The invention relates to an engine for a vehicle, in particular a motorcycle, having a crankshaft and a generator driven by the crankshaft via a driven gear. Further, the invention relates to a vehicle, in particular a motorcycle, having an engine.
Such a vehicle and such a conventional engine is known, for example, from JP-A-2000-45921. This engine is mounted on the vehicle with the axis of a crankshaft parallel to the width direction of the vehicle, and with a generator disposed at the left end of a crankcase. The generator is covered with a cover attached to the left end of the crankcase so as to protrude outwardly, and made up of a stator fixed inside the cover, a rotor fixed to the left end of the crankshaft, and the like.
The rotor is formed in the shape of a bottomed cylinder opening leftwardly, and has a boss at its axial center, to which the crankshaft is fixed on the same axis. In order for the rotor to be fixed to the crankshaft, a structure is adopted in which the rotor is fastened to the crankshaft with the foregoing boss fitted in a tapered surface formed in the crankshaft. The stator is supported on the foregoing cover and inserted in the rotor from outside.
Apart from the foregoing construction in which the generator is disposed at the end of the crankshaft, another conventional engine for a motorcycle is disclosed, for example, in JP-A-Hei05-91693, in which a generator is disposed rearwardly of a cylinder and upwardly of a crankcase. This generator is mounted on a vertical wall of the crankcase extending vertically, and made up of an annular stator fixed inside a cover attached to the vertical wall from the left side, a rotor rotating inside the stator about its axis, and the like.
The rotor is made up of a shaft parallel to a crankshaft and an excitation coil, and supported at both ends on the cover and the vertical wall of the crankcase for rotation.
The rotor shaft is coupled at its inner end to a drive shaft by spline fitting, and connected to the crankshaft through the drive shaft and a chain.
In such engines for a motorcycle with a generator as described above, it is required that the position of the center of gravity of the vehicle can be lowered as much as possible with the engine mounted thereon. This is because driving becomes easier when the position of the center of gravity of the motorcycle is lowered.
Of the foregoing conventional engines for a motorcycle, the engine with the generator disposed at one end of the crankshaft raises a problem that the bank angle becomes smaller when the engine is mounted on the vehicle at a relatively low position for the purpose of lowering the center of gravity of the vehicle. The reason for the smaller bank angle is that the generator protruded laterally from one side of the crankcase is apt to come in contact with the road surface when the vehicle is tilted.
On the other hand, in the engine for a motorcycle with the generator disposed rearwardly of the cylinder and upwardly of the crankcase, the generator does not cause a narrower bank angle even when the engine is mounted on the vehicle at a low position. However, since the generator of a relatively large weight is located higher than the crankshaft in the engine of this type, it is difficult to lower the position of the center of gravity as much as expected even when mounting the engine on the vehicle at a low position at best.
US 4,513,838 A discloses a motorized two-wheeled vehicle having an internal combustion engine (4) and, at its rear portion, a transmission (5), so that an output of the internal combustion engine (4) can be transmitted by the transmission (5) to a rear wheel (3). The internal combustion engine (4) is a six-cylinder in-line engine comprising a crankshaft (8) having a sprocket (23) on a middle portion of said crankshaft (8). The sprocket (23) is in engagement with a further sprocket (21) through a chain (22) wherein a further sprocket (21) is located on an intermediate shaft (18). A generator (19) is connected by a friction clutch (26) to the intermediate shaft (18) (column 2, lines 53 to 65; column 3, lines 35 to 55; Figure 3).
Thus, it is an objective of the present invention to provide a compact engine for a vehicle which has a small weight and a vehicle, in particular a motorcycle, having said engine.
According to the present invention, this object is solved by an engine for a vehicle as mentioned above, with the improvement that:
According to the invention, since power of the crankshaft is transmitted to the generator through the driven gear connected to one axial end face of the rotor of the generator, the rotor shaft can be formed to be small in diameter and light in weight so as to have a minimum rigidity required to support the rotor for rotation.
Preferably, the driven gear which is disposed on the same axis as the rotor is meshed with a drive gear provided on the crankshaft. Moreover, preferably the generator is disposed rearwardly of and in the vicinity of the crankshaft.
