JP2897172B2 - Noise reduction structure of air cleaner for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction structure in which intake noise of an air cleaner for an internal combustion engine can be reduced by a resonance duct. About improvement.

[0002]

2. Description of the Related Art FIGS. 7 and 8 show an air cleaner for an internal combustion engine.
As shown in the figure, an air cleaner case 31 containing a built-in element, an inlet duct 32 connected to the primary side of the case 31 for introducing outside air, and a secondary side of the air cleaner case 31 for vaporizing filtered air. And a supply duct 33 for supplying to the intake manifold or the intake manifold. However, the air cleaner 30 has a problem that the intake noise generated from the engine side is emitted outward from the vicinity of the external opening of the introduction duct 32.

[0003] Conventionally, this type of air cleaner often adopts a silencing structure for reducing the intake noise. Conventionally, as such a silencing structure, a structure in which a side branch (resonance duct) 34 having a predetermined length is connected to an air cleaner case 31 as shown in FIG. 7 or a predetermined structure as shown in FIG. There is a structure in which a resonator 35 having a capacity is connected and connected via a pipe 35a. In the case of the structure in which the resonator 35 is connected, sound having a frequency corresponding to the length and cross-sectional area of the pipe 35a and the volume of the resonator 35 can be attenuated. In the case of the structure in which the side branch 34 is connected, the length is reduced. Sound of the corresponding frequency can be attenuated.

[0004]

However, in the case of the above-mentioned conventional silencing structure, there is a problem that only sounds in a very narrow frequency range can be attenuated. In the case of the side branch method,
In order to enlarge the attenuable area, it is conceivable to provide a plurality of side branches having different lengths. Since the damping effect cannot be obtained in the portion, it is considered that the damping effect as a whole does not improve so much after all.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a silencing structure of an air cleaner for an internal combustion engine that can reduce sound in a wide frequency range while avoiding a complicated structure. .

[0006]

According to the present invention, a resonance duct having an opening at one end and a closed end at the other end is connected to an air cleaner case, and the duct attenuates sound in a predetermined frequency range by resonance. In the noise reduction structure of the air cleaner for an internal combustion engine, the cross section of the resonance duct is substantially rectangular or substantially elliptical, and the axial length thereof is changed along the longitudinal direction of the cross section. I have.

[0007]

According to the sound deadening structure of the present invention, the resonance duct has a rectangular or elliptical cross section, and its length is changed along the longitudinal direction of the cross section. The same operation as when the resonance duct is provided can be obtained, and the sound in the frequency region corresponding to each length in the longitudinal direction of the cross-sectional shape can be attenuated, so that the attenuable frequency region can be expanded. In this case, there is only one resonance duct, and the structure does not become complicated as in the case where the plurality of side branches are provided.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to 4 are views for explaining a muffling structure of an air cleaner for a two-stroke engine according to an embodiment of the present invention. FIG. 1 is a sectional side view of the air cleaner, FIG. FIG. 3 is a side view of the motorcycle, and FIG. 4 is a view showing the damping characteristics.

In the drawing, reference numeral 1 denotes a motorcycle on which an air cleaner according to the embodiment is mounted, which is a head pipe 2a at a front end of a body frame 2 and which pivots a front fork 4 for supporting a front wheel 3 to the left and right. Support, center bracket part 2b
Thus, a rear arm 6 for pivotally supporting the rear wheel 5 is pivotably supported up and down, and an engine unit 7 is suspended and supported by a front main frame portion 2c.

The engine unit 7 is an air-cooled two-cycle single-cylinder engine in which a cylinder body 7b and a cylinder head 7c are stacked and fastened to the front of a crankcase 7a in a forwardly inclined state. The above cylinder body 7
The front end of the exhaust pipe 8 is connected to the front side wall of the b, and the exhaust pipe 8 extends rearward on the right side of the vehicle below the crankcase 7a. A carburetor 10 is connected to an intake port formed on the back of the crankcase 7a via a cab joint 9, and an air cleaner 11 of the present embodiment is connected to an intake port of the carburetor 10. .

The air cleaner 11 comprises an air cleaner case 12, a pair of introduction ducts 13 connected to a primary side thereof, and a supply duct 14 connected to a secondary side. The introduction ducts 13 are connected to left and right side walls of a lid case 17 of the air cleaner case 12, which will be described later, and are opened rearward. The upstream end of the supply duct 14 is connected to a bottom wall 15 a of a bottom case 15 of the air cleaner case 12 described below, and the downstream end thereof is connected to the carburetor 10.

The air cleaner case 12 has a three-part structure including a bottom case 15, an intermediate case 16, and a lid case 17. The lid case 17 is cup-shaped, and has a central convex portion 16b of a partition 16a of the intermediate case 16.
The intermediate case 16 is detachably fastened to the intermediate case 16 with a bolt 18 screwed into the intermediate case 16. The intermediate case 16 and the lid case 1
7, a cylindrical element 19 is arranged. This element 19 is a cylindrical element body 20
And a frame 21 disposed inside the frame to support the element body 20.

