JPH09112276A - Exhaust timing controller for 2-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase output in a range of low speeds of an engine and improve service. SOLUTION: In this controller 28, a nearly circular hole 32 open to an exhaust passage 20 near the exhaust port 30 of a cylinder 10 is integrated with a cylinder body 8 and an exhaust valve 36 is slidably received in the hole 32 via a valve guide 34. A nearly circular cylindrical valve guide 34 is inserted into the hole 34 and on the valve guide 34 is formed a valve sliding part 40 whose upper wall 40a and lower wall 40b are flat and which open to the exhaust passage 20 in the shape of a letter C and the exhaust valve 36 which has a flat upper surface 36a1 and a lower surface 36a2 and is shaped like a plate is slidably assembled in the valve sliding part 40.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an exhaust timing control device for a two-cycle engine.

[0002]

2. Description of the Related Art For example, a two-cycle engine for a motorcycle has an exhaust timing control device (exhaust device) that adjusts the exhaust timing according to the engine speed so that a high output can be obtained in the entire engine speed range. Some are equipped. An example of a conventional exhaust timing control device will be described with reference to FIGS. As shown in FIG. 5, the cylinder body a
The exhaust passage d having the exhaust port c on the inner wall of the cylinder b.
The exhaust timing control device e is arranged above the exhaust passage d.

As shown in FIG. 6, the exhaust timing control device e is provided on both the left and right sides with a rib f integrally formed on the cylinder body a interposed therebetween. As shown in FIG. 5, each exhaust timing control device e has a substantially circular hole g opened in the exhaust passage d near the exhaust port c and formed in the cylinder body a, and a valve guide h in the hole g. And an exhaust valve i slidably disposed therethrough.

As shown in FIG. 7 (a), the valve guide h is provided with a flange portion j that is locked to the rear end portion of the hole g, and the upper surface of the flange portion j has the upper surface of the hole g. A guide part k is formed integrally with the upper wall in an arc shape and has a lower surface in a flat shape. Further, the flange portion j is provided with a through hole j1 which is open on both front and rear surfaces.

The front portion of the exhaust valve i has a substantially cylindrical shape, and as shown in FIG. 6, a sliding portion m constituting the front portion.
Has a planar upper surface that is in sliding contact with the lower surface of the guide portion k, and the outer peripheral surface other than the upper surface is formed into a cylindrical surface shape so as to match the inner peripheral surface of the hole g. As shown in FIG. 7B, a drive shaft portion n inserted into the through hole j1 of the valve guide h projects rearward from the upper rear surface of the sliding portion m.
Further, at the rear end of the drive shaft portion n, a spacer q is fitted and a pin hole n1 penetrating in the left-right direction is formed,
The left and right exhaust valves i, i are connected by passing the connecting pin p through the pin hole n1.

According to the exhaust timing control device e, the exhaust valve i is housed in the hole g at the time of high engine speed,
When the engine speed enters the low speed range, the connecting pin p is driven forward by an actuator (not shown), and the sliding portion m projects into the exhaust passage d while sliding on the inner peripheral surfaces of the guide portion k and the hole g. . Then, the sliding part m stops when its front edge reaches the exhaust port c and is located on the same plane as the inner wall of the cylinder b. This slightly lowers the upper edge position of the exhaust port c and delays the exhaust timing. On the other hand, when the engine speed increases from this state, the exhaust valve i is retracted into the hole g, the upper edge position of the exhaust port c is raised, and the exhaust timing corresponds to the high engine speed.

As described above, in the conventional exhaust timing control device e, the exhaust valve i is slid on the inner peripheral surface of the guide portion k of the valve guide h and the hole g, so that the exhaust valve i is moved to the exhaust passage d. The exhaust valve i is retracted and the exhaust timing is appropriately changed according to the engine speed. As a conventional exhaust timing control device having substantially the same function as the exhaust timing control device e, there is a device described in Japanese Patent Laid-Open No. 2-169821.

[0008]

The conventional exhaust timing control device has the following problems. (1) Since the sliding portion m of the exhaust valve i has a substantially columnar shape, when the sliding portion m projects into the exhaust passage g, the exhaust passage g
The volume of the engine becomes small, which may affect the engine output in the low speed range due to the reflected wave from the open end of the muffler. (2) Since the sliding portion m mainly slides on the inner peripheral surface of the hole g, if the inner peripheral surface of the hole g is worn, the cylinder body a itself must be replaced, which is not very convenient for service. Not preferable.
Particularly, in the one disclosed in JP-A-2-169821, since the exhaust valve is incorporated without a guide component, the guide of the exhaust valve depends only on the hole integrally formed in the cylinder body. Serious problems will occur.

The present invention has been made in view of the problems of the conventional exhaust timing control device, and has improved the output in the low engine speed range and the serviceability.
An object is to provide an exhaust timing control device for a cycle engine.

