Air-breathing two-stroke engine

Abstract

In an air intake-type two-stroke engine 10, an exhaust port 20, a scavenging port 22, etc. are opened and closed by a piston 12. A fuel injection valve 60 is disposed at an upper end section 24a of a scavenging passage 24. The fuel injection valve 60 is preferably installed such that the axis Lax of the fuel injection valve 60 is directed toward the scavenging port 22. The fuel injection timing is set such that fuel injection occurs in the latter half of a scavenging process or in the latter half of a combustion process.

Description

[Technical Field]

[0001] The present invention relates to a piston valve type two-stroke engine used in a work machine, and more particularly to an air-breathing two-stroke engine. [Background technology]

[0002] Two-stroke engines are used as the power source for portable work equipment such as brush cutters, chainsaws, and blowers. Among two-stroke engines, piston valve engines are the most common. In piston valve two-stroke engines, the intake port, exhaust port, and scavenging port, which open on the inner wall of the cylinder, are opened and closed by a piston. A feature of piston valve two-stroke engines is that they are easy to construct into a small, lightweight engine.

[0003] In a two-stroke engine, one cycle is completed with one reciprocating movement of the piston. That is, during the upward stroke of the piston, compression occurs in the cylinder, while fresh air (generally an air-fuel mixture) is filled into the crankcase. During the downward stroke of the piston due to combustion, the mixture is pre-compressed in the crankcase, and exhaust and scavenging occur in the cylinder during the latter half of the downward stroke. During the scavenging process, the pre-compressed mixture is discharged from the crankcase through the scavenging port into the cylinder, thereby scavenging the air in the cylinder. Due to the structure and mechanism of these two-stroke engines, two-stroke engines inherently have the problem of fuel "blow-by."

[0004] One solution to this problem of blow-by is the stratified scavenging engine (US Pat. No. 6,289,856 B1 (Patent Document 1)). Taking a stratified scavenging engine equipped with a carburetor as an example, first, lead air is charged into the upper part of the scavenging passage and the air-fuel mixture is introduced into the crankcase. The air-fuel mixture introduced into the crankcase is pre-compressed during the piston's downward stroke. Then, in the early stage of the scavenging process, the lead air in the scavenging passage is discharged into the cylinder, and then the air-fuel mixture in the crankcase is discharged into the cylinder.

[0005] The use of fuel injection valves instead of carburetors in two-stroke engines is also being considered. Regarding the placement of the fuel injection valve, a direct-injection two-stroke engine has been developed in which the fuel injection valve is placed facing the inside of the cylinder. WO 2020 / 256624 A1 (Patent Document 2) discloses a stratified scavenging engine in which the fuel injection valve is placed facing the crankcase. In a two-stroke engine using a fuel injection valve, air is supplied to the crankcase, where it is precompressed and used for scavenging.

[0006] US 10,858,985 B2 (Patent Document 3) discloses an air-breathing two-stroke engine. An air-breathing two-stroke engine is characterized by the use of a scavenging passage to supply fresh air to the crankcase. Here, "fresh air" refers to air filtered by an air cleaner. An air-breathing two-stroke engine has piston grooves on the circumferential surface of its piston, which can communicate with the scavenging passage at a predetermined timing. During the intake process, air filtered by the air cleaner is supplied to the crankcase through the intake passage, intake port, piston groove, and scavenging passage. Similar to other types of two-stroke engines, air-breathing two-stroke engines discharge fresh air from the crankcase into the cylinders through the scavenging passages and scavenging ports during the scavenging process.

