JPS5963319A - Decompressor of two-stroke engine - Google Patents

Abstract

PURPOSE:To reduce a compressing pressure so as to provide easier starting operation for an engine by forming a small port in communication with the inside of a valve body positioned recess, in the upper part of an exhaust port of a cylinder and opening the port at the side of said valve positioned recess when the valve body is turned backward from the exhaust passage. CONSTITUTION:When an engine is demanded to be started, a valve body 5 is turned on the position shown by a solid line to open a small port 7. Even after a piston 3 closes an exhaust port 2a during the elevating stroke of said piston 3, part of mixture remaining on the upper face of the piston 3 is released through said small port 7 from a combustion chamber 1 into a valve positioned recess 6 which is communicated with an exhaust passage 4 to restrict boost in pressure which acts on the upper face of the piston 3, whereby providing smooth starting operation. Once the engine is started, the valve body 5 is turned to the most projecting position shown by a two-dotted line and then turned reversely in the reopening direction for the port, (namely, in the upward direction in the drawing) in association with increase in power or speed of the engine, setting the characteristic of the engine for high speed run mode.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a two-stroke engine in which an exhaust port formed in a cylinder is movable up and down by a valve body, and a decompression is constructed between the inside of the cylinder near the exhaust port and the inside of the exhaust passage. It is characterized in that a small hole is provided, the small hole is configured to be openable and closable by a valve body, and the opening on the side of the accommodation recess opens when the valve body retreats from the exhaust passage.

In general, for two-stroke engines, a decompression device is known, which is a device that connects the inside of the cylinder to the exhaust passage through a small hole as a device to reduce the compression pressure inside the cylinder in order to facilitate cranking during startup. (For example, Japanese Utility Model Application Publication No. 50-90927). However, these small holes act to reduce the compression pressure inside the cylinder even after the engine has started, reducing the engine's output.
Alternatively, the air-fuel mixture in the combustion chamber is discharged to the exhaust passage.
There is a problem with Marino that consumes fuel needlessly.

The inventor studied a simple configuration to eliminate such problems, and as a result, developed an exhaust structure that is known as a technology for efficiently operating a two-stroke engine.

Focusing on a device (for example, Utility Model Application Publication No. 54-9221) in which a valve body forming the upper part of the exhaust port is provided at the exhaust port of a cylinder and the upper edge of the valve body is raised when the engine output is high, the behavior of the valve body was investigated. It is unique in that it is configured to be used to open and close the small holes of the decompression device.

This will be explained below with reference to illustrated embodiments.

In the figure, 1 is a combustion chamber formed by a cylinder 2, a cylinder head, and a piston 3.

4 is an exhaust passage, which is led from an exhaust port 2a opened in the wall surface of the cylinder 2. The exhaust passage 4 is provided with a valve body 5 located near the exhaust port 2a and forming an upper edge 2b of the exhaust port 2&. As shown in FIG. 3, the valve body 5 has an approximately hourglass-shaped outer periphery, and a portion of the outer periphery is cut off to form the exhaust passage 4.
is formed, and the cut edge 4& forms the upper edge of the exhaust port 2a. Reference numeral 6 denotes a housing recess for the valve body 5 provided on the back side of the exhaust port 2a facing the exhaust passage 4;
The inside communicates through a small hole 7 into the combustion chamber 1 above the exhaust port 2a of the cylinder 2. The valve body 5 is configured to be rotatable from the position shown by the solid line to the position shown by the two-dot chain line in FIG. It is configured to be openable and closable when it rotates clockwise from its position and closes when it projects into the exhaust passage, as shown by the two-dot chain line.

Next, the operation of the embodiment will be explained. When trying to start the engine, the valve body 5 is turned off manually or in conjunction with the operation of a cold starting device such as a choke valve (not shown) or a starting operator as shown in FIG. , rotate to the position shown by the solid line, and open the small hole 7. Therefore, during the upward stroke of the piston 3 due to cranking, even after the piston 3 closes the exhaust port 2Bt, a part of the air-fuel mixture on the upper surface of the piston 3 passes through the small hole 7 and is stored in the combustion chamber 1 leading to the exhaust passage 4. The pressure that escapes into the recess 6 and acts on the upper surface of the piston 3 does not increase, allowing the starting operation to be performed easily. Once the engine has started, the edge 4a of the valve body 5 rotates to the most protruding position shown by the two-dot chain line in FIG. The part 4a is rotated in the open direction (upward in the figure) to set the engine characteristics to high speed. That is, the small hole 7 is closed by the valve body 5 at least during output operation excluding idle link operation, and the piston 3
All of the air-fuel mixture on the top surface is used for combustion. Of course, it is equally possible to set it to close during idling operation.

Note that the small hole T is not necessarily limited to the embodiment of this embodiment.
For example, as shown in FIG. 5, the same effect can be obtained by continuously cutting upward from the exhaust port 2a to form a groove Ta. It is also possible to form the groove 7a by casting,
By doing so, it is also possible to improve productivity.

This invention provides a recess for accommodating the valve body facing the exhaust passage on the back side of the exhaust port formed in the cylinder as described above, and extends into the recess into the exhaust passage to close the upper edge of the exhaust port. 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. Since a small hole leading to the engine is provided, the compression pressure can be reduced through the opening, and the starting operation can be easily performed.

Further, in order to improve engine characteristics, the opening on the side of the solidification storage recess is configured to be openable and closable by the valve body, and the opening on the side of the solidification storage recess is configured to open when the valve body retreats from the exhaust passage. A simple configuration in which the provided valve body is moved back greatly at the time of startup, and the upper part of the cylinder exhaust port and the inside of the valve body housing recess are communicated through a small hole, makes the starting operation easy. Since the hole is closed by the valve body during normal operation of the engine, the air-fuel mixture in the combustion chamber will not flow out into the exhaust passage, resulting in economical operation.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is a sectional view showing the main parts of the engine, FIG. 2 is an enlarged sectional view of the main parts, and FIG. 3 is an external view of the valve body. Figure 4 is the PJ of Figure 2.
-IV sectional view is a sectional view corresponding to 4th porcelain showing another embodiment from FIG. 4... Exhaust passage, 4a... Edge, 511...
・Valve body, 6...Accommodation recess, 7...Small hole, 7a@
-1111 groove. Patent Applicant Yamaha Motor Co., Ltd. Agent Masaki Yamakawa (1 person) Figure 1 Figure 3 u Figure 4 Figure 2 Figure 5

Claims (1)

[Scope of Claims] (1) A recess for accommodating the valve body is provided on the back side of the exhaust port formed in the cylinder facing the exhaust passage, and the valve body is advanced into the exhaust passage into the accommodating recess and the valve body is placed in the upper part of the exhaust port. In a two-stroke engine that supports a valve body forming a cylinder, and is configured so that the opening timing of the exhaust port can be adjusted by moving the upper edge up and down during engine operation, there is another member above the exhaust port of the cylinder. A decompressor is provided with a small hole leading into the accommodation recess, the opening on the side of the accommodation port b1 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. Device. e) The decompression device according to claim 1, wherein the small hole 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 JfX recess R is formed into a substantially drum shape. The decompression device according to claim 1, wherein the decompression device is automatically moved to an open position.