JPH03178845A - Device for reducing noise in car room - Google Patents

Abstract

PURPOSE:To remove not only a confined noise but also other noise components together by making an applicable step size variable in accordance with an output condition of a car audio equipment and controlling a speaker so as to minimize an input of a microphone, by means of a controller. CONSTITUTION:Engine vibration X(n) is converted into a car room noise Y(n) closely to ears and observed through a car room space transmission path by a transmission function G. Here the engine vibration itself is caused by an engine speed secondary component, but the noise Y(n) contains a component except the above described engine speed secondary component by the transmission function G. An engine vibration signal X(n) and an output signal e(n) from a microphone are always input. In a controller 5, and a filter coefficient train H is adequately controlled base on these signals by an LMS method or the like to generate a speaker output y(n) so as to cancel the car room noise Y(n). In this case a car audio output condition is fed to the controller 5, and the corresponding step size mu is selected to perform an applicable control.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vehicle interior noise reduction device, and particularly to a device for actively reducing low-frequency noise in a closed space of a vehicle such as an automobile that has a periodic sound source. It is related to the device.

[Conventional technology]

Noise inside a vehicle such as a car is caused by the resonance phenomenon that occurs in the cabin, which forms a closed space, under certain conditions.
The vibrational force that is the cause of this is thought to be due to the rotational vibration component of the engine.

The measures initially taken to reduce such noise were passive, such as improving the coupling rigidity of the engine system, which is the source of vibration, and improving the coupling rigidity of the transmission system. has tuned each mount, and increased the rigidity of the panel for the sounding body inside the vehicle.
Furthermore, as a countermeasure against resonance, mass dampers, dynamic dampers, etc. were applied to the resonant parts.

Such passive means increase cost and weight, and are insufficiently effective.

On the other hand, in the case of a four-cylinder engine, the main cause of such cabin noise is thought to be the engine rotation order component, which is the two-explosion component of one revolution of the crankshaft, or the so-called two-blow-off component of the engine revolution. , Japanese Patent Application Laid-Open No. 59-9699 and Japanese Utility Model Application Laid-open No. 62-127 are known as conventional techniques that attempt to actively reduce the muffled sound caused by such factors.
Publication No. 051 and the like have already been proposed.

In these conventional technologies, an ignition pulse is detected as a signal of engine rotation, and this pulse signal is processed in various ways to generate the inverse of each frequency component (rotational order component) of the noise observed at the driver's listening point in the vehicle interior. By separately adding sound from a speaker that has the same phase and magnitude as the noise component, the noise level at the listening point is canceled out and reduced by the interference effect.

[Problem to be solved by the invention]

However, the above-mentioned conventional example is a device for reducing only the muffled noise caused by engine rotation 2 in the cabin noise, and is a device for reducing only the muffled sound caused by engine rotation 2.
Even if a noise component due to a rotational order component (explosion order component) other than the blowing component exists, it cannot be removed, and the noise reduction will not be optimal.

In addition, it is constantly affected by changes over time in the vehicle's engine system, mounting system, electrical system, etc., changes in the temperature characteristics of the electrical signal system, changes in the number of occupants, changes in the cabin temperature, etc., and the intrusion of some external disturbance. There was a problem that it was impossible to deal with the problem or the immediate response of the control could not be obtained.

Therefore, it is an object of the present invention to realize a simple device that can remove not only the muffled noise caused by the two-fire components of engine rotation in the passenger compartment, but also other noise components, and that can quickly respond to various changes in vehicle conditions. [Means for Solving the Problems] In order to solve the above-mentioned problems, the vehicle interior noise reduction device according to the present invention includes an engine vibration detection means and a detection signal of the detection means to detect vibrations of the vehicle body. An adaptive controller that identifies the inverse transfer function of the transfer function up to the ears of the system, a speaker that outputs the output signal of the controller into the vehicle interior, a means for detecting the output state of the car audio, and a means for detecting all vehicle interior noise. Equipped with a microphone, 1 controller has 3
The adaptive step size is varied according to the output state of the car audio, and the speaker is controlled so that the input to the microphone is minimized.

[Function] In the vehicle interior noise reduction device according to the present invention, as shown in the equivalent block diagram of FIG. 1, G is the overall transfer function of the vehicle interior vibration system excited by engine vibration, and
Transfer function by engine mount (MTC;), transfer function by torque rod based on engine vibration,
This is due to the transfer function of the cab mount, etc., and the engine vibration is observed in the form of the engine vibration converted to the cabin noise Y (n) at the ear via the cabin space transmission path using this transfer function G.

In this case, the engine vibration itself is due to the two engine rotation components, but the cabin noise Y (
n) includes components other than the engine rotation two components due to the transfer function G.

This transfer function G is an unknown value, and the controller 5 identifies the inverse transfer function G-1 of this transfer function.
The controller 5 always inputs the engine vibration signal X (n) detected by the engine vibration detection means and the output signal e (n) from the microphone, and based on these signals, performs the well-known LMS (Least Mean 5
The speaker output y (n) is generated by adaptively controlling the filter coefficient sequence H using the square method or the like to cancel the above-mentioned vehicle interior noise Y (n).

Here, the update amount of the filter coefficient sequence H is the step size μ
If the step size μ is large, the amount of update each time will be large, so the convergence of the adaptive operation will be faster, but since the amount of update will be large every time the step size μ is large, the optimum value may be exceeded. On the other hand, when the step size μ is small, it gradually approaches the optimum value, so it is easy to settle on the optimum value, but since the amount of update at one time is small, it takes time for convergence.

