Active noise reduction device

Abstract

To provide an inexpensive active type noise reduction device which can effectively reduce noise at a head position of an occupant even if the head position of the occupant changes.SOLUTION: An active type noise reduction device 11 includes: a reference distance detection device 15 for detecting a reference distance Lr being a distance from a canceling sound output device 13 to a head position of an occupant; and a control device 16 for controlling the canceling sound output device 13 on the basis of a reference signal x, an error signal e and the reference distance Lr. The control device 16 generates a first canceling sound estimation signal y^m2 being an estimation signal of canceling sound y at a position of an error detection device 14, generates a second canceling sound estimation signal y^e1 being the estimation signal of the canceling sound y at the head position of the occupant by adjusting time delay and amplitude of the first canceling signal estimation signal y^m2 on the basis of the reference distance Lr, and updates a control filter W for controlling the canceling sound output device 13 on the basis of the second canceling sound estimation signal y^e1.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] Active noise reduction devices have been known that reduce noise by interfering with the noise with a canceling sound that is in opposite phase to the noise. Such active noise reduction devices include, for example, a canceling sound output device that outputs a canceling sound to cancel the noise, an error detection device that detects the error between the noise and the canceling sound and generates an error signal corresponding to the error, and a control device that controls the canceling sound output device based on the error signal.

[0003] For example, Patent Document 1 discloses a speaker that outputs a canceling sound, a microphone that outputs an error signal, and an active noise control device that generates a control signal for causing the speaker to output the canceling sound based on the error signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-162849 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional active noise reduction devices, the area where the control effect (noise reduction effect) is high is limited to a part of the area around an error detection device such as a microphone. Therefore, when the head position of the occupant changes, there is a risk that the noise at the head position of the occupant may not be sufficiently reduced.

[0006] In view of the above background, an object of the present invention is to provide an inexpensive active noise reduction device that can effectively reduce noise at the position of an occupant's head, even when the position of the occupant's head changes. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, one aspect of the present invention is an active noise reduction device (11) for reducing noise in an interior space (5) of a moving body (1), the active noise reduction device (11) comprising: a reference signal generation device (12) for generating a reference signal corresponding to the noise; a noise cancellation output device (13) for outputting a noise cancellation signal for canceling the noise; an error detection device (14) for detecting an error between the noise and the noise cancellation signal and generating an error signal corresponding to the error; a reference distance detection device (15) for detecting a reference distance, which is a distance from the noise cancellation output device to a head position of an occupant; and a control device (16) that controls the noise cancellation output device based on the error signal and the reference distance, wherein the control device generates a first noise cancellation estimation signal that is an estimation signal of the noise cancellation at the position of the error detection device based on the reference signal, adjusts a time delay and an amplitude of the first noise cancellation estimation signal based on the reference distance, and generates a second noise cancellation estimation signal that is an estimation signal of the noise cancellation at the position of the occupant's head, and updates a control filter (W) for controlling the noise cancellation output device based on the second noise cancellation estimation signal.

[0008] According to this aspect, by updating the control filter based on the second noise cancellation estimation signal (the noise cancellation estimation signal at the occupant's head position), the characteristics of the control filter can be changed to follow changes in the occupant's head position. Therefore, even if the occupant's head position changes, the noise at the occupant's head position can be effectively reduced. Furthermore, since the second noise cancellation estimation signal is generated by adjusting the time delay and amplitude of the first noise cancellation estimation signal (the noise cancellation estimation signal at the position of the error detection device), there is no need to use a filter with a high computational load to generate the second noise cancellation estimation signal. Therefore, the computational load of the control device can be reduced, and the control device can be configured using a relatively inexpensive processor.

[0009] In the above aspect, the control device may set a correction coefficient according to the reference distance, and correct the update amount of the control filter by multiplying the update amount of the control filter by the correction coefficient.

[0010] According to this aspect, the update amount of the control filter can be adjusted in accordance with the reference distance, and therefore the update amount of the control filter can be maintained at an appropriate value.

[0011] In the above aspect, the control device may adjust the amplitude of the first cancellation estimation signal using an amplitude adjustment coefficient that decreases as the reference distance increases, and the correction coefficient may be set to an inverse number of the amplitude adjustment coefficient.

