Active noise control device

Abstract

The present invention provides an active noise control device. A coordination control unit (24) causes a booming noise control signal processing unit (20) to start feedforward signal processing. When a secondary path filter (C^) converges, the converged secondary path filter (C^) is set as a narrowband noise control signal processing unit (22), causing the narrowband noise control signal processing unit (22) to start feedback signal processing. Thus, even if the transmission characteristics change, the sound pressure of the noise can be reduced.

Description

Technical Field

[0001] The invention relates to an active noise control device. Background Art

[0002] Japanese Patent Application Laid-Open No. 2007-025527 discloses an active noise reduction device. This device controls a speaker to output an interference sound that reduces the sound pressure of noise such as road noise. This device controls the speaker based on a signal from a microphone located at the location where the noise pressure is to be reduced. Summary of the Invention

[0003] In the active noise control device disclosed in Japanese Patent Application Laid-Open No. 2007-025527, the transmission characteristic used when generating the signal for controlling the speaker is fixed. This transmission characteristic represents the sound transmission characteristic between the speaker and the microphone. Therefore, if the actual transmission characteristic between the speaker and the microphone changes, there is a concern that the speaker may not be able to output interference sound that reduces the sound pressure of the noise, and thus fail to reduce the sound pressure of the noise.

[0004] The purpose of the present invention is to solve the above-mentioned technical problems.

[0005] An embodiment of the present invention is an active noise control device that performs active noise control to control a loudspeaker based on an error signal output by a detector that detects a synthetic sound at a control point, wherein the synthetic sound is a synthetic sound of noise transmitted from a vibration source and a canceling sound output from the loudspeaker to cancel the noise. The active noise control device includes a feedforward signal processing unit, a feedback signal processing unit, and a coordination control unit, wherein the feedforward signal processing unit performs feedforward signal processing, which is to output an FF control signal for controlling the loudspeaker based on the vibration frequency of the vibration source; the feedback signal processing unit performs feedback signal processing, which is to output an FB control signal for controlling the loudspeaker based on a component of the error signal in a frequency band centered on a predetermined frequency; and the coordination control unit coordinates and controls the feedforward signal processing unit and the feedback signal processing unit. The signal processing unit includes a feedforward signal processing unit having an FF secondary path filter updating unit, which adaptively updates the FF secondary path filter in sequence, wherein the FF secondary path filter is a filter related to the transmission characteristics of the sound from the speaker to the detector; the feedback signal processing unit includes an FB secondary path filter signal processing unit, which uses the FB secondary path filter to perform signal processing, wherein the FB secondary path filter is a filter related to the transmission characteristics of the sound from the speaker to the detector; the coordination control unit causes the feedforward signal processing unit to start the feedforward signal processing; and when the FF secondary path filter converges, the converged FF secondary path filter is set as the FB secondary path filter, and the feedback signal processing unit starts the feedback signal processing.

[0006] The active noise control device of the present invention can reduce the sound pressure of noise even if the transmission characteristics vary.

[0007] The above-mentioned objects, features and advantages will be easily understood from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A diagram illustrating an overview of active noise control performed in an active noise control device.

[0009] Figure 2 Schematic diagram showing the structure of an active noise control device.

[0010] Figure 3 This is a control block diagram of the booming sound control signal processing unit and the narrowband noise control signal processing unit.

[0011] Figure 4 This is a control block diagram of the roaring sound control signal processing unit.

[0012] Figure 5 This is a control block diagram of the reference signal generation unit.

[0013] Figure 6 This is a control block diagram of the narrowband noise control signal processing unit.

[0014] Figure 7 This is a control block diagram of the control target signal extraction unit.

[0015] Figure 8 This is a diagram showing the initial value table.

[0016] Figure 9 This is a diagram of the updated value table.

[0017] Figure 10 This is a flowchart showing the flow of the cooperative control process performed in the cooperative control unit.

[0018] Figure 11 This is a flowchart showing the flow of a convergence determination process of an update value in the cooperative control unit.

[0019] Figure 12 This is a flowchart showing the flow of the cooperative control process performed in the cooperative control unit. DETAILED DESCRIPTION

[0020] [First embodiment]

[0021] Figure 1 1 is a diagram illustrating an overview of active noise control performed in active noise control device 10 .

[0022] As the engine 12 rotates or the propeller shaft rotates during vehicle travel, a periodic noise known as engine roar is generated within the cabin 14 of the vehicle 13. Furthermore, the wheels 16 vibrate due to the forces exerted on them by the road surface during travel. This vibration is transmitted to the vehicle body via the suspension, generating road noise within the cabin 14. Road noise particularly peaks in the 40-50 Hz frequency band, which is stimulated by the acoustic resonance characteristics within a confined space like the cabin 14. This narrowband component, centered around the peak frequency and having a certain bandwidth, produces a "booming" sound also known as drumming noise, which can easily cause discomfort to passengers.

[0023] The active noise control device 10 of the present embodiment causes the speaker 18 provided in the vehicle interior 14 to output a canceling sound, thereby reducing the sound pressure of the engine roar and low-frequency noise at a control point in the vehicle interior 14 .

[0024] Figure 2Schematic diagram showing the structure of active noise control device 10 . Active noise control device 10 includes a booming sound control signal processing unit 20 , a narrowband noise control signal processing unit 22 , a coordination control unit 24 , an initial value table 26 , and an update value table 28 .

[0025] Figure 3 1 is a control block diagram of the booming sound control signal processing unit 20 and the narrowband noise control signal processing unit 22 .

[0026] The roaring sound control signal processing unit 20 performs feedforward signal processing. The feedforward signal processing generates the FF control signal u0_a, which is a signal for causing the speaker 18 to output a canceling sound that cancels the engine roaring sound. Figure 1 ) to generate the FF control signal u0_a based on the engine speed Ne detected. The roaring sound control signal processing unit 20 corresponds to the feedforward signal processing unit of the present invention.

[0027] The narrowband noise control signal processing unit 22 performs feedback signal processing. This feedback signal processing generates an FB control signal u0_b, which is used to cause the speaker 18 to output a canceling sound that cancels low-frequency noise. This FB control signal u0_b is generated based on the error signal e output from the microphone 32 located at the control point. The narrowband noise control signal processing unit 22 corresponds to the feedback signal processing unit of the present invention.

[0028] In this embodiment, in order to set the vicinity of the passenger's ear as the control point, as shown in FIG. Figure 1 As shown, a microphone 32 is provided on a headrest 36 of a seat 34 in a vehicle cabin 14. A synthesized sound of a control point noise d and a control point cancellation sound y is input to the microphone 32. The microphone 32 outputs an error signal e.

[0029] return Figure 2 The coordination control unit 24 coordinates the updating of the secondary path filter C^, which will be described later, between the booming sound control signal processing unit 20 and the narrowband noise control signal processing unit 22. The updating of the secondary path filter C^ will be described in detail later.

[0030] Initial value table 26 is a table-format memory area provided in a storage unit (described later). Initial value table 26 stores the initial values ​​of secondary path filter C^. Update value table 28 is a table-format memory area provided in the storage unit. Update value table 28 stores the updated values ​​of secondary path filter C^.

[0031] The active noise control device 10 includes a calculation unit and a storage unit (not shown). The calculation unit realizes the booming sound control signal processing unit 20, the narrowband noise control signal processing unit 22, and the coordination control unit 24 described above.

[0032] The computing unit is constituted by a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit).

[0033] The calculation unit includes a determination unit and a control unit (not shown). The determination unit and the control unit are realized by the calculation unit executing a program stored in the storage unit.

[0034] Furthermore, at least a portion of the determination unit and the control unit may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, at least a portion of the determination unit and the control unit may be formed by an electronic circuit including discrete components.

[0035] The storage unit may be composed of volatile memory (not shown) and non-volatile memory (not shown). Examples of volatile memory include RAM (Random Access Memory). Examples of non-volatile memory include ROM (Read Only Memory) and flash memory. Data, etc., may be stored in volatile memory. Programs, tables, maps, etc., may be stored in non-volatile memory. At least a portion of the storage unit may also be provided in a processor, integrated circuit, or the like as described above.

[0036] [Structure of the roaring sound control signal processing unit]

[0037] Figure 4 1 is a control block diagram of the roaring sound control signal processing unit 20. Hereinafter, the sound transmission path from the engine 12 to the microphone 32 is referred to as a primary path. Also, the sound transmission path from the speaker 18 to the microphone 32 is referred to as a secondary path.

