Abstract:
A vehicle that is operable by motor power and/or by muscular power, in particular an electric bicycle, including a crankshaft drive having a bottom bracket bearing shaft, a front sprocket that transmits a drive torque for the vehicle to a chain, an electric drive and a friction gear for continuously varying a transmission ratio, the friction gear and the electric drive being configured on the crankshaft drive, and the friction gear being coupled to the crankshaft drive and adapted for transmitting a rider-produced torque to the front sprocket.

Description:
BACKGROUND INFORMATION 
     The present invention relates to a vehicle that is operable by motor power and/or by muscular power, in particular an electric bicycle, having a friction gear. 
     Electric bicycles of various designs are known from the related art, for example. There are electric bicycles where the electric drive is configured in the area of the bottom bracket bearing (mid-engine design). A rear wheel is then driven by a chain. In this case, a gearshift device, for example, a derailleur or hub gear or the like may be configured on the rear wheel. Other alternative configurations, specifically of gearshift devices, would be desirable here. 
     SUMMARY OF THE INVENTION 
     The vehicle that is operable by motor power and/or by muscular power in accordance with the present invention, in particular an electric bicycle having the features of claim  1 , has the advantage of permitting an especially compact design of an electric drive and of a gearshift device. One particular advantage is that the gearshift device makes it possible for a transmission to be continuously varied. In this case, an especially compact design is made possible by the present invention. In addition, a continuous variation of a transmission may allow an especially effective interplay between a pedal drive and an electric drive, making the present invention especially suited for an electric bicycle. The transmission may be readily varied even under load and, in particular, noise may even be avoided in the case of a change in the transmission ratio, so that varying the transmission ratio in accordance with the present invention is a very noiseless process. This is achieved in accordance with the present invention in that the vehicle features a crankshaft drive having a bottom bracket bearing shaft, a front sprocket, and an electric drive. Moreover, the vehicle includes a continuously variable friction gear for continuously varying the transmission ratio. The friction gear is thereby configured on the crankshaft drive, is coupled thereto, and is adapted for transmitting a rider-produced torque to the front sprocket. With regard to the continuously variable friction gear, it is also advantageous that a gear shifting under load is possible, and that a rider does not notice any sudden transmission changes. An especially advantageous driving feel results herefrom, in particular in combination with the electric drive, since the torque thereof and the speed are likewise steplessly controllable. 
     Preferred embodiments of the present invention are recited in the dependent claims. 
     To achieve an especially compact design, the friction gear is preferably configured within a housing of the crankshaft drive. 
     The friction gear is preferably a traction mechanism drive, in particular a CVT transmission having a traction mechanism and two V-pulleys. 
     It is also preferred that the vehicle have a first planetary gear via which the electric drive is connected to the front sprocket, thereby driving the same. A bushing or the like, for example, may provide a coupling between the planetary gear and the front sprocket. The bushing is preferably mounted via a freewheel on the bottom bracket bearing shaft. 
     The electric drive preferably drives the front sprocket via the friction gear. Here, the advantage is derived that the friction gear makes possible a continuously variable transmission, so that, depending on the control of the electric drive, an optimal transmission ratio may be rendered possible by the friction gear. 
     It is also preferred that the friction gear be coupled via the first planetary gear to the front sprocket. At the same time, it is especially preferred that a planetary gear be configured between the electric drive and the friction gear. 
     A ring gear of the planetary gear preferably features an external toothing via which the planetary gear is driven by the output of the electric drive. 
     In accordance with another preferred embodiment of the present invention, a rider-operated actuator may vary a transmission of the friction gear. If the friction gear is a CVT transmission, a control motor is preferably used to adjust one of the two V-pulleys. 
     An especially compact design is obtained when the bottom bracket bearing shaft extends through a component of the friction gear, in particular through one of the V-pulleys of the CVT transmission. 
     It is also preferred that the vehicle have a second planetary gear, the second planetary gear being configured between the bottom bracket bearing shaft and the friction gear. This permits an even better adaptation and transmission of the rider-applied torque. 
     The vehicle also preferably includes a control unit and a force sensor for recording a rider-applied force. This makes it possible to determine a force value, the control unit being adapted for controlling the electric drive of the vehicle on the basis of the recorded force value. Additionally or alternatively, a rider-applied torque may also be used for controlling the electric drive. The force sensor is preferably configured on the ring gear of the second planetary gear. This allows the force sensor to be readily integrated in the motor gear assembly. 
     Another preferred embodiment of the present invention provides that the friction gear be mounted above the bottom bracket bearing shaft. It is also preferred that the electric motor be mounted below the bottom bracket bearing shaft. 
