JP2894597B2 - 2 cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stroke engine in which the cooling effect on the top of a piston is particularly enhanced and the fluctuation of the piston is eliminated.

[0002]

2. Description of the Related Art Conventionally, in a two-stroke engine of this type, at the inlet of a scavenging passage, a crank chamber side end of a cylinder body is cut off and a ventilation hole is formed in a piston skirt for cooling the piston. When fresh air flows from the crank chamber to the combustion chamber, a part of the fresh air is caused to flow from the vent hole formed in the piston skirt portion through the inside of the piston to the scavenging passage ( H. TRZEBIATOWSKY, "MOTOR-RADER MOTORROLL
ER ・ MOPEDS UND IHRE INSTA-NDHALTUNG ”P. 177).

[0003]

However, in the above-described conventional two-stroke engine, since the end of the crank chamber of the cylinder body is notched as described above, the cooling of the top of the piston exposed to high-temperature combustion gas is performed. If the notch of the cylinder body is positioned upward to effectively perform the operation, the length of the cylinder wall of the cylinder body cannot be sufficiently taken toward the crank chamber side, causing the piston to fluctuate. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a two-stroke engine capable of improving the cooling effect of the piston top and eliminating the problem of the piston flicker. is there.

[0005]

According to the present invention, there is provided a two-stroke engine having a scavenging passage having one end opened in a crank chamber and the other end opened in a cylinder via a scavenging port. The inner surface of the top has a curved shape that curves in the circumferential direction of the piston pin, and the ventilation hole that communicates with the scavenging port located at a position substantially opposite to the exhaust port in the cylinder is located above the piston pin of the piston skirt. And the gap between the upper edge of the vent hole and the outer periphery of the top of the piston is set to be larger than the height of the scavenging port in the cylinder axial direction.

Therefore, according to the present invention, the vent communicates with the scavenging port after the piston closes the scavenging port when the piston is raised.
From inside the scavenging passage to the inside of the piston that is the pressure source
Scavenging port, flow into the piston through the vent
The flow is created and serves to cool the top of the piston, which effectively cools the top of the piston. At this time, since the flow of scavenging gas from the scavenging port arranged at a position substantially opposite to the exhaust port to the combustion chamber has a larger component in the cylinder axis direction than the flow of scavenging air from the other scavenging ports to the combustion chamber, The flow of the scavenging air guided into the piston from the ventilation hole also has a large component in the axial direction of the cylinder. Therefore, the scavenging air effectively cools the inner surface of the top of the piston.

Further, since the ventilation hole is formed above the piston pin and the inner surface of the top of the piston is formed in a curved shape curved in the circumferential direction of the piston pin,
The scavenging gas flowing into the piston from the ventilation hole flows smoothly along the inner surface of the top of the piston, and this flow is not interrupted by the piston pin and the small end of the connecting rod. Cools effectively.

Further, according to the present invention, it is not necessary to form a notch in the cylinder body, so that the cylinder wall can secure a sufficient length toward the crank chamber side, thereby eliminating the fluctuation of the piston. be able to.

[0009]

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

FIG. 1 is a longitudinal sectional side view of a two-stroke engine according to the present invention, and FIG. 2 is a sectional view of a single piston (A-A in FIG. 1).
FIG.

In FIG. 1, reference numeral 1 denotes a cylinder body, on which an upper cylinder head 2 and a lower crankcase 3 are connected. A cylinder 4 is formed at the center of the cylinder body 1.
A piston 5 is fitted in the cylinder 4 so as to be slidable up and down. The upper end of a connecting rod 6 is connected to the piston 5 via a piston pin 7, and the lower end of the connecting rod 6 is connected to a crankshaft 8 via a crankpin 9. The inner surface of the top of the piston 5 is formed in a curved shape that is curved upward in the circumferential direction of the piston pin 7. The crankshaft 8 is disposed in a crank chamber 10 in the crankcase 3 so as to be rotatable in a direction perpendicular to the plane of FIG.

A combustion chamber is formed in a space defined by the piston 5 and the cylinder head 2 in the cylinder 4, and an ignition plug 11 is screwed on the top of the cylinder head 2. Further, a plurality of scavenging ports 12a,
12b, 12c and the exhaust port 13 are open.
The scavenging port 12a is disposed at a position substantially opposed to the exhaust port 13 in the cylinder 4.

A plurality of scavenging passages 14 and an exhaust passage 15 are formed in the cylinder body 1. Each end of the scavenging passage 14 is connected to the scavenging ports 12a, 12b, 1b.
It opens into the cylinder 4 via 2c, and the other end opens into the crank chamber 10. One end of the exhaust passage 15 is opened into the cylinder 4 via the exhaust port 13, and an exhaust pipe (not shown) is connected to the other end.

A vent hole 17 is formed in the skirt portion of the piston 5 above the piston pin 7 to selectively communicate with the scavenging port 12a. Here, the vent hole 17 is formed at a position where the distance between the upper edge thereof and the outer peripheral portion of the top of the piston 5 is larger than the height of the scavenging port 12a in the cylinder axial direction.

On the other hand, an intake passage 18 is formed in the crankcase 3, one end of the intake passage 18 opens into the crank chamber 10, and the carburetor 1
9 are connected. A reed valve type check valve 20 is provided in the intake passage 18 for allowing only the mixture (fresh air) to flow in the direction of the crank chamber 10. An air cleaner (not shown) is connected to the upstream side of the carburetor 19.

Next, the operation of the present two-stroke engine will be described.

In the scavenging process, the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber in the previous cycle is discharged from the exhaust port 13 to the atmosphere through the exhaust passage 15 and the exhaust pipe, and the exhaust gas remaining in the cylinder 4 Is effectively exhausted by scavenging air flowing from the scavenging ports 12a to 12c.

