Active noise reduction device

Abstract

To effectively reduce noise at a peak frequency by tracking a change of peak frequency of noise due to a change of input conditions.SOLUTION: An active noise reduction device 11 comprises: a negating sound generation device 13 that generates a negating sound y to negate a noise d; an error detection device 14 that detects an error between the noise d and the negating sound y and generates an error signal e that corresponds to the error; and a control device 15 that controls the negating sound generation device 13 on the basis of the error signal e. The control device 15 extracts noise components Ak0, Ak1 at a plurality of frequencies fk on the basis of the error signal e, determines a control target frequency fc from among the plurality of frequencies fk on the basis of the noise components Ak0, Ak1 in the plurality of frequencies fk, selects a value of a prescribed control parameter on the basis of the control target frequency fc, and generates a control signal u for controlling the negating sound generation device 13, on the basis of the selected value of the control parameter.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an active noise reduction device that reduces noise by interfering with the noise with a canceling sound that is in the opposite phase to the noise. [Background technology]

[0002] In a typical vehicle, the wheels vibrate due to the force they receive from the road surface, and when this vibration is transmitted to the vehicle body via the suspension, road noise is generated inside the vehicle cabin. In particular, narrow-band road noise (more specifically, road noise with a constant bandwidth and a peak around 40 to 50 Hz) excited by the acoustic resonance characteristics of a closed space such as a vehicle cabin is also known as drumming noise. Drumming noise reaches the ears of occupants as a muffled "rumble" sound, which can be quite unpleasant for them.

[0003] Patent Document 1 proposes an active noise reduction device for reducing such drumming noise. This active noise reduction device uses only the noise signal at the control point detected by a microphone as a control input, and generates a control sound by adjusting the amplitude and phase of the noise signal.

[0004] More specifically, referring to FIG. 1 of Patent Document 1, a processing circuit 101 extracts the f0 component of a noise signal detected by a microphone. Here, the f0 component refers to the component at the control target frequency f0 (ω0=2πf0 in the figure). An adjustment circuit 108 adjusts the amplitude and phase of the f0 component of the noise signal extracted by the processing circuit 101 to generate a control sound.

[0005] The processing circuit 101 described above is composed of a SAN filter (adaptive notch filter) having coefficients A and B, and a generator that generates reference signals (sine and cosine waves). The frequency of the reference signal is set to the controlled frequency f0. The coefficients A and B of the SAN filter are updated by an adaptive algorithm so that the error signal e1 (e1 = e + Vout1) generated by the noise signal e detected by the microphone and the output Vout1 of the SAN filter is minimized. As a result, Vout1 = -e. More specifically, since the output Vout1 of the SAN filter is a narrowband signal centered at the controlled frequency f0, Vout1 = -e at the controlled frequency f0. In other words, the f0 component of the noise signal is extracted. Figure 5 of Cited Document 1 shows the characteristics of the processing circuit 101.

[0006] The adjustment circuit 108 corrects the acoustic characteristics C (including the characteristics of the vehicle interior space and electronic devices) from the speaker to the microphone and generates a control sound. Referring to FIG. 8 of Patent Document 1, the adjustment circuit 108 is composed of a SAN filter for noise extraction having coefficients A and B, and a notch filter having coefficients Sa and Sb and representing the characteristics of the adjustment circuit 108. As a setting example, if the acoustic characteristic C is measured in advance as C^ and the notch filter is set to the reciprocal of C^ at the control target frequency f0, 1 / C^, the following equation (1) is established at the microphone position. Note that "e" in the following equation (1) represents the sound pressure of the noise signal after control, and "d" in the following equation (1) represents the sound pressure of the noise signal before control.

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[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-25527 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, with regard to the narrow-band road noise (hereinafter simply referred to as "noise") described above, the sound pressure of the noise inside a vehicle cabin is determined by the product of the noise input conditions (wheel vibration due to forces received from the road surface) and the noise's transfer characteristics (vehicle body characteristics, vehicle cabin acoustic characteristics, etc.). The resonance frequency of the noise's transfer characteristics does not change depending on the vehicle's driving conditions (road surface conditions, vehicle speed, etc.). On the other hand, the noise input conditions change depending on the vehicle's driving conditions, and the peak frequency of the noise can change by several Hz accordingly. Conventional active noise reduction devices only reduce noise whose peak frequency is a preset fixed frequency, so they cannot follow changes in the noise's peak frequency, resulting in the problem of noise remaining at the peak frequency.

[0009] In view of the above background, an object of the present invention is to provide an active noise reduction device that can effectively reduce noise at peak frequencies by following changes in the peak frequency of noise due to changes in input conditions. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, one aspect of the present invention is an active noise reduction device (11) comprising: a noise cancellation generating device (13) that generates a noise cancellation to cancel out the noise; an error detecting device (14) that detects an error between the noise and the noise cancellation and generates an error signal corresponding to the error; and a control device (15) that controls the noise cancellation generating device based on the error signal, wherein the control device extracts noise components at a plurality of frequencies based on the error signal, determines a frequency to be controlled from among the plurality of frequencies based on the noise components at the plurality of frequencies, selects a value of a predetermined control parameter based on the frequency to be controlled, and generates a control signal for controlling the noise cancellation generating device based on the value of the selected control parameter.

[0011] According to this aspect, by determining the frequency to be controlled from among a plurality of frequencies, the frequency to be controlled can be made to follow changes in the peak frequency of the noise caused by changes in the input conditions, thereby effectively reducing the noise at the peak frequency.