[0007] The air-breathing two-stroke engine disclosed in Patent Document 3 is equipped with a fuel injector. Regarding the arrangement of this fuel injector, Patent Document 3 discloses an embodiment in which the fuel injector is arranged in the longitudinal middle portion of the scavenging passage. In this embodiment, a reed valve is arranged at the entrance of the scavenging passage, i.e., at the upstream opening of the scavenging passage. The reed valve allows gas to move from the crankcase to the scavenging passage. In other words, the reed valve prohibits gas from moving from the scavenging passage to the crankcase. Summary of the Invention [Problem to be solved by the invention]

[0008] Known lubricating oil supply methods for two-stroke engines include a mixed fuel supply method and a separate fuel supply method. Work machines generally use a mixed fuel supply method, in which lubricating oil is mixed with fuel. For example, if a direct injection system is used, in which a fuel injection valve is located inside the cylinder, it becomes impossible to supply lubricating oil to the crankcase along with the fuel, so a separate fuel supply method must be used. However, the separate fuel supply method requires the addition of an oil supply device to lubricate the crankcase, which has the disadvantage of making the overall engine structure more complex and larger.

[0009] The inventors of this invention devised this invention by noting that in air-breathing two-stroke engines, the scavenging passage is used not only for the scavenging process but also for the intake process, and that air flows toward the crankcase during the intake process. Specifically, during the scavenging process, air in the crankcase precompressed by the descending piston is discharged into the cylinder through the scavenging passage and scavenging port. Meanwhile, during the intake process, air purified by the air cleaner is introduced into the crankcase through the intake port, piston groove, and scavenging passage. As described above, the use of scavenging passages during the intake process is a distinctive feature of air-breathing two-stroke engines. Looking at the scavenging passages in air-breathing two-stroke engines, the air flows through them in opposite directions during the intake and scavenging processes, with air moving back and forth through the scavenging passages.

[0010] The object of the present invention is to provide an air-breathing two-stroke engine that can increase design freedom, including the lubricating oil supply method, and improve combustion efficiency and exhaust gas reduction effects without increasing the size of the engine. [Means for solving the problem]

[0011] The air-breathing two-stroke engine according to the present invention is characterized in that the fuel injection valve is located at the upper end of the scavenging passage. In an air-breathing two-stroke engine, locating the fuel injection valve at the upper end of the scavenging passage increases the degree of freedom in design. In an embodiment, this can be combined with at least one of the injection direction and fuel injection timing of the fuel injection valve to improve combustion efficiency and the effect of reducing exhaust gas emissions. Here, the upper end of the scavenging passage is directly connected to the scavenging port. In other words, the upper end opening of the scavenging passage forms the scavenging port.

[0012] The tip portion of the fuel injection valve is called a "nozzle portion," and an injection hole is formed at the tip of the nozzle portion. The nozzle portion has a length, and therefore the fuel injection valve has an axis.

[0014] fruit In one embodiment, the axis of the fuel injection valve is , tilted downwards and directed The fuel injection valve may be installed at the upper end of the scavenging passage so as to face the crankcase side of the scavenging passage. The lower end opening of the scavenging passage is in communication with the crankcase. fruit In this embodiment, the fuel discharged from the fuel injection valve can be supplied to the crank chamber. By supplying the fuel discharged from the fuel injection valve to the crank chamber, an air-fuel mixture with a uniform density can be produced in the crank chamber.

[0015] One method for setting the fuel injection timing is to open the fuel injection valve located at the upper end of the scavenging passage in the latter half of the scavenging process to inject fuel. By setting the fuel injection timing in the latter half of the scavenging process, it is possible to lubricate the crankcase while preventing blow-by.

[0016] Another method for setting the fuel injection timing is to open the fuel injector later in the combustion process to inject fuel. Setting the fuel injection timing later in the combustion process allows for cylinder cooling while lubricating the crankcase. In either case, the fuel injector must be located near the piston opening and closing positions. This configuration eliminates the need for a reed valve linked to the fuel injector.

