Title of Invention

"A POWER UNIT FOR A MOTORCYCLE"

Abstract

A power unit for a motorcycle, said: power unit (P) with its front portion swingably supported by a body frame (F), said power unit (P) having an engine (E) disposed in front of a rear wheel (WR); a transmission case (84) continuous to a crank case (28) of said engine (E) and extending on one side of said rear wheel (WR); and a transmission means (17) contained in said transmission case (84) disposed between said rear wheel (WR) rotatably supported by a rear portion of said transmission case (84) and one end of a crank shaft (27) of said engine (E); and a starter/generator (18) connected to the other end of said crank shaft (27); characterized in that said starter/genera tor (18) is connected to said crank shaft (27) in such a manner as to be disposed outside a side end, opposed to said transmission case (84) , of said rear wheel (WR).

Full Text

The present invention relates to a power unit for a motorcycle: said power unit with its front portion swingably supported by a body frame, said power unit having an engine disposed in front of a rear wheel; a transmission case continuous to a crank case of said engine and extending on one side of said rear wheel; and a transmission means contained in said transmission case and disposed between said rear wheel rotatably supported by a rear portion of said transmission case and one end of a crank shaft of said engine; and a starter/generator connected to the other end of said crank shaft; characterized in that said starter/generator is connected to said crank shaft in such a manner as to be disposed outside a side end, opposed to said transmission case, of said rear wheel. [Prior Art] A vehicle in which a starter/generator is connected to a crank shaft of an engine of a power unit swingably supported by a body frame has been known, for example, from Japanese Patent Laid-open No. Eei 8-175473. [Problem to be Solved by the Invention] The starter/generator has a function as a starter motor for rotating a crank shaft of an engine upon starting of the engine, and a function as a generator driven by a rotational power of the crank shaft. With respect to the function as the starter, since a torque required to start the engine varies depending on the kind of engine mounted on a motorcycle, the performance required for the function as the starter motor differs depending on the kind of engine and also the shape of the starter/generator varies depending on the kind of engine. Meanwhile, in a motorcycle of a type in which a power unit is swingably supported by a body frame, a crank shaft of an engine disposed in front of a rear wheel is close to the rear wheel. Accordingly if the arrangement of the starter/generator is changed, the power unit must be designed to avoid the interference between the starter/generator and the rear wheel depending on the kind of engine, or the rear wheel must be shifted rearwardly in order to be separated apart from the starter/generator, thereby causing extension of the wheel base. In view of the foregoing, the present invention has been made, and a first object of the present invention is to provide a motorcycle capable of certainly preventing interference between a starter/generator and a rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. The motorcycle with a hybrid type power unit has been known, for example, from Japanese Patent Laid-open No.Hei8-175473.supply smeller equivalent The above-described prior art motorcycle, in which a motor is connected to the axle of a rear wheel in such a manner as to put the rear wheel between the power unit and the motor, has a problem. Since the motor which is relatively heavy is connected to the axle of the rear wheel, that is, the heavy substance is applied to a position separated rearwardly from a swinging fulcrum of the power unit, a non-suspended weight of a rear cushion provided between a body frame and the rear wheel is increased, tending to degrade the riding comfort and steering stability. In view of the foregoing, the present invention has been made, and a second object of the present invention is to provide a motorcycle with a hybrid type power unit, wherein the power unit is configured in such a manner as to prevent a motor from exerting adverse effect on the swinging characteristic of the power unit. [Means for Solving the Problem] To achieve the above first object, according to an invention described in claim 1, there is provided a motorcycle including: a power unit with its front portion swingably supported by a body frame, the power unit including an engine disposed in front of a rear wheel; a transmission case continuous to a crank case of the engine and extending on one side of the rear wheel; and a transmission means contained in the transmission case in such a manner as to be disposed between the rear wheel rotatably supported by a rear portion of the transmission case and one end of a crank shaft of the engine; and a starter/generator connected to the other end of the crank shaft; wherein the starter/generator is connected to the crank shaft in such a manner as to be disposed outside a side end, opposed to the transmission case, of the rear wheel. With this configuration, since the starter/generator is disposed outside the rear wheel irrespective of the kind of engine, it is possible to certainly prevent interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. iOJHrU According to an invention described in claim 2, in addition to the configuration of the invention described in claim 1, the engine is a four-cycle engine. 4Q-e±2T Incidentally, a four-cycle engine has a cylinder head longer than that of a two-cycle engine in the direction along the axial line of the cylinder. In a motorcycle on which the four-cycle engine is mounted, since the wheel base is larger than that of a motorcycle on which the two-cycle engine is mounted and a starting torque required for starting the four-cycle engine is larger than that of the two-cycle engine, the starter/generator must be enlarged. Accordingly, by applying the invention described in claim 1 to the motorcycle on which the four-cycle engine is mounted in accordance with the configuration described in claim 2, it is possible to significantly achieve the effect of certainly preventing interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. According to an invention described in claim 3, in addition to the configuration of the invention described in claim 2, the engine is mounted with its cylinder axial line directed substantially in the horizontal direction. With this configuration, it is possible to significantly achieve the effect of certainly preventing interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. To achieve the above second object, according to an invention described in claim 4, there is provided a motorcycle with a hybrid type power unit characterized in that the output of the engine is assisted by the starter/generator. With this configuration, since the motor is connected to a portion, near a swinging fulcrum of the power unit, of the crank shaft, the power unit can be configured in such a manner as to prevent the non-suspended weight of a rear cushion from being increased. This makes it possible to improve the riding comfort and the steering stability by preventing the motor from exerting adverse effect on the swinging characteristic of the power unit. According to an invention described in claim 5, in addition to the configuration of the invention described in claim 4, the motorcycle with a hybrid type power unit further includes a control unit for controlling the operations of the engine and the motor in such a manner as to stop the engine upon stopping of the motorcycle and start the engine upon starting the movement of the motorcycle, and to operate the motor for a specific time upon starting the movement of the motorcycle. With this configuration, it is possible to control the stopping/starting of the engine in accordance with the stopping/starting the movement of the motorcycle and hence to efficiently operate the engine while preventing useless fuel consumption and emission of exhaust gas. Further, it is possible to readily start the motorcycle by imparting an assist force generated by the motor to the output of the engine upon acceleration for starting the movement of the motorcycle. According to an invention described in claim 6, in addition to the configuration of the invention described in claim 4 or 5, the motor is capable of imparting a starting torque to the engine upon starting of the engine. With this configuration, the motor can be used not only as an assist motor for assisting the output of the engine but also as a starter motor. [Brief Description of the Drawings] [Fig. 1] Fig. 1 is a side view of a scooter type motorcycle in a first embodiment. (Fig. 2] Fig. 2 is a sectional view, taken along line 2-2 of Fig. 1, showing a power unit. [Fig. 3] Fig. 3 is an enlarged sectional view of an engine and a compressor shown in Fig. 2. [Fig. 4] Fig. 4 is an enlarged sectional view taken on line 4-4 of Fig. 3. [Fig. 5] Fig. 5 is a diagram showing opening/closing timings of an intake valve, an exhaust valve, and a supercharging valve. [Fig. 6] Fig. 6 is an enlarged sectional view of a starter/generator shown in Fig. 2. [Fig. 7] Fig. 7 is a circuit diagram showing