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

engine

[0001] The present invention relates to engines, and more particularly to opposed-piston engines.

[0002] Conventionally, opposed-piston engines have generally been structured so that pistons with opposing piston heads move linearly within a single horizontally arranged cylinder, as shown in Patent Documents 1 and 2. Within this cylinder, the area where the piston heads face each other functions as a combustion chamber, and a gas mixture of fuel and air ignites and explodes, moving the piston and supplying power to an external actuator such as a generator.

[0003] However, the engine described in the patent document has a small combustion chamber volume, making it difficult to achieve a high compression ratio, and there are also issues with insulating the combustion chamber. Also, the intake and exhaust valves of conventional opposed-piston engines open directly into 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 facing each other inside a horizontal cylinder. A combustion chamber is formed between the left and right piston heads and communicates with the outside of the horizontal cylinder. Furthermore, the engine described in Patent Document 3 has an extension that extends laterally from the combustion chamber. A spark plug is provided in this extension.

[0005] JP 2007-46534 JP 8-93498 Re-Tabulation 2013 / 047878

[0006] However, the opposed-piston engines described in the above-mentioned patent documents have room for improvement in terms of optimizing the decompression mechanism.

[0007] Specifically, the opposed-piston engine described in Patent Document 3 is provided with a centrifugal decompression mechanism. However, because the centrifugal decompression mechanism is configured to change shape in response to centrifugal force, the mechanical configuration itself is complex. Furthermore, if the engine is provided with multiple cylinder chambers, a centrifugal decompression mechanism must be provided for each cylinder chamber, which further complicates and increases the size of the entire engine.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide an engine with a simplified decompression mechanism.

[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 a portion forming the extension space, a decompression valve arranged so as to be able to advance and retreat relative to the decompression valve mounting hole, and a decompression valve advancement and retreat mechanism that moves the decompression valve forward and backward, wherein the decompression valve advancement and retreat mechanism has 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] In addition, 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 at a portion that forms the first extension space and a second decompression valve mounting hole formed in the engine block at a portion that forms the second extension space, and the decompression valve includes a first decompression valve disposed so as to be able to advance and retreat relative to the first decompression valve mounting hole and a second decompression valve disposed so as to be able to advance and retreat relative to the second decompression valve mounting hole. and a second decompression valve arranged to be retractable, wherein the springs include a first spring arranged to apply a biasing force to the first decompression valve and a second spring arranged to apply a biasing force to the second decompression valve, wherein 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, and 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.

[0011] In addition, in an engine according to one embodiment of the present invention, the decompression valve advance / retreat mechanism has a shaft rotated by the actuator, a cam connected to the shaft so as to be rotatable relative to the shaft, and a rocker arm that rotates by contacting the cam, and the rocker arm is characterized in that one side of the rocker arm contacts the cam and the other side of the rocker arm contacts the first decompression valve and the second decompression valve.

[0012] In addition, in the engine according to one embodiment of the present invention, the actuator is a linear actuator.

[0013] An engine according to an embodiment of the present invention includes an engine block, a cylinder chamber formed within the engine block, an extension space formed within the engine block and extending laterally from the cylinder chamber, a decompression valve mounting hole formed in the engine block at a portion defining the extension space, a decompression valve disposed so as to be able to advance and retreat relative to the decompression valve mounting hole, and a decompression valve advancement / retraction mechanism for advancing and retreating the decompression valve, the decompression valve advancement / retraction mechanism including 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 when pressed by the actuator. According to the engine according to the embodiment of the present invention, the use of the spring and the actuator to close and open the extension space by the decompression valve simplifies the configuration of the decompression valve advancement / retraction mechanism, thereby enabling the overall engine to be simplified and compact.

[0014] In addition, 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 at a portion that forms the first extension space and a second decompression valve mounting hole formed in the engine block at a portion that forms the second extension space, and the decompression valve includes a first decompression valve disposed so as to be able to advance and retreat relative to the first decompression valve mounting hole and a second decompression valve disposed so as to be able to advance and retreat relative to the second decompression valve mounting hole. and a retractable second decompression valve, the springs including a first spring arranged to apply a biasing force to the first decompression valve and a second spring arranged 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, and 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. According to an engine according to an embodiment of the present invention, the first decompression valve and the second decompression valve close the first decompression valve mounting hole and the second decompression valve close the second decompression valve mounting hole by the first spring and the second spring attached to the first decompression valve, respectively. Furthermore, the first decompression valve and the second decompression valve open the first decompression valve mounting hole and the second decompression valve mounting hole using a common actuator, so that the first decompression valve and the second decompression valve can be moved forward and backward using a small number of actuators.

