engine

Abstract

Provided is an engine having a simplified decompression mechanism.　An engine 10 comprises an engine block 11, a cylinder chamber 12 formed inside the engine block 11, and an extension space 33 that is formed inside the engine block 11 and that extends laterally from the cylinder chamber 12. The engine 10 further comprises a decompression valve attachment orifice 22 formed in the part of the engine block 11 where the extension space 33 is formed, a decompression valve 23 disposed so as to be able to advance into and withdraw from the decompression valve attachment hole 22, and a decompression valve advancing / withdrawing mechanism 50 that causes the decompression valve 23 to advance and withdraw.

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to engines, and in particular to opposed-piston engines. [[BACKGROUND ART]]

[0002] Conventionally, as disclosed in Patent Document 1 and Patent Document 2, an opposed-piston engine generally has a structure in which pistons having mutually opposed piston heads perform linear motion within one horizontally arranged cylinder. In this cylinder, the region where the piston heads face each other functions as a combustion chamber, and when a mixed gas of fuel and air ignites and explodes, the pistons operate, and power is supplied to an external actuator such as a generator.

[0003] However, in the engines described in the aforementioned patent documents, the small combustion chamber volume makes it difficult to achieve a high compression ratio, and there are also problems with thermal insulation of the combustion chamber. In addition, the intake and exhaust valves of conventional opposed-piston engines are directly open to the combustion chamber, which has the drawback of increasing the volume of the combustion chamber.

[0004] To solve this problem, the engine described in Patent Document 3 was invented. In the engine described in Patent Document 3, independent left and right pistons are arranged to face each other in a horizontal cylinder. Also, one combustion chamber is formed between the left and right piston heads so as to communicate with the outside of the horizontal cylinder. Furthermore, in the engine described in Patent Document 3, an extension portion extending laterally from the combustion chamber is formed. A spark plug is provided in the extension portion. [[PRIOR ART DOCUMENTS]] [[PATENT DOCUMENTS]]

[0005] [[Patent Document 1]] Japanese Patent Laid-Open No. 2007-46534 [[Patent Document 2]] Japanese Patent Laid-Open No. 8-93498 [[Patent Document 3]] International Publication No. 2013 / 047878 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the opposed-piston engine described in the aforementioned patent document had room for improvement in terms of optimizing the decompression mechanism.

[0007] Specifically, the opposed-piston engine described in Patent Document 3 was equipped with a centrifugal decompression mechanism. However, because the centrifugal decompression mechanism is configured to change shape in response to centrifugal force, there was a problem in that the mechanical configuration itself was complex. Furthermore, when the engine is equipped with multiple cylinder chambers, it is necessary to equip each cylinder chamber with a centrifugal decompression mechanism, which led to the problem of the entire engine becoming even more complex and larger.

[0008] This invention has been made in view of these problems, and its objective is to provide an engine with a simplified decompression mechanism. [Means for solving the problem]

[0009] An engine according to one embodiment of the present invention comprises an engine block, a cylinder chamber formed inside the engine block, an extension space formed inside the engine block and extending laterally from the cylinder chamber, a decompression valve mounting hole formed in the engine block in the portion forming the extension space, a decompression valve disposed to be movable back and forth relative to the decompression valve mounting hole, and a decompression valve reciprocating mechanism for moving the decompression valve back and forth, wherein the decompression valve reciprocating mechanism comprises a spring and an actuator, and the decompression valve closes the decompression valve mounting hole when biased by the spring, and opens the decompression valve mounting hole when pressed by the actuator.

[0010] Furthermore, in an engine according to one embodiment of the present invention, the cylinder chamber has a first cylinder chamber and a second cylinder chamber, the extension space has a first extension space formed in the first cylinder chamber and a second extension space formed in the second cylinder chamber, the decompression valve mounting hole has a first decompression valve mounting hole formed in the engine block in the portion forming the first extension space and a second decompression valve mounting hole formed in the engine block in the portion forming the second extension space, the decompression valve has a first decompression valve disposed to move back and forth relative to the first decompression valve mounting hole and a second decompression valve mounted to move back and forth relative to the second decompression valve mounting hole The present invention relates to a second decompression valve that is retractably disposed, wherein the spring comprises a first spring disposed to apply a biasing force to the first decompression valve and a second spring disposed to apply a biasing force to the second decompression valve, wherein the first decompression valve closes the mounting hole of the first decompression valve when biased by the first spring and opens the mounting hole of the first decompression valve when pressed by the actuator, and the second decompression valve closes the mounting hole of the second decompression valve when biased by the second spring and opens the mounting hole of the second decompression valve when pressed by the actuator.

[0011] Furthermore, in an engine according to one embodiment of the present invention, the decompression valve advancement mechanism comprises a shaft rotated by the actuator, a cam rotatably connected to the shaft, and a rocker arm that rotates by contacting the cam, wherein one side of the rocker arm contacts the cam and the other side contacts the first decompression valve and the second decompression valve.

[0012] Furthermore, in the engine according to one embodiment of the present invention, the actuator is characterized in that it is a linear actuator. [Effects of the Invention]

[0013] An engine according to one embodiment of the present invention comprises an engine block, a cylinder chamber formed inside the engine block, an extension space formed inside the engine block and extending laterally from the cylinder chamber, a decompression valve mounting hole formed in the engine block in the portion forming the extension space, a decompression valve disposed to be movable back and forth relative to the decompression valve mounting hole, and a decompression valve reciprocating mechanism for moving the decompression valve back and forth, wherein the decompression valve reciprocating mechanism comprises a spring and an actuator, and the decompression valve closes the decompression valve mounting hole when biased by the spring, and opens the decompression valve mounting hole when pressed by the actuator. According to the engine according to the embodiment of the present invention, by closing and opening the extension space by the decompression valve using a spring and an actuator, the configuration of the decompression valve reciprocating mechanism can be simplified, and the overall engine can be simplified and miniaturized.

[0014] Furthermore, in an engine according to one embodiment of the present invention, the cylinder chamber has a first cylinder chamber and a second cylinder chamber, the extension space has a first extension space formed in the first cylinder chamber and a second extension space formed in the second cylinder chamber, the decompression valve mounting hole has a first decompression valve mounting hole formed in the engine block in the portion forming the first extension space and a second decompression valve mounting hole formed in the engine block in the portion forming the second extension space, the decompression valve has a first decompression valve disposed to move back and forth relative to the first decompression valve mounting hole and a second decompression valve mounted to move back and forth relative to the second decompression valve mounting hole The engine comprises a second decompression valve that is retractably disposed, and the spring comprises a first spring disposed to apply a biasing force to the first decompression valve and a second spring disposed to apply a biasing force to the second decompression valve, wherein the first decompression valve closes the mounting hole of the first decompression valve when biased by the first spring and opens the mounting hole of the first decompression valve when pressed by the actuator, and the second decompression valve closes the mounting hole of the second decompression valve when biased by the second spring and opens the mounting hole of the second decompression valve when pressed by the actuator.According to the engine of the embodiment of the present invention, the first decompression valve and the second decompression valve close the mounting hole of the first decompression valve and the second decompression valve by the first spring and the second spring attached to them, respectively. Furthermore, the first and second decompression valves open their respective mounting holes using a common actuator. Therefore, the first and second decompression valves can be moved forward and backward with fewer actuators.