[0038] The booming sound control signal processing unit 20 includes a reference signal generating unit 38, a control signal generating unit 40, a first estimated canceling sound signal generating unit 42, a reference signal generating unit 44, a second estimated canceling sound signal generating unit 46, an estimated noise signal generating unit 48, a first hypothetical error signal generating unit 50, a second hypothetical error signal generating unit 52, a primary path filter updating unit 54, a secondary path filter updating unit 56, and a control filter updating unit 58.

[0039] Figure 5 3 is a control block diagram of the reference signal generating unit 38. The reference signal generating unit 38 includes a frequency conversion unit 60, a cosine signal generator 62, and a sine signal generator 64.

[0040] Frequency conversion unit 60 calculates the vibration frequency f of engine 12 based on engine speed Ne. Cosine signal generator 62 generates reference signal xc_a (= cos(2π × f × t)), which is a cosine signal of vibration frequency f. Sine signal generator 64 generates reference signal xs_a (= sin(2π × f × t)), which is a sinusoidal signal of vibration frequency f. Here, t represents time.

[0041] return Figure 4 The control signal generating unit 40 generates the FF control signal u0_a and the FF control signal u1_a based on the reference signal xc_a and the reference signal xs_a. The control signal generating unit 40 corresponds to the FF control signal generating unit of the present invention.

[0042] In the control signal generation unit 40, an adaptive notch filter (e.g., a SAN (Single-frequency Adaptive Notch) filter) is used as the control filter W. The control filter W is updated and optimized by the control filter update unit 58 described later. The control filter W has a filter coefficient W0 for adjusting the amplitude of the cosine wave component of the canceling sound output from the speaker 18. The control filter W has a filter coefficient W1 for adjusting the amplitude of the sine wave component of the canceling sound output from the speaker 18.

[0043] The control signal generating unit 40 includes a first control filter 40 a , a second control filter 40 b , a third control filter 40 c , a fourth control filter 40 d , an inverting amplifier 40 e , an adder 40 f , and an adder 40 g .

[0044] The first control filter 40a has a filter coefficient W0. The second control filter 40b has a filter coefficient W1. The third control filter 40c has a filter coefficient W0. The fourth control filter 40d has a filter coefficient W1.

[0045] The reference signal xc_a whose amplitude is adjusted by the first control filter 40a and the reference signal xs_a whose amplitude is adjusted by the second control filter 40b are added together by the adder 40f to generate the FF control signal u0_a. The FF control signal u0_a is converted into an analog signal by the digital / analog converter 41 and output to the speaker 18.

[0046] The third control filter 40c receives the reference signal -xs_a whose polarity is inverted by the inverting amplifier 40e. The reference signal -xs_a whose amplitude is adjusted by the third control filter 40c and the reference signal xc_a whose amplitude is adjusted by the fourth control filter 40d are added together by the adder 40g to generate the FF control signal u1_a.

[0047] In the first estimated cancellation sound signal generating unit 42 described next, the FF control signal u0_a is used as a real number component, and the FF control signal u1_a is used as an imaginary number component.

[0048] The first estimated canceling sound signal generating unit 42 generates a first estimated canceling sound signal y1_a^ based on the FF control signal u0_a and the FF control signal u1_a.

[0049] In the first estimated cancellation sound signal generator 42, an adaptive notch filter (e.g., a SAN filter) is used as the secondary path filter Cff^. The secondary path filter Cff^ is updated by the secondary path filter updater 56, described later, so that it converges to the sound transmission characteristic C in the secondary path. The secondary path filter Cff^ is represented by Cff^=C0^+iC1^ using filter coefficients C0^ and C1^. Here, i represents an imaginary number.

[0050] The first estimated canceling sound signal generation unit 42 includes a first secondary path filter 42 a , a second secondary path filter 42 b , and an adder 42 c .

[0051] The first secondary path filter 42a has a filter coefficient C0^. The second secondary path filter 42b has a filter coefficient C1^. The FF control signal u0_a, whose amplitude has been adjusted in the first secondary path filter 42a, and the FF control signal u1_a, whose amplitude has been adjusted in the second secondary path filter 42b, are added together in the adder 42c to generate a first estimated cancellation sound signal y1_a^.

[0052] The reference signal generator 44 generates a reference signal r0_a and a reference signal r1_a based on the reference signal xc_a and the reference signal xs_a. The reference signal generator 44 corresponds to the FF reference signal generator of the present invention.

[0053] In the reference signal generator 44, an adaptive notch filter (e.g., a SAN filter) is used as the secondary path filter Cff. The reference signal generator 44 includes a third secondary path filter 44a, a fourth secondary path filter 44b, a fifth secondary path filter 44c, a sixth secondary path filter 44d, an inverting amplifier 44e, an adder 44f, and an adder 44g.

[0054] The third secondary path filter 44a has a filter coefficient C0 ^. The fourth secondary path filter 44b has a filter coefficient C1 ^. The fifth secondary path filter 44c has a filter coefficient C0 ^. The sixth secondary path filter 44d has a filter coefficient C1 ^.

[0055] The fourth-stage path filter 44b receives the reference signal -xs_a, whose polarity has been inverted by the inverting amplifier 44e. The reference signal xc_a, whose amplitude has been adjusted by the third-stage path filter 44a, and the reference signal -xs_a, whose amplitude has been adjusted by the fourth-stage path filter 44b, are added together by the adder 44f to generate the reference signal r0_a.

[0056] The reference signal xs_a whose amplitude is adjusted in the fifth secondary path filter 44c and the reference signal xc_a whose amplitude is adjusted in the sixth secondary path filter 44d are added together in the adder 44g to generate a reference signal r1_a.

[0057] The second estimated cancellation sound signal generator 46 generates a second estimated cancellation sound signal y2_a^ based on the reference signal r0_a and the reference signal r1_a. The second estimated cancellation sound signal generator 46 includes a fifth control filter 46a, a sixth control filter 46b, and an adder 46c. The fifth control filter 46a has a filter coefficient W0. The sixth control filter 46b has a filter coefficient W1.

[0058] The reference signal r0_a whose amplitude is adjusted by the fifth control filter 46a and the reference signal r1_a whose amplitude is adjusted by the sixth control filter 46b are added together by the adder 46c to generate the second estimated cancellation sound signal y2_a^.

[0059] The estimated noise signal generator 48 generates an estimated noise signal d_a^ based on the reference signal xc_a and the reference signal xs_a. The estimated noise signal generator 48 uses an adaptive notch filter (e.g., a SAN filter) as the primary path filter H^. The primary path filter H^ is updated by the primary path filter updater 54 (described later) to converge to the sound transmission characteristic H in the primary path. The primary path filter H^ is represented by H^=H0^+iH1^ using the filter coefficients H0^ and H1^. Note that i represents an imaginary number.

[0060] The estimated noise signal generator 48 includes a first primary path filter 48a, a second primary path filter 48b, an inverting amplifier 48c, and an adder 48d. The first primary path filter 48a has a filter coefficient H0^, and the second primary path filter 48b has a filter coefficient H1^.

[0061] The second primary path filter 48b receives the reference signal -xs_a, whose polarity has been inverted by the inverting amplifier 48c. The reference signal xc_a, whose amplitude has been adjusted by the first primary path filter 48a, and the reference signal -xs_a, whose amplitude has been adjusted by the second primary path filter 48b, are added together by the adder 48d to generate the estimated noise signal d_a^.

[0062] The first virtual error signal generator 50 generates a first virtual error signal e1_a based on the error signal e, the estimated noise signal d_a^, and the first estimated cancellation sound signal y1_a^. The first virtual error signal generator 50 includes an inverting amplifier 50a, an inverting amplifier 50b, and an adder 50c.

[0063] The error signal e converted into a digital signal by the analog / digital converter 51, the estimated noise signal -d_a^ obtained by inverting the polarity by the inverting amplifier 50a, and the first estimated cancellation sound signal -y1_a^ obtained by inverting the polarity by the inverting amplifier 50b are added together by the adder 50c to generate the first virtual error signal e1_a.

[0064] The second virtual error signal generator 52 generates a second virtual error signal e2_a based on the estimated noise signal d_a^ and the second estimated canceling sound signal y2_a^. The second virtual error signal generator 52 includes an adder 52a. The adder 52a adds the estimated noise signal d_a^ and the second estimated canceling sound signal y2_a^ to generate the second virtual error signal e2_a.

[0065] The primary path filter updating unit 54 adaptively updates the primary path filter Ĥ in sequence using an adaptive algorithm (eg, LMS (Least Mean Square) algorithm) to minimize the first virtual error signal el_a.

