JPH0513954Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] 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 open 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's summery. This two-stroke internal combustion engine is equipped with a supercharger.

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.
In other words, in a vertical U-shaped flow within the cylinder,
This is because the mainstream of fresh air moves downwards in the cylinder. For this reason, ignition by the spark plug installed in the cylinder head and generation of a flame kernel are inhibited, and the flame propagation speed is reduced.
Misfires and combustion fluctuations are more likely to occur.

The applicant of the present application previously developed a two-stroke internal combustion engine in which a fresh air valve and an exhaust valve were provided in the cylinder head.
At low loads, including idle, a portion of the exhaust gas discharged from the exhaust port when the exhaust valve opens is re-introduced into the combustion chamber while being swirled around the cylinder axis, thereby reducing the residual exhaust gas on the piston side. In response, we proposed a two-stroke internal combustion engine that collects fresh air on the cylinder head side and performs stratified combustion. Furthermore, when the load is high, a large amount of fresh air is supplied, so the swirl of exhaust gas disappears, and cross-scavenging in which fresh air replaces exhaust gas occurs in the cylinder. Furthermore, a four-stroke internal combustion engine equipped with a mechanical supercharger is well known, as described in Japanese Patent Application Laid-Open No. 19935/1983.

[Problem that the invention attempts to solve]

However, as mentioned above, in a two-stroke internal combustion engine that re-enters a portion of the exhaust from the exhaust port during low load to create an exhaust swirl and stratify the fresh air swirl toward the cylinder head, a supercharger is installed in the fresh air supply passage. If this is provided, stratified combustion during low load operation may be inhibited. That is, in a two-stroke internal combustion engine having a supercharger, supercharging is performed even in a low-load operating range where stratified charge combustion is performed, and the pressure at the fresh air port is relatively high. For this reason,
The flow rate of the fresh air flowing in from the fresh air port is high, and the strength of the swirl of the fresh air may become larger than necessary. However, if the strength of the fresh air swirl is large, the fresh air (air mixture) will diffuse throughout the combustion chamber, and there will be cases where it will not be possible to form an ignitable mixture near the spark plug.

The present invention aims to solve the above-mentioned problems and to enable stable stratified combustion in a two-stroke internal combustion engine that generates exhaust backflow swirl in a low-load operating region.

[Means for solving problems]

According to the present invention, the first fresh air port causes a swirl of fresh air flowing into the engine combustion chamber, the second fresh air port linearly introduces fresh air into the combustion chamber, and the first fresh air port a fresh air valve that opens and closes a second fresh air port; an exhaust port that discharges exhaust gas from the combustion chamber; an exhaust valve that opens and closes the exhaust port; and a fresh air flow that passes through the second intake port during low engine load operation. and an intake control valve that substantially shuts off the air, the exhaust valve is opened earlier than the fresh air valve during the downward stroke of the piston to exhaust the exhaust gas in the combustion chamber, and then the exhaust gas in the exhaust port flows back into the combustion chamber. In a two-stroke engine, the two-stroke engine is further provided with a means for causing exhaust gas flowing back from the exhaust port to swirl around the cylinder axis in the same direction as fresh air flowing in from the first fresh air port. A throttle valve is provided in the fresh air supply passage that supplies fresh air to the fresh air port, a supercharger is arranged downstream of the throttle valve, and the supercharger is connected to the fresh air supply passage by bypassing the supercharger. a bypass passage that connects the throttle valve and the downstream side of the supercharger; and a bypass control valve that controls the flow rate of fresh air passing through the bypass passage, between the throttle valve and the supercharger. There is provided a two-stroke internal combustion engine characterized in that the control valve is opened when the pressure of the fresh air supply passage becomes equal to or less than a predetermined value.

〔Example〕

FIG. 1 is a diagram showing a six-cylinder two-stroke internal combustion engine 10 to which the present invention is applied, FIG. 2 is a diagram showing the vicinity of the combustion chamber of one cylinder in detail in FIG. 1, and FIG. FIG. 3 is a vertical cross-sectional view through the fresh air valve and the exhaust valve.

