Patent Publication Number: US-2022234680-A1

Title: Electric bicycle driving device and method therefor

Description:
TECHNICAL FIELD 
     The present invention relates to driving of an electric bicycle, and more particularly, to a technique for driving a chainless electric bicycle. 
     BACKGROUND ART 
     An electric bicycle includes a motor for rotating wheels and a battery for supplying power to the motor. Electric bicycles are driven in a way that a motor rotates wheels or in a way that assists a force with which a user presses a pedal. In a chainless electric bicycle among the electric bicycles, a force with which a user presses a pedal is converted into electricity by a generator connected to the pedal, the electricity is stored in a battery, and a motor is turned on by the electricity stored in the battery so that the electric bicycle is moved. 
     In a typical bicycle, when a user presses pedals with his or her feet, a pedaling force is transmitted to wheels through a chain so that the bicycle is moved. Since the chain is connected from the pedals of the bicycle to the wheels, there are problems in that a length of the chain is long, a structure of the chain is complicated, and the chain comes out of a gear or gets caught in the user&#39;s pants, etc. 
     In order to solve the above problems, chainless electric bicycles have recently been developed and used. 
     However, in a chainless electric bicycle, there is no load applied to pedals, and thus a user cannot feel a pedaling feeling. The pedaling feeling refers to a counter torque that is felt by a user when the user presses a pedal. As the counter torque increases, an occupant feels that the pedal is heavy, and as the counter torque decreases, the occupant feels that the pedal is light. 
     A pedaling feeling that the user feels when driving a bicycle with a chain depends on various driving factors, such as an amount of torque when the user applies to the pedal, a gradient of a road surface, and the like. The user is generally familiar with the pedaling feeling that the user can feel when driving a bicycle with a chain. However, when the pedaling feeling cannot be reproduced in a chainless electric bicycle, the user may feel a sense of difference and feel uncomfortable. 
     A pedaling feeling of a real bicycle with a chain is generated because pedals and a driving wheel are mechanically connected by a chain. In this case, a value obtained by multiplying a rotational position of the driving wheel by a gear ratio is identical to a value of a rotational position of the pedal. That is, in the bicycle with a chain, a rotational position of the pedal is synchronized with a rotational position of the driving wheel. On the other hand, in the chainless electric bicycle, pedals and a driving wheel are not mechanically connected and power generated due to the rotation of the pedal is transmitted to the driving wheel by electronic control, and thus the pedals and the driving wheel are independently rotated. Therefore, since a rotational position of the pedal and a rotational position of the driving wheel of the chainless electric bicycle are not synchronized unlike in the bicycle with a chain, the user feels a sense of difference. 
     Further, in the bicycle with a chain, a gradient of a road surface and an acceleration of the pedal are directly reflected to the rotation of the driving wheel so that a driving torque of the driving wheel is increased. Therefore, even when the rotational position of the pedal is rapidly changed, the driving wheel immediately follows the rotation of the pedal. However, in the chainless electric bicycle, when the gradient of the road surface or the acceleration of the pedal is not reflected to the rotation of the driving wheel through electronic control, a response of the driving wheel becomes slow even when the rotational position of the pedal is rapidly changed, and thus a driving torque is not sufficiently applied to the driving wheel and the user feels a sense of difference. 
     In the chainless electric bicycle, since the pedal is not connected to the driving wheel, a speed command or torque command which is applied to a motor is adjusted based on a pedal torque. 
     However, in the case in which the speed command is used, it is difficult to adjust an acceleration of the motor, and in the case in which the torque command is used, a speed difference may occur in an electric bicycle with two or more motors due to a difference in condition of the road surface on which wheels, on which the motors are mounted, are placed. Accordingly, there is a problem in that the user cannot feel a pedaling feeling or a driving feeling unlike in the bicycle with a chain. 
     DISCLOSURE 
     Technical Problem 
     The present invention is to solve the problems of the related art as described above and is directed to providing a technique for providing a pedaling feeling and a driving feeling to a user of a chainless electric bicycle as in a bicycle with a chain. 
     The present invention is also directed to providing a technique for allowing a user to feel a pedaling feeling as in a bicycle with a chain by synchronizing a rotational position of a pedal and a rotational position of a driving wheel of a chainless electric bicycle. The present invention is also directed to providing a technique for allowing a rotational position of the driving wheel to rapidly follow a rotational position of the pedal by additionally increasing a driving torque of a driving wheel by reflecting a gradient of a road surface on which a chainless electric bicycle travels and an acceleration of a pedal. 
     Meanwhile, other objects that are not specified in the present invention will be additionally considered within the range that may be easily inferred from the following detailed descriptions and effects thereof. 
