Two-stroke internal combustion engines and engine implements

Abstract

To provide a two-cycle internal combustion engine which can prevent the blow-through of an air-fuel mixture at scavenging, and can supply the air-fuel mixture which is adapted to an operation state of the engine into a combustion chamber.SOLUTION: A two-cycle internal combustion engine comprises: a fuel injection valve 25 for supplying fuel into a crank chamber 8; an intake passage 17 for sucking only air by negative pressure at an operation of a piston 4; and a scavenging passage 18 for making the crank chamber 8 and a combustion chamber 6 communicate with each other. An intake port 42 and the scavenging passage 18 communicate with each other via a piston groove 44, and air is sucked into the crank chamber 8 through the intake passage 17, the intake port 42, the piston groove 44, a scavenging port 14 and the scavenging passage 18. Then, air which passes through the intake passage 17 is introduced into the scavenging passage 18, and air which is stagnated in the scavenging passage 18 at a finish of air intake is involved in the scavenging.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a two-stroke internal combustion engine and an engine-powered implement powered by a two-stroke internal combustion engine. [Background technology]

[0002] Two-stroke internal combustion engines are often used as a power source for portable work machines such as brush cutters, chainsaws, and power blowers. In two-stroke internal combustion engines, a mixture of fuel and air is generated in the carburetor, and this mixture is drawn into the crankcase. Two-stroke internal combustion engines have a scavenging passage that connects the crankcase and the combustion chamber. As the piston moves within the cylinder, the pre-compressed mixture in the crankcase is introduced into the combustion chamber through the scavenging passage, and this mixture scavenges the air. Summary of the Invention [Problem to be solved by the invention]

[0003] Two-stroke internal combustion engines have the well-known problem of "blow-by," where the scavenging mixture introduced into the combustion chamber is expelled directly from the cylinder exhaust. Blow-by wastes fuel and contributes to air pollution.

[0004] To solve this problem, a so-called "stratified scavenging two-stroke engine" is known (Ref. 98 / 057053), which is configured so that the gases introduced into the cylinder are air and then the air-fuel mixture. This technology has an intake passage for supplying air and an intake passage for supplying the air-fuel mixture, and the movement of the piston reciprocating within the cylinder fills the upper part of the scavenging passage with air and the crankcase with the air-fuel mixture. This allows the air stagnating in the upper part of the scavenging passage to participate in scavenging, reducing blow-by with so-called leading air.

[0005] In this configuration, the supply amounts and timing of both the lead air and the mixture are dependent on the negative pressure generated in the combustion chamber and the amount of air trapped in the upper part of the scavenging passage, making precise control impossible. One possible solution for regulating the supply distribution of the lead air and the mixture is to adjust the intake ratio of air and the mixture by appropriately setting the cross-sectional area of ​​each intake passage. However, even with such a solution, precise control to achieve optimal supply distribution across a wide range of engine speeds is not possible. Furthermore, to avoid engine damage, a setting that prioritizes the amount of mixture supplied (i.e., a rich mixture) is necessary to ensure reliable operation across the entire engine speed range.

[0006] Furthermore, two-stroke internal combustion engines are widely used in portable work machines, and due to their characteristics, they are frequently used not only in high-speed, high-load ranges, but also in acceleration and deceleration from low to high speeds, and in intermediate speed and light-load ranges. Even in such two-stroke internal combustion engines, it is desirable to supply the lead air and air-fuel mixture to the combustion chamber that are optimal for the engine's operating conditions. More specifically, it is necessary to accurately control the lead air amount and air-fuel mixture amount under the various operating conditions described above, to set a sufficient lead air supply amount regardless of the air-fuel mixture supply amount required for each operating range of the engine, and to maintain the compactness of the engine.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a two-stroke internal combustion engine that can prevent the air-fuel mixture from blowing by during scavenging and can supply an air-fuel mixture suitable for the operating state of the engine to the combustion chamber.

[0008] The present invention also provides an engine working machine powered by the two-stroke internal combustion engine. [Means for solving the problem]

[0009] In order to solve the above problems, the two-stroke internal combustion engine of the present invention comprises a cylinder defining a combustion chamber and having an exhaust port, an intake port, and a scavenging port; an ignition device for igniting the air-fuel mixture in the combustion chamber; a piston that reciprocates within the cylinder due to combustion expansion in the combustion chamber; a crank chamber communicating with the inside of the cylinder; a crankshaft disposed within the crank chamber and operatively connected to the piston; a fuel injection valve that injects fuel into the crank chamber; and a piston that is ignited by a negative pressure when the piston is operating. pure The engine is provided with an intake passage that takes in only air, and a scavenging passage that connects the crank chamber and the combustion chamber. ,before the piston has a piston groove, and the intake port and the scavenging passage communicate with each other via the piston groove; As the piston moves toward the top dead center, pure air supplied from the intake passage flows into the front The air is drawn into the crank chamber through the intake port, the piston groove, the scavenging port, and the scavenging passage. Thus, the entire scavenging passage is filled with pure air, and pure air flows into the crank chamber to generate an air-fuel mixture therein. The fuel remaining in the scavenging passage at the end of intake pure It is characterized in that air participates in scavenging.

[0010] According to the present invention, fuel is injected into the crank chamber by the fuel injection valve. pure Air is introduced into the transfer passage. pure Air is drawn into the crankcase. At the end of the intake, the air flows into the scavenging passage. pure Air is stagnated in the crankcase through the scavenging passage. pure Air is mixed with fuel to form an air-fuel mixture. The air-fuel mixture in the crankcase is introduced into the combustion chamber through the scavenging passage by the action of the piston. The air-fuel mixture in the combustion chamber is compressed by the piston, ignited by the ignition device, and burns and expands. As this combustion and expansion pushes the piston back, scavenging and exhaust occur. In other words, the air-fuel mixture remaining in the scavenging passage pure Air is pumped into the combustion chamber to participate in scavenging, which expels the combustion gases through the exhaust port.

