JPH04246221A - Noise suppressing device - Google Patents

Abstract

PURPOSE:To obtain a noise suppressing device which can extend noise eliminating frequency area, simplify construction, miniaturize, and reduce cost. CONSTITUTION:A noise suppressing device of resonance type is provided with a resonant noise suppressing chamber 4 or a side branch resonant tube which is connected to an air hose 3 through a connecting hole 5. In the device, a bellows 6 which varies the length of the connecting hole 5 or side branch resonant tube by telescoping it due to pressure in the resonant noise eliminating chamber 4 or side branch resonant tube is provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffling device for muffling noise generated in an air flow pipe, and more particularly to a muffling device having a structure that widens the muffling frequency range.

0002

2. Description of the Related Art The frequency of noise generated in air flow pipes may change depending on various conditions. For example, the frequency of intake noise generated in an intake pipe or exhaust sound generated in an exhaust pipe of an internal combustion engine changes moment by moment approximately in proportion to the rotational speed of the internal combustion engine. In order to keep such changing noise constantly low, it is necessary to provide the air flow pipe with a muffling device having a wide muffling frequency range. There are various ways to widen the silencing frequency range of a silencing device depending on the silencing mechanism. For example, the following silencing devices are known.

[0003] Japanese Utility Model Publication No. 60-23245 discloses that the opening area of a through hole communicating with an intake pipe and a resonance silencing chamber is made variable by a slide cylinder, and the slide cylinder is used as an engine for detecting the rotational speed of an internal combustion engine. A resonance type muffler is shown in which the aperture area is changed according to the rotational speed by being driven by a /V converter and a potentiometer connected thereto (first conventional example).

Japanese Utility Model Application Publication No. 59-39760 discloses a bellows system in which the opening area of a resonance hole that communicates between a conduit and a resonance silencing chamber is made variable by a slide valve, and the slide valve is actuated by the negative pressure of the resonance silencing chamber. A resonance type muffling device is disclosed in which the opening area is changed in proportion to the negative pressure by driving with the above (second conventional example).

[0005] Japanese Utility Model Publication No. 61-202617 discloses that the cross-sectional area of a communication pipe that communicates the flow air pipe and the resonance muffling chamber is made variable by a bellows, and the bellows is expanded and contracted by back pressure in the communication pipe. A resonance type muffling device is shown in which the cross-sectional area is changed according to the back pressure (third conventional example).

[0006] Japanese Utility Model Application Publication No. 59-41664 discloses that the volume of a resonant silencing chamber communicating with the intake pipe is made variable by a bellows, and by expanding and contracting the bellows by the intake negative pressure, the volume is adjusted to the intake negative pressure. A resonance type muffling device is shown in which the noise is changed according to the noise level (fourth conventional example).

[0007]

[Problems to be Solved by the Invention] However, in the above-mentioned first conventional example, a control device such as an F/V converter,
Since an actuator such as a potentiometer is required, the structure becomes complicated and the cost increases significantly.

In addition, in the above-mentioned second to fourth conventional examples, since the bellows was used for the purpose of varying the opening area of the resonance hole, the cross-sectional area of the communication pipe, or the volume of the resonance silencing chamber, the resonance silencing The bellows must be prepared as an addition to the parts constituting the chamber and the communication hole, which increases the number of parts and material costs.

An object of the present invention is to solve the above-mentioned problems and provide a silencing device that not only can widen the silencing frequency range but also has a simple and compact structure and can suppress cost increases. be.

0010

[Means for Solving the Problems] In order to achieve the above object, the silencing device of the present invention as set forth in claim 1 is a resonant type silencing device in which a resonant silencing chamber is provided which communicates with the flow air pipe through a communication hole. The muffling device is characterized in that a bellows is provided that expands and contracts due to the negative pressure in the resonance muffling chamber to change the length of the communication hole.

[0011] Further, the muffling device of the present invention as set forth in claim 2 is a side branch resonant type muffling device provided with a side branch resonant pipe communicating with a flow air pipe, in which the muffling device expands and contracts due to the negative pressure in the side branch resonant pipe. The present invention is characterized in that a bellows is provided for changing the length of the side branch resonance tube.

[0012] Here, the "flow air pipe" is not limited to any particular pipe as long as it is a pipe through which gas flows, and may include, for example, an intake pipe or an exhaust pipe of an internal combustion engine. In addition, a "resonant silencing chamber" is not limited to a specific shape or size as long as it has a volume necessary to resonate at a desired silencing frequency; room,
One example is a cylindrical muffling chamber provided coaxially around the outer periphery of the air flow pipe. In addition, "communicating hole" includes not only a simple hole with almost no length, but also a tubular hole with a clear length, and examples of the opening shape include circular, oval, oval, triangular, quadrilateral, etc. Can be done.