a configuration of an electric circuit associated with a commutator of a rotating electrical machine. [Fig. 8] Fig. 8 is a circuit diagram showing a connection state of the commutator and brushes. [Fig. 9] Fig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 6. [Fig. 10] Fig. 10 is a view showing a state in which a weight roller is tilted in a containing recessed portion. [Fig. 11] Fig. 11 is a diagram showing a control system for the engine and the rotating electrical machine. [Fig. 12(a), 12 (b) and 12(c)] Fig. 12(a) , 12 (b) and 12(c) are Diagrams showing changes in throttle opening, rotational speed of a crank shaft, and output torque of the crank shaft with elapsed time upon starting of the engine. [Fig. 13] Fig. 13 is a diagram showing a relationship between the output of a motor, an engine rotational speed, and a throttle opening upon impartment of an assist torque. [Figs. 14(a), 14(b) and 14(c)] Figs. 14 (a), 14(b) and 14 (c) are diagrams showing changes in throttle opening, rotational speed of a crank shaft, and output torque of the crank shaft with elapsed time upon impartment of an assist torque. [Fig. 15] Fig. 15 is a circuit diagram, similar to Fig. 7, showing a second embodiment. [Fig. 16] Fig. 16 is a sectional view, similar to Fig. 2, showing a power unit in a third embodiment. [Fig. 17] Fig. 17 is an enlarged view showing an essential portion shown in Fig. 16. [Mode for Carrying Out the Invention] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figs. 1 to 14 show a first embodiment of the present invention, wherein Fig. 1 is a side view of a scooter type motorcycle; Fig. 2 is a sectional view, taken on line 2-2 of Fig. 1, showing a power unit; Fig. 3 is an enlarged sectional view of an engine and a compressor shown in Fig. 2; Fig. 4 is an enlarged sectional view taken on line 4-4 of Fig. 3; Fig. 5 is a diagram showing opening/closing timings of an intake valve, an exhaust valve, and a supercharging valve; Fig. 6 is an enlarged sectional view of a starter/generator shown in Fig. 2; Fig. 7 is a circuit diagram showing a configuration of an electric circuit associated with a commutator of a rotating electrical machine; Fig. 8 is a circuit diagram showing a connection state of the commutator and brushes; Fig. 9 is an enlarged sectional view taken on line 9-9 of Fig. 6: Fig. 10 is a view showing a state in which a weight roller is tilted in a containing recessed portion; Fig. 11 is a diagram showing a control system for the engine and the rotating electrical machine; Figs. 12 (a) , 12 (b) and 12 (c) are diagrams showing changes in throttle opening, rotational speed of a crank shaft, and output torque of the crank shaft with elapsed time upon starting of the engine; Fig. 13 is a diagram showing a relationship between the output of a motor, an engine rotational speed, and a throttle opening upon impartment of an assist torque; and Figs. 14 (a), 14(b) and 14 (c) are diagrams showing changes in throttle opening, rotational speed of a crank shaft, and output torque of the crank shaft with elapsed time upon impartment of the assist torque. Referring first to Fig. 1, a body frame F of the scooter type motorcycle in this embodiment includes a head pipe 12 for steerably supporting a front fork 11 from which a front wheel WF is suspended; a down tube 13 extending downwardly from the head pipe 12; and a rear frame 14 extending rearwardly from the lower end of the down tube 13. The rear frame 14 includes a pair of front frames 14a extending rearwardly from the lower end of the down tube 13 substantially in the horizontal direction; a pair of intermediate frames 14b extending rearwardly, upwardly from the rear ends of the front frames 14a; and a rear frame 14c for connecting the rear ends of the intermediate frames 14b to each other. The frames 14a, 14b and 14c form an approximately elliptic shape in a plan view. The body frame F is covered with a body cover 15 having a floor board 15a for supporting the feet of a driver, and a seat 16 on which the driver is to be sit is provided on the rear portion of the body cover 15. The front portion of a power unit P is supported by the intermediate frames 14b of the rear frame 14 in such a manner as to be swingably supported around an axis parallel to a rotational axis of a rear wheel WR, and the rear wheel WR is rotatably supported by the rear portion of the power unit P. Referring to Fig. 2, the power unit P includes a water-cooled type four-cycle/single-cylinder engine E disposed in front of the rear wheel WR, a transmission means 17 provided between the engine E and the rear wheel WR, and a starter/generator 18 connected to the engine E. As seen best in Figs. 3 and 4, a cylinder block 20 of the engine E is disposed such that the axial line of a cylinder 21 provided in the cylinder block 20 extends substantially, horizontally along the longitudinal direction of the motorcycle. A combustion chamber 24 is formed between a cylinder head 22 connected to the cylinder block 20 and a piston 23 slidably fitted in the cylinder 21. The piston 23 is connected to a crank shaft 27 having the rotational axis parallel to the rotational axis of the rear wheel WR via a connecting rod 25 and a crank pin 26 . The crank shaft 27 is rotatably supported by a crank case 28 integrally formed on the cylinder block 20 via first and second ball bearings 29 and 30. The cylinder head 22 has an intake port 31, an exhaust port 32, and supercharging port 33 which are connected to the combustion chamber 24. An intake valve 34 and an exhaust valve 35 for opening/closing the intake port 31 and the exhaust port 32 respectively are mounted in the cylinder head 22 in such a manner as to be arranged in an approximately V-shape on a view projected on plane containing the rotating axis of the crank shaft 27 and the axial line of the cylinder 21. A supercharging valve 36 for opening/closing the supercharging port 33 and an ignition plug 37 facing to the combustion chamber 24 are mounted in the cylinder head 22 in such a manner as to be arranged in an approximately V-shape in the direction substantially perpendicular to an arrangement line of the intake valve 34 and the exhaust valve 35. These intake valve 34, the exhaust valve 35 and the supercharging valve 36 are biased by springs in the direction where they close the intake port 31, the exhaust port 32, and the supercharging port 33, respectively. One end of a valve system cam shaft 38, having the axial line parallel to the axial line of the crank shaft 27, is rotatably supported by the cylinder head 22 via a third bearing 39. An intermediate portion of the valve system cam shaft 38 in the longitudinal direction is also rotatably supported by the cylinder head 22 via a fourth ball bearing 40. The valve system cam shaft 38 is provided with an intake cam 41 and an exhaust cam 42 disposed between the third and fourth ball bearings 39 and 40, and with a supercharging cam 43 disposed outside the fourth ball bearing 40. The intake cam 41 and the exhaust cam 42 are engaged with the intake valve 34 and the exhaust valve 35 via an intake rocker arm 44 and an exhaust rocker arm 45, respectively, and the supercharging cam 43 formed into a taper shape is directly engaged with the supercharging valve 36. A driven sprocket 48 is fixed on the valve system cam shaft 38 on the side opposed to the fourth ball bearing 40 at a position adjacent to the supercharging cam 43. On the other hand, a drive sprocket 49 is fixed on the crank shaft 27 on the outside of the second ball bearing 30 at a position corresponding to that of the driven sprocket 48. An endless cam chain 50 is wound around the drive sprocket 49 and the driven sprocket 48. With these drive sprocket 49, the driven sprocket 48 and the cam chain 50, the valve system cam shaft 38 is rotated at a rotational number being half that of the crank shaft 27. Thus, the intake valve 34, the exhaust valve 35, and the supercharging valve 36 are opened/closed with timings shown in Fig. 5, and the supercharging valve 36 is opened directly before the intake valve 34 is sit to be closed. [0026] A containing chamber 51 for containing the drive sprocket 49, the driven sprocket 48 and the cam chain 50 is formed in both the cylinder block 20 and the cylinder head 22. An opening 52 is formed at a portion, facing to the other end of the valve system cam shaft 38, of the cylinder head 22 in such a manner as to be opened to the containing chamber 51. The opening 52 is blocked with a cover member 53. An opening 54 is formed at a portion, facing to the crank shaft 27, of the crank case 28 in such a manner as to be opened to the containing chamber 51. The opening 54 is blocked with the starter/generator 18. [0027] In the containing chamber 51, a drive gear 55 is fixed on the crank shaft 27 at a position between the drive sprocket 49 and the second ball bearing 30, and an oil pump (not shown) is driven by the drive gear 55. [0028] An intake device 58 (see Fig. 1) containing an air cleaner 66 and a carburetor 57 is connected to the intake port 31; an exhaust device (not shown) is connected to the exhaust port 32; and a reciprocating type compressor 60 is connected to the supercharging port 33. The compressor 60, driven by the valve system cam shaft 38, is disposed adjacent to the outer side of the cover member 53 connected to the cylinder head 22 in