JPS6312818A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To stratify fresh air and exhaust gas, so as to improve the ignitionability, by setting an exhaust system adapted to control the pressure fluctuation of back pressure of an exhaust port, in light load range of an engine, and setting means which contain a mask, adapted to give a swirl to the exhaust gas blown back to a combustion chamber. CONSTITUTION:In light load range of an engine, an intake air control valve 16 is closed, and on the other hand, an exhaust gas control valve 34 is opened. Then, exhaust valves 31a, 31b are opened according to the descendent motion of a piston 3, to blow the exhaust gas toward exhaust ports 32a, 32b, respectively, and this exhaust gas is blown back to a combustion chamber 2. At this time, a swirl of exhaust gas is formed by the eccentric port 32b and a mask 5, and at the same time, the lower part of the swirl is guided to a slanting recessed part 8 of the top face of the piston 3. On the other hand, fresh air passed through a throttle valve 13 and a supercharger 14, is led slowly into the combustion chamber 2 through an intake valve 21a, and gathered near a sparking plug 4 on the cylinder head 6 side. In this way, the fresh air on the cylinder head 6 side and the exhaust gas on the piston 3 side, are stratified, and consequently, the ignitionability is improved.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a two-stroke internal combustion engine, particularly an intake valve operated in synchronization with a crank angle, which has an exhaust valve and which generates a swirl approximately around the cylinder axis. The present invention relates to a two-stroke internal combustion engine.

[Conventional technology]

Tokuko Showa 60. No. 5,770 discloses an open chamber two-stroke internal combustion engine having an intake valve and an exhaust valve. In this two-stroke internal combustion engine, both valves open when the piston is at bottom dead center. When fresh air flows in from the intake valve, it is supplied downward along the cylinder, forming a vertical loop-shaped flow. The interface between fresh air and exhaust gas moves first to the vicinity of the intake valve, then to the center of the cylinder, and then to the exhaust valve, ensuring exhaust and fresh air replacement throughout the cylinder.

However, although this two-stroke internal combustion engine does not have any problems under high load, in the idle range or light load range, the amount of fresh air is small and a large amount of exhaust gas remains in the cylinder. (spark plugs) cannot be gathered near them. That is, in a loop-shaped flow, the main stream of fresh air moves downwards in the cylinder. As a result, ignition by the spark plug provided in the cylinder head and generation of a flame kernel are inhibited, and the flame propagation speed is reduced, making misfires and combustion fluctuations more likely to occur. Also shown is a piston with a recessed portion on its top surface, but these four portions are not intended to form an exhaust swirl around the cylinder axis.

Incidentally, in US Pat. No. 4,543,928, a swirl of air is formed around the axis of the cylinder, and stratification is performed between the air on the piston side and the air-fuel mixture on the cylinder head side.

However, it does not form a swirl of exhaust gas and stratify the air between the exhaust gas and fresh air, and it is of a pre-chamber type.

[Problem that the invention seeks to solve]

The present invention provides a two-stroke internal combustion engine that has an intake valve operated in synchronization with the crank angle and that forms a swirl around the cylinder axis, even under operating conditions where the amount of fresh air is small, especially in the light load range. By collecting fresh air near the cylinder head (spark plug) before the compression stroke, a stratified state of fresh air and exhaust gas is maintained to facilitate ignition.

[Means for solving problems]

According to the present invention, a fresh air supply system having a supercharging means, an intake valve and In a two-stroke internal combustion engine having an exhaust valve, the exhaust system suppresses pressure fluctuations in the back pressure of the exhaust port at least in the idle range and light load range, and the exhaust port opens the exhaust valve earlier than the intake valve when the piston descends at a high speed. a piston having a cylindrical recess on the top surface; A two-stroke internal combustion engine is provided, which has fresh air gently flowing into the exhaust swirl from an intake valve.

