JP3546259B2 - Active noise reduction system for vehicle interior noise - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an active silencer that actively silences vehicle interior noise such as an automobile, and is particularly suitable for preventing deterioration of control performance due to gain variation due to individual differences in amplifiers that drive silencing speakers. Active silencer.
[0002]
[Prior art]
2. Description of the Related Art As a conventional active noise reduction device for vehicle interior noise, for example, there is a device shown in Japanese Patent Publication No. 1-501344 (British Patent 8624053). In this prior art, a plurality of loudspeakers are arranged in a closed space, a sound pressure at a predetermined position in a vehicle cabin is measured by a microphone 4, and a signal synchronized with rotation of an engine as a noise source is generated by a reference signal generator. generate. Then, based on the measured value of the microphone and the signal generated by the reference signal generator, a drive signal for each speaker that minimizes the sound pressure level in the closed space is calculated, and the vehicle interior noise is canceled from the speaker. A secondary sound of the same amplitude and opposite phase is output to the vehicle interior. In the calculation at this time, a driving signal of each speaker is obtained using an adaptive filter using a least mean square algorithm (hereinafter, referred to as an LMS algorithm) which is a kind of the steepest descent method. In this case, control is performed so that the sum of the sound pressure levels at the respective locations where the plurality of microphones are arranged is minimized.
[0003]
Here, the reference signal generator generates a sine wave having a frequency synchronized with the engine rotation (for example, a frequency twice as high as the rotation speed in a four-cylinder engine). The adaptive filter controls the phase and amplitude of the sine wave so that the sound pressure level to the microphone is minimized. If the sound component to be controlled by the adaptive filter is a single frequency, an output signal for one speaker can be generated by a digital filter having at most two taps. At this time, the sum of the squares of the filter coefficients is an amount proportional to the output power.
[0004]
By the way, the engine muffled sound to be controlled is a vibration generated due to a change in combustion gas pressure due to the rotation of the engine, an unbalanced inertia force of a crankshaft, etc., propagates in a vehicle cabin and is generated and confined in the vehicle cabin. It is noise. That is, it is vibration noise generated by vibrating a specific portion of the vehicle body by using the engine as a vibration source. The magnitude of the noise mainly depends on the rotation speed, and although there are some differences in the vibration modes excited due to acceleration / deceleration speed, vehicle weight, etc., the time averaged for each rotation speed region The average value is almost the same level, and the average value of the output power of the above-described filter for each rotation speed region is also approximately the same level.
[0005]
[Problems to be solved by the invention]
In the conventional silencer using the adaptive control described above, the control system may diverge depending on conditions. If the phase and amplitude of the noise to be controlled change rapidly with respect to the adaptation time of the control system, the change cannot be followed, and the secondary sound output from the silencing speaker increases in reverse. A divergence phenomenon occurs, giving the passenger discomfort. In order to avoid this, for example, it is necessary to take measures such as stopping the muffling control when the volume of the speaker exceeds a certain threshold for a certain period of time or longer, assuming that the sound has diverged. Since it is difficult to directly detect the volume of the speaker, an appropriate method is to provide a threshold value for the output power of the above-mentioned digital filter, and to consider the divergence when the output power exceeds the threshold value for a certain period of time. Can be considered.
[0006]
However, in the case where a function of stopping the secondary sound output by simply applying this method is provided, there is an inconvenience because each gain varies due to individual differences in the manufacture of the drive amplifier of each speaker. For example, when the gain of the speaker drive amplifier is lower than the design value, the output power of the filter for obtaining the actual speaker volume required for silencing becomes relatively large. At this time, if the output power exceeds the above-mentioned threshold value, the secondary sound output stop function operates even though the control system is not diverging, and the noise reduction control is turned off, so that the noise cannot be reduced. Occurs.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an active silencer that avoids divergence regardless of manufacturing variations of a speaker drive amplifier.
[0008]
[Means for Solving the Problems]
The above object is to detect the output voltage of the amplifier driving the speaker, determine whether the detected output voltage of the actually obtained amplifier is equal to the design value with respect to the output power of the filter calculated by the controller, and perform the detection. If the output voltage is larger than the value calculated by the controller, it is determined that the gain of the speaker drive amplifier is larger than the design value and the power threshold of the filter is reduced, and conversely, the detected output voltage is the value calculated by the controller. If smaller, the gain is determined by determining that the gain of the speaker drive amplifier is smaller than the design value and increasing the threshold value of the filter power.
[0009]
Another object of the present invention is to set the expected value of the output power in each rotation speed region obtained when the gain of the speaker drive amplifier is equal to the design value in advance in the ROM memory of the controller, and At the time of control, the filter power is obtained for each rotation speed region, the deviation from the set expected value is calculated every moment, the sum of the deviation in each rotation speed region is obtained every moment, and the sum of the sum after a lapse of a certain time is calculated. When the value is positive and larger than a certain set value, it is determined that the gain of the speaker drive amplifier is smaller than the design value, and the threshold value of the power of the filter is made larger. Is negative and smaller than a certain set value, this is achieved by determining that the gain of the speaker drive amplifier is larger than the design value and making the threshold smaller.
