Patent Publication Number: US-2022230618-A1

Title: Active noise control device and vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-007119 filed on Jan. 20, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an active noise control device and a vehicle. 
     Description of the Related Art 
     JP 2006-335136 A discloses an active vibration noise control device including a sensor, a noise computation unit, and a controller. The sensor measures vibration of a vehicle body. The noise computation unit calculates noise in the vehicle compartment based on the vibration of the vehicle body. The controller controls an active part for generating a control sound according to the noise in the vehicle compartment. 
     SUMMARY OF THE INVENTION 
     However, in JP 2006-335136 A, it is not always possible to suitably reduce noise when resonance occurs in the sensor. 
     An object of the present invention is to provide an active noise control device and a vehicle which can reduce noise suitably. 
     An active noise control device according to one aspect of the present invention causes an actuator to output a canceling sound based on a control signal in order to reduce noise in a vehicle compartment of a vehicle, and includes a basic signal generating unit configured to generate a basic signal corresponding to a resonance frequency of a vibration sensor provided at the vehicle, a first adaptive filter configured to generate a sensor resonance simulation signal simulating a signal acquired while the vibration sensor is resonating by performing a filtering process on the basic signal, a computation unit configured to calculate a second reference signal that is a difference between a first reference signal acquired by the vibration sensor and the sensor resonance simulation signal, and a second adaptive filter configured to generate the control signal by performing a filtering process on the second reference signal, the filtering process being different from the filtering process performed by the first adaptive filter. 
     A vehicle according to another aspect of the present invention includes the active noise control device as described above. 
     According to the present invention, it is possible to provide an active noise control device and a vehicle which can reduce noise suitably. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an outline of active noise control; 
         FIG. 2  is a block diagram illustrating a part of a vehicle provided with the active noise control device according to the first embodiment; 
         FIG. 3  is a block diagram illustrating a part of a vehicle provided with an active noise control device according to a second embodiment; and 
         FIG. 4  is a block diagram illustrating a part of a vehicle provided with an active noise control device according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Preferred embodiments of an active noise control device and a vehicle according to the present invention will be described in detail below with reference to the accompanying drawings. 
     First Embodiment 
     An active noise control device and a vehicle according to a first embodiment will be described with reference to  FIGS. 1 and 2 .  FIG. 1  is a diagram illustrating an outline of active noise control. 
     An active noise control device  10  causes an actuator  16  to output a canceling sound for reducing noise (vibration noise) in a vehicle compartment  14  of a vehicle  12 . 
     The noise in the vehicle compartment  14  may include, for example, road noise. Road noise is noise that is transmitted to an occupant in the vehicle compartment  14  when a wheel vibrates due to force received from the road surface and the vibration of the wheel is transmitted to the vehicle body via a suspension. 
     The vehicle  12  is provided with a vibration sensor  18  that detects vibration of the vehicle  12 . Signals r 1  detected by vibration sensor  18  are supplied to the active noise control device  10 . That is, signals indicating vibration are supplied to the active noise control device  10 . 
     A microphone  20  is further provided in the vehicle compartment  14 . The microphone  20  detects residual noise (cancellation error noise) due to interference between the noise and the canceling sound output from the actuator  16 . The residual noise detected by the microphone  20  is supplied to the active noise control device  10 . That is, an error signal e detected by the microphone  20  is supplied to the active noise control device  10 . 
     The active noise control device  10  generates a control signal u for outputting a canceling sound from the actuator  16 , based on the signal r 1  detected by the vibration sensor  18  and the error signal e detected by the microphone  20 . More specifically, the active noise control device  10  generates the control signal u such that the error signal e detected by the microphone  20  is minimized. Since the actuator  16  outputs the canceling sound based on the control signal u that minimizes the error signal e detected by the microphone  20 , the noise in the vehicle compartment  14  can be suitably canceled out by the canceling sound. In this way, the active noise control device  10  can reduce noise transmitted to an occupant in the vehicle compartment  14 . 
     Resonance occurs in the vibration sensor  18 . The signal r 1  acquired by the resonant vibration sensor  18  includes resonance noise. When such a canceling sound is simply generated based on the signal r 1  including relatively large resonance noise, it is not always possible to suitably cancel out the noise in the vehicle compartment  14  by the canceling sound. Although it is conceivable to remove such resonance noise using a low-pass filter, the use of a low-pass filter causes signal delay, which leads to a decrease in the noise control effect. As a result of intensive studies, the inventors of the present application have conceived the active noise control device  10  as described below. 
       FIG. 2  is a block diagram illustrating a part of a vehicle equipped with the active noise control device according to the present embodiment. 
     As shown in  FIG. 2 , the active noise control device  10  includes a reference signal generating unit  22  and a control signal generating unit  24 . 
     The reference signal generating unit  22  includes resonance frequency storage units  26 X to  26 Z, basic signal generating units  28 X to  28 Z, first adaptive filters  30 X to  30 Z, computation units  32 X to  32 Z, and first filter coefficient updating units  34 X to  34 Z. 
     The control signal generating unit  24  includes second adaptive filters  36 X,  36 Y, and  36 Z, acoustic characteristic filters  38 X,  38 Y, and  38 Z, second filter coefficient updating units  40 X,  40 Y, and  40 Z, and computation units  42 . 