[0015] In an engine according to an embodiment of the present invention, the decompression valve advancement / retraction mechanism includes a shaft rotated by the actuator, a cam connected to the shaft so as to be rotatable relative to the shaft, and a rocker arm that rotates by contacting the cam, one side of the rocker arm contacting the cam and the other side of the rocker arm contacting the first decompression valve and the second decompression valve. According to the engine according to an embodiment of the present invention, the configuration of the decompression valve advancement / retraction mechanism can be simplified by operating multiple decompression valves with a single actuator.

[0016] In addition, in an engine according to an embodiment of the present invention, the actuator is a linear actuator. According to the engine according to an embodiment of the present invention, the linear actuator can operate the decompression valves in multiple cylinder chambers, thereby simplifying the configuration of the decompression valve advance / retreat mechanism and the engine.

[0017] 1 is a perspective view of an engine according to an embodiment of the present invention; FIG. 1 is a perspective view of an engine according to an embodiment of the present invention, showing a first engine block; FIG. 2 is a perspective view of an engine according to an embodiment of the present invention, showing a second engine block; FIG. 3 is a perspective view of an engine according to an embodiment of the present invention, showing a first abutment surface of a first engine block; FIG. 4 is a perspective view of an engine according to an embodiment of the present invention, showing a second abutment surface of a second engine block; FIG. 5 is a perspective view of an engine according to an embodiment of the present invention, showing engine parts, etc.; FIG. 6 is a cross-sectional view of a wall portion of an engine block that forms a cylinder chamber and an extension space; FIG. 7 is a perspective view of an engine according to an embodiment of the present invention, showing a decompression valve and each valve; FIG. 8 is a perspective view of an engine according to an embodiment of the present invention, showing a decompression valve and each valve; FIG. 9 is a cross-sectional view of an engine according to an embodiment of the present invention, showing a decompression valve and each valve; FIG. 10 is a perspective view of an engine according to an embodiment of the present invention, showing a decompression valve and a decompression valve advancement / retraction mechanism in a closed state; FIG. 11 is a cross-sectional view of an engine according to an embodiment of the present invention, showing a decompression valve and a decompression valve advancement / retraction mechanism in a closed state; FIG. 12 is a perspective view of an engine according to an embodiment of the present invention, showing a decompression valve and a decompression valve advancement / retraction mechanism in an open state; FIG. 13 is a cross-sectional view of an engine according to an embodiment of the present invention, showing a decompression valve and a decompression valve advancement / retraction mechanism in an open state;

[0018] An engine 10 according to an embodiment of the present invention will be described in detail below with reference to the drawings. In the following description, the front-rear direction refers to the direction in which pistons (described later) reciprocate along the axial direction of cylinder chambers (described later). The left-right direction refers to the direction in which cylinder spaces (described later) are arranged. The left-right direction is also synonymous with the width direction. In the following description, identical components are generally designated by the same reference numerals, and repeated description will be omitted. Furthermore, in this embodiment, the configuration recited in the claims will be mainly illustrated and described. Therefore, parts of the engine 10 other than those components, such as a crankshaft rotation synchronization mechanism, a lubricating oil supply mechanism, a fuel supply mechanism, electrical components, drive mechanisms for driving various valves, belts, etc., are not illustrated.

[0019] FIG. 1 is a perspective view showing an engine 10. As shown in FIG.

[0020] The engine 10 is an opposed-piston engine having a plurality of pistons arranged in opposing directions. The internal configuration and operation of the engine 10 will be described later with reference to Figure 2A and subsequent figures.

[0021] The engine 10 is configured to operate using gasoline, diesel, hydrogen, or the like as fuel. The engine 10 can be used as a drive source for various devices. The engine 10 is used as a drive source for vehicles, generators, water heaters, flight devices, drones, series hybrid drones, parallel hybrid drones, and the like. A series hybrid drone is a drone in which a generator is driven by the engine 10, and the power generated by the generator drives a motor, which in turn drives a rotor, thereby generating lift to keep the drone afloat. A parallel hybrid drone is a drone in which a main rotor is mechanically rotated by the engine 10, and the lift generated by the rotation of the main rotor keeps the drone afloat. The engine 10 of this embodiment is an opposed-piston engine, and is lightweight and low-vibration, making it particularly suitable as a drive source for series hybrid drones, parallel hybrid drones, and the like.

[0022] Specifically, engine 10 mainly comprises a cylinder chamber 12, an intake valve 18, and an exhaust valve 19. These components constituting engine 10 are housed in an engine block 11. The cylinder chamber 12, the intake valve 18, the exhaust valve 19, etc. will be described with reference to FIG. 6A and other figures.

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

[0024] A third crankshaft 163 and a fourth crankshaft 173 extend from the right side of the engine 10. Rotational power can be extracted to the outside from the third crankshaft 163 and the fourth crankshaft 173. In addition, crankshafts can also be extended from the left side of the engine 10 to extract rotational power from these crankshafts to the outside.

[0025] A second spark plug 262 is attached to the right side of the engine block 11. Similarly, a first spark plug 261 (not shown here) is attached to the left side of the engine block 11. The first spark plug 261 and the second spark plug 262 penetrate the respective side surfaces of the second engine block 112, and electrodes formed at their tip ends are exposed to an extension space 33 (described below). This configuration will be described later with reference to FIG. 6A and other figures. Furthermore, an exhaust port 25 is formed on the top surface of the engine block 11. The exhaust port 25 is a path through which gases generated after combustion inside the engine 10 are discharged.

[0026] Furthermore, the engine 10 has a decompression valve advancing / retracting mechanism 50. The decompression valve advancing / retracting mechanism 50 is a mechanism that advances and retracts a decompression valve 23, which will be described later. In FIG. 1, a portion of the decompression valve advancing / retracting mechanism 50 is disposed on the upper surface of the engine block 11. The decompression valve advancing / retracting mechanism 50 will be described later with reference to FIG. 7 and other figures.

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

[0028] 2A, the rearward facing surface of the first engine block 111 is defined as a first abutment surface 40. The first abutment surface 40 is a flat surface that abuts against a second abutment 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 each formed in a generally cylindrical shape extending forward from the first abutment surface 40. The first cylinder chamber front portion 1211 and the second cylinder chamber front portion 1221 are adjacent to each other in the left-right direction. The first cylinder chamber front portion 1211 is a generally cylindrical space and forms the front portion of the first cylinder chamber 121 (described later). The second cylinder chamber front portion 1221 is a generally cylindrical space and forms the front portion of the second cylinder chamber 122 (described later).

[0030] The first extension space front portion 3311 is a portion of the first contact surface 40 recessed forward, 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 described below.

[0031] The second extension space front portion 3321 is a portion of the first contact surface 40 recessed forward, and is continuous with the upper end of the second cylinder chamber front portion 1221. The second extension space front portion 3321 constitutes the front portion of the second extension space 332 described below.

[0032] 2B , the surface of the second engine block 112 facing forward is the second abutment surface 41. The second abutment surface 41 is a flat surface that abuts against the first abutment surface 40 of the first engine block 111 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 abutment surface 41. The first cylinder chamber rear portion 1212 and the second cylinder chamber rear portion 1222 are adjacent to each other in 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 first extension space rear portion 3312 is a portion of the second abutment surface 41 recessed rearward, and is continuous with the upper end of the first cylinder chamber rear portion 1212. The first extension space rear portion 3312, together with the first extension space front portion 3311 described above, constitutes the first extension space 331, which will be described later.

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

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

[0037] 3A is a diagram showing the first contact surface 40 of the first engine block 111. The first contact surface 40 is formed with an intake valve mounting hole 35. 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 first extension space front portion 3311. The first intake valve mounting holes 351 are circular through-holes that penetrate the wall portion of the first engine block 111 in the front-to-rear direction. A first intake valve 181 (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 second extension space front portion 3321. The second intake valve mounting holes 352 are circular through-holes that penetrate a wall formed inside the first engine block 111. A second intake valve 182, which will be described later, is disposed in each of the second intake valve mounting holes 352.