     It is especially preferred that the vehicle according to the present invention be an electric bicycle, making it possible to eliminate a gearshift device on a rear wheel of the electric bicycle by using the continuously variable friction gear in accordance with the present invention. By configuring both the electric drive, as well as the gearshift device in the form of the friction gear on the bottom bracket bearing, an especially low center of gravity of the electric bicycle is also thereby made possible, thereby positively influencing the handling properties of the electric bicycle. 
    
    
     
       DRAWING 
       Preferred exemplary embodiments of the present invention are described in detail in the following with reference to the accompanying drawing. Like or functionally equivalent parts are denoted by the same reference numerals in the exemplary embodiments. In the drawing: 
         FIG. 1  shows a schematic view of a component of an electric bicycle in accordance with a first exemplary embodiment of the present invention; 
         FIG. 2  shows a schematic view of a crankshaft drive of an electric bicycle in accordance with the first exemplary embodiment of the present invention; 
         FIG. 3  shows a schematic view of a crankshaft drive of an electric bicycle in accordance with a second exemplary embodiment of the present invention; 
         FIG. 4  shows a schematic view of a crankshaft drive of an electric bicycle in accordance with a third exemplary embodiment of the present invention; and 
         FIG. 5  shows a schematic partial view of the crankshaft drive of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     An electric bicycle  1  in accordance with a first preferred exemplary embodiment of the present invention is described in detail in the following with reference to  FIGS. 1 and 2 . 
     As is readily apparent from  FIG. 1 , electric bicycle  1  includes a crankshaft drive  2  within which an electric drive  3  (see  FIG. 2 ) is integrated. A front sprocket  4  transmits a tractive force via a chain  5  to a pinion  6  configured on a rear wheel  9 . Reference numerals  7  and  8  denote crank arms having pedals of the electric bicycle. 
       FIG. 2  shows crankshaft drive  2  in detail. Besides the two crank arms  7 ,  8 , crankshaft drive  2  includes a bottom bracket bearing shaft  20  that is supported on a first bottom bracket bearing  21 , a second bottom bracket bearing  22 , and a third bottom bracket bearing  23 . A rider-applied pedal force is transmitted by the pedals to bottom bracket bearing shaft  20 . Arrow A indicates a rotation of the bottom bracket bearing shaft. 
     Also configured on bottom bracket bearing shaft  20  is an input V-pulley  11  of a CVT transmission  10 . In addition, CVT transmission  10  includes an output V-pulley  12 , as well as a traction mechanism  13 , for example, a belt that joins the two V-pulleys. Output V-pulley  12  is secured to an intermediate shaft  14  on which a first gear wheel  26  of a first gear stage  25  is also configured. 
     In addition, first gear stage  25  includes a second gear wheel  27 , as well as an intermediate gearwheel  28  for reversing the direction of rotation within first gear stage  25 . 
     As is also readily apparent from  FIG. 2 , second gear wheel  27  is coupled to a planetary-gear carrier  18  of a planetary gear  15 . Planetary gear  15  also includes a sun gear  16 , planetary gear wheels  17 , as well as a ring gear  19 . 
     Sun gear  16  is configured on a bushing  53  upon which front sprocket  4  is also mounted (compare  FIG. 2 ). Bushing  53  is mounted via second and third bottom bracket bearing  22 ,  23  on bottom bracket bearing shaft  20 . 
     Ring gear  19  of planetary gear  15  also features an external toothing that meshes with a motor pinion  51  of electric drive  3 . Motor pinion  51  is mounted on a motor output shaft  46 . A control unit  60  controls electric drive  3 . 
     Second gear wheel  27  of first gear stage  25  is mounted by a first bearing  31  on bottom bracket bearing shaft  20 . In addition, ring gear  19  of planetary gear  15  is mounted by a second bearing  32  on the bottom bracket bearing shaft. 
     CVT transmission  10  may be shifted by the rider via an actuator (not shown). Thus, the electric bicycle may do without a gearshift control at the hub of rear wheel  9 . 
     Overall, therefore, a pedal force of a rider is transmitted via bracket bearing shaft  20  and CVT transmission  10  into planetary gear  15 . If a propulsion by electric drive  3  is additionally or exclusively desired, then this torque of electric drive  3  is likewise transmitted into planetary gear  15  and, from there, acts via sun gear  16  and bushing  53  on front sprocket  4 . 
     Thus, the friction gear configured as CVT transmission  10  assumes the function of a gearshift device of the bicycle. In this case, a transmission ratio of CVT transmission  10  may be varied continuously. The drive unit according to the present invention having a gear on the crankshaft drive may thereby be very compact and of small construction. Motor output shaft  46  extends parallel to bottom bracket bearing shaft  20  and also parallel to intermediate shaft  14  at the output of CVT transmission  10 . 