The engine body 10 is composed of a cylinder block 12 and a cylinder head 14, and a combustion chamber 18 is formed above a piston 16. A fresh air port 20 and an exhaust port 22 are formed in opposing arrangement in the cylinder head 14, and each has a fresh air valve 24 and an exhaust valve 26 which are poppet valves.

As shown in FIG. 2, two fresh air valves 24 and two exhaust valves 26 are provided, and a spark plug 28 is provided approximately in the center of the combustion chamber 18. The exhaust valve 26 is designated E _s and E, while the fresh air valve 2
4 is represented by FA and FB. This is Shinkiben 24
This shows that there are differences in the functions of
The fresh air valve represented by FA is called a low-load fresh air valve, and FB
The fresh air valve represented by is called a high-load fresh air valve.

As shown in FIGS. 1 and 2, the cylinder head 14 has two fresh air manifolds 30, 3.
2 can be installed. One fresh air manifold 3
Each branch pipe of 0 is connected to the fresh air port 20 on the side where the low-load fresh air valve FA is arranged, and each branch pipe of the other fresh air manifold 32 is connected to the fresh air port 20 on the side where the high-load fresh air valve FB is arranged. air port 20. Both fresh air 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 centerline of the cylinder in a direction substantially perpendicular to the longitudinal axis of the engine, and at least the arrangement of the low-load fresh air valve FA Fresh air port 20 on the side where
opens tangentially into the combustion chamber 18 . And fresh air port 20 or fresh air manifold 30, 32
A fuel injection valve 34 is arranged in each branch pipe. Further, a check valve 36 made of a reed valve is arranged upstream of the fuel injection valve 34.

As shown in FIG. 1, air is taken in from an air cleaner 38, its flow rate controlled by a throttle valve 40, and supercharged by a supercharger 42. An intercooler 43 is arranged downstream of the supercharger 42, and the two fresh air manifolds 30 and 32 are both connected to the intercooler 43.

As shown in FIGS. 1 and 4, the supercharger 4
2 is composed of a roots type pump, and a belt 44
It is driven by the engine's crankshaft. A bypass passage 45 bypasses the supercharger 42 and is connected to the fresh air supply passage. That is, the upstream connection point of the bypass passage 45 is the throttle valve 40.
and the supercharger 42, and the downstream connection point is downstream of the intercooler 43, which is further downstream than the supercharger 42. A negative pressure operated bypass control valve 46 is disposed in the middle of the bypass passage 45 . The bypass control valve 46 has a valve member 46b fixed to a diaphragm 46a, and a negative pressure chamber 46c is formed behind the diaphragm 46a. A spring 46d is disposed within the negative pressure chamber 46c, and the diaphragm 4
6a is biased in the valve closing direction. Negative pressure downstream of the throttle valve 40 is introduced into the negative pressure chamber 46c through a pipe 46e. A solenoid valve 47 is arranged in the middle of the negative pressure introduction pipe 46e,
Negative pressure or atmospheric pressure can be selectively supplied to the negative pressure chamber 46c. The bypass control valve 46 opens when negative pressure is supplied, and closes when atmospheric pressure is supplied.

A pressure sensor 48 is arranged in the fresh air supply passage between the throttle valve 40 and the supercharger 42. Solenoid valve 4
A control unit (ECU) 49 is provided to control 7. The control unit (ECU) 49 is configured as a microcomputer, and includes a central processing unit (CPU) 49a that has calculation and control functions, and a read-only memory (ROM) that stores programs.
49b, and a random access memory (RAM) 49c for storing data, etc., which are interconnected by a bus 49d, and are connected to the pressure sensor 48 and the like via an input/output (A/O) interface means 49e. It is connected to a solenoid valve 47.

FIG. 5 shows a flowchart of the control of the solenoid valve 47, and in step 100 it is determined whether the detected absolute pressure P is greater than a predetermined value _P0 .
If YES, it is determined that the negative pressure level downstream of the throttle valve 40 is not large, and the process proceeds to step 101.
Atmospheric pressure is supplied to the bypass control valve 46 to close it. On the other hand, if NO, it is determined that the negative pressure level downstream of the throttle valve 40 is large, and negative pressure is supplied to the bypass control valve 46 to open it. When the bypass control valve 46 opens, fresh air downstream of the supercharger 42 flows to the upstream side of the supercharger 42 through the bypass passage 45, and the supercharging pressure decreases. That's why the new air valve
The flow rate of fresh air flowing into the combustion chamber from the FA decreases,
The intensity of the swirl generated within the combustion chamber is reduced.