     Technical Solution 
     One aspect of the present invention provides a device for driving a chainless electric bicycle, which includes a motor configured to drive a driving wheel, a generator configured to generate power using a pedal, a generator position sensor configured to measure a value of a rotational position of the generator, a motor position sensor configured to measure a value of a rotational position of the motor, and a controller configured to calculate a difference value obtained by subtracting a value obtained by multiplying the value of the rotational position of the motor by a gear ratio from the value of the rotational position of the generator and control the generator or the motor on the basis of the difference value. 
     Preferably, the controller may control the generator or the motor so that the difference value becomes zero. 
     Further, when the difference value is greater than zero, the controller may control the generator to increase a counter torque with respect to a driving direction of the generator or may control the motor to increase a driving torque of the motor, and when the difference value is smaller than zero, the controller may control the generator to reduce the counter torque with respect to the driving direction of the generator or may control the motor to reduce the driving torque of the motor. 
     The device may further include a generator current sensor configured to measure a generator driving current between a battery and the generator and a motor current sensor configured to measure a motor driving current between the battery and the motor, wherein the controller may control the generator by controlling the generator driving current using a target generator current generated based on the difference value as a reference value and using the measured generator driving current as a feedback value and may control the motor by controlling the motor driving current using a target motor current generated based on the difference value as a reference value and using the measured motor driving current as a feedback value. 
     When the difference value is greater than zero, the controller may increase the generator driving current or increase the motor driving current, and when the difference value is smaller than zero, the controller may reduce the generator driving current or reduce the motor driving current. 
     The device may further include a gradient sensor configured to measure a gradient of a road on which the electric bicycle travels, wherein the controller may calculate a rotational acceleration of the pedal using the rotational position of the generator and further increase the motor driving current on the basis of a value of the gradient of the road, which is received from the gradient sensor, and the rotational acceleration of the pedal. 
     Another aspect of the present invention provides a method of driving an electric bicycle, which includes receiving a value of a rotational position of a generator from a generator position sensor, receiving a value of a rotational position of a motor from a motor position sensor, calculating a difference value obtained by subtracting a value obtained by multiplying the value of the rotational position of the motor by a gear ratio from the value of the rotational position of the generator, and controlling the generator or the motor on the basis of the difference value. 
     Preferably, in the controlling of the generator or the motor, the generator or the motor may be controlled so that the difference value becomes zero. 
     In the controlling of the generator or the motor, when the difference value is greater than zero, the generator may be controlled to increase a counter torque with respect to a driving direction of the generator or the motor may be controlled to increase a driving torque of the motor, and when the difference value is smaller than zero, the generator may be controlled to reduce the counter torque with respect to the driving direction of the generator or the motor may be controlled to reduce the driving torque of the motor. 
     In particular, the method may further include receiving a value of a gradient of a road on which the electric bicycle travels from a gradient sensor, calculating a rotational acceleration of a pedal using the rotational position of the generator, and controlling a driving torque of the motor to be further increased on the basis of the value of the gradient of the road and the rotational acceleration of the pedal. 
     Further, the method may further include measuring a generator driving current between a battery and the generator using a generator current sensor and measuring a motor driving current between the battery and the motor using a motor current sensor, wherein, in the controlling of the generator or the motor, the generator driving current is controlled using a target generator current generated based on the difference value as a reference value and using the measured generator driving current as a feedback value, and the motor driving current is controlled using a target motor current generated based on the difference value as a reference value and using the measured motor driving current as a feedback value. 
     In the controlling of the generator or the motor, when the difference value is greater than zero, the generator driving current may be increased or the motor driving current may be increased, and when the difference value is smaller than zero, the generator driving current may be reduced or the motor driving current may be reduced. 
     Still another aspect of the present invention provides a device for driving a chainless electric bicycle, which includes a motor configured to drive a driving wheel, a generator configured to generate power using a pedal, a generator position sensor configured to measure a value of a rotational position of the generator, a motor position sensor configured to measure a value of a rotational position of the motor, a generator current sensor configured to measure a current of the generator, a motor current sensor configured to measure a current of the motor, and a controller configured to calculate a target pedal torque on the basis of a difference between a position of the generator which is measured by the generator position sensor and a position of the motor which is measured by the motor position sensor and control the current of the generator to reach the calculated target pedal torque. 
     Preferably, the controller may calculate a target motor acceleration according to the calculated target pedal torque, calculate an acceleration of the motor from a change in the measured position of the generator, and control the current of the motor so that the acceleration of the motor reaches the calculated target motor acceleration. 
     Yet another aspect of the present invention provides a method of controlling a device for driving a chainless electric bicycle which includes receiving a position of a generator from a generator position sensor, receiving a position of a motor from a motor position sensor, calculating a target pedal torque on the basis of a difference between the position of the generator and the position of the motor, and controlling a current of the generator to reach the calculated target pedal torque. 
     The method may further include, after the controlling of the current of the generator, determining a target motor acceleration according to the calculated target pedal torque, calculating an acceleration of the motor from a change in a detected position of a pedal, and controlling a current of the motor so that the acceleration of the motor reaches the determined target motor acceleration. 
