JPH0828277A - Exhaust control device for engine - Google Patents

Abstract

PURPOSE:To improve the output of an engine within the wide range of ' the low speed rotation area of an engine to the high speed rotation area thereof without exerting effect on appearance of an exhaust device or complicating constitution of the exhaust device. CONSTITUTION:An exhaust control device for an engine comprises an exhaust route 4 through which exhaust gas in the cylinder of an engine is taken out to the outside; and a muffler 6 involving the release end of the exhaust route 4. Thus, in a muffler 6, the exhaust route 4 comprises two exhaust routes having different lengths to release ends 4a1 and 4b1. The two exhaust routes are constituted in such a manner that one is a long exhaust route 4a for an engine low speed rotation area and the other is a short exhaust route being shorter than the long exhaust route 4a and used in an engine high speed rotation area. A switching valve 10 capable of switching the exhaust route 4 into either the long exhaust route 4a or the short exhaust route is disposed in the muffler 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust control device.

[0002]

2. Description of the Related Art For example, a two-cycle or four-cycle engine used in a motorcycle is equipped with an exhaust device for exhausting exhaust gas generated in a combustion chamber in a cylinder into the atmosphere. This exhaust device is mainly composed of an exhaust pipe whose upstream portion is connected to an exhaust port of a cylinder and a silencer (muffler) which is connected to a downstream portion of the exhaust pipe and which includes an open end of the exhaust pipe. There is. Further, in this exhaust system, the positive pressure wave and the negative pressure wave generated inside the exhaust pipe by the open end are utilized to enhance the filling efficiency in the cylinder by the so-called exhaust pulsation effect to improve the engine output. .

By the way, since the timing of obtaining the exhaust pulsation effect depends on the engine speed and the length of the exhaust pipe, when the length of the exhaust pipe is constant, the exhaust pulsation effect is obtained over the entire engine revolution range. Can't get Therefore, in a motorcycle or the like, the length of the exhaust pipe is set according to the main engine rotation range. That is, the exhaust pipe of a low rotation type engine is lengthened, and the exhaust pipe of a high rotation type engine is shortened to set the length of the exhaust pipe according to the engine. Therefore, as shown in FIG. 9, in the conventional engine, the output in either the high speed region or the low speed region is sacrificed.

Therefore, a technique is known in which the length of the exhaust pipe is changed according to the engine speed. For example,
In Japanese Patent No. 44925, an exhaust pipe is branched by a two-way valve outside the silencer, one branch path is lengthened for a low speed rotation range, and the other branch path is shortened for a high speed rotation range. A back pressure reducing device is disclosed in which any one of two branch passages is selected as an exhaust pipe depending on the rotation speed.

[0005]

However, in the back pressure reducing device disclosed in Japanese Utility Model Laid-Open No. 57-44925, since the exhaust pipe is branched outside the silencer, the branch portion and the noise reduction are suppressed. The exhaust pipe for low-speed rotation outside the unit is exposed to the outside. Therefore, when the exhaust device is arranged in the lower part of the vehicle and concealed like a four-wheeled vehicle, the appearance of the vehicle is not affected, but in motorcycles where the exhaust device is exposed, this back pressure reduction device is used. Is not preferred. Further, since the exhaust pipe is branched outside the silencer, a heat insulating device for preventing heat damage provided in the exhaust pipe is separately required for the two exhaust pipes, which complicates the structure of the exhaust device. At the same time, there arises a problem that the cost is high.

The present invention has been made in view of the problems of the prior art, and does not affect the appearance of the exhaust system,
Moreover, it is an object of the present invention to provide an exhaust control device for an engine, which does not complicate the structure of the exhaust device and improves the output of the engine in a wide range from the low speed region to the high speed region of the engine.

[0007]

The present invention has the following constitution in order to solve the above problems. That is, according to the present invention, the upstream portion is connected to the cylinder of the engine to guide the exhaust gas inside the cylinder to the outside of the cylinder and to release the exhaust gas from the release end outside the cylinder, and to the downstream portion of the exhaust path. In an exhaust system of an engine including a silencer connected to the open end, the exhaust path has two paths having different lengths to the open ends in the silencer. The two paths are the long exhaust path through which exhaust flows when the engine runs at low speed,
The exhaust path is a path shorter than the long exhaust path and the exhaust flows when the engine rotates at high speed. The exhaust path is provided in the muffler, and the exhaust path is either the long exhaust path or the short exhaust path. The exhaust control device for an engine is characterized in that switching means capable of switching is provided in the path.

