JPH04287732A - Active noise control device for vehicle - Google Patents

Abstract

PURPOSE:To satisfactorily reduce load noise without making a detecting system large-sized and complex by efficiently detecting the vibration frequency of the load noise generated from individual wheels with one frequency detector. CONSTITUTION:One frequency detector 10 is installed at a position at nearly the same distance from individual wheels on the cross member 20 of a vehicle body floor 2, and its detection signal is fed to a controller 14. The controller 14 receives the detection signal P of a microphone 12 provided at the ear position EA and drives a loud speaker 16.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control device that reduces noise transmitted to the cabin of a vehicle by interfering with control sound emitted from a control sound source such as a loudspeaker. The present invention relates to an active noise control device suitable for reducing road noise (tire noise) containing random, broadband frequency components.

0002

2. Description of the Related Art Hitherto, active noise control devices of this type are known, for example, as described in British Patent Publication No. 2149614. This conventional device is applied to closed spaces such as aircraft cabins and similar cabins, and includes a plurality of microphones that are fixedly installed in the closed space to detect sound pressure at the positions, and two microphones located in the closed space. A plurality of loudspeakers that emit secondary sounds, a frequency detector that detects frequencies f0 to fn of a single noise source such as an engine located outside a closed space, and detection signals of a plurality of microphones and a frequency detector. and a signal processor that drives a plurality of loudspeakers based on the detection signal. The signal processor generates detection signals Pn (n=1, 2,..., m) of a plurality of microphones,
That is, the sum of squares of the sound pressure P: is used as an evaluation function, and each speaker is adaptively controlled using the LMS method, which is one of the steepest descent methods, so as to minimize this evaluation function P.

[0003] Thereby, the secondary sound radiated from the loudspeaker and the primary sound transmitted from the noise source interfere with each other, thereby reducing residual noise at each observation position. In this way, this conventional device uses a frequency detector (in a vehicle, for example, a muffled sound synchronized with engine rotation) as the target noise (in a vehicle, for example, a muffled sound synchronized with the rotation of the engine). Since the speaker drive signal is generated by processing the reference input signal from the crank angle pulse detector (which outputs a predetermined number of pulses), only one frequency detector needs to be installed at one location.

0004

[Problem to be solved by the invention] The above-mentioned conventional device is
Consider the case where the method is applied to reducing vehicle road noise. Road noise is an irregular and wide-ranging sound that is caused by the vibrations caused by tires coming into contact with the undulations of the road surface and propagates through the suspension system, vehicle body members, and vehicle floor to the occupant's ears. It has the characteristic that it contains a frequency component and increases as the vehicle speed increases. Furthermore, since each wheel is a sound source, road noise has the peculiarity that it includes sounds that are generated without correlation to each other.

For this reason, when the above-mentioned conventional device is applied to such road noise reduction, there is a low correlation between the vibration at one wheel position and the sound pressure at the ear position of the driver's seat in the vehicle, and the vibration at any one wheel position is low. There is a problem in that simply using the output reference signal of the frequency detector for the vehicle does not necessarily have a sufficient effect of reducing road noise at the passenger's ear position.

[0006] Therefore, in order to improve the road noise reduction effect, in the case of a normal vehicle, at least a frequency detector is installed for each wheel, and the four channels of reference input are used.
A configuration that aims to improve detection accuracy is possible. Furthermore, it is conceivable that vibration frequency detectors are provided separately in the X, Y, and Z axis directions at each detection position, resulting in a total of 12 channels of detection configuration, in which each is controlled individually. However, in these multi-channel configurations, the entire system becomes large and
A problem arises in that the computational processing load increases and the manufacturing cost increases.