[0012] In the above aspect, the control device may calculate absolute values ​​of noise components at multiple frequencies (step ST1), calculate correction values ​​of the noise components at multiple frequencies by correcting the absolute values ​​of the noise components at multiple frequencies (steps ST2 and ST3), identify the maximum value of the correction values ​​of the noise components at multiple frequencies by comparing the correction values ​​of the noise components at multiple frequencies (step ST4), and determine the frequency corresponding to the maximum correction value of the noise components as the frequency to be controlled (step ST5).

[0013] According to this aspect, by correcting the absolute values ​​of the noise components at multiple frequencies and then comparing them, it is possible to appropriately determine the frequency to be controlled, and it is possible to improve the ability of the frequency to be controlled to follow changes in the peak frequency of the noise.

[0014] In the above aspect, the control device may correct the absolute values ​​of the noise components at a plurality of frequencies based on a correction table that defines correction coefficients for each frequency according to the human hearing characteristics (step ST3).

[0015] According to this aspect, the user of the active noise reduction device (for example, a vehicle occupant) can easily feel the noise reduction effect.

[0016] In the above aspect, the control device may correct the absolute values ​​of the noise components at a plurality of frequencies based on the target volume reduction for each frequency (step ST2).

[0017] According to this aspect, the absolute value of the noise component after sound reduction can be converted to the absolute value of the noise component before sound reduction based on the target sound volume reduction for each frequency, thereby making it possible to more appropriately determine the frequency to be controlled.

[0018] In the above aspect, the control device may extract noise components at multiple frequencies and calculate absolute values ​​of the noise components at multiple frequencies at a predetermined sample period, and calculate the current absolute values ​​of the noise components at each frequency based on the previous absolute values ​​of the noise components at each frequency and the current absolute values ​​of the noise components at each frequency (step ST1).

[0019] According to this aspect, it is possible to prevent the frequency to be controlled from being frequently switched due to noise or the like contained in the noise components of each frequency.

[0020] In the above aspect, the control device may store a control parameter table (T1, T3) that specifies the value of the control parameter for each frequency, and may select the value of the control parameter corresponding to the frequency to be controlled by referring to the control parameter table based on the frequency to be controlled.

[0021] According to this aspect, it is possible to generate a control signal using the optimum control parameter value according to the frequency to be controlled. [Effects of the Invention]

[0022] According to the above aspect, it is possible to provide an active noise reduction device that can effectively reduce noise at peak frequencies by following changes in the peak frequency of noise due to changes in input conditions. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing a vehicle to which an active noise reduction device according to a first embodiment is applied; [Figure 2] FIG. 1 is a functional block diagram showing an active noise reduction device according to a first embodiment; [Figure 3] 1 is a table showing a control parameter table according to a first embodiment; [Figure 4] A functional block diagram showing a control signal output unit according to the first embodiment. [Figure 5]Flowchart showing a process for determining a frequency to be controlled according to the first embodiment [Figure 6] 1 is a table showing a correction table according to a first embodiment; [Figure 7] Graph showing drumming noise reduction effect [Figure 8] 10 is a table showing a control parameter table according to the second embodiment. [Figure 9] A functional block diagram showing a control signal output unit according to a second embodiment. [Figure 10] A functional block diagram showing a control target signal generator according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, the "^" (hat) next to various symbols indicates an identified value or an estimated value. While the "^" is placed above various symbols in figures and formulas, it is placed after the various symbols in the main text.

[0025] (First embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

[0026] <Active Noise Reduction Device 11> 1 is a schematic diagram showing a vehicle 1 to which an active noise reduction device 11 (hereinafter abbreviated as "noise reduction device 11") according to a first embodiment is applied. When a wheel 2 vibrates due to a force received from a road surface S and the vibration of the wheel 2 is transmitted to a vehicle body 4 via a suspension 3, a drumming noise d (an example of noise) is generated inside a vehicle interior 5. The drumming noise d is a narrow-band road noise having a peak around 40 to 50 Hz.

[0027] The noise reduction device 11 is a feedback control type ANC (Active Noise Control Device) for reducing such drumming noise d. More specifically, the noise reduction device 11 generates a canceling sound y that is in the opposite phase to the drumming noise d, and reduces the drumming noise d by causing the generated canceling sound y to interfere with the drumming noise d.

[0028] 1 and 2, noise reduction device 11 includes a plurality of speakers 13 (an example of a cancellation sound generating device) that generate a cancellation sound y to cancel out drumming noise d, a plurality of error microphones 14 (an example of an error detecting device) that detect an error (synthetic sound) between drumming noise d and cancellation sound y and generate an error signal e corresponding to the detected error, and a control device 15 that controls the plurality of speakers 13 based on the error signal e. Note that symbol C in Fig. 2 indicates the transfer characteristic of a secondary path from speaker 13 to error microphone 14.

[0029] <Speaker 13> 1, each speaker 13 of the noise reduction device 11 constitutes, for example, a part of the audio system of the vehicle 1 and is installed in the door of the vehicle 1. Note that in other embodiments, the speaker 13 may be provided separately from the audio system of the vehicle 1, or may be installed in a location other than the door of the vehicle 1 (for example, in the headrest 6a of the passenger seat 6 or on the floor below the passenger seat 6).

[0030] <Error Mic 14> Each error microphone 14 of the noise reduction device 11 is installed, for example, on the headrest 6a of the passenger seat 6. Note that in other embodiments, the error microphone 14 may be installed in a location other than the passenger seat 6 of the vehicle 1 (for example, on the ceiling above the passenger seat 6).

