Two-cycle internal combustion engine and engine working machine

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 working machine 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, chain saws, 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 crank chamber. Two-stroke internal combustion engines have a scavenging passage that connects the crank chamber and the combustion chamber. As the piston moves in the cylinder, the mixture precompressed in the crank chamber is introduced into the combustion chamber through the scavenging passage, and scavenging is performed by this mixture. 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," which means that the scavenging mixture introduced into the combustion chamber is expelled directly from the cylinder exhaust. Blow-by wastes fuel and is a source of air pollution.

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

[0005] In this configuration, the supply amount and timing of both the leading air and the mixture are determined subordinately by the negative pressure generated in the combustion chamber and the amount of air stagnating in the upper part of the scavenging passage, and precise control is not possible. As one idea, in order to regulate the supply distribution of the leading air and the mixture, a countermeasure such as appropriately setting the cross-sectional area of ​​each intake passage and adjusting the intake ratio of air and the mixture can be adopted. However, even with such a countermeasure, precise control that realizes optimal supply distribution in all operating ranges of a wide rotation speed range is not possible. In addition, in order to avoid damage to the engine, it is necessary to set the mixture supply amount with priority (rich) so that reliable operation can be maintained in all rotation speed ranges.

[0006] In addition, two-stroke internal combustion engines are widely used in portable work machines, and due to their characteristics, they are frequently used not only in the high rotation and high load ranges, but also in the acceleration and deceleration from low rotation to high rotation, and in the intermediate rotation speed and light load ranges. 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 most suitable for the engine operating conditions. More specifically, it is required to accurately control the lead air amount and the air-fuel mixture amount in the various operating conditions as described above, to set a sufficient lead air supply amount regardless of the 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 blow-by of the air-fuel mixture 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 aims to provide an engine working machine using the above-mentioned two-stroke internal combustion engine as a power source. [Means for solving the problem]

[0009] In order to achieve the above object, a two-stroke internal combustion engine according to 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 an air-fuel mixture in the combustion chamber, a piston reciprocating in the cylinder by combustion and expansion in the combustion chamber, a crank chamber communicating with the inside of the cylinder, a crankshaft disposed in 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 air by negative pressure during operation of the piston, and a scavenging passage communicating between the crank chamber and the combustion chamber, wherein air passing through the intake passage is introduced into the scavenging passage, the piston has a piston groove, the intake port and the scavenging passage are communicated via the piston groove, air is drawn into the crank chamber through the intake passage, the intake port, the piston groove, the scavenging port and the scavenging passage, and air remaining in the scavenging passage at the end of intake takes part in scavenging.

[0010] According to the present invention, fuel is injected into the crank chamber by the fuel injection valve. Air passing through the intake passage is introduced into the scavenging passage. The air introduced into the scavenging passage is sucked into the crank chamber. At the end of the intake, air remains in the scavenging passage. The air introduced into the crank chamber through the scavenging passage is mixed with fuel to form an air-fuel mixture. The air-fuel mixture in the crank chamber is introduced into the combustion chamber through the scavenging passage by the operation of the piston. The air-fuel mixture in the combustion chamber is compressed by the piston, ignited by an ignition device, and combusted and expanded. During the process in which the piston is pushed back by this combustion and expansion, scavenging and exhaust are performed. That is, the air remaining in the scavenging passage is forced into the combustion chamber and participates in scavenging, and the combustion gas is exhausted from the exhaust port by this scavenging.

[0011] As described above, according to the present invention, since fuel is supplied into the crank chamber by the fuel injection valve, the timing of fuel supply can be easily controlled, and a mixture suitable for the operating state of the engine can be supplied. In addition, since the intake passage takes in only air, and the air passing through the intake passage is introduced into the scavenging passage, the intake passage can be easily formed. Since the intake passage takes in only air, it is easy to control the intake air, and it can also contribute to improving the reliability of air control. When the intake is completed, air remains in the scavenging passage, and this air participates in scavenging, so that the mixture is prevented from blowing through during scavenging, and the composition of the exhaust gas is improved. In addition, the intake port and the scavenging passage are communicated through the piston groove, and air is sucked into the crank chamber through the intake passage, the intake port, the piston groove, the scavenging port, and the scavenging passage. With this configuration, the sucked air comes into direct contact with the peripheral surface of the piston, and the cooling performance of the piston is also improved.

