JPH0141852Y2 - - Google Patents

Description

[Detailed explanation of the idea] (Technical field) The present invention relates to a silencer for automobiles.

(Prior art) Examples of conventional silencers include the one shown in Figure 1 (Fourth Report on Automobile Pollution Prevention Technology (Environment Agency, Automobile Pollution Prevention Technology Evaluation Committee,
(Published in May 1981)) is known.

In FIG. 1, 1 is an outer cylinder whose both ends are closed by closing plates 2 and 3, and inside the outer cylinder 1 is a partition plate 4,
5 defines U-turn type expansion chambers 6, 7 and a resonance chamber 8 sequentially from the closing plate 2 side. Also 9
An exhaust introduction pipe communicates with the engine via an exhaust manifold (not shown), and the exhaust introduction pipe 9 penetrates the expansion chamber 6 and opens into the expansion chamber 7. Furthermore, 10 is an exhaust outlet pipe that opens to the atmosphere, and the exhaust outlet pipe 10 penetrates the resonance chamber 8 and the expansion chamber 7, projects into the expansion chamber 6, and is open. Further, the expansion chamber 6 and the expansion chamber 7 communicate with each other through a hole 11 formed in the partition plate 4, and the expansion chamber 7 and the resonance chamber 8 are connected to the axis of the exhaust inlet pipe 9 in the partition plate 5. They are communicated by a cervical canal 12 disposed on the same line.

In such a silencer for an automobile, the exhaust gas introduced into the expansion chamber 7 from the exhaust introduction pipe 9 makes a U-turn in the expansion chamber 7, flows through the hole 11 to the expansion chamber 6, and then makes a U-turn in the expansion chamber 6. and is discharged to the atmosphere through the exhaust outlet pipe 10. The noise transmitted from the engine is transmitted through the exhaust introduction pipe 9, the expansion chamber 7 and the hole 11.
In the expansion type noise reduction element constituted by the expansion chamber 6 and the expansion chamber 6, noise mainly in the medium and high frequency range is reduced.
Further, this noise is reduced in a low frequency region in a Helmholtz resonator (resonance type muffling element) composed of the cervical canal 12 and the resonance chamber 8.

However, in such conventional automobile silencers, the exhaust gas expands and contracts twice in the U-turn expansion chambers 6 and 7, and then makes a U-turn before being released into the atmosphere. When the rotation speed becomes high and the load increases and the flow velocity of the exhaust gas increases, the pressure loss of the exhaust gas increases and the secondary air flow noise increases. As a result, there were problems in that engine output decreased, fuel consumption deteriorated, and exhaust noise increased.

(Purpose of the invention) Therefore, the present invention defines a first chamber and a second chamber in the outer cylinder, passes the exhaust introduction pipe through the first chamber, and opens its outlet end into the second chamber. A plurality of small holes communicating with the first chamber are bored in the part of the exhaust introduction pipe that penetrates the first chamber, and the number of small holes per unit area of the pipe wall increases as the small holes go downstream. The exhaust outlet pipe is bored through the second chamber and its inlet end is opened to the first chamber, and the exhaust outlet pipe has a plurality of holes in the portion passing through the second chamber that communicate with the second chamber. By drilling small holes, the number of small holes per unit area of the pipe wall increases as you go downstream, allowing exhaust to be discharged through two systems without making a U-turn. The purpose is to reduce secondary airflow noise and exhaust pressure loss, reduce exhaust noise, and improve engine output and fuel efficiency.

(Structure of the invention) The automobile silencer of the invention includes an outer cylinder in which a first chamber and a second chamber are defined, and a structure that penetrates through the first chamber.
an exhaust introduction pipe whose outlet end opens into the second chamber; and an exhaust outlet pipe which passes through the second chamber and whose inlet end opens into the first chamber, the exhaust introduction pipe passing through the first chamber. A small hole communicating with the first chamber is bored in the part, and the opening density of the small hole with respect to the first chamber of the exhaust inlet pipe increases as it goes downstream, and the second chamber of the exhaust outlet pipe is penetrated. By drilling a plurality of small holes that communicate with the second chamber in the part where the exhaust outlet pipe is located, and by increasing the opening density of the small holes toward the second chamber of the exhaust outlet pipe toward the downstream, secondary airflow noise can be reduced. This reduces the pressure loss of the exhaust gas.