According to a further preferred embodiment, a starter motor for rotating the crankshaft at a time of engine start is provided, the starter motor being coupled to the driven gear. Therein, preferably a clutch for engaging and disengaging the starter motor and the driven gear is provided on a rotary shaft of the rotor.
Additionally, it is preferred that an output gear for driving a propulsion device, in particular a rear wheel, is formed on a crank web on the other end side of the crankshaft as the drive gear.
Further preferably, a transmission is driven by the crankshaft, in particular by the output gear, wherein preferably the transmission and the generator are disposed side by side on one side and on the other side in axial direction of the crankshaft.
Moreover, preferably the engine is a parallel multi-cylinder engine with at least three cylinders.
Still further, preferably the drive gear is formed on a second crank web from one end of the crankshaft, and/or the output gear is formed on a crank web at the other end of the crankshaft, wherein preferably the generator is located on the one end side in an axial direction of the crankshaft with respect to the driven gear, while the transmission is located on the other end side in the axial direction of the crankshaft with respect to a gear meshing with the output gear.
Also, since according to a preferred embodiment, rotation of the starter motor is transmitted to the crankshaft through the driven gear connected to one axial end face of the rotor of the generator, mounting rigidity of parts constituting the transmission path through which rotation of the starter motor is transmitted to the crankshaft is improved and the parts can be formed to be small in size and light in weight.
Therefore, according to a further preferred embodiment, the generator and the transmission allow weight balancing of the engine in the direction of the crankshaft.
Moreover, a layout space for the transmission can be secured while protrusion of the generator on one end side in the axial direction of the crankshaft is kept small. That is, these two components can be disposed rearwardly of the cylinder side by side in the vehicle width direction, without significantly increasing the total width of the engine including these two components. Therefore, both of these components can be disposed in the vicinity of the crankshaft, effecting lowering of the center of gravity of the engine as such.
Further, since the driven gear is connected to one axial end face of the rotor of the generator, the rotor shaft can be formed to be small in size and light in weight.
Therefore, the clutch provided on the rotary shaft of the rotor can be made smaller which also further reduces the overall weight of the engine.
For a vehicle of the above kind, the above object is solved in an inventive manner in that said engine is configured according to at least one of the claims 1 to 9. Thereby, the position of the center of gravity of the vehicle can be lowered and driving abilities of the vehicle can be further improved.
Also, since according to a preferred embodiment rotation of the starter motor is transmitted to the crankshaft through the driven gear connected to one axial end face of the rotor of the generator, mounting rigidity of parts constituting the transmission path through which rotation of the starter motor is transmitted to the crankshaft is improved and the parts can be formed.
Preferably, a crankshaft of the engine has its axis directed in a vehicle width direction.
Thereby, according to a preferred embodiment, the generator and the transmission allow weight balancing of the engine in the vehicle width direction. Therefore, in a vehicle, such as e.g. a motorcycle carrying the engine, according to this invention, the center of gravity can be positioned low and centrally in the vehicle width direction, thereby providing easier driving.
Further preferred embodiments are subject to the subclaims.
In the following, an embodiment of the invention will be described in greater detail with reference to the accompanying drawings, wherein:
In these figures, reference numeral 1 designates an engine for a motorcycle of this embodiment. The engine is a water-cooled, four-stroke and four-cylinder type, and mounted on a body frame (not shown) of the motorcycle, with the axis of a crankshaft 2 parallel to the vehicle width direction. A cylinder 3 of the engine 1 is formed such that its cylinder axis extends obliquely upwardly toward the front from the crankshaft 2.
A crankcase 4 supporting the crankshaft 2 for rotation is formed so as to be divided into a lower crankcase 5 and an upper crankcase 6. In Fig. 1, reference numeral 7 designates a cylinder head, 8 a head cover, and 9 an oil pan.
The crankshaft 2 is provided with crank webs 11-18 at eight locations in the axial direction, as shown in Fig. 2, and configured such that a #2 web 12 second from the left in the figure and a rightmost #8 web 18 constitute gears, respectively.
