JPH0627968A - In-cabin noise reducing device - Google Patents

Abstract

PURPOSE:To provide the LMS(Least Mean Square) type in-cabin noise reducing device which is inexpensive, superior in after-market performance, and high in reliability and stability. CONSTITUTION:An ignition pulse signal to an ignition coil is made into a signal of frequency of a component of 0.5X n (integer)th order of engine rotation through the waveform shaping and thinning of an ignition signal converting circuit 2 and the signal is outputted as a primary source to an adaptive filter 3 and to an LMS arithmetic circuit 6 through a speaker-micrphone transmission characteristic correcting circuit 7. The primary source is composed as a canceling signal by the adaptive filter 3 and outputted as a sound for canceling a vibration noise from a speaker 4. Then the noise reduced state at a listening point is detected by an error microphone 5 as an error signal, which is sent to the LMS arithmetic circuit 6; and this LMS arithmetic circuit 6 updates the filter coefficient W (N) of the adaptive filter 3 so that the error signal becomes minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle interior noise reduction device for reducing vehicle interior noise by canceling noise.

[0002]

2. Description of the Related Art Various techniques for reducing vehicle interior noise by generating a sound (cancellation sound) having the same amplitude and opposite phase as the noise generated in the vehicle due to engine vibration as a main factor, from an additional sound source. Is proposed.

As such a technique, for example, Japanese Patent Laid-Open No. Hei 3
No. 5255, numerical data of a basic sine wave having an opposite phase in synchronism with a secondary component of engine rotation is stored in advance, and the engine rotation speed obtained from a crank angle sensor and the engine obtained from a pressure sensor are stored. By modifying the phase and amplitude of the basic sine wave with a load, there is disclosed a vehicle interior noise reduction device capable of producing a canceling sound without requiring a vibration sensor or the like for directly detecting engine vibration.

However, in order to finely deal with various noise waveforms under various operating conditions, it is necessary to store a huge amount of data, and noise reduction is required under various operating conditions. It is difficult to do so stably with. Further, in order to effectively reduce the noise generated by the engine vibration that is different for each vehicle, the above data must be set for each vehicle.

[0005]

By the way, recent LS
By the I technique, LMS (Least Mean Square) algorithm (in order to simplify the calculation formula for obtaining the optimum filter coefficient, the fact that the correction formula of the filter is recursive is used, the mean square error is approximated by the instantaneous square error. The desired theory) or MEFX (Multiple Error Filtered) which is an extension of this LMS algorithm to multiple channels.
X) A vehicle interior noise reduction device using an algorithm has begun to be put into practical use. In the vehicle interior noise reduction device using the LMS algorithm, when the vehicle interior noise generated mainly due to the engine vibration is silenced, a signal highly correlated with the engine vibration is used as a noise vibration source signal (primary source) by a vibration sensor or the like. It detects and synthesizes the cancellation signal (cancellation signal) for noise from this primary source by the optimum filter, and the cancellation sound is generated from the speaker. Then, the noise reduction state at the listening point is detected as an error signal by the error microphone, and from this error signal and the primary source, by the LMS algorithm,
The filter coefficient of the optimum filter is updated to optimize the noise reduction at the listening point.

According to the noise reduction device using this LMS algorithm, noise reduction can be stably performed under various operating conditions without storing a huge amount of data as described in the prior art. Therefore, it is possible to effectively reduce the noise that is different for each vehicle.

However, in order to obtain a signal having a high correlation with the engine vibration, a vibration sensor or the like for detecting the engine vibration is required, and this vibration sensor is highly accurate and reliable in order to obtain the signal serving as the primary source. However, there is a problem that the noise reduction device becomes expensive. In addition, since a new detector such as a vibration sensor is required for the engine, it is difficult to equip a vehicle that is not equipped with the noise reduction device with the noise reduction device afterwards.

The present invention has been made in view of the above circumstances, and is an LMS algorithm which uses a signal having a high correlation with a highly accurate and reliable stable engine vibration and a high correlation without using a sensor such as a vibration sensor. It is an object of the present invention to provide a vehicle interior noise reduction device that can be easily installed even in a vehicle not equipped with the noise reduction device, as a noise reduction device utilizing the noise reduction device.

