JPH076387B2 - Exhaust control device for 2-cycle engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust timing control system for a two-cycle engine.

[0002]

2. Description of the Related Art Conventionally, in a two-cycle engine, an exhaust timing control device delays the exhaust timing by greatly advancing the valve body position into the exhaust passage even during idling operation in which the engine rotation speed is slow.

[0003]

However, if the exhaust timing is late when the engine is started, especially during idling operation,
There was a problem that exhaust gas was not sufficiently discharged and exchange with fresh air was not performed sufficiently, and as a result, combustion in the combustion chamber could not be completed completely and smooth idling operation could not be obtained.

Further, in the compression stroke of the engine, the exhaust passage is closed promptly, so that the compression of the air-fuel mixture above the piston becomes strong, which causes a problem in the rotation of the crank.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to establish a communication period between the combustion chamber and the exhaust passage as much as possible during engine starting to idling operation. By increasing the length, improving the exchange with fresh air and lowering the compression ratio,
It is an object of the present invention to provide an exhaust control device for a two-cycle engine that can prevent irregular combustion during idling operation and perform smooth operation.

[0006]

In order to achieve the above object, the exhaust control system for a two-cycle engine according to the present invention operates the valve body position from the engine start to the idling operation in the opening direction to open the combustion chamber. The air-fuel mixture and the exhaust gas are controlled to be discharged into the exhaust passage, and during the output operation, the valve body position is controlled in the opening direction from the lowermost position as the engine speed increases. Is.

[0007]

Since the exhaust control device for a two-cycle engine configured as described above is used, exhaust from the combustion chamber from engine start to idling operation is promptly exhausted, and replacement with fresh air is sufficient. Done. Further, the compression of the air-fuel mixture above the piston is partly discharged into the exhaust passage and the compression timing is delayed, so the compression ratio becomes low, and the influence of the compression on the crank is reduced.

[0008]

Embodiments of the present invention will be described with reference to the accompanying drawings. Reference numeral 1 in the drawing denotes a combustion chamber, which is formed by a cylinder 2, a cylinder head 2 ', and a piston 3.

Reference numeral 4 denotes an exhaust passage, which is guided from an exhaust port 2a opened on the wall surface of the cylinder 2. The exhaust passage 4 is provided with a valve body 5 that forms an upper edge 2b of the exhaust port 2a.

As shown in FIG. 3, the valve body 5 has a substantially drum-shaped outer circumference, and a part of the outer circumference is cut off to form an exhaust passage 4. Normally, the cut edge 4a is the exhaust port 2a. Forming the upper edge of.

Reference numeral 6 denotes a housing recess of the valve body 5 provided on the rear surface of the exhaust port 2a facing the exhaust passage 4, and the housing recess 6 is located above the exhaust port 2a of the cylinder 2 through a groove 7. To the combustion chamber 1 of.

The valve body 5 is configured to be rotatable from a position shown by a solid line to a position shown by a chain double-dashed line in FIG. 2, and the groove 7 is formed while the valve body 5 is at a position shown by a solid line retracted from the exhaust passage 4. It communicates with the ventilation passage 4 and rotates clockwise from that position,
At the position where the edge 4a coincides with the upper edge of the exhaust port 2a, the communication with the ventilation passage 4 by the groove 7 is released.

The exhaust control device for a two-cycle engine having the above-described structure is used. When the engine is started, it is operated manually or an operator of a cold starter such as a choke valve (not shown). The valve element 5 is rotated to the position shown by the solid line in FIG.

Since the groove 7 communicates with the ventilation passage 4 by this rotation, the piston 3 is closed even after the piston 3 closes the exhaust port 2a during the upward stroke of the piston 3 due to cranking.
A part of the air-fuel mixture on the upper surface is discharged from the combustion chamber 1 to the exhaust passage 4 through the groove 7, and the pressure acting on the upper surface of the piston 3 does not become high. The exhaust air can be exhausted sufficiently and exchanged with fresh air can be done sufficiently.

When the engine is started, the idling operation is completed and the output operation is started, the valve body 5 once has its edge portion 4a shown in FIG.
It rotates to the lowermost position indicated by the middle two-dot chain line, and thereafter, as the engine output or the engine speed increases, the edge 4a is manually or automatically rotated in the opening direction (upward in the figure) to improve the engine characteristics. Set to high speed.

That is, the groove 7 is closed by the valve body 5 during the output operation except the idling operation, and all the air-fuel mixture on the upper surface of the piston 3 is used for combustion.

[0017]

As described above, according to the present invention, the opening timing of the exhaust port can be adjusted by the valve body according to the number of revolutions of the engine during the output operation of the engine. The output characteristics can be improved.

Particularly, since the valve body position is operated in the opening direction from the engine start to the idling operation to control the mixture and exhaust gas in the combustion chamber to be discharged into the exhaust passage, the mixture mixture above the piston is controlled. Since a part of the compression is discharged into the exhaust passage and the compression timing is delayed, the compression ratio can be suppressed to a low level, the influence of the compression on the crank is reduced, and the crank rotation is smoothed. It can be continued.

Furthermore, since the exhaust gas discharge timing after the explosion stroke is accelerated, the fresh air in the combustion chamber can be sufficiently replaced, so that irregular combustion in the engine during idling operation can also be prevented.

From the above, an engine with good startability is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of a two-cycle engine according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is an external view of a valve body.

FIG. 4 is a view on arrow EE of FIG.

[Explanation of symbols]

 1 combustion chamber 2 cylinder 2a exhaust port 4 exhaust passage 5 valve body 6 accommodation recess

Claims (1)

[Claims] 1. A recess for accommodating a valve body is provided on a back surface of an exhaust port formed in a cylinder, facing the exhaust passage, and the accommodating recess extends into the exhaust passage to form an upper edge of the exhaust port. A valve element is supported, and the opening timing of the exhaust port can be adjusted by moving the upper edge up and down during engine output operation.
In the cycle engine, the valve body position is operated in the opening direction from the engine start to the idling operation, and the air-fuel mixture and the exhaust gas in the combustion chamber are controlled to be discharged into the exhaust passage. An exhaust control device for a two-cycle engine, characterized in that the body position is controlled from the lowermost position in the opening direction as the engine speed increases.