[0010]

The present invention has the following configuration to achieve the above object. That is, according to the present invention, a substantially circular hole that opens to the exhaust passage near the exhaust port of the cylinder is integrally formed in the cylinder body, and the exhaust valve is slidably accommodated in the hole through a valve guide. The exhaust valve is projected into the exhaust passage from the hole to lower the upper edge position of the exhaust port at the front edge of the exhaust valve, and the exhaust valve is retracted from the exhaust passage into the hole to exhaust the exhaust gas. In an exhaust timing control device for a two-cycle engine that returns the upper edge position of the mouth to the position before the projection of the exhaust valve, a substantially cylindrical valve guide is fitted in the hole, and the valve guide has an upper wall and a lower wall. A valve sliding contact portion that is flat and opens in a substantially U shape toward the exhaust passage is formed, and a substantially plate-shaped exhaust valve having a flat upper surface and a lower surface can be slid on the valve sliding contact portion. To incorporate An exhaust timing control device of a two-stroke engine, characterized.

According to the present invention, since the upper surface and the lower surface of the exhaust valve are in sliding contact with the upper wall and the lower wall of the valve sliding contact portion of the valve guide, the hole of the cylinder body is hardly worn. Therefore, if the valve guide is worn due to sliding of the exhaust valve, it is sufficient to replace only the valve guide, which improves serviceability.

Further, since the exhaust valve has a substantially plate shape,
Even if the exhaust valve projects into the exhaust passage in the low engine speed range, the amount of change in the volume of the exhaust passage is smaller than that in the case where the substantially cylindrical exhaust valve projects. Therefore, the output can be improved in the low engine speed range.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a two-cycle engine according to this embodiment. FIG. 2 is an enlarged view of part A in FIG. FIG. 3 is a view on arrow B in FIG. FIG.
(A) is a side view of the valve guide according to the present embodiment, and (b) is a side view of the exhaust valve according to the present embodiment.

In this embodiment, the present invention is applied to an exhaust timing control system for a two-cycle engine of a motorcycle. As shown in FIG. 1, a two-cycle engine (hereinafter, referred to as an engine) 2 according to the present embodiment is fixed to a crankcase 6 that rotatably supports a crankshaft 4 and a front upper surface of the crankcase 6. And a cylinder body 8.

The cylinder body 8 is formed with a cylinder 10 having a central axis extending in the vertical direction.
On the inner wall of the piston, the piston 14 slides up and down by the connecting rod 12. An intake passage 18 communicating with the carburetor 16 is provided on one side of the cylinder body 8, and an exhaust passage 20 is formed obliquely downward on the other side of the cylinder body 8. The intake passage 18 is provided with a reed valve 22 that opens and closes the passage. A cylinder head 26 having an ignition plug 24 at the center is fastened to the upper end surface of the cylinder 10.

As shown in FIG. 2, the exhaust timing control device 28 of the present embodiment has a cylinder body 8 having a substantially circular hole 32 that opens into the exhaust passage 20 in the vicinity of the exhaust port 30 of the cylinder 10.
The exhaust valve 36 is slidably accommodated in the hole 32 through the valve guide 34, whereby the exhaust valve 36 is projected from the hole 32 into the exhaust passage 20 and the front of the exhaust valve 36. The upper edge position of the exhaust port 30 is lowered at the edge, and the exhaust valve 36 is retracted from the inside of the exhaust passage 20 into the hole 32 to return the upper edge position of the exhaust port 30 before the projection of the exhaust valve 36. As shown in FIG. 3, the exhaust timing control device 28 is provided on both left and right sides with a rib 38 formed integrally with the cylinder body 8 interposed therebetween.

The holes 32 are formed in the cylinder 1 as shown in FIG.
A step portion 32a is formed in the opening on the side opposite to the cylinder formed obliquely upward as viewed from the 0 side. The valve guide 34 is shown in FIG.
As shown in FIG. 3, the outer shape is a substantially columnar shape corresponding to the inner shape of the hole 32 and is fitted into the hole 32. As shown in FIG. 2, a flange portion 34a fitted to the step portion 32a is provided at the rear end portion of the valve guide 34. Then, the valve guide 34
As shown in FIG. 4A, a valve sliding contact portion 40 is formed in which the upper wall 40a and the lower wall 40b are planar and open to the exhaust passage 20 in a substantially U shape. From the rear wall of the valve sliding contact portion 40 to the rear end surface of the valve guide 34,
A substantially circular through hole 34b is formed. Further, on the left and right sides of the rear end of the valve guide 34, arcuate receiving surfaces 34c for restricting the rear position of the exhaust valve 36 are provided.