[0008]

According to the present invention, when the exhaust path is switched to the long exhaust path by the switching means when the engine is rotating at a low speed, the exhaust gas introduced into the silencer has a long open end. It flows in the long exhaust path. On the other hand, if the switching means switches the exhaust path to the short exhaust path when the engine is rotating at high speed, the exhaust gas flows through the short exhaust path that is short to the release end. Therefore, the desired exhaust pulsation effect is obtained at each of the low speed rotation and the high speed rotation of the engine, and the long exhaust path, the short exhaust path, and the switching means are provided in the silencer, so that the exhaust gas is exhausted. The heat insulation device for preventing heat damage provided in the pipe is simplified.
At the same time, the exhaust control device cannot be seen from the outside even when applied to a motorcycle, for example.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the engine exhaust control device of the present invention is applied to a motorcycle engine.
FIG. 1 is a side view of the scooter according to this embodiment. FIG. 2 is a side view showing the overall configuration of the engine. FIG.
FIG. 4 is a vertical cross-sectional view of the exhaust system when the engine rotates at a low speed. FIG. 4 is a vertical cross-sectional view of the exhaust system when the engine rotates at high speed. FIG. 5 is a perspective view of the branch pipe showing the state of the switching valve when the engine rotates at a low speed. Figure 6
FIG. 6 is a perspective view of a branch pipe showing a turning state of a switching valve. FIG. 7 is a perspective view of the branch pipe showing the state of the switching valve when the engine rotates at high speed. FIG. 8 is a graph showing the relationship between the engine speed and the engine output in each of the long exhaust path and the short exhaust path.

The scooter 12 according to this embodiment has a structure shown in FIG.
As shown in FIG. 3, the swing unit type engine 2 is provided below the seat 14 and the cylinder 2a is tilted substantially horizontally forward. This engine 2 is shown in FIG.
As shown in (4), it is a four-cycle engine and has an exhaust device 8. As shown in FIGS. 2 and 3, the exhaust device 8 has an upstream portion connected to the cylinder 2a of the engine 2 to guide the exhaust gas in the cylinder 2a to the outside of the cylinder 2a and release the exhaust gas from the release end outside the cylinder 2a. The exhaust passage 4 is provided with an exhaust pipe 16 (described later). Further, the exhaust device 8 is provided with a silencer 6 which is connected to the downstream portion of the exhaust path 4 and which includes the open end.

As shown in FIG. 3, the muffler 6 is provided with an outer cylinder 6a whose tip is fixed to the outer circumference of the exhaust pipe 16 near the cylinder 2a and which is formed in a slightly tapered shape. 6a The three silencing chambers arranged in the longitudinal direction are partitioned by the partition plate 6b and the partition plate 6c. The three silencing chambers are located in the central portion and include a first silencing chamber 6A that includes the open end of the exhaust path 4 and a partition plate 6b.
The second silencing chamber 6B is formed on the front side of the first silencing chamber 6A with the partitioning plate 6c interposed therebetween, and the third silencing chamber 6C is formed on the rear side of the first silencing chamber 6A with the partition plate 6c sandwiched therebetween.

The partition plate 6b has a first silencing chamber 6A.
The baffle pipe 6d that guides the exhaust gas released in step S6 into the second silencing chamber 6B is fixed, and the partition plate 6b and the partition plate 6c are fixed.
A baffle pipe 6e that guides the exhaust gas in the second muffling chamber 6B directly into the third muffling chamber 6C is supported by. Further, on the rear end wall of the muffler 6, there is provided a tail pipe 6f for discharging exhaust gas from the third muffler chamber 6C to the atmosphere.

As shown in FIGS. 3 and 4, the exhaust path 4 has open ends 4a1 and 4a in the silencer 6, respectively.
There are two paths having different lengths up to b1. These two paths are a long exhaust path 4a (see FIG. 3) through which exhaust flows when the engine rotates at a low speed, and a path shorter than the long exhaust path 4a. It is composed of a short exhaust path 4b (see FIG. 4) through which exhaust flows when the engine rotates at high speed.

The exhaust pipe 16 includes a main exhaust pipe 16a for guiding exhaust gas from the cylinder 2a into the silencer 6, and the main exhaust pipe 1
6a and a short exhaust pipe 16b which sends exhaust gas to the first silencing chamber 6A, and a short exhaust pipe 16b which is connected to the rear end of the short exhaust pipe 16b and exhausts from the short exhaust pipe 16b to the first silencing chamber 6
A branch pipe 16c that is released coaxially with the center axis 16b1 of the short exhaust pipe 16b in A or that bends the flow direction of the exhaust gas from the short exhaust pipe 16c slightly to the center axis 16b1 of the short exhaust pipe 16b. The exhaust pipe is connected to the rear end of the branch pipe 16c, is curved in a U-shape in the third silencing chamber 6C, and the exhaust end is exposed by exposing the open end 4a1 in the first silencing chamber 6A.
And a long exhaust pipe 16d which is released in A.

