Patent Publication Number: US-11661138-B2

Title: Drive train and sprocket arrangement for human-powered vehicle

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a drive train and a sprocket arrangement for a human-powered vehicle. 
     Discussion of the Background 
     For example, a human-powered vehicle includes a drive train to transmit a human power to a wheel. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, a drive train for a human-powered vehicle comprises a drive unit, a sprocket arrangement, and a total gear range quotient. The drive unit includes a motor configured to impart propulsion to the human-powered vehicle. The sprocket arrangement is operatively coupled to the drive unit. The sprocket arrangement comprises a plurality of rear sprockets and a plurality of gear ratios respectively corresponding to the plurality of rear sprockets. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. The total gear range quotient is obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is larger than 5. 
     With the drive train according to the first aspect, it is possible to provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a second aspect of the present invention, the drive train according to the first aspect is configured so that the total gear range quotient is equal to or larger than 7. 
     With the drive train according to the second aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a third aspect of the present invention, the drive train according to the first or second aspect is configured so that the total gear range quotient is equal to or larger than 9. 
     With the drive train according to the third aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a fourth aspect of the present invention, the drive train according to any one of the first to third aspects further comprises a rear derailleur configured to shift a chain relative to the plurality of rear sprockets. 
     With the drive train according to the fourth aspect, it is possible to change a gear position in the plurality of rear sprockets. 
     In accordance with a fifth aspect of the present invention, the drive train according to the fourth aspect further comprises a front derailleur. 
     With the drive train according to the fifth aspect, it is possible to change a gear position in a plurality of front sprockets. 
     In accordance with a sixth aspect of the present invention, the drive train according to any one of the first to fifth aspects further comprises at least one internal transmission device. 
     With the drive train according to the sixth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a seventh aspect of the present invention, the drive train according to the sixth aspect is configured so that the at least one internal transmission device includes a rear internal transmission device configured to be disposed on a rear wheel. 
     With the drive train according to the seventh aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with an eighth aspect of the present invention, the drive train according to the sixth or seventh aspect is configured so that the at least one internal transmission device includes a front internal transmission device configured to be coupled to a crank assembly. 
     With the drive train according to the eighth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a ninth aspect of the present invention, the drive train according to any one of the first to eighth aspects is configured so that a total number of the plurality of rear sprockets is equal to or smaller than 10. 
     With the drive train according to the ninth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a tenth aspect of the present invention, the drive train according to the ninth aspect is configured so that the total number of the plurality of rear sprockets is equal to or larger than 5. 
     With the drive train according to the tenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with an eleventh aspect of the present invention, the drive train according to any one of the first to tenth aspects is configured so that the sprocket arrangement includes at least one individual sprocket-space provided between two adjacent rear sprockets among the plurality of rear sprockets. The two adjacent rear sprockets are adjacent to each other without another rear sprocket therebetween in an axial direction with respect to a rotational center axis of the plurality of rear sprockets. A force-transmission coefficient obtained by dividing the total gear range quotient by a total number of the at least one individual sprocket-space is equal to or smaller than 1. 
     With the drive train according to the eleventh aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a twelfth aspect of the present invention, the drive train according to any one of the first to tenth aspects is configured so that the sprocket arrangement includes at least one individual sprocket-space provided between two adjacent rear sprockets among the plurality of rear sprockets. The two adjacent rear sprockets are adjacent to each other without another rear sprocket therebetween in an axial direction with respect to a rotational center axis of the plurality of rear sprockets. A force-transmission coefficient obtained by dividing the total gear range quotient by a total number of the at least one individual sprocket-space is larger than 1. 
     With the drive train according to the twelfth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the drive train including the drive unit. 
     In accordance with a thirteenth aspect of the present invention, a sprocket arrangement for a human-powered vehicle comprises a plurality of rear sprockets and a gear range quotient. The plurality of rear sprockets includes a largest rear sprocket and a smallest rear sprocket. The gear range quotient is obtained by dividing a total tooth-number of the largest rear sprocket by a total tooth-number of the smallest rear sprocket. The gear range quotient is larger than 6.01. 
