JPS63205415A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the combustivity by specifying the valve timing, as well as furnishing a means to make a part of the exhaust gas reflow in to a combustion chamber while swirling around the cylinder shaft, in an engine in which suction valves and exhaust valves are arranged at a cylinder head. CONSTITUTION:When a six-cylinder engine is used, two suction valves 24 and two exhaust valves 26 are furnished at a cylinder head 14 of each cylinder respectively. One of two exhaust ports 22 is formed in almost a straight line to the branch pipe 50a of an exhaust maniford 50, opened in the tangent direction at a combustion chamber 18, while the other exhaust port 22 is formed making an angle. And when the exhaust gas is released and a part of it is made reflow in to the combustion chamber 18, it reflows in through the exhaust port 22 formed almost in a straight line by the effect of inertia, and a swirl S can be formed in the combustion chamber 18. Further more, the valve timing is set to open the exhaust valves 26 of the other cylinder, in the period from the closing of the suction valves 24 to the closing of the exhaust valves 26 of one cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-stroke internal combustion engine in which a cylinder head is provided with an intake valve and an exhaust valve.

[Conventional technology]

Japanese Patent Publication No. 60-5770 discloses an open chamber type two-stroke internal combustion engine having an intake valve and an exhaust valve. In this two-stroke internal combustion engine, the intake valve and exhaust valve open almost simultaneously when the piston is at bottom dead center, and the fresh air flowing in from the intake valve is directed downward, reverses at the top of the piston, and enters the cylinder. It forms a vertical U-shaped flow. The interface between fresh air and exhaust air is first near the intake valve, then in the lower middle part of the cylinder, and then moves closer to the exhaust valve, such that exhaust and fresh air are replaced throughout the cylinder. It has become.

However, although such a two-stroke internal combustion engine has no problems in a high load range, it has problems with combustion at idle or with a light load. At idle or in a light load range, the amount of fresh air supplied is small and a large amount of exhaust gas remains in the cylinder, so the fresh air is dispersed into the residual exhaust gas and becomes thinner, causing the fresh air to ignite the cylinder head. It cannot be collected near the plug.

That is, in a vertical U-shaped flow within the cylinder, the main stream of fresh air moves downward in the cylinder. For this reason, ignition by the spark plug provided in the cylinder head and generation of a flame kernel are inhibited, and flame propagation speed is reduced, making misfires and combustion fluctuations more likely to occur.

Furthermore, it is conventionally known to form a swirl around a cylinder axis in intake air. For example, U.S. Pat.
No. 43928 supplies air from two oppositely arranged intake valves to form a swirl around the cylinder axis. The exhaust valve is located in a subchamber formed at the center of the top of the cylinder. Therefore, in the internal combustion engine disclosed in this patent, combustion starts in the pre-chamber and then spreads into the swirling cylinder, causing swirls in the exhaust gas and residual exhaust gas. It does not create stratification between gas and fresh air.

The applicant of this application previously discovered that during low loads including idle, part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened is re-introduced into the combustion chamber while swirling around the cylinder axis. We proposed a two-stroke internal combustion engine that can perform stratified charge combustion by collecting fresh air on the cylinder head side against residual exhaust gas on the cylinder head side.

[Problem that the invention seeks to solve]

As mentioned above, in a two-stroke internal combustion engine, exhaust gas remains in the combustion chamber because exhaust gas is exhausted by scavenging, and at idle or in a light load range, the ratio of fresh air supplied to the residual exhaust gas in the combustion chamber becomes small, resulting in combustion failure. There was a problem with stability. The present invention, as described in the above-mentioned prior application, burns a part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened, especially under operating conditions with a small amount of fresh air, such as when idling or in a light load range. The air is swirled around the cylinder axis and re-introduced into the chamber to form a stratification of fresh air and residual exhaust gas, and the formed stratification can be maintained until the piston is raised; The purpose of this is to enable the ignition plug to easily ignite a rich air-fuel mixture layer formed near the cylinder head. In particular, in order to swirl some of the exhaust gas discharged from the exhaust port when the exhaust valve opens and re-enter the combustion chamber while swirling it around the cylinder axis, it is necessary to wait until exhaust blowdown occurs when the exhaust valve opens. It is preferable to open the intake valve after a predetermined period of time has elapsed, and if there is exhaust blowdown from another cylinder while the intake valve is open, stratification of fresh air and exhaust gas formed in the cylinder may occur. A problem arises in which the image disappears.

[Means for solving problems]

A two-stroke internal combustion engine according to the present invention includes a fresh air supply system having a supercharging means, an intake valve and an intake valve that are driven in synchronization with a crank angle to open and close an intake port and an exhaust port provided in a cylinder head portion. In a two-stroke internal combustion engine having an exhaust valve, a means is provided for causing part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened to re-enter the combustion chamber while swirling it around the cylinder axis,
Three cylinders are connected by one exhaust manifold, and the pulp timing is such that the exhaust valve opens, then the intake valve opens, then the intake valve closes, then the exhaust valve closes, and the intake valve closes. This is characterized in that the exhaust valves of other cylinders are set to open between the time the exhaust valve closes and the exhaust valve closes.

[For production]

According to the present invention, stratification is achieved in the following manner at least in a low load range including idle. That is, when the exhaust valve opens during the downward stroke of the piston, a weak exhaust blowdown occurs, and the inside of the exhaust port becomes positive pressure. The exhaust blowdown ends in a predetermined short time, and as the piston continues to descend, the inside of the cylinder becomes negative pressure with respect to the exhaust port, and a portion of the exhaust gas that was once exhausted flows back into the combustion chamber. In the present invention, a means for swirling the re-inflowing exhaust gas around the cylinder axis is provided, and the exhaust gas is swirled around the cylinder axis within the combustion chamber. After that, the intake valve opens. During idling and in a light load range, the amount of fresh air supplied is small, and the fresh air flows in relatively slowly. Therefore, the fresh air that slowly flows in slowly rides on the exhaust gas that is swirling around the cylinder axis, and the fresh air collects near the cylinder head while riding on the exhaust swirl. Therefore, there is fresh air on the cylinder head side and residual exhaust gas on the piston side, which forms a stratification.

Additionally, three cylinders are connected by one exhaust manifold, and combustion cycles are performed in these cylinders at 120 degree intervals. The opening period of the exhaust system is greater than 120 degrees, so that before the exhaust valve of one cylinder closes, the exhaust valve of the next cylinder opens. If there is exhaust blowdown when the next cylinder's exhaust valve opens, exhaust gas can flow to the exhaust manifold and to the previous cylinder that is open.

At this time, the intake valve of the previous cylinder is closed, so exhaust gas does not flow back into the intake port of the previous cylinder due to this exhaust blowdown. In this case, the blowdown exhaust gas is temporarily stored in the previous cylinder,
This exhaust gas re-flows into the next cylinder while swirling. Therefore, the expansion space for the exhaust gas is increased, and the blowdown of the exhaust gas is completed in a short time.
The opening timing of the intake valve can be made earlier by that amount.
This allows for improved output.

〔Example〕

Fig. 1 is a vertical cross-sectional view passing through the intake valve and exhaust valve of Fig. 3, and Fig. 2 is a 6-cylinder two-citrate internal combustion engine 1 to which the present invention is applied.
FIG. 3 is a diagram showing the vicinity of the combustion chamber of one cylinder in FIG. 2 in detail. The engine body 10 is composed of a cylinder block 12 and a cylinder head 14, and is located above a piston 16.

□ Combustion chamber 18 is formed. An intake port 20 and an exhaust port 22 are formed in the cylinder head 14 in a facing arrangement,
An intake valve 24 and an exhaust valve 26 each consisting of a poppet valve.
It has the following.

As shown in FIG. 3, two intake valves 24 and two exhaust valves 26 are provided, and a spark plug 28 is inserted into the combustion chamber.
It is provided approximately in the center of 8. Exhaust valves 26 are designated Es and E, while intake valves 24 are designated FA and FB. This indicates that the functions of the intake valves 24 are different from each other, and henceforth, the intake valve represented by FA will be referred to as a low-load intake valve, and the intake valve represented by FB will be referred to as a high-load intake valve. Make it.