such a manner as to block the opening 52 of the containing chamber 51. [0029] The compressor 60 has a cylinder body 62 having a cylinder hole 61 extending in parallel to the axial line of the cylinder 21 of the engine E; first and second pump cylinder heads 63 and 64 connected to the cylinder body 62 in such a manner as to close both ends of the cylinder hole 61; and a pump piston 67 slidably fitted in the cylinder hole 61 in such a manner as to form a first pump chamber 65 between the first pump cylinder head 63 and the pump piston 67 and to form a second pump chamber 66 between the second pump cylinder head 64 and the pump piston 67. [0030] A pump crank shaft 68 having the same rotational axial line as that of the valve system cam shaft 38 of the engine E is rotatably supported by an intermediate portion of the cylinder body 62 in the axial direction via fifth and sixth ball bearings 69 and 70. One end of the pump crank shaft 68, rotatably passing through the cylinder body 62 and the cover member 53, is connected to the other end of the valve system cam shaft 38 in the containing chamber 51 in such a manner as to be coaxial with the valve system cam shaft 38 and not to be rotated relative to the valve system cam shaft 38. In other words, the pump crank shaft 68 is rotated with the valve system cam shaft 38. An annular seal member 71 is provided between the cover member 53 and the pump crank shaft 68. [0031] The pump piston 67 is connected to the pump crank shaft 68 via a connecting rod 72. The pump piston 67 has an operational hole 73 for allowing the pump crank shaft 68 to pass there through in such a manner as not to interfere with the reciprocating operation of the pump piston 67 accompanied by the rotation of the pump crank shaft 68. [0032] Annular discharge chambers 74 and 75 are provided in the first and second pump cylinder heads 63 and 64, respectively, and suction chambers 76 and 77 are provided in such a manner as to be surrounded by the discharge chambers 74 and 75, respectively. Both the discharge chambers 74 and 75 are communicated to each other and also both the suction chambers 76 and 77 are communicated to each other. [0033] Both the suction chambers 76 and 77 are communicated to the intake device 58. Suction valves (not shown), which are opened when the pressures of the pump chambers 65 and 66 are reduced, are provided between the suction chambers 76 and 77 and the pump chambers 65 and 66, and discharge valves (not shown), which are opened when the pressures of the pump chambers 65 and 66 are increased, are provided between the discharge chambers 74 and 75 and the pump chambers 65 and 66. A discharge conduit 78 with one end communicated to one of the discharge chambers 74 and 65 (for example, the discharge chamber 74) is provided between the pump cylinder heads 63 and 64, and the other end of the discharge conduit 78 is communicated to one end of a discharge passage 79 provided in the second pump cylinder 64. A conduit portion 81 forming a passage 80 communicated to the other end of the discharge passage 79 is integrally formed in the cover member 53 for blocking the opening 52. The conduit portion 81 is air-tightly fitted to the cylinder head 22 of the engine E in such a manner that the other end of the passage 80 is communicated to the supercharging port 33. [0034] With this reciprocating type compressor 60, air is forced from the supercharging port 33 into the combustion chamber 24 in accordance with opening of the supercharging valve 36 directly before the intake valve 34 is sit to be closed upon operation of the engine E. As a result, the filling efficiency is improved to increase the output torque of the engine E. [0035] Referring again to Fig. 2, a transmission case 84 extending on the left side of the rear wheel WR in a state in which the motorcycle is directed forwardly in the running direction is connected to the crank case 28 of the engine E. The transmission case 84 includes a case main body 85 connected to the crank case 28; a left cover 86 fastened from left to the case main body 85 to form a first transmission chamber 88 between the case main body 85 and the left cover 86; and a right cover 87 fastened to the rear right portion of the case main body 85 to form a second transmission chamber 89 between the case main body 85 and the right cover 87. [0036] A supporting arm 90 projects from the front portion of the case main body 85 of the transmission case 84 in such a manner as to be disposed on one side of the cylinder block 20 of the engine E. The supporting arm 90 is swingably supported by the intermediate frames 14b of the rear frame 14 of the body frame F. [0037] An axle 91 of the rear wheel WR is rotatably supported by the rear portion of the case main body 85 and the right cover 87 of the transmission case 84. As shown in Fig. 1, a rear cushion 92 is provided between the rear portion of the case main body 85 and the intermediate frames 14b of the rear frame 14 of the body frame F. [0038] The transmission means 17 provided between the engine E and the rear wheel WR includes a V-belt type continuously variable transmission 93 contained in the first transmission chamber 88 and a reduction gear train 94 provided between the continuously variable transmission 93 and the axle 91. [0039] The continuously variable transmission 93 includes a drive side transmission pulley 95 connected to one end of the crank shaft 27; a driven side transmission pulley 98 mounted around a driven shaft 96 via a centrifugal clutch 97; and an endless V-belt 99 wound around both the transmission pulleys 95 and 98. In addition, the driven shaft 96, having the axial line parallel to the crank shaft 27, is rotatably supported by both the rear portion of the case main body 85 and the right cover 87. [0040] The drive side transmission pulley 95 includes a fixed pulley half 95b fixed around the crank shaft 27 and a movable pulley half 95a axially slidably mounted around the crank shaft 27. A V-shaped annular groove 100 is formed between both the pulley halves 95a and 95b, and the V-belt 99 is inserted in the annular groove 100. A ramp plate 101 is fixed to the crank shaft 27 on the back side of the movable pulley half 95a, and a plurality of weight rollers 102 are contained between the movable pulley half 95a and the ramp plate 101 in a floating state. As the rotational speed of the crank shaft 27 is increased, the weight rollers 102 are moved radially outwardly from the crank shaft 27 due to the centrifugal forces applied thereto, to make the movable pulley half 95a closer to the fixed pulley half 95b. As a result, the contact radius of the V-belt 99 with both the pulley halves 95a and 95b becomes large. [0041] The driven side transmission pulley 98 includes a supporting cylinder 103 connected to the driven shaft 96 via a centrifugal clutch 97 and rotatably supported by the driven shaft 96; a fixed pulley half 98a integrally formed on the supporting cylinder 103; and a movable pulley half 98b which is supported by the supporting cylinder 103 in such a manner as to be movable close to or apart from the fixed pulley half 98a and which is biased by a spring toward the fixed pulley half 98a. The V-belt 99 is inserted in a V-shaped annular groove 104 formed between both the pulley halves 98a and 98b. As the contact radius of the V-belt 99 with the drive side transmission pulley 95 becomes large, the movable pulley half 98b is moved in the axial direction such that the contact radius of the V-belt 99 with the driven side transmission pulley 98 becomes small. In this way, the continuously variable transmission between the crank shaft 27 and the driven shaft 96 is performed on the basis of the rotation of the crank shaft 27. [0042] A kick shaft 106 is rotatably supported by the left cover 86 of the transmission case 84, and a kick pedal 105 (see Fig. I) is provided at the outer end of the kick shaft 106. A kick type starter 107 for transmitting a power of the kick shaft 106 to the crank shaft 27 in accordance with the activation of the kick pedal 105 is provided on the inner surface side of the left cover 86 at a position between the kick shaft 106 and the crank shaft 27. [0043] The reduction gear train 94 is provided between the driven shaft 96 and the axle 91 and is contained in the second transmission chamber 89. The rotational power of the driven shaft 96 of the continuously variable transmission mechanism 93 is reduced by the reduction gear train 94 and is transmitted to the axle 91 of the rear wheel WR via the reduction gear train 94. [0044] The starter/generator 18 includes a rotating electrical machine 110 and a centrifugal governor 111. The starter/generator 18 is connected to the other end of the crank shaft 27 of the engine E, that is, connected to the end, opposed to the side to which the continuously variable transmission mechanism 93 of the transmission means 17 is connected, of the crank shaft 27. To be more specific, the starter/generator 18 is disposed outside the side end, opposed to the transmission case 84, of the rear wheel WR. [0045] The function of the rotating electrical machine 110 is switchable among a function as a starter motor for imparting a starting torque to the engine E, a function as an assist motor for imparting an assist torque to the engine E, and a function as a generator driven by a power of the