JPS6131289B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a two-stroke engine.

A two-stroke engine generally has twice the work stroke for the same rotational speed as a four-stroke engine, and has the advantage of being able to generate large output with a small and lightweight engine.
As is well known, gas exchange in the engine cylinder chamber is performed by pushing out the burned gas in the engine cylinder chamber with fresh air, that is, by scavenging air.
It is difficult to perform complete gas exchange, and it is also difficult to avoid so-called fresh air blow-through, in which fresh air passes through the engine cylinder chamber and is exhausted together with the burned gas. Normally, in a two-stroke gasoline engine that supplies a homogeneous air-fuel mixture created by a carburetor or fuel injection method into the engine cylinder chamber, the fuel (gasoline) in the fresh air blowing through is discharged unburned to the exhaust system. Therefore, it is unavoidable that the HC emission concentration will increase. The higher the air supply ratio in a 2-stroke engine is, the higher the engine load is, the more fresh air blows through.During maximum torque operation, nearly half of the supplied fuel blows through, resulting in high air blow-through. In the load operation range, the HC emission concentration increases significantly. In contrast,
In low-load, low-speed operating ranges, the air supply ratio is low and the air supply efficiency is high, so there is little loss of fresh air due to blow-through, but the scavenging efficiency is low and a large amount of burned gas remains in the engine cylinder chamber. However, since the fresh air is severely diluted by the burned gas, it becomes difficult to ignite the fresh air, resulting in irregular combustion, which causes rapid deterioration of engine performance due to torque fluctuations, decreased output, increased fuel consumption, etc. Also, at this time, unburned fuel is discharged from the non-combustion cycle, so the HC concentration in the exhaust gas increases significantly.

By the way, during low load operation where irregular combustion as described above occurs, in a two-stroke engine, the amount of burned gas remaining in the engine cylinder chamber is high compared to the amount of fresh air supplied into the engine cylinder chamber, and therefore the engine cylinder It is known that a so-called active heat atmosphere is created in a room where the fuel can be activated by a large amount of high-temperature residual burned gas, and this active heat atmosphere is present at the end of the engine's compression stroke. When the fuel is activated, it generates radicals and self-ignites, resulting in self-ignited combustion. If such self-igniting combustion is performed continuously in each combustion cycle, a quiet, high-performance engine can be operated even in a low-load operating range. Since it can be carried out even when
Fuel efficiency can be improved.

It is known that in conventional two-stroke engines, combustion may occur by self-ignition at low load and high speeds, rather than by ignition by the spark plug, but this combustion can cause problems such as piston melting and damage. This is abnormal combustion caused by so-called hot spot ignition, and is not caused by self-ignition as described above. In conventional two-stroke engines, self-ignition combustion as described above does not occur because fresh air flows into the engine cylinder chamber, especially when the air-fuel mixture supply port (scavenging port) is opened. The fresh air flowing into the room at a high flow rate causes turbulent flow of the burned gas remaining in the engine cylinder chamber, and heat dissipates from the engine cylinder wall. This is presumed to be because the temperature decreases and the active heat atmosphere necessary for self-ignition has already disappeared at the end of the engine compression stroke.

Therefore, one object of the present invention is to maintain an active heat atmosphere necessary for self-ignition until the end of the compression stroke of the engine in a stable state, and to operate with continuous self-ignition combustion. Our goal is to provide cycle engines.

When self-igniting combustion is performed, a relatively large amount of burned gas must remain in the engine cylinder chamber in order to secure the thermal energy necessary for fuel activation within the engine cylinder chamber. In this case, the scavenging efficiency is low, and the amount of fresh air flowing into the engine cylinder chamber is inevitably reduced. In medium and high load operating ranges, especially in high speed and high load operating ranges, in order to obtain the necessary engine output, the amount of fresh air flowing in increases and the inflow speed also becomes high, making it impossible to operate using the combustion mechanism described above. Become. Therefore, in such an operating range, it is preferable to increase the scavenging efficiency and the air supply efficiency and combust the air-fuel mixture by spark ignition from the ignition plug.

Therefore, another object of the present invention is to operate by self-igniting combustion as described above in the low load operating range, and to increase the scavenging efficiency and the condensation efficiency in the medium and high load operating range, and to increase the efficiency of the spark plug. A two-stroke engine configured to operate by spark ignition combustion is provided.

According to the invention, such objects include an engine case having a bore, an engine piston movably disposed within the bore and defining an engine cylinder chamber, and an engine piston opening into the engine cylinder chamber at the top of the engine cylinder chamber. a mixture supply port and an air supply port; first and second scavenging valves that open and close the mixture supply port and the air supply port, respectively; a scavenging port that is opened and closed by the engine piston, a mixture supply device, a mixture passage that guides the mixture from the mixture supply device to the mixture supply port, and a mixture that flows through the mixture passage. A mixture control valve that controls the flow, a compressed air source device, an air passage that guides air from the compressed air source device to the air port, and an air control valve that controls the flow of air flowing through the air passage. This is accomplished by a two-stroke engine, such as a 2-stroke engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings.

The attached FIG. 1 is an illustrative sectional view showing one embodiment of the two-stroke engine according to the present invention, and FIG. 2 is an illustrative sectional view showing the top of the engine cylinder chamber of the two-stroke engine shown in FIG. 1. FIG. The engine case 1 is constituted by an assembly of a cylinder head 2, a cylinder block 3, and a crank case 4, and has a bore 5 therein whose upper end is closed by the cylinder head 2. . An engine piston 6 is disposed within the bore 5 so as to be movable in the vertical direction as shown in the figure, and the engine piston 6 has an engine cylinder chamber 7 on the upper side in the figure and a crank chamber on the lower side in the figure. 8 has been determined. The engine piston 6
One end of a connecting rod 9 is connected to the piston pin 10, and the other end of the connecting rod 9 is connected to a crank pin 12 of a crankshaft 11 supported by the crank case 4. ing. As a result, the reciprocating movement of the engine piston 6 is caused by the crankshaft 1
1 is extracted as rotational force. In this case, the piston stroke and the cross-sectional area of the cylinder chamber may be designed so that the compression ratio is 4 to 10.

A spark plug 18 is provided in the center of the cylinder head 2, and two mixture supply ports 13 and two air supply ports 14 are provided alternately around the spark plug 18. The mixture supply port 1
3 and the air supply port 14 are respectively opened and closed by first and second scavenging valves 15 and 16 of the tabet valve type. Although the first and second scavenging valves 15, 16 are not shown in the drawings, they may be configured to be opened and closed by a well-known engine shaft valve mechanism, such as an overhead cam type.
In this case, the air supply port 14 is opened by the second scavenging valve 16 later than the opening timing of the exhaust port 19, which will be described later, and earlier than the opening timing of the mixture supply port 13, and the air-fuel mixture The supply port 13 is opened by the first scavenging valve 15 after the air supply port 14 is opened. The exhaust port 19 opens into the engine cylinder chamber 7 at a side peripheral portion of the engine cylinder chamber 7, and is opened and closed by the reciprocating movement of the engine piston 6.

The mixture supply port 13 is connected to the crank chamber 8 via a mixture passage 20 . A mixture control valve 21 is provided in the middle of the mixture passage 20, preferably as close as possible to the crank chamber 8, for controlling the flow of the mixture flowing through the passage.
is provided. This air-fuel mixture control valve 21 is operated based on a control signal from a control device 22, which will be described later. The crankcase 4 has a mixture intake port 23 that opens into the crank chamber 8.
The air-fuel mixture is supplied to the engine piston 3 through an air cleaner 24, a carburetor 25, an air-fuel mixture supply pipe 26, and a reed valve 27 as the engine piston 6 rises. The carburetor 25 may be constituted by a general carburetor including a throttle valve 28, a float chamber, and various fuel supply systems, but when air is supplied from the air supply port 14, the amount of air supplied corresponds to the amount of air supplied from the air supply port 14. It is preferable to include a correction fuel supply system that corrects the air-fuel ratio of the air-fuel mixture.

