JP7694464B2 - Two-stroke engine - Google Patents

Description

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

2. Description of the Related Art Reed valve type two-stroke engines are known in the art (for example, see 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 in the crankcase decreases when the engine is running. At this time, gas (air or a mixture) is drawn into the crankcase via the intake passage and the reed valve. The reed valve then closes as the pressure in the crankcase increases. This prevents gas (including fuel) from flowing back from the crankcase to the intake passage.

Patent Document 1 also proposes providing a pressing part that constantly presses the valve body of the reed valve in the valve closing direction.

Japanese Patent Application Publication No. 62-99622

Due to the structure of a two-stroke engine, fuel (e.g., gasoline or hydrogen) is mixed into the air drawn into the crankcase. For this reason, two-stroke engines are required to prevent gas (including fuel) from leaking from inside the crankcase to outside the engine when the engine is stopped.

As described in Patent Document 1, by constantly pressing the valve element of the reed valve in the closing direction, it is possible to hold the reed valve in a closed state when the engine is stopped. This makes it possible to suppress gas leakage when the engine is stopped.

However, in this case, the reed valve is constantly pressed in the closing direction, so when the engine is running, it is necessary to open the reed valve with a large force against the pressing force of the pressing part. This can lead to a decrease in the reed valve opening speed in the above two-stroke engine, which can result in a decrease in intake efficiency.

A two-stroke engine that solves the above problem has an intake passage connected to a crankcase, and a reed valve that is provided in the intake passage and opens in response to a decrease in the internal pressure of the crankcase when the engine is operating. The engine has a biasing section that biases the valve body of the reed valve in a closing direction, and the biasing section biases the valve body in such a way that the biasing force when the engine is stopped is greater than the biasing force when the engine is operating.

According to the above configuration, when the engine is stopped, the reed valve can be held in a closed state by the biasing force of the biasing section, thereby preventing gas in the crankcase from leaking outside the two-stroke engine. Furthermore, when the engine is running, the biasing force biasing the valve element of the reed valve in the closing direction can be reduced compared to when the engine is stopped. This reduces the force required to open the reed valve when the engine is running. This makes it possible to prevent a decrease in the opening speed of the reed valve when the engine is running, thereby preventing a decrease in intake efficiency.

In the above two-stroke engine, it is preferable that the biasing portion sets the biasing force to "0" when the engine is operating.
According to the above-mentioned configuration, although a biasing portion is provided that biases the valve element of the reed valve in the valve closing direction, the biasing force of the biasing portion can be prevented from acting on the valve element during engine operation, thereby making it possible to effectively prevent a decrease in intake efficiency.

In the above two-stroke engine, the reed valve comprises a valve body having a valve port and a valve seat, the valve body that opens and closes the valve port, and a stopper member that is provided in a position to sandwich the valve body between the valve body and the valve body, and the biasing unit comprises a position change unit that changes the position of the stopper member, and a control unit that controls the operation of the position change unit, and the position change unit operates in a manner that switches the position of the stopper member between a closed position in which the stopper member is pressed against the valve body with the valve body sandwiched therebetween, and an open position in which the stopper member is separated from the valve body, and it is preferable that the control unit 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.

According to the above configuration, when the engine is stopped, the stopper member can be used to press the valve body of the reed valve against the valve seat of the valve body. This allows the reed valve to be held in a closed state. When the engine is operating, the stopper member can be separated from the valve body of the reed valve. This prevents the biasing force of the biasing portion from acting on the valve body when the engine is operating.

In the above two-stroke engine, the reed valve preferably comprises a valve body having a valve port and a valve seat, and the valve element that opens and closes the valve port, and the biasing unit preferably comprises an electromagnet provided in the valve body that generates a magnetic force that attracts the valve element, and a control unit that controls the supply of electricity to 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.

With the above configuration, when the engine is stopped, the magnetic force generated by the electromagnet can press the valve element of the reed valve against the valve seat of the valve body. This allows the reed valve to be held in a closed state. When the engine is running, the electromagnet does not generate magnetic force, so the force required to open the reed valve can be reduced.