     With the sprocket arrangement according to the thirteenth aspect, it is possible to provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a fourteenth aspect of the present invention, the sprocket arrangement according to the thirteenth aspect is configured so that a total number of the plurality of rear sprockets is equal to or smaller than 10. 
     With the sprocket arrangement according to the fourteenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a fifteenth aspect of the present invention, the sprocket arrangement according to the fourteenth aspect is configured so that the total number of the plurality of rear sprockets is equal to or larger than 5. 
     With the sprocket arrangement according to the fifteenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a sixteenth aspect of the present invention, the sprocket arrangement according to any one of the thirteenth to fifteenth aspects is configured so that the gear range quotient is equal to or larger than 7. 
     With the sprocket arrangement according to the sixteenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a seventeenth aspect of the present invention, the sprocket arrangement according to any one of the thirteenth to sixteenth aspects is configured so that the gear range quotient is equal to or larger than 9. 
     With the sprocket arrangement according to the seventeenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with an eighteenth aspect of the present invention, the sprocket arrangement according to any one of the thirteenth to seventeenth aspects is configured so that the sprocket arrangement includes at least one individual sprocket-space provided between two adjacent rear sprockets among the plurality of rear sprockets. The two adjacent rear sprockets are adjacent to each other without another rear sprocket therebetween in an axial direction with respect to a rotational center axis of the plurality of rear sprockets. A force-transmission coefficient obtained by dividing the total gear range quotient by a total number of the at least one individual sprocket-space is equal to or smaller than 1. 
     With the sprocket arrangement according to the eighteenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a nineteenth aspect of the present invention, the sprocket arrangement according to any one of the thirteenth to seventeenth aspects is configured so that the sprocket arrangement includes at least one individual sprocket-space provided between two adjacent rear sprockets among the plurality of rear sprockets. The two adjacent rear sprockets are adjacent to each other without another rear sprocket therebetween in an axial direction with respect to a rotational center axis of the plurality of rear sprockets. A force-transmission coefficient obtained by dividing the total gear range quotient by a total number of the at least one individual sprocket-space is equal to or larger than 1. 
     With the sprocket arrangement according to the nineteenth aspect, it is possible to effectively provide a wide gear range and a well-balanced combination of the plurality of sprockets in the sprocket arrangement. 
     In accordance with a twentieth aspect of the present invention, a drive train for a human-powered vehicle comprises at least one internal transmission device and a total gear range quotient. The at least one internal transmission device has a plurality of gear ratios. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. The total gear range quotient is obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is equal to or larger than 6.37. 
     With the drive train according to the twentieth aspect, it is possible to provide the drive train having a wide gear range and a well-balanced combination of the plurality of sprockets. 
     In accordance with a twenty-first aspect of the present invention, the drive train according to the twentieth aspect is configured so that the at least one internal transmission device includes a rear internal transmission device configured to be disposed on a rear wheel. 
     With the drive train according to the twenty-first aspect, it is possible to provide the drive train having a wide gear range and a well-balanced combination of the plurality of sprockets. 
     In accordance with a twenty-second aspect of the present invention, the drive train according to the twentieth or twenty-first aspect is configured so that the at least one internal transmission device includes a front internal transmission device configured to be coupled to a crank assembly. 
     With the drive train according to the twenty-second aspect, it is possible to provide the drive train having a wide gear range and a well-balanced combination of the plurality of sprockets. 
     In accordance with a twenty-third aspect of the present invention, a drive train for a human-powered vehicle comprises a plurality of gear ratios and a total gear range quotient. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. The total gear range quotient is obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is equal to or larger than 6.95. 
     With the drive train according to the twenty-third aspect, it is possible to provide the drive train having a wide gear range and a well-balanced combination of the plurality of sprockets. 
     In accordance with a twenty-fourth aspect of the present invention, the drive train according to the twenty-third aspect is configured so that the total gear range quotient is equal to or larger than 9. 
     With the drive train according to the twenty-fourth aspect, it is possible to provide the drive train having a wide gear range and a well-balanced combination of the plurality of sprockets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG.  1    is a side elevational view of a human-powered vehicle including a drive train in accordance with a first embodiment. 
         FIG.  2    is a schematic diagram of the drive train of the human-powered vehicle illustrated in  FIG.  1   . 
