JPS63173812A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To improve combustibility by providing a cylinder head with fresh air ports and exhaust ports which are respectively opened and closed by fresh air valves and exhaust valves, and providing meens for swirling a part of exhaust gas to be again let flow into a combustion chamber when the exhaust valve is opened. CONSTITUTION:Two fresh air ports 24 and two exhaust ports 26 are formed on a cylinder head 14 and opened and closed by fresh air valves 20 and exhaust valves 22 which are respectively driven in synchronization with a crank angle. In an exhaust stroke at the time of low load operation of such an engine, when pressure in a combustion chamber 18 is lowered less than the pressure of the exhauat port 26, a part of exhaust gas discharged from the combustion chamber is again let flow into the combustion chamber 18 due to a pressure difference between the exhaust port 26 and the combustion chamber 18. In order to conduct inflow of the exhaust gas again while a swirl is generated, masks 26a partially surrounding opening portions of the exhaust ports 26 are formed on the wall surface of the cylinder head 14. In this arrangement, stratification is promoted between fresh air and the residual exhaust to improve ignition-ability.

Description

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

[Conventional technology]

Japanese Patent Publication No. 60-5770 discloses an oven chamber type two-stroke internal combustion engine having an intake (fresh air) 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 two-stroke internal combustion engines do not have any problems in high load ranges, they have problems with combustion during idling or in light load ranges. 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.

Furthermore, JP-A-55-117021 discloses that combustion can be improved by performing activated thermal atmosphere combustion, and that if the cylinder head, cylinder block, etc. are made of ceramic, the inside of the cylinder can be maintained at a high temperature. are doing.

[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 provides a two-stroke internal combustion engine in which a fresh air boat and an exhaust port are provided in the cylinder head.
The purpose is to achieve stratification between fresh air and residual exhaust gas, gather fresh air near the cylinder head, and facilitate ignition, especially under operating conditions with a small amount of fresh air, such as when idling or under light load. .

[Means for solving problems]

The two-stroke internal combustion engine according to the present invention includes a fresh air supply system having a supercharging means, a fresh air boat provided in the cylinder head portion, and a fresh air driven in synchronization with the crank angle to open and close the exhaust port. In a two-stroke internal combustion engine having a valve and an exhaust valve, a means is provided for causing a portion of the exhaust gas discharged from the exhaust port when the exhaust valve is opened to re-inflow into the combustion chamber while swirling it around the cylinder axis. It is characterized by a catalyst attached to the boat.

[For production]

According to the present invention, stratification is achieved in the following manner at least in idle and light load ranges. That is,
When the exhaust valve opens during the downward stroke of the piston, a weak exhaust blowdown occurs, creating positive pressure in the exhaust port. The exhaust blowdown ends in a 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 fresh air valve opens.

At idle and in a light load range, the amount of new air supplied is small and 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, ignition becomes easier. Moreover, since the fresh air is on top of the high-temperature exhaust gas, it is activated and becomes more easily ignited. Furthermore, in the present invention, a catalyst is attached to the fresh air boat, and the fresh air in the fresh air boat is activated by the action of the exhaust gas flowing back into the fresh air boat and the catalyst immediately after the fresh air valve is opened. This helps ensure good combustion even at low temperatures in the internal combustion engine.

〔Example〕

Figure 1 is a vertical sectional view through the fresh air valve and exhaust valve in Figure 3;
FIG. 2 is a diagram showing a six-cylinder two-stroke internal combustion engine 10 to which the present invention is applied, and FIG. 3 is a diagram showing the vicinity of the combustion chamber of one cylinder in detail in FIG. 2. As shown in FIG. 1, the opening main body IO is composed of a cylinder block 12 and a cylinder head 14, and a combustion chamber 18 is formed above a piston 16. This two-stroke internal combustion engine has cylinder head 1
The cylinder head 14 has a fresh air valve 20 and an exhaust valve 22, each of which is a poppet valve.Therefore, a fresh air boat 24 and an exhaust port 26 are formed in the cylinder head 14.

As shown in FIG. 3, two fresh air valves 20 and two exhaust valves 22 are provided, and a spark plug 28 is inserted into the combustion chamber.
It is provided approximately in the center of 8. In FIG. 3, the exhaust valves 22 are both designated E, while the fresh air valves 20 are designated FA, F.
It is represented by B.