[0031] <Control device 15> The control device 15 of the noise reduction device 11 is an electronic control unit (ECU) that includes an arithmetic processing unit (a processor such as a CPU or an MPU) and a storage device (a memory such as a ROM or a RAM). The control device 15 may be configured as a single piece of hardware, or may be configured as a unit consisting of multiple pieces of hardware.

[0032] Referring to FIG. 2, the control device 15 includes, as functional components, an A / D conversion unit 21, a plurality of noise component extraction units 22, a control target frequency determination unit 23, a parameter selection unit 24, a control signal output unit 25, and a D / A conversion unit 26.

[0033] The A / D conversion unit 21 of the control device 15 converts the error signal e output from the error microphone 14 from an analog signal to a digital signal, and outputs the converted error signal e to a plurality of noise component extraction units 22. Hereinafter, when simply referred to as "error signal e," it refers to the error signal e that has passed through the A / D conversion unit 21.

[0034] <Noise component extraction unit 22> Each noise component extraction unit 22 of the control device 15 extracts noise components Ak0, Ak1 at a predetermined extraction frequency fk (k=1, 2, ...) based on the error signal e at a predetermined sampling period. More specifically, the noise component extraction unit 22 extracts the noise components Ak0, Ak1 at the extraction frequency fk as a complex signal having a real part and an imaginary part. The noise component extraction unit 22 outputs the extracted noise components Ak0, Ak1 together with the extraction frequency fk to the controlled frequency determination unit 23.

[0035] The extraction frequency fk is set to a different value for each noise component extraction unit 22. The extraction frequency fk is set to a frequency (a frequency in the vicinity of 40 to 50 Hz) that can be a peak frequency of the drumming noise d. The number k of extraction frequencies fk (i.e., the number of noise component extraction units 22) is set to an arbitrary integer equal to or greater than 2.

[0036] ​The noise component extraction unit 22 includes a cosine wave generation circuit 31, a sine wave generation circuit 32, an extraction signal generation unit 33, and an adder .

[0037] The cosine wave generating circuit 31 generates an extracted cosine wave signal xck based on the extraction frequency fk and outputs the generated extracted cosine wave signal xck to the extraction signal generating unit 33. The sine wave generating circuit 32 generates an extracted sine wave signal xsk based on the extraction frequency fk and outputs the generated extracted sine wave signal xsk to the extraction signal generating unit 33.

[0038] The extraction signal generation unit 33 is configured by an extraction filter Ak. The extraction filter Ak is an adaptive notch filter (SAN filter). The extraction signal generation unit 33 includes a first extraction filter unit 35, a second extraction filter unit 36, an adder 37, a first extraction update unit 38, and a second extraction update unit 39.

[0039] The first extraction filter unit 35 has an extraction filter coefficient Ak0. The extraction filter coefficient Ak0 forms the real part of the coefficient of the extraction filter Ak and also forms the real part of the noise component (complex signal) extracted by the noise component extraction unit 22. The first extraction filter unit 35 performs filtering on the extracted cosine wave signal xck output from the cosine wave generation circuit 31.

[0040] The second extraction filter unit 36 ​​has an extraction filter coefficient Ak1. The extraction filter coefficient Ak1 forms the imaginary part of the coefficient of the extraction filter Ak and also forms the imaginary part of the noise component (complex signal) extracted by the noise component extraction unit 22. The second extraction filter unit 36 ​​performs filtering on the extracted sine wave signal xsk output from the sine wave generation circuit 32.

[0041] The adder 37 generates an extracted signal ak by adding the extracted cosine wave signal xck that has passed through the first extraction filter unit 35 and the extracted sine wave signal xsk that has passed through the second extraction filter unit 36. The adder 37 outputs the generated extracted signal ak to the adder 34.

[0042] The first extraction / update unit 38 updates the extraction filter coefficient Ak0 at the above-mentioned sample period using an adaptive algorithm such as an LMS (Least Mean Square) algorithm. More specifically, the first extraction / update unit 38 updates the extraction filter coefficient Ak0 so that the virtual error signal ek (details of which will be described later) output from the adder 34 is minimized.

[0043] The second extraction / update unit 39 updates the extraction filter coefficient Ak1 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the second extraction / update unit 39 updates the extraction filter coefficient Ak1 so that the virtual error signal ek output from the adder 34 is minimized.

[0044] The adder 34 generates a virtual error signal ek by adding the extraction signal ak and the error signal e output from the extraction signal generation unit 33. The adder 34 outputs the generated virtual error signal ek to the extraction signal generation unit 33.

[0045] <Control target frequency determination unit 23> The controlled frequency determiner 23 of the control device 15 determines a controlled frequency fc from among the plurality of extracted frequencies fk based on the extracted frequency fk and noise components Ak0, Ak1 (extraction filter coefficients) output from the plurality of noise component extractors 22. The controlled frequency determiner 23 outputs the determined controlled frequency fc to the parameter selector 24, and also outputs the determined controlled frequency fc and the corresponding noise components Ac0, Ac1 to the control signal output unit 25. The method of determining the controlled frequency fc by the controlled frequency determiner 23 will be described later.

[0046] <Parameter selection section 24> 3, the parameter selection unit 24 of the control device 15 stores a control parameter table T1. The control parameter table T1 is a table that defines the values ​​of various control parameters for each frequency. In this embodiment, the control parameters include a feedback gain (FB gain), a feedback phase (FB phase), a target volume reduction, etc.

