JPS6227247B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stroke engine in which the shape of the top surface of the piston is improved.

Conventionally, by providing a roughly spherical recess that opens upward on the top surface of the piston, the shape of the combustion chamber when the spark plug fires near top dead center is set to be roughly hemispherical with the spark plug in the center. The aim was to shorten the flame propagation distance, or combustion time, and improve combustion efficiency. By the way, in a two-stroke engine, it is necessary to send the burnt gas in the combustion chamber to the outside through the exhaust port by using a scavenging air flow, but since the scavenging air flow does not flow into the recess in a sufficient amount, some of the burnt gas remains in the recess. remains unavoidable, which has the disadvantage of reducing scavenging efficiency.

In an attempt to eliminate this drawback, JP-A-57-
The piston shape of Publication No. 44754 has been proposed.
This is shown in FIGS. 1 and 2. In FIG. 1, an exhaust port 11, a scavenging port 12, and a sub-scavenging port 13
A piston 15 is fitted into a cylinder 14 having a diameter. A recess 16 is provided on the upper surface 15a of the piston 15.
A groove 17 is formed in communication with the recess 16. During the scavenging stroke, the scavenging air 18 shown in FIG. The combustion gas in the recess 16 is expelled by this swirling flow.

However, the swirling flow is caused by the recess 16 in FIG.
is formed in a plane (horizontal plane) perpendicular to the recess direction 20, and the velocity component in the recess direction 20 is extremely small.
6 cannot be smoothly pushed upward,
Improvement in scavenging efficiency cannot be expected. Furthermore, since a swirling flow is generated when the piston 15 descends to the position shown in FIG. 1 and the sub-scavenging port 13 and the groove 17 match, the piston 15 then rises and ignites near top dead center. Since the swirling flow weakens when the swirling flow occurs, an improvement in combustion efficiency due to the mixing effect of the swirling flow cannot be expected.

This invention was made to eliminate the above-mentioned conventional drawbacks, and it improves scavenging efficiency by smoothly expelling the burnt gas in the recess on the upper surface of the piston, and also generates a strong swirling flow of the air-fuel mixture at the time of ignition. The purpose is to improve combustion efficiency in this way.

Embodiments of the present invention will be described below with reference to the drawings.

3 to 5 show a first embodiment of the invention. In FIG. 3, the upper surface 1 of the piston 15
5a has a substantially spherical recess 16 that opens upward.
The shape of the combustion chamber 22 is set to be approximately hemispherical with the spark plug 23 in the center, thereby shortening the flame propagation distance, that is, the combustion time, and improving combustion efficiency. There is. Further, a guide groove 25 is formed on the upper surface 15a of the piston 15, and extends obliquely downward from the outer circumference toward the bottom of the recess 16. , are located approximately 180° apart from the exhaust port 11 in the circumferential direction.

The upper surface 15a of the piston 15 and the cylinder head 2 at a position facing the guide groove 25 in FIG. 3, that is, at a circumferential position corresponding to the exhaust port 11.
The lower surface 26a of the piston 15 is set to have a shape that widens upward and downward toward the center side, so that when the piston 15 approaches the top dead center, the piston 15 The recess 16 is compressed from the outer circumference of the piston 15 by
It forms an airflow generation space 27 that generates an upward mixed airflow. In addition, in FIGS. 3 and 4, 12 is a scavenging port, and 28 is an intake port.

In the above configuration, as shown in FIG. 3, when the piston 15 rises and approaches the top dead center, the recess 16 is moved from the outer circumference of the piston 15 into the guide groove 25 under the compression force of the piston 15. A mixed air flow A is generated toward the bottom, and a mixed air flow B is generated within the air flow generation space 27 from the outer periphery of the piston 15 toward the upper part of the recess 16.