engine E. The power unit P is of a hybrid type including the engine E, the transmission means 17, and the motor (rotating electrical machine 110) for assisting the output of the engine E. [0046] Referring to Fig. 6, the rotating electrical machine 110 includes an inner rotor 112 fixed to the other end of the crank shaft 27, an outer stator 113 surrounding the inner rotor 112, a commutator 114 fixedly supported by the outer stator 113, and a brush assembly 115 disposed between the commutator 114 and the inner rotor 112 and biased by a spring toward the commutator 114 . [0047] The inner rotor 112 includes a rotor boss 116 and a magnet 117 provided around the outer periphery of the rotor boss 116. A taper shaft 27a coaxially provided to the other end of the crank shaft 27 is fitted in the rotor boss 116. The rotor boss 116 is fixed to the other end of the crank shaft 27 by screwing a nut 118 in the leading end, projecting from the rotor boss 116, of the crank shaft 27. A rotor cover 119 for covering the magnet 117 is fixed to the rotor boss 116. [0048] The outer stator 113 includes a stator core 120 and coils 121 of, for example, a single-phase/six-pole type are wound around the stator core 120. The stator core 120 is fixed to a stator case 122. The stator case 122 is formed into a bowl shape in such a manner as to cover a portion, positioned inside the stator core 120 in the axial line direction of the crank shaft 27, of the coils 121, the commutator 114, and the brush assembly 115. The stator case 122 is fastened to the crank case 28 such that the opening 54 provided in the crank case 28 of the engine E is blocked with an end wall 122a of the stator case 122. The crank shaft 27 rotatably passes through a central opening of the end wall 122a of the stator case 122, and an annular seal member 123 is provided between the inner periphery of the central opening of the end wall 122a and the outer periphery of the crank shaft 27. [0049] The commutator 114 includes a commutator holder 124 which is formed from a non-conductive material such as a synthetic resin into an approximately disk shape and which has at its central portion a through-hole 124 allowing the crank shaft 27 to loosely pass therethrough. As shown in Fig. 7, a first annular conductive passage 125; a second annular conductive passage 126 coaxially surrounding the first conductive passage 125; and commutator pieces 27 of the number corresponding to that of poles of the coils 121, for example, six pieces, which are spaced at equal intervals around the second conductive passage 126, are provided on the surface, opposed to the brush assembly 115, of the commutator holder 124. The commutator holder 124 is disposed in proximity to the inner surface of the end wall 122a of the stator case 122, and is fixedly supported by the stator core 120. [0050] The first conductive passage 125 is connected to a minus terminal of a battery 128, and a second conductive passage 126 is connected to a plus terminal of the battery 128 via a relay switch 131. Each of the commutator pieces 127 is connected to a connection point between adjacent two of the coils 121 having respective poles in the outer stator 113. [0051] A relay coil 132 and a stator switch 129 are connected in series between the plus side terminal and the minus side terminal of the battery 128. The relay coil 132 and the relay switch 131 constitute a stator relay 130. That is to say, the relay switch 131 is made conductive in accordance with excitation of the relay coil 132 due to conduction of the relay switch 129. [0052] The brush assembly 115 includes a brush holder 133 made from a non-conductive material. The brush holder 133 is disposed between the commutator 114 and the inner rotor 112 in such a manner as to be rotatable around the axial line of the crank shaft 27 together with the inner rotor 112 and to be reciprocatingly movable in the axial line of the crank shaft 27. A coil shaped spring 134 surrounding the crank shaft 27 is provided between the brush holder 133 and the rotor boss 116 of the inner rotor 112. The brush holder 133, that is, the brush assembly 115 is biased toward the commutator 114 by the elastic force of the spring 134. [0053] As seen best in Fig. 8, a minus side common brush 135, three minus side individual brushes 136, a plus side common brush 137, and three plus side individual brushes 138 are held on the brush holder 133 while being biased toward the commutator 114 by springs. The minus side common brush 135 is usually in slide-contact with the first conductive passage 125 of the commutator 114. The minus side individual brushes 136 are commonly connected to the minus side common brush 135 and are allowed to be in slide-contact with the commutator pieces 127 of the commutator 114. The plus side common brush 137 is usually in slide-contact with the second conductive passage 126 of the commutator 114. The plus side individual brushes 138 are commonly connected to the plus side common brush 137 and are allowed to be in slide-contact with the commutator pieces 127 of the commutator 114. [0054] Referring again to Fig. 6, the centrifugal governor 111 includes a rotating body 140 integrally formed on the rotor boss 116 of the inner rotor 112 to be thus fixed to the crank shaft 27, a moving body 141 disposed opposite to the rotating body 140, and a plurality of weight rollers 142 interposed between the rotating body 140 and the moving body 141. [0055] As seen best in Fig. 9, the rotating body 140 is integrally formed on a portion, opposed to the brush assembly 115, of the rotor boss 116. A cylindrical portion 143 disposed coaxially with the crank shaft 27, a circular recessed portion 144 surrounding the cylindrical portion 143, an annular groove 145 opened to the inner peripheral edge of the recessed portion 144 and continuous to the outer surface of the cylindrical portion 143 at the same level, and containing recessed portions 146 disposed at a plurality (for example, six pieces) of locations spaced at equal intervals in the peripheral direction of the recessed portion 144, are provided on the outer end surface of the rotating body 140, that is, on the surface, opposed to the brush assembly 115, of the rotating body 140. [0056] The cylindrical portion 143 has an inside diameter allowing a nut 118 to be screwed in the other end of the crank shaft 27 to pass therethrough. The nut 118 is screwed in the other end of the crank shaft 27 in the cylindrical portion 143. [0057] Each containing recessed portion 146 extends from the annular groove 145 along the radial direction of the rotating body 140 in such a manner as to be made shallower as nearing the outer side of the rotating body 140 in the radial direction. [0058] The moving body 141 includes a guide cylinder portion 147 fitted in the annular groove 145 of the rotating body 140 in such a manner as to be slidable along the axial line direction of the crank shaft 27, and a disk-like contact plate portion 148 protruded radially outwardly from the outer end of the guide cylinder portion 147 and contained in the recessed portion 144 of the rotating body 140. The contact plate portion 148 of the moving body 141 is opposed to the rotating body 140. [0059] One ends of a plurality (for example, pair) of connecting shafts 149 having axial lines parallel to the crank shaft 27 and passing through the rotating body 140 and the rotor boss 116 are connected to the brush holder 133 of the brush assembly 115, and the other ends of the connecting shafts 149 are connected to the contact plate portion 148 of the moving body 141. Accordingly, the contact plate portion 148, that is, the moving body 141 is not rotatable relative to the rotating body 140, that is, the inner rotor 112, but are movable close to or apart from the rotating body 140 in the axial line direction of the crank shaft 27 . Since the brush holder 133 is biased toward the fixed commutator 114 by a spring 134, the moving body 141 is also elastically biased to the rotating body 140. [0060] Short-column shaped weight rollers 142 are contained in the containing recessed portions 146 in such a manner as to be interposed between the rotating body 140 and the contact plate portion 148 of the moving body 141. The containing recessed portions 146 are provided in one of the opposed surface portions of the rotating body 140 and the moving body 141 (the bpposed surface portion, to the moving body 141, of the rotating body 140 in this embodiment) at a plurality, for example, six pieces of locations spaced at intervals in the peripheral direction. [0061] In such a centrifugal governor lli, as the centrifugal forces applied to the weight rollers 142 are increased depending on the rotation of the crank shaft 27 and the rotating body 140, the weight rollers 142 are moved in the containing recessed portions 146 radially outwardly of the rotating body 140. In this case, since the depth of each containing recessed portion 146 becomes shallower as nearing the outer side of the rotating body 140 in the radial direction, the moving body 141 is pushed by the weight rollers 142 to be moved apart from the rotating body 140. Accordingly, when the rotational speed of the crank shaft 27 comes to not less than a specific value less than an idling rotational speed, the brush assembly 115 is moved apart from the commutator 114, so that the