[0010]
[Action]
If the gain of the speaker drive amplifier is not the desired design value, it is determined whether the gain is larger or smaller than the design value based on the detection value of the output voltage detection circuit or the average value of the power of the filter. By raising and lowering the divergence determination threshold based on this determination, erroneous divergence determination based on a gain error can be avoided.
[0011]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of an active noise reduction device for vehicle interior noise according to an embodiment of the present invention. In this active silencer, noise in the passenger compartment is detected by four microphones 4 and two speakers 5 generate sound (secondary sound) for silencing control. Now, when the engine 1 rotates, a rotation signal 101 obtained from a tachogenerator, a crank angle sensor or the like is input to the microprocessor 3 in the active silencer 2. The microprocessor 3 also receives a sound pressure signal 102 obtained by the microphone 4. The microprocessor 3 generates a sine wave (reference signal 100) having twice the frequency of the engine speed based on the rotation signal 101 on the programmed software, and generates the reference signal 100 and each sound pressure signal 102. (There are four), the output signals 103 (two) of the loudspeaker 5 that minimize the sum of the squares of the sound pressure signal 102 are calculated. The signal 103 is subjected to D / A conversion, amplified by the power amplifier 6, and output as sound from the speaker 5 into the vehicle interior.
[0012]
When filtering the reference signal 100 to generate the signal 103, the microprocessor 3 generates the signal 103 at the time of the n-th sampling according to the following equation (1).
[0013]
(Equation 1)
_{ym (n) = wm 0 ·} x (n) + wm 1 · x (n-1)
Here, x: reference signal 100
y: output signal wm ₀ to speaker 5: filter coefficient m: (= 0, 1) is a speaker number (there are two).
[0014]
Now, if the frequency of the reference signal 100 is f and the sampling frequency is fs constant,
[0015]
(Equation 2)
x (n) = sin (2πn / N)
Where N = fs / f
Therefore, the above equation (1) is transformed into the following equation (3).
[0016]
[Equation 3]
ym (n) = Wmsin (2πn / N + φ)
However ^{_{Wm 2 = wm 0 2 + wm}} 1 2 + 2wm 0 · wm 1 cos (2π / N)
tanφm = wm ₁ sin (2π / N) / (wm ₀ + wm ₁ cos (2π / N))
Wm: output power of the filter (hereinafter referred to as W power).
[0017]
These filter coefficients are adaptively corrected by the LMS algorithm so that the evaluation function (sum of sound pressure squares) is minimized. (For details of the LMS algorithm, refer to the document “A Multiple Error LMS Algorithm and It's Application to the Active Control of Sound and Vibration” (“A Multiple Error LMS Algorithm and It's Application”). The Active Control Sound and Vibration "IEEE Transactions on Acoustic Speech, and Signal Processing, Vol. ASSP-35, No. 10 October, 1987).
[0018]
By the way, when the phase and amplitude of the vehicle interior noise to be controlled suddenly change, the adaptation cannot catch up, and there is a risk that the control system diverges. As shown in FIG. 2 (a), at this time, the value of W power is monitored by setting a threshold value, and if the W power under control exceeds this threshold value for a certain period of time, it is determined that divergence has occurred. By activating the sound stop processing, it is possible to avoid an increase in noise due to divergence and to avoid giving the occupant a discomfort. On the other hand, as shown in FIG. 2B, when the gain of the speaker drive amplifier is considerably lower than the design value due to manufacturing variations of the amplifier, the W power value increases as a whole. Depending on the engine speed (that is, the reference signal 100), the threshold value may be exceeded. At this time, if this is determined to be a divergence phenomenon and the silencing function is stopped, the function of the active silencer cannot be exhibited. Therefore, in this embodiment, an output voltage detection circuit 10 of a speaker drive amplifier as shown in FIG. 3 is prepared. The circuit 10 extracts both signals of the AC voltage output from the speaker drive amplifier 6 and drives a voice coil (not shown) inside the speaker 5, amplifies a potential difference between the two signals by a differential amplifier 22, and amplifies the signal. The A / D converter 23 obtains a digital voltage proportional to the magnitude of the peak voltage of the signal thus obtained, and outputs the digital voltage to the microprocessor 2.
[0019]
By adding the voltage detection circuit 10 to the active silencer as shown in FIG. 4, the microprocessor 3 of the active silencer 2 can use the output of the A / D converter 23 (FIG. 3) to actually drive the speaker. The output voltage of the amplifier 6 can be known, and it can be determined whether or not the detected output voltage of the amplifier 6 actually obtained with respect to the output power of the filter calculated by the controller is as designed. If the detected output voltage is larger than the value calculated by the controller, it is determined that the gain of the speaker drive amplifier 6 is larger than the design value, and the power threshold of the filter is made smaller. Conversely, if the detected output voltage is smaller than the value calculated by the controller, it is determined that the gain of the speaker drive amplifier 6 is smaller than the design value, and the power threshold of the filter is made larger.