         FIG.  3    is a schematic diagram of a plurality of rear sprockets of the drive train illustrated in  FIG.  2   . 
         FIG.  4    is a table showing a plurality of gear ratios of the drive train illustrated in  FIG.  2   . 
         FIG.  5    is a table showing a plurality of gear ratios of a drive train in accordance with a modification of the first embodiment. 
         FIG.  6    is a table showing a plurality of gear ratios of a drive train in accordance with another modification of the first embodiment. 
         FIG.  7    is a schematic diagram of a drive train of a human-powered vehicle in accordance with a second embodiment. 
         FIG.  8    is a schematic diagram of a drive train of a human-powered vehicle in accordance with a third embodiment. 
         FIG.  9    is a table showing a plurality of gear ratios of the drive train illustrated in  FIG.  8   . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiment(s) will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
     First Embodiment 
     Referring initially to  FIG.  1   , a human-powered vehicle  10  includes a drive train  12  in accordance with an embodiment. For example, the human-powered vehicle  10  is a vehicle to travel with a motive power including at least a human power of a user who rides the human-powered vehicle  10 . Examples of the user who rides the human-powered vehicle  10  include a rider. The human-powered vehicle  10  has an arbitrary number of wheels. For example, the human-powered vehicle  10  has at least one wheel. In this embodiment, the human-powered vehicle  10  preferably has a smaller size than that of a four-wheeled automobile. However, the human-powered vehicle  10  can have an arbitrary size. For example, the human-powered vehicle  10  can have a larger size than that of the four-wheeled automobile. Examples of the human-powered vehicle  10  include a bicycle, a tricycle, and a kick scooter. In this embodiment, the human-powered vehicle  10  is a bicycle. An electric assisting system including an electric motor can be applied to the human-powered vehicle  10  to assist muscular motive power of the user. Namely, the human-powered vehicle  10  can be an E-bike. While the human-powered vehicle  10  is illustrated as a road bike having a motor, the technology disclosed in the present application can be applied to mountain bikes or any type of human-powered vehicles  10 . 
     As seen in  FIG.  1   , the human-powered vehicle  10  includes a handlebar  1 , a saddle  2 , a vehicle body  3 , an operating device  4 , a front wheel  5 , and a rear wheel  6 . The operating device  4  is mounted to the handlebar  1 . The operating device  4  includes a rear brake operating device via which a user operates a rear braking device B 1  and a front operating device via which a user operates a front braking device B 2 . 
     In the present application, the following directional terms “front,” “rear,” “forward,” “rearward,” “left,” “right,” “transverse,” “upward” and “downward” as well as any other similar directional terms refer to those directions which are determined on the basis of a user who sits on the saddle  2  of the human-powered vehicle  10  with facing the handlebar  1 . Accordingly, these terms, as utilized to describe components, should be interpreted relative to the human-powered vehicle  10  equipped with the components as used in an upright riding position on a horizontal surface. 
     As seen in  FIG.  2   , the drive train  12  for the human-powered vehicle  10  comprises a drive unit  14 . The drive unit  14  includes a motor  16  configured to impart propulsion to the human-powered vehicle  10 . The drive train  12  comprises a crank assembly  18  rotatably mounted to the vehicle frame  3 . The crank assembly  18  includes a crank axle  18 A and crank arms  18 B and  18 C. The crank arms  18 B and  18 C are secured to the crank axle  18 A. For example, the drive unit  14  is configured to apply an assist rotational force to the crank assembly  18 . 
     The drive unit  14  comprises a pedaling-force sensor  20  configured to sense a pedaling force applied to the crank assembly  18  from a rider. The drive unit  14  includes a motor controller  19  configured to control the motor  16  to add the assist rotational force to the drive train  12  in response to the pedaling force sensed by the pedaling-force sensor  20 . However, the motor controller  19  is configured to control the motor  16  to add the rotational force to the drive train  12  regardless of the pedaling force. For example, the motor controller  19  is configured to control the motor  16  to add the rotational force to the drive train  12  in response to a user input received by the operating device  4 . 
