Noise reduction device, vehicle, and noise reduction method

1. An active noise reduction device, comprising:

a reference signal inputter to which a reference signal that has a correlation with noise in a space in a vehicle is input, the reference signal being output by a reference signal source attached to the vehicle;

an adaptive filter that is applied to the reference signal that is input to the reference signal inputter to generate a cancelling signal, the cancelling signal being used to output a cancelling sound for reducing the noise; and

a filter coefficient updater that calculates a coefficient of the adaptive filter based on a predetermined update equation,

wherein, at a first timing at which the output of the cancelling sound is started, the filter coefficient updater reads a first coefficient as an initial value of the predetermined update equation, the first coefficient being the coefficient of the adaptive filter calculated by the filter coefficient updater at a second timing that is prior to the first timing,

wherein, at the first timing, the filter coefficient updater uses a corrected first coefficient obtained by multiplying the first coefficient by a correction coefficient that is greater than 0 and less than 1 as the initial value of the predetermined update equation, instead of using the first coefficient, and

wherein the correction coefficient, which is greater than 0 and less than 1, is determined according to a length of a period from the second timing to the first timing.

2. The active noise reduction device according to claim 1 ,

wherein the second timing is a timing at which an ignition power supply of the vehicle is turned off, and

the first timing is immediately after the second timing, and is a timing at which the active noise reduction device is turned on.

3. The active noise reduction device according to claim 1 ,

wherein the second timing is before the active noise reduction device is shipped.

4. The active noise reduction device according to claim 3 ,

wherein the second timing is immediately after the vehicle is moved under a plurality of different moving conditions.

5. The active noise reduction device according to claim 3 , further comprising a storage that stores the first coefficient,

wherein the active noise reduction device has a function of prohibiting processing of storing the first coefficient in the storage.

6. The active noise reduction device according to claim 1 ,

wherein the active noise reduction device selectively operates in either a first operation mode or a second operation mode, and

the filter coefficient updater uses the first coefficient as the initial value of the update equation at the first timing at which the output of the cancelling sound in the first operation mode is started, and uses a second coefficient as the initial value of the update equation at a timing at which the output of the cancelling sound in the second operation mode is started, the second coefficient being a coefficient that is different from the first coefficient and is the coefficient of the adaptive filter calculated by the filter coefficient updater prior to the timing at which the output of the cancelling sound in the second operation mode is started.

7. The active noise reduction device according to claim 1 ,

wherein the correction coefficient decreases in value as the length of the period from the second timing to the first timing increases in length.

8. The active noise reduction device according to claim 1 ,

wherein the filter coefficient updater stores the first coefficient in a nonvolatile storage at the second timing, and reads the first coefficient stored in the nonvolatile storage as the initial value of the update equation at the first timing.

9. The active noise reduction device according to claim 1 ,

wherein the filter coefficient updater stores the first coefficient in a volatile storage at the second timing, and reads the first coefficient stored in the volatile storage as the initial value of the update equation at the first timing.

10. The active noise reduction device according to claim 9 ,

wherein the filter coefficient updater stores the first coefficient in a nonvolatile storage at the second timing when a notification of interruption of a supply of power to the active noise reduction device is received or when an interruption of the supply of power is detected.

11. A vehicle comprising:

the active noise reduction device according to claim 1 ; and

the reference signal source.

12. The active noise reduction device according to claim 1 ,

wherein the filter coefficient updater determines whether the length of the period from the second timing to the first timing is greater than or equal to a threshold value,

the filter coefficient updater uses a first correction coefficient as the correction coefficient in response to the length of the period being greater than or equal to the threshold value, and

the filter coefficient updater uses a second correction coefficient, different than the first correction coefficient, as the correction coefficient in response to the length of the period being less the threshold value.

13. The active noise reduction device according to claim 12 ,

wherein the second correction coefficient is greater than the first correction coefficient.

14. The active noise reduction device according to claim 1 ,

wherein the filter coefficient updater determines whether the length of the period from the second timing to the first timing is greater than or equal to a plurality of different threshold values, and

the filter coefficient updater determines the correction coefficient in three or more stages, from among a plurality of correction coefficients, depending on whether the length of the period is greater than or equal to the plurality of different threshold values.

15. An active noise reduction device, comprising:

a reference signal inputter to which a reference signal that has a correlation with noise in a space in a vehicle is input, the reference signal being output by a reference signal source attached to the vehicle;

an adaptive filter that is applied to the reference signal that is input to the reference signal inputter to generate a cancelling signal, the cancelling signal being used to output a cancelling sound for reducing the noise; and

a filter coefficient updater that calculates a coefficient of the adaptive filter based on a predetermined update equation,

wherein, at a first timing at which the output of the cancelling sound is started, the filter coefficient updater reads a first coefficient as an initial value of the predetermined update equation, the first coefficient being the coefficient of the adaptive filter calculated by the filter coefficient updater at a second timing that is prior to the first timing,

wherein, at the first timing, the filter coefficient updater uses a corrected first coefficient obtained by multiplying the first coefficient by a correction coefficient that is greater than 0 and less than 1 as the initial value of the predetermined update equation, instead of using the first coefficient, and

wherein the correction coefficient decreases in value as a difference between a temperature of the space at the second timing and a temperature of the space at the first timing increases in value.

16. The active noise reduction device according to claim 15 ,

wherein the filter coefficient updater determines whether the difference between the temperature of the space in the vehicle at the second timing and the temperature of the space in the vehicle at the first timing is greater than or equal to a threshold value,

the filter coefficient updater uses a first correction coefficient as the correction coefficient in response to the difference being greater than or equal to the threshold value, and

the filter coefficient updater uses a second correction coefficient, different than the first correction coefficient, as the correction coefficient in response to the difference being less the threshold value.

17. The active noise reduction device according to claim 16 ,

wherein the second correction coefficient is greater than the first correction coefficient.

18. An active noise reduction method executed by an active noise reduction device, the active noise reduction method comprising:

generating a cancelling signal by applying an adaptive filter to a reference signal, the reference signal having a correlation with noise in a space in a vehicle and being output by a reference signal source attached to the vehicle, the cancelling signal being used to output a cancelling sound for reducing the noise; and

calculating a coefficient of the adaptive filter based on a predetermined update equation,

wherein the calculating includes, at a first timing at which the output of the cancelling sound is started, reading a first coefficient as an initial value of the predetermined update equation, the first coefficient being the coefficient of the adaptive filter calculated by the active noise reduction device at a second timing that is prior to the first timing,

wherein the calculating further includes, at the first timing, multiplying the first coefficient by a correction coefficient that is greater than 0 and less than 1 to obtain a corrected first coefficient, and using the corrected first coefficient as the initial value of the predetermined update equation instead of the first coefficient, and

wherein the correction coefficient, which is greater than 0 and less than 1, is determined according to a length of a period from the second timing to the first timing.