[0011] As described above, according to the present invention, fuel is supplied into the crank chamber by the fuel injection valve, so that the timing of fuel supply can be easily controlled and an air-fuel mixture suitable for the operating state of the engine can be supplied. pure Only air is drawn in and passes through the intake passage. pure Since the air is introduced into the scavenging passage, the intake passage can be easily formed. pure By only drawing in air, it becomes easier to control the intake air, and it also contributes to improving the reliability of air control. pure Air stagnates, and this pure Since air is involved in scavenging, the mixture is prevented from blowing by during scavenging, improving the exhaust gas composition. In addition, the intake port and scavenging passage are connected via the piston groove, pure Air is drawn into the crankcase through the intake passage, intake port, piston groove, scavenging port, and scavenging passage. This configuration allows the drawn air to come into direct contact with the circumferential surface of the piston, improving piston cooling performance.

[0012] Furthermore, according to the present invention, only an air passage needs to be arranged on the intake side, eliminating the need for the intake passages and intake ports for supplying the air-fuel mixture that are provided in conventional stratified scavenging engines, and therefore the cylinder, manifold, etc. can be easily formed. This configuration also simplifies the air control valve, contributing to easier and more reliable control of the intake air volume. More specifically, regarding the cylinder configuration, whereas conventionally, air ports and air-fuel mixture ports had to be arranged vertically or circumferentially, the present invention eliminates the need for a port for supplying the air-fuel mixture, significantly increasing the design freedom of the port openings in the cylinder.

[0013] The piston has a piston groove, and the intake port and the scavenging passage communicate with each other via the piston groove. With this configuration, the intake port is opened and closed by the piston, eliminating the need for a check valve.

[0014] In one embodiment, the piston groove may be provided with a hole communicating with the crank chamber. In this case, air can also flow from the intake port to the crank chamber through the hole. pure Since air flows in, the amount of air supplied to the crankcase can be increased.

[0015] In one embodiment, a communication portion that communicates the intake passage with the crank chamber may be provided between the lower end of the piston and the lower end of the intake port. In this case, air also flows from the intake port into the crank chamber through the communication portion, thereby increasing the amount of air supplied to the crank chamber.

[0016] In one embodiment, the piston may have a notch at its lower end, and the communication portion may be formed by the notch. In this case, air flows from the intake port into the crank chamber through the notch.

[0017] In one embodiment, a downwardly expanding portion may be provided at the lower end of the intake port, and the communication portion may be formed by the expanding portion. In this case, air flows from the intake port to the crank chamber through the expanding portion. pure Air flows in.

[0018] In one embodiment, the scavenging passage may have a branch passage communicating with the piston groove at a position closer to the crank chamber than the scavenging port. In this case, air flows from the intake port through the branch passage to the crank chamber. pure Since air flows in, the amount of air supplied to the crankcase can be increased.

[0019] In one embodiment, the fuel injection valve is configured to inject fuel from the scavenging passage into the crank chamber. pure The fuel may be injected in a direction that does not obstruct the inflow of air.

[0020] In one embodiment, the fuel injection valve may be a high-pressure fuel injection valve that receives fuel pressure from at least one of an electric fuel pump and a pump that is operated by rotation of the crankshaft, thereby enabling fuel to be injected at a targeted location.

[0021] In one embodiment, the fuel injection valve may inject fuel at high pressure toward a portion of the cylinder or crank chamber that needs to be cooled, whereby the portion that needs to be cooled is effectively cooled by the fuel injected at high pressure from the fuel injection valve.

[0022] In one embodiment, the fuel injection valve may be a high-pressure fuel injection valve that can inject fuel even under the maximum internal pressure of the crank chamber during the operation of the piston. In this way, the timing of fuel injection into the crank chamber can be optimized, thereby improving the components of exhaust gas, for example by preventing fuel from mixing with the air stagnating in the scavenging passage.

[0023] In one embodiment, the intake passage may open to only one intake port, which makes it easier to form the intake passage than the conventional configuration in which an air-fuel mixture port and two air ports are provided, and greatly contributes to the compactness of the work machine.

[0024] In one embodiment, a booster passage communicating the crank chamber and the combustion chamber may be provided separately from the scavenging passage, and the timing of fuel supply by the fuel injection valve may be controlled by a control device, thereby performing homogeneous combustion during full-load operation, while fuel flows into the combustion chamber via the booster passage to perform stratified combustion during light-load operation. In this case, homogeneous combustion is performed during full-load operation, and stratified combustion is performed during light-load operation. This improves thermal efficiency during light-load operation as well as full-load operation.

[0025] As one embodiment, a bottom dead center side booster port that communicates the crank chamber with the booster passage, and a fuel supply configuration that positions the fuel supplied from the fuel injection valve near the bottom dead center side booster port during light load operation may be provided. In this case, since the fuel supplied from the fuel injection valve is introduced (flows into) the vicinity of the bottom dead center side booster port during light load operation, the fuel easily flows into the combustion chamber via the booster passage. pure Air is introduced into the combustion chamber through the scavenging passages. pure By introducing air and fuel mixture through separate passages, it is suitable for stratified combustion during light load operation.

[0026] In one embodiment, the fuel supply configuration may include both a first configuration in which the fuel injection valve is disposed near the bottom dead center side booster port, and a second configuration in which fuel is injected from the fuel injection valve at an injection pressure that can remain near the bottom dead center side booster port.