[0009]

In order to achieve the above object, a vehicle interior noise reduction device according to the present invention, as shown in FIG. 1, comprises an ignition signal of an engine composed of high-order components of a predetermined value set in advance. Ignition signal converting means M1 for converting as a noise vibration source signal of a frequency spectrum, cancel signal combining means M2 for combining the noise vibration source signal as a cancel signal by an adaptive filter, and the cancel signal generated from a sound source as a canceling sound for noise. Canceling sound generating means M3, error signal detecting means M4 for detecting the noise reduction state at the listening point as an error signal, and cancel signal updating means M5 for updating the filter coefficient of the adaptive filter based on the error signal and the ignition signal. It is equipped with and.

[0010]

[Operation] In the above structure, first, the ignition signal converting means M1 converts the ignition signal of the engine into a noise vibration source signal having a frequency spectrum composed of higher order components of a predetermined value. Next, the cancel signal synthesizer M2 synthesizes the noise and vibration source signal as a cancel signal by an adaptive filter. Next, the canceling sound generating means M3
Thus, the cancel signal is generated from the sound source as a canceling sound for noise. Then, the noise reduction state at the listening point is detected as an error signal by the error signal detecting means M4 and sent to the cancel signal updating means M5, and the cancel signal updating means M5 makes the adaptation based on the error signal and the ignition signal. Update the filter coefficient of the filter.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 2 and the following shows an embodiment of the present invention, and FIG. 2 is a schematic explanatory view of a system operation principle of a vehicle interior noise reduction device, and FIG.
Is an explanatory diagram of an ignition signal conversion circuit, FIG. 4 is an explanatory diagram of a correlation between a primary source and vibration noise, (a) is a shaped / processed ignition signal pulse, (b) is engine-related vibration noise,
(C) is a shaped / processed ignition signal pulse viewed from the frequency domain, (d) is engine-related vibration noise viewed from the frequency domain, and FIG. 5 is an operation explanatory view of the vehicle interior noise reduction device.

In FIG. 2, reference numeral 1 denotes a 4-cylinder 4-cycle engine. A vehicle interior noise reduction device for reducing vehicle interior noise by the engine 1 includes an ignition signal conversion circuit 2 as ignition signal conversion means M1 and a cancel signal. Synthesis means M
2, an adaptive filter 3 as an offset canceling sound generating means M3, an amplifier (not shown) and a speaker 4, an error microphone 5 as an error signal detecting means M4, and an LMS arithmetic circuit 6 as a canceling signal updating means M5. , Speaker-microphone transfer characteristic correction circuit 7 and various filter circuits (circuits such as LP filters), A / D converter, D /
It is configured by an A converter (neither is shown) or the like.

As shown in FIG. 3, the ignition signal conversion circuit 2 is composed of a waveform shaping circuit 2a and a thinning circuit 2b. An ignition coil (not shown) input to the ignition signal conversion circuit 2 is used. The ignition pulse signal (Ig pulse signal) to) is 1 pulse for two engine revolutions in synchronization with the engine revolution, and is 0.5 × n of the engine revolution.
The signal is shaped / decimated into a signal having a frequency of an (integer) next component, and is output to the adaptive filter 3 and the speaker-microphone transfer characteristic correction circuit 7 as a noise vibration source signal (primary source).

This is because the vibration noise associated with the 4-cycle engine (FIG. 4 (b)) is caused by the engine 1 rotating twice (720 ° C.).
In order to complete the four strokes of intake / compression / explosion / exhaust in A), there is vibration noise that makes the engine 2 revolutions in one cycle. A spectrum in which the sine wave component that becomes 1 cycle in the above is the fundamental wave, and the higher-order component is the main component (Fig. 4
This is because (d)) is set (it is composed of 0.5 × n (integer) order components). Therefore, by shaping and processing the Ig pulse signal as described above, it is possible to obtain a primary source having a very high correlation with the vibration noise to be silenced (FIGS. 4A and 4C).