     The drive train  12  for the human-powered vehicle  10  comprises a sprocket arrangement  22 . The sprocket arrangement  22  is operatively coupled to the drive unit  14 . The sprocket arrangement  22  for the human-powered vehicle  10  comprises a plurality of rear sprockets RS. The sprocket arrangement  22  comprises a plurality of front sprockets FS mounted to the crank assembly  18 . The drive train  12  comprises a chain C engaged with the plurality of front sprockets FS and the plurality of rear sprockets RS to transmit a rotational force from the plurality of front sprockets FS to the plurality of rear sprockets RS. In the present application, the “sprocket” indicates a member engageable with the chain C and does not include a gear provided in an internal transmission device. 
     As seen in  FIG.  1   , the drive train  12  further comprises a rear derailleur RD configured to shift the chain C relative to the plurality of rear sprockets RS. The drive train  12  further comprises a front derailleur FD configured to shift the chain C relative to the plurality of front sprockets FS. The rear derailleur RD is configured to shift the chain C among a plurality of rear gear positions respectively corresponding to the plurality of rear sprockets RS in response to a gear-shift operation which is input to the operating device  4 . The front derailleur FD is configured to shift the chain C among a plurality of front gear positions respectively corresponding to the plurality of front sprockets FS in response to a gear-shift operation which is input to the operating device  4 . 
     In this embodiment, the rear derailleur RD includes a chain guide RD 1  and an electric actuator RD 2  configured to move the chain guide RD 1  in response to a user input received by the operating device  4 . The front derailleur FD includes a chain guide FD 1  and an electric actuator FD 2  configured to move the chain guide FD 1  in response to a user input received by the operating device  4 . The rear derailleur RD is electrically connected to the operating device  4  with a wire communication or a wireless communication. The front derailleur FD is electrically connected to the operating device  4  or the rear derailleur RD with a wire communication or a wireless communication. However, the rear derailleur RD and/or the front derailleur FD can be operated with a mechanical cable. 
     The drive train  12  includes a power supply PS. The power supply PS is electrically connected to the operating device  4 , the motor  16 , the rear derailleur RD, and the front derailleur FD to supply electricity to the operating device  4 , the motor  16 , the rear derailleur RD, and the front derailleur FD. The power supply PS includes a battery PS 1  and a battery holder PS 2 . Examples of the battery PS 1  include a primary battery such as a lithium manganese dioxide battery, and a secondary battery such as a lithium-ion secondary battery. In this embodiment, the battery PS 1  is the secondary battery. The battery PS 1  is detachably attached to the battery holder PS 2  to supply electricity to the gear shifting device RD, the additional gear shifting device FD, and other electric components. For example, the battery PS 1  includes a plurality of battery cells. The battery holder PS 2  is mounted to the vehicle body  3  ( FIG.  1   ) and is electrically connected to the operating device  4 , the motor  16 , the gear shifting device RD, and the additional gear shifting device FD to supply electricity from the battery PS 1  to the operating device  4 , the motor  16 , the rear derailleur RD, and the front derailleur FD to supply electricity to the operating device  4 , the rear derailleur RD, and the front derailleur FD. The battery holder PS 2  can be provided in the vehicle body  3  ( FIG.  1   ). The drive train  12  can include another power supply configured to supply electricity to the rear derailleur RD and/or the front derailleur FD instead of or in addition to the power supply PS. 
     As seen in  FIG.  3   , a total number of the plurality of rear sprockets RS is equal to or smaller than 10. The total number of the plurality of rear sprockets RS is equal to or larger than 5. In this embodiment, the total number of the plurality of rear sprockets RS is 10. The plurality of rear sprockets RS includes first to tenth rear sprockets RS 1  to RS 10 . However, the total number of the plurality of rear sprockets RS is not limited to this embodiment. 
     The sprocket arrangement  22  includes at least one individual sprocket-space provided between two adjacent rear sprockets among the plurality of rear sprockets RS. The two adjacent rear sprockets RS are adjacent to each other without another rear sprocket therebetween in an axial direction D 1  with respect to a rotational center axis A 1  of the plurality of rear sprockets RS. 
     In this embodiment, the sprocket arrangement  22  includes a plurality of individual sprocket-spaces S provided between two adjacent rear sprockets among the plurality of rear sprockets RS. Specifically, the plurality of individual sprocket-spaces S includes first to ninth individual sprocket-spaces S 1  to S 9 . A total number of the plurality of individual sprocket-spaces S is nine. However, the total number of the plurality of individual sprocket-spaces S is not limited to this embodiment. 
