Abstract:
Apparatus and method for controlling an electric motor providing assistance to a bicycle rider based on measuring the mechanical power generated by the rider. The power generated by the rider is measured by measuring tension in a bicycle chain (or belt) and RPM. A chain (or belt) roller is carried at the free end of a cantilevered beam and the chain (or belt) rides over the roller. The resulting deflection of the cantilevered beam provides a measurement of chain tension. A control signal for the electric motor is generated based on a smoother version of the power generated by the rider.

Description:
The present application claims the priority of U.S. Provisional Patent Application Ser. No. 61/489,163 filed May 23, 2011, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to electric bicycles and in particular to controlling electric motor assistance to propelling the electric bicycle based on a rider&#39;s pedaling. 
     There is both a desire among consumers, and regulations requiring, that the electric motor power provided to the drive train of electric assisted bicycles be tied to the rider&#39;s manual power input via the pedals. That is, electric power is delivered to the drive train only if the rider manually rotates the pedals and then, such electric power must match or be some percentage of the actual power manually provided by the rider. Such electric bike systems are alternately referred to as Pedal Assist, PAS or Pedelec. 
     In order for such Pedal Assist systems to work, an accurate measurement of the power manually generated by the rider through the pedals must be made. Known systems for measuring the power provided by the rider are expensive to manufacture and there is a need for a power measuring device and method which is low cost with relation to the entire electric bicycle cost. Further, complex systems are often prone to failure and there is a need for a durable and low or zero maintenance system. Complex systems may further require calibration and adjustment and there is a need for a system which is easy to calibrate and adjust to obtain the desired accuracy. 
     Additionally, there is a need for a measurement device which can be fit onto existing bicycles with little or no modification to the existing vehicle thus allowing for a kit which can be attached by the consumer or manufacturer of existing bicycles. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an apparatus and method for controlling an electric motor providing assistance to a bicycle rider based on measuring the mechanical power generated by the rider. The power generated by the rider is measured by measuring tension in a bicycle chain (or belt) and RPM. A chain (or belt) roller is carried at the free end of a cantilevered beam and the chain (or belt) rides over the roller. The resulting deflection of the cantilevered beam provides a measurement of chain tension. A control signal for the electric motor is generated based on a smoother version of the power generated by the rider. 
     In accordance with one aspect of the invention, there is a provided control system for an electric bicycle. The control system includes: an electric motor for assisting a rider pedaling the bicycle; a bicycle chain; a sensor measuring tension in the bicycle chain to generate raw chain tension data; a processor computing a control signal for the electric motor. The control system computed: revolutions per minute of a crank assembly using the raw chain tension data; a smoothed value of the raw chain tension data; average power generated by pedaling; and a control signal for the electric motor proportional to the average power generated by pedaling. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is a left side view of a sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 1B  is a right side view of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 1C  is a top view of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 2  is a perspective view of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 3  is a perspective view of a second embodiment of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 4  is a perspective view of a housing of the second embodiment of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 5A  is a left side view of the housing of the second embodiment of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 5B  is a top view of the housing of the second embodiment of the sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 5C  is a front view of the housing of the second embodiment of the view sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 5D  is a rear view of the housing of the second embodiment of the view sensor assembly according to the present invention for measuring rider generated torque in a bicycle chain. 
         FIG. 6  is a right side view of a bicycle having the sensor attached to the bicycle according to the present invention. 
         FIG. 7  is a right side view of a bicycle chain, pedals, and sprockets and the sensor configured for measuring chain torque according to the present invention. 
         FIG. 8  is a right side view of a bicycle having the sensor attached to the bicycle and an electric motor for providing assistance according to the present invention. 