[0012] According to this aspect, when the amplitude adjustment coefficient decreases as the reference distance increases, the correction coefficient can be increased, thereby preventing an excessive decrease in the update amount of the control filter and maintaining the update performance of the control filter.

[0013] In the above aspect, the control device may adjust the amplitude of the first cancellation estimation signal using an amplitude adjustment coefficient that decreases as the reference distance increases, and the correction coefficient may be set so that a product of the amplitude adjustment coefficient and the correction coefficient is less than 1.

[0014] According to this aspect, when the update accuracy of the control filter decreases as the reference distance increases, it is possible to prevent an excessive increase in the update amount of the control filter, thereby avoiding a situation in which the performance of the control filter is degraded due to the update of the control filter.

[0015] In the above aspect, the control device may store a correction coefficient table that defines the relationship between the reference distance and the correction coefficient.

[0016] According to this aspect, the correction coefficient can be set arbitrarily depending on the reference distance, and therefore the degree of freedom in setting the correction coefficient can be increased.

[0017] In the above aspect, the control device may generate the first cancellation estimation signal by updating the estimate value of the transfer characteristic of the cancellation and correcting the reference signal based on the updated estimate value of the transfer characteristic of the cancellation.

[0018] According to this aspect, when the transfer characteristics of the canceling sound change, the change in the transfer characteristics of the canceling sound can be learned and the first canceling estimation signal can be generated based on the learning result, thereby making it possible to more effectively reduce noise at the position of the occupant's head.

[0019] In the above aspect, the noise cancellation output device and the error detection device may be installed in a headrest (6 a) of a passenger seat (6) provided in the interior space, and the control device may generate the second noise cancellation estimation signal by adjusting only the time delay and amplitude of the first noise cancellation estimation signal.

[0020] According to this aspect, the noise cancellation output device, the error detection device, and the occupant's head can be brought sufficiently close to one another. As a result, most of the noise cancellation reaches the error detection device and the occupant's head directly from the noise cancellation output device, increasing the dependency of noise cancellation on time delay and distance attenuation. Therefore, by adjusting only the time delay and amplitude of the first noise cancellation estimation signal, the second noise cancellation estimation signal can be generated with high accuracy. [Effects of the Invention]

[0021] According to the above aspects, it is possible to provide an inexpensive active noise reduction device that can effectively reduce noise at the position of the occupant's head, even if the position of the occupant's head changes. [Brief explanation of the drawings]

[0022] [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] Schematic diagram showing the noise reduction mechanism and prerequisites according to the first embodiment. [Figure 4] Graph showing road noise reduction effect [Figure 5] FIG. 10 is a functional block diagram showing an active noise reduction device according to a second embodiment. [Figure 6] 10 is a table showing a correction coefficient table according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] (First embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

[0025] <Active Noise Reduction Device 11> FIG. 1 is a schematic diagram showing a vehicle 1 (an example of a moving body) to which an active noise reduction device 11 (hereinafter simply referred to 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, road noise d is generated in a vehicle cabin 5 (an example of an interior space of a moving body). The noise reduction device 11 according to the first embodiment is a feedback-control type ANC device (Active Noise Control Device) for reducing such road noise d. More specifically, the noise reduction device 11 generates a canceling sound y that is in opposite phase to the road noise d and causes the generated canceling sound y to interfere with the road noise d, thereby reducing the road noise d. Note that in other embodiments, the noise reduction device 11 may also reduce noise other than the road noise d generated as the vehicle 1 travels (for example, aerodynamic noise transmitted from an undercover attached to the underside of the vehicle body 4).

[0026] 1 and 2, the noise reduction device 11 includes a vibration sensor 12 (an example of a reference signal generating device) that generates a reference signal x corresponding to road noise d, a plurality of speakers 13 (an example of a noise canceling output device) that generates a cancellation sound y to cancel out the road noise d, a plurality of error microphones 14 (an example of an error detecting device) that detect an error (synthetic sound) between the road noise d and the cancellation sound y and generate an error signal e corresponding to the detected error, and a distance from the plurality of speakers 13 to the head position of an occupant (hereinafter referred to as a "reference distance L"). r a reference distance detection device 15 for detecting a reference signal x, an error signal e, and a reference distance L r and a control device 16 that controls the plurality of speakers 13 based on the received signal.

