JPH09112370A - Sound absorbing duct for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound absorbing duct having high sound insulation characteristic over the range from a low frequency area to a high frequency area by a method wherein columnar support bodies to hold a sound absorbing material are arranged at intervals of a fixed distance along the inner circumferential parts of an inner cylinder and/or an outer cylinder. SOLUTION: Columnar support bodies 21 are arranged on an inner cylinder 19 along the inner circumference of an intake duct 23. Sound absorbing materials 22 are held between an outer cylinder 20 and the columnar support body 21. By fixing the sound absorbing material 22 as described above, the sound absorbing material 22 is prevented from being sucked out by the flow of intake air. Further, a sound absorbing duct part and an intake duct 23 are interconnected through a rubber band 24. The end part of the columnar support body 21 is not welded to the outer cylinder 20. To prevent bending of the columnar support body 21 during welding of the inner and outer cylinders 19 and 20, there is a need for a gape to be provided between the columnar support body 21 and the outer cylinder 20. By installing a sound absorbing duct at the intake system of an internal combustion engine, a sound insulation duct having high sound insulation ability throughout a range of from a lower frequency region to a high frequency region is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorbing duct for an internal combustion engine capable of reducing intake noise of the internal combustion engine.

[0002]

2. Description of the Related Art Intake noise of an internal combustion engine is considered to be caused by pulsation of intake air due to opening / closing of a valve in a combustion chamber. In order to reduce the intake noise of the internal combustion engine, as shown in FIG.
Sound absorbing material and resonator are installed. In FIG.
Reference numeral 1 is an intake duct, 2 and 5 are resonators, 3 is an air cleaner, 4 is an air filter, and 7 is an internal combustion engine. In particular, the resonator 2 is intended for countermeasures against intake noise in the low frequency range, and has a volume of 1000 cc or more.

As a measure for reducing the intake sound seen from the frequency range, generally, as a measure against the intake sound in the high frequency range (mainly 800 Hz or more), a sound absorbing material such as felt is installed in a part of the intake duct to reduce the low frequency. As a measure against the intake noise, a resonator and side branch are installed in the intake duct.

Since the sound absorbing material has a characteristic that the sound absorbing performance is enhanced in a high frequency region, it is effective to use it in a frequency region of 800 Hz or higher. Examples of the sound absorbing material include fibrous sound absorbing materials (felt, etc.). This sound absorbing material is formed by opening chemical fibers or natural fibers, adding a binder resin, and heating.

The binder resin can be appropriately selected and used from known synthetic resins, and in particular, heat-fusible resins such as polyethylene, polypropylene and polyester resins are preferably used. A phenol resin is particularly preferably used as the thermosetting resin. Unlike the fiber material, these binder resins are components that do not contribute to sound absorption. Further, since the binder resin is mixed in about 1/3 of the weight of the fiber material, the sound absorbing performance per unit weight is low. Such a sound absorbing material is used by being attached to a back cover of an air cleaner or the like in order to reduce turbine noise particularly in an internal combustion engine equipped with a turbocharger.

A general resonator used for reducing intake noise of an internal combustion engine has a structure as shown in FIG. This resonator is a device for reducing the noise on the relatively low frequency side generated from the pulsation of intake air, and is generally a cavity type resonator, and the frequency characteristics are designed by the volume of the cavity, the diameter and length of the neck, etc. It is possible.

This resonator forms a mass-spring system in which the air in the neck 9 which is in contact with the sound absorbing duct 1 serves as a mass and the air in the cavity 10 serves as a spring, so that the air in the neck corresponding to the mass at a certain frequency is formed. Violently vibrates, and at that time the sound energy is attenuated.

The set frequency is expressed by the following equation 1, and is characterized in that the sound pressure reducing effect is high near the set frequency.

(Equation 1) Where FO is the resonance frequency (Hz), C is the speed of sound (340 m / s)
, S is the cross-sectional area of the neck (m ² ), t is the length of the neck (m), d
Is the diameter of the hole (m), and V is the volume of the cavity (m ³ ).

FIG. 3 shows the characteristic of the sound absorption coefficient with respect to the typical frequency of the resonator. As shown in FIG. 3, it can be seen that the sound absorption effect is difficult to be exhibited outside the set frequency range.

By adopting the structure of the resonator shown in FIG. 2, the resonance frequency can be set by the above formula 1 according to the inner diameter d and the length t of the neck 9 of the resonator and the volume V of the cavity 10.