The air supply port 14 communicates with an air passage 29, and an air control valve 30 is provided in the middle of the air passage 29 to control the flow of air flowing through the passage. In this case, the air passage 29 is configured so that even when the air flowing into the engine cylinder chamber 7 from the air port 14 flows into the engine cylinder chamber, a swirl is generated with a velocity component in the tangential direction of the engine cylinder chamber. has been done. The air control valve 30 is operated based on a control signal from the control device 22. Air is supplied to the air passage 29 from an air cleaner 31 via an air supply pipe 32 and a scavenging air pump 33.

The control device 22 receives a throttle valve opening signal from the carburetor 25, and outputs a valve opening amount control signal to the mixture control valve 21 and the air control valve 30 in accordance with the throttle valve opening signal. It is configured as follows. As a result, the mixture control valve 21 is located near the fully closed position to throttle the mixture passage 20 until the opening of the throttle valve 28 reaches a certain predetermined value, and as the opening of the throttle valve 28 increases thereafter. The valve is gradually opened, and when the throttle valve 25 reaches a throttle valve opening of about a medium load, it is fully opened, and when the throttle valve opening is larger than that, it is held at the fully open position. The air control valve 30 is held at the fully closed position until the mixture control valve 21 is opened to a certain degree, for example, close to fully open, and as the mixture control valve 21 is opened, In other words, as the opening degree of the throttle valve 28 increases, it gradually opens, and when the throttle valve 28 becomes fully open, it is held at the fully open position.

Next, the operation of the two-stroke engine constructed as described above will be explained.

During engine operation, as the engine piston 6 rises, the mixture is drawn into the crank chamber 8 from the mixture intake port 23 via the air cleaner 24, the carburetor 25, the mixture supply pipe 26, and the reed valve 27. is compressed as it descends,
This compressed air-fuel mixture then passes through the first scavenging valve 15.
When the mixture supply port 13 is opened, the mixture is supplied into the engine cylinder chamber 7 from the mixture supply port 13 via the mixture control valve 21 and the mixture passage 20. When the engine is idling or operating under low load, the air control valve 30 is closed, so the second scavenging valve 16 is connected to the air supply port 1.
Even if the air-fuel mixture control valve 2 is opened, air will not be supplied into the engine cylinder chamber 7.
1 throttles the mixture passage 17, the flow of the mixture is throttled when passing through the mixture control valve 21, resulting in a peak flow velocity when the mixture starts to flow into the engine cylinder chamber 7. The maximum mixture flow rate is reduced, and the mixture is kept at a relatively low flow rate that is uniform throughout the inlet period, and is prevented from occurring when passing through the mixture control valve 21. The turbulence disappears from the mixture control valve 21 through the mixture passage 20 to the mixture supply port 13, and slowly flows into the engine cylinder chamber 7 as a laminar flow.

By supplying the air-fuel mixture into the engine cylinder chamber at low speed and low pressure in this way,
A sufficient amount of high-temperature burnt gas remains in the engine cylinder chamber, and the burnt gas does not flow or become turbulent, and the burnt gas is distributed in layers with the air-fuel mixture in the engine cylinder chamber. As a result, heat dissipation to the cylinder wall is suppressed.
As a result, a stable and favorable active heat surrounding air is created in the engine cylinder chamber. This active thermal atmosphere is maintained until the end of the compression stroke because the gas flow in the engine cylinder chamber is very small and there is little loss of thermal energy during the compression stroke, during which time the air-fuel mixture crosses the boundary with the burnt gas. is activated by the heat of the burnt gas and generates radicals (C ₂ , CH,
Combustion intermediate products such as OOH, CHO, H, etc.) are generated, and this radical-containing state is adiabatically compressed by the engine piston, causing self-ignition at the end of the compression stroke, resulting in self-ignition combustion. In such an operating range, the carburetor may be adjusted to create an air-fuel mixture with an air-fuel ratio selected within the range of 12-20. As mentioned above, by creating an active thermal atmosphere in a stable state within the engine cylinder chamber, the air-fuel mixture reliably undergoes self-ignition combustion in each combustion cycle, and as a result, the engine can operate quietly with little noise and vibration. Furthermore, the concentration of harmful components in the exhaust gas is significantly reduced compared to the spark ignition method.

