Patent Publication Number: US-7216615-B2

Title: Engine device for motorcycles

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an engine device for motorcycles. 
   2. Description of Related Art 
   An engine device for motorcycles has been conventionally provided with a motor type starting device for starting an engine. The motor type starting device transmits drive force of the starter motor, for example, to a crankshaft through a reduction gear train housed in a side space within the crankcase (See Japanese Patent Document JP-A-Hei 6-341327, for example). 
   Such a reduction gear train is made up of a plurality of transmission gears each supported for rotation on a plurality of the respective support shafts disposed parallel to a motor shaft of the starter motor and the crankshaft. 
   Sometimes, however, a generator, which is usually provided integrally for rotation at the end of a crankshaft, is provided integrally for rotation at the end of a generator shaft disposed parallel to and offset from the crankshaft, depending on the layout of the vehicle body. 
   Therefore, some of transmission gears of the reduction gear train in the motor type starting device are configured such that they are supported on the generator shaft, but such a transmission gear is required to have an outside diameter greater than that of the rotor of the generator having a relatively large diameter. 
   Thus, the starter motor, which transmits drive force to the crankshaft through a reduction gear train having a relatively large outside diameter, is disposed at the upper part of the crankcase distant from the crankshaft. The starter motor has a strong influence on the weight balance of the vehicle in the longitudinal or the lateral direction because of its heavy weight and might cause a deviation of the weight balance because of its disposition distant from the crankshaft. 
   In addition, in the case where a V-type engine is provided with a motor type starting device, the starter motor can be disposed forward of the engine only at the upper part of the crankcase. In this case, the starter motor which is disposed away from the crankshaft, is disposed further forward of a cylinder block of the engine, and a running wind hitting against cooling fins might be blocked in an air-cooled engine. 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a good engine device for motorcycles in which a starter motor for transmitting drive force to a crankshaft through a reduction gear train can be disposed closer to the crankcase in order to solve the foregoing problem. 
   The object of the present invention is achieved by an engine device for motorcycles comprising a starter motor having a motor shaft, a crankshaft, and an engine having a reduction gear train placed between the starter motor and the crankshaft for transmitting drive force of the starter motor to the crankshaft. The reduction gear train is provided with a first support shaft connected at one end to the motor shaft of the starter motor and at the other end to the crankshaft, and the motor shaft is located at a position closer to the crankshaft than the first support shaft. 
   According to the engine device for motorcycles described above, the power transmission path of a starter motor to the crankshaft can be reversed toward the crankshaft through a first support shaft of a reduction gear train. Thus, the starter motor can be disposed closer to the crankshaft. 
   In the foregoing engine device for motorcycles, it is preferable that the starter motor has a pinion gear disposed at the end of the motor shaft. The reduction gear train comprises a first support shaft disposed parallel to the motor shaft of the starter motor, first gears supported for rotation on the first support shaft; a second support shaft disposed parallel to the first support shaft, second gears supported for rotation on the second support shaft, and a starter gear provided on the crankshaft. 
   The first gears have a first gear meshing the pinion gear of the starter motor, and a second gear. The second gears have a third gear meshing the second gear, and a fourth gear connected to the crankshaft. The motor shaft is located at a position closer to the second support shaft than the first support shaft. 
   According to this arrangement, the power transmission path of the starter motor to a crankshaft can be reversed toward the crankshaft through first and second support shafts of a reduction gear train. Thus, the starter motor can be disposed closer to the second support shaft. 
   Further, in the foregoing engine device for motorcycles, it is preferable that the reduction gear train comprises a third support shaft disposed parallel to the second support shaft, third gears supported for rotation on the third support shaft, and a starter gear provided on the crankshaft disposed parallel to the third support shaft. The third gears have a fifth gear meshing the fourth gear, and a sixth gear meshing the starter gear on the crankshaft. The motor shaft is located closer to the third support shaft than the first support shaft. 
   According to this arrangement, the power transmission path of a starter motor to a crankshaft can be reversed toward the crankshaft through first to third support shafts of a reduction gear train. Thus, the starter motor can be disposed closer to the third support shaft. 
   Further, in the foregoing engine device for motorcycles, it is preferable that there is provided a torque limiter supported on the second support shaft, and the third gear is supported on the second support shaft through the torque limiter. 
   According to this arrangement, the starter motor can be protected at starting of the engine. 
   Further, in the foregoing engine device for motorcycles, it is preferable that there is provided a one-way clutch supported on the third support shaft, and the fifth gear is supported on the third support shaft through the one-way clutch. 
