2-stroke engine

Abstract

To provide a two cycle engine which enables lubrication and cooling to be performed at a large end with a small amount of a mixed fuel.SOLUTION: An engine 1 includes: a crank case 6 connected to a cylinder 2; a crank mechanism 7 which is disposed in a crank chamber 6a and rotates around a crank shaft 7a; a connecting rod 10 having a small end part 21 connected to a piston 4 and a large end part 22 connected to the crank mechanism 7; and a fuel injection nozzle 30 which is attached to the crank case 6 and injects a mixed fuel in a tangential direction of a circular track of the large end part 22 to spray the mixed fuel to the large end part 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piston valve type two-stroke engine. [Background technology]

[0002] As described in Patent Document 1, a fuel-injected two-stroke engine has been known in which a main scavenging passage and an auxiliary scavenging passage are formed in a cylinder block. In this two-stroke engine, a fuel injection device is attached to the crankcase. The fuel injection device is oriented so as to inject fuel toward the scavenging inlet of the auxiliary scavenging passage. Other known fuel injection methods include a method of injecting fuel into the intake path leading to the crankcase and a method of directly injecting fuel into the combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-224741 Summary of the Invention [Problem to be solved by the invention]

[0004] The injection method described in Patent Document 1 provides a two-stroke engine with excellent starting and responsiveness. However, no particular consideration has been given to the supply of lubricating oil to the crankshaft and bearings. Conventionally, in order to lubricate the crankshaft and bearings, it has been necessary to provide a separate passage for lubricating oil or to install an oil pump, etc. Insufficient lubrication can lead to problems such as seizure.

[0005] The inventors discovered that in a piston valve type two-stroke engine, lubrication and cooling of the big end of the connecting rod located inside the crankcase are important. Fuel such as gasoline is mixed with oil and supplied (injected) as a mixed fuel. From the standpoint of fuel economy and environmental considerations, a two-stroke engine that can be lubricated and cooled with a small amount of mixed fuel is desired.

[0006] An object of the present invention is to provide a two-stroke engine that can lubricate and cool the big end with a small amount of mixed fuel. [Means for solving the problem]

[0007] One aspect of the present invention is a piston valve type two-stroke engine (1) in which an intake port is opened and closed by a piston (4) that reciprocates axially within a bore portion (3) of a cylinder (2), the engine comprising: a crankcase connected to the cylinder (2) and having a crank chamber (6a); a crank mechanism (7) disposed in the crank chamber (6a) and rotating about a crankshaft (7a); a connecting rod having a small end (21) connected to the piston (4) and a big end (22) connected to the crank mechanism (7); and a fuel injector (30) attached to the crankcase and injecting a fuel mixture in a tangential direction of a circumferential orbit of the big end (22) to spray the fuel mixture onto the big end (22).

[0008] In this two-stroke engine (1), a fuel injector (30) attached to the crankcase sprays a fuel mixture onto the big end (22) of the connecting rod. The fuel injector (30) injects the fuel mixture in a direction tangential to the circumferential orbit of the big end (22). The oil contained in the fuel mixture lubricates and cools the big end (22). The fuel (gasoline, etc.) contained in the fuel mixture also cools the big end (22). This allows the big end (22) to be lubricated and cooled with a small amount of fuel mixture. Furthermore, because the fuel mixture is injected into the crankcase, not into the combustion chamber or bore (3), there is no need to consider the pressure resistance and heat resistance of the peripheral configuration of the fuel injector (30).

[0009] The injection port 31 of the fuel injector 30 may protrude into the crank chamber 6a. This configuration allows the mixed fuel to be injected from a position closer to the big end 22, making it easier to achieve the desired lubrication and cooling effects.

[0010] The crank mechanism (7) may have a pair of crank webs (7b) connected to the crankshaft (7a) and spaced apart in the axial direction of the crankshaft (7a), and the injection port (31) of the fuel injector (30) may be disposed at a position passing through the gap (G) between the pair of crank webs (7b). With this configuration, the injection port (31) can be brought closer to the big end (22), and the big end (22) can be cooled more reliably and effectively.

[0011] The fuel injector (30) may be configured to inject the mixed fuel into the big end (22) at least when the piston (4) is at top dead center. With this configuration, the fuel injection is timed to coincide with the scavenging, making it easier to introduce the fuel sprayed onto the big end (22) into the scavenging holes.