As the engine load increases, that is, as the opening amount of the throttle valve 28 increases, the mixture control valve 21
will be opened gradually. As a result, the intake efficiency increases, but at the same time, the speed at which the air-fuel mixture flows into the engine cylinder chamber increases, so when the load reaches a certain value, an active thermal atmosphere is no longer created in the engine cylinder chamber, and the air-fuel mixture self-ignites. The spark plug 18 then ignites a spark. In such a loaded operating state, all the air control valves 30 are opened, and compressed air is supplied to the air supply port 14 by the scavenging air pump 33. Since the air supply port 14 is opened toward the engine cylinder chamber 7 earlier than the mixture supply port 13 by the second scavenging valve 16, at this time, there is no air inside the engine cylinder chamber 7.
Air is supplied in a swirl manner from the air supply port 14 before the air-fuel mixture, and the air first performs uniflow type scavenging. Then, the air-fuel mixture is supplied into the engine cylinder chamber 7 from the air-fuel mixture supply port 13 . The air-fuel mixture supplied into the engine cylinder chamber 7 is turbulent by air flowing into the engine cylinder chamber while swirling from the air supply port 14, and is then adiabatically compressed by the engine piston 6 and ignited at the end of the compression stroke. A spark is ignited by the plug 18, resulting in spark ignition combustion. In this way, after the burned gas in the engine cylinder chamber is scavenged by air, the air-fuel mixture is supplied into the engine cylinder chamber.
The fuel components in the air-fuel mixture supplied into the engine cylinder chamber do not blow through from the exhaust port.
Moreover, uniflow scavenging is performed well. As a result, both air supply efficiency and scavenging efficiency improve,
The air-fuel mixture in the engine cylinder chamber is reliably ignited by the spark plug, resulting in good combustion.

In such a spark ignition operating range, the air-fuel mixture is diluted by scavenging air in the engine cylinder chamber, so the carburetor can handle a mixture that is richer than in the above-mentioned self-ignition operating range, for example, with an air-fuel ratio of about 6 to 16. It may be adjusted to create a mixture. Further, it is preferable that the air-fuel ratio of the air-fuel mixture at this time is variably adjusted continuously or stepwise in accordance with the amount of air remaining in the engine cylinder chamber after scavenging.

Although the present invention has been described in detail with respect to specific embodiments above, it will be understood by those skilled in the art that the present invention is not limited thereto and that various embodiments can be made within the scope of the present invention. It should be obvious.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view showing one embodiment of a two-stroke engine according to the present invention, and FIG. 2 is a plan view diagrammatically showing the top of the engine cylinder chamber of the two-stroke engine shown in FIG. It is. 1...Engine case, 2...Cylinder head, 3
...Cylinder block, 4...Crankcase, 5...
Bore, 6... Engine piston, 7... Engine cylinder chamber, 8... Crank chamber, 9... Connecting rod, 10... Piston pin, 11... Crankshaft, 12... Crank pin, 13... Air mixture supply port, 14... Air Supply port, 15...first scavenging valve, 16...second scavenging valve, 18...spark plug, 1
9... Exhaust port, 20... Mixture passage, 21... Mixture control valve, 22... Control device, 23... Mixture intake port, 24... Air cleaner, 25... Carburetor, 2
6...Mixture mixture supply pipe, 27...Reed valve, 28...Throttle valve, 29...Air supply passage, 30...Air control valve, 31...Air cleaner, 32...Air supply pipe, 3
3...Scavenging air pump.

Claims (1)

[Claims] 1. An engine case having a bore, an engine piston that is movably disposed within the bore and defines an engine cylinder chamber, and a mixture supply port and air supply that open into the engine cylinder chamber at the top of the engine cylinder chamber. a port, first and second exhaust valves that open and close the air-fuel mixture supply port and the air supply port, respectively; opening into the engine cylinder chamber at a side circumference of the engine cylinder chamber and opened and closed by the engine piston; an exhaust port, a mixture supply device, a mixture passage that guides the mixture from the mixture mixing device to the mixture supply port, and a mixture control that controls the flow of the mixture flowing through the mixture passage. The compressed air source device includes a valve, a compressed air source device, an air passageway that guides air from the compressed air source device to the air port, and an air control valve that controls the flow of air flowing through the air passageway. 2-stroke engine.