The adaptive filter 3 is an LMS which will be described later.
This is an FIR (Finite Impulse Response) filter having a filter coefficient W (n) that can be updated by the arithmetic circuit 6. This FIR filter has a tap number of 256 in this embodiment. The number of taps is 2
The number of taps is not limited to 56, and a filter with a larger number of taps may be used as long as sufficient calculation speed and cost performance can be obtained, and if sufficient accuracy is obtained,
A filter with a smaller number of taps may be used. The primary source from the ignition signal conversion circuit 2 input to the adaptive filter 3 is output as a cancellation signal that is a canceling sound signal that cancels vibration noise by the convolution product sum with the filter coefficient W (n). It

The cancel signal from the adaptive filter 3 is output to a speaker 4 inside the vehicle through a D / A converter and an amplifier (not shown), and the speaker 4 sets the driver's head inside the vehicle. Is output as a canceling sound for the vibration noise at the listening point 8. In the present embodiment, the speaker 4 is used in common with the audio speaker mounted in the vehicle compartment (FIG. 5), but separately,
It may be arranged as a sound source speaker for muffling.

An error microphone 5 is arranged near the listening point 8. The error microphone 5 detects the result of interference between vibration noise and canceling sound, and the LMS arithmetic circuit 6
Error signal. In the speaker-microphone transfer characteristic correction circuit 7, the speaker-microphone transfer characteristic CMN is obtained and set in advance, and the speaker-microphone transfer characteristic CMN is transferred to the primary source from the ignition signal conversion circuit 2. It is adapted to be corrected by being multiplied by the characteristic CMN and input to the LMS arithmetic circuit 6. This L
In the MS arithmetic circuit 6, the instantaneous square error is obtained from the error signal from the error microphone 5 and the corrected primary source, and the adaptive filter 3 of the adaptive filter 3 is set so that the error signal from the error microphone 5 is minimized. Filter coefficient W
Update (n).

A reference character C in the drawing indicates a vehicle body transmission characteristic when vibration noise propagates from the engine 1 to the listening point 8.

Further, the ignition signal conversion circuit 2, the adaptive filter 3, the LMS operation circuit 6, the speaker-microphone transfer characteristic correction circuit 7, the filter circuit, the A / D converter, and the D / D converter.
The A converter and the like are housed in one place, and are provided in the vehicle rear part or the like as the vehicle interior noise reduction device control unit 9.

Next, the operation of the embodiment having the above construction will be described. First, engine vibration noise is
From the inside to the inside of the vehicle through a mount or the like (not shown), and the sounds of intake and exhaust also propagate inside the vehicle. As shown in FIG. 4, each of these engine-related vibration noises is composed of a spectrum of a 0.5 × n (integer) order component in the frequency domain, and is multiplied by the vehicle body transfer characteristic C to obtain the listening point 8 Reach

On the other hand, the ignition pulse signal (Ig pulse signal) to the ignition coil (not shown) of the engine 1 is 1 pulse for 2 revolutions of the engine in synchronization with the rotation of the engine and 0.5 × n ( It is shaped / decimated into a signal having a frequency of an (integer) order component, and is output to the adaptive filter 3 and the speaker-microphone transfer characteristic correction circuit 7 as a noise vibration source signal (primary source).

Next, the primary source from the ignition signal conversion circuit 2 input to the adaptive filter 3 is
By a convolution product sum with the filter coefficient W (n), a cancellation signal that is a canceling sound signal that cancels vibration noise is output to the speaker 4 inside the vehicle through a D / A converter and an amplifier (not shown). The listening point 8 from the speaker 4
It is output as a canceling sound for the vibration noise in. At this time, the cancellation sound output from the speaker 4 is multiplied by the speaker-microphone transfer characteristic CMN and reaches the listening point 8.

Therefore, at the listening point 8, the engine-related vibration noise and the canceling noise interfere with each other to reduce the vibration noise, and at the same time, the error microphone 5 disposed near the listening point 8 is reduced. As a result, the result of the interference between the vibration noise and the canceling noise is detected and sent to the LMS arithmetic circuit 6 as an error signal.