[0012] Scavenging holes (14) are formed in the cylinder (2), and the inlets (14a) of the scavenging holes (14) that open toward the crankcase (6a) may be located at the same height in the axial direction as the injection ports (31) of the fuel injectors (30). This configuration facilitates introducing fuel sprayed onto the big end (22) into the scavenging holes (14). Since the mixed fuel accumulates near the inlets (14a) of the scavenging holes (14), the fuel is easily introduced into the scavenging holes (14). This reduces the amount of wasted fuel that is not introduced into the scavenging holes (14), thereby achieving an effect of reducing fuel consumption. Furthermore, transient response and starting performance are improved. [Effects of the Invention]

[0013] According to the present invention, lubrication and cooling of the big end can be achieved with a small amount of mixed fuel. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a vertical cross-sectional view of a two-stroke engine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a vertical cross-sectional view showing a state in which the piston is located at the bottom dead center. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5(a) is an exploded perspective view showing the crank mechanism and the connecting rod, and FIG. 5(b) is a side view showing the crank mechanism and the connecting rod. [Figure 6] FIG. 2 is a block diagram showing a schematic configuration relating to injection control of a mixed fuel in a fuel injector. [Figure 7] FIG. 7(a) is a diagram showing the injection timing of the mixed fuel in the two-stroke engine of FIG. 1, and FIG. 7(b) is a diagram showing the injection timing of the mixed fuel in a two-stroke engine according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. In the following description, when "upper and lower" are used, it is based on the case where the cylinder body 2a is erected so that the bore portion 3 of the cylinder 2 extends vertically, with the opening into which the piston 4 is inserted facing downward. "Up" corresponds to one side in the direction of the axis L of the bore portion 3, and "lower" corresponds to the lower side in the direction of the axis L.

[0016] As shown in Figures 1, 2, and 3, engine (two-stroke engine) 1 is a two-stroke engine that uses a scavenging method called a sinusoidal scavenging system and is installed in, for example, a brush cutter or a backpack power sprayer. Engine 1 includes a cylinder 2, a piston 4 that reciprocates within a bore 3 within cylinder 2, a crankcase 6 connected below cylinder 2 and having a crank chamber 6a, and a crank mechanism 7 disposed within the crank chamber 6a of crankcase 6. A piston pin 8 disposed within piston 4 and a crank pin 9 of crank mechanism 7 disposed within crankcase 6 are connected by a connecting rod 10. Piston 4 is disposed within bore 3 and is capable of reciprocating along axis L between a combustion chamber 11 and the crank chamber 6a. In the following description, connecting rod 10 will be referred to as connecting rod 10.

[0017] The cylinder 2 is formed with a combustion chamber 11, a cylindrical bore portion 3 connected to the combustion chamber 11 and into which the piston 4 is inserted, an intake port 12 and an exhaust port 13 communicating with the bore portion 3, a pair of intake-side scavenging ports 14, and a pair of exhaust-side scavenging ports 16. The cylinder 2 has a cylinder body 2a and a pair of scavenging cassettes 2b fitted into a lower portion of the cylinder body 2a. The pair of scavenging cassettes 2b are fitted and fixed in two openings formed in the bore portion 3 so as to face each other in the radial direction. The pair of intake-side scavenging ports 14 and the pair of exhaust-side scavenging ports 16 are formed, for example, by the cylinder body 2a and the pair of scavenging cassettes 2b (see FIG. 2).

[0018] The bore 3 has a cylindrical bore surface 3a and extends along the axis L inside the cylinder 2. The bore 3 is open on its bottom dead center side (the lower side in the figure) and communicates with the crank chamber 6a. A recessed combustion chamber 11 is formed at the end of the bore 3 on the top dead center side, and a discharge electrode such as an ignition plug 18 is disposed inside the combustion chamber 11. An ignition plug mounting hole 19 into which the ignition plug 18 is mounted is provided near the combustion chamber 11 in the cylinder body 2a.

[0019] The intake port 12 and the exhaust port 13 are each connected to the bore portion 3, and the exhaust port 13 is positioned slightly closer to the top dead center than the intake port 12 in the direction of the axis L. The intake port 12 and the exhaust port 13 are positioned at approximately 180° offset from each other in the circumferential direction of the bore portion 3 so as to face each other in the radial direction of the bore portion 3.