[0047] The parameter selection unit 24 selects a value of a control parameter according to the control target frequency fc by referring to the control parameter table T1 based on the control target frequency fc output from the control target frequency determination unit 23. The parameter selection unit 24 outputs the selected value of the control parameter to the control signal output unit 25.

[0048] <Control signal output unit 25> 4, the control signal output unit 25 of the control device 15 generates a control signal u for controlling the speaker 13, based on the control target frequency fc and the noise components Ac0 and Ac1 output from the control target frequency determination unit 23, and the value of the control parameter output from the parameter selection unit 24. The control signal output unit 25 outputs the generated control signal u to the D / A conversion unit 26.

[0049] The control signal output unit 25 is configured by a SAN filter and includes a cosine wave generating unit 41, a sine wave generating unit 42, a first control filter unit 43, a second control filter unit 44, an adder 45, and a gain adjusting unit 46.

[0050] The cosine wave generating unit 41 generates a controlled cosine wave signal uc=cos(ωt+φd) based on the controlled frequency fc output from the controlled frequency determining unit 23 and the value of the FB phase (one of the control parameters) output from the parameter selecting unit 24. More specifically, the cosine wave generating unit 41 generates the controlled cosine wave signal uc by shifting the phase of the reference cosine wave cos(ωt) corresponding to the controlled frequency fc by an angle φd corresponding to the FB phase. The cosine wave generating unit 41 outputs the generated controlled cosine wave signal uc to the first control filter unit 43.

[0051] The sine wave generation unit 42 generates a control sine wave signal us = sin(ωt + φd) based on the control target frequency fc output from the control target frequency determination unit 23 and the value of the FB phase (one of the control parameters) output from the parameter selection unit 24. More specifically, the sine wave generation unit 42 generates the control sine wave signal us by shifting the phase of the reference sine wave sin(ωt) corresponding to the control target frequency fc by an angle φd corresponding to the FB phase. The sine wave generation unit 42 outputs the generated control sine wave signal us to the second control filter unit 44.

[0052] The first control filter unit 43 has a control filter coefficient A. The first control filter unit 43 performs a filter process on the control cosine wave signal uc output from the cosine wave generation unit 41. The control filter coefficient A is sequentially updated using the noise component Ac0 output from the control target frequency determination unit 23.

[0053] The second control filter unit 44 has a control filter coefficient B. The second control filter unit 44 performs a filter process on the control sine wave signal us output from the sine wave generation unit 42. The control filter coefficient B is sequentially updated using the noise component Ac1 output from the control target frequency determination unit 23.

[0054] The adder 45 generates a control signal u by adding the control cosine wave signal uc that has passed through the first control filter unit 43 and the control sine wave signal us that has passed through the second control filter unit 44. The adder 45 outputs the generated control signal u to the gain adjustment unit 46.

[0055] The gain adjustment unit 46 adjusts the gain of the control signal u output from the adder 45 based on the FB gain (one of the control parameters) output from the parameter selection unit 24. The gain adjustment unit 46 outputs the control signal u with the adjusted gain to the D / A conversion unit 26.

[0056] <D / A conversion unit 26> 2, D / A conversion unit 26 of control device 15 converts control signal u output from control signal output unit 25 from a digital signal to an analog signal and outputs the analog signal to speaker 13. As a result, speaker 13 generates a canceling sound y according to control signal u.

[0057] <Control target frequency determination process> The controlled frequency determiner 23 of the control device 15 executes a controlled frequency determination process at the above-mentioned sample period. In the controlled frequency determination process, the controlled frequency determiner 23 determines a controlled frequency fc based on the extracted frequency fk and noise components Ak0, Ak1 output from the plurality of noise component extractors 22. In the following description of the controlled frequency determination process, (n) added to various symbols indicates a value extracted or calculated at the current sample time (current value). On the other hand, (n-1) added to various symbols indicates a value extracted or calculated at the previous sample time (previous value).

[0058] Referring to FIG. 5, when the controlled frequency determination process is started, the controlled frequency determination unit 23 calculates the current value |Ak(n)| of the absolute values ​​of the noise components Ak0 and Ak1 for each extracted frequency fk using the following equation (2) (step ST1).

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[0059] However, in the above equation (2), the current value |Ak(n)| of the absolute value of the noise components Ak0 and Ak1 is calculated based only on the current values ​​of the noise components Ak0 and Ak1. When using such a calculation method, there is a risk that the control target frequency fc will frequently change due to noise contained in the noise components Ak0 and Ak1.

[0060] Therefore, the controlled target frequency determiner 23 may calculate the current value |Ak(n)| of the absolute value of the noise components Ak0 and Ak1 based on the current values ​​of the noise components Ak0 and Ak1 and the previous value |Ak(n-1)| of the absolute value of the noise components Ak0 and Ak1. That is, the controlled target frequency determiner 23 may set the time-averaged value of the absolute values ​​of the noise components Ak0 and Ak1 within a predetermined time as the current value |Ak(n)| of the absolute value of the noise components Ak0 and Ak1. For example, the controlled target frequency determiner 23 may calculate the current value |Ak(n)| of the absolute value of the noise components Ak0 and Ak1 using the following equation (3) instead of the above equation (2):

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[0061] Next, the controlled frequency determination unit 23 corrects the absolute value |Ak(n)| of the noise components Ak0 and Ak1 based on the control effect (the effect of reducing the drumming noise d). More specifically, the controlled frequency determination unit 23 calculates a first correction value |Axk(n)| of the absolute value |Ak(n)| of the noise components Ak0 and Ak1 by correcting the absolute value |Ak(n)| of the noise components Ak0 and Ak1 based on the target volume reduction (one of the control parameters) for each frequency (step ST2). For example, the controlled frequency determination unit 23 calculates the first correction value |Axk(n)| using the following equation (4). Note that "TR" in the following equation (4) indicates the target volume reduction for each frequency.