The two-stroke engine is preferably a hydrogen fuelled internal combustion engine.
According to the above configuration, in a two-stroke engine that uses hydrogen as fuel, it is possible to suppress a decrease in intake efficiency while suppressing leakage of gas containing hydrogen from inside the crankcase.

1 is a schematic diagram of a two-stroke engine of a first embodiment at bottom dead center; FIG. 2 is a schematic diagram of the two-stroke engine of the embodiment at top dead center; FIG. FIG. 2 is an exploded perspective view of the reed valve of the embodiment. FIG. 2 is a perspective view of a reed valve according to the embodiment. FIG. 4 is a side view of the reed valve when the stopper member of the embodiment is in an open position. FIG. 4 is a side view of the reed valve when the stopper member of the embodiment is in a closed position. FIG. 11 is an exploded perspective view of a reed valve of a two-stroke engine according to a second embodiment. FIG. 2 is a perspective view of a reed valve according to the embodiment. 4 is a side cross-sectional view of the reed valve of the embodiment. FIG. 11 is a side view of the reed valve of the two-stroke engine of the third embodiment at a low temperature. FIG. 4 is a side view of the reed valve of the embodiment at a high temperature.

First Embodiment
A first embodiment of a two-stroke engine will now be described with reference to FIGS.
As shown in Figures 1 and 2, a two-stroke engine (hereinafter, referred to as an internal combustion engine 20) has a cylinder bore 21. The inner circumferential surface of the cylinder bore 21 is cylindrical. A piston 22 is provided inside the cylinder bore 21 so as to be able to reciprocate in the axial direction of the cylinder bore 21. Inside the internal combustion engine 20, a combustion chamber 24 is defined by the inner circumferential surface of the cylinder bore 21, the top surface of the piston 22, and the lower surface of a cylinder head 23. An ignition plug 25 is provided in the combustion chamber 24.

The internal combustion engine 20 has a crankcase 26. A crankshaft 27 is rotatably disposed inside the crankcase 26. The internal combustion engine 20 has a connecting rod 28. The connecting rod 28 connects the crankshaft 27 and the piston 22.

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. The other end of the intake passage 29 is connected to an intake pipe (not shown) that constitutes the intake system of the internal combustion engine 20. In this embodiment, a mixture generating device for mixing air and hydrogen fuel to generate a mixture is provided in the middle of the intake pipe. As the mixture generating device, for example, a fuel injection valve that injects hydrogen fuel into the intake pipe is used. In this embodiment, a mixture gas containing air and hydrogen fuel is sucked into the crankcase 26 through the intake passage 29. A reed valve 40 is provided in the intake passage 29. The reed valve 40 opens in response to a decrease in the internal pressure of the crankcase 26 during engine operation. The specific structure of the reed valve 40 will be described in detail later.

The internal combustion engine 20 has an intake port 31 that connects the combustion chamber 24 and 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. The air-fuel mixture in the crankcase 26 is introduced into the combustion chamber 24 through the intake port 31.

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 on the inner peripheral surface of the cylinder bore 21. The other end of the exhaust port 32 is connected to an exhaust pipe (not shown) that constitutes the exhaust system of the internal combustion engine 20. Combustion gas in the combustion chamber 24 is discharged to the exhaust pipe through the exhaust port 32.

The internal combustion engine 20 operates as follows.
In the intake compression stroke, when the piston 22 rises toward the top dead center, the air-fuel mixture is compressed in the combustion chamber 24. As the piston 22 rises, the pressure inside the crankcase 26 is reduced, and the internal pressure of the crankcase 26 decreases. This causes the reed valve 40 to open. At this time, the air-fuel mixture is drawn into the crankcase 26 through the reed valve 40 and the intake passage 29.

After that, when the piston 22 approaches top dead center and decelerates, it becomes difficult to reduce the pressure inside the crankcase 26. 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, the ignition operation is performed by the spark plug 25 at a predetermined ignition timing. This causes the mixture to ignite and burn in the combustion chamber 24.

During the exhaust scavenging process, the piston 22 descends toward the bottom dead center due to the expansion force of the combustion gas in the combustion chamber 24. When the piston 22 descends to a position that connects the combustion chamber 24 with the exhaust port 32, the combustion gas is exhausted from the combustion chamber 24 to the exhaust pipe via the exhaust port 32. In this way, the combustion chamber 24 is scavenged.

When the piston 22 descends, the internal pressure of the crankcase 26 basically increases. Therefore, the reed valve 40 is kept closed at this time. Meanwhile, as scavenging of the combustion chamber 24 progresses, 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, this pressure difference causes the mixed gas in the crankcase 26 to be introduced into the combustion chamber 24 via the intake port 31. When the piston 22 reaches bottom dead center, the piston 22 then begins to rise.

(Reed valve)
The structure of the reed valve 40 will now be described.
As shown in FIGS. 3 and 4 , the reed valve 40 includes a valve body 41 , two valve bodies 43 , and two stopper members 44 .

(Valve body)
The valve body 41 is made of a metal material (e.g., an aluminum alloy). The cross section of the valve body 41 perpendicular to the flow path of the intake passage 29 (see FIG. 1) is substantially isosceles triangular. The valve body 41 is attached to the intake passage 29 in such a manner that the apex of the isosceles triangle protrudes downstream (lower left side in FIG. 1) of the intake passage 29. The inside of the valve body 41 is a gas passage 411 through which the mixed gas passes. The upstream end of the gas passage 411 opens at a portion of the valve body 41 that corresponds to the base of the isosceles triangle. Three valve ports 451 and three valve seats 452 are provided on each of two side walls 45 that correspond to the hypotenuse of the isosceles triangle of the valve body 41.

(Valve body)
Each of the two valve bodies 43 is formed in a thin plate shape from a metal material (e.g., an iron-based material). Each valve body 43 is provided on a 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 to close three valve ports 451 provided in the opposing side wall 45. The valve body 43 has a cantilever structure with one end (hereinafter, a base end portion 431) fixed to the valve body 41.

In this embodiment, when the downstream pressure P1 (see FIG. 1) of the reed valve 40 becomes low during engine operation, the difference between the downstream pressure P1 and the upstream pressure P2 of the reed valve 40 causes the valve body 43 to elastically deform in a direction away from the valve orifice 451. As a result, the valve body 43 is separated from the valve seat 452, and the reed valve 40 is in an open state.

On the other hand, when the downstream pressure P1 does not decrease significantly or increases during engine operation, the valve element 43 is pressed against the valve body 41 and does not elastically deform. At this time, the valve element 43 is seated on the valve seat 452, i.e., the valve element 43 blocks the valve port 451, and the reed valve 40 is in a closed state. In this way, the reed valve 40 opens and closes according to the difference between the downstream pressure P1 and the upstream pressure P2.

(Stopper member)
Each of the two stopper members 44 is formed in a plate shape from a metal material (e.g., aluminum alloy). The stopper members 44 are provided separately on two side walls 45 of the valve body 41. Each stopper member 44 is provided at a position where the valve body 43 is sandwiched between the stopper member 44 and the side walls 45 of the valve body 41. The stopper member 44 has a cantilever structure in which one end (hereinafter, the base end portion 441) is 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.

(Using device)
5 and 6, the internal combustion engine 20 of this embodiment has a biasing device 50 as a biasing portion that biases the valve body 43 of the reed valve 40 in the valve closing direction. The biasing device 50 will be described below.

The urging device 50 includes a position changing unit 51 that changes the position of the stopper member 44 , and a control unit 52 that controls the operation of the position changing unit 51 .
(Position change unit)
The position change unit 51 has two rotation shafts 511 and a connecting mechanism 512 .

As shown in Figures 3 and 4, the rotating shaft 511 is cylindrical. The rotating shaft 511 is integrally provided to the base end 441 of the stopper member 44 in such a manner that it extends along the base end 441. The rotating shaft 511 is provided separately for each of the two stopper members 44.

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 allows rotation about the axis of the rotating shaft 511 .
As shown in Figures 5 and 6, the reed valve 40 is capable of rotating the stopper member 44 around the axis of the rotary shaft 511 by rotating the rotary shaft 511. Specifically, as shown by arrow A in Figure 6, by rotating the rotary shaft 511 in one direction, the rotation position of the stopper member 44 becomes a position where the stopper member 44 is pressed against the valve body 41 with the valve body 43 sandwiched therebetween (hereinafter, referred to as the closed position). Also, as shown by arrow B in Figure 5, by rotating the rotary 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, referred to as the open position).

As shown in Figs. 5 and 6, the connecting mechanism 512 is interposed 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 connecting mechanism 512. The connecting mechanism 512 is a power transmission mechanism that transmits the power generated by the actuator 521 to the two rotating shafts 511. In this embodiment, a gear mechanism is used as the connecting mechanism 512.

(Control Unit)
The control unit 52 includes the actuator 521 and a control device 522 .
The actuator 521 is connected to the input shaft of the connecting mechanism 512. In this embodiment, a rotating machine is used as the actuator 521. In this embodiment, the operation of the position change unit 51 is controlled through the operation control of the actuator 521, so that the positions of the two stopper members 44 of the reed valve 40 can be switched between the "closed position" and the "open position".

The control device 522 is an electronic control device having an arithmetic processing unit and a memory device. The control device 522 takes in output signals from various sensors, such as the output signal from the operation switch 53. The operation switch 53 is a switch that is turned on when the operation of the internal combustion engine 20 is started and turned off when the operation of the internal combustion engine 20 is stopped. The control device 522 performs various calculations based on the output signals from the sensors, and executes operation control of the position change unit 51 (more specifically, the actuator 521) based on the results of the calculations.

In this embodiment, the actuator 521 is controlled so that the stopper member 44 is in the closed position when the engine is stopped, and is in the open position when the engine is running.

(When the engine is stopped)
In this embodiment, the stopper member 44 is controlled to the closed position when the engine is stopped as follows. That is, when the operation of the internal combustion engine 20 is stopped, the actuator 521 is controlled to move the stopper member 44 to the "closed position" (as shown in FIG. 6). This moves the stopper member 44 to the "closed position." Note that in this embodiment, the fact that the operation of the internal combustion engine 20 has been stopped is determined when the operation switch 53 has been turned off. Thus, in this embodiment, the stopper member 44 is in the closed position during the period when the operation of the internal combustion engine 20 is stopped, i.e., when the engine is stopped.

According to this 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. This allows the valve body 43 of the reed valve 40 to be pressed against the valve seat 452 and tightly attached. In this way, according to this embodiment, when the engine is stopped, the stopper member 44 is used to hold the reed valve 40 in a closed state. Therefore, when the engine is stopped, it is possible to prevent 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 of the reed valve 40 and the valve seat 452.

The valve body 43 of the reed valve 40 is repeatedly elastically deformed as it opens and closes. This can cause the valve body 43 to change over time, such as the tip portion of the valve body 43, which is the portion opposite the base end portion 431, deforming in a manner that warps away from the side wall 45 of the valve body 41. If this change occurs over time, a gap may be created 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 risk of mixed gas leaking from inside the crankcase 26 to outside the internal combustion engine 20 through the gap.

In this regard, according to this embodiment, when the engine is stopped, the valve body 43 is sandwiched between the stopper member 44 and the valve body 41, and the valve body 43 is pressed against the valve body 41 by the stopper member 44. Therefore, the tip portion of the valve body 43 that has deformed over time is pressed against the valve body 41 while being deformed (corrected) into a shape that conforms to the outer surface of the valve body 41. This allows the valve body 43 of the reed valve 40 to be tightly attached to the valve seat 452. Thus, according to this embodiment, even if the valve body 43 has deformed over time, the reed valve 40 can be brought into a closed state and maintained in the closed state.

(Engine operation)
In this embodiment, the stopper member 44 is set to the open position during engine operation as follows. That is, when operation of the internal combustion engine 20 is started, the actuator 521 is controlled to set the position of the stopper member 44 to the "open position" (as shown in FIG. 5). As a result, the position of the stopper member 44 is set to the "closed position." Note that in this embodiment, the start of operation of the internal combustion engine 20 is determined when the operation switch 53 is turned on. Thus, in this embodiment, the position of the stopper member 44 is in the open position while the internal combustion engine 20 is operating, that is, during engine operation.

In this embodiment, when the reed valve 40 is closed during engine operation, the stopper member 44 is separated from the valve body 43. This allows the biasing force of the stopper member 44 biasing the valve body 43 to be "0". According to this embodiment, although the stopper member 44 can bias the valve body 43 in the valve closing direction, the biasing force of the stopper member 44 can be prevented from acting on the valve body 43 during engine operation. This reduces the force required to open the reed valve 40 during engine operation. This prevents a decrease in the opening speed of the reed valve 40 during engine operation, thereby preventing a decrease in intake efficiency.

According to this embodiment, the following advantageous effects can be obtained.
(1) When the engine is stopped, the stopper member 44 is in a closed position where it is pressed against the valve body 41 with the valve body 43 sandwiched therebetween. When the engine is operating, the stopper member 44 is in an open position where it is separated from the valve body 43. This makes it possible to suppress a decrease in intake efficiency when the engine is operating, while suppressing leakage of mixed gas from inside the crankcase 26 to the outside of the internal combustion engine 20 when the engine is stopped.

(2) When the engine is operating, the force exerted on the valve body 43 by the stopper member 44 can be set to "0". This effectively prevents a decrease in intake efficiency when the engine is operating.

Second Embodiment
Hereinafter, the second embodiment of the two-stroke engine will be described with reference to FIGS. 7 to 9, focusing on the differences from the first embodiment.

The two-stroke engine of this embodiment differs from the two-stroke engine of the first embodiment in that the stopper member is fixed to the valve body and that an electromagnet is provided to attract the valve body.

The stopper member and electromagnet of this embodiment will be described below. Note that in the following, the same reference numerals (or corresponding reference numerals) will be used for the same components as those of the two-stroke engine of the first embodiment illustrated in Figures 1 to 6 above, and detailed descriptions of these components will be omitted.

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 metal material (e.g., an aluminum alloy). The stopper members 64 are provided separately on the two side walls 45 of the valve body 61. Each stopper member 64 is provided at a position where the valve body 43 is sandwiched between the stopper member 64 and the side wall 45 of the valve body 61. One end (base end 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 641 is supported. The stopper member 64 extends from the base end 641 toward the tip end, which is the part opposite to the base end 641, in a manner that it moves away from the valve body 43. The stopper member 64 is intended to suppress further deformation of the valve body 43 through contact with the valve body 43.

The reed valve 60 of this embodiment does not have a position change portion 51 (see FIG. 5), specifically, a rotating shaft 511 and a connecting mechanism 512. The stopper member 64 of this embodiment is structured so that its position does not change.

(electromagnet)
The electromagnets 70 are provided on the two side walls 45 of the valve body 61, respectively.
Specifically, an attachment groove 453 is provided in each side wall 45 of the valve body 61. This attachment groove 453 has three peripheral portions 66 and two connecting portions 67. Each peripheral portion 66 is annular and 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.

The electromagnet 70 has three coil portions 71 and two connection portions 72. The coil portions 71 are annular and extend 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. Each of the two electromagnets 70 is attached to the mounting groove 453 of the side wall 45. More specifically, the coil portions 71 of the electromagnet 70 are fitted into the peripheral portion 66 of the mounting groove 453. Furthermore, the connection portions 72 of the electromagnet 70 are fitted into the connecting portions 67 of the mounting groove 453.

