JPH0733771B2 - 2-cycle internal combustion engine - Google Patents

Description

The present invention relates to a two-cycle internal combustion engine.

[Prior Art] A pair of air supply valves and a pair of exhaust valves are provided, and a mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between each exhaust valve and the intake valve. When the exhaust valve lift amount is small, the opening between the exhaust valve peripheral portion located on the intake valve side and the valve seat is closed, and each intake air is supplied from the pair of intake ports so that the flow rate of fresh air is equal. A two-cycle internal combustion engine having an air port has already been proposed by the present applicant (see Japanese Patent Application No. 62-31559). In this two-cycle internal combustion engine, the exhaust gas that flows back into the combustion chamber from the exhaust port after the blowdown occurs when the exhaust valve is opened is guided by the mask wall, and the swirl flow around the cylinder axis is introduced into the combustion chamber by this backflow exhaust gas. I am trying to generate it. During low engine load operation, the velocity of the fresh air flowing from the air supply port is slow, so the fresh air swirls with the swirl flow of the backflow exhaust gas, and as a result, the fresh air does not diffuse to the lower region of the combustion chamber and The combustion chamber is stratified to gather in the upper region. On the other hand, during high engine load operation, the velocity of the fresh air flowing from the air supply port is high, so the fresh air descends toward the piston top surface, then changes the flow direction at the piston top surface, thus performing loop scavenging. Be done. At this time, if the flow rate of fresh air flowing in from both air supply ports is different, that is, if there is a difference in the strength of fresh air flowing in from both air supply ports, the weaker new air flow will be laterally moved by the stronger new air flow. Since it is pushed, it does not flow in a clean loop shape, and thus good loop scavenging cannot be obtained as a whole. However, in this two-cycle internal combustion engine, since the fresh air flowing from both air supply ports has the same strength, both new air flows in a loop shape, and thus good loop scavenging is performed.

[Problems to be Solved by the Invention]

However, in this two-cycle internal combustion engine, when the lift of the exhaust valve increases, the opening between the exhaust valve and the valve seat opens in the combustion chamber over the entire circumference of the exhaust valve, and as a result, a part of the fresh air flowing from the intake port Fresh air blows through because it flows along the inner wall surface of the cylinder head and then flows over the mask wall into the exhaust port. However, if a part of the fresh air blows into the exhaust port in this way, this fresh air does not contribute to the loop scavenging, so that there is a problem that strong loop scavenging cannot be performed.

[Means for Solving the Problems]

According to the present invention, in order to solve the above-mentioned problems, a pair of air supply valves and a pair of air supply ports are arranged symmetrically with respect to a plane including a cylinder axis, and the shape of each air supply valve and the shape of each air supply port. Are formed in substantially the same shape, a mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between each air supply valve and the exhaust valve, and each mask wall is positioned on the exhaust valve side. The opening between the periphery of each air supply valve and the valve seat is closed for the full opening period of the air supply valve, each mask wall is arranged symmetrically with respect to the plane including the cylinder axis, and the shape of each mask wall is substantially They are formed in the same shape.

[Work]

By closing the opening between the periphery of each intake valve located on the exhaust valve side and the valve seat with the mask wall for the full opening period of the intake valve, the fresh air flowing in from the intake port is blown into the exhaust port. Instead, the fresh air flowing from both air supply ports flows toward the top of the piston in a clean loop.

〔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 ridge 5 is formed on the inner wall surface 3a of the cylinder 3, which projects toward the combustion chamber 4 and extends along the diameter of the inner wall surface 3a of the cylinder head 3 and extends over the entire diameter. As shown in FIG. 1, this raised portion 5 has a triangular cross section having a ridge 5a at its lower end, and the root portion of this raised portion 5 is shown in FIGS.
It is shown at 5b in the figure. A pair of air supply valves 6 are arranged on one side of the raised portion 5, and a pair of exhaust valves 7 are arranged on the other side of the raised portion 5.
Are placed.

Further, the central portion 5c of the raised portion 5 is curved toward the exhaust valve 7 side, and the spark plug 8 is arranged on the air supply valve 6 side of the curved central portion 5c. Therefore, the spark plug 8 is located substantially on the cylinder axis and is arranged on the air supply valve 6 side with respect to the raised portion 5. A mask wall 10 is formed on the raised portion 5 for each air supply valve 6 so as to cover the opening between the periphery of the air supply valve 6 located on the exhaust valve 7 side and the valve seat 9. These mask walls 10
Are arranged very close to the peripheral edge of the corresponding air supply valve 6 and have an arcuate cross-section extending along the peripheral edge of the air supply valve 6, and these mask walls 10 are the maximum indicated by the chain line in FIG. It extends toward the combustion chamber 4 below the air supply valve 6 at the lift position. 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 10 during the entire opening period of the air supply valve 6. On the other hand, a constant space is provided between the peripheral portion of the exhaust valve 7 and the root portion 5b of the raised portion 5, and therefore the opening between the peripheral portion of the exhaust valve 7 located on the intake valve 6 side and the valve seat 11 is formed. Is not closed by the ridge 5. Therefore, when the exhaust valve 7 opens, the entire opening formed between the exhaust valve 7 and the valve seat 11 opens into the combustion chamber 4.

