JPH0261322A - Combustion chamber structure for two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To feed fresh air so well as well as to secure good scavenging by installing a mask wall, closing an opening between a peripheral edge of a feed valve being situated at the exhaust valve side and a valve seat, over the whole valve opening period of the feed valve, and a fresh air guide wall higher in a level than that of the mask wall respectively. CONSTITUTION:Respective inner wall parts 3b, 3c of a cylinder head 3 are connected to each other via a peripheral wall 8 of a recess groove 5. At this time, this peripheral wall 8 is made up of a pair of mask walls 8a extending in a circular form along a peripheral edge of each feed valve 6, a fresh air guide wall 8b being situated between the feed valves 6 and a pair of fresh air guide walls 8c being situated between the peripheral edge in an inner wall surface 3a of the cylinder head 3. An opening between the peripheral edge of the feed valve 6 being situated at the side of exhaust valves 7 closes the mask wall 8a over the whole valve opening period of the feed valves 6. On the other hand, the paired fresh air guide walls 8c is made higher in level than that of the paired mask walls 8a. With this formation, fresh air is fed up to the inmost part of a combustion chamber 4.

Description

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

(Prior Art) In a two-stroke internal combustion engine, a mask wall extending from the inner wall surface of a cylinder head toward a combustion chamber is formed between an air intake valve and an exhaust valve, and the air intake valve is positioned on the exhaust valve side by this mask wall. The opening between the peripheral edge and the valve seat is closed during the full opening period of the air supply valve, and the air supply valve extends from the end of the mask wall to the peripheral edge of the inner wall surface of the cylinder head in a direction perpendicular to the air intake port axis. The applicant has already proposed a two-stroke internal combustion engine in which a fresh air guide wall facing toward the periphery of the combustion chamber on the valve side is formed on the inner wall surface of the cylinder head (Japanese Patent Application No. 1983-102).
(See No. 659). In this two-stroke internal combustion engine, the opening between the intake valve periphery and the valve seat located on the exhaust valve side is covered by a mask wall during the full opening period of the intake valve, so fresh air flowing in from the intake port is Instead of blowing through into the exhaust port, most of the fresh air flows into the combustion chamber from the intake valve opening on the opposite side of the mask wall, descends along the inner wall of the cylinder below the intake valve, and then flows onto the top surface of the piston. It changes direction and flows in a loop. In this way, since most of the fresh air is used for loop scavenging, good loop scavenging can be obtained. Further, a part of the fresh air flowing in from the air supply port is guided by the fresh air guide wall toward the top surface of the piston, and then changes its direction upward. In this way, in this two-stroke internal combustion engine, most of the fresh air that flows in from the intake port flows in a loop, so that good loop scavenging can be ensured.

[Problems to be Solved by the Invention] In order to perform good scavenging, it is necessary for fresh air to flow deep into the combustion chamber, that is, to flow close to the top surface of the piston.

However, in the above-mentioned two-stroke internal combustion engine, the fresh air guide wall and the mask wall have the same height. Therefore, since the height of the fresh air guide wall is low, the fresh air guided by the fresh air guide wall is directed toward the top surface of the piston. It does not reach the vicinity, but changes direction in the center of the combustion chamber and heads toward the exhaust valve. Therefore, this fresh air does not contribute much to the scavenging action, and there is a problem that the combustion chamber cannot be sufficiently scavenged even though the fresh air is guided by the fresh air guide wall.

(Means for Solving the Problems) In order to solve the above problems, according to the present invention, a mask 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. The mask wall closes the opening between the peripheral edge of the air intake valve located on the exhaust valve side and the valve seat during the full opening period of the air intake valve, and air is supplied from near the end of the mask wall to the peripheral edge of the inner wall of the cylinder head. A fresh air guide wall that extends transversely to the port axis and faces toward the periphery of the combustion chamber on the intake valve side is formed on the inner wall surface of the cylinder head, and the height of the fresh air guide wall is lower than the height of the mask wall. It is also expensive.

[For production]

By making the height of the fresh air guide wall higher than the height of the mask wall, the fresh air guided by the fresh air guide wall reaches near the top surface of the piston, that is, deep into the combustion chamber.

