JPH01277619A - Combustion chamber of two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the generation of knocking by allowing a gap in which the fresh air flows to be formed between a mask wall and the peripheral edge part of an air feeding valve, when the lift quantity of the air feeding valve is small and preventing the flow of the fresh air between the mask wall and the peripheral edge part of the air feeding valve when the lift quantity of the air feeding valve is large. CONSTITUTION:When an air feeding valve 6 is at the max. lift position, the peripheral edge part of the air feeding valve 6 is set cose to a mask wall 9a, and the fresh air does not flow between the peripheral edge part of the air feeding valve 6 and the mask wall 9a. Further, when the lift quantity of the air feeding valve 6 is small, a gap is formed between the peripheral edge part of the air feeding valve 6 and the mask wall 9a, and the fresh air flows between the peripheral edge part of the air feeding valve 6 and the mask wall 9a. Therefore, the whole in a combustion chamber can be scavenged, and the generation of knocking in the high speed operation can be prevented.

Description

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

[Conventional technology]

In order to ensure good loop scavenging in the combustion chamber in a two-stroke diesel engine, there is an opening between the intake valve periphery and the valve seat located on the cylinder axis side, and an opening between the exhaust valve periphery and the valve seat located on the cylinder axis side. A wall is installed to close the opening of the air supply valve and exhaust valve when the lift amount is small.
Furthermore, a two-stroke diesel engine is known in which an air supply boat and an exhaust boat are arranged upwardly extending parallel to the cylinder axis (Japanese Patent Laid-Open No. 104613/1983). This 2
Between cycle diesel machines, the intake air that flows in from the air supply boat flows along the inner wall of the cylinder toward the top of the piston, then changes direction on the top of the piston and flows along the inner wall of the cylinder toward the exhaust boat. Loop scavenging can be performed.

However, in this two-stroke diesel engine, when the lift amount of the intake valve and exhaust valve becomes large, the opening formed between the intake valve and the valve seat opens into the combustion chamber around the entire circumference of the intake valve, and the exhaust valve opens into the combustion chamber. Openings formed between the valve and the valve seat extend around the entire circumference of the exhaust valve and open into the combustion chamber. As a result, the intake air flowing in from the opening of the intake valve located on the cylinder axis side advances along the inner wall surface of the cylinder and flows out into the exhaust boat through the opening of the exhaust valve. Therefore, in this two-stroke diesel engine, only the - part of the intake air is used for loop scavenging, making it impossible to ensure good loop scavenging.

Therefore, in order to ensure strong loop scavenging, a Max wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between the intake valve and the exhaust valve, and this Max wall is located on the exhaust valve side. The present applicant has already proposed a two-stroke internal combustion engine in which the opening between the intake valve periphery and the valve seat is closed during the entire opening period of the intake valve (Japanese Patent Application No. 82-2).
(See No. 88390).

In this two-stroke internal combustion engine, the openings between the intake valve and the valve seat located on the exhaust valve side are mutually closed during the period when the intake valve is fully open, so that all the fresh air is absorbed into the inner wall of the cylinder below the intake valve. , thus creating a strong loop scavenging.

[Problem to be solved by the invention]

However, when strong loop scavenging is performed in this way, the scavenging air flows in a loop along the peripheral wall of the combustion chamber, and fresh air is not sent into the center of the combustion chamber, so high-temperature already existing air flows in the center of the combustion chamber. Fuel gas will remain. As a result, there is a problem in that knocking occurs particularly when the engine rotates at high speeds because the fresh air is heated by the residual burnt gas.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, a maxi wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between the intake valve and the exhaust valve, and the periphery of the intake valve is located on the exhaust valve side. When the lift amount of the air supply valve is small, a gap is created between the Maxu wall and the periphery of the air supply valve where fresh air can flow, and the lift amount of the air supply valve is increased. When is large, the Max wall is formed so that fresh air does not substantially flow between the Max wall and the peripheral edge of the air supply valve.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block 1,
3 is a cylinder head fixed on the cylinder block 1, 4 is a combustion chamber formed between the inner wall surface 3a of the cylinder head 3 and the top surface of the piston 2, and 6 is a groove 5 on the inner wall surface 3a of the cylinder head. is formed, and the air supply valve 6 is disposed on the cylinder head inner wall surface portion 3b forming the bottom wall surface of the groove 5. On the other hand, the cylinder head inner wall surface portion 3C excluding the groove 5 is substantially flat, and the exhaust valve 7 is disposed on this cylinder head inner wall surface portion 3C.