[0015] Furthermore, in an engine according to one embodiment of the present invention, the decompression valve advancement mechanism includes a shaft rotated by the actuator, a cam rotatably connected to the shaft, and a rocker arm that rotates by contacting the cam, wherein one side of the rocker arm contacts the cam and the other side contacts the first decompression valve and the second decompression valve. According to the engine according to the embodiment of the present invention, the configuration of the decompression valve advancement mechanism can be simplified by operating multiple decompression valves with a single actuator.

[0016] Furthermore, in an engine according to one embodiment of the present invention, the actuator is a linear actuator. According to the engine according to the embodiment of the present invention, the decompression valves in multiple cylinder chambers can be operated by a linear actuator that operates in a straight line, so the decompression valve advance / retraction mechanism and the engine configuration can be simplified. [Brief explanation of the drawing]

[0017] [Figure 1] This is a perspective view showing an engine according to an embodiment of the present invention. [Figure 2A] This figure shows an engine according to an embodiment of the present invention, and is a perspective view showing the first engine block. [Figure 2B] This figure shows an engine according to an embodiment of the present invention, and is a perspective view showing the second engine block. [Figure 3A] This figure shows an engine according to an embodiment of the present invention, and is a diagram showing the first contact surface of the first engine block. [Figure 3B] This figure shows an engine according to an embodiment of the present invention, and is a diagram showing the second contact surface of the second engine block. [Figure 4] This figure shows an engine according to an embodiment of the present invention, and is a perspective view showing the engine section and other components. [Figure 5]FIG. 1 is a diagram showing an engine according to an embodiment of the present invention, and is a cross-sectional view showing a wall portion of an engine block that forms a cylinder chamber and an extension space. [Figure 6A] FIG. 2 is a diagram showing an engine according to an embodiment of the present invention, and is a perspective view showing a decompression valve, each valve, and the like. [Figure 6B] FIG. 3 is a diagram showing an engine according to an embodiment of the present invention, and is a perspective view showing a decompression valve, each valve, and the like. [Figure 7] FIG. 4 is a diagram showing an engine according to an embodiment of the present invention, and is a perspective view showing a decompression valve in a closed state and a decompression valve advancing / retracting mechanism. [Figure 8] FIG. 5 is a diagram showing an engine according to an embodiment of the present invention, and is a cross-sectional view showing a decompression valve in a closed state and a decompression valve advancing / retracting mechanism. [Figure 9] FIG. 6 is a diagram showing an engine according to an embodiment of the present invention, and is a perspective view showing a decompression valve in an open state and a decompression valve advancing / retracting mechanism. [Figure 10] FIG. 7 is a diagram showing an engine according to an embodiment of the present invention, and is a cross-sectional view showing a decompression valve in an open state and a decompression valve advancing / retracting mechanism. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an engine 10 according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the front-rear direction refers to a direction in which a piston, which will be described later, reciprocates along the axial direction of a cylinder chamber, which will be described later. The left-right direction refers to a direction in which cylinder spaces, which will be described later, are arranged. Further, the left-right direction is synonymous with the width direction. In the following description, the same members are in principle denoted by the same reference numerals, and repeated descriptions are omitted. Furthermore, in the present embodiment, the configuration described in the claims is mainly illustrated and described. Therefore, parts other than the configuration included in the engine 10, such as a crankshaft rotation synchronization mechanism, a lubricating oil supply mechanism, a fuel supply mechanism, electrical components, a drive mechanism for driving each valve, a belt, and the like, are not illustrated.

[0019] FIG. 1 is a perspective view showing the engine 10.

[0020] Engine 10 is an opposed-piston engine having multiple pistons arranged opposite each other. The internal configuration and operation of engine 10 will be described later with reference to Figures 2A and later.

[0021] Engine 10 is configured to operate using gasoline, diesel fuel, hydrogen, etc. Engine 10 can be used as a power source for various devices. Engine 10 is used as a power source for vehicles, generators, water heaters, flying devices, drones, series hybrid drones, parallel hybrid drones, etc. A series hybrid drone is a drone in which engine 10 drives a generator, the electricity generated from the generator rotates a motor, the motor rotates a rotor, and the lift generated by the rotation of the rotor makes the drone float in the air. A parallel hybrid drone is a drone in which engine 10 mechanically rotates a main rotor, and the lift generated by the rotation of the main rotor makes the drone float. The engine 10 of this embodiment is an opposed-piston type engine, and because it is lightweight and has low vibration, it is particularly suitable as a power source for series hybrid drones, parallel hybrid drones, etc.

[0022] Specifically, the engine 10 mainly comprises a cylinder chamber 12, an intake valve 18, and an exhaust valve 19. Each of these components constituting the engine 10 is housed in the engine block 11. The cylinder chamber 12, intake valve 18, and exhaust valve 19 will be explained with reference to Figure 6A, etc.

[0023] The engine 10 also has an engine block 11, which is the main body. The engine block 11 is made of, for example, a cast aluminum alloy. The engine block 11 consists of a first engine block 111, a second engine block 112, a third engine block 113, and a fourth engine block 114. These parts are fastened together by fastening members such as stud bolts (not shown).

[0024] A third crankshaft 163 and a fourth crankshaft 173 are routed out from the right side of the engine 10. Rotational power can be extracted externally from the third crankshaft 163 and the fourth crankshaft 173. In addition, a crankshaft can be routed out from the left side of the engine 10, and rotational power can also be extracted externally from this crankshaft.

[0025] Furthermore, a second spark plug 262 is mounted on the right side of the engine block 11. Similarly, a first spark plug 261 (not shown here) is mounted on the left side of the engine block 11. The first spark plug 261 and the second spark plug 262 penetrate each side of the second engine block 112, and the electrodes formed at their tips are exposed to the extension space 33, which will be described later. This configuration will be described later with reference to Figure 6A, etc. Furthermore, an exhaust port 25 is formed on the upper surface of the engine block 11. The exhaust port 25 is a path through which gases after combustion inside the engine 10 are discharged.