     The active noise control device  10  includes a computation device (computational processing device) (not shown). The computation device may be configured by a processor such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or the like. However, the present invention is not limited to this feature. A DDS (Direct Digital Synthesizer), a DCO (Digitally Controlled Oscillator), or the like can be included in the computation device. In addition, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or the like can be included in the computation device. 
     The active noise control device  10  includes a storage device (not shown). Such a storage device may be configured by a volatile memory (not shown) and a nonvolatile memory (not shown). Examples of the volatile memory include, for example, a RAM or the like. Examples of the nonvolatile memory include, for example, a ROM, a flash memory, or the like. Programs, tables, maps, and the like may be stored, for example, in the nonvolatile memory. 
     The resonance frequency storage units  26 X to  26 Z are provided in the storage device. The basic signal generating units  28 X to  28 Z, the first adaptive filters  30 X to  30 X, the computation units  32 X to  32 Z, and the first filter coefficient updating units  34 X to  34 Z can be realized by programs, which are stored in the storage device, being executed by the computation device. 
     The second adaptive filters  36 X,  36 Y, and  36 Z, the acoustic characteristic filters  38 X,  38 Y, and  38 Z, the second filter coefficient updating units  40 X,  40 Y, and  40 Z, and the computation units  42  can be realized by programs, which are stored in the storage device, being executed by the computation device. 
     The vehicle  12  may be provided with a vibration sensor  18 , in particular an acceleration sensor. More specifically, for example, a three-axis acceleration sensor can be used as the vibration sensor  18 . The three axes are the X-axis, the Y-axis and the Z-axis. The vibration in the X-axis direction detected by the vibration sensor  18  is supplied to the active noise control device  10  as a first reference signal rx 1 . The vibration in the Y-axis direction detected by the vibration sensor  18  is supplied to the active noise control device  10  as a first reference signal ry 1 . The vibration in the Z-axis direction detected by the vibration sensor  18  is supplied to the active noise control device  10  as a first reference signals rz 1 . The reference character r 1  is used when describing the first reference signal in general. The reference characters rx 1 , ry 1 , and rz 1  are used when describing individual first reference signals. 
     As described above, the microphone  20  that detects the residual noise due to interference between the noise and the canceling sound is provided in the vehicle compartment  14  (see  FIG. 1 ). That is, the microphone  20  for detecting the error signal e is provided in the vehicle compartment  14 . 
     As described above, the vehicle compartment  14  (see  FIG. 1 ) is provided with the actuator  16  that outputs a canceling sound based on the control signal u. As examples of the actuator  16 , there may be cited a speaker. 
     As described above, the reference signal generating unit  22  includes the resonance frequency storage units (resonance frequency storing units)  26 X,  26 Y,  26 Z. The resonance frequency storage units  26 X,  26 Y,  26 Z store resonance frequency information indicating the resonance frequencies f 0   x , f 0   y , and f 0   z  of the vibration sensor  18 . The resonance frequency storage unit  26 X stores the resonance frequency f 0   x  of the vibration sensor  18  in the X-axis direction. The resonance frequency storage unit  26 Y stores the resonance frequency f 0   y  of the vibration sensor  18  in the Y-axis direction. The resonance frequency storage unit  26 Z stores the resonance frequency f 0   z  of the vibration sensor  18  in the Z-axis direction. The reference character  26  is used when describing the resonance frequency storage unit in general. The reference characters  26 X,  26 Y, and  26 Z are used when describing individual resonance frequency storage units. The reference character f 0  is used when describing the resonance frequency in general. The reference characters f 0   x , f 0   y , and f 0   z  are used when describing individual resonance frequencies. 
     As described above, the reference signal generating unit  22  includes the basic signal generating units  28 X,  28 Y, and  28 Z. The basic signal generating unit  28 X generates a basic signal sx corresponding to the resonance frequency f 0   x  of the vibration sensor  18  in the X-axis direction based on the resonance frequency information stored in the resonance frequency storage unit  26 X. The basic signal generating unit  28 Y generates a basic signal sy corresponding to the resonance frequency f 0   y  of the vibration sensor  18  in the Y-axis direction based on the resonance frequency information stored in the resonance frequency storage unit  26 Y. The basic signal generating unit  28 Z generates a basic signal sz corresponding to the resonance frequency f 0   z  of the vibration sensor  18  in the Z-axis direction based on the resonance frequency information stored in the resonance frequency storage unit  26 Z. The reference character  28  is used when describing the basic signal generating unit in general. The reference characters  28 X,  28 Y, and  28 Z are used when describing the individual basic signal generating units. The reference character s is used when describing the basic signal in general. The reference characters sx, sy, and sz are used when describing the individual basic signals. The basic signal generating unit  28  can be realized by a direct digital synthesizer, a digitally controlled oscillator, or the like, but is not limited thereto. 