[0020]
FIG. 5 is a diagram illustrating a process in an active silencer according to another embodiment of the present invention. In the present embodiment, the expected value of the W power is set in advance for each engine speed region, a deviation from the expected value is obtained every moment when the control is started, and the value is integrated in each speed region. The magnitude of the gain is determined. If the gain of the speaker drive amplifier is as designed, the deviation should be close to zero over time. However, if the gain differs from the design value and is small or large, the deviation moves in the positive direction or the negative direction as a whole. Therefore, after a certain period of time has elapsed since the start of the control, the sum of the integrated values of the deviations obtained in each rotation speed region is obtained. If the sum is a positive value and larger than a certain set value, it is determined that the gain is small, and the threshold value of W power is increased. Conversely, if the sum is a negative value and smaller than a certain set value, it is determined that the gain is large, and the threshold value of the W power is lowered. In this embodiment, the integrated value of the deviation is obtained in each rotation speed region before obtaining the total sum. However, the procedure may be further simplified, and the deviation obtained every moment may be integrated as it is to directly obtain the total sum.
[0021]
Here, the rise or fall of the threshold value of the W power may be set to a value proportional to the total value. In addition, this series of processing may be performed not only once after the control is started (usually when the ignition is turned on) but also periodically at predetermined intervals. These control algorithms and parameters required for the control are stored in a ROM 31 shown in FIG. 1, data measured every moment are stored in a RAM 32, and a series of processes are all performed inside a microprocessor of a controller. Can be performed as software processing.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that the active silencer of the same performance can be comprised regardless of the manufacturing variation of the speaker drive amplifier gain.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an active silencer according to one embodiment of the present invention.
FIG. 2 is an explanatory diagram of a relationship between output power of a filter and a threshold.
FIG. 3 is a configuration diagram of a voltage detection circuit of a speaker drive amplifier output.
FIG. 4 is a configuration diagram of an active silencer in which the voltage detection circuit shown in FIG. 3 is arranged.
FIG. 5 is an explanatory diagram of a threshold change processing procedure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Active silencer, 3 ... Microprocessor, 4 ... Microphone, 5 ... Speaker, 6 ... Power amplifier, 100 ... Reference signal, 101 ... Engine rotation signal, 102 ... Sound pressure signal, 103 ... Output signal, 31 ... ROM, 32 ... RAM.

Claims (4)

Noise detection means for detecting the sound pressure in the passenger compartment, a controller for calculating the amplitude and phase of a secondary sound for actively canceling the detected noise, and a control signal for the calculated secondary sound from the controller An active noise reduction apparatus for vehicle interior noise , comprising: a drive amplifier that amplifies the signal; and a speaker that is driven by an amplifier output of the drive amplifier and outputs the calculated secondary sound.
Means for determining whether or not the output power of the control signal is at a level equal to or higher than a preset threshold value; and determining that the secondary sound is diverged when the output power is equal to or higher than the threshold value, from the speaker. Means for stopping the operation , a detecting means for detecting the amplifier output of the driving amplifier , and comparing the detected value of the detecting means with the value of the output power of the control signal. An active noise reduction apparatus for vehicle interior noise, comprising: a divergence threshold value correction unit that determines that there is a deviation between a gain as a design value and an actual gain and corrects the threshold value. Noise detection means for detecting the sound pressure in the passenger compartment, a controller for calculating the amplitude and phase of a secondary sound for actively canceling the detected noise, and a control signal for the calculated secondary sound from the controller An active noise reduction apparatus for vehicle interior noise , comprising: a drive amplifier that amplifies the signal; and a speaker that is driven by an amplifier output of the drive amplifier and outputs the calculated secondary sound.
Means for determining whether or not the output power of the control signal is at a level equal to or higher than a preset threshold value; and determining that the secondary sound is diverged when the output power is equal to or higher than the threshold value, from the speaker. Means for stopping the control signal, means for storing in advance the expected value of the output power of the control signal of the amplitude and phase of the secondary sound, and the value of the deviation between the calculated output power value of the control signal and the expected value And a divergence threshold value correcting unit that corrects the threshold value by determining that there is a difference between a gain as a design value of the drive amplifier and an actual gain in accordance with the threshold value. apparatus. 3. The active noise reduction apparatus according to claim 2, wherein the expected value is set for each vibration frequency range of a vibration source that vibrates the vehicle interior. 4. The active vehicle interior noise according to claim 3, wherein an integrated value of the deviation is obtained for each vibration frequency region, a total value of the integrated values is obtained, and the threshold value is corrected according to the total value. Silencer.

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