The directions of both air mixture flows A and B are approximately 180 degrees from each other.
5, the two air mixture flows A and B form a swirling flow 29 in a plane (vertical plane) along the recess direction 20 of the recess 16, as shown in FIG. Therefore, the indentation direction 20 that this swirling flow 29 has
Since the velocity component v of is large, the burned gas in the recess 16 is smoothly expelled above the recess 16. The expelled burned gas goes through the next combustion stroke and is then discharged to the outside from the exhaust port 11 in FIG. will improve.

Furthermore, since a swirling flow 29 is formed when the piston 15 approaches the top dead center, a strong swirling flow 29 exists at the time of ignition, and the stirring of the air-fuel mixture progresses.
Combustion efficiency is improved.

Additionally, in general, a large amount of end gas, which is incompletely combusted gas, remains at a location 180 degrees away from the exhaust port 11 in the circumferential direction, and knocking is likely to occur due to self-ignition of this end gas. , a guide groove 25 is provided at the above location, and the cylinder head 26 and piston 1 at the above location are accommodated accordingly.
Since the clearance with 5 is increased, the pressure of the end gas is lowered, and the knocking can be effectively prevented.

Furthermore, in the above embodiment, as shown in FIG. 4, the groove width of the guide groove 25 becomes narrower as it approaches the center, so the passage area of the guide groove 25 becomes narrower as it approaches the center. The rate of increase can be reduced, and as a result, the flow velocity of the air mixture A shown in FIG. 3 passing through the guide groove 25 can be increased, and a stronger swirling flow 29 can be obtained.

6 and 7 show a second embodiment of the invention. In FIG. 6, a protrusion 31 is provided in the guide groove 25.
is provided. As shown in FIG. 7, this protrusion 31 is located at the center of the guide groove 25 in the circumferential direction, receives the air mixture B, and deflects it downward in FIG. 6. Therefore, the swirling flow 29
is strengthened, and scavenging efficiency and combustion efficiency are further improved.

FIGS. 8 and 9 show a third embodiment of the invention. In FIG. 8, a protrusion 31 is provided on the cylinder head 26 side, and this protrusion 31 is
As shown in FIG. 9, it is located over almost the entire width of the guide groove 25, and also receives the mixed air flow B and deflects it downward in FIG. 8, thereby obtaining a strong swirling flow 29.

As explained above, according to the present invention, although the structure is such that the recess 16 is provided on the upper surface of the piston 15 to improve combustion efficiency, the swirling flow generated by the guide groove 25 and the airflow generation space 27 is This makes it possible to effectively eliminate the burned gas in the recess, thereby increasing the scavenging efficiency, and further improving the combustion efficiency due to the strong swirling flow.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing a conventional example, and Figure 2 is a vertical cross-sectional view of a conventional example.
3 is a longitudinal sectional view showing the first embodiment of the present invention, FIG. 4 is a sectional view taken along line 3 in FIG. 3, and FIG. 6 is a longitudinal sectional view showing the second embodiment, FIG. 7 is a sectional view taken along line - in FIG. 6, and FIG. 8 is a longitudinal sectional view showing the third embodiment. FIG. 9 is a longitudinal cross-sectional view showing the embodiment, and is a cross-sectional view taken along the line - - in FIG. 8. 11...Exhaust port, 12...Scavenging port, 14...Cylinder, 15...Piston, 15a...Top surface, 1
6... Recess, 25... Guide groove, 26... Cylinder head, 26a... Lower surface, 27... Air flow generation space, 31... Protrusion.

Claims (1)

[Claims] 1. A generally spherical recess that opens upward on the top surface of the piston, and a guide that extends obliquely downward from a position on the outer periphery of the piston that is approximately 180° apart from the exhaust port in the circumferential direction toward the bottom of the recess. A groove is provided between the upper surface of the piston and the lower surface of the cylinder head at a position in the circumferential direction corresponding to the exhaust port, and when the piston approaches top dead center, it receives the compressive force from the piston, and the outer circumference of the piston A two-stroke engine comprising an airflow generation space that generates a mixed airflow upwardly from the recess.