   According to this arrangement, although at starting of the engine, the one-way clutch can transmit drive force of a starter motor to the crankshaft, after the engine start, the one-way clutch does not transmit the rotation of the crankshaft to the starter motor, so that no reverse driving of the starter motor happens. 
   Further, in the foregoing engine device for motorcycles, it is preferable that the third support shaft is a generator shaft provided at one end with a generator. 
   According to this arrangement, even if a generator is provided integrally for rotation at the end portion of a generator shaft disposed parallel to and offset from the crankshaft, the starter motor can be disposed closer to the crankshaft. 
   Further, in the foregoing engine device for motorcycles, it is preferable that the starter motor is disposed further forward of the engine. 
   According to this arrangement, since the position of a starter motor disposed forward of the cylinder block of an air-cooled, V-type engine, for example, is lowered, the area required to hide cooling fins is reduced and no running wind hitting against the cooling fins of the cylinder block is blocked, providing a satisfactory engine cooling. 
   Further, in the foregoing engine device for motorcycles, it is preferable that there is provided a body frame having the engine mounted thereon, and the starter motor is disposed between cooling fins formed on the engine, and the generator. 
   According to this arrangement, since a starter motor is disposed between the body frame, the cooling fins of the engine, and the generator, mounting space of the vehicle body can be utilized effectively. 
   According to the foregoing engine device for motorcycles, the power transmission path of a starter motor to the crankshaft can be reversed toward the crankshaft through a reduction gear train and the starter motor can be disposed closer to the crankshaft. Thus, deviation of the weight balance of the engine device due to the heavy weight of the starter motor can be reduced. 
   Further, since the position of a starter motor disposed forward of the engine at the upper part of the crankcase can be lowered, the area required to hide cooling fins of an air-cooled engine is reduced, which improves the cooling property of the engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a right side view of a motorcycle having an engine device for motorcycles according to the present invention mounted thereon; 
       FIG. 2  is an enlarged right side view of a portion of the engine device for motorcycles shown in  FIG. 1 ; 
       FIG. 3  is an enlarged front view of a portion of the engine device for motorcycles shown in  FIG. 1 ; 
       FIG. 4  is a sectional plan view of the engine device for motorcycles shown in  FIG. 1 ; 
       FIG. 5  is an enlarged sectional plan view of a portion of the engine device for motorcycles shown in  FIG. 4 ; and 
       FIG. 6  is a schematic right side view showing an arrangement of a reduction gear train shown in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Now, a preferred embodiment of the engine device for motorcycles according to the present invention is described below in detail with reference to the accompanying drawings. 
     FIG. 1  is a right side view of a motorcycle on which an engine device for motorcycles according to the present invention is mounted.  FIG. 2  is an enlarged right side view of a portion of the engine device for motorcycles shown in  FIG. 1 .  FIG. 3  is an enlarged front view of a portion of the engine device for motorcycles shown in  FIG. 1 .  FIG. 4  is a sectional plan view of the engine device for motorcycles shown in  FIG. 1 .  FIG. 5  is an enlarged sectional plan view of a portion of the engine device for motorcycles shown in  FIG. 4 .  FIG. 6  is a schematic right side view showing an arrangement of the reduction gear train shown in  FIG. 2 . 
   A motorcycle  1 , as shown in  FIG. 1 , is a cruiser type motorcycle. This motorcycle  1  has a structure schematically described below. 
   A front fork  3  is supported for rotation by a head pipe (not shown) fixed to the forward end of a body frame  2  of double cradle type. A front wheel  4  is supported at the lower end of the front fork  3 , while handlebars  5  are disposed at the upper end thereof. 
   A fuel tank  6  and a seat  7  are disposed at the upper part of the body frame  2 , and further a rear wheel  9  is supported at the rear end of a rear arm  8  pivotally mounted for up and down swinging movement to a rear arm bracket  2   b  of the body frame  2 . 
   A rear suspension  10  is disposed between the rear arm  8  and body frame  2 . A footrest board  11  for supporting the driver&#39;s foot is disposed at each side of left and right down tubes  2   a  of the body frame  2 . 
   A front fender  12  for covering the upper side of the front wheel  4  is mounted to the front fork  3 . A rear fender  13  for covering approximately the upper half of the rear wheel  9  is mounted on a rear frame (not shown) extending rearward from the upper end of the rear arm bracket  2   b , and a rear seat  14  is provided on the upper surface of the rear fender  13 . 
