ . When reducing noise, the evaluation function is set to e _min ²
Although to a, it is taken as the target level e _h ² instead of minimizing the evaluation function when you want to emphasize certain sounds. Therefore, when emphasizing a specific sound, the control algorithm of the expression (5) converges to one of the quadratic surfaces showing the square value of the sound pressure on the iso-square sound pressure surface shown by hatching in FIG.
The filter coefficients W ₀ and W ₁ are determined.

FIG. 6 is a flowchart for updating the filter coefficient when a specific sound is emphasized as described above.

Firstly, the equation (5) to set the target level e _h serving as a reference level to be converged in the step S _1. Then the engine rotational order component e ₂ is separated as in step S _2. In step S _3, if the engine rotational order component e ₂ exceeds the target level e _h is determined, if exceeded in step S _4, the (5) is a type of convergence coefficient α is positive, step S
_Move to ₅ . Further, the engine rotational order component e ₂ in step S ₃ is convergence factor in step S ₆ if it is determined to be below the target level e _h alpha moves to step S ₅ is negative. In step S ₅ the (5) is the sign of α convergence coefficient of formula is changed in response to the step S ₄ or step S _6, it is the filter coefficient is updated in step S ₇ accordingly.

As a result, as shown in FIG.
The next component and its fourth harmonic component, which is a harmonic component thereof, are emphasized by, for example, the level P, and the other frequency components are set to a level difference d or more to create a comfortable sound room with a light feeling in the vehicle interior. it can. Therefore, in a sports car, it is possible to create a sound field according to the type of vehicle in a vehicle compartment, for example, while driving while listening to a comfortable engine sound with a light feeling. In addition, even if it is not a sports car, it can respond to a user's request to drive while listening to the engine sound and the acceleration sound.

FIG. 6 is a three-dimensional map showing the frequency on the horizontal axis, the sound pressure level on the vertical axis, and the rotation speed on the depth. It is known that the second and fourth components of the engine rotational speed change clearly and smoothly as an example of the characteristic having an excellent tone color.

In order to realize this characteristic by the active noise control, it is necessary to change the setting of the target level by the target level setting unit 17 according to the engine speed, thereby providing a light feeling according to the engine speed. A comfortable sound quality can be created. In addition, the target level can be changed not only by the engine speed but also by the engine load. For example, when the load is large, the noise level can be increased to create a sound-enhancing room that matches the feeling of an actual person. Further, the engine load can be detected by the throttle opening. This is because the throttle opening has a characteristic that is almost uniquely determined with respect to the engine load.

The present invention is not limited to the above embodiment. For example, the frequency of the signal to be emphasized may be only the second-order component of the engine rotation, and when several harmonic components are simultaneously emphasized, the signal may include not only the fourth-order component but also higher components. is there. Further, it is also possible to emphasize sounds other than the engine sound. Also,
The setting of the target level can be freely changed by manual operation of the occupant. Furthermore, the target level can be raised by detecting the occupant's falling asleep, and the occupant can be encouraged to wake up. In the above embodiment, the control device using a single filter has been described. However, a Filtered-XLMS algorithm using two digital filters may be used. Further, even if the evaluation point for noise reduction and the microphone are spatially separated from each other, control can be performed by estimating the residual noise at the evaluation point based on the predetermined position. Furthermore, it is also possible to apply to vibration control and the like.

[0057]

As is clear from the above, according to the structure of the present invention, it is possible to emphasize sounds of a specific frequency and reduce sounds of other frequencies. A sound field can be created in the passenger compartment accordingly.

[Brief description of the drawings]

FIG. 1 is an overall control block diagram according to an embodiment of the present invention.

FIG. 2 is a control block diagram showing a part of the control block in detail.

FIG. 3 is a schematic diagram of a control algorithm.

FIG. 4 is a flowchart according to one embodiment.

FIG. 5 is an explanatory diagram of the operation and effect.

FIG. 6 is an explanatory diagram of a relationship between a rotation order and a timbre.

FIG. 7 is a control block diagram according to a conventional example.

[Explanation of symbols]

 Reference Signs List 3 loudspeaker 3 (control sound source) 5 Microphone (residual noise detecting means) 9 Adaptive digital filter 9a Main adaptive digital filter 9b Secondary adaptive digital filter 9c Secondary adaptive digital filter 11 Signal separating means 13 Adaptive controller 13a Main adaptive controller 13b Secondary Adaptive controller 13c sub-adaptive controller 21 crank angle signal sensor (noise generation state detecting means) 23 signal extracting means

Claims (1)

(57) [Claims] 1. A control sound source for generating a control sound causing interference with noise to reduce noise at an evaluation point, means for detecting residual noise at a predetermined position after the interference, and a signal relating to a noise generation state of the noise source. Means for detecting, and means for extracting a signal of a target frequency from an output signal of the noise generation state detecting means,
A main adaptive filter for inputting an output signal of the noise generation state detecting means, filtering with a predetermined filter coefficient and outputting a drive signal of the control sound source, and a signal of the extracted target frequency and inputting a predetermined filter coefficient A sub-adaptive filter that filters and outputs a drive signal of the control sound source, a unit that separates an output signal of the residual noise detection unit into a signal of a target frequency and other signals, and that the other signals are minimized. A main adaptive controller that updates the filter coefficient of the main adaptive filter and a sub-adaptive controller that updates the filter coefficient of the sub-adaptive filter so that the signal of the separated target frequency becomes a target level. Active noise control device.