JPH0588367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to the improvement of a two-stroke gasoline engine suitable as an engine for small vehicles such as motorcycles.

[Conventional technology]

Conventionally, two-stroke gasoline engines have been widely used in motorcycles and other small vehicles because they have a simple structure, are lightweight, and can provide high output, and there is an increasing demand for increased output per unit displacement.

In general, to improve the specific power of an engine,
It is necessary to effectively supply the air-fuel mixture into the combustion chamber, and this has conventionally been made possible in two-stroke engines by increasing the opening area of the scavenging port or exhaust port into the combustion chamber.

However, if the opening area is set large, the scavenging port and exhaust port will get closer together, and the inner wall of the cylinder that separates both ports will become narrower, allowing the air-fuel mixture that was once sucked into the combustion chamber to be released to the outside from the exhaust port. This caused so-called blow-by, which not only hindered output improvement but also caused fuel wastage.

[Purpose and structure of the invention]

The purpose of this invention is to improve the above-mentioned problems, improve the output of the engine, or burn fuel effectively. Therefore, a combustion chamber is formed, and the inner wall of the cylinder has scavenging ports adjacent to both sides of the exhaust port, which is a so-called sinule-type port arrangement, and the top surface of the piston has a peripheral edge facing the scavenging ports. The feature is that a recess is formed along the exhaust port, and a step portion that rises relatively sharply upward is formed on the exhaust port side of the recess.

〔Example〕

Hereinafter, the present invention will be explained with reference to the illustrated embodiment. In the figure, 1 indicates a two-stroke engine. The engine 1 has a combustion chamber 1d surrounded by a cylinder 1a, a piston 1b sliding inside the cylinder 1a, and a cylinder head 1c covering the top of the cylinder 1a. 1e is an ignition plug with an electrode facing into the combustion chamber 1d, and 1f is a connecting rod, which connects the piston 1b to a crankshaft (not shown); there is no particular difference from the conventional engine.

An intake port 2, a scavenging port 3, and an exhaust port 4 are opened on the inner wall of the cylinder 1a. The scavenging ports 3 consist of a pair arranged symmetrically with the piston 1b in between, and are composed of two each. In other words, the scavenging port 3 is arranged adjacent to both sides of the exhaust port 4, forming a so-called sinule shape. A reed-type check valve 2a that only allows inward airflow is installed in the intake port 2, and its downstream end is connected to the crank chamber 5 and auxiliary scavenging air through a through hole 1h formed in the piston 1b. It is connected to the combustion chamber 1d via the port 2b.

Here, as shown in FIGS. 2 and 4, a recess 6 is formed on the top surface of the piston 1b along the periphery facing the scavenging port 3. The recess 6 has a step 6a that rises relatively sharply upward at the end on the exhaust port 4 side, and the other side has a gentle slope. As shown in FIG. 2, a step 6b, which is a second step similar to that on the exhaust port 4 side, may also be provided at the end on the intake port 2 side.

Next, to explain the operation of this embodiment, first,
When the piston 1b rises, each port is closed on its top surface, the volume of the combustion chamber 1d is rapidly reduced, and the compression stroke progresses. On the other hand, the through hole 1h formed in the piston 1b and the intake port 2 match, and the low pressure in the crank chamber 5 acts on the check valve 2a, which is opened and the air-fuel mixture flows from the intake port 2 into the crank chamber 5. Inhaled.

Just before the piston 1b reaches top dead center, the combustion chamber 1
On the d side, ignition is performed by the spark plug, an explosion and a subsequent expansion stroke begin, and the piston 1b shifts to a downward stroke.

In the downward stroke, the exhaust port 4 is first opened to start the exhaust stroke, and the burnt gas is ejected into the exhaust port 4 due to internal pressure. Then piston 1b
When the engine moves downward, each scavenging port 3 and, slightly later, the auxiliary scavenging port 2b open to start the scavenging stroke, but during this time, the air-fuel mixture sucked into the crank chamber 5 in the previous suction stroke by the piston 1b is removed. is compressed, and the pressure inside the crank chamber 5 increases.