   As shown in  FIG. 2 , the engine device for motorcycles according to this embodiment includes a starter motor  70  having a motor shaft  70   a , a crankshaft  21 , and an engine  15  having a reduction gear train  101  placed between the starter motor  70  and crankshaft  21  for transmitting drive force of the starter motor  70  to the crankshaft  21 . 
   The engine  15  is an air-cooled, four-stroke, V-type two-cylinder, OHV engine, which is mounted inside the cradle of the body frame  2 . 
   The engine  15  has a structure schematically described below. 
   A forward cylinder block  7  and a rear cylinder block  18  are disposed longitudinally of the vehicle such that they make a given bank angle to each other. A forward cylinder head  19  and a rear cylinder head  20  are placed on the upper mating surfaces of the forward and rear cylinder blocks  17 ,  18  in tiers, respectively, to be fastened with head bolts. Further, head covers  24   a ,  24   b  are mounted on the upper mating surfaces of the cylinder heads  19 ,  20 . 
   On the outside circumferential walls of the forward and rear cylinder blocks  17 ,  18  and the forward and rear cylinder heads  19 ,  20  are integrally formed numerous cooling fins  50 ,  51  approximately at right angles to the bore axes. Because of a running wind directly hitting against the cylinder blocks  17 ,  18  and the cylinder heads  19 ,  20 , heat from the engine is radiated through the cooling fins  50 ,  51 , thereby cooling the engine  15 . 
   The crankcase  16  has a structure in which a crankcase section  16   a  containing the crankshaft  21  and a mission case section  16   b  containing a transmission mechanism  90  (described later) are formed integrally, as shown in  FIG. 4 . 
   The crankshaft  21  is disposed horizontally in the lateral direction of the vehicle and set so as to rotate clockwise as viewed from the right side of the vehicle. The crankshaft  21  has a crank pin  21   a  common to the forward and rear cylinders, left and right crank webs  21   b ,  21   b  and left and right crank journals  21   c ,  21   c.    
   In each cylinder bore of the forward and rear cylinder blocks  17 ,  18  is inserted a piston (not shown) for sliding movement, and the piston is connected to a crank pin  21   a  of the crankshaft  21  common to the forward and rear cylinders through a connecting rod. 
   An intake valve opening and an exhaust valve opening formed in the forward and the rear cylinder head  19 ,  20  are opened and closed by an intake and an exhaust valve (not shown). Specifically, a forward and a rear camshaft  31 ,  31  are driven for rotation by the crankshaft  21  to advance and retract an intake and an exhaust push rod (not shown) in up and down direction and then rotate an intake and an exhaust rocker arm (not shown) for opening and closing the openings. 
   The camshafts  31 ,  31  are disposed, in the crankcase  16 , parallel to the crankshaft  21  and driven for rotation through an intermediate shaft  29  and a timing gear  30  by a drive gear  28  fixed to the right end portion of the crankshaft  21 . 
   The intake and the exhaust pushrods are housed in cylindrical casings  36 ,  36  disposed to be exposed to the right side, along the cylinder axes of the forward and rear cylinder blocks  17 ,  18 , respectively. 
   Each exhaust valve opening of the forward and rear cylinder heads  19 ,  20  leads to the outside wall of the V-bank through a joint exhaust port. To The forward and rear exhaust ports are connected forward and rear exhaust pipes  42 ,  43 , as shown in  FIG. 1 . The exhaust pipes  42 ,  43  extend rearward on the right side of the vehicle body to be joined together, to the downstream end of which is connected a muffler  44  disposed at the right side of the rear wheel  9 . 
   The transmission mechanism  90  is disposed in the transmission case section  16   b  of the crankcase  16 , and configured such that a main shaft  87  having an import gear group  89 . A drive shaft  88 , having an output gear group  91  meshing the import gear group  89 , are each disposed parallel to the crankshaft  21 . 
   When a foot-operated shift lever is controlled in a rocking manner, a shift drum (not shown) is rotated and shift forks move in the axial directions to connect any specified gears of the import gear group  89  and output gear group  91  to the main shaft  87  and drive shaft  88 , so that switching is performed between lowest speed and highest speed stages. 
   The right end portion of the drive shaft  88  is protruded outwardly from the transmission case section  16   b , and a drive sprocket  86  mounted on the protruded drive shaft  88  is coupled with a follower sprocket located at one end of a drive shaft (not shown) disposed in the transfer case through a chain. Further, a belt pulley provided at the other end of the drive shaft is coupled with a follower pulley of the rear wheel  9  through a drive belt. 