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[0062] The absolute value |Ak(n)| of the noise components Ak0 and Ak1 calculated in step ST1 above corresponds to the noise components Ak0 and Ak1 after sound reduction (after control). However, what is desired to be canceled by the sound cancellation y from the speaker 13 is not the drumming noise d after sound reduction (after control), but the drumming noise d before sound reduction (before control). Therefore, the controlled frequency determination unit 23 corrects the absolute value |Ak(n)| of the noise components Ak0 and Ak1 using the above equation (4) to convert the values ​​corresponding to the noise components Ak0 and Ak1 after sound reduction (after control) into values ​​corresponding to the noise components Ak0 and Ak1 before sound reduction (before control). For example, when the target sound reduction is 6 dB, the coefficient β in the above equation (4) is approximately 2.

[0063] Next, the controlled frequency determiner 23 corrects the first correction value |Axk(n)| based on the evaluation criterion (human hearing characteristics). More specifically, the controlled frequency determiner 23 corrects the first correction value |Axk(n)| based on the correction table T2 to calculate the second correction value |Ayk(n)| of the absolute value |Ak(n)| of the noise components Ak0 and Ak1 (step ST3).

[0064] 6, correction table T2 is a table that defines a correction coefficient for each frequency according to the human hearing characteristics. In this embodiment, correction table T2 defines the correction coefficient for each frequency based on so-called A-weighting. Note that in other embodiments, correction table T2 may define the correction coefficient for each frequency based on an evaluation criterion other than the human hearing characteristics.

[0065] For example, the controlled frequency determiner 23 calculates the second correction value |Ayk(n)| by correcting the first correction value |Axk(n)| using the following equation (5): Note that α in the following equation (5) represents a correction coefficient set based on the correction table T2.

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[0066] Referring to FIG. 5, next, the control target frequency determination unit 23 identifies the maximum value of the second correction value |Ayk(n)| by comparing the second correction values ​​(|Ay1(n)|, . . . , |Ayk(n)|) at all the extracted frequencies fk (step ST4).

[0067] Next, the controlled object frequency determination unit 23 determines the extracted frequency fk corresponding to the maximum value of the second correction value |Ayk(n)| as the controlled object frequency fc (step ST5). With the above, the controlled object frequency determination process ends.

[0068] <Effects> In the first embodiment, the control device 15 extracts noise components Ak0, Ak1 at a plurality of extraction frequencies fk based on the error signal e, determines a control target frequency fc from among the plurality of extraction frequencies fk based on the noise components Ak0, Ak1 at the plurality of extraction frequencies fk, selects a value of a predetermined control parameter based on the control target frequency fc, and generates a control signal u for controlling the speaker 13 based on the selected value of the control parameter. By determining the control target frequency fc from among the plurality of extraction frequencies fk in this manner, the control target frequency fc can be made to follow changes in the peak frequency of the drumming noise d due to changes in the driving conditions of the vehicle 1. As a result, the drumming noise d at the peak frequency can be effectively reduced.

[0069] Next, the drumming noise d reduction effect described above will be further explained with reference to Fig. 7. Fig. 7(a) shows the state before the peak frequency of the drumming noise d changes in a conventional noise reduction device and in the noise reduction device 11 of this embodiment (as an example, a state where the peak frequency of the drumming noise d is around 46 Hz). Fig. 7(b) and Fig. 7(C) show the state after the peak frequency of the drumming noise d changes in the conventional noise reduction device and in the noise reduction device 11 of this embodiment (as an example, a state where the peak frequency of the drumming noise d is around 53 Hz).

[0070] 7(a) and 7(b), in conventional noise reduction device 11, the control target frequency fc is constant, and the control target frequency fc does not change even if the peak frequency of drumming noise d changes. As a result, the control target frequency fc cannot follow changes in the peak frequency of drumming noise d, and drumming noise d remains at the peak frequency (see ellipse Z1 in FIG. 7(b)).

[0071] 7(a) and 7(c), in noise reduction device 11 of this embodiment, the controlled frequency fc is variable, and the controlled frequency fc also changes automatically in accordance with changes in the peak frequency of drumming noise d. As a result, the controlled frequency fc can be made to follow changes in the peak frequency of drumming noise d, and the drumming noise d can be effectively reduced at the peak frequency (see ellipse Z2 in FIG. 7(c)).

[0072] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Figures 8 to 10. Note that descriptions that overlap with the first embodiment of the present invention will be omitted as appropriate.

[0073] <Parameter selection section 24> 8, the parameter selection unit 24 of the control device 15 stores a control parameter table T3. The control parameter table T3 is a table that defines the values ​​of various control parameters for each frequency. In this embodiment, the control parameters include step size parameters μ1 and μ2, a ​​target volume reduction, an FB gain upper limit value (feedback gain upper limit value), etc.

[0074] The step size parameters μ1 and μ2 are parameters for adjusting the update amount of the SAN filter used in the control signal output unit 25 (details will be described later). As the values ​​of the step size parameters μ1 and μ2 increase, the update amount of the SAN filter also increases. As the values ​​of the step size parameters μ1 and μ2 decrease, the update amount of the SAN filter also decreases.

[0075] The parameter selection unit 24 selects the value of the control parameter corresponding to the control target frequency fc by referring to the control parameter table T3 based on the control target frequency fc output from the control target frequency determination unit 23. The parameter selection unit 24 outputs the selected value of the control parameter to the control signal output unit 25.