[0066] The primary path filter updating unit 54 includes a first primary path filter coefficient updating unit 54a and a second primary path filter coefficient updating unit 54b. The first primary path filter coefficient updating unit 54a and the second primary path filter coefficient updating unit 54b update the filter coefficient H0^ and the filter coefficient H1^ according to the following equation. In the equation, n represents the number of time steps (n = 0, 1, 2, ...). The active noise control device 10 performs feedforward signal processing at a predetermined cycle. The time step represents the length of the cycle. The time step number indicates the number of cycles of feedforward signal processing. μ0 H , μl H Represents the step size parameter.

[0067] H0^ n+1 =H0^ n -μ0 H ×e1_a n ×xc_a n

[0068] H1^ n+1 =H1^ n -μ1 H ×e1_a n ×xs_a n

[0069] The secondary path filter updating unit 56 sequentially adaptively updates the secondary path filter Cff^ using an adaptive algorithm (e.g., an LMS algorithm) to minimize the first virtual error signal e1_a. The secondary path filter updating unit 56 uses the first virtual error signal e1_a instead of the error signal e to update the secondary path filter Cff^. The first virtual error signal e1_a corresponds to the error signal of the present invention. The secondary path filter updating unit 56 corresponds to the FF secondary path filter updating unit of the present invention.

[0070] The secondary path filter updating unit 56 includes a first secondary path filter coefficient updating unit 56a and a second secondary path filter coefficient updating unit 56b. The first secondary path filter coefficient updating unit 56a and the second secondary path filter coefficient updating unit 56b update the filter coefficients C0^ and C1^ according to the following equations. Where n represents the number of time steps (n = 0, 1, 2, ...). C 、μ1 C In addition, C0^(f)_u and C1^(f)_u are filter coefficients of the update value Cff^(f)_u corresponding to the vibration frequency f stored in the above-mentioned update value table 28.

[0071] C0^ n+1 =C0^(f)_u-μ0 C ×e1_a n×u0_a n

[0072] C1^ n+1 =C1^(f)_u-μ1 C ×e1_a n ×u1_a n

[0073] The control filter update unit 58 sequentially adaptively updates the control filter W using an adaptive algorithm (e.g., the LMS algorithm) to minimize the second virtual error signal e2_a. The control filter update unit 58 uses the second virtual error signal e2_a instead of the error signal e to update the control filter W. The second virtual error signal e2_a corresponds to the error signal of the present invention. The control filter update unit 58 corresponds to the FF control filter update unit of the present invention.

[0074] The control filter updating unit 58 includes a first control filter coefficient updating unit 58a and a second control filter coefficient updating unit 58b. The first control filter coefficient updating unit 58a and the second control filter coefficient updating unit 58b update the filter coefficient W0 and the filter coefficient W1 according to the following equation. Where n represents the number of time steps (n = 0, 1, 2, ...). μ0 W 、μ1 W Represents the step size parameter.

[0075] W0 n+1 =W0 n -μ0 w ×e2_a n ×r0_a n

[0076] W1 n+1 =W1 n -μ1w×e2_a n ×r1_a n

[0077] [Structure of Narrowband Noise Control Signal Processing Unit]

[0078] Figure 6 This is a control block diagram of the narrowband noise control signal processing unit 22. The narrowband noise control signal processing unit 22 includes a control target signal extraction unit 66, a control signal generation unit 68, a first estimated cancellation sound signal generation unit 70, a reference signal generation unit 72, a second estimated cancellation sound signal generation unit 74, an estimated noise signal generation unit 76, a first virtual error signal generation unit 78, a second virtual error signal generation unit 80, an adjustment filter update unit 82, a secondary path filter update unit 84, and a control filter update unit 86.

[0079] Figure 73 is a control block diagram of the control target signal extraction unit 66. The control target signal extraction unit 66 includes a cosine signal generator 88, a sine signal generator 90, a decimation signal generation unit 92, and a decimation filter update unit 96.

[0080] The cosine signal generator 88 generates a reference signal xc_b (= cos(2π×fx×t)) for the cosine signal of the control target frequency fx. The sine signal generator 90 generates a reference signal xs_b (= sin(2π×fx×t)) for the sine signal of the control target frequency fx. Here, t represents time. The control target frequency fx is different from the vibration frequency f of the booming sound control signal processing unit 20 and is preset. The control target frequency fx is set near the peak frequency of the low-frequency noise. The control target frequency fx corresponds to the prescribed frequency of the present invention.

[0081] The extraction signal generating section 92 generates an extraction signal efr and an extraction signal efi based on the reference signal xc_b and the reference signal xs_b.

[0082] In the decimation signal generation unit 92, an adaptive notch filter (e.g., a SAN filter) is used as the decimation filter A. The decimation filter A is updated and optimized in the decimation filter update unit 96, described later. The decimation filter A has filter coefficients A0 and A1 that align the amplitude and phase of the reference signal xc_b and the reference signal xs_b with the component of the control target frequency fx contained in the low-frequency noise.

[0083] The decimation signal generating unit 92 includes a first decimation filter 92a, a second decimation filter 92b, a third decimation filter 92c, a fourth decimation filter 92d, an inverting amplifier 92e, an adder 92f, and an adder 92g.

[0084] The first decimation filter 92a has a filter coefficient A0. The second decimation filter 92b has a filter coefficient A1. The third decimation filter 92c has a filter coefficient A0. The fourth decimation filter 92d has a filter coefficient A1.

[0085] The reference signal xc_b whose amplitude is adjusted by the first decimation filter 92a and the reference signal xs_b whose amplitude is adjusted by the second decimation filter 92b are added together by the adder 92f to generate the decimation signal efr.

[0086] The third decimation filter 92c receives the reference signal -xs_b, whose polarity is inverted by the inverting amplifier 92e. The reference signal -xs_b, whose amplitude is adjusted by the third decimation filter 92c, and the reference signal xc_b, whose amplitude is adjusted by the fourth decimation filter 92d, are added together by the adder 92g to generate the decimation signal efi.

[0087] The differential signal generating section 94 generates a differential signal e0_b based on the error signal e and the extracted signal efr. The differential signal generating section 94 includes an adder 94a. The error signal e and the extracted signal efr are added together in the adder 94a to generate the differential signal e0_b.

[0088] The decimation filter updating unit 96 adaptively updates the decimation filter A in sequence using an adaptive algorithm (eg, LMS algorithm) to minimize the differential signal e0_b.

[0089] The decimation filter updating unit 96 includes a first decimation filter coefficient updating unit 96a and a second decimation filter coefficient updating unit 96b. The first decimation filter coefficient updating unit 96a and the second decimation filter coefficient updating unit 96b update the filter coefficient A0 and the filter coefficient A1 according to the following equation. In the equation, m represents the number of time steps (m = 0, 1, 2, ...). The active noise control device 10 performs feedback signal processing at a predetermined cycle. The time step represents the length of the cycle. The time step number indicates the number of cycles in which the feedback signal processing occurs. μ0 A 、μ1 A Represents the step size parameter.

[0090]

[0091]

[0092] return Figure 6 The control signal generating section 68 generates the FB control signal u0_b and the FB control signal u1_b based on the extraction signal efr and the extraction signal efi. The control signal generating section 68 corresponds to the FB control signal generating section of the present invention.

[0093] In the control signal generation unit 68, an adaptive notch filter (e.g., a SAN filter) is used as the control filter V. The control filter V is updated and optimized by the control filter update unit 86, described later. The control filter V has a filter coefficient V0 for adjusting the amplitude of the cosine wave component of the canceling sound output from the speaker 18, and a filter coefficient V1 for adjusting the amplitude of the sine wave component.

[0094] The control signal generating unit 68 includes a first control filter 68 a , a second control filter 68 b , a third control filter 68 c , a fourth control filter 68 d , an inverting amplifier 68 e , an adder 68 f , and an adder 68 g .

[0095] The first control filter 68a has a filter coefficient V0. The second control filter 68b has a filter coefficient V1. The third control filter 68c has a filter coefficient V0. The fourth control filter 68d has a filter coefficient V1.

[0096] The extracted signal efr, whose amplitude has been adjusted by the first control filter 68a, and the extracted signal efi, whose amplitude has been adjusted by the second control filter 68b, are added together by the adder 68f to generate the FB control signal u0_b. The FB control signal u0_b is converted into an analog signal by the digital-to-analog converter 69 and output to the speaker 18.

[0097] The third control filter 68c receives the extracted signal -efi, whose polarity has been inverted by the inverting amplifier 68e. The extracted signal -efi, whose amplitude has been adjusted by the third control filter 68c, and the extracted signal efr, whose amplitude has been adjusted by the fourth control filter 68d, are added together by the adder 68g to generate the FB control signal u1_b.