[0026] Furthermore, the engine 10 has a decompression valve retraction mechanism 50. The decompression valve retraction mechanism 50 is a mechanism that moves the decompression valve 23, which will be described later, forward and backward. In Figure 1, a part of the decompression valve retraction mechanism 50 is located on the upper surface of the engine block 11. The decompression valve retraction mechanism 50 will be described later with reference to Figure 7, etc.

[0027] Figure 2A is a perspective view showing the first engine block 111.

[0028] Referring to Figure 2A, the rearward-facing surface of the first engine block 111 is designated as the first contact surface 40. The first contact surface 40 is a flat surface and contacts the second contact surface 41 of the second engine block 112, which will be described later.

[0029] The first engine block 111 has a first cylinder chamber front portion 1211 and a second cylinder chamber front portion 1221, which are formed in a substantially cylindrical shape extending forward from the first contact surface 40. The first cylinder chamber front portion 1211 and the second cylinder chamber front portion 1221 are adjacent to each other along the left-right direction. The first cylinder chamber front portion 1211 is a substantially cylindrical space and forms the front portion of the first cylinder chamber 121, which will be described later. The second cylinder chamber front portion 1221 is a substantially cylindrical space and forms the front portion of the second cylinder chamber 122, which will be described later.

[0030] The first extension space front portion 3311 is a portion in which the first contact surface 40 is recessed toward the front, and is continuous with the upper end of the first cylinder chamber front portion 1211. The first extension space front portion 3311 constitutes the front portion of the first extension space 331, which will be described later.

[0031] The front portion 3321 of the second extension space is a part in which the first contact surface 40 is recessed toward the front, and is continuous with the upper end of the front portion 1221 of the second cylinder chamber. The front portion 3321 of the second extension space constitutes the front part of the second extension space 332, which will be described later.

[0032] Referring to Figure 2B, the forward-facing surface of the second engine block 112 is designated as the second contact surface 41. The second contact surface 41 is a flat surface and contacts the first contact surface 40 of the first engine block 111, as described above.

[0033] The second engine block 112 has a first cylinder chamber rear portion 1212 and a second cylinder chamber rear portion 1222 formed rearward from the second contact surface 41. The first cylinder chamber rear portion 1212 and the second cylinder chamber rear portion 1222 are adjacent to each other along the left-right direction. The first cylinder chamber rear portion 1212 is a substantially cylindrical space and forms the rear portion of the first cylinder chamber 121, which will be described later. The second cylinder chamber rear portion 1222 is a substantially cylindrical space and forms the rear portion of the second cylinder chamber 122, which will be described later.

[0034] The rear portion 3312 of the first extension space is a part in which the second contact surface 41 is recessed toward the rear, and is continuous with the upper end of the rear portion 1212 of the first cylinder chamber. The rear portion 3312 of the first extension space, together with the front portion 3311 of the first extension space described above, constitutes the first extension space 331, which will be described later.

[0035] The rear portion 3322 of the second extension space is a portion in which the second contact surface 41 is recessed toward the rear, and is continuous with the upper end of the rear portion 1222 of the second cylinder chamber. The rear portion 3322 of the second extension space, together with the front portion 3321 of the second extension space described above, constitutes the second extension space 332, which will be described later.

[0036] A first spark plug mounting hole 371 and a first decompression valve mounting hole 221 are formed in the rear portion 3312 of the first extension space. Furthermore, a second spark plug mounting hole 372 and a second decompression valve mounting hole 222 are formed in the rear portion 3322 of the second extension space. A first spark plug 261, which will be described later, is installed in the first spark plug mounting hole 371. A first decompression valve 231, which will be described later, is installed in the first decompression valve mounting hole 221. A second spark plug 262, which will be described later, is installed in the second spark plug mounting hole 372. A second decompression valve 232, which will be described later, is installed in the second decompression valve mounting hole 222.

[0037] Figure 3A shows the first contact surface 40 of the first engine block 111. An intake valve mounting hole 35 is formed in the first contact surface 40. The intake valve mounting hole 35 has a first intake valve mounting hole 351 and a second intake valve mounting hole 352.

[0038] Two first intake valve mounting holes 351 are formed inside the front portion 3311 of the first extension space. The first intake valve mounting holes 351 are through holes that penetrate the wall portion of the first engine block 111 in a circular manner in the front-rear direction. A first intake valve 181, which will be described later, is disposed in each of the first intake valve mounting holes 351.

[0039] Two second intake valve mounting holes 352 are formed inside the front portion 3321 of the second extension space. The second intake valve mounting holes 352 are through holes that penetrate the wall formed inside the first engine block 111 in a circular shape. A second intake valve 182, which will be described later, is disposed in each of the second intake valve mounting holes 352.

[0040] Figure 3B shows the second contact surface 41 of the second engine block 112. The second contact surface 41 has an exhaust valve mounting hole 36, a spark plug mounting hole 37, and a decompression valve mounting hole 22. The exhaust valve mounting hole 36 has a first exhaust valve mounting hole 361 and a second exhaust valve mounting hole 362. The spark plug mounting hole 37 has a first spark plug mounting hole 371 and a second spark plug mounting hole 372. The decompression valve mounting hole 22 is formed in the portion of the engine block 11 that forms the extension space 33. Specifically, the decompression valve mounting hole 22 has a first decompression valve mounting hole 221 and a second decompression valve mounting hole 222.

[0041] The first exhaust valve mounting hole 361 is a hole formed in the rear portion 3312 of the first extension space. The first exhaust valve mounting hole 361 penetrates the wall formed inside the second engine block 112 in a circular shape. The first exhaust valve 191, which will be described later, is installed in the first exhaust valve mounting hole 361.

[0042] The first plug mounting hole 371 is a through hole formed in the lower left side of the rear portion 3312 of the first extension space, on the outer side in the width direction. The first plug mounting hole 371 is a through hole that penetrates the left side portion of the second engine block 112. The first spark plug 261, which will be described later, is installed in the first plug mounting hole 371.

[0043] The first decompression valve mounting hole 221 is a through hole formed in the lower right side of the first extension space rear portion 3312, on the inner side in the width direction. The first decompression valve mounting hole 221 is a hole that penetrates a wall formed inside the second engine block 112. The first decompression valve 231, which will be described later, is installed in the first decompression valve mounting hole 221.

[0044] The second exhaust valve mounting hole 362 is a hole formed in the rear portion 3322 of the second extension space. The second exhaust valve mounting hole 362 penetrates the wall formed inside the second engine block 112 in a circular shape. The second exhaust valve 192, which will be described later, is installed in the second exhaust valve mounting hole 362.