[0027] In one embodiment, the fuel supply configuration may include both a first configuration in which the fuel injection valve is positioned so that fuel is injected toward the bottom dead center side booster port, and a second configuration in which fuel is injected from the fuel injection valve at an injection pressure that can reach the bottom dead center side booster port.

[0028] In one embodiment, during full-load operation, fuel may be supplied from the fuel injection valve when the piston is positioned near top dead center, and during light-load operation, fuel may be supplied from the fuel injection valve just before the piston reaches bottom dead center. This improves the homogeneity of the air-fuel mixture in the crankcase during full-load operation, making it suitable for homogeneous combustion. On the other hand, during light-load operation, the fuel supplied from the fuel injection valve flows into the combustion chamber through the booster passage before mixing with the air filling the crankcase. Since the air filling the crankcase is introduced into the combustion chamber through the scavenging passage without being mixed with the fuel, this is suitable for stratified combustion.

[0029] In one embodiment, a pair of scavenging ports that communicate the scavenging passage and the combustion chamber may be arranged on an inner peripheral surface of the cylinder, the exhaust port may be arranged on one of the arcuate surfaces between the pair of scavenging ports, and a top dead center side booster port that communicates the combustion chamber and the booster passage may be arranged on the other of the arcuate surfaces between the pair of scavenging ports. In this case, during light load operation, fuel flows into the combustion chamber via the booster passage, and the pair of scavenging ports flows into the combustion chamber. pure A rich mixture is introduced into the combustion chamber from a booster port for supplying a mixture, which is provided separately from the scavenging passage. pure By mixing with air, a rich mixture is formed near the ignition point of the ignition device, which improves the reliability of stratified charge combustion during light load operation.

[0030] As described above, according to the present invention, it is possible to supply lead air and air-fuel mixture to the combustion chamber that are optimal for the engine's operating conditions, not only in the high-speed, high-load range of a two-stroke internal combustion engine, but also during acceleration and deceleration from low speed to high speed, and in the intermediate speed and light-load range. Furthermore, by combining the arrangement, timing control, and directionality of the fuel injection device, it is possible to accurately control the lead air amount and air-fuel mixture amount. Furthermore, because only the air port for intake air is open in the cylinder, it is possible to set a sufficient lead air supply amount, and this also contributes to a simpler and more compact structure on the intake side (opposite the exhaust side) of the engine.

[0031] In one embodiment, the intake passage may be provided with a check valve, which prevents spit-back air from the combustion chamber in the previous cycle from entering the intake passage, allowing for more precise control of the amount of air supplied and the amount of fuel injected in the next cycle.

[0032] As one embodiment, an engine working machine may be provided that includes the two-stroke internal combustion engine as a power source. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a schematic diagram of a two-stroke internal combustion engine according to one embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram of the operating stroke of the engine of FIG. 1. [Figure 3] FIG. 2 is a block diagram showing the flow of air (pure air containing no fuel) and fuel in the engine of FIG. 1. [Figure 4] FIG. 2 is a schematic diagram of a two-stroke internal combustion engine according to another embodiment of the present invention. [Figure 5] FIG. 2 is a schematic diagram of a two-stroke internal combustion engine according to another embodiment of the present invention. [Figure 6] FIG. 2 is a schematic diagram of a two-stroke internal combustion engine according to another embodiment of the present invention. [Figure 7] FIG. 2 is a schematic diagram of a two-stroke internal combustion engine according to another embodiment of the present invention. [Figure 8] 1A and 1B are explanatory diagrams of a two-stroke internal combustion engine according to another embodiment of the present invention during full load operation, in which FIG. 1A is a schematic front view of the engine, FIG. 1B is a diagram showing the fuel supply timing during full load operation of the engine, and FIG. 1C is a schematic plan view of the engine. [Figure 9] 9A and 9B are explanatory diagrams of the two-stroke internal combustion engine of FIG. 8 during light load operation, where FIG. 9A is a schematic front view of the engine, and FIG. 9B is a diagram showing the fuel supply timing during light load operation of the engine. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0035] The two-stroke internal combustion engine (hereinafter simply referred to as "engine") according to the present invention is an air-cooled engine that is mounted primarily as a power source in portable engine-powered implements. Examples of implements that can use the engine of the present invention include handheld, shoulder-mounted, or backpack-mounted portable implements, such as chainsaws, brushcutters, power cutters, hedge trimmers, and power blowers.

[0036] As shown in FIG. 1, an engine 1 according to one embodiment of the present invention includes a cylinder block 2 and a piston 4 that reciprocates within a cylinder 3 that constitutes the cylinder block 2. A combustion chamber 6 is defined by a cylinder head 5 that constitutes one end of the cylinder block 2 and the piston 4, while a crank chamber 8 is defined by a crankcase 7 that constitutes the other end of the cylinder block 2 and the piston 4. A spark plug 9 that constitutes an ignition device is fixed to the cylinder head 5 and protrudes into the combustion chamber 6. A crankshaft 10 is rotatably supported within the crankcase 7, and this crankshaft 10 is connected to a piston pin 4a of the piston 4 by a connecting rod 11. Combustion expansion (explosion) in the combustion chamber 6 causes the piston 4 to reciprocate within the cylinder 3, thereby driving the crankshaft 10 to rotate via the connecting rod 11, and a rotational driving force is output to an output shaft (not shown) connected to the crankshaft 10.

[0037] An exhaust port 12 and at least one scavenging port 14 are opened on the inner wall of the cylinder 3, and these ports 12, 14 are controlled to open and close at predetermined timing by the reciprocating motion of the piston 4. The exhaust port 12 communicates with a muffler 15a via an exhaust pipe 15. The scavenging port 14 communicates with the crank chamber 8 via a scavenging passage 18.