     Advantageous Effects 
     According to the present invention, by synchronizing a rotational position of a driving wheel and a rotational position of a pedal of a chainless electric bicycle, a user can feel a pedaling feeling as in a bicycle with a chain. 
     Further, by additionally controlling a driving torque of a driving wheel by reflecting a gradient of a road surface on which a chainless electric bicycle travels and an acceleration of a pedal, a rotational position of a driving wheel can rapidly follow a rotational position of a pedal. 
     Further, it is possible to more effectively improve a pedaling feeling as in a bicycle with a chain regardless of a road surface on which a chainless electric bicycle travels. 
     Further, by applying an acceleration command to a motor, an acceleration of the motor can be adjusted. 
     Meanwhile, it is added that effects, which are not explicitly described herein but are described in the following specification expected by the technical features of the present invention, and their potential effects are treated as those described in the specification of the present invention. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a schematic structure of a device for driving a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 2  illustrates a structure of a controller for driving a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 3  illustrates a structure of a generator controller of a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 4  illustrates a structure of a motor controller of a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 5  illustrates a more detailed structure of a motor acceleration controller according to an embodiment of the present invention. 
         FIG. 6  is a flowchart illustrating a method of driving a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 7  is a flowchart illustrating a method of controlling a generator or a motor of a chainless electric bicycle according to an embodiment of the present invention. 
         FIG. 8  is an additional flowchart illustrating a method of controlling a motor according to an embodiment of the present invention. 
         FIG. 9  is a control flowchart illustrating a device for driving an electric bicycle according to another embodiment of the present invention. 
     
    
    
     The accompanying drawings are exemplified by reference for understanding the technical idea of the present invention and the scope of the present invention is not limited thereby. 
     MODES OF THE INVENTION 
     Hereinafter, configurations of the present invention guided by various embodiments of the present invention and effects resulting from the configurations will be described with reference to the accompanying drawings. In descriptions of the present invention, when detailed descriptions of related known configurations or functions are deemed to unnecessarily obscure the gist of the present invention, they will be omitted. 
     It should be understood that, although terms “first,” “second,” and the like may be used herein to describe various elements, the elements are not limited by the terms. The terms are only used to distinguish one element from another element. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present invention. Further, as used herein, the singular forms “a” and “an” are intended to also include the plural forms, unless the context clearly indicates otherwise. Unless otherwise defined, all terms in the embodiments of the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. 
     Hereinafter, the configurations of the present invention guided by various embodiments of the present invention and effects resulting from the configurations will be described with reference to the accompanying drawings. 
       FIG. 1  illustrates a structure of a system for driving a chainless electric bicycle according to an embodiment of the present invention. 
     A device  10  for driving a chainless electric bicycle according to the embodiment of the present invention includes a controller  20 , a generator position sensor  31 , a generator current sensor  33 , a motor current sensor  35 , and a motor position sensor  37  to control a generator  40  and a motor  50 . When a user presses a pedal  42 , the generator  40  converts a pedaling force into electricity and stores the electricity in a battery  60 , and the motor  50  is driven by the electricity stored in the battery  60  so that a wheel  52  connected to the motor  50  is driven. 
     The controller  20  includes a generator controller  22 , a motor controller  24 , and one or more processors or microcontroller units (MCUs). 
     The generator  40  is mechanically connected to the pedal  42 . Therefore, a rotational position of the pedal  42  is synchronized with a rotational position of the generator  40 , and the rotational position of the pedal  42  may be measured by measuring a rotational position P P  (P P  also denotes a rotational position of the pedal because the generator and the pedal are mechanically connected. Hereinafter, all physical values for the rotation of the generator also refer to a corresponding physical value for the rotation of the pedal) of the generator  40  by the generator position sensor  31 . P P  may be expressed as a value of an angle. In the overall driving of the device  10  for driving the chainless electric bicycle for the purpose of synchronizing the rotational position P P  of the pedal  42  and a rotational position P M  of a driving wheel  52 , P P  is used as a reference value. The generator position sensor  31  transmits a value of the rotational position P P  to the controller  20 . 
     The motor  50  is mechanically connected to the driving wheel  52 . Therefore, a rotational position of the driving wheel  52  is synchronized with a rotational position of the motor  50 , and a rotational position of the driving wheel  52  may be measured by measuring the rotational position P M  (P M  also denotes a rotational position of the driving wheel because the motor and the driving wheel are mechanically connected. Hereinafter, all physical values for the rotation of the motor also refer to a corresponding physical value for the rotation of the driving wheel) of the motor  50  by the motor position sensor  37 . P M  may be expressed as a value of an angle. In the overall driving of the device  10  for driving the chainless electric bicycle for the purpose of synchronizing the rotational position P P  of the pedal  42  and the rotational position P M  of the driving wheel  52 , P M  is used as a feedback value. The motor position sensor  37  transmits a value of the rotational position P M  to the controller  20 . 