The present invention is intended to replace the functions of a plurality of resonators with a single sound absorbing mechanism in the current intake system having such a complicated structure. Also,
Taking an automobile as an example, the engine room and auxiliary equipment occupy most of the space in the engine room, and there is no extra space. To secure the space to install the resonator,
Although it is general to form the shape of the resonator so as to match the effective space, there is also a drawback that the shape becomes complicated and the processing cost becomes high.

As a practical example so far, a large number of small holes are provided in the intake pipe connecting the carburetor and the air cleaner,
Further, a type in which a sound absorbing material is attached (Japanese Patent Laid-Open No. 53-1486).
17), an air cleaner with a built-in resonator (Japanese Patent Laid-Open No. 62-110722), and a resonance frequency variable type resonator (Japanese Laid-Open Patent Publication No. 55-60444). Further, as a material using a sound absorbing material, a material in which the sound absorbing material is installed in the vicinity of the opening end of the intake duct has been proposed (Japanese Patent Laid-Open No. 53-14867).

[0013]

However, the conventional sound absorbing material itself does not have the rigidity enough to maintain the shape against the flow or vibration of the intake air. Therefore, at present, fixing methods such as fittings and fixing methods using double cylinders are adopted. The conventional fixing means for the sound absorbing material requires a step of making a hole in the sound absorbing material, a step of caulking with a metal fitting, a step of inserting a double cylinder into the inside, and the like, which deteriorates workability. Therefore, there are problems that it is difficult to automate the assembly process when the sound absorbing material is installed in the intake duct, and there are many manual assembly processes. Further, it is difficult to reduce the intake sound to the low frequency range only with the sound absorbing material, and it has been necessary to ensure a wide range of sound absorbing performance in combination with the expansion duct.

As an example of installing a sound absorbing material in the air cleaner, as shown in FIG. 4, a back lid 11 of the air cleaner 3 is provided.
It is possible to hold the sound absorbing material with metal fittings. In FIG. 4, 14 is a metal fitting for holding the sound absorbing material 13,
Reference numeral 12 is a rivet for fixing the metal fitting to the back lid 11 of the air cleaner. In this case, a step of installing the sound absorbing material 13 and the metal fitting 14 and a step of hitting the rivet 12 are required, which deteriorates workability.

Further, in order to support and fix the sound absorbing material in the duct, it is possible to install a cylindrical inner cylinder.
One example is shown in FIG. As shown in FIG. 5, reference numeral 15 is an intake duct having an expanded portion for holding the sound absorbing material 13,
An inner cylinder 17 having a small hole is installed therein, and rings 16 for fixing are installed at both ends thereof. The inner cylinder 17 is provided with a small hole 18 so that the intake sound reaches the sound absorbing material.

The inner cylinder itself can be manufactured by molding a resin material such as polypropylene by blow molding or injection, but the hole processing for air permeability is complicated, and it takes a considerable amount of time in the process. It requires man-hours. In other words, it is difficult to process the shape of the support member having the sound absorbing material and the air-permeable supporting member in one processing step, which causes an increase in manufacturing cost.

Therefore, according to the present invention, the inner cylinder and the outer cylinder are injection-molded, and the sound absorbing material is installed around the inner part of the outer cylinder or the columnar part of the inner cylinder and assembled with the other member in the assembly at the time of manufacturing. It is an object of the present invention to provide a sound-absorbing duct which can be easily manufactured by thermal welding and has a high sound deadening characteristic in a low frequency range to a high frequency range by being installed in an intake system of an internal combustion engine.

[0018]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
In an air intake duct in which a sound absorbing material is installed in the gap between the outer cylinder and the inner cylinder, along the inner peripheral portion of the inner cylinder and / or the outer cylinder,
The present invention is achieved by a sound absorbing duct for an internal combustion engine, characterized in that columnar supports for holding the sound absorbing material are formed at regular intervals.

That is, according to the present invention, in the sound absorbing duct in which the sound absorbing material is installed in the gap between the outer cylinder and the inner cylinder, a plurality of pillar-shaped sound absorbing material supports are provided in the inner cylinder and / or the outer cylinder part which also serve as a part of the duct. And the columnar support is installed along the inner peripheral portion of the inner cylinder and / or the outer cylinder, so that the sound absorbing material can be easily and reliably installed, and a ventilation portion is secured in the support. belongs to.