As shown in FIGS. 2 and 3, the cylinder head 1
Two intake manifolds 30 and 32 are attached to 4. Each branch pipe of one intake manifold 30 is connected to the intake port 20 on the side where the low-load intake valve FA is arranged, and each branch pipe of the other intake manifold 32 is connected to the intake port 20 on the side where the high-load intake valve FB is arranged. Connected to port 20. Both intake ports 20 extend substantially parallel to each other in a direction substantially perpendicular to the longitudinal axis of the engine, and are located on either side of the center line of the cylinder in a direction substantially perpendicular to the longitudinal axis of the engine, with at least one of the low-load intake valves FA being arranged. The side intake port 20 opens tangentially into the combustion chamber 18 . A fuel injection valve 34 is arranged in each branch pipe of the intake port 20 or the intake manifolds 30 and 32, respectively. Further, a check valve 36 made of a reed valve is arranged upstream of the fuel injection valve 34.

As shown in FIG. 2, air is taken in from an air cleaner 38, its flow rate controlled by a throttle valve 40, and supercharged by a supercharger 42. Supercharger 4
An intercooler 44 is disposed downstream of the two intake eyebrows 30 and 32, and both of the two intake eyebrow bolts 30 and 32 are connected to this intercooler 44. The supercharger 42 can be a mechanical supercharger driven by the output of an engine such as a Roots pump. Further, an air flow meter 46 is arranged upstream of the throttle valve 40.

A butterfly-type intake control valve 48 is disposed at a gathering portion of the intake manifold 32 on the high-load side. While the intake valve 24 and the exhaust valve 26 are driven by a camshaft in synchronization with the crankshaft of the engine, the intake control valve 48 is opened and closed according to the load and rotational speed of the engine. The intake control valve 48 is closed during low load, including at least when the engine is idling, and therefore, at this time, air is supplied only from the intake manifold 30 on the low load side.

The intake control valve 48 is opened during high engine loads, so that at this time air is supplied through both the high load side intake manifold 32 and the low load side intake manifold 30.

As shown in FIG. 2, two exhaust manifolds 50 are provided for six cylinders, one exhaust manifold 5
0 is connected to the 1st, 2nd, and 3rd cylinders, and the other exhaust manifold 50 is connected to the 4th, 5th, and 6th cylinders. A catalyst 52 is disposed at each gathering portion of each exhaust manifold 50, and each exhaust manifold 50 further passes through a muffler 54 and terminates independently of each other. In this case, the firing order is
The order is the 1st, 6th, 2nd, 4th, 3rd and 5th cylinders. Each exhaust manifold 50 has three branch pipes, so one branch pipe is connected to the exhaust port 22 for one cylinder.

FIG. 3 shows one such branch 50a, which is mounted approximately at right angles to the longitudinal axis of the engine. Incidentally, each cylinder has two exhaust ports 22, and these two exhaust ports 22 are merged into one port within the cylinder head 14. The exhaust port 22 on which the exhaust valve 26, which is indicated with Es, is disposed is formed approximately at right angles to the longitudinal axis of the engine so as to be in line with the branch pipe 50a, and opens tangentially into the combustion chamber 18. do. The other exhaust port 22 merges at an angle to form a side exhaust port 22 formed approximately perpendicular to the longitudinal axis of the engine. The configuration of the exhaust port 22 is such that the exhaust gas exhaust speed can be increased by having two exhaust valves 26, and the exhaust gas is exhausted to the exhaust port 22 and the exhaust manifold 50, and a part of it is When re-inflowing into the combustion chamber 18, there is almost no re-inflow from the exhaust port 22 on the angled side due to the effect of inertia flowing in a straight line. This re-inflowing exhaust gas mainly passes through the exhaust port 22 of the cylinder and is configured to form a swirl S around the cylinder axis.

This swirl S is in a clockwise direction as viewed in FIG. The exhaust port 22 (on the Es side) that forms this swirl S faces in a straight line with the intake port 20 having the intake valve FB on the high load side, and is opposed to the intake port 20 having the intake valve FA on the low load side. They are arranged to face each other with an offset across the center line. Therefore, when fresh air supplied from the intake port 20 having the intake valve FA on the low load side generates a swirl at low load, the swirl is generated in the same clockwise direction as the swirl S of the re-inflowing exhaust gas. become. When the load is low, the intake control valve 48 is closed, so there is no flow of fresh air from the intake port 20 on the high load side facing the exhaust port 22 that forms the swirl S.
There is nothing to disturb the swirl S of the re-entering exhaust gas (thus, the swirl S can be maintained).