[0045] The second plug mounting hole 372 is a through hole formed in the lower right side of the second extension space rear portion 3322, on the outer side in the width direction. The second plug mounting hole 372 is a through hole that penetrates the right side portion of the second engine block 112. The second spark plug 262, which will be described later, is installed in the second plug mounting hole 372.

[0046] The second decompression valve mounting hole 222 is a through hole formed in the lower left side of the second extension space rear portion 3322, on the widthwise inner side. The second decompression valve mounting hole 222 is a hole that penetrates the wall formed inside the second engine block 112. The second decompression valve 232, which will be described later, is installed in the second decompression valve mounting hole 222.

[0047] Figure 4 is a perspective view of the engine section 13, which is housed in the aforementioned engine block 11, as seen from the front.

[0048] The engine section 13 includes a first engine section 14, a second engine section 15, a third engine section 16, and a fourth engine section 17. The first engine section 14 and the second engine section 15 constitute one opposing engine section. The third engine section 16 and the fourth engine section 17 also constitute one opposing engine section. By having multiple opposing engine sections in the engine 10, it is possible to increase power output while ensuring the lightweight and low vibration of the engine 10.

[0049] The cylinder chamber 12 comprises a first cylinder chamber 121 and a second cylinder chamber 122 adjacent to the first cylinder chamber 121. The first cylinder chamber 121 and the second cylinder chamber 122 are adjacent to each other along the left-right direction. In Figure 4, the first cylinder chamber 121 and the second cylinder chamber 122 are shown by dotted lines. Inside the first cylinder chamber 121, a first piston 141 and a second piston 151 are arranged opposite each other to reciprocate. Inside the second cylinder chamber 122, a third piston 161 and a fourth piston 171 are arranged opposite each other to reciprocate.

[0050] The first engine section 14 includes a first piston 141, a first connecting rod 142, and a first crankshaft 143. The first connecting rod 142 rotatably connects the first piston 141 and the first crankshaft 143.

[0051] The second engine section 15 is positioned opposite the first engine section 14. The second engine section 15 includes a second piston 151, a second connecting rod 152, and a second crankshaft 153. The second connecting rod 152 rotatably connects the second piston 151 and the second crankshaft 153.

[0052] The third engine section 16 includes a third piston 161, a third connecting rod 162, and a third crankshaft 163. The third connecting rod 162 rotatably connects the third piston 161 and the third crankshaft 163.

[0053] The fourth engine section 17 is positioned opposite the third engine section 16. The fourth engine section 17 includes a fourth piston 171, a fourth connecting rod 172, and a fourth crankshaft 173. The fourth connecting rod 172 rotatably connects the fourth piston 171 and the fourth crankshaft 173.

[0054] The first crankshaft 143 of the first engine section 14 and the third crankshaft 163 of the third engine section 16 are integrally continuous. Therefore, the first piston 141 of the first engine section 14 and the third piston 161 of the third engine section 16 reciprocate simultaneously.

[0055] Similarly, the second crankshaft 153 of the second engine section 15 and the fourth crankshaft 173 of the fourth engine section 17 are integrally continuous. Therefore, the second piston 151 of the second crankshaft 153 and the fourth piston 171 of the fourth engine section 17 reciprocate simultaneously.

[0056] The engine section 13 has a configuration in which opposing engine sections consisting of a first engine section 14 and a second engine section 15, and opposing engine sections consisting of a third engine section 16 and a fourth engine section 17 are arranged side by side along the left-right direction. Furthermore, the first engine section 14 and the third engine section 16 rotate the first crankshaft 143 and the third crankshaft 163. In addition, the second engine section 15 and the fourth engine section 17 rotate the second crankshaft 153 and the fourth crankshaft 173. With this configuration, a large amount of power can be generated even with a compact configuration.

[0057] The extension space 33 is a space that extends laterally upward from the middle of the cylinder chamber 12 in the front-rear direction. The extension space 33 has a first extension space 331 and a second extension space 332. The first extension space 331 is a space that extends upward from the middle of the first cylinder chamber 121 in the front-rear direction. The second extension space 332 is a space that extends upward from the middle of the second cylinder chamber 122 in the front-rear direction. The first extension space 331 and the second extension space 332 are the parts in which the valves and plugs are installed, as will be described later. The specific shape of the extension space 33 is shown in Figure 6A, etc.

[0058] The combustion chamber 34 is a space within the cylinder chamber 12 that is sandwiched between the pistons. The combustion chamber 34 has a first combustion chamber 341 and a second combustion chamber 342. The first combustion chamber 341 is a space within the first cylinder chamber 121 that is sandwiched between the first piston 141 and the second piston 151, and where the fuel-air mixture burns. The first combustion chamber 341 is continuous with the first extension space 331. The second combustion chamber 342 is a space within the second cylinder chamber 122 that is sandwiched between the third piston 161 and the fourth piston 171, and where the fuel-air mixture burns. The second combustion chamber 342 is continuous with the second extension space 332.

[0059] Figure 5 is a cross-sectional view along the BB cross-section line of Figure 4, showing the wall portion of the engine block 11 that forms the first cylinder chamber 121 and the first extension space 331.

[0060] As described above, the first cylinder chamber 121 is a space that is substantially cylindrical in shape. The first cylinder chamber 121 has a front part 1211 on the front side and a rear part 1212 connected to the rear end of the front part 1211. At approximately the center of the first cylinder chamber 121 in the front-rear direction, the first extension space 331 protrudes upward from the upper surface of the first cylinder chamber 121. The front part 1211, the rear part 1212, and the first extension space 331 are in communication with each other.

[0061] The first cylinder chamber 121 and the first extension space 331 in this configuration are spaces surrounded by walls formed inside the engine block 11.

[0062] Specifically, the front portion 1211 of the first cylinder chamber is a substantially cylindrical space surrounded by the first cylinder wall portion 1281. The first cylinder wall portion 1281 is a cylindrical wall formed inside the first engine block 111. The front and rear ends of the first cylinder wall portion 1281 are open.

[0063] The rear portion 1212 of the first cylinder chamber is a roughly cylindrical space surrounded by the second cylinder wall portion 2282. The second cylinder wall portion 2282 is a cylindrical wall formed inside the second engine block 112. The front and rear ends of the second cylinder wall portion 2282 are open.

[0064] The first extension space 331 is the space enclosed by the first extension wall portion 1291 and the second extension wall portion 2292. The first extension wall portion 1291 is a roughly tongue-shaped portion that extends upward from the upper end of the first cylinder wall portion 1281 at the rear end of the first cylinder wall portion 1281. The second extension wall portion 2292 is a roughly tongue-shaped portion that extends upward from the upper end of the second cylinder wall portion 2282 at the front end of the second cylinder wall portion 2282.

