JP3055348B2 - Two-stroke engine intake structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake structure for a two-stroke engine provided with a reed valve device.

2. Description of the Related Art In a two-stroke engine, an air-fuel mixture is sucked into a crankcase, and several types of valve devices have been devised to control the flow and shutoff thereof.

[0002] The above-mentioned valve device includes, for example, a reed valve system, a piston valve system, a piston reed valve system,
The rotary disc valve system is generally used, but the reed valve system is particularly simple in structure, has good accelerator response at low speeds, and has a high torque engine. Has been adopted.

A reed valve of a reed valve device adopting a reed valve system is a thin and elastic metal plate-shaped one having a fixed end provided in an intake passage. FIGS. 5 and 6 show a general example of a two-stroke engine which is a stop valve and includes a reed valve device.

[0004] The engine 1 having the reed valve device includes:
A valve chamber 3 is formed in a part of the crankcase 2, and a carburetor 5 serving as an engine intake system is connected to an outer end of the valve chamber 3 via an intake passage 4. That is, the air-fuel mixture is sucked into the crankcase 2 through the valve chamber 3, and the reed valve device 6 is provided in the valve chamber 3.

The reed valve device 6 has a wedge-shaped valve seat 9 whose base end 7 is opened and an upper and lower surface on which a valve opening 8 is opened contracts toward the front end. The valve port 8 is provided with a thin and elastic metal plate-shaped reed valve 10. The reed valve 10 has a free end at the front end and a rear end fixed to the valve seat 9.

[0006] The reed valve device 6 is mounted so that the front end thereof faces the inside of the crankcase 2 and the entrance of the valve chamber 3 is closed by the flange 11 of the base end 7.

Due to the negative pressure in the crankcase 2 in the compression process due to the rise of the piston 13 in the cylinder 12 of the engine 1, the air-fuel mixture flows from the intake passage 4 to the valve seat 9.
While the reed valve 10 is pushed open and sucked through, the piston 13 descends and the inside of the crankcase 2 returns to positive pressure, the reed valve 10 immediately closes the valve port 8 and prevents the backflow of the air-fuel mixture. I do. Thus, the reed valve device 6
Controls opening and closing of the intake passage 4 with a kind of check valve function.

[0008]

When observing the inflow state of the air-fuel mixture in the reed valve device 6 constructed as described above, most of the air-fuel mixture is found to be at the leading end 1 of the reed valve.
0a, but a part is reed valve side edge 10b.
Some are trying to escape from the side.

However, the reed valve side edge 10b
Because the inner walls 3a of the valve chamber oppose each other with a slight gap 14, the mixture is prevented from flowing out smoothly, and the suction efficiency of the entire reed valve device 6 is reduced.

On the other hand, if the gap 14 between the side edge portion 8a of the valve port 8 and the inner side walls 3a of the valve chamber is made excessively large, the compression ratio in the crankcase 2 may be reduced. Adversely affect.

The present invention has been made in consideration of the above-mentioned circumstances, and makes the outflow of the air-fuel mixture from the side edge of the reed valve smooth, increases the flow rate of the air-fuel mixture to increase the suction efficiency, and thereby achieves full rotation. It is an object of the present invention to provide a two-stroke engine intake structure that improves the engine performance in a region.

Another object of the present invention is to provide an intake structure for a two-stroke engine that does not lower the compression ratio in the crankcase.

[0013]

According to a first aspect of the present invention, there is provided an intake structure for a two-stroke engine connected to an intake passage of an engine intake system. A valve chamber was formed in the case, and a reed valve device was provided in the valve chamber.
In the intake structure of a cycle engine, the reed valve device has a wedge-shaped valve seat whose base end is opened and whose upper and lower surfaces contract toward the front end. While the reed valve is provided, the reed valve device is mounted so that the front end thereof faces the inside of the crankcase, and the entrance of the valve chamber is closed by a flange at the base end.
A gentle mountain-shaped curved surface bulging outward is formed on both inner side walls of the valve chamber, and these curved surfaces form an inflated portion having a substantially rectangular cross-sectional shape between both side surfaces of the valve seat. Projecting portions projecting toward both side surfaces of the valve seat are provided at required portions of both inner side walls of the valve chamber opposite to both side surfaces of the valve seat of the inflated portion. And a gap between the inner wall of the valve chamber and the inner wall of the valve chamber.