[0017] The advantages and other objects of the present invention will become apparent from the following detailed description of the preferred embodiment. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a piston valve type two-stroke engine, specifically an air-breathing two-stroke engine, according to the present invention. [Figure 2] FIG. 2 is a diagram illustrating a specific example in which a fuel injection valve is disposed at the upper end of a scavenging passage of an air-intake two-stroke engine. [Figure 3] Figure 3 is a chart showing the opening and closing timing of each port and the ignition timing in an air-breathing two-stroke engine. [Figure 4] FIG. 4 is a chart showing an example of fuel injection timing for an air-breathing two-stroke engine. [Figure 5] FIG. 5 is a chart showing another example of fuel injection timing for an air-breathing two-stroke engine. [Figure 6] FIG. 6 is a diagram for explaining a modified example of the fuel injection direction of the fuel injection valve disposed at the upper end of the scavenging passage. [Figure 7] FIG. 7 is a chart for explaining conventional fuel supply timing as a comparative example. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0019] A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. Figure 1 is a schematic diagram of a two-stroke engine according to the present invention, which is used as a power source for portable working machines such as, but not limited to, chainsaws and brush cutters.

[0020] The illustrated two-stroke engine 10 is a single-cylinder, air-cooled engine. The engine 10 has a combustion chamber 14 formed by a piston 12 that reciprocates up and down, and an ignition plug 16 is located at the upper end of the combustion chamber 14. An intake port 18, an exhaust port 20, and a scavenging port 22 are opened on the inner circumferential surface of the cylinder, and these ports 18, 20, and 22 are opened and closed by the piston 12. In other words, the engine 10 is a piston-valve engine.

[0021] The scavenging ports 22 are configured by a total of four ports: a pair of first scavenging ports 22A on the intake port 18 side that face each other across the intake port 18, and a pair of second scavenging ports 22B on the exhaust port 20 side. However, the number of scavenging ports 22 is arbitrary, and for example, the scavenging ports 22 may be configured by a pair of scavenging ports. Upper end portions 24a of the scavenging passages 24 are connected to each scavenging port 22. In other words, the upper end openings of the scavenging passages 24 form the scavenging ports 22. Each scavenging passage 24 is configured as a passage extending in the vertical direction, and the lower end openings 24b of the scavenging passages 24 communicate with the crank chamber 26. As is well known, a crankshaft (not shown) is arranged in the crank chamber 26, and this crankshaft is connected to the piston 12 via a connecting rod (not shown).

[0022] 1, reference symbol 24A denotes a first scavenging passage connected to the first scavenging port 22A, and the first scavenging passage 24A is located on the intake port 18 side. Reference symbol 24B denotes a second scavenging passage connected to the second scavenging port 22B, and the second scavenging passage 24B is located on the exhaust port 20 side.

[0023] An air cleaner 32 is disposed at the upstream end of a common intake passage 30 connected to the intake port 18. Air filtered by the air cleaner 32 is supplied to the common intake passage 30. A throttle valve 34, which is an air amount control valve, is disposed midway along the common intake passage 30. Meanwhile, a muffler 42 is disposed in an exhaust passage 40 connected to the exhaust port 20.

[0024] The piston 12 has a piston groove 50 on its circumferential surface. When the piston 12 is inserted into the cylinder, the piston groove 50 is composed of a first piston groove 50A and a second piston groove 50B provided on the left and right sides of the exhaust port 20. The first piston groove 50A is disposed opposite the first and second scavenging passages 24A, 24B located on one side of the cylinder and communicates with these first and second scavenging passages 24A, 24B during the intake process. The second piston groove 50B is disposed opposite the first and second scavenging passages 24A, 24B located on the other side of the cylinder and communicates with these first and second scavenging passages 24A, 24B during the intake process.

[0025] The intake port 18 is composed of a first intake port 18A and a second intake port 18B. The first intake port 18A is located on one side of the cylinder in relation to the first piston groove 50A. The second intake port 18B is located on the other side of the cylinder in relation to the second piston groove 50B. The first and second intake ports 18A, 18B are connected to the common intake passage 30 via first and second branch intake passages 31A, 31B. That is, the downstream portion of the common intake passage 30 branches into two. The first branch intake passage 31A is connected to the first intake port 18A, and the second branch intake passage 31B is connected to the second intake port 18B.