[0020] The intake-side scavenging holes 14 are used to introduce fuel-containing fresh air into the bore 3 and the combustion chamber 11 during the scavenging stroke, and extend along the axis L inside the sidewall of the cylinder 2. The fresh air is a fuel mixture consisting of a gasoline-oil fuel mixture and air for engine operation. The ends of the intake-side scavenging holes 14 on the top dead center side communicate with the bore 3 at positions approximately the same as the exhaust ports 13 in the axis L. The intake-side scavenging holes 14 are arranged spaced apart from one another in the circumferential direction of the bore 3. More specifically, the intake-side scavenging holes 14 are arranged approximately symmetrically in the radial direction with respect to an imaginary line connecting the intake port 12 and the exhaust port 13. The intake-side scavenging holes 14 are arranged so that the fresh air introduced into the bore 3 is directed toward the intake port 12.

[0021] The end portion (inlet 14a, described later) of the intake-side scavenging port 14 on the bottom dead center side is connected to the crank chamber 6a. The end portion (not shown) of the exhaust-side scavenging port 16 on the bottom dead center side is connected to the crank chamber 6a.

[0022] The exhaust-side scavenging holes 16 are used to introduce EGR (Exhaust Gas Recirculation) gas, which is post-combustion exhaust gas having a lower fuel content than the working gas, into the bore 3 and the combustion chamber 11 during the scavenging stroke, and extend inside the side wall of the cylinder 2 along the axial line L. Ends of the exhaust-side scavenging holes 16 on the top dead center side communicate with the bore 3 at positions substantially similar to the positions of the exhaust ports 13 in the axial line L. The exhaust-side scavenging holes 16 are arranged spaced apart from each other in the circumferential direction of the bore 3. More specifically, the exhaust-side scavenging holes 16 are arranged substantially symmetrically with respect to an imaginary line connecting the intake port 12 and the exhaust port 13 in the radial direction. The exhaust-side scavenging holes 16 are arranged so that the EGR gas introduced into the bore 3 is directed toward the intake port 12. The piston 4 may be provided with a communication passage that connects the exhaust port 13 and the exhaust-side scavenging port 16 when the piston 4 is near top dead center, and through which exhaust gas after combustion is taken in as EGR gas from the exhaust port 13 to the exhaust-side scavenging port 16.

[0023] As described above, engine 1 is a piston valve type two-stroke engine in which intake port 12 is opened and closed by piston 4 reciprocating within bore portion 3. In engine 1, of the components that make up fresh air, air is introduced through intake port 12, while a mixed fuel containing gasoline and oil is injected into crank chamber 6a to cool big end 22 of connecting rod 10. As a result, the air and mixed fuel are mixed within crank chamber 6a of crankcase 6, and the above-mentioned fuel mixture is generated.

[0024] The configurations of the crank mechanism 7 and the connecting rod 10 will be described with reference to Figures 5(a) and 5(b). As shown in Figure 5(a), the crank mechanism 7 has a crankshaft 7a, a pair of crank webs 7b connected to the crankshaft 7a, and a pair of connecting portions 7c provided on radially opposite sides of the crank webs 7b. The connecting rod 10 has a small end 21 that is rotatably connected to the piston 4 via the piston pin 8 by inserting the piston pin 8 into a pin insertion hole 21a, a big end 22 that is rotatably connected to the connecting portion 7c of the crank mechanism 7 via the crank pin 9 by inserting the crank pin 9 into a pin insertion hole 22a, and a rod main body 23 that connects the small end 21 and the big end 22.

[0025] The crank webs 7b, connecting portion 7c, and crankshaft 7a are molded as a single unit. A crank pin 9 inserted into the pair of connecting portions 7c is joined and fixed to these connecting portions 7c, and the entire crank mechanism 7 forms a rigid body. The pair of crank webs 7b are fan-shaped with the crankshaft 7a at its center and are guided by the cylindrical wall surface of the crank chamber 6a to rotate about the crankshaft 7a. When the connecting rod 10 moves up and down in conjunction with the reciprocating motion of the piston 4, the big end 22 of the connecting rod 10 moves (rotates) in a circumferential orbit together with the crank pin 9 and connecting portion 7c, and the reciprocating motion of the piston 4 is converted into rotational motion of the crankshaft 7a.

[0026] As shown in Figure 5(b), the pair of crank webs 7b extend parallel to each other and are spaced apart in the axial direction of the crankshaft 7a. A gap G is formed between the pair of crank webs 7b. During rotation of the crank mechanism 7, the big end 22 of the connecting rod 10 and the gap G between the crank webs 7b are always located on opposite sides in the radial direction. The circumferential path of the big end 22 and the circumferential path of the gap G overlap.