     As described above, the reference signal generating unit  22  includes the first adaptive filters  30 X,  30 Y,  30 X. The first adaptive filter  30 X generates a sensor resonance simulation signal mx that simulates a signal acquired while the vibration sensor  18  is resonating in the X-axis direction by performing a filtering process on the reference signal sx. The first adaptive filter  30 Y generates a sensor resonance simulation signal my that simulates a signal acquired while the vibration sensor  18  is resonating in the Y-axis direction by performing a filtering process on the reference signal sy. The first adaptive filter  30 Z generates a sensor resonance simulation signal mz that simulates a signal acquired while the vibration sensor  18  is resonating in the Z-axis direction by performing a filtering process on the reference signal sz. The reference character  30  is used when describing the first adaptive filter in general, whereas the reference characters  30 X,  30 Y, and  30 Z are used when describing the individual first adaptive filters. The reference character m is used when describing the sensor resonance simulation signal in general. The reference characters mx, my, and mz are used when describing the individual sensor resonance simulation signals. As the first adaptive filter  30 , for example, a notch filter or the like can be used. As examples of such a notch filter, there may be cited a SAN (single-frequency adaptive notch) filter, but the present invention is not limited to this feature. The notch filter is used as the first adaptive filter  30  because the notch filter has an advantage of having a shorter delay time than a low-pass filter or the like. The frequency (notch frequency) blocked by the first adaptive filter  30  is the resonance frequency f 0 . The filter coefficients Wrx, Wry, and Wrz of the first adaptive filters  30 X,  30 Y, and  30 Z can be updated by the first filter coefficient updating units  34 X,  34 Y, and  34 Z, as will be described later. The reference character Wr is used when describing the filter coefficient in general. The reference characters Wrx, Wry, and Wrz are used when describing the individual filter coefficients. When the magnitude of the component of the resonance frequency f 0  is relatively large in the first reference signal r 1 , the filter coefficient Wr of the first adaptive filter  30  can be set such that the amount of attenuation for the component of the resonance frequency f 0  is relatively small in the first adaptive filter  30 . On the other hand, when the magnitude of the component of the resonance frequency f 0  is relatively small in the first reference signal r 1 , the filter coefficient Wr of the first adaptive filter  30  can be set such that the amount of attenuation for the component of the resonance frequency f 0  is relatively large in the first adaptive filter  30 . 
     The first adaptive filter  30  is not limited to a notch filter. The first adaptive filter  30  can also be configured by a bandpass filter or the like. Even when a bandpass filter is used as the first adaptive filter  30 , the filter coefficient Wr of the first adaptive filter  30  can be set as follows. That is, when the magnitude of the component of the resonance frequency f 0  is relatively large in the first reference signal r 1 , the filter coefficients Wr of the first adaptive filter  30  can be set such that the amount of attenuation for the component of the resonance frequency f 0  is relatively small in the first adaptive filter  30 . On the other hand, when the magnitude of the component of the resonance frequency f 0  is relatively small in the first reference signal r 1 , the filter coefficients Wr of the first adaptive filter  30  can be set such that the amount of attenuation for the component of the resonance frequency f 0  is relatively large in the first adaptive filter  30 . 
     As described above, the reference signal generating unit  22  includes the computation units  32 X,  32 Y, and  32 Z. The computation unit  32 X calculates the second reference signal rx 2  that is a difference between the first reference signal rx 1  acquired by the vibration sensor  18  and the sensor resonance simulation signal mx. More specifically, the computation unit (subtractor)  32 X generates the second reference signal rx 2  by subtracting the sensor resonance simulation signal mx from the first reference signal rx 1  acquired by the vibration sensor  18 . The computation unit  32 Y calculates the second reference signal ry 2  that is a difference between the first reference signal ry 1  acquired by the vibration sensor  18  and the sensor resonance simulation signal my. More specifically, the computation unit (subtractor)  32 Y generates the second reference signal ry 2  by subtracting the sensor resonance simulation signal my from the first reference signal ry 1  acquired by the vibration sensor  18 . The computation unit  32 Z calculates the second reference signal rz 2  which is a difference between the first reference signal rz 1  acquired by the vibration sensor  18  and the sensor resonance simulation signal mz. More specifically, the computation unit (subtractor)  32 Z generates the second reference signal rz 2  by subtracting the sensor resonance simulation signal mz from the first reference signal rz 1  acquired by the vibration sensor  18 . The reference character  32  is used when describing the computation unit in general. The reference characters  32 X,  32 Y, and  32 Z are used when describing the individual computation units. The reference character r 2  is used when describing the second reference signal in general. The reference characters rx 2 , ry 2 , and rz 2  are used when individual second reference signals are described. 
     As described above, the reference signal generating unit  22  includes the first filter coefficient updating units  34 X,  34 Y, and  34 Z. The first filter coefficient updating unit  34 X updates the filter coefficient Wrx of the first adaptive filter  30 X such that the magnitude of the component of the resonance frequency f 0   x  of the vibration sensor  18  in the X-axis direction is minimized in the second reference signal rx 2 . The first filter coefficient updating unit  34 Y updates the filter coefficient Wry of the first adaptive filter  30 Y such that the magnitude of the component of the resonance frequency f 0   y  of the vibration sensor  18  in the Y-axis direction is minimized in the second reference signal ry 2 . The first filter coefficient updating unit  34 Z updates the filter coefficient Wrz of the first adaptive filter  30 Z such that the magnitude of the component of the resonance frequency f 0   z  of the vibration sensor  18  in the Z-axis direction is minimized in the second reference signal rz 2 . The reference character  34  is used when describing the first filter coefficient updating unit in general. The reference characters  34 X,  34 Y, and  34 Z are used when describing each of the first filter coefficient updating units. In updating the filter coefficient Wr, for example, an LMS (Least Mean Square) algorithm can be used, but the present invention is not limited to this feature. 
     The filter coefficient Wr can be updated by the first filter coefficient updating unit  34  as follows, for example. 
     The following expression (1) is established among the first reference signal r 1 , the second reference signal r 2 , and the basic signal s. 
         r 2= r 1− Wr·s   (1)
 