[For production]

According to the present invention, stratification is achieved at least in the idle range and light load range by the following steps. In other words, during the downward stroke of the piston, a weak exhaust blowdown occurs immediately after the exhaust valve opens, and the exhaust port pressure momentarily increases, but the pressure fluctuation at the exhaust port is suppressed and the cylinder internal pressure quickly returns to atmospheric pressure. Become. At this time, because the piston descends at a high speed, the pressure inside the cylinder becomes negative, and the high-temperature exhaust gas from the exhaust port flows back into the cylinder. At this time, the exhaust swirl forming means, ie, the mask, forms an exhaust swirl approximately around the cylinder axis. The lower part of this exhaust swirl is guided into a recess in the suntop surface.

Then, after the cylinder internal pressure drops and the intake valve opens, the pressure at the intake port is regulated by the throttle valve and throttled by the intake valve, so the backflow of exhaust gas from the exhaust port is still progressing. When the piston descending speed further decreases and the intake valve lift increases, fresh air whose pressure is regulated by the throttle valve and supercharged by the supercharging means slowly flows in so as to ride on the exhaust swirl.

Therefore, stratification of fresh air on the head side and exhaust gas on the piston side is obtained. Then, even after the bottom dead center is reached and the inflow of fresh air ends, stratification is maintained by the exhaust swirl approximately around the cylinder axis, and the adiabatic compression stroke begins. Note that by suppressing the exhaust pulsation, the exhaust gas does not flow out again into the exhaust system, fresh air flows out, or backflow of fresh air occurs, so that the exhaust swirl approximately around the cylinder axis is not disturbed.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a six-cylinder two-stroke internal combustion engine according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the main parts thereof, and FIG. 3 is a sectional view of the two-stroke internal combustion engine. In these figures, 1 is the internal combustion engine body, 10 is an intake system, and 30 is an exhaust system. In the internal combustion engine main body l, 2 is the combustion chamber (
3 is a piston having a recess 8 on its inertia surface, 4 is a spark plug, 5 is a mask, 6 is a cylinder head, and 7 is a cylinder block. In the intake system 10, 11 is an air cleaner, 12 is an air flow meter, 13 is a throttle valve, 14 is a mechanical supercharger (supercharger), 15 is an intercooler, 16 is an intake control valve, 17a, 17b is a surge tank, 18a , 18b is a reed valve, 19a, 1
9b is a fuel injection valve, 20a, 20b are intake ports, 21
a and 21b are intake valves. In the exhaust system 30, 31a and 31b are exhaust valves, 32a and 32b are exhaust ports, 33 is an exhaust manifold, 34 is an exhaust control valve, 35 is a catalyst, and 36 is a muffler.

Intake air flows in from an air cleaner 11, and the amount of air is adjusted by a throttle valve 13. An air flow meter 12 is provided between the air cleaner 11 and the throttle valve 13 to measure the amount of intake air.

A mechanical supercharger 14 is provided downstream of the throttle valve 13 to supercharge the intake air, and cools the intake air whose temperature has increased due to supercharging by an intercooler 15 provided downstream. Improve volumetric efficiency of air. The mechanically driven supercharger 14 is, for example, a Roots-type pump supercharger, which supercharges intake air by performing a pumping action within a housing.

Downstream of the intercooler 15, the intake system 10 is divided into a light load intake passage 10a and a high load intake passage 10b, and the high load intake passage 10b is provided with an intake control valve 16. This intake control valve 16 is a normal butterfly valve, and is closed in the idle region and light load region of the engine.
It is opened in high load ranges (including medium load ranges, the same applies hereinafter).

Each intake passage 10a, 10b has a surge tank 17.
downstream of the surge tanks 17a, 17b are branched into respective cylinders by branch pipes, and connected to the combustion chamber 2 via intake ports 20a, 20b formed in the cylinder head 6. These intake ports 20a, g
Ob opens directly into the combustion chamber 2 from the cylinder head 6 side. Fuel injection valves 19a and 119b are provided in the intake ports 20a and 20b of each cylinder, respectively, and check valves 18a and 18b such as reed valves may be provided upstream of these fuel injection valves 19a and 19b, respectively, as necessary. good. One fuel injection valve 19a injects fuel toward the periphery of the spark plug 4 of the combustion chamber 2 in all operating ranges, and the other high-load fuel injection valve 19b injects fuel in the high-load range when the intake control valve 16 is open. The injector only injects fuel toward the center of the combustion chamber 2, and has a larger nozzle so that a larger injection amount can be obtained than the fuel injector 19a. The intake air mixed with the injected fuel flows from the intake ports 20a, 20b to the poppet type intake valve 21a,
It flows into the combustion chamber 2 via 21b.

