Engine

Abstract

An engine (E) according to the present disclosure comprises: a crankshaft (2) that converts the reciprocating motion of a piston (3) into rotational motion; a shaft body (30) to which power is transmitted from the crankshaft (2); and a cover body (28) that covers the shaft body (30) from the outside in the axial direction. One end of the shaft body (30) in the axial direction is rotatably supported by the cover body (28), and the other end of the shaft body (30) is supported at one end of the crankshaft (2) in the axial direction so as to be rotatable relative to the crankshaft (2).

Description

engine Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-061958, filed April 8, 2024, the entire contents of which are incorporated herein by reference.

[0002] This disclosure relates to engines having a crankshaft that converts reciprocating piston motion into rotational motion.

[0003] In engines equipped with a crankshaft that converts the reciprocating motion of pistons into rotational motion, there is a type in which a shaft supported for relative rotation with respect to the crankshaft is connected to one axial end of the crankshaft via a coupling (see, for example, Patent Document 1). In the engine disclosed in Patent Document 1, the shaft is rotatably supported by a separate case adjacent to the crankcase.

[0004] Japanese Patent Application Publication No. 3-204395

[0005] In such an engine, the shaft is disposed adjacent to the crankshaft in the axial direction, which results in an increased size in the axial direction.

[0006] The disclosure of the present application provides an engine that can be prevented from becoming large.

[0007] An engine according to one aspect of the present disclosure includes a crankshaft that converts reciprocating motion of a piston into rotational motion, a shaft body supported at one axial end of the crankshaft so as to be rotatable relative to the crankshaft, and a cover body that covers the shaft body from the axial outside and rotatably supports the one axial end of the shaft body. The other axial end of the shaft body is supported by the crankshaft, and power is transmitted from the crankshaft.

[0008] According to the engine of the present disclosure, the other end of the shaft is supported by the crankshaft, so the crankcase can be prevented from becoming larger in the axial direction compared to when the shaft is supported by the crankcase.

[0009] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present disclosure. In particular, any combination of two or more of the claims is included in the present disclosure.

[0010] The present disclosure will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation, and should not be used to define the scope of the present disclosure. The scope of the present disclosure is defined by the accompanying claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts. Fig. 1 is a side view of an engine according to a first embodiment of the present disclosure. Fig. 2 is a front view of the engine. Fig. 3 is a side view of the engine as seen from the opposite side to Fig. 1. Fig. 4 is a cross-sectional view of a reduction mechanism of the engine.

[0011] A preferred embodiment of the present disclosure will be described below with reference to FIGS. 1 to 4. The engine E of this embodiment is a reciprocating engine. The engine E of this embodiment is used, for example, in an airplane in which a propeller is disposed at the tip of the fuselage. In this case, the engine E is housed within the fuselage, and engine power is transmitted to the propeller Pr. The use of the engine E is not limited to this, and it can also be used, for example, as a drive source for an airplane in which a propeller is disposed on the wing, or for a ship equipped with a propeller. The engine E of this embodiment can also be used as a drive source for vehicles such as motorcycles and four-wheeled vehicles.

[0012] In the following description, the "width direction WD" refers to the direction in which the crankshaft 2 of the engine E extends. In other words, the "axial direction of the crankshaft" coincides with the width direction WD. In the width direction WD, the direction toward the width center is referred to as the "inner width direction," and the direction away from the width center is referred to as the "outer width direction." The "reciprocating direction VD" refers to the direction in which the pistons of the engine E reciprocate. The direction perpendicular to both the "width direction WD" and the "reciprocating direction VD" is referred to as the "perpendicular direction PD."

[0013] The engine E of this embodiment is an in-line cylinder engine with multiple cylinders aligned in the direction of the extension of the crankshaft 2. However, the number of cylinders is not limited, and may be, for example, one cylinder. Furthermore, although the engine E of this embodiment is a gasoline engine, the fuel is not limited to gasoline. The crankshaft 2 is formed in a crank shape, and converts the reciprocating motion of the piston 2, which occurs due to repeated combustion strokes, into rotational motion.

[0014] The engine E has a crankcase 4 that supports the crankshaft 2, a cylinder 6 that protrudes upward from the crankcase 4, and a cylinder head 8 that is connected to one upper end of the cylinder 6 in the reciprocating direction. In the following description, in the reciprocating direction VD of the piston 2, the direction in which the cylinder 6 protrudes from the crankcase 4 is referred to as "upper," and the opposite side is referred to as "lower."