The present invention has been made in view of such problems with conventional devices, and also satisfactorily reduces vehicle road noise, simplifies the configuration for detecting the noise reference frequency, and improves the performance of the device. The purpose is to avoid increasing the size.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the invention as set forth in claim 1 provides a control sound source capable of generating control sound into a vehicle cabin to which noise is transmitted from a noise source on the road surface and between the wheels; a frequency detector for detecting the frequency of noise generated by the noise source; a noise detection means for detecting sound pressure at a predetermined sound receiving point in the vehicle interior; a detection value of the noise detection means; and a detection value of the frequency detector. and a controller that drives the control sound source so that the detected value of the noise detection means is minimized based on They are placed at equidistant positions or in the vicinity.

[0009] Furthermore, the invention according to claim 2 has a structure in which the members in the configuration according to claim 1 are connected at one point approximately equidistant from each ring by a plurality of highly rigid rod-shaped members connected to a noise source. A frequency detector is provided at the connection point.

0010

[Operation] In the present invention, the rigidity of the member on which the frequency detector is installed is higher than that of other materials such as floor panels, so the vibrations of road noise generated by each wheel are transmitted to the detector position at a high speed. However, the vibrations generated by the four wheels overlap and are detected by a frequency detector. This eliminates the need for a four-channel configuration for detecting road noise for each wheel, so it is not necessary to increase the size of the device. and,
By using the control sound radiated from the control sound source, it is possible to satisfactorily reduce the high-power radiated sound (that is, the sound that makes up most of the noise) from the floor panel, which transmits vibrations at a slow speed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 4 of the accompanying drawings. In this embodiment, an ordinary passenger car is used as the vehicle, and road noise (tire noise) is reduced.

In FIG. 1, reference numeral 2 indicates a vehicle body floor, 4 indicates a wheel, 6 indicates a suspension between the vehicle body 2 and the wheels 4, and 8 indicates an active noise control device mounted on this vehicle. Here, the contact between the road surface and the wheels 4 becomes a source of noise.

The active noise control device 8 includes a frequency detector 10 that detects the frequency of noise from a noise source as a reference signal.
, a microphone 12 as a noise detection means installed in the vehicle interior, and a controller 1 installed at a predetermined position in the vehicle.
4 and a loudspeaker 16 as a control sound source. The frequency detector 10 is composed of, for example, a vibration sensor, and is installed on the cross member 20 at approximately the intersection point A of the center console 2a of the vehicle body floor 2 and the front cross member 20 in the center, and transmits the detection signal x to the controller. Output to 14. The installation position A is approximately equidistant from the four wheels, and the front cross member 20 is located close to the side members 2 on both sides.
1.

The microphone 12 is installed, for example, near the head rest of the seat, and supplies a signal P corresponding to the sensed sound pressure to the controller. Furthermore, controller 1
4 calculates a speaker drive signal SX that minimizes the evaluation function based on the detection signals x and P using, for example, the LMS method, which is one of the steepest descent methods described above, and sends this signal SX to the loudspeaker 16. Output. The loudspeaker 16 is
It is installed in a position such as the front dash of the vehicle interior and opens into the vehicle interior, and generates control sound (cancelling sound) in response to the speaker drive signal SX supplied from the controller 16. In FIG. 1, EA is the reference ear position of the occupant, that is, the sound receiving point.

The floor structure shown in FIG. 1 is obtained by combining a general monocoque body 22 shown in FIG. 2 with a power train (power transmission mechanism) 24 shown in FIG. 3. At this time, the power train 24 is necessarily connected to the side members 21 and the front cross member 20 in a highly rigid manner.

[0016] The fact that active noise control is possible will now be explained. First, as a prerequisite for active noise control to be possible, from the noise source (tire position) to the ear position E.
It is necessary that the signal transmission time from the noise source to the ear position EA via the controller 14 and loudspeaker 16 is shorter than the signal transmission time to A.

The vibroacoustic transmission time from the noise source to the ear position EA can be estimated by the following formula. That is, the transmission speed Ct of longitudinal waves and the transmission speed Cy of transverse waves of vibroacoustic waves are approximately expressed as follows: Ct=E/ρ Cy=(E·I/(A·ρ))1/4·ω1/2. E: modulus of longitudinal elasticity, I: moment of inertia, ρ: density of member, A: cross-sectional area of member, ω: angular velocity (
=2πf).