[0098] The first estimated canceling sound signal generating unit 70 generates a first estimated canceling sound signal y1_b^ based on the FB control signal u0_b and the FB control signal u1_b.

[0099] In the first estimated cancellation sound signal generation unit 70, an adaptive notch filter (e.g., a SAN filter) is used as the secondary path filter Cfb^. This filter is updated by the secondary path filter update unit 84 (described later) to converge to the sound transmission characteristic C in the secondary path. The secondary path filter Cfb^ is represented by Cfb^=C2^+iC3^ using filter coefficients C2^ and C3^. Here, i represents an imaginary number.

[0100] The first estimated canceling sound signal generation unit 70 includes a first secondary path filter 70 a , a second secondary path filter 70 b , and an adder 70 c .

[0101] The first secondary path filter 70a has a filter coefficient C2^. The second secondary path filter 70b has a filter coefficient C3^. The FB control signal u0_b, whose amplitude has been adjusted in the first secondary path filter 70a, and the FB control signal u1_b, whose amplitude has been adjusted in the second secondary path filter 70b, are added together in an adder 70c to generate a first estimated cancellation sound signal y1_b^.

[0102] The reference signal generation unit 72 generates a reference signal r0_b and a reference signal r1_b based on the extracted signal efr and the extracted signal efi. The reference signal generation unit 72 corresponds to the FB secondary path filter signal processing unit of the present invention.

[0103] In the reference signal generator 72, an adaptive notch filter (e.g., a SAN filter) is used as the secondary path filter Cfb^. The reference signal generator 72 includes a third secondary path filter 72a, a fourth secondary path filter 72b, a fifth secondary path filter 72c, a sixth secondary path filter 72d, an inverting amplifier 72e, an adder 72f, and an adder 72g.

[0104] The third secondary path filter 72a has a filter coefficient of C2^. The fourth secondary path filter 72b has a filter coefficient of C3^. The fifth secondary path filter 72c has a filter coefficient of C2^. The sixth secondary path filter 72d has a filter coefficient of C3^.

[0105] The fourth-stage path filter 72b receives the extracted signal -efi, whose polarity has been inverted by the inverting amplifier 72e. The extracted signal efr, whose amplitude has been adjusted by the third-stage path filter 72a, and the extracted signal -efi, whose amplitude has been adjusted by the fourth-stage path filter 72b, are added together by the adder 72f to generate the reference signal r0_b.

[0106] The extraction signal efr whose amplitude is adjusted in the fifth secondary path filter 72c and the extraction signal efi whose amplitude is adjusted in the sixth secondary path filter 72d are added together in the adder 72g to generate a reference signal r1_b.

[0107] The second estimated canceling sound signal generator 74 generates a second estimated canceling sound signal y2_b^ based on the reference signal r0_b and the reference signal r1_b. The second estimated canceling sound signal generator 74 includes a fifth control filter 74a, a sixth control filter 74b, and an adder 74c.

[0108] The reference signal r0_b whose amplitude is adjusted by the fifth control filter 74a and the reference signal r1_b whose amplitude is adjusted by the sixth control filter 74b are added together by the adder 74c to generate the second estimated cancellation sound signal y2_b^.

[0109] Estimated noise signal generation unit 76 generates estimated noise signal d_b^ based on extracted signal efr and extracted signal efi. Estimated noise signal generation unit 76 uses an adaptive notch filter (e.g., a SAN filter) as adjustment filter P, which adjusts the characteristics of extracted signal efr and extracted signal efi. Adjustment filter P is updated by adjustment filter update unit 82, described later. Adjustment filter P is represented by P = P0 + iP1 using filter coefficients P0 and P1. "i" represents an imaginary number.

[0110] The estimated noise signal generating unit 76 includes a first adjustment filter 76a, a second adjustment filter 76b, an inverting amplifier 76c, and an adder 76d. The first adjustment filter 76a has a filter coefficient P0, and the second adjustment filter 76b has a filter coefficient P1.

[0111] The second adjustment filter 76b receives the extracted signal -efi, whose polarity has been inverted by the inverting amplifier 76c. The extracted signal efr, whose amplitude has been adjusted by the first adjustment filter 76a, and the extracted signal -efi, whose amplitude has been adjusted by the second adjustment filter 76b, are added together by the adder 76d to generate the estimated noise signal d_b^.

[0112] The first virtual error signal generator 78 generates a first virtual error signal e1_b based on the error signal e, the estimated noise signal d_b^, and the first estimated cancellation sound signal y1_b^. The first virtual error signal generator 78 includes an inverting amplifier 78a, an inverting amplifier 78b, and an adder 78c.

[0113] The error signal e converted into a digital signal by the analog / digital converter 79, the estimated noise signal -d_b^ obtained by inverting the polarity by the inverting amplifier 78a, and the first estimated cancellation sound signal -y1_b^ obtained by inverting the polarity by the inverting amplifier 78b are added together by the adder 78c to generate the first virtual error signal e1_b.

[0114] The second virtual error signal generator 80 generates a second virtual error signal e2_b based on the estimated noise signal d_b^ and the second estimated cancellation sound signal y2_b^. The second virtual error signal generator 80 includes an adder 80a. The adder 80a adds the estimated noise signal d_b^ and the second estimated cancellation sound signal y2_b^ to generate the second virtual error signal e2_b.

[0115] The adjustment filter updating unit 82 adaptively updates the adjustment filter P sequentially using an adaptive algorithm (eg, LMS algorithm) so as to minimize the first virtual error signal el_b.

[0116] The adjustment filter updating unit 82 includes a first adjustment filter coefficient updating unit 82a and a second adjustment filter coefficient updating unit 82b. The first adjustment filter coefficient updating unit 82a and the second adjustment filter coefficient updating unit 82b update the filter coefficient P0 and the filter coefficient P1 according to the following equation. Where m represents the number of time steps (m = 0, 1, 2, ...). μ0 P 、μ1 P Represents the step size parameter.

[0117] P0 m+1 =P0 m -μ0P ×e1_b m ×efr

[0118] P1 m+1 =P1 m -μ1 P ×e1_b m ×efi

[0119] The secondary path filter updater 84 sequentially adaptively updates the secondary path filter Cfb^ using an adaptive algorithm (e.g., the LMS algorithm) to minimize the first virtual error signal el_b. The secondary path filter updater 84 uses the first virtual error signal el_b instead of the error signal e to update the secondary path filter Cfb^. The first virtual error signal el_b corresponds to the error signal of the present invention. The secondary path filter updater 84 corresponds to the FB secondary path filter updater of the present invention.

[0120] The secondary path filter updating unit 84 includes a first secondary path filter coefficient updating unit 84a and a second secondary path filter coefficient updating unit 84b. The first secondary path filter coefficient updating unit 84a and the second secondary path filter coefficient updating unit 84b update the filter coefficients C2^ and C3^ according to the following equations. Here, m represents the number of time steps (m = 0, 1, 2, ...). μ2 C 、μ3 C Represents the step size parameter.

[0121] C2^ m+1 =C2^ m -μ2 C ×e1_b m ×u0_b m

[0122] C3^ m+1 =C3^ m -μ3 C ×e1_b m ×u1_b m

[0123] The control filter update unit 86 sequentially adaptively updates the control filter V using an adaptive algorithm (e.g., the LMS algorithm) to minimize the second virtual error signal e2_b. The control filter update unit 86 uses the second virtual error signal e2_b instead of the error signal e to update the control filter V. The second virtual error signal e2_b corresponds to the error signal of the present invention. The control filter update unit 86 corresponds to the FB control filter update unit of the present invention.

[0124] The control filter updating unit 86 includes a first control filter coefficient updating unit 86a and a second control filter coefficient updating unit 86b. The first control filter coefficient updating unit 86a and the second control filter coefficient updating unit 86b update the filter coefficient V0 and the filter coefficient V1 according to the following equation. Where m represents the number of time steps (n = 0, 1, 2, ...). μ0 V 、μ1 V Represents the step size parameter.

[0125] V0 m+1 =V0 m -μ0 v ×e2_b m ×r0_b m

[0126] V1 m+1 =V1 m -μ1 V ×e2_b m ×r1_b m

[0127] [Coordinated Control]

[0128] Figure 8 Schematic diagram showing the initial value table 26 . Figure 9 28 is a schematic diagram of the update value table 28.