     The generator position sensor  31 , the generator current sensor  33 , the motor position sensor  37 , and the motor current sensor  35  are all electrically connected to the controller  20 . The generator position sensor  31  measures the rotational position P P  of the generator  40 , the generator current sensor  33  measures a generator driving current I P_current , the motor position sensor  37  measures the rotational position P M  of the motor  50 , and the motor current sensor  35  measures a motor driving current I M_current . Values that are measured by the generator position sensor  31 , the generator current sensor  33 , the motor position sensor  37 , and the motor current sensor  35  are transmitted to the controller  20  and are used to control the generator  40  or the motor  50  using the controller  20 . 
     Preferably, in order to additionally control the motor, the device  10  for driving the chainless electric bicycle may further include a gradient sensor  39 , and the gradient sensor  39  may also be electrically connected to the controller  20 . The gradient sensor  39  may include at least one of a gyro sensor, an acceleration sensor, and a geomagnetic sensor to measure a gradient of a road surface on which the electric bicycle travels. The gradient sensor  39  measures a gradient S S  of the road surface and transmits a value of the gradient S S  to the controller  20 . The transmitted value of the gradient S S  is used when additionally controlling the motor  50  in addition to the control of the motor  50  based on P P  and P M . 
     The controller  20  controls the generator  40  and the motor  50  on the basis of the rotational position P P  of the generator  40  which is measured by the generator position sensor  31 , the generator driving current I P_current  which is measured by the generator current sensor  33 , the rotational position P M  of the motor  50  which is measured by the motor position sensor  37 , and the motor driving current I M_current  which is measured by the motor current sensor  35 . The control of the generator  40  and the control of the motor  50  by the controller  20  mean the control of the generator driving current I P_current  and the control of the motor driving current I M_current  and, as a result, mean the control of the driving of the generator  40  and the control of the driving of the motor  50 . The control of the driving of the generator  40  and the control of the driving of the motor  50  by the controller  20  are performed independently. 
     Further, the controller  20  may additionally control the motor  50  to be driven on the basis of the gradient S S  of the road surface which is measured by the gradient sensor  39 . 
     The controller  20  may also be referred to as a controller, a microcontroller, a microprocessor, a microcomputer, or the like. Meanwhile, the controller  20  may be implemented by hardware, firmware, software, or a combination thereof. 
     When the embodiment of the present invention is implemented by hardware, application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable-gate arrays (FPGAs), or the like may be provided in the controller  20 . 
     The generator controller  22  and the motor controller  24  in the controller  20  control the generator driving current I P_current  between the battery  60  and the generator  40  and the motor driving current I M_current  between the battery  60  and the motor  50 , respectively. A generator driver and a motor driver may be implemented with a field effect transistor (FET). 
     When the electric bicycle is driven, the generator driving current I P_current  and the motor driving current I M_current  may each flow from the battery  60  toward the generator  40  and the motor  50 , but when the electric bicycle performs regenerative braking, the generator driving current I P_current  and the motor driving current I M_current  may each flow from the generator  40  and the motor  50  toward the battery  60 . That is, the generator driving current I P_current  and the motor driving current I M_current  may flow bidirectionally. The generator driving current I P_current  and the motor driving current I M_current  are measured by the generator current sensor  33  and the motor current sensor  35 , respectively. The measured generator driving current I P_current  and the measured motor driving current I M_current  are transmitted to the controller  20  as a feedback value for generator current control and a feedback value for motor current control, respectively. 
       FIG. 2  illustrates, in more detail, a structure of the controller  20  for driving the chainless electric bicycle according to the embodiment of the present invention. 
     The controller  20  receives the rotational position P P  of the generator which is measured by the generator position sensor  31  and the rotational position P M  of the motor which is measured by the motor position sensor  37 , and then calculates a difference value P Δ  obtained by subtracting P M_geared , which is the product of the value of the rotational position P M  and a gear ratio G R , from the value of the rotational position P P . The gear ratio G R  is a value that may be adjusted by an occupant, and in the case of a bicycle with a chain, P M_geared , which is the product of P M  and GR, is physically identical to P P . That is, a difference value P Δ  in the bicycle with a chain is zero. Therefore, in order for the user to feel a pedaling feeling for the electric bicycle as in the bicycle with a chain, P Δ  should be set to zero. When P Δ  becomes zero, the rotation of the pedal and the rotation of the driving wheel are synchronized. 
     According to an embodiment of the present invention, after the difference value P Δ  of P P  and P M_geared  is commonly calculated by the controller  20 , the control of the generator  40  and the control of the motor  50  are independently performed by the controller  20 . The control of the generator  40  by the controller  20  is performed by the operation of the generator driver through generator position control, generator speed control, and generator current control by the controller  20 . Further, the control of the motor  50  by the controller  20  is performed by the operation of the motor driver through motor position control, motor speed control, and motor current control by the controller  20 . 
