JPH0715262B2 - Combustion chamber structure of two-cycle internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a combustion chamber structure of a two-cycle internal combustion engine.

[Conventional technology]

A pair of air supply valves are arranged on one side of the mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber, and a pair of exhaust valves are arranged on the other side of the mask wall, and the pair of exhaust valves are positioned on the exhaust valve side by this mask wall. The applicant has already proposed a two-cycle internal combustion engine in which the opening between the periphery of the air supply valve and the valve seat is closed over the pre-open period of the air supply valve (Japanese Patent Application No. 62-16).
See 9684). In this two-cycle internal combustion engine, the mask wall prevents fresh air that has flowed in from the air supply port from immediately flowing out into the exhaust port, so that not only can fuel be prevented from passing through, but the mask wall can also be used to supply air. Since fresh air flowing in from the port flows downward along the inner wall surface of the cylinder bore, good loop scavenging can be secured.

[Problems to be solved by the invention]

However, in this two-cycle internal combustion engine, if the diameter of the intake valve is increased in order to increase the supply amount of fresh air, the new airflow flowing from the peripheral portion of the intake valve farthest from the cylinder axis is blocked by the cylinder head inner wall surface. Therefore, there is a problem that it is difficult to sufficiently increase the supply amount of fresh air.

[Means for solving problems]

In order to solve the above problems, according to the present invention, a pair of air supply valves are provided, and the pair of air supply valves are arranged on one side of the mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber and the mask wall. The exhaust valve is arranged on the other side, and the opening between the air valve peripheral portion located on the exhaust valve side and the valve seat is closed by the mask wall for the full opening period of the air intake valve, and the cylinder head around the air intake valve is closed. The peripheral portion of the inner wall surface and the peripheral portion of the top portion of the cylinder bore are deleted.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a cylinder block, 2 is a piston reciprocating in the cylinder block 1,
Reference numeral 3 denotes a cylinder head fixed on the cylinder block 1, and 4 denotes a combustion chamber formed between the inner wall surface 3a of the cylinder head 3 and the top surface of the piston 2. Cylinder head 3
A concave groove 5 is formed on the inner wall surface 3a of the cylinder head, so that the cylinder head inner wall surface 3a forms a bottom wall surface of the groove 5 and a cylinder head inner wall surface portion 3b.
On the other hand, it is constituted by the cylinder head inner wall surface portion 3c protruding toward the combustion chamber 4. A pair of air supply valves 6 are arranged on the cylinder head inner wall surface portion 3b, and a pair of exhaust valves 7 are arranged on the cylinder head inner wall surface portion 3c. The cylinder head inner wall surface portions 3b and 3c are connected to each other through a peripheral wall 8 of a groove 5 which is substantially vertical. A pair of air supply valves 6 are arranged on one side of the peripheral wall 8 and a pair on the other side. The exhaust valve 7 of is disposed. The peripheral wall 8 is disposed very close to the peripheral edge of the air supply valve 6 and extends in an arc shape along the peripheral edge of the air supply valve 6, and a fresh air guide wall formed between the both air supply valves 6. 8b and a fresh air guide wall 8c formed between the peripheral wall surface of the combustion chamber 4 and the air supply valve 6. The mask wall 8a extends below the intake valve 6 at the maximum lift position to the combustion chamber 4
Therefore, the opening between the periphery of the air supply valve 6 located on the exhaust valve 7 side and the valve seat 9 is closed by the mask wall 8a over the entire opening period of the air supply valve 6. Become. An ignition plug 12 is arranged on the inner wall surface portion 3c of the cylinder head so as to be located at the center of the combustion chamber 4.

In the cylinder head 3, an air supply port 10 is formed for each air supply valve 6, and an exhaust port 11 is formed for the exhaust valve 7.
Is formed. The air supply port 10 is connected to a supercharger via a throttle valve (not shown), and a fuel injection valve (not shown) is arranged in the exhaust port 10.

As can be seen from FIGS. 1 and 2, the outer peripheral edges of the air supply valve 6 and the exhaust valve 7 extend to the vicinity of the extension surface of the cylinder bore 1a. The peripheral edge portion 13 of the cylinder head inner wall surface 3a around the air supply valve 6 and the exhaust valve 7 is removed outward beyond the extension surface of the cylinder bore 1a, and the cylinder head inner wall surface peripheral edge portion 13 has a substantially spherical shape. . On the other hand, the top peripheral portion 14 of the cylinder bore 1a around the intake valve 6 and the exhaust valve 7 is also deleted, and the top peripheral portion 14 of the cylinder bore has a substantially cylindrical shape.
The cylinder head inner wall peripheral portion 13 and the cylinder bore top peripheral portion 14 are smoothly connected to each other without a step.