[0129] Initial value table 26 stores the initial values ​​of the secondary path filters Cff^ of booming sound control signal processing unit 20 in association with frequencies. When active noise control device 10 is shipped, the initial values ​​Cff^(f)_i of all secondary path filters Cff^ are set to "0." At the start of active noise control, coordination control unit 24 writes the initial values ​​Cff^(f)_i stored in initial value table 26 into updated value table 28 as updated values ​​Cff^(f)_u.

[0130] The vibration frequency f input to the roaring sound control signal processing unit 20 varies depending on the engine speed Ne. The coordination control unit 24 selects an update value Cff^(f)_u corresponding to the current vibration frequency f from the update value table 28 for each cycle and sets it as the secondary path filter Cff^ of the roaring sound control signal processing unit 20. The secondary path filter update unit 56 of the roaring sound control signal processing unit 20 uses the update value Cff^(f)_u to update the secondary path filter Cff^. The updated secondary path filter Cff^ is written into the update value table 28 as the update value Cff^(f)_u.

[0131] As described above, the control target frequency fx set by the narrow-band noise control signal processing unit 22 is a predetermined fixed value. At the start of feedback signal processing, the coordination control unit 24 selects an update value Cff^(fx)_u corresponding to the control target frequency fx from the update value table 28 and sets it in the secondary path filter Cfb^ of the narrow-band noise control signal processing unit 22. Specifically, the filter coefficient C2^ of the secondary path filter Cfb^ of the narrow-band noise control signal processing unit 22 is set to the filter coefficient C0^(fx)_u of the updated value Cff^(fx)_u, and the filter coefficient C3^ is set to the filter coefficient C1^(fx)_u of the updated value Cff^(fx)_u. Unlike the secondary path filter updating unit 56 of the booming sound control signal processing unit 20 , the secondary path filter updating unit 84 of the narrowband noise control signal processing unit 22 updates the secondary path filter Cfb^ using the secondary path filter Cfb^ updated in the previous cycle.

[0132] Whenever the booming sound control signal processing unit 20 updates the secondary path filter Cff^, the coordination control unit 24 writes the updated secondary path filter Cff^ into the update value table 28 as the updated value Cff^(f)_u corresponding to the vibration frequency f. Furthermore, when active noise control ends, the coordination control unit 24 writes the updated value Cff^(f)_u stored in the update value table 28 into the initial value table 26 as the initial value Cff^(f)_i. However, the initial value Cff^(fx)_i is written with the latest secondary path filter Cfb^ updated by the secondary path filter updating unit 84 of the narrow-band noise control signal processing unit 22.

[0133] Figure 10 2 is a flowchart showing the flow of the cooperative control process performed in the cooperative control unit 24. The cooperative control process is executed every time active noise control is started.

[0134] In step S1 , the coordination control unit 24 writes the initial value Cff^(f)_i of the initial value table into the updated value Cff^(f)_u of the updated value table 28 , and then moves to step S2 .

[0135] In step S2 , the coordination control unit 24 causes the booming sound control signal processing unit 20 to start feedforward signal processing, and then the process shifts to step S3 .

[0136] In step S3 , the coordination control unit 24 determines whether the initial value Cff^(fx)_i corresponding to the control target frequency fx is “0.” If the initial value Cff^(fx)_i is “0,” the process proceeds to step S4 , and if not, the process proceeds to step S9 .

[0137] In step S4 , the coordination control unit 24 determines whether the elapsed time from the start of the feedforward signal processing is less than the predetermined time Ta. If the elapsed time is less than the predetermined time Ta, the process proceeds to step S5 , and if the elapsed time is greater than the predetermined time Ta, the process proceeds to step S8 .

[0138] In step S5, the cooperative control unit 24 performs a convergence determination process on the update value Cff^(fx)_u corresponding to the control target frequency fx, and then moves to step S6. The convergence determination process will be described in detail later.

[0139] In step S6 , the coordination control unit 24 determines whether the update value Cff ^(fx)_u has converged. If the update value Cff ^(fx)_u has converged, the process proceeds to step S7 . Otherwise, the process returns to step S4 .

[0140] In step S7, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to begin feedback signal processing, and then the process shifts to step S10. When feedback signal processing begins in step S7, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the updated value Cff^(fx)_u from the updated value table 28. At this point, the updated value Cff^(fx)_u has already converged. Consequently, feedback signal processing can begin using the updated value Cff^(fx)_u that has been fully learned and converged during feedforward signal processing.

[0141] As described above, when the elapsed time from the start of the feedforward signal processing in step S4 is equal to or longer than the predetermined time Ta, the process proceeds to step S8.

[0142] In step S8, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to begin feedback signal processing, and then the process shifts to step S10. When feedback signal processing begins in step S8, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the updated value Cff^(fx)_u from the updated value table 28. At this point, the updated value Cff^(fx)_u has not yet converged. Consequently, if the elapsed time from the start of feedforward signal processing exceeds the predetermined time Ta, feedback signal processing is initiated even if the updated value Cff^(fx)_u has not yet converged, thereby reducing the sound pressure of low-frequency noise.

[0143] As described above, when the initial value Cff^(fx)_i is not "0" in step S3, the process proceeds to step S9.

[0144] In step S9, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to start feedback signal processing, and then the process shifts to step S10. When feedback signal processing starts in step S9, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the initial value Cff^(fx)_i in the initial value table 26.

[0145] In step S10 , the cooperative control unit 24 determines whether active noise control has been completed. If active noise control has been completed, the process proceeds to step S11 . If active noise control has not been completed, the process of step S10 is repeated.

[0146] In step S11, the coordinated control unit 24 rewrites the initial value Cff^(f)_i stored in the initial value table 26 with the updated value Cff^(f)_u stored in the updated value table 28, thereby terminating the coordinated control process. However, the latest secondary path filter Cfb^ updated by the secondary path filter update unit 84 of the narrow-band noise control signal processing unit 22 is written to the initial value Cff^(fx)_i in the initial value table 26.

[0147] Figure 11 4 is a flowchart showing the flow of a convergence determination process of the update value Cff^(fx)_u in the cooperative control unit 24 .

[0148] In step S21, the coordination control unit 24 determines the state of the feedforward signal processing. If the feedforward signal processing is stable, the process proceeds to step S22, and if the feedforward signal processing is unstable, the process proceeds to step S25.

[0149] The coordination control unit 24 determines that the feedforward signal processing is stable when the modulus |Cff^·W| of the combined filter of the secondary path filter Cff^ and the control filter W is less than the modulus |H^| of the primary path filter H^. On the other hand, the coordination control unit 24 determines that the feedforward signal processing is unstable when the modulus |Cff^·W| is greater than the modulus |H^|.

[0150] In step S22 , the coordination control unit 24 determines whether the update value Cff ^(fx)_u is updated. If the update value Cff ^(fx)_u is updated, the process proceeds to step S23 , and if not, the process proceeds to step S26 .

[0151] In step S23, the coordination control unit 24 determines whether the update value Cff^(fx)_u has been updated more than the predetermined number of times Ma. If so, the process proceeds to step S24; if not, the process proceeds to step S26.

[0152] In step S24 , the coordination control unit 24 determines whether the update value Cff^(fx)_u has converged, and then ends the convergence determination process.

[0153] As described above, after determining that the feedforward signal processing is unstable in step S21, the process proceeds to step S25. In step S25, the coordination control unit 24 resets the number of updates of the update value Cff^(fx)_u, and then proceeds to step S26.

[0154] After step S25, the process proceeds to step S26. Alternatively, if it is determined in step S22 that the updated value Cff^(fx)_u has not been updated, as described above, the process proceeds to step S26. Alternatively, if it is determined in step S23 that the updated value Cff^(fx)_u has been updated less than the predetermined number Ma, the process proceeds to step S26. In step S26, the coordination control unit 24 determines that the updated value Cff^(fx)_u has not converged, and terminates the convergence determination process.

[0155] [Effects]

[0156] The active noise control device 10 of this embodiment includes a coordination control unit 24 that coordinates and controls the booming sound control signal processing unit 20 and the narrowband noise control signal processing unit 22. The coordination control unit 24 causes the booming sound control signal processing unit 20 to start feedforward signal processing before causing the narrowband noise control signal processing unit 22 to start feedback signal processing. The coordination control unit 24 sets the secondary path filter Cff^ corresponding to the control target frequency fx to the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 when the secondary path filter update unit 56 of the booming sound control signal processing unit 20 updates the secondary path filter Cff^ corresponding to the control target frequency fx (= updated value Cff^(fx)_u). Thereafter, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to start feedback signal processing.