Returning to FIG. 1, a butterfly type fresh air control valve 51 is disposed at the collecting portion of the fresh air manifold 32 on the high load side. While the fresh air valve 24 and the exhaust valve 26 are driven by a camshaft in synchronization with the engine crankshaft, the fresh air control valve 51 is opened and closed according to the engine load and rotation speed. be. The fresh air control valve 51 is closed when the load is low, including at least when the engine is idling. Therefore, at this time, air is supplied only from the fresh air manifold 30 on the low load side. The fresh air control valve 51 is opened when the engine is under high load, so that at this time air is supplied through both the fresh air manifold 32 on the high load side and the fresh air manifold 30 on the low load side.

Furthermore, as shown in FIG. 1, two exhaust manifolds 50 are provided for six cylinders, one exhaust manifold 50 is connected to the first, second and third cylinders, and the other exhaust manifold 50 is connected to the fourth cylinder. ，
Connected to 5th and 6th cylinder. Each exhaust manifold 5
A catalyst 52 is arranged in each of the collecting parts of 0,
Each exhaust manifold 50 further terminates independently of one another through a muffler 54. In this case, the ignition 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. 2 shows one such branch 50a, which is mounted approximately at right angles to the longitudinal axis of the engine. By the way, each cylinder has 2
There are two exhaust ports 22, and these two exhaust ports 22 are merged into one port within the cylinder head 14. Exhaust valve 26 indicated with E _s
The exhaust port 22 in which is arranged is the branch pipe 50a.
It is formed substantially at right angles to the longitudinal axis of the engine so as to be in line with the engine, and is connected tangentially to the combustion chamber 18 . The other exhaust port 22 merges at an angle with the exhaust port 22 on the side formed substantially perpendicular to the longitudinal axis of the engine. The configuration of this exhaust port 22 is that the exhaust gas exhaust speed can be increased by having two exhaust valves 26, and the exhaust gas is discharged to the exhaust port 22 and the exhaust manifold 50, and one of the exhaust gases is discharged to the exhaust manifold 50. When the E _s re-enters the combustion chamber 18, there is almost no re-inflow from the angled exhaust port 22 due to the effect of inertia flowing in a straight line.
This re-inflowing exhaust gas mainly passes through the exhaust port 22 in which the exhaust valve 26 shown with is located is arranged, so that this re-inflowing exhaust gas can form a swirl S around the cylinder axis.

This swirl S is in a clockwise direction as viewed in FIG. Then, this swirl S is formed (E _s
side) exhaust port 22 is the fresh air valve FB on the high load side.
facing in a straight line with the fresh air port 20 having
The fresh air port 20 having the fresh air valve FA on the low load side faces the fresh air port 20 with an offset across the center line. Therefore, when the fresh air supplied from the fresh air port 20 having the fresh air valve FA on the low load side generates a swirl at low load, the swirl is the same as the swirl S of the re-inflowing exhaust gas. The direction will be clockwise. When the load is low, the fresh air control valve 48 is closed, so there is no flow of fresh air from the fresh air port 20 on the high load side facing the exhaust port 22 that forms the swirl S, and the swirl S of the re-inflowing exhaust gas is prevented. There is no obstruction and thus the swirl S can be maintained.

As shown in FIGS. 2 and 3, on the inner wall of the cylinder head 14, that is, on the upper wall of the combustion chamber 18,
A mask 56 is formed. This mask 56 is formed so as to traverse the combustion chamber 18 substantially parallel to the longitudinal axis of the engine and to block between the fresh air valve 24 and the exhaust valve 26 . This mask 56 is formed of a plateau-like ridge that rises at a sharp angle in most of the center, and has a gentle slope at the side edges. The spark plug 28 is placed on the fresh air 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 E26 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 E _s tends to swirl by itself as described above, and furthermore, if there is a flow toward the center of the combustion chamber 18 away from the swirl and toward the fresh air valve 24, this also flows through the mask 56. is interrupted by Therefore, the re-inflowing exhaust gas from the exhaust valve _Es is passed through the mask 56.
The flow has no choice but to pass through the gently sloped side edges of the combustion chamber 18 and increasingly along the cylindrical surfaces of the cylinders. Further, during high load, fresh air supplied in parallel from the two fresh air ports 20 hits the mask 56, is directed downward, and is prevented from blowing directly through the exhaust port 22. Since the spark plug 28 is located on the side of the fresh air 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 decreases below the pressure at the exhaust port due to the downward movement of the piston 16, a portion of the exhaust gas exhausted from the combustion chamber by exhaust blowdown is transferred to the exhaust port 22 and the combustion chamber 18. The pressure difference causes the air to flow back into the combustion 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 forms a swirl S around the cylinder axis within the combustion chamber 18, as shown in FIGS. 1 and 3. In the past, 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.

