JPH0249921A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To suppress generation of NOx by furnishing two air supply passages coupled with a combustion chamber via respective air supply valves, forming a mask wall along that peripheral part of each air supply valve on its exhaust valve side, and by arranging an air supply control valve closing at low load on No.2 air supply passage. CONSTITUTION:No.1, No.2 air supply valves 6a, 6b are arranged on an inner wall surface portion 3b constituting a bottom wall surface of a groove 5, which is provided on the inner wall surface 3a of a cylinder head 3, and No.1, No.2 exhaust valves 7a, 7b are arranged in an approx. flat inner wall surface portion 3c except the mentioned groove 5. These wall surface portions 3b, 3c are connected together via the surrounding wall 9 of this groove 5, but this surrounding wall 9 is positioned very close to the peripheries of the abovementioned air supply valves 6a, 6b, being composed of a pair of mask walls 9a stretching in the form of a circular arc along their perimeters and also new air guide walls 9b, 9c. An air supply control valve, not illustrated, closed when the engine bears a low load is interposed on No.2 air supply passage in communication with No.2 air supply port 12b.

Description

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

[Conventional technology]

The first air supply passage includes a first air supply passage connected to the combustion chamber via the first air supply valve, and a second air supply passage connected to the combustion chamber via the second air supply valve. A two-stroke internal combustion engine is known in which an air supply control valve that closes during low-load engine operation is disposed in two air supply passages (see Japanese Patent Laid-Open No. 61-291427). In this two-stroke internal combustion engine, after the exhaust valve is opened and blowdown occurs, the burned gas flowing back into the combustion chamber generates a swirling flow around the cylinder axis within the combustion chamber. When such a swirling flow is generated, as the piston descends, the burned gas also swirls and descends. Next, the intake valve opens, and fresh air is supplied into the combustion chamber from almost the entire circumference of the intake valve. In this way, the fresh air flows in from almost the entire circumference of the intake valve, so the inflow speed of the fresh air is slow, and therefore the fresh air collects in the area above the burnt gas without stirring the swirling burnt gas. Therefore, the inside of the combustion chamber becomes stratified. As a result, since fresh air exists around the ignition frame, good ignition can be achieved.

[Problem to be solved by the invention]

However, when the combustion chamber is stratified in this way, the fuel component in the fresh air that exists at the interface between the high-temperature burnt gas and the low-temperature fresh air is heated by the high-temperature burnt gas, so the fuel at this interface This results in the problem of self-ignition. Also, since the burnt gas is given a swirling flow, some heat escapes to the cylinder inner wall surface, but the amount of heat is not very large. Therefore, when fresh air is ignited, the combustion temperature becomes quite high and a large amount There is a problem that NOx is generated. In addition, if the burnt gas and fresh air are separated, the burnt gas will not perform the internal EGR effect that reduces the combustion rate, and therefore the combustion rate will increase, causing the combustion pressure to rise and the combustion temperature to decrease. Therefore, there is a problem in that a large amount of NOx is generated from this point as well.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, the first air supply passage is connected to the combustion chamber through the first air supply valve, and the first air supply passage is connected to the combustion chamber through the second air supply valve. A mask wall is provided in the second air supply passage to close the opening between the valve seat and the peripheral edge of each air supply valve located on the exhaust valve side, and a mask wall is provided in the second air supply passage to close the opening between the valve seat and the peripheral edge of each air supply valve located on the exhaust valve side. A supply air control valve is installed.

[For production]