[0157] Thus, narrowband noise control signal processing unit 22 can begin feedback signal processing using the secondary path filter Cff^, whose learning has progressed in the previously initiated feedforward processing. This improves the sound pressure reduction performance of low-frequency noise, particularly immediately after feedback signal processing begins. Furthermore, it can suppress unusual noise from speaker 18 immediately after feedback signal processing begins.

[0158] Furthermore, in the active noise control device 10 of this embodiment, when the coordination control unit 24 determines that feedforward signal processing is stable, it counts the number of updates of the secondary path filter Cff^ corresponding to the control target frequency fx. If the counted number of updates is equal to or greater than a predetermined number, the coordination control unit 24 determines that the secondary path filter Cff^ corresponding to the control target frequency fx has converged.

[0159] With this, the coordination control unit 24 can accurately determine the convergence of the secondary path filter Cff^ corresponding to the control target frequency fx.

[0160] Furthermore, in the active noise control device 10 of the present embodiment, when the coordination control unit 24 determines that the feedforward signal processing is unstable, it resets the number of updates of the secondary path filter Cff^ corresponding to the control target frequency fx.

[0161] If feedforward signal processing becomes unstable, it is assumed that the secondary path filter Cff^ corresponding to the control target frequency fx has not been updated in the convergence direction. Therefore, by recounting the number of updates to the secondary path filter Cff^ corresponding to the control target frequency fx, the coordination control unit 24 can accurately determine whether the secondary path filter Cff^ corresponding to the control target frequency fx has converged.

[0162] [Second embodiment]

[0163] In the active noise control device 10 of this embodiment, the coordination control unit 24 sets the initial value of the control filter V of the narrowband noise control signal processing unit 22 before starting feedback signal processing. Furthermore, before starting feedback signal processing, the coordination control unit 24 sets the secondary path filter C^ of the booming sound control signal processing unit 20 to a correction value C_eq^ that reflects the influence of the FB control signal u0_b.

[0164] [Setting the initial value of the control filter V]

[0165] The sensitivity function S, which is a transfer function between the error signal e and the noise d, is expressed by the following equation.

[0166]

[0167] Here, E is the frequency characteristic of the error signal e, and D is the frequency characteristic of the noise d. When the secondary path transmission characteristic C is replaced by the secondary path filter Cfb^, the control filter V is expressed as follows.

[0168]

[0169] For example, when the sound pressure of low-frequency noise is reduced by approximately 6 dB, the sensitivity function S is approximately 0.5. In this case, the coordination control unit 24 sets the initial value of the control filter V of the narrowband noise control signal processing unit 22 to 1 / Cfb^ and starts feedback signal processing.

[0170] [Setting of correction value C_eq^]

[0171] like Figure 3 As shown, from the perspective of booming sound control signal processing unit 20, error signal e is influenced by FB control signal u0_b. Therefore, before coordinating control unit 24 begins feedback signal processing, it calculates correction value C_eq^ for secondary path filter Cff^ to reflect the influence of FB control signal u0_b. This correction value C_eq^ is then set as update value Cff^(fx)_u corresponding to control target frequency fx in update value table 28. Correction value C_eq^ is expressed by the following equation.

[0172]

[0173] Here, U0_a is the frequency characteristic of the FF control signal u0_a. When the secondary path transmission characteristic C is replaced by the secondary path filter Cfb^, the correction value C_eq^ is expressed by the following equation.

[0174]

[0175] After coordinating control unit 24 begins feedback signal processing, it uses correction value C_eq^ as updated value Cff^(fx)_u corresponding to control target frequency fx in update value table 28. When vibration frequency f is fx, this updated value Cff^(fx)_u is applied to secondary path filter Cff^ in booming sound control signal processing unit 20. In other words, secondary path filter Cff^ is set to correction value C_eq^.

[0176] [Effects]

[0177] In the active noise control device 10 of this embodiment, before starting feedback signal processing, the coordination control unit 24 determines the initial value of the control filter V based on the secondary path filter Cfb^. The coordination control unit 24 then sets the initial value of the control filter V in the narrowband noise control signal processing unit 22. Furthermore, the coordination control unit 24 determines a correction value C_eq^ for the secondary path filter Cff^ based on the initial value of the control filter V and the secondary path filter Cfb^. The correction value C_eq^ is then used as the update value Cff^(fx)_u corresponding to the control target frequency fx in the update value table 28.

[0178] As a result, the influence of the FB control signal u0_b can be reflected in the secondary path filter C^ of the roaring sound control signal processing unit 20, thereby improving the sound pressure reduction performance of the engine roaring sound.

[0179] [Third embodiment]

[0180] In the present embodiment, the cooperative control process performed by the cooperative control unit 24 is partially different from that in the first embodiment.

[0181] Figure 12 1 is a flowchart showing the flow of the cooperative control process performed in the cooperative control unit 24 .

[0182] In step S31 , the coordination control unit 24 writes the initial value Cff^(f)_i of the initial value table 26 into the updated value Cff^(f)_u of the updated value table 28 , and then proceeds to step S32 .

[0183] In step S32 , the coordination control unit 24 causes the booming sound control signal processing unit 20 to start feedforward signal processing, and then the process shifts to step S33 .

[0184] In step S33 , the coordination control unit 24 determines whether the initial value Cff^(fx)_i corresponding to the control target frequency fx is “0.” If the initial value Cff^(fx)_i is “0,” the process proceeds to step S34 , and if not, the process proceeds to step S41 .

[0185] In step S34 , the coordination control unit 24 determines whether the elapsed time from the start of the feedforward signal processing is less than the predetermined time Ta. If so, the process proceeds to step S35 , and if not, the process proceeds to step S38 .

[0186] In step S35, the cooperative control unit 24 performs a convergence determination process on the update value Cff^(fx)_u corresponding to the control target frequency fx, and then moves to step S36. The convergence determination process is the same as that of the first embodiment.

[0187] In step S36 , the coordination control unit 24 determines whether the update value Cff ^(fx)_u has converged. If so, the process proceeds to step S37 . Otherwise, the process returns to step S34 .

[0188] In step S37, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to begin feedback signal processing, and then the process shifts to step S42. When feedback signal processing begins in step S37, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the updated value Cff^(fx)_u from the updated value table 28. At this point, the updated value Cff^(fx)_u has already converged. Consequently, feedback signal processing can begin using the updated value Cff^(fx)_u that has been fully learned and converged during feedforward signal processing.

[0189] As described above, when the elapsed time from the start of the feedforward signal processing in step S34 is equal to or longer than the predetermined time Ta, the process proceeds to step S38.

[0190] In step S38, the coordination control unit 24 determines whether the initial value Cff^(fx-F)_i is "0." If the initial value Cff^(fx-F)_i is "0," the process proceeds to step S39; if the initial value Cff^(fx-F)_i is not "0," the process proceeds to step S40. Here, F is pre-set to a relatively low frequency, such as 1 Hz or 2 Hz. That is, fx-F is a frequency lower than the control target frequency fx and near the control target frequency fx. The vibration frequency f changes depending on the engine speed Ne. As the engine 12 changes from a low speed to a high speed, if the initial value Cff^(fx)_i is "0," the initial value Cff^(f)_i corresponding to a vibration frequency f higher than the control target frequency fx is unlikely to be set to a value other than "0." Therefore, fx-F is set to a frequency lower than the control target frequency fx. Alternatively, instead of presetting F, F may be dynamically set so that the initial value Cff^(fx-F)_i is not "0" and fx-F becomes the frequency closest to the control target frequency fx.

[0191] In step S39, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to begin feedback signal processing, and then the process shifts to step S42. When feedback signal processing begins in step S39, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the updated value Cff^(fx)_u from the updated value table 28. At this point, the updated value Cff^(fx)_u has not yet converged. Consequently, if the elapsed time from the start of feedforward signal processing exceeds the predetermined time Ta, feedback signal processing is initiated even if the updated value Cff^(fx)_u has not yet converged, thereby reducing the sound pressure of low-frequency noise.

[0192] In step S40, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to begin feedback signal processing, and then the process shifts to step S42. Upon initiation of feedback signal processing in step S40, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the initial value Cff^(fx-F)_i from the initial value table 26. This sets the secondary path filter Cfb^ to the initial value Cff^(fx-F)_i that closely approximates the secondary path transmission characteristic C, thereby reducing the sound pressure of low-frequency noise.

[0193] As described above, when the initial value Cff^(fx)_i is not "0" in step S33, the process proceeds to step S41.

[0194] In step S41, the coordination control unit 24 causes the narrowband noise control signal processing unit 22 to start feedback signal processing, and then moves to step S42. When feedback signal processing starts in step S41, the secondary path filter Cfb^ of the narrowband noise control signal processing unit 22 is set to the initial value Cff^(fx)_i in the initial value table 26.

