JPH02169819A - Two cycle engine - Google Patents

Abstract

PURPOSE:To improve a cooling efficiency on a piston inner surface and a connecting rod small end part by boring, in a piston skirt part, an air feed hole opening to a communicating hole communicating with a scavenging passage and a cylinder inner circumference surface at the time of an initial scavenging process. CONSTITUTION:A communicating hole 16 which opens to a cylinder 4 inner circumference surface, located below scavenging ports 12, is bored on the intermediate part of a scavenging passage 14. An air feed hole 17 which opens to the communicating hole 16 at least when scavenging ports 12 are opened by a piston 5, is bored on the skirt part of a piston 5. Thereby, since the air feed hole 17 is in its opened condition with respect to the communicating hole 16 at least at the time of an initial scavenging process, new air having a large flowing speed is supplied into the cylinder 4 through the air feed hole 17, the communicating hole 16 and the scavenging passage 14 after cooling the inner surface of the piston 5 and the small end part of a connecting rod 6. Since the inner surface of the piston 5 and the small end part of the connecting rod 6 are cooled by the new air having the large flowing speed at the time of an initial scavenging process, the cooling efficiency is improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a two-stroke engine.

(Prior Art) In this type of two-stroke engine, conventionally, for the purpose of piston cooling, the crank chamber side end of the cylinder body is cut out at the entrance of the scavenging passage, and a ventilation hole is bored in the piston skirt. It is known that when fresh air flows from the crank chamber to the combustion chamber, the - part of the MTR air is prevented from flowing into the scavenging passage through the vent hole bored in the piston skirt through the inside of the piston. H,TRZ
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However, in the above-mentioned conventional two-stroke engine, the end of the crank chamber of the cylinder body was notched as described above, so in order to effectively cool the top of the piston exposed to high-temperature combustion gas, the cylinder body was cut out. If the notch is positioned upward, the length of the cylinder wall of the cylinder body cannot be sufficiently extended toward the crank chamber, which causes a problem of causing fluctuation of the piston.

Therefore, the present applicant drilled a communication hole in the cylinder wall to communicate the scavenging passage with the inside of the cylinder, and also drilled a ventilation hole in the piston skirt that opens into the communication hole when the scavenging port is open. We first proposed that the above-mentioned problem could be solved by establishing a
No. 094).

(Problem to be Solved by the Invention) However, in the two-stroke engine according to the above proposal, the vent hole is not necessarily open to the communication hole at the moment the piston opens the scavenging port and the scavenging stroke begins. Therefore, there is a possibility that fresh air having a high flow rate at the beginning of the scavenging stroke cannot be effectively utilized for cooling the inner surface of the piston and the small end of the connecting rod.

The present invention has been made in view of the above problems, and an object thereof is to provide a two-stroke engine that can improve the cooling efficiency of the inner surface of the piston and the small end of the conrod.

(Means for Solving the Problems) In order to achieve the above object, the present invention has a scavenging port that opens on the inner peripheral surface of the cylinder and is opened and closed by a piston, one end of which is inside the crank chamber, and the other end of which is connected to the scavenging port. In a two-stroke engine that has scavenging passages that communicate with each other in the cylinders through the scavenging ports, a communication hole that opens to the inner circumferential surface of the cylinder below the scavenging port is bored in the middle part of the scavenging passage, and at least the piston The present invention is characterized in that when the scavenging port is opened, a vent hole opening into the communication hole is provided in the piston skirt portion.

(Function) At least at the beginning of the scavenging process, the ventilation holes are open to the communication holes, so fresh air with a high flow rate is
After cooling the inner surface of the piston and the small end of the connecting rod, the air is supplied into the cylinder through a ventilation hole, a communication hole, and a scavenging passage. In this way, the inner surface of the piston and the small end of the connecting rod are
Since the air is cooled at a high flow rate of 1 ft'A at the beginning of the scavenging stroke, the cooling efficiency is increased.

(Example) An example of the present invention will be described below based on the activated drawings.

FIG. 1 is a longitudinal sectional side view of a two-stroke engine according to the present invention, and FIGS. 2 and 3 are explanatory views of the operation of the two-stroke engine.

In the m1 diagram, 1 is the cylinder body.

A cylinder head 2 is connected to the upper part of this, and a crankcase 3 is connected to the lower part thereof. A cylinder 4 is formed in the center of the cylinder body 1, and a piston 5 is mounted inside the cylinder 4 so as to be slidable up and down. A small end of a connecting rod 6 is connected to the piston 5 via a piston pin 7, and a large end of the connecting rod 6 is connected to a web 8a of a crankshaft 8 via a crank pin 9. Incidentally, the crankshaft 8 is disposed within the crank chamber IO in the crankcase 3 so as to be freely rotatable in a direction perpendicular to the paper plane of FIG.

A combustion chamber S is formed in a space defined by the piston 5 and the cylinder head 2 in the cylinder 4, and a spark plug 11 is screwed onto the top of the combustion window S. Further, scavenging ports 12 and exhaust ports 13 are opened in the cylinder 4.