[0027] In addition, the symbol H in Fig. 2 m indicates the transfer characteristic (transfer characteristic of the primary path) of the road noise d from the noise source (the road surface S in this embodiment) to the error microphone 14. Also, the symbol C in FIG.m indicates the transfer characteristic of the canceling sound y from the speaker 13 to the error microphone 14 (transfer characteristic of the secondary path).

[0028] <Vibration sensor 12> 1, the vibration sensor 12 of the noise reduction device 11 is installed, for example, on the suspension 3. The vibration sensor 12 detects the acceleration of the suspension 3 corresponding to the road noise d, and generates a reference signal x corresponding to the acceleration of the suspension 3. Note that in other embodiments, the vibration sensor 12 may be installed at a location other than the suspension 3 of the vehicle 1. Also, in other embodiments, the reference signal x corresponding to the road noise d may be generated by a reference microphone (not shown).

[0029] <Speaker 13> Each speaker 13 of the noise reduction device 11 is installed, for example, in a headrest 6a of a passenger seat 6 provided in the vehicle interior 5. In other embodiments, the speaker 13 may be installed in a location other than the headrest 6a of 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 at a location other than the headrest 6a of the passenger seat 6.

[0031] <Reference distance detection device 15> The reference distance detection device 15 of the noise reduction device 11 is configured, for example, by an occupant monitoring system equipped with an occupant camera that captures images of occupants. The reference distance detection device 15 determines the reference distance L based on the image of the occupant captured by the occupant camera. r Detect the reference distance L r to the control device 16. In another embodiment, the reference distance detection device 15 outputs the reference distance L r Alternatively, the distance sensor may be configured to directly detect the distance.

[0032] <Control device 16> The control device 16 of the noise reduction device 11 is an electronic control unit (ECU) including an arithmetic processing unit (a processor such as a CPU or MPU) and a storage device (a memory such as a ROM or RAM). The control device 16 may be configured as one piece of hardware, or may be configured as a unit composed of a plurality of pieces of hardware.

[0033] Referring to FIG. 2, the control device 16 includes, as functional components, a first A / D conversion unit 21, a control signal output unit 22, a D / A conversion unit 23, a second A / D conversion unit 24, an acoustic characteristic update unit 25, a reference signal correction unit 26, an acoustic characteristic adjustment unit 27, an adjustment amount determination unit 28, and a control filter update unit 29.

[0034] <First A / D Conversion Unit 21> The first A / D conversion unit 21 of the control device 16 converts the reference signal x output from the vibration sensor 12 from an analog signal to a digital signal, and outputs the converted reference signal x to the control signal output unit 22, the acoustic characteristic update unit 25, and the reference signal correction unit 26. Hereinafter, when simply described as the "reference signal x", it means the reference signal x that has passed through the first A / D conversion unit 21.

[0035] <Control Signal Output Unit 22> The control signal output unit 22 of the control device 16 is constituted by a control filter W. An FIR filter (finite impulse response filter) is used for the control filter W. However, in other embodiments, a SAN filter (adaptive notch filter) may be used for the control filter W. The control signal output unit 22 generates a control signal u by performing filter processing on the reference signal x using the control filter W, and outputs the generated control signal u to the D / A conversion unit 23 and the acoustic characteristic update unit 25. <00002​​​​​​

[0037] <Second A / D conversion unit 24> The second A / D conversion unit 24 of the control device 16 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 the acoustic characteristic update unit 25. Hereinafter, when simply referred to as "error signal e," it refers to the error signal e that has passed through the second A / D conversion unit 24.

[0038] <Acoustic characteristics update section 25> The acoustic characteristic update unit 25 of the control device 16 updates the estimated value of the acoustic characteristic in the vehicle compartment 5 based on the reference signal x, the control signal u, and the error signal e. The acoustic characteristic update unit 25 includes a canceling noise estimation signal generation unit 31, a noise estimation signal generation unit 32, and an adder 33.

