JP2016108957A - Silencer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silencer which enables an inner pipe to be easily attached to a division plate, and which suppresses generation of whistling noises.SOLUTION: A silencer has an outer shell 2. An inner cylinder 10 is provided in the outer shell 2. A plurality of through-holes 15A and 15B are formed on a peripheral wall of the inner cylinder 10. The silencer is formed so that the relational expression, 0<L2/(4×L1)<1/6, can hold, when L1 represents a minimum distance between an inner peripheral surface of the outer shell 2 and the through-hole 15A and L2 represents a minimum distance between the adjacent through-holes 15A and 15B.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a silencer, for example, a silencer used as a silencer for an internal combustion engine or the like mounted on an automobile.

  A muffler is mounted on a vehicle using an internal combustion engine as a power source for the purpose of reducing noise generated from the internal combustion engine.

  In such a silencer, since the flow velocity of the gas flowing through the silencer is in a wide range of 5 to 120 m / s, a whistling sound that is an abnormal sound may be generated.

  Therefore, conventionally, a large number of small holes are formed in the inner pipe, and a louver that opens in the circumferential direction is provided outside the small hole, so that the opening can be connected between the inner pipe and the housing provided on the outer peripheral portion thereof. There is known a silencer that suppresses outflow of exhaust pulsation radiated into a resonance chamber composed of a formed air layer and suppresses the generation of whistling noises that are abnormal sounds (see Patent Document 1).

  Further, a silencer is known in which an inner pipe provided with a plurality of small holes is provided with irregularities so that the flow of exhaust gas is disturbed and generation of whistling noise is suppressed by canceling resonance action (Patent Literature). 2).

JP 2004-36589 A JP-A-8-35416

  In the silencers described in Patent Documents 1 and 2, since any inner pipe has a shape that protrudes outside the diameter of the raw pipe due to louvers or unevenness, a partition plate is provided in the housing to provide a resonance chamber or expansion. In a silencer that provides a chamber, in order to insert the inner pipe through the mounting hole formed in the partition plate during assembly, it is necessary to make the diameter of the mounting hole larger than the inner pipe diameter of the inner pipe. A gap is generated between the partition plate and the inner pipe cannot be press-fitted into the partition plate. Further, when the inner pipe is attached to the partition plate by welding, the welding cannot be easily performed, and there is a problem in assembling.

  Therefore, the present invention has an object to provide a silencer that can easily assemble an inner pipe to a partition plate without providing the louver or unevenness as described above, and suppress the generation of whistling noise. To do.

In order to solve the above problems, the present invention has an outer shell, and an inner cylinder is provided in the outer shell.
A plurality of through holes are formed in the peripheral wall of the inner cylinder,
When the minimum distance between the inner peripheral surface of the outer shell and the through hole is L1, and the minimum distance between adjacent through holes is L2,
It is formed so that the relational expression of 0 <L2 / (4 × L1) <1/6 holds.

  According to the present invention, the whistle blowing is such that the minimum distance L1 between the inner peripheral surface of the outer shell and the through hole and the minimum distance L2 between adjacent through holes are 0 <L2 / (4 × L1) <1/6. By suppressing the generation of noise, there is no need to change the inner tube diameter of the inner cylinder, and the inner cylinder can be easily assembled to the partition plate, etc. Can be reduced.

1 is a cross-sectional view in the axial direction of a silencer according to a first embodiment of the present invention. AA sectional view taken on the line AA of FIG. The elements on larger scale explaining the arrangement | sequence of the through-hole in FIG. The perspective view for demonstrating reduction of a whistling sound in this invention. The graph for demonstrating the synthetic | combination sound in the case of set it as (alpha) = 0.1. The graph for demonstrating the synthetic | combination sound in the case of being set to (alpha) = 0.25. An axial direction sectional view showing an example of a silencer concerning Example 3 of the present invention.

  The silencer of the present invention can be used as any silencer used for internal combustion engines such as vehicles, general-purpose engines, stationary combustion apparatuses, and the like. The following embodiments will be described based on an example in which the present invention is applied to a silencer used in an internal combustion engine such as a vehicle.

[Example 1]
1 to 4 show a first embodiment of the present invention.

  FIG. 1 is a cross-sectional view of the silencer 1 in the axial direction, and FIG. 2 is a cross-sectional view taken along line AA of FIG.

  As shown in FIG. 2, the silencer 1 has an outer shell 2 which is an outer shell formed in a cylindrical shape with an oval cross section, and an outer plate 3 is provided at both ends of the axial direction XX. 4 is fixed. The outer plate 3 has an inlet pipe insertion hole 3a, and the outer plate 4 has an outlet pipe insertion hole 4a.

