JPH0518330A - Silencing structure of air cleaner for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide the silencing structure of an air cleaner for an internal combustion engine which can reduce the sound in wide frequency region while avoiding the complication of structure. CONSTITUTION:The silencing structure of an air cleaner for an internal combustion engine is constituted by connecting a resonance duct 24, which has an opening at one end and the other end of which is blocked, to an air cleaner case 12 in common, and attenuating the sound in the specified frequency area by resonance by that duct 24. In this case, the shape of the cross section of the resonance duct 24 is made approximately elliptic, and the length in its axial direction is changed in the longitudinal direction of the ellipse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound deadening structure capable of reducing the intake sound of an air cleaner for an internal combustion engine by means of a resonance duct. Regarding improvement.

[0002]

2. Description of the Related Art An air cleaner for an internal combustion engine is shown in FIGS.
As shown in FIG. 2, an air cleaner case 31 containing an element, an introduction duct 32 connected to the primary side of the case 31 and introducing the outside air, and a secondary side of the air cleaner case 31 are connected to vaporize the filtered air. And a supply duct 33 that supplies 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.

Therefore, conventionally, this type of air cleaner often employs a sound deadening structure for reducing the intake noise. As such a sound deadening structure, conventionally, for example, as shown in FIG. 7, a side branch (resonance duct) 34 of a predetermined length is connected to the air cleaner case 31, or as shown in FIG. There is a structure in which a resonator 35 having a volume is connected and connected via a pipe 35a. In the case of the structure in which the resonator 35 is connected, the sound of the frequency corresponding to the length and cross-sectional area of the pipe 35a and the volume of the resonator 35 can be attenuated, and in the case of the structure in which the side branch 34 is connected, the length of the structure can be reduced. The sound of the corresponding frequency can be attenuated.

[0004]

However, the above-mentioned conventional sound deadening structure has a problem that it can only attenuate the sound in a very narrow frequency range. In the case of the side branch method,
To expand the attenuable range, it is possible to provide multiple side branches with different lengths, but this causes a problem that the structure becomes complicated, and the frequency range between the attenuation frequencies by each side branch is increased. Since the damping effect cannot be obtained in the part, it is considered that the damping effect as a whole does not improve so much.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a sound deadening structure for an air cleaner for an internal combustion engine capable of reducing noise in a wide frequency range while avoiding complication of the structure. ..

[0006]

SUMMARY OF THE INVENTION According to the present invention, a resonance duct having an opening at one end and closed at the other end is connected to an air cleaner case in communication therewith, and the duct attenuates sound in a predetermined frequency range by resonance. In the sound-deadening structure for an air cleaner for an internal combustion engine as described above, the cross-sectional shape of the resonance duct is substantially rectangular or substantially elliptical, and its axial length is changed along the longitudinal direction of the cross-section. There is.

[0007]

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

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 are views for explaining a sound deadening structure of an air cleaner for a two-cycle engine according to an embodiment of the present invention, FIG. 1 is a sectional side view of the air cleaner, FIG. 2 is a partial sectional rear view of the air cleaner, FIG. 3 is a side view of the motorcycle, and FIG. 4 is a diagram showing damping characteristics.

In the figure, reference numeral 1 is a motorcycle equipped with the air cleaner of the embodiment, which is a head pipe 2a at the front end of a vehicle body frame 2 and a front fork 4 which pivotally supports the front wheel 3 and which can be steered left and right. Support, central bracket 2b
The rear arm 6 that pivotally supports the rear wheel 5 is pivotally supported up and down, and the engine unit 7 is suspended and supported by the 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 laminated and fastened to the front of a crankcase 7a in a forwardly inclined state. The cylinder body 7
A front end of an exhaust pipe 8 is connected to a front side wall of b, and the exhaust pipe 8 extends rearward on the right side of the vehicle through below the crankcase 7a. Further, a carburetor 10 is connected to an intake port formed on the back surface of the crankcase 7a via a cab joint 9, and an air cleaner 11 of this embodiment is connected to the suction port of the carburetor 10. ..

The air cleaner 11 comprises an air cleaner case 12, a pair of introduction ducts 13 and 13 connected to the primary side of the air cleaner case 12, and a supply duct 14 connected to the secondary side. Each of the introduction ducts 13 is connected to left and right side walls of a lid case 17 of the air cleaner case 12, which will be described later, and opens rearward. The upstream end of the supply duct 14 is connected to a bottom wall 15a of a bottom case 15 of the air cleaner case 12 described later, 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 the partition wall 16a of the intermediate case 16.
It is detachably fastened to the intermediate case 16 with a bolt 18 screwed in. This intermediate case 16 and lid case 1
A cylindrical element 19 is arranged between the element 7 and the element 7. This element 19 is a cylindrical element body 20.
And a frame 21 that is arranged inside and that supports the element body 20.

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

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

Next, the function and effect of the structure of this embodiment will be described. Generally, in an air cleaner, the intake sound from the engine side is attenuated according to the shapes, dimensions, etc. of the supply duct, the air cleaner case, the introduction duct, etc., and then emitted to the outside. It is known that, in this case, when a pipe whose one end is closed is connected to an air cleaner case, the sound of 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 whose effective length is continuously changed by connecting the resonance duct 24 by obliquely cutting the opening 24a is communicatively connected, it is possible to attenuate the sound in the frequency region corresponding to the change range of the effective length. In other words, the attenuable frequency range can be expanded compared to the conventional structure using the side branch or the resonator. The bottom wall 24b of the resonance duct 24 may be formed obliquely as shown by the chain double-dashed line in FIG. In this way, the change range of the effective length of the resonance duct becomes larger, so that 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 attenuation amount. In the figure, the characteristic curve A (broken line) is
The characteristics of the air cleaner having the same shape as that of the present embodiment is shown as it is, that is, the case where the sound deadening structure is not provided. The characteristics when the side branch and the resonator as shown in FIGS. 7 and 8 are provided are shown. The characteristic curve D (solid line) shows the characteristic of the sound deadening structure according to the structure of this 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 region of frequencies f1 'to f2' can be attenuated.

5 and 6 show modifications of the above embodiment,
In the figure, the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions. In this modification, the entire resonance duct 25 is attached to the bottom case 1.
5 and is integrally formed with the bottom case 15, and the opening 25a is inclined in the front-rear direction of the air cleaner case 12. Also in this modification, there is an effect that the attenuable frequency range can be expanded, and since the resonance duct does not project to the outside of the case, it is possible to avoid the problem of a large arrangement space.

[0019]

As described above, according to the sound deadening structure for an air cleaner for an internal combustion engine according to the present invention, the resonance duct connected to the air cleaner case is constructed so that its effective length continuously changes. However, there is an effect that the attenuable frequency range can be expanded without complication.

[Brief description of drawings]

FIG. 1 is a sectional side view showing a sound deadening structure of an air cleaner according to an embodiment of the present invention.

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

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

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

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

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

FIG. 7 is a perspective view showing a conventional sound deadening structure.

FIG. 8 is a perspective view showing another conventional sound deadening structure.

[Explanation of symbols]

 7 2-cycle engine unit 12 Air cleaner case 24,25 Resonance duct 24a, 25a Opening

Claims (1)

Claim: What is claimed is: 1. A resonance duct, which has an opening at one end and is closed at the other end, is communicatively connected to an air cleaner case, and the duct attenuates sound in a predetermined frequency region by resonance. In the sound deadening structure of the air cleaner for the internal combustion engine,
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 oval, and an axial length of the resonance duct is changed along a longitudinal direction of the cross section.