These intake valves 20a and 20b are opened and closed, respectively, in synchronization with the crank angle at timings described below.

The air-fuel mixture flowing into the combustion chamber 2 from the intake bows 1-20a and 20b is made to flow as shown in FIGS. 4 and 5, respectively. That is, from the intake port 20a, as shown in FIG. 4, the air flows from substantially the entire circumference of the umbrella portion of the intake valve 21a, and from the intake port 20b, as shown in FIG. , i.e., a region close to the wall of the cylinder 2 of the combustion chamber, the flow is caused to flow directly downward along the cylinder wall. For this reason, for example, a mask wall 22 as shown by the broken line in FIGS. 3 and 5 is formed on the inner wall of the intake port 20b in a region close to the intake valve 21b and close to the center of the cylinder 2. There is. Therefore, a large amount of high-speed air-fuel mixture (
The fresh air is guided toward the cylinder wall along the sloped portion of the mask wall 22, flows directly into the combustion chamber 2, and quickly flows directly downward along the cylinder wall.

Two exhaust ports 32a, 32b are also formed in the cylinder head 6, which open directly into the combustion chamber 2 from the cylinder Rad 6 side at positions facing the intake ports 20a, 20b. These exhaust ports 32a and 32b are also opened and closed, respectively, by poppet type exhaust valves 31a and 31b, which are operated in synchronization with the crank angle at timings as will be described later. 2
The two exhaust ports 32a and 32b are exhaust valves 313 and 31b.
They merge near the downstream and are connected to the exhaust manifold 33. The exhaust manifold 33 has branch pipe collection parts 33a for the first to third cylinders and fourth to sixth cylinder pipe collection parts in the branch pipe collection parts for each cylinder.
An exhaust control valve 34 is provided to allow separation or communication between the cylinder and the branch pipe collecting portion 33b. Further, the two separated branch pipe collection parts 33a and 33b are connected to the exhaust pipe 38 through a two-pronged branch pipe 37 that is collected into one downstream. here,
In the illustrated six-cylinder two-stroke internal combustion engine, assuming that the stroke order is repeated in the order of the first, sixth, second, fourth, third, and fifth cylinders every 60 degrees of crank angle, the first to fifth cylinders Within each group, the three cylinder group and the fourth to sixth cylinder groups, the cylinder stroke is repeated every 120 degrees.

A catalyst 35 and a muffler 36 are provided downstream of the exhaust pipe 38. The exhaust control valve 34 is simply for controlling exhaust pressure and does not require much sealing performance when closed, so a normal butterfly valve is sufficient. However,
Of course, a valve with a high sealing property when closed, such as a poppet valve, may also be used. This exhaust control valve 34 is controlled to open in the idle range and light load range of the engine, and closed in the high load range.

The combustion chamber 2 of each cylinder is formed between a cylinder head 6, a piston 3, and a cylinder block 7, and an ignition plug 4 is arranged in the upper center of the cylinder head 6 side.

A mask 5 is formed around the exhaust valves 31a, 31b of the cylinder head 6, and these masks 5 allow exhaust to flow from the exhaust ports 32a, 32b to the poppet type exhaust valves 31a, 3.
A swirl is created in the exhaust gas when it flows back into the combustion chamber 2 through the entire circumference of the cylinder 1b, and a moderate swirl is created within the combustion chamber 2, especially in the idle region and light load region, approximately around the axis of the cylinder (combustion chamber 2). It has a shape that forms.

