JP2595632B2 - Variable exhaust timing device - Google Patents

Description

The present invention relates to a variable exhaust timing device for a two-stroke engine, and more particularly to a variable exhaust timing device capable of satisfactorily operating an exhaust timing valve.

(Prior Art) In a two-stroke engine, as shown in FIG.
Is provided. The exhaust timing valve 2 is provided so as to be able to advance and retreat toward the exhaust port 4 in synchronization with the engine speed by an operating mechanism 3 linked to the crank. In other words, the exhaust timing valve 2 is projected to the exhaust port 4 to delay the exhaust timing in the low and middle engine speed range, and the exhaust timing valve 2 in the high engine speed range.
And the exhaust timing is advanced.

Such an exhaust timing valve 2 is advanced and retracted along a valve guide 5, and the valve guide 5 is screw-fixed to a cylinder block 6. Also,
The operating mechanism 3 for moving the exhaust timing valve 2 forward and backward is accommodated in an operating chamber 7 attached to the cylinder block 6.

(Problems to be Solved by the Invention) In the low and middle engine speed range of the engine, the exhaust timing valve 2 protrudes toward the exhaust port 4 as shown in FIG. At this time, since the exhaust timing valve 2 is exposed to high-temperature exhaust gas, if the engine is driven under a low load for a long period of time in the low and middle engine speed range, the oil content in the exhaust gas will be about 150 ° C. to about 5 ° C.
When heated to 50 ° C., it is carbonized and becomes tar, and adheres to the outer surface of the exhaust timing valve 2. This tar is
When the exhaust timing valve 2 moves forward and backward, the exhaust timing valve 2 may enter a small gap between the sliding surfaces 8 and 9 between the exhaust timing valve 2 and the valve guide 5 and hinder the smooth operation of the exhaust timing valve 2. . In particular, the operability of the exhaust timing valve 2 is significantly reduced due to the high viscosity of the tar at the time of cooling.

The present invention has been made in view of the above facts, and provides an exhaust timing variable device that can operate the exhaust timing valve satisfactorily even if tar enters between the exhaust timing valve and the valve guide. The purpose is to:

[Configuration of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, an exhaust timing variable device according to the present invention is disposed near an exhaust port of an engine, and is provided so as to be able to advance and retreat toward the exhaust port. A timing valve, and a valve guide that slides on the exhaust timing valve and guides the movement of the exhaust timing valve. The exhaust timing valve and the valve guide are provided in two sets in parallel with the exhaust port. The two sliding contact surfaces of the valve guide and the valve guide are both formed in a planar shape, and the outer surface of the operating portion of the exhaust timing valve is formed in a satin shape including the sliding contact surface.

(Action) Therefore, according to the variable exhaust timing device of the present invention, the oil in the exhaust is carbonized by the heat of the exhaust to generate tar, and the tar is in contact with the sliding surfaces of the exhaust timing valve and the valve guide. Even when the exhaust timing valve enters, the outer surface of the operating portion of the exhaust timing valve is formed in a satin shape including the sliding contact surface, so that the oil film is cut off in the tar between the sliding contact surfaces and the viscosity is reduced. In addition, since the sliding contact surface is formed in a satin shape, the contact area of the sliding contact surface is reduced by that amount, and the operating resistance of the exhaust timing valve is reduced.
For these reasons, even when tar enters between the exhaust timing valve and the valve guide, the operation of the exhaust timing valve can be favorably performed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

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

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

In the cylinder block 11, an exhaust timing valve 17 and a valve guide 18 are arranged near the upper portion of the exhaust port 15. The exhaust timing valve 17 and the valve guide 18 are arranged in parallel above the scavenging port 15 as shown in FIG. Of these, the exhaust timing valve 17 is
19, a rod portion 20, and a stopper portion 21. The stopper portion 21 is fitted and fixed to the rod portion 20. The operating portion 19 slides on the guide portion 22 of the valve guide 18, and the rod portion 20 passes 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.
Thus, the exhaust timing valve 17 is guided by the valve guide 18 and moves toward and away from the exhaust port 15.

A working chamber 25 is attached to the cylinder block 11, and an exhaust timing valve 17 is provided in the working chamber 25.
The rod portion 20, the stopper portion 21, and the operating mechanism 26 are accommodated.

The operating mechanism 26 includes an operating arm 27, a driven pulley 28, and a cable 29. The cable 29 is wound around a drive pulley (not shown) interlocked with the crank and the driven pulley 28, and rotates the driven pulley 28 according to the engine speed. The operating arm 27 is connected to a driven pulley 28 via a shaft (not shown), and a pin 30 fitted to the stopper 21 of the exhaust timing valve 17.
Engages. When the operating mechanism 26 reaches the high engine speed range, the driven pulley 28 is rotated by the cable 29, and the operating arm 27 is rotated accordingly. As shown in FIG. From the exhaust port 15.