The cylinder head inner wall surface portion 3b and the cylinder head inner wall surface portion 3C are connected to each other via the peripheral wall 9 of the groove 5. This concave groove circumferential wall 9 includes a max wall 9a that 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 fresh air guide wall located between the air supply valve 6. 9b
and a fresh air guide wall 9c located between the peripheral wall of the cylinder head inner wall surface 3a and the air supply valve 6. Each Max wall 9a extends toward the combustion chamber 4 below the intake valve 6 at the maximum lift position.

In the embodiment shown in FIGS. 1 to 3, the intake valve 6 is arranged at an angle so that the valve shaft of the intake valve 6 extends toward the center of the combustion chamber 4. are arranged almost vertically. Furthermore, as shown in FIG.
When the air supply valve 6 is at the maximum lift position, the air supply valve 6
The peripheral edge of is approaching the makusu wall 9a. Therefore, when the air supply valve 6 is at the maximum lift position, fresh air does not flow between the peripheral edge of the air supply valve 6 and the mask wall 9a. On the other hand, when the lift amount of the air supply valve 6 is small, the peripheral edge of the air supply valve 6 and the mask wall 9
A gap is formed between the gaps a through which fresh air can flow, and therefore, when the lift amount of the air supply valve 6 is small, fresh air flows between the peripheral edge of the air supply valve 6 and the mask wall 9d. In the embodiment shown in FIG. 3, the mask wall 9a is formed so that the gap between the peripheral edge of the air supply valve 6 and the mask wall 9a gradually becomes smaller as the lift amount of the air supply valve 6 increases. The shape of the mask wall 9a is such that when the lift amount of the air intake valve 6 is large, there is substantially no gap between the peripheral edge of the air intake valve 6 and the mask wall 9a, and when the lift amount of the air intake valve 6 is small ( This may be any shape that allows fresh air to flow between the peripheral edge of the air supply valve 6 and the mass 2993.

On the other hand, as shown in FIG. 1 and FIG. It extends almost parallel to the line connecting the centers. Spark plug 1
1 is arranged on the cylinder head inner wall surface portion 3c so as to be located at the center of the cylinder head inner wall surface 3a.

Inside the cylinder head 3, an air supply boat 1 is provided for an air supply valve 6.
2 is formed, and an exhaust port 13 is formed for the exhaust valve 7. Each air supply boat 12 is connected to an air cleaner via, for example, a mechanical supercharger driven by an engine and a throttle valve. Further, a fuel injection valve 14 is disposed within the air supply boat 12, and fuel is injected from the fuel injection valve 14 toward the back surface of the air supply valve 6.

FIG. 4 shows an example of the opening period of the intake valve 6 and the exhaust valve 7. In the example shown in FIG. 4, the exhaust valve 7 opens before the intake valve 6, and the exhaust valve 7 closes before the intake valve 6.

When the piston 2 moves down one step and the exhaust valve 7 opens, the combustion chamber 4
The high-pressure burnt gas inside flows out into the exhaust port 13. Then, when the air supply valve 6 opens, the high-pressure burned gas flows from the air supply boat 12 into the combustion chamber 4.
Fresh air containing fuel flows into the tank. At this time, as shown by arrow St in FIG. 5, some of the fresh air descends along the inner wall surface of the cylinder below the air supply valve 6, and then advances along the top surface of the piston 2. On the other hand, the remaining fresh air passes downward through the gap between the mask wall 9a and the peripheral edge of the air supply valve 6, as shown by arrow S2 in FIG. Therefore, the scavenging air flow S1 scavenges the peripheral part of the combustion chamber 4, and the scavenging air flow S2 scavenges the central part of the combustion chamber 4.

Next, when the piston 2 further descends, as shown in FIG. 6, there is virtually no gap between the peripheral edge of the air supply valve 6 and the mask wall 9a, so the fresh air containing fuel flows to the side opposite to the mask wall 9a. The air flows into the combustion chamber 4 from the opening of the intake valve 6 . This fresh air then changes direction at the top of the piston 2 and heads toward the exhaust valve 7, as shown by arrow S in FIG. 13, thus performing loop scavenging. By the way, in the embodiment shown in FIGS. 1 and 2, the length of the mask wall 9a extending in an arc shape is relatively long, and when the lift amount of the air supply valve 6 is large, the air supply valve 6
Of the openings formed between the valve seat 10 and the valve seat 10, approximately 1/3 of the openings located on the exhaust valve 7 side are closed by the mask wall 9a, and approximately 2/3 of the openings located on the opposite side of the exhaust valve 7. Fresh air is supplied from Further, in this embodiment, the fresh air flowing in from the air supply valve 6 is guided downward along the inner wall surface of the cylinder by the fresh air guide walls 9b and 9c. Therefore, in this embodiment, when the lift amount of the air supply valve 6 becomes large, most of the fresh air is directed toward the top surface of the piston 2 along the inner wall surface of the cylinder, thus achieving good loop scavenging. Become.