[0015] The crankcase 4 is divided into two parts, a lower crankcase 4a and an upper crankcase 4b. In this embodiment, the upper crankcase 4b and the cylinder 6 are integrally formed by molding. However, the upper crankcase 4b and the cylinder 6 may be separate bodies. In the following description, the integrated upper crankcase 4b and the cylinder 6 are referred to as a cylinder block 10.

[0016] The engine E further has a head cover 12 connected to the upper end of the cylinder head 8, and an oil pan 14 connected to the lower end of the crankcase 4. The oil pan 14 stores oil, which is a type of engine lubricating fluid.

[0017] Lubricated engine parts include bearings, piston sliding surfaces in the combustion chamber, cam sliding surfaces, and power transmission parts such as gears and chains. Cooled engine parts include the back surface of the piston and parts that generate heat due to sliding.

[0018] An intake port 16 opens at one end (right side in FIG. 1) of the cylinder head 8 in the orthogonal direction PD, and an exhaust port 18 opens at the other end (left side in FIG. 1) of the cylinder head 8 in the orthogonal direction PD.

[0019] The intake port 16 and the exhaust port 18 are passages formed inside the cylinder head 8. The upstream end of the intake port 16 opens to one end side of the cylinder head 8 in the orthogonal direction PD, and the downstream end opens to a combustion chamber 20 inside the cylinder 6. The upstream end of the exhaust port 18 opens to the combustion chamber 20 inside the cylinder 6, and the downstream end opens to the other end side of the cylinder head 8 in the orthogonal direction PD. An intake port 16 is formed for each cylinder. Similarly, an exhaust port 18 is formed for each cylinder.

[0020] External air is supplied as intake air from the intake port 16 to the combustion chamber 20, and fuel is injected into the combustion chamber 20 from the injector 22 to form a fuel-air mixture. The mixture in the combustion chamber 20 is ignited by the spark plug 24 and burns. Exhaust gas after combustion is discharged to the outside of the engine from the exhaust port 18.

[0021] Fig. 2 is a cross-sectional view taken along an imaginary plane including two axes of the output shaft and the input shaft. As shown in Fig. 2, the engine E of the present disclosure includes a transmission mechanism for transmitting the rotation of the crankshaft. In this embodiment, the transmission mechanism is a reduction mechanism 26 that reduces the rotation of the crankshaft 2. The reduction mechanism 26 is provided on one end side (left side in Fig. 2) in the width direction WD of the engine E. In other words, the reduction mechanism 26 is disposed in an area on one side of the crankcase 4 in the width direction.

[0022] The reduction gear mechanism 26 is covered by a gear cover 28. More specifically, the gear cover 28 covers the reduction gear mechanism 26 from the outside in the axial direction. The gear cover 28 is detachably attached to the cylinder block 10 by fastening members 29 such as bolts.

[0023] The reduction gear mechanism 26 has an input shaft 30 to which power is transmitted from the crankshaft 2, and an output shaft 32 that is gear-connected to the input shaft 30. A small-diameter input gear 34 is provided on the input shaft 30, and a large-diameter output gear 36 is provided on the output shaft 32, with the input gear 34 and the output gear 36 meshing together. In other words, the rotational force of the crankshaft 2 is transmitted to the input shaft 30, reduced by the gear connection between the gears 34, 36, and then transmitted to the output shaft 32. This allows the gear ratio to be changed to suit the output.

[0024] The axes of the input shaft 30 and the output shaft 32 are arranged parallel to the axis of the crankshaft 2. The input shaft 30 is arranged on one side of the crankshaft 2 in the width direction. The input shaft 30 is arranged coaxially with the crankshaft 2. Power is transmitted to the input shaft 30 from the crankshaft 2 via a damper structure 40, which is a coupling structure described below. In other words, the input shaft 30 is connected to the crankshaft 2 so as to be capable of relative angular displacement within an allowable angular range. The output shaft 32 is arranged offset in the reciprocating direction VD from the input shaft 30. As shown in FIG. 3 , when viewed from the width direction WD, the output shaft 32 is arranged in a position overlapping the wall surface of the crankcase 4. As shown in FIG. 4 , one axial end of the crankshaft 2 is rotatably supported by the crankcase 4.

[0025] 2, in this embodiment, an aircraft propeller Pr is connected to the output shaft 32. The propeller Pr may be directly connected to the output shaft 32, or may be connected to the output shaft 32 via a power transmission member. In addition to the aircraft propeller Pr, for example, a vehicle wheel, a turbine or compressor rotor blade, a pump impeller, etc. may also be connected to the output shaft 32.

[0026] When the propeller Pr is connected to the output shaft 32, a reaction force caused by the rotation of the propeller Pr generates an axial force, i.e., a thrust force, on the output shaft 32. Specifically, a force in one direction in the width direction WD, in other words, a force in a direction away from the crankcase 4 (a direction of escape), is applied to the output shaft 32.

[0027] The engine E of this embodiment is disposed within the fuselage of a propeller-driven aircraft, with the aircraft's propeller Pr connected to the output shaft 32. In this case, the propeller shaft and crankshaft 2 may be disposed along the fuselage centerline, which extends in the longitudinal direction of the fuselage of the propeller-driven aircraft. Furthermore, with the aircraft's wings facing horizontally, the engine E of this embodiment may be in an upright position, i.e., the piston reciprocation direction VD may coincide with the vertical direction. This allows the engine E to be housed compactly within the fuselage.

[0028] As shown in Figure 4, the input shaft 30 and output shaft 32 of the reduction gear mechanism 26 are connected by inclined gears 34, 36, whose tooth traces are oblique to the axes. In this embodiment, the input and output gears 34, 36 are "helical gears." By using helical gears, the meshing ratio can be increased compared to spur gears, and they are advantageous in terms of strength and noise reduction.

[0029] The helix angle of the output gear 36 is preferably set so that, when power is transmitted from the input gear 34, a thrust load is generated on the opposite side to the thrust load received by the rotation of the propeller. This makes it possible to suppress the thrust load generated on the bearing supporting the output gear 36. Furthermore, the helix angle of the input gear 34 is preferably set so that a thrust load is generated on the opposite side to the thrust load received from the output shaft 32 due to the rotation of the propeller. This makes it possible to suppress the thrust load generated on the bearing supporting the input gear 34.

[0030] In the engine E of this embodiment, power is transmitted from the crankshaft 2 to the input shaft 30 via a rotating body 40, which is a joint structure. The rotating body 40 is disposed coaxially with one end 2a (the left end in FIG. 4 ) of the crankshaft 2, and the input shaft 30 is connected to one end 2a of the crankshaft 2 via the rotating body 40.

[0031] In this embodiment, the rotating body 40 is a damper structure 40 that suppresses torsional vibrations of the crankshaft 2. More specifically, the damper structure 40 of this embodiment is an engine torque damper, specifically a spring damper, that reduces rotational fluctuations of the engine that occur during deceleration and acceleration. The damper structure 40 may reduce rotational fluctuations caused by combustion timing of the engine or by torsional deformation of the crankshaft 2.

[0032] The damper structure 40 includes two rotating members 40a, 40b and a damping member 40c that dampingly connects the two rotating members 40a, 40b. The rotating members 40a, 40b are made up of a crank-side rotating body member 40a on the crankshaft 2 side and an input-shaft-side rotating member 40b on the input shaft 30 side. The crank-side rotating member 40a is bolted coaxially to the end of the crankshaft 2. The input-shaft-side rotating member 40b is coupled to the input shaft 30 coaxially and prevented from rotating.

[0033] The damping member 40c connects the crank-side rotating member 40a and the input-shaft-side rotating member 40b so that they can rotate relative to each other within an allowable range. The damping member 40c is, for example, a spring or rubber having damping characteristics. By coupling the input shaft 30 and the output shaft 32 via this damper structure 40, rotational fluctuations occurring in the crankshaft 2 are suppressed and the rotational force of the crankshaft 2 is transmitted to the input shaft 30.

[0034] An axially recessed recess 42 is formed at one axial end 2a of the crankshaft 2. The recess 42 is cylindrical and coaxial with the axis of the crankshaft 2. A flange-shaped flange 2b extending radially is formed at one axial end 2a of the crankshaft 2. A plurality of threaded holes 2ba are formed in the flange 2b and spaced at equal intervals in the circumferential direction.

[0035] The recess 42 and the flange portion 2b are disposed adjacent to one side in the axial direction of a support portion where one axial end of the crankshaft 2 is supported by the crankcase 4. The recess 42 and the flange portion 2b have a radially overlapping region. In other words, the flange portion 2b is formed radially outward of the recess 42. By radially overlapping the recess 42 and the flange portion 2b, the axial dimension can be made smaller than when the recess 42 and the flange portion 2b are aligned in the axial direction.