〔Example〕

Referring to FIGS. 1 to 4, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block I, and 3 is a cylinder block.
is the cylinder head fixed on the cylinder block l,
4 indicates a combustion chamber formed between the inner wall surface 3a of the cylinder head 3 and the top surface of the piston 2, respectively. A groove 5 is formed on the inner wall surface 3a of the cylinder head, and a pair of intake valves 6 are formed on the inner wall surface portion 3b of the cylinder head forming the bottom wall surface of the groove 5.
is placed. On the other hand, the cylinder head inner wall surface portion 3c excluding the groove 5 is substantially flat, and a pair of exhaust valves 7 are arranged on this cylinder head inner wall surface portion 3c. Cylinder head inner wall surface portion 3b and cylinder head inner wall surface portion 3c
are connected to each other via the peripheral wall 8 of the groove 5. This concave groove peripheral wall 8 includes a pair of mask walls 8a extending in an arc shape along the peripheral edge of the air supply valve 6, a fresh air guide wall 8h located between the air supply valves 6, and a peripheral edge of the cylinder head inner wall surface 3a. and a pair of fresh air guide walls 8c located between the air supply valves 6. Each mask wall 8a extends toward the combustion chamber 4 below the intake valve 6 at the maximum lift position shown by the broken line in FIG. The opening between the valve seats 9 is closed by the mask wall 8a throughout the opening period of the air supply valve 6. Furthermore, the pair of fresh air guide walls 8c are located in substantially the same plane, and the fresh air guide walls 3b and 8c extend substantially parallel to the line connecting the centers of the resupply valves 6.

The ignition plug 10 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. On the other hand, the exhaust valve 7 is not provided with a mask wall that covers the opening between the exhaust valve 7 and the valve seat 11. Therefore, when the exhaust valve 7 opens, a mask wall is formed between the exhaust valve 7 and the valve seat 11. The entire opening opens into the combustion chamber 4.

In the cylinder head 3, there is an air intake port 1 for the air intake valve 6.
2 is formed, and an exhaust port 13 is formed for the exhaust valve 7. Each air supply port 12 is connected to an air cleaner (not shown) via a mechanical supercharger 14 driven by an engine and an air supply duct 15, for example.
A throttle valve 16 is disposed within the throttle valve 5 . each air supply port)
Fuel injection valves 17 are arranged on the upper wall surface of the fuel injection valve 12, and rigid fuel with a small spread angle is injected from each fuel injection valve 17 toward a region 18 of the air supply valve 6 shown by hatching in FIG. . This region 18 is located on the ignition plug lO side with respect to the axis of the air supply port 12, and on the opposite side from the ignition plug 10 with respect to a line connecting the valve stems of both the intake valves 6.

As mentioned above, each fresh air guide wall 8b, 8c is connected to both air supply valves 6.
It extends almost parallel to the line connecting the centers of That is,
In other words, each fresh air guide wall 8b8C extends transversely to the axis of the air supply port 12 from near the end of the mask wall 8a, and in the embodiment shown in FIGS. 1 to 4, each fresh air guide wall 8b.

8c extends from the end of the mask wall 8a in a direction perpendicular to the axis of the air supply port 12. Furthermore, these fresh air guide walls 8b and 8c face toward the periphery of the combustion chamber 4 on the intake valve 6 side. Further, in the embodiment shown in FIGS. 1 to 4, a pair of fresh air guide walls 8C extend to the bottom wall surface of the cylinder head inner wall surface 3a.

That is, the bottom wall surface of the cylinder head inner wall surface 3a has a pair of bottom wall surface portions 3d that protrude into the combustion chamber 4 in a U-shape, and each fresh air guide wall 8c is connected to the cylinder head inner wall surface portion 3b.
It extends from to this bottom wall surface portion 3d. Therefore, the height of the fresh air guide wall 8C is higher than the height of the mask wall 8a. On the other hand, the mask wall 8a located on the fresh air guide wall 8C side has an extension portion 8d extending to the bottom wall surface portion 3d, and this extension portion 8d also forms a fresh air guide wall. As can be seen from FIG. 3, the fresh air guide wall 8d extends to the fresh air guide wall 8c while being curved, and the height of the fresh air guide wall 8d increases as it approaches the fresh air guide wall 8c. On the other hand, the first
As shown in the figure and FIG. 2, a burnt gas guide wall 8e is formed on the opposite side of the fresh air guide wall 8c. This burnt gas guide wall 8e consists of a curved surface extending from the cylinder head inner wall surface portion 3c to the bottom wall/surface portion 3d.