[0039] The cancellation estimation signal generator 31 includes a secondary path filter unit 35 and a secondary path update unit 36 ​​.

[0040] The secondary path filter unit 35 is configured by a secondary path filter C^. The secondary path filter C^ has a transfer characteristic C of the cancellation sound y from the speaker 13 to the error microphone 14. m The secondary path filter C^ is a filter corresponding to an estimated value of . An FIR filter is used as the secondary path filter C^. However, in other embodiments, a SAN filter may be used as the secondary path filter C^.

[0041] The secondary path filter unit 35 performs filtering on the control signal u using the secondary path filter C^, thereby generating the cancellation estimated signal y^. m1 Generate the cancellation estimated signal y^ m1 is an estimated signal of the canceling sound y at the position of the error microphone 14 (hereinafter referred to as the "microphone position"). The secondary path filter unit 35 generates the canceling sound estimated signal y^ m1 is output to the adder 33.

[0042] The secondary path update unit 36 ​​updates the secondary path filter C^ using an adaptive algorithm such as an LMS (Least Mean Square) algorithm. More specifically, the secondary path update unit 36 ​​updates the secondary path filter C^ so that the virtual error signal e1 (details of which will be described later) output from the adder 33 is minimized.

[0043] The noise estimation signal generator 32 includes a primary path filter unit 38 and a primary path update unit 39 .

[0044] The primary path filter unit 38 is configured by a primary path filter H^. The primary path filter H^ has a transfer characteristic H m The primary path filter H^ is a filter corresponding to an estimated value of . An FIR filter is used as the primary path filter H^. However, in other embodiments, a SAN filter may be used as the primary path filter H^.

[0045] The primary path filter unit 38 generates a noise estimation signal d^ by filtering the reference signal x using the primary path filter H^. The noise estimation signal d^ is a noise estimation signal obtained by subtracting the road noise d^ at the microphone position from the reference signal x. m and road noise d at the occupant's head position. e The primary path filter unit 38 outputs the generated noise estimation signal d̂ to the adder 33 and the control filter update unit 29.

[0046] The primary path update unit 39 updates the primary path filter H^ using an adaptive algorithm such as an LMS algorithm. More specifically, the primary path update unit 39 updates the primary path filter H^ so that the virtual error signal e1 (details of which will be described later) output from the adder 33 is minimized.

[0047] The adder 33 outputs the error signal e and the cancellation estimation signal y^. m1and the noise estimation signal d̂, thereby generating a virtual error signal e1. The adder 33 outputs the generated virtual error signal e1 to the canceling estimation signal generator 31 and the noise estimation signal generator 32.

[0048] <Reference signal correction unit 26> The reference signal corrector 26 of the control device 16 is configured with a secondary path filter C^, similar to the canceling noise estimation signal generator 31. When the secondary path filter C^ is updated in the canceling noise estimation signal generator 31, the updated secondary path filter C^ is output to the reference signal corrector 26, and the secondary path filter C^ is updated in the reference signal corrector 26. In other words, the secondary path filter C^ set in the reference signal corrector 26 is not a fixed value, but a value that is successively updated based on the signal from the canceling noise estimation signal generator 31.

[0049] The reference signal correction unit 26 performs a filter process on the reference signal x to obtain the cancellation estimated signal y^ m2 More specifically, the reference signal corrector 26 corrects the reference signal x based on the updated secondary path filter C^ to generate the cancellation estimation signal y^. m2 Generate the cancellation estimated signal y^ m2 is the cancellation estimated signal y^ m1 Similarly to the above, the reference signal correction unit 26 generates the estimated signal y^ of the cancellation sound at the microphone position. m2 is output to the acoustic characteristic adjustment unit 27.

[0050] <Acoustic characteristic adjustment section 27> The acoustic characteristic adjustment unit 27 of the control device 16 adjusts the cancellation estimation signal y^ m2 By adjusting the time delay and amplitude (distance attenuation) of e1 (An example of a second cancellation estimation signal) is generated. e1 is an estimated signal of the cancellation sound y at the position of the occupant's head. The acoustic characteristic adjustment unit 27 adjusts the generated cancellation sound estimated signal y^ e1 is output to the control filter update unit 29.

