JPH01195908A - Engine exhauster - Google Patents

Abstract

PURPOSE:To improve the reliability of an exhaust system and to reduce internal noise effectively by arranging a gate valve in the upstream of a silencer arranged in one branch exhaust path and arranging an exhaust silencer in the other branch exhaust path. CONSTITUTION:A common exhaust path 1 is branched into first and second exhaust paths 4, 5 at a branch section 3 in the downstream of a catalyst converter 2. A gate valve 6 is placed in the first exhaust path 4. The exhaust resistance of a low speed exhaust silencer is set higher than that of a high speed exhaust silencer 11. Consequently, the durability or reliability of the exhaust system can be improved and exhaust noise can be reduced effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine exhaust system, and in particular, it is provided with an exhaust silencer for high speeds and an exhaust silencer for low speeds, and is equipped with an exhaust silencer for high speeds and an exhaust silencer for low speeds. The present invention relates to an exhaust system in which these can be switched by hand.

(Prior Art) In recent years, as engines have become more powerful, there has been a demand for exhaust silencers with low exhaust resistance and high silencing power. However, there is a problem in that exhaust noise cannot be effectively reduced by simply providing one exhaust silencer because the muffling methods are different for high-frequency sounds that occur mainly at high speeds and low-frequency sounds that occur mainly at low speeds.

Therefore, at the branch part of the common exhaust passage downstream of the catalytic converter, the common exhaust passage is branched into a first branch exhaust passage and a second branch exhaust passage.
A high-speed exhaust silencer configured to reduce high-frequency noise is interposed in the second branch exhaust passage (which may also be a branch exhaust passage), and a low-speed exhaust silencer configured to reduce low-frequency noise is installed in the second branch exhaust passage. An exhaust system has been proposed that is equipped with a so-called dual-type exhaust silencer, which is equipped with an on-off valve that switches the inflow path of exhaust gas to these two exhaust silencers depending on the operating state of the engine. For example, see Japanese Unexamined Patent Application Publication Nos. 59-74325).

However, if such an on-off valve is placed immediately downstream of the catalytic converter, exhaust gas heated by the catalytic converter will flow into the on-off valve, impairing the reliability of the on-off valve. is placed at a position immediately upstream of the high-speed exhaust exhaust sensor in the first branch exhaust passage in order to separate it from the catalytic converter as much as possible and to simplify the structure.

(Problem to be Solved by the Invention) However, in the above conventional exhaust system equipped with a dual type exhaust silencer, the exhaust systems on the first branch exhaust passage side and the second branch exhaust passage side arranged on the left and right sides are heavy and heavy. Since the exhaust passage becomes unbalanced, a difference in stress occurs in the branch part due to the swing phase difference between the first and second branch exhaust passages, causing problems such as damage to the branch part.

The present invention has been made in view of the above-mentioned conventional problems. Reduces the swing phase difference between the second branch exhaust passages,
A dual-type design that improves the vibration characteristics of the exhaust system, reduces uneven stress generated at the branch parts, and effectively prevents damage to the branch parts, improving the reliability of the exhaust system. An object of the present invention is to provide an exhaust system for an engine provided with an exhaust silencer.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a catalytic converter interposed in a common exhaust passage, and two branch exhausts that branch from the common exhaust passage at a branching part downstream of the catalytic converter. In an engine exhaust system in which a silencer is provided in each of the branch exhaust passages, an on-off valve that is controlled according to the operating load of the engine is provided upstream of the silencer in one of the branch exhaust passages. An exhaust system for an engine is provided, characterized in that the other branch exhaust passage is provided with an exhaust silencer having an internal structure having a greater exhaust resistance than the silencer on the side in which the on-off valve is interposed.

(Operations and Effects of the Invention) According to the present invention, the exhaust silencer (hereinafter referred to as the first exhaust silencer) on the side of the branch exhaust passage in which the on-off valve is provided and the other on-off valve is not provided. Exhaust silencer on the branch exhaust passage side (hereinafter referred to as the second silencer)
The structure is different from that of the first exhaust silencer, and in order to increase the exhaust resistance, the second exhaust silencer has more partition walls than the first exhaust silencer, and is heavier. Therefore, the total weight of the on-off valve and the first exhaust silencer provided on one branch exhaust passage side can be set to be approximately equal to the weight of the second exhaust silencer provided on the other branch exhaust passage side. Since the vibration phase difference between the two branched exhaust passages can be reduced, the vibration characteristics of the exhaust system can be improved and uneven stress can be prevented from being generated at the branched portion. For this reason,
The reliability of the exhaust system can be improved.