[0040] 3B is a view showing the second contact surface 41 of the second engine block 112. The second contact surface 41 is formed with an exhaust valve mounting hole 36, a 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 plug mounting hole 37 has a first plug mounting hole 371 and a second plug mounting hole 372. The decompression valve mounting hole 22 is formed in the engine block 11 in a portion 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 installation hole 361 is a hole formed in the first extension space rear portion 3312. The first exhaust valve installation hole 361 passes through a circular wall formed inside the second engine block 112. A first exhaust valve 191, which will be described later, is disposed in the first exhaust valve installation hole 361.

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

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

[0044] The second exhaust valve installation hole 362 is a hole formed in the second extension space rear portion 3322. The second exhaust valve installation hole 362 passes through a circular wall formed inside the second engine block 112. A second exhaust valve 192, which will be described later, is disposed in the second exhaust valve installation hole 362.

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

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

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

[0048] The engine section 13 has 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 form one opposing engine section. The third engine section 16 and the fourth engine section 17 form one opposing engine section. By having multiple opposing engine sections in the engine 10, it is possible to increase the output while ensuring the lightweight and low vibration characteristics of the engine 10.

[0049] The cylinder chamber 12 includes 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 in the left-right direction. In FIG. 4 , the first cylinder chamber 121 and the second cylinder chamber 122 are indicated by dotted lines. A first piston 141 and a second piston 151 are disposed in the first cylinder chamber 121 so as to reciprocate, and are opposed to each other. A third piston 161 and a fourth piston 171 are disposed in the second cylinder chamber 122 so as to reciprocate, and are opposed to each other.

[0050] The first engine section 14 has 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 disposed opposite the first engine section 14. The second engine section 15 has 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 has 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 disposed to face the third engine section 16. The fourth engine section 17 has 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 connected to each other. 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 an opposed engine section consisting of a first engine section 14 and a second engine section 15 and an opposed engine section consisting of a third engine section 16 and a fourth engine section 17 are arranged side by side in the left-right direction. Furthermore, the first engine section 14 and the third engine section 16 rotate a first crankshaft 143 and a third crankshaft 163. Furthermore, the second engine section 15 and the fourth engine section 17 rotate a second crankshaft 153 and a fourth crankshaft 173. With this configuration, a large amount of power can be generated even in a compact configuration.

[0057] The extension space 33 is a space that extends laterally, i.e., upward, from a central portion of the cylinder chamber 12 in the front-to-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 a central portion of the first cylinder chamber 121 in the front-to-rear direction. The second extension space 332 is a space that extends upward from a central portion of the second cylinder chamber 122 in the front-to-rear direction. The first extension space 331 and the second extension space 332 are portions in which various valves and plugs are installed, as described below. The specific shape of the extension space 33 is shown in FIG. 6A and other figures.

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

[0059] FIG. 5 is a cross-sectional view taken along the line BB in FIG. 4, showing the wall portion of the engine block 11 that defines the first cylinder chamber 121 and the first extension space 331. As shown in FIG.

[0060] As described above, the first cylinder chamber 121 is a substantially cylindrical space. The first cylinder chamber 121 has a first cylinder chamber front portion 1211 on the front side and a first cylinder chamber rear portion 1212 connected to the rear end of the first cylinder chamber front portion 1211. A first extension space 331 protrudes upward from the top surface of the first cylinder chamber 121 at approximately the center of the first cylinder chamber 121 in the front-to-rear direction. The first cylinder chamber front portion 1211, the first cylinder chamber rear portion 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 configured as described above are spaces surrounded by walls formed inside the engine block 11 .

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

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

[0064] The first extension space 331 is a space surrounded by the first extension wall portion 1291 and the second extension wall portion 2292. The first extension wall portion 1291 is a generally tongue-shaped portion that extends upward from the upper end portion 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 generally tongue-shaped portion that extends upward from the upper end portion 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 portion 1281 and the second cylinder wall portion 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 described above.

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

[0068] The extension space 33 is connected to the cylinder chamber 12 and is a space that serves as the starting point of combustion in the combustion stroke described below. Specifically, the extension space 33 is a space that extends continuously upward from the center in the front-to-rear direction of the cylinder chamber 12. As 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 generally tongue-shaped portion having its largest surface facing the front-to-rear direction. The first extension space 331 has a first side surface 3313 and a second side surface 3314. The first side surface 3313 faces forward. The second side surface 3314 faces backward.