brushes 135, 136, 137 and 138 are moved apart from the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 of the commutator 114. [0062] Since the weights of the weight rollers 142 are set such that the brushes 135, 136, 137 and 138 are moved apart from the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 by the centrifugal forces applied to the weight rollers 142 when the rotational speed of the engine E comes to not less than the specific value less than the idling rotational speed, the outside diameter of each weight roller 142 is relatively small. [0063] When the outside diameter of the weight roller 142 is relatively small as described above, a slight gap is formed between each end of the weight roller 142 and each inner side surface of the containing recessed portion 146 as shown in Fig. 10, with a result that the weight roller 142 is liable to be tiled in the containing recessed portion 146. In the case where the weight roller 142 is tilted in the containing recessed portion 146, if outer edges of both the ends of the weight roller 142 are not chamfered or chamfered in taper shapes, there may occur a problem that the outer edges of the both the ends of the weight roller 142 bite the inner side surfaces of the containing recessed portion 146, to be thus locked therewith. To cope with such a problem, in this embodiment, arcuate surfaces 142a each having an outwardly swelled arcuate shape in vertical cross-section are formed on the outer edges of both the ends of the weight roller 142. [0064] Each containing recessed portion 146 is filled with grease 150 as a lubricant. [0065] A pulser rotor 151 projecting outwardly from the outer periphery of the rotating body 140 is fastened to an end, opposed to the brush assembly 115, of the rotating body 140 in such a manner as to block the recessed portion 144. A cooling fan 152, which is disposed outwardly from the pulser rotor 151, is also fastened to the rotating body 140 together with the pulser rotor 151. That is to say, the pulser rotor 151 is fixed to the outer end of the crank shaft 27 in such a manner as to substantially seal the containing recessed portions 146 of the centrifugal governor 111. [0066] A rotational speed sensor 153 is mounted to the stator case 122 in such a manner as to face to the outer periphery of the pulser rotor 151. The rotational speed of the crank shaft 27, that is, the rotational speed of the engine E is detected by the rotational speed sensor 153. [0067] The engine E and the starter/generator 18 are covered with a shroud 155 shown by a chain line in Fig. 2. The shroud 155 has a cooling wind inlet '156 at a position corresponding to that of the cooling fan 152 of the starter/generator 18. Accordingly, cooling air is sucked in the shroud 155 from the cooling wind inlet 156 by rotation of the cooling fan 152 accompanied by rotation of the crank shaft 27, to cool the engine E and the rotating electrical machine 110 with the cooling wind. A radiator 158 for circulating cooling water between the radiator 158 and the water jacket 157 provided in both the cylinder block 20 and the cylinder head 22 of the engine E is fixed in front of the starter/generator 18 in such a .manner that part of the radiator 158 is located in the course of a flow passage of the cooling wind flowing from the cooling fan 152 in the shroud 155 and the remainder of the radiator 158 projects from the shroud 155. [0068] Referring to Fig. 11, an ignition device 161 connected to the ignition plug 37 of the engine E is controlled by a control unit 162. A detection value of the rotational speed sensor 153 for detecting the rotational speed of the engine E, a detection value of a throttle sensor 164 additionally provided on a throttle grip 163, a signal from an idle switch 165 for permitting or restricting idling of the engine E, and a detection value of a vehicle speed sensor 166 for detecting the vehicular speed, are input in the control unit 162. [0069] The control unit 162 can switch the operational mode between an engine stopping/vehicle starting mode and an idling permissible mode in accordance with operation of the idling switch 165. In the engine stopping/vehicle starting mode, the engine E is stopped when the motorcycle is stopped, more specifically, when the detection value sent from the vehicle speed sensor 166 indicates the stopping state of the motorcycle, and also the engine E is started when the motorcycle is intended to be started in the stopping state, more specifically, when the throttle grip 163 is operated in the stopping state of the vehicle. In the idling permissible mode, idling for warming upon starting of the engine E is permissible. [0070] The rotating electrical machine 110 is provided with an electrification control circuit 167. The control unit 162 controls the electrification control circuit 167 by switching the control mode among a starting control mode, an assist control mode, and a power generation control mode. In the starting control mode, the rotating electrical machine 110 functions as the starter motor upon starting of the engine E irrespective of the above engine stopping/vehicle starting mode and idling permissible mode. In the assist control mode, the rotating electrical machine 110 functions as an assist motor upon starting the movement of the motorcycle under the above engine stopping/vehicle starting mode or the idling permissible mode. In the power generation control mode, the rotating electrical machine 110 functions as the generator during running of the motorcycle irrespective of the above engine stopping/vehicle starting mode and idling permissible mode. [0071] The electrification control circuit 167 includes, as shown in Fig. 7, FETs (Field Effect Transistors) 168 as electrification control elements each being interposed between a connection point between adjacent two of the coils 121 having respective poles and the minus side terminal of the battery 128; FETs 169 as electrification control elements each being interposed between a connection point between adjacent two of the coils 121 having respective poles and the plus side terminal of the battery 128; diodes 170 connected in parallel to the FETs 168; and diodes 171 connected in parallel to the FETs 169. [0072] The starting control mode of the control unit 162 is executed upon detection of either of a state in which the engine rotational speed is equal to or less than a specific value less than the idling rotational speed, a state in which the starter switch 129 is depressed, and a state in which the brushes 135, 136, 137 and 138 of the brush assembly 115 are in contact with the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 of the commutator 114. In this starting control mode, the FETs 168 and 169 of the electrification control circuit 167 are each turned into a non-conductive state. According to this control mode, in the stopping state of the engine E, the brush assembly 115 is located in proximity to the commutator 114 side in such manner that the brushes 135, 136, 137 and 138 are in slide-contact with the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 of the commutator 114, so that the rotating electrical machine 110 acts as a brush motor. As a result, a current is carried from the battery 128 to each coil 121 of the outer stator 113 by conduction of the relay switch 131 in accordance with conducting operation of the starter switch 129, to rotate the inner rotor 112, thereby imparting a starting torque from the inner rotor 112 to the crank shaft 27. [0073] The engine E is started by the impartment of the starting torque from the rotating electrical machine 110 functioning as the starter motor. And, when the rotational speed of the engine E is equal to or more than the above-described specific value, the centrifugal governor 111 moves the brush assembly 115 in such a manner that the brushes 135, 136, 137 and 138 are separated apart from the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 of the commutator 114, to thereby stop the impartment of the starting torque from the rotating electrical machine 110 to the engine E. [0074] In the assist control mode upon starting the movement of the motorcycle under the engine stopping/vehicle starting mode, the control unit 162 controls the rotating electrical machine 110 in such a manner that the rotating electrical machine 110 imparts an assist torque to the engine E for a specific time T after the engine rotational speed comes to not less than a specific rotational speed NS larger than the idling rotational speed NS. According to this assist control mode, the control unit 162 controls the conduction/non-conduction of the FETs 168 and 169 of the electrification control circuit 167 on the basis of the detection values sent from the rotational speed sensor 153 and the throttle sensor 164, so that the rotating electrical machine 110 acts as the brushless motor. [0075] In this assist control mode, when the throttle opening is increased by activation of the throttle grip 163 to start the motorcycle under the engine starting/vehicle starting mode as shown in Fig. 12(a), the crank shaft 27 is additionally rotated by the rotating electrical machine 110 until a specific time T is elapsed after the engine rotational speed comes to not less than the specific rotational speed NS as shown in Fig. 12 (b) . As a result, the rotational