     Thus, the present invention provides that both a gearshift device, as well as an electric drive  3  be configurable on crankshaft drive  2 . Electric drive  3  and the gearshift device configured as CVT transmission  10  are preferably configured in a shared housing of crankshaft drive  2 . As is readily apparent from  FIG. 2 , intermediate shaft  14  is located above bottom bracket bearing shaft  20 , and electric drive  3  is located below bottom bracket bearing shaft  20 . CVT transmission  10  may thereby render possible a continuously variable transmission of a rider-applied torque. This makes possible an especially effective interplay of the rider-applied torque and of the torque provided by electric drive  3 . In particular, CVT transmission  10  also allows the transmission to be varied under load, so that, even if a transmission ratio changes, electric drive  3  may be continuously driven, as needed, and generate additional torque for a propulsion. 
       FIG. 3  shows a crankshaft drive in accordance with a second exemplary embodiment of the present invention, where, in contrast to the first exemplary embodiment, in addition to the torque applied by the rider by pedaling, the output torque of electric drive  3  is also input into CVT transmission  10 . In this case, a planetary gear  15  is configured between bottom bracket bearing shaft  20  and CVT transmission  10 , as well as between electric drive  3  and CVT transmission  10 . Sun gear  16  of planetary gear  15  is thereby fixedly mounted on bottom bracket bearing shaft  20  and thus receives the torque produced by pedaling. Electric drive  3  transmits a torque via a motor output shaft  46  and a motor pinion  51  to a ring gear  19  of planetary gear  15 . Ring gear  19  features an external toothing here that meshes with motor pinion  51 . Planetary gear  15  is output via a planetary-gear carrier  18  that is coupled to a hollow shaft  34 . Hollow shaft  34  is supported via a fourth and fifth bottom bracket bearing  35 ,  36  on bottom bracket bearing shaft  20  and is fixedly coupled to input V-pulley  11  of CVT transmission  10  (compare  FIG. 3 ). 
     Connected downstream of CVT transmission  10 , in turn, is a first gear stage  25  having a first gear wheel  26 , a second gear wheel  27 , and an intermediate gear wheel  28  for reversing a direction of rotation. Second gear wheel  27  is configured directly on bushing  53  upon which front sprocket  4  is mounted. 
     The second exemplary embodiment thereby has the advantage that transmission of both the torque applied by the rider by pedaling, as well as of the torque applied by electric drive  3  may be carried out via CVT transmission  10  in the desired manner. Electric drive  3  may be controlled to preferably always be operated within the optimal speed range, and an optimal transmission is then carried out via CVT transmission  10  as a function of a torque applied by the rider by pedaling. 
       FIGS. 4 and 5  show a crankshaft drive  2  in accordance with a third exemplary embodiment of the present invention. As in the case of the first exemplary embodiment, in the third exemplary embodiment, only one rider-applied torque may be varied via CVT transmission  10 . Electric drive  3  transmits the torque thereof into a first planetary gear  15 , as in the first exemplary embodiment. In addition, in the third exemplary embodiment, a second planetary gear  55  having a sun gear  56 , planetary gear wheels  57 , a planetary-gear carrier  58  and a ring gear  59  are also provided. Ring gear  59  is fixed. A torque applied by the rider by pedaling is introduced via planetary-gear carrier  58  that is coupled to bottom bracket bearing shaft  20  into second planetary gear  55 . An output from second planetary gear  55  via sun gear  56  drives a hollow shaft  34 . Hollow shaft  34  is supported on bottom bracket bearing shaft  20  via a fourth and fifth bottom bracket bearing  35 ,  36 . Hollow shaft  34  is directly coupled to input V-pulley  11  of CVT transmission  10 . 
     Also configured on fixed ring gear  59  of second planetary gear  55  is a tension rod  43  that is coupled to a tensioning spindle  44  for pretensioning CVT transmission  10 . Tension rod  43  is pretensioned by a spring  45  (compare  FIG. 5 ). 
     In addition, a force sensor  61 , which is adapted for determining the pedal force applied by the rider, is configured on fixed ring gear  59 . Force sensor  61  is connected to control unit  60 . A control motor  62  and an adjustment spindle  63  are provided to adjust the transmission ratio of CVT transmission  10 . In particular, a spacing of output V-pulley  12  of CVT transmission  10  is varied by adjustment spindle  63 . 
     When a rider pedals via crank arms  7 ,  8 , a torque is exerted on fixed ring gear  59  of second planetary gear  55  and is transmitted to tension rod  43 . If the rider pedals more vigorously during operation, thereby increasing the torque, a tensioning spindle  44  is rotated at a higher rate. At the same time, at the opposite side of tensioning spindle  44 , force sensor  61  on ring gear  59  measures a force that corresponds to the force applied by the rider. On the basis of this force, control unit  60  determines an optimal transmission ratio of CVT transmission  10  and drives control motor  62  accordingly. Thus, in the case of the third exemplary embodiment, optimal transmission ratio may be ensured on CVT transmission  10  by a simple and compact pedal-force measurement.