Furthermore, at low speeds, the second exhaust silencer reduces low-frequency sounds that cause muffled noise, so it is possible to effectively reduce muffled sounds in low-speed driving ranges.

Further, according to the present invention, since the exhaust resistance of the first exhaust silencer is small, the exhaust pressure of the engine at high speed can be effectively reduced, and a decrease in engine output can be prevented.

(Example) Examples of the present invention will be specifically described below.

As shown in Figure 1, a common exhaust passage for the engine! for,
A catalytic converter 2 using a three-way catalyst consisting of an oxidation catalyst that oxidizes hydrocarbons, unburned fuel, etc. and converts it into carbon dioxide and water, and a reduction catalyst that reduces nitrogen oxides and converts them into nitrogen. It is set up.

When hydrocarbons, unburned fuel, etc. are oxidized in this catalytic converter 2, reaction heat is generated, so when the exhaust gas contains a large amount of hydrocarbons, unburned fuel, etc. The gas temperature is set to rise considerably.

The common exhaust passage 1 (at the branch part 3 slightly downstream of the catalytic converter 2, the first branch exhaust passage 4 and the second branch exhaust passage 5
It is branched into. An on-off valve 6 is interposed in the first branch exhaust passage 4 to open and close it. This on-off valve 6
reliability decreases when exposed to high-temperature exhaust gas,
As described above, since the exhaust gas discharged from the catalytic converter 2 may reach a high temperature, the on-off valve 6 is arranged as far downstream as possible based on the layout.

An actuator 7 using, for example, a negative pressure responsive diaphragm device is provided for the on-off valve 6, and the actuator 7 receives a signal from a control unit 8 and performs a predetermined operation as described later. At high speeds, the on-off valve 6 is opened, and at predetermined low speeds, the on-off valve 6 is closed.

Immediately downstream of the on-off valve 6 of the first branch exhaust passage 4, a high-speed exhaust silencer 11, which will be explained in detail later, is interposed, while in the second branch exhaust passage 5, an extension of the common exhaust passage l is provided. In terms of direction, a low speed exhaust silencer 12, which will be described in detail later, is interposed at a position that substantially corresponds to the high speed exhaust silencer 11.

As shown in FIG. 2, the high-speed exhaust silencer 11 is provided with a slightly elongated cylindrical outer cylinder 16.
The space defined inside by the second partition wall 1
7 and a second partition wall 18.
From the left side of the figure), the 1st/l! ! A sound chamber 21, a second silencing chamber 22, and a third silencing chamber 23 are provided. and,
In order to introduce exhaust gas into the high-speed exhaust silencer 11, a high-speed side exhaust introduction passage 24 is provided, and the high-speed side exhaust introduction passage 24 is connected to the first branch exhaust passage 4 (see Fig. 1). . This high-speed side exhaust introduction passage 24 is connected to the outer cylinder 16.
The second silencing chamber 22 is inserted through the front wall of the first silencing chamber 21 and the first silencing chamber 21.
It communicates with In addition, the first
A large number of small-diameter holes 25 are bored in the portion through which the silencing chamber 21 passes. In the exhaust sound of the exhaust gas passing through the high-speed side exhaust introduction passage 24, a high frequency portion is absorbed by the sound absorbing material in the first silencing chamber 21 through the small diameter hole 25. Furthermore, when the exhaust gas flows from the high-speed side exhaust introduction passage 24 into the second muffling chamber 22 (expansion chamber), it expands slightly, thereby relatively reducing low-frequency noise.

The second silencing chamber 22 communicates with a third silencing chamber 23 (resonance chamber) via a communication path 27, and the resonance effect of the third silencing chamber 23 reduces exhaust noise at a predetermined frequency. ing. The exhaust gas in the second muffling chamber 22 is discharged into the atmosphere through the high-speed tail pipe 28.

In addition, as shown in Fig. 3, the exhaust silencer 1 for low speed
2 is provided with a slightly elongated cylindrical outer cylinder 31 having approximately the same volume as the outer cylinder 16 of the high-speed exhaust silencer 11 (see Fig. 2), and is defined inside by the outer cylinder 3I. The space is partitioned by a first partition wall 32, a second partition wall 33, and a third partition wall 34, and in order from the upstream side (left side in FIG. 2), a first silencing chamber 35 and a second silencing chamber 36. and third
A silencing chamber 37 and a fourth silencing chamber 38 are provided. In order to introduce exhaust gas into the low-speed exhaust silencer 12, a low-speed side exhaust introduction passage 41 is provided, and the low-speed side exhaust introduction passage 41 is connected to the second branch exhaust passage 5 (see FIG. 1).
It is connected to the. This low speed side exhaust introduction passage 4! penetrates the front wall of the outer cylinder 31 and the first silencing chamber 35 and communicates with the second silencing chamber 36 . Then, when the exhaust gas flows from the low-speed exhaust introduction passage 41 into the second muffling chamber 36 (expansion chamber), it expands slightly, thereby relatively reducing low-frequency noise.