[0026] During the intake process of the air-breathing two-stroke engine 10, fresh air filtered by the air cleaner 32 is drawn into the crankcase 26 through two channels, the first and second branch intake passages 31A, 31B. Specifically, in the first channel, fresh air supplied to the crankcase 26 passes through the common intake passage 30, the first branch intake passage 31A, the first intake port 18A, and the first piston groove 50A, and then enters the first and second scavenging passages 24A, 24B through the upper ends 24a of the first and second scavenging passages 24A, 24B located on one side of the cylinder, and is then introduced into the crankcase 26 through the lower end openings 24b of the first and second scavenging passages 24A, 24B on one side of the cylinder.

[0027] In the second channel, fresh air supplied to the crank chamber 26 passes through the common intake passage 30, the second branch intake passage 31B, the second intake port 18B, and the second piston groove 50B, and then enters the first and second scavenging passages 24A, 24B through the upper ends 24a of the first and second scavenging passages 24A, 24B located on the other side of the cylinder, and is then introduced into the crank chamber 26 through the lower end openings 24b of the first and second scavenging passages 24A, 24B on the other side of the cylinder.

[0028] In the scavenging process of the two-stroke engine 10, fresh air pre-compressed in the crank chamber 26 is discharged as a scavenging flow into the combustion chamber 14 through each of the four scavenging ports 22, namely, a pair of first scavenging ports 22A on the intake port 18 side and a pair of second scavenging ports 22B on the exhaust port 20 side.

[0029] The air-breathing two-stroke engine 10 is preferably a scavenging engine. Specifically, scavenging is performed by directing fresh air discharged from the scavenging ports 22 toward the intake ports 18, which are opposite the exhaust ports 20.

[0030] The air-breathing two-stroke engine 10 has a fuel injector 60, which supplies a mixed fuel. The mixed fuel contains lubricating oil. Referring to FIG. 2, the fuel injector 60 is disposed in at least one of the scavenging passages 24A or 24B. The fuel injector 60 is assembled to the upper end 24a of the scavenging passage 24.

[0031] Referring to FIG. 2, one typical mounting mode of the fuel injection valve 60 will be described below. The fuel injection valve 60 discharges atomized mixed fuel. The fuel injection valve 60 includes a nozzle portion 60a at its tip, and the nozzle portion 60a has a length. The mixed fuel is discharged from the tip of the nozzle portion 60a. Reference symbol Lax indicates the axis of the fuel injection valve 60. As can be seen from FIG. 2, in a preferred mode, the fuel injection valve 60 is arranged to discharge mixed fuel toward the opening region of the scavenging port 22, and is preferably arranged to discharge fuel toward the center of the scavenging port 22, i.e., the center of the upper end opening of the scavenging passage 24.

[0032] It is preferable to install the fuel injection valve 60 at the upper end 24a of the scavenging passage 24 so that its axis Lax, i.e., its fuel discharge direction, is approximately parallel to the inclination direction of the ceiling portion Tc at the upper end of the scavenging passage 24. Air precompressed in the crank chamber 26 is discharged into the cylinder through the scavenging passage 24 in the scavenging process. At this time, a scavenging flow is formed through the scavenging passage 24 and the scavenging ports 22. The scavenging flow has directionality. Setting the fuel injection direction of the fuel injection valve 60 so that it is approximately parallel to the inclination direction of the ceiling portion Tc at the upper end of the scavenging passage 24 has the advantage that the flow direction of the fuel injected from the fuel injection valve 60 is less likely to be affected by the scavenging flow that flows from the inside of the scavenging passage 24 toward the inside of the cylinder.

[0033] As described above, the fuel injection valve 60 is installed at the upper end 24a of the scavenging passage 24 with the axis Lax of the fuel injection valve 60 directed toward the scavenging port 22. Most preferably, the fuel injection valve 60 is installed so that the axis Lax of the fuel injection valve 60 is approximately parallel to the inclination direction of the ceiling portion Tc at the upper end of the scavenging passage 24. This arrangement prevents fuel from adhering to or accumulating on the opening edge of the scavenging port 22, and ensures that all of the fuel is sent into the cylinder.