[0027] As shown in FIG. 1, the engine 1 is equipped with a fuel injection nozzle (fuel injector) 30 that sprays a fuel mixture toward the big end 22 of the connecting rod 10. The fuel injection nozzle 30 is attached to the upper part of the crankcase 6 near the position where the fuel injection nozzle 30 is connected to the cylinder body 2a. The tip portion of the fuel injection nozzle 30, which includes an injection port 31 from which the fuel mixture is injected, is fitted from the outside to the inside of the crankcase 6. The injection port 31 of the fuel injection nozzle 30 is oriented, for example, in a direction that intersects both the axial direction L of the bore portion 3 and the axial direction of the crankshaft 7a. More specifically, the injection port 31 of the fuel injection nozzle 30 is oriented in a direction that intersects both the axial direction L of the bore portion 3 and the axial direction of the crankshaft 7a.

[0028] 4 is a cross-sectional view taken along line IV-IV in FIG. 1. As shown in FIG. 4, the fuel injection nozzle 30 is disposed in the diameter direction of the bore portion 3 (bore surface 3a) in a plan view. The injection port 31 of the fuel injection nozzle 30 protrudes slightly into the crank chamber 6a. The injection port 31 is disposed at a position where it passes through the gap G (see FIG. 5(b)) between the pair of crank webs 7b during rotation of the crank mechanism 7. Because the injection port 31 is structured so as to face the gap G, no other members are present between the injection port 31 and the pin insertion hole 22a.

[0029] 1 and 4, the inlets 14a of a pair of intake-side scavenging holes 14 are located near the sides of the injection nozzle 31. The pair of inlets 14a open toward the crankcase 6a. The pair of inlets 14a also communicate with a pair of exhaust-side scavenging holes 16. The circumferential distance between the injection nozzle 31 and the inlets 14a is shorter than one-fourth the length of the circumferential surface of the bore surface 3a (the inner circumferential surface of the bore portion 3). That is, the injection nozzle 31 and one of the intake-side scavenging holes 14 are arranged within a range of a central angle of 90° based on the axis L of the bore portion 3. The injection nozzle 31 and the other of the intake-side scavenging holes 14 are arranged within a range of a central angle of 90° based on the axis L of the bore portion 3. The inlets 14a of the intake-side scavenging holes 14 are located at the same height as the injection nozzle 31 of the fuel injection nozzle 30 in the direction of the axis L. In other words, the injection port 31 of the fuel injection nozzle 30 is located at the same height as the upper end of the crankcase 6.

[0030] As shown in FIGS. 1 and 7(a), the fuel injection nozzle 30 injects the mixed fuel in a direction tangential to the circumferential orbit of the big end 22. The period during which the mixed fuel is injected from the fuel injection nozzle 30 includes at least the time when the piston 4 is positioned at top dead center (at which time the pin big end 22 is also at its highest position) and may continue, for example, until 30° after top dead center. In other words, the period during which the mixed fuel is injected from the fuel injection nozzle 30 may start when the piston 4 is positioned at top dead center (0°) or slightly before that (approximately several to 15° before), and may end 30° after top dead center. The fuel injection nozzle 30 is configured to spray the mixed fuel onto the big end 22 of the connecting rod 10. The fuel injection nozzle 30 injects the mixed fuel while the big end 22 passes in front of the injection port 31.

[0031] As shown in FIG. 6 , the injection timing of the mixed fuel from the fuel injection nozzle 30 is controlled by the ECU 40, which controls the engine 1. The ECU 40 controls the valve 50, which opens and closes the intake path to the intake port 12, and the fuel injection nozzle 30 based on throttle opening information input from the throttle sensor S1 and rotation angle information of the crank mechanism 7 input from the angle sensor S2. The injection timing (injection period) described above can be appropriately adjusted by the ECU 40 based on the state of the engine 1. The fuel injection nozzle 30 is an electronically controlled injector and can adjust the injection amount of the mixed fuel with high precision. For example, even when the required mixed fuel (gasoline amount) is minimum, the ECU 40 injects the mixed fuel from the fuel injection nozzle 30 at the controllable limit (minimum amount). In this embodiment, the fuel injection nozzle 30 is configured to spray the mixed fuel toward the big end 22 at least when the piston 4 is positioned at top dead center. Note that FIG. 6 omits the mixed fuel line (path) connected to the fuel injection nozzle 30.

