JP2838544B2 - Exhaust system for two-cycle engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for a two-stroke engine provided with an exhaust valve for adjusting an exhaust timing and an exhaust chamber for adjusting an exhaust equivalent pipe length in an exhaust passage.

(Prior art)

It is known that the output of the two-stroke engine can be increased by increasing the charging efficiency of the mixed gas.
As a method of increasing the charging efficiency of such a mixed gas, the exhaust timing is adjusted so as to be slower in the low-speed rotation region and to be earlier in the higher-speed rotation region, or to use the reflected wave of the exhaust pulsation wave for unburned gas. Or to prevent the mixed gas from blowing out from the exhaust port.

JP-A-59-218331 discloses that the opening area of the upper edge of the exhaust port is changed in the exhaust passage in the vertical direction in accordance with the engine speed in order to implement such a method for increasing the efficiency of filling the two mixed gases. There is disclosed a two-stroke engine in which an exhaust valve is provided to open and close a communication passage of an exhaust chamber provided in the exhaust passage by the exhaust valve. With such a configuration, in the low-speed rotation range, the exhaust valve closes the upper edge of the exhaust port to delay the exhaust timing, and opens the exhaust chamber to increase the equivalent length of the exhaust pipe, thereby reflecting the exhaust pulsation wave. In the high-speed rotation range, the exhaust valve opens the upper edge of the exhaust port to accelerate the exhaust timing, and closes the exhaust chamber to shorten the equivalent length of the exhaust pipe, thereby reducing the exhaust pulsation wave. A blow-by is suppressed by a reflected wave.

However, in all of the conventional two-stroke engines of this type, the communication path to the exhaust passage of the exhaust chamber is formed such that an extension of the communication path extends inside the exhaust port (toward the cylinder). According to the study of the present inventors, due to the configuration of such a communication path, a part of the exhaust gas exiting the exhaust port is directly blown into the exhaust chamber, and the back pressure near the inlet of the exhaust chamber communication path increases. I knew that I was letting it go. Also, due to this back pressure rise phenomenon,
Exhaust gas flowing out of the exhaust port is subject to flow resistance, resulting in diminished output improvement effect due to the provision of the exhaust valve and the exhaust chamber.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust system for a two-stroke engine that further improves the output performance of an exhaust valve and an exhaust chamber in view of the conventional problems described above.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an exhaust valve that changes an opening area of an upper edge portion of an exhaust port in an up-down direction in response to a rotation speed of an engine near an exhaust port in an exhaust passage. A two-stroke engine configured to open and close a communication path between an exhaust chamber attached to the exhaust path and the exhaust path,
The extension line is formed so as to intersect the inner wall of the exhaust passage outside the exhaust port, and the outlet of the communication passage facing the exhaust passage is always directed to the downstream direction of the exhaust passage when opened. It is characterized by the following.

〔Example〕

FIG. 1 shows a two-stroke engine according to an embodiment of the present invention, in which 1 is a cylinder and 2 is a piston. An intake port 3 communicating with an intake passage 4 is opened at a lower portion of the cylinder 1, and an exhaust port 5 communicating with an exhaust passage 6 is opened at an upper portion facing the intake port 3.

An exhaust valve 7 that changes the opening area of the upper edge of the exhaust port 5 is provided near the exhaust port 5. This exhaust valve 7 is a lower valve portion 7a extending in the lateral direction.
And a valve body extending upward from the lower valve portion 7a
7b, the opening area of the upper edge of the exhaust port 5 is changed in the vertical direction according to the rotation speed of the engine. That is, the exhaust valve 7 is moved up and down by the rod 10 attached to the upper part of the valve body 7b, and the upper edge of the exhaust port is closed as shown in the low-speed rotation range, but it rises as the rotation speed increases. Thus, the upper edge of the exhaust port is opened.

An exhaust chamber 8 is provided near the exhaust valve 7, and the exhaust chamber 8 communicates with the exhaust passage 6 through a communication passage 9. The communication passage 9 is closed by raising the exhaust valve 7. The extension of the communication passage 9 always intersects the inner wall of the exhaust passage 6 outside the exhaust port 5 irrespective of the position where the exhaust valve 7 is raised, so that the communication passage 9 does not extend into the cylinder 1. ing. Further, the outer portion of the lower valve portion 7a is formed obliquely downward and when the communication passage 9 is opened due to the lowering of the exhaust valve 7, the outlet 9a of the communication passage 9 always facing the exhaust passage 6.
Are directed to the downstream direction of the exhaust passage 6.

In such a configuration, when the engine is in the low speed rotation range, the exhaust valve 7 is in a state where the upper edge of the exhaust port 5 is closed to the lowest position. Therefore, the exhaust timing at this time is delayed, and the charging efficiency of the mixed gas during low-speed rotation is increased. At this time, the exhaust valve 7
Since the communication path 9 of the exhaust chamber 8 is not closed, the exhaust pipe equivalent pipe length is set to the longest state, and the reflected wave of the exhaust pulsation wave acts to push the unburned mixed gas back into the cylinder 1. Therefore, the charging efficiency of the mixed gas is also increased by the exhaust pulsation wave.