speed of the crank shaft 27 is increased by addition of the assist rotational speed given by the rotating electrical machine 110 to the rotational speed of the engine E as shown by a hatching portion in Fig. 12(b). Further, the output torque of the crank shaft 27 is also increased by addition of the assist torque generated by the rotating electrical machine 110 to the engine torque as shown by a hatching portion in Fig. 12 (c) . [0076] In this case, the output torque of the rotating lectrical machine 110 functioning as the assist motor is changed depending on the engine rotational speed and the throttle opening in such a manner as to be increased linearly with the increased throttle opening. To change the output torque of the rotating electrical machine 110 as described above, the conduction/non-conduction of the FETs 168 and 169 of the electrification control circuit 167 are controlled by the control unit 162. [0077] Even in the assist control mode upon starting the movement of the motorcycle under the idling permissible mode, the control unit 162 controls the conduction/non-conduction of the FETs 168 and 169 of the electrification control circuit 167 on the basis of the detection values sent from the rotational speed sensor 153 and the throttle sensor 164. [0078] In this assist control mode, when the throttle opening is increased by activation of the throttle grip 163 to start the movement of the motorcycle after warming I by idling as shown in Fig. 14(a), the crank shaft 27 is additionally rotated by the rotating electrical machine 110 after the engine rotational speed comes to not less than the specific rotational speed NS as shown in Fig. 14 (b) . As a result, the rotational speed of the crank shaft 27 is increased by addition of the assist rotational speed given by the rotating electrical machine 110 to the rotational speed of the engine E as shown by a hatching portion in Fig. 14 (b). Further, the output torque of the crank shaft 27 is also increased by addition of the assist torque given by the rotating electrical machine 110 to the engine torque as shown by a hatching portion in Fig. 14 (c) . [0079] In this way, the rotating electrical machine 110 functions as the starter motor configured as the brush motor under the starting control mode, and functions as the assist motor configured as the brushless motor under the assist control mode. Since a torque required for the starter motor is relatively large, the rotating electrical machine 110 functioning as the starter motor is configured as the brush motor. In this case, the rotating electrical machine 110 can output a large torque by allowing a large current to flow in the coils 121. On i the other hand, since a torque required for the assist motor upon starting the movement of the vehicle is relatively small and further it must be controlled to be accurately outputted depending on the engine rotational speed and the throttle opening, the rotating electrical machine 110 functioning as the assist motor is configured as the brushless motor. In this case, inexpensive electrification control elements not required to withstand a large current (FETs 168 and 169 in this . embodiment) can be used. Also, the brushless motor generally requires a rotational speed sensor capable of detecting the absolute angle for starting the brushless motor; however, in this embodiment, since the rotating electrical machine 110 functions as the brushless motor in the rotational state of the engine E, the reference angle can be easily detected, to thereby simplify the structure of the rotational speed sensor. [0080] In the case of using the brushless motor as the starter motor, expensive electrification control elements withstanding a large current must be used; while in the case of using the brush motor as the assist motor, since the motor is frequently, repeatedly turned on/off, the maintenance due to wear of brushes becomes complicated. [0081] The power generation control mode is executed in the case where the assist control mode is not set in the state in which the engine E is rotated at the rotational speed equal to or more than the specific rotational speed NS. In this power generation control mode, the control unit 162 makes conductive the FETs 168 connected to the minus side connection terminal of the battery 128 in a state in which the FETs 169 connected to the plus connection terminal of the terminal 128 are made non-conductive. With this control, as shown by a solid arrow in Fig. 7, the power generation voltage of the coils 121 is increased. Then, the control unit 162 makes non-conductive the FETs 168 connected to the minus side connection terminal of the battery 128 in the state in which the FETs 169 connected to the plus side connection terminal of the battery 128 is kept non-conductive. With this control, as shown by a broken arrow in Fig. 7, the battery 128 is charged by the power generation voltage increased in the coils 121. [0082] In the power generation control mode, the control unit 162 controls a ratio between intervals of conduction and non-conduction of the FETs 168, that is, the duty ratio depending on the voltage of the battery 128. To be more specific, the ratio between intervals of conduction and non-conduction of the FETs 168 is controlled by the control unit 162 such that when the voltage of the battery 128 is less than a specific value, the charging current is made large by setting the duty ratio at a large value, while when the voltage of the battery 128 is equal to or more than the specific value, the charging current is made small by setting the duty ratio at a small value. [0083] The control unit 162 controls the ratio between intervals of conduction and non-conduction of the FETs 168 depending on the throttle opening and the engine rotational speed. To be more specific, upon return of throttle or full-close of throttle opening, the ratio between intervals of conduction and non-conduction of the FETs 168 is controlled by the control unit 162 such that the power generation amount is increased by making large the duty ratio in order that the rotating electrical machine 110 functions as a regenerative brake. [0084] The function of the first embodiment will be described below. The power unit P is of a hybrid type including the engine E, the transmission means 17 for transmitting the output of the engine E to the rear wheel WR, and the rotating electrical machine 110 as the starter motor or assist motor capable of generating a power for assisting the output of the engine E. In such a power unit P, the rotating electrical machine 110 is connected to the end portion, opposed to the transmission means 17, of the crank shaft 27. That is to say, the rotating electrical machine 110 is connected to a portion, near a position of the body frame F taken as the swinging fulcrum of the power unit P, of the crank shaft 27. Accordingly, the hybrid type power unit P can be configured in such a manner as to prevent the non-suspended weight of the rear cushion 92 from being increased. This prevents the rotating electrical machine 110 from exerting adverse effect on the swinging characteristic of the power unit P, to thereby improve the driving comfort and steering stability. [0085] Further, in the embodiment, the operation of the engine E and the rotating electrical machine 110 are controlled by the control unit 162. Specifically, the control unit 162 stops the engine E upon stopping of the vehicle and starts the engine E upon starting the movement of the vehicle, and further the control unit 162 controls the rotating electrical machine 110 such that the rotating electrical machine 110 functions as the assist motor upon starting the movement of the vehicle. Accordingly, it is possible to control the stopping/starting of the engine E in accordance with the stopping/starting the movement of the vehicle, and hence to efficiently operate the engine E while preventing useless fuel consumption and emission of exhaust gas. Further, it is possible to readily start the movement of the vehicle by adding the assist force given by the rotating electrical machine 110 to the output of the engine upon acceleration for starting the movement of the vehicle. [0086] Since the rotating electrical machine 110 is controlled by the control unit 162 in such a manner as to impart a starting torque to the engine E upon starting of the engine E, the rotating electrical machine 110 can be used not only as the assist motor for assisting the output of the engine E but also as the starter motor. [0087] The rotating electrical machine 110 constitutes the starter/generator 18 in cooperation with the centrifugal governor 111. The starter/generator 18 is located outside the side end, opposed to the transmission case 84, of the rear wheel WR, and is connected to the crank shaft 27 of the engine E. Accordingly, the starter/generator 18 is located outside the rear wheel WR irrespective of the kind of the engine E, thereby certainly preventing interference between the starter/generator 18 and the rear wheel WR while avoiding both the change in design and extension of a wheel base in accordance with the kind of the engine E. [0088] The engine E, which is configured as the four-cycle engine in this embodiment, has the cylinder head 22 longer than that of a two-cycle engine in the direction along the axial line of the cylinder. In