As shown in FIG. 3, a mask 56 is formed on the inner wall of the cylinder throat 14, that is, on the earthen wall of the combustion chamber 18. As shown in FIG. This mask 56 traverses the combustion chamber 18 substantially parallel to the longitudinal axis of the engine, and is formed by a steeply rising terrace-like ridge in most of its center, with a gentle slope at the side edges. The spark plug 28 is placed on the intake valve 24 side.

This mask 56 also helps form the swirl S. That is, not only is there almost no exhaust gas re-inflowing from the exhaust valve (E) 26 as described above, but even if there is inflow, it is blocked by the mask 56. The re-inflowing exhaust gas from the exhaust valve Es tends to swirl by itself as described above, and furthermore, if it deviates from the swirl and flows toward the center of the combustion chamber 18, this is also blocked by the mask 56. Therefore, the re-inflowing exhaust gas from the exhaust valve Es has no choice but to pass through the gently sloped region of the side edge of the mask 56, and increasingly flows along the combustion chamber 18 and the cylindrical surface of the cylinder. Also, during high loads, two intake ports 20
The fresh air supplied in parallel from the exhaust port 22 hits the mask 56, is directed downward, and is prevented from blowing through to the exhaust port 22. Since the spark plug 28 is located on the side of the intake valve 24, it can come into contact with a richer air-fuel mixture even when the load is low.

To explain the pressure of exhaust gas here, when the engine is under low load, there is a weak exhaust blowdown immediately after the exhaust valve 26 is opened, and the inside of the exhaust port becomes positive pressure, and the exhaust pressure in the combustion chamber 18 rapidly decreases. do. When the pressure in the combustion chamber 18 falls below the pressure at the exhaust port due to the downward movement of the piston 16, a portion of the exhaust gas discharged from the combustion chamber due to exhaust blowdown is combusted due to the pressure difference between the exhaust port 22 and the combustion chamber 18. It will now flow back into chamber 18 (backflow).

Thus, when the engine is under low load, there is a backflow of exhaust gas into the combustion chamber immediately after the weak exhaust blowdown.

In the present invention, the exhaust gas flowing back into the combustion chamber is
As shown in the figures and FIG. 3, a swirl S around the cylinder axis is formed within the combustion chamber 18. Conventionally, it has been proposed to generate a swirl in the intake air taken in from the intake port, but a major feature of the present invention is to generate a swirl in the exhaust gas flowing back.

Figure 4 shows the opening period (FO) of the intake valve 24 and the opening period (EO) of the exhaust valve 26, which are driven in synchronization with the crankshaft.
). In a two-stroke internal combustion engine, there are only two strokes: an expansion stroke in which the piston 16 descends from top dead center TDC to bottom dead center BDC, and a compression stroke in which it ascends from bottom dead center BDC to top dead center TDC. The intake and suction are performed near the bottom dead center BDC between these two strokes, and basically include scavenging to perform gas exchange while pushing out the exhaust gas with fresh air pushed in by the supercharger 42. When the load is high, the amount of fresh air and fuel is large, so there is little exhaust gas remaining in the cylinder, so there are few combustion problems, but when the load is idling and the load is low, the amount of fresh air and fuel is small, and the residual exhaust gas is small. Combustion must be carried out in a large amount of gas, and when fresh air and exhaust gas mix, the air-fuel ratio becomes diluted, making ignition combustion extremely difficult.

In the present invention, the exhaust valve 26 opens at a point 80 degrees before bottom dead center BDC, and since the downward speed of the piston 16 is fast at this time, the pressure in the combustion chamber 18 decreases after a weak exhaust blowdown at idle and low load. The back pressure in the exhaust port 22 and the negative pressure in the combustion chamber 18 ensure that a backflow of exhaust gas occurs. The opening period of the exhaust valve 26 is set to be 120 degrees or more, and in FIG.
degree, and closes at 60 degrees after bottom dead center BDC. In addition, the intake valve 24 is operated at a point in time when a backflow of exhaust gas occurs after the exhaust valve 26 opens, for example, 70 minutes before bottom dead center BDC.
It opens at 40 degrees and closes at 40 degrees after bottom dead center BDC before the exhaust valve 26 closes.