[0051] The acoustic characteristic adjustment unit 27 includes a delay unit 41 and an amplitude adjuster 42. The delay unit 41 adjusts the delay characteristic Z -d Using the cancellation estimation signal y^ m2 More specifically, the delay 41 adjusts the time delay of the cancellation estimation signal ŷ. m2 The amplitude adjuster 42 delays the cancellation estimation signal ŷ by d samples using the amplitude adjustment coefficient a. m2 More specifically, the amplitude adjuster 42 adjusts the amplitude of the cancellation estimation signal ŷ. m2 By multiplying by the amplitude adjustment coefficient a, the cancellation estimated signal y^ m2 Adjust the amplitude of the

[0052] <Adjustment amount determining section 28> The adjustment amount determination unit 28 of the control device 16 determines the reference distance L output from the reference distance detection device 15. r Based on this, the adjustment amount of the time delay by the acoustic characteristic adjustment unit 27 is determined. More specifically, the adjustment amount determination unit 28 determines the delay characteristic Z of the delay unit 41 by the following equation (1): -d In the following formula (1), "round" indicates the calculation of rounding off the decimal point, "c" indicates the speed of sound, and "F" in the following formula (1) is S indicates the sampling frequency.

number

[0053] The adjustment amount determination unit 28 determines the reference distance L output from the reference distance detection device 15. r The adjustment amount of the amplitude to be adjusted by the acoustic characteristic adjustment unit 27 is determined based on the above. More specifically, the adjustment amount determination unit 28 determines the amplitude adjustment coefficient a of the amplitude adjuster 42 by the following equation (2). Note that, L in the following equation (2) m indicates the distance from the speaker 13 to the error microphone 14, N (N=1, 2, ...) in the following equation (2) indicates a parameter for adjusting the amplitude, and σ in the following equation (2) indicates an adjustment constant (a constant with a relatively small value for preventing the denominator on the right side of the following equation (2) from becoming zero or the amplitude from becoming excessive).

number

[0054] <Control filter update unit 29> The control filter update unit 29 of the control device 16 is configured by a control filter W, similar to the control signal output unit 22. The control filter update unit 29 updates the cancellation estimated signal y^ output from the acoustic characteristic adjustment unit 27. e1 The control filter W is updated based on the above. The control filter update unit 29 includes a control filter unit 45, an adder 46, and a control update unit 47.

[0055] The control filter unit 45 uses the control filter W to generate the cancellation estimation signal y^ e1 By filtering the noise cancellation estimated signal y^ e2 Generate the cancellation estimated signal y^ e2 is the cancellation estimated signal y^ e1 Similarly, it is an estimated signal of the cancellation sound y at the head position of the occupant. e2 can be expressed by the following equation (3).

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[0056] The adder 46 outputs the cancellation estimation signal y^ e2 and the noise estimation signal d^ are added to obtain the virtual error signal e e The adder 46 generates the generated virtual error signal e e is output to the control update unit 47.

[0057] The control update unit 47 uses an adaptive algorithm such as an LMS algorithm to update the control filter W. More specifically, the control update unit 47 updates the virtual error signal e output from the adder 46. e The control filter W is updated so that is minimized.

[0058] When the control filter W is updated in the control filter update unit 29 in this manner, the updated control filter W is output to the control signal output unit 22, and the control filter W is updated in the control signal output unit 22. In other words, the control filter W set in the control signal output unit 22 is not a fixed value, but a value that is successively updated based on the signal from the control filter update unit 29.

[0059] <Noise reduction mechanism and prerequisites> Next, the noise reduction mechanism and prerequisites of the noise reduction device 11 will be described with reference to Fig. 3. Note that multiple curved lines p in Fig. 3 indicate wavefronts of road noise d transmitted from the noise source (surfaces where the sound pressure of the road noise d is equal).