the motorcycle in which the four-cycle engine E is mounted, since the wheel base is larger than that of a motorcycle in which the two-cycle engine is mounted and a starting torque required for starting the four-cycle engine E is larger than that of the two-cycle engine, the starter/generator 18 must be enlarged. In this embodiment, however, since the starter/generator 18 is located outside the side end, opposed to the transmission case 84, of the rear wheel WR, it is possible to significantly achieve the effect of certainly preventing interference between the starter/generator 18 and the rear wheel WR while avoiding both the change in design and extension of the wheel base in accordance with the kind of the engine E. [0089] Further, since the engine E is mounted on the motorcycle with its cylinder axial line directed substantially in the horizontal direction, it is possible to more significantly achieve the effect of certainly preventing interference between the starter/generator 18 and the rear wheel WR while avoiding both the change in design and extension of the wheel base in accordance with the kind of the engine E. [0090] In the centrifugal governor 111 of the starter/generator 18, a plurality of the weight rollers 142 interposed between the rotating body 140 and the moving body 141 are contained in the containing recessed portions 146 provided in the surface portion, opposed to the moving body 141, of the rotating body 140 at a plurality of the locations spaced in the peripheral direction. Further, the weights of the weight rollers 142 are set such that the brushes 135, 136, 137, and 138 are separated apart from the first conductive passage 125, the second conductive passage 126, and the commutator pieces 127 by the centrifugal forces applied to the weight rollers 142 when the rotational speed of the engine E comes to not less than a specific rotational speed smaller than the idling rotational speed, and consequently the outside diameter of each weight roller 142 is relatively small. Accordingly, each weight roller 142 is liable to be tilted in the associated containing recessed portion 146 due to the fact that a slight gap is present between each outer edge of the weight roller 142 and the associated inner side surface of the containing recessed portion 146. In this embodiment, however, since the arcuate portion 142a having an arcuate shape swelled outwardly in vertical cross - section is formed on the entire periphery of each outer edge of the weight roller 142, even if the weight roller 142 is tilted in the containing recessed portion 146 and the outer edge of the weight roller 142 is brought into contact with the inner side surface of the containing recessed portion 146, the contact surface pressure between the weight roller 142 and the inner side surface of the containing recessed portion 146 becomes relatively low, so that the outer edge of the weight roller 142 is easy to slide on the inner side surface of the containing recessed portion 146, thereby preventing occurrence of a failure of operation of the centrifugal governor 111 due to lock of the weight roller 142 as much as possible. [0091] Since each containing recessed portion 146 is filled with the grease 150, the contact of each outer edge of the weight roller 142 and the inner side surface of the containing recessed portion 146 is lubricated by the grease 150. This makes it possible to more effectively prevent occurrence of a failure of operation of the centrifugal governor 111 due to lock of the weight roller 142. [0092] The containing recessed portions 146 are substantially sealed with the pulser rotor 151 for detecting the engine rotational speed, which pulser rotor is fixed at the outer end of the crank shaft 27 in such a manner as to cover the rotating body 140 and the moving body 141. Accordingly, it is possible to seal the containing recessed portions 146 without use of any specialized part other than the pulser rotor 151 and prevent permeation of dust into the grease 150, and hence to keep the desirable lubricating state between the weight rollers 142 and the containing recessed portions 146. [0093] Fig. 15 shows a second embodiment of the present invention. In this embodiment, coils 121 of an outer stator 113 are configured to have three-phases. An electrification control circuit 167' includes three FETs 168 interposed between the three-phase coils 121 and a minus side terminal of a battery 128; three FETs 169 interposed between the three-phase coils 121 and a plus side terminal of the battery 128; diodes 170 connected in parallel to the FETs 168; and diodes 171 connected in parallel to the FETs 169. [0094] While the embodiments of the present invention have been described, the present invention is not limited thereto, and it is to be understood that many changes in design may be made without departing from the spirit or scope of the claims. [0095] For example, in the above embodiments, the charging voltage of the battery 128 in the power generation control mode is adjusted by changing the duty ratio; however, it may be adjusted by using a conventional regulator. In this case, the FETs 168 and 169 can be used as three-phase rectifier. [0096] Further, in the above embodiments, the starting torque upon starting of the engine E, the assist torque upon starting the movement of the vehicle, and the power generation voltage are obtained by means of the coils 121 of the outer stator 113; however, the starting torque, the assist torque and the power generation voltage can be obtained by means of different coils, respectively. Also, the same coils provided with intermediate taps may be used for obtaining the starting torque, the assist torque, and the power generation voltage. [0097] Figs. 16 and 17 show a third embodiment of the present invention. In this embodiment, parts corresponding to those in the previous embodiments are designated by the same reference numerals. [0098] In a motor tricycle having a left rear wheel WRL and a right rear wheel WRR, a power unit P' swingably supported by a body frame includes a water-cooled type four-cycle/single-cylinder engine E' including a compressor 60; a transmission means 17 provided between the engine E' and the left and right rear wheels WRL and 1 WRR; and a starter/generator 18 connected to the engine E' . [0099] In the engine E', a left crank case 28L and a right crank case 28R are connected to a cylinder block 20' provided with a cylinder 21 in which a piston 23 is slidably fitted. The left crank case 28L constitutes part of a transmission case 84' for containing the transmission means 17. [0100] A crank shaft 27 is rptatably supported by the left and right crank cases 28L and 28R via first and second ball bearings 29 and 30. The transmission means 17 is connected to one end of the crank shaft 27. [0101] A valve system cam shaft 38 for opening/closing an intake valve and an exhaust valve (not shown) and further a supercharging valve 36 is rotatably supported by the cylinder head 22 of the engine E' via third and fourth ball bearings 39 and 40. [0102] A cam chain 50 is wound around a drive sprocket 49 and a driven sprocket 48. The drive 'sprocket 49, located outside the right crank case 28R, is fixed to the crank shaft 27. The driven sprocket 48 is fixed to the valve system cam shaft 38 at a position corresponding to that of the drive sprocket 49. A containing chamber 51' for containing the drive sprocket 49, the driven sprocket 48 and the cam chain 50 extends upwardly from the right crank case 28R to the cylinder head 22 through the cylinder block 20'. Further, an opening 54' opened to the containing chamber 51' is provided in the right crank case 28R at a position corresponding to that of the crank shaft 27. The opening 54' is blocked with a stator case 122' of a starter/generator 18'. [0103] The starter/generator 18' includes a rotating electrical machine 110 and a centrifugal governor 111. An outer stator 113 of the rotating electrical machine 110 is supported by the stator case 122'. An inner rotor 112 of the rotating electrical machine 110 is fixed to an end portion, opposed to the transmission means 17, of the crank shaft 27. The crank shaft 27 rotatably passes through the stator case 122'. A ball bearing 175 and an annular seal member 123 are provided between the crank shaft 27 and the stator case 122'. [0104] In this way, the first ball bearing 29 is provided between the crank shaft 27 and the left crank case 28L; the second ball bearing 30 is provided between the crank shaft 27 and the right crank case 28R; and the ball bearing 175 is provided between the crank shaft 27 and the stator case 122'. Accordingly, since the three points, spaced in the axial direction, of crank shaft 27 are rotatably supported, it is possible to suppress rotational runout of the crank shaft 27 which is relatively longer because the crank shaft 27 is connected to the starter/generator 18'. This makes it possible to certainly prevent interference between the inner rotor 112 and the outer stator 113 of the rotating electrical machine 110 of the starter/generator 18' due to the rotational runout of the crank shaft 27. [0105] In the containing chamber 51', a drive gear 55 is fixed to the crank shaft 27 at a position between the drive sprocket 49 and the second ball bearing 30. On the other hand, an oil pump 176 is provided