The lower exhaust manifold 5o in FIG. 2 is connected to the 1st, 2nd and 3rd cylinders which are out of phase by 120 degrees, and is independent from the cylinder group connected to the other exhaust manifold 5o. Assuming that FIG. 4 shows the valve timing of the first cylinder, the opening period of the exhaust valve 26 of the second cylinder, which is the next combustion cylinder, is shown by EO2, and furthermore, the opening period of the exhaust valve 26 of the second cylinder, which is the next combustion cylinder, is shown as EO2. The opening period of the exhaust valve 26 is indicated by EO3. The opening timings of these exhaust valves 26 are shifted by 120 degrees, and the opening timing of the exhaust valve 26 of the second cylinder is 40 degrees after the bottom dead center BDC of the first cylinder. Therefore, after the exhaust valve 26 of the first cylinder opens, the intake valve 24 of the first cylinder opens, and after the intake valve 24 of the first cylinder closes, the exhaust valve 26 of the first cylinder closes. After the intake valve 26 of the first cylinder closes and before the exhaust valve 26 of the first cylinder closes, the exhaust valve 26 of the other second cylinder opens.

FIG. 5 is a diagram illustrating the backflow and swirl generation of exhaust gas during idle and low load, and the resulting stratification of fresh air and residual exhaust gas. At this time, the intake control valve 48 is closed and fresh air is supplied to the low-load intake valve (
FA) 20 side only. This supply of fresh air is slow because the amount of air is small and the supercharging pressure is low. As shown in FIG. 5(a), when the temperature reaches 80 degrees before the bottom dead center BDC, the exhaust valve 26 opens and a weak exhaust blowdown with a pressure P occurs. This exhaust blowdown ends in a short time when the engine is idling or under low load. for example,
The pressure at the exhaust port 22 during weak exhaust blowdown at idle and low load is instantaneously 2-3 kg/
cnl, but it soon drops to about 1.05 kg/cJ and stabilizes while maintaining positive back pressure.

As the piston 16 descends, the inside of the combustion chamber 18 becomes negative pressure,
As shown in FIG. 5(b), the exhaust gas re-inflows in the direction of the arrow Q, and a swirl S of the exhaust gas is formed within the combustion chamber 18 due to the structure of the exhaust port 22 and the swirl forming means such as the mask 56. be done.

7 Foreshock 0 degrees before bottom dead center BDC, low load intake valve (FA)
20 opens. The fresh air is metered by the throttle valve 40, and the supercharging pressure of the supercharger 42 is also relatively low. In addition, since it takes time for the intake valve 24 to substantially fully open, fresh air does not flow in immediately, and even when the low-load intake valve (FA) 20 is opened, the exhaust gas backflows and swirls are formed. continues. In this way, the formation of the exhaust swirl continues for a considerable period of time, and this swirl is formed around the cylinder axis.

After that, as shown in FIGS. 5(C) and (d),
When the intake valve 24 is substantially fully opened, fresh air enters.

At this time, since the descending speed of the piston 16 is also low, almost no negative pressure is formed in the combustion chamber, and as mentioned above, the supercharging pressure is also low, so fresh air slowly enters the combustion chamber 18.

Therefore, the incoming fresh air slowly rides on the exhaust swirl and is supplied so as to rotate in the same direction as described above, so that it swirls together with the exhaust swirl on the exhaust swirl. In this way, the fresh air gathers at a portion of the 14 cylinder heads near the spark plug 28 side, that is,
Stratification of the fresh air on the nozzle 14 side to the cylinder and the exhaust gas from the piston 16 is achieved. This stratification of fresh air and exhaust gas is maintained even after the piston 16 descends to the bottom dead center, as shown in FIG. 5(e). Furthermore, piston 16
Even if it passes the bottom dead center and begins to rise, the movement speed is slow for a while, and the catalyst 52 provided in each exhaust manifold 50 prevents the pressure of the exhaust port 22 and the exhaust manifold 50 from decreasing, so that the air from the combustion chamber 18 Outflow of fresh air to the exhaust port 22, so-called blow-by of fresh air, hardly occurs.

In addition, it has been confirmed that the catalyst 52 provided in each exhaust manifold 50 has the effect of reflecting pressure during exhaust blowdown, and this reflected pressure causes the piston 16 to move upward past the bottom dead center. Later, back pressure is applied to the combustion chamber 18,
Venting fresh air is effective in preventing this. Then, the intake valve 24 closes and the supply of fresh air to that cylinder ends.

