JP4623621B2 - Low noise duct - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low noise duct that is used as an intake duct for introducing outside air into a combustion chamber of a vehicle engine or an air conditioning duct for a vehicle, and is useful for reducing noise.
[0002]
[Prior art]
In recent years, a variety of methods have been adopted so far, for example, in a vehicle air intake duct, in order to reduce noise outside the vehicle. As a typical method, (1) a hole is formed in the duct, and a sheet of glass wool, foamed urethane, non-woven fabric, etc. is attached to absorb the sound so as to close the hole, and (2) generated in the duct. Air column resonance attenuation method using porous materials (fibers, sintered products, etc.) aiming at attenuation of resonances (JP-A-62-84525, etc.), (3) noise in a specific frequency band in the chamber There are attenuation methods using a muffler (resonator) that attenuates diffuse reflection in a single or composite specification.
[0003]
[Problems to be solved by the invention]
However, the methods (1) to (3) have the following problems. Since the glass wool of (1) is expected to be dispersed by the negative pressure of the intake air (it will be scattered apart) as it is, post-processing to maintain the shape is necessary. The urethane foam is basically unsuitable for use in the engine room. One is hydrolysis, which requires a water-stop cover. In addition, heat deterioration is likely to occur, and durability is difficult.
The above (2) is not a method to eliminate noise itself, but rather to increase the noise caused by air column resonance coming from the duct length by reducing the resonance by letting the sound pressure escape from the middle of the duct pipe, and as a result, aim to reduce noise. There was no structure to mute the noise itself. Moreover, like a resonator, it was not possible to target only a specific frequency band. In addition, problems such as inhalation of hot air can be considered. Furthermore, as can also be said to (1), since a communicating porous material is used, there is a possibility that dust and dirt may be mixed into the intake duct, so the so-called primary intake on the intake side from the air cleaner. It could only be used for parts.
The above (3) basically requires a large-capacity chamber, and a large space must be secured in the engine room, and the cost is high.
[0004]
The present invention solves the above-mentioned problems, and achieves low noise without dust intrusion or the like and requires almost no installation space, and is useful for not only an intake duct but also an air conditioning duct or the like. The purpose is to provide.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the gist of the invention described in claim 1 is that a duct body that forms a gas flow path, a part of the duct body at a predetermined portion of the duct body, and a general part of the duct wall A membrane-shaped portion that is integrally formed and whose thickness is thinner than the thickness of the general portion, and surrounds the outer peripheral edge of the membrane- like portion and rises outward from the duct wall of the duct body, A ridge part integrally formed and a separate cap attached to the ridge part so as to cover the film part so that the film part can resonate with sound waves. It is in a low noise duct characterized by the above. A low noise duct according to a second aspect of the present invention is the low noise duct according to the first aspect, wherein the duct body is made of an elastomeric material.
[0006]
If the film-like part formed integrally with the general part and having a thickness smaller than the thickness of the general part as in the invention of claim 1 is capable of resonance vibration with respect to the sound wave, the sound is reduced by the film resonance. it can. Since the sound can be reduced by forming a film-like portion by reducing the thickness of a part of the duct body without making a hole in the duct body, dust or the like does not enter the duct . If a separate cap is attached to the raised part so as to cover the membrane part, an air layer thickness is created between the membrane part and the bottom of the cap. The frequency can be absorbed. If the duct body is made of an elastomeric material as in the invention of claim 2, the sound absorption effect can be further enhanced by the viscoelastic properties of the elastomer.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the low noise duct according to the present invention will be described in detail. 1 to 7 show an embodiment of the low noise duct according to the present invention. FIG. 1 is an overall perspective view thereof, FIG. 2 is a view taken along line AA in FIG. 1, and FIG. (B) is a perspective view of a cap different from (a), FIG. 4 is a partial longitudinal sectional view of a low noise duct different from FIG. 1, and FIG. 5 is for calculating the required space. FIG. 6 is a longitudinal sectional view of a membrane-like portion with a cap used for calculating a required space, and FIG. 7 is a longitudinal sectional view showing an example of a location where the membrane-like portion is installed in a low noise duct. is there. Applies to vehicle intake ducts.
[0008]
The low noise duct of the present embodiment includes a duct body 1, a membrane part 3, a raised part 24, and a cap 4. The duct body 1 is a conduit that forms a gas flow path O for taking in outside air. The duct wall 21 has a wall thickness t ₁ that occupies almost the entire portion, and the wall thickness t ₂ that occupies a portion of the duct wall 21. The membrane portion 3 is made by integral molding. The duct body 1 here is an air cleaner upstream side duct body from the air inlet to the air cleaner, but it can also be applied to a secondary side duct body heading from the air cleaner to the engine. Reference numeral 22 denotes a suction part for introducing the atmosphere, and reference numeral 23 denotes a connection part on the air cleaner side, and a fitting sealing material 5 (see FIG. 7) is appropriately wound around the outer peripheral surface thereof.
