The present invention relates to a muffling structure of a vent pipe and a muffling structure of a case.
Noise tends to be produced in a vent pipe (such as a duct, an intake pipe, and an exhaust pipe) and a case (such as a case for an air cleaner) provided with a vent pipe. Among them, loud noise tends to be produced in a vent pipe and a case provided in an internal combustion engine, a fuel cell, a blower, and any other intake system. A muffling structure is therefore typically provided in a vent pipe and a case provided with a vent pipe to eliminate the noise. For example, the following Patent Documents 1 and 2 have been known as conventional techniques on a muffling structure of a vent pipe.
Patent Document 1 (Japanese Patent Laid-Open No. 2007-231881) discloses a muffling structure in which a porous portion is provided in a vent pipe. In the muffling structure, the porous portion can function to muffle sound in a wide frequency range.
On the other hand, Patent Document 2 (Japanese Patent Laid-Open No. 2007-231882) discloses a muffling structure using a Helmholtz resonator. In the muffling structure, the Helmholtz resonator can effectively function to muffle sound in a specific frequency range. Further, disposed external to a vent pipe in the muffling structure, the Helmholtz resonator unlikely hinders ventilation, which allows preventing vent resistance in the vent pipe from deterioration.
In the conventional technique disclosed in Patent Document 1, however, the vent resistance in the vent pipe deteriorates because the porous portion provided in the vent pipe hinders ventilation. On the other hand, the Helmholtz resonator can only function to muffle sound in a specific frequency range. Therefore, the conventional technique disclosed in Patent Document 2 cannot muffle sound in a wide frequency range.
The present invention has been made in view of the problems of the conventional techniques. An object of the present invention is to provide a muffling structure of a vent pipe and a muffling structure of a case, which is capable of muffling sound in a wide frequency range and preventing vent resistance in the vent pipe or the case from deterioration.
To solve the problems described above, the present invention provides the following means.
A first aspect of the present invention is a muffling structure of a vent pipe, characterized in that the vent pipe is a primary duct, and that the muffling structure includes vent holes formed in peripheral wall of the primary duct, a cover so provided outside the peripheral wall as to cover the vent holes, activated charcoal contained in the cover, and a ventilative member interposed between the activated charcoal and the peripheral wall.
The first aspect of the present invention is also characterized in that the vent holes are provided in the peripheral wall except the bottom thereof.
A second aspect of the present invention is a muffling structure of a case provided with a vent pipe for introduction purposes and a vent pipe for discharge purposes, characterized in that the muffling structure includes an inner pipe that is disposed in the case and communicates with the introduction vent pipe or the discharge vent pipe, vent holes formed in a peripheral wall of the inner pipe, a cover so provided outside the peripheral wall as to cover the vent holes, activated charcoal contained in the cover, and a ventilative member interposed between the activated charcoal and the peripheral wall.
The second aspect of the present invention is also characterized in that the vent holes are provided in the peripheral wall except the bottom thereof.
The present application claims the priority based on International Application (PCT/JP2008/53815) filed on Mar. 4, 2008, and the contents of which is hereby incorporated in the present application.
The present invention is capable of muffling sound in a wide frequency range and preventing vent resistance in a vent pipe or a case from deterioration.
The present inventors have focused on the fact that activated charcoal has a muffling effect and attained the present invention by using the muffling effect of activated charcoal. To confirm an advantageous effect of the present invention, the present inventors have used a test apparatus 10 shown in
The test apparatus 10 shown in
The noise meter 1 is disposed in a position spaced apart from an upstream end of the primary duct 2 by 100 mm and inclined to the upstream end by 45 degrees. The primary duct 2 is 56 mm in inner diameter and 620 mm in length. The silencer 3 is attached to a substantially central portion of the primary duct 2. One hundred vent holes (10 mm in diameter) are formed in the peripheral wall of the primary duct 2. The silencer 3 has a muffling portion having a volume of 0.5 liter. A bag-like body formed of a ventilative sheet is disposed in the silencer 3. The bag-like body contains 300 cc of particulate activated charcoal (approximately 20 angstroms in average pore diameter). The ventilative sheet is made of a nonwoven fabric and specifically approximately 3 mm in thickness and approximately 80 to 100 μm in pore diameter (average pore size). The volume of the air cleaner 4 is 5 liters. The rubber hose with bellows 6 is 70 mm in inner diameter and 350 mm in length. The volume of the four-cylinder gasoline engine 8 is 2.3 liters.
First, when the silencer 3 is attached to the primary duct 2, the sound pressure (dB) of noise is lowered over all the frequency range, as compared with those in Comparative Examples 1 to 4, as shown in
When the silencer 3 is attached to the primary duct 2, noise is significantly lowered over a wide frequency range (Hz), as compared with the case where no silencer is attached to the primary duct 2, as shown in
A muffling structure of a vent pipe of the present invention will next be described with reference to
The silencer 310 shown in
The silencer 320 shown in
The silencer 330 shown in
In the silencer 340 shown in
The silencer 350 shown in
In a vent pipe provided with any of the silencers of Examples 1 to 5, the activated charcoal can function to muffle sound in a wide frequency range. Further, in any of the cases, no obstacle that may cause vent resistance is provided in the vent pipe. Each of the silencers can therefore prevent vent resistance from deterioration.
A description of a muffling structure of a case of the present invention will next be made with reference to
The case 400 shown in
The silencer 410 is attached to an inner pipe 411, which is provided in the case 400 in such a manner as to communicate with the vent pipe 401. The silencer 410 includes a cover 412, a bag-like body 413, and activated charcoal 414. Vent holes 411a are formed in the peripheral wall of the inner pipe 411, and the cover 412 is so provided as to cover the vent holes 411a. The bag-like body 413 containing the activated charcoal 414 is disposed in the space created by the peripheral wall of the inner pipe 411 and the inner wall of the cover 412.
In the case 400 provided with the silencer 410, the activated charcoal 414 can function to muffle sound in a wide frequency range. Further, although the silencer 410 is attached to the inner pipe 411, no obstacle that may cause vent resistance is provided in the inner pipe 411. The silencer 410 can therefore also prevent vent resistance from deterioration.
The above description is intended to allow the present invention to be readily understood but is not intended to limit the present invention. The present invention, of course, can be changed and modified without departing from the substance and purpose thereof and encompasses equivalents thereof.
For example, as other embodiments of the present invention, silencers 500, 510, 520, 530, and 540 shown in
First, the silencer 500 shown in
Each of the silencer 510 shown in
The silencer 510, however, differs from the silencer 500 in that a nonwoven fabric 514, a compressing plate 515, and a plate spring 516 are provided between the activated charcoal 512 and the lid 501b in this order from the activated charcoal 512 toward the lid 501b.
The silencer 520 differs from the silencer 500 in that the nonwoven fabric 514, a compressing plate 517, and springs 518 are provided between the activated charcoal 512 and the lid 501b in this order from the activated charcoal 512 toward the lid 501b.
The silencer 530 differs from the silencer 500 in that a foam member (such as sponge) 519 is provided between the activated charcoal 512 and the lid 501b.
The silencer 540 shown in
Each of the silencers (that is, the silencers 500, 510, 520, 530, and 540 shown in
The present inventor has investigated an optimum shape of the silencer as indicated in the following items (1) to (7):
Activated charcoal to be used is believed to be more excellent in muffling characteristics when the surface area thereof is larger. When activated charcoal is packed in a container efficiently (at a high density), activated charcoal having a smaller particle diameter is more advantageous. However, powdery activated charcoal having a very small diameter may clog the ventilative sheet and disperse into the atmosphere at the time of packing. It is therefore necessary to control the particle diameter distribution when the powdery activated charcoal is used. Further, since vibration causes activated charcoal to rub against each other into powder, hardness is also an important factor to prevent deterioration of the activated charcoal during use. It is therefore desirable to use activated charcoal controlled under the following conditions: the diameter (initial) equivalent to those of activated charcoal particles obtained under the JIS K1474 test method that pass through a sieve whose aperture size ranges from 0.5 mm to 4.5 mm defined by JIS Z8801, and the hardness being 95% or greater defined by JIS K1474.