[0038] Engine 1 is of pure air containing no fuel The intake passage 17 is provided for supplying air. The intake passage 17 is provided with an intake passage 17 for supplying air by the negative pressure generated when the piston 4 is in operation. (This refers to pure air that does not contain fuel. The same applies hereinafter in this specification.) Only air is drawn in. A throttle valve 19, such as a butterfly type, is disposed in the intake passage 17, and an air cleaner 20 is disposed upstream of the throttle valve 19. The opening of the throttle valve 19 is adjusted by the operator operating an output operating member (such as a throttle trigger or throttle lever) of the work machine.

[0039] The intake passage 17 is connected to a scavenging passage 18. A check valve 23 is provided in the intake passage 17 to prevent backflow of air from the scavenging passage 18. The intake passage 17 is connected to an intake port 24 formed at the end of the scavenging passage 18 on the scavenging port 14 side. The intake passage 17 guides air purified by an air cleaner 20 to the scavenging passage 18. The intake passage 17 opens to the intake port 24 at only one location.

[0040] During the intake stroke, when the crank chamber 8 is under negative pressure, the air purified by the air cleaner 20 passes through the intake passage 17, the check valve 23, the intake port 24, and the scavenging passage 18 in this order, before being drawn into the crank chamber 8. At the end of the intake stroke, air remains in the scavenging passage 18. During the scavenging stroke, this remaining air flows into the cylinder 3 through the scavenging port 14, prior to the air-fuel mixture in the crank chamber 8. Due to this air-leading scavenging, the combustion gas in the combustion chamber 6 is discharged from the exhaust port 12.

[0041] The engine 1 is equipped with a fuel injection valve 25 for supplying fuel into the crank chamber 8. The fuel is mixed with air in the crank chamber 8 to form an air-fuel mixture. In the illustrated example, the fuel injection valve 25 is disposed in the lower part of the crankcase 7.

[0042] A fuel tank 26 and a fuel pump 27 are connected to the fuel injection valve 25. Fuel in the fuel tank 26 is supplied to the fuel injection valve 25 by operation of the fuel pump 27, and fuel injection is controlled by opening and closing the fuel injection valve 25.

[0043] The opening and closing of the fuel injection valve 25 is controlled by a control device 28 including a microcomputer. A detection signal from at least one sensor 29 (29a to 29g) that detects the operating state of the engine 1 is input to the control device 28. Based on the detection by the sensor 29, the control device 28 controls the supply of fuel to the crank chamber 8 by the fuel injection valve 25.

[0044] Examples of the at least one sensor 29 include an intake air temperature sensor 29a that detects intake air temperature and emits a signal, an intake air pressure sensor 29b that detects intake air pressure and emits a signal, a throttle valve opening sensor 29c that detects the opening of the throttle valve 19 and emits a signal, a crank chamber pressure sensor 29d that detects the pressure in the crank chamber 8 and emits a signal, a crank chamber temperature sensor 29e that detects the temperature of the crank chamber 8 and emits a signal, an engine speed sensor 29f that detects the speed of the engine 1 and emits a signal, and a crank angle sensor 29g that detects the crank angle and emits a signal. The signals from these sensors 29a to 29g are input to the control device 28.

[0045] Based on various signals from sensors 29a to 29g, control device 28 issues a fuel injection signal to fuel injection valve 25 at an appropriate timing according to a predetermined program, and also issues an ignition signal to spark plug 9, which constitutes an ignition device, at a predetermined timing. This causes fuel to be supplied to crank chamber 8 and the air-fuel mixture in combustion chamber 6 to be ignited.

[0046] Next, the operation of the engine 1 in Fig. 1 will be described with reference to Fig. 2. In Fig. 2, (a) is a diagram illustrating scavenging, (b) is a diagram illustrating intake and compression, (c) is a diagram illustrating combustion expansion (explosion), and (d) is a diagram illustrating exhaust. Note that fuel injection into the crank chamber 8 may be performed at any appropriate time, but as an example, it is performed at the end of the intake stroke.

[0047] Referring to Figures 2(a) and (b), when the piston 4 closes the scavenging ports 14 as it rises from bottom dead center, the rising of the piston 4 creates a negative pressure in the crank chamber 8. As a result, air is drawn into the crank chamber 8 from the intake passage 17 through the intake ports 24 and the scavenging passages 18. As an example, fuel is injected from the fuel injection valve 25 at the end of the intake stroke. In the combustion chamber 6, the air-fuel mixture is compressed until the piston 4 reaches top dead center. When the piston 4 reaches top dead center, the intake of air into the crank chamber 8 ends. At this point, the crank chamber 8 is filled with a mixture of fuel and air, and air is stagnant in the scavenging passages 18.

[0048] Referring to FIG. 2(c), when the piston 4 reaches top dead center, ignition is performed by the spark plug 9. This causes the air-fuel mixture to burn and expand (explode) in the combustion chamber 6, pushing the piston 4 down to bottom dead center, rotating the crankshaft 10 and generating power. The downward movement of the piston 4 pre-compresses the air-fuel mixture in the crank chamber 8. At this time, the check valve 23 operates to prevent air from flowing out of the intake port 24.

[0049] Referring to FIG. 2(d), when the exhaust port 12 opens as the piston 4 descends, the combustion gas flows out into the exhaust pipe 15. Next, as shown in FIG. 2(a), the scavenging port 14 opens, and the pre-compressed air-fuel mixture in the crank chamber 8 is sent through the scavenging passage 18 into the combustion chamber 6. At this time, air that has been stagnating in the scavenging passage 18 flows into the combustion chamber 6 as leading air ahead of the air-fuel mixture in the crank chamber 8, expelling the combustion gas into the exhaust port 12. This reduces the blow-by of the air-fuel mixture during scavenging. The piston 4 moves again toward top dead center as the crankshaft 10 rotates, and the same process is repeated thereafter.