  Further, an inner plate 5 is provided in the outer shell 2, and a first silencing chamber 7 and a second silencing chamber 8 are defined by the inner plate 5. The first silencing chamber 7 and the second silencing chamber 8 communicate with each other through a communication hole 5 a formed in the inner plate 5. The inner plate 5 has an inlet pipe insertion hole 5b and an outlet pipe insertion hole 5c.

  An inlet pipe 10 that is an inner cylinder is press-fitted into the inlet pipe insertion holes 3 a and 5 b of the outer plate 3 and the inner plate 5 and fixed.

  Further, the outlet pipe 11 which is an inner cylinder is press-fitted into the inlet pipe insertion holes 4 a and 5 c of the outer plate 4 and the inner plate 5 and fixed. The inlet pipe 10 or the outlet pipe 11 may be assembled to the outer plates 3 and 4 and the inner plate 5 by welding instead of press fitting.

  As shown in FIG. 3, a plurality of through holes 15 having the same inner diameter d are formed in the peripheral wall of the inlet pipe 10. A louver or the like as in the prior art is not formed on the periphery of the through hole 15. Further, the through holes 15 may be provided in substantially the entire axial direction of the inlet pipe 10 or may be provided only in a part of the axial direction. Moreover, the through-hole 15 may be provided in the whole circumferential direction centering on the axial center of the inlet pipe 10, or may be provided only in a part in the circumferential direction. Moreover, it is preferable to set all the distance L2 between the adjacent through-holes 15 and 15 the same.

  Next, generation of a whistling sound and reduction of the whistling sound will be described.

  In FIG. 4, an explanation will be given assuming that any one of the through holes 15 is 15A, and one through hole adjacent to the through hole 15A is 15B.

  When the exhaust gas flows through the inlet pipe 10 in the direction of arrow B in FIG. 4, a vortex lump formed at the upstream peripheral edge 15a of the through hole 15A collides with the downstream peripheral edge 15b to cause pressure fluctuation. This pressure fluctuation is amplified when the air layer between the through hole 15A of the inlet pipe 10 and the outer shell 2 serves as a resonator, and a whistling sound is generated.

The frequency f ₁ (Hz) of the pressure fluctuation generated when the vortex block collides with the peripheral edge 15b on the downstream side is:
When the flow rate of the exhaust gas is u (m / s) and the inner diameter of the through hole 15 is d (m),
f ₁ = 0.5 × u / d (1)
It becomes.

Further, the frequency f ₂ (Hz) when the air layer between the through hole 15A and the outer shell 2 serves as a resonator is:
If the speed of sound is c (m / s) and the distance between the through hole 15A and the inner peripheral surface of the outer shell 2 is L1,
f ₂ = c / (4 × L1) (2)
Thus, the whistling sound is generated in the through hole 15A when f ₁ = f ₂ .

Next, when α = propagation time when sound is transmitted from the through hole 15A to the through hole 15B / one cycle time of pressure fluctuation generated in the through hole 15A, the distance between the adjacent through holes 15A and 15B is L2. From equation (1), f ₁ = f ₂ ,
α = (L2 / c) / (2 × d / u)
= (L2 / c) / (4 × L1 / c)
= L2 / (4 × L1) (3)
It becomes.

In addition, the whistling sound p ₁ (t) generated in the through hole 15A is
θ = ωt (rad), ω: angular frequency (rad / s), a: amplitude of sound generated in the through hole 15A,
p ₁ (t) = asin ωt = acos (ωt + π / 2)

  The whistling sound generated in the through-hole 15A propagates to the through-hole 15B, and when the through-hole 15B functions as a resonator, the whistling sound generated in the through-hole 15A is delayed in phase from the whistling sound generated in the through-hole 15A. Occur.

The phase delay t ′ due to the propagation of sound from the through hole 15A to the through hole 15B is expressed by the following equations (2) and (3):
t ′ = L2 / c = α × (4 × L1) / c = α / f
In the through-hole 15B, the phase delay t ″ due to the time from when the sound enters until it comes out is expressed by the following equation (2):
t ″ = 2 × L1 / c = 1 / (2 × f)

Therefore, the sound p ₂ (t) generated in the through hole 15B is
p ₂ (t) = asin (ωt−t′−t ″)
= Asin ω (t−α / f−1 / (2 × f))
= Cos (ωt-2πα-π + π / 2)

The synthesized sound p (t) generated by the interference between the whistling sound generated in the through hole 15A and the phase delayed sound generated in the through hole 15B is
p (t) = p ₁ (t) + p ₂ (t)
= Cos (ωt + π / 2) + acos (ωt-2πα-π + π / 2)

Assuming that the amplitude of the synthesized sound is A, basic acoustics by Shigeru Yoshikawa and Satoshi Fujita (Kodansha 2002) p50-51
A ² = a ² + a ² +2 aacos (−2πα−π)
It becomes.