The first step is to close the air supply control valve during low engine load operation.
The flow rate of fresh air flowing through the air supply passage is increased. In addition, because a portion of the opening of the air intake valve is closed by the mask wall, the flow rate of fresh air flowing in from the air intake valve becomes even faster, and since this fresh air reaches the top of the piston, it is separated from the burned air. Even when the engine is operating at low load, the burnt gas is sufficiently mixed with the burnt gas, and the fresh air provides strong turbulence to the burned gas, increasing the amount of heat escaping to the cylinder inner wall surface. Therefore, the combustion temperature decreases, and the burned gas effectively acts as internal EGR gas.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block 1,
Reference numeral 3 indicates a cylinder head fixed on the cylinder block 1, and reference numeral 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. A groove 5 is formed on the inner wall surface 3a of the cylinder head, and a first intake valve 6 is formed on the inner wall surface portion 3b of the cylinder head forming the bottom wall surface of the groove 5.
A pair of air supply valves consisting of a second air supply valve 6b and a second air supply valve 6b are arranged. 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 consisting of a first exhaust valve 7a and a second exhaust valve 7b are arranged on this cylinder head inner wall surface portion 3C. Ru. 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 peripheral wall 9 includes a pair of masks Q9a arranged very close to the peripheral edges of each of the air supply valves 6a and 6b and extending in an arc shape along the peripheral edges of each of the air supply valves 6a and 5b, and a pair of masks Q9a that are arranged in close proximity to the peripheral edges of each of the air supply valves 6a and 5b, .

6b, and a pair of fresh air guide walls 9c located between the peripheral wall of the cylinder head inner wall surface 3a and each intake valve 6a, 6b. Each mask wall 9a extends toward the combustion chamber 4 below the intake valves 6a, 6b at their maximum lift position, and therefore
・Each air supply valve 6a, 6b periphery and valve seat 1 located on the 7b side
The opening between 0 and 0 is closed by the mask wall 9a throughout the opening period of the air supply valves 6a and 6b. Further, each fresh air guide wall 9b, 9c is located in substantially the same plane, and furthermore, these fresh air guide walls 9b.

9C extends approximately parallel to a line connecting the centers of both intake valves (3a and 6b).The ignition plug 11 is arranged on the cylinder head inner wall surface 3C so as to be located at the center of the cylinder head inner wall surface 3a. ing.

Inside the cylinder head 3 there is a first air supply port 12a and a second air supply port 12a.
a pair of air supply boats consisting of the first air supply boat) 12b;
A pair of exhaust ports consisting of the exhaust port 13a and the second exhaust boat 13b are formed.

The second exhaust port 13b is aligned with the first air supply boat 12a and extends on the opposite side from the first air supply boat 12a. On the other hand, the first exhaust port) 13a is the second air supply port) 12b.
and extends on the opposite side from the second air supply port 12b. Further, the first air supply port 12a and the second exhaust port 13a are tangentially connected in the combustion chamber 4 toward the same peripheral direction of the combustion chamber 4, and the second air supply port 12b and the second exhaust port 13b is tangentially connected within the combustion chamber 4 toward the same peripheral direction of the combustion chamber 4 in the opposite direction.

As shown in FIG. 3, the first intake port 12a of each cylinder
are connected to the surge tank 15 via independent air supply branch pipes 14a, and the second air supply ports 12b of each cylinder are connected to the independent air supply branch pipes 14. It is connected to the surge tank 15 via b. An air supply control valve 16 is disposed within each air supply branch pipe 14b, which closes during low engine load operation and opens during high engine load operation. The surge tank 15 is connected to an air cleaner via an engine-driven mechanical supercharger 17 and a throttle valve (not shown).

Referring again to FIGS. 1 and 2, the cylinder head 3
There is an air blast valve 20 that blows out fuel together with compressed air.
is installed. This air blast valve 20 includes a compressed air passage 22 having a nozzle opening 21 formed at its tip, a valve element 23 for controlling the opening and closing of the nozzle opening 21, an actuator 24 for driving the valve element 23, and a compressed air passage. It consists of a compressed air passage 25 branched from 22 and a fuel injection valve 26 that injects fuel into the compressed air passage 25.

The compressed air passage 25 is connected to a discharge port of an engine-driven air pump 27, so the compressed air passage 2225 is filled with compressed air.

FIG. 4 shows the air supply valves 6a and 6b and the exhaust valve 7a.

7b shows the valve opening period. As shown in FIG. 4, the exhaust valves 7a and 7b open before the intake valves 6a and 6b, and the exhaust valves 7a and 7b close before the intake valves 6a and 5b. Further, fuel is injected from the fuel injection valve 26 into the compressed air passage 25 before the bottom dead center. Next is the exhaust valve after bottom dead center? a.