[0076] <Control target signal generator 27> 9 and 10, the control device 15 according to the second embodiment includes, in addition to the components of the control device 15 according to the first embodiment, a controlled signal generation unit 27. The controlled signal generation unit 27 has a cosine wave generation circuit 27A, a sine wave generation circuit 27B, a first filter unit 27C, a second filter unit 27D, a first adder 27E, a third filter unit 27F, a fourth filter unit 27G, and a second adder 27H.

[0077] The cosine wave generating circuit 27A generates a cosine wave signal rc based on a reference frequency f0 corresponding to the controlled frequency fc. The sine wave generating circuit 27B generates a sine wave signal rs based on the reference frequency f0.

[0078] The first filter unit 27C has a first filter coefficient A0 corresponding to the noise component Ac0. The first filter unit 27C performs filtering on the cosine wave signal rc. The second filter unit 27D has a second filter coefficient A1 corresponding to the noise component Ac1. The second filter unit 27D performs filtering on the sine wave signal rs. The first adder 27E generates the control target signal efr by adding the cosine wave signal rc that has passed through the first filter unit 27C and the sine wave signal rs that has passed through the second filter unit 27D.

[0079] The third filter unit 27F has a first filter coefficient A0. The third filter unit 27F performs filtering on the sine wave signal rs. The fourth filter unit 27G has a coefficient obtained by inverting the polarity of the second filter coefficient A1. The fourth filter unit 27G performs filtering on the cosine wave signal rc. The second adder 27H generates the control target signal efi by adding the sine wave signal rs that has passed through the third filter unit 27F and the cosine wave signal rc that has passed through the fourth filter unit 27G.

[0080] <Control signal output unit 25> Referring to FIG. 9, the control signal output unit 25 of the control device 15 includes a control signal generation unit 51, a cancellation estimation signal generation unit 52, a noise estimation signal generation unit 53, a reference signal generation unit 54, a control filter update unit 55, and a virtual error signal generation unit 56.

[0081] The control signal generating unit 51 is configured by a control filter W. A SAN filter is used as the control filter W. The control signal generating unit 51 includes a first control filter unit 61, a second control filter unit 62, a first adder 63, a third control filter unit 64, a fourth control filter unit 65, and a second adder 66.

[0082] The first control filter unit 61 has a control filter coefficient W0. The control filter coefficient W0 forms the real part of the coefficient of the control filter W. The first control filter unit 61 performs filtering on the control target signal efr output from the control target signal generation unit 27.

[0083] The second control filter unit 62 has a control filter coefficient W1. The control filter coefficient W1 forms the imaginary part of the coefficient of the control filter W. The second control filter unit 62 performs filtering on the control target signal efi output from the control target signal generation unit 27.

[0084] The first adder 63 generates a control signal u0 by adding the control target signal efr that has passed through the first control filter unit 61 and the control target signal efi that has passed through the second control filter unit 62. The first adder 63 outputs the generated control signal u0 to the D / A conversion unit 26 and the cancellation estimation signal generation unit 52.

[0085] The third control filter unit 64 has a coefficient obtained by inverting the polarity of the control filter coefficient W0. The third control filter unit 64 performs filtering on the control target signal efi output from the control target signal generation unit 27.

[0086] The fourth control filter unit 65 has a control filter coefficient W1. The fourth control filter unit 65 performs filtering on the control target signal efr output from the control target signal generation unit 27.

[0087] The second adder 66 generates a control signal u1 by adding the control target signal efi that has passed through the third control filter unit 64 and the control target signal efr that has passed through the fourth control filter unit 65. The second adder 66 outputs the generated control signal u1 to the cancellation estimation signal generation unit 52.

[0088] The canceling noise estimation signal generation unit 52 is configured by a secondary path filter C^. The secondary path filter C^ is a filter corresponding to an estimated value of the transfer characteristic C of the secondary path from the speaker 13 to the error microphone 14. A SAN filter is used as the secondary path filter C^. The canceling noise estimation signal generation unit 52 includes a first secondary path filter unit 71, a second secondary path filter unit 72, an adder 73, a first secondary path update unit 74, and a second secondary path update unit 75.

[0089] The first secondary path filter unit 71 has a secondary path filter coefficient C^0. The secondary path filter coefficient C^0 forms the real part of the coefficient of the secondary path filter C^. The first secondary path filter unit 71 performs filtering on the control signal u0 output from the control signal generation unit 51.

[0090] The second secondary path filter unit 72 has a secondary path filter coefficient C^1. The secondary path filter coefficient C^1 forms the imaginary part of the coefficient of the secondary path filter C^. The second secondary path filter unit 72 performs filtering on the control signal u1 output from the control signal generation unit 51.

[0091] The adder 73 generates a first cancellation estimation signal y^1 by adding the control signal u0 that has passed through the first secondary path filter unit 71 and the control signal u1 that has passed through the second secondary path filter unit 72. The first cancellation estimation signal y^1 is a signal that corresponds to an estimated value of the cancellation y. The adder 73 outputs the generated first cancellation estimation signal y^1 to the virtual error signal generation unit 56.

[0092] The first secondary path updater 74 updates the secondary path filter coefficient C^0 at a predetermined sampling period using an adaptive algorithm such as an LMS algorithm. More specifically, the first secondary path updater 74 updates the secondary path filter coefficient C^0 so that the virtual error signal ex (details of which will be described later) output from the virtual error signal generator 56 is minimized.