In the cylinder head 3, there is an air supply port 12 for the air supply valve 6.
Is formed, and the 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, and a throttle valve 16 is arranged in the air supply duct 15. A fuel injection valve 17 is disposed on the upper wall surface of each air supply port 12, and a rigid fuel having a small divergence angle is directed from each fuel injection valve 17 toward a region 18 of the air supply valve 6 shown by hatching in FIG. Is jetted. This area 18
Is located on the spark plug 8 side with respect to the axis of the air supply port 12 and on the side opposite to the spark plug 8 with respect to the line connecting the valve stems of both air supply valves 6.

As can be seen from FIG. 2, the pair of air supply valves 6 are arranged symmetrically with respect to the plane aa including the cylinder axis, and the pair of air supply ports 12 are also arranged symmetrically with respect to the plane aa. Further, the shape of each air supply valve 6 is substantially the same,
The shape of each air supply port 12 is also substantially the same. Further, the valve lift curves of the air supply valves 6 are substantially the same, and therefore, when the air supply valve 8 is opened, the amount of fresh air flowing in from each air supply port 12 is substantially the same. The raised portion 5 has a shape symmetrical with respect to the plane aa, and the mask walls 10 are also arranged symmetrically with respect to the plane aa. Further, each mask wall 10 has substantially the same shape. The exhaust valves 7 are also arranged symmetrically with respect to the plane aa, and the exhaust valves 7 have substantially the same shape.

FIG. 4 shows an example of a valve opening period of each air supply valve 6 and each exhaust valve 7, and an example of a 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.

FIG. 5 shows valve lifts of the intake valve 6 and the exhaust valve 7 and pressure changes P ₁ , P ₂ , Q ₁ , Q ₂ in the exhaust port 13. These pressure changes P ₁ , P ₂ , Q ₁ , Q ₂ will be described later.

Next, the scavenging action and the stratification action will be described with reference to FIGS. 6 and 7. FIG. 6 shows a low load operation, and FIG. 7 shows a high load operation. Further, FIGS. 6 (A) and 7 (A) show immediately after the air supply valve 6 is opened, and FIGS. 6 (B) and 7 (B) show that the piston 2 is almost dead. It shows when there is a point.

First, the engine low load operation will be described with reference to FIG.

When the piston 2 descends and the exhaust valve 7 opens, the high-pressure combustion gas in the combustion chamber 4 flows into the exhaust port 13, and as a result, the pressure in the exhaust port 13 temporarily changes as indicated by P ₁ in FIG. Positive pressure. This positive pressure P ₁ propagates in the exhaust passage toward the downstream side, is reflected at the gathering portion of the exhaust passages of the cylinders, becomes negative pressure this time, and propagates again into the exhaust port 13. Therefore, when the air supply valve 6 is opened, a negative pressure is generated in the exhaust port 13 as shown by P ₂ in FIG. The time when this negative pressure is generated depends on the length of the exhaust passage. The combustion pressure is low during engine low load operation, so the positive pressure P ₁ and the negative pressure P ₂ generated in the exhaust port 13 are relatively small.

When the air supply valve 6 is opened, fresh air containing fuel flows into the combustion chamber 4 from the air supply port 12, but since the mask wall 10 is provided to the opening of the air supply valve 6, The fuel mainly flows into the combustion chamber 4 through the opening of the air supply valve 6 on the side opposite to the mask wall 10. On the other hand, when the intake valve 6 is opened, a negative pressure is generated in the exhaust port 13 as indicated by P ₂ in FIG. 5, so that the burnt gas in the upper portion of the combustion chamber 4 is exhausted by this negative pressure. It is sucked into 13. Due to the movement of the burnt gas, the fresh air and the fuel are pulled toward the exhaust valve 7 as shown by an arrow R ₁ in FIG. 6 (A), so that the fuel is around the spark plug 8 (FIG. 2). Be guided to. Then the sixth
As shown in FIG. 3B, when the piston 2 descends, the fresh air containing fuel moves downward along the cylinder inner wall surface below the air supply valve 6 as indicated by R ₂ . However, during engine low load operation, the amount of fresh air flowing into the combustion chamber 4 is small and the inflow speed is slow, so the fresh air does not reach the top surface of the piston 2 and remains in the upper portion 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,
Since the residual burned gas collects in the lower portion of the combustion chamber 4, the inside of the combustion chamber 4 is stratified. Thus, the air-fuel mixture is surely ignited by the spark plug 8.