The columnar support is installed at a constant interval because of the shape design for simultaneously processing the support and the ventilation part. In other words, by using a plurality of columnar supports, it is not necessary to process the ventilation part, and injection molding can be performed. Although processing by blow molding is also possible, injection molding is advantageous in order to secure dimensional accuracy of the contact surface between the inner cylinder and the outer cylinder.

The sound absorbing duct portion has an enlarged cross-sectional shape with respect to an ordinary intake duct having a circular cross section or a quadrangular cross section. In particular, the cross-sectional shape of the air intake duct does not matter. Intake noise can be reduced by the volume expansion effect of the expanded volume of the duct and the sound absorbing effect of the sound absorbing material.

In the present invention, the fiber base material constituting the sound absorbing material is preferably a fiber assembly containing natural fibers and / or synthetic fibers as main components. With the current general technology, the smallest fineness, about 0.0001 denier, can be obtained. In order to improve the sound absorption performance, the fineness should be small. This is because sound absorption by the fibrous body is absorbed by the sound energy being converted into thermal energy by vibrating the fiber. That is, in the case of ultrafine fibers, the number of fibers per unit volume increases, so that the sound absorbing performance can be improved. Particularly, according to the melt blown manufacturing method in which the molten resin is extruded by applying pressure from the pores to form fibers, ultrafine fibers of several microns level can be obtained. Melt-blown fibers have already been put to practical use for winter clothes and medical applications.

By using synthetic fibers, the sound absorbing material performance can be arbitrarily designed in accordance with the required performance specifications such as the fiber diameter, the fiber length and the compounding ratio. The average fiber diameter of this synthetic fiber is preferably in the range of 0.1 to 60 μm.
If the average fiber diameter of the synthetic fibers is less than 0.1 μm, the rigidity of the fibers themselves is too small, and it is difficult to mold the sound absorbing material. On the other hand, when it exceeds 60 μm, the sound absorbing performance is rather deteriorated.

In the case of polyester fibers produced by the melt spinning method, the average fiber diameter is preferably in the range of 10 to 40 μm. Melt-spun polyester fibers are the most common and economical. It is difficult to produce fibers having a diameter of less than 10 μm by the melt spinning method, and 40 μm is required to secure sound absorbing performance depending on the surface area of the fibers.
It is effective that it is m or less.

Further, in the sound absorbing material containing polyethylene fiber as a main component, the sound absorbing material has a fiber structure composed of a binder fiber having a core-sheath structure and a main fiber, and is heat-molded in advance so as to maintain shape retention. It becomes possible to prevent the fibers from coming off. Even in the case where the binder fibers are not included, the fibers can be physically entangled with each other and the shape can be maintained by using a processing method such as needle punching.

The surface density of the sound absorbing material is 50 to 4000 g / m ^2.
Is preferably within the range. Area density of sound absorbing material is 50g
If it is less than / m ² , the performance as a sound absorbing material cannot be secured. On the other hand, when it exceeds 4000 g / m ² , the performance is not improved and the efficiency is poor although the weight or the cost associated therewith is exceeded. Furthermore, as the surface density increases, the amount of ventilation of the sound absorbing material itself decreases, so that the performance of the sound absorbing material cannot be exhibited and the sound absorbing effect is the same as that of the duct only.

In order to prevent the fibers of the sound absorbing material placed in the expansion duct from falling out, one side surface of the fiber assembly or the entire surface of the fiber assembly is covered, and the average fiber length is 1 to 100 cm, the average fiber diameter is 1 to 30 μm, A non-woven fabric made of synthetic fiber having an area density of 20 to 200 g / m ² is preferably installed as the surface skin. This skin is formed in the form of a cloth-like non-woven fabric or woven fabric. In the case of a non-woven fabric, it is formed by a needle punching method or by heat-sealing a part of the cloth, but the skin produced by these methods has high rigidity and sufficient air permeability can be secured. Further, the use of only long fibers having a length of 10 cm or more as the constituent fibers is effective for further improving the rigidity of the cloth, but is not particularly limited.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION In a sound absorbing duct of the present invention, an inner cylinder and an outer cylinder are injection-molded, and a sound absorbing material is installed around an inner part of the outer cylinder or a columnar part of the inner cylinder when assembled during manufacturing.
It can be manufactured by combining with the other member and heat welding. By installing such a sound-absorbing duct in the intake system of an internal combustion engine, it has become possible to obtain a sound-absorbing duct having a high sound deadening characteristic in a low frequency region to a high frequency region.