A cylindrical recess 8 is formed in the top surface of the piston 3, as shown in FIG. The side surface of this recess 8 is a cylindrical wall having an axis that coincides with the cylinder axis C, but the bottom surface 8b
is an inclined surface with a larger depth near the exhaust valves 31a and 31b, and has a shape convenient for escape of the mask 5 provided around the exhaust valve on the inner wall of the cylinder head 7.

Intake valves 21a, 21b and exhaust valves 31a, 31 of each cylinder
Although not shown, cams b are operated by appropriate cams attached to a camshaft that rotates at the same rotational speed as the crankshaft, and are opened and closed at predetermined timings as shown in FIG. That is, the intake valves 31a and 31b open first at about -125 degrees with respect to the bottom dead center (BDC), and then the intake valves 21a and 21b open at about -90 degrees. Also, approximately +40 from the bottom dead center (B D C)
Exhaust valves 31a, 31b close at about +6°
The intake valves 21a and 21b close at 0 degrees. Note that the fuel injection valves 19a and L9b inject fuel between approximately +45 degrees and 140 degrees with respect to bottom dead center (BDC).

As shown in the figure, the stroke order is 1st, 6th, 2nd,
Assuming that the operation is repeated in the order of the fourth, third, and fifth cylinders, the open/close states of the exhaust valves 31a, 31b of each cylinder will be as shown in FIG. That is, in FIG. 7, the portion indicated by a solid line with respect to the crank angle of the first cylinder corresponds to the exhaust valve 31 of each cylinder.
This is the period when a and 31b are open. On the other hand, the exhaust control valve 34 is controlled to open at least in the idle range and light load range of the engine, as described above. Therefore, in the idle range and light load range, the branch pipes of the exhaust manifolds 33 of all cylinders are in a state of communication with each other.

Looking at this for the first cylinder, in Fig. 7, the exhaust valve of the third cylinder is still open in the region where the exhaust valves 31a and 31b begin to open, and the exhaust valve of the sixth cylinder is open in the middle region. The exhaust valve of the second cylinder begins to open in the region M where it begins to open and ends. In particular, due to the influence of the exhaust pressure from another cylinder group (sixth cylinder), the exhaust port is substantially always at positive pressure, and the exhaust pulse supercharging effect of each cylinder does not occur. The same applies to the other cylinders, and the exhaust pressures of each cylinder interfere with each other, and the back pressure is controlled as described later. On the other hand, since the exhaust control valve 34 is closed in the high-load operating range of the engine, in the intermediate range in FIG. Therefore, the exhaust port of the first cylinder receives interference from the exhaust pressure (M) of the second cylinder, producing a supercharging effect due to the exhaust pulse.

Note that in order to suppress pulsation that occurs immediately after exhaust blowdown at low rotation speeds, an exhaust valve may be provided near the exhaust port, or a method of connecting resonance chambers may be combined.

Next, the operation of the two-stroke internal combustion engine according to the present invention will be explained.

First, in the idle range and light load range of the engine, the intake control valve 16 is closed, while the exhaust control valve 34 is open. During the downward stroke of the piston 3, when the piston 3 reaches a position at a crank angle of -125 degrees from the top dead center (TDC) in FIG.
1a and 31b begin to open. Therefore, around the time point (A) in FIG. 6, the exhaust gas after combustion flows out (weak blowdown P) from the exhaust valves 31a and 31b that have just started to open, as shown in 819A. In the idle range and light load range, the combustion pressure in the cylinder is low and the amount of exhaust gas is small, so this blowdown (P) ends in a short time. That is, at the exhaust ports 32a and 32b, the exhaust pressure momentarily decreases to 2 due to the initial weak exhaust blowdown (P).
~3kg/-, but soon 1.05 ksr/
The temperature decreases to about cti and stabilizes. This tendency becomes more stable as the engine speed increases. Then, at point (B) in Fig. 6, when the crank angle is about -90 degrees, the descending speed of the piston 3 is considerably large, the cylinder internal pressure becomes negative pressure, and as shown in the region of Fig. 7, other Affected by the exhaust pressure of the cylinder group (6th cylinder). Therefore, the high temperature exhaust gas that has blown down into the exhaust ports 32a and 32b flows back (Q) into the combustion chamber 2.

