JPH0352981Y2 - - Google Patents

Description

[Detailed explanation of the idea] Industrial applications The present invention relates to a two-stroke internal combustion engine.

BACKGROUND TECHNOLOGY Compact two-stroke internal combustion engines such as those for portable power working machines generally discharge combustion gas in the cylinder to the exhaust port by using the scavenging flow of the air-fuel mixture blown into the cylinder from the scavenging port. In order to effectively blow out and reverse this scavenging air flow for efficient exhaust, it is necessary to change the shape and number of scavenging ports to suit the optimum conditions for each model, and to create complex structures on the top of the piston. However, it is difficult to obtain a complete scavenging effect with a simple configuration, and therefore sufficient improvements in engine performance, especially engine output characteristics and fuel efficiency characteristics, have not been achieved. It has not been.

Problems to be Solved by the Invention Therefore, an object of the present invention is to provide a two-stroke internal combustion engine that has a simple structure, further enhances the scavenging effect, and can more completely improve engine characteristics.

Means for Solving the Problem That is, according to the present invention, a piston is arranged in a cylinder so as to be able to reciprocate, and the combustion gas in the combustion chamber of the cylinder is discharged to the exhaust port by a scavenging air flow from the scavenging port. In a two-stroke internal combustion engine, a medium-height crown spherical surface at the top of the piston is formed by a spherical surface drawn with a predetermined radius around a point on a line offset by a predetermined dimension in the lateral direction from the central axis of the piston. Features.

Effect: Therefore, by setting the direction of the crown spherical surface at the top of the piston to match the engine, scavenging can be performed with an optimal deflector effect for blowing out and reversing the scavenging air flow.

Embodiments Next, the present invention will be described based on embodiments shown in the drawings.

The two-stroke internal combustion engine of the illustrated embodiment is a high-speed engine used in chainsaws, etc.
As shown in the figure, it has a cylinder 1, and the cylinder 1
has an intake port 2 and an exhaust port 3 on opposite sides.
Scavenging ports 4 are formed on both sides located substantially perpendicularly to the intake port 2 and exhaust port 3, and a piston 5 is provided within the cylinder 1 so as to be able to reciprocate. There is. A crankcase 6 is coupled to the lower end of the cylinder 1, and the crankcase 6 rotatably supports a crankshaft 8 in its crank chamber 7. The crankshaft 8 is connected to the piston 5 by a connecting rod 9, and is driven to rotate by the reciprocating motion of the piston 5. The intake port 2
is connected to a carburetor 10 and sucks a mixture of fuel and air into the crank chamber 7, and as the piston 5 descends, the mixture flows into the crank chamber 7.
It is designed to be pre-compressed inside. Said scavenging port 4
is in communication with the crank chamber 7, and blows out the air-fuel mixture precompressed in the crank chamber 7 into the combustion chamber 11 of the cylinder 1 as a scavenging air flow, so that the combustion gas in the combustion chamber 11 is The air is discharged from the exhaust port 3 to the outside through the muffler 12. Further, an ignition plug 13 is obliquely disposed at the head of the cylinder 1, and the ignition plug 13 generates discharge fireworks in the combustion chamber 11 of the cylinder 1 to burn the air-fuel mixture and cause an explosion. The force is used to push down the piston 5.

The top portion 14 of the piston 5 is formed with a crown spherical surface, and this crown spherical surface is formed along a line Y offset by a predetermined dimension D in the lateral direction from the central axis X-X of the piston 5, as shown in FIG. −
It is formed by a spherical surface drawn with radius R centered on point O on Y. Therefore, the piston 5
Compared with the crown spherical surface of the conventional piston top 14' (shown by a dotted line in FIG. 2) drawn with the same radius R from the point O' on the central axis XX, the crown spherical surface of this embodiment is as follows. One side crown edge 1
5 is the crown edge 16 on the diametrically opposite side;
The entire crown spherical surface is formed to be inclined toward the crown end edge 16 at a lower level.

In the case of the high-speed engine shown in FIG. 1, the piston 5 formed in this manner has its high-level crown edge 15 located on the intake port 2 side of the cylinder 1, and the low-level crown edge 15 located on the side of the intake port 2 of the cylinder 1. 16 is placed in the cylinder 1 so that it is located on the exhaust port 3 side of the cylinder 1.

With the above-described configuration, the crown spherical surface of the top 14 of the piston 5 can blow out the scavenging air flow from the scavenging port 4 into the combustion chamber 11 and
It has a deflector effect and a guiding effect on the reversal of the scavenging airflow within the airflow chamber 1, thereby further improving the scavenging efficiency. Furthermore, if the internal combustion engine is a low-speed engine other than a high-speed type, the scavenging efficiency can be similarly improved by changing the direction of the spherical surface of the crown 14 of the piston 5 according to the type of engine. .

Effects of the invention With the structure of the invention explained above, the invention has the following effects:
By appropriately setting the direction of the crown spherical surface at the top of the piston according to the engine type, high scavenging efficiency can be achieved by providing the optimal deflector effect and guiding action for blowing out the scavenging air flow and reversing the scavenging air flow. As a result, engine performance characteristics, particularly engine output characteristics, fuel efficiency characteristics, etc., can be improved, and furthermore, manufacturing is easy.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a high-speed two-stroke internal combustion engine showing one embodiment of the present invention, and FIG. 2 is a side view of a piston of the internal combustion engine shown in FIG. 1. 1...Cylinder, 3...Exhaust port, 4...Scavenging port, 5...Piston, 11...Combustion chamber, 14...
top of the piston.

Claims (1)

[Scope of utility model registration request] In a two-stroke internal combustion engine, a piston 5 is disposed in a cylinder 1 so as to be able to reciprocate, and combustion gas in a combustion chamber 11 of the cylinder is discharged to an exhaust port 3 by a scavenging air flow from a scavenging port 4. The mid-height crown spherical surface of the top portion 14 is formed of a spherical surface drawn with a predetermined radius R centered on a point O on a line Y-Y offset by a predetermined dimension D in the lateral direction from the piston center axis X-X. A two-stroke internal combustion engine featuring: