2-Stroke Engine

Abstract

To provide a two-stroke engine capable of suppressing leakage of gas from an inside of a crankcase while suppressing deterioration of intake efficiency.SOLUTION: A two-stroke engine includes: an intake passage which is connected to a crankcase; and a reed valve 40 which is provided in the intake passage and is opened in accordance with decrease of an internal pressure of the crankcase during operation of the engine. The two-stroke engine has an energizing device 50 for energizing a valve element 43 of the reed valve 40 to a valve close direction. The energizing device 50 energizes the valve element 43 in such a manner that energizing force at engine stop is larger than energizing force at engine operation.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, a reed valve type two-stroke engine has been known (for example, Patent Document 1). The two-stroke engine described in Patent Document 1 has an intake passage connected to a crankcase and a reed valve provided in the intake passage. The reed valve opens as the pressure inside the crankcase decreases during engine operation. At this time, gas (air or mixture) is inhaled into the crankcase through the intake passage and the reed valve. The reed valve closes as the pressure inside the crankcase increases thereafter. This prevents the backflow of gas (including fuel) from the crankcase to the intake passage.

[0003] Also, Patent Document 1 proposes providing a pressing portion that constantly presses the valve body of the reed valve in the closing direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a two-stroke engine, due to its structure, fuel (for example, gasoline fuel or hydrogen fuel) is mixed into the air inhaled into the crankcase. Therefore, it is required to suppress the leakage of gas (including fuel) from the inside of the crankcase to the outside of the engine when the engine stops.

[0006] As described in Patent Document 1, by constantly pressing the valve body of the reed valve in the valve closing direction, it becomes possible to hold the reed valve in the closed state when the engine stops. Thereby, it becomes possible to suppress gas leakage when the engine stops.

[0007] However, in this case, since the reed valve is constantly pressed in the valve closing direction, during engine operation, it is necessary to open the reed valve with a large force against the pressing force of the pressing portion. Therefore, in the above two-stroke engine, there is a possibility of causing a decrease in intake efficiency, such as a decrease in the opening speed of the reed valve.

Means for Solving the Problem

[0008] The two-stroke engine for solving the above problem has an intake passage connected to a crankcase and a reed valve provided in the intake passage that opens as the internal pressure of the crankcase decreases during engine operation. In the two-stroke engine, it has a biasing portion that biases the valve body of the reed valve in the valve closing direction, and the biasing portion biases the valve body in such a manner that the biasing force when the engine stops is greater than the biasing force when the engine is running.

[0009] According to the above configuration, when the engine stops, the reed valve can be held in the closed state by the biasing force of the biasing portion, so that it is possible to suppress the gas in the crankcase from leaking to the outside of the two-stroke engine. Moreover, during engine operation, the biasing force that biases the valve body of the reed valve in the valve closing direction can be made smaller compared to when the engine stops. Therefore, the force required to open the reed valve during engine operation can be reduced. Thereby, it becomes possible to suppress a decrease in the opening speed of the reed valve during engine operation, so that a decrease in intake efficiency can be suppressed.

[0010] In the above two-stroke engine, it is preferable that the biasing portion makes the biasing force during engine operation "0". According to the above configuration, although there is a biasing portion that biases the valve body of the reed valve in the valve closing direction, it is possible to prevent the biasing force of the biasing portion from acting on the valve body during engine operation. Therefore, it is possible to suitably suppress a decrease in intake efficiency.

[0011] In the above two-stroke engine, the reed valve includes a valve body having a valve port and a valve seat, a valve body that opens and closes the valve port, and a stopper member provided at a position that sandwiches the valve body between the valve body and the valve body. The biasing portion includes a position changing portion that changes the position of the stopper member, and a control portion that controls the operation of the position changing portion. The position changing portion operates in a manner that switches the position of the stopper member between a closed position where the stopper member is pressed against the valve body in a manner that sandwiches the valve body, and an open position where the stopper member is separated from the valve body. The control portion preferably sets the stopper member to the closed position when the engine is stopped, and sets the stopper member to the open position when the engine is operating.

[0012] According to the above configuration, when the engine is stopped, the valve body of the reed valve can be pressed against the valve seat of the valve body by using the stopper member. Thereby, the reed valve can be held in a valve-closed state. When the engine is operating, the stopper member can be separated from the valve body of the reed valve. Thereby, although the biasing portion is provided, it is possible to prevent the biasing force of the biasing portion from acting on the valve body during engine operation.

[0013] In the above two-stroke engine, the reed valve preferably includes a valve body having a valve port and a valve seat, a valve body that opens and closes the valve port, an electromagnet provided on the valve body that generates a magnetic force that attracts the valve body, and a control unit that controls energization of the electromagnet in a manner that generates a magnetic force in the electromagnet when the engine is stopped and does not generate a magnetic force in the electromagnet when the engine is operating.

[0014] According to the above configuration, when the engine stops, the valve body of the reed valve can be pressed against the valve seat of the valve body by the generated magnetic force of the electromagnet. Thereby, the reed valve can be held in the closed state. When the engine is running, since the electromagnet does not generate magnetic force, the force required for opening the reed valve can be reduced.

[0017] The above two-stroke engine is preferably an internal combustion engine using hydrogen as fuel. According to the above configuration, in a two-stroke engine using hydrogen as fuel, it is possible to suppress a decrease in intake efficiency and suppress leakage of gas containing hydrogen from the crankcase.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

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Figure 4

Figure 5

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Figure 8

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Figure 10

Figure 11

Best Mode for Carrying Out the Invention

[0019] (First Embodiment) Hereinafter, a first embodiment of a two-stroke engine will be described with reference to FIGS. 1 to 6. As shown in FIGS. 1 and 2, a two-stroke engine (hereinafter, internal combustion engine 20) has a cylinder bore 21. The inner peripheral surface of the cylinder bore 21 has a cylindrical shape. Inside the cylinder bore 21, a piston 22 is provided in a reciprocating manner in the axial direction of the cylinder bore 21. Inside the internal combustion engine 20, a combustion chamber 24 is defined by the inner peripheral surface of the cylinder bore 21, the top surface of the piston 22, and the bottom surface of the cylinder head 23. An ignition plug 25 is provided in the combustion chamber 24.

[0020] The internal combustion engine 20 has a crankcase 26. Inside the crankcase 26, a crankshaft 27 is rotatably provided. The internal combustion engine 20 has a connecting rod 28. The crankshaft 27 and the piston 22 are connected by the connecting rod 28.

[0021] The internal combustion engine 20 has an intake passage 29. One end of the intake passage 29 is connected to the crankcase 26 in a manner that opens on the inner wall surface of the crankcase 26. An intake pipe (not shown) constituting the intake system of the internal combustion engine 20 is connected to the other end of the intake passage 29. In this embodiment, in the middle of the intake pipe, a mixture generation device for mixing air and hydrogen fuel to generate a mixture is provided. As the mixture generation device, for example, a fuel injection valve that injects hydrogen fuel into the intake pipe is adopted. In this embodiment, a mixed gas containing air and hydrogen fuel is inhaled into the inside of the crankcase 26 through the intake passage 29. A reed valve 40 is provided in the intake passage 29. The reed valve 40 opens as the internal pressure of the crankcase 26 decreases during engine operation. The specific structure of the reed valve 40 will be described in detail later.

[0022] The internal combustion engine 20 has an intake port 31 that communicates the combustion chamber 24 with the crankcase 26. The intake port 31 opens at the inner peripheral surface of the cylinder bore 21 and the inner wall surface of the crankcase 26. Through the intake port 31, the air-fuel mixture in the crankcase 26 is introduced into the combustion chamber 24.

[0023] The internal combustion engine 20 has an exhaust port 32. One end of the exhaust port 32 is connected to the cylinder bore 21 in a manner that opens at the inner peripheral surface of the cylinder bore 21. An exhaust pipe (not shown) that constitutes the exhaust system of the internal combustion engine 20 is connected to the other end of the exhaust port 32. Through this exhaust port 32, the combustion gas in the combustion chamber 24 is discharged into the exhaust pipe.

[0024] The internal combustion engine 20 operates as follows. In the intake compression process, when the piston 22 rises toward the top dead center, the air-fuel mixture in the combustion chamber 24 is compressed. Also, as the piston 22 rises, the inside of the crankcase 26 is depressurized, and the internal pressure of the crankcase 26 becomes low. As a result, the reed valve 40 opens. At this time, the mixed gas is inhaled into the crankcase 26 through the reed valve 40 and the intake passage 29.

[0025] After that, when the piston 22 approaches the top dead center and decelerates, it becomes difficult for the inside of the crankcase 26 to be depressurized. As a result, the internal pressure of the crankcase 26 increases, and the reed valve 40 is closed. At this time, the intake of the mixed gas into the crankcase 26 is stopped. Then, at a predetermined ignition timing, the ignition operation is performed by the spark plug 25. As a result, the air-fuel mixture ignites and burns in the combustion chamber 24.

[0026] In the exhaust scavenging process, the piston 22 descends toward the bottom dead center under the expansion force of the combustion gas in the combustion chamber 24. Then, when the piston 22 descends to a position where the combustion chamber 24 and the exhaust port 32 communicate, the combustion gas is discharged from the combustion chamber 24 into the exhaust pipe through the exhaust port 32. In this way, the scavenging of the combustion chamber 24 is performed.

[0027] When the piston 22 descends, basically, the internal pressure of the crankcase 26 increases. Therefore, at this time, the reed valve 40 remains in the closed state. On the other hand, as the scavenging of the combustion chamber 24 proceeds, the internal pressure of the combustion chamber 24 decreases. When the internal pressure of the combustion chamber 24 becomes lower than the internal pressure of the crankcase 26, due to this pressure difference, the mixed gas in the crankcase 26 is introduced into the combustion chamber 24 through the intake port 31. Then, when the piston 22 reaches the bottom dead center, thereafter the piston 22 starts to rise.

[0028] (Reed Valve) Hereinafter, the structure of the reed valve 40 will be described. As shown in FIGS. 3 and 4, the reed valve 40 includes a valve body 41, two valve elements 43, and two stopper members 44.

[0029] (Valve Body) The valve body 41 is formed of a metallic material (for example, an aluminum alloy). The valve body 41 has a substantially isosceles triangular cross-section perpendicular to the flow path of the intake passage 29 (see FIG. 1). The valve body 41 is attached to the intake passage 29 in such a manner that the apex of the isosceles triangle protrudes downstream of the intake passage 29 (the lower left side in FIG. 1). The inside of the valve body 41 forms a gas passage 411 through which the mixed gas passes. The upstream end of the gas passage 411 opens at a portion corresponding to the base of the isosceles triangle in the valve body 41. Two side walls 45 corresponding to the hypotenuses of the isosceles triangle in the valve body 41 are each provided with three valve openings 451 and three valve seats 452.

[0030] (Valve Element) Each of the two valve bodies 43 is formed in a thin plate shape from a metal material (for example, an iron-based material). Each valve body 43 is provided on the side wall 45 of the valve body 41 in a manner extending along the side wall 45. The valve body 43 is fixed to the side wall 45 in a manner closing three valve openings 451 provided in the opposing side wall 45. The valve body 43 has a cantilever structure with one end (hereinafter, the base end portion 431) fixed to the valve body 41.

[0031] In this embodiment, when the downstream pressure P1 (see FIG. 1) of the lead valve 40 becomes low during engine operation, due to the difference from the upstream pressure P2 of the lead valve 40, the valve body 43 elastically deforms in a direction away from the valve opening 451. As a result, the valve body 43 is in a state of being separated from the valve seat 452, and at this time, the lead valve 40 is in an open valve state.

[0032] On the other hand, when the downstream pressure P1 does not become so low or becomes high during engine operation, the valve body 43 is pressed against the valve body 41, so the valve body 43 does not elastically deform. At this time, since the valve body 43 is in a state of seating on the valve seat 452, that is, the valve body 43 is in a state of closing the valve opening 451, the lead valve 40 is in a closed valve state. Thus, the lead valve 40 opens and closes according to the difference between the downstream pressure P1 and the upstream pressure P2.

[0033] (Stopper member) Each of the two stopper members 44 is formed in a plate shape from a metal material (for example, an aluminum alloy). The stopper members 44 are respectively provided on the two side walls 45 of the valve body 41. Each stopper member 44 is provided at a position sandwiching the valve body 43 between the side wall 45 of the valve body 41. The stopper member 44 has a cantilever structure with one end (hereinafter, the base end portion 441) supported by the valve body 41. Each stopper member 44 has three through holes 442. The stopper member 44 is basically for regulating the maximum opening degree of the valve body 43. The stopper member 44 suppresses further deformation of the valve body 43 through contact with the valve body 43.

[0034] (Biasing device) As shown in FIGS. 5 and 6, the internal combustion engine 20 of the present embodiment has a biasing device 50 as a biasing portion that biases the valve body 43 of the lead valve 40 in the valve closing direction. Hereinafter, the biasing device 50 will be described.

[0035] The biasing device 50 includes a position changing portion 51 that changes the position of the stopper member 44, and a control portion 52 that controls the operation of the position changing portion 51. (Position changing portion) The position changing portion 51 has two rotating shafts 511 and a connecting mechanism 512.

[0036] As shown in FIGS. 3 and 4, the rotating shaft 511 has a cylindrical shape. The rotating shaft 511 is integrally provided on the base end portion 441 of the stopper member 44 in a manner that extends along the base end portion 441. The rotating shaft 511 is provided separately on the two stopper members 44.

[0037] Further, the rotating shaft 511 is attached to the side wall 45 of the valve body 41 via an attachment member 513 in a manner that can rotate about the axis of the rotating shaft 511 as the rotation center. As shown in FIGS. 5 and 6, the lead valve 40 can rotate the stopper member 44 about the axis of the rotating shaft 511 as the rotation center by rotating the rotating shaft 511. Specifically, as shown by the arrow A in FIG. 6, by rotating the rotating shaft 511 in one direction, the rotation position of the stopper member 44 becomes a position where it is pressed against the valve body 41 with the valve body 43 interposed therebetween (hereinafter, the closed position). Also, as shown by the arrow B in FIG. 5, by rotating the rotating shaft 511 in the other direction, the rotation position of the stopper member 44 becomes a position where the stopper member 44 is separated from the valve body 43 (hereinafter, the open position).

[0038] As shown in FIGS. 5 and 6, the coupling mechanism 512 is provided between the two rotating shafts 511 and the actuator 521. In this embodiment, the two rotating shafts 511 and the actuator 521 are connected via the coupling mechanism 512. The coupling mechanism 512 is a power transmission mechanism that transmits the generated power of the actuator 521 to the two rotating shafts 511. In this embodiment, a gear mechanism is employed as the coupling mechanism 512.

[0039] (Control unit) The control unit 52 includes the above actuator 521 and a control device 522. The actuator 521 is connected to the input shaft of the coupling mechanism 512. In this embodiment, a rotary machine is employed as the actuator 521. In this embodiment, by controlling the operation of the actuator 521, the operation of the position changing unit 51 is controlled, so that the positions of the two stopper members 44 of the lead valve 40 can be switched to either the "closed position" or the "open position".

[0040] The control device 522 is an electronic control device having an arithmetic processing unit and a storage device. Output signals of various sensors, such as the output signal of the operation switch 53, are input to the control device 522. The operation switch 53 is a switch that is turned on when starting the operation of the internal combustion engine 20 and turned off when stopping the operation of the internal combustion engine 20. The control device 522 performs various calculations based on the output signals of the sensors, and based on the calculation results, executes the operation control of the position changing unit 51 (specifically, the actuator 521).

[0041] In this embodiment, operation control of the actuator 521 is executed, such as setting the stopper member 44 to the closed position when the engine is stopped and setting the stopper member 44 to the open position when the engine is operating.

[0042] (When the engine is stopped) In the present embodiment, when the engine is stopped, the stopper member 44 is controlled to the closed position as follows. That is, when the operation of the internal combustion engine 20 is stopped, the operation control of the actuator 521 is executed in such a manner that the position of the stopper member 44 is set to the "closed position" (the mode shown in FIG. 6). As a result, the position of the stopper member 44 becomes the "closed position". In the present embodiment, it is determined that the operation of the internal combustion engine 20 has been stopped when the operation switch 53 is turned off. Thus, in the present embodiment, during the period when the operation of the internal combustion engine 20 is stopped, that is, when the engine is stopped, the position of the stopper member 44 becomes the closed position.

[0043] According to the present embodiment, when the engine is stopped, the stopper member 44 is pressed against the valve body 43 and the valve body 41 with the valve body 43 sandwiched between the stopper member 44 and the valve body 41. As a result, the valve body 43 of the reed valve 40 can be pressed against the valve seat 452 to achieve close contact. Thus, according to the present embodiment, when the engine is stopped, by using the stopper member 44, the reed valve 40 can be held in the closed state. Therefore, when the engine is stopped, it is possible to suppress the leakage of the mixed gas in the crankcase 26 to the outside of the internal combustion engine 20 through the gap between the valve body 43 and the valve seat 452 of the reed valve 40.

[0044] Here, the valve body 43 of the reed valve 40 repeatedly undergoes elastic deformation as it opens and closes. Therefore, over time, the valve body 43 may change in such a manner that the tip portion, which is the portion opposite to the base end portion 431 of the valve body 43, warps in a direction away from the side wall 45 of the valve body 41. When such a change over time occurs, there is a possibility that a gap may be formed between the tip portion of the valve body 43 and the valve body 41 when the engine is stopped. In this case, there is a possibility that the mixed gas may leak from the inside of the crankcase 26 to the outside of the internal combustion engine 20 through the above-described gap.

[0045] In this regard, according to the present embodiment, when the engine stops, the valve body 43 is pressed against the valve body 41 by the stopper member 44 with the valve body 43 sandwiched between the stopper member 44 and the valve body 41. Therefore, the tip portion of the valve body 43 deformed due to changes over time is pressed against the valve body 41 while being deformed (corrected) into a shape along the outer surface of the valve body 41. As a result, the valve body 43 of the reed valve 40 can be brought into close contact with the valve seat 452. As described above, according to the present embodiment, even when the valve body 43 is deformed due to changes over time, the reed valve 40 can be closed and held in the closed state.

[0046] (During engine operation) In the present embodiment, the stopper member 44 is set to the open position during engine operation as follows. That is, when the operation of the internal combustion engine 20 is started, the operation control of the actuator 521 is executed in a manner of setting the position of the stopper member 44 to the "open position" (the manner shown in FIG. 5). As a result, the position of the stopper member 44 becomes the "closed position". In the present embodiment, it is determined that the operation of the internal combustion engine 20 has started when the operation switch 53 is turned on. Thus, in the present embodiment, during the period when the internal combustion engine 20 is operating, that is, during so-called engine operation, the position of the stopper member 44 becomes the open position.

[0047] In the present embodiment, when the reed valve 40 is closed during engine operation, the stopper member 44 is separated from the valve body 43. As a result, the biasing force for biasing the valve body 43 by the stopper member 44 can be set to "0". According to the present embodiment, although the valve body 43 can be biased in the closing direction by the stopper member 44, during engine operation, the biasing force by the stopper member 44 can be prevented from acting on the valve body 43. Therefore, the force required for opening the reed valve 40 during engine operation can be reduced. As a result, a decrease in the opening speed of the reed valve 40 during engine operation can be suppressed, and a decrease in the intake efficiency can be suppressed.

[0048] According to this embodiment, the following operational effects can be obtained. (1) When the engine is stopped, the position of the stopper member 44 is set to the closed position where the stopper member 44 is pressed against the valve body 41 in a manner that sandwiches the valve body 43 therebetween. When the engine is operating, the position of the stopper member 44 is set to the open position where the stopper member 44 is separated from the valve body 43. Therefore, it is possible to suppress a decrease in intake efficiency during engine operation while suppressing leakage of the mixed gas from the inside of the crankcase 26 to the outside of the internal combustion engine 20 when the engine is stopped.

[0049] (2) During engine operation, the biasing force that biases the valve body 43 by the stopper member 44 can be set to "0". Therefore, it is possible to preferably suppress a decrease in intake efficiency during engine operation.

[0050] (Second Embodiment) Hereinafter, the second embodiment of the two-stroke engine will be described with a focus on the differences from the first embodiment, with reference to FIGS. 7 to 9.

[0051] The two-stroke engine of this embodiment is different from the two-stroke engine of the first embodiment in that the stopper member is fixed to the valve body and an electromagnet that attracts the valve body is provided on the valve body.

[0052] Hereinafter, the stopper member and the electromagnet according to this embodiment will be described. In the following, the same reference numerals (or corresponding reference numerals) will be given to the same configurations as those of the two-stroke engine of the first embodiment illustrated in FIGS. 1 to 6 above, and detailed descriptions of those configurations will be omitted.

[0053] As shown in FIGS. 7 to 9, the reed valve 60 of this embodiment has two stopper members 64 and two electromagnets 70. (Stopper Member) Each of the two stopper members 64 is formed in a plate shape from a metallic material (e.g., an aluminum alloy). The stopper members 64 are respectively provided on the two side walls 45 of the valve body 61. Each stopper member 64 is provided at a position that sandwiches the valve element 43 between itself and the side wall 45 of the valve body 61. One end (base end portion 641) of the stopper member 64 is fixed to the valve body 61. The stopper member 64 has a cantilever structure in which the base end portion 641 is supported. The stopper member 64 extends in a manner that moves away from the valve element 43 as it goes from the base end portion 641 toward the tip portion, which is the portion on the side opposite to the base end portion 641. The stopper member 64 is for suppressing further deformation of the valve element 43 through contact with the valve element 43.

[0054] Note that the lead valve 60 of the present embodiment does not have a position changing portion 51 (see FIG. 5), specifically, a rotation shaft 511 and a connection mechanism 512. The stopper member 64 of the present embodiment has a structure in which its position does not change.

[0055] (Electromagnet) The electromagnets 70 are respectively provided on the two side walls 45 of the valve body 61. Specifically, mounting grooves 453 are provided on each side wall 45 of the valve body 61. Each mounting groove 453 has three peripheral portions 66 and two connecting portions 67. Each peripheral portion 66 forms an annulus that extends along the inner edge of the valve port 451 of the side wall 45. Each connecting portion 67 extends in a manner that connects adjacent peripheral portions 66 to each other.

[0056] The electromagnet 70 has three coil portions 71 and two connection portions 72. The coil portions 71 form an annulus that extends along the inner edge of the valve port 451 of the side wall 45. The connection portions 72 are shaped to connect adjacent coil portions 71 to each other. Each of the two electromagnets 70 is attached to the mounting groove 453 of the side wall 45. Specifically, the coil portion 71 of the electromagnet 70 fits into the peripheral portion 66 of the mounting groove 453. Also, the connection portion 72 of the electromagnet 70 fits into the connecting portion 67 of the mounting groove 453.

[0057] (Control device) The internal combustion engine 20 has a control device 73 as a control unit. The control device 73 performs various calculations based on the output signals of the sensors, and based on the calculation results, executes the operation control (energization control) of the electromagnet 70.

[0058] In this embodiment, energization control of the electromagnet 70 is executed such that the electromagnet 70 is "on (energized)" when the engine is stopped, while the electromagnet 70 is "off (non-energized)" when the engine is operating.

[0059] (When the engine is stopped) In this embodiment, the electromagnet 70 is "turned on" when the engine is stopped as follows. That is, when the operation of the internal combustion engine 20 is stopped, the electromagnet 70 is "turned on". In this embodiment, the fact that the operation of the internal combustion engine 20 has stopped is determined by the operation switch 53 being turned off. Thus, in this embodiment, the electromagnet 70 is "turned on" during the period when the operation of the internal combustion engine 20 is stopped, that is, during so-called engine stop.

[0060] At this time, when the electromagnet 70 is "turned on", the electromagnet 70 generates a magnetic force. Then, due to the magnetic force generated by the electromagnet 70, the valve body 43 is attracted toward the valve body 61 side, and the valve body 43 is pressed against the valve seat 452 of the valve body 61. As a result, the reed valve 40 can be held in the closed state. Therefore, it is possible to suppress the mixed gas in the crankcase 26 from leaking to the outside of the internal combustion engine 20 through the gap between the valve body 43 and the valve seat 452 of the reed valve 40.

[0061] Also, according to this embodiment, when the engine is stopped, the valve body 43 is pressed against the valve body 61 by the suction force generated by the magnetic force generated by the electromagnet 70. Therefore, the tip portion of the valve body 43 deformed due to changes over time can be corrected to a shape along the outer surface of the valve body 61 while being pressed against the valve body 61. Therefore, according to this embodiment, even when the valve body 43 is deformed due to changes over time, the reed valve 40 can be closed and held in the closed state.

[0062] (During engine operation) In this embodiment, the electromagnet 70 is turned "OFF" during engine operation as follows. That is, when the operation of the internal combustion engine 20 is started, the electromagnet 70 is turned "OFF". In this embodiment, the start of the operation of the internal combustion engine 20 is determined by the fact that the operation switch 53 is turned on. Thus, in this embodiment, the electromagnet 70 is turned "OFF" during the period when the internal combustion engine 20 is operating, that is, during so-called engine operation.

[0063] In this embodiment, during engine operation, the electromagnet 70 does not generate magnetic force. At this time, since the valve body 43 is not attracted by the electromagnet 70, the biasing force that biases the valve body 43 in the closing direction by the electromagnet 70 becomes "0". Thus, according to this embodiment, although it is possible to bias the valve body 43 in the closing direction by the magnetic force generated by the electromagnet 70, during engine operation, the attractive force by the electromagnet 70, that is, the biasing force in the closing direction, can be prevented from acting on the valve body 43. Therefore, the force required for opening the lead valve 40 during engine operation can be reduced. As a result, the decrease in the opening speed of the lead valve 40 during engine operation can be suppressed, and thus the decrease in the intake efficiency can be suppressed.

[0064] According to this embodiment, the following operational effects can be obtained. (3) An electromagnet 70 that generates a magnetic force for attracting the valve body 43 is provided on the valve body 61. During engine stop, the electromagnet 70 is energized to generate magnetic force, and during engine operation, the energization of the electromagnet 70 is controlled so as not to generate magnetic force. Therefore, while suppressing the decrease in intake efficiency during engine operation, it is possible to suppress the leakage of the mixed gas from the inside of the crankcase 26 to the outside of the internal combustion engine 20 during engine stop.

[0065] (4) During engine operation, the biasing force that biases the valve body 43 in the closing direction by the electromagnet 70 can be made "0". Therefore, the decrease in intake efficiency during engine operation can be suitably suppressed.

[0066] (Third Embodiment) Hereinafter, the third embodiment of the two-stroke engine will be described with reference to FIGS. 10 and 11, focusing on the differences from the first and second embodiments.

[0067] In the two-stroke engine of this embodiment, the material of the stopper member and the peripheral structure of the same stopper member are different from those of the two-stroke engines of the first and second embodiments.

[0068] Hereinafter, the stopper member of this embodiment will be described in detail. In the following, the same reference numerals (or corresponding reference numerals) are given to the same configurations as those of the two-stroke engine of the first embodiment illustrated in FIGS. 1 to 6 and the same configurations as those of the two-stroke engine of the second embodiment illustrated in FIGS. 7 to 9. And the detailed description of those configurations hereinafter is omitted.

[0069] (Stopper Member) As shown in FIGS. 10 and 11, the reed valve 80 of this embodiment has two stopper members 84. Each of the two stopper members 84 is formed in a plate shape by a bimetal. The bimetal is formed by bonding two metals having different coefficients of thermal expansion. The stopper members 84 are respectively provided on two side walls 45 of the valve body 81. Each stopper member 84 is provided at a position that sandwiches the valve element 43 between the side wall 45 of the valve body 81. One end (base end portion 841) of the stopper member 84 is fixed to the valve body 81. The stopper member 84 has a cantilever structure in which the base end portion 841 is supported.

[0070] In this embodiment, the stopper member 84 corresponds to the biasing portion. Further, the reed valve 80 of this embodiment does not have a position changing portion 51 (rotating shaft 511 and connecting mechanism 512), an actuator 521, and a control device 522 (see FIG. 5). The reed valve 80 of this embodiment does not have an electromagnet 70 and a control device 73 (see FIG. 9).

[0071] In the present embodiment, based on the results of various experiments and simulations conducted by the inventor, the temperature characteristics of the bimetal constituting the stopper member 84 are defined in a manner that satisfies both of the following (Condition A) and (Condition B).

[0072] (Condition A) When the temperature of the stopper member 84 has sufficiently decreased when the engine stops, the stopper member 84 has a shape (the shape shown in FIG. 10) in which it is pressed against the side wall 45 of the valve body 81 with the valve element 43 sandwiched therebetween.

[0073] (Condition B) When the temperature of the stopper member 84 has risen to a certain extent during engine operation, the stopper member 84 has a shape (for example, the shape shown in FIG. 11) that bends in a direction away from the valve element 43.

[0074] Also, in the present embodiment, based on the results of various experiments and simulations conducted by the inventor, the elastic modulus of the bimetal constituting the stopper member 84 is defined in a manner that satisfies the following (Condition C).

[0075] (Condition C) When the internal combustion engine 20 is operated with the temperature of the stopper member 84 being low, such as during cold start or warm-up operation of the internal combustion engine 20, the stopper member 84 can be opened together with the valve element 43 in accordance with the difference between the downstream pressure P1 (see FIG. 1) and the upstream pressure P2.

[0076] (At low temperatures) As shown in FIG. 10, the stopper member 84 is shaped such that it is pressed against the side wall 45 of the valve body 81 with the valve element 43 sandwiched therebetween at low temperatures. When the engine stops, since the temperature of the internal combustion engine 20 decreases, the temperature of the stopper member 44 of the reed valve 40 also decreases. According to the present embodiment, at such a time when the engine stops, by utilizing the deformation of the stopper member 44 constituted by a bimetal, the stopper member 44 together with the valve element 43 can be pressed against the valve seat 452 of the valve body 81. At this time, the reed valve 40 is held in the closed state. Thereby, the reed valve 40 can be held in the closed state. Therefore, it is possible to suppress the mixture gas in the crankcase 26 from leaking to the outside of the internal combustion engine 20 through the gap between the valve element 43 of the reed valve 80 and the valve seat 452.

[0077] (At high temperatures) As shown in FIG. 11, the stopper member 84 is shaped to bend in a direction away from the valve element 43 at high temperatures. Thereby, when the temperature of the stopper member 84 becomes somewhat high during engine operation and when the reed valve 40 is closed, the biasing force by the stopper member 84 can be prevented from acting on the valve element 43.

[0078] According to the present embodiment, although the valve element 43 can be biased in the closing direction by the stopper member 84 at low temperatures, the biasing force by the stopper member 84 can be prevented from acting on the valve element 43 at high temperatures. Therefore, the force required for opening the reed valve 80 during engine operation can be reduced. Thereby, a decrease in the opening speed of the reed valve 80 during engine operation can be suppressed, and thus a decrease in the intake efficiency can be suppressed.

[0079] According to the present embodiment, the following operational effects can be obtained. (5) The stopper member 84 is configured by a bimetal. The stopper member 84 has a shape that is pressed against the valve body 81 in a manner sandwiching the valve element 43 therebetween at low temperatures. The stopper member 84 has a shape that bends in a direction away from the valve element 43 at high temperatures. Therefore, it is possible to suppress a decrease in intake efficiency during engine operation while suppressing leakage of the mixed gas from inside the crankcase 26 to the outside of the internal combustion engine 20 when the engine is stopped.

[0080] (6) During engine operation, the biasing force that biases the valve element 43 in the valve closing direction by the stopper member 84 can be set to "0". Therefore, it is possible to suitably suppress a decrease in intake efficiency during engine operation.

[0081] (Modification example) Note that each of the above embodiments can be implemented with the following modifications. Each of the above embodiments and the following modification examples can be implemented in combination with each other as long as there is no technical contradiction.

[0082] · In each embodiment, the configuration of the biasing portion that biases the valve element 43 in the valve closing direction is not limited to the biasing device 50 in the first embodiment, the electromagnet 70 in the second embodiment, or the bimetal stopper member 84 in the third embodiment, and can be arbitrarily changed. The key is that any configuration is acceptable as long as it can bias the valve element 43 in such a manner that the biasing force of the biasing portion when the engine is stopped is greater than the biasing force of the biasing portion when the engine is operating.

[0083] For example, instead of providing a rotary machine as the actuator 521 in the first embodiment, a linear motor may be provided. According to this configuration, the stopper member 44 can be pressed against the valve body 43 and the valve body 43 together against the valve body 41 by pressing the stopper member 44 in the thickness direction by the linear motor.