[0014]

In the present invention having the above structure, the reed valve device has a wedge-shaped valve seat whose base end is opened and whose upper and lower surfaces contract toward the front end. An elastically deformable reed valve is provided at the mouth, while the reed valve device is mounted so as to close the inlet of the valve chamber by a flange at a base end with its distal end directed into the crankcase, A gentle mountain-shaped curved surface bulging outward is formed on both inner side walls of the valve chamber, and these curved surfaces form an inflated portion having a substantially rectangular cross-sectional shape between both side surfaces of the valve seat. Projections protruding toward both side surfaces of the valve seat are provided at required portions of both inner side walls of the valve chamber facing the both side surfaces of the valve seat. Since the gap between both side surfaces of the valve seat and both inner side walls of the valve chamber is reduced, the outflow of the air-fuel mixture from the side edge of the reed valve is smoothed, and the flow rate of the air-fuel mixture is increased to increase the suction efficiency. It is possible to provide an intake structure of a two-stroke engine that improves the engine performance in all rotation ranges and does not lower the compression ratio in the crankcase.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional plan view showing an example of a two-cycle engine provided with a reed valve device to which the present invention is applied, and FIG. 2 is a longitudinal side view of the engine.

1 and 2, the engine 2
A cylinder 22 is formed above the cylinder 1 and the cylinder 2
2, a crankcase 23 is provided continuously below. A piston 24 housed in the cylinder 22 slides up and down in the cylinder 22 to rotate a crankshaft 27 via a connecting rod 25 and a crankpin 26. Above piston 2
4 reciprocating stroke, the exhaust port 28 of the exhaust passage 28
and the scavenging port 29a of the scavenging passage 29 communicating with the inside of the crankcase 23 is opened and closed. Further, the pressure in the crankcase 23 changes according to the reciprocating stroke of the piston 24.

On the other hand, an intake pipe 31 connected to a carburetor 30 serving as an engine intake system is connected to a crankcase 23. A valve chamber 32 is formed in the crankcase 23 at the connection portion, and a reed valve device 33 is provided in the valve chamber 32.

The intake passage 34 that leads from the intake pipe 31 to the crankcase 23 via the valve chamber 32 is controlled to open and close by the reed valve device 33.

The reed valve device 33 is based on a wedge-shaped valve seat 35 whose upper and lower surfaces are contracted toward the distal end and whose base end is open, and a thin and elastic valve port 36 is provided on the upper and lower surfaces thereof. A metal plate-shaped reed valve 37 is provided. The reed valve front end 37a is a free end, while the reed valve rear end 37b constitutes a base end. 38 and fixed together. The stopper plate 38 adjusts the opening of the reed valve 37.

The reed valve device 33 configured as described above closes the valve chamber 32 with the distal end portion directed toward the inside of the crankcase 23 by the flange 39 formed at the base end portion of the valve seat 35, and closes the intake pipe 31. It is pinched by the connection part.

FIG. 3 is an enlarged view of the vicinity of the valve chamber 32 of FIG. 2, and FIG. 4 is a cross-sectional view taken along the line AA of FIGS. 1 and 3.

As shown in FIGS. 1 and 3, the valve chamber 32 has a gentle mountain-shaped curved surface 40 bulging outward on both inner side walls 32 a of the valve chamber 32. As shown in FIG. 4, an expansion section 41 having a substantially rectangular cross-sectional shape is formed between them. On the other hand, valve seats 35 are provided at required portions on both inner side walls 32a of the valve chamber facing the both sides of the valve seat 35 on the curved surface 40.
The protrusions 42 having shapes corresponding to both side surfaces of the valve seat 3 are provided.
5 protrudes toward both side surfaces of the valve seat 5 to reduce a gap between both side surfaces of the valve seat 35 and both inner side walls 32a of the valve chamber.

The maximum width of the expansion section 41 is, for example, 5 to 5.
10mm, from there into the crankcase 23 inward
It is set to converge at an inclination angle of ２０20 °.

Next, the operation of this embodiment will be described.

When the piston 24 in the cylinder 22 rises and the pressure inside the crankcase 23 becomes negative, the air-fuel mixture in the intake pipe 31 is sucked into the crankcase 23 via the reed valve device 33. At this time, the air-fuel mixture introduced into the valve seat 35 pushes and opens the reed valve 37, and the reed valve tip portion 37 a and the side edge portion 37 c are opened from the valve port 36.
Through the crankcase 23.

Next, when the piston 24 descends, the negative pressure changes to a positive pressure, the reed valve 37 returns by elasticity, closes the valve port 36, and the sucked air-fuel mixture is primarily compressed in the crankcase 23.