This shows that the functions of the fresh air valves 20 are different from each other.Hereafter, the fresh air valve 20 represented by FA will be referred to as a low-load fresh air valve, and the fresh air valve 20 represented by FB will be referred to as a high-load fresh air valve. I'll call it Shinkiben.

As shown in FIGS. 2 and 3, the cylinder head 1
4 is fitted with two fresh air manifolds 30,32. Each branch pipe of one fresh air manifold 30 is connected to the fresh air boat 24 on the side where the low load fresh air valve FA20 is arranged, and each branch pipe of the other fresh air manifold 32 is connected to the fresh air boat 24 on the side where the high load fresh air valve FB20 is arranged. is connected to the fresh air boat 24 on the side where the Each fresh air boat 24 or fresh air manifold 30.3
A fuel injection valve 34 is arranged in each of the two branch pipes.

As shown in FIG. 2, air is taken in from an air cleaner 38, controlled by a throttle valve 40, and further supercharged by a supercharger (S/C) 42. An intercooler 44 is arranged downstream of the supercharger 42, and the two fresh air manifolds 30, 32 are both 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.

A butterfly-type fresh air control valve 48 is disposed at a collecting portion of the fresh air manifold 32 on the high load side. While the fresh air valve 20 and exhaust valve 22 are driven in synchronization with the crankshaft of the engine, the fresh air control valve 48 is opened and closed according to the load and rotational speed of the engine. The fresh air control valve 4 is closed at least when the engine is idling and at low load, so that at this time air is supplied only from the fresh air manifold 30 on the low load side. The fresh air control valve 48 is opened during high engine loads, so that at this time air is supplied through both the high load side fresh air manifold 32 and the low load side fresh air manifold 30. Note that the fresh air boat FB24 is provided with a check valve 36 made of a reed valve to prevent backflow of fresh air.

FIG. 4 shows the characteristics of the flow of fresh air supplied from the low-load fresh air valve FA and the high-load fresh air valve FB, respectively. This characteristic is not obtained by the valve alone, but is obtained by the arrangement of the related fresh air boat 24, the characteristics of the cylinder head wall surface shape around the valve, etc. even if the shape of the valve is the same. The low-load fresh air valve FA allows a small amount of air to flow almost uniformly around the valve when the valve is opened, as shown by the arrow in (a). The other high-load fresh air valve FB is (
As shown by the arrow in b), it is formed so that air flows in a biased direction. This direction is along the vertical walls of the cylinder, so that at high loads a large amount of fresh air coming through the boat on the high load side first moves down the cylinder along one wall and then It changes direction at the top surface of the piston 16 and rises along the opposite wall surface, and by flowing in a U-shape in this way, it can be efficiently replaced with exhaust gas. In order to allow the air to flow in a biased direction, for example, as shown in FIG. 4(b), a bias wall 49 is provided inside the boat.
Alternatively, it is possible to provide a weir on the wall of the throat 14 in the cylinder.

Further, even if the cylinder head wall shape around the high-load fresh air valve FB is similar to that of the low-load fresh air valve FA, fresh air can be efficiently replaced with exhaust gas.

As shown in FIGS. 1 and 3, the fresh air manifold 30 or fresh air boat 24 on the low load side has a catalyst having honeycomb-shaped pores between the fresh air valve 20 and the fuel injection valve 34. 50 are placed. Furthermore, the combustion chamber side of the fresh air boat 24 is coated with a heat insulating ceramic layer.

As shown in Figure 3, two exhaust ports 2 for each cylinder
6 are combined into one boat within the cylinder head 14. As shown in FIG. 2, the exhaust system is divided into two groups of cylinders that do not interfere in terms of firing order, and two exhaust manifolds 54 are connected to exhaust ports 26 for three cylinders each. The collecting portion 56 of the exhaust manifold 54 is further joined by a common exhaust pipe 58 and then connected to a muffler 62. In addition, the gathering portion 5 of each exhaust manifold 54
6, a catalyst 60 is disposed on each side.