At that time, the exhaust swirl forming means, that is, the eccentric port 32b
and the mask 5, a swirl (R) approximately centered on the cylinder axis is formed. The lower part of this exhaust swirl is smoothly guided into the recess 8 on the top surface of the piston 3. The swirl at this time is a slow rotation to prevent heat dissipation of the exhaust gas in the cylinder. Next, the intake valves 21a, 21b
After the opening of the throttle valve 13, the pressure in the intake port 20a becomes
Since the lift amount of the intake valve 21a is small and the intake valve 21a is throttled, there is no inflow of fresh air and the exhaust port 3'2a
, 32b proceeds. When the piston further lowers and its descending speed becomes slower, the intake valve lift increases, resulting in the states shown in FIG. 6 (C) and FIG. The fresh air (mixture) supercharged into the intake valve 21 from the intake port 20a.
It flows into the combustion chamber 2 via a. At this time, as described above, the air flows from the intake port 20a substantially from the entire circumference of the umbrella portion of the intake valve 21a as shown in FIG. 4, and the descending speed of the piston 3 is small in this operating range. So,
The drop in cylinder internal pressure is small, so the flow rate of fresh air is low, and the fresh air slowly flows onto the exhaust swirl and collects at a portion near the ignition plug 4 on the cylinder head 6 side in the upper part of the combustion chamber 2. Therefore, fresh air (S) on the cylinder head side (upper layer)
This results in stratification of the exhaust gas (R) on the piston 3 (lower layer) side. Since the exhaust gas (R) is swirling approximately around the cylinder axis, even if the piston 3 reaches the bottom dead center and is in the state shown in Figure 6 (D) and Figure 8, it will not become fresh air (S). The stratified state between the exhaust gas (R) and the exhaust gas (R) is maintained. Even in the state shown in FIG. 6 (E) and FIG. 8 E, where the intake valve 21a is closed and the inflow of fresh air has substantially ended, the stratified state between the fresh air (S) and the exhaust air (R) is maintained. Since this stratified state is maintained until the end of the compression stroke, the fresh air on the cylinder head 6 side is activated by the high-temperature exhaust gas on the piston 3 side, and in the idle region, it is easily activated by the spark plug 4 at the end of the compression stroke. Ignition occurs, flame propagation progresses, and reliable combustion is obtained.In addition, in the light load range after warm-up, the temperature of the exhaust gas inside the cylinder increases, the activation of fresh air progresses, and as a result of adiabatic compression during the compression stroke, the ignition plug 4, self-ignition combustion becomes possible. In states D and E, the exhaust pressure (back pressure) from other cylinders is affected as shown in the region and M in Figure 7, and in the idle region and light load region, the exhaust gas is substantially reduced. The back pressure of the ports 32a and 32b is always positive pressure. Therefore, since the supercharging effect caused by the exhaust pulse is stopped, there is no outflow of fresh air into the exhaust system (so-called fresh air blow-through) or backflow of fresh air, and the lower part of the exhaust swirl is lower than the piston 3. Since it is guided by the recess 8, the swirl (R) is not disturbed.

Therefore, reliable stratified combustion is achieved.

As described above, in the idle range and light load range of the engine, the exhaust control valve 34 is opened to prevent the supercharging effect of the exhaust pulse, to generate an exhaust swirl due to υF air jib blowdown, and to open the intake control valve 16. By closing,
The fresh air is guided from the intake port 20a to the cylinder head 6 side of the combustion chamber 2, and stratification of the fresh air and exhaust swirl is realized.
When the engine is idling or cold, the ignition plug 4 ensures reliable ignition combustion, and when the exhaust temperature is high, such as during light load after warming up, self-ignition combustion of fresh air is realized.