That is, the long exhaust passage 4a is connected to the main exhaust pipe 1.
6a, short exhaust pipe 16b, branch pipe 16c, long exhaust pipe 16d
And the short exhaust path 4b is a path constituted by the open end 4a1 and the main exhaust pipe 16a, the short exhaust pipe 16b, and the branch pipe 1.
6c and the open end 4b1. Therefore, the long exhaust path 4a is at least the long exhaust pipe 16d.
The length of the pipe is longer than the short exhaust path 4b.

Further, in the exhaust control system of the present embodiment, the branch pipe 16c has a switching valve 10 (which can switch the exhaust path 4 to either the long exhaust path 4a or the short exhaust path 4b). An example of switching means) is provided.

As shown in FIGS. 5 to 7, the switching valve 10 includes a flat plate-shaped first valve body 10a for opening and closing the open end 4b1 of the short exhaust path 4b, and a branch pipe 16c constituting the long exhaust path 4a. Flat plate-shaped second valve body 1 for opening and closing the pipeline 16c1 of
0b and the pin 10c are integrally formed.
Is rotatably attached to the branch pipe 16c. The switching valve 10 includes the first valve body 10a.
Closes the open end 4b1 and the second valve body 10b closes the conduit 1
6c1 is biased by a torsion spring or the like (not shown) in the direction of opening 6c1 (the direction indicated by reference character P in FIG. 5). The urging force of the torsion spring or the like causes the switching valve 10 to rotate in the direction opposite to the sign P by the pressure of the exhaust gas when the engine rotates at high speed,
The first valve body 10a opens the open end 4b1 and the second valve body 1
0b is set to a size such that it can block the conduit 16c1.

An opening 16c2 is provided in the side wall of the conduit 16c1 of the branch pipe 16c, and the second valve body 10 is provided with the opening 16c2.
The portion b closes the opening 16c2 and constitutes a part of the side wall along the side wall when the engine rotates at a low speed. Therefore, the flow passage area of the pipeline 16c1 is the second
It does not decrease due to the presence of the valve body 10b.

(Operation of this Embodiment) The present embodiment having the above-described structure operates as follows. When the engine is running at a low speed, the open end 4b1 of the short exhaust path 4b is closed by the first valve body 10a as shown in FIG. 5, so the exhaust gas that has passed through the short exhaust pipe 16b is branched as shown in FIG.
Flowing into the long exhaust pipe 16d through the conduit 16c1 of the above, flowing in a U-shaped curve in the long exhaust pipe 16d, and releasing the open end 4a1.
Is released into the first silencing chamber 6A.

On the other hand, when the engine is rotating at high speed, as shown in FIGS. 6 and 7, the first valve body 10a opens the release end 4b1 as the pressure of the exhaust gas increases at high engine speed, and the second valve body 10b is opened. Since the pipe line 16c1 of the branch pipe 16c is closed, the exhaust gas that has passed through the short exhaust pipe 16b does not flow through the long exhaust pipe 16d as shown in FIG.
On the central axis 16 of the short exhaust pipe 16b in the first silencing chamber 6A
It is released coaxially with b1.

Exhaust gas released and expanded in the first muffling chamber 6A is sent to the second muffling chamber 6B through the baffle pipe 6d and expanded again at both low speed rotation and high speed rotation of the engine. The baffle pipe 6e guides and expands into the third silencing chamber 6C. As a result, the exhaust gas having the exhaust energy sufficiently absorbed is discharged into the atmosphere through the tail pipe 6f.

(Effects of this Embodiment) With the above-described operation, this embodiment has the following effects (1) to (4). (1) Exhaust gas passes through the long exhaust path 4a and is released during low-speed engine rotation, and exhaust gas is released through the short exhaust path 4b during low engine speed range. When the predetermined length is matched with, the output of the engine 2 is improved when the engine 2 is rotating at low speed and at high speed, as shown in FIG. Therefore, by appropriately setting the engine speed at which the switching valve 10 switches and the biasing force of the torsion spring or the like that causes the switching valve 10 to rotate at this speed, the engine 2 can be operated at high speeds in the low speed range. The engine output can be improved in a wide rotation range up to the rotation range.