Before and after the valve 7b closes, the on-off valve 23, that is, the air blast valve 20, is opened. At this time, fuel is injected into the combustion chamber 4 from the nozzle port 21 together with compressed air.

As described above, the air supply control valve 16 is closed when the engine is operating at low load. Therefore, at this time, the air supply valves 6a, 6
b opens, the air supply branch pipe 14a and the first air supply port) 1
Fresh air is supplied only from the first air supply valve 6a via 2a. In this way, when the engine is operating at low load, the first air supply port 12
Since fresh air is supplied only from the first air supply port 12a, the fresh air flows at a high speed within the first air supply port 12a. On the other hand, air supply valves 5a and 5b
When the valve opens, fresh air flows into the combustion chamber 4 from the first air supply port 12a, but the mask wall 9a
, fresh air flows into the combustion chamber 4 from the opening of the air supply valve 6a on the opposite side to the mask wall 9a. Next, this fresh air changes direction at the top surface of the piston 2 as shown by the arrow S in FIG. 5 and reaches the exhaust valve. Head to a, 7b. As a result, the burnt gas in the combustion chamber 4 is pushed out into the exhaust boats 13a, 13b by this scavenging airflow, thus performing loop scavenging. In this way, when the engine is operating at low load, fresh air is supplied only from the first air supply port 12a, and a considerable portion of the opening of the air supply valve 6a is masked.
Since the intake valve 6a is closed by l 9 a, the inflow speed of fresh air into the combustion chamber 4 from the opening of the intake valve 6a becomes faster, thus causing a scavenging air flow S+:) to flow inside the combustion chamber 4 at high speed. Become. Furthermore, 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 the air supply valve 6a is
Among the openings formed between the valve seat 10 and the exhaust valve 7b,
Approximately 1/3 of the openings located on the sides are closed by the mask wall 9a, and fresh air is supplied from approximately 2/3 of the openings located on the opposite side to the exhaust valve 7a. Furthermore, in this embodiment, the air supply valve 6
The fresh air flowing in from a is guided downward along the inner wall surface of the cylinder by the fresh air guide wall 9b9C. Therefore, in this embodiment, when the air supply valve 6a is opened, most of the fresh air flows along the inner wall surface of the cylinder toward the top surface of the piston 2, thus achieving good loop scavenging.

In this way, when the engine is operating at low load, the scavenging air flow S flows through the combustion chamber 4 at a high speed, so that the high temperature residual gas in the combustion chamber 4 and the low temperature fresh air are sufficiently mixed, and thus the residual gas temperature decreases. I am forced to do it. Furthermore, since the residual gas is strongly disturbed by fresh air, the heat of the residual gas escaping to the cylinder inner wall surface increases, and thus the residual gas temperature becomes even lower.

Since the residual gas temperature decreases in this way, the combustion temperature decreases, and since the residual gas acts as an internal EGR, NO
The generation of X will be suppressed.

On the other hand, during high-load engine operation, the air supply control valve 16 is opened, so that at this time both air supply ports H2a, 1
Fresh air is supplied from 2b. On the other hand, since no mask wall is provided for the exhaust valves 7a and 7b, the exhaust valves 7a and
When the valve 7b opens, the burnt gas in the combustion chamber 4 is immediately discharged to the exhaust port 13a13b, that is, a strong blowdown occurs, and the pressure in the combustion chamber 4 is immediately reduced. Therefore, good scavenging is performed by strong loop scavenging using fresh air flowing in from the air supply ports 12a and 12b, resulting in high engine output.

Another embodiment is shown in FIG. In this embodiment, a check valve 30 made of a reed valve that allows flow only from the surge tank 15 into the combustion chamber 4 is arranged in the air supply branch pipe 14a of each cylinder. As shown in FIG. 4, when the piston 2 passes the bottom dead center and begins to rise, the exhaust valves 7a and 7b close first, and then the air supply valves 5a and 5b close. So the exhaust valve? a.