     As seen in  FIG.  2   , a total number of the plurality of front sprockets FS is equal to or smaller than two. In this embodiment, the total number of the plurality of front sprockets FS is two. The plurality of front sprockets FS includes first and second front sprockets FS 1  and FS 2 . However, the total number of the plurality of front sprockets FS is not limited to this embodiment. 
     As seen in  FIG.  4   , the drive train  12  for the human-powered vehicle  10  comprises a plurality of gear ratios. In this embodiment, the sprocket arrangement  22  comprises a plurality of gear ratios. The plurality of gear ratios respectively corresponds to the plurality of rear sprockets RS. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. In this embodiment, combinations of the plurality of rear sprockets RS and the plurality of front sprockets FS provide the plurality of gear ratios. 
     In this embodiment, a total number of sprocket teeth of the first rear sprocket RS 1  is 63. A total number of sprocket teeth of the second rear sprocket RS 2  is 50. A total number of sprocket teeth of the third rear sprocket RS 3  is 40. A total number of sprocket teeth of the fourth rear sprocket RS 4  is 32. A total number of sprocket teeth of the fifth rear sprocket RS 5  is 26. A total number of sprocket teeth of the sixth rear sprocket RS 6  is 21. A total number of sprocket teeth of the seventh rear sprocket RS 7  is 17. A total number of sprocket teeth of the eighth rear sprocket RS  8  is 14. A total number of sprocket teeth of the ninth rear sprocket RS 9  is 11. A total number of sprocket teeth of the tenth rear sprocket RS 10  is 9. The total number of sprocket teeth can also be referred to as a total tooth-number. However, the total tooth-number of each of the plurality of rear sprockets RS is not limited to this embodiment. 
     A total number of sprocket teeth of the first front sprocket FS 1  is 28. A total number of sprocket teeth of the second front sprocket FS 2  is 38. However, the total tooth-number of each of the plurality of front sprockets FS is not limited to this embodiment. 
     The drive train  12  comprises a total gear range quotient obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is larger than 5. The total gear range quotient is equal to or larger than 6.95. The total gear range quotient is equal to or larger than 7. The total gear range quotient is equal to or larger than 9. The total gear range quotient is equal to or smaller than 11. 
     The largest gear ratio is obtained by dividing the largest total tooth-number in the plurality of front sprockets FS by the smallest total tooth-number in the plurality of rear sprockets RS. The smallest gear ratio is obtained by dividing the smallest total tooth-number in the plurality of front sprockets FS by the largest total tooth-number in the plurality of rear sprockets RS. 
     In this embodiment, the largest gear ratio is 4.22 if the total tooth-number of the second front sprocket FS 2  is 38 and the total tooth-number of the tenth rear sprocket RS 10  is 9. The smallest gear ratio is 0.44 if the total tooth-number of the first front sprocket FS 1  is 28and the total tooth-number of the first rear sprocket RS 1  is 63. The total gear range quotient is 9.5 if the largest gear ratio is 4.22 and the smallest gear ratio is 0.44. However, the total gear range quotient is not limited to this embodiment and the above ranges. The largest gear ratio and the smallest gear ratio are not limited to this embodiment. 
     The force-transmission coefficient obtained by dividing the total gear range quotient by the total number of the at least one individual sprocket-space is larger than 1. In this embodiment, the force-transmission coefficient is 1.06 if the total gear range quotient is 9.50 and the total number of the plurality of individual sprocket-spaces S is 9. However, the force-transmission coefficient is not limited to this embodiment and the above range. As seen in  FIG.  5   , for example, the force-transmission coefficient obtained by dividing the total gear range quotient by the total number of the at least one individual sprocket-space can be equal to or smaller than 1. In the modification of  FIG.  5   , the largest gear ratio is 4.22, the smallest gear ratio is 0.48, the total gear range quotient is 8.75, and the force-transmission coefficient is 0.97. 