[0050] The flow of air and fuel in the engine 1 of FIG. 1 can be simply shown as a block diagram in FIG.

[0051] According to the engine 1 of this embodiment, fuel is supplied into the crank chamber 8 by the fuel injection valve 25, which makes it easy to control the timing of fuel supply and enables the supply of an air-fuel mixture suited to the operating state of the engine 1. In addition, air remains in the scavenging passage 18 at the end of intake, and this remaining air participates in scavenging as leading air, preventing the air-fuel mixture from blowing by during scavenging and improving the exhaust gas composition. Since the intake passage 17 is configured to take in only air, it is easy to control the intake air and it also contributes to improving the reliability of air control. In addition, since the intake passage 17 communicates with the scavenging passage 18 via the check valve 23, it contributes to simplifying the piston 4 and the scavenging passage 18.

[0052] The arrangement and type of the fuel injection valve 25 may be as follows, for example.

[0053] In one preferred embodiment, the fuel injection valve 25 may be configured to inject fuel in a direction that does not lead to the scavenging passage 18. In this way, the fuel is less likely to be mixed with the air remaining in the scavenging passage 18.

[0054] In one preferred embodiment, fuel injection valve 25 may be a high-pressure fuel injection valve that receives fuel pressure from at least one of an electric fuel pump and a pump operated by the rotation of crankshaft 10. In this way, fuel can be injected at a targeted location. For example, it is possible to inject fuel at a location in engine 1 where seizure is likely to occur.

[0055] In a preferred embodiment, the fuel injection valve 25 may inject fuel at high pressure toward a portion of the cylinder 3 or the crank chamber 8 that needs to be cooled. In this manner, the portion that needs to be cooled is effectively cooled by the fuel injected at high pressure from the fuel injection valve 25. Examples of the portion that needs to be cooled include portions where frictional heat is generated, such as the connection between the connecting rod 11 and the piston pin 4a and the connection between the connecting rod 11 and the crankshaft 10. Furthermore, fuel may be injected at high pressure onto the inner wall of the piston 4 to cool the piston 4.

[0056] The fuel for a two-stroke internal combustion engine is a mixed fuel made by mixing gasoline with lubricating oil. Therefore, when fuel (mixed fuel) is supplied into the crankcase 8, the lubricating oil contained in the fuel quickly and responsively lubricates the piston 4 and the cylinder 3. This prevents the engine 1 from seizing. In this case, fuel may be injected using at least one of a temperature signal, an RPM signal, an intake pressure signal, and an opening signal to prevent the engine 1 from seizing. For example, fuel may be injected when a high temperature is detected during high-speed operation. It is also possible to prevent seizure by injecting fuel when the engine is suddenly stopped during high-speed operation.

[0057] In one preferred embodiment, the fuel injection valve 25 may be a high-pressure fuel injection valve that can inject fuel even under the maximum internal pressure of the crank chamber 8 during the operation of the piston 4. In this way, the timing of fuel injection into the crank chamber can be optimized, thereby improving the exhaust gas composition by, for example, preventing gasoline from being mixed with the lead air.

[0058] As a preferred embodiment, as shown in FIG. 1 , the fuel injection valve 25 may be installed on the side where the fuel tank 26 is located with respect to a plane including the axis X of the cylinder 3 and the axis Y of the crankshaft 10. This configuration allows the fuel tank 26 and the fuel injection valve 25 to be positioned close to each other, thereby shortening the piping between them and contributing to a more compact and lightweight work machine. Furthermore, by arranging the fuel injection valve 25 so that the fuel inlet 25c of the fuel injection valve 25 faces the fuel tank 26, it becomes easier to form the piping from the fuel tank 26 to the fuel injection valve 25. Furthermore, in this case, the short distance between the fuel tank 26 and the fuel injection valve 25 allows fuel to be delivered to the fuel injection valve 25 quickly, resulting in smooth starting of the engine 1. In particular, in the case of a high-pressure fuel injection valve with an electric fuel pump installed in the fuel tank 26, the short distance between the electric fuel pump and the fuel injection valve 25 allows fuel to be delivered quickly, resulting in smooth starting of the engine 1.

[0059] In one preferred embodiment, fuel injection valve 25a may have fuel inlet 25c at its rear end and inject fuel upward, and fuel tank 26 may be disposed below crank chamber 8. In this case, the same effects as those described above can be obtained.

[0060] The fuel injector 25 may be electrically or mechanically controlled. In the latter case, for example, a mechanically openable and closable fuel injector may be operatively connected to the crankshaft 10 so that the fuel injector opens and closes at a predetermined timing during the working stroke of the piston 4.

[0061] Next, a modified example of Fig. 1 will be described with reference to Fig. 4. In the following description, components that are the same as or equivalent to those in the example of Fig. 1 are given the same reference numerals as in Fig. 1, and duplicated descriptions will be omitted. Fig. 4(a) shows a state in which the piston is at top dead center, and Fig. 4(b) shows a state in which the piston is at bottom dead center.

[0062] In an engine 40 shown in Fig. 4, only one intake port 42 opens on the inner wall of a cylinder 41. This intake port 42 is connected to the intake passage 17. The intake port 42 is opened and closed by a piston 43. The piston 43 shown in Fig. 4 has a piston groove 44 on its circumferential surface, and the intake passage 17 and the scavenging port 14 are connected to each other via this piston groove 44 at a predetermined timing.