[0065] The first cylinder chamber 121 is a substantially cylindrical space having a first central axis 1213 extending along the front-rear direction. The first cylinder chamber 121 has a first side surface 1214. The first side surface 1214 is a surface formed by the inner surfaces of the first cylinder wall 1281 and the second cylinder wall 2282. A first extension space 331 extends from the first side surface 1214. Specifically, the first extension space 331 is a space that extends upward in a direction perpendicular to the first central axis 1213 of the first cylinder chamber 121. The first extension space 331 communicates with the first cylinder chamber 121.

[0066] The same applies to the second cylinder chamber 122 mentioned above.

[0067] Figure 6A is a perspective view showing the cylinder chamber 12 and the valves, etc., from the upper right rear side. Figure 6B is a perspective view showing the cylinder chamber 12 and the valves, etc., from the upper left front side.

[0068] The extension space 33 is connected to the cylinder chamber 12 and serves as the starting point for combustion in the combustion stroke described later. Specifically, the extension space 33 is a space that extends continuously upward from the central part in the front-to-back direction of the cylinder chamber 12. As part of the extension space 33, a first extension space 331 is formed in the first cylinder chamber 121, and a second extension space 332 is formed in the second cylinder chamber 122.

[0069] The first extension space 331 is a roughly tongue-shaped portion having its largest surface facing the front-to-back direction. The first extension space 331 has a first side surface 3313 and a second side surface 3314. The first side surface 3313 is the surface facing forward. The second side surface 3314 is the surface facing backward.

[0070] The second extension space 332 is a roughly tongue-shaped portion having its largest surface facing the front-to-back direction. The second extension space 332 has a first side surface 3323 and a second side surface 3324. The first side surface 3323 is the surface facing forward. The second side surface 3324 is the surface facing backward.

[0071] The intake valve 18 has a first intake valve 181 and a second intake valve 182.

[0072] The first intake valve 181 is provided so as to be able to move forward and backward relative to the first side surface 3313 of the first extension space 331 from the front side. Two first intake valves 181 are provided here. Each first intake valve 181 is attached to the first intake valve mounting hole 351 shown in Figure 3A. The first intake valve 181 is for drawing in a fuel-air mixture into the first cylinder chamber 121. When the first intake valve 181 enters the first extension space 331, it opens the first intake valve mounting hole 351 shown in Figure 3A, allowing air to be drawn into the first extension space 331 and the first cylinder chamber 121. On the other hand, when the first intake valve 181 retracts from the first extension space 331, it closes the first intake valve mounting hole 351 shown in Figure 3A.

[0073] The second intake valve 182 is provided so as to be able to move forward and backward relative to the first side surface 3323 of the second extension space 332 from the front side. Two second intake valves 182 are provided here. Each second intake valve 182 is attached to the second intake valve mounting hole 352 shown in Figure 3A. The second intake valve 182 is for drawing in a fuel-air mixture into the second cylinder chamber 122. When the second intake valve 182 enters the second extension space 332, it opens the second intake valve mounting hole 352 shown in Figure 3A, allowing air to be drawn into the second extension space 332 and the second cylinder chamber 122. On the other hand, when the second intake valve 182 retracts from the second extension space 332, it closes the second intake valve mounting hole 352 shown in Figure 3A.

[0074] The exhaust valve 19 has a first exhaust valve 191 and a second exhaust valve 192.

[0075] The first exhaust valve 191 is provided so as to be able to move back and forth relative to the second side surface 3314 of the first extension space 331 from the rear side. There is one first exhaust valve 191 in this case. The first exhaust valve 191 is attached to the first exhaust valve mounting hole 361 shown in Figure 3B. The first exhaust valve 191 is for exhausting the combustion gas from the first cylinder chamber 121. When the first exhaust valve 191 enters the first extension space 331, it opens the first exhaust valve mounting hole 361 shown in Figure 3B, allowing exhaust from inside the first cylinder chamber 121 through the first exhaust valve mounting hole 361. On the other hand, when the first exhaust valve 191 retracts from the first extension space 331, it closes the first exhaust valve mounting hole 361 shown in Figure 3B.

[0076] The second exhaust valve 192 is provided so as to be able to move back and forth relative to the second side surface 3324 of the second extension space 332 from the rear side. There is one second exhaust valve 192 in this case. The second exhaust valve 192 is attached to the second exhaust valve mounting hole 362 shown in Figure 3B. The second exhaust valve 192 is for exhausting the combustion gas from the second cylinder chamber 122. When the second exhaust valve 192 enters the second extension space 332, it opens the second exhaust valve mounting hole 362 shown in Figure 3B, allowing exhaust from inside the second cylinder chamber 122 through the second exhaust valve mounting hole 362. On the other hand, when the second exhaust valve 192 retracts from the second extension space 332, it closes the second exhaust valve mounting hole 362 shown in Figure 3B.

[0077] The number of intake valves 18 is greater than the number of exhaust valves 19. For example, with respect to the first extension space 331, there is one first exhaust valve 191 and two first intake valves 181. In this way, the first spark plug 261 is exposed to the extension space 33 from the side of the fewer number of first exhaust valves 191, allowing for effective use of the space around the first extension space 331.

[0078] The spark plug 26 is a component disposed on the side where the exhaust valve 19 is provided, that is, on the rear side of the extension space 33. The electrode formed at the tip of the spark plug 26 is disposed inside the extension space 33. The spark plug 26 has a first spark plug 261 and a second spark plug 262.

[0079] The first spark plug 261 is a component located to the left of the first exhaust valve 191. The front end of the first spark plug 261 penetrates the second side surface 3314 and is located inside the first extension space 331.

[0080] The second spark plug 262 is a component located to the right of the second exhaust valve 192. The front end of the second spark plug 262 penetrates the second side surface 3324 and is located inside the second extension space 332.

[0081] The decompression valve 23 is a valve that performs decompression in the initial stages of engine 10 operation, by opening the extension space 33 to the outside, thereby releasing the pressure in the cylinder chamber 12 and improving the starting performance of the engine 10. The decompression valve 23 has a first decompression valve 231 and a second decompression valve 232. The first decompression valve 231 faces the first extension space 331 from the second side surface 3314. The second decompression valve 232 faces the second extension space 332 from the second side surface 3324. The operation of the first decompression valve 231 and the second decompression valve 232 will be described later with reference to Figures 7 and later.