The gear formed on the #2 web 12 is connected to a generator 21 (described later) and a balancer 22 (see Fig. 1). The balancer 22, not shown in the figure, has a structure in which a balance weight is provided on a rotary shaft extending in the vehicle width direction in front of the crankshaft 2, and a gear on the rotary shaft meshes with the gear formed on the #2 web 12. On the other hand, a rear wheel drive system 23 is connected to the gear formed on the #8 web 18 of the crankshaft 2, as shown in Fig. 2. In this embodiment, a drive gear is constituted by the gear formed on the #2 web 12, while an output gear is constituted by the gear formed on the #8 web 18.
The rear wheel drive system 23 connected to the gear formed on the #8 web 18 has the same construction as that in a conventional engine for a motorcycle. That is, the rear wheel drive system 23 includes: a large reduction gear 24 meshed with the gear formed on the #8web 18; a clutch (not shown) disposed at the right side of and on the same axis as the large reduction gear 24; a multi-stage transmission 25 disposed at the left side of and on the same axis as the large reduction gear 24 and having an input shaft and an output shaft parallel to the input shaft; a chain transmission device (not shown) for transmitting power from the output shaft to a rear wheel; and the like. To the right end of the crankshaft 2 is mounted a sprocket 26 for a timing chain (not shown) for driving a valve drive device to be wound around, as shown in Fig. 2.
The generator 21, as shown in Fig. 1, is disposed rearwardly of and in the vicinity of the crankshaft 2, that is, at a position obliquely rearwardly of and upwardly of the crankshaft 2 and rearwardly of the cylinder 3, with its axis parallel to the crankshaft 2. The mounting position of the generator 21 of this embodiment is set such that the generator 21 and the input shaft portion (forward end) of the transmission 25 are disposed side by side on the left side and on the right side of the vehicle, as shown in Fig. 2.
The generator 21 includes: a driven gear 31 meshed with the gear formed on the #2 web 12; a rotor 32 and a stator 33 located on the left side (left side also in Fig. 3) of the driven gear 31; a rotary shaft 34 supporting the driven gear 31 and the rotor 32; a cover 35 supporting the rotary shaft 34 for rotation in cooperation with the upper crankcase 6; and the like, as shown in Fig. 3. The generator 21 is housed in a generator housing 36 of the upper crankcase 6.
The rotary shaft 34 of the generator 21 is supported, at the right end, on a left vertical wall 6a of the upper crankcase 6 for rotation through a bearing 37, and, at the left end, on the cover 35 for rotation through a bearing 38. The cover 35 is formed, centrally, with a boss 39 for the attachment of the left bearing 38 and the stator 33, and fixed to the upper crankcase 6 with a fixing bolt 40.
The outer peripheral portion of the cover 35 is formed in the shape of a bowl opening rightwardly, and closely attached to the generator housing 36 of the upper crankcase 6 throughout the portion such that the inside and the outside of the cover are defined liquid-tightly. The boss 39 of the cover 35 is formed in the shape of a cylinder; the bearing 38 is fitted in its hollow portion from the left side; and the stator 33 is attached to the right end face from the right side. Also, a cap 41 is screwed in the opening at the left end of the boss 39.
The stator 33 is formed in the shape of a ring having a hollow portion of a larger diameter than that of the rotary shaft 34, and fixed to the boss 39 so as to be inserted in the rotor 32 (described later), with the rotary shaft 34 passing through the hollow portion. Fixing of the stator 33 to the boss 39 is performed by positioning the stator 33 relative to the boss 39 using a knock pin designated by reference numeral 42 in Fig. 3, and screwing a fixing bolt 43 passing through the stator 33 into the boss 39. The knock pin 42 and fixing bolt 43 are provided in a radially inner part of the stator 33 that overlaps with the bearing 38 when viewed in the axial direction of the rotary shaft 34.
The rotary shaft 34 is formed, in its axial center, with an oil passage 44 passing through in the axial direction. The oil passage 44 is connected, at the right end, to an oil chamber 45 of the upper crankcase 6, and oil is supplied from an oil pump (not shown) through the oil chamber 45. Oil supplied into the oil passage 44 is supplied to the supporting portions of the driven gear 31 and a starter gear 47 through a plurality of branched passages 46 extending in radial directions of the rotary shaft 34, and supplied to the bearing 38 from the left end of the oil passage 44 through a space inside the cap 41.