   The main shaft  87  is provided, at the left end thereof, with a clutch mechanism  95 . The clutch mechanism  95  has a structure in which numerous clutch plates  98  are disposed between an outer drum  96  mounted for relative rotation on the main shaft  87  and an inner drum  97  connected to the main shaft  87  for rotation therewith. The clutch mechanism  95  is adapted to transmit or cut off engine power to the main shaft  87  when a push rod  99  inserted in the axial center of the main shaft  87  is advanced/retracted by an oil piston  100   a  of an oil cylinder member  100 . 
   The crankshaft  21  has the left and the right crank journal  21   c  supported by bosses  16   c  formed on a left and a right sidewall of the crankcase section  16   a . A crank gear  85  is fixed by key-engagement to the left end portion of the crankshaft  21  with a second balancer gear  59  placed between the crank gear  85  and the boss. 
   Further, forwardly of the crankshaft  21  is disposed, parallel to the crankshaft  21 , a generator shaft  75  having a generator  77  mounted thereon at the right end. The generator  77  includes a rotor  78  fitted on the generator shaft  75  at the right end and rotating together in one body and a coil assembly  78  supported fixedly on a starter gear cover  61 . 
   The generator shaft  75  has a transmission gear (sixth gear)  76   b  meshing the starter gear  22  provided on the crankshaft  21 . A first balancer gear  57  mounted at the left end of the generator shaft  75  engages with the second balancer gear  59  through an intermediate gear  58 . The second balancer gear  59  is supported for rotation on a balancer housing  60  fixed to the crankcase section  16   a  of the crankcase  16 . 
   In this arrangement, the first balancer gear  57  rotates in the opposite direction at a speed twice as fast as the crankshaft  21 , and the second balancer gear  59  rotates in the opposite direction at the same speed as the crankshaft  21 . 
   Further, the engine  15  according to this embodiment has a reduction gear train  101  that is placed between a starter motor  70  disposed at the upper part of the crankcase  16  and the crankshaft  21  and transmits drive force of the starter motor  70  to the crankshaft  21 , as shown in  FIGS. 2 and 3 . 
   As shown in  FIGS. 4 and 5 , a starter gear cover  61  is mounted fluid-tightly on the right side of the crankcase section  16   a  of the crankcase  16  and there is provided a starter gear chamber separate from the crankcase section  16   a.    
   In the starter gear chamber, a reduction gear train  101  is housed to transmit drive force of the starter motor  70  to the crankshaft  21 . 
   The reduction gear train  101  of this embodiment includes a first support shaft  71  disposed parallel to the motor shaft  70   a  of the starter motor  70 . First gears  72  are supported for rotation on the first support shaft  71 . A second support shaft  73  is disposed parallel to the first support shaft  71 . Second gears  74  are supported for rotation on the second support shaft  73 . A generator shaft (third support shaft)  75  is disposed parallel to the second support shaft  73 . Third gears  76  are supported for rotation on the generator shaft  75 . A starter gear  22  is disposed on the crankshaft  21  and parallel to the generator shaft  75 . 
   The first support shaft  71 , one side of which is connected to the motor shaft  70   a  and the other side of which is connected to the crankshaft  21 , has one end supported for fitting on the crankcase  16  and the other end supported for fitting on the starter gear cover  61 . 
   The second support shaft  73  is supported, at both ends, for rotation on the crankcase  16  and starter gear cover  61  through bearings. 
   The generator shaft  75  has a left and a right journal  75   a ,  75   a  supported by bosses  16   d  formed on the left and the right wall of the crankcase section  16   a.    
   The first gears  72  are formed integrally of a large first gear  72   a  meshing a pinion gear  70   b  disposed at one end of the motor shaft  70   a , and a small second gear  72   b  meshing a third gear  74   a  of the second gears  74 . 
   The second gears  74  have a third gear  74   a  supported on the second support shaft  73  through a torque limiter  81 , and a fourth gear  74   b  meshing a fifth gear  76   a  of the third gears  76  and rotating with the second support shaft  73  in one body. 
   The third gears  76  have a fifth gear  76   a  supported on the generator shaft  75  through a one-way clutch  80 , and a transmission gear (sixth gear)  76   b  meshing the starter gear  22 . The starter motor  70  has the motor shaft  70   a  located closer to the generator shaft  75  than the first support shaft  71 , as shown in  FIG. 6 . 
   That is, the starter motor  70  is disposed between the down tubes  2   a  of the body frame  2  located forwardly of the engine  15 , the cooling fins  50  formed on the engine  15 , and the generator  77 , as shown in  FIGS. 2 and 3 . 
