JPH01240724A - Exhaust gas timing changing device - Google Patents

Abstract

PURPOSE:To satisfactorily operate an exhaust timing valve by matte-finishing at least one of the slide surfaces of an exhaust timing valve and a valve guide. CONSTITUTION:An exhaust timing valve 17 and a valve guide 18 are provided in the vicinity of an exhaust port 15 in an engine. A matte-finished surface 33 is formed by shot-peening, sand-blasting or the like in a slide contact surface 31 of the exhaust timing valve 17 which makes contact with a slide surface of a valve guide 18. Even though tar enters between both slide surfaces, the viscosity of the tar is reduced since an oil film is broken. Thereby it is possible to satisfactorily operate the exhaust timing valve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a variable exhaust timing device for a two-stroke engine, and particularly relates to a variable exhaust timing device [F] that can improve the operation of an exhaust timing valve.

(Prior Art) In a two-stroke engine, as shown in FIG. 4, an exhaust timing valve 2 is provided in an exhaust passage 1 to determine exhaust timing. The exhaust timing valve 2 is provided so as to be movable toward the exhaust port 4 in synchronization with the engine rotational speed by an actuation mechanism 3 linked to a crank.

In other words, in the low and medium speed range of the engine, the exhaust timing valve 2 is made to protrude into the tiller port 4 to delay the exhaust timing.
Furthermore, in the high engine speed range, the exhaust timing valve 2 is moved back to advance the exhaust timing.

Such an exhaust timing valve 2 has a valve guide 5.
The valve guide 5 is moved forward and backward along the cylinder block 6, and the valve guide 5 is screwed to the cylinder block 6. Further, an actuation mechanism 3 for advancing and retracting the exhaust timing valve 2 is housed in an actuation chamber portion 7 attached to the cylinder block 6.

(Problem to be Solved by the Invention) Now, in the low and medium rotation range of the engine, the exhaust timing valve 2 protrudes toward the exhaust port 4 as shown in FIG. At this time, the exhaust timing valve 2 is exposed to high-temperature exhaust gas, so if the engine continues to run under low load for a long time in the low-to-medium speed range, the oil content in the exhaust gas will heat up to about 50°C to about 550°C. The fuel is carbonized and becomes tar, which adheres to the outer surface of the exhaust timing valve 2. When the exhaust timing valve 2 moves forward and backward, this tar is deposited on the tank contact surface 8 between the exhaust timing valve 2 and the valve guide 5.
There is a risk that the particles may enter the small gap 9 and disturb the smooth operation of the exhaust timing valve 2. In particular, when the engine is cold, the viscosity of tar is high, so the operability of the exhaust timing valve 2 is significantly reduced.

This invention was made in consideration of the above facts,
An object of the present invention is to provide an exhaust timing variable device capable of properly operating an exhaust timing valve even if tar enters between the exhaust timing valve and a valve guide.

[Structure of the Invention] (Means for Solving the Problems) This invention provides an exhaust timing valve that is disposed near the exhaust port of an engine and is movable toward the exhaust port, and a slider on the exhaust timing valve. The exhaust timing valve has a valve guide that is in contact with the exhaust timing valve and guides the movement of the exhaust timing valve, and is characterized in that at least one of the surfaces of the exhaust timing valve and the valve guide that come in contact with the two tanks is formed in a matte finish.

(Function) Therefore, according to the exhaust timing variable device according to the present invention, the oil in the exhaust gas is carbonized by the heat of the exhaust gas and tar is generated, and this tar is transferred to the contact surfaces of the exhaust timing valve and the valve guide. Even if the tar enters the gap, since the sliding contact surface is formed in a matte finish, an oil film is formed on the tar between the contact surfaces and the viscosity decreases. Furthermore, since the sliding contact surface is formed in a matte finish, the contact area of the layer contact surface is reduced accordingly, and the operating resistance of the exhaust timing valve is reduced. For these reasons, even if tar enters between the exhaust timing valve and the valve guide, the exhaust timing valve can operate satisfactorily.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view showing an embodiment of the variable exhaust timing device according to the present invention applied to a two-cycle one-engine engine.

Reference numeral 10 indicates a two-cycle engine, and a cylinder 12 is fitted into a cylinder block 11 of the two-stroke engine 10, and a piston 13 is slidably accommodated in the cylinder 12. The side wall of the cylinder 12 includes a scavenging port (not shown) for guiding fresh air into the combustion chamber 14 and a scavenging port (not shown) for guiding fresh air into the combustion chamber 14.
Exhaust ports 15 for discharging the combustion gas burned therein are respectively opened. An exhaust passage 16 extends outward from the exhaust port 15.

An exhaust timing valve 17 and a valve guide 18 are arranged in the cylinder block 11 near the top of the exhaust port 15 . Two sets of these exhaust timing valves 17 and valve guides 18 are arranged in parallel above the scavenging port 15, as also shown in FIG.

Of these, the exhaust timing valve 17 has an actuating part 19, a rod part 20, and a stopper part 21, and the stopper part 21 is fitted and fixed to the rod part 20. Actuation part 19
is in sliding contact with the guide portion 22 of the valve guide 18, and the rod portion 20 is inserted through the insertion portion 23 of the valve guide 18. The valve guide 18 is fixed to the cylinder block 11 by a set screw 24. In this way, the exhaust timing valve 17 is guided by the valve guide 18 and moves back and forth toward the exhaust port 15.