[0029]

【Example】

Example 1 FIG. 6 shows an example in which a columnar support 21 is installed on the inner cylinder 19.
The columnar support 2 is attached to the inner cylinder 19 along the inner circumference of the intake duct 23.
1 is installed. The sound absorbing material 22 is held between the outer cylinder 20 and the columnar support 21. By fixing the sound absorbing material in this way, the sound absorbing material is prevented from being sucked out by the flow of the intake air.

Further, since the space is provided between the supports, the intake noise can reach the sound absorbing material 22.
Since the sound absorbing duct is installed as a part of the intake duct, a connecting portion is required. In the first embodiment, the sound absorbing duct portion and the intake duct 23 are connected by the rubber band 24. The end of the columnar support 21 and the outer cylinder 20 are not welded.
This is because it is necessary to provide a gap between the columnar support body 21 and the outer cylinder 20 in order to prevent the columnar support body from being bent at the time of welding the inner and outer cylinders in consideration of variations in molding accuracy of the resin. . FIG. 7 shows a cross-sectional view of the plane AA '.

In this embodiment, the cross-sectional shape of the intake duct is φ
It is a cylinder of 50 mm. Since the expansion ratio of the sound absorbing duct to the diameter of the intake duct was set to 2, the outer diameter of the sound absorbing duct was φ1.
It becomes 00 mm. Since it is preferable that the sound absorbing material is synthetic fiber as described above, polypropylene fiber manufactured by the melt blow method is used in this embodiment. The basis weight is 800 g / m ² .

Example 2 Example 2 is shown in FIG. Example 2 differs from Example 1 in that
In order to further fix the end portion of the columnar support 21 installed in the inner cylinder 19, a fixing portion 2 of the columnar support 2 is attached to a part of the outer cylinder 20.
5 is provided. An enlarged view is shown in FIG. t1 is the length of the gap provided between the columnar support 21 and the outer cylinder 20. L indicates the height of the fixed portion 25, which is 5 of the gap t1.
If it is about twice, it is effective enough. With such a configuration, it is possible to prevent the columnar support 21 from being deformed inside the sound absorbing duct even if the columnar support and the outer cylinder are not fixed.

Example 3 Example 3 is shown in FIG. In the third embodiment, the columnar support 21 is integrally formed on the inner circumference of the outer cylinder 20. The sound absorbing material 22 can be easily installed by securing a place for installing the sound absorbing material in advance. In this case as well, a gap is provided between the columnar support 21 and the inner cylinder 19. Further, as shown in Example 2, it is also possible to form a protruding portion for fixing the support body at the end of the columnar support body 21.

Example 4 Example 4 is shown in FIG. In the fourth embodiment, columnar supports 28 and 29 are formed on both sides of the inner cylinder 26 and the outer cylinder 27, respectively, and small holes are formed at the end and center of the support. The small hole 33 in the central portion is connected to the space 31 formed by the sound absorbing material 30 divided from the support. The small holes 32 and 34 connect the sound absorbing duct and the sound absorbing material. FIG. 12 shows an enlarged schematic view of the columnar supports 28 and 29. Since resonance can be generated between the small hole 33 and the space 31, it is possible to obtain a function as a kind of resonator in the target frequency range. The resonance frequency can be expressed by Equation 2 below, and the resonance frequency can be set by the shape of the hole and the volume of the space.

[0035]

(Equation 2) Where f ₀ is the resonance frequency (Hz), C is the speed of sound (340 m /
s), V is the volume of the cavity (m ³ ), n is the number of holes, S ₁ is the area of the hole (m ² ), t is the depth of the hole (m), and d is the diameter of the hole (m). is there. FIG. 12 shows a configuration diagram of the columnar supports 28 and 29.

Test Example The sound absorbing duct obtained in the above example was subjected to the following test. The sound absorbing duct of each example was assembled to the duct of the intake system of a 4-cylinder engine installed in a semi-anechoic chamber. In this system, the insertion loss (IL), which is the difference between the sound pressure at the intake manifold side end connected to the engine and the sound pressure at the intake duct side opening, was measured.