On the other hand, since the combustion pressure becomes high during engine high load operation, the positive pressure generated in the exhaust port 13 becomes high as indicated by Q ₁ in FIG. 5, and the negative pressure which is a reflected wave of this positive pressure Q ₁ The pressure Q ₂ also increases. Further, the peak of the negative pressure Q ₂ occurs slightly later than the peak of the negative pressure P ₂ .

During engine high load operation, the amount of fresh air flowing into the combustion chamber 4 is large, and the inflow speed is high. Therefore, when the exhaust valve 6 opens, a large amount of fresh air flows into the combustion chamber 4 at high speed.
Next, when the burned gas in the upper portion of the combustion chamber 4 is sucked into the exhaust port 13 by the negative pressure Q ₂ generated in the exhaust port 13, as shown by arrows S ₁ and S ₂ in FIG. 7 (A). The fresh air turns toward the center of the combustion chamber 4. Next, when the piston 2 further descends, the fresh air moves downward along the cylinder inner wall surface below the air supply valve 6 and reaches the top surface of the piston 2 as indicated by S ₃ in FIG. 7 (B). Therefore, the burned gas in the combustion chamber 4 is gradually driven by fresh air and discharged into the exhaust port 13 as indicated by an arrow T in FIG. 7 (B). Will be done.

By the way, as described above, in the embodiment shown in FIGS. 1 to 3, the air supply valves 6, the mask walls 10 and the air supply ports 12 are arranged symmetrically with respect to the plane aa, respectively. Have the same shape. Therefore, the strength of the fresh air flowing from each air supply port 12 is substantially equal, and the combustion chamber 4
Since the inner shape is symmetrical with respect to the plane aa, the fresh air flowing into the combustion chamber 4 from each air supply port 12 produces a symmetrical loop-shaped flow with respect to the plane aa.
As a result, the fresh air flows in the combustion chamber 4 in a clean loop shape, and thus a strong loop scavenging can be obtained during engine high load operation.

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. Again 2
In a cycle internal combustion engine, the amount of residual burned gas is large, and even when there is a large amount of residual burned gas, it is necessary to collect the air-fuel mixture around the spark plug 8 in order to ensure good ignition combustion. It is necessary to perform proper stratification. In the embodiment shown in FIGS. 1 to 3, the provision of the mask wall 10 prevents the fresh air and the air-fuel mixture from flowing out into the exhaust port 13 along the inner wall surface 3a of the cylinder head 3, which is favorable. Not only can loop scavenging be secured, but good stratification can also be secured.

Further, by disposing the spark plug 8 on the side of the air supply valve 6 with respect to the raised portion 5, it becomes easier for the air-fuel mixture to gather around the spark plug 8, so that good ignition of the air-fuel mixture by the spark plug 8 is ensured. You can In particular, the air-fuel mixture is likely to stay in the region surrounded by the curved center portion 5c of the raised portion 5, and the ignition plug 8 is arranged in this region, so that the ignitability is improved.

Further, since the fuel injected from the combustion injection valve 17 collides with the rear surface of the bulk portion of the air supply valve 6 and is atomized and immediately supplied into the combustion chamber 4, combustion adheres to the inner wall surface of the air supply port 12. There is nothing to do.

FIG. 8 and FIG. 9 show another embodiment of the two-cycle internal combustion engine which can ensure better loop scavenging.
In this embodiment, the concave groove 20 is formed on the cylinder head inner wall surface 3a, and the air supply valve 6 is arranged on the cylinder head inner wall surface portion 3b forming the bottom wall surface of the concave groove 20. On the other hand, the cylinder head inner wall surface portion 3c excluding the concave groove 20 is substantially flat, and the exhaust valve 7 is arranged on the 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 21 of the concave groove 20. The concave groove peripheral wall 21 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. 21b
And a fresh air guide wall 21c located between the peripheral wall of the cylinder head inner wall surface 3a and the air supply valve 6. Each mask wall 2
1a extends toward the combustion chamber 4 below the intake valve 6 at the maximum lift position, and therefore the opening between the peripheral edge of the intake valve 6 located on the exhaust valve 7 side and the valve seat 9 is an intake valve. It will be closed by the mask wall 21a over the entire 6 valve opening period. Further, the fresh air guide walls 21b and 21c are located substantially in the same plane, and these fresh air guide walls 21b and 21c extend substantially parallel to the line connecting the centers of both air supply valves 6. There is. The spark plug 8 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.