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

In this embodiment, the electromagnet 70 is controlled so that the electromagnet 70 is turned "on (energized)" when the engine is stopped, and turned "off (not energized)" when the engine is operating.

(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." Note that in this embodiment, the fact that the operation of the internal combustion engine 20 has been stopped is determined when the operation switch 53 is turned off. In this manner, 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 a so-called engine stop.

At this time, the electromagnet 70 is turned "on" and generates a magnetic force. The magnetic force generated by the electromagnet 70 attracts the valve body 43 toward the valve body 61, and the valve body 43 is pressed against the valve seat 452 of the valve body 61. This makes it possible to hold the reed valve 40 in a closed state. This makes it possible to prevent 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.

In addition, according to this embodiment, when the engine is stopped, the valve body 43 is pressed against the valve body 61 by the attractive force generated by the magnetic force of the electromagnet 70. Therefore, the tip portion of the valve body 43, which has been deformed over time, can be pressed against the valve body 61 while being corrected to a shape that conforms to the outer surface of the valve body 61. Therefore, according to this embodiment, even if the valve body 43 has been deformed over time, the reed valve 40 can be brought into a closed state and maintained in the closed state.

(Engine operation)
In this embodiment, the electromagnet 70 is turned "off" during engine operation as follows. That is, when operation of the internal combustion engine 20 is started, the electromagnet 70 is turned "off." Note that in this embodiment, the start of operation of the internal combustion engine 20 is determined when the operation switch 53 is turned on. In this manner, in this embodiment, the electromagnet 70 is turned "off" during the period when the internal combustion engine 20 is operating, that is, during engine operation.

In this embodiment, the electromagnet 70 does not generate a magnetic force when the engine is operating. At this time, the valve body 43 is not attracted by the electromagnet 70, so the force of the electromagnet 70 urging the valve body 43 in the valve closing direction is "0". Thus, according to this embodiment, although the magnetic force generated by the electromagnet 70 can urge the valve body 43 in the valve closing direction, the attraction force of the electromagnet 70, i.e., the urging force in the valve closing direction, can be prevented from acting on the valve body 43 during engine operation. Therefore, the force required to open the reed valve 40 during engine operation can be reduced. This makes it possible to suppress a decrease in the opening speed of the reed valve 40 during engine operation, thereby suppressing a decrease in intake efficiency.

According to this embodiment, the following advantageous effects can be obtained.
(3) The electromagnet 70 that generates a magnetic force that attracts the valve disc 43 is provided in the valve body 61. When the engine is stopped, the electromagnet 70 generates a magnetic force, and when the engine is running, the supply of current to the electromagnet 70 is controlled in such a manner that the electromagnet 70 does not generate a magnetic force. As a result, it is possible to suppress a decrease in intake efficiency when the engine is running, while suppressing leakage of mixed gas from inside the crankcase 26 to the outside of the internal combustion engine 20 when the engine is stopped.

(4) When the engine is running, the force exerted by the electromagnet 70 on the valve body 43 in the valve closing direction can be set to "0". This effectively prevents a decrease in intake efficiency when the engine is running.

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.

The two-stroke engine of this embodiment differs from the two-stroke engine of the first embodiment and the two-stroke engine of the second embodiment in the material of the stopper member and the surrounding structure of the stopper member.

The stopper member of this embodiment will be described in detail below. Note that in the following, the same reference numerals (or corresponding reference numerals) are used for configurations similar to those of the two-stroke engine of the first embodiment illustrated in Figures 1 to 6 above, and configurations similar to those of the two-stroke engine of the second embodiment illustrated in Figures 7 to 9 above. Detailed descriptions of these configurations will be omitted below.

(Stopper member)
As shown in Figures 10 and 11, the reed valve 80 of this embodiment has two stopper members 84. Each of the two stopper members 84 is formed into a plate shape using a bimetal. A bimetal is formed by bonding two metals having different thermal expansion coefficients. The stopper members 84 are provided on the two side walls 45 of the valve body 81, respectively. Each stopper member 84 is provided at a position where the valve body 43 is sandwiched between the stopper member 84 and the side wall 45 of the valve body 81. One end (base end 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 841 is supported.