[0009]
As described above, the membrane portion 3 constitutes a part of the duct body 1 at a predetermined portion of the duct body 1 and is integrally formed with the general portion 2 of the duct wall 21 and has a thickness t _{2 of the} thickness of the general portion 2. is a portion which is thinner than the thickness t _1. In forming the duct body 1, a part of the duct wall 21 is thinned to form the membrane portion 3. Here, the film-like portion 3 is formed into a thin film disk shape in plan view. Although the film-like part 3 is thin, it bears a part of the duct wall 21 related to the duct body 1 and forms the gas flow path O together with the general part 2. The membrane portion 3 is thinly formed with a thickness of 0.5 mm to 3 mm, so that it can resonate with sound waves. Since the membrane portion thickness t ₂ will not vibrate and become too thick, preferably as thin as possible of. On the other hand, if it is too thin, the film will be broken during cold or heat aging. Varies how much can be thin by the strength of the material, but if for example using a chloroprene rubber to set the thickness t ₂ of the membrane portion 3 to about 1 mm to 3 mm.
[0010]
The material of the duct body 1 (film-like part 3, general part 2) is selected so that the thin-walled film-like part 3 can resonate and vibrate with sound waves. For example, EPDM (ethylene propylene diene rubber), CR (chloroprene rubber), NBR (acrylonitrile butadiene rubber), TPO (olefin thermoplastic elastomer), TPE (amide thermoplastic elastomer) used for general purpose hoses. ), NR (natural rubber), etc. are selected. Elastomer materials such as EPDM, CR, and NBR are more preferable. The reason why an elastomeric material is good for the membrane portion 3, that is, the duct body 1, is that it has both physical properties of elasticity corresponding to hardness and viscoelasticity in which viscosity corresponding to viscosity is combined, and molecular motion. This is because energy loss occurs due to friction caused by the above, and the energy is efficiently converted. In the case of elastomer, when kinetic energy is applied, it deforms and returns to its original state when stress is removed. In the meantime, there is friction between molecules. Produced and changed for thermal energy. The conversion of friction energy into heat energy by the movement of the molecular chain is considered to be a noise attenuation mechanism. For these reasons, an elastomer material having excellent viscoelastic properties and vibration damping ability is particularly preferable.
[0011]
The position (part) where the film-like portion 3 is set in the duct body 1 is provided at a portion where the pressure amplitude of the internal sound of the duct becomes an antinode. This is to increase the sound wave absorption effect, and is the same as when setting a Helmholtz-type silencer. For example, as shown in FIG. 7, in an intake duct composed of a straight pipe having a constant duct inner diameter and a full length Z, there is a portion that becomes an antinode of the pressure amplitude of the internal sound of the duct at the center of the duct (distance Z / 2 from the end) A membrane portion 3 is provided in the center of the duct. And this time, the point of the center of the duct and the air cleaner connection part (suction part) is a node of the pressure amplitude, and there is a part where the antinode of the pressure amplitude is at the middle point (distance of Z / 4 from the end). The film-like part 3 is set in By doing so, the pressure amplitude belly is further eliminated, and the sound pressure level can be lowered. In the present embodiment, as shown in FIGS. 1 and 2, a film-like portion 3 is provided in the approximate center of the duct.
[0012]
The raised portion 24 is a portion that is formed so as to surround the outer peripheral edge of the film-like portion 3 and to bulge outward from the duct wall 21 of the duct body 1 when the duct body 1 is molded. The raised portion 24 is a cylindrical body 24a as shown in FIGS. Since the bulge 24 is thinned by forming the film-like portion 3 in a part of the duct 1, the ridge 24 is provided to ensure rigidity. The raised portion 24 here also plays a role of holding the cap 4. A cylindrical body 24a that swells outward from the duct wall 21 is formed so as to surround the periphery of the membrane portion 3, and an external flange 241 is provided at the tip thereof. The code | symbol 25 shows the recess of the undercut part formed in the base end part of the cylindrical body 24a.
[0013]
As described above, the duct main body 1 in which the general portion 2 including the raised portion 24 and the membrane-like portion 3 are integrated to form the gas flow path O is, for example, to ensure the thinness of the membrane-like portion 3. It can be made by rubber injection molding. In rubber-based injection molding, a material automatically supplied and preheat plasticized is automatically weighed and injected into a mold that has been clamped, and a vulcanized product can be obtained in a predetermined heating time set in advance.
