JPH0658063B2 - 2-cycle engine - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a two-stroke engine.

(Prior Art) In a two-cycle engine, the unburned gas (HC) is contained in the exhaust gas discharged during idling. This is because the scavenging air flow that is pushed into the cylinder from the scavenging port at the time of idling blows through to the scavenging port.

It is known that as a measure for preventing blow-by of the scavenging airflow during idling, the separation distance (exhaust lead) between the upper end of the exhaust port and the upper end of the scavenging port may be shortened. Therefore, in the conventional two-cycle engine, the scavenging timing is adjusted by setting the exhaust lead of the scavenging port on the inner wall surface of the cylinder to be short, but the blow-through prevention effect is not always sufficient. .

(Object of the Invention) An object of the present invention is to provide a two-cycle engine that prevents blow-by of a scavenging airflow during idling, reduces the amount of unburned gas in exhaust gas, and improves fuel efficiency.

(Structure of the Invention) In the present invention to achieve the above object, the main scavenging port and the auxiliary scavenging port are opened on the inner peripheral surface of the cylinder, the main scavenging port is on the side closer to the exhaust port, and the auxiliary scavenging port is on the far side. In each two-stroke engine,
The exhaust lead of the auxiliary scavenging port is shorter than the exhaust lead of the main scavenging port, and a wall surface for guiding the scavenging air from the auxiliary scavenging port inward from the piston peripheral portion is formed on the upper surface of the piston. It is what

(Examples) Hereinafter, the present invention will be described with reference to Examples shown in the drawings.

Reference numeral 1 is a cylinder head, 2 is a cylinder, and 3 is a crankcase. A spark plug 4 is attached to a position of the cylinder head 1 above the cylinder 2. A piston 5 is inserted into the cylinder 2, and the reciprocating motion of the piston 5 rotationally drives the crankshaft 6 in the crankcase 3.

An intake passage 7 is provided on one side of the cylinder 2, and an exhaust passage 8 is provided on the opposite side. On the inner peripheral surface of the cylinder 2, three intake ports 9, 9, 9 communicating with the intake passage 7 are opened at a lower portion and an intermediate portion respectively, and an exhaust port 10 communicating with the exhaust passage 8 is provided at an intermediate portion. It is open. Further, main scavenging ports 11, 11 and auxiliary scavenging ports 12, 12 communicating with the crankcase 3 are opened in an intermediate region between the intake port 9 and the exhaust port 10. The main exhaust port 11 and the auxiliary scavenging port 12 are arranged symmetrically across the diagonal line of the intake port 9 and the exhaust port 10, and the main scavenging port 11 is on the side near the exhaust port 10 and the auxiliary scavenging port 12 is located. Are located on the far side.

Wall surfaces 5b, 5b that guide the scavenging air from the auxiliary scavenging ports 12, 12 inward from the piston peripheral portion are formed on the upper surface of the piston 5, and the auxiliary scavenging ports 12,
Corresponding to No. 12, notches 5a and 5a are provided respectively. The notches 5a and 5a are respectively formed in the piston 5
The grooves extend inward of the upper surface and communicate with each other at the center of the upper surface. Therefore, the separation distance from the upper end of the exhaust port 10 to the upper ends of the respective scavenging ports 11 and 12, the exhaust leads are shorter in the auxiliary scavenging ports 12, 12 than the main scavenging port 10 by the depth of the notches 5a, 5a. ing.

In the above-described two-cycle engine, when the piston 5 rises, the air-fuel mixture above the piston 5 is compressed and the lower side of the piston 5 is made negative pressure. Is sucked into the crankcase 3 via the. Next, when the ignition plug 4 is ignited, the compressed air-fuel mixture on the upper side of the piston 5 burns and explodes, causing the piston 5 to descend, and the upper surface of the piston 5 is connected to the exhaust port 10.
When passing through, the burnt gas inside is exhausted from the exhaust port 10. At the same time, the air-fuel mixture in the crankcase 3 compressed by the lowering of the piston 5 is ejected from the scavenging ports 11 and 12 into the cylinder 2 to perform a scavenging action.

When performing such a scavenging action, a wall surface 5b that guides the scavenging air from the auxiliary scavenging port 12 is formed on the upper surface of the piston 5, and the exhaust lead of the auxiliary scavenging port 12 is exhausted from the main scavenging port 11. Since it is shorter than the lead, there is a gap in the timing of opening, so that the auxiliary scavenging port 12 first opens and then the main scavenging port 11 opens. Moreover, since the wall surface 5b is directed inward from the peripheral edge portion of the piston 5, the scavenging airflow ejected from the auxiliary scavenging port 12 is guided by the wall surface 5b as shown by an arrow A and prevented from spreading to the exhaust port 10 side. Suddenly exhaust port 10
It doesn't blow through. At this time, the scavenging air flow easily flows along the wall surface 5b because the upper edge of the auxiliary scavenging port 12 opens at the notch 5a on the upper surface of the piston 5 at the stage when the preload of the air-fuel mixture becomes the highest, so that it easily flows along the wall surface 5b. 1
The effect of preventing diffusion to the 0 side can be enhanced. Then
In such a state, the scavenging airflow flows from the main scavenging port 11 in the direction opposite to the exhaust port 10 as shown by the arrow B, and therefore the scavenging airflow can be further prevented from occurring. In addition, the scavenging air flow is the auxiliary scavenging port 12
When jetted out from the exhaust port 10 as indicated by arrow A, the burnt gas above the piston can be efficiently expelled from the exhaust port 10 as indicated by arrow C. Therefore, in the above-described two-cycle engine, blow-by of the scavenging airflow during idling is prevented, and the amount of unburned gas (HC) contained in the exhaust gas can be reduced. Moreover, it is possible to improve fuel efficiency.

(Effect of the Invention) As described above, the present invention opens the main scavenging port and the auxiliary scavenging port on the inner peripheral surface of the cylinder, and the main scavenging port is on the side closer to the exhaust port and the auxiliary scavenging port is on the far side. In the arranged two-cycle engine, the exhaust lead of the auxiliary scavenging port is made shorter than the exhaust lead of the main scavenging port, and the scavenging air from the auxiliary scavenging port is guided inward from the peripheral edge of the piston to the upper surface of the piston. Since the wall surface is formed, the scavenging air flow from the auxiliary scavenging port is guided by the wall surface formed on the upper surface of the piston to prevent sudden blow-through to the exhaust port. Therefore, the amount of unburned gas contained in the exhaust gas at the time of idling can be reduced, and the fuel consumption can be improved.

[Brief description of drawings]

The figure shows a two-stroke engine according to an embodiment of the invention,
FIG. 1 is a perspective view schematically showing a main part of the two-cycle engine shown in FIG. 3, FIG. 2 is a development view of a cylinder of the engine, FIG. 3 is a longitudinal sectional view of the engine, and FIG. Of FIG.
It is a IV-IV arrow line view. 2 ... Cylinder, 5 ... Piston 5a ... Notch, 5b ... Wall surface 9 ... Intake port, 10 ... Exhaust port 11 ... Main scavenging port, 12 ... Auxiliary scavenging port

Claims (1)

[Claims] 1. A two-cycle engine in which a main scavenging port and an auxiliary scavenging port are opened on an inner peripheral surface of a cylinder, and the main scavenging port is arranged on a side closer to an exhaust port and the auxiliary scavenging port is arranged on a far side. The exhaust lead of the auxiliary scavenging port is shorter than the exhaust lead of the main scavenging port, and a wall surface for guiding the scavenging air from the auxiliary scavenging port inward from the peripheral edge of the piston is formed on the upper surface of the piston. A two-cycle engine that does.