[0082] The configuration and operation of the decompression valve retraction mechanism 50 will be described with reference to Figures 7 to 10. Figure 7 is a perspective view showing the decompression valve 23 and the decompression valve retraction mechanism 50 in the closed state. Figure 8 is a cross-sectional view showing the decompression valve 23 and the decompression valve retraction mechanism 50 in the closed state. Figure 9 is a perspective view showing the decompression valve 23 and the decompression valve retraction mechanism 50 in the open state. Figure 10 is a cross-sectional view showing the decompression valve 23 and the decompression valve retraction mechanism 50 in the open state.

[0083] Referring to Figure 7, the configuration of the decompression valve advance / retraction mechanism 50 will be explained. Figure 7 is a perspective view showing the decompression valve advance / retraction mechanism 50 when the decompression valve 23 is in the closed position.

[0084] As mentioned above, the decompression valve advance / retraction mechanism 50 is a mechanism configured to advance and retract the decompression valve 23. Specifically, the decompression valve advance / retraction mechanism 50 mainly comprises a spring 51, an actuator 52, a shaft 53, a cam 54, and a rocker arm 55.

[0085] Actuator 52 is, for example, a linear actuator 521. The linear actuator 521 is configured to perform linear, repetitive motion. The linear actuator 521 has a fixed part 522 and an extendable part 523. The extendable part 523 extends and retracts relative to the fixed part 522, driven by a motor or the like built into the fixed part 522. The rear end of the fixed part 522 is attached to the upper surface of the engine block 11 shown in Figure 1 via a bracket 57. The rear end of the fixed part 522 is also attached to the upper surface of the bracket 57 via a connecting part 58. At the connecting part 58, the fixed part 522 of the linear actuator 521 is rotatable. In this way, as will be described later, the linear extension and retraction motion of the linear actuator 521 can be converted into the rotational motion of the cam 54.

[0086] The arm 56 is a plate-shaped member and is positioned between the linear actuator 521 and the shaft 53. The left end of the arm 56 is rotatably connected to the front end of the extension portion 523. The right end of the arm 56 is connected to the upper end of the shaft 53 in a manner that prevents relative rotation.

[0087] The shaft 53 is a roughly rod-shaped member that extends linearly in the vertical direction. As described above, the upper end of the shaft 53 is connected to the arm 56 in a way that prevents relative rotation. The lower end of the shaft 53 is connected to the cam 54 in a way that prevents relative rotation.

[0088] The cam 54, when viewed from above, is a component that exhibits a roughly fan shape, starting from the portion connected to the shaft 53. When viewed from above, the shape of the cam 54 is an irregular fan shape. That is, the cam 54 has a side portion 541 that faces radially outward. When viewed from above, the side portion 541 has a first side end portion 542, which is one end, and a second side end portion 543, which is the other end. Here, the first side end portion 542 is closer to the rotation center of the shaft 53, i.e., the connection portion between the cam 54 and the shaft 53, than the second side end portion 543. Also, the side portion 541 of the cam 54 is in contact with the rear end of the rocker arm 55. As will be described later, by having the shape of the cam 54, the amount and force of pressure applied to the rocker arm 55 in a forward direction can be adjusted by rotating the cam 54.

[0089] The rocker arm 55 is a component made of a bent metal plate or the like. The left end of the rocker arm 55 is connected to the rear end of the first decompression valve 231. The right end of the rocker arm 55 is connected to the rear end of the second decompression valve 232. The middle portion of the rocker arm 55 protrudes rearward and contacts the side portion 541 of the cam 54. The rocker arm 55 is arranged to swing in the front-rear direction with its upper end as the center of rotation.

[0090] The spring 51 is configured to provide a biasing force to the decompression valve 23. The spring 51 has a first spring 511 and a second spring 512.

[0091] The first spring 511 is positioned so as to provide a rearward biasing force to the first decompression valve 231, with the rear portion of the first decompression valve 231 inserted inside it. The first decompression valve 231 closes the first valve seat ring 281 when biased by the first spring 511.

[0092] The second spring 512 is positioned so as to provide a rearward biasing force to the second decompression valve 232, with the rear portion of the second decompression valve 232 inserted inside it. The second decompression valve 232 closes the second valve seat ring 282 when biased by the second spring 512.

[0093] The first valve seat ring 281 is a substantially ring-shaped member that is press-fitted from the inside into the first decompression valve mounting hole 221 shown in Figure 3B. The front end of the first decompression valve 231 is inserted into the first valve seat ring 281. The front end of the first decompression valve 231 closes the first valve seat ring 281, preventing the aforementioned first extension space 331 and first cylinder chamber 121 from being decompressed. On the other hand, the front end of the first decompression valve 231 is pushed forward of the first valve seat ring 281, creating a gap between the first decompression valve 231 and the first valve seat ring 281, through which the aforementioned first extension space 331 and first cylinder chamber 121 are decompressed.

[0094] The second valve seat ring 282 is a substantially ring-shaped member that is press-fitted from the inside into the second decompression valve mounting hole 222 shown in Figure 3B. The front end of the second decompression valve 232 is inserted into the second valve seat ring 282. The front end of the second decompression valve 232 closes the second valve seat ring 282, preventing the aforementioned second extension space 332 and second cylinder chamber 122 from being decompressed. On the other hand, the front end of the second decompression valve 232 is pushed forward of the second valve seat ring 282, creating a gap between the second decompression valve 232 and the second valve seat ring 282, through which the aforementioned second extension space 332 and second cylinder chamber 122 are decompressed.

[0095] In the state shown in Figure 7, i.e., when decompression does not occur, the decompression valve advance / retraction mechanism 50 does not strongly press the first decompression valve 231 and the second decompression valve 232. As a result, the rearward biasing force of the first spring 511 and the second spring 512 causes the first decompression valve 231 and the second decompression valve 232 to block the first valve seat ring 281 and the second valve seat ring 282.

[0096] Specifically, based on instructions from the arithmetic control unit, which is a CPU (not shown), the linear actuator 521 extends. When this happens, the front end of the extended portion 523 pushes the left end of the arm 56 forward. As a result, the arm 56, shaft 53, and cam 54 rotate counterclockwise when viewed from above, with the central axis of the shaft 53 as the center of rotation. This causes the side portion 541 near the first side end 542 to contact the rear end of the rocker arm 55. As mentioned above, the side portion 541 near the first side end 542 is close to the center of rotation of the cam 54. Therefore, the amount and force of pressure applied by the cam 54 to the rocker arm 55 decreases. As a result, the first decompression valve 231 and the second decompression valve 232 are biased rearward by the first spring 511 and the second spring 512, closing the openings of the first valve seat ring 281 and the second valve seat ring 282. As a result, the aforementioned decompression does not occur. During normal operation of engine 10, the decompression valve 23 is closed in this manner.

[0097] Figure 8 shows a partial cross-section of the engine 10 when the second decompression valve 232 is in the closed position.

