Patent Publication Number: US-2016229487-A1

Title: Vehicle operable by motor and by muscle power having gear-change assistance

Description:
FIELD OF THE INVENTION 
     The present invention relates to a vehicle operable by motor and by muscle power having a gear-change assistance device, and a method for operating such a vehicle for an improved gear change. 
     BACKGROUND INFORMATION 
     Electric bicycles are believed to be understood in various designs from the related art. In general, in bicycles having derailleur gears with multiple chain rings, so-called “climbing aids” are used, which carry along the chain when shifting to a larger chain ring and make the transfer from the smaller to the larger chain ring easier. These climbing aids are situated at predefined positions on the larger chain ring. In the case of multiple chain rings on the crank drive, the positions of the climbing aids are fixed in relation to the positions of the pedals. The climbing aids are typically situated in this case in such a way that during a shifting procedure, a minimal crank torque may be always generated by the bike rider. In electric bicycles, the problem arises that pedal position and location of the chain ring are no longer uniquely fixed in relation to one another, since the two parts are separated by a freewheel. However, in particular with multiple chain rings on the crank drive, increased wear thus results during the shifting procedure. 
     SUMMARY OF THE INVENTION 
     The vehicle according to the present invention, which is operable by motor power and/or muscle power, in particular an electric bicycle, having the features described herein has the advantage over the related art in that a shift assistance may be provided during every shifting procedure of the vehicle and therefore wear on gearwheels and chain of the vehicle may be significantly reduced. In particular, the present invention also enables the use of multiple chain rings having different numbers of teeth on the crank drive of the vehicle, without an excessively high torque being applied during the shifting procedure, even with the motor-driven assistance of the bike rider. This is achieved according to the present invention in that the vehicle includes, in addition to an electric drive and a power supply, a chain, a crank drive, and a gearshift having at least one first and one second gearwheel and a chain transfer assistance unit. This chain transfer assistance unit is situated on one of the gearwheels and assists a transfer of the chain from the first to the second gearwheel during a gear change. The chain transfer assistance unit may be, for example, an element protruding laterally on the gearwheel, over which the chain also runs during the gear change. 
     According to the present invention, a control unit is provided, which controls the electric drive, the control unit being configured to drive the electric drive during a gear change. The chain is moved in such a way that the chain transfer assistance unit is moved into a gear-change position, in which the chain transfer assistance unit optimally assists the gear change. 
     The descriptions herein specify refinements of the present invention. 
     The chain transfer assistance units may be particularly situated on one of the gearwheels, in particular laterally to a gearwheel. A simply constructed and effective assistance may thus be provided during the gear change. 
     Furthermore, the vehicle may include a sensor, which detects a gear-change intent of the bike rider. The sensor reports the gear-change intent of the bike rider to the control unit, which then generates a signal for the electric drive to move the chain transfer assistance unit into the gear-change position. 
     The vehicle particularly may include a manual shift unit and the sensor for detecting the gear-change intent is situated on the manual shift unit, which may be actuated by the bike rider. The manual shift unit is, for example, a shift lever or a shift twist grip. 
     Furthermore, the vehicle may include an electric actuator for actuating the gearshift. The signal generated on the electric actuator for the gear change may be also the signal for the electric drive to move the chain transfer assistance unit into the gear-change position. 
     The first and second gear wheels of the gearshift may be particularly situated on the crank drive of the vehicle. In this case, the two gearwheels therefore form two chain rings having different numbers of teeth, a chain being able to change with the aid of a front derailleur between the two chain rings, for example. 
     Furthermore, the vehicle may include a freewheel, which is provided between the output of the crank and a chain ring, which is engaged with the chain. The freewheel may be particularly provided as switchable, i.e., the bike rider may determine, for example, with the aid of a switch, whether or not the freewheel is to be activated. 
     According to another embodiment of the present invention, the electric drive is situated in the area of the crank drive. A relatively low center of gravity may thus be achieved in an electric bicycle, for example. Moving the chain transfer assistance unit rapidly into position may also be achieved. 