In the above-described suction stroke, the state when the air-fuel mixture pushes open the reed valve 37 and flows into the crankcase 23 will be examined in detail.
The negative pressure in the inside is also propagated to the expansion section 41, and a large amount of the air-fuel mixture is generated by the suction effect, so that the reed valve side edge 37c
Out of the expansion section 41.

Due to this effect, the reed valve tip 37
The intake efficiency of the air-fuel mixture into the crankcase 23 is increased in accordance with the outflow amount from the crankshaft a, and the engine response over the entire rotation range is good and the output is improved.

Normally, when the above-described expansion portion 41 is provided in the valve chamber 32, the compression ratio in the crankcase 23 is reduced, but the expansion portion 4 having a substantially rectangular cross-sectional shape is used.
Since the projecting portions 42 having shapes corresponding to both side surfaces of the valve seat 35 are formed at required portions of both inner side walls 32a of the valve chamber opposed to both side surfaces of the first valve seat 35, the compression ratio in the crankcase 23 is reduced. Is minimized and does not adversely affect the scavenging action in the cylinder 22.

[0031]

As described above, according to the intake structure of a two-stroke engine according to the present invention, a valve chamber is formed in a crankcase connected to an intake passage of an engine intake system, and a reed valve is provided in the valve chamber. In the intake structure of a two-stroke engine provided with a device, the reed valve device has a wedge-shaped valve seat whose base end is opened and whose upper and lower surfaces contract toward the front end. An elastically deformable reed valve is provided at the valve port, while the reed valve device is mounted so as to close the inlet of the valve chamber by a flange at a base end with its distal end directed into the crankcase. A gentle mountain-shaped curved surface swelling outward is formed on both inner side walls of the valve chamber, and these curved surfaces are substantially formed between both side surfaces of the valve seat. Protruding portions projecting toward both side surfaces of the valve seat at required portions of both inner side walls of the valve chamber facing the both side surfaces of the valve seat. These protrusions reduce the gap between both side surfaces of the valve seat and both inner side walls of the valve chamber, smoothing outflow of the air-fuel mixture from the side edges of the reed valve and increasing the flow rate of the air-fuel mixture. As a result, it is possible to provide an intake structure of a two-stroke engine in which the intake efficiency is increased, the engine performance in the entire rotation range is improved, and the compression ratio in the crankcase is not reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view of a two-cycle engine showing one embodiment of an intake structure of a two-cycle engine according to the present invention.

FIG. 2 is a vertical side view of the engine shown in FIG.

FIG. 3 is an enlarged view of the vicinity of a valve chamber in FIG. 2;

FIG. 4 is a sectional view taken along the line AA in FIGS. 1 and 3;

FIG. 5 is a cross-sectional plan view of a two-stroke engine provided with a conventional reed valve device.

FIG. 6 is a longitudinal sectional side view of the engine shown in FIG. 5;

[Explanation of symbols]

 Reference Signs List 21 engine 22 cylinder 23 crankcase 24 piston 30 carburetor 31 intake pipe 32 valve chamber 32a both inner side walls of valve chamber 33 reed valve device 34 intake passage 35 valve seat 36 valve port 37 reed valve 39 flange 40 curved surface 41 inflated portion 42 projecting portion

Claims (1)

(57) [Claims] 1. In a two-stroke engine intake structure in which a valve chamber is formed in a crankcase connected to an intake passage of an engine intake system and a reed valve device is provided in the valve chamber, the reed valve device 33 includes: A wedge-shaped valve seat 35 whose base end is opened and the upper and lower surfaces contract toward the front end is provided. A resiliently deformable reed valve 37 is provided in a valve port 36 on the upper and lower surfaces of the valve seat 35. The reed valve device 33 is mounted so that the front end thereof faces the inside of the crankcase 23, and the entrance of the valve chamber 32 is closed by a flange 39 at the base end. A gentle mountain-shaped curved surface 40 is formed which bulges into a curved shape. The curved surface 40 has a substantially rectangular cross-sectional shape between the curved surface 40 and both side surfaces of the valve seat 35. The projecting portions projecting toward both side surfaces of the valve seat 35 at required portions of both inner side walls 32a of the valve chamber facing the both side surfaces of the valve seat 35. 42 are provided, and the valve seat 35 is
Characterized in that a clearance between both side surfaces of the valve body and both inner side walls 32a of the valve chamber is reduced.