JPH06301388A - Vibration radiation sound decreasing device - Google Patents

Abstract

PURPOSE:To provide the device which decreases the noises of a low-frequency range generated in the passenger room of an airplane, etc., and decreases the noises generated in consequence of the vibrations of the plane together with the plane vibrations by exciting the vibrating plane with a vibration mode of the opposite phase from the phase of the plane vibrations and of the same frequency and amplitude as the frequency and amplitude of the plane vibrations. CONSTITUTION:This device consists of a vibration sensor B which detects the vibration mode of the plane frame consisting of outside plates 1 and frames 2 which are the major cause for the low-frequency range noises, a controller C which determines the resonance mode of the plane frames from the vibration mode signal 6 from this vibration sensor B and calculates and outputs a second vibration mode signal 7 effective for negating this resonance mod and an exciter A which excites the plane frame by the excitation force meeting the output signal from this controller C. The device is constituted to decrease the noises by decreasing the vibrations of the plane frames which are the source for the noises from the decrease of the noises by using the vibration attenuation by the conventional vibration-damping materials and to particularly decrease the noises of the low-frequency range which are heretofore particularly difficult to be decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is caused by vibration of a machine body frame by monitoring the vibration of the machine body frame and exciting the machine body frame with a vibration force having a phase opposite to the vibration to reduce the vibration. The present invention relates to a device for reducing low frequency noise in a passenger room.

[0002]

2. Description of the Related Art Conventionally, as shown in FIGS. 4 and 5, a frame 2 attached to a skin 1 of an aircraft including a helicopter, or a stringer as the case may be, is used as a constraining layer to reduce noise in a low frequency range generated in an aircraft cabin. The effect was obtained by attaching the vibration damping material 4.

As for the noise in the passenger compartment in the low frequency range, as shown by the dotted line in FIG. 3, the structure of the aircraft body, mainly the outer skin 1 and the frame 2
It becomes large in the frequency range corresponding to the vibration mode of the body frame consisting of, but conventionally, as shown in FIG. 4, a damping material 4 and a restraining layer 5 for restraining the damping material 4 are attached to the frame 2 in order to reduce the vibration of the body frame. By relying on these stiffnesses, we focus on the frequencies corresponding to the vibration modes of the aircraft frame that increase the noise in the cabin, and greatly reduce the vibration of the aircraft frame, thereby reducing low-frequency noise in the cabin. No measures such as letting it happen were taken.

[0004]

The following problems have been encountered in the noise reduction by the conventional damping material with constraining layer.

(1) In the noise reduction by the vibration damping material 4, the vibration damping effect of the vibration does not largely change depending on the frequency, and the vibration damping of the vibration damping material 4 only reduces the vibration of the body frame. Therefore, the vibration damping effect does not change significantly even at the frequency corresponding to the vibration mode of the body frame, and the vibration still remains at the frequency corresponding to the vibration mode.

(2) When the damping material 4 is attached to the frame 2 as shown in FIG. 4, it is necessary to closely attach the damping material 4 to the two orthogonal surfaces of the frame 2 in order to exert the damping effect. Therefore, the constraining layer 5 must be continuously attached for 2 m or more in the longitudinal direction of the frame, and the frame 2 is attached to the outer plate 1.
Since it is necessary to form the member in such a manner that it is curved along the shape of, the manufacturing and mounting of these members become a very troublesome work, resulting in an increase in cost.

(3) Since the damping material 4 is attached to the frame 2, it becomes difficult to inspect the frame 2 on or near the surface where the damping material 4 is attached, and it is inspected for cracks and corrosion that are indispensable for the strength members of the aircraft. But it was very difficult.

The present invention solves the drawbacks and problems of the above-described conventional reduction device, effectively reduces the noise in the low frequency range that has been difficult to reduce in the airframe, and reduces the conventional noise. An object of the present invention is to provide a vibration radiated sound reducing device that avoids the difficulty in working due to installation of the device or the problem in checking structural materials.

[0009]

Therefore, the vibration radiated sound reducing apparatus of the present invention detects the vibration mode of the machine frame constituting the machine body in the apparatus for reducing the low frequency band noise caused by the machine vibration. A vibration sensor that outputs a signal, a control device that inputs a vibration mode signal from the vibration sensor and calculates and outputs a second vibration mode signal that cancels the vibration mode, and a control device that inputs the second vibration mode signal And a vibration exciter that vibrates the body frame according to the second vibration mode signal.