(Example) Hereinafter, the present invention will be explained based on the drawings.

FIG. 2 is a diagram showing a first embodiment of the present invention.

First, to explain the configuration, in Fig. 2, 2
Reference numeral 1 denotes an outer cylinder whose both ends are closed by closing plates 22 and 23, and inside the outer cylinder 21, partition plates 24 and 25 sequentially open a first chamber 26 and a second chamber from the closing plate 22 side.
A chamber 27 and a third chamber 28 are defined. Second
The chamber 27 has an exhaust gas introduction pipe 29 that penetrates the first chamber 26.
The outlet end of the exhaust inlet pipe 29 protrudes and is open.
A plurality of small holes 30 communicating with the first chamber 26 are bored in the portion that penetrates the first chamber 26 . The plurality of small holes 30 are formed such that the number of small holes 30 per unit area of the pipe wall of the exhaust gas introduction pipe 29 increases toward the downstream side (outlet end) of the exhaust gas introduction pipe 29. That is, the opening amount (opening density) of the small holes per unit length of the tube increases toward the downstream side. The inlet end of the exhaust introduction pipe 29 communicates with the engine via an exhaust manifold (not shown). And the second chamber 27 and the third chamber 2
8 is communicated with the partition plate 25 through a cervical pipe 31 arranged so that its axis coincides with that of the exhaust gas introduction pipe 29. Further, 32 is an exhaust outlet pipe, and the exhaust outlet pipe 32 passes through the second chamber 27 and the third chamber 28, and its inlet end is open to the first chamber 26, and its outlet end is open to the atmosphere. . The exhaust outlet pipe 32 has a plurality of small holes 33 in the part that penetrates the second chamber 27.
is drilled. The plurality of small holes 33 correspond to a unit area of the wall of the exhaust outlet pipe 32 as it goes downstream (outlet end) of the exhaust outlet pipe 32.
The holes are drilled so that the number of holes increases. That is, the opening density of the small holes 33 of the exhaust outlet pipe 32 with respect to the second chamber 27 increases as it goes downstream.

Next, the effect will be explained.

Exhaust gas sent from the engine (not shown) to the exhaust introduction pipe 29 via the exhaust manifold is passed through the small holes 30.
It is discharged into the first chamber 26 through the outlet, and is also discharged into the second chamber 27 from its outlet end. 1st room 26
The exhaust gas discharged into the air enters the exhaust outlet pipe 32 from the inlet end of the exhaust outlet pipe 32 and is discharged to the outside of the atmosphere. The exhaust gas released into the second chamber 27 passes through the small hole 33.
It is discharged to the atmosphere through the exhaust outlet pipe 32. Therefore, the exhaust gas from the engine does not make a U-turn, but instead flows through the first path via the first chamber 26 and the second chamber 27.
The exhaust gas is discharged to the atmosphere through two routes, including the second route via which the exhaust gas pressure loss can be reduced.

On the other hand, the noise propagated from the engine through the exhaust inlet pipe 29 into the automobile silencer is caused by the exhaust gas expanding in the first chamber 26 through the small hole 30 and the exhaust exit pipe 29.
2, and the exhaust gas introduction pipe 29
The air expands when being discharged from the air into the second chamber 27 and contracts when flowing into the exhaust outlet pipe 32 through the small hole 33, thereby muffling the sound.

Generally, the exhaust pressure is proportional to the square of the exhaust flow velocity V (V ² ) passing through a small hole in the exhaust pipe, and the magnitude of the secondary air flow noise generated when passing through the small hole is 6 of the exhaust flow velocity V. It is proportional to the power (V ⁶ ). Therefore, as the velocity of the exhaust gas passing through the small holes increases, the secondary airflow noise further increases. Incidentally, the exhaust flow rate passing through this small hole changes depending on the pressure difference between the inside and outside of the exhaust pipe.