Further, when the step size μ is large, the effect of disturbance is easier than when it is small.

Now, if we assume that car audio is being output into the vehicle interior with the step size μ fixed, the car audio sound, which is unrelated to the process by which engine vibration becomes sound, is continuously fed to the microphone. This results in external noise, which disturbs the system and prevents the adaptive operation from being performed correctly.

Therefore, in the present invention, a means for detecting the output state of the car audio is provided, and by sending the output state of the car audio to the controller, a corresponding step size μ
By selecting and performing adaptive operation, it is possible to identify the optimal inverse transfer function.

Therefore, if the adaptive controller of the present invention changes the step size in response to the external noise from the car audio, all of the detected signals from the engine vibration among the information input to the microphone inside the vehicle will be subject to control. Since noise other than the order components of the engine can also be canceled out, cabin noise can be reduced more completely and quickly.

[Embodiment] Fig. 2 shows an embodiment of the vehicle interior noise reduction device according to the present invention, in which 1 is the interior of the vehicle, 2 is the engine of the automobile 1, and 3 is the engine vibration of the engine 2. 4 is a microphone that detects the noise level in the vehicle interior; 5 is an inverse transfer function of the transfer function of the vibration system of the vehicle body excited by the vibration of the engine by the outputs of sensors 3 and 4; 6 is a speaker that generates a sound that reduces noise, 7 is an amplifier that amplifies the signal from the controller 5 and drives the speaker 6, 8 is a car audio device, and 9 is a car audio device. This is a circuit for detecting the output state of 8.

An embodiment of this car audio output detection circuit 9 is shown in FIG. 3, and in the case of FIG. 81, and an A/D converter 82 that converts the output of the comparator 81 into a digital signal, and in this embodiment, the car audio device 8
It detects whether it is in the on state or in the off state and notifies the controller 5.

In addition, in the case of FIG. 8B, the line output from the car audio device 8 is converted to direct current by the diode D1, smoothed by the resistors R1 and R2 and the capacitor CI, and then converted into a digital signal by the A/D converter 82. In this embodiment, the volume of the car audio device 8 is outputted and detected in an analog manner.

FIG. 4 shows an embodiment of the controller shown in FIG. 2. In this embodiment, it is composed of an adaptive digital filter, and adaptive algorithms include the well-known steepest descent method, learning identification method, etc. Examples include the LMS method, and the LMS method is used here.

In addition, n Z bows represent delay elements for delaying engine vibration X (n) for each sample, and n h(0
)~h (n-1) is a filter (tap) coefficient for multiplication for each delay element Z-1, and each filter coefficient is determined by the LMS algorithm, that is, h(i+1)=h(i)
+2 updated every sample according to e(n)X(ni). However, i=0...n, μ is the step size described above.

In this case, the step size μ is determined in accordance with ○N10FF of the car audio device 8 as shown in FIG. Choose a smaller size so that

Further, in the case as shown in FIG. 3(b), the step size μ is changed in inverse proportion to the output voltage from the A/D converter 82 as shown in FIG. That is, the larger the output volume of the car audio device 8, the greater the influence of the disturbance sound, so the step size μ is made smaller (or may be made zero).

After variably setting the step size μ as described above, a convolution operation is performed in which the filter coefficient is multiplied by the engine vibration X(n) of each sample and the output signal is sent to the speaker 6 via the amplifier 7. y(n) is found.

By subtracting this speaker output y (n) from the sound pressure Y (n) actually observed near the driver's ear, the output from the microphone 4 e (n) = Y (r
o y (nl is generated, and based on this, LM
By updating the filter coefficients using the S algorithm, it is possible to gradually identify the inverse transfer function G-1 of the transfer function G of the vibration system in the vehicle interior, and to make the microphone output e (nl converge to the minimum value) I can do it.

It should be noted that the engine vibration signal It can be converged.

(Effects of the Invention) As described below, the vehicle interior noise reduction device according to the present invention uses an adaptive controller in which the adaptive step size is variably set according to the output state of the car audio. The inverse transfer function of the transfer function of the cabin vibration system up to the ears is identified from the engine vibration signal and the microphone output, and the speaker cancels out the cabin noise caused by the engine vibration. In addition to being able to cancel out all the rotational order components caused by engine explosion other than the engine explosion, as shown in FIG. It can be seen that residual noise is suppressed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the principle of a vehicle interior noise reduction device according to the present invention. FIG. 2 is a schematic configuration diagram showing an embodiment of the vehicle interior noise reduction device according to the present invention. FIG. 3 is a diagram showing an embodiment of a car audio output detection circuit used in the present invention, FIG. 4 is a diagram showing an embodiment of a controller used in the present invention, and FIG. 5 is a diagram showing an embodiment of a car audio output detection circuit used in the present invention. FIG. 6 is a graph showing the relationship between the step size and the step size used in the present invention, and is a rotational order ratio analysis diagram showing the effects of the present invention. In the figure, 1 is a vehicle interior, 2 is an engine, 3 is an engine vibration sensor, 4 is a microphone, 5 is a controller, 6 is a driver, 8 is a car audio device, and 9 is a car audio output detection circuit. . In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] An engine vibration detection means, an adaptive controller that identifies an inverse transfer function of a transfer function from the detection signal of the detection means to the ear of the vibration system of the vehicle body, and a speaker that outputs an output signal of the controller into the vehicle interior; The controller includes means for detecting the output state of the car audio and a microphone for detecting all vehicle interior noise, and the controller changes the adaptive step size according to the output state of the car audio so that the input of the microphone is minimized. A vehicle interior noise reduction device characterized by controlling the speaker.