Fresh air compressed in the combustion chamber 4 is pushed out into each air supply boat 12a, 12b via the air supply valve 6a, 6b after the air supply valve 7b closes until the air supply valve 5a, 5b closes. It will be done. As a result, immediately after the air supply valves 6a, 6b close, the pressure within each air supply port 6a, 6b becomes temporarily high. When the engine is operating at low load, the intake control valve 16 is closed, but since there is some leakage, the pressure inside the second air supply boat 12b drops quickly. On the other hand, the check valve 30 completely blocks the flow of fresh air from the first air supply port 12a toward the surge tank 10, so that the inside of the first air supply boat 12a is maintained at a high pressure. Therefore, when the intake valves 6a and 6b open next time, the high-pressure fresh air accumulated in the first air intake boat 12a is injected into the combustion chamber 4 at high speed, and this fresh air causes residual gas to be removed. A strong turbulence is applied to the air, and at the same time, fresh air and residual gas are strongly mixed. As a result, the combustion temperature is further reduced, and thus the generation of NOx can be further suppressed.

FIGS. 7 and 8 show an embodiment in which the backflow of exhaust gas from the exhaust port 13a into the combustion chamber 4 is utilized to further promote mixing of fresh air and residual gas. In this embodiment, an air supply control 40 is arranged in the second air supply port 12b, which closes during low engine load operation and opens during high engine load operation.
An exhaust control valve 41 is disposed within the second exhaust port 13b, which closes during low engine load operation and opens during high engine load operation.

Further, a fuel injection valve 42 is arranged in the first air supply boat 12a, and fuel is supplied from the fuel injection valve 42 to the first air supply port).
The air is injected onto the back surface of the air supply valve 6a of the air supply valve 12a. The rest of the structure is the same as the embodiment shown in FIGS. 1 and 2, so the explanation will be omitted.

FIG. 9 shows the valve lifts of the intake valves 5a, 6b and the exhaust valves 7a7b and the pressure changes in the exhaust boat 13a. When the exhaust control valve 41 is open, the exhaust port) 13
The pressure inside b also changes as shown in FIG. That is, when the piston 2 descends and the exhaust valves 7a and 7b open, the high-pressure burnt gas in the combustion chamber 4 flows into the exhaust port 13a, and when the exhaust control valve 41 is open, the exhaust port 13a=13.
b. As a result, the pressure inside the exhaust boats 13a, 13b temporarily becomes positive pressure, as shown in FIG.

This positive pressure propagates downstream in the exhaust ports 13a and 13b, is reflected at the confluence of the exhaust passages of each cylinder, and then returns to the exhaust ports 13a and 13b as negative pressure. . Therefore, as shown in FIG. 9, when positive pressure is generated, negative pressure is subsequently generated.

Next, this negative pressure propagates downstream again within the exhaust ports 13a and 13b and is reflected at the confluence of the exhaust passages of each cylinder, and this time becomes positive pressure and flows through the exhaust ports 13a and 13b.
Come back inside. When the exhaust valves 7a and 7b are opened in this way, the exhaust ports 43a, 1 are opened as shown in FIG.
Positive pressure and negative pressure are alternately generated in 3b, causing exhaust pulsation.

When the engine is operating at low load, both the air supply control valve 40 and the exhaust control valve 41 are closed, as described above.

So the exhaust valve? When valves a and 7b open, the burnt gas in the combustion chamber 4 is discharged into the first exhaust bow 13a, and the pressure in the combustion chamber 4 rapidly decreases. Next, when the pressure in the first exhaust port 13a becomes positive due to exhaust pulsation, the exhaust gas in the first exhaust port 13a flows back into the combustion chamber 4, and the exhaust gas in the first exhaust port 13a flows back into the combustion chamber 4.
A swirling flow is generated in the combustion chamber 4 as indicated by X in the figure and FIG. 10. Next, when the intake valves 6a and 6b open, fresh air flows into the combustion chamber 4 at a high speed only from the first intake port 12a, as shown by arrow S in FIG.