FIG. 6 is a diagram showing the valve opening engine (FO) of the fresh air valve 24 driven in synchronization with the crankshaft and the valve opening period (EO) of the exhaust valve 26. 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 is performed near the bottom dead center BDC between these two strokes, and basically includes scavenging for 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 remaining exhaust gas is small. Combustion must be carried out in a large amount of exhaust gas, and when fresh air and exhaust mix together, the air-fuel ratio becomes diluted, making ignition combustion extremely difficult.

In the present invention, the exhaust valve 26 is located at the bottom dead center BDC.
Opens at 80 degrees forward, at this time piston 16
Since the downward speed of the combustion chamber 18 is fast, the pressure in the combustion chamber 18 decreases after a weak exhaust blowdown at idle and low load, and the back pressure of the exhaust port 22 and the negative pressure in the combustion chamber 18 ensure a backflow of exhaust gas. It is starting to occur in The exhaust valve 26 closes at 40 degrees after bottom dead center BDC. In addition, the fresh air valve 24 is an exhaust valve 26.
It opens at a time point at which backflow of exhaust gas occurs after the exhaust valve 26 opens, for example, at a time point 60 degrees before bottom dead center BDC, and closes at a time point 60 degrees after bottom dead center BDC after the exhaust valve 26 is closed.

FIG. 7 is a diagram illustrating the backflow of exhaust gas and the generation of swirl 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,
Fresh air is supplied only from the low-load fresh air valve FA20 side. During idle and low load, the throttle valve 40 is closed and the negative pressure level downstream of the throttle valve 40 becomes high, so the bypass control valve 4 is closed.
Valve 6 is open and the supercharging pressure is low. For this reason, the flow velocity of fresh air flowing into the combustion chamber from the low-load intake valve FA is low, and the generated swirl is also weak. As shown in Figure 7a, before bottom dead center BDC
When the temperature reaches 80 degrees, the exhaust valve 26 opens and a weak exhaust blowdown of 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 or under low load momentarily becomes about 2 to 3 kg/ ^cm2 , but soon
The pressure drops to around 1.05Kg/cm ² and stabilizes while maintaining positive back pressure.

As the piston 16 descends, the inside of the combustion chamber 18 becomes negative pressure, and as shown in FIG.
A swirl S of exhaust gas is formed within the combustion chamber 18 by the swirl forming means such as the mask 56 . When the temperature reaches 60 degrees before bottom dead center BDC, low load fresh air valve FA20
opens. Fresh air is metered by the throttle valve 40, and since the bypass control valve 46 is open, the supercharging pressure of the supercharger 42 is also relatively low. Also, new air valve 24
Since it takes time for the valve to become substantially fully open, fresh air does not flow in immediately, and backflow of exhaust gas and swirl formation continue even when the low-load fresh air valve FA20 is initially opened. 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 Figure 7c and d,
Fresh air enters when the fresh air valve 24 is substantially fully opened. At this time, since the descending speed of the piston 16 is also slow, almost no negative pressure is formed in the combustion chamber, and as mentioned above, the supercharging pressure is also small, so fresh air slowly enters the combustion chamber 18. Therefore, the swirl of the incoming fresh air is weak, and the fresh air rides slowly on the exhaust swirl without diffusing throughout the combustion chamber, and swirls together with the exhaust swirl on the exhaust swirl. In this way,
The fresh air collects in a region close to the spark plug 28 side on the cylinder head 14 side.
A stratified ratio of fresh air on the piston 16 side and exhaust gas on the piston 16 side is achieved. This stratification of fresh air and exhaust gas is maintained even after the piston 16 has descended to the bottom dead center, as shown in FIG. 7e. Furthermore, piston 16
Even after passing the bottom dead center and starting to rise, the movement speed is slow for a while, and the catalyst 52 provided in each exhaust manifold 50 prevents the pressure from decreasing in the exhaust port 22 and the exhaust manifold 50, so that air from the combustion chamber 18 Outflow of fresh air to the exhaust port 22, so-called blow-by of fresh air, hardly occurs. Furthermore, 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
After passing the bottom dead center and starting to rise, back pressure is applied to the combustion chamber 18, which is effective in preventing fresh air from blowing through. Then, the fresh air valve 24 closes and the supply of fresh air to that cylinder ends.