[0093] The second secondary path update unit 75 updates the secondary path filter coefficient C^1 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the second secondary path update unit 75 updates the secondary path filter coefficient C^1 so that the virtual error signal ex output from the virtual error signal generation unit 56 is minimized.

[0094] The noise estimation signal generation unit 53 is composed of a primary path filter H^. The primary path filter H^ is a filter corresponding to an estimated value of the transfer characteristic H of the path (primary path) from the noise source (in this embodiment, the road surface S) to the error microphone 14. A SAN filter is used as the primary path filter H^. The noise estimation signal generation unit 53 includes a first primary path filter unit 81, a second primary path filter unit 82, an adder 83, a first primary path update unit 84, and a second primary path update unit 85.

[0095] The first primary path filter unit 81 has a primary path filter coefficient H^0. The primary path filter coefficient H^0 forms the real part of the coefficient of the primary path filter H^. The first primary path filter unit 81 performs filtering on the control target signal efr output from the control target signal generation unit 27.

[0096] The second primary path filter unit 82 has a coefficient obtained by inverting the polarity of the primary path filter coefficient H^1. The primary path filter coefficient H^1 forms the imaginary part of the coefficient of the primary path filter H^. The second primary path filter unit 82 performs filtering on the control target signal efi output from the control target signal generation unit 27.

[0097] The adder 83 generates a noise estimation signal d^ by adding the control-target signal efr that has passed through the first primary path filter unit 81 and the control-target signal efi that has passed through the second primary path filter unit 82. The noise estimation signal d^ is a signal that corresponds to an estimated value of the drumming noise d. The adder 83 outputs the generated noise estimation signal d^ to the virtual error signal generation unit 56.

[0098] The first primary path update unit 84 updates the primary path filter coefficient H^0 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the first primary path update unit 84 updates the primary path filter coefficient H^0 so that the virtual error signal ex output from the virtual error signal generation unit 56 is minimized.

[0099] The second primary path update unit 85 updates the primary path filter coefficient H^1 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the second primary path update unit 85 updates the primary path filter coefficient H^1 so that the virtual error signal ex output from the virtual error signal generation unit 56 is minimized.

[0100] The reference signal generation unit 54 is configured with a secondary path filter C^, similar to the canceling sound estimation signal generation unit 52. When the coefficients (C^0, C^1) of the secondary path filter C^ are updated in the canceling sound estimation signal generation unit 52, the updated coefficients of the secondary path filter C^ are output to the reference signal generation unit 54, and the coefficients of the secondary path filter C^ are updated in the reference signal generation unit 54. In other words, the coefficients of the secondary path filter C^ set in the reference signal generation unit 54 are not fixed values ​​but are values ​​that are successively updated based on the signal from the canceling sound estimation signal generation unit 52.

[0101] The reference signal generation unit 54 includes a third secondary path filter unit 91, a fourth secondary path filter unit 92, a first adder 93, a fifth secondary path filter unit 94, a sixth secondary path filter unit 95, and a second adder 96.

[0102] The third secondary path filter unit 91 has a secondary path filter coefficient C 0. The third secondary path filter unit 91 performs filtering on the control object signal efr output from the control object signal generation unit 27.

[0103] The fourth secondary path filter unit 92 has a coefficient obtained by inverting the polarity of the secondary path filter coefficient C^1. The fourth secondary path filter unit 92 performs filtering on the control object signal efi output from the control object signal generation unit 27.

[0104] The first adder 93 generates a reference signal r0 by adding the control object signal efr that has passed through the third secondary path filter unit 91 and the control object signal efi that has passed through the fourth secondary path filter unit 92. The first adder 93 outputs the generated reference signal r0 to the control filter update unit 55.

[0105] The fifth secondary path filter unit 94 has a secondary path filter coefficient C 0. The fifth secondary path filter unit 94 performs filtering on the control object signal efi output from the control object signal generation unit 27.

[0106] The sixth secondary path filter unit 95 has a secondary path filter coefficient C^1. The sixth secondary path filter unit 95 performs filtering on the control object signal efr output from the control object signal generation unit 27.

[0107] The second adder 96 generates a reference signal r1 by adding the control object signal efi that has passed through the fifth secondary path filter unit 94 and the control object signal efr that has passed through the sixth secondary path filter unit 95. The second adder 96 outputs the generated reference signal r1 to the control filter update unit 55.

[0108] Like the control signal generating unit 51, the control filter updating unit 55 is configured by a control filter W. The control filter updating unit 55 includes a fifth control filter unit 101, a sixth control filter unit 102, an adder 103, a first control updating unit 104, and a second control updating unit 105.

[0109] The fifth control filter unit 101 has a control filter coefficient W0. The fifth control filter unit 101 performs filtering on the reference signal r0 output from the reference signal generator .

[0110] The sixth control filter unit 102 has a control filter coefficient W1. The sixth control filter unit 102 performs filtering on the reference signal r1 output from the reference signal generator 54.

[0111] The adder 103 generates a second cancellation estimation signal y^2 by adding the reference signal r0 that has passed through the fifth control filter unit 101 and the reference signal r1 that has passed through the sixth control filter unit 102. The second cancellation estimation signal y^2 is a signal that corresponds to an estimated value of the cancellation y. The adder 103 outputs the generated second cancellation estimation signal y^2 to the virtual error signal generation unit 56.

[0112] The first control update unit 104 updates the control filter coefficient W0 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the first control update unit 104 updates the control filter coefficient W0 so that the virtual error signal ey (described in detail later) output from the virtual error signal generation unit 56 is minimized.