By the way, the cylinder body l has a scavenging passage 14...
・And exhaust passages 15 are formed, and each scavenging passage 14
The - end opens into the cylinder 4 via the scavenging port 12, and the other end opens into the crank chamber 10. Moreover, the - end of the exhaust passage 15 is connected to the exhaust bow)-1.
It opens into the cylinder 4 through the exhaust passage 1.
The other end of 5 is connected to an exhaust pipe (not shown).

A scavenging port 1 is provided in the middle of the scavenging passage 14.
A communication hole 16 is bored in the inner circumferential surface of the cylinder 4 below the piston 5, and a ventilation hole 17 is bored in the skirt portion of the piston 5. As shown in FIG. 3, the ventilation hole 17 is designed to remain open to the communication hole 16 at least at the moment when the piston 5 descends and the scavenging ports 12 open and the scavenging stroke begins. Its dimensions and location have been determined.

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 IO, and a carburetor 19 is connected to the other end of the intake passage 18. There is.

A reed check valve 20 is provided in the intake passage 18 to allow the air-fuel mixture (fresh air) to flow only in the direction of the crank chamber 10 . Note that an air sonar (not shown) is connected to the upstream side of the carburetor 19.

Next, I will explain the operation of the wood 2-cycle engine.

When the piston 5 is at the top dead center position as shown in FIG.
In this state, when the compressed air-fuel mixture in the combustion chamber S is ignited and burned by the spark plug 11, the piston 5 receives combustion pressure on its upper surface and begins to descend.

Then, when the exhaust port 13 opens, the high temperature and high pressure exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber S,
The gas is discharged to the atmosphere from the exhaust port 13 through the exhaust passage and exhaust pipe, but as shown in Figure 0'53, the scavenging ports 12... eventually begin to open.

Fresh air compressed in the crank chamber IO is scavenging passage 14
This fresh air is supplied into the combustion chamber S from the scavenging port 12 through..., and this fresh air effectively discharges the exhaust gas remaining in the combustion chamber S. At this time, a part of the fresh air in the crank chamber 10 flows through the piston 5 as shown by the arrow in FIG. 3, cools the inner surface of the piston 5 and the small end of the connecting rod 6, and then 17 and the communication hole 16 to the scavenging passage 1
4 and finally introduced into the combustion chamber S in the cylinder 4 through the scavenging ports 12 .

As described above, in this embodiment, since the vent hole 17 is open to the communication hole 16 at least at the beginning of the scavenging stroke when the scavenging port 12 starts to be heard, the inner surface of the piston 5 and the small The end is J1i1
The fresh air having a high flow rate at the beginning of the air stroke efficiently cools the air, increasing its cooling efficiency.

Then, when the piston 5 moves upward from the bottom dead center position shown in FIG.
The fresh air supplied into the engine is compressed by the upwardly moving piston 5, and then ignited and combusted by the spark plug 11, and thereafter the same operation as described above is repeated. Incidentally, the upward movement of the piston 5 generates negative pressure in the crank chamber 10, and the air-fuel mixture formed by the carburetor 19 due to this negative pressure is introduced into the crank chamber 10 through the check valve 20. , and is then primarily compressed by the descending piston 5.

(2) Effect of A Ming) As is clear from the following explanation, according to the present invention, there is a scavenging port that opens on the inner circumferential surface of the cylinder and is closed by the piston, one end of which is inside the crank chamber, and the other end of which is located above. In a two-stroke engine having scavenging passages that communicate with the cylinders through scavenging ports, a communication hole that opens to the inner circumferential surface of the cylinder below the scavenging port is bored in the middle of the scavenging passage, and at least a piston is connected to the cylinder. When the scavenging port is set to lJI I:l, since the piston skirt is provided with a vent hole that opens to the communication hole 1i1, the inner surface of the piston and the small end of the connecting rod can maintain the flow velocity at the beginning of the scavenging stroke when the scavenging port begins to open. It is effectively cooled by a portion of the large fresh air, and the effect of increasing the cooling efficiency can be obtained.

[Brief explanation of the drawing]

1A is a longitudinal cross-sectional view i'Ilj of the two-stroke engine according to the 2-cycle engine 1, and FIGS. 2 and 3 are explanatory diagrams of the operation of the same two-cycle engine. 4... Cylinder, 5... Piston, 10... Crank chamber, 12... Scavenging port, 14... Scavenging passage,
16...Communication hole, 17...Vent hole.

Claims (1)

[Claims] In a two-stroke engine, the scavenging passage has a scavenging port that opens on the inner circumferential surface of the cylinder and is opened and closed by a piston, and a scavenging passage that communicates with the crank chamber at one end and into the cylinder via the scavenging port at the other end. A communication hole that opens to the inner circumferential surface of the cylinder below the scavenging port is formed in the middle, and at least when the piston opens the scavenging port, a ventilation hole that opens to the communication hole is formed in the piston skirt. A two-stroke engine characterized by the following features: