JPH0452371B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a two-stroke engine in which a narrow passage communicating between the upper part of the exhaust port of the cylinder and the exhaust passage is opened in conjunction with the engine starting operation. This invention relates to an engine decompression device.

(Prior Art) Generally, in two-stroke engines, a decompression device is used, which is a device that reduces the compression pressure in the cylinder to facilitate cranking during startup. The device is known. (For example, see Utility Model Application Publication No. 50-90927.) However, in this decompression device, the opening and closing of a narrow passage for reducing the compression pressure in the cylinder is performed in conjunction with the accelerator lever, so the engine Even when the load is low after startup, the narrow passage communicates the inside of the cylinder with the exhaust passage, acting to reduce the compression pressure inside the cylinder. Therefore, when the load is low, the output of the engine is reduced or the air-fuel mixture in the combustion chamber is discharged to the exhaust passage, resulting in unnecessary fuel consumption.

(Problem to be solved by the invention) On the other hand, as a technique for efficiently operating a two-stroke engine, a valve body is provided at the exhaust port of the cylinder to form the upper edge of the exhaust port, and when the engine rotates at high speed and has high output, Structures that raise the edge are known.

(For example, see Japanese Utility Model Application Publication No. 54-9221.) This invention has the disadvantage that in a decompression device for a two-stroke engine, the compression pressure in the cylinder decreases even when the load is low after starting the engine due to narrow passages communicating with each other. This problem was solved by providing a valve body at the exhaust port of the cylinder that forms the upper edge of the exhaust port, so that when the engine is started, the inside of the cylinder is communicated with the exhaust passage through a narrow passage. The technical challenge is to make this possible.

(Means for Solving the Problems) The present invention provides a decompression device for a two-stroke engine, in which a recess for accommodating a valve body is provided on the back side of an exhaust port formed in a cylinder facing an exhaust passage, and A valve body extending into the exhaust passage and forming an upper edge of the exhaust port is supported, and the opening timing of the exhaust port can be adjusted by moving the upper edge up and down while the engine is operating. There is a relatively narrow passage (small hole) above the exhaust port that leads into the valve body housing recess.
a groove), the opening on the side of the accommodation recess is configured to be openable and closable by the valve body, and the opening on the side of the accommodation recess opens when the valve body retreats from the exhaust passage; The technical means includes a control means for retracting the valve body from the exhaust passage in conjunction with the engine starting operation at the time of starting, and opening the opening of the narrow passage on the side of the accommodation recess.

(Function) When the engine is started, the valve body in the accommodation recess is retracted from the exhaust passage by the action of the control means in conjunction with the engine starting operation, and the opening of the narrow passage on the accommodation recess side is opened. The passage communicates the exhaust passage, the accommodation recess, and the combustion chamber. Even after the piston closes the exhaust port while the piston is rising due to cranking, a portion of the air-fuel mixture on the top of the piston escapes from the combustion chamber to the exhaust port through the narrow passage and accommodation recess, and the pressure acting on the top of the piston is high. It doesn't light up and the starting operation is easy. When the engine starting operation is completed, the opening of the narrow passage on the side of the accommodation recess is closed by the action of the control means, and communication between the accommodation recess and the combustion chamber is cut off, and a normal operating state is established.

(Example) The illustrated example will be described. A combustion chamber 1 is formed by a cylinder 2, a cylinder head 2', and a piston 3. Reference numeral 4 denotes an exhaust passage, which is led from an exhaust port 2a opened in the wall surface of the cylinder 2. The exhaust passage 4 has an upper edge 2b at the opening of the exhaust port 2a, and a valve body 5 is provided near the upper edge 2b and forms the upper edge of the exhaust port 2a. As shown in FIG. 3, the outer periphery of the valve body 5 is approximately drum-shaped, and part of the outer periphery is cut off to form a part of the exhaust passage 4, and the cut edge 4a is located above the exhaust port 2a. form a rim. The outer circumferential surface of the portion of the valve body 5 that is not part of the exhaust passage 4 is a series of curved surfaces without openings such as holes, and corresponds to and contacts the opening of the small hole 7 to the accommodation recess 6, which will be described later. This forms a sealing surface that closes this opening.

Reference numeral 6 denotes a housing recess for the valve body 5 provided on the back surface of the exhaust port 2a facing the exhaust passage 4, and inside the housing recess 6 is a small hole 7 (this is the first embodiment of the narrow passage). 2 and 4) into the combustion chamber 1 above the exhaust port 2a of the cylinder 2. The valve body 5 is rotatably arranged around pins protruding from both ends thereof, and can be moved from the position shown by the solid line to the position shown by the two-dot chain line in FIG. 2, or vice versa from the position shown by the two-dot chain line in FIG. It is operated by a control means described later to the position shown by the solid line. Valve body 5
When the small hole 7 is at the position indicated by the solid line and retreated from the inside of the exhaust passage 4, the opening of the small hole 7 on the accommodation recess 6 side is opened, and the small hole 7 communicates the combustion chamber with the accommodation recess 6 and the exhaust passage 4. . When the valve body 5 is rotated clockwise in FIG. 2 from the position indicated by the solid line and is at the position indicated by the two-dot chain line, a part of the valve body 5 protrudes into the exhaust passage 4 and is accommodated in the small hole 7. The opening on the recess side is closed by the valve body 5, and communication between the combustion chamber and the accommodation recess 6 and exhaust passage 4 is cut off. Further, when the valve body 5 is in the position shown by the two-dot chain line, the opening timing of the exhaust port is delayed compared to when it is in the position shown by the solid line.

The valve body 5 is controlled by a control means, which includes a manual operation means, a cold start device (a cold start valve, a
There are means for interlocking with the operation of a starting operator (such as a start switch) and means for interlocking with the operation of a starting operator (such as a starting switch). During the engine starting operation, the control means rotates the valve body 5 to the position shown by the solid line in FIG. 2 in conjunction with the engine starting operation, and the opening of the small hole 7 on the side of the accommodation recess 6 is opened. hand,
The small hole 7 communicates the combustion chamber with the accommodation recess 6 and the exhaust passage 4. Therefore, when starting the engine,
During the upward stroke of the piston 3 due to cranking,
Even after the piston 3 closes the exhaust port 2a, a part of the air-fuel mixture on the upper surface of the piston 3 escapes from the combustion chamber 1 through the small hole 7 to the accommodation recess 6 and further to the exhaust passage 4.
The pressure acting on the upper surface of the piston 3 does not increase and the starting operation can be performed easily.

When the engine starting operation is completed, the control means rotates the valve body 5 to the most protruding position shown by the two-dot chain line in FIG. The opening of the small hole 7 on the side of the accommodation recess is closed by the valve body 5. Thereafter, as the engine output or engine speed increases, the edge 4a is rotated manually or automatically (for example, the valve body 5 is linked to the governor) in the opening direction (to the upper position shown in FIG. 1) to open the engine. Set the characteristic to high speed. That is, the small hole 7 is closed by the valve body 5 at least during output operation excluding idling operation, and all the air-fuel mixture on the upper surface of the piston 3 is provided for combustion. During idling, the engine may be operated with the small holes 7 open in order to stabilize combustion, and of course the small holes 7 may be closed.

The groove 7a shown in FIG. 5 is a second embodiment of a narrow passage, and is formed by continuously cutting upward from the exhaust port 2a. It is also possible to manufacture the groove 7a by casting, in which case productivity can be improved.

If the opening on the side of the accommodation recess of the relatively narrow passage (small hole 7, groove 7a) is closed by being closed by the sealing surface of the valve body 5, and the opening on the side of the accommodation recess is closed by shifting the sealing surface, the opening on the side of the accommodation recess is closed. can be opened and closed reliably and easily, and the amount of decompression can be easily adjusted.

(Effects of the Invention) In the present invention, a recess for accommodating a valve body is provided on the back surface of an exhaust port formed in a cylinder facing an exhaust passage, and the valve body is advanced into the exhaust passage into the accommodating recess, and the exhaust port In a two-stroke engine in which a valve body forming an upper edge is supported and the opening timing of the exhaust port can be adjusted by moving the upper edge up and down during engine operation, a valve body is provided above the exhaust port. A narrow passage connecting the receiving recess and the combustion chamber is provided, which reduces the compression pressure and facilitates the starting operation.

Further, in the present invention, the opening on the side of the accommodation recess of the narrow passage is configured to be openable and closable by the valve body, and the opening on the side of the accommodation recess opens when the valve body retreats from inside the exhaust passage. , control means is provided for retracting the valve body from within the exhaust passage in conjunction with the engine starting operation to open the opening on the accommodation recess side of the narrow passage, which is provided to improve engine characteristics. A simple configuration in which the valve body is moved back greatly at the time of starting, and the upper part of the exhaust port of the cylinder and the opening on the side of the housing recess of the valve body are communicated through a narrow passage, makes the starting operation easy. ,
Moreover, since the opening on the side of the accommodation recess in the narrow passage is closed by the valve body at low load after the engine has started, the air-fuel mixture in the combustion chamber does not flow out into the exhaust passage, making economical operation possible. Become.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a sectional view showing the main parts of the engine, FIG. 2 is an enlarged sectional view of the main parts, FIG. 3 is an external view of the valve body, and FIG. The figure is a cross-sectional view taken along the line shown in FIG. 2, and FIG. 5 is a cross-sectional view corresponding to FIG. 4 showing another embodiment. 2...Cylinder, 2a...Exhaust port, 4...Exhaust passage, 5...Valve body, 6...Accommodation recess, 7...Small hole, 7a...Groove.

Claims (1)

[Scope of Claims] 1. A recess for accommodating a valve body is provided on the back side of an exhaust port formed in the cylinder facing the exhaust passage, and the upper edge of the exhaust port is inserted into the recess and extends into the exhaust passage. In a two-stroke engine configured to support a valve body to be formed and to adjust the opening timing of the exhaust port by moving the upper edge up and down during engine operation, a recess for housing the valve body is provided above the exhaust port of the cylinder. a narrow passage leading to the exhaust passageway, the opening on the side of the accommodation recess is configured to be openable and closable by the valve body, and the opening on the side of the accommodation recess opens when the valve body retreats from the inside of the exhaust passage; The decompression device is characterized in that a control means is provided for retracting the valve body from the exhaust passage in conjunction with the engine starting operation to open an opening on the accommodation recess side of the narrow passage. . 2. The decompression device according to claim 1, wherein the narrow passage is formed in the shape of a groove continuously cut upward from the upper edge of the exhaust port. 3. The decompression device according to claim 1, wherein the accommodation recess is formed in a substantially hourglass shape. 4. The decompression device according to claim 1, wherein the valve body is automatically moved to a position where the opening on the side of the accommodation recess of the narrow passage is opened when the engine is started.