[0018] Therefore, when the transverse wave transmission speed is calculated for a typical member used in a car body structure, assuming that the member is steel, the result is as shown in Fig. 4. In the figure, curve a is a hollow prism (50 x 53 mm), and curve b is a round bar (20 mm diameter).
, curve c is for a plate (300 x 300 x 6 mm). From these results, the transmission speed of a member with high rigidity (in this example, a hollow prismatic column) is significantly faster than that of a member with low rigidity (in this example, a round bar, plate), and the higher the frequency, the faster the transmission speed becomes. It can be seen that the speed is also faster. Note that although the longitudinal wave has a constant value (approximately 5000 m/s) regardless of the frequency, experiments have shown that its energy is small and can be almost ignored as road noise.

Now let us consider the transmission time. Based on the data in FIG. 4, let us calculate the time it takes for a 150 Hz sound to travel to each point in FIG. 1. According to the above formula, the transmission time from the front wheel, which is one of the sound sources, to the installation position A of the frequency detector 10, which is 1.5 m away, is approximately 5 msec. The transmission time to the center position B of the floor panel 2b, which is 1.2 m away for the 21 section and 0.3 m for the panel 2b section, is about 10 msec. In other words, since the floor panel 2b has low rigidity and a slow transmission speed, the signal propagates to installation position A, which follows a path consisting only of members 21 and 20, which are highly rigid structures, about 5 msec faster than to point B. It should be noted that it is not the members 20 and 21 that emit the high-energy sound, but the floor panel 2b, which has a wide surface and has a large vibration amplitude.

As a result, the active noise control device 8 takes approximately 5 msec from monitoring the vibration of the front cross member 20 to causing the loudspeaker 16 to emit the control sound.
Since there is sufficient time for this, active noise control becomes possible.

Next, the effects of this embodiment will be explained. Noise vibrations generated between the road surface and the tires are transmitted to the vehicle body members 21, 20 and the vehicle floor 2 via the suspension 6 (see arrows in Figure 1), and then the vibrations become noise (road noise). radiated into the passenger compartment.

At this time, the noise vibrations are transmitted through the members 21 and 20 faster than through the floor panel 2b, and the vibrations transmitted earlier are detected by the frequency detector 10, and the detection signal x is sent to the controller. 14. Since the controller 14 calculates the speaker drive signal SX based on the detection signal x and outputs it to the loudspeaker 16, the loudspeaker 16 emits a control sound that can reduce road noise at appropriate phase timing.

[0023] In parallel with this, the noise vibrations that have reached the floor panel 2b with a delay are radiated from the floor panel 2b into the vehicle interior as high-power road noise. Therefore, the road noise (transverse waves) radiated from the floor panel 2b and the control sound that reduces this mainly reach the ear position EA of the occupant, and the road noise that the occupant can hear is reduced. This reduced residual sound is further sensed by microphone 12 and controller 14 drives loudspeaker 16 to further reduce this residual sound. As a result,
Road noise audible to passengers is minimal.

As described above, in this embodiment, the position of the highly rigid member where the noise vibration transmission speed is high, and
Active noise control is performed by detecting the frequency of noise vibration at a single position A that is approximately equidistant from the ring. Therefore, even if a detector for detecting the frequency of road noise of each wheel is not provided for each suspension 6, noise vibrations of each wheel can be detected in a combined (summed) state. Therefore, there is no need to make the system large and complicated as a four-channel detection configuration, and a simple configuration is sufficient, yet efficient noise control is possible.

Furthermore, since the detection point A has high rigidity, it is affected by rigid vibrations and elastic vibrations of the vehicle body, and low frequency components generated by these vibrations are also detected by the frequency detector 10. Ru. Therefore, there is an advantage that the same noise control device 8 exerts a reduction effect on such low-frequency components as well, and simultaneously reduces unpleasant sounds caused by such low-frequency vibrations. Furthermore,
Even when the vehicle body is vibrated due to the occurrence of large vehicle interior cavity resonance, the frequency detector 10 detects the vibration at the detection point A with the resonance vibration superimposed, so that noise caused by the resonance is detected. active reduction is also achieved.