Fuel is injected at an appropriate time before fresh air valve 24 closes. Therefore, at idle and under light load, the rich air-fuel mixture gathers at a portion of the cylinder head 14 near the spark plug 28, and the spark plug 28
This allows for easy ignition and reliable combustion. This air-fuel mixture is placed on top of the exhaust gas, is activated by the high-temperature exhaust gas, and forms an active thermal atmosphere containing radical fuel components, increasing ignitability. It is possible to carry out combustion.

Since the fresh air control valve 51 is opened during medium to high loads, fresh air is supplied through both fresh air ports 24. 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, since there is a mask 56 that crosses the center of the cylinder head 14, the fresh air does not blow directly into the exhaust port 22, but flows downward, and then hits the piston 16 and flows upward, forming a U-shape. Scavenging can be carried out using the flow of air.

[Effect of idea]

As explained above, according to the present invention, during low-load operation when the negative pressure level generated downstream of the throttle valve becomes large, the bypass control valve is opened to lower the supercharging pressure, and fresh air flows in from the low-load fresh air valve. By weakening the swirl of fresh air, diffusion of fresh air into the combustion chamber can be prevented and good stratified charge combustion can be achieved during low load operation.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a six-cylinder two-stroke internal combustion engine to which the present invention is applied, Figure 2 is a diagram showing the vicinity of the combustion chamber of one cylinder in Figure 1, and Figure 3 is a diagram showing the fresh air valve in Figure 2. 4 is a detailed view of the vicinity of the supercharger in FIG. 1, FIG. 5 is a flowchart showing an example of bypass valve control, and FIG. 6 is a diagram showing valve timing. 7 are explanatory diagrams illustrating stratification during low load. 14...Cylinder head, 16...Piston,
18... Combustion chamber, 20... Fresh air port, 22...
Exhaust port, 24...fresh air valve, 26...exhaust valve,
40...throttle valve, 42...supercharger, 45...
...Bypass passage, 46...Bypass control valve, 56
……mask.

Claims (1)

[Claims for Utility Model Registration] A first fresh air port that creates a swirl of fresh air flowing into the engine combustion chamber, a second fresh air port that linearly introduces fresh air into the combustion chamber, and A fresh air valve that opens and closes the first and second fresh air ports, an exhaust port that discharges exhaust gas from the combustion chamber, an exhaust valve that opens and closes the exhaust port, and a fresh air that passes through the second intake port during low engine load operation. and an intake control valve that substantially blocks fresh air flow, the exhaust valve is opened earlier than the fresh air valve during the downward stroke of the piston to exhaust the exhaust gas in the combustion chamber, and then the exhaust gas in the exhaust port is introduced into the combustion chamber. In a two-stroke engine, the two-stroke engine is provided with means for causing the exhaust gas flowing back from the exhaust port to swirl about the cylinder axis in the same direction as the fresh air flowing in from the first fresh air port. a throttle valve in a fresh air supply passage that supplies fresh air to the second fresh air port; a supercharger disposed downstream of the throttle valve; and a turbocharger in the fresh air supply passage bypassing the supercharger. a bypass passage that connects the engine and the throttle valve and the downstream side of the supercharger; and a bypass control valve that controls the flow rate of fresh air passing through the bypass passage, the throttle valve and the supercharger A two-stroke internal combustion engine characterized in that the control valve is opened when the fresh air supply passage pressure during the period falls below a predetermined value.