Oil supplied to the bearing 38 flows rightwardly through small clearances between its inner and outer races, between the rotary shaft 34 and boss 39, and between the rotary shaft 34 and stator 33 into the rotor 32. The oil flowing into the rotor 32 further flows through a cutout 32a formed in the outside circumferential portion of the rotor 32 into the housing 36, and returns to the oil pan 9 through an unillustrated passage. This formation of the oil passage 44 allows efficient cooling of the rotor 32 and stator 33 by oil. For the purpose of adopting the foregoing construction, the connecting portion of the stator 33 and cover 35 is configured such that they are in contact with each other throughout the circumferential portion for the prevention of oil leakage.
The rotor 32 of the generator 21 is formed in the shape of a bottomed cylinder opening leftwardly, as shown in Fig. 3, and fixed to the rotary shaft 34 for rotating together therewith, with the rotary shaft 34 press-fitted in a boss 51 in the axial center of the rotor 32. The outside circumferential portion of the rotor 32, to the inside circumferential surface of which a permanent magnet 52 is fixed, has a diameter large enough to accommodate the stator 33.
The boss 51 of the rotor 32 is formed to protrude leftwardly and rightwardly from a bottom wall 53 of the rotor 32 in the shape of a bottomed cylinder. The left end of the boss 51 is in abutment against a stopper 34a formed integrally with the rotary shaft 34 from the right side. Also, a sleeve 55 is connected to the right end of the boss 51 through a spacer 54. These spacer 54 and sleeve 55 are fitted on the rotary shaft 34 for rotation and placed between the bearing 37 supporting the right end of the rotary shaft 34 and the boss 51, to restrict rightward movement of the boss 51.
The driven gear 31 is supported for rotation on the boss 51 of the rotor 32 at the portion protruded rightwardly from the bottom wall 53. The driven gear 31 is connected, at one side on the left side of the vehicle, to the rotor 32 through a damper rubber 56 (described later) such that the rotor 32 moves together with the driven gear 31. On the other hand, the driven gear 31 is provided, at the other side on the right side of the vehicle, with a cylindrical body 57 protruded on the same axis, and the starter gear 47 is connected to the cylindrical body 57 through a one-way clutch 58 mounted inside the cylindrical body 57.
Also, the driven gear 31 is formed integrally, at the outside circumferential portion, with an annular projection 59 protruding leftwardly. The annular projection 59 is fitted for rotation on the outside circumferential portion of the bottom wall 53 of the rotor 32 such that the driven gear 31 is positioned on the same axis as the rotor 32. Further, the driven gear 31 is formed to be smaller in outside diameter than the gear formed on the #2 web 12, as shown in Fig. 1. Therefore, the driven gear 31 rotates at a greater speed than the crankshaft 2.
The damper rubber 56, as is familiar in a conventional shaft joint or the like, is placed between a leftwardly protruded transmission wall 60 provided on the driven gear 31 and a rightwardly protruded transmission wall 61 provided on the bottom wall 53 of the rotor 32. A plurality of the transmission walls 60 of the driven gear 31, not shown in the figure, are arranged radially as seen in the axial direction, and a plurality of the transmission walls 61 of the rotor 32 are respectively arranged between the plurality of the transmission walls 60 of the driven gear 31.
As described above, since the rotor 32 is connected to the driven gear 31 through the damper rubbers 56, shocks transmitted from the driven gear 31 to the rotor 32 can be mitigated by the damper rubbers 56 when the crankshaft 2 abruptly changes its rotational speed.
The starter gear 47 is supported on the sleeve 55 on the rotary shaft 34 for rotation, and a starter motor 63 is connected to the starter gear 47 through an intermediate gear 62 (described later). A boss 64 in the axial center of the starter gear 47 is formed such that its left end extends into the cylindrical body 57 of the driven gear 31. The one-way clutch 58 is placed between the boss 64 and cylindrical body 57. The one-way clutch 58 is adapted to transmit power from the starter gear 47 to the driven gear 31 only. That is, the starter motor 63 is coupled to the driven gear 31 in an interlocking relation therewith through the intermediate gear 62, starter gear 47 and one-way clutch 58.
