JPH059457Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a variable exhaust timing device, and specifically relates to a variable exhaust timing device for a two-stroke engine.

[Prior art]

In a 2-stroke engine, a valve body is disposed on the upper wall of the housing that forms the exhaust passage so that it can freely protrude and retract.The valve body is made to protrude in the low speed range of the engine, and the tip of the valve body is inserted into the upper part of the exhaust port of the cylinder. by blocking the upper part of the exhaust port and delaying the exhaust timing.
Some engines are equipped with a variable exhaust timing device that retracts the tip of the valve body from the exhaust port of the cylinder in a high speed range of the engine, thereby accelerating the exhaust timing.

As such a variable exhaust timing device,
There is one that was provided earlier (Utility Application No. 61-001589).
In this device, a hole with a circular cross section is bored in the upper wall of the exhaust passage toward the exhaust port of the cylinder, and a guide sleeve whose lower end surface forms the upper surface of the exhaust port is installed in the hole. A semi-cylindrical valve body is slidably attached to the guide sleeve.

By the way, if the cylinder is a sleeve casting type, the cylinder sleeve may be displaced in the axial direction due to combustion pressure etc. during casting, and if the cylinder is a plating type, A buildup of plating may occur on the edge of the exhaust port. In such a case, when assembling the guide sleeve, the tip of the guide sleeve may hit or ride on the raised part of the cylinder sleeve or plating, making it impossible to install the guide sleeve in the specified position. . As a result, when the guide sleeve comes to press down on the valve body, the operability of the valve body decreases.

Furthermore, when the engine is in use, if carbon adheres to the tip of the guide sleeve and gets into the gap between the guide sleeve and the cylinder sleeve, the guide sleeve will be displaced toward the valve body, which may result in a decrease in the operability of the valve body as described above.

[Purpose of invention]

An object of the present invention is to provide a variable exhaust timing device that can ensure stable operability of a valve body.

[Structure of the idea]

In the variable exhaust timing device of the present invention, a hole with a circular cross section is bored in the upper wall of the exhaust passage toward the exhaust port of the cylinder, and a guide sleeve whose lower end surface forms the upper surface of the exhaust port is inserted into the hole. At the same time, a semi-cylindrical valve body is slidably attached to the guide sleeve, and the valve body protrudes and blocks the upper part of the exhaust port with its tip, thereby delaying the exhaust timing. The variable device is a variable device that forms a gap between the circumferential surface of the distal end of the guide sleeve and the housing.

In the variable exhaust timing device of the present invention, even if the cylinder sleeve shifts in the axial direction or a build-up of plating occurs at the exhaust port, the gap formed between the guide sleeve and the housing will allow it to escape.
The guide sleeve is disposed at a predetermined position, and even if carbon adheres to the guide sleeve during use of the engine, the carbon will adhere to the gap and will not displace the guide sleeve.

〔Example〕

FIG. 1 shows a part of a two-stroke engine equipped with a variable exhaust timing device according to the present invention.
The figure shows the shape of the exhaust port, and FIG. 3 shows the operating state of the variable exhaust timing device according to the present invention.

The illustrated engine 1 has a cylinder sleeve 3 in a housing 2 . This cylinder sleeve 3 is formed with an exhaust port 4 as shown in FIG. The exhaust port 4 has a semicircular opening 4a at its upper portion. On the other hand, the housing 2 includes an exhaust passage 5 that is continuous from the exhaust port 4.
A circular hole 6 is formed in the upper wall 2a forming the exhaust passage 5 toward the exhaust port 4. A guide sleeve 7 is attached to the upper half of the hole 6, and a valve body 8 is slidably disposed in the lower half of the hole 6.

The guide sleeve 7 has a surface 7a forming the upper wall 2a of the exhaust passage 5 at its tip, and a tip peripheral surface 7a.
b has been removed and is formed to have a larger curvature than the base peripheral surface 7c. Therefore, when the guide sleeve 7 is inserted into the hole 6, even if the cylinder sleeve 3 is displaced with respect to the housing 2, the tip of the guide sleeve 7 will not hit the cylinder sleeve 3. Moreover, once the guide sleeve 7 is fixed at a predetermined position, the upper edge of the exhaust port 4 of the cylinder sleeve 3 and the guide sleeve 7
A gap A is ensured between the guide sleeve 7 and the tip of the guide sleeve 7, and carbon and the like are accommodated in the gap A, so that the guide sleeve 7 is not displaced.

The valve body 8 has a surface 8a forming the upper wall 2a of the exhaust passage 5 at its distal end, and the distal end circumferential surface 8b is formed with a larger curvature than the base circumferential surface 8c. Therefore, when the valve body 8 is slid within the hole 6, even if there is a buildup of plating on the periphery of the opening of the hole 6, the movement of the valve body 8 will be prevented by these. Nothing happens. Note that this valve body 8 is actuated via a lever 9 by an actuator (not shown).

In the variable exhaust timing device configured as described above, the valve body 8 is maintained in the state shown in FIG. 1 in the extremely low rotational speed range when the engine is stopped and idling. When the rotation of the crankshaft increases and reaches a low rotational speed range, the tip of the valve body 8 is projected to the position shown in FIG. block. When the rotation of the crankshaft further increases and reaches a high rotational speed range, the tip of the valve body 8 moves to the upper wall 2 above the exhaust passage 5 as shown in FIG.
Re-immerse yourself in a.

Also, when the rotation of the crankshaft becomes slow, the valve body 8
returns to the initial position by following the reverse operation to the above.

In the above embodiments, a sleeve casting type cylinder is shown, but the device of the present invention is also suitable for a plating type cylinder. In a plating type cylinder, a plating buildup may occur on the edge of the exhaust port 4, but the distal end peripheral surface 7b of the guide sleeve 7 escapes the plating protrusion and is attached to a predetermined position.

[Effect of idea]

As described above, in the variable exhaust timing device according to the present invention, since a gap is formed between the circumferential surface of the tip end of the guide sleeve and the housing, the guide sleeve can be placed at a predetermined position without being displaced. Therefore, the operation of the valve body is not hindered. Furthermore, even if carbon adheres to the tip of the guide sleeve during use of the engine, the guide sleeve will not be displaced by the carbon, thus ensuring stable operation of the valve body.

[Brief explanation of drawings]

Figure 1 is a conceptual longitudinal sectional view showing a part of a two-stroke engine equipped with a variable exhaust timing device according to the present invention, Figure 2 is a front view showing the shape of its exhaust port, and Figure 3 is a FIG. 2 is a conceptual end view of essential parts showing the operating state of the variable exhaust timing device according to the present invention. 1...Engine, 2...Housing, 2a...
Upper wall, 3... cylinder sleeve, 4... exhaust port,
4a...Semicircular opening, 5...Exhaust passage, 6...
... Hole, 7... Guide sleeve, 7a... Surface, 7b
...Tip circumferential surface, 7c... Base circumferential surface, 8... Valve body,
8a...surface, 8b...tip circumferential surface, 8c...base circumferential surface, A...gap.

Claims (1)

[Scope of utility model registration request] On the upper wall of the exhaust passage toward the cylinder exhaust port,
A hole with a circular cross section is bored, a guide sleeve whose lower end surface forms the upper surface of the exhaust port is installed in the hole, and a semi-cylindrical valve body is slidably attached to the guide sleeve, An exhaust timing variable device in which the valve body protrudes to block the upper part of the exhaust port with its tip to delay the exhaust timing, characterized in that a gap is formed between the guide sleeve and the housing. Variable timing device.