[0013] Furthermore, the "side branch resonance pipe" is not limited to a particular shape or size as long as it has a length necessary to resonate at a desired silencing frequency. These may include tubes or resonant tubes extending radially from the airflow conduit. Further, the "bellows" may be provided in a part of the communication hole or the side branch resonance tube, or may be provided in the entirety.

[0014]

[Operation] First, when the flow rate of gas flowing in the airflow pipe is low, the frequency of noise generated in the airflow pipe is generally low. At this time, the negative pressure in the flow air pipe is weak, and the negative pressure generated in the resonance silencing chamber or side branch resonance pipe is also weak.
The bellows hardly contracts, and the length of the communicating hole or side branch resonant tube hardly decreases. Then, the resonance silencing frequency of the resonant silencing chamber or side branch resonant tube is kept low and matches the frequency of the noise.

[0015] Next, when the flow rate of the gas flowing in the air flow pipe is high, the frequency of the noise generated in the air flow pipe generally becomes high. At this time, the negative pressure in the flow air pipe becomes stronger, and the negative pressure generated in the resonance silencing chamber or side branch resonance pipe also becomes stronger, so the bellows contracts and reduces the length of the communication hole or side branch resonance pipe. . Then, the silencing frequency due to resonance of the resonant silencing chamber or the side branch resonant tube becomes high, and can be synchronized with the frequency of the noise.

[0016] In this way, by changing the silencing frequency in synchronization with the noise frequency, the silencing frequency range can be efficiently expanded. In addition, the structure for expanding the silencing frequency range can be constructed from the bellows, which is a simple, small, and small number of parts, and the bellows forms part or all of the communicating hole or side branch resonance pipe. so you can use it like so:
This is effective in reducing the number of parts or material costs.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention is embodied in a resonance type muffling device provided in an intake pipe of an internal combustion engine will be described with reference to FIGS. 1 to 3. A resonance muffling chamber 4 formed in a box shape made of synthetic resin is provided adjacent to the outside of an air hose 3 serving as an intake pipe connecting an air cleaner 1 and a fuel injection device 2 of an internal combustion engine. The air hose 3 and the resonance muffling chamber 4 are communicated with each other via a tubular communication hole 5. The resonance frequency of the resonant silencing chamber 4, that is, the silencing frequency f0, is expressed by the following equation 1.

[0018]

[Equation 1] f0 = (C/2π)・√(S/(V・Lp
)) Here, C = 331.5 + 0.61t: Speed of sound (m/sec) S = πD2 /4: Cross-sectional area of communication hole 5 D:
Diameter V of communication hole 5: Volume of resonance silencing chamber 4 Lp = L1 +0.8D L1: Length t of communication hole 5: Temperature (℃)

Cross-sectional area S of the communicating hole 5 and resonance muffling chamber 4
Since the volume V is constant, the shorter the length L1 of the communicating hole 5, the higher the silencing frequency f0 becomes. Now, since the frequency fi of the intake noise generated in the air hose 3 increases approximately in proportion to the rotational speed of the internal combustion engine, the length L1 of the communication hole 5 should be adjusted appropriately as the rotational speed of the internal combustion engine increases. If the silencing frequency f0 is decreased at a certain rate of decrease, the intake sound frequency fi
It can be increased by synchronizing with

Therefore, in this embodiment, attention is paid to the fact that as the rotational speed of the internal combustion engine increases, the air pressure inside the air hose 3 decreases and the negative pressure becomes stronger. A bellows 6 whose length can be changed is provided. The bellows 6 is formed of rubber into a bellows shape so as to constitute the entire communication hole 5, and expands and contracts by the negative pressure generated in the resonance muffling chamber 4 communicating with the air hose 3.

Next, the operation and effect of the silencer of the first embodiment constructed as above will be explained. First, when the rotational speed of the internal combustion engine is low, the intake sound frequency fi is also low. At this time, since the negative pressure inside the air hose 3 is weak and the negative pressure generated in the resonance muffling chamber 4 is also weak, the bellows 6 hardly contracts as shown in FIG.
hardly decreases. Then, as is clear from Equation 1 above, the silencing frequency f0 due to the resonance of the resonant silencing chamber 4
is kept low and corresponds to the intake sound frequency fi mentioned above. Of course, this coincidence is based on the premise that the volume V of the resonant silencing chamber 4 and the cross-sectional area S of the communication hole 5 are appropriately set, but this setting can be easily done based on Equation 1 above. It can be carried out.