(2) Long exhaust path 4a and short exhaust path 4
Each exhaust pipe such as a branch pipe 16c constituting b and the switching valve 1
Since 0 is provided inside the silencer 6, the exhaust control device cannot be seen from the outside. Therefore, the appearance of the rear part of the scooter 12 is not affected. Further, the heat insulating device for preventing heat damage in the exhaust pipe 16 can be simplified.

(3) Exhaust gas that has passed through the short exhaust path 4b during high-speed engine rotation is exhausted from the open end 4b1 to the exhaust pipe 16
Since it is released coaxially with the central axis of the exhaust gas, the exhaust resistance is reduced. Therefore, the performance of the engine 2 at the time of high speed rotation can be improved.

On the other hand, JP-A-61-101619
In the exhaust device for an internal combustion engine disclosed in the publication, a long hole is provided in the peripheral wall of the tail end of the exhaust pipe, and a slide piece having a circular hole corresponding to the long hole is provided at the tail end to slide the slide piece. By moving it, the position of the circular hole that becomes the open end is changed in the central axis direction of the exhaust pipe, the length from the exhaust port of the cylinder to the open end is made variable, and an exhaust pulsation effect is obtained in the entire engine rotation range. I am trying.

However, in this exhaust system for an internal combustion engine, since the elongate hole is formed in the peripheral wall of the tail end of the exhaust pipe, the exhaust gas flowing through the exhaust pipe along the central axis of the exhaust pipe is discharged from the circular hole. When discharged, the flow direction changes to a right angle. Therefore, the exhaust resistance increases, and the performance of the internal combustion engine may deteriorate.

(4) When the engine is running at low speed, the exhaust gas sent from the cylinder 2a into the muffler 6 passes through the long exhaust path 4a and flows in the muffler 6 near the rear end wall having the lowest temperature. Heat dispersion is improved.

The present embodiment is a preferred embodiment of the present invention, and the technical scope of the present invention is not limited to this embodiment. For example, the switching valve 10 need not be biased and controlled by an elastic member such as a torsion spring or a coil spring, but may be controlled to be opened / closed by a wire or the like according to the engine speed. Further, the exhaust control device of the present invention is not necessarily a four-cycle engine,
It can also be applied to the exhaust system of a two-cycle engine.

[0029]

As described above, according to the present invention, there is no influence on the appearance of the exhaust system, and the structure of the exhaust system is not complicated. The engine output can be improved in a wide range up to the range.

[Brief description of drawings]

FIG. 1 is a side view of a scooter according to this embodiment.

FIG. 2 is a side view showing the overall configuration of the engine according to the present embodiment.

FIG. 3 is a vertical cross-sectional view of the exhaust device according to the present embodiment when the engine rotates at a low speed.

FIG. 4 is a vertical cross-sectional view of the exhaust device according to the present embodiment when the engine rotates at high speed.

FIG. 5 is a perspective view of a branch pipe showing a state of a switching valve during low speed engine rotation according to the present embodiment.

FIG. 6 is a perspective view of a branch pipe showing a turning state of the switching valve according to the present embodiment.

FIG. 7 is a perspective view of a branch pipe showing a state of a switching valve during high speed engine rotation according to the present embodiment.

FIG. 8 is a graph showing a relationship between an engine speed and an engine output in each of a long exhaust path and a short exhaust path according to the present embodiment.

FIG. 9 is a graph showing the relationship between the engine speed and the engine output when the exhaust pipe is lengthened and when the exhaust pipe is shortened.

[Explanation of symbols]

 2 engine 2a cylinder 4 exhaust path 4a long exhaust path 4a1 open end of long exhaust path 4b short exhaust path 4b1 open end of short exhaust path 6 silencer 8 exhaust device 10 switching valve (one example of switching means) 10a first valve body 10b Second valve body 16 Exhaust pipe 16a Main exhaust pipe 16b Short exhaust pipe 16c Branch pipe 16d Long exhaust pipe

Claims (1)

[Claims] 1. An exhaust path, an upstream part of which is connected to a cylinder of an engine to guide the exhaust gas inside the cylinder to the outside of the cylinder and to release the exhaust gas from an open end outside the cylinder, and a downstream part of the exhaust path. And a muffler including the open end, the exhaust path includes two paths in the muffler having different lengths to the respective open ends. The two paths are composed of a long exhaust path through which exhaust flows when the engine rotates at a low speed, and a short exhaust path that is shorter than the long exhaust path and through which exhaust flows when the engine rotates at a high speed. An exhaust control device for an engine, comprising switching means capable of switching an exhaust path to either the long exhaust path or the short exhaust path.