     The basic signal s corresponds to the resonance frequency f 0  of the vibration sensor  18 , and is expressed by the following expression (2). 
         s =cos(2·π· f 0· t )+ i ·sin(2·π· f 0· t )  (2)
 
     The first reference signal r 1  includes a component having the same frequency as that of the basic signal s and a component q having a frequency different from that of the basic signal s. Therefore, the first reference signal r 1  is expressed by the following expression (3). 
         r 1= A·s+q   (3)
 
     The first filter coefficient updating unit  34  acquires a filter coefficient Wr that minimizes a square error as follows. That is, the first filter coefficient updating unit  34  acquires the filter coefficient Wr that minimizes the square of the second reference signal r 2 . 
       | r 2| 2 →min
 
     The minimum square of the second reference signal r 2  means that the magnitude of the component of the resonance frequency f 0  of the vibration sensor  18  is minimized in the second reference signal r 2 . 
     The expression |r 2 | 2  is a quadratic function of the filter coefficient Wr. 
     Further, when a relationship such as the following expression (4) is established, a filter coefficient Wr of the first adaptive filter  30  is Wreso. 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         
                            
                           
                             r 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                            
                         
                         2 
                       
                     
                     
                       ∂ 
                       Wr 
                     
                   
                   = 
                   0 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In the case of Wr&gt;Wreso, the following expression (5) is obtained. 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         
                            
                           
                             r 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                            
                         
                         2 
                       
                     
                     
                       ∂ 
                       Wr 
                     
                   
                   &gt; 
                   0 
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Note that Wreso corresponds to an amplitude of the component of the resonance frequency f 0  of the vibration sensor  18 . 
     On the other hand, in the case of Wr&lt;Wreso, the following expression (6) is obtained. 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         
                            
                           
                             r 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                            
                         
                         2 
                       
                     
                     
                       ∂ 
                       Wr 
                     
                   
                   &lt; 
                   0 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Then, assuming that the filter coefficient of the first adaptive filter  30  before the update is Wr(n), the filter coefficient Wr(n+1) of the first adaptive filter  30  after the update is expressed by the following expression (7). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           Wr 
                           