When the scavenging stroke starts, the air-fuel mixture that has been primarily compressed in the crank chamber 5 flows obliquely upward from each scavenging port 3 toward the side wall surface of the intake port 2 in the combustion chamber 1d, and auxiliary scavenging air flows into the part where they join. port 2
Auxiliary scavenging air is blown out from b. That is, when the intake port 2 is closed by the piston 1b, the pressure on the downstream side of the check valve 2a increases due to fresh air flowing in due to inertia, and when the auxiliary scavenging port 2b is subsequently opened, this pressure increases. The pressurized air-fuel mixture is supplied from the auxiliary scavenging port 2b into the combustion chamber 1d to promote scavenging.

Each scavenging air flow rises along the side wall surface of the intake port 2, reverses itself at the cylinder head 1c, and descends to remove the burnt gas remaining in the combustion chamber 1d from the exhaust port 2.
The piston 1b reaches the top surface of the piston 1b just before the piston 1b closes the exhaust port 4.
In this way, one stroke completes, and the above operation is no different from that of conventionally known two-stroke engines.

Next, in this invention, the exhaust port 4 and the scavenging port 3 are opened adjacent to each other, and the scavenging port 3 is arranged at symmetrical positions with the piston 1b sandwiched therebetween. Further, a recess 6 is formed on the top surface of the piston 1b along the peripheral edge facing the scavenging port 3,
At the end of the recess 6 on the exhaust port 4 side, a stepped portion 6a rising relatively sharply upward is formed.

Therefore, in the downward stroke of the piston 1b, when the exhaust port 4 is opened and then the scavenging port 3 is opened, most of the scavenging air injected from there into the combustion chamber 1d flows toward the intake port 2 side of the cylinder inner wall. . At this time, although a portion tends to flow into the adjacent exhaust port 4 in a short-circuit manner, the flow is diverted upward by the step portion 6a, thereby preventing blow-through.

Note that if a second step 6b rising upward is formed on the opposite side of the recess 6, there will be a tendency to divert the scavenging air supplied from the left and right scavenging ports 3 upward, and the scavenging air from the left and right scavenging ports Collision of the scavenging air flowing in from No. 3 is reduced, the speed of swirling in the combustion chamber is less reduced, and stable combustion can be obtained in the subsequent explosion stroke.

〔Effect of the invention〕

As explained above, this invention has a recess formed on the top surface of the piston, located in front of the scavenging port and along the periphery, and a stepped portion rising upwardly at the end of the recess on the exhaust port side. Therefore, even if the scavenging port 3 is brought closer to the exhaust port 4, there is less fresh air blowing through, and the opening area of the scavenging port 3 can be increased. Therefore, as shown in Fig. 8, in the two-stroke engine, improvements can be seen as shown by the broken line compared to the output characteristics of the conventional engine shown by the solid line, and in particular, it is possible to increase relatively low-speed torque. effective.

[Brief explanation of drawings]

The drawings show one embodiment of the invention.
2 is a longitudinal sectional view of the engine, FIG. 2 is a sectional view thereof, FIG. 3 is a side view showing the piston taken out, and FIG. 4 is a sectional view thereof. FIG. 5 is a sectional view equivalent to FIG. 2 showing another embodiment, FIG. 6 is a side view equivalent to FIG. 3 showing the piston,
FIG. 7 is a sectional view thereof. FIG. 8 is a characteristic diagram of the engine according to the present invention. 1d...Combustion chamber, 2...Intake port, 3...Scavenging port, 4...Exhaust port, 6...Recess, 6
a, 6b... step section.

Claims (1)

[Claims] 1. A combustion chamber is constituted by a cylinder, a cylinder head covering the top of the cylinder, and a piston sliding inside the cylinder, and scavenging ports are provided on the inner wall of the cylinder adjacent to both sides of an exhaust port. The piston has a sinule-shaped port arrangement, and a recess is formed on the top surface of the piston along the periphery facing the scavenging port, and a step that rises relatively sharply upward is formed on the exhaust port side of the recess. The combustion chamber of a two-stroke engine. 2. The combustion chamber for a two-stroke engine according to claim 1, wherein the recess also forms a second step rising relatively sharply upward on the opposite side of the step. 3. A combustion chamber for a two-stroke engine according to claim 1, wherein the recess forms a second step portion that gently rises upward on the opposite side of the step portion.