The boss 64 of the starter gear 47 is positioned between the spacer 54 on the rotary shaft 34 and a spacer 65 on the sleeve 55, and axial movement of the boss 64 is restricted by these two spacers 54 and 65. The spacer 65 on the sleeve 55 is held by a circlip 66 locked on the sleeve 55 for the prevention of slipping out.
The intermediate gear 62 is formed integrally with a small gear 62a meshing with the starter gear 47 and a large gear 62b meshing with a pinion 63a of the starter motor 63, and supported for rotation on the vertical wall 6a of the upper crankcase 6 by a cylindrical support shaft 67 and a fixing bolt 68. The starter motor 63 is disposed upwardly of the crankshaft 2 and centrally in the vehicle width direction, as shown in Fig. 1 and Fig. 2. Rotation of the starter motor 63 is transmitted to the crankshaft 2 through a power transmission system made up of the pinion 63a, intermediate gear 62, starter gear 47, one-way clutch 58, and driven gear 31.
In the engine 1 for a motorcycle as described above, rotation of the crankshaft 2 is transmitted from the #2 web 12 to the driven gear 31 and from the driven gear 31 through the damper rubbers 56 to the rotor 32, to drive the generator 21. At this time, power is transmitted from the transmission walls 60 of the driven gear 31 through the damper rubbers 56 to the transmission walls 61 of the rotor 32. That is, in this engine 1 for a motorcycle, power transmission from the driven gear 31 to the rotor 32 located axially away from the driven gear 31 can be performed without using the rotary shaft 34 of the rotor 32.
Therefore, the rotary shaft 34 can be designed to have a minimum rigidity required to support members (rotor 32, driven gear 31, and the like) provided on the shaft. As a result, the rotary shaft 34 can be formed to be smaller in outside diameter and lighter in weight compared with a rotor shaft of a conventional generator used for power transmission.
Therefore, in the engine 1 for a motorcycle according to this embodiment, the rotary shaft 34 can be made lighter, and weight reduction of the power transmission system can be effected by adopting the construction in which rotation of the crankshaft 2 is transmitted not through a component such as a chain but directly to the generator 21, as described above, so that, in spite of the fact that the generator 21 is positioned relatively high, the center of gravity of the engine itself can be positioned relatively low. As a result, if the engine 1 is mounted at a low position of the motorcycle, lowering of the center of gravity of the vehicle can be effected. Since the engine 1 has the generator 21 provided rearwardly of and in the vicinity of the crankshaft 2, the generator 21 does not cause a decreased bank angle in a motorcycle carrying this engine 1.
Also, since rotation of the starter motor 63 of the engine 1 for a motorcycle according to this embodiment is transmitted to the crankshaft 2 through the driven gear 31 connected to one axial end face of the rotor 32 of the generator 21, mounting rigidity of parts constituting the transmission path through which rotation of the starter motor 63 is transmitted is improved and the parts can be formed to be small in size and light in weight.
Further, in the engine 1 for a motorcycle according to this embodiment, the driven gear 31 of the generator 21 is meshed with the gear formed on the #2 web 12 of the crankshaft 2, while the large reduction gear 24 is meshed with the #8 web 18, and the generator 21 and transmission 25 are provided side by side on one side and on the other side in the vehicle width direction, so that the weight of the engine 1 can be balanced in the vehicle width direction by the generator 21 and transmission 25.
Therefore, in a motorcycle carrying the engine 1 according to this embodiment, the center of gravity can be positioned low and centrally in the vehicle width direction.
In the generator 21 according to this embodiment, the driven gear 31 is formed to be smaller in outside diameter than the gear formed on the #2 web 12 of the crankshaft 2, and the rotor 32 rotates at a greater speed than the crankshaft 2. Since the rotor 32 rotates at a relatively high speed, the generator 21 can be formed such that its rotor 32 and stator 33 have relatively small outside diameters. Therefore, downsizing of the generator 21 can be effected, and the shaft distance between the generator 21 and crankshaft 2 can be decreased without causing interference of the generator 21 with the crankshaft 2. As a result, the engine 1 can be formed with a compact structure as a whole.