[0026] According to the calculation of the transmission time described above, even if the position of the frequency detector 10 differs by about 0.5 m, the resulting delay or advance is only about 1 msec. Therefore, in consideration of the seating position of the occupant, the frequency detector 10 may be installed at a position slightly closer to the front than a position equidistant from the four wheels.

Next, other embodiments will be explained using FIGS. 5 and 6. The frame structure 30 of the vehicle body shown in FIG. 5 is a structure without a cross member, which is called a peripheral frame, and also generates unpleasant low-frequency noise. In such a case, a highly rigid bar 3 as a member is placed in an X shape.
2 and 32, and set the point where they cross at approximately the same distance from each ring. Then, at that cross point,
As shown in FIG. 3, a frequency detector 34 for detecting vibrations is connected so that road noise vibrations from each wheel can be detected in a combined state. The other configurations are the same as those of the previous embodiment. Even in the case where there is no cross member, by adding the highly rigid bars 32, 32, the vibrations of the highly rigid parts around the frame structure 30 can be transmitted to the detector 34 at a high transmission speed. It is possible to obtain the same effects as in the example.

[0028] In addition to the above-mentioned body members, the vehicle body member in the present invention may be, for example, a rear cross member or a member for installing a seat.

[0029]

As described above, the present invention provides a frequency detector for detecting a noise frequency as a reference signal at a position equidistant from each wheel of a highly rigid member that supports a vehicle and a power train, or at a position equidistant from each wheel. Since it is installed nearby, the time required for the noise vibration to reach the frequency detector is
Due to the high rigidity of the member, it is short, and one frequency detector can detect the combined road noise generated between the four wheels and the road surface, making it an ideal detection position for road noise. , four-wheel road noise can be efficiently reduced using a simple one-channel detection configuration. This makes it possible to avoid the need to increase the size and complexity of the device by installing four-channel detection mechanisms for the four wheels in order to reduce road noise. This reduces manufacturing costs and improves road noise. A reduction effect can be obtained.

Furthermore, the secondary effect is that it can also reduce low frequency vibrations caused by rigid vibrations and elastic vibrations of the vehicle body, as well as vibrations caused by large cavity resonances in the vehicle interior. can get.

[Brief explanation of the drawing]

FIG. 1 is a partially block configuration diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view showing a monocoque body of a passenger car.

FIG. 3 is a perspective view showing the power train.

FIG. 4 is a graph showing the relationship between transverse waves and vibration frequency using members with different rigidities as parameters.

FIG. 5 is a perspective view of a frame structure according to another embodiment of the present invention.

6 is a partially enlarged view showing how the frequency detector is mounted in the embodiment of FIG. 5; FIG.

[Explanation of symbols]

2 Vehicle floor 4 Wheels 8 Active noise control device 10 Frequency detector 12 Microphone 14 Controller 16 Loudspeaker 20 Cross member 21 Side member 32 High rigidity bar 34 Frequency detector

Claims (2)

[Claims] 1. A control sound source capable of generating control sound into a vehicle interior through which noise is transmitted from a road surface and a noise source between wheels; a frequency detector that detects the frequency of noise generated by the noise source; noise detection means for detecting sound pressure at a predetermined sound receiving point; and the control so that the detection value of the noise detection means is minimized based on the detection value of the noise detection means and the detection value of the frequency detector. and a controller for driving a sound source, and the frequency detector is provided at or near a position equidistant from each wheel of a highly rigid member that supports the vehicle and the power train. Noise control device. 2. The member includes a structure in which a plurality of highly rigid rod-shaped members connected to a noise source are connected at one point approximately equidistant from each ring, and the frequency detector is located at the position of the connection point. The active noise control device for a vehicle according to claim 1, further comprising: an active noise control device for a vehicle.