In this test, the speaker was used as the vibration source, and the IL measurement was carried out by the reverse arrangement method in which vibration was applied from the intake port side. As a test result, the difference in sound pressure level at each frequency was expressed in dB, and averaged in a low frequency range of 500 Hz or less, a medium frequency range of 500 to 1 KHz, and a high frequency of 1 KHz or more.

Further, the same experiment was conducted using a general duct instead of the sound absorbing duct of the present invention, the average was taken in each frequency range, and the performance of the sound absorbing duct of the present invention was examined with this numerical value as a standard. Table 1 shows the test results.

[0039]

[Table 1]

As shown in Table 1, the various sound-absorbing ducts of the present invention prepared in the examples exhibited excellent sound-absorbing characteristics in the low frequency region, the medium frequency region and the high frequency region.

[0041]

In the sound-absorbing duct of the present invention, the inner cylinder and the outer cylinder are injection-molded, and the sound-absorbing material is installed around the inner part of the outer cylinder or the columnar part of the inner cylinder during the assembly at the time of manufacture. It can be easily manufactured by combining with a member and heat welding. Further, by installing the sound absorbing duct of the present invention in the intake system of an internal combustion engine, it becomes possible to obtain a sound absorbing duct having high sound deadening characteristics in a low frequency region to a high frequency region.

[Brief description of the drawings]

FIG. 1 is an intake system of a current internal combustion engine.

FIG. 2 is a schematic diagram of a resonator.

FIG. 3 is a characteristic of a resonator.

FIG. 4 is a back cover sound absorbing material.

FIG. 5 is a double cylindrical sound absorbing material.

FIG. 6 is an explanatory diagram of the first embodiment.

FIG. 7 is an explanatory diagram of capturing of the first embodiment.

FIG. 8 is an explanatory diagram of a second embodiment.

FIG. 9 is a partially enlarged view of the second embodiment.

FIG. 10 is an explanatory diagram of the third embodiment.

FIG. 11 is an explanatory diagram of the fourth embodiment.

FIG. 12 is an explanatory diagram of the fourth embodiment.

[Explanation of symbols]

 1 Air Intake Duct 2 Resonator 1 3 Air Cleaner 4 Air Filter 5 Resonator 2 6 Resonator 3 7 Internal Combustion Engine 8 Sound Absorbing Material 9 Resonator Neck 10 Space Inside Resonator 11 Air Cleaner Back Cover 12 Rivet 13 Sound Absorbing Material 14 Metal Fitting 15 Intake Cylinder 16 Ring 17 Inner Cylinder 18 Small Hole 19 Inner Cylinder 20 of the Present Invention 20 Outer Cylinder of the Present Invention 21 Columnar Support 22 Sound Absorbing Material 23 Intake Duct 24 Connection Rubber Band 25 Fixed Part of Columnar Support 26 Inner Cylinder of the Present Invention 27 Outer cylinder 28 Columnar support formed on the inner cylinder 29 Columnar support formed on the outer cylinder 30 Sound absorbing material 31 Space 32 Inner cylinder side support end small hole 33, 34 Support end small hole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Nemoto 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Kyoichi Watanabe 2 Takara-cho, Kanagawa-ku, Yokohama, Nissan Nissan Motor Co., Ltd. (72) Inventor Hiroshi Sugawara 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (4)

[Claims] 1. A columnar support for holding the sound absorbing material along an inner peripheral portion of the inner cylinder and / or the outer cylinder in an air intake duct in which a sound absorbing material is installed in a gap between the outer cylinder and the inner cylinder. A sound absorbing duct for an internal combustion engine, wherein a body is formed at regular intervals. 2. The sound absorbing duct for an internal combustion engine according to claim 1, wherein a groove or a projection portion for fixing the columnar support is provided at a portion where the columnar support is in contact with the inner cylinder and / or the outer cylinder. . 3. The sound absorbing duct for an internal combustion engine according to claim 1, wherein columnar supports are provided on both sides of the inner cylinder and the outer cylinder, and a plurality of small holes are formed in the columnar supports. 4. The sound absorbing material is divided into a plurality of parts, some of the small holes formed in the support body communicate with the space formed by the support body, the outer cylinder and the sound absorbing material, and the other small holes are The sound absorbing duct for an internal combustion engine according to claim 3, wherein the sound absorbing material is in contact with a space in which the sound absorbing material is installed.