The exhaust valve 26 of the second cylinder opens after the supply of fresh air ends and before the exhaust valve closes. When the exhaust valve 26 of the second cylinder opens, there is a blowdown of the exhaust gas, and the exhaust gas flows to the exhaust manifold 50.
can flow into the cylinder. Therefore, the expansion space for the exhaust gas flowing out from the second cylinder is increased, and the blowdown of the exhaust gas is completed in a short time. Therefore, the time from when the exhaust valve 26 opens to when the intake valve 24 opens can be shortened, and the opening period of the intake valve 24 can be adjusted so that sufficient fresh air is supplied even under high load. It can be set appropriately. Exhaust gas temporarily stored in the first cylinder re-enters the second cylinder when exhaust blowdown ends.
This forms a swirl. Note that in order to avoid disturbing the swirl formed in the combustion chamber 18, it is important to avoid receiving exhaust blowdown from other cylinders while the intake valve 24 is open.

Fuel is injected at an appropriate time before the intake valve 24 closes. Therefore, during idling and light load, the rich air-fuel mixture gathers at a portion of the cylinder head 14 near the ignition plug 28, and is easily ignited by the ignition plug 28, resulting in reliable combustion. Then, this air-fuel mixture and the next fresh air are on top of the exhaust gas, and are activated by the high-temperature exhaust gas, forming an active thermal atmosphere containing radical fuel components, and increasing ignitability. It is possible to carry out combustion inside.

When the load is medium to high, the intake control valve 48 is opened, so fresh air is supplied through both intake ports 24, and in particular, a large amount of air can pass through the intake port FB24 on the high load side. . When the amount of fresh air increases in this way, the swirl effect of the re-inflowing exhaust gas disappears, and a large amount of fresh air is used to perform cross-scavenging.At this time, the mask 56 that crosses the center of the cylinder head 14 Therefore, the fresh air supplied toward the exhaust port 22 hits the mask 56 and flows downward, and as a result, the fresh air first flows downward and then hits the piston 16 and flows upward, scavenging air in a U-shaped flow. conduct.

(Effects of the Invention) As explained above, according to the present invention, stratification is formed between fresh air and residual exhaust gas especially during idling and low load, and this stratification is maintained to ensure reliable exhaust purification performance. It is possible to obtain a two-stroke internal combustion engine that can perform excellent combustion and can perform good combustion from low to high loads.In particular, since exhaust blowdown can be completed quickly, the intake air can be reduced accordingly. Since the valve can be opened quickly and negative pressure can be created in the combustion chamber after exhaust blowdown, the inflow of fresh air can be helped, and a large amount of fresh air can be supplied even under high loads.

[Brief explanation of the drawing]

Figure 1 is a vertical section and top view passing through the intake valve and exhaust valve in Figure 3, Figure 2 is a diagram showing a 6-cylinder two-stroke internal combustion engine to which the present invention is applied, and Figure 3 is 1 in Figure 2. FIG. 4 is a diagram showing the vicinity of the combustion chamber of the cylinder in detail, FIG. 4 is a diagram showing valve timing, and FIG. 5 is an explanatory diagram illustrating stratification at low load. 14... Cylinder head, 16... Piston, 18
...Combustion chamber, 20...Intake port, 22.
...Exhaust port, 24...Intake valve, 26...Exhaust valve, 42...Supercharger, 48...Intake control valve, 56...Mask. Electrical Figure 1 Figure 3121 24... Intake valve 56... Mask Figure 4 Figure 5

Claims (1)

[Claims] In a two-stroke internal combustion engine that has a fresh air supply system having a supercharging means, and an intake valve and an exhaust valve that are driven in synchronization with the crank angle to open and close the intake port and exhaust port provided in the cylinder head part. , a means is provided to allow part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened into the combustion chamber while swirling it around the cylinder axis, and the three cylinders are connected by one exhaust manifold, and the valve timing is adjusted. However, after the exhaust valve opens, the intake valve opens, and after the intake valve closes, the exhaust valve closes, and after the intake valve closes until the exhaust valve closes. A two-stroke internal combustion engine characterized in that the exhaust valves of other cylinders are opened at the same time.