In this embodiment, the stopper member 84 corresponds to the biasing portion. 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, or a control device 522 (see FIG. 5). The reed valve 80 of this embodiment does not have an electromagnet 70 or a control device 73 (see FIG. 9).

In this embodiment, based on the results of various experiments and simulations conducted by the inventors, the temperature characteristics of the bimetal that constitutes the stopper member 84 are determined in a manner that satisfies both the following (Condition A) and (Condition B).

(Condition I) When the temperature of the stopper member 84 drops sufficiently during engine stoppage, the stopper member 84 assumes a shape (as shown in FIG. 10) in which it is pressed against the side wall 45 of the valve body 81 with the valve body 43 sandwiched therebetween.

(Condition B) When the temperature of the stopper member 84 rises to a certain level during engine operation, the stopper member 84 assumes a bent shape (for example, the shape shown in FIG. 11) in a direction away from the valve body 43.

In addition, in this embodiment, the elastic modulus of the bimetal that constitutes the stopper member 84 is determined to satisfy the following (Condition C) based on the results of various experiments and simulations conducted by the inventors.

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

(At low temperatures)
As shown in FIG. 10, at low temperatures, the stopper member 84 is shaped to be pressed against the side wall 45 of the valve body 81 with the valve body 43 sandwiched therebetween. When the engine is stopped, the temperature of the internal combustion engine 20 is low, and therefore the temperature of the stopper member 44 of the reed valve 40 is also low. According to this embodiment, when the engine is stopped, the stopper member 44, which is made of a bimetal, can be pressed against the valve seat 452 of the valve body 81 together with the valve body 43 by utilizing the deformation of the stopper member 44. At this time, the reed valve 40 is held in a closed state. This allows the reed valve 40 to be held in a closed state. Therefore, it is possible to prevent 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 80.

(At high temperatures)
11 , at high temperatures, the stopper member 84 is bent in a direction away from the valve body 43. This prevents the biasing force of the stopper member 84 from acting on the valve body 43 when the temperature of the stopper member 84 becomes high to a certain degree during engine operation and when the reed valve 40 is closed.

According to this embodiment, although the stopper member 84 can bias the valve body 43 in the valve closing direction at low temperatures, the biasing force of the stopper member 84 can be prevented from acting on the valve body 43 at high temperatures. This reduces the force required to open the reed valve 80 when the engine is running. This makes it possible to suppress a decrease in the opening speed of the reed valve 80 when the engine is running, thereby suppressing a decrease in intake efficiency.

According to this embodiment, the following advantageous effects can be obtained.
(5) The stopper member 84 is made of a bimetal. At low temperatures, the stopper member 84 is shaped to be pressed against the valve body 81 with the valve body 43 sandwiched therebetween. At high temperatures, the stopper member 84 is shaped to bend in a direction away from the valve body 43. This makes it possible to suppress a decrease in intake efficiency when the engine is operating, while suppressing leakage of mixed gas from inside the crankcase 26 to the outside of the internal combustion engine 20 when the engine is stopped.

(6) When the engine is operating, the force exerted by the stopper member 84 on the valve body 43 in the valve closing direction can be set to "0". This effectively prevents a decrease in intake efficiency when the engine is operating.

(Example of change)
The above-described embodiments may be modified as follows: The above-described embodiments and the following modifications may be combined with each other to the extent that no technical contradiction occurs.

- In each embodiment, the configuration of the biasing part that biases the valve body 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 bimetallic stopper member 84 in the third embodiment, and can be changed as desired. In short, any configuration can be used that is capable of biasing the valve body 43 in such a way that the biasing force of the biasing part when the engine is stopped is greater than the biasing force of the biasing part when the engine is operating.

For example, instead of providing a rotating machine as the actuator 521 in the first embodiment, a linear motor may be provided. With this configuration, the linear motor can press the stopper member 44 in the thickness direction, thereby pressing the stopper member 44 together with the valve body 43 against the valve body 41.