By the way, when the duct main body 1 is seen as a molded product, the recess 25 of the undercut part exists. In resin molding, if there is an undercut, the mold must be removed by sliding the undercut portion. However, in rubber-based injection molding, the mold can be removed by force using the properties of rubber. The bent part of the duct wall 21 of the duct main body 1 can be removed from the mold by expanding the molded product by forcibly removing air or blowing air by utilizing the characteristics of rubber.
Compared to the elastic deformation of rubber and elastomer, there is a limit to the flexibility of the elastic deformation of the thermoplastic elastomer, and there is a certain limit to the undercut treatment by forced removal. In addition to the above-described viewpoint of the sound absorbing effect, the material of the duct main body 1 is more preferably a rubber such as EPDM, CR, NBR, or an elastomer based material.
[0014]
The cap 4 is a separate bottomed cylindrical body that is attached to the raised portion 24 so as to cover the membrane portion 3. The cap 4 is a part for securing an air layer L between the film-shaped part 3 and the bottom part 42 behind the film-shaped part 3 by covering the film-shaped part 3, and is made of metal, resin, composite material or the like. It has rigidity. The cap 4 used in this embodiment is a bottomed cylindrical body as shown in FIG. The cap 4 is attached to the raised portion 24 so that the opening side of the cap 4 faces the membrane portion 3 and the cap 4 is pushed into the cylindrical wall of the raised portion 24. A protrusion 43 is formed on the opening edge of the cap 4. When the cap 4 is attached to the raised portion 24, the protrusion 43 fits into the recess 25 and the cap 4 is fixedly held. Furthermore, the cap 4 is securely attached and held on the raised portion 24 by fastening with the wire clamp 6 or the like from the outer peripheral surface of the cylindrical body 24a as necessary. Reference numeral 61 denotes a clamp, and reference numeral 62 denotes a wire. Instead of the protrusion 43 may be a flange 44 as shown in FIG. 3 (b). Further, the cap 4 is attached to the raised portion 24 to protect the film-like portion 3 from being torn or damaged. In a vehicle intake duct or a vehicle air-conditioning duct, traveling pebbles or the like may jump and break the membrane-like portion 3, and once it breaks, the noise attenuation function of the membrane-like portion 3 is lost. The cap 4 protects the film-like part 3 and exhibits a stable sound absorbing performance.
[0015]
When the cap 4 is attached to the raised portion 24, an air layer thickness L is formed behind the membrane-like portion 3. When considering a silencing mechanism by resonance of the membrane portion 3, the resonance frequency is theoretically the product (M × L) of the surface density M (kg / m ² ) of the membrane portion 3 and the air layer thickness L behind. Inversely proportional to the square root. Therefore, the target frequency can be absorbed by appropriately setting the film thickness t ₂ of the film-like portion 3 and the air layer thickness L. Furthermore, it requires less installation space than a resonator.
[0016]
For example, consider resonance with a frequency f = 200 Hz in a resonator as shown in FIG.
f = (c / 2π) {πr ² /V(L+0.8×2r)} ^1/2 (1)
In the equation (1), c = 340 [m / sec], r = 17.5 × 10 ⁻³ [m], L = 25 × 10 ⁻³ [m], f = 200 [Hz], which are sound velocity values. To obtain V = 1.33 × 10 ⁻³ [m ³ ] = 1333 [cm ³ ], and assuming that a × b is a 10 cm square prism as shown in FIG. Less than 3cm is required.
On the other hand, when resonance of the frequency f = 200 Hz is considered in the film-like portion 3 as shown in FIG. 6 (FIG. 2),
f = (c / 2π) (ρ / ML) 1/2 (2)
It becomes. Here, the density ρ of air = 1.2 kg / m ³ , the surface density M [kg / m ² ], and the thickness of the air layer [m]. When the thickness of the film-like part 3 is 1 [mm], the specific gravity is 1.15 and the surface density M = 1.15 [kg / m ² ], and if this is substituted into the equation (2), L = 76.5 [Mm] is obtained. If the thickness of the film-shaped part 3 is 2 [mm], L = 38.3 [mm] is obtained, and if the thickness of the film-shaped part 3 is 3 [mm], L = 25.5 [mm] is obtained. As described above, when the film-like portion 3 is used, the installation space can be reduced as compared with the resonator.
[0017]
As can be seen from the equation (2), the area of the film-like portion 3 is not related to the resonance frequency. However, since the volume reduction increases as the area increases, it is preferable that the area of the membrane portion 3 is set large as long as the strength of the duct can be secured.