[0012] Furthermore, according to the present invention, since only an air passage needs to be arranged on the intake side, the intake passage and intake port for supplying the mixture, which are provided in conventional stratified scavenging engines, are not required, and the cylinder, manifold, etc. can be easily formed. This configuration simplifies the air control valve, which contributes to facilitating and improving the reliability of intake air volume control. In more detail about the cylinder configuration, while conventionally it was necessary to arrange the air port and the mixture port vertically or circumferentially, the present invention does not require a port for supplying the mixture, so the design freedom of the port opening in the cylinder is significantly improved.

[0013] The piston has a piston groove, and the intake port and the scavenging passage are communicated via the piston groove. With this configuration, the intake port is opened and closed by the piston, so there is no need to provide a check valve.

[0014] In one embodiment, the piston groove may be provided with a hole communicating with the crank chamber, in which case air also flows from the intake port into the crank chamber through the hole, thereby increasing the amount of air supplied to the crank chamber.

[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 lower end provided with a notch, 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, the intake port may be provided at a lower end with a portion enlarged downward, the enlarged portion forming the communication portion, in which case air flows from the intake port into the crank chamber through the enlarged portion.

[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 into the crank chamber, so that the amount of air supplied to the crank chamber can be increased.

[0019] In one embodiment, the fuel injection valve may inject fuel in a direction that does not hinder the inflow of air from the scavenging passage into the crank chamber.

[0020] As one embodiment, the fuel injection valve may be a high-pressure fuel injection valve receiving fuel pressure from at least one of an electric fuel pump and a pump operated by rotation of the crankshaft, thereby making it possible to inject fuel 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 capable of injecting 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 the exhaust gas, for example by preventing fuel from being mixed with the air remaining 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 a mixture port and two air ports are provided, and contributes greatly to the compactness of the working 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, so that homogeneous combustion is performed during full load operation, while fuel flows into the combustion chamber through the booster passage and stratified combustion is performed 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, the engine may include a bottom dead center 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 booster port during light load operation. In this case, the fuel supplied from the fuel injection valve is introduced (flows into) the vicinity of the bottom dead center booster port during light load operation, so that the fuel easily flows into the combustion chamber through the booster passage. Meanwhile, air is introduced into the combustion chamber from a scavenging passage, and the air-fuel mixture is introduced from a different passage, which is suitable for stratified combustion during light load operation.

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

[0027] As 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 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 booster port.

[0028] In one embodiment, fuel may be supplied from the fuel injection valve when the piston is at the top dead center during full load operation, and fuel may be supplied from the fuel injection valve just before the piston reaches the bottom dead center during light load operation. In this way, the homogeneity of the mixture in the crank chamber is improved during full load operation, which is 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 crank chamber. The air filling the crank chamber is introduced into the combustion chamber from the scavenging passage without being mixed with fuel, which 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 the 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 arcuate surface between the pair of scavenging ports. In this case, during light load operation, fuel flows into the combustion chamber through the booster passage, and air flows into the combustion chamber from the pair of scavenging ports. A rich mixture is mixed with the air in the combustion chamber from a booster port for supplying the mixture, which is provided separately from the scavenging passage, to form a rich mixture near the ignition part of the ignition device. This improves the reliability of stratified combustion during light load operation.