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

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

[0072] The first intake valve 181 is provided so as to be movable 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 a first intake valve installation hole 351 shown in FIG. 3A . The first intake valve 181 is used to draw an air-fuel 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 installation hole 351 shown in FIG. 3A , allowing air to be drawn into the first extension space 331 and the first cylinder chamber 121. When the first intake valve 181 retreats from the first extension space 331, it closes the first intake valve installation hole 351 shown in FIG. 3A .

[0073] The second intake valve 182 is provided so as to be movable 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 a second intake valve installation hole 352 shown in FIG. 3A . The second intake valve 182 is used to draw an air-fuel 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 installation hole 352 shown in FIG. 3A , allowing air to be drawn into the second extension space 332 and the second cylinder chamber 122. When the second intake valve 182 retreats from the second extension space 332, it closes the second intake valve installation hole 352 shown in FIG. 3A .

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

[0075] The first exhaust valve 191 is provided so as to be movable from the rear side toward and away from the second side surface 3314 of the first extension space 331. Here, one first exhaust valve 191 is provided. The first exhaust valve 191 is attached to the first exhaust valve installation hole 361 shown in FIG. 3B . The first exhaust valve 191 is used to exhaust post-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 installation hole 361 shown in FIG. 3B , allowing exhaust from the inside of the first cylinder chamber 121 through the first exhaust valve installation hole 361. On the other hand, when the first exhaust valve 191 retreats from the first extension space 331, it closes the first exhaust valve installation hole 361 shown in FIG. 3B .

[0076] The second exhaust valve 192 is provided so as to be movable forward and backward from the rear side relative to the second side surface 3324 of the second extension space 332. Here, one second exhaust valve 192 is provided. The second exhaust valve 192 is attached to the second exhaust valve installation hole 362 shown in FIG. 3B . The second exhaust valve 192 is used to exhaust post-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 installation hole 362 shown in FIG. 3B , allowing exhaust from the interior of the second cylinder chamber 122 through the second exhaust valve installation hole 362. On the other hand, when the second exhaust valve 192 retreats from the second extension space 332, it closes the second exhaust valve installation hole 362 shown in FIG. 3B .

[0077] The number of intake valves 18 is greater than the number of exhaust valves 19. For example, for the first extension space 331, the number of first exhaust valves 191 is one, and the number of first intake valves 181 is two. In this way, the first spark plug 261 is exposed to the extension space 33 from the side of the first exhaust valves 191, which are fewer in number, and the space around the first extension space 331 can be used effectively.

[0078] The spark plug 26 is a component that is disposed on the side where the exhaust valve 19 is provided, i.e., on the rear side of the extension space 33. The spark plug 26 has an electrode formed at its tip that 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 disposed on the left side of the first exhaust valve 191. The front end of the first spark plug 261 penetrates the second side surface 3314 and is disposed inside the first extension space 331.

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

[0081] The decompression valve 23 is a valve that, by connecting the extension space 33 to the outside during the initial operation of the engine 10, releases pressure in the cylinder chamber 12 and performs decompression to improve the startability 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 a second side surface 3314. The second decompression valve 232 faces the second extension space 332 from a 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 Figure 7 and subsequent figures.

[0082] The configuration and operation of the decompression valve advancing and retracting 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 advancing and retracting mechanism 50 in a closed state. Figure 8 is a cross-sectional view showing the decompression valve 23 and the decompression valve advancing and retracting mechanism 50 in a closed state. Figure 9 is a perspective view showing the decompression valve 23 and the decompression valve advancing and retracting mechanism 50 in an open state. Figure 10 is a cross-sectional view showing the decompression valve 23 and the decompression valve advancing and retracting mechanism 50 in an open state.

[0083] The configuration of the decompression valve advancing and retracting mechanism 50 will be described with reference to Fig. 7. Fig. 7 is a perspective view showing the decompression valve advancing and retracting mechanism 50 when the decompression valve 23 is closed.

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

[0085] The actuator 52 is, for example, a linear actuator 521. The linear actuator 521 is configured to be capable of linearly reciprocating motion. The linear actuator 521 has a fixed portion 522 and an extending portion 523. The extending portion 523 extends and retracts relative to the fixed portion 522 using a motor or the like built into the fixed portion 522 as a drive source. The rear end of the fixed portion 522 is attached to the upper surface of the engine block 11 shown in FIG. 1 via a bracket 57. The rear end of the fixed portion 522 is also attached to the upper surface of the bracket 57 by a connecting portion 58. The fixed portion 522 of the linear actuator 521 is rotatable at the connecting portion 58. In this manner, the linear extension and retraction motion of the linear actuator 521 can be converted into the rotational motion of the cam 54, as described below.

[0086] The arm 56 is a plate-shaped member and is disposed 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 part 523. The right end of the arm 56 is connected to the upper end of the shaft 53 so as not to rotate relative to it.

[0087] The shaft 53 is a generally rod-shaped member that extends linearly in the vertical direction. As described above, the arm 56 is connected to the upper end of the shaft 53 so as not to rotate relative to the shaft 53. The cam 54 is connected to the lower end of the shaft 53 so as not to rotate relative to the shaft 53.

[0088] When viewed from above, the cam 54 is a member that has a generally fan-shaped configuration starting from the portion connected to the shaft 53. When viewed from above, the shape of the cam 54 is a distorted fan-shaped configuration. That is, the cam 54 has a side surface 541 that faces radially outward. When viewed from above, the cam 54 has a first side surface end 542, which is an end on one side, and a second side surface end 543, which is an end on the other side. Here, the first side surface end 542 is closer to the center of rotation of the shaft 53, i.e., the connection portion between the cam 54 and the shaft 53, than the second side surface end 543. In addition, the side surface 541 of the cam 54 contacts the rear end of the rocker arm 55. As will be described later, the shape of the cam 54 allows the amount and force of pressure that presses the rocker arm 55 forward to be adjusted by rotating the cam 54.

[0089] The rocker arm 55 is a member 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 so that it can swing in the front-to-rear direction around its upper end as the center of rotation.

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

[0091] The first spring 511 is disposed so that the rear portion of the first decompression valve 231 is inserted therein and applies a rearward biasing force to the first decompression valve 231. The first decompression valve 231 is biased by the first spring 511 to close the first valve seat ring 281.

[0092] The second spring 512 is disposed so that the rear portion of the second decompression valve 232 is inserted therein and applies a rearward biasing force to the second decompression valve 232. The second decompression valve 232 is biased by the second spring 512 to close the second valve seat ring 282.

[0093] The first valve seat ring 281 is a generally ring-shaped member that is press-fitted from the inside into the first decompression valve mounting hole 221 shown in FIG. 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 blocks the first valve seat ring 281, preventing the first extension space 331 and the 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, forming a gap between the first decompression valve 231 and the first valve seat ring 281, allowing air to decompress the first extension space 331 and the first cylinder chamber 121 through this gap.

[0094] The second valve seat ring 282 is a generally ring-shaped member that is press-fit from the inside into the second decompression valve mounting hole 222 shown in FIG. 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 blocks the second valve seat ring 282, preventing the second extension space 332 and the 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, forming a gap between the second decompression valve 232 and the second valve seat ring 282, allowing air to decompress the second extension space 332 and the second cylinder chamber 122 through this gap.

[0095] 7, i.e., in a state where decompression is not performed, the decompression valve advancing and retracting mechanism 50 does not strongly press the first decompression valve 231 and the second decompression valve 232. As a result, the rearward biasing forces of the first spring 511 and the second spring 512 cause 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, the linear actuator 521 enters an extended state based on instructions from a calculation control unit (CPU, not shown). This causes the front end of the extension portion 523 to push the left end of the arm 56 forward. As a result, the arm 56, shaft 53, and cam 54 rotate counterclockwise around the central axis of the shaft 53 as viewed from above. This causes the side surface portion 541 near the first side surface end 542 to come into contact with the rear end of the rocker arm 55. As described above, the side surface portion 541 near the first side surface end 542 is closer to the rotation center of the cam 54. Therefore, the amount and force of pressure exerted by the cam 54 on the rocker arm 55 are reduced. 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 decompression valve 23 is closed in this manner during normal operation of the engine 10.

[0097] FIG. 8 is a partial cross section of the engine 10 when the second decompression valve 232 is closed.

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

[0099] When the decompression valve advancing / retreating mechanism 50 applies a small pressing force and a small amount of pressing force to the second decompression valve 232, the second decompression valve 232 is positioned rearward due to the biasing force of the second spring 512. Therefore, the front end of the second decompression valve 232 closes the second valve seat ring 282. As a result, the second extension space 332 and the second cylinder chamber 122 are in a non-decompressed state, which is the normal operating state of the engine 10. In other words, 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] FIG. 9 illustrates the state of the decompression valve advancing and retracting mechanism 50 when the decompression valve 23 is set to the open state (decompressed state).

[0101] The operation of the decompression valve advance / retract mechanism 50 when the decompression valve 23 is changed from a closed state to an open state will now be described. First, the linear actuator 521 is contracted based on instructions from a calculation control unit (not shown). Specifically, the driving force of the motor built into the fixed portion 522 retracts most of the extension portion 523 into the fixed portion 522. This pulls the left end of the arm 56 rearward. As a result, the arm 56, shaft 53, and cam 54 rotate clockwise around the central axis of the shaft 53, which extends vertically. At the same time, when viewed from above, the linear actuator 521 rotates counterclockwise around the connecting portion 58. When this rotation is complete, the second side end 543 of the cam 54 abuts against the rear end of the rocker arm 55. As mentioned above, the shape of the cam 54 in a plan view is not exactly fan-shaped. The second side end 543 is farther 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 abuts against 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. As a result, a gap for decompression is formed 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. As a result, a gap for decompression is formed between the second decompression valve 232 and the second valve seat ring 282.

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

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

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

[0105] The operation of the decompression valve advancing and retreating mechanism 50 is controlled by an arithmetic and control unit. The arithmetic and control unit controls the operation of the actuator 52 based on an input signal input from a rotation sensor that senses the rotation speed of the engine 10.

[0106] Specifically, when the rotation speed of the engine 10 is below a predetermined rotation speed, i.e., at the beginning of the operation of the engine 10, the decompression valve advance / retreat mechanism 50 presses the second decompression valve 232 forward, as shown in Figure 10, thereby connecting the second cylinder chamber 122 and the second extension space 332 to the outside and reducing the pressure.

[0107] Thereafter, when the engine 10 speed exceeds a predetermined speed, i.e., when the initial stage of operation of the engine 10 is completed, the decompression valve advancing / retreating mechanism 50 closes the second cylinder chamber 122 and the second extension space 332 by not pressing the second decompression valve 232 forward, as shown in Figure 8. This allows the engine 10 to enter a normal operating state.

[0108] The following describes normal operation of the engine 10. The first engine section 14 and the second engine section 15 of the engine section 13 configured as described above operate by repeating an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke as follows.

[0109] 4, during the intake stroke, the first piston 141 and the second piston 151 move from the center toward the outside inside the first cylinder chamber 121, thereby drawing an air-fuel mixture, which is a mixture of fuel and air, into the first cylinder chamber 121. At the same time, the first crankshaft 143 and the second crankshaft 153 rotate. Referring to FIGS. 6A and 6B, during 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. Therefore, the air-fuel 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 FIG. 3A.

[0110] 4, during the compression stroke, the inertia of the rotating first crankshaft 143 and second crankshaft 153 pushes the first piston 141 and the second piston 151 toward the center, compressing the air-fuel mixture inside the first cylinder chamber 121. Referring to FIG. 6A, the first intake valve 181 closes the first extension space 331, and the first exhaust valve 191 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 Fig. 6A ignites in the first extension space 331, causing the air-fuel mixture to combust inside the first extension space 331 and the first cylinder chamber 121 shown in Fig. 4, thereby pushing the first piston 141 and the second piston 151 to their outer ends, which are at bottom dead center. Referring to Fig. 6A , as in the compression stroke, during this stroke, the first intake valve 181 closes the first extension space 331, and the first exhaust valve 191 closes the first extension space 331. That is, the states of the first intake valve 181 and the first exhaust valve 191 are the same as those in the compression stroke described above.

[0112] 4, during the exhaust stroke, the inertia of the rotating first crankshaft 143 and second crankshaft 153 pushes the first piston 141 and the second piston 151 inward, and the burned gas present inside the first cylinder chamber 121 is discharged to the outside. Referring to FIGS. 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 burned gas inside the first cylinder chamber 121 is discharged to the outside through the first exhaust valve installation hole 361 shown in FIG.