     The controller  20  controls the generator  40  and the motor  50  so that the occupant of the electric bicycle feels the pedaling feeling to be heavier, lighter, or the same as before, depending on whether P Δ  is a positive number, a negative number, or zero. 
     First, when P Δ  is a positive number, that is, when the rotational position P P  of the generator is greater than P M_geared , which is the product of the rotational position P M  of the motor and the gear ratio G R , the generator  40  is relatively ahead of the motor  50  in rotational position and the motor  50  is behind the generator  40 . Therefore, in order to adjust P Δ  to zero, the generator  40  and the motor  50  should be controlled so that the occupant feels the pedaling feeling heavy. 
     To this end, until P Δ  becomes zero, the counter torque with respect to a driving direction of the generator  40  should be increased so that a driving torque of the motor  50  is increased or the motor  50  follows the rotation of the generator  40 . Therefore, until P Δ  becomes zero, the controller  20  should control at least one of the generator  40  and the motor  50  by increasing the generator driving current I P_current  or the motor driving current I M_current . 
     When P Δ  is the positive number, the control of the generator  40  is performed by the operation of the generator driver through the generator position control, the generator speed control, and the generator current control by the controller  20 . In the generator position control, the controller  20  increases a target generator speed ω P_ref  on the basis of P Δ  and outputs the increased target generator speed ω P_ref . Next, in the generator speed control, the controller  20  increases a target generator current I P_ref  using the increased target generator speed ω P_ref  as a reference value and using a generator rotation speed ω P  calculated by differentiating the rotational position P P  of the generator as a feedback value, and outputs the increased target generator current I P_ref . Next, in the generator current control, the controller  20  controls the generator driver so that the generator driving current I P_current  is increased using the increased target generator current I P_ref  as a reference value and using the generator driving current I P_current  which is measured and transmitted by the generator current sensor  33  as a feedback value. The generator driver controls the generator  40  so that a counter torque is increased by increasing the generator driving current I P_current  between the battery  60  and the generator  40  according to the generator current control. 
     When P Δ  is the positive number, the control of the motor  50  is performed by the operation of the motor driver through the motor position control, the motor speed control, and the motor current control by the controller  20 . The controller  20  increases a target motor speed ω M_ref  on the basis of P Δ  in the motor position control and outputs the increased target motor speed ω M_ref . A gain may be applied to the target motor speed ω M_ref  according to the user&#39;s driving mode setting. The driving mode means that the user manually sets how heavy the default pedaling feeling is. Therefore, the target motor speed ω M_ref  that is increased and output based on P Δ  is input to the motor speed control after the gain is applied according to the driving mode setting. Next, in the motor speed control, the controller  20  increases a target motor current I M_ref  using the increased target motor speed ω M_ref  as a reference value and using the motor rotation speed ω M  calculated by differentiating the rotational position P P  of the motor of the motor as a feedback value, and outputs the increased target motor current I M_ref . Next, in the motor current control, the controller  20  controls the motor driver so that the motor driving current I M_current  is increased using the increased target motor current I M_ref  as a reference value and using the motor driving current I M_current  which is measured and transmitted by the motor current sensor  35  as a feedback value. The motor driver controls the motor  50  so that a torque is increased by increasing the motor driving current I M_current  between the battery  60  and the motor  50  according to the motor current control. 
     Further, when P Δ  is a negative number, that is, when the rotational position P P  of the generator is smaller than P M_geared , which is the product of the rotational position P M  of the motor and the gear ratio G R , the generator  40  is relatively behind the motor  50  in the rotational position and the motor  50  is ahead of the generator  40 . Therefore, in order to adjust P Δ  to zero, the generator  40  and the motor  50  should be controlled so that the occupant feels the pedaling feeling light. To this end, until P Δ  becomes zero, the counter torque with respect to the driving direction of the generator  40  should be reduced so that the driving torque of the motor  50  is reduced or the motor  50  follows the rotation of the generator  40 . Therefore, until P Δ  becomes zero, the controller  20  should control the generator  40  or the motor  50  by reducing the generator driving current I P_current  or the motor driving current I M_current . 
     When P Δ  is the negative number, the control of the generator  40  is performed by the operation of the generator driver through the generator position control, the generator speed control, and the generator current control by the controller  20 . In the generator position control, the controller  20  reduces the target generator speed ω P_ref  on the basis of P Δ  and outputs the reduced target generator speed ω P_ref . Next, in the generator speed control, the controller  20  reduces the target generator current I P_ref  using the reduced target generator speed ω P_ref  as the reference value and using the generator rotation speed ω P  calculated by differentiating the rotational position P P  of the generator as the feedback value, and outputs the target generator current I P_ref . However, a minimum value of the target generator current I P_ref  cannot be less than zero. That is, the pedaling feeling cannot be reduced by rotating (when the target generator current I P_ref &lt;0) the pedal through the generator faster than the speed of the pedal that the occupant presses the pedal in the direction in which the pedal rotates. Next, in the generator current control, the controller  20  controls the generator driver so that the generator driving current I P_current  is reduced using the reduced target generator current I P_ref  as the reference value and using the generator driving current I P_current  which is measured and transmitted by the generator current sensor  33  as the feedback value. The generator driver controls the generator  40  so that the counter torque is reduced by reducing the generator driving current I P_current  between the battery  60  and the generator  40  according to the generator current. 