[0030] As described above, according to the present invention, it is possible to supply the leading air and mixture to the combustion chamber that are most suitable for the operating state of the engine, not only in the high revolution and high load range of a two-stroke internal combustion engine, but also in the acceleration and deceleration from low revolution to high revolution, and in the intermediate revolution and light load range. In addition, by combining the arrangement, timing control, and directivity of the fuel injection device, it is possible to accurately control the leading air amount and the mixture amount. Since only the air port for intake air is opened in the cylinder, it is possible to set a sufficient leading air supply amount, and it also contributes to simplifying the structure of the intake side (opposite exhaust side) of the engine and making it compact.

[0031] In one embodiment, the intake passage may be provided with a check valve. By providing the 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 backflow of air from the combustion chamber in the previous cycle from entering the intake passage.

[0032] As one embodiment, an engine working machine may be provided that includes the two-stroke internal combustion engine as a power source. [Brief description 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. [Diagram 2] FIG. 2 is an explanatory diagram of the operating stroke of the engine of FIG. [Diagram 3] FIG. 2 is a block diagram showing the air and fuel flows 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. [Diagram 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 is a schematic front view of a two-stroke internal combustion engine according to another embodiment of the present invention during full load operation, 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 (a) is a schematic front view of the engine, and (b) is a diagram showing the fuel supply timing during light load operation of the engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 mainly mounted as a power source in portable engine working machines. Examples of working machines in which the engine of the present invention can be used include portable working machines such as hand-held, shoulder-mounted, or backpack-mounted machines, such as chainsaws, brush cutters, power cutters, hedge trimmers, and power blowers.

[0036] As shown in FIG. 1, an engine 1 according to an embodiment of the present invention includes a cylinder block 2 and a piston 4 that reciprocates and slides in 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, and a crank chamber 8 is defined by a crank case 7 that constitutes the other end of the cylinder block 2 and the piston 4. An ignition plug 9 that constitutes an ignition device is fixed to the cylinder head 5, and the ignition plug 9 protrudes into the combustion chamber 6. A crankshaft 10 is rotatably supported in the crank case 7, and the crankshaft 10 and a piston pin 4a of the piston 4 are connected by a connecting rod 11. The piston 4 reciprocates and slides in the cylinder 3 due to combustion expansion (explosion) in the combustion chamber 6, so that the crankshaft 10 is rotationally driven 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 in the inner wall of the cylinder 3, and these ports 12, 14 are controlled to open and close at a 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] The engine 1 is equipped with an intake passage 17 for supplying air. The intake passage 17 draws in only air by the negative pressure generated when the piston 4 is in operation. A throttle valve 19, such as a butterfly type, is disposed within 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 a 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 only one intake port 24.

[0040] During the intake stroke when the crank chamber 8 becomes 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, and is 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 from the scavenging port 14 into the cylinder 3 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 includes 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 fuel injection valve 25 is controlled to open and close by a control device 28 including a microcomputer. A detection signal from at least one sensor 29 (29a to 29g) that detects the operating condition 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 the intake air temperature and issues a signal, an intake air pressure sensor 29b that detects the intake air pressure and issues a signal, a throttle valve opening sensor 29c that detects the opening of the throttle valve 19 and issues a signal, a crank chamber pressure sensor 29d that detects the pressure in the crank chamber 8 and issues a signal, a crank chamber temperature sensor 29e that detects the temperature of the crank chamber 8 and issues a signal, an engine speed sensor 29f that detects the speed of the engine 1 and issues a signal, and a crank angle sensor 29g that detects the crank angle and issues a signal. The signals of 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 injector 25 at appropriate timing according to a predetermined program, and also issues an ignition signal to spark plug 9 constituting an ignition device at a predetermined timing. This causes fuel to be supplied to crank chamber 8 and ignites the mixture in combustion chamber 6.