[0098] The second decompression valve mounting hole 222 is a through-hole that penetrates the inner wall of the engine 10 in the front-rear direction. A vent hole 24 is formed extending from a portion of the second decompression valve mounting hole 222 toward the exhaust port 25. The vent hole 24 is a through-hole that linearly penetrates a thickened portion inside the engine 10. The vent hole 24 is a path through which the air-fuel mixture that escapes from the first cylinder chamber 121 and the first extension space 331 to the exhaust port 25 during decompression passes. The vent hole 24 is also formed corresponding to the first decompression valve mounting hole 221 described above.

[0099] If the pressing force and amount applied by the decompression valve advance / retraction mechanism 50 to the second decompression valve 232 are small, the biasing force of the second spring 512 causes the second decompression valve 232 to be positioned to the rear. As a result, the front end of the second decompression valve 232 closes the second valve seat ring 282. This results in the second extension space 332 and the second cylinder chamber 122 being in an uncompressed state, which is the normal operating state of the engine 10. In other words, the gas inside the second cylinder chamber 122 and the second extension space 332 does not escape to the outside through the second decompression valve mounting hole 222 and the vent hole 24.

[0100] Figure 9 illustrates the state of the decompression valve advance / retraction mechanism 50 when the decompression valve 23 is in the open state (decompression state).

[0101] The operation of the decompression valve advance / retraction mechanism 50 when moving the decompression valve 23 from the closed state to the open state will be explained. First, based on instructions from the calculation control unit (not shown here), the linear actuator 521 enters a retracted state. That is, the driving force of the motor built into the fixed part 522 causes most of the extension part 523 to be pulled into the fixed part 522. As a result, the left end of the arm 56 is pulled towards the rear. Consequently, the arm 56, shaft 53, and cam 54 rotate clockwise around the central axis of the shaft 53, which extends vertically, as the center of rotation. At the same time, the linear actuator 521, when viewed from above, rotates counterclockwise around the connection part 58 as the center of rotation. When this rotation is completed, the second side end 543 of the cam 54 comes into contact with the rear end of the rocker arm 55. As mentioned earlier, the shape of the cam 54 in plan view is not a precise sector shape. The second side end 543 is further from the central axis of the shaft 53 than the first side end 542. Therefore, when the second side end 543 of the cam 54 contacts the rocker arm 55, the first decompression valve 231 and the second decompression valve 232 are pushed forward. As a result, the front end portion of the first decompression valve 231 protrudes forward beyond the front end of the first valve seat ring 281. This creates a gap for decompression between the first decompression valve 231 and the first valve seat ring 281. Similarly, the front end portion of the second decompression valve 232 protrudes forward beyond the front end portion of the second valve seat ring 282. This creates a gap for decompression between the second decompression valve 232 and the second valve seat ring 282.

[0102] Figure 10 shows a cross-section of the engine 10 when the second decompression valve 232 is open. Here, the gas flow during decompression is indicated by the dotted arrows.

[0103] As described above, in the decompression valve advance / retraction mechanism 50, the linear actuator 521 contracts, causing the front end of the second decompression valve 232 to protrude forward of the front surface of the second valve seat ring 282. This creates a gap for decompression between the second decompression valve 232 and the second valve seat ring 282. During decompression, the gas inside the second cylinder chamber 122 and the second extension space 332 enters the second decompression valve mounting hole 222 through the gap between the second decompression valve 232 and the second valve seat ring 282, and is then discharged through the vent hole 24 to the exhaust port 25.

[0104] The same applies to the first decompression valve 231 and the first valve seat ring 281 shown in Figure 9. That is, the first decompression valve 231 opens and closes the first valve seat ring 281 simultaneously with the second decompression valve 232.

[0105] The operation of the decompression valve advance / retraction mechanism 50 is controlled by the calculation control unit. The calculation control unit controls the operation of the actuator 52 based on the input signal received from the rotation sensor that senses the rotational speed of the engine 10.

[0106] Specifically, when the rotational speed of the engine 10 is below a predetermined rotational speed, that is, in the initial stages of operation of the engine 10, the decompression valve advance / retraction mechanism 50, as shown in Figure 10, pushes the second decompression valve 232 forward, thereby connecting the second cylinder chamber 122 and the second extension space 332 to the outside and reducing the pressure.

[0107] Subsequently, when the rotational speed of the engine 10 exceeds a predetermined rotational speed, that is, when the initial operation of the engine 10 is completed, the decompression valve advance / retraction mechanism 50 closes the second cylinder chamber 122 and the second extension space 332 by not pushing the second decompression valve 232 forward, as shown in Figure 8. As a result, the engine 10 returns to its normal operating state.

[0108] The normal operation of engine 10 is described below. The first engine section 14 and the second engine section 15 of the engine section 13 with the above configuration operate by repeatedly performing the intake stroke, compression stroke, combustion stroke, and exhaust stroke as follows.

[0109] In the intake stroke, as shown in Figure 4, the first piston 141 and the second piston 151 move from the center outward within the first cylinder chamber 121, drawing the fuel-air mixture into the first cylinder chamber 121. Simultaneously, the first crankshaft 143 and the second crankshaft 153 rotate. Referring to Figures 6A and 6B, in the intake stroke, the first intake valve 181 opens the first extension space 331, while the first exhaust valve 191 closes the first extension space 331. Thus, the fuel-air mixture can be drawn into the first cylinder chamber 121 via the first intake valve mounting hole 351 and the first extension space 331 shown in Figure 3A.

[0110] During the compression stroke, as shown in Figure 4, the inertia of the rotating first crankshaft 143 and second crankshaft 153 pushes the first piston 141 and second piston 151 toward the center, compressing the air-fuel mixture inside the first cylinder chamber 121. Referring to Figure 6A, the first intake valve 181 closes the first extension space 331, and the first exhaust valve 191 also closes the first extension space 331. Therefore, the first extension space 331 and the first cylinder chamber 121 are closed, allowing the air-fuel mixture to be compressed inside the first cylinder chamber 121.

[0111] During the combustion stroke, the first spark plug 261 shown in Figure 6A ignites in the first extension space 331, causing the fuel-air mixture to burn inside the first extension space 331 and the first cylinder chamber 121 shown in Figure 4. This pushes the first piston 141 and the second piston 151 to their outer ends, which are at bottom dead center. Referring to Figure 6A, similar to the compression stroke, in this stroke, the first intake valve 181 closes the first extension space 331, and the first exhaust valve 191 also closes the first extension space 331. That is, the state of the first intake valve 181 and the first exhaust valve 191 is the same as in the compression stroke described above.