[0032] The mixed fuel injected from the injection port 31 may be radial or linear. The type of nozzle may be selected as appropriate. The injection direction (central axis of injection) of the fuel injection nozzle 30 intersects with the axis L and crosses the bore portion 3 in a plan view. The central axis of injection of the fuel injection nozzle 30 is, for example, perpendicular to the axis L. The central axis of injection of the fuel injection nozzle 30 is also, for example, perpendicular to the axial direction of the crankshaft 7a.

[0033] Next, we will explain the operation of the engine 1. First, as the piston 4 rises from bottom dead center to top dead center, the intake-side scavenging port 14, the exhaust-side scavenging port 16, and the exhaust port 13 are closed by the piston 4, and fresh air in the combustion chamber 11 is compressed. As the piston 4 further rises, the intake port 12 communicates with the crank chamber 6a via the bore portion 3, and air is introduced into the crank chamber 6a (see FIGS. 1 and 2).

[0034] When the piston 4 reaches near top dead center, the air-fuel mixture explodes in the combustion chamber 11, causing the piston 4 to descend toward bottom dead center. Meanwhile, in the crank chamber 6a, when the piston 4 is near top dead center, the fuel mixture is injected from the fuel injection nozzle 30 under the control of the ECU 40. The fuel mixture is sprayed onto the big end 22 of the connecting rod 10, thereby lubricating and cooling the big end 22. The injection of the fuel mixture is stopped immediately after the piston 4 begins to descend (by 30° after top dead center at the latest). The air and fuel mixture are mixed in the crank chamber 6a, generating fresh air.

[0035] As the piston 4 continues to descend, the exhaust port 13 opens and the combustion gas is exhausted (see FIG. 3). Then, slightly after the exhaust port 13 opens, the intake-side scavenging port 14 and the exhaust-side scavenging port 16 are exposed inside the bore portion 3, and the scavenging stroke begins. The injection of the mixed fuel occurs close to the start of the scavenging stroke. In addition, the distance from the injection port 31 to the inlet 14a of the intake-side scavenging port 14 is short. The mixed fuel (fresh air) is reliably and easily introduced into the intake-side scavenging port 14. In the first half of the scavenging stroke, the exhaust-side scavenging port 16 is filled with EGR gas, and the intake-side scavenging port 14 is filled with fresh air.

[0036] When the intake-side scavenging port 14 opens to the bore portion 3, fresh air starts to be introduced into the bore portion 3 through the intake-side scavenging port 14. As the piston 4 descends, fresh air flows into the bore portion 3 from the intake-side scavenging port 14. At the same time, the exhaust-side scavenging port 16 opens, allowing EGR gas and fresh air to flow in this order through the exhaust-side scavenging port 16. This results in stratified scavenging.

[0037] As the piston 4 reaches bottom dead center, the pair of crank webs 7b of the crank mechanism 7 pass near the fuel injection nozzle 30, but the injection port 31 passes through the gap G between the pair of crank webs 7b, so there is no interference between them.

[0038] In the engine 1 of this embodiment, the fuel injection nozzle 30 attached to the crankcase 6 sprays mixed fuel onto the big end 22 of the connecting rod 10. In doing so, the fuel injection nozzle 30 injects the mixed fuel in a direction tangential to the circumferential orbit of the big end 22. The oil contained in the mixed fuel lubricates and cools the big end 22. The gasoline contained in the mixed fuel also cools the big end 22. As a result, a small amount of mixed fuel is required to lubricate and cool the big end 22. Furthermore, because the mixed fuel is injected into the crankcase 6 rather than into the combustion chamber 11 or bore 3, there is no need to consider the pressure resistance and heat resistance of the peripheral configuration of the fuel injection nozzle 30.

[0039] The injection port 31 of the fuel injection nozzle 30 protrudes into the crank chamber 6a. This allows the mixed fuel to be injected from a position closer to the big end 22, making it easier to achieve the desired lubrication and cooling effects described above.

[0040] The injection port 31 of the fuel injection nozzle 30 is positioned so that it passes through the gap G between the pair of crank webs 7b. This allows the injection port 31 to be closer to the big end 22, enabling the big end to be cooled more reliably and effectively.