[0046] Next, the operation of the engine 1 in Fig. 1 will be described with reference to Fig. 2. In Fig. 2, (a) is an explanatory diagram of scavenging, (b) is an explanatory diagram of intake and compression, (c) is an explanatory diagram of combustion expansion (explosion), and (d) is an explanatory diagram of 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] 2(a) and (b), when the piston 4 closes the scavenging port 14 while ascending from the bottom dead center, the piston 4 causes a negative pressure in the crank chamber 8. As a result, air is drawn from the intake passage 17 through the intake port 24 and the scavenging passage 18 into the crank chamber 8. 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 mixture is compressed until the piston 4 reaches the top dead center. When the piston 4 reaches the 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 retained in the scavenging passage 18.

[0048] 2(c), when the piston 4 reaches the 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 the 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 from the intake port 24.

[0049] Referring to FIG. 2(d), when the exhaust port 12 opens due to the downward movement of the piston 4, the combustion gas flows out to the exhaust pipe 15. Next, as shown in FIG. 2(a), the scavenging port 14 opens, and the precompressed air-fuel mixture in the crank chamber 8 is sent to the combustion chamber 6 through the scavenging passage 18. At this time, air that has been retained in the scavenging passage 18 flows into the combustion chamber 6 as leading air prior to the air-fuel mixture in the crank chamber 8, and expels the combustion gas to the exhaust port 12. This reduces the blow-by of the air-fuel mixture during scavenging. The piston 4 moves again toward the top dead center due to the rotation of the crankshaft 10, and the same action 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, so that the timing of fuel supply can be easily controlled, and an air-fuel mixture suitable for the operating state of the engine 1 can be supplied. In addition, air remains in the scavenging passage 18 at the end of the intake, and this remaining air participates in scavenging as leading air, so that the mixture is prevented from being blown away during scavenging, and the composition of the exhaust gas is improved. 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] As a 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 mix with the air remaining in the scavenging passage 18.

[0054] As a preferred embodiment, the fuel injection valve 25 may be a high-pressure fuel injection valve receiving fuel pressure from at least one of an electric fuel pump and a pump operated by the rotation of the crankshaft 10. In this way, fuel can be injected at a targeted location. For example, it is possible to inject fuel at a location of the 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 in the cylinder 3 or the crank chamber 8 that needs to be cooled. In this way, 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 a connection portion between the connecting rod 11 and the piston pin 4a, or a connection portion between the connecting rod 11 and the crankshaft 10. Also, 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 crank chamber 8, the lubricating oil contained in the fuel lubricates the piston 4 and the cylinder 3 promptly and quickly. This prevents the engine 1 from seizing. In this case, the 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 seizing by injecting fuel when the engine is suddenly stopped during high-speed operation.

[0057] As a preferred embodiment, the fuel injection valve 25 may be a high-pressure fuel injection valve capable of injecting 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 components of the exhaust gas, for example by preventing gasoline from being mixed with the leading 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 arranged with respect to a plane including the axis X of the cylinder 3 and the axis Y of the crankshaft 10. With this configuration, the fuel tank 26 and the fuel injection valve 25 are located close to each other, so that the piping between them can be short, which contributes to the miniaturization and weight reduction of the working machine. In addition, 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 is easy to form the piping from the fuel tank 26 to the fuel injection valve 25. In addition, in this case, since the distance between the fuel tank 26 and the fuel injection valve 25 is short, fuel can be sent to the fuel injection valve 25 quickly, and the engine 1 can be started smoothly. In particular, in the case of a high-pressure fuel injection valve in which an electric fuel pump is installed in the fuel tank 26, since the distance between the electric fuel pump and the fuel injection valve 25 is short, fuel can be sent quickly, and the engine 1 can be started smoothly.

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

[0060] The fuel injector 25 may be electrically controlled or mechanically controlled. In the latter case, for example, a mechanically openable and closable fuel injector may be operatively connected to the crankshaft 10 and opened and closed at a predetermined timing during the operating 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 description 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 in Fig. 4, only one intake port 42 opens in the inner wall of a cylinder 41. This intake port 42 communicates with the intake passage 17. The intake port 42 is opened and closed by a piston 43. The piston 43 in Fig. 4 has a piston groove 44 on its circumferential surface, and the intake passage 17 and the scavenging port 14 communicate with each other via this piston groove 44 at a predetermined timing.