The synthesized sound does not become larger than the whistling sound generated in the through hole 15A, that is, 0 <A / a <1 where the amplitude A of the synthesized sound is smaller than the amplitude a of the sound generated in the through hole 15A.
0 <α = L2 / (4 × L1) <1/6
At the time.

  For example, when α = 0.1, the phase difference generated while sound is transmitted from the through hole 15A to the through hole 15B is π / 5, and the sound emitted from the through hole 15A and the sound emitted from the through hole 15B are As shown in FIG. 5, the synthesized sound is smaller than the sound emitted from the through hole 15A.

  Thus, when α <1/6, the sound emitted from the through hole 15A and the sound emitted from the through hole 15B interfere with each other and cancel each other, so that the synthesized sound is produced by the whistle blowing generated in the through hole 15A. It becomes smaller than the noise.

  On the other hand, when α = 0.25, the phase difference generated while sound is transmitted from the through hole 15A to the through hole 15B is π / 2, and the sound emitted from the through hole 15A and the sound emitted from the through hole 15B are As shown in FIG. 6, the synthesized sound is larger than the sound emitted from the through hole 15A.

  Thus, when α> 1/6, the sound emitted from the through hole 15A and the sound emitted from the through hole 15B are amplified by interference, and the synthesized sound is produced by the whistling sound generated in the through hole 15A. Become bigger.

  As described above, the distance between the through hole 15 and the outer shell 2 differs depending on the position where the through hole 15 is formed. The influence at the through hole 15 is great. Further, since the interference action between the most adjacent through holes 15A and 15B is strong, L1 at 0 <α = L2 / (4 × L1) <1/6 uses the minimum distance between the through hole 15 and the outer shell 2. , L2 is a silencer that suppresses the generation of whistling noise by setting the positions of the through hole 15 and the inlet pipe 10 so that this relational expression is established using the minimum distance between the adjacent through holes 15A and 15B. 1 can be used.

  Further, in the silencer designed in this way, the silencer designed so that α = 0.16 does not generate a whistling sound, and the silencer designed so that α = 0.23 does not produce a whistling sound. It was also confirmed from experiments that the generation of whistling noise can be suppressed by setting α <1/6.

  In addition, since the relationship between the minimum distance L1 between the through-hole 15 and the outer shell 2 and the distance L2 between the adjacent through-holes 15 can be set to a predetermined relationship, the generation of whistling noise can be suppressed. There is no need to change the tube diameter as in the prior art. Therefore, the inlet pipe 10 can be easily assembled by being press-fitted into the inlet pipe insertion holes 3a and 5b of the outer plate 3 and the inner plate 5 or welded. The manufacturing cost can be reduced.

[Example 2]
In the first embodiment, the inlet pipe 10 is formed with a plurality of through holes 15 that satisfy the relationship 0 <L2 / (4 × L1) <1/6, but the outlet pipe 11 has 0 <L2 / (4 × L1). ) A plurality of through-holes 15 satisfying a relationship of <1/6 may be formed, or through-holes satisfying a relationship of 0 <L2 / (4 × L1) <1/6 are formed in the inlet pipe 10 and the outlet pipe 11. A plurality of 15 may be formed.

Since other structures are the same as those of the first embodiment, the description thereof is omitted.
Also in the second embodiment, the same effect as the first embodiment is obtained.

[Example 3]
The present invention is not limited to the structure of the silencer 1 shown in the drawing according to the first embodiment, and may have any outer shell and an inner cylinder having a plurality of through holes formed in the outer shell. It can be applied to a silencer of any structure.

  As the outer shell, which is an outer shell, a metal plate wound, one formed by spinning, one formed by press molding, or the like can be used. Can be set to

  For example, as shown in FIG. 7, the present invention is applied to a silencer 20 in which both ends of a cylindrical outer shell 21 have a tapered diameter and the inner cylinder 22 is inserted into the outer shell 21. Can do. A through hole 15 similar to that of the first embodiment is formed in the inner cylinder 22.

  Also in the third embodiment, the same effects as in the first and second embodiments are obtained.

1,20 silencer 2,21 outer shell 10,11,22 inner cylinder 15 through hole

Claims (1)

An outer shell, and an inner cylinder in the outer shell;
A plurality of through holes are formed in the peripheral wall of the inner cylinder,
When the minimum distance between the inner peripheral surface of the outer shell and the through hole is L1, and the minimum distance between adjacent through holes is L2,
A muffler characterized in that the relational expression of 0 <L2 / (4 × L1) <1/6 holds.

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