         FIG. 9  is a right side view of a bicycle having the sensor attached to the bicycle and an electric motor for providing assistance according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A left side view of a sensor assembly  12  according to the present invention for measuring rider generated torque in a bicycle chain  34  (see  FIG. 7 ) is shown in  FIG. 1A , a right side view of the sensor assembly  12  is shown in  FIG. 1B , a top side view of the sensor assembly  12  is shown in  FIG. 1C , and a perspective view of the sensor assembly  12  is shown in  FIG. 2 . A displacement transducer located in the non-fixed end  16   a  of a cantilevered beam  16  measures the deflection of the non-fixed end  16   a  to determine the tension in the chain  34 . For example, a magnet  17  may be located in the non-fixed end  16   a  of the cantilevered beam  16  and a Hall effect sensor  18  may be positioned in a fixed enclosure  13  so that one of the poles of the magnet  17  is directly over the Hall effect sensor  18 . The distance between the magnet  17  surface and the Hall effect sensor is typically ⅛ inches. The sensor assembly  12  is fitted with a chain roller  14  and guide  20  for cooperation with the chain  34  (see  FIG. 7 ). 
     The cantilevered beam  16  is a preferred embodiment, but any apparatus for measuring chain tension by measuring a force normal to the chain path is intended to come within the scope of the present invention, for example, a plunger and coil spring. 
     When force is exerted on the chain roller  14  by the chain  34 , the non-fixed end  16   a  of the beam  16  moves. The movement causes the magnet  17  to move closer the fixed Hall sensor  18 . The Hall sensor  18  senses a change in the magnetic field and causes its electrical output to vary with the position in the magnet  17 . 
     The design of the cantilevered beam  16  is such that it is not stressed to the point where it would fail over time. Typically the total movement of the magnet  17  relative to the fixed Hall sensor  18  is less then approximately ⅛ inch. The scale or size of the component parts of the system can vary to fit the application and force to be measured. 
     The fixed enclosure  13  carrying the Hall sensor  18  is sealed and waterproof to survive extreme wet and dirty conditions. 
     The sensor assembly  12  is typically powered with approximately +5 volts and a common wire. A third wire carries the sensor signal that represents the force applied to the cantilevered beam  16 . 
     The base analog Hall sensor  18  generates a high level electrical signal that is ratio metric to the power supply. This high signal level eliminates the need for high gain signal conditioning that would be required for a similar strain gauge based measurement system. 
     A perspective view of a second embodiment of the sensor assembly  12   a  according to the present invention for measuring rider generated torque in a bicycle chain is shown in  FIG. 3 , a perspective view of a housing  24  of the sensor assembly  12   a  is shown in  FIG. 4 , a left side view of the housing  24  is shown in  FIG. 5A , a top view of the housing  24  is shown in  FIG. 5B , a front view of the housing  24  is shown in  FIG. 5C , and a rear view of the housing  24  is shown in  FIG. 5D . The housing  24  includes an arm  16  being an integral part of the housing  24 . Such single piece housing and arm provides a consistent measurement. A cavity  26  in the housing  24  is provided for a circuit  10 . 
     A right side view of a bicycle  30  having the sensor assembly  12  or  12   a  attached to the bicycle frame  31  according to the present invention is shown in  FIG. 6  and a right side view of a bicycle chain  34 , crank  40  and sprockets  36  and  38  are shown in  FIG. 7 . To measure human power applied to pedaling the bicycle  30 , the sensor assembly  12  or  12   a  is fitted with the chain roller  14  and the guide  20  (see  FIGS. 1A-5D ). The complete sensor assembly  12  or  12   a  is preferably mounted to a fixed location on the bicycle frame  31  where the chain roller  14  is directly under the chain  34  and to the rear of the crank  40 . The cantilevered beam  16  or  16   a  is allowed to bend with chain force on the chain roller  14 . The chain  34  is adjusted so that it places force on the roller proportional to the pedal force applied to the crank. 