[0113] The same operation is performed for 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 between the two pistons, the first piston 141 and the second piston 151, which reciprocate within the single first cylinder chamber 121. This allows for a higher compression ratio of the mixed gas compared to conventional engines. Furthermore, because the first piston 141 and the second piston 151 face each other within the first cylinder chamber 121, the cylinder head required in conventional engines is unnecessary, resulting in a simple and lightweight configuration of the engine unit 13. Furthermore, the components constituting the engine unit 13, i.e., the first piston 141 and the second piston 151, the first crankshaft 143 and the second crankshaft 153, etc., are positioned opposite each other and operate in an opposing manner. This cancels out vibrations generated by the components of the engine unit 13, thereby reducing external vibrations generated by the engine unit 13 as a whole. Therefore, by incorporating an engine unit 13 having such a structure in a flight device, the flight device can be made smaller, lighter, and with less vibration. In particular, the reduced vibration can prevent adverse effects on precision equipment such as attitude control, motor output control, and other arithmetic and control devices, GPS sensors, etc. It can also prevent damage to delivery packages transported by the flight device due to vibration.

[0115] Although the embodiments of the present invention have been described above, the present invention is not limited to these and can be modified within the scope of the present invention. In addition, the above-described embodiments can be combined with each other.

[0116] 10 Engine 11 Engine block 111 First engine block 112 Second engine block 113 Third engine block 114 Fourth engine block 12 Cylinder chamber 121 First cylinder chamber 1211 First cylinder chamber front part 1212 First cylinder chamber rear part 122 Second cylinder chamber 1221 Second cylinder chamber front part 1222 Second cylinder chamber rear part 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 Fourth engine section 171 Fourth piston 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 hole 221 First decompression valve mounting hole 222 Second decompression valve mounting hole 23 Decompression valve 231 First decompression valve 232 Second decompression valve 24 Vent hole 25 Exhaust port 26 Spark plug 261 First spark plug 262 Second spark plug 281 First valve seat ring 282 Second valve seat ring 33 Extension space 331 First extension space 3311 First extension space front portion 3312 First extension space rear portion 3313 First side surface 3314 Second side surface 332 Second extension space 3321 Second extension space front portion 3322 Rear portion of second extension space 3323 First side surface 3324 Second side surface 34 Combustion chamber 341 First combustion chamber 342 Second combustion chamber 35 Intake valve installation hole 351 First intake valve installation hole 352 Second intake valve installation hole 36 Exhaust valve installation hole 361 First exhaust valve installation hole 362 Second exhaust valve installation hole 37 Plug installation hole 371First plug installation hole 372 Second plug installation hole 40 First contact surface 41 Second contact surface 50 Decompression valve advance / retract mechanism 51 Spring 511 First spring 512 Second spring 52 Actuator 521 Linear actuator 522 Fixed portion 523 Extension portion 53 Shaft 54 ​​Cam 541 Side portion 542 First side end portion 543 Second side end portion 55 Rocker arm 56 Arm 57 Bracket 58 Connection portion

Claims

1. An engine comprising: 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 a portion forming the extension space; a decompression valve arranged to be able to advance and retreat relative to the decompression valve mounting hole; and a decompression valve advancement and retreat mechanism for advancing and retreating the decompression valve, wherein the decompression valve advancement and retreat mechanism has a spring and an actuator, the decompression valve closes the decompression valve mounting hole when biased by the spring, and the decompression valve opens the decompression valve mounting hole when pressed by the actuator.

2. 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 a portion forming the first extension space and a second decompression valve mounting hole formed in the engine block in a portion forming the second extension space; the decompression valve has a first decompression valve arranged to be able to advance and retreat relative to the first decompression valve mounting hole and a second decompression valve arranged to be able to advance and retreat relative to the second decompression valve mounting hole; the spring has a first spring arranged to apply a biasing force to the first decompression valve and a second spring arranged to apply a biasing force to the second decompression valve, 2. The engine according to claim 1, wherein the first decompression valve closes the first decompression valve mounting hole by being biased by the first spring and opens the first decompression valve mounting hole by being pressed by the actuator, and the second decompression valve closes the second decompression valve mounting hole by being biased by the second spring and opens the second decompression valve mounting hole by being pressed by the actuator.

3. The engine described in claim 2, characterized in that the decompression valve advance / retract mechanism has a shaft rotated by the actuator, a cam connected to the shaft so as to be rotatable relative to the shaft, and a rocker arm that rotates by contacting the cam, one side of the rocker arm contacting the cam and the other side contacting the first decompression valve and the second decompression valve.

4. The engine according to claim 3, wherein said actuator is a linear actuator.

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