[0018]
By the way, in the membrane resonance of the formula (2), as described above, the resonance frequency is theoretically the square root of the product (M × L) of the surface density M (kg / m ² ) of the membrane portion 3 and the air layer thickness L behind. Inversely proportional to However, if the surface density M of the film-like portion 3 is constant or lower than a certain frequency, that is, the measured value of the resonance frequency becomes substantially constant above a predetermined air layer, and the difference from the theoretical formula increases. Because of such a phenomenon, it is numerically suitable for a frequency of 160 Hz or higher, and this mechanism is not suitable for noise reduction in a low frequency range. On the other hand, even if the space layer L behind is not secured, the membrane portion 3 resonates at a specific frequency and can absorb sound waves inside the duct. For this reason, the cap 4 is a protective cap that protects the film-like portion 3 from being torn or damaged, and the cylindrical body 24a provided with a through hole 411 (or mesh) as shown in FIG. can do.
[0019]
Further development can be made into a low-noise duct as shown in FIG. In the low noise duct of FIG. 4, the thickness t _{2 of} the membrane portion, the shape of the membrane portion 3 and the like are appropriately set according to the target frequency, but the thickness t ₂ is the same as in the low noise duct of FIGS. Is subject to certain restrictions. In the low noise duct of FIG. 4, a part of the duct is thinned by the membrane portion 3, so that a ridge 24 as a reinforcing rib 24 b is provided on the outer peripheral edge of the membrane portion 3 to ensure rigidity. preferable.
[0020]
The low noise duct configured in this manner reduces the sound by reducing the thickness of a part of the duct body 1 to form the film-shaped part 3 and causing the film-shaped part 3 to resonate with sound waves. The above formula (2) can be applied, and the size can be reduced as compared with other silencers such as a resonator. And it demonstrates its power in reducing noise with a frequency of 160 Hz or higher.
Further, since the duct body 1 is only partially thinned to form the membrane portion 3 and the duct wall 21 is not perforated, the duct body 1 is perforated by perforating the duct body 1 as in the prior art (1). There is no worry of dust and dirt getting into the engine unlike the case of attaching a sound absorbing material such as glass wool or using a porous material for the duct body 1 of the prior art (2). Therefore, it can also be used for an air intake duct between the air cleaner and the engine. There is no risk of inhaling hot hot air from the engine compartment.
And, if the cap 4 is attached so as to cover the membrane portion 3, the cap 4 protects and solves the risk of the membrane portion 3 being broken by jumping pebbles, gravel, etc. during driving, etc. And can take measures to reduce noise. There is no problem of clogging that tends to occur when the porous materials (1) and (2) are used.
In addition, since the membrane part 3 and the general part 2 constituting the duct body 1 are manufactured by integral molding, manufacturing is easy and cost reduction is possible, and recycling is facilitated because they are made of the same material. . When an elastomer material is used for the membrane portion 3 (duct body 1), the viscoelastic property of the elastomer material exhibits a sound absorbing effect, and the vibration damping ability can be further enhanced.
[0021]
In addition, in this invention, it is not restricted to what is shown to the said embodiment, According to the objective and a use, it can change variously in the range of this invention. The shape, size, material and the like of the duct body 1, the general part 2, the membrane part 3, the cap 4 and the like can be appropriately selected according to the application. Although the embodiment is applied to an intake duct, it can also be applied to a vehicle air-conditioning duct or the like.
[0022]
【The invention's effect】
As described above, the low-noise duct according to the present invention does not intrude dust and the like, and exhibits excellent effects such as reducing the installation space and selectively enabling noise reduction.
[Brief description of the drawings]
FIG. 1 is an overall perspective view of one embodiment of a low noise duct according to the present invention.
FIG. 2 is a view taken along the line AA in FIG. 1;
3A is a perspective view of the cap of FIG. 2, and FIG. 3B is a perspective view of a cap according to another embodiment different from FIG.
4 is a partial longitudinal sectional view of a low noise duct different from that of FIG. 1; FIG.
FIG. 5 is a perspective view of a resonator used for calculating a required space.
FIG. 6 is a longitudinal sectional view of a cap-like film-like portion used for calculating a required space.
FIG. 7 is a longitudinal sectional view showing an example of a membrane-like portion installation location in a low noise duct.
[Explanation of symbols]
1 the duct body 2 generally portion 21 duct wall 24 ridges 3 membrane portion 4 caps _{t 1, t 2} thickness O gas flow path

Claims (2)

A duct body forming a gas flow path;
A part of the duct body is formed at a predetermined portion of the duct body, and is formed integrally with the general part of the duct wall, and the thickness of the film part is smaller than the thickness of the general part.
A bulge that surrounds the outer periphery of the membrane and swells outward from the duct wall of the duct body, and is integrally formed with the duct body;
A separate cap attached to the raised portion so as to cover the membrane-like portion ,
A low-noise duct characterized in that the membrane-like part can resonate with sound waves. Low noise duct made claims 1 Symbol placement in the duct body elastomeric material.

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