[0036] An input shaft-side rotating member 40b of a damper structure 40 is attached to the other end 30a (right end in FIG. 4) of the input shaft 30. Furthermore, the crankshaft-side rotating member 40a of the damper structure 40 is attached to a flange portion 2b formed on one end 2a of the crankshaft 2. This allows the rotation of the crankshaft 2 to be transmitted to the input shaft 30 via the damper structure 40. Furthermore, the damper structure 40 absorbs short-term rotational fluctuations that occur in the crankshaft 2 and transmits them to the input shaft.

[0037] A protrusion 44 is formed on the other end 30a of the input shaft 30. The protrusion 44 is formed in a cylindrical shape and protrudes axially inward (toward the other end) from the other end 30a of the input shaft 30 of the reduction mechanism 26, i.e., from the portion where the damper structure 40 is attached.

[0038] A protrusion 44 of the input shaft 30 is inserted into a recess 42 of the crankshaft 2. Specifically, the protrusion 44 is formed closer to the crankshaft 2 than the portion of the other end 30a of the input shaft 30 where the damper structure 40 is attached. In this embodiment, a needle roller bearing 46, which is a type of rolling bearing, is press-fitted into the recess 42 of the crankshaft 2, and the protrusion 44 of the input shaft 30 is press-fitted into the inner ring portion of the bearing 46. This allows the input shaft 30 to be angularly displaced relative to the crankshaft 2.

[0039] That is, power is transmitted to the input shaft 30 from the crankshaft 2 via the damper structure 40. The input shaft 30 is supported at one end 2a of the crankshaft 2 in the axial direction so as to be angularly displaceable relative to the crankshaft 2.

[0040] The crankshaft 2 has a recess 42 formed in the flange portion 2b, which has a larger radial dimension than the adjacent portion. This increases the support rigidity and makes it easier to form the diameter of the recess 42 large. This makes it easier to fit a bearing into the recess 42. Furthermore, a crankcase portion that supports the crankshaft 2 is disposed axially adjacent to the recess 42. This increases the support rigidity of the input shaft 30 by the crankshaft 2 compared to when the recess 42 and the crankcase support portion are spaced apart.

[0041] Thus, in this embodiment, the input shaft 30 transmits power from the crankshaft 2 and constitutes a shaft body that is supported at one end 2a of the crankshaft 2 in the axial direction so as to be rotatable relative to the crankshaft 2.

[0042] Although the rolling bearing 46 is not limited to a needle roller bearing 46, the use of a needle roller bearing 46 reduces the diameter of the support portion (recess 42). This allows the input shaft 30 to be inserted and supported on the crankshaft 2 without reducing the diameter of the input shaft 30, thereby reducing the amount of axial protrusion of the input shaft 30. Furthermore, radial positioning of the damper structure 40 and the crankshaft 2 during assembly, or so-called centering, can be performed by press-fitting the reduction input shaft 30 into the inner ring of the bearing 46 provided on the crankshaft 2.

[0043] In this embodiment, the recess 42 is formed on one end 2 a of the crankshaft 2 and the protrusion 44 is formed on the other end 30 a of the input shaft 30, but the recess and protrusion may be reversed. That is, the protrusion may be formed on one end 2 a of the crankshaft 2 and the recess may be formed on the other end 30 a of the input shaft 30.

[0044] The input shaft 30 is provided with a thrust movement suppression member 48 that receives a load in the thrust direction of the input shaft 30. In this embodiment, a circlip (retaining ring) 48 is used as the thrust movement suppression member 48. The circlip 48 is provided in a portion of the input shaft 30 between the damper structure 40 and the input and output gears 34, 36.

[0045] This prevents the input gear 34 from moving relative to the input shaft 30, even if a thrust load is generated by the power transmission between the input gear 34 and the output gear 36. Furthermore, it is preferable that the input shaft 30 be prevented from moving in the thrust direction by bearings provided on both ends.

[0046] One end 30b (the left end in FIG. 4) of the input shaft 30 is rotatably supported by the gear cover 28. More specifically, the one end 30b of the input shaft 30 is supported by the gear cover 28 via a rolling bearing 50. In this embodiment, a ball bearing is used as the rolling bearing 50. However, the rolling bearing 50 is not limited to a ball bearing. In this manner, the one end 30b of the input shaft 30 is supported by the gear cover 28, and the other end 30a is supported by the crankshaft 2. In other words, the input shaft 30, to which the damper structure 40 is attached, is supported at both ends.