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 22 is opened, and the inside of the exhaust boat 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 26 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 an intake boat, but a major feature of the present invention is to generate a swirl in the exhaust gas flowing back. In order to generate a swirl in the exhaust, the same means as in the case of generating a swirl in the intake air can be adopted. For example, the shape of the exhaust port may be twisted, or the exhaust port may be placed around the cylinder. can be connected tangentially to. In this embodiment, as shown in FIG.
is formed. Further, an inclined guide surface may be formed on the cylinder head wall surface extending from the opening of the exhaust port 26 to the opening of the fresh air boat 24. This guide surface on the exhaust side cooperates with the weir on the fresh air side to help swirl the exhaust gas in the direction of arrow S, prevent the fresh air from flowing in the direction of arrow S, and as a whole more securely align the cylinder axis. This causes a swirl to be generated around the .

Figure 5 shows the opening period (FO) of the fresh air valve 20 and the opening period (E) of the exhaust valve 22, which are driven in synchronization with the crankshaft.
FIG. 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 the piston 16 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.
Combustion must be carried out in a large amount of residual exhaust 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 22 opens at a point 8 degrees before bottom dead center BDC, and since the downward speed of the piston 16 is fast at this time, the combustion chamber 18 opens after a weak exhaust blowdown during idling and low load. The pressure drops and the back pressure in the exhaust port 26 and the negative pressure in the combustion chamber 18 ensure that a backflow of exhaust gas occurs. The exhaust valve 22 closes at 40 degrees after the bottom dead center BDC, when the compression stroke has not progressed much.

In addition, the fresh air valve 20 opens at a point when exhaust gas backflow occurs after the exhaust valve 22 opens, for example, at a point 60 degrees before the bottom dead center BDC, and closes at the bottom dead center after the exhaust valve 22 closes. After BDC 6
Closes at 0 degrees.

FIG. 6 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 fresh air valve F.
Only from the A20 side. This supply of fresh air is slow and has a small volume and does not have a specific direction as described with reference to FIG. As shown in FIG. 6(a), the exhaust valve 22 opens 8 degrees before the bottom dead center BDC, 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 under low load momentarily drops to about 2 to 3 kg/crl, but quickly drops to about 1.05 kg/cIJ, and the back pressure of the positive pressure increases. Stabilize while maintaining pressure.

As the piston 16 descends, the inside of the combustion chamber 18 becomes negative pressure,
As shown in FIG. 6(b), the exhaust gas re-inflows in the direction of arrow Q, and the exhaust gas is swirled in the combustion chamber 18 by swirl forming means such as the structure of the exhaust port 26, the mask 26a, and the guide surface. S is formed. 60 before bottom dead center BDC
degree, the low-load fresh air valve FA20 opens. The fresh air is metered by the throttle valve 40, and the supercharging pressure of the supercharger 42 is also relatively low. Furthermore, since it takes time for the fresh air valve 20 to substantially fully open, fresh air does not flow in immediately, and even when the low-load fresh air valve FA20 is first opened, the exhaust gas backflow and swirl formation continue. There is. In this way, the formation of the exhaust swirl continues for a considerable period of time, and since this swirl is formed around the cylinder axis, it is maintained without disappearing until after the end of the compression stroke.

Therefore, during this period, exhaust gas also flows back into the fresh air boat 24. This backflow exhaust gas heats the fresh air and also heats the catalyst 5.
0 and heats the catalyst 5o to promote the heating effect of fresh air. The ceramic layer 52 prevents this backflow exhaust gas and the heated fresh air from being cooled even when the internal combustion engine is at a low temperature, thereby helping to form a hot atmosphere for activating the fresh air.

Additionally, the catalyst 50 provides fresh air flow resistance and helps fresh air to be slowly supplied to the combustion chamber 18 at low loads. Since the catalyst is placed in the fresh air port 24 on the low load side, when both fresh air ports 24 are opened during high load, fresh air tends to flow toward the fresh air port 24 on the high load side. Therefore, it becomes possible to further utilize the flow characteristics of the high-load fresh air valve FB20.