[0195] In step S42, the cooperative control unit 24 determines whether the active noise control has been completed. If the active noise control has been completed, the process proceeds to step S43. If the active noise control has not been completed, the process of step S42 is repeated.

[0196] In step S43, the coordinated control unit 24 rewrites the initial value Cff^(f)_i stored in the initial value table 26 with the updated value Cff^(f)_u stored in the updated value table 28, and ends the coordinated control process. However, the latest secondary path filter Cfb^ updated by the secondary path filter update unit 84 of the narrow-band noise control signal processing unit 22 is written to the initial value Cff^(fx)_i in the initial value table 26.

[0197] [Effects]

[0198] When the vehicle continues traveling at a low engine speed Ne, the vibration frequency f does not reach fx. In this case, the learning of the update value Cff^(fx)_u may not progress, and the update value Cff^(fx)_u may not converge.

[0199] In the active noise control device 10 of this embodiment, if the updated value Cff^(fx)_u does not converge even after the elapsed time from the start of feedforward signal processing by the booming sound control signal processing unit 20 reaches a predetermined time Ta or longer, the feedback signal processing by the narrowband noise control signal processing unit 22 is initiated. This can prevent a situation where the sound pressure of low-frequency noise persists for a long period of time without decreasing.

[0200] Furthermore, in the active noise control device 10 of this embodiment, when the initial value Cff(fx)_i is 0, the narrow-band noise control signal processing unit 22 begins feedback signal processing using the initial value Cff^(fx-F)_i corresponding to a frequency fx-F near the control target frequency fx. The actual secondary path transfer characteristic C continuously changes with changes in the frequency of the canceling sound output from the speaker 18. Therefore, the difference between the transfer characteristic C for the control target frequency fx and the transfer characteristic C for the frequency fx-F is small. By using the initial value Cff^(fx-F)_i for which learning has progressed, instead of the initial value Cff^(fx)_i for which learning has not progressed, as the secondary path filter C^, to perform feedback signal processing, the sound pressure reduction performance of low-frequency noise can be particularly improved immediately after the start of feedback signal processing. Furthermore, the generation of unusual noise from the speaker 18 immediately after the start of feedback signal processing can be suppressed.

[0201] [Technical Concepts Achievable by Implementation Methods]

[0202] The following describes the technical ideas that can be grasped from the above-mentioned embodiments.

[0203] An active noise control device (10) performs active noise control to control a loudspeaker (18) based on an error signal output by a detector (32) that detects a synthetic sound at a control point, wherein the synthetic sound is a synthetic sound of noise transmitted from a vibration source and a canceling sound output from the loudspeaker (18) to cancel the noise. The active noise control device (10) comprises a feedforward signal processing unit (20), a feedback signal processing unit (22), and a coordination control unit (24), wherein the feedforward signal processing unit (20) performs feedforward signal processing, wherein the feedforward signal processing is to output an FF control signal for controlling the loudspeaker based on the vibration frequency of the vibration source; the feedback signal processing unit (22) performs feedback signal processing, wherein the feedback signal processing is to output an FB control signal for controlling the loudspeaker based on a component in a frequency band centered on a predetermined frequency of the error signal; and the coordination control unit (24) coordinates and controls the A feedforward signal processing unit and a feedback signal processing unit, wherein the feedforward signal processing unit includes an FF secondary path filter updating unit (56) for adaptively updating the FF secondary path filter in sequence, wherein the FF secondary path filter is a filter related to the transmission characteristics of the sound from the speaker to the detector; the feedback signal processing unit includes an FB secondary path filter signal processing unit (72) for performing signal processing using the FB secondary path filter, wherein the FB secondary path filter is a filter related to the transmission characteristics of the sound from the speaker to the detector; the coordination control unit causes the feedforward signal processing unit to start the feedforward signal processing; and when the FF secondary path filter converges, the converged FF secondary path filter is set as the FB secondary path filter, and causes the feedback signal processing unit to start the feedback signal processing.

[0204] In the above-mentioned active noise control device, the feedforward signal processing unit may include a reference signal generating unit (38), an FF control signal generating unit (40), an FF reference signal generating unit (44), the FF secondary path filter updating unit and an FF control filter updating unit (58), wherein the reference signal generating unit (38) generates a reference signal corresponding to the vibration frequency; the FF control signal generating unit (40) processes the reference signal through the FF control filter as an adaptive notch filter to generate the FF control signal; the FF reference signal generating unit (44) processes the reference signal through the FF secondary path filter as an adaptive notch filter to generate the FF reference signal; the FF secondary path filter updating unit adaptively updates the FF secondary path filter in sequence according to the error signal and the FF control signal to minimize the size of the error signal; the FF control filter updating unit adaptively updates the FF secondary path filter in sequence according to the error signal and the FF control signal to minimize the size of the error signal; and the FF control filter updating unit adaptively updates the FF secondary path filter in sequence according to the error signal and the FF control signal. The FF reference signal is used to adaptively update the FF control filter in sequence so as to minimize the size of the error signal. The feedback signal processing unit includes a sampling signal generating unit (92), an FB control signal generating unit (68), the FB secondary path filter signal processing unit, and an FB control filter updating unit (86), wherein the sampling signal generating unit (92) extracts a component of a frequency band centered on a predetermined frequency of the error signal to generate a sampling signal; the FB control signal generating unit (68) processes the sampling signal through an FB control filter as an adaptive notch filter to generate an FB control signal; the FB secondary path filter signal processing unit processes the sampling signal through an FB secondary path filter as an adaptive notch filter to generate an FB reference signal; and the FB control filter updating unit (86) adaptively updates the FB control filter in sequence based on the error signal and the FB reference signal so as to minimize the size of the error signal.

[0205] In the above-mentioned active noise control device, the coordination control unit may determine whether the feedforward signal processing is stable, count the number of updates of the FF secondary path filter if the feedforward signal processing is stable, and determine that the FF secondary path filter has converged if the number of updates is greater than a predetermined number.

[0206] In the active noise control device described above, the coordination control unit may reset the counted number of updates when the feedforward signal processing becomes unstable.

[0207] In the above-mentioned active noise control device, the coordination control unit may determine an initial value of the FB control filter based on the converged FF secondary path filter before causing the feedback signal processing unit to start the feedback signal processing, and set the FB control filter of the feedback signal processing unit to the initial value of the FB control filter.

[0208] In the active noise control device described above, before causing the feedback signal processing unit to start the feedback signal processing, the coordination control unit may determine a correction value for the FF secondary path filter based on the converged initial values ​​of the FF secondary path filter and the FB control filter, and set the FF secondary path filter of the feedforward signal processing unit to the correction value.

[0209] In the above-mentioned active noise control device, it is also possible to have an initial value table (26) and an update value table (28), wherein the initial value table (26) stores the initial value of the FF secondary path filter and the frequency in a table form; the update value table (28) stores the update value of the FF secondary path filter and the frequency in a table form; the feedback signal processing unit has a FB secondary path filter update unit (84), the FB secondary path filter update unit (84) adaptively updates the FB secondary path filter in sequence according to the error signal and the FB control signal to minimize the size of the error signal; and the coordination control unit updates the initial value table when the active noise control starts. The initial value of the FF secondary path filter is written into the update value table as an update value of the FF secondary path filter. During the active noise control, whenever the FF secondary path filter is updated in the FF secondary path filter updating unit, the coordination control unit writes the updated FF secondary path filter into the update value table as the update value of the FF secondary path filter corresponding to the vibration frequency. When the active noise control ends, the coordination control unit writes the update value of the FF secondary path filter in the update value table as the initial value of the FF secondary path filter, and writes the FB secondary path filter into the initial value table as the initial value of the FF secondary path filter corresponding to the prescribed frequency.

[0210] The active noise control device may include an initial value table that stores, in tabular form, initial values ​​of the FF secondary path filter in correspondence with frequencies. When the initial value of the FF secondary path filter corresponding to the prescribed frequency is not zero, the coordination control unit sets the FB secondary path filter to the initial value of the FF secondary path filter and causes the feedback signal processing unit to start the feedback signal processing. When the initial value of the FF secondary path filter corresponding to the prescribed frequency is zero, the coordination control unit sets the FB secondary path filter to the initial value of the FF secondary path filter corresponding to the vibration frequency lower than the prescribed frequency and causes the feedback signal processing unit to start the feedback signal processing.