[0047] The output shaft 32 is rotatably supported at both ends by the crankcase 4 and the gear cover 28. More specifically, the other end 32a (the right end in FIG. 4) of the output shaft 32 is supported by the cylinder block 10 via a rolling bearing 52, and one end 32b (the left end in FIG. 4) of the output shaft 32 is supported by the gear cover 28 via a rolling bearing 54.

[0048] In this embodiment, tapered roller bearings are used as the rolling bearings 52, 54. By supporting the output shaft 32 with the tapered roller bearings 52, 54, it is possible to support the thrust force of the pair of "helical gears" 34, 36. However, the rolling bearings 52, 54 are not limited to tapered roller bearings.

[0049] The outer diameter D1 of the portion of the output shaft 32 that is supported by the gear cover 28 is set to be larger than the outer diameter D2 of the portion of the output shaft 32 that is supported by the crankcase 4. In other words, the one end 32b of the output shaft 32 is set to have a larger diameter than the other end 32a of the output shaft 32.

[0050] In other words, the inner ring diameter of the bearing 54 on the gear cover 28 side is larger than the inner ring diameter of the bearing 52 on the crankcase 4 side. In addition, in this embodiment, the bearing 54 on the gear cover 28 side is formed to have a larger width dimension than the bearing 52 on the crankcase 4 side.

[0051] The bearing 54 on the gear cover 28 side is inclined radially inward toward one side (outside) in the width direction WD so as to receive a thrust load directed toward one side (outside) in the width direction WD, i.e., toward the propeller side of the output shaft 30. The bearing 52 on the crankcase 4 side is inclined radially outward toward one side (outside) in the width direction WD so as to receive a thrust load directed toward the other side (inside) in the width direction WD, i.e., toward the side opposite the propeller side of the output shaft 30. In this way, the two bearings 52, 54 can receive loads on both sides in the thrust direction, respectively.

[0052] One end 32b of the output shaft 32 has a flange structure with a larger diameter than the remaining portion. This flange structure allows a large number of bolt holes 32ba to be arranged in one end (tip) 32b of the output shaft 32. As a result, a large fastening force can be provided to withstand the torque acting on the output shaft 32 from the propeller Pr.

[0053] An output shaft opening 28a facing outward in the width direction WD is formed in the gear cover 28, and a shaft end face 32c of the output shaft 32, i.e., the end face 32c of the flange structure, is exposed from this output shaft opening 28a. A bolt hole 40fa is provided in the flange 40f for connecting the rotating body 30. The propeller Pr is connected to one end 32b of the output shaft 32 by tightening a fastening member 55 such as a bolt into a bolt hole 32ba in one end 32b of the output shaft 32.

[0054] 2, the gear cover 28 is supported by the crankcase 4 at the supported portion 56. More specifically, the gear cover 28 is detachably attached to the crankcase 4 at the supported portion 56 using fastening members 29.

[0055] The gear cover 28 is formed with a reinforcing rib 68 that connects the portion 28b of the gear cover 28 that supports the output shaft 32 and the supported portion 56. The reinforcing rib 68 is provided on the outer surface of the gear cover 28 and protrudes radially relative to the remaining portion. In this embodiment, a plurality of reinforcing ribs 68 extending radially of the output shaft 32 are arranged at intervals around the circumferential direction of the output shaft 32. The reinforcing ribs 68 extend radially from the portion 28b that supports the output shaft 32. While two reinforcing ribs 68 are depicted in FIG. 2, some of them are omitted for ease of explanation; in reality, more reinforcing ribs 68 are provided. The reinforcing ribs 68 reinforce the bearing portion 28b of the gear cover 28. This improves the support rigidity of the output shaft 32 while reducing the thickness of the gear cover 28.

[0056] In this embodiment, the reaction force of the propeller Pr is suppressed by the thrust force generated by the power transmission of the helical gears 34, 36. A "spring member" 70 that is biased in the axial direction (width direction WD) is provided on the output shaft 32. In this embodiment, a disc spring 70 is used as the spring member 70. By providing the spring member 70, the spring member 70 can also suppress the reaction force of the propeller Pr.

[0057] According to the above configuration, one end 30b of the input shaft 30 is supported by the gear cover 28, and the other end 30a is supported by the crankshaft 2. In other words, since the input shaft 30 is supported at both ends, the support rigidity is high. Furthermore, since the other end 30a of the input shaft 30 is supported by the crankshaft 2, it is possible to prevent the crankcase 4 from becoming large in the axial direction (width direction WD) compared to when the input shaft 30 is supported by the crankcase 4.

[0058] Power is transmitted from the crankshaft 2 to the input shaft 30 via a damper structure 40 disposed coaxially with the crankshaft 2. The damper structure 40 of this embodiment is a spring damper that suppresses torsional vibration of the crankshaft 2. In an in-line multi-cylinder engine, the crankshaft 2 is long, so torsional vibration is likely to occur when torque is applied. However, by providing the damper structure 40, torque fluctuations in the engine output can be suppressed and resonance can be prevented. Furthermore, by transmitting power via the damper structure 40, the crankshaft 2 and the input shaft 30 can rotate relative to each other, and power can be transmitted between them.

[0059] A recess 42 is formed on one end 2a of the crankshaft 2, a protrusion 44 is formed on the other end 30a of the input shaft 30, a roller bearing 46 is press-fitted into the recess 42 of the crankshaft 2, and the protrusion 44 of the input shaft 30 is press-fitted into the inner ring of the roller bearing 46. This configuration makes it easy to center the crankshaft 2 and the input shaft 30. In addition, by using a needle roller bearing as the roller bearing 46, the outer diameter of the bearing is reduced, preventing the diameters of the crankshaft 2 and the input shaft 30 from becoming smaller and making it easier for the crankshaft 2 to support the input shaft 30.

[0060] A circlip 48 is provided on the input shaft 30 to receive a thrust load acting on the input gear 34. According to this configuration, by combining the roller bearing 46 and the circlip 48, the thrust load support burden on the roller bearing 46 can be reduced.

[0061] The input shaft 30 and the output shaft 32 are connected by inclined gears 34, 36, whose tooth traces are inclined relative to the shafts. With this configuration, the reaction force of the propeller Pr connected to the output shaft 32, i.e., the load in the thrust direction, can be suppressed by the inclined gears 34, 36.

[0062] An axially biased disc spring 70 is provided on the output shaft 32. With this configuration, the reaction force of the propeller Pr connected to the output shaft 32, i.e., the load in the thrust direction, can be borne not only by the inclined gears 34, 36 but also by the disc spring 70.

[0063] Both ends of the output shaft 32 are supported by the gear cover 28 and the crankcase 2, respectively. With this configuration, the output shaft 32 is supported at both ends, resulting in high support rigidity. Furthermore, both ends 32a, 32b of the output shaft 32 are supported by tapered roller bearings 52, 54, respectively. This allows the outer diameter of the bearings to be smaller than that of ball bearings, even while bearing the thrust load resulting from the reaction force of the propeller Pr. By reducing the outer diameter of the bearings, it is possible to ensure space for arranging the damper structure 40 and reduce the axial distance between the input and output shafts 30, 32, particularly on the inner side in the width direction WD (the crankcase 4 side).

[0064] The outer diameter of the portion (one end 32b) of the output shaft 32 of the reduction mechanism 26 that is supported by the gear cover 28 is larger than the outer diameter of the portion (the other end 32a) that is supported by the crankcase 4. In other words, the other end 32a of the output shaft 32 of the reduction mechanism 26 has a flange structure that allows the larger diameter to accommodate a large number of bolts 55. This configuration makes it possible to withstand radial and axial loads caused by the rotation of the propeller Pr connected to the output shaft 32. Furthermore, fastening with a large number of bolts 55 makes it possible to withstand the torque of the propeller Pr.

[0065] The gear cover 28 is formed with a reinforcing rib 68 that connects a portion 28b of the gear cover 28 that supports the output shaft 32 of the reduction mechanism 26 and a supported portion 56 that is supported by the crankcase 4. This configuration can improve the support rigidity of the bearing portion 28b of the gear cover 28.

[0066] As shown in Figure 4, a passage 60 is formed in the crankshaft 2 to guide the lubricating liquid OL. The lubricating liquid OL is supplied from the shaft end of the crankshaft 2 to an internal passage 62 in the input shaft 30. This allows the lubricating liquid OL to be guided to the bearing 46 between the crankshaft 2 and the input shaft 30. The lubricating liquid OL can be guided to the bearings 50, 54 of the input and output shafts 30, 32 via the internal passage 62 in the input shaft 30 and the internal passage 64 in the output shaft 32.

[0067] The bearings may be rolling bearings or plain bearings as long as they are rotatably supported. Furthermore, any existing bearing may be selectively used. While a speed reduction mechanism that reduces the rotation of the crankshaft at a predetermined reduction ratio has been used as the transmission mechanism, a mechanism that increases the speed at a predetermined speed increase ratio or transmits power at a constant speed may also be used.

[0068] When the transmission mechanism is a gear pair, the power may be transmitted by a spur gear. Also, a helical gear, a double helical gear, or the like may be used as a gear with teeth that are inclined to the axis. As for the transmission mechanism, in addition to gear transmission, the power may be transmitted by a chain or a belt.

[0069] In the above embodiment, a propeller Pr for propulsion is used as the rotating body attached to the output shaft 32, but a rotating blade for a purpose other than propulsion may also be used. Such a rotating blade may be a fan or impeller for blowing air or compressing a fluid. The rotating body attached to the output shaft 32 is preferably one that generates a thrust force as a reaction force to its rotation, but a rotating body that does not generate a thrust force may also be connected to the output shaft 32.

[0070] The present disclosure is not limited to the above embodiments, and various additions, modifications, and deletions are possible without departing from the spirit and scope of the present disclosure. For example, the engine of the above embodiment can also be applied to saddle-type vehicles such as motorcycles, tricycles, and four-wheeled buggies (all-terrain vehicles). The engine may be used in an outboard motor or as a propulsion source for aircraft. Additionally, the engine may be used as a propulsion source for four-wheeled vehicles or small personal watercraft. The engine may be equipped with a supercharger such as a turbocharger or supercharger. Therefore, such devices are also included within the scope of the present disclosure.

Claims

1. An engine comprising: a crankshaft that converts the reciprocating motion of a piston into rotational motion; a shaft body to which power is transmitted from the crankshaft and which is supported at one axial end of the crankshaft so as to be rotatable relative to the crankshaft; and a cover body that covers the shaft body from the axial outside and rotatably supports one axial end of the shaft body.

2. An engine as set forth in claim 1, wherein the shaft receives power from the crankshaft via a rotor disposed coaxially with the crankshaft.

3. An engine according to claim 2, wherein the rotating body is a damper structure that suppresses torsional vibration of the crankshaft.

4. An engine according to any one of claims 1 to 3, wherein one axial end of the crankshaft is formed with a recess recessed in the axial direction, and the other axial end of the shaft is formed with a protrusion that is press-fitted into the recess, and a bearing is press-fitted into the recess of the crankshaft.

5. An engine according to any one of claims 1 to 4, further comprising a thrust movement suppressing member provided on the shaft for receiving a load in the thrust direction of the shaft.

6. An engine according to any one of claims 1 to 5, further comprising a transmission mechanism for transmitting the rotation of the crankshaft, wherein the shaft constitutes the input shaft of the transmission mechanism, and the input and output shafts of the transmission mechanism are connected by an inclined gear whose teeth are oblique to the axis.

7. An engine according to any one of claims 1 to 6, further comprising a transmission mechanism for transmitting the rotation of the crankshaft, wherein the shaft constitutes the input shaft of the transmission mechanism, and a spring member biased in the axial direction is provided on the output shaft of the transmission mechanism.

8. An engine according to any one of claims 1 to 7, further comprising a transmission mechanism for transmitting the rotation of the crankshaft, wherein the shaft constitutes the input shaft of the transmission mechanism, and both ends of the output shaft of the transmission mechanism are supported by the cover body and the crankcase.

9. An engine according to claim 8, wherein the outer diameter of the portion of the output shaft of the transmission mechanism that is supported by the cover body is larger than the outer diameter of the portion that is supported by the crankcase.

10. An engine as claimed in claim 8 or 9, wherein the cover body is supported by the engine body at the supported portion, and a reinforcing rib is formed on the cover body to connect the portion of the cover body that supports the output shaft of the transmission mechanism to the supported portion.

11. An engine according to any one of claims 1 to 10, further comprising a transmission mechanism for transmitting the rotation of the crankshaft, the shaft body constituting the input shaft of the transmission mechanism, and a rotor attached to the output shaft of the transmission mechanism.

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