Next, in a high engine load range, the intake control valve 16 opens, while the exhaust control valve 34 closes. During the downward stroke of the piston 3, at the point in time (a) in FIG. 6, the exhaust valves 31a and 31b begin to open, as shown in FIG. 9A. The exhaust gas after combustion rapidly flows out (blowdown P) from the exhaust valves 31a and 31b that have just started to open. In a high load range, the exhaust volume is large, resulting in strong exhaust blowdown, and the duration of the blowdown (P) is also long. Blowdown is the crank angle -
It almost ends at 90 degrees. Therefore, the discharge of a large amount of exhaust gas is completed. When reaching (b) in Figure 6, Figure 9B
As shown in FIG. 2, when the crank angle is about -80 degrees, the intake valves 21a and 21b are substantially opened and the inflow of fresh air (T) is started.

Therefore, the supercharged fresh air (mixture) is transferred to the intake port 20a.
, 20b starts flowing into the combustion chamber 2 via the intake valves 21a and 21b. In addition, in the high load range, the intake control valve 16 is open as described above, so fresh air flows through both intake ports 20.
A, 20b, but a large amount of fresh air flows quickly from the intake bow 20b directly downward in the combustion chamber 2 along the cylinder wall as shown in FIG. As shown in Figure B, so-called cross scavenging begins between the exhaust air (U) and fresh air (T).In this case as well, the recess 8 of the piston 3 guides the fresh air (T). , the exhaust gas flows out smoothly.Next, (b
), (C) and Fig. 9 B, C (crank angle -80 degrees ~
At around -50 degrees), the pressure at the exhaust ports 32a and 32b temporarily becomes negative due to the effect of the exhaust pulse caused by the strong exhaust blowdown, which helps fresh air flow into the cylinder. Part (V) Force<tn air ports 32a, 32b
and is temporarily stored in the exhaust manifold 33. Next, at the time of Fig. 6(d) and Fig. 9, there is a strong exhaust blowdown from another cylinder (second cylinder) whose exhaust valve has begun to open, as shown in area M of Fig. 7. Exhaust port 32a receives strong positive pressure.

32b and the exhaust manifold 33 is forced into the combustion chamber 2 so as to flow back (W). When this fresh air flows back into the combustion chamber 2, a strong fresh air swirl (X) is formed in the upper part of the combustion chamber 2 on the cylinder head 6 side by the eccentric exhaust port 32b and the mask 5. Intake valve 21a, 2
In the states shown in FIG. 6(e) and FIG. 9(E) where 1b is closed, fresh air no longer blows back.

As described above, when the engine is in a high load range, the intake control valve 16 is opened (by which a large amount of fresh air is quickly guided below the combustion chamber 2 along the cylinder wall of the combustion chamber 2, realizing cross scavenging. At the same time, by closing the exhaust control valve 34, a positive and negative pressure pulse is generated in the exhaust gas, and the exhaust pulse supercharging effect between the cylinders helps the inflow of fresh air. By heating the fresh air that is stored and flowing back into the cylinder, an appropriate amount of fresh air can be supplied into the cylinder, and the strong fresh air swirl increases the turbulence of the fresh air and improves flame propagation.

In addition, although the above-mentioned embodiment explained the case of a 6-cylinder 2-stroke internal combustion engine, the present invention is not limited to this, and can be applied to, for example, a 3-cylinder or 1 to 2-cylinder 2-stroke internal combustion engine. .

In the case of a three-cylinder engine, as a means of suppressing pressure fluctuations in the back pressure at the exhaust port in the idle range and light load range, the exhaust pipes for each cylinder are provided independently, and a bypass valve is provided to connect these exhaust pipes with each other. . By closing the bypass valve in the idle region or light load region, the equivalent pipe length of each exhaust pipe becomes longer, making it virtually unaffected by the exhaust pulse of the cylinder, and in this region, pressure fluctuations in the back pressure at the exhaust port are suppressed. It will be done. Further, in the case of one cylinder, an exhaust control valve is provided in the exhaust pipe and a passage bypassing the exhaust control valve is provided. By closing the exhaust control valve in the idle range or light load range, the equivalent pipe length of the exhaust pipe becomes longer, and pressure fluctuations in the back pressure of the exhaust port are suppressed in this range.