[0060] The head position of an occupant (assumed to be the driver here) can change significantly in the front-to-rear direction depending on the occupant's driving posture, but it is difficult to change in the up-to-down direction. Therefore, when the speaker 13 and the error microphone 14 are provided on the headrest 6a of the occupant's seat 6, it is estimated that the occupant's head position and the error microphone 14 are at approximately the same height. Here, road noise d is transmitted from the occupant's feet toward the occupant's head inside the vehicle interior 5. Therefore, if the occupant's head position and the error microphone 14 are at approximately the same height, the road noise d at the microphone position m and road noise at the passenger's head position d e That is, the following equation (4) holds true for the road noise d.

number

[0061] On the other hand, when the speaker 13 and the error microphone 14 are provided on the headrest 6a of the passenger seat 6, if the position of the passenger's head changes significantly in the front-rear direction, the reference distance Lr also changes significantly. Accordingly, due to the effects of time delay and distance attenuation, the cancellation sound y e also changes significantly.

[0062] Therefore, the control device 16 calculates the cancellation estimation signal y^ m2 By adjusting the time delay and amplitude (distance attenuation) of e1 In other words, the control device 16 generates the cancellation y m By adjusting the time delay and amplitude (distance attenuation) of e That is, the following equation (5) holds for the cancellation y.

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[0063] In order to use such a noise reduction mechanism, it is required that most of the cancellation sound y reaches the error microphone 14 and the head position of the occupant directly from the speaker 13 so that the cancellation sound y depends heavily on time delay and distance attenuation. In other words, in order to use such a noise reduction mechanism, it is a prerequisite that the speaker 13, the error microphone 14, and the head position of the occupant are sufficiently close to each other.

[0064] <Effects of the first embodiment> The control device 16 according to the first embodiment updates the primary path filter H^ and the secondary path filter C^ based on the reference signal x and the error signal e. In other words, the control device 16 updates the estimated value of the acoustic characteristics of the interior space based on the reference signal x and the error signal e. Therefore, even if the acoustic characteristics of the interior space change in response to the displacement of the error microphone 14, the characteristics of the control filter W can also be changed to follow this change in the acoustic characteristics. As a result, the error microphone 14 can be disposed on a movable part such as the headrest 6a, allowing the error microphone 14 to be brought closer to the position of the occupant's head.

[0065] On the other hand, the area where the control effect (noise reduction effect) of the noise reduction device 11 is high is limited to a part of the area (see circle A in FIG. 1 ) around the error microphone 14. Therefore, if the occupant's head moves away from the error microphone 14 depending on the driving posture of the occupant, there is a risk that the control effect of the noise reduction device 11 that the occupant can feel will decrease.

[0066] Therefore, the control device 16 calculates the cancellation estimation signal y^ based on the reference distance Lr. m2 By adjusting the time delay and amplitude of (the estimated signal of the cancellation y at the microphone position), the cancellation estimated signal y^ e1 (Estimated signal of noise cancellation y at the occupant's head position) is generated, and the estimated noise cancellation signal y^ e1 The control filter W is updated based on the error microphone 14. This allows the characteristics of the control filter W to be changed so as to follow changes in the head position of the occupant. Therefore, when the occupant's head moves away from the error microphone 14, it is possible to prevent a decrease in the control effect of the noise reduction device 11 that the occupant can feel.

[0067] By the way, when trying to reduce wideband noise using the noise reduction device 11, the cancellation estimation signal y^ m2 By filtering using an FIR filter, the cancellation estimated signal y^ e1 However, it is possible to generate the cancellation estimated signal y^ using an FIR filter in this way. e1 When generating the cancellation estimated signal y^ e1The calculation load on the control device 16 for generating the equation (2) becomes large.

[0068] Therefore, the control device 16 calculates the cancellation estimation signal y^ m2 Delay characteristic Z -d By adjusting only the amplitude adjustment coefficient a, the cancellation estimated signal y^ e1 As a result, even when reducing wideband noise, the cancellation estimation signal y^ e1 Therefore, when reducing broadband noise, it is not necessary to use an FIR filter to generate the cancellation estimation signal y^. e1 This can significantly reduce the computational load on the control device 16 for generating the equation (1).