[0063] According to the engine 40 of FIG. 4, the crank chamber 8 becomes negative pressure as the piston 43 moves toward the top dead center. Then, 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 through 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 directly contacts the peripheral surface of the piston 43, the cooling performance of the piston 43 is improved. Also, since the intake port 42 is opened and closed by the piston 43, unlike the engine 1 of FIG. 1, there is no need to provide a check valve on the intake passage 17.

[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 are given the same reference numerals as in Fig. 4, and duplicated description will be omitted.

[0065] In an engine 50 in Fig. 5, a hole 52 communicating with the crank chamber 8 is provided in the piston groove 44 of a piston 51. Air also flows into the crank chamber 8 from the intake port 42 through the hole 52, so that 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 are given the same reference numerals as in Fig. 4, and duplicated description will be omitted.

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

[0068] 6(a), the lower end of the intake port 42 may be provided with a downwardly expanding portion 61a, and the expanding portion 61a may form 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 the 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 are given 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 communicating with the piston groove 44 at a position closer to the crank chamber 8 than the scavenging port 14. In this case, since the branch passage 71 is located below the scavenging port 14, the communication time between the piston groove 44 and the branch passage 71 due to the operation of the piston 43 can be extended, and the intake amount can be increased to improve the output.

[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 the engine 40 of 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 in the cylinder 41 by combustion and expansion in the combustion chamber 6, a crank chamber 8 that communicates with the inside of the cylinder 41, a crankshaft 10 that is disposed in 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 air that is sucked in by 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 in the latter half of the intake stroke participates in scavenging.

[0074] As shown in Fig. 8(c), in the engine 80, a pair of scavenging passages 18 are provided. As a result, a pair of scavenging ports 14 that communicate between the scavenging passages 18, 18 and the combustion chamber 6 are provided on the inner peripheral surface of the cylinder 41. The intake passage 17 branches into two branch passages 17a, 17b, and each of the branch passages 17a, 17b communicates with a pair of intake ports 42, 42 provided in the cylinder 41. Each of the intake ports 42, 42 communicates with each of the scavenging ports 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 FIG. 8(a) and FIG. 9(a), in the engine 80, a booster passage 81 that communicates between 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 communicates with the crank chamber 8 via a bottom dead center side booster port 81b formed in the crankcase 7. The booster passage 81 is for realizing stratified charge combustion by allowing fuel in the crank chamber 8 to flow into the combustion chamber 6 during light load operation of the engine 80. 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 a mixture are separately introduced into the combustion chamber 6, and stratified charge combustion is performed.

[0076] In this embodiment, at least the fuel supply timing by the fuel injection valve 25 is controlled by the control device 28, so that homogeneous combustion is performed 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, and stratified combustion is performed. This improves the 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 be different 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 located near the top dead center side, 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 end side 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 located on the bottom dead center side, more preferably, immediately before the piston 43 reaches the vicinity of the bottom dead center. As a result, during operation under a light load, 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 mixture, air filled in the crank chamber 8 is introduced from the scavenging passages 18, 18, and an air layer and a mixture layer are generated in the combustion chamber 6, thereby achieving stratified combustion.

[0079] Preferably, the control device 28 also controls the fuel injection mode by 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 in full load operation, it is preferable that the fuel is forcefully injected radially from the fuel injection valve 25 as shown in Fig. 8(a). This makes it easy for the fuel to be scattered throughout the crank chamber 8, so that the fuel and air are easily mixed homogeneously throughout the entire crank chamber 8.