In other words, when exhaust gas is directly released into the atmosphere from the small hole in the exhaust pipe as shown in Figure 3a, the atmospheric pressure
P _O is constant as shown in Figure 3b, but the pressure P in the exhaust pipe is decreasing from upstream P ₁ to downstream P ₂ , so the exhaust flow rate passing through the small hole is As shown by the arrows in Figure 3a, it is faster on the upstream side where the pressure difference with atmospheric pressure P _O is large, and slow on the downstream side where the pressure difference with atmospheric pressure P _O is small.

Therefore, as shown in FIG. 4a, when the exhaust gas introduction pipe 34 penetrates the first chamber 37, the exhaust gas discharged into the first chamber 37 passes through the exhaust outlet pipe 38 and is discharged to the atmosphere. Therefore, the pressure distribution in the first chamber 37 is the pressure on the closing plate 45 side as shown in FIG. 4b.
The pressure _P4 on the partition plate 46 side is lower than _P3 . On the other hand, the pressure P inside the exhaust gas introduction pipe 34 is
As in the case of figure b, the pressure increases as you go downstream.
The pressure decreases from P ₁ to P ₂ . Therefore, if the small holes 35 are uniformly formed in the exhaust gas introduction pipe 34, the velocity of the exhaust gas passing through the small holes 35 increases as it goes downstream, as shown in FIG. 4a. . However, in this embodiment, the small holes 35 of the exhaust gas introduction pipe 34 are formed so that the opening density increases toward the downstream side, so that the exhaust flow rate passing through the small holes 35 on the downstream side is large. This prevents the secondary airflow noise from increasing.

Further, as shown in FIG. 5a, the exhaust outlet pipe 38
passes through the second chamber 39, the exhaust introduction pipe 3
The exhaust gas diffused into the second chamber 39 from the small hole 4
2 into the exhaust outlet pipe 38, the pressure in the second chamber 39 decreases as it moves toward the partition plate 40, but the exhaust gas discharged from the exhaust introduction pipe 34 into the second chamber 39 flows into the partition plate 40. 40 and the cervical canal 41, the pressure in the second chamber 39 near the partition plate 40 and the cervical canal 41 increases rapidly. On the other hand, the pressure inside the exhaust outlet pipe 38 is increased from the first chamber 37 to the exhaust outlet pipe 3.
Since the exhaust gas flowing into the exhaust gas 8 undergoes contraction when flowing in, the pressure P ₇ on the upstream side is higher than the pressure P ₈ on the downstream side. Therefore, the pressure difference between the pressures _P6 and ₈ is larger than the pressure difference between the pressures _P5 and _P7 . As a result, if the small holes 42 are formed in the exhaust outlet pipe 38 with a uniform opening density, the velocity of the exhaust gas passing through the small holes 42 increases toward the downstream side, as shown by the arrows in FIG. 5a. Therefore, it becomes larger. However, in this embodiment, the exhaust outlet pipe 38
Since the small holes 42 are formed so that the opening density increases toward the downstream side, the exhaust airflow passing through the small holes 42 on the downstream side is prevented from increasing, and secondary airflow noise is reduced. Growth is prevented.

In this example, an increase in secondary airflow noise generated within an automobile silencer is prevented, so
The exhaust frequency characteristics when the engine is operated at high load and high rotation speed can be shown as shown in Figure 6, and compared to the noise level of the conventional automobile silencer (indicated by the solid line B), Example noise level (dashed line A
) is not only reduced in the entire frequency range, but is particularly reduced in the medium to high frequency range to the high frequency range.