[0113] The second control update unit 105 updates the control filter coefficient W1 at the above-mentioned sample period using an adaptive algorithm such as an LMS algorithm. More specifically, the second control update unit 105 updates the control filter coefficient W1 so that the virtual error signal ey output from the virtual error signal generation unit 56 is minimized.

[0114] When the coefficients (W0, W1) of the control filter W are updated in the control filter update unit 55, the updated coefficients of the control filter W are output to the control signal generation unit 51, and the coefficients of the control filter W are updated in the control signal generation unit 51. In other words, the coefficients of the control filter W set in the control signal generation unit 51 are not fixed values, but are values ​​that are successively updated based on the signal from the control filter update unit 55.

[0115] The virtual error signal generating unit 56 includes a first polarity inverting circuit 111 , a second polarity inverting circuit 112 , a first adder 113 , and a second adder 114 .

[0116] The first polarity inversion circuit 111 inverts the polarity of the first cancellation estimation signal y^1 output from the cancellation estimation signal generation unit 52. The second polarity inversion circuit 112 inverts the polarity of the noise estimation signal d^ output from the noise estimation signal generation unit 53.

[0117] The first adder 113 generates a virtual error signal ex by adding the error signal e, the first canceling estimation signal y^1 that has passed through the first polarity inversion circuit 111, and the noise estimation signal d^ that has passed through the second polarity inversion circuit 112. The first adder 113 outputs the generated virtual error signal ex to the canceling estimation signal generation unit 52 and the noise estimation signal generation unit 53.

[0118] The second adder 114 generates a virtual error signal ey by adding the noise estimation signal d^ output from the noise estimation signal generation unit 53 and the second cancellation estimation signal y^2 output from the control filter update unit 55. The second adder 114 outputs the generated virtual error signal ey to the control filter update unit 55.

[0119] <Effects> In the second embodiment, the control device 15 uses an adaptive algorithm to update the control filter W, the primary path filter H^, and the secondary path filter C^. This allows the control device 15 to learn the acoustic characteristics in the vehicle interior 5 while the feedback control is being performed, thereby enhancing the drumming noise d reduction effect.

[0120] <Modification> In the second embodiment, the control device 15 uses an adaptive algorithm to update all of the control filter W, the primary path filter H^, and the secondary path filter C^. On the other hand, in another embodiment, the control device 15 may use an adaptive algorithm to update only some of the control filter W, the primary path filter H^, and the secondary path filter C^. For example, the control device 15 may update the primary path filter H^ and the secondary path filter C^ using an adaptive algorithm, and then use the updated values ​​of the primary path filter H^ and the secondary path filter C^ to calculate the control filter W using a formula.

[0121] In the first and second embodiments described above, the noise reduction device 11 is applied to the vehicle 1 to reduce the drumming noise d. On the other hand, in other embodiments, the noise reduction device 11 may be applied to the vehicle 1 to reduce noise other than the drumming noise d (for example, noise from a drive source such as an internal combustion engine or an electric motor), or may be applied to a moving body other than the vehicle 1 (for example, an aircraft, etc.).

[0122] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment and its modifications, and can be modified in a wide range of ways. [Explanation of symbols]

[0123] 11: Active noise reduction device 13: Speaker (an example of a noise canceling device) 14: Error microphone (an example of an error detection device) 15: Control device Ak0: Noise component Ak1: Noise component T1: Control parameter table T2: Correction table T3: Control parameter table d: Drumming noise (an example of noise) e: error signal fc: Control target frequency fk: Extraction frequency (an example of multiple frequencies) u: control signal y :Cancellation sound

Claims

1. a noise cancelling generating device that generates a noise cancelling sound to cancel out the noise; an error detection device that detects an error between the noise and the cancellation sound and generates an error signal corresponding to the error; a control device that controls the cancellation generating device based on the error signal, The control device extracting noise components at a plurality of frequencies based on the error signal; calculating absolute values ​​of the noise components at the plurality of frequencies; calculating corrected values ​​of the noise components at the plurality of frequencies by correcting the absolute values ​​of the noise components at the plurality of frequencies; comparing the correction values ​​of the noise components at the plurality of frequencies to identify a maximum value of the correction values ​​of the noise components at the plurality of frequencies; determining a frequency corresponding to the maximum value of the correction value of the noise component as a frequency to be controlled; selecting a value of a predetermined control parameter based on the controlled frequency; An active noise reduction system that generates a control signal for controlling the cancellation generating device based on the selected value of the control parameter.

2. 2. The active noise reduction device according to claim 1, wherein the control device corrects absolute values ​​of the noise components at the plurality of frequencies based on a correction table that defines correction coefficients for each frequency according to human hearing characteristics.

3. 3. The active noise reduction device according to claim 1, wherein the control device corrects absolute values ​​of the noise components at the plurality of frequencies based on the target volume reduction for each frequency.

4. The control device extracting the noise components at the plurality of frequencies and calculating the absolute values ​​of the noise components at the plurality of frequencies at a predetermined sampling period; An active noise reduction device according to any one of claims 1 to 3, wherein a current value of the absolute value of the noise component for each frequency is calculated based on a previous value of the absolute value of the noise component for each frequency and a current value of the noise component for each frequency.

5. The control device storing a control parameter table that defines the value of the control parameter for each of the frequencies; An active noise reduction device according to any one of claims 1 to 4, wherein the control parameter table is referenced based on the frequency to be controlled, thereby selecting the value of the control parameter corresponding to the frequency to be controlled.

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