Next, as the rotational speed of the internal combustion engine increases, the intake sound frequency fi also increases. At this time, air hose 3
As the negative pressure inside becomes stronger and the negative pressure generated in the resonance muffling chamber 4 also becomes stronger, the bellows 6 contracts as shown in FIG.
The length L1 of the communication hole 5 is decreased. Then, as is clear from Equation 1 above, the silencing frequency f0 due to the resonance of the resonant silencing chamber 4 becomes high, and can be synchronized with the intake sound frequency fi. Of course, this synchronization is based on the premise that the reduction rate of the length L1 of the communication hole 5 is appropriately set, but this setting can be easily performed by selecting the bellows 6 or the like.

As described above, according to the silencing device of the first embodiment, the silencing frequency range can be efficiently expanded by changing the silencing frequency f0 in synchronization with the intake sound frequency fi. Further, the structure for expanding the silencing frequency range can be constructed from the bellows 6, which is a simple, small, and small number of parts. As a result, the structure is simpler and more compact than conventional silencers of this type, and cost increases can also be suppressed.

Next, a second embodiment of the silencer shown in FIGS. 4 and 5 will be explained. This second embodiment is a side branch resonance type muffler, and instead of the resonance muffler chamber 4 and the communication hole 5 in the first embodiment, the air hose 3 is provided with a side branch resonance pipe 7 communicating therewith. ing. The resonance frequency, that is, the silencing frequency f0 of this side branch resonance tube 7 is expressed by the following equation 2.

[0025]

[Math. 2] f0 = (2n-1)C/4L2 where, n
=1,2,...C =331.5+0.61t: Speed of sound (m/sec)
L2: Length t of side branch resonance tube 7: Temperature (
℃)

Therefore, the length L of the side branch resonance tube 7
2 is shorter, the silencing frequency f0 becomes higher. Therefore,
As in the first embodiment, if the length L2 of the side branch resonance pipe 7 is decreased at an appropriate reduction rate as the rotational speed of the internal combustion engine increases, the silencing frequency f0 can be synchronized with the intake sound frequency fi. can be made higher. Therefore, in this embodiment, a bellows 6 is provided which expands and contracts due to the negative pressure inside the side branch resonance tube 7 to change the length L2 of the side branch resonance tube 7. The bellows 6 is formed of rubber into a bellows shape so as to constitute a part of the side branch resonance tube 7.

According to this second embodiment, when the rotation speed of the internal combustion engine is low, the bellows 6 hardly contracts, as shown in FIG. 4, and the length L2 of the side branch resonance pipe 7 decreases.
hardly decreases. Therefore, the silencing frequency f0 is kept low and matches the intake sound frequency fi. Furthermore, as the rotational speed of the internal combustion engine increases, the bellows 6 contracts, reducing the length L2 of the side branch resonance tube 7, as shown in FIG. Therefore, the silencing frequency f0 becomes high and can be synchronized with the intake sound frequency fi. Therefore, this second embodiment also has the same effects as the first embodiment.

It should be noted that the present invention is not limited to the configuration of the above-mentioned embodiments, but can be modified and embodied as desired without departing from the spirit of the invention.

[0029]

[Effects of the Invention] Since the silencing device of the present invention is constructed as described above, it is possible not only to widen the silencing frequency range, but also to have a simple and compact structure, thereby suppressing an increase in cost. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a bellows in an extended state in a first embodiment.

FIG. 2 is a sectional view of the bellows in a contracted state in the first embodiment.

FIG. 3 is a front view showing the installed state of the first embodiment.

FIG. 4 is a cross-sectional view of the bellows in an extended state in the second embodiment.

FIG. 5 is a sectional view of the bellows in a contracted state in the second embodiment.

[Explanation of symbols]

3 Air hose as a flow air conduit 4 Resonance muffling chamber 5 Communication hole
6 Bellows 7 Side branch resonance tube

Claims (2)

[Claims] 1. A resonance type muffling device including a resonant muffling chamber communicating with a flow air pipe through a communication hole, wherein a bellows expands and contracts depending on the air pressure in the resonant muffling chamber to change the length of the communication hole. A silencing device characterized by being provided with. 2. A side branch resonance type silencer provided with a side branch resonance tube communicating with a flow air pipe, wherein the side branch resonance tube expands and contracts depending on the air pressure inside the side branch resonance tube to change the length of the side branch resonance tube. A silencer characterized by having a bellows.