Next, a second embodiment is shown in FIG. In explaining this embodiment, the same components as those of the automobile silencer of the first embodiment are given the same reference numerals, and the explanation thereof will be omitted. In the first embodiment, in order to increase the opening density of the plurality of small holes 43, 44 toward the downstream side, the number of small holes 43, 44 per unit area of the pipe wall is increased toward the downstream side. It was drilled to do so. However, in this embodiment, the number of small holes 43, 44 per unit area of the tube wall is made uniform from the upstream side to the downstream side, and the small holes 43, 44 are made uniform from the upstream side to the downstream side.
The small holes 43 and 44 are bored so that the diameter of the holes 44 becomes larger toward the downstream side. That is, in this way, the opening density of the small holes 43 and 44 is increased toward the downstream side. Further, regarding the shape of the small hole 43, since the exhaust gas in the exhaust introduction pipe 29 is released into the first chamber 26 through the small hole 43, the small hole 43 is designed so that the exhaust gas can be smoothly released.
3 is bent toward the first chamber 26 and burred. Exhaust outlet pipe 32
Regarding the small hole 44, the exhaust gas discharged into the second chamber 27 flows into the exhaust outlet pipe 32 through the small hole 44,
The exhaust gas released into the first chamber 26 constricts from the inlet end of the exhaust outlet pipe 32 and travels straight through the exhaust outlet pipe 32, so that the exhaust gas from the second chamber 27 flows smoothly into the exhaust outlet pipe 32 through the small hole 44. A small hole 44 is provided so that the air can flow in and smoothly go straight through the exhaust outlet pipe 32.
The peripheral edge is bent toward the second chamber 27 and further bent toward the inside of the exhaust outlet pipe 32 to perform a double burring process. Therefore, small hole 4
3, 44 and the inside of the exhaust outlet pipe 32 becomes smooth, and the pressure loss of the exhaust inside the automobile silencer can be further reduced.

(Effects) According to the present invention, the exhaust gas is discharged through two systems without making a U-turn, so it is possible to reduce the pressure loss of the exhaust gas, and it also allows the exhaust gas to pass through the small hole on the downstream side of the exhaust inlet pipe and the exhaust outlet pipe. Since the exhaust flow velocity of the exhaust gas is reduced, it is possible to significantly reduce noise at medium to high frequencies or higher, particularly secondary airflow noise generated in an automobile muffler. Therefore,
Engine output and fuel efficiency can be improved, and external noise can be significantly reduced.

In addition, in the first embodiment, the small holes were drilled with the same diameter, making it easy to work the small holes, and in the second embodiment, the periphery of the small holes was bent. Therefore, there is an effect that the pressure loss of exhaust gas can be further reduced.

[Brief explanation of drawings]

FIG. 1 is a front sectional view showing a conventional automobile silencer. FIG. 2 is a front sectional view of the first embodiment of the automobile silencer according to the present invention. Figure 3 a, b, Figure 4 a, b, and Figure 5 a, b are diagrams showing the relationship between pressure changes inside and outside the exhaust pipe and the exhaust flow velocity passing through the small hole. FIG. 3 is a diagram illustrating the exhaust sound frequency characteristics of the automobile silencer according to the present invention in comparison with a conventional example when operating under high load rotation. FIG. 7 is a front sectional view showing a second embodiment of the automobile silencer according to the present invention. 21...Outer cylinder, 26...First chamber, 27...Second
Chamber, 29... Exhaust introduction pipe, 30, 43... Small hole,
32...Exhaust outlet pipe, 33, 44...Small hole.

Claims (1)

[Scope of utility model registration request] an outer cylinder having a first chamber and a second chamber defined therein; an exhaust introduction pipe that passes through the first chamber and has an outlet end opening into the second chamber; and an inlet end that passes through the second chamber. and an exhaust outlet pipe opening into the first chamber, and a plurality of small holes communicating with the first chamber are bored in a portion of the exhaust introduction pipe that penetrates the first chamber, and the exhaust introduction pipe is formed by the small holes. The opening density for the first chamber of the exhaust outlet pipe increases as it goes downstream, and
A plurality of small holes communicating with the second chamber are formed in the portion penetrating the chamber, and the opening density of the small holes with respect to the second chamber of the exhaust outlet pipe increases as it goes downstream. Automobile silencer.