[0069] Fig. 4 is a graph showing the effect of reducing road noise d at the position of the occupant's head (particularly the position of the occupant's ears). As shown in Fig. 4, when the noise reduction device 11 of this embodiment (i.e., the noise reduction device 11 that updates the control filter W based on the occupant's head position) is turned on, the road noise d can be reduced over a wide frequency band compared to when a conventional noise reduction device (i.e., a noise reduction device that updates the control filter W without considering the occupant's head position) is turned on or when the noise reduction device 11 is turned off.

[0070] <Modification of the first embodiment> In the first embodiment described above, the control device 16 calculates the cancellation estimation signal y^ m2 Delay characteristic Z -d On the other hand, when the precondition of the noise reduction mechanism as described above (the condition that the speaker 13, the error microphone 14, and the head position of the occupant are sufficiently close to each other) is difficult to be met, the control device 16 adjusts only the noise cancellation estimation signal y^ m2 Delay characteristic Z -d In addition to the amplitude adjustment coefficient a, other parameters may also be adjusted.

[0071] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Figures 5 and 6. Note that descriptions that overlap with the first embodiment of the present invention will be omitted as appropriate.

[0072] <Active Noise Reduction Device 51> 5 is a functional block diagram showing an active noise reduction device 51 (hereinafter abbreviated as "noise reduction device 51") according to the second embodiment. Note that the configuration of the noise reduction device 51 other than the control filter update unit 54 and adjustment amount determination unit 55 of the control device 53 is the same as in the first embodiment, and therefore description thereof will be omitted.

[0073] <Control filter update unit 54> The control filter update unit 54 of the control device 53 has a control filter unit 56, an adder 57, an estimated signal correction unit 58, and a control update unit 59. Note that the configurations of the control filter unit 56 and the adder 57 of the control filter update unit 54 are similar to the configurations of the control filter unit 45 and the adder 46 of the control filter update unit 29 according to the first embodiment, and therefore description thereof will be omitted.

[0074] The estimated signal correction unit 58 calculates the cancellation estimated signal y^ using the correction coefficient b. e1 The estimated signal corrector 58 corrects the corrected cancellation estimated signal y^. e1 is output to the control update unit 59.

[0075] The control update unit 59 uses an adaptive algorithm such as an LMS algorithm to update the control filter W. More specifically, the control update unit 59 updates the virtual error signal e output from the adder 57. e The control filter W is updated so that is minimized. For example, the control update unit 59 updates the control filter W according to the following equation (6). Note that μ in the following equation (6) represents a step size parameter.

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[0076] <Adjustment amount determining section 55> The adjustment amount determination unit 55 of the control device 53 determines the reference distance L output from the reference distance detection device 15. r The correction coefficient b is set based on the following: A method for setting the correction coefficient b by the adjustment amount determination unit 55 will be described below.

[0077] <Method 1 for setting correction coefficient b> Reference distance L r When the amplitude adjustment coefficient a decreases in response to an increase in , the update amount of the control filter W also decreases. If the update amount of the control filter W decreases excessively, there is a risk that the update performance (learning speed) of the control filter W will decrease.

[0078] Therefore, the adjustment amount determination unit 55 sets the correction coefficient b to the reciprocal of the amplitude adjustment coefficient a in order to reduce the dependency of the update amount of the control filter W on the amplitude adjustment coefficient a. r When the amplitude adjustment coefficient a decreases as the amplitude of the control filter W increases, the correction coefficient b can be increased. This makes it possible to prevent an excessive decrease in the update amount of the control filter W and maintain the update performance of the control filter W.

[0079] <Method 2 for setting correction coefficient b> Reference distance L r When θ increases, the precondition for the noise reduction mechanism described above (the condition that the speaker 13, the error microphone 14, and the head position of the occupant are sufficiently close to each other) no longer holds true, and therefore there is a risk that the update accuracy of the control filter W will decrease.

[0080] Therefore, the adjustment amount determination unit 55 sets the correction coefficient b so that the product of the amplitude adjustment coefficient a and the correction coefficient b is less than 1. As a result, the reference distance L rWhen the amount of update of the control filter W increases, it is possible to prevent an excessive increase in the amount of update of the control filter W. Therefore, it is possible to avoid a situation in which the performance of the control filter W is deteriorated due to the update of the control filter W.

