JP2007278185A - Tube structure of muffler for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tube structure of a muffler for an internal combustion engine which can achieve an inexpensive constitution without using a control valve and acquire the reduction effect of discharge sound in a wide frequency range. <P>SOLUTION: In a tube structure of a muffler for an internal combustion engine, a tube 2 is formed as a double tube structure composed of an inner tube 3 and an outer tube 4 containing the inner tube 3 thereinside. A plurality of small holes 5 are provided to the inner tube 3 so as to make an opening ratio thereof to the total area of the inner tube 1-7%. By this constitution, acoustic characteristics particularly at a low frequency can be improved without using an expensive control valve. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tube structure of a muffler for an internal combustion engine for reducing noise generated from an exhaust system of the internal combustion engine provided in an automobile or the like.

Conventionally, a muffler shell (outer cylinder) inside an muffler for an internal combustion engine mounted on an automobile is divided into a plurality of chambers, and two outlet pipes are provided, depending on the engine speed (exhaust gas amount). Some control valves are opened and closed to switch between the case of one discharge mainly discharging exhaust gas from one outlet pipe and the case of two discharges discharging both exhaust gases from two outlet pipes. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 11-153019 (FIG. 6)

  However, as in the technique described in Patent Document 1, when a control valve is used and the exhaust gas flow rate is switched as necessary within a range from low rotation to high rotation, a drive system and a control system for operating the control valve Cost is inevitable and cost increase is inevitable.

  In view of the above circumstances, the present invention provides a muffler tube structure for an internal combustion engine that can obtain an effect of reducing discharge noise in a wide frequency range with an inexpensive device configuration without using a control valve. Objective.

  The present invention relates to a tube structure of an muffler for an internal combustion engine, wherein the tube has a double tube structure including an inner tube and an outer tube in which the inner tube is disposed, and the inner tube has a total area of the inner tube. A plurality of small holes are provided so that the aperture ratio is 1% to 7%.

  The present invention may be applied to a tail tube of a muffler for an internal combustion engine, or may be applied to a center tube.

  When the present invention is applied to a tail tube, the tube has a double-pipe structure composed of an inner tube and an outer tube in which the inner tube is provided. Small holes are provided so that the aperture ratio is 1% to 7%. Moreover, it is preferable that the tube length of an inner tube shall be 100 mm or more. Further, the length of the outer tube is made longer than the length of the inner tube. Further, it is desirable that the double pipe be closed on the upstream side in the exhaust gas flow direction and open on the downstream side.

  The opening diameter of the small holes is preferably φ5 (diameter 5 mm) or less. Further, it is desirable that the small holes are formed not over a part of the inner tube but over the whole. For example, small holes of φ5 or less are arranged in one row or in multiple rows in the inner tube length direction.

  According to the tube structure of the muffler for an internal combustion engine of the present invention, the small hole is formed in the inner pipe so that the opening ratio is 1% to 7% with respect to the total area of the inner pipe. By distributing the holes, attenuation of low frequency (150 Hz or less) is possible, and pressure loss and air flow noise can be greatly reduced.

  Moreover, according to the tube structure of the muffler for an internal combustion engine of the present invention, the acoustic characteristics can be improved without using an expensive control valve, so that the cost can be greatly reduced.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  In this embodiment, an acoustic control characteristic is improved particularly in a low frequency range (150 Hz or less) by utilizing a characteristic that the passing efficiency with respect to the frequency when the sound wave passes through the small hole without using an expensive control valve. To do. Specifically, because the wavelength of the low frequency is long, the portion where there are few small holes makes it difficult for sound waves to pass through the small holes, and the phenomenon that the number of small holes increases gradually becomes easier. It is a thing.

  FIG. 1 is a cross-sectional view of a principal part showing a tube structure of an internal combustion engine muffler in which the present invention is applied to a tail tube. In this example, the tail tube 2 for discharging the exhaust gas in the muffler shell 1 to the outside has a double tube structure constituted by an inner tube 3 and an outer tube 4 in which the inner tube 3 is provided. In the tail tube 2, the tube length L 1 of the inner tube 3 is set to 100 mm or more, and the tube length L 2 of the outer tube 4 is made longer than the tube length L 2 of the inner tube 3. The double pipe has a closed pipe on the upstream side in the exhaust gas flow direction and an open pipe on the downstream side. And the small hole 5 is formed in the inner tube | pipe 3 so that the opening ratio may become 1%-7% with respect to this inner tube | pipe whole area.

  In FIG. 1A, the connecting portion 3 a of the inner tube 3 is expanded in diameter relative to the muffler shell 1 with respect to other portions, and the end portion 4 a of the outer tube 4 is connected to the muffler shell 1. . 1B, the end 4a of the outer tube 4 is reduced in diameter relative to other parts, and the end 4a is connected to the inner tube 3.

  When a plurality of small holes 5 are formed in the inner tube 3 of the tail tube 2 having a double tube structure, the small hole opening ratio is 1% to 1% in the low frequency range (150 Hz or less) even if the small holes 5 are opened. At 7%, the small hole 5 is difficult to be recognized as a boundary condition, and the sound wave passes through the inner tube 3 without passing through the small hole 5, so that the acoustic silencing effect becomes large. As the muffler's noise reduction characteristics, the more the tail tube is squeezed (the smaller the tube diameter), the greater the noise reduction effect and the greater the pressure loss and airflow noise. Doing so improves the sound deadening characteristics. At an aperture ratio of 1% to 7%, the sound wave gradually shifts from the characteristic of completely passing through the inner tube 3 to the characteristic of passing through the outer tube 4 through the small hole 5 as the frequency increases. According to this, the silencing effect from the low frequency to the medium frequency is increased.