Therefore, in this embodiment, the swirling flow X is generated by the exhaust gas flowing backward during low-load engine operation, and the scavenging flow S flows at high speed in the combustion chamber 4, further promoting the mixing of residual gas and fresh air. . Furthermore, since the residual gas is swirled and turbulent by the fresh air, the amount of heat escaping to the inner wall surface of the cylinder increases, and the temperature of the residual gas further decreases. As a result, the combustion temperature is further reduced, and the generation of NOx is greatly suppressed. Also in this embodiment, since no mask wall is provided for each exhaust valve 7a, 7b, the exhaust valves 7a, 7b open even when the combustion pressure is high, such as during high engine load operation. The burnt gas immediately flows out into the exhaust port H3a, 13b. Therefore, the scavenging efficiency is improved, resulting in higher engine output.

Still another embodiment is shown in FIG. 11 and FIG. 12. In this embodiment, an air suction tube 43 is disposed within the first exhaust port 13a. The opening at the tip of the air suction tube 43 is closed by the back surface of the exhaust valve 7a when the exhaust valve 7a is closed, and is oriented toward the periphery of the combustion chamber 4 when the exhaust valve 7a is open. Placed. This air suction tube 43 is connected to, for example, an air cleaner (not shown) via a reed valve 44 that allows flow only toward the tip opening.

After the exhaust valve 7a is opened, when negative pressure is generated in the first exhaust bow 13a due to exhaust pulsation, air is ejected from the opening at the tip of the air suction tube 43, and as shown in FIGS.
As shown by Y in Figure 3, this air causes the combustion chamber 4 to
A swirling flow is generated within. The swirling direction of this swirling flow Y is the same direction as the swirling flow X. Therefore, a strong swirling flow is generated in the combustion chamber 4, and the mixing of fresh air and residual gas becomes even better. Furthermore, when the air ejected from the air suction tube 43 is supplied into the combustion chamber 4, the amount of exhaust gas flowing back into the combustion chamber 4 decreases, and therefore the gas temperature in the combustion chamber 4 decreases, which further reduces NOx. Occurrence can be controlled. Furthermore, the occurrence of self-ignition can be controlled by lowering the gas temperature within the combustion chamber 4,
Furthermore, since the ignition plug 11 can be scavenged by the air ejected from the air suction tube 43, good ignition can be ensured. Furthermore, by improving ignitability, it is possible to expand the lean limit.

〔Effect of the invention〕

Since fresh air flows into the combustion chamber at high speed when the engine is operating at low load, residual gas and fresh air are mixed well, and the residual gas is strongly turbulent by the fresh air. As a result, the combustion temperature decreases because the residual gas temperature decreases,
In this way, the generation of NOX can be suppressed.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of the two-stroke internal combustion engine taken along line I-I in Figure 2, Figure 2 is a diagram showing the inner wall surface of the cylinder head, and Figure 3 is the two-stroke internal combustion engine in Figure 1. 4 is a diagram showing the opening period of the supply/exhaust valve, air blast valve, etc., FIG. 5 is a side sectional view showing the position where the piston is lowered, and FIG. 6 is a diagram showing another embodiment. FIG. 7 is a side sectional view of another embodiment of the two-stroke internal combustion engine taken along the line ■-■ in FIG. 8, and FIG. 8 is the cylinder head of FIG. 7. A diagram showing the inner wall surface of
Fig. 9 is a diagram showing the pressure change inside the exhaust port, Fig. 10 is a side sectional view showing the position where the piston has descended, and Fig. 11 is a diagram showing the pressure change inside the exhaust port.
The figure is a side cross-sectional view of yet another embodiment taken along the line XI-XI in Figure 12, Figure 12 is a view showing the inner wall surface of the cylinder head in Figure 11, and Figure 13 is a view of the piston being lowered. FIG. 5a, 5b...Air supply valve, 7a, 7b...Exhaust valve,
9a... Mask wall, 12a... First air supply port, 12b... Second air supply port, 13a... First exhaust boat, 13b... Second exhaust boat, 16.40.
...Air supply control valve, 41...Exhaust control valve.

Claims (1)

[Claims] A first air supply passage connected to the combustion chamber via the first air supply valve; a second air supply passage connected to the combustion chamber via the second air supply valve; A mask wall is provided to close the opening between the peripheral edge of each air supply valve located on the valve side and the valve seat, and a second
A two-stroke internal combustion engine that has an air supply control valve located in the air supply passage that closes when the engine is operating at low load.