[0112] During the exhaust stroke, as shown in Figure 4, the inertia of the rotating first crankshaft 143 and second crankshaft 153 pushes the first piston 141 and second piston 151 inward, and the post-combustion gases present inside the first cylinder chamber 121 are discharged to the outside. Referring to Figures 6A and 6B, the first intake valve 181 closes the first extension space 331, while the first exhaust valve 191 opens the first extension space 331. As a result, the post-combustion gases inside the first cylinder chamber 121 are released to the outside through the first exhaust valve mounting hole 361 shown in Figure 3B.

[0113] The same applies to the third engine section 16, the fourth engine section 17, the second intake valve 182, and the second exhaust valve 192.

[0114] In the engine unit 13 according to this embodiment, the stroke can be divided by two first pistons 141 and second pistons 151 that reciprocate within a single first cylinder chamber 121. Therefore, the compression ratio of the fuel mixture can be increased compared to a conventional engine. Furthermore, since the first piston 141 and second piston 151 face each other within the first cylinder chamber 121, a cylinder head required in a typical engine is unnecessary, resulting in a simple and lightweight engine unit 13. In addition, each component constituting the engine unit 13, namely the first piston 141 and second piston 151, the first crankshaft 143 and second crankshaft 153, etc., are arranged and operate in opposition to each other. As a result, vibrations generated from each component of the engine unit 13 cancel each other out, reducing the vibrations generated from the engine unit 13 as a whole to the outside. Therefore, by mounting an engine unit 13 with such a structure on an aircraft, miniaturization, weight reduction, and vibration reduction of the aircraft can be achieved. In particular, reducing vibrations can prevent adverse effects on precision equipment such as attitude control, motor output control, and GPS sensors. It can also prevent damage to cargo transported by the aircraft due to vibrations.

[0115] Although embodiments of the present invention have been described above, the present invention is not limited thereto, and modifications are possible without departing from the spirit of the invention. Furthermore, the above-described embodiments can be combined with each other. [Explanation of Symbols]

[0116] 10 Engines 11 Engine Block 111 First engine block 112 Second engine block 113 Third engine block 114. Fourth engine block 12 Cylinder Chambers 121 First Cylinder Chamber 1211 Front of the first cylinder chamber 1212 Rear of the first cylinder chamber 122 Second Cylinder Chamber 1221 Front of the second cylinder chamber 1222 Rear of the second cylinder chamber 13 Engine section 14. First Engine Section 141 First Piston 142 First Connecting Rod 143 First Crankshaft 15. Second Engine Section 151 Second piston 152 Second Connecting Rod 153 Second crankshaft 16. Third Engine Section 161 Third piston 162 Third Connecting Rod 163 Third crankshaft 17. Engine No. 4 171 Piston No. 4 172 Fourth Connecting Rod 173 Fourth crankshaft 18 Intake valve 181 First intake valve 182 Second intake valve 19 Exhaust valve 191 First exhaust valve 192 Second exhaust valve 22 Decompression valve mounting holes 221 First decompression valve mounting hole 222 Second decompression valve mounting hole 23 Decompression valve 231 First decompression valve 232 Second decompression valve 24 ventilation holes 25 Exhaust Ports 26 Spark plugs 261 First spark plug 262 Second Spark Plug 281 First valve seat ring 282 Second valve seat ring 33 Extension space 331 1st extension space 3311 First extension space front 3312 First extension space rear 3313 1st side 3314 Second side 332 Second extension space 3321 Second extension space front 3322 Second extension space rear 3323 1st side 3324 Second side 34 Combustion chamber 341 First Combustion Chamber 342 Second Combustion Chamber 35 Intake valve mounting hole 351 First intake valve mounting hole 352 Second intake valve mounting hole 36 Exhaust valve mounting hole 361 First exhaust valve mounting hole 362 Second exhaust valve mounting hole 37 Plug mounting holes 371 First plug installation hole 372 Second plug installation hole 40 First contact surface 41 Second contact surface 50 Decompression valve advance / retraction mechanism 51 Spring 511 First spring 512 Second spring 52 Actuators 521 Linear Actuator 522 Fixed part 523 Extension part 53 shaft 54 Cam 541 Side part 542 First side edge 543 Second side edge 55 Rocker arm 56 Arm 57 Bracket 58 Connection part

Claims

1. The engine comprises an engine block, a cylinder chamber formed inside the engine block, an extension space formed inside the engine block and extending outward from the cylinder chamber, a decompression valve mounting hole formed in the engine block in the portion forming the extension space, a decompression valve disposed to be movable back and forth relative to the decompression valve mounting hole, a decompression valve retraction mechanism for moving the decompression valve back and forth, a first engine section, and a second engine section, wherein the first engine section has a first piston, a first connecting rod, and a first crankshaft, and the second engine section has a second piston, a second connecting rod An engine comprising a piston and a second crankshaft, wherein the first piston and the second piston are arranged to face each other inside the cylinder chamber, the extension space extends from the cylinder chamber in a direction perpendicular to the direction in which the first piston and the second piston reciprocate, in the portion sandwiched between the first piston and the second piston, and the decompression valve advance / retraction mechanism comprises a spring and an actuator, wherein the decompression valve closes the decompression valve mounting hole when biased by the spring, and opens the decompression valve mounting hole when pressed by the actuator.

2. The cylinder chamber comprises a first cylinder chamber and a second cylinder chamber. The extension space comprises a first extension space formed in the first cylinder chamber and a second extension space formed in the second cylinder chamber. The decompression valve mounting hole comprises a first decompression valve mounting hole formed in the engine block in the portion forming the first extension space, and a second decompression valve mounting hole formed in the engine block in the portion forming the second extension space. The decompression valve comprises a first decompression valve disposed to be movable forward and backward relative to the first decompression valve mounting hole, and a second decompression valve disposed to be movable forward and backward relative to the second decompression valve mounting hole. The spring comprises a first spring disposed to apply a biasing force to the first decompression valve and a second spring disposed to apply a biasing force to the second decompression valve. The first decompression valve closes the first decompression valve mounting hole when biased by the first spring, and opens the first decompression valve mounting hole when pressed by the actuator. The engine according to claim 1, characterized in that the second decompression valve closes the second decompression valve mounting hole when biased by the second spring, and opens the second decompression valve mounting hole when pressed by the actuator.

3. The engine according to claim 2, wherein the decompression valve advancement mechanism comprises a shaft rotated by the actuator, a cam connected to the shaft so as not to rotate relative to it, and a rocker arm that rotates by contacting the cam, and the rocker arm is such that one side contacts the cam and the other side contacts the first decompression valve and the second decompression valve.

4. The engine according to claim 3, characterized in that the actuator is a linear actuator.

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