As can be seen from FIG. 9, also in this embodiment, the pair of air supply valves 6 are arranged symmetrically with respect to the plane aa including the cylinder axis, and the pair of air supply ports 12 are also arranged symmetrically with respect to the plane aa. Has been done. Further, the shape of each air supply valve 6 is substantially the same, and the shape of each air supply port 12 is also substantially the same. Further, the valve lift curves of the air supply valves 6 are substantially the same, and therefore, when the air supply valves 6 are opened, the amounts of fresh air flowing in from the air supply ports 12 are substantially the same.
Further, each mask wall 21a has a symmetrical shape with respect to the plane aa, and the fresh air guide wall 21b and each fresh air guide wall 21c are also arranged symmetrically with respect to the plane aa. Further, each mask wall 21a and each fresh air guide wall 21c have substantially the same shape. The exhaust valves 7 and the exhaust ports 13 are also arranged symmetrically with respect to the plane aa, and the exhaust valves 7 and the exhaust ports 13 have substantially the same shape.

In this embodiment, the length of the mask wall 21a extending in an arc shape is longer than that in the embodiment shown in FIGS. 1 to 3, and the exhaust gas is exhausted from the opening formed between the air supply valve 6 and its valve seat 9. The mask wall 21a closes the approximately 1/3 opening located on the valve 7 side, and fresh air is supplied from the approximately 2/3 opening located on the opposite side of the exhaust valve 7. Further, in this embodiment, the fresh air flowing from the air supply valve 6 is guided downward by the fresh air guide walls 21b and 21c along the inner wall surface of the cylinder. Therefore, in this embodiment, when the exhaust valve 6 is opened, most of the fresh air flows toward the top surface of the piston 2 along the inner wall surface of the cylinder as indicated by an arrow U in FIG. Will be performed.

By the way, also in the embodiment shown in FIGS. 9 and 10, each air supply valve 6, each air supply port 12, each mask wall 21a and each fresh air guide wall 21c are arranged symmetrically with respect to the plane aa. , And each has substantially the same shape. Therefore, the strength of the fresh air flowing in from each air supply port 12 is substantially equal, and the shape of the combustion chamber 4 is symmetrical with respect to the plane aa, so that the air from each air supply port 12 to the combustion chamber Four
The fresh air that has flowed in produces a symmetrical loop-shaped flow with respect to the plane aa. As a result, in this embodiment as well, fresh air flows in the combustion chamber 4 in a clean loop shape, so that strong loop scavenging is obtained during engine high load operation.

Although the present invention has been described so far as applied to a two-cycle gasoline engine, it goes without saying that the present invention can be applied to a two-cycle diesel engine.

〔The invention's effect〕

The opening between the periphery of the intake valve 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 fresh air is burned with substantially the same strength from each intake port. A strong loop scavenging can be ensured by allowing the fresh air that has flowed into the chamber to flow in a loop shape symmetrically with respect to the plane including the cylinder axis.

[Brief description of drawings]

FIG. 1 is a side sectional view of a two-cycle internal combustion engine, FIG. 2 is a view showing an inner wall surface of a cylinder head, FIG. 3 is a plan sectional view of a cylinder head, and FIG. 4 is a line showing an opening period of a supply / exhaust valve. 5 and 5 are views showing the valve lift of the air supply / exhaust valve and changes in pressure in the exhaust port, FIG. 6 is a diagram for explaining the operation during low load operation, and FIG. 7 is the operation during high load operation. FIG. 8 is a side sectional view of a two-cycle internal combustion engine showing another embodiment, FIG. 9 is a view showing the inner wall surface of the cylinder head of FIG. 8, and FIG. 10 is a view for explaining the operation. FIG. 3 ... Cylinder head, 4 ... Combustion chamber, 5 ... Raised part, 6 ... Air supply valve, 7 ... Exhaust valve, 8 ... Spark plug, 10,21a ... Mask wall, 12 ... Air supply port.

Claims (1)

[Claims] 1. A pair of air supply valves and a pair of air supply ports are arranged symmetrically with respect to a plane including a cylinder axis, and the shape of each air supply valve and the shape of each air supply port are substantially the same. And a mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between each air supply valve and the exhaust valve, and each mask wall surrounds each air supply valve peripheral portion and valve located on the exhaust valve side. Two cycles in which the openings of the seats are closed for the full opening period of the air supply valve, the mask walls are arranged symmetrically with respect to the plane including the cylinder axis, and the shapes of the mask walls are formed to be substantially the same. Internal combustion engine.