JPH0715260B2 - 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]

In order to perform loop scavenging in a two-cycle diesel engine, the opening between the intake valve peripheral portion located on the cylinder axis side and the valve seat and the opening between the exhaust valve peripheral portion located on the cylinder axis side and the valve seat are provided to the intake valve and the exhaust. A two-cycle diesel engine is known in which a mask wall that closes when the valve lift amount is small is provided, and further, an air supply port and an exhaust port are extended upward in parallel with the cylinder axis (Japanese Patent Laid-Open No. 52-52160).
-104613 publication). In this two-cycle diesel engine, the intake air flowing in from the air supply port goes to the piston top surface along the cylinder inner wall surface, then turns on the piston top surface and flows along the cylinder inner wall surface toward the exhaust port Scavenging can be performed.

[Problems to be solved by the invention]

However, in this two-cycle diesel engine, when the lift amount of the intake valve and the exhaust valve becomes large, the opening formed between the intake valve and the valve seat opens in the combustion chamber over the entire circumference of the intake valve, and the exhaust valve and the valve The opening formed between the seats opens in the combustion chamber over the entire circumference of the exhaust valve. As a result, the intake air that has flowed in from the opening of the air supply valve located on the cylinder axis side travels along the inner wall surface of the cylinder head, and flows out into the exhaust port through the opening of the exhaust valve. Like this 2
Not only is it difficult to obtain good loop scavenging because some intake air is not used for loop scavenging in cycle diesel engines, but fuel blow-through occurs when a mixture is supplied from the air intake port It will be.

Also, when the height of the mask wall is increased in a case where the intake valve and the exhaust valve are arranged so as to approach each other as the two-cycle diesel engine opens, the tip of the mask wall becomes a knife edge shape. As a result, there arises a problem that the heat load cannot be endured. Further, in this two-cycle diesel engine, when trying to increase the valve diameters of the intake valve and the exhaust valve, the height of the mask wall inevitably becomes low, so that further blow-through of fuel occurs and good loop scavenging is obtained. The problem of being unable to do so arises.

[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 peripheral edge of the air supply valve located on the exhaust valve side and the valve seat is closed by the mask wall for the full opening period of the air supply valve, and the axis of each air supply valve is The plane including the axis is substantially parallel to the cylinder axis, and the axes of the air supply valves are inclined in this plane so as to approach each other toward the combustion chamber.

〔Example〕

1 to 4, 1 is a cylinder block, 2 is a piston that reciprocates 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, 3c are connected to each other via a peripheral wall 8 of a groove 5 which is substantially vertical, and an air supply valve 6 is arranged on one side of the peripheral wall 8 and an exhaust valve 7 on the ground side. Are placed. 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 toward the combustion chamber 4 below the air supply valve 6 at the maximum lift position, so that the opening between the periphery of the air supply valve 6 on the exhaust valve 7 side and the valve seat 9 is supplied. It will be closed by the mask wall 8a over the entire opening period of the air valve 6. 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. The exhaust port 11 is connected to a supercharger via a throttle valve (not shown), and a fuel injection valve (not shown) is arranged in the exhaust port 11.

A plane K (Fig. 1) including the axis of each air supply valve 6 is substantially parallel to the cylinder axis, and a plane L (Fig. 1) including the axis of each exhaust valve 7 is also substantially parallel to the cylinder axis. ing. Furthermore, these planes K and L are also substantially parallel. On the other hand, as shown in FIG. 1, the axis of the intake valve 6 is inclined so as to approach each other in the plane K as it goes toward the combustion chamber 4, and the axis of the exhaust valve 7 is also flat as shown in FIG. Within L, they are arranged so as to be closer to each other toward the combustion chamber 4.

FIG. 5 shows an example of the valve 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. 5, 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, but after a while, the pressure in the exhaust port 11 becomes almost atmospheric pressure. Next, when the piston 2 further descends, the inside of the combustion chamber 4 becomes negative pressure,
As shown in FIG. 6, the burnt gas in the exhaust port 11 is indicated by an arrow R.
As shown by, the backflow occurs in the combustion chamber 4. The lower the negative pressure operation, the lower the combustion pressure. Therefore, after the exhaust valve 7 opens, the exhaust port
Since the time until the pressure in 11 becomes almost atmospheric pressure is short, the backflow R of burnt gas occurs earlier as the engine load decreases. When the piston 2 further descends, the fuel flows into the combustion chamber 4 together with the fresh air from the air supply port 10. However, since the mask wall 8a is provided to the opening of the air supply valve 6, the fresh air and the fuel are supplied. It goes downward along the inner wall surface of the cylinder below the valve 6. Therefore, as shown by an arrow S in FIG. 6, the burned gas in the combustion chamber 4 is gradually pushed by the fresh air and discharged into the exhaust port 11, and thus the loop scavenging is performed in the combustion chamber 4. On the other hand, some fuel is fresh air guide wall
Down along 8b, this fuel is conducted 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, 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.

[Advantages of the Invention] Since good loop scavenging can be ensured while preventing blow-through of fuel, engine output can be improved.

[Brief description of drawings]

1 is a sectional view of the two-cycle internal combustion engine taken along line I-I in FIG. 3, FIG. 2 is a sectional view taken along line II-II in FIG. 3, and FIG. FIG. 4 is a bottom view, FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, FIG. 5 is a diagram showing the opening period of the supply / exhaust valve, and FIG. 6 is a diagram for explaining the operation. is there. 6 ... Air supply valve, 7 ... Exhaust valve, 8 ... Recessed groove, 8a ... Mask wall, 10
… Air supply port, 11… Exhaust port, 12… Spark plug.

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,
Combustion of a two-cycle internal combustion engine in which a plane including the axis of each intake valve is substantially parallel to the cylinder axis and the axes of each intake valve are inclined so that they approach each other in the plane toward the combustion chamber. Room structure.