JP2551086B2 - Variable exhaust timing device - Google Patents

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-cycle engine.

(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.
To advance and retreat to accelerate the exhaust timing.

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 actuation mechanism 3 for advancing and retracting the exhaust timing valve 2 is housed in the actuation chamber 7 attached to the cylinder block 6 together with the rear portion of the exhaust timing valve 2.

(Problems to be Solved by the Invention) In the low and middle engine speed range, the exhaust timing valve 2 projects toward the exhaust port 4 as shown in FIG. Exhaust pressure in the exhaust port 4 and the exhaust passage 1 acts through a gap between the exhaust timing valve 2, the valve guide 5, and the cylinder block 6. Since there is no escape path for pressure in the working chamber 7, the pressure P ₁ in the working chamber 7 becomes higher than the pressure P ₂ in the exhaust passage 1 as shown by the solid line A in FIG. Therefore, even if it is desired to retract the exhaust timing valve 2 in the high engine speed region, it is difficult to retract the exhaust timing valve 2 by the amount that the pressure P ₁ is higher than the pressure P ₂ , and the exhaust timing valve 2 may malfunction. is there.

Therefore, conventionally, a pressure vent hole that connects the working chamber 7 and the ventilation passage 1 is formed to reduce the pressure P ₁ in the working chamber 7 in the low and middle engine speed range as shown by the chain line B in FIG. There is something. However, in this case, part of the exhaust gas is guided into the working chamber 7 through the pressure release hole even in the high engine speed region, so that the engine output may decrease in the high engine engine speed region.

The present invention has been made in consideration of the above facts, and an object of the present invention is to provide an exhaust timing variable device capable of favorably operating an exhaust timing valve and suitably maintaining an engine output.

[Structure of Invention]

(Means for Solving the Problem) The present invention is directed to an exhaust timing valve which is arranged in the vicinity of an exhaust port of an engine and is capable of advancing and retracting toward the exhaust port; A valve guide for guiding the movement of the valve; and a working chamber for accommodating a rear portion of the exhaust timing valve and an operating mechanism connected to the rear portion of the exhaust timing valve, wherein the exhaust timing valve has a groove formed therein. The groove is provided so as to communicate and block the exhaust passage communicating with the exhaust port and the working chamber, respectively, according to the advance / retreat of the exhaust timing valve.

(Operation) Therefore, according to the exhaust timing variable device of the present invention, when the exhaust timing valve is projected, the working chamber communicates with the exhaust passage through the groove of the exhaust timing valve, so that the pressure in the working chamber is almost equal to that of the exhaust passage. They can be made equal, and the exhaust timing valve can be favorably retracted. Further, since the exhaust passage and the working chamber are shut off when the exhaust timing valve is retracted, the exhaust gas flowing through the exhaust passage in the high engine speed range is not guided to the working chamber, and the engine output in the high engine speed range is reduced. Never.

Embodiment An embodiment of the present invention will be described below 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 from the exhaust port 15 to the outside.

In the cylinder block 11, an exhaust timing valve 17 and a valve guide 18 are arranged near the upper part of the exhaust port 15. The exhaust timing valve 17 is shown in FIGS. 2 (A) and (B).
As also shown in FIG. 3, it comprises 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,
The rod portion 20 and the stopper portion 21 as the rear portion of the exhaust timing valve 17 and the operating mechanism 26 are housed in the operating chamber 25.

This actuation mechanism 26, as shown in FIG.
7. It has a driven pulley 28 and a cable 29. The cable 29 is wound around a drive pulley (not shown) interlocked with a crank and the driven pulley 28 to rotate the driven pulley 28 according to the engine speed. The operating arm 27 is connected to the driven pulley 28 via a shaft (not shown) and engages with the pin 30 fitted to the stopper portion 21 of the exhaust timing valve 17. In such an operating mechanism 26, when the engine reaches a high rotation speed range, the driven pulley 28 is rotated by the cable 29, and the operating arm 27 is accordingly rotated.
Rotates and causes the exhaust timing valve 17 to retract from the exhaust port 15 as shown in FIG. 3 (B).

Now, as shown in FIGS. 1 to 3, a groove 31 extending in the longitudinal direction of the exhaust timing valve 17 is formed in the operating portion 19 of the exhaust timing valve 17. The upper end 31A of this groove 31
Is on the back 32 of the actuating part 19 and the lower end 31B of the groove 31 is
It is formed at a substantially central position of 9 in the longitudinal direction. The lower end 31B of the groove 31 is located inside the exhaust passage 16 as shown in FIGS. 1 and 2A when the exhaust timing valve 17 projects to the exhaust port 15, and the exhaust timing valve 17 is disposed at the exhaust port. As shown in FIG. 2 (B) when the vehicle retreats from 15, the exhaust passage 16
It is set so as to be located on the outer working surface sliding surface 33.