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 before the intake valve 6, and the exhaust valve 7 closes before the intake valve 6. Further, the fuel injection period is set from the time when the intake valve 6 opens until before the bottom dead center BDC.

FIG. 6 shows the valve lift of the intake valve 6 and the exhaust valve 7 and the pressure change P in the exhaust port 13.9. P 2+ Q+,
It shows Qz. These pressure changes P r, P t
, Q+, and Qg will be described later.

The scavenging action and stratification action will be explained with reference to FIGS. 7 and 8. FIG. 7 shows the state of low load operation, and FIG. 8 shows the state of high load operation. In addition, Fig. 7 (A) and Fig. 8 (8) show the state immediately after the air supply valve 6 is opened, and Fig. 7 (B) and Fig. 8 (B) show the piston 2 almost at the bottom. It shows when it is at a point.

First, with reference to FIG. 7, the operation during low engine load operation will be explained.

When the piston 2 descends and the exhaust valve 7 opens, the high-pressure burned gas in the combustion chamber 4 flows out into the exhaust port 13, and as a result, the pressure in the exhaust port 13 increases as shown by P in FIG. Temporarily becomes positive pressure.

This positive pressure P propagates downstream in the exhaust passage, is reflected at the gathering part of the exhaust passages of each cylinder, and then becomes negative pressure and propagates into the exhaust port 13 again. Therefore, when the air supply valve 6 is opened, negative pressure is generated within the exhaust port 13, as indicated by P2 in FIG. The timing at which this negative pressure occurs depends on the length of the exhaust passage. When the engine is operating at low load, the combustion pressure is low, and therefore the positive pressure P I + negative pressure P2 generated within the exhaust port 13 is relatively small.

When the air intake valve 6 opens, fresh air containing fuel flows into the combustion chamber 4 from the air intake port 12, but because the mask wall 8a is provided to the opening of the air intake valve 6, fresh air and Fuel mainly flows into the combustion chamber 4 through the opening of the intake valve on the side opposite to the mask wall 8a. - On the other hand, when the intake valve 6 opens, negative pressure is generated in the exhaust port 13 as shown by P2 in FIG. It is sucked out within 13. Due to the movement of this burnt gas, fresh air and fuel are drawn toward the exhaust valve 7 as shown by arrow R7 in FIG. 7 (8).
Fuel is thus directed around the spark plug 10 (FIG. 2). Next, as shown in FIG. 7(B), when the piston 2 descends, the fresh air containing fuel flows into the air supply valve 6 as shown by R2.
It goes downward along the inner wall surface of the lower cylinder. However, when the engine is operating at low load, the amount of fresh air flowing into the combustion chamber 4 is small and the speed of the fresh air flowing into the combustion chamber 4 is slow, so that the fresh air does not reach the top surface of the piston 2 and remains in the upper part of the combustion chamber 4. Therefore, when the piston 2 rises, the air-fuel mixture gathers in the upper part of the combustion chamber 4, and residual burnt gas gathers in the lower part of the combustion chamber 4, so that the inside of the combustion chamber 4 becomes stratified. In this way, the air-fuel mixture is reliably ignited by the ignition plug 10.

On the other hand, during high-load engine operation, the combustion pressure increases, so the positive pressure generated in the exhaust port 13 increases as shown by Q in FIG. 6, and the negative pressure that is the reflected wave of this positive pressure Q1 increases. Q2 also becomes larger.

Further, the peak of the negative pressure Q2 occurs slightly later than the peak of the negative pressure P2.

When the engine is operated under high load, the amount of fresh air flowing into the combustion chamber 4 is large, and the speed of the air flowing into the combustion chamber 4 is high. Therefore, when the intake valve 6 opens, a large amount of fresh air flows into the combustion chamber 4 at a high speed.