     As seen in  FIG.  3   , the plurality of rear sprockets RS includes a largest rear sprocket and a smallest rear sprocket. In this embodiment, the largest rear sprocket is the first rear sprocket RS 1 . The smallest rear sprocket is the tenth rear sprocket RS 10 . As seen in  FIG.  4   , the sprocket arrangement  22  comprises a gear range quotient obtained by dividing a total tooth-number of the largest rear sprocket by a total tooth-number of the smallest rear sprocket. The gear range quotient is larger than 6.01. The gear range quotient is equal to or larger than 7. The gear range quotient is equal to or smaller than 11. In this embodiment, the total gear range quotient is 7 if the total tooth-number of the largest rear sprocket RS 1  is 63 and the total tooth-number of the smallest rear sprocket RS 10  is 9. However, the total gear range quotient is not limited to this embodiment. As seen in  FIG.  6   , for example, the gear range quotient can be equal to or larger than 9. In the modification of  FIG.  6   , the total tooth-number of the largest rear sprocket RS 1  is 81, the total tooth-number of the smallest rear sprocket RS 1  is 9, and the gear range quotient is 9. 
     Second Embodiment 
     A human-powered vehicle  210  including a drive train  212  in accordance with a second embodiment will be described below referring to  FIG.  7   . The drive train  212  has the same structure and/or configuration as those of the drive train  12  except for the internal transmission device. Thus, elements having substantially the same function as those in the first embodiment will be numbered the same here and will not be described and/or illustrated again in detail here for the sake of brevity. 
     As seen in  FIG.  7   , the drive train for the human-powered vehicle  210  comprises the drive unit  14  and the sprocket arrangement  22 . In this embodiment, the drive train  212  further comprises at least one internal transmission device  224 . The at least one internal transmission device  224  includes a rear internal transmission device  226  configured to be disposed on the rear wheel  6 . The at least one internal transmission device  224  includes a front internal transmission device  228  configured to be coupled to the crank assembly  18 . 
     For example, the rear internal transmission device  226  includes a planetary gear structure. The rear internal transmission device  226  has at least one gear ratio to increase a rotational speed of the rear wheel  6  relative to a rotational speed of the plurality of rear sprockets RS. 
     The front internal transmission device  228  is provided between the crank assembly  18  and the plurality of front sprockets FS. For example, the front internal transmission device  228  includes a planetary gear structure. The front internal transmission device  228  has at least one gear ratio to increase a rotational speed of the plurality of front sprockets FS relative to a rotational speed of the crank assembly  18 . 
     In this embodiment, for example, the sprocket arrangement  22  has the same gear ratios as the gear ratios shown in  FIG.  5    of the first embodiment. However, the sprocket arrangement  22  can have other gear ratios by utilizing the gear ratios of the at least one internal transmission device  224 . At least one of the rear internal transmission device  226  and the front internal transmission device  228  can be omitted from the drive train  212 . 
     Third Embodiment 
     A human-powered vehicle  310  including a drive train  312  in accordance with a third embodiment will be described below referring to  FIGS.  8  and  9   . The drive train  312  has the same structure and/or configuration as those of the drive train  12  except for the internal transmission device and the sprocket arrangement. Thus, elements having substantially the same function as those in the above embodiments will be numbered the same here and will not be described and/or illustrated again in detail here for the sake of brevity. 
     As seen in  FIG.  8   , the drive train  312  for the human-powered vehicle  310  comprises at least one internal transmission device  324 . In this embodiment, the sprocket arrangement  22  is omitted from the drive train  312 . Instead, the drive train  312  comprises a front sprocket FS 31  and a rear sprocket RS 31 . A total number of sprocket teeth of the front sprocket FS 31  is equal to a total number of sprocket teeth of the rear sprocket FS 32 . The total number of sprocket teeth can also be referred to as a total tooth-number. However, the total tooth-number of the front sprocket FS 31  can be different from the total tooth-number of the rear sprocket FS 32 . 
     In this embodiment, the at least one internal transmission device  324  includes a rear internal transmission device  326  configured to be disposed on the rear wheel  6 . The at least one internal transmission device  324  includes a front internal transmission device  328  configured to be coupled to the crank assembly  18 . 
