JPH0118822Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in pistons for two-stroke engines.

FIG. 1 shows a sectional view of the main parts of a two-stroke engine 1. As shown in FIG.

As is well known, in the two-stroke engine 1, high-temperature exhaust gas (arrow A) after combustion is transferred to the exhaust port 3 by fresh air (arrow B) supplied from the scavenging port 2.
The system is designed to extrude and discharge the liquid from the inside. Also,
Since the two-stroke engine 1 performs one combustion in two strokes in which the piston 4 reciprocates within the cylinder sleeve 5, the heat load of the exhaust gas on the piston 4 is greater than in a four-stroke engine (not shown). . In particular, this tendency is greater in the portion of the piston 4 located near the exhaust port 3 than in the portion of the piston 4 located near the scavenging port 2.

On the other hand, in the conventional piston 4, as shown in the enlarged cross-sectional view of FIG. Increase this part 4
Along with the decrease in hardness of a, there was a drawback that the piston 4 in this part was likely to seize. In Fig. 1, numeral 6 is the cylinder head, 7 is the cylinder block, 8 is the crankcase, 9 is the crankshaft, and 10 is the cylinder head.
11 is a connecting rod, 12 is an inlet port, and 13 is a reed valve.

In order to solve the above-mentioned problems, conventionally, as described in Japanese Patent Application Laid-Open No. 57-146037, the wall thickness of the piston head of a two-stroke engine is made thinner on the exhaust side than on other parts. As a result, the heat from the piston head on the exhaust side, which tends to become high, is transferred to the piston head on the scavenging side, which is easily cooled by fresh air drawn into the combustion chamber through the crankcase, resulting in a high temperature. There is one in which the piston head on the exhaust side, which is easy to cool, is indirectly cooled.

However, with the conventional piston described above,
The heat accumulated in the piston head on the exhaust side is mainly transferred to the piston head on the scavenging side, which has a small heat radiation area and is easily heated by combustion in the combustion chamber, and the transferred heat is sucked in through the crankcase. Since the configuration uses hot fresh air to cool the system, the cooling efficiency is limited and is not always sufficient.

In view of the above-mentioned circumstances, this idea more efficiently dissipates the heat accumulated in the piston head on the exhaust side, which tends to reach high temperatures, thereby reducing the heat load on the piston located on the exhaust port side as much as possible. An object of the present invention is to provide a piston for a two-stroke engine.

In order to achieve the above-mentioned purpose, this invention:
The wall thickness of the piston located near the exhaust port side is made thicker than the wall thickness of other pistons including the scavenging port side, ensuring a large heat dissipation area mainly for the heat accumulated in the piston head on the exhaust side. The heat is transferred to the piston skirt, which is difficult to heat due to combustion in the combustion chamber, and the heat transferred to the piston skirt is sucked into the crankcase, which has a lower temperature than the fresh air sucked into the combustion chamber. The system uses fresh air to cool the area directly.

Hereinafter, one embodiment of a two-stroke engine piston according to the present invention will be described in detail.

FIG. 3 is an enlarged sectional view showing a piston 30 for a two-stroke engine according to the present invention. It goes without saying that this piston 30 is arranged at the same position as the conventional two-stroke engine piston 4 shown in FIG.

The piston 30 has a cross-sectional shape that is asymmetrical with respect to the left-right direction in the drawing. Moreover, the wall thickness T of the portion 30a of the piston 30 that forms the piston ring groove from the top, that is, the portion 30a corresponding to the exhaust port 3 of the two-stroke engine 1 shown in FIG. It is formed thicker than the wall thickness. Therefore,
Since the portion 30a of the piston 30 corresponding to the exhaust port 3 has a thicker wall thickness, the skirt portion 3 of the piston 30 is mainly thicker than other portions of the piston 30.
The heat transfer efficiency to 0b is improved, and therefore a wide heat radiation area by the skirt portion 30b is ensured. Further, the exhaust port 3 of the piston 30
The heat transferred to the skirt portion 30b from the portion 30a corresponding to Since the skirt portion 30b is in direct contact with air over a wide area,
In other words, the cooling efficiency of the portion 30a of the piston 30 corresponding to the exhaust port 3 is improved.

In addition, according to the above-mentioned piston 30, since the wall thickness of a part of the piston 30 is made asymmetrically thick, the balance of the entire piston 30 will be lost if left as is. This can be compensated for by making it thicker or thinner considering the weight and balance.

As explained above, in this design, the wall thickness of the piston located near the exhaust port side is made thicker than the wall thickness of other pistons including the scavenging port side, so that the air remains in the piston head on the exhaust side. Heat is mainly transferred to the piston skirt, which has a large heat dissipation area, and the heat transferred to the piston skirt is sucked into the crankcase, which has a lower temperature than the fresh air sucked into the combustion chamber. By cooling with fresh air, the heat load on the piston located near the exhaust port is reduced as much as possible, which reduces the hardness of the piston and the resulting piston seizure. Therefore, it is possible to provide a two-stroke engine with stable power characteristics.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of essential parts of a two-stroke engine, FIG. 2 is an enlarged cross-sectional view of a conventional two-stroke engine piston, and FIG. be. 1...Two-stroke engine, 2...Scavenging port, 3...Exhaust port, 30...Piston for two-stroke engine.

Claims (1)

[Scope of utility model registration request] The circumferential wall of the head of the two-cycle engine piston located on the exhaust port side of the cylinder is formed to be thicker than the circumferential wall of the piston head of other parts including the scavenging port side, and the piston on the exhaust port side A piston for a two-stroke engine, characterized in that heat accumulated in the head is mainly transmitted to the skirt side of the piston.