JPH0715261B2 - 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 a cycle diesel engine, but fuel blow-through occurs when a mixture is supplied from the air supply port There is a problem.

[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 intake 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 intake valve, and the intake valve peripheral portion and the valve are closed. A partial mask wall that closes the opening between the seats when the lift amount of the intake valve is small is formed between the pair of intake valves, and an ignition plug is arranged between the partial mask wall and the exhaust valve.

〔Example〕

Referring to FIGS. 1 to 3, 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 arranged 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 partial mask wall 8b formed between the both air supply valves 6. 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 intake valve 6 at the maximum lift position as shown by the broken line in FIG.
Therefore, the opening between the peripheral portion 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. On the other hand, the partial mask wall 8b extends from between the pair of mask walls 8a to between the pair of air supply valves 6. The height of the partial mask wall 8b is lower than the height of the mask wall 8a. Therefore, when the lift amount of the air supply valve 6 is small, the opening formed between the air supply valve 6 and its valve seat 9 is closed by the partial mask wall 8b, and when the lift amount of the air supply valve 6 becomes large, Between the valve seats 9 is the combustion chamber 4
Open inside. In the embodiment shown in FIGS. 1 to 3, the lower wall surface of the partial mask wall 8b is parallel to the cylinder head inner wall surface portion 3b. It can be inclined and arranged, or can be formed on the extension surface of the cylinder head inner wall surface portion 3c. The spark plug is arranged on the cylinder head inner wall surface portion 3c between the partial mask wall 8b and the pair of exhaust valves 7 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 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.

FIG. 4 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. 4, 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 starts to flow into the exhaust port 11. Then, 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, but the fresh air and the fuel are supplied because the mask wall 8a is provided to the opening of the air supply valve 6. It goes downward along the inner wall surface of the cylinder below the air valve 6. Therefore, as shown by the arrow S in FIG.
The burnt gas in the inside is gradually pushed by the fresh air and discharged into the exhaust port 11, so that the loop scavenging is performed in the combustion chamber 4. Next, when the lift amount of the air supply valve 6 increases, fresh air containing fuel flows into the partial mask wall 8b, and this fresh air is guided around the spark plug 12. Therefore, the air-fuel mixture is easily ignited by the spark plug 12. It should be noted that if the height of the partial mask wall 8b is too low, the fuel blows into the exhaust port 11, and if the height of the partial mask wall 8b is too high, a sufficient amount of fuel is supplied around the spark plug 12. Can't lead. Therefore, the height of the partial mask wall 8b is
It is selected so that the air-fuel mixture is formed around the spark plug 12 without being blown into the interior of the spark plug 12.

In the two-cycle internal combustion engine in which the intake valve 6 and the exhaust valve 7 can be seen, the above-mentioned 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 inner wall surface 3a of the cylinder head by providing the mask wall 8a, not only the fuel blow-through can be prevented, but also the mask wall 8a and the fresh air guide wall. 8c and when the lift amount of the air supply valve 6 is small, the fresh air is guided by the partial mask wall 8b so as to descend along the inner wall surface of the cylinder, so that good loop scavenging can be secured.

Another embodiment is shown in FIGS. 6 and 7. In this embodiment, a concave groove is formed on the inner wall surface portion 3c of the cylinder head around the spark plug 12.
13 is formed, and the spark plug 12 is arranged on the bottom wall surface of the groove 13. The lower wall surface of the partial mask wall 8b is smoothly connected to the bottom wall surface of the concave groove 13. In this embodiment, the peripheral wall of the concave groove 13 can prevent the fuel from being discharged into the exhaust port 11.

〔The invention's effect〕

Since good loop scavenging can be ensured while preventing blow-through of fuel, it is possible to improve engine output and ensure good ignition.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a two-cycle internal combustion engine taken along the line II of FIG. 2, FIG. 2 is a bottom view of a cylinder head, and FIG.
The figure is a sectional view taken along the line III-III in FIG. 2, FIG. 4 is a diagram showing the opening period of the supply / exhaust valve, FIG. 5 is a diagram for explaining the operation, and FIG. FIG. 7 is a bottom view of the cylinder head showing the embodiment of FIG. 7, and FIG. 7 is a sectional view taken along the line VII-VII in FIG. 6 ... Air supply valve, 7 ... Exhaust valve, 5 ... Recessed groove, 8a ... Mask wall, 8b
… Partial 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,
A partial mask wall that closes the opening between the air supply valve peripheral portion and the valve seat when the lift amount of the air supply valve is small is formed between the pair of air supply valves, and an ignition plug is provided between the partial mask wall and the exhaust valve. Combustion chamber structure of the arranged two-cycle internal combustion engine.