                             ( 
                             
                               n 
                               + 
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                             Wr 
                             
                               ( 
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                             α 
                             · 
                             
                               
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                               · 
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                               · 
                               r 
                             
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                         = 
                           
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                             Wr 
                             
                               ( 
                               n 
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                           - 
                           
                             
                               2 
                               · 
                               α 
                               · 
                               r 
                             
                             ⁢ 
                             
                                 
                             
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                         = 
                           
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                             Wr 
                             
                               ( 
                               n 
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                           - 
                           
                             
                               μ 
                               · 
                               r 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
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                               · 
                               s 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     The values α and μ are step-size parameters. The relationship between μ and α is expressed by the following expression (8). 
       μ=2·α  (8)
 
     As described above, in the present embodiment, the filter coefficient Wr of the first adaptive filter  30  is updated such that the magnitude of the component of the resonance frequency f 0  of the vibration sensor  18  is minimized in the second reference signal r 2 . Therefore, according to the present embodiment, the magnitude of the component of the resonance frequency f 0  of the vibration sensor  18  is sufficiently reduced in the second reference signal r 2  even when the resonance frequency f 0  has fluctuated and/or even when the magnitude of the component of the resonance frequency f 0  has fluctuated. For this reason, according to the present embodiment, it is possible to acquire a good second reference signal r 2  corresponding to vibration of the vehicle  12 . 
     As described above, the control signal generating unit  24  includes the second adaptive filters  36 X,  36 Y, and  36 Z. The second adaptive filter  36 X generates the control signal u 0   x  by performing on the second reference signal rx 2  a filtering process that is different from the filtering process performed by the first adaptive filter  30 X. The second adaptive filter  36 Y generates the control signal u 0   y  by performing on the second reference signal ry 2  a filtering process that is different from the filtering process performed by the first adaptive filter  30 Y. The second adaptive filter  36 Z generates the control signal u 0   z  by performing on the second reference signal rz 2  a filtering process that is different from the filtering process performed by the first adaptive filter  30 Z. The reference character  36  is used when describing the second adaptive filter in general. The reference characters  36 X,  36 Y, and  36 Z are used when describing the individual second adaptive filters. The reference character u 0  is used when describing a control signal in general. The reference characters u 0   x , u 0   y , and u 0   x  are used when describing the individual control signals. As the second adaptive filter  36 , for example, an FIR (Finite Impulse Response) filter or the like can be used, but the present invention is not limited to this feature. The filter coefficients of the second adaptive filters  36 X,  36 Y, and  36 Z are updated by second filter coefficient updating units  40 X,  40 Y, and  40 Z, as described later. The FIR filter generates the control signal u 0  by performing a convolution operation on the second reference signal r 2 . 
     As described above, the control signal generating unit  24  includes the acoustic characteristic filters  38 X,  38 Y, and  38 Z. The acoustic characteristic filter  38 X corrects the second reference signal rx 2  by performing a filtering process on the second reference signal rx 2  according to an acoustic characteristic (transfer characteristic) from the actuator  16  to the microphone  20 . The acoustic characteristic filter  38 Y corrects the second reference signal ry 2  by performing the filtering process on the second reference signal ry 2  according to the acoustic characteristic from the actuator  16  to the microphone  20 . The acoustic characteristic filter  38 Z corrects the second reference signal rz 2  by performing the filtering process on the second reference signal rz 2  according to the acoustic characteristic from the actuator  16  to the microphone  20 . The acoustic characteristic from the actuator  16  to the microphone  20  is acquired in advance. That is, the transfer characteristic Ĉ from the actuator  16  to the microphone  20  is acquired in advance. The reference character  38  is used when describing the acoustic characteristic filter in general. The reference characters  38 X,  38 Y, and  38 Z are used when describing the individual acoustic characteristic filters. 