In this embodiment, as described above, the distance between the upper edge of the ventilation hole 17 and the outer periphery of the top of the piston 5 is larger than the height of the scavenging port 12a in the cylinder axial direction.
As shown in FIG. 1, when the piston 5 rises during the scavenging stroke,
Top the scavenging port 12a, 12b, although the vent holes 17 of the piston 5 after closing 12c communicates with the scavenging port 12a, this time, a negative pressure source when the piston 5 rise in
The scavenging air is transferred from the scavenging passage 14 to the inside of the piston 5.
12a, flows into the piston 5 through the vent hole 17.
As a result, a top flow of the piston 5 is cooled, and the top surface of the piston 5 is effectively cooled.

In order to effectively cool the top of the piston 5, it is desirable to form the ventilation hole 17 near the top of the piston 5, but in practice, a piston ring is fitted around the upper periphery of the piston 5. Therefore, it is practically impossible to form the ventilation hole 17 near the top of the piston 5.

On the other hand, generally, the scavenging ports 12b, 1
The scavenging air flowing into the combustion chamber from 2c is directed away from the exhaust passage 15 in order to prevent the scavenging air from flowing into the exhaust passage 15, while the scavenging air flowing into the combustion chamber from the scavenging port 12a is The peripheral residual gas is directed in the cylinder axis direction in order to push the residual gas toward the exhaust passage 15. For this reason, the flow of scavenging gas from the scavenging port 12a, which opens at a position substantially opposite to the exhaust passage 15, to the combustion chamber has a larger component in the cylinder axial direction than the flow from the other scavenging ports 12b, 12c to the combustion chamber. As a result, although the vent hole 17 is formed at a position lower than the vicinity of the top of the piston 5, the flow of the scavenging gas guided through the vent hole 17 into the piston 5 also has a large component in the cylinder axial direction, Therefore, the inner surface of the top of the piston 5 is effectively cooled by this scavenging.

Further, the ventilation hole 17 is formed above the piston pin 7 and the inner surface of the top of the piston 5 is formed into a curved surface curved in the circumferential direction of the piston pin 7. The scavenging gas flowing into the interior of the piston 5 from 17 flows smoothly along the inner surface of the top of the piston 5, and this flow is not interrupted by the piston pin 7 and the small end of the connecting rod 6, so that the scavenging flow 5 is effectively cooled.

Further, according to the present invention, the cylinder body 1
Since there is no need to form a notch in the cylinder wall, a sufficient length of the cylinder wall can be secured toward the crank chamber 10, thereby eliminating the fluctuation of the piston 5.

When the scavenging ports 12a to 12c and the exhaust port 13 are closed by the piston 5, the air-fuel mixture supplied into the cylinder 4 is compressed by the piston 5.

On the other hand, a negative pressure is generated in the crank chamber 10 by the upward movement of the piston 5, and the air-fuel mixture formed by the carburetor 19 is pulled by the negative pressure and passes through the check valve 20 to pass through the check valve 20. Introduced within.

When the piston 5 reaches the vicinity of the top dead center, the air-fuel mixture compressed in the cylinder 4 by the spark plug 11 is ignited and burned. And the piston 5 moves downward. When the piston 5 moves downward, the scavenging ports 12a to 12c and the exhaust port 13 open in the cylinder 4 and exhaust gas is exhausted from the exhaust port 13 to the atmosphere through the exhaust passage 15 and the exhaust pipe. Exhaust gas remaining in the scavenging ports 12a to 12c is effectively exhausted by scavenging air flowing in from the scavenging ports 12a to 12c, and thereafter, the same operation as described above is repeated. The air-fuel mixture introduced into the crank chamber 10 is compressed by the downward movement of the piston 5.

[0026]

As is apparent from the above description, according to the present invention, a scavenging passage having one end opened in the crank chamber and the other end opened in the cylinder via the scavenging port is provided.
In a cycle engine, the inner surface of the top of the piston is formed into a curved shape curved in the circumferential direction of the piston pin, and a ventilation hole communicating with a scavenging port arranged substantially in the cylinder with respect to the exhaust port is provided with a piston in the piston skirt portion. Since the hole is formed above the pin and the distance between the upper edge of the ventilation hole and the outer periphery of the top of the piston is set to be larger than the height of the scavenging port in the cylinder axial direction, the cooling effect of the top of the piston can be enhanced. At the same time, the effect of eliminating the problem of the piston flicker can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view of a two-stroke engine according to the present invention.

FIG. 2 is a cross-sectional view (a cross-sectional view along the line AA in FIG. 1) of the piston alone.

[Explanation of symbols]

 Reference Signs List 4 cylinder 5 piston 7 piston pin 10 crank chamber 12a to 12c scavenging port 13 exhaust port 14 scavenging passage 17 ventilation hole

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-195316 (JP, A) JP-A-2-169819 (JP, A) JP-A-55-146230 (JP, A) 102724 (JP, U)

Claims (1)

(57) [Claims] 1. A two-stroke engine having a scavenging passage having one end opened in a crank chamber and the other end opened in a cylinder via a scavenging port, wherein an inner surface of a piston top is formed into a curved surface curved in a circumferential direction of a piston pin. A vent hole communicating with a scavenging port disposed substantially in the cylinder with respect to the exhaust port is formed above the piston pin of the piston skirt portion, and the upper edge of the vent hole and the top of the piston are formed. A two-stroke engine characterized in that an interval with an outer peripheral portion is set larger than a height of a scavenging port in a cylinder axial direction.