[0041] The fuel injection nozzle 30 is configured to inject the mixed fuel into the big end 22 at least when the piston 4 is positioned at top dead center. This synchronizes the fuel injection with the scavenging timing, making it easier to introduce the fuel sprayed onto the big end 22 into the intake-side scavenging port 14.

[0042] The inlet 14a of the intake-side scavenging port 14 is located at the same height as the injection port 31 of the fuel injection nozzle 30 in the direction of the axis L. This makes it easier to introduce the fuel sprayed onto the big end 22 into the intake-side scavenging port 14. Because the mixed fuel remains near the inlet 14a of the intake-side scavenging port 14, the fuel is easily introduced into the intake-side scavenging port 14. This makes it possible to reduce the amount of wasted fuel that is not introduced into the intake-side scavenging port 14, which also has the effect of reducing fuel consumption. Furthermore, transient response and starting performance are improved.

[0043] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the configuration is not limited to one in which the fuel injection nozzle 30 injects the mixed fuel into the big end 22 at least when the piston 4 is positioned at top dead center. For example, as shown in FIG. 7(b), the fuel injection nozzle 30 may spray the mixed fuel into the big end 22 of the connecting rod 10 while the piston 4 is on its way to top dead center. The fuel injection nozzle 30 may be attached to, for example, the lower part of the crankcase 6, in order to inject the mixed fuel in a tangential direction to the circumferential orbit of the big end 22. The injection port 31 may be directed upward.

[0044] The present invention is not limited to a configuration in which four scavenging holes, i.e., a pair of intake-side scavenging holes 14 and a pair of exhaust-side scavenging holes 16, are provided in the cylinder 2, but may be a configuration in which one intake-side scavenging hole 14 and one exhaust-side scavenging hole 16 are provided. The present invention is not limited to a configuration in which the intake-side scavenging hole 14 introduces fresh air and the exhaust-side scavenging hole 16 introduces EGR gas. The present invention is also applicable to a stratified scavenging engine that uses air. Furthermore, only a pair of scavenging holes that are radially opposed to each other may be provided between the intake port 12 and the exhaust port 13. Only one scavenging hole may be provided for the cylinder 2. [Explanation of symbols]

[0045] 1...engine (two-stroke engine), 2...cylinder, 3...bore portion, 4...piston, 6...crankcase, 6a...crank chamber, 7...crank mechanism, 7a...crankshaft, 7b...crank web, 9...crankpin, 11...combustion chamber, 12...intake port, 13...exhaust port, 14...intake side scavenging hole (scavenging hole), 16...exhaust side scavenging hole (scavenging hole), 21...small end, 22...big end, 30...fuel injection nozzle (fuel injector), 31...injection port, G...gap, L...axis (of bore portion).

Claims

1. In a two-stroke engine (1) of a piston valve type in which an intake port is opened and closed by a piston (4) that reciprocates axially within a bore portion (3) of a cylinder (2), a crankcase (6) connected to the cylinder (2) and having a crank chamber (6a); a crank mechanism (7) disposed in the crank chamber (6a) and rotating around a crankshaft (7a); a connecting rod having a small end (21) connected to the piston (4) and a big end (22) connected to the crank mechanism (7); a fuel injector (30) attached to the crankcase (6) and configured to inject a mixed fuel in a tangential direction of a circumferential orbit of the big end (22) to spray the mixed fuel onto the big end (22), The fuel injector (30) is attached to the crankcase (6) near a position where the crankcase (6) is connected to the cylinder (2), an injection port (31) of the fuel injector (30) protrudes further into the crank chamber (6a) than a bore surface (3a) of the bore portion (3) when viewed in the axial direction of the bore portion (3).

2. The crank mechanism (7) has a pair of crank webs (7b) connected to the crankshaft (7a) and spaced apart in the axial direction of the crankshaft (7a), 2. The two-stroke engine according to claim 1, wherein the injection port (31) of the fuel injector (30) is arranged at a position passing through a gap (G) between the pair of crank webs (7b).

3. 3. The two-stroke engine according to claim 1, wherein the fuel injector is configured to inject the mixed fuel into the big end of the piston at least when the piston is at top dead center.

4. The cylinder (2) is formed with a scavenging hole (14), 4. The two-stroke engine according to claim 1, wherein an inlet (14a) of the scavenging port (14) opening toward the crankcase (6a) is positioned at the same height as the injection port (31) of the fuel injector (30) in the axial direction.

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