In addition, when this two-stroke internal combustion engine is configured as a diesel engine, the intake air before fuel injection is stratified with the exhaust gas, and the fuel is directly injected after the air is sufficiently heated, resulting in low compression. It is also possible to cause self-igniting combustion even at a certain ratio.

Note that if one of the exhaust valves 31a, 31b is made to open earlier than the other, and the mask provided around the exhaust valve that opens earlier is made higher (deeper) to produce a stronger exhaust swirl than the other mask, the exhaust The piston recess 8 deepened toward the valve side can serve as an effective escape for such a mask. This makes it possible to obtain a desired exhaust swirl. Further, if the exhaust port on the side that opens earlier of the exhaust valve is oriented in the tangential direction of the cylinder so that the exhaust flows back in the tangential direction, an exhaust swirl can be effectively obtained in combination with the above-mentioned mask.

〔Effect of the invention〕

As described above, according to the present invention, the exhaust swirl is not disturbed by the concave portion of the piston even in the idle region and light load region where there is a large amount of residual exhaust gas, so that stable stratification between exhaust gas and fresh air is achieved. By locating fresh air near the cylinder head, ignition becomes easier. Therefore, there is no misfire. Furthermore, since the exhaust gas is located on the piston side and fresh air does not touch the top surface of the piston, quenching of the top surface of the piston does not occur. Furthermore, heat dissipation of the exhaust gas can be prevented by insulating the top surface of the piston by the exhaust swirl, and the temperature of fresh air can be increased by the exhaust gas. At the boundary between the exhaust gas and fresh air, which maintains a stratified state, the fresh air is activated by the exhaust heat,
When the temperature of the exhaust gas is high, it is also possible to perform self-ignition combustion at the end of compression stroke. In addition, in high load range,
The piston recess smoothly guides fresh air to perform cross-scavenging, ensuring high filling efficiency and high output. Further, the recessed portion on the top surface of the piston can be used as a relief for the mask, which is the swirl forming means, and the mask can be formed into a desired shape (that is, a desired height).

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a six-cylinder two-stroke internal combustion engine according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing its main parts, FIG. 3 is a sectional view of the two-stroke internal combustion engine, and FIGS. Fifth
The figure shows the flow of fresh air from two intake valves, Figure 6 shows the opening/closing timing of the exhaust valve and intake valve, and the injection timing of the fuel injection valve, and Figure 7 shows the exhaust valve between the cylinders. Fig. 8 is a diagram to explain the state of exhaust gas and fresh air in the idle or light load range, and Fig. 9 is a diagram to explain the state of exhaust gas and fresh air in the high load range. This is a diagram. 1...2 cycle internal combustion engine body 2...Combustion chamber 3...Piston 5.5a15b...Mask 8...Four parts at the top of the piston 14...Supercharger 16...Intake control valves 21a, 21b ...Intake valves 31a, 31b...Exhaust valves 20a, 20b...Intake ports 32a, 32b...Exhaust port 34...Exhaust control valve Fig. 1 Fig. 2 Fig. 20a, 20b---Intake port no. 3 Figure 8-= 1 Figure 4 Figure 5 Figure 6 Crank angle Figure 7 Exhaust Figure 8 Exhaust Figure 9 Cross scavenging start Cross scavenging air vent prevents fresh air backflow swirl

Claims (1)

[Claims] 1. A fresh air supply system having supercharging means, and an intake valve and 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. In a two-stroke internal combustion engine, the exhaust system suppresses fluctuations in the back pressure of the exhaust port at least in the idle range and light load range, and the exhaust system opens the exhaust valve earlier than the intake valve when the piston descends at a high speed. means including a mask formed on the inner wall surface of the cylinder head around the exhaust valve for causing the exhaust gas to flow back into the combustion chamber and giving the backflowing exhaust gas a swirl approximately around the cylinder axis; and a piston having a cylindrical recess on the top surface. A two-stroke internal combustion engine that is equipped with an intake valve and allows fresh air to flow gently onto the exhaust swirl. 2. The two-stroke internal combustion engine according to claim 1, wherein the recess has an inclined bottom surface such that the depth toward the exhaust valve becomes greater.