The sliding portions 31 and 32 are formed on the operating portion 19 of the exhaust timing valve 17 and the guide portion 22 of the valve guide 18, respectively. These sliding contact surfaces 31, 32 are both planar in shape and come into contact with each other to serve as guide surfaces when the exhaust timing valve 17 moves.

As shown in FIGS. 1 to 3, the outer surface of the operating portion 19 of the exhaust timing valve 17 has a matte surface 33 formed substantially over the entire surface including the sliding contact surface 31. The pear surface 33 is formed by performing cold working such as shot peening or sand blasting on the surface of the operating portion 19.

In the low engine speed range, the exhaust timing valve 17 is connected to the exhaust port 15 as shown by the solid lines in FIGS.
, And the exhaust timing is delayed. At this time, if the low-load running is continued for a long time, the exhaust timing valve 17 comes into direct contact with the high-temperature exhaust gas, and
Therefore, the oil component in the exhaust gas is carbonized into tar, and adheres to the exhaust timing valve 17. The adhering tar is discharged by the exhaust timing valve 17 and the valve guide as the exhaust timing valve 17 moves forward and backward.
18 between the sliding surfaces 31, 32 and the exhaust timing valve 17
Between the operating part 19 and the cylinder block 11. However, since the matte surface 33 is formed on the entire surface of the operating portion 19 of the exhaust timing valve 17, oil that has entered the space between the sliding contact surfaces 31 and 32 and between the operating portion 19 and the cylinder block 11 is cut off. Viscosity decreases. In particular, the viscosity significantly decreases during the cold period.

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 contact area between the sliding contact surfaces 31 and 32 and the contact area between the operating portion 19 and the cylinder block 11 are reduced, and The operating resistance of the timing valve 17 is reduced. As a result of the reduction in the viscosity of these tars and the reduction in the operating resistance of the exhaust timing valve 17, the tars
The exhaust timing valve 17 operates satisfactorily even if it enters between the exhaust timing valve 17 and the cylinder block 11.

Further, since the matte surface 33 of the exhaust timing valve 17 can be formed by simple cold working, the cost does not increase.

In the above embodiment, the matte surface 33 is formed on the exhaust timing valve 17, but the matte surface is formed on the sliding contact surface 32 of the valve guide 18 and the sliding contact surface of the cylinder block 11 with the exhaust timing valve 17. May be formed, or the exhaust timing valve 17,
A matte surface may be formed on all of the valve guide 18 and the cylinder block 11.

〔The invention's effect〕

As described above, according to the variable exhaust timing apparatus of the present invention, two sets of the exhaust timing valve and the valve guide are arranged in parallel to the exhaust port, and both sliding contact surfaces of the exhaust timing valve and the valve guide are formed in a planar shape. On the other hand, the outer surface of the operating portion of the exhaust timing valve is
Since it is formed in a satin shape including the sliding surfaces, even if tar enters between the sliding surfaces of the two sets of exhaust timing valves and valve guides arranged side by side, the oil film on the tar between the sliding surfaces will break. As a result, the viscosity of the tar is reduced, the operation of the exhaust timing valve can be improved, and the sliding contact surface is divided into two sets by the two sets of exhaust timing valves and valve guides arranged in parallel. Since the amount of tar adhering to the surface is different, the sliding resistance is different, so that the initial operability of the exhaust timing valve is also improved. Even if the contact area of the contact surface decreases, the operating resistance of the timing valve decreases, and tar enters between the exhaust timing valve and the valve guide, the operation of the exhaust timing valve is balanced, smooth and smooth. It can be carried out in good.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of an exhaust timing variable device according to the present invention applied to a two-stroke engine, FIG. 2 is a cross-sectional view showing a state in which an exhaust timing valve is retracted in FIG. FIG. 1 is a sectional view taken along the line III-III of FIG. 1, and FIG. 4 is a sectional view showing a conventional exhaust timing variable device. 10… 2 cycle engine, 15… Exhaust port, 17… Exhaust timing valve, 18… Valve guide, 31,32… Sliding contact surface, 33… Pear ground.

Claims (1)

(57) [Claims] An exhaust timing valve disposed near an exhaust port of an engine and movably provided toward the exhaust port, and a valve guide slidingly contacting the exhaust timing valve to guide movement of the exhaust timing valve. And two sets of the exhaust timing valve and the valve guide are arranged side by side with respect to the exhaust port, and both sliding contact surfaces of the exhaust timing valve and the valve guide are formed in a planar shape. An exhaust timing variable device characterized in that the outer surface is formed in a satin shape including a sliding contact surface.