[0034] An upper end 24a of the scavenging passage 24 is open into the cylinder through the scavenging port 22. That is, the upper end opening of the scavenging passage 24 is the scavenging port 22. The axis Lax of the fuel injection valve 60 is directed toward the scavenging port 22, that is, toward the upstream opening of the scavenging passage 24. That is, the fuel injection valve 60 is installed so that the extension of the axis Lax of the fuel injection valve 60 passes through the scavenging port 22 and extends into the cylinder.

[0035] The scavenging passage 24 in which the fuel injection valve 60 is disposed is preferably the first scavenging passage 24A that is connected to the first scavenging port 22A on the intake port 18 side. This configuration prevents the lubricating oil components injected from the fuel injection valve 60 from flowing into the exhaust port 20, further reducing blow-by.

[0036] FIG. 3 is a chart showing the timing of opening and closing ports and ignition timing in an air-breathing two-stroke engine 10. The arrows indicate the direction of crankshaft rotation. The left half of the figure shows the piston 12's upward stroke, where it moves from bottom dead center (BDC) to top dead center (TDC). The right half of the figure shows the piston 12's downward stroke, where it moves from top dead center (TDC) to bottom dead center (BDC). The ignition timing of the spark plug 16 is set to occur just before the piston 12 reaches top dead center (TDC) during the piston's upward stroke. During the piston's downward stroke, the scavenging ports 22 open immediately after the exhaust port 20 opens, initiating the scavenging process.

[0037] The fuel injection timing of the fuel injection valve 60 installed at the upper end 24a of the scavenging passage 24 is preferably set to coincide with the upward stroke of the piston 12, i.e., the scavenging process. By coordinating the fuel injection timing with the location of the fuel injection valve 60 (located at the upper end 24a of the scavenging passage 24) and the scavenging process, i.e., the opening timing of the scavenging port 22 by the piston 12, it is possible to add fuel components to only a portion of the upper part of the scavenging passage 24 of the air that is filled into the scavenging passage 24 via the crankcase 26 during the intake process. This is because the space and time that the air remains in the scavenging passage 24 are short.

[0038] Compared to a case where the fuel injection valve 60 is arranged in the middle or lower region of the scavenging passage 24, the air-intake two-stroke engine 10 of the embodiment has the advantage that the air and fuel components are less likely to mix inside the scavenging passage 24, and an air layer and a mixture layer can be introduced into the cylinder sequentially. As a result, the air scavenging effect in the scavenging process can be maintained. In addition, because the distance from the fuel injection valve 60 to the inside of the cylinder is short, there are advantages that the directionality of the injected fuel can be easily controlled and tuned.

[0039] Furthermore, in the air-intake two-stroke engine 10, the fuel injection valve 60 is located close to the scavenging port 22, so the fuel components injected by the fuel injection valve 60 are less likely to be homogenized with the surrounding gas in the scavenging passage 24, and the fuel components injected by the fuel injection valve 60 are injected directly into the cylinder. In addition, the injection of fuel reduces the temperature of the upper part of the scavenging passage 24, which contributes to cooling the cylinder and piston 12.

[0040] FIG. 4 is a chart showing specific fuel injection timings of the fuel injection valve 60. The opening and closing of each port and the timing of ignition correspond to the chart shown in FIG. 3. Referring to FIG. 4, when the scavenging process enters the latter half in which the scavenging port 22 is opened, the fuel injection valve 60 is opened and fuel injection is performed. The closing timing of the fuel injection valve 60 is immediately before the scavenging port 22 is closed, that is, immediately before the end of the scavenging process. That is, during the latter half of the scavenging process, that is, from the point when the piston 12 starts to rise from bottom dead center (BDC) to immediately before the end of the scavenging process, the fuel mixture is supplied from the fuel injection valve 60 to the cylinder through the upper end 24a of the scavenging passage 24 and the scavenging port 22. The period during which fuel is supplied to the scavenging passage 24 is short, and the exhaust port 20 is closed immediately after the fuel injection valve 60 injects the fuel mixture. The arrangement of the fuel injection valve 60, the direction of the axis Lax of the fuel injection valve 60 (the axis Lax passes through the scavenging port 22 and extends into the cylinder), and the timing of fuel injection shown in FIG. 4 combine to prevent fuel blow-by.