The area in which communication holes are formed affects the muffling effect, and providing communication holes in a largest possible area in the longitudinal direction of the duct (enlarging the silencer accordingly) enhances the muffling effect. Providing communication holes across the entire length of the duct is, however, not realistic. In consideration of a realistic amount of activated charcoal and a realistic shape of the silencer, communication holes (and a silencer) may be provided over one-sixth the entire length of the duct in a central portion in the longitudinal direction of the duct. In air-column resonance in a duct, since the primary resonance frequency range most affects the overall muffling effect, a central portion of the duct, where the level of the primary resonance can be greatly reduced and decrease in sound pressure at C2 can be minimized, is an optimum position. It is noted that the diameter of communication holes does not affect the muffling characteristics. Further, the muffling effect does not greatly vary when communication holes whose size is at least 10% of the projected area of the silencer are evenly distributed.
Consider changing the height of a silencer containing activated charcoal (vertical dimension from communication holes). The muffling effect reaches a plateau when the height is approximately 80 mm irrespective of the diameter of the duct. Increasing the height from 80 mm will not enhance the muffling effect. It is therefore effective to limit the height of the silencer to 80 mm at maximum. Further, consider changing the length of a silencer containing activated charcoal (in the longitudinal direction of the duct). It is most preferable to provide communication holes over approximately one-sixth the entire length of the duct in a central portion of the duct, as having been concluded in the section of communication holes in the peripheral wall of a duct. Further, when the area where communication holes are formed is fixed and only the length of the silencer is changed, the muffling effect is hardly affected. The silencer therefore only needs to be long enough to ensure the area in which the communication holes are formed. Moreover, the width of a silencer containing activated charcoal only needs to be equal to the inner diameter of the duct. In consideration of the factors described above, the amount of activated charcoal that is not only effective in muffling sound but also practical can be determined by the following equation: the length (the entire length of the duct/6)×the width (the inner diameter of the duct)×the height (80 mm), which are the inner dimensions of the silencer, =an optimum amount of activated charcoal (cc). When a duct is 56 mm in inner diameter and 600 mm in length, the optimum amount of activated charcoal is 100×56×80≈450 cc.
A silencer containing activated charcoal having a fixed volume shows a substantially same muffling effect irrespective of the shape of the silencer, such as a box-shape silencer and a cylindrical silencer.
(5) Position where Silencer is Disposed
When a silencer containing activated charcoal and having communication holes formed over a length of 100 mm is attached to a longitudinally central portion of a duct, the muffling effect is large in primary resonance, whereas the muffling effect is small in secondary resonance. When a silencer containing activated charcoal is attached to each end portion of a duct (in the position spaced apart from each end by one-fourth the entire length of the duct), the muffling effect is small in primary resonance, whereas the muffling effect is large in secondary resonance. It is most effective to dispose a silencer containing activated charcoal in a node position of the wavelength corresponding to a resonant frequency in question. When a plurality of silencers are attached to node positions of resonant frequencies of primary resonance, secondary resonance, and higher-order resonance, the muffling effect for each of the resonant frequency ranges is large but this approach is not realistic. Since it is most effective to address the primary resonant frequency of the duct when a high priority is placed on the overall muffling effect, a single silencer containing activated charcoal attached to a central portion of the duct provides a large muffling effect, which is the same conclusion as the conclusion on the area in which communication holes are formed.
(6) Comparison with Other Sound-Absorbing Materials
When the contents of the silencer is changed and comparison is made among activated charcoal, glass wool, and sponge (sound-absorbing sponge dedicated to automobile use), the activated charcoal provides the best muffling effect over all frequencies and at C2 and excels in muffling characteristics for each sound pressure level and for each order of the resonance components.
(7) Comparison with Porous Medium
When a silencer containing a porous medium is compared with a silencer containing activated charcoal, the sound at the intake tip is substantially the same, and the silencer containing activated charcoal is better in terms of transmitted sound and vent resistance. Further, a porous medium disadvantageously sucks warm air in an engine room, whereas a silencer containing activated charcoal will not suck warm air because there are no openings that communicate with the atmosphere other than the communication holes in the peripheral wall of the duct.
Number | Date | Country | Kind |
---|---|---|---|
PCT/JP2008/053815 | Mar 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2009/053198 | 2/23/2009 | WO | 00 | 9/30/2010 |