     As described above, the control signal generating unit  24  includes the second filter coefficient updating units  40 X,  40 Y, and  40 Z. The second filter coefficient updating unit  40 X updates the filter coefficient Wx of the second adaptive filter  36 X such that the error signal e, which is acquired by detecting the residual noise due to the interference between the noise and the canceling sound by the microphone  20 , is minimized. The second filter coefficient updating unit  40 Y updates the filter coefficient Wy of the second adaptive filter  36 Y such that the error signal e, which is acquired by detecting the residual noise due to the interference between the noise and the canceling sound by the microphone  20 , is minimized. The second filter coefficient updating unit  40 Z updates the filter coefficient Wz of the second adaptive filter  36 Z such that the error signal e, which is acquired by detecting the residual noise due to the interference between the noise and the canceling sound by the microphone  20 , is minimized. The reference character  40  is used when describing the second filter coefficient updating unit in general. The reference characters  40 X,  40 Y, and  40 Z are used when describing the individual second filter coefficient updating units. The reference character W is used when describing the filter coefficient in general. The reference characters Wx, Wy, and Wz are used when describing the individual filter coefficients. When the filter coefficient W is updated, for example, a filtered-X LMS algorithm can be used, but the present invention is not limited to this feature. 
     Although one vibration sensor  18  is illustrated in  FIG. 2 , a plurality of the vibration sensors  18  may be provided in the vehicle  12 . Components such as those described above may be provided for each of the vibration sensors  18 . 
     As described above, the control signal generation unit  24  further includes the computation units  42 . The control signals u 0  output from the respective second adaptive filters  36  are input to the computation units  42 . The computation units  42  add the control signals u 0  supplied from the respective second adaptive filters  36 . The computation units (adders)  42  supply a control signal u generated by adding the plurality of control signals u 0  to the actuator  16  via a power amplifier  15 . 
     As described above, in the present embodiment, the second reference signal r 2  is generated based on a difference between the first reference signal r 1  acquired by the vibration sensor  18  and the sensor resonance simulation signal m that simulates a signal acquired while the vibration sensor  18  is resonating. Since the second reference signal r 2  is generated by the difference between the first reference signal r 1  and the sensor resonance simulation signal m, the magnitude of the component of the resonance frequency f 0  of the vibration sensor  18  is reduced in the second reference signal r 2 . According to the present embodiment, since the control signal u for causing the actuator  16  to output a canceling sound is generated based on such a second reference signal r 2 , it is possible to provide the active noise control device  10  that is capable of reducing noise suitably even when the vibration sensor  18  resonates. 
     Second Embodiment 
     An active noise control device and a vehicle according to a second embodiment will be described with reference to  FIG. 3 .  FIG. 3  is a block diagram illustrating a part of a vehicle equipped with the active noise control device according to the present embodiment. The same components as those of the active noise control device and the like according to the first embodiment shown in  FIGS. 1 and 2  are denoted by the same reference characters, and description of such features is either omitted or simplified. 
     In the present embodiment, a resonance frequency identifying unit  44 X is further provided. The resonance frequency identifying unit  44 X identifies the resonance frequency f 0   x  of the vibration sensor  18  in the X-axis direction by performing frequency analysis on the first reference signal rx 1 . Further, in the present embodiment, a resonance frequency identifying unit  44 Y is further provided. The resonance frequency identifying unit  44 Y identifies the resonance frequency f 0   y  of the vibration sensor  18  in the Y-axis direction by performing frequency analysis on the first reference signal ry 1 . Further, in the present embodiment, a resonance frequency identifying unit  44 Z is further provided. The resonance frequency identifying unit  44 Z identifies the resonance frequency f 0   z  of the vibration sensor  18  in the Z-axis direction by performing frequency analysis on the first reference signal rz 1 . The reference character  44  is used when describing the resonance frequency identifying unit in general. The reference characters  44 X,  44 Y, and  44 Z are used when describing the individual resonance frequency identifying units. The resonance frequency identifying unit  44  can identify the resonance frequency f 0  of the vibration sensor  18  by, for example, performing a Fourier transform on the first reference signal r 1  supplied from the vibration sensor  18  and analyzing a frequency spectrum acquired by the Fourier transform. The resonance frequency identifying unit  44 X stores the identified resonance frequency f 0   x  in the X-axis direction in the resonance frequency storage unit  26 X. The resonance frequency identifying unit  44 Y stores the identified resonance frequency f 0   y  in the Y-axis direction in the resonance frequency storage unit  26 Y. The resonance frequency identifying unit  44 Z stores the identified resonance frequency f 0   z  in the Z-axis direction in the resonance frequency storage unit  26 Z. The resonance frequency identifying unit  44  identifies the resonance frequency f 0  as appropriate. The resonance frequency information indicating the resonance frequency f 0  is updated as appropriate in the resonance frequency storage unit  26 . 
     The basic signal generating unit  28 X generates a basic signal sx corresponding to the resonance frequency f 0   x  identified by the resonance frequency identifying unit  44 X. More specifically, the basic signal generating unit  28 X reads out resonance frequency information indicating the resonance frequency f 0   x  identified by the resonance frequency identifying unit  44 X from the resonance frequency storage unit  26 X, and generates the basic signal sx corresponding to the resonance frequency f 0   x  based on the resonance frequency information. The basic signal generating unit  28 Y generates a basic signal sy corresponding to the resonance frequency f 0   y  identified by the resonance frequency identifying unit  44 Y. More specifically, the basic signal generating unit  28 Y reads out resonance frequency information indicating the resonance frequency f 0   y  identified by the resonance frequency identifying unit  44 Y from the resonance frequency storage unit  26 Y, and generates the basic signal sy corresponding to the resonance frequency f 0   y  based on the resonance frequency information. The basic signal generating unit  28 Z generates a basic signal sz corresponding to the resonance frequency f 0   z  identified by the resonance frequency identifying unit  44 Z. More specifically, the basic signal generating unit  28 Z reads out resonance frequency information indicating the resonance frequency f 0   z  identified by the resonance frequency identifying unit  44 Z from the resonance frequency storage unit  26 Z, and generates the basic signal sz corresponding to the resonance frequency f 0   z  based on the resonance frequency information. 
     As described above, the present embodiment is further provided with the resonance frequency identifying unit  44  that identifies the resonance frequency f 0  of the vibration sensor  18  by performing frequency analysis on the first reference signal r 1 . According to the present embodiment, since such a resonance frequency identifying unit  44  is provided, the resonance frequency information can be accurately updated even when the resonance frequency f 0  of the vibration sensor  18  has fluctuated. Therefore, according to the present embodiment, it is possible to provide active noise control device  10  capable of reducing noise more suitably. 
     Third Embodiment 
     An active noise control device and a vehicle according to a third embodiment will be described with reference to  FIG. 4 .  FIG. 4  is a block diagram illustrating a part of a vehicle equipped with the active noise control device according to the present embodiment. The same components as those of the active noise control device and the like according to the first or second embodiment shown in  FIGS. 1 to 3  are denoted by the same reference characters, and description of such features is either omitted or simplified. 
     In the present embodiment, the sampling rate of each component included in the reference signal generating unit  22  is set to be twice or more as high as the sampling rate of each component included in the control signal generating unit  24 . The sampling rate in the first adaptive filter  30 X is set to be twice or more as high as the sampling rate in the second adaptive filter  36 X. Further, the sampling rate in the first adaptive filter  30 Y is set to be twice or more as high as the sampling rate in the second adaptive filter  36 Y. Furthermore, the sampling rate in the first adaptive filter  30 Z is set to be twice or more as high as the sampling rate in the second adaptive filter  36 Z. 
     When the first reference signal r 1  acquired by using the vibration sensor  18  is sampled at a relatively low sampling rate, aliasing noise (folding noise) corresponding to a component of the resonance frequency f 0  is mixed into the control signal u, and the noise cannot always be cancelled suitably. On the other hand, in the present embodiment, since the processing for generating the second reference signal r 2  is performed at a relatively high sampling rate, aliasing noise corresponding to the component of the resonance frequency f 0  can be prevented from being mixed into the control signal u. 
     A downsampling unit  46 X is provided between the first adaptive filter  30 X and the second adaptive filter  36 X. The second reference signal rx 2  output from the computation unit  32 X is input to the downsampling unit  46 X. Then, the second reference signal rx 2  downsampled by the downsampling unit  46 X is input to the second adaptive filter  36 X and the acoustic characteristic filter  38 X. 
     Further, a downsampling unit  46 Y is further provided between the first adaptive filter  30 Y and the second adaptive filter  36 Y. The second reference signal ry 2  output from the computation unit  32 Y is input to the downsampling unit  46 Y. Then, the second reference signal ry 2  downsampled by the downsampling unit  46 Y is input to the second adaptive filter  36 Y and the acoustic characteristic filter  38 Y. 
     Further, a downsampling unit  46 Z is further provided between the first adaptive filter  30 Z and the second adaptive filter  36 Z. The second reference signal rz 2  output from the computation unit  32 Z is input to the downsampling unit  46 Z. Then, the second reference signal rz 2  downsampled by the downsampling unit  46 Z is input to the second adaptive filter  36 Z and the acoustic characteristic filter  38 Z. The reference character  46  is used when describing the downsampling unit in general, and the reference characters  46 X,  46 Y, and  46 Z are used when describing the individual downsampling units. 
     As described above, the sampling rate in the first adaptive filter  30  may be set to be twice or more as high as the sampling rate in the second adaptive filter  36 , and the downsampling unit  46  may be further provided between the first adaptive filter  30  and the second adaptive filter  36 . According to the present embodiment, since the filtering process for generating the second reference signal r 2  is performed at a relatively high sampling rate, aliasing noise corresponding to the component of the resonance frequency f 0  can be suitably prevented from being mixed into the control signal u. Therefore, according to the present embodiment, it is possible to provide the active noise control device  10  that is capable of reducing noise more suitably. 
     Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made thereto without departing from the essence and gist of the present invention. 
     The embodiments described above can be summarized in the following manner. 
     The active noise control device ( 10 ) causes the actuator ( 16 ) to output the canceling sound based on the control signal (u) in order to reduce noise in the vehicle compartment ( 14 ) of the vehicle ( 12 ), and includes the basic signal generating unit ( 28 X,  28 Y,  28 Z) configured to generate the basic signal (sx, sy, sz) corresponding to the resonance frequency (f 0   x , f 0   y , f 0   z ) of the vibration sensor ( 18 ) provided at the vehicle, the first adaptive filter ( 30 X,  30 Y,  30 Z) configured to generate the sensor resonance simulation signal (mx, my, mz) simulating the signal acquired while the vibration sensor is resonating by performing a filtering process on the basic signal, the computation unit ( 32 X,  32 Y,  32 Z) configured to calculate the second reference signal (rx 2 , ry 2 , rz 2 ) that is a difference between the first reference signal (rx 1 , ry 1 , rz 1 ) acquired by the vibration sensor and the sensor resonance simulation signal, and the second adaptive filter ( 36 X,  36 Y,  36 Z) configured to generate the control signal by performing a filtering process on the second reference signal, the filtering process being different from the filtering process performed by the first adaptive filter. According to such a configuration, the second reference signal is generated by the difference between the first reference signal acquired by the vibration sensor and the sensor resonance simulation signal that simulates a signal acquired while the vibration sensor is resonating. Since the second reference signal is generated by the difference between the first reference signal and the sensor resonance simulation signal, the magnitude of the component of the resonance frequency of the vibration sensor is reduced in the second reference signal. According to such a configuration, since the control signal for outputting the canceling sound from the actuator is generated based on such a second reference signal, it is possible to provide an active noise control device capable of suitably reducing noise even when the vibration sensor has resonated. 
     The active noise control device may further include the first filter coefficient updating unit ( 34 X,  34 Y,  34 Z) configured to update the filter coefficient (Wrx, Wry, Wrz) of the first adaptive filter in a manner that a magnitude of a component of the resonance frequency of the vibration sensor is minimized in the second reference signal. According to such a configuration, the magnitude of the component of the resonance frequency of the vibration sensor can be sufficiently reduced in the second reference signal even when the resonance frequency has fluctuated and/or even when the magnitude of the component of the resonance frequency has fluctuated. Therefore, according to such a configuration, it is possible to provide an active noise control device that is capable of acquiring a much better second reference signal corresponding to vibration of the vehicle, and reducing noise more suitably even when the vibration sensor has resonated. 
     The active noise control device may further include the resonance frequency storage unit ( 26 X,  26 Y,  26 Z) configured to store resonance frequency information indicating the resonance frequency of the vibration sensor, wherein the basic signal generating unit is configured to generate the basic signal corresponding to the resonance frequency of the vibration sensor based on the resonance frequency information stored in the resonance frequency storage unit. 
     The active noise control device may further include the resonance frequency identifying unit ( 44 X,  44 Y,  44 Z) configured to identify the resonance frequency of the vibration sensor by performing frequency analysis on the first reference signal, wherein the basic signal generating unit may be configured to generate the basic signal corresponding to the resonance frequency identified by the resonance frequency identifying unit. According to such a configuration, even when the resonance frequency of the vibration sensor has fluctuated, the resonance frequency information can be accurately updated. Therefore, according to such a configuration, it is possible to provide an active noise control device that is capable of reducing noise more suitably. 
     The sampling rate of the first adaptive filter may be twice or more as high as the sampling rate of the second adaptive filter, and the active noise control device may further include the downsampling unit ( 46 X,  46 Y,  46 Z) located between the first adaptive filter and the second adaptive filter. According to such a configuration, since the filtering process for generating the second reference signal is performed at a relatively high sampling rate, aliasing noise corresponding to the component of the resonance frequency can be suitably prevented from being mixed into the control signal. Therefore, according to such a configuration, it is possible to provide an active noise control device that is capable of reducing noise more suitably. 
     The active noise control device may further include the second filter coefficient updating unit ( 40 X,  40 Y,  40 Z) configured to update the filter coefficient (Wx, Wy, Wz) of the second adaptive filter in a manner that the error signal (e) is minimized, the error signal being acquired by detecting, with the microphone ( 20 ), residual noise due to interference between the noise and the canceling sound. According to such a configuration, since the filter coefficient of the second adaptive filter is suitably updated, it is possible to provide an active noise control device that is capable of reducing noise more suitably. 
     The vehicle includes the active noise control device as described above.