JPS61294121A - Combustion chamber of 2-stroke engine - Google Patents

Abstract

PURPOSE:To enable increase of the open area of a scavenging port and to improve improvement of the output of an engine, by a method wherein a recessed part is formed in the top surface of a piston along a peripheral edge positioned facing the scavenging port, and a suddenly-rising stepped part is formed on the exhaust port side of the recessed part. CONSTITUTION:A 2-stroke engine 1 has a combustion chamber 1d surrounded with a cylinder 1a, a piston 1b, sliding on the interior of the cylinder, and a cylinder head 1c covering the top part of the cylinder 1a. A suction port 2, scavenging ports 3, and an exhaust port 4 are open to the inner wall of the cylinder 1a, and the scavenging ports 3 are disposed adjacent to both sides of the exhaust port 4. With this constitution, a recessed part 6 is formed in the top surface of the piston 1b along the peripheral edge positioned facing the scavenging ports 3. A stepped part 6a is formed in the end part on the exhaust port 4 side of the recessed part 6. This reduces blow-by of fresh air even when the scavenging ports 3 approach the exhaust port 4, and enables increase of the opening area of the scavenging port 3.

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 a simple structure, are lightweight, and can provide high output, so they have been widely used in motorcycles and other small vehicles, and there is a growing demand for increased output per unit displacement.

Generally, in order to improve the specific output of an engine, it is necessary to effectively supply a mixture into the combustion chamber.
In stroke engines, this has been made possible by increasing the opening area of the scavenging ports and exhaust ports into the combustion chamber.

However, if the opening area is set large, the scavenging port and exhaust port will approach each other, and the inner wall of the cylinder that separates both ports will become narrower, causing 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-through, which was not only a hindrance to improving output, but also a cause of wasted fuel.

[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 more effectively. 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 cinnular port arrangement. The feature is that a recess is formed, and a step portion that rises relatively sharply upward is formed on the exhaust port side of the recess.

〔Example〕

The present invention will be explained below 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 1b1 that slides inside the cylinder 1a, and a cylinder head 1C that covers the top of the cylinder 1a. 1e is a spark plug with an electrode facing into the combustion chamber 1d, 1f is a connecting rod, and piston 1
b is connected to a crankshaft (not shown), and there is no particular difference from conventional engines.

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,
It is composed of two pieces each.

In other words, the scavenging port 3 is arranged adjacent to both sides of the exhaust port 4, forming a so-called syringe shape. The intake port 2 is equipped with a reed-type check valve 2a that allows only inward airflow, and its downstream end is connected to the crank chamber 5 and the auxiliary cylinder through a through hole 1h formed in the piston 1b. It is connected to the combustion chamber 1d via the scavenging port 2b.

As shown in FIGS. 2 and 4, a recess 6 is formed on the top surface of the piston 1b at 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. 3- As in the embodiment, a stepped portion 6b, which is a second stepped portion, similar to that on the exhaust port 4 side may also be provided at the end portion on the intake port 2 side.

Next, to explain the operation of this embodiment, when the piston 1b rises, each port is closed on its top surface.
The volume of the combustion chamber 1d decreases rapidly 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.

Immediately before the piston 1b reaches the top dead center, ignition is performed by the ignition plug on the side of the combustion chamber 1d, 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. Subsequently, when the piston 1b descends, each scavenging port 3 and later the auxiliary scavenging port 2b open to start the scavenging stroke. The intake air-fuel mixture 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. B) Auxiliary scavenging air is blown out from 2b.

That is, when the intake port 2 is closed by the piston 1b, the pressure on the downstream side of the check valve 2a rises due to fresh air flowing in due to inertia, and when the auxiliary scavenging bow 2b is subsequently opened, this pressure rises. The air-fuel mixture is supplied from the auxiliary scavenging air 2b into the combustion chamber 1d to promote scavenging.

Each scavenging air flow stays on the side wall surface of the intake port 2 and rises, reverses itself at the cylinder head 1C, and descends, pushing out the burnt gas remaining in the combustion chamber 1d to the exhaust port 4, and progresses toward the piston 1b. Just before closing the exhaust port 4, the piston 1b
reach the top of 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 a target position sandwiching the piston 1b. In addition, a recess 6 is formed on the top surface of the piston 1b at the peripheral edge facing the scavenging port 3, and at the end of the recess 6 on the exhaust port 4 side, there is a step that rises relatively sharply upward. The portion 6a 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 to the intake port 2 (llll) on the inner wall of the cylinder. .

At this time, a portion of the gas tends to flow into the adjacent exhaust port 4 in a short-circuit manner, but the flow is diverted upward by the step portion 6a, thereby preventing blow-through.

In addition, on the opposite side of the recess 6, there is also a second
By forming the stepped portion 6b, the scavenging air supplied from the left and right scavenging ports 3 tends to be diverted upward, the collision of the scavenging air flowing from the left and right scavenging ports 3 is reduced, and the speed at which the scavenging air swirls in the combustion chamber is increased. There is little decrease in combustion, 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, in the two-stroke engine, as shown in FIG. 8, improvements can be seen as shown by the broken line compared to the output characteristics of the conventional engine shown by the solid line,
In particular, it has the effect of making it possible to increase relatively low-speed torque.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a longitudinal cross-sectional view of the engine, FIG. 2 is a cross-sectional view taken along the line ■-■, FIG. FIG. 4 is a sectional view taken along the TV-IV line. FIG. 5 is a sectional view corresponding to FIG. 2 showing another embodiment, and FIG. 6 is a third sectional view showing the piston.
FIG. 7 is a side view corresponding to the figure, and FIG. 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, 6a, 6b...Step part.

Claims (3)

[Claims] (1) A combustion chamber is composed of a cylinder, a cylinder head that covers the top of the cylinder, and a piston that slides inside the cylinder.Scavenging ports are provided on the inner wall of the cylinder adjacent to both sides of the exhaust port, and the port is in the form of a cinnular shape. A recess is formed on the top surface of the piston along the periphery facing the scavenging port, and a stepped portion rising relatively sharply upward is formed on the exhaust port side of the recess. Combustion chamber of a stroke engine. (2) A combustion chamber for a two-stroke engine according to claim 1, wherein the recess also forms a second step that rises relatively sharply upwards 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.