     When P Δ  is the negative number, the control of the motor  50  is performed by the operation of the motor driver through the motor position control, the motor speed control, and the motor current control by the controller  20 . The controller  20  reduces the target motor speed ω M_ref  on the basis of P Δ  in the motor position control and outputs the reduced target motor speed ω M_ref . As described above, the target motor speed ω M_ref  that is reduced and output based on P Δ  is input to the motor speed control after the gain is applied according to the driving mode setting. Next, in the motor speed control, the controller  20  reduces the target motor current I M_ref  using the reduced target motor speed ω M_ref  as the reference value and using the motor rotation speed ω M  calculated by differentiating the rotational position P P  of the motor as the feedback value and outputs the reduced target motor current I M_ref . Next, in the motor current control, the controller  20  controls the motor driver so that the motor driving current I M_current  is reduced using the reduced target motor current I M_ref  as the reference value and using the motor driving current I M_current  which is measured and transmitted by the motor current sensor  35  as the feedback value. The motor driver controls the motor  50  so that the torque is reduced by reducing the motor driving current I M_current  between the battery  60  and the motor  50  according to the motor current control. 
     Further, when P Δ  is zero, that is, when the rotational position P P  of the generator is equal to P M_geared , which is the product of the rotational position P M  of the motor and the gear ratio G R , the generator  40  and the motor  50  are synchronized in the rotational position. Therefore, in order to adjust P Δ  to zero, the generator  40  and the motor  50  should be controlled so that the occupant maintains and feels the pedaling feeling. To this end, until P Δ  becomes zero, the counter torque with respect to the driving direction of the generator  40  should be maintained, and the driving torque of the motor  50  should be maintained so that the motor  50  follows the rotation of the generator  40 . Therefore, in order to maintain P Δ  at zero, the controller  20  should control the generator  40  and the motor  50  so that the generator driving current I P_current  and the motor driving current I M  current are maintained in current states. 
     When P Δ  is zero, the control of the generator  40  is performed by the operation of the generator driver through the generator position control, the generator speed control, and the generator current control by the controller  20 . In the generator position control, the controller  20  maintains and outputs the target generator speed WP ref on the basis of P A . Next, in the generator speed control, the controller  20  maintains and outputs the target generator current I P_ref  using the maintained target generator speed ω P_ref  as the reference value and using the generator rotation speed ω P  calculated by differentiating the rotational position P P  of the generator as the feedback value. Next, in the generator current control, the controller  20  controls the generator driver so that the generator driving current I P_current  is maintained using the maintained target generator current I P_ref  as the reference value and using the generator driving current I P_current  which is measured and transmitted by the generator current sensor  33  as the feedback value. The generator driver controls the generator  40  so that the counter torque is maintained by maintaining the generator driving current I P_current  between the battery  60  and the generator  40  according to the generator current control. 
     When P Δ  is zero, the control of the motor  50  is performed by the operation of the motor driver through the motor position control, the motor speed control, and the motor current control by the controller  20 . In the motor position control, the controller  20  maintains and outputs the target motor speed ω M_ref  on the basis of P A . As described above, the target motor speed ω M_ref  that is maintained and output based on P Δ  is input to the motor speed control after the gain is applied according to the driving mode setting. Next, in the motor speed control, the controller  20  maintains and outputs the target motor current I M_ref  using the maintained target motor speed ω M  ref as the reference value and using the motor rotation speed ωm calculated by differentiating the rotational position P P  of the motor as the feedback value. Next, in the motor current control, the controller  20  controls the motor driver so that the motor driving current I M_current  is maintained using the maintained target motor current I M  ref as the reference value and using the motor driving current I M_current  measured and transmitted by the motor current sensor  35  as the feedback value. The motor driver controls the motor  50  so that the torque is maintained by maintaining the motor driving current I M_current  between the battery  60  and the motor  50  according to the motor current control. 
     As a result of the driving control for at least one of the generator  40  and the motor  50  of the controller  20 , the rotational position P M  of the motor  50  is synchronized with the rotational position P P  of the generator  40 . That is, in terms of overall control of the device  10  for driving the chainless electric bicycle, the rotational position P P  of the generator  40  is used as the reference value and the rotational position P M  of the motor  50  is used as the feedback value. 