[0063] In the engine 40 of FIG. 4, negative pressure is created in the crank chamber 8 as the piston 43 moves toward top dead center. When the piston groove 44 and the scavenging port 14 overlap during the upward movement of the piston 43, the crank chamber 8 communicates with the intake passage 17 via the scavenging passage 18, the scavenging port 14, the piston groove 44, and the intake port 42. Therefore, due to the negative pressure in the crank chamber 8, air is drawn into the crank chamber 8 through the intake passage 17, the intake port 42, the piston groove 44, the scavenging port 14, and the scavenging passage 18. Since the drawn air comes into direct contact with the circumferential surface of the piston 43, the cooling performance of the piston 43 is improved. Furthermore, because the intake port 42 is opened and closed by the piston 43, there is no need to provide a check valve in the intake passage 17, unlike the engine 1 of FIG. 1.

[0064] Next, a modified example of Fig. 4 will be described with reference to Fig. 5. In the following description, components that are the same as or equivalent to those in the example of Fig. 4 will be assigned the same reference numerals as in Fig. 4, and duplicated description will be omitted.

[0065] In the engine 50 of Figure 5, a hole 52 communicating with the crank chamber 8 is provided in the piston groove 44 of the piston 51. Air also flows into the crank chamber 8 from the intake port 42 through the hole 52, so the amount of air supplied to the crank chamber 8 can be increased.

[0066] Next, a modified example of Fig. 4 will be described with reference to Fig. 6. In the following description, components that are the same as or equivalent to those in the example of Fig. 4 will be assigned the same reference numerals as in Fig. 4, and duplicated description will be omitted.

[0067] 6, a communication part 61 that connects the intake passage 17 and the crank chamber 8 is provided between the lower end of the piston 43 and the lower end of the intake port 42. In this case, when the piston 43 reaches top dead center, air also flows from the intake port 42 into the crank chamber 8 through the communication part 61, thereby increasing the amount of air supplied to the crank chamber 8.

[0068] 6(a), the communication portion 61 may be formed such that a downwardly expanding portion 61a is provided at the lower end of the intake port 42, and this expanding portion 61a forms the communication portion 61. In this case, air flows from the intake port 42 into the crank chamber 8 through the expanding portion 61a.

[0069] 6(b), a notch 61b may be provided at the lower end of the piston 62, and this notch 61b may form the communicating portion 61. In this case, air flows from the intake port 42 into the crank chamber 8 through the notch 61b.

[0070] Next, a modified example of Fig. 4 will be described with reference to Fig. 7. In the following description, components that are the same as or equivalent to those in the example of Fig. 4 will be assigned the same reference numerals as in Fig. 4, and duplicated description will be omitted.

[0071] In the engine 70 of Fig. 7, the scavenging passage 18 has a branch passage 71 that communicates with the piston groove 44 at a position closer to the crank chamber 8 than the scavenging ports 14. In this case, since the branch passage 71 is located below the scavenging ports 14, the time during which the piston groove 44 and the branch passage 71 communicate with each other due to the operation of the piston 43 can be extended, thereby increasing the amount of intake air and improving power.

[0072] Next, another embodiment of the present invention will be described with reference to Figures 8 and 9. The example of Figures 8 and 9 is an embodiment based on a modified example of engine 40 in Figure 4, which is a modified example of Figure 1. Therefore, components that are the same as or equivalent to those in the examples of Figures 1 and 4 are given the same reference numerals, and duplicated descriptions may be omitted.

[0073] 8 and 9 also includes a cylinder 41 that defines a combustion chamber 6 and has an exhaust port 12, an ignition device (spark plug 9) that ignites the air-fuel mixture in the combustion chamber 6, a piston 43 that reciprocates within the cylinder 41 due to combustion and expansion in the combustion chamber 6, a crank chamber 8 that communicates with the interior of the cylinder 41, a crankshaft 10 that is disposed within the crank chamber 8 and operatively connected to the piston 43, a fuel injection valve 25 that injects fuel into the crank chamber 8, an intake passage 17 that supplies only the air that is sucked in by the negative pressure when the piston 43 is operating, and a scavenging passage 18 that communicates between the crank chamber 8 and the combustion chamber 6. Air passing through the intake passage 17 is introduced into the scavenging passage 18, and the air that remains in the scavenging passage 18 during the latter half of the intake stroke participates in scavenging.

[0074] As shown in Figure 8(c), an engine 80 is provided with a pair of scavenging passages 18. As a result, a pair of scavenging ports 14 that connect the scavenging passages 18, 18 to the combustion chamber 6 are present on the inner peripheral surface of the cylinder 41. The intake passage 17 branches into two branch passages 17a, 17b, and each branch passage 17a, 17b communicates with a pair of intake ports 42, 42 provided in the cylinder 41. Each intake port 42, 42 communicates with each scavenging port 14, 14 at a predetermined timing via each of two piston grooves 44, 44 provided on the peripheral surface of the piston 43.

[0075] As shown in FIGS. 8(a) and 9(a), in an engine 80, a booster passage 81 that connects the crank chamber 8 and the combustion chamber 6 is disposed separately from the pair of scavenging passages 18, 18. The booster passage 81 communicates with the combustion chamber 6 via a top dead center-side booster port 81a formed in the cylinder 41, and with the crank chamber 8 via a bottom dead center-side booster port 81b formed in the crankcase 7. The booster passage 81 allows fuel in the crank chamber 8 to flow into the combustion chamber 6 during light load operation of the engine 80, thereby achieving stratified charge combustion. That is, during light load operation of the engine 80, the operation of the piston 43 causes fuel in the crank chamber 8 to flow into the combustion chamber 6 through the booster passage 81. At the same time, air in the crank chamber 8 flows into the combustion chamber 6 through the scavenging passages 18, 18. In this way, air and an air-fuel mixture are introduced separately into the combustion chamber 6, and stratified charge combustion is performed.