FIG. 3 shows an example of the opening period of the intake valve 6 and the exhaust valve 7 and an example of the fuel injection period. In the example shown in FIG. 3, the exhaust valve 7 opens earlier than the intake valve 6, and the exhaust valve 7 closes earlier than the intake valve 6. Further, the fuel injection period is set after the air supply valve 6 is opened and before the bottom dead center BDC.

When the piston 2 descends and the exhaust valve 7 opens, the high-pressure burned gas in the combustion chamber 4 flows into the exhaust port 11 as shown by arrows S ₁ and S ₂ in FIG. At this time, since a large gap exists between the outer peripheral edge of the exhaust valve 7 and the peripheral edge portion 13 of the inner wall surface of the cylinder head, the burned gas is quickly discharged into the exhaust port 11. Next, when the piston 2 further descends, as shown by an arrow T in FIG. 4, the fuel flows into the combustion chamber 4 from the intake port 10 together with the fresh air, but the mask wall 8a is provided to the opening of the intake valve 6. Therefore, the fresh air flows downward along the inner wall surface of the cylinder bore 1a below the air supply valve 6. At this time, the outer peripheral edge of the air supply valve 6 and the peripheral edge portion 13 of the inner wall surface of the cylinder head 13
Since there is a large gap between them, the inflow resistance to fresh air is small, and thus a large amount of fresh air goes downward along the inner wall surface of the cylinder bore 1a below the air supply valve 6.
Therefore, as shown by an arrow R in FIG. 4, the burnt gas in the combustion chamber 4 is gradually pushed by the fresh air and is exhausted from the exhaust port 11
It is discharged into the interior of the combustion chamber 4, and thus loop scavenging is performed in the combustion chamber 4. On the other hand, a part of the fuel descends along the fresh air guide wall 8b, and this fuel is guided around the spark plug 12. The air-fuel mixture formed around the spark plug 12 is ignited by the spark plug 12.

In a two-cycle internal combustion engine equipped with the air supply valve 6 and the exhaust valve 7, such loop scavenging has the highest scavenging efficiency. In the present invention, since the air-fuel mixture does not flow out into the exhaust port 11 along the cylinder head inner wall surface 3a by providing the mask wall 8a, not only the blow-through of fuel can be prevented, but also
Since the fresh air is guided by the mask wall 8a and the fresh air guide walls 8b and 8c so as to descend along the inner wall surface of the cylinder bore 1a, good loop scavenging can be secured.

Further, in the present invention, even if the valve diameters of the air supply valve 6 and the exhaust valve 7 are increased and the lift amounts of the air supply valve 6 and the exhaust valve 7 are increased, the height of the mask wall 8a is freely increased accordingly. be able to. Therefore, even if the valve diameter of the air supply valve 6 is increased and the lift amount is increased to increase the amount of fresh air supplied into the combustion chamber 4, the fresh air performs a good loop scavenging, thus improving the engine output. can do.

〔The invention's effect〕

The inflow resistance of fresh air can be reduced by eliminating the peripheral edge of the cylinder head inner wall surface and the peripheral edge of the cylinder bore around the air supply valve. As a result, the inflow of fresh air can be increased, and the engine output can be improved.

[Brief description of drawings]

FIG. 1 is a side sectional view of a two-cycle internal combustion engine, FIG. 2 is a bottom view of the cylinder head of FIG. 1, FIG. 3 is a diagram showing an opening period of a supply / exhaust valve, and FIG. FIG. 5 ... concave groove, 6 ... air supply valve, 7 ... exhaust valve, 8a ... mask wall, 10
... Air supply port, 11 ... Exhaust port, 12 ... Spark plug, 13 ... Cylinder head inner wall peripheral edge, 14 ... Cylinder bore top peripheral edge.

Claims (1)

[Claims] 1. A pair of air supply valves, wherein a pair of air supply valves are arranged on one side of a mask wall extending from an inner wall surface of a cylinder head toward a combustion chamber and an exhaust valve is arranged on the other side of the mask wall. Then, the opening between the intake valve peripheral portion located on the exhaust valve side and the valve seat is closed by the mask wall over the full opening period of the intake valve,
A combustion chamber structure of a two-cycle internal combustion engine in which a peripheral portion of an inner wall surface of a cylinder head around a supply valve and a peripheral portion of a top portion of a cylinder bore are removed.