  FIG. 2 is a cross-sectional view of the main part showing the tube structure of an internal combustion engine muffler in which the present invention is applied to a long tail tail tube. 2A is an example in which the tail tube 2 in FIG. 1A is elongated, and FIG. 2B is an example in which the tail tube 2 in FIG. 1B is elongated.

  In the case of a long tail, the tail tube throttling effect increases as the tube length increases, but the sound deadening effect increases. The ratio of the throttle may be determined comprehensively based on the sound deadening characteristics, pressure loss, and airflow sound characteristics, but it is more effective to set the throttle portion length (particularly, the tube length L1 of the inner tube 3) to 100 mm or more. When the tail tube length cannot be obtained, a part of the tail tube 2 is inserted into the muffler shell 1 as shown in FIG. In addition, if the tube length of the inner tube 3 is made longer than the outer tube 4, the blowing sound from the inner tube end becomes larger.

  4 and 5 are views showing a tube structure of a muffler for an internal combustion engine in which the present invention is applied to a center tube. In FIG. 4, the center tube 8 provided between the prima muffler 6 and the rear muffler 7 has a double tube structure including an inner tube 9 and an outer tube 10 in which the inner tube 9 is provided. A plurality of small holes are formed so that the opening ratio is 1 to 7% with respect to the total area of the inner tube. In FIG. 4, both ends of the center tube 8 are connected to the end faces of the pre-muffler 6 and the rear muffler 7, respectively, but in FIG. 5, the end of the center tube 8 is inserted into the rear muffler 7.

  As described above, when the present invention is applied to the tail tube 2 and the center tube 8, it is possible to attenuate in a low frequency region by distributing the small holes using the acoustic characteristics, and the exhaust gas passes through the small holes, and the double tube. The air flow noise and pressure loss can also be reduced.

 For example, when the small hole 5 is not formed in the inner tube 3, the air flow noise and pressure loss are greatly increased. However, by forming the small hole 5 having an aperture ratio of several percent in the inner tube 3, the air flow sound and pressure are increased. Loss can also be reduced.

  In addition, according to the present embodiment, low-frequency attenuation can be achieved without using an expensive control valve or the like, so that the muffler itself can be reduced in cost. Further, according to the present embodiment, when the control valve is used, airflow noise is generated in the valve main body when the exhaust gas passes through the valve, but in the structure of the present invention, there is no generation of airflow noise and abnormal noise. .

  FIG. 6 is a characteristic diagram showing the relationship between the small hole aperture ratio and the discharge sound in each frequency band when the diameter of the inner tube is φ38.1 and the diameter of the outer tube is φ54.0. FIG. 6 is a characteristic diagram showing the relationship between the small hole aperture ratio and the discharge sound in each frequency band when the diameter of the outer tube is φ45.0 and the diameter of the outer tube is φ54.0.

  When experimenting with an inner tube diameter of φ38.1 and an outer tube diameter of φ54.0, the aperture ratio of the small hole opening in the inner tube is effective from 1% to attenuate low frequencies below 150 Hz. The effect is good up to 7%, and after 7%, the effect is lost. Further, the airflow sound and pressure loss are saturated at 3% to 5%. A similar result is obtained when the diameter of the inner tube is φ45.0 and the diameter of the outer tube is φ54.0.

  Thus, since the range which has an effect on a design is 1%-7%, it is thought that 1%-7% which is a small hole opening ratio of an inner pipe is applicable for the exhaust system for vehicles. In addition, since it is easier to pass a small hole with a diameter of φ5 or less as an acoustic boundary at 150 Hz or less, it is preferable to use φ5 or less. However, φ1 is too small and clogging may occur due to carbon or the like. It seems to be better to avoid using it. In addition, it is a small hole opening position of the inner tube, but it is desirable to divide and open the tube in the length direction of the tube without concentrating it in one place, and there is a characteristic that it is difficult to become an acoustic boundary. It is also advantageous in terms of pressure loss. Moreover, although the small hole 5 changes according to an aperture ratio, the opening of a length direction may be 1 row or multiple rows.

It is principal part sectional drawing which shows the tube structure of the muffler for internal combustion engines which applied this invention to the tail tube. It is principal part sectional drawing which shows the tube structure of the muffler for internal combustion engines which applied this invention to the tail tube of a long tail. It is principal part sectional drawing which shows the tube structure of the muffler for internal combustion engines of the example which inserted a part of tail tube in the muffler shell, and ensured tube length. It is a figure which shows the tube structure of the muffler for internal combustion engines which applied this invention to the center tube. It is a figure which shows the other example of the tube structure of the muffler for internal combustion engines which applied this invention to the center tube. It is a characteristic view showing the relationship between the small hole aperture ratio and the discharge sound in each frequency band when the diameter of the inner tube is φ38.1 and the diameter of the outer tube is φ54.0. It is a characteristic view showing the relationship between the small hole aperture ratio and the discharge sound in each frequency band when the diameter of the inner tube is φ45.0 and the diameter of the outer tube is φ54.0.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Muffler shell 2 ... Tail tube 3, 9 ... Inner tube 4, 10 ... Outer tube 5 ... Small hole 6 ... Prim muffler 7 ... Rear muffler 8 ... Center tube

Claims (1)

In the tube structure of the muffler for internal combustion engines,
The tube (2) has a double-pipe structure with an inner tube (3) and an outer tube (4) in which the inner tube (3) is disposed.
A muffler tube for an internal combustion engine, wherein the inner pipe (3) is provided with a plurality of small holes (5) so that the opening ratio is 1% to 7% with respect to the total area of the inner pipe. Construction.

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