Claims

1. An active noise control device (10) for controlling a speaker (18) based on an error signal output by a detector (32) for detecting a synthetic sound at a control point, wherein the synthetic sound is a synthetic sound of noise transmitted from a vibration source and a cancelling sound output from the speaker (18) to cancel the noise, wherein: It has a feedforward signal processing unit (20), a feedback signal processing unit (22) and a coordination control unit (24), wherein: The feedforward signal processing unit (20) performs feedforward signal processing, wherein the feedforward signal processing is to output an FF control signal for controlling the speaker according to the vibration frequency of the vibration source; The feedback signal processing unit (22) performs feedback signal processing, wherein the feedback signal processing is to output an FB control signal for controlling the speaker based on a component of a frequency band centered on a predetermined frequency of the error signal; The coordination control unit (24) coordinates and controls the feedforward signal processing unit and the feedback signal processing unit, The feedforward signal processing unit includes an FF secondary path filter updating unit (56) for adaptively updating the FF secondary path filter in sequence, wherein the FF secondary path filter is a filter related to the transmission characteristics of the sound from the speaker to the detector. The feedback signal processing section includes an FB secondary path filter signal processing section (72) for performing signal processing using an FB secondary path filter, wherein the FB secondary path filter is a filter related to the transmission characteristics of sound from the speaker to the detector. The coordination control unit performs the following processing: causing the feedforward signal processing unit to start the feedforward signal processing, When the FF secondary path filter converges, the converged FF secondary path filter is set as the FB secondary path filter, and the feedback signal processing unit is caused to start the feedback signal processing.

2. The active noise control device according to claim 1, characterized in that: The feedforward signal processing unit comprises a reference signal generating unit (38), an FF control signal generating unit (40), an FF reference signal generating unit (44), an FF first estimated cancellation sound signal generating unit (42), an FF second estimated cancellation sound signal generating unit (46), an FF estimated noise signal generating unit (48), an FF first virtual error signal generating unit (50), an FF second virtual error signal generating unit (52), the FF secondary path filter updating unit and an FF control filter updating unit (58), wherein: The reference signal generating unit (38) generates a reference signal corresponding to the vibration frequency; The FF control signal generating unit (40) performs signal processing on the reference signal through an FF control filter as an adaptive notch filter to generate the FF control signal; The FF reference signal generating unit (44) performs signal processing on the reference signal through the FF secondary path filter as an adaptive notch filter to generate an FF reference signal; The FF first estimated cancellation sound signal generating unit (42) processes the FF control signal through the FF secondary path filter to generate a FF first estimated cancellation sound signal; The FF second estimated cancellation sound signal generating unit (46) performs signal processing on the FF reference signal through the FF control filter to generate a FF second estimated cancellation sound signal; The FF estimated noise signal generating unit (48) performs signal processing on the reference signal through an FF primary path filter as an adaptive notch filter to generate an FF estimated noise signal; The FF first virtual error signal generating unit (50) generates a FF first virtual error signal based on the error signal, the FF estimated noise signal and the FF first estimated cancellation sound signal; The FF second virtual error signal generating unit (52) generates a FF second virtual error signal based on the FF estimated noise signal and the FF second estimated cancellation sound signal. The FF secondary path filter updating unit adaptively updates the FF secondary path filter in sequence according to the FF first virtual error signal and the FF control signal, so as to minimize the magnitude of the FF first virtual error signal; The FF control filter updating unit (58) adaptively updates the FF control filter in sequence according to the FF second virtual error signal and the FF reference signal so as to minimize the magnitude of the FF second virtual error signal. The feedback signal processing unit includes an extraction signal generating unit (92), an FB control signal generating unit (68), the FB secondary path filter signal processing unit, an FB second estimated cancellation sound signal generating unit, an FB estimated noise signal generating unit, an FB second virtual error signal generating unit, and an FB control filter updating unit (86), wherein: The extraction signal generating unit (92) extracts a component of a frequency band centered on a predetermined frequency of the error signal to generate an extraction signal; The FB control signal generating unit (68) generates the FB control signal by performing signal processing on the extracted signal using an FB control filter as an adaptive notch filter; The FB secondary path filter signal processing unit generates an FB reference signal by performing signal processing on the decimated signal using the FB secondary path filter as an adaptive notch filter; The FB second estimated cancellation sound signal generating unit performs signal processing on the FB reference signal through the FB control filter to generate a FB second estimated cancellation sound signal; The FB estimation noise signal generating unit performs signal processing on the extracted signal using an adjustment filter as an adaptive notch filter to generate an FB estimation noise signal; The FB second virtual error signal generating unit generates a FB second virtual error signal based on the FB estimated noise signal and the FB second estimated cancellation sound signal; The FB control filter updating unit (86) adaptively updates the FB control filter in sequence based on the FB second virtual error signal and the FB reference signal so as to minimize the magnitude of the FB second virtual error signal.

3. The active noise control device according to claim 1 or 2, characterized in that: The coordination control unit performs the following processing: determining whether the feedforward signal processing is stable, Counting the number of updates of the FF secondary path filter when the feedforward signal processing is stable, When the number of updates is equal to or greater than a predetermined number of times, it is determined that the FF secondary path filter has converged.

4. The active noise control device according to claim 3, characterized in that: The coordination control unit resets the counted number of updates when the feedforward signal processing is unstable.

5. The active noise control device according to claim 1, 2 or 4, characterized in that: Before causing the feedback signal processing unit to start the feedback signal processing, the coordination control unit obtains an initial value of an FB control filter, which is an adaptive notch filter, based on the converged FF secondary path filter, and sets the FB control filter of the feedback signal processing unit to the initial value of the FB control filter.

6. The active noise control device according to claim 5, characterized in that: Before causing the feedback signal processing unit to start the feedback signal processing, the coordination control unit calculates a correction value for the FF secondary path filter based on the converged initial values ​​of the FF secondary path filter and the FB control filter, and sets the FF secondary path filter of the feedforward signal processing unit to the correction value.

7. The active noise control device according to claim 1, 2, 4 or 6, characterized in that: There is an initial value table (26) and an updated value table (28), wherein, The initial value table (26) stores the initial value of the FF secondary path filter and the frequency in a corresponding relationship in a table form; The update value table (28) stores the update value of the FF secondary path filter in a corresponding relationship with the frequency in a table form. The feedback signal processing unit includes an extraction signal generating unit, an FB control signal generating unit, an FB first estimated cancellation sound signal generating unit, an FB estimated noise signal generating unit, an FB first virtual error signal generating unit and an FB secondary path filter updating unit (84), wherein: The extraction signal generating unit extracts a component of a frequency band centered on a predetermined frequency of the error signal to generate an extraction signal; The FB control signal generating unit generates the FB control signal by performing signal processing on the extracted signal using an FB control filter as an adaptive notch filter; The FB first estimated cancellation sound signal generating unit performs signal processing on the FB control signal through the FB secondary path filter to generate a FB first estimated cancellation sound signal; The FB estimation noise signal generating unit performs signal processing on the extracted signal using an adjustment filter as an adaptive notch filter to generate an FB estimation noise signal; The FB first virtual error signal generating unit generates a FB first virtual error signal based on the error signal, the FB estimated noise signal, and the FB first estimated cancellation sound signal; The FB secondary path filter updating unit (84) adaptively updates the FB secondary path filter in sequence according to the FB first virtual error signal and the FB control signal, so as to minimize the magnitude of the FB first virtual error signal. The coordination control unit writes the initial value of the FF secondary path filter in the initial value table as the update value of the FF secondary path filter into the update value table when the active noise control starts. Whenever the FF secondary path filter is updated in the FF secondary path filter updating unit during the active noise control, the coordination control unit writes the updated FF secondary path filter as an update value of the FF secondary path filter corresponding to the vibration frequency into the update value table. When the active noise control ends, the coordination control unit writes the updated value of the FF secondary path filter in the updated value table as the initial value of the FF secondary path filter into the initial value table, and writes the value of the FB secondary path filter as the initial value of the FF secondary path filter corresponding to the specified frequency into the initial value table.

8. The active noise control device according to claim 1, 2, 4 or 6, characterized in that: An initial value table is provided, which stores the initial value of the FF secondary path filter and the frequency in a corresponding relationship in a table form. When the initial value of the FF secondary path filter corresponding to the predetermined frequency is not zero, the coordination control unit sets the FB secondary path filter to the initial value of the FF secondary path filter and causes the feedback signal processing unit to start the feedback signal processing. When the initial value of the FF secondary path filter corresponding to the prescribed frequency is 0, the coordination control unit sets the FB secondary path filter to the initial value of the FF secondary path filter corresponding to the vibration frequency lower than the prescribed frequency, and causes the feedback signal processing unit to start the feedback signal processing.

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