In addition, a control rod inserted into the through hole of the stopper member may be provided as the biasing portion. In this configuration, when the engine is stopped, the valve body 43 is pressed in the valve closing direction by the control rod inserted into the through hole. As a result, the valve body 43 is pressed against the valve seat 452 of the valve body. Therefore, the reed valve can be held in a closed state. On the other hand, when the engine is operating, the pressure on the valve body 43 by the control rod is released. As a result, the biasing force of the control rod in the valve closing direction of the valve body 43 becomes "0". Therefore, although it is possible to bias the valve body 43 in the valve closing direction by the control rod, it is possible to prevent the biasing force of the control rod from acting on the valve body 43 during engine operation. Therefore, the force required to open the reed valve during engine operation can be reduced. As a result, the decrease in the opening speed of the reed valve during engine operation can be suppressed, and therefore the decrease in intake efficiency can be suppressed.

- In each embodiment, the biasing force of the biasing part during engine operation does not necessarily have to be "0". If the biasing force of the biasing part when the engine is stopped is greater than the biasing force of the biasing part during engine operation, the valve body 43 may be biased by the biasing part even during engine operation.

With this configuration, the reed valve can be held in a closed state when the engine is stopped, preventing gas in the crankcase from leaking outside the internal combustion engine. Furthermore, when the engine is running, the force biasing the valve element of the reed valve in the closing direction can be reduced compared to when the engine is stopped. This reduces the force required to open the reed valve when the engine is running. This makes it possible to prevent a decrease in the reed valve opening speed when the engine is running, thereby preventing a decrease in intake efficiency.

The two-stroke engines according to the above embodiments can also be applied to direct injection type internal combustion engines that inject fuel (hydrogen fuel, gasoline fuel, etc.) directly into the combustion chamber, and to internal combustion engines that inject hydrogen fuel into the crankcase.

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

Claims (4)

A two-stroke engine having an intake passage connected to a crankcase, and a reed valve provided in the intake passage and opening in response to a decrease in internal pressure of the crankcase during engine operation,
a biasing portion that biases the valve element of the reed valve in a valve closing direction,
The biasing portion biases the valve body in such a manner that the biasing force when the engine is stopped is greater than the biasing force when the engine is operating, and the biasing force when the engine is operating is set to "0." A two-stroke engine having an intake passage connected to a crankcase, and a reed valve provided in the intake passage and opening in response to a decrease in 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 element that opens and closes the valve port, and a stopper member provided at a position to sandwich the valve element between the valve body and the stopper member,
a biasing portion that biases the valve body of the reed valve in a valve closing direction,
The biasing unit includes a position changing unit that changes a position of the stopper member, and a control unit that controls an operation of the position changing unit,
the position changing unit operates to change the position of the stopper member to either a closed position in which the stopper member is pressed against the valve body with the valve body sandwiched therebetween, or an open position in which the stopper member is separated from the valve body,
The control unit 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, thereby making the biasing force of the biasing part when the engine is stopped greater than the biasing force of the biasing part when the engine is operating. A two-stroke engine having an intake passage connected to a crankcase, and a reed valve provided in the intake passage and opening in response to a decrease in internal pressure of the crankcase during engine operation,
The reed valve includes a valve body having a valve port and a valve seat, and a valve element that opens and closes the valve port,
a biasing portion that biases the valve body of the reed valve in a valve closing direction,
The biasing portion is
an electromagnet provided in the valve body for generating a magnetic force that attracts the valve element;
a control unit that controls current flow to the electromagnet in a manner that causes the electromagnet to generate a magnetic force when the engine is stopped and does not generate a magnetic force when the engine is operating , thereby making the biasing force of the biasing unit when the engine is stopped greater than the biasing force of the biasing unit when the engine is operating. The two-stroke engine is a hydrogen-fueled internal combustion engine.
A two-stroke engine according to any one of claims 1 to 3 .

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