[0081] <Method 3 for setting correction coefficient b> Referring to FIG. 6, the adjustment amount determination unit 55 determines the reference distance L r and the correction coefficient b. For example, similar to the method 2 for setting the correction coefficient b, the correction coefficient b is set so that the product of the amplitude adjustment coefficient a and the correction coefficient b is less than 1.

[0082] The adjustment amount determination unit 55 determines the reference distance L r By using the correction coefficient table T in this way, the correction coefficient b is set. r Since the correction coefficient b can be arbitrarily set depending on the condition, the degree of freedom in setting the correction coefficient b can be increased.

[0083] <Effects of the second embodiment> The control device 53 according to the second embodiment is configured to calculate the reference distance L r The update amount of the control filter W is corrected by multiplying the update amount of the control filter W by the correction coefficient b. r The update amount of the control filter W can be adjusted in accordance with the change in the control filter W, and the update amount of the control filter W can be maintained at an appropriate value.

[0084] 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]

[0085] 1: Vehicle (an example of a moving object) 5: Vehicle cabin (an example of the interior space of a moving object) 6: Passenger seat 6a: Headrest 11: Active noise reduction device 12: Vibration sensor (an example of a reference signal generator) 13: Speaker (an example of a noise canceling device) 14: Error microphone (an example of an error detection device) 15: Reference distance detection device 16: Control device 51: Active noise reduction device 53: Control device a: Amplitude adjustment coefficient b: Correction coefficient C^: Secondary path filter (estimated transfer characteristic of cancellation) d: Road noise (an example of noise) e: error signal Lr: Reference distance T: Correction coefficient table W: Control filter x :Reference signal y :Cancellation sound y^ m2 : Cancellation estimation signal (first cancellation estimation signal) y^ e1 : Cancellation estimation signal (second cancellation estimation signal)

Claims

1. An active noise reduction device for reducing noise in an interior space of a moving body, comprising: a reference signal generator for generating a reference signal corresponding to the noise; a noise canceling output device that outputs a noise canceling sound to cancel 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 reference distance detection device for detecting a reference distance that is a distance from the noise canceling device to a head position of an occupant; a control device that controls the noise canceling device based on the reference signal, the error signal, and the reference distance; The control device generating a first cancellation estimation signal, which is an estimation signal of the cancellation at the position of the error detection device, based on the reference signal; generating a second noise cancellation estimation signal that is an estimation signal of the noise cancellation at the head position of the occupant by adjusting a time delay and an amplitude of the first noise cancellation estimation signal based on the reference distance; An active noise reduction device that updates a control filter for controlling the noise cancellation output device based on the second noise cancellation estimation signal.

2. The control device setting a correction coefficient according to the reference distance; 2. The active noise reduction device according to claim 1, wherein the update amount of the control filter is corrected by multiplying the update amount of the control filter by the correction coefficient.

3. the control device adjusts the amplitude of the first cancellation estimation signal using an amplitude adjustment coefficient that decreases as the reference distance increases; 3. An active noise reduction system according to claim 2, wherein the correction coefficient is set to the reciprocal of the amplitude adjustment coefficient.

4. the control device adjusts the amplitude of the first cancellation estimation signal using an amplitude adjustment coefficient that decreases as the reference distance increases; 3. An active noise reduction device according to claim 2, wherein the correction coefficient is set so that the product of the amplitude adjustment coefficient and the correction coefficient is less than one.

5. 5. An active noise reduction device according to claim 2, wherein said control device stores a correction coefficient table that defines the relationship between said reference distance and said correction coefficient.

6. The control device updating the estimate of the transfer characteristic of the cancellation; An active noise reduction device according to any one of claims 1 to 5, wherein the first cancellation estimation signal is generated by correcting the reference signal based on an estimated value of the updated transfer characteristic of the cancellation.

7. the noise canceling device and the error detecting device are installed in a headrest of a passenger seat provided in the interior space, The active noise reduction device according to any one of claims 1 to 6, wherein the control device generates the second cancellation estimation signal by adjusting only the time delay and amplitude of the first cancellation estimation signal.

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