[0076] In this embodiment, the control device 28 controls at least the fuel supply timing by the fuel injection valve 25, thereby performing homogeneous combustion during full-load operation as shown in Figures 8(a) and 8(b). On the other hand, during light-load operation as shown in Figures 9(a) and 9(b), fuel flows into the combustion chamber 6 via the booster passage 81, performing stratified combustion. This improves thermal efficiency during light-load operation as well as full-load operation.

[0077] The timing of fuel supply by the fuel injector 25 is controlled by the control device 28 so as to differ between full-load operation and light-load operation of the engine 80. That is, during full-load operation of the engine 80, fuel is supplied from the fuel injector 25 at a timing when the piston 43 is positioned near the top dead center, as shown in FIG. 8(b). In this configuration, the air-fuel mixture generated by mixing in the crank chamber 8 is introduced into the combustion chamber 6 from the lower ends of the scavenging passages 18, 18. As a result, during full-load operation, the homogeneity of the air-fuel mixture in the crank chamber 8 is improved, which is suitable for homogeneous combustion.

[0078] On the other hand, when the engine 80 is operating under a light load, as shown in Fig. 9(b), fuel is supplied from the fuel injector 25 when the piston 43 is positioned near the bottom dead center, more preferably just before the piston 43 reaches the vicinity of the bottom dead center. As a result, during light load operation, the fuel supplied from the fuel injector 25 is likely to flow into the combustion chamber 6 via the booster passage 81 before being mixed with air in the crank chamber 8. In addition to this flow of the air-fuel mixture, air filled in the crank chamber 8 is introduced from the scavenging passages 18, 18, creating an air layer and an air-fuel mixture layer in the combustion chamber 6, thereby achieving stratified combustion.

[0079] Preferably, the control device 28 also controls the fuel injection mode of the fuel injection valve 25 so that it differs between full-load operation and light-load operation of the engine 80. That is, when the engine 80 is operating at full load, it is preferable that fuel be injected radially and forcefully from the fuel injection valve 25, as shown in Fig. 8(a). This makes it easier for the fuel to be dispersed throughout the crank chamber 8, making it easier for the fuel and air to be mixed homogeneously throughout the crank chamber 8.

[0080] On the other hand, when the engine 80 is operating under a light load, it is preferable that fuel be supplied from the fuel injection valve 25 so that the fuel is positioned near the bottom dead center side booster port 81b. To achieve this type of fuel supply, the engine 80 is provided with a fuel supply configuration 82 that positions the fuel supplied from the fuel injection valve 25 near the bottom dead center side booster port 81b when the engine 80 is operating under a light load. This fuel supply configuration 82 makes it easier for the fuel to flow into the combustion chamber 6 via the booster passage 81 when the engine 80 is operating under a light load. This is therefore suitable for stratified charge combustion during light load operation.

[0081] 9(a), the fuel supply configuration 82 may include both a first configuration 82a in which the fuel injector 25 is disposed near the bottom dead center booster port 81b, and a second configuration 82b in which the fuel injector injects fuel at an injection pressure that allows the fuel to remain near the bottom dead center booster port 81b. As described above, the injection pressure of the fuel injector 25 is controlled by the control device 28.

[0082] 9(a), a configuration may be adopted in which both a first configuration 82c in which fuel injection valve 25 is disposed so as to inject fuel toward bottom dead center side booster port 81b and a second configuration 82d in which fuel is injected from fuel injection valve 25 at an injection pressure that allows the fuel to reach bottom dead center side booster port 81b are provided. In this case as well, the injection pressure of fuel injection valve 25 is controlled by control device 28.

[0083] Next, a preferred positional relationship between the exhaust port, two scavenging ports, and the top dead center side booster port will be described. As shown in Figure 8(c), two scavenging ports are arranged on the inner peripheral surface of the cylinder. The exhaust port is arranged on one of the arcuate surfaces of the inner peripheral surface of the cylinder between these two scavenging ports. The top dead center side booster port is arranged on the other arcuate surface of the inner peripheral surface of the cylinder between the two scavenging ports. The opening position of the top dead center side booster port in the axial direction of the cylinder may be lower than the exhaust port (towards bottom dead center), or may be at approximately the same height as the scavenging ports.

[0084] With this configuration, during light-load operation, fuel flows into the combustion chamber through the booster passage, and air flows into the combustion chamber through the two scavenging ports. The fuel flowing into the combustion chamber through the booster passage is rich and contains almost no air. The air flowing into the combustion chamber through the two scavenging ports contains almost no fuel. As shown in Figure 9(a), the fuel flowing into the combustion chamber through the top-dead-center booster port is carried toward the cylinder head along the other arcuate surface of the cylinder's inner circumferential surface by the air flowing into the combustion chamber through the two scavenging ports. By introducing air and the air-fuel mixture separately into the combustion chamber 6 in this way, stratified-charge combustion during light-load operation is further ensured.

[0085] The configuration in which a booster passage is provided and the timing of fuel supply from the fuel injection valve is controlled to perform stratified combustion during light load operation is not limited to the embodiment shown in Figures 8 and 9, but can of course also be applied to the embodiments shown in Figures 1 to 7.

[0086] In such engines, it is important to more precisely control the ratio of air supplied through the intake passage to the mixture containing fuel components supplied by the fuel injection device. For this purpose, it is desirable to provide a well-known check valve (see check valve 23 in Figure 1) in the intake passage, more preferably near the intake port. By providing a check valve, the amount of air supplied and the amount of fuel injected in the next cycle can be more precisely controlled by preventing the return air from the combustion chamber in the previous cycle from being mixed into the intake passage.