     The rear internal transmission device  326  is provided between the rear sprockets RS 31  and the hub assembly  6 A of the rear wheel  6 . For example, the rear internal transmission device  326  includes a planetary gear structure. The rear internal transmission device  326  has at least one gear ratio to increase a rotational speed of the rear wheel  6  relative to a rotational speed of the rear sprockets RS 31 . 
     The front internal transmission device  328  is provided between the crank assembly  18  and the front sprockets FS 31 . For example, the front internal transmission device  328  includes a planetary gear structure. The front internal transmission device  328  has at least one gear ratio to increase a rotational speed of the front sprocket FS 31  relative to a rotational speed of the crank assembly  18 . 
     As seen in  FIG.  9   , the at least one internal transmission device  324  has a plurality of gear ratios. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. The drive train  212  comprises a total gear range quotient obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is equal to or larger than 6.37. 
     In this embodiment, the rear internal transmission device  326  has a plurality of rear gear ratios GR 1  to GR 10 . The front internal transmission device  326  has a plurality of front gear ratios GF 1  and GF 2 . The plurality of gear ratios of the drive train  312  is defined by the rear gear ratios GR 1  to GR 10  and the front gear ratios GF 1  and GF 2 . The largest gear ratio is 4.20. The smallest gear ratio is 0.44. 
     The drive train  312  for the human-powered vehicle  310  comprises a plurality of gear ratios. The plurality of gear ratios includes a largest gear ratio and a smallest gear ratio. The drive train  312  for the human-powered vehicle  310  comprises a total gear range quotient obtained by dividing the largest gear ratio by the smallest gear ratio. The total gear range quotient is equal to or larger than 6.95. The total gear range quotient is equal to or larger than 9. 
     In this embodiment, the total gear range quotient is 9.54 if the largest gear ratio is 4.2 and the smallest gear ratio is 0.44. However, the largest gear ratio, the smallest gear ratio, and the total gear range quotient are not limited to this embodiment and the above ranges. 
     Other Modifications 
     In the above embodiments and the above modifications, the total number of the rear sprockets RS is 10, and the total number of the front sprockets FS is 2. However, the total number of the rear sprockets RS and the total number of the front sprockets FS are not limited to the above embodiments and the above modifications. The total number of the rear sprockets RS can be larger than 10. The total number of the front sprockets FS can be larger than 2. In such modifications, it is possible to reduce a difference between the total number of a rear sprocket and the total number of another rear sprocket adjacent to the rear sprocket. It is possible to reduce a difference between the total number of a front sprocket and the total number of another front sprocket adjacent to the front sprocket. 
     In the third embodiment, the drive train  312  can include a sprocket arrangement as well as the other embodiments and the modifications. 
     The term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. This concept also applies to words of similar meaning, for example, the terms “have,” “include” and their derivatives. 
     The terms “member,” “section,” “portion,” “part,” “element,” “body” and “structure” when used in the singular can have the dual meaning of a single part or a plurality of parts. 
     The ordinal numbers such as “first” and “second” recited in the present application are merely identifiers, but do not have any other meanings, for example, a particular order and the like. Moreover, for example, the term “first element” itself does not imply an existence of “second element,” and the term “second element” itself does not imply an existence of “first element.” 
     The term “pair of,” as used herein, can encompass the configuration in which the pair of elements have different shapes or structures from each other in addition to the configuration in which the pair of elements have the same shapes or structures as each other. 
     The terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. 
     The phrase “at least one of” as used in this disclosure means “one or more” of a desired choice. For one example, the phrase “at least one of” as used in this disclosure means “only one single choice” or “both of two choices” if the number of its choices is two. For other example, the phrase “at least one of” as used in this disclosure means “only one single choice” or “any combination of equal to or more than two choices” if the number of its choices is equal to or more than three. For instance, the phrase “at least one of A and B” encompasses (1) A alone, (2), B alone, and (3) both A and B. The phrase “at least one of A, B, and C” encompasses (1) A alone, (2), B alone, (3) C alone, (4) both A and B, (5) both B and C, (6) both A and C, and (7) all A, B, and C. In other words, the phrase “at least one of A and B” does not mean “at least one of A and at least one of B” in this disclosure. 
     Finally, terms of degree such as “substantially,” “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. All of numerical values described in the present application can be construed as including the terms such as “substantially,” “about” and “approximately.” 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.