The primary source output to the speaker-microphone transfer characteristic correction circuit 7 is multiplied by the speaker-microphone transfer characteristic CMN obtained in advance and sent to the LMS arithmetic circuit 6. Then, in this LMS operation circuit 6, an instantaneous square error is obtained from the error signal from the error microphone 5 and the corrected primary source,
An algorithm for updating the filter coefficient W (n) of the adaptive filter 3 is performed so that the error signal from the error microphone 5 is minimized.

As described above, since the ignition pulse generally used for various controls in the automobile is used as a primary source, it is possible to construct an inexpensive and highly reliable vehicle interior noise reduction device without using a new sensor. You can

Since the engine-related vibration noise has factors such as engine vibration transmission noise, intake and exhaust noise, etc., rather than detecting a partial vibration of the engine with a vibration sensor or the like and using it as a primary source, More effective noise reduction can be realized.

Further, since a primary source having a very high correlation with engine-related vibration noise can be obtained without using a new sensor such as a vibration sensor, it is easy for a vehicle not equipped with a vehicle interior noise reduction device. It becomes possible to mount it on.

In this embodiment, an example of the noise reduction device using the LMS algorithm of 1 channel (1 error microphone, 1 speaker) has been described, but the MEFX (Multipl) in which the LMS algorithm is expanded to multiple channels.
It can also be applied to a vehicle interior noise reduction device (for example, a device with four error microphones, four speakers, etc.) that uses the e Error Filtered X) algorithm. By shaping and processing the ignition signal of the engine, the primary source can be changed. It can be highly correlated with engine-related vibration noise.

[0029]

As described above, according to the present invention, the engine ignition signal is converted into the noise vibration source signal having the frequency spectrum composed of the high-order components of the predetermined value. LMS that uses highly accurate and reliable stable engine vibration and a highly correlated signal as a primary source without using sensors such as sensors
System noise reducer, the noise reducer is also inexpensive, and it is possible to easily install it on a vehicle not equipped with the noise reducer.

[Brief description of drawings]

FIG. 1 is a block diagram of the concept of the present invention.

FIG. 2 is a schematic explanatory diagram of a system operation principle of a vehicle interior noise reduction device according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of an ignition signal conversion circuit according to an embodiment of the present invention.

4A and 4B are explanatory diagrams showing a correlation between a primary source and vibration noise according to an embodiment of the present invention, in which FIG. 4A is a molded / processed ignition signal pulse, and FIG. 4B is engine-related vibration noise.
(C) is a shaped / processed ignition signal pulse viewed from the frequency domain, and (d) is an explanatory diagram of engine-related vibration noise viewed from the frequency domain.

FIG. 5 is an operation explanatory view of the vehicle interior noise reduction device according to the embodiment of the present invention.

[Explanation of symbols]

 M1 Ignition signal conversion means M2 Cancel signal synthesis means M3 Cancellation sound generation means M4 Error signal detection means M5 Cancel signal update means W (n) Filter coefficient 1 Engine 2 Ignition signal conversion circuit 3 Adaptive filter 4 Speaker 5 Error microphone 6 LMS arithmetic circuit 7 Speaker-microphone transfer characteristic correction circuit 8 Listening point

Front page continuation (72) Inventor Kazuyuki Kondo 1-7-2 Nishishinjuku, Shinjuku-ku, Tokyo Fuji Heavy Industries Ltd. (72) Inventor Keitaro Yokota 1-2-7 Nishishinjuku, Shinjuku-ku, Tokyo Fuji Heavy Industries Ltd. In the company

Claims (1)

[Claims] 1. An ignition signal converting means for converting an engine ignition signal as a noise vibration source signal having a frequency spectrum composed of high-order components of a predetermined value, and a cancellation signal for the noise vibration source signal by an adaptive filter. A canceling signal synthesizing means for synthesizing the canceling signal, a canceling sound generating means for generating the canceling signal from the sound source as a canceling sound for noise, an error signal detecting means for detecting a noise reduction state at the listening point as an error signal, and the error signal A vehicle interior noise reduction device comprising: a cancellation signal updating means for updating the filter coefficient of the adaptive filter based on the ignition signal.