The intermediate case 16 and the bottom case 15 are fastened by bolts 22. A relatively large space E is formed on the secondary side of the element 19 by the two cases. A drain hole 15b is formed in a rear portion of the bottom wall 15a of the bottom case 15, and the hole 15b is closed by an auxiliary element 23 arranged in the case.
The auxiliary element 23 is for filtering the external air when the external air is sucked from the drain hole 15b by the pulsation of the intake air.

A resonance duct 24 is mounted at the center of the bottom wall 15a of the bottom case 15. The resonance duct has an elliptical cross section, an opening 24a at the upper end, and a lower end closed by a bottom wall 24b. This resonance duct 24
The flange portion 24c formed near the center in the height direction is fitted in the mounting hole 15c of the bottom wall 15a. Therefore, the upper portion is located in the space E of the air cleaner case 12, and the lower portion is located in the air cleaner case. 12 project outward. The opening 24a is obliquely inclined in the vehicle width direction, so that the effective length of the resonance duct 24 changes continuously along the major axis of the ellipse.

Next, the operation and effect of the structure of this embodiment will be described. Generally, in an air cleaner, the intake noise from the engine side is attenuated according to the shape, dimensions, and the like of the supply duct, the air cleaner case, the introduction duct, and the like, and then emitted outward. It is known that, in this case, when a pipe having one end closed is connected to an air cleaner case, sound having a frequency corresponding to the effective length of the pipe can be further attenuated.

In this embodiment, the air cleaner case 12
In addition, since the resonance duct 24 having the effective length continuously changed is connected to the resonance duct 24 by cutting the opening 24a obliquely, the sound in the frequency region corresponding to the change range of the effective length can be attenuated. That is, the attenuable frequency range can be expanded as compared with the conventional structure using the side branch or the resonator. Note that the bottom wall 24b of the resonance duct 24 may be formed obliquely as shown by a two-dot chain line in FIG. In this way, the range of change of the effective length of the resonance duct becomes larger, and therefore the attenuable frequency range can be further expanded.

FIG. 4 is an experimental result showing the relationship between the frequency of the intake sound and the amount of attenuation. In the figure, the characteristic curve A (dashed line)
The characteristics of the air cleaner having the same shape as the present embodiment as it is, that is, the characteristics in the case where the sound deadening structure is not provided, are shown. The characteristics when the side branch and the resonator as shown in FIGS. 7 and 8 are provided are shown. A characteristic curve D (solid line) shows the characteristic of the sound deadening structure according to the structure of the present embodiment. As is clear from the figure, when the side branch is provided, the sound of the frequency f1 can be more effectively attenuated, and when the resonator is provided, the sound of the frequency f2 can be more effectively attenuated. On the other hand, in the case of the present embodiment, it can be seen that the sound in the frequency range from the frequency f1 'to f2' can be attenuated.

FIGS. 5 and 6 show modifications of the above embodiment.
In the drawings, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding parts. In this modification, the entire resonance duct 25 is connected to the bottom case 1.
5 and is formed integrally with the bottom case 15, and the opening 25 a is inclined in the front-rear direction of the air cleaner case 12. This modification also has the effect of expanding the attenuable frequency range, and furthermore, since the resonance duct does not protrude outside the case, it is possible to avoid a problem that the arrangement space becomes large.

[0019]

As described above, according to the noise reduction structure of the air cleaner for an internal combustion engine according to the present invention, the resonance duct connected to the air cleaner case is configured so that its effective length changes continuously. However, there is an effect that the attenuable frequency region can be expanded without complicating.

[Brief description of the drawings]

FIG. 1 is a cross-sectional side view showing a muffling structure of an air cleaner according to one embodiment of the present invention.

FIG. 2 is a partial cross-sectional rear view of the muffling structure of the embodiment.

FIG. 3 is a side view of a motorcycle having the structure of the embodiment.

FIG. 4 is a frequency-attenuation characteristic diagram for explaining the effect of the embodiment.

FIG. 5 is a sectional side view showing a modification of the above embodiment.

FIG. 6 is a partial cross-sectional rear view of the modification.

FIG. 7 is a perspective view showing a conventional silencing structure.

FIG. 8 is a perspective view showing another conventional silencing structure.

[Explanation of symbols]

 7 Two-cycle engine unit 12 Air cleaner case 24, 25 Resonance duct 24a, 25a Opening

Claims (1)

(57) [Claims] An air cleaner for an internal combustion engine, wherein a resonance duct having an opening at one end and a closed end at the other end is connected to an air cleaner case, and the duct attenuates sound in a predetermined frequency range by resonance. In the silencing structure,
A sound deadening structure for an air cleaner for an internal combustion engine, wherein a cross-sectional shape of the resonance duct is substantially rectangular or substantially elliptical, and an axial length of the resonance duct is changed along a longitudinal direction of the cross section.