   In the motor type starting device having a reduction gear train  101  as described above, when starter motor  70  is energized to rotate the pinion gear  70   b  starting of the engine, the rotation is transmitted to the third gear  74   a  of the second gears  74  through the first gears  72 . Then, the rotation transmitted to the third gear  74   a  is transmitted to the second support shaft  73  through the torque limiter  81 , for the rotation of the fourth gear  74   b.    
   When the fourth gear  74   b  rotates, the rotation is transmitted to the fifth gear  76   a . Then, an inner ring  80   a  of the one-way clutch  80  rotates with the fifth gear  76   a , and in turn an outer ring  80   b  rotates in the same direction to rotate the rotor  78  and generator shaft  75  of the generator  77 . 
   When the generator shaft  75  rotates, the rotation is transmitted to the starter gear  22  through the transmission gear  76   b , for the rotation of the crankshaft  21 . In this way, rotary motion of the crankshaft  21  causes the engine  15  to start. 
   That is, according to the engine  15  of the engine device of this embodiment described above, driving force of the starter motor  70  can be transmitted to the crankshaft  21  through the first gear  72   a  and second gear  72   b  of the first gears  72  supported for rotation on the first support shaft  71  disposed at a position more distant than the motor shaft  70   a  of the starter motor  70 . 
   Therefore, the power transmission path of the starter motor  70  to the crankshaft  21  can be reversed toward the crankshaft  21  through the first support shaft  71  of the reduction gear train  101 , and the starter motor  70  can be disposed closer to the crankshaft  21 . 
   As a result, deviation of the weight balance of the engine  15  due to the heavy weight of the starter motor  70  can be decreased. 
   Further, if a generator  77  is provided integrally for rotation at the end portion of the generator shaft  75  disposed parallel to and offset from the crankshaft  21 , as in the engine  15 , the fifth gear  76   a  supported on the generator shaft  75  is required to have an outside diameter larger than that of the rotor  78  of the generator  77  having a relatively large diameter, and the second support shaft  73  should be correspondingly disposed further away from the crankshaft  21 . 
   However, since in the engine  15  of this embodiment, the starter motor  70  can be disposed closer to the crankshaft  21 , as described above, the influence on the weight balance of the vehicle in the longitudinal or the lateral direction can be reduced when the generator shaft  75  is disposed parallel to and offset from the crankshaft  21 . Further, in the engine  15  of this embodiment, the starter motor  70  can be disposed closer also to the second support shaft  73  and generator shaft  75 . 
   In addition, since the third gear  74   a  of this embodiment is supported on the second support shaft  73  through the torque limiter  81 , the starter motor  70  can be protected at starting of the engine. 
   Further, the fifth gear  76   a  of this embodiment is supported on the generator shaft  75  through the one-way clutch  80 . Therefore, at starting of the engine, the one-way clutch  80  can transmit the drive force of the starter motor  70  to the crankshaft  21 , but after the engine start, since the one-way clutch  80  does not transmit the rotation of the crankshaft  21  toward the starter motor  70 , no reverse driving of the starter motor happens. 
   In addition, since the engine  15  of this embodiment is an air-cooled, V-type two-cylinder engine, the starter motor  70  disposed at the upper part of the crankcase  16 , is disposed further forward of the forward cylinder block  17 . However, as shown in  FIGS. 2 and 3 , the starter motor  70  can be provided at a lower position, so that the area required to hide the cooling fins  50  is reduced and running wind hitting against the cooling fins  50  of the forward cylinder block  17  is not blocked, which provides a satisfactory engine cooling. 
   Further, the mounting space of the vehicle body can be utilized effectively since the starter motor  70  is disposed between the cooling fins  50  of the engine  15 , the generator  77 , and the down tube  2   a  of the body frame  2  located forwardly of the engine  15 . 
   It should be understood that the configuration of the starter motor, first to third support shafts, first to third gears, first to sixth gears, torque limiter, one-way clutch, generator, and engine type or the like, is not limited to that of the foregoing embodiment, but various modes can be adopted, based on the spirits of the present invention. 
   For example, although in the foregoing embodiment, the third gear  74   a  of the second gears  74  is supported on the second support shaft  73  through the torque limiter  81 , the second gear can be formed of integrated third and forth gears. 
   Further, although in the foregoing embodiment, the fifth gear  76   a  of the third gear  76  is supported on the generator shaft  75  through the one-way clutch  80 , a structure is possible in which the fifth gear is fixed to the generator shaft  75  and the starter gear is supported on the crankshaft through the one-way clutch.