When the engine is in the high speed range, the exhaust valve 7 makes the upper edge of the exhaust port 5 completely open,
The communication passage 9 of the exhaust chamber 8 is closed. Therefore, the exhaust timing is advanced, and the equivalent length of the exhaust pipe is shortened so as to correspond to the high-speed rotation range, thereby preventing the unburned mixed gas from flowing through.

Further, in the engine described above, since the extension of the communication passage 9 always intersects with the inner wall of the exhaust passage 6 so that the engine does not pass through the exhaust port 5 into the cylinder 1, the exhaust gas is exhausted from the exhaust port 5. The exhaust gas is not directly blown into the exhaust chamber 8. Therefore, the exhaust gas can flow smoothly without increasing the back pressure near the outlet of the communication passage 9 unlike a conventional engine. Therefore, the flow of the new mixed gas into the cylinder is smoothed, the charging efficiency is improved, and the output is further increased.

Moreover, when the communication passage 9 is in the open state, the outlet 9a is always directed to the downstream side of the exhaust passage 6, so that
Part of the exhaust gas exiting the exhaust port 5 can be more effectively prevented from directly blowing into the exhaust chamber 8 from the opening to the full opening, so that a new mixed gas flows into the cylinder. And the filling efficiency can be further improved.

In the two-cycle engine described above, the exhaust valve 7
The opening and closing of the upper edge of the exhaust port 5 and the opening and closing of the communication passage 9 are performed in a mutually opposite relationship. In general, the upper edge of the exhaust port 5 is closed and the communication passage 9 is opened in the low-speed rotation region, and the upper edge of the exhaust port 5 is opened and the communication passage 9 is closed in the high-speed rotation region. In the middle speed region, the upper edge of the exhaust port 5 and the communication passage 9 are all in the intermediate state.

However, in the present invention, particularly preferably, as shown in the graph of FIG. 2, the rotation speed Rc at which the communication passage 9 is closed in the high-speed rotation region is set to be smaller than the rotation speed Re at which the upper edge of the exhaust port 5 is completely opened. It is desirable that the rotation speed is also increased by the rotation speed r. By doing so, it is possible to effectively use the exhaust inertia effect in the high-speed rotation range, and it is possible to further increase the output in the high-speed rotation range.

〔The invention's effect〕

As described above, the present invention provides an exhaust valve that changes the opening area of the upper edge of the exhaust port in the vertical direction in response to the rotation speed of the engine near the exhaust port in the exhaust passage. A two-stroke engine configured to open and close a communication passage between an exhaust chamber provided in the exhaust passage and the exhaust passage, such that an extension of the communication passage intersects an inner wall of an outer exhaust passage by the exhaust port. And the outlet of the communication passage facing the exhaust passage at the time of opening is always directed to the downstream direction of the exhaust passage, so that the following excellent effects can be obtained.

That is, the communication path between the exhaust chamber and the exhaust passage is formed such that the extension line intersects the inner wall of the exhaust passage outside the exhaust port, so that the exhaust passage does not pass through the cylinder. Therefore, it becomes difficult for a part of the exhaust gas from the exhaust port to directly blow into the exhaust chamber, thereby preventing the back pressure from increasing near the outlet of the communication passage and allowing the exhaust gas to flow smoothly to the outside. . As a result, the flow of the new mixed gas into the cylinder can be made smooth, the filling efficiency can be improved, and the output performance can be further improved.

In addition, since the outlet of the communication passage facing the exhaust passage is always directed to the downstream direction of the exhaust passage when the communication passage is opened, part of the exhaust gas flows directly into the exhaust chamber from the start of opening of the communication passage to full opening. More effectively prevent
Output performance can be further improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a two-stroke engine according to an embodiment of the present invention, and FIG. 2 shows an example of timing of opening and closing an upper edge of an exhaust port and opening and closing a communication passage by an exhaust valve in the engine of the present invention. It is a graph. 1 ... cylinder, 2 ... piston, 5 ... exhaust port,
6 exhaust passage, 7 exhaust valve, 8 exhaust chamber, 9 communication passage, 9a outlet.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02B 25/20 F02B 27/06 F02B 25/14

Claims (1)

(57) [Claims] An exhaust valve for changing an opening area of an upper edge portion of an exhaust port in a vertical direction in response to a rotation speed of an engine is provided near an exhaust port in an exhaust passage, and the exhaust valve is provided by the exhaust valve. A two-stroke engine configured to open and close a communication passage between an exhaust chamber and the exhaust passage provided in the exhaust passage, wherein the communication passage is formed such that an extension of the communication passage intersects an exhaust passage inner wall outside the exhaust port, And an exhaust device for a two-stroke engine, wherein an outlet of the communication passage facing the exhaust passage is always directed to a downstream direction of the exhaust passage when opened.