     Furthermore, the present invention relates to a method for operating a vehicle operable by motor and/or muscle power, for example, an electric bicycle. The vehicle includes an electric drive, a power supply, a gearshift having a first and a second gear wheel and a chain transfer assistance unit, a chain, a crank drive, and a control unit to control the electric drive. The chain transfer assistance unit is situated on a gearwheel. The method includes the steps of detecting a gear-change intent and driving the electric drive to move the chain, so that the chain transfer assistance unit is moved into a gear-change position, in which a gear change is assisted by the chain transfer assistance unit. 
     One exemplary embodiment of the present invention is described in detail hereafter with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of a vehicle according to one specific embodiment of the present invention. 
         FIG. 2  shows a schematic illustration of a chain ring arrangement according to the present invention having two chain rings. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an electric bicycle  1  according to one exemplary embodiment of the present invention. 
     Electric bicycle  1  according to the present invention includes a crank drive  2  and an electric drive  3 , which is situated in the area of the crank drive. Furthermore, electric bicycle  1  includes a gearshift  4  having a chain  5 , a plurality of pinions  6  on a rear wheel  19 , and a front shifter having a chain ring arrangement  7 . The front shifter includes two gearwheels  7   a,    7   b  as chain rings. 
     Reference numerals  8  and  9  identify cranks of crank drive  2 . 
     Furthermore, a power supply  11  is provided on a frame of the electric bicycle, which supplies electric drive  3  with power. 
     Electric bicycle  1  furthermore includes a control unit  10 , which is situated in this exemplary embodiment on the handlebar of the electric bicycle. Furthermore, a shift unit  12  is situated on the handlebar, which is shifted manually by a bike rider. A sensor  13  is provided on shift unit  12 , which detects a gear-change intent of the bike rider. Sensor  13  is connected to control unit  10 . 
     As is apparent from  FIG. 2 , a chain transfer assistance unit  14 , which is situated laterally on gearwheel  7   a,  is provided on larger gearwheel  7   a.    
     Chain transfer assistance unit  14  assists, in the event of a gear change, as shown in  FIG. 2 , a transfer of chain  5  from a first, small gearwheel  7   b  to a second, larger gearwheel  7   a.  A position of chain transfer assistance unit  14  may be situated in such a way that a torque exerted by the bike rider on the crank drive is minimal in this position. This is the case in particular when one of cranks  8 ,  9  is located at a bottom dead center or in the vicinity of the bottom dead center. 
     Control unit  10  is configured in such a way that in the event of a gear change, which the bike rider initiates via shift unit  12 , sensor  13  transmits a corresponding signal to control unit  10 . Control unit  10  thereupon drives electric drive  3 , to move chain transfer assistance unit  14  into a gear-change position, in which the gear change is maximally assisted. Since a freewheel (not shown) is provided between crank drive  2  and chain rings  7 , this may also take place when the bike rider stops pedaling or the pedaling slows. Electric drive  3  may rotate chain rings  7  independently of a pedal actuation by the bike rider, so that chain transfer assistance unit  14  is movable into an optimum position. 
     According to the present invention, wear on chain  5  and chain rings  7  may thus be minimized, since chain transfer assistance unit  14  is always positioned in the optimum position for the transfer of the chain from the first to the second gearwheel. 
     According to the present invention, in particular in the case of so-called front derailleurs on the crank drive, a gearshift may be implemented which has multiple chain rings. 
     If a torque sensor is furthermore situated on crank drive  2 , as may also be the case, control unit  10  may drive electric drive  3  in each case in such a way that the shifting procedure may be carried out with an optimum torque. The control unit may detect the torque applied by the bike rider during the shifting procedure and provide the amount of torque which is lacking for the optimum torque for the shifting procedure by way of electric drive  3 , or also limit it if the bike rider wishes to carry out the shifting procedure using an excessively large amount of torque.