     The rotational position of the driving wheel  52  and the rotational position of the pedal  42  may be synchronized by the driving control of at least one of the generator  40  and the motor  50 , and as a result, the pedaling feeling that the occupant of the electric bicycle feels may become similar to a real bicycle. 
       FIG. 3  illustrates a structure of the generator controller  22  for additional motor control according to another embodiment of the present invention. 
     When a pedal acceleration increases or a gradient of a road surface increases, it is difficult for the motor  50  to follow the rotation of the generator  40  because a rotation speed of the generator  40  increases rapidly, and thus an additional target motor current I A_ref  may be input to the motor current control in an overlapping manner with the target motor current I M_ref  to be used as a reference value in an overlapping manner. The gradient of the road surface may be obtained from the gradient sensor  39 . That is, the additional motor control using the additional target motor current I A_ref  may be performed on the motor  50  in an overlapping manner. However, a minimum value of the additional target motor current I A_ref  cannot be less than zero. 
     In order to enable the rotation of the motor  50  to rapidly follow the rotation of the generator  40 , the additional motor control may be performed to further increase the driving torque of the motor  50 . When the rotational position of the generator  40  is rapidly changed because the gradient of the road surface is large or the rotational acceleration of the pedal  42  is large, the rotational position control of the motor  50  by the electronic control cannot follow the rotational position of the generator  40 , and thus the additional motor control is performed. 
     A generator rotational acceleration α P  is calculated by differentiating the generator rotation speed ω P  again which is calculated through differentiation from the rotational position P P  of the generator, a gradient S S  of the road surface is measured by the gradient sensor  39 , and then the generator rotational acceleration α P  and the gradient S S  of the road surface is input to a predetermined additional control table to generate an additional target motor current I A_ref , and thus the additional motor control is performed by the generator controller  22 . Preferably, the generator rotational acceleration α P  may be input to the table after a gain is applied according to a driving mode set by the user. 
     As the generator rotational acceleration α P  increases and the gradient S S  of the road surface increases, a larger additional motor current command I A_ref  may be generated. Preferably, when the generator rotational acceleration α P  is greater than or equal to a predetermined acceleration or the gradient of the road surface is greater than or equal to a predetermined gradient, the additional motor current command I A_ref  may be generated. However, a minimum value of the additional target motor current I A_ref  cannot be less than zero. 
     The additional target motor current I A_ref  is used as a reference value for motor current control of the motor controller  24  in an overlapping manner with the target motor current I M_ref . By the additional motor control, a larger motor driving current I M_current  may be provided to the motor  50  and a driving torque of the motor  50  may be additionally increased. As a result, the motor  50  rotates more and thus may rapidly follow a position change caused by the rapid rotation of the generator  40 . 
       FIG. 4  illustrates a structure of the motor controller  24  according to another embodiment of the present invention. 
     The motor controller  24  may further include a motor acceleration controller  26  to control the acceleration of the motor  50 . That is, the motor  50  is driven by controlling an acceleration of the motor rather than a speed of the motor. 
     The motor controller  24  receives a motor acceleration command value Acc M_ref  calculated using the user&#39;s pedal torque, and the motor acceleration controller calculates a motor acceleration Acc M  from a rotational position P M  of the motor. Based on the above two values, the motor acceleration controller  26  controls the acceleration of the motor. 
       FIG. 5  illustrates a more detailed structure of the motor acceleration controller  26  according to another embodiment of the present invention. 
     The motor acceleration controller  26  receives a motor acceleration reference value Acc M_ref  calculated using a pedal torque and generates a current i 1  on the basis of a reference acceleration. The reference acceleration is calculated by calculating a motor control current according to an acceleration assuming that a weight on the bicycle is an average weight on a flat ground with a gradient of 0%. 
     Next, an additional current i 2  is generated by reflecting the gradient measured by the gradient sensor and a current i 3  is generated by adding the additional current i 2  to the reference current i 1 . As the gradient is increased, more additional current is required, and thus the additional current should be generated. 
     When there is a weight sensor, an additional current i 4  is generated by reflecting the weight and a current i 5  is generated by adding the additional current i 4  to the current command. 
     Meanwhile, a motor acceleration Acc M  calculated using a motor rotation speed RP M  is used as a feedback to control the motor acceleration reference value Acc M_ref  calculated using the pedal torque, and a motor acceleration current i 6  is generated so that the target motor acceleration Acc M_ref  and the actual motor acceleration Acc M  become identical. 
     Finally, I M_ref , which is a motor acceleration command current, is generated by adding the current i 6  generated using the target motor acceleration and the current i 5  to which the gradient and the weight are applied to drive the motor. 
     As described above, since the motor acceleration command instead of the motor torque command or the motor speed command is used for motor control, the acceleration of the motor  50  may be adjusted. As a result, variation of the acceleration may be reduced, and thus a more improved pedaling feeling and driving feeling may be realized. 
