JP2595486B2 - 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 comes into sliding contact with a valve guide 5 and is guided by the valve guide 5 to move forward and backward. The valve guide 5 is fixed to a cylinder block 6 by screws. The operating mechanism 3 for moving the exhaust timing valve 2 forward and backward is housed in an operating chamber 7 attached to the cylinder block 6 together with the rear part of the exhaust timing valve 2.

(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 vehicle continues to run under a low load for a long period of time in the low-to-medium rotation region, the oil content in the exhaust gas will be about 150 ° C. to about 550 ° C.
When heated to ° C., it is carbonized and becomes tar and adheres to the outer surface of the exhaust timing valve 2. When the exhaust timing valve 2 moves forward and backward, the tar penetrates into a small gap between the sliding contact surfaces 8 and 9 between the exhaust timing valve 2 and the valve guide 5 to make the exhaust timing valve 2 operate smoothly. May hinder. Then, the exhaust timing valve 2 may be stuck, which may cause a malfunction of the exhaust timing valve.

The present invention has been made in view of the above facts,
It is an object of the present invention to provide a variable exhaust timing device capable of satisfactorily operating the exhaust timing valve even when tar enters both sliding surfaces of the exhaust timing valve and the valve guide.

[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. And at least one of the sliding surfaces of the valve guide is provided with a plurality of grooves extending in the direction of movement of the exhaust timing valve.

(Operation) Therefore, according to the variable exhaust timing apparatus of the present invention, the oil in the exhaust is carbonized by the heat of the exhaust to generate tar, and the tar is brought into sliding contact between the exhaust timing valve and the valve guide. Even if it enters between the surfaces, since the groove is formed in the sliding contact surface, the tar is guided into the groove, and the adhesion to the sliding contact surface can be reduced. As a result, the sticking of the exhaust timing valve is prevented. Can be prevented. Further, since the groove is formed in the sliding contact surface, the contact area of the sliding contact surface is reduced by the amount of the groove, and the operating resistance of the exhaust timing valve is reduced. For these reasons, even when tar enters between the sliding surfaces of the exhaust timing valve and the valve guide, the exhaust timing valve guided in sliding contact with the valve guide can be favorably operated.

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 on 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. Two sets of these exhaust timing valves 17 and valve guides 18 are arranged above the exhaust port 15. The exhaust timing valve 17 includes an operating portion 19, a rod portion 20, and a stopper portion 21, and 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 is provided in the working chamber 25.
The rear portion of the 17 rod portion 20, the stopper portion 21, and the operating mechanism 26 are housed.

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 is engaged with a pin 30 fitted to the stopper 21 of the exhaust timing valve 17. In such an operating mechanism 26, when the engine reaches a high engine speed range, a driven pulley 28 rotates by a cable 29,
As a result, the operation arm 27 rotates, and the exhaust timing valve 17 is retracted from the exhaust port 15 as shown by the dashed line A.

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 surfaces 31 and 32 have a planar shape as shown in FIG.
It will be the guide surface for 17 moves. Of which, the valve guide
A plurality of grooves 33 are engraved on the sliding surface 32 of the 18. These grooves 33
As shown in FIG. 3, a plurality of, for example, three are formed in the moving direction of the exhaust timing valve 17. Each groove 33 is formed over almost the entire area of the valve guide 18, and the lower end 34 of the groove 33 in the figure is provided so as to open to the lower end surface 35 of the valve guide 18.

In the low-medium engine speed range, the exhaust timing valve 17 projects toward the exhaust port 15 as shown by the solid line in FIG. 1, and the exhaust timing is delayed. At this time, if the vehicle continues to run at low load for a long time, the exhaust timing valve 17 comes into direct contact with the high-temperature exhaust gas and is heated to about 150 ° C to about 550 ° C. Adhere to the exhaust timing valve 17. When the exhaust timing valve 17 is retracted, the tar contacts the sliding surfaces 31 and 3 of the exhaust timing valve 17 and the valve guide 18.
Although it invades between the two, most of it is guided into the groove 33. Groove 3
The tar accumulated in 3 will eventually pass from the lower end 34 of the groove 33 to the exhaust passage 1
It is discharged into 6.

Thus, even if tar enters between the sliding contact surfaces 31 and 32 of the exhaust timing valve 17 and the valve guide 18,
Almost all of the tar is guided into the groove 33, and the tar does not adhere to the contact surfaces of the sliding contact surfaces 31, 32. Therefore, the exhaust timing valve 17 does not adhere to the tar. In addition, since the groove 33 is formed in the contact surface 32, the sliding contact surface
The contact area between 32 and 31 is reduced and the exhaust timing valve 17
Operating resistance is reduced. By preventing the sticking of the exhaust timing valve 17 by the tar and reducing the operating resistance, the exhaust timing valve 17 can be satisfactorily operated even if the tar enters between the sliding contact surfaces 31 and 32.

In the above embodiment, the lower end 34 of the groove 33 is the valve guide.
Although the opening at the lower end surface 35 of 18 has been described, when the amount of tar is small, the lower end of the groove 33 is
It may not be open at the lower end surface 35 of the 18.

In the above embodiment, the groove 33 is formed on the sliding surface 32 of the valve guide 18. However, the groove 33 may be formed on the sliding surface 31 of the exhaust timing valve 17. Further, it may be formed on both contact surfaces 31, 32.

[Effects of the Invention] 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 with the exhaust port, and the sliding contact of the exhaust timing valve and the valve guide is performed. A plurality of grooves extending in the direction of movement of the exhaust timing valve are formed on at least one of the surfaces, so that a groove for collecting or collecting tar can be formed on the sliding contact surface. The contact area of the surface can be reduced, the operating resistance of the exhaust timing valve can be reduced, and the sliding can be performed smoothly and smoothly. On the other hand, the oil in the exhaust becomes tar and easily enters between the sliding contact surfaces. However, by guiding the invading tar into the groove, even if tar invades between the sliding surfaces, the tar is prevented from adhering to the sliding surfaces and is reduced, so that the exhaust timing valve is reduced. Can be favorably performed.

In addition, although the state of the sliding contact surface is basically uniform with one set of the exhaust timing valve and the valve guide, two sets of the exhaust timing valve and the valve guide are arranged side by side, and if the two groups are divided, the state of the sliding contact surface is improved. Although different possibilities arise, the reciprocating operation of the exhaust timing valve can be balanced, and the grooves formed in the two sets of sliding contact surfaces are used for collecting or collecting tar, so that both sliding contact surfaces can be used. It is possible to prevent and reduce the adhesion of tar to the exhaust gas, thereby improving the operability of the exhaust timing valve while maintaining the balance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an exhaust timing variable device according to the present invention applied to a two-stroke engine, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. FIG. 1 is a front view of a valve guide, 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 surface, 33 ... groove.

Claims (1)

(57) [Claims] An exhaust timing valve disposed in the vicinity of an exhaust port of an engine and movably provided toward the exhaust port; and a valve guide for slidingly contacting the exhaust timing valve to guide the 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 extend in at least one of the sliding contact surfaces of the exhaust timing valve and the valve guide in the direction of movement of the exhaust timing valve. A variable exhaust timing device comprising a plurality of grooves.