[0080] On the other hand, when the engine 80 is operating under a light load, it is preferable that the fuel is supplied from the fuel injector 25 so that the fuel is located near the bottom dead center side booster port 81b. In order to realize such fuel supply, the engine 80 is provided with a fuel supply configuration 82 that positions the fuel supplied from the fuel injector 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 through 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 have 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) by a phantom line, another specific example of the fuel supply configuration 82 may include a first configuration 82c in which the fuel injector 25 is disposed so as to inject fuel toward the bottom dead center booster port 81b, and a second configuration 82d in which the fuel injector 25 injects fuel at an injection pressure that allows the fuel to reach the bottom dead center booster port 81b. In this case as well, the injection pressure of the fuel injector 25 is controlled by the control device 28.

[0083] Next, a preferred arrangement of the exhaust port, the two scavenging ports, and the top dead center side booster port will be described. As shown in FIG. 8(c), two scavenging ports are provided on the inner peripheral surface of the cylinder. The exhaust port is provided 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 provided 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 (bottom dead center side), and may be at approximately the same height as the scavenging ports.

[0084] With the above 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 that flows into the combustion chamber through the booster passage is a rich fuel that contains almost no air. Also, the air that flows into the combustion chamber through the two scavenging ports contains almost no fuel. As shown in FIG. 9(a), the fuel that flows into the combustion chamber from the top dead center side booster port is carried toward the cylinder head along the other arc surface of the inner circumferential surface of the cylinder by the air that flows into the combustion chamber through the two scavenging ports. In this way, the air and the mixture are introduced separately into the combustion chamber 6, which further improves the reliability of stratified combustion during light load operation.

[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 in Figures 8 and 9, and can of course be applied to the embodiments in Figures 1 to 7.

[0086] In such engines, it is important to more precisely control the ratio between the air supplied from the intake passage and the mixture containing the fuel component supplied by the fuel injection device. For this purpose, it is desirable to provide a known check valve (see check valve 23 in FIG. 1) in the intake passage, more preferably in the vicinity of 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 without the backflow from the combustion chamber in the previous cycle 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 includes design changes and the like that do not deviate from the gist of the present invention. In addition, the above-mentioned embodiments can be combined by utilizing each other's technologies as long as there are no particular contradictions or problems in the purpose, configuration, etc. [Explanation of symbols]

[0088] 1 2-stroke internal combustion engine 3 Cylinder 4 Piston 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 piston that reciprocates within the cylinder by combustion and expansion in the combustion chamber; a crank chamber that communicates with the inside of the cylinder; a crankshaft that is disposed within the crank chamber and operatively connected to the piston; a fuel injection valve that injects fuel into the crank chamber; an intake passage that draws in only air by negative pressure when the piston is in operation; and a scavenging passage that communicates the crank chamber with the combustion chamber, wherein air passing through the intake passage is introduced into the scavenging passage, the piston has a piston groove, the intake port and the scavenging passage are communicated via the piston groove, and air is drawn into the crank chamber through the intake passage, the intake port, the piston groove, the scavenging port and the scavenging passage, and air remaining in the scavenging passage at the end of intake takes part in scavenging.

2. 2. The two-stroke internal combustion engine of claim 1, wherein said piston groove is provided with a hole communicating with said 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, the communication portion being 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 crank chamber 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 impede the inflow of 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 receiving fuel pressure from at least one of an electric fuel pump and a pump operated 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 a 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 between the crank chamber and the combustion chamber is provided 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 communicates between the crank chamber and the booster passage; and a fuel supply configuration 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 in the vicinity of the bottom dead center booster port, and a second configuration in which fuel is injected from the fuel injection valve at an injection pressure that allows fuel to remain in the vicinity of the bottom dead center 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 disposed so as to inject fuel 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 capable of reaching 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 immediately 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 communicating between the scavenging passage and the combustion chamber are arranged on an inner circumferential 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 communicating between the combustion chamber and the booster passage is arranged on the other arcuate surface between the pair of scavenging ports.

18. 18. A two-stroke internal combustion engine according to claim 1, further comprising a check valve in the intake passage.

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

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