An actuation chamber portion 25 is attached to the cylinder block 11, and the rod portion 20 and stopper portion 21 of the exhaust timing valve 17, as well as the actuation mechanism 26 are accommodated in the actuation chamber portion 25.

The actuation mechanism 26 includes an actuation arm 27, a driven pulley 28, and a pulley 29.

The cable 29 is wound between a drive pulley (not shown) linked to the crank and the driven pulley 28,
The driven boo 928 is rotated according to the engine speed. The operating arm 27 is connected to a driven pulley 28 via a shaft (not shown), and is also connected to the exhaust timing valve 17.
It engages with the bottle 30 fitted into the stopper part 21 of. Such an operating mechanism 26, when the engine reaches a high speed range,
The driven pulley 28 is rotated by the cable 29, and the actuating arm 27 is accordingly rotated, thereby retracting the exhaust timing valve 17 from the exhaust port 15, as shown in FIG.

Now, sliding contact surfaces 31 and 32 are provided on the operating portion 19 of the exhaust timing valve 17 and the guide portion 22 of the valve guide 18, respectively. Both of these sliding contact surfaces 31 and 32 have a planar shape, and contact each other to close the exhaust timing valve 1.
This serves as a guide surface when moving 7.

Further, the outer surface of the actuating portion 19 in the exhaust timing valve 17 is connected to the sliding surface 31 as shown in FIGS. 1 to 3.
A pear-shaped surface 33 is formed over almost the entire surface including the pear-shaped surface. This matte surface 33 is formed by subjecting the surface of the actuating portion 19 to cold working such as shot peening or sandblasting.

In the engine low and medium speed range, the exhaust timing valve 17 is positioned at the exhaust port 1 as shown by the solid line in FIGS. 1 and 3.
5, and the exhaust timing is delayed.

At this time, if you continue to drive at a low load for a long time, the exhaust timing valve 17 will come into direct contact with the high temperature exhaust gas and the temperature will rise to about 50°C.
Since it is heated to about 550° C., the oil in the exhaust gas becomes carbonized and becomes tar, which adheres to the exhaust timing valve 17. As the exhaust timing valve 17 advances and retreats, this attached tar is spread between the tank contact surfaces 31 and 32 of the exhaust timing valve 17 and the valve guide 18, and between the operating part 19 of the exhaust timing valve 17 and the cylinder block 11. to invade. However, since the matte surface 33 is formed on the entire surface of the actuating part 19 of the exhaust timing valve 17, the area between the sliding surfaces 31 and 32 and the actuating part 19
Then, the tar that has entered between the cylinder blocks 11 breaks out in the oil film, and the viscosity of the tar decreases. In particular, the viscosity decreases significantly when cold.

Moreover, since the matte surface 33 is formed on almost the entire surface of the operating portion 19 of the exhaust timing valve 17, the sliding surfaces 31 and 32
as well as the contact area between the actuating part 19 and the cylinder block 11.
The contact area with the exhaust timing valve 17 is reduced, and the operating resistance of the exhaust timing valve 17 is reduced.

These tar viscosity reduction and exhaust timing valve 1
As a result of the reduction of the operating resistance of 7, the tar
Even if it enters the exhaust timing valve 17 and the cylinder block 111, the exhaust timing valve 17
works well.

Further, since the matte surface 33 of the exhaust timing valve 17 can be formed by simple cold working, there is no increase in cost.

In the above embodiment, the exhaust timing valve 17 is provided with a satin surface 33, but the sliding surface 32 of the valve guide 18 and the sliding surface of the cylinder block 11 with the exhaust timing valve 17 are provided with a satin surface. Alternatively, the exhaust timing valve 17, the valve guide 18, and the cylinder block 11 may all have a satin surface.

(Effects of the Invention) As described above, according to the variable exhaust timing device according to the present invention, at least one of the contact surfaces of both the exhaust timing valve and the valve guide is formed in a satin-finish shape. Even if tar enters between the contact surfaces of both layers of the valve guide, an oil film is formed in the tar between the sliding contact surfaces, and the viscosity of the tar provides resistance, thereby improving the operation of the exhaust timing valve.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the exhaust timing variable device according to the present invention applied to a two-stroke engine, and FIG. 2 is a V sectional view showing the exhaust timing valve in a retracted state in FIG. 1, M3. The figure is a sectional view taken along the line ■--■ in FIG. 1, and FIG. 4 is a sectional view showing a conventional variable exhaust timing device. 10...2-cycle engine, 15...Exhaust port, 1
7...Exhaust timing valve, 18...Valve guide, 31.32...Sliding surface, 33...Pearl surface. Applicant's agent Hisaha Hata 2ro 3rd session

Claims (1)

[Claims] It has an exhaust timing valve that is arranged near the exhaust port of the engine and is movable toward the exhaust port, and a valve guide that slides in contact with the exhaust timing valve and guides the movement of the exhaust timing valve. An exhaust timing variable device characterized in that at least one of the sliding contact surfaces of the exhaust timing valve and the valve guide is formed in a matte finish.