[0010]

[Function] The vibration of the machine frame is measured by the vibration sensor, the machine frame vibration mode is found by the control device, the output of the exciter is calculated by the control device so as to reduce the machine frame vibration mode, and the vibration is excited. It is possible to reduce noise in the low frequency range due to the vibration of the machine body frame inside the machine body by outputting to the machine and exciting the machine body frame with the shaker.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vibration radiation noise reducing apparatus of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 are views showing a vibration radiated sound reducing apparatus as an embodiment of the present invention. A small vibration exciter A is attached to a frame 2 which constitutes a structural member of an aircraft such as an aircraft including a helicopter. The structural member vibrates due to the exciting force of the propulsion engine or the air flow, and noise in the low frequency range propagates in the passenger compartment. This low-frequency noise not only makes passengers or occupants uncomfortable, but it is technically difficult to reduce it. Of the structural members, the vibration of the body frame composed of the frame 2 and the outer plate 1 is applied to the frame 2
The vibration mode signal 6 of the airframe from the vibration sensor B is monitored by the vibration sensor B attached to the controller C.
Send to. The vibration mode consists of the resonance frequency and the amplitude of the machine frame, and the controller C calculates the machine frame vibration mode shown by the dotted line in FIG. 3 based on the input vibration mode signal, and cancels this vibration mode. A second vibration mode having the same amplitude and opposite phase to the vibration mode input to the control device is calculated, and this second vibration mode signal 7 is sent to the small vibration exciter A. The small vibration exciter A is attached to the frame 2, and the vibration of the machine frame is canceled by vibrating the machine frame based on the second vibration mode signal from the control device C, so that the machine frame vibration mode shown by the dotted line in FIG. It is possible to suppress the formation of noise and reduce the low frequency noise generated in the passenger compartment.

Although the present embodiment has been described for the purpose of reducing noise in the cabin of an aircraft, the vibration radiation noise reducing apparatus of the present invention is not limited to these embodiments, and may be, for example, on land. It is also effective when applied to a vehicle or the like that travels.

Also, for the sake of convenience of explanation, it has been explained that the vibration force of the (small) vibration exciter A is caused by the second vibration mode having the same amplitude as that of the vibration mode of the machine body frame. Any vibration mode that effectively reduces the vibration may be used. Further, the machine body frame has been described as consisting of the outer plate 1 and the frame 2, but if the frame is not required for structural strength, it may be composed of only the outer plate 1 or reinforced with other structural members.

[0015]

As described above, according to the vibration radiated sound reducing apparatus of the present invention, in order to reduce the low frequency band noise caused by the vibration of the machine body, the vibration mode of the machine body frame constituting the machine body is detected and the signal is output. A vibration sensor, a control device that inputs a vibration mode signal from the vibration sensor and calculates and outputs a second vibration mode signal that cancels the vibration mode, and a second vibration mode signal that inputs the second vibration mode signal. The machine frame vibration mode is monitored by a simple configuration requirement consisting of a shaker that excites the machine frame according to the vibration mode signal.
The output of the exciter is adjusted by the control device to prevent formation of the aircraft frame vibration mode, thereby suppressing the radiated sound due to the aircraft frame vibration and effectively reducing the low frequency noise generated in the cabin. It can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a vibration radiation noise reduction device of the present invention.

FIG. 2 is a diagram in which a small vibrator as a vibrator constituting the present invention is attached to a frame.

FIG. 3 is a diagram showing a body frame vibration mode of an aircraft.

FIG. 4 is a view in which a conventional constraining layer and a damping material are attached to a frame.

FIG. 5 is a cross-sectional view showing a state in which a conventional constraining layer and a damping material are attached to a frame.

[Explanation of symbols]

 A Small exciter as an exciter B Vibration sensor C Controller 1 Outer plate 2 Frame 3 Floor beam 4 Damper 5 Restraint layer 6 Vibration mode signal 7 Second vibration mode signal

Claims (1)

[Claims] 1. A vibration sensor for detecting a vibration mode of a machine body frame constituting a machine body and outputting the signal in a device for reducing low frequency band noise caused by machine body vibration,
A control device that inputs a vibration mode signal from the vibration sensor and calculates and outputs a second vibration mode signal that cancels the vibration mode; and a control device that inputs the second vibration mode signal and responds to the second vibration mode signal. And a vibration exciter that vibrates the machine body frame.