[0084] Alternatively, as a biasing portion, a control rod inserted through the through-hole of the stopper member may be provided. In this configuration, when the engine stops, the valve body 43 is pressed in the valve closing direction by the control rod inserted through the through-hole. As a result, the valve body 43 is pressed against the valve seat 452 of the valve body. Therefore, the lead valve can be held in the closed state. On the other hand, during engine operation, the pressing of the valve body 43 by the control rod is released. As a result, the biasing force of the valve body 43 in the valve closing direction by the control rod becomes "0". Therefore, although the valve body 43 can be biased in the valve closing direction by the control rod, during engine operation, the biasing force by the control rod can be prevented from acting on the valve body 43. Therefore, the force required for opening the lead valve during engine operation can be reduced. As a result, a decrease in the opening speed of the lead valve during engine operation can be suppressed, and a decrease in the intake efficiency can be suppressed.

[0085] · In each embodiment, the biasing force of the biasing portion during engine operation does not necessarily have to be "0". If the biasing force of the biasing portion when the engine stops is greater than the biasing force of the biasing portion during engine operation, the valve body 43 may be biased by the biasing portion even during engine operation.

[0086] According to this configuration, when the engine stops, the lead valve can be held in the closed state, so that the gas in the crankcase can be prevented from leaking to the outside of the internal combustion engine. Moreover, during engine operation, the biasing force for biasing the valve body of the lead valve in the valve closing direction can be reduced as compared with when the engine stops. Therefore, the force required for opening the lead valve during engine operation can be reduced. As a result, it becomes possible to suppress a decrease in the opening speed of the lead valve during engine operation, and a decrease in the intake efficiency can be suppressed.

[0087] · The two-stroke engine according to each of the above embodiments can also be applied to a direct injection type internal combustion engine that directly injects fuel (such as hydrogen fuel or gasoline fuel) into the combustion chamber, or an internal combustion engine that injects hydrogen fuel into the crankcase.

Explanation of Signs

[0088] 20 Internal combustion engine (two-stroke engine) 29 Intake passage 40, 60, 80 Reed valve 41, 61, 81 Valve body 43 Valve element 44, 64, 84 Stopper member 451 Valve port 452 Valve seat 50 Biasing device 51 Position changing part 511 Rotating shaft 52 Control part 521 Actuator 522 Control device 53 Operation switch 70 Electromagnet 73 Control device

Claims

1. In a two-stroke engine having an intake passage connected to a crankcase and a reed valve provided in the intake passage and opening in accordance with a decrease in the internal pressure of the crankcase during engine operation, it has a biasing portion that biases the valve body of the reed valve in the closing direction, the biasing portion biases the valve body in such a manner that the biasing force at engine stop is greater than the biasing force at engine operation, and the biasing force at engine operation is made "0". A two-stroke engine.

2. In a two-stroke engine having an intake passage connected to a crankcase and a reed valve provided in the intake passage and opening in accordance with a decrease in the internal pressure of the crankcase during engine operation, the reed valve includes a valve body having a valve port and a valve seat, a valve body that opens and closes the valve port, and a stopper member provided at a position sandwiching the valve body between the valve body and the valve body, it has a biasing portion that biases the valve body of the reed valve in the closing direction, the biasing portion includes a position changing portion that changes the position of the stopper member and a control portion that controls the operation of the position changing portion, the position changing portion operates in such a manner as to switch the position of the stopper member between a closed position where the stopper member is pressed against the valve body in a manner sandwiching the valve body and an open position where the stopper member is separated from the valve body, The control portion sets the stopper member in the closed position at engine stop and sets the stopper member in the open position at engine operation, so that the biasing force of the biasing portion at engine stop is greater than the biasing force of the biasing portion at engine operation. A two-stroke engine.

3. In a two-stroke engine having an intake passage connected to a crankcase and a reed valve provided in the intake passage and opening in accordance with a decrease in the internal pressure of the crankcase during engine operation, The lead valve includes a valve body having a valve port and a valve seat, and a valve element for opening and closing the valve port. The lead valve has a biasing portion that biases the valve element of the lead valve in the closing direction. The biasing portion includes an electromagnet provided on the valve body that generates a magnetic force for attracting the valve element, and a control unit that controls energization of the electromagnet in such a manner that the electromagnet generates a magnetic force when the engine is stopped and does not generate a magnetic force when the engine is operating, so that the biasing force of the biasing portion when the engine is stopped is made greater than the biasing force of the biasing portion when the engine is operating. The two-stroke engine is provided with this control unit.

4. The two-stroke engine is an internal combustion engine that uses hydrogen as fuel. The two-stroke engine according to any one of claims 1 to 3.

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