The driven gear 31 is connected to the starter motor 63 through the one-way clutch 58, starter gear 47, intermediate gear 62, and the like, so that the engine 1 can be started using the driven gear 31 for transmitting rotation of the crankshaft 2 to the generator 21. Therefore, the number of parts can be reduced compared with when a gear exclusively for starting to which the starter motor is connected is provided on the crankshaft 2.
Also, the driven gear 31 is formed to be smaller in outside diameter than the gear formed on the #2 web 12, and the one-way clutch 58 is placed between the driven gear 31 and starter gear 47, so that a clutch with a relatively small capacity can be used for the one-way clutch 58. This is because, when the driven gear 31 is rotated by the starter motor 63, rotation of the driven gear 31 is reduced in speed to be transmitted to the crankshaft 2.
Since the one-way clutch 58 may be such a clutch with a relatively small capacity, and since the one-way clutch 58 is mounted on the rotary shaft 34 of a small diameter and may be formed to be small in outside diameter, a small-sized one can be used for the one-way clutch 58. Therefore, downsizing of the generator 21 is not prevented by the one-way clutch 58.
Also, the driven gear 31 is connected to the rotor 32 through the damper rubbers 56, and, when the crankshaft 2 has significantly large rotational fluctuations, the shocks are mitigated by the damper rubbers 56, so that the face width of the driven gear 31 can be decreased accordingly. Further, since the annular projection 59 formed on the outside circumferential portion of the driven gear 31 is fitted on the outside circumferential portion of the rotor 32, compared with when the driven gear 31 is supported only at its axially central portion supported for rotation on the boss 51 of the rotor 32 for the prevention of the inclination or the like of the drive gear 31 relative to the shaft 34, the thickness of that portion can be decreased to a relatively small value. Therefore, downsizing of the generator 21 in the axial direction can be effected.
Since no power is transmitted from the rotary shaft 34 to the rotor 32 of the generator 21, a simple construction can be adopted for the mounting structure of the rotor 32 to the rotary shaft 34. In this embodiment, since the rotor 32 is mounted to the rotary shaft 34 by press-fitting, the mounting structure of the rotor 32 can be simplified compared with when a fixing structure is adopted in which the rotor is fitted on a tapered surface on the rotary shaft to be fastened. In addition, since the rotor 32 is positioned on the rotary shaft 34 with the help of the stopper 34a formed integrally with the rotary shaft 34, the spacer 54 and sleeve 55 mounted on the rotary shaft 34, or the like, the rotor 32 can be positioned easily without using a positioning circlip.
Also, the sleeve 55 is fitted on the rotary shaft 34 for rotation and supports the starter gear 47 for rotation, so that, if there is a difference in the number of revolutions between the rotary shaft 34 and starter gear 47, the sleeve 55 rotates in sliding relation to one or both of these members. Therefore, the resistance produced in the sliding surfaces on the inside and outside circumferential sides of the sleeve 55 can be reduced as little as possible. Further, since rightward movement of the starter gear 47 is restricted by the circlip 66 locked on the sleeve 55, it is not necessary to form an annular groove for a circlip in the rotary shaft 34. This can increase rigidity of the rotary shaft 34, allowing the rotary shaft 34 to be even smaller in outside diameter.
Further, since the generator 21 according to this embodiment is arranged such that the bearing 38 supporting the left end of the rotary shaft 34 is press-fitted in the boss 39 of the cover 35 from the left side and the stator 33 is supported by the inside circumferential portion of the boss 39, the stator 33 can be formed to be smaller in outside diameter, effecting downsizing. That is, if a construction is adopted in which the bearing 38 is press-fitted in the boss 39 from the right side, the fixing bolt 43 for fixing the stator 33 to the boss 39 must be provided radially further outwardly than the bearing 38 and the outside diameter of the stator 33 must be increased accordingly. However, in this embodiment, the fixing bolt 43 can be positioned radially inwardly such that the fixing bolt 43 overlaps with the bearing 38 when viewed in the axial direction, allowing the stator 33 to be relatively small in diameter.