Next, the burnt gas in the upper part of the combustion chamber 4 is sucked out into the exhaust port 13 by the negative pressure Q2 generated in the exhaust port 13, as shown by arrows S I and S z in FIG. 8(A). The fresh air is directed towards the center of the combustion chamber 4. Then, when the piston 2 further descends, Fig. 8 (B)
As shown at 33, the fresh air heads downward along the inner wall surface of the cylinder below the intake valve 6 and reaches the top surface of the piston 2. Therefore, the burnt gas in the combustion chamber 4 is as shown in Fig. 8 (B).
As shown by the arrow T, the fresh air is gradually driven away and discharged into the exhaust port 13, and thus loop scavenging is performed within the combustion chamber 4.

In the embodiment shown in FIGS. 1 to 4, fresh air guide walls 8b and 8c are formed on both sides of the mask wall 8a, so that the fresh air is guided by these fresh air guide walls 8b+8c and passes through the piston 2. Head to the top. By the way, in this embodiment, the height of the fresh air guide wall 8c is higher than the mask wall 8a, and the fresh air guide wall 8c extends to the bottom wall surface portion 3d of the cylinder head. It reaches near the top surface of the piston 2 as shown by arrow S4 in FIG. 2(B). Therefore, the fresh air guided by the fresh air guide wall 8c also performs a strong scavenging action, thus ensuring a good scavenging action. Further, since fresh air is guided to the top surface of the piston 2 by the fresh air guide wall 8d, even better scavenging action can be ensured.

Furthermore, since the fresh air is guided to the vicinity of the top surface of the piston 2 by the fresh air guide walls 8c and 8d, even if the fresh air guide wall 8c is brought closer to the exhaust valve 7, the fresh air does not blow through into the exhaust port 13. There isn't. Therefore, the fresh air guide wall 8c can be moved closer to the exhaust valve 7, so that the opening area of the air supply valve 6 can be increased. As a result, the amount of fresh air flowing in can be increased, so that the engine output can be increased.

Further, when the exhaust valve 7 is opened, a part of the burnt gas is guided by the burnt gas guide wall 8e and flows smoothly into the exhaust port 13. As a result, burned gas is more easily discharged from the combustion chamber 4, so that even better scavenging action can be ensured. It goes without saying that the present invention can also be applied to a two-stroke diesel engine.

[Effect of the invention] The opening between the peripheral edge of the air supply valve located on the exhaust valve side and the valve seat is covered by a mask wall during the full opening period of the air supply valve, and the fresh air guided by the fresh air guide wall is directed to the piston. Since the air can be sent to the vicinity of the top surface, good scavenging action can be ensured.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of a two-stroke internal combustion engine, Fig. 2 is a view showing the inner wall surface of the cylinder head, and Fig. 3 is an arrow I in Fig. 1.
Fig. 4 is a plan sectional view of the cylinder head, Fig. 5 is a line diagram showing the opening period of the exhaust valve, and Fig. 6 is a diagram showing the valve lift of the supply and exhaust valve and the exhaust. FIG. 7 is a diagram showing the pressure change in the port, FIG. 7 is a diagram for explaining the operation during low load operation, and FIG. 8 is a diagram for explaining the operation during high load operation. 3... Cylinder head, 4... Combustion chamber, 6...
...Air supply valve, 7...Exhaust valve, 8a.
...Mask wall, 8b, 8c, 8d... Fresh air guide wall, 12... Air supply port.

Claims (1)

[Claims] A mask 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 opening between the peripheral edge of the intake valve located on the exhaust valve side and the valve seat is opened by the mask wall to supply air. The valve is closed during the full opening period of the valve, and extends transversely to the intake port axis from near the edge of the mask wall to the peripheral edge of the inner wall surface of the cylinder head, and extends toward the periphery of the combustion chamber on the intake valve side. A combustion chamber structure for a two-stroke internal combustion engine in which a facing fresh air guide wall is formed on an inner wall surface of a cylinder head, and the height of the fresh air guide wall is higher than the height of a mask wall.