[0041] As described above, the air-breathing two-stroke engine 10 is characterized in that fresh air moves back and forth through the scavenging passage 24 during two processes: the scavenging process and the intake process. That is, during the scavenging process, fresh air moves up through the scavenging passage 24 from the lower end opening 24b to the upper end 24a of the scavenging passage 24. On the other hand, during the intake process, fresh air moves down through the scavenging passage 24 from the upper end 24a to the lower end opening 24b of the scavenging passage 24.

[0042] The air-breathing two-stroke engine 10 is capable of solving the problem of fuel blow-by while achieving lubrication of the crankcase 26, which will be described next, by combining, first, a characteristic of an air-breathing two-stroke engine in that fresh air flows back and forth through the scavenging passage 24 in two processes, that is, the scavenging process and the intake process, and second, the above-mentioned arrangement of the fuel injection valve 60 (arranged at the upper end 24a of the scavenging passage 24), the fuel injection direction of the fuel injection valve 60 (the above-mentioned direction of the axis Lax), and the timing of fuel injection (fuel injection in the latter half of the scavenging process).

[0043] At the upper end 24a of the scavenging passage 24, a portion of the mixed fuel injected in the latter half of the scavenging process immediately enters the cylinder through the scavenging ports 22, but the scavenging ports 22 close immediately thereafter. By injecting fuel at this timing, the mixture required for combustion can be injected only in the later half of scavenging, thereby reducing blow-by. In addition, because the scavenging ports 22 are closed by the piston 12 immediately after injection, the remainder of the injected fuel components remains in the scavenging passage 24, for example, by adhering to the wall surface of the scavenging passage 24. When the crank chamber 26 becomes negative pressure in the next intake process, the mixed fuel remaining in the scavenging passage 24 is introduced into the crank chamber 26 along with the flow of fresh air (air) that passes through the scavenging passage 24. The mixed fuel that enters the crank chamber 26 along with this fresh air ensures lubrication of the crank chamber 26. This means that there is no need to add a separate oil supply device, and it is possible to supply lubricating oil components to the combustion chamber 14 and crank chamber 26 simply by setting the fuel injection timing at one location for a specified period during one cycle of the two-stroke engine.

[0044] Furthermore, in the system of the present invention, the fuel injection timing is linked to the opening and closing timing of the scavenging port of the piston valve, and all fuel components in excess of the blow-by are sucked into the crank chamber 26 side, so there is no need for additional opening and closing parts such as the reed valve disclosed in Patent Document 3, and there is no need for opening and closing control of the opening and closing parts.

[0045] FIG. 5 is a chart showing a modified fuel injection timing. The fundamental difference from the first fuel injection timing described above with reference to FIG. 4 is that in the modified fuel injection timing, fuel is injected during the piston 12's downward stroke from top dead center to bottom dead center, when the intake port 18 and the scavenging port 22 communicate with each other via the piston groove 50. That is, fuel components are injected into the cylinder from the fuel injector 60 during the latter part of the combustion period. Immediately after that, when the piston 12 closes the scavenging port, the scavenging port 22 faces the piston skirt, which is a friction surface, and then communicates with the piston groove 50. As described above, fuel components injected during the latter part of the combustion period that do not reach the cylinder adhere to the piston skirt and are subsequently introduced into the piston groove 50 that communicates with the piston. The fuel components that adhere to the piston skirt are used directly for piston lubrication. The fuel components introduced into the piston groove 50 are drawn into the crank chamber 26 and used for lubrication of the crank chamber 26. At this time, the gas flows in the order of intake passage 30, piston groove 50, scavenging passage 24, and crank chamber 26, so the fuel components injected in the scavenging passage 24 are directed toward the crank chamber 26 along the gas flow, and no fuel is blown back into the intake passage 30.