The exhaust valve 36 is shown in FIGS. 3 and 4 (b).
As shown in, the flat upper surface 36a1 and the lower surface 36a
It is a substantially plate-shaped member provided with 2, and is slidably incorporated in the valve sliding contact portion 40. That is, the exhaust valve 36
Is a sliding portion 36a having substantially the same thickness as the vertical width of the valve sliding contact portion 40 and having left and right side surfaces formed in an arc shape along the hole 32, and a central portion of the rear end surface of the sliding portion 36a. The drive shaft portion 36b protrudes and is inserted into the through hole 34b of the valve guide 34. The drive shaft portion 36b includes
As shown in FIG. 2, when the exhaust valve 36 is projected, a cylindrical spacer 42 that is in contact with the rear surface of the flange portion 34a of the valve guide 34 is fitted. Furthermore, the left and right drive shaft portions 36b,
36b is provided with a pin hole 36b1 penetrating left and right, and as shown in FIG. 3, the pin holes 36b1 and 36b1 are provided.
The left and right exhaust valves 36, 36 are connected by fitting both ends of the connecting pin 44 into the.

According to the present embodiment having such a configuration, the sliding portion 36a is housed in the valve sliding contact portion 40 at the time of high engine rotation, and when the engine rotational speed enters the low speed region, the actuator (not shown) is used. The connecting pin 44 is driven forward, the sliding portion 36a projects into the exhaust passage 20 while sliding on the upper wall 40a and the lower wall 40b of the valve sliding contact portion 40, and as shown in FIG. When it comes into contact with the collar portion 34a, it stops. At this time, the sliding portion 36
The front edge of a reaches the exhaust port 30 and is located flush with the inner wall of the cylinder 10. This slightly lowers the upper edge position of the exhaust port 30 and delays the exhaust timing. on the other hand,
When the engine speed increases from this state, the sliding portion 36
The a is immersed in the valve sliding contact portion 40 until its rear end abuts on the receiving surface 34c of the valve guide 34. As a result, the upper edge position of the exhaust port 30 is raised so that the exhaust timing corresponds to the high engine speed.

According to the exhaust timing control device 28 constructed and operated as described above, the upper surface 36a1 and the lower surface 36a2 of the exhaust valve 36 slide on the upper wall 40a and the lower wall 40b of the valve sliding contact portion 40 of the valve guide 34. Since they are in contact with each other, the inner wall of the hole 32 formed integrally with the cylinder body 8 is hardly worn. Therefore, the upper wall 40 of the valve guide 34
When the a and the lower wall 40b are worn, it is sufficient to replace only the valve guide 34, so that the serviceability is improved.

Further, since the sliding portion 36a of the exhaust valve 36 has a substantially plate shape, the exhaust passage 2 is provided in the low engine speed region.
Even if it projects in 0, the amount of change in the volume of the exhaust passage 20 is smaller than that of a conventional exhaust valve having a substantially cylindrical shape. Specifically, the volume of the exhaust passage 20 at the time of valve projection becomes larger than that of the conventional one (see FIG. 5) by the amount of the substantially semi-cylindrical space indicated by the symbol D in FIGS. 2 and 3. Therefore,
It is possible to obtain smooth output characteristics from the engine low speed range to the high speed range.

The present embodiment is a preferred embodiment of the present invention, and the technical scope of the present invention is not limited to this embodiment.

[0023]

As described above, according to the present invention, 2
In the exhaust timing control device for a cycle engine, it is possible to improve the output and serviceability in the low engine speed range.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a two-cycle engine according to this embodiment.

FIG. 2 is an enlarged view of a portion A in FIG.

FIG. 3 is a view taken in the direction of arrow B in FIG. 2;

4A is a side view of a valve guide according to the present embodiment, and FIG. 4B is a side view of an exhaust valve according to the present embodiment.

FIG. 5 is a sectional view of a main part of a cylinder body showing a conventional exhaust timing control device.

FIG. 6 is a view as viewed in the direction of arrow C in FIG. 5;

FIG. 7A is a side view of a valve guide according to a conventional example,
(B) is a side view of an exhaust valve according to a conventional example.

[Explanation of symbols]

 2 2 cycle engine 8 Cylinder body 10 Cylinder 20 Exhaust passage 28 Exhaust timing control device 30 Exhaust port 32 Hole 34 Valve guide 36 Exhaust valve 36a1 Upper surface 36a2 Lower surface 40 Valve sliding part 40a Upper wall 40b Lower wall

Claims (1)

[Claims] 1. A substantially circular hole that opens into an exhaust passage near the exhaust port of a cylinder is integrally formed in a cylinder body, and an exhaust valve is slidably accommodated in the hole through a valve guide. The exhaust valve from above into the exhaust passage to lower the upper edge position of the exhaust port at the front edge of the exhaust valve, and the exhaust valve is retracted into the hole from within the exhaust passage. In an exhaust timing control device for a two-cycle engine that returns the upper edge position of the exhaust valve to a position before the protrusion of the exhaust valve, a substantially columnar valve guide is fitted into the hole, and
The valve guide is provided with a valve sliding contact portion having an upper wall and a lower wall which are flat and open in a substantially U shape toward the exhaust passage, and a substantially plate-like exhaust having a flat upper surface and a lower surface. An exhaust timing control device for a two-cycle engine, wherein a valve is slidably incorporated in the valve sliding contact portion.