Therefore, when the exhaust timing valve 17 is projected,
Groove 31 and exhaust timing valve 17 and valve guide
The exhaust passage 16 and the inside of the working chamber 25 communicate with each other through a gap 18 and are provided so that the exhaust passage 16 and the inside of the working chamber 25 are shut off when the exhaust timing valve 17 is retracted.

 Next, the operation will be described.

As shown in FIGS. 1 and 2 (A), the exhaust timing valve 17 has the exhaust port in the low and middle engine speed range.
Since it projects toward 15, the working chamber 25 communicates with the exhaust passage 16 through the gap between the exhaust timing valve 17 and the valve guide 18 and the groove 31. Therefore, the pressure P ₁ in the exhaust chamber 25 becomes substantially equal to the pressure P ₂ in the exhaust passage 16, and the backward movement of the exhaust timing valve 17 by the operating mechanism 26 is not hindered. Therefore, the exhaust timing valve 17 can be favorably retracted.

Further, in the high engine speed region, as shown in FIG. 2 (B), when the exhaust timing valve 17 retracts from the exhaust port 15, the groove 31 is not located in the exhaust passage 16, so
The working chamber 25 and the exhaust passage 16 are shut off. As a result, since the exhaust gas flowing through the exhaust passage 16 is not guided into the working chamber 25, the engine output in the high engine speed range does not decrease, and the high output can be maintained as shown by the solid line C in FIG. .

As another embodiment, if the volume of the working chamber 25 is set to an appropriate size, the exhaust passage 16 and the exhaust chamber 25 communicate with each other through the groove 31 and the like in the engine low and middle speed range,
The exhaust pressure pulsating wave will flow from the exhaust passage 16 to the working chamber 25. As a result, the charging efficiency of fresh air in the engine low-medium speed range is enhanced, and the engine output in the engine low-medium speed range is as shown in the broken line E in FIG. ) Better than.

In both of the above embodiments, in the engine low / medium speed range, the exhaust passage 16 passes through the gap between the exhaust timing valve 17 and the valve guide 18 in addition to the groove 31.
Although the one communicating with the inside of the valve 25 has been described, the insertion portion 23 of the valve guide 18 is provided with a through hole 34 shown by a broken line in FIG. 2A, and the working chamber 25 and the exhaust passage 16 are provided with the groove 31 and the through hole 34. You may be connected by.

〔The invention's effect〕

As described above, according to the exhaust timing variable device of the present invention, a groove is formed in the exhaust timing valve that is guided and moved by the valve guide, and the groove includes the exhaust passage communicated with the exhaust port and the exhaust timing valve. Since the working chamber that accommodates the working mechanism of No. 2 is provided so as to cut off the communication in accordance with the advance and retreat of the exhaust timing valve, when the exhaust timing valve is projected, the working chamber and the exhaust passage are connected to each other and Is almost equal to that in the exhaust passage, the exhaust timing can be favorably retracted, and the exhaust timing valve can be favorably operated. At the same time, since the working chamber and the exhaust passage are cut off when the exhaust timing valve is retracted, the exhaust gas flowing through the exhaust passage does not flow to the working chamber, and the engine output in the high engine speed region can be preferably maintained.

[Brief description of 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-cycle engine, and FIGS. 2 (A) and 2 (B) are views showing the operation of an exhaust timing valve. FIG. 4 is a graph showing the relationship between engine speed and engine output in one embodiment, FIG. 4 is a sectional view showing a conventional exhaust timing varying device, and FIG. 5 is a two-cycle engine equipped with a conventional exhaust timing varying device. 3 is a graph showing the relationship between the engine speed and the working chamber internal pressure. 10 …… 2-cycle engine, 15 …… exhaust port, 16 …… exhaust passage, 17 …… exhaust timing valve, 18 …… valve guide, 25 …… working chamber, 26 …… working mechanism, 31 …… groove,
31A …… The upper end of the groove, 31B …… The lower end of the groove.

Claims (1)

(57) [Claims] 1. An exhaust timing valve which is arranged near an exhaust port of an engine and is provided so as to be able to move forward and backward toward the exhaust port, and a valve guide which slides on the exhaust timing valve to guide the movement of the exhaust timing valve. And a working chamber for housing a working mechanism connected to the rear portion of the exhaust timing valve and the rear portion of the exhaust timing valve, wherein a groove is formed in the exhaust timing valve, and the groove is communicated with the exhaust port. An exhaust timing variable device, wherein the exhaust passage and the working chamber are provided so as to communicate with each other and shut off in accordance with the advance and retreat of the exhaust timing valve.