Then, the second muffler 36 is connected to the fourth muffler through the first communication path 43.
It communicates with a silencing chamber 38 (resonance chamber), and the resonance effect of the fourth silencing chamber 38 reduces exhaust noise at a predetermined frequency. Furthermore, the second silencing chamber 36 is connected to the second communication path 44
The exhaust gas in the second muffling chamber 36 expands slightly when it flows into the third muffling chamber 37 through the second communication passage 44, thereby reducing low-frequency noise. It has become.

Further, a third silencing chamber 37 and a third silencing chamber 35 are connected to each other.
A communication passage 45 is provided, and when the exhaust gas in the third silencing chamber 37 flows into the first silencing chamber 35 through the third communication passage 45, it expands slightly, thereby reducing low frequency sounds.

The exhaust gas in the first muffling chamber 35 is discharged into the atmosphere through the low-speed tail pipe 46.

The low-speed exhaust silencer 12 has more partition walls than the high-speed exhaust silencer 11 shown in FIG. l! The exhaust resistance is considerably larger, and the weight is also considerably thicker.The weight of the low-speed exhaust silencer 12 is the sum of the weight f of the on-off valve 6 and the weight of the high-speed exhaust silencer 11. is set to be approximately equal to .

In such a sliding construction, the first branch exhaust passage 4 side and the second
Since the weights of the exhaust systems on the branch exhaust passage 5 side are almost equal,
The phase difference between the left and right deflections of the exhaust system becomes smaller, and the branch part 3
Since uneven stress is not generated in the exhaust system, the durability and reliability of the exhaust system can be improved.

Hereinafter, a method of controlling the on-off valve 6 by the control unit will be explained.

If the engine speed is below a predetermined value (for example, 2500 r,
At low speeds (p, m, below), the on-off valve 6 is closed. At this time, all exhaust gases are transferred to the common exhaust passage l and the second
A low speed exhaust silencer 12 is connected to the branch exhaust passage 5.
The low-frequency sound that flows into the vehicle and becomes particularly loud at low speeds as described above is effectively reduced.

On the other hand, the engine speed exceeds a predetermined value (for example, 25
At high speeds (exceeding 0 Or, p, m), the on-off valve 6 is opened. At this time, the common exhaust passage 1 communicates with both the first branch exhaust passage 4 and the second branch exhaust passage 5, but as described above, the exhaust resistance of the low-speed exhaust silencer 12 is greater than the exhaust resistance of the high-speed exhaust silencer 2. Since the resistance is considerably greater than the resistance, most of the exhaust gas actually flows into the high-speed exhaust silencer 11 through the first branch exhaust passage 4, and high-frequency noise, which becomes particularly loud at high speeds, is effectively reduced.

In this way, according to the present invention, even at high speeds, without reducing the durability or reliability of the exhaust system,
Exhaust gas noise can be effectively reduced even at low speeds.

In this embodiment, the on-off valve 6 is controlled according to the engine speed, but it may also be controlled depending on whether the intake air amount (engine load) exceeds a predetermined value. Alternatively, the on-off valve may be controlled based on both the engine speed and the intake air amount.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of an engine exhaust system showing an embodiment of the present invention. FIG. 2 is an explanatory longitudinal cross-sectional view of the high-speed exhaust silencer shown in FIG. 1. FIG. 3 is an explanatory longitudinal cross-sectional view of the low-speed exhaust silencer shown in FIG. 1. l... common exhaust passage, 2... catalytic converter, 3...
... Branch, 4.5... 1st. Second branch exhaust passage, 6
...Opening/closing valve, 8...Control unit, ll.
...Exhaust silencer for high speed, 12...Exhaust silencer for low speed.

Claims (1)

[Claims] (1) A catalytic converter is interposed in the common exhaust passage, and two branch exhaust passages are provided that branch from the common exhaust passage at a branch part downstream from the catalytic converter, and a silencer is provided in each of the branch exhaust passages. In the engine exhaust system installed, an on-off valve controlled according to the operating load of the engine is provided upstream of the silencer in one branch exhaust passage, while the above-mentioned on-off valve is interposed in the other branch exhaust passage. An exhaust system for an engine, comprising an exhaust silencer having an internal structure with greater exhaust resistance than a side silencer.