Also, since this generator 21 is formed with an oil passage 44 inside the rotary shaft 34, oil can be supplied easily to members (driven gear 31, damper rubbers 56, starter gear 47, one-way clutch 58, and the like) on the rotary shaft 34. Further, since the generator 21 according to this embodiment is arranged such that oil flows from the oil passage 44 through the left bearing 38 to the stator 33, the bearing 38 and stator 33 can be cooled by oil.
Also, since the generator 21 is rotated at an increased speed, its diameter can be decreased for a required output, allowing the generator 21 to be placed in the vicinity of the crankshaft 2. Since a generator is located higher than a crankshaft, in general, the foregoing placement of the generator 21 in the vicinity of the crankshaft 2 allows lowering of the center of gravity. Further, since rotation of the driven gear 31 is reduced in speed to be transmitted to the crankshaft 2 at the time of engine start, the capacity of the starter clutch (not shown) can be decreased, allowing downsizing. That is, members disposed higher than the crankshaft 2 are decreased in size and weight, so that further lowering of the center of gravity can be effected.
In this embodiment, the drive gear is formed on the second crank web 12 from one end of the crankshaft 2, while the output gear is formed on the crank web 18 at the other end of the crankshaft 2; and the generator 21 is located on the one end side in the axial direction of the crankshaft 2 with respect to the driven gear 31, while the transmission 25 is located on the one end side in the axial direction of the crankshaft 2 with respect to the gear meshing with the output gear. In general, a transmission is greater than a generator in dimension in the vehicle width direction. Therefore, in this embodiment, a layout space for the transmission 25 can be secured while protrusion of the generator 21 on the one end side in the axial direction of the crankshaft is kept small. That is, these two components can be disposed rearwardly of the cylinder side by side in the vehicle width direction, without significantly increasing the total width of the engine including these two components. Therefore, both of these components can be disposed in the vicinity of the crankshaft 2, effecting lowering of the center of gravity.
Of course, the vehicle of this invention is not restricted to a motorcycle. Any kind of vehicle, in particular straddle type vehicles such as snow mobiles, water jets or the like are comprised in the invention.
As described above, an engine for a vehicle, in particular a motorcycle, is proposed having a crankshaft with its axis directed in a vehicle width direction, a generator driven by the crankshaft, and a starter motor for rotating the crankshaft at the time of engine start, in which the generator is disposed rearwardly of and in the vicinity of the crankshaft; a driven gear disposed on the same axis as a rotor of the generator is connected to one axial end face of the rotor, in an interlocking relation with the rotor; a drive gear provided on the crankshaft is meshed with the driven gear; and the starter motor is coupled to the driven gear in an interlocking relation therewith.
Therein, the drive gear is formed on a crank web on one end side of the crankshaft, while an output gear with which a transmission for driving a rear wheel is meshed is formed on a crank web on the other end side of the crankshaft, and the transmission and the generator are disposed side by side on one side and on the other side in the vehicle width direction.
Moreover, the engine is a preferably parallel multi-cylinder engine with no less than three cylinders; the drive gear is formed on a second crank web from one end of the crankshaft, while an output gear is formed on a crank web at the other end of the crankshaft; and the generator is located on the one end side in an axial direction of the crankshaft with respect to the driven gear, while a transmission is located on the one end side in the axial direction of the crankshaft with respect to a gear meshing with the output gear.
Also, a clutch for engaging and disengaging the starter motor and the driven gear is provided on a rotary shaft of the rotor.
As further described above, in order to provide an engine for a motorcycle allowing the position of the center of gravity of the motorcycle to be lowered, it is proposed that a generator 21 is disposed rearwardly of and in the vicinity of the crankshaft 2. A driven gear 31 disposed on the same axis as a rotor 32 of the generator 21 is connected to one axial end face of the rotor 32, in an interlocking relation with the rotor 32. A drive gear provided on the crankshaft 2 is meshed with the driven gear 31. A starter motor 63 is coupled to the driven gear 31 in an interlocking relation therewith.