     Meanwhile, in the case in which the motor speed command is used for motor control, the motor speed command is changed with time. Therefore, when a bandwidth of a speed controller is not large enough, an output may be unstable. However, since the motor acceleration command has a constant value corresponding to the pedal torque, the output may be relatively stable. 
     A magnitude of the current, which is supplied to the motor, of the speed controller may be greater than that of the acceleration controller. Even when a command value is given to exhibit the same acceleration performance, a maximum current appears in different aspects according to a control method. In the case in which the acceleration controller is used, it is possible to control the speed only with a smaller current. 
     Further, when the motor is accelerated using the acceleration controller, less current than that of the conventional speed controller is supplied to the motor, and thus it is possible to improve thermal characteristics and reduce a size of a hardware system. 
       FIG. 6  is a flowchart illustrating a method of driving a chainless electric bicycle according to an embodiment of the present invention. 
     According to an embodiment of the present invention, a method of driving a chainless electric bicycle, which is performed by a driving device including a controller, includes an operation S 100  of receiving a measured value of a rotational position P P  of a generator  40 , an operation S 200  of receiving a measured value of a rotational position P M  of a motor  50 , an operation S 300  of calculating a difference value P Δ  obtained by subtracting a value P M_geared  obtained by multiplying the value of the rotational position P M  of the motor  50  by a gear ratio from the value of the rotational position P P  of the generator  40 , and an operation S 400  of controlling the generator  40  or the motor  50  on the basis of the difference value P A . 
       FIG. 7  is a flowchart illustrating the operation of controlling the generator  40  or the motor  50  according to the embodiment of the present invention. 
     Referring to  FIG. 7 , after the operation S 300  of calculating the difference value is performed, the operation S 400  of controlling at least one of the generator  40  and the motor  50  may include at least one of operations S 412  to S 414  of controlling the generator  40  by controlling a generator driving current I P_current  between a battery and the generator  40  and at least one of operations S 422  to S 424  of controlling the motor  50  by controlling a motor driving current I M_current  between the battery and the motor  50 . The operations S 412  to S 414  of controlling the generator  40  and the operations S 422  to S 424  of controlling the motor  50  may be performed independently of each other. 
     The method of driving the chainless electric bicycle according to the embodiment of the present invention may further include an operation S 411  of measuring the generator driving current I P_current  and an operation S 421  of measuring the motor driving current I M_current . The control of the generator driving current I P_current  (S 412  to S 414 ) may be performed using a target generator current I P_ref  generated based on the difference value P Δ  as a reference value and using the measured generator driving current I P_current  as a feedback value. The control of the motor driving current I M_current  (S 422  to S 424 ) may be performed using a target motor current I M_ref  generated based on the difference value P Δ  as a reference value and using the measured motor driving current I M_current  as a feedback value. 
     Further, the operations S 412  to S 414  of controlling the generator  40  may include the operation S 412  of controlling the generator  40  by increasing the generator driving current I P_current  until the difference value P Δ  becomes zero when the difference value P Δ  is a positive number, the operation S 413  of controlling the generator  40  by reducing the generator driving current I P_current  until the difference value P Δ  becomes zero when the difference value P Δ  is a negative number, or the operation S 414  of controlling the generator  40  by maintaining the generator driving current I P_current  when the difference value P Δ  is zero. The control of the generator  40  may be completed by performing the operations S 412  to S 414  of controlling the generator  40 . 
     Further, the operations S 422  to S 424  of controlling the motor  50  may include the operation S 422  of controlling the motor  50  by increasing the motor driving current I M  current until the difference value P Δ  becomes zero when the difference value P Δ  is a positive number, the operation S 423  of controlling the motor by reducing the motor driving current I M_current  until the difference value P Δ  becomes zero when the difference value P Δ  is a negative number, or the operation S 424  of controlling the motor  50  by maintaining the motor driving current I M_current  when the difference value P Δ  is zero. The control of the motor  50  may be completed by performing the operations S 422  to S 424  of controlling the motor  50  or may be completed after additional operations S 425  to S 427  of controlling the motor  50  are further performed. 
       FIG. 8  is a flowchart illustrating a method of additionally controlling the motor  50  according to an embodiment of the present invention. 
     The method of driving the chainless electric bicycle according to the embodiment of the present invention may further include the operation S 425  of measuring a gradient S S  of a road on which the electric bicycle travels, the operation S 426  of calculating a pedal rotational acceleration α P  using a rotational position P P  of the generator  40 , and the operation S 427  of additionally controlling the motor  50  on the basis of the gradient S S  of the road and the pedal rotational acceleration α P . 
     Further, the operation S 427  of additionally controlling the motor  50  may be performed by additionally increasing the motor driving current I M_current  when the gradient S S  of the road is greater than or equal to a predetermined gradient or the pedal rotational acceleration α P  is greater than or equal to a predetermined acceleration. 
     As a result of the performing of driving control on at least