on the inner surface side of the left crank case 28L, and a rotational shaft 177 of the oil pump 176 rotatably passes through the right crank case 28R and projects in the containing chamber 51'. A bowl-like rotational member 178 is fixed to an end portion of the rotational shaft 177 in the containing chamber 51', and a driven gea'r 179 fixed to the outer periphery of the rotational member 178 is meshed with the drive gear 55. A water pump 180 operated together with the oil pump 176 is mounted to the stator case 122' in such a manner as to face to the containing chamber 51'. Part of the water pump 180 is covered with the rotational member 178. [0106] A connecting rod 25 connected to the piston 23 is connected to a crank pin 26 provided between a pair of crank arms 27a of the crank shaft 27 via a roller bearing 181. A passage 182 with a bottom, opened to the first ball bearing 29 side, is coaxially provided in the crank pin 26, and also a passage 183 having an inner end opened to the passage 182 and an outer end opened in the outer surface of the crank pin 26 is provided in the crank pin 26. Oil is supplied to the roller bearing 181 via both the passages 182 and 183. [0107] A ring member 185 is mounted on the surface, on the first ball bearing 29 side, of one crank arm 27a on the first ball bearing 29 side such that the inner peripheral edge of the ring member 185 faces to the opening end of the passage 182. The ring member 185 forms an oil sump 184 between the crank arm 27a and the same. On the other hand, a ring-shaped guide member 186 having on its inner peripheral edge a cylindrical projection 186a projecting in the ring member 185 is mounted on the inner surface of the left crank case 28L. Accordingly, oil scattered in a crank chamber 187 formed between the left and right crank cases 28L and 28R is introduced to the opening end of the passage 182 through a space between the guide member 186 and the ring member 185, and part of oil is accumulated in the oil sump 184 by the centrifugal action caused by rotational of the crank shaft 27. [0108] The rotating electrical machine 110 of the starter/generator 18' is controlled in the same manner as described in the first and second embodiments. [0109] According to the third embodiment, unlike the first and second embodiments, the starter/generator 18' is not disposed outside the right rear wheel WRR, it is impossible to obtain the effect of preventing interference between the starter/generator 18' and the right rear wheel WRR while avoiding both the change in design and extension of the wheel base in accordance with the kind of the engine E'; however, since the rotating electrical machine 110 is connected to the end portion, opposed to the transmission means 17, of the crank shaft 27, it is possible to improve the riding comfort and steering stability of the motor tricycle by preventing the rotating electrical machine 110 from exerting adverse effect on the swinging characteristic of the hybrid type power unit P'. [0110] While the third embodiment of the present invention have been described, the present invention is not limited thereto, and it is to be understood that the configuration in the third embodiment can be applied not only to the motor tricycle but also to a motorcycle without departing from the spirit or scope of the claims. [0111] For example, in the above embodiments, the charging voltage of the battery 128 in the power generation control mode is adjusted by changing the duty ratio; however, it may be adjusted by using a conventional regulator. In this case, the FETs 168 and 169 can be used as three-phase rectifier. [0112] Further, in the above embodiments, the starting torque upon starting of the engine E, the assist torque upon starting the movement of the vehicle, and the power generation voltage are obtained by means of the coils 121 of the outer stator 113; however, the starting torque, the assist torque and the power generation voltage can be obtained by means of different coils, respectively. Also, the same coils provided with intermediate taps may be used for obtaining the starting torque, the assist torque, and the power generation voltage. [0113] [Effect of the Invention] As described above, according to the invention described in claim 1, it is possible to certainly prevent interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. [0114] According to the invention described in claim 2, it is possible to significantly achieve the effect of certainly preventing interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. [0115] I According to the invention described in claim 3, it is possible to more significantly achieve the effect of certainly preventing interference between the starter/generator and the rear wheel while avoiding both the change in design and extension of the wheel base depending on the kind of engine. [0116] According to the invention described in claim 4, the hybrid type power unit can be configured in such a manner as to prevent the non- suspended weight of a rear cushion from being increased. This makes it possible to improve the riding comfort and the steering stability of the motorcycle by preventing the motor from exerting adverse effect on the swinging characteristic of the power unit. 10117] According to the invention described in claim 5, it is possible to control the stopping/starting of the engine in accordance with the stopping/starting the movement of the motorcycle and hence to efficiently operate the engine while preventing useless fuel consumption and emission of exhaust gas. Further, it is possible to readily start the movement of the motorcycle by imparting an assist force generated by the motor to the output of the engine upon acceleration for starting the movement of the motorcycle. [0118] According to the invention described in claim 6, the motor can be used not only as the assist motor for assisting the output of the engine but also as the starter motor. [Explanation of Reference Numerals] 17: transmission means, 18: starter/generator, 27: crank shaft, 28: crank case, 84: transmission case, 110: rotating electrical machine as motor, 162: control unit, E, E': engine, F: body frame, P, P': power unit, WR: rear wheel Fig. 5 valve lift, exhaust valve 35, intake valve 34, supercharging valve 36, engine crank angle Fig. 11 162: control unit, 161: ignition device, 167: electrification control circuit, 153: rotational speed sensor, 112: inner rotor, 111: centrifugal governor, 115: brush assembly, 114: commutator, 129: starter SW, 130: starter relay, 128: battery Fig. 12(a) throttle opening, full-open, full-close, time Fig. 12(b) rotational speed of crank shaft, time Fig. 12(c) output torque of crank shaft, time Fig. 13 output torque of rotating electrical machine throttle opening engine rotational speed Fig. 14(a) throttle opening, full-open, full-close, time Fig. 14(b) rotational speed of crank shaft, time Fig. 14(c) output torque of crank shaft, time WE CLAIM: 1. A power unit for a motorcycle, said power unit (P) with its front portion swingably supported by a body frame (F) , said power unit (P) having an engine (E) disposed in front of a rear wheel (WR); a transmission case (84) continuous to a crank case (28) of said engine (E) and extending on one side of said rear wheel (WR); and a transmission means (17) contained in said transmission case (84) and disposed between said rear wheel (WR) rotatably supported by a rear portion of said transmission case (84) and one end of a crank shaft (27) of said engine (E); and a starter/generator (18) connected to the other end of said crank shaft (27); characterized in that said starter/generator (18) is connected to said crank shaft (27) in such a manner as to be disposed outside a side end, opposed to said transmission case (84) , of said rear wheel (WR). 2. A motorcycle as claimed in claim 1, wherein said engine (E) is a four¬ cycle engine. 3. A motorcycle as claimed in claim 2, wherein said engine (E) is mounted with its cylinder axial line directed in the horizontal direction. 4. A motorcycle with a hybrid type power unit as claimed in claim 1, wherein the output of said engine (E, E') is assisted by said starter/generator (18). 5. A motorcycle with a hybrid type power unit as claimed in claim 4, wherein having a control unit (162) for controlling the operations of said engine (E, E') and said motor (110) to stop said engine (E, E') upon stopping of said motorcycle and start said engine (E, E') upon starting the movement of said motorcycle, and to operate said motor (110) for a specific time upon starting the movement of said motorcycle. 6. A motorcycle with a hybrid type power unit as claimed in claim 4 or 5, wherein said motor (110) is capable of imparting a starting torque to said engine (E, E*) upon starting of said engine (E, E1). 7. A motorcycle substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

1104-del-1999-abstract.pdf

1104-del-1999-assignment.pdf

1104-del-1999-claims.pdf

1104-del-1999-correspondence-others.pdf

1104-del-1999-correspondence-po.pdf

1104-del-1999-description (complete).pdf

1104-del-1999-drawings.pdf

1104-del-1999-form-1.pdf

1104-del-1999-form-13.pdf

1104-del-1999-form-19.pdf

1104-del-1999-form-2.pdf

1104-del-1999-form-3.pdf

1104-del-1999-form-5.pdf

1104-del-1999-gpa.pdf

1104-del-1999-petition-137.pdf

1104-del-1999-petition-138.pdf