In this way, in the embodiments shown in FIGS. 1 to 3, the scavenging air flow S
The burnt gas in the entire combustion chamber 4 can be scavenged by S2, and thus the occurrence of knocking can be suppressed. Furthermore, when the lift amount of the intake valve 6 is small, fresh air flows in from the entire opening between the intake valve 6 and the valve seat 1o, so the amount of fresh air supplied into the combustion chamber 4 increases, and thus further increases. Scavenging efficiency can be improved.

Another embodiment is shown in FIGS. 7 to 9. In this embodiment, a mask wall 15 is also provided for the exhaust valve 7. As shown in FIG. 8, this mask wall 15 extends in an arc shape along the peripheral edge of the exhaust valve 7 located on the side of the air supply valve 6, and as shown in FIG. - 5 extends parallel to the valve axis of the exhaust valve 7. Therefore, the opening formed between the exhaust valve 7 located on the side of the air supply valve 6 and its valve seat 16 is closed by the mask wall 7 during the period when the exhaust valve 7 is fully open.

As mentioned above, when the exhaust valve 7 opens, the burnt gas in the combustion chamber 4 suddenly flows out into the exhaust port 13, so that the pressure in the exhaust port 13 temporarily becomes positive due to blowdown. . Thereafter, the pressure inside the exhaust boat 13 repeats negative pressure and positive pressure, resulting in so-called exhaust pulsation. - Once blowdown occurs, the pressure in the combustion chamber 4 rapidly decreases, and therefore, when the pressure in the exhaust boat 13 becomes positive due to exhaust pulsation, the exhaust gas in the exhaust boat 13 will then flow into the combustion chamber 4. flow backwards. However, in the embodiments shown in FIGS. 7 to 9, the mask wall 15 is provided for the exhaust valve 7, so that the exhaust gas R flowing backward flows onto the inner wall surface of the cylinder below the exhaust valve 7, as shown in FIG. flows downward along. Therefore, the backflowing exhaust gas is not mixed into the fresh air, so misfires can be prevented.

FIG. 11 shows another embodiment of FIGS. 7 to 9. In this embodiment, a mask wall 15' is provided only around the exhaust valve 7 near the ignition plug 11. Therefore, in this embodiment, compared to the embodiments shown in FIGS. 7 to 9, the exhaust valve 7 is
The opening area of the exhaust boat 13 becomes larger, and the burned gas easily flows out into the exhaust boat 13 during blowdown. In addition,
In this embodiment as well, the mask wall 15' prevents backflow exhaust gas from entering the fresh air in the center of the combustion chamber 4.

〔Effect of the invention〕

Since the entire combustion chamber can be scavenged, it is possible to prevent knocking, which occurs particularly when the engine is operated at high speed.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of a two-stroke internal combustion engine, Figure 2 is a diagram showing the inner wall surface of the cylinder head, Figure 3 is an enlarged side sectional view of the cylinder head, and Figure 4 shows the opening period of the supply and exhaust valves. 5 is a diagram showing when the lift amount of the air supply valve is small, and FIG. 6 is a diagram showing when the lift amount of the air supply valve is large.
FIG. 7 is a side sectional view of a two-stroke internal combustion engine showing another embodiment, FIG. 8 is a view showing the inner wall surface of the cylinder head of FIG. 7, and FIG. 9 is an enlarged side sectional view of the cylinder head of FIG. 7. 10 are diagrams showing when the lift amount of the supply/exhaust valve is large, and FIG. 11 is a diagram showing the inner wall surface of the cylinder head of still another embodiment. 6...Air supply valve, 7...Exhaust valve, 9a, 15
．． 15'...Mask wall, 14...Fuel injection valve.

Claims (1)

[Claims] A Max wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between the intake valve and the exhaust valve, and the Max wall faces the opening between the intake valve periphery and the valve seat located on the exhaust valve side. When the lift amount of the air supply valve is small, a gap is created between the Max wall and the periphery of the intake valve, and when the lift amount of the air intake valve is large, a gap is created between the Max wall and the periphery of the air intake valve. A combustion chamber of a two-stroke internal combustion engine that has a wall that prevents fresh air from flowing between the two sections.