[0046] Returning to Fig. 4, in the embodiment shown in Fig. 4 in which the main injection period is the upward stroke of the piston 12, it is preferable that the direction of the axis Lax of the fuel injector 60 is perpendicular to the cylinder axis direction, i.e., horizontal, or inclined downward toward the crank chamber 26 (Fig. 6). The lower end opening 24b of the scavenging passage 24 communicates with the crank chamber 26. Therefore, in the typical arrangement of the fuel injector 60 shown in Fig. 6, the fuel discharged from the fuel injector 60 during the upward stroke of the piston is introduced into the crank chamber 26, accompanied by the air flow toward the crank chamber 26 through the scavenging passage 24. The fuel components introduced into the crank chamber 26 are used to lubricate the crank chamber 26, and are also introduced from the scavenging passage 24 into the cylinder and used for combustion in the latter half of the scavenging process of the next cycle.

[0047] As explained above, the configuration in which the fuel injection valve 60 is disposed at the upper end 24a of the scavenging passage 24 of the air-intake, piston valve, two-stroke engine 10 allows the opening and closing of the piston 12 to be used as a valve for switching the direction of fuel introduction. Fuel components can be supplied to both the cylinder side and the crank chamber 26 side without the need to provide a lubrication device for the crank chamber 26 or a valve structure for controlling the presence and timing of fuel introduction.

[0048] FIG. 7 is a chart illustrating the fuel supply timing of a conventional two-stroke engine in which a fuel injector 60 is disposed in the crankcase 26 as a comparative example. The fuel injector 60 opens during the piston's downward stroke, supplying fuel to the crankcase 26. In this conventional example, the fuel supplied to the crankcase 26 mixes with air in the crankcase 26 until the scavenging port opens and the scavenging process begins in the next cycle, which has the advantage of allowing a uniform mixture to be supplied to the combustion chamber. Another advantage is that the crankcase 26 can be smoothly lubricated. However, as mentioned above, this conventional method does not solve the problem of fuel blow-by. [Explanation of symbols]

[0049] 10. Air-breathing two-stroke engine of the embodiment 12 pistons 14 Combustion chamber 18 Intake port 20 exhaust port 22 Scavenging port 24 scavenging passage 24a Upper end of scavenging passage 24b Lower end opening of scavenging passage 26 Crankcase 30 Common intake passage 31A First branch intake passage 31B Second branch intake passage 50 piston groove 60 Fuel injection valve 60a Nozzle portion of fuel injection valve Lax Axis of fuel injection valve Tc Ceiling part at the top of the scavenging passage

Claims

1. an intake port communicating with the intake passage and opening to an inner peripheral surface of the cylinder; an exhaust port communicating with the exhaust passage and opening to an inner peripheral surface of the cylinder; The upper end of the scavenging passage that communicates with the crankcase is connected to the inner peripheral surface of the cylinder. a scavenging port opening to the A piston that forms a combustion chamber and reciprocates up and down; a piston groove formed on a peripheral surface of the piston and capable of communicating with the intake port and the scavenging passage; During the intake process, fresh air is supplied to the crankcase through the intake passage, the intake port, the piston groove, and the scavenging passage; In a scavenging process in which the scavenging port is opened to scavenge air in the cylinder, fresh air pre-compressed in the crankcase is discharged into the cylinder through the scavenging passage and the scavenging port, In an air-breathing two-stroke engine, the intake port, the exhaust port, and the scavenging port are opened and closed by the piston, a fuel injection valve is disposed at an upper end of the scavenging passage; The fuel injection timing of the fuel injection valve is set to the latter half of the scavenging process, The closing timing of the fuel injection valve is different from the closing timing of the scavenging port, the closing timing of the fuel injection valve is immediately before the closing timing of the scavenging port, An air-intake two-stroke engine, characterized in that the axial direction of the fuel injection valve is oriented at an angle downward toward the crank chamber.

2. 2. The air-breathing two-stroke engine according to claim 1, the air-breathing two-stroke engine is a Sinuer type two-stroke engine, In an air-breathing two-stroke engine, during the scavenging process, fresh air discharged from the scavenging port into the cylinder is directed toward the intake port side, which is opposite to the exhaust port.

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