[0087] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and the present invention also includes design changes within the scope of the present invention. Furthermore, the above-described embodiments can be combined by utilizing each other's technologies as long as there are no particular contradictions or problems in their purposes, configurations, etc. [Explanation of symbols]

[0088] 1. Two-stroke internal combustion engine 3 cylinders 4 pistons 6 Combustion chamber 9 Spark plug (ignition device) 10 crankshaft 12 Exhaust port 14 Scavenging port 17 Intake passage 18 scavenging passage 23 Check valve 25 Fuel injection valve 42 Intake port 44 Piston groove 52 holes 61 Communication part 61a Enlarged section 61b Notch 71 Branch Passage

Claims

1. a cylinder defining a combustion chamber and having an exhaust port, an intake port, and a scavenging port; an ignition device for igniting the air-fuel mixture in the combustion chamber; a piston reciprocating within the cylinder by combustion expansion in the combustion chamber; a crank chamber communicating with the interior of the cylinder; a crankshaft disposed within the crank chamber and operatively connected to the piston; a fuel injection valve for injecting fuel into the crank chamber; an intake passage for drawing in only pure air by negative pressure when the piston is operating; and a scavenging passage communicating the crank chamber and the combustion chamber; a piston groove, the intake port and the scavenging passage are communicated via the piston groove, and as the piston moves toward top dead center, pure air supplied from the intake passage is drawn into the crankcase through the intake port, the piston groove, the scavenging port and the scavenging passage, so that the entire scavenging passage is filled with pure air, and pure air flows into the crankcase to generate an air-fuel mixture therein, and the pure air remaining in the scavenging passage at the end of the intake stroke participates in scavenging.

2. 2. The two-stroke internal combustion engine according to claim 1, wherein the piston groove is provided with a hole communicating with the crankcase.

3. 3. The two-stroke internal combustion engine according to claim 1, further comprising a communication portion between a lower end of the piston and a lower end of the intake port, the communication portion providing communication between the intake passage and the crank chamber.

4. 4. The two-stroke internal combustion engine according to claim 3, wherein a notch is provided in a lower end of the piston, and the communication portion is formed by the notch.

5. 4. The two-stroke internal combustion engine according to claim 3, further comprising a downwardly expanding portion at a lower end of said intake port, said communicating portion being formed by said expanding portion.

6. 6. The two-stroke internal combustion engine according to claim 1, wherein the scavenging passage has a branch passage communicating with the piston groove at a position closer to the crankcase than the scavenging port.

7. 7. The two-stroke internal combustion engine according to claim 1, wherein the fuel injection valve injects fuel in a direction that does not obstruct the inflow of pure air into the crank chamber.

8. 8. The two-stroke internal combustion engine according to claim 1, wherein the fuel injection valve is a high-pressure fuel injection valve that receives fuel pressure from at least one of an electric fuel pump and a pump that operates by rotation of the crankshaft.

9. 9. The two-stroke internal combustion engine according to claim 8, wherein the fuel injection valve injects fuel at high pressure toward a portion in the cylinder or the crank chamber that needs to be cooled.

10. 10. The two-stroke internal combustion engine according to claim 8, wherein the fuel injection valve is a high-pressure fuel injection valve capable of injecting fuel even under the maximum internal pressure of the crank chamber during the operation of the piston.

11. 11. A two-stroke internal combustion engine according to claim 1, wherein the intake passage opens into only one intake port.

12. 12. The two-stroke internal combustion engine according to claim 1, wherein a booster passage communicating the crank chamber and the combustion chamber is arranged separately from the scavenging passage, and a timing of fuel supply by the fuel injection valve is controlled by a control device, thereby performing homogeneous combustion during full-load operation, while performing stratified combustion by allowing fuel to flow into the combustion chamber via the booster passage during light-load operation.

13. 13. The two-stroke internal combustion engine according to claim 12, further comprising: a bottom dead center side booster port that connects the crank chamber and the booster passage; and a fuel supply structure that introduces fuel supplied from the fuel injection valve into the vicinity of the bottom dead center side booster port during light load operation.

14. 14. The two-stroke internal combustion engine according to claim 13, wherein the fuel supply configuration includes both a first configuration in which the fuel injection valve is disposed near the bottom dead center side booster port, and a second configuration in which fuel is injected from the fuel injection valve at an injection pressure that can remain near the bottom dead center side booster port.

15. 14. The two-stroke internal combustion engine according to claim 13, wherein the fuel supply configuration includes both a first configuration in which the fuel injection valve is positioned so that fuel is injected toward the bottom dead center side booster port, and a second configuration in which fuel is injected from the fuel injection valve at an injection pressure that can reach the bottom dead center side booster port.

16. 16. The two-stroke internal combustion engine according to claim 12, wherein during full load operation, fuel is supplied from the fuel injection valve at a timing when the piston is located near top dead center, and during light load operation, fuel is supplied from the fuel injection valve at a timing just before the piston reaches near bottom dead center.

17. 17. The two-stroke internal combustion engine according to claim 12, wherein a pair of scavenging ports that communicate between the scavenging passage and the combustion chamber are arranged on an inner peripheral surface of the cylinder, the exhaust port is arranged on one of the arcuate surfaces between the pair of scavenging ports, and a top dead center side booster port that communicates between the combustion chamber and the booster passage is arranged on the other of the arcuate surfaces between the pair of scavenging ports.

18. 18. A two-stroke internal combustion engine according to any one of claims 1 to 17, further comprising a check valve in the intake passage.

19. An engine implement comprising the two-stroke internal combustion engine according to any one of claims 1 to 18 as a power source.

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