     A right side view of a bicycle  30   a  having the sensor assembly  12  or  12   a  attached to the bicycle, and an electric motor  50  for providing assistance according to the present invention, is shown in  FIG. 8 , and a right side view of a bicycle  30   b  with a derailer  60  having the sensor assembly  12  or  12   a  attached to the bicycle, and a high speed electric motor  50   a  for providing assistance, is shown in  FIG. 9 . By placing the torque sensor on a pedal chain  34   a  which is then connected directly to a low speed (under 300 RPM) motor, and then connecting said motor  50  via a second chain  34   b  or belt to a rear wheel transmission (e.g., the derailleur  60 ) commonly used on bicycles, all energy generated by the rider and motor  50  would have the benefit of being fed into a multispeed transmission gaining the same benefit an unaided rider would gain from said transmission. By placing the chain  34   a  from the crank  40  to the motor  50  on a freewheel  48 , the rider would have the option of running the motor  50  directly into the transmission  60  without having to pedal in localities where pedal assist is not a regulatory requirement. 
     Alternately, the high speed motor  50   a  could be used in exactly the same manner if the pedal chain  34   a  were connected to an intermediate shaft  54  with the sensor assembly  12  mounted as previously described. The high speed motor  50   a  could be connected via chain  52  or belt to the same intermediate shaft  54  through a free wheel allowing for a speed reduction through gear ratios which would bring down the rotational speed coming off the motor  50   a  to a rate which would match up with the manual pedal speed of the rider. The chain or belt  34   a  would then connect to a rear transmission  60  and would transfer all force generated by either or both the motor  50   a  and rider into the transmission  60 . 
     In some applications where the analog output electrical signal must interface with an existing device, a simple signal conditioner can be built into the system. The electrical signal can also be easily configured to a pulse width modulated configuration within the sensor enclosure if the system requires a non-analog or digital signal from the sensor. 
     At startup, the device may establish a “zero position” for the sensor assembly  12  or  12   a  under the assumption that there is no significant force or torque placed on the pedals by the rider. Should tension subsequently drop below that initial “zero position”, each subsequent low measurement would create a new “zero position” for that riding. All measurement above “zero position” will be measured as force or torque generated by the rider. 
     Data from the sensor assembly  12  or  12   a  is provided to a processor to control the motor  50 . When the rider begins to pedal the bicycle (or any pedal driven vehicle), the action of pedal rotation produces an uneven chain tension measurement as the rider cycles through each crank rotation. One rotation will consist of two peaks as the right and left foot each rotate the pedal crank  360  degrees. The processor processes the raw tension data to detect peaks in the tension to compute RPM. The processor then computes torque in the crank from the measured chain tension times the crank sprocket radius and multiplies the torque times the computed RPM to compute the power generated by the rider. 
     In cases where the power generated by the rider using the crank and the power of the motor are fed into some kind of a transmission to increase efficiency, the processor may use crank sprocket torque and pedal rotation speed to determine optimum gear position in the transmission and shift the transmission. During instances in which the crank sprocket torque is increasing while the crank RPM (or vehicle speed measured at the wheel) is steady or decreasing, the processor may shift to a lower gear or gear ratio. During instances in which the pedal torque is decreasing while the rotational pedal speed (or vehicle speed measured at the wheel) is increasing, the processor shift to a higher gear or gear ratio. 
     Software may incorporate a sleep and wake up function which keeps the sensor assembly  12  or  12   a  from outputting a motor signal when first powered up. If the pedals have no force applied, the sensor assembly  12  or  12   a  will enter a preset sleep condition. This is a safety feature to prevent torque sensor output and motor activation while the rider is not on the bike. 
     The sensor assembly  12  or  12   a  may further include a speed sensor input to determine when the bicycle  30  is in motion. The speed sensor may detect wheel rotation and true vehicle speed and the sensor assembly  12  or  12   a  may limit the torque sensor output based on bicycle or vehicle speed as may be required in some installations by regulation. The speed sensor may also be used to restrict or prevent the torque sensor output until the sensor detects the vehicle wheel is in motion. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.