After that, as shown in FIG. 6(c), the fresh air valve 2 is opened.
When 0 is practically at full throttle, fresh air comes in. At this time, the fresh air flows slowly from the entire circumference of the valve as explained with reference to FIG. Fresh air enters the combustion chamber 18 slowly because no pressure is built up and the supercharging pressure is low as described above. Therefore,
The incoming fresh air slowly rides on the exhaust swirl, and rather than passing downward through the exhaust swirl, the fresh air swirls on the exhaust swirl together with the exhaust swirl. In this way, fresh air gathers at a portion of the cylinder head 14 near the spark plug 28 side, that is, the cylinder head 1
Stratification of the fresh air on the 4 side and the exhaust air on the piston 16 side is achieved. This stratification of fresh air and exhaust air is shown in Figure 6 (d).
As shown in , the piston 16 descends to the bottom dead center,
It then rises a little, closes the exhaust valve 22, and is maintained even when the fresh air valve 20 closes. Note that the exhaust port 26 is maintained at positive pressure and is applied from the exhaust valve 22 to the combustion chamber 18.
Since the movement of the piston 16 until the exhaust valve 22 closes is also slow, fresh air flows out from the combustion chamber 18 to the exhaust port 26, so-called fresh air blow-through hardly occurs.

During idling and under light load, fresh air gathers in the cylinder head 14 near the spark plug 28 side, as described above, and the fuel injected from the fuel injection valve 34 before the fresh air valve 20 closes also collects in the fresh air. As a result, the air-fuel ratio does not become too thin near the spark plug 28, and the spark plug 28 easily ignites the fuel to ensure reliable combustion. The fresh air is placed on top of the exhaust gas, and is activated by the high-temperature exhaust gas to form an activated thermal atmosphere containing radical fuel components.

Therefore, when the internal combustion engine is in a low temperature state, the spark plug 28 ignites the engine, but after warming up, adiabatic compression in the compression stroke enables self-ignition combustion with low fuel consumption and excellent exhaust purification performance. In the present invention, the fresh air is heated by the action of the catalyst 50 disposed in the fresh air port 24, and can be activated quickly when it enters the combustion chamber 18, so that the fresh air is sufficiently activated. Stable combustion can be achieved even at low temperatures.

Since the fresh air control valve 48 is opened during medium to high loads, fresh air is supplied through both fresh air boats 24, and in particular, a large amount of air can pass through the fresh air port FB24 on the high load side. It becomes like this.

As explained with reference to FIG. 4, the fresh air valve FB20 on the high load side is provided so that fresh air mainly flows downward along the cylinder wall, and the fresh air flows through the cylinder wall on one side. This creates a U-shaped flow that descends along the opposite wall, changes direction with the piston, and ascends along the opposite wall. This allows more exhaust gas to be pushed out and improves scavenging efficiency. . Note that by providing the fresh air control valve 48 in each fresh air port FB24, it is possible to eliminate the check valve 36.

〔Effect of the invention〕

As explained above, according to the present invention, stratification is achieved between fresh air and residual exhaust gas especially at idle and low load, and the fresh air is heated by the catalyst placed in the fresh air port to achieve stable combustion. It is possible to obtain a two-stroke internal combustion engine that can perform good combustion from low loads to high loads.

[Brief explanation of the drawing]

Figure 1 is a vertical sectional view through the fresh air valve and exhaust valve in Figure 3, Figure 2 is a diagram showing a six-cylinder two-stroke internal combustion engine to which the present invention is applied, and Figure 3 is a single-cylinder diagram in Figure 2. Figure 4 is a diagram explaining the flow of fresh air entering the combustion chamber from the fresh air valve, Figure 5 is a diagram showing valve timing, and Figure 6 is a diagram showing the vicinity of the combustion chamber at low load. FIG. 2 is an explanatory diagram illustrating backflow of exhaust gas and supply of fresh air. 14... Cylinder head, 16... Piston, 18... Combustion chamber, 20... Fresh air valve, 22... Exhaust valve, 24... Fresh air port, 26... Exhaust boat, 26a...Mask, 48...Fresh air control valve, 50...Catalyst.

Claims (1)

[Claims] A two-stroke internal combustion engine with a fresh air supply system that includes supercharging means, and a fresh air valve and exhaust valve that are driven in synchronization with the crank angle to open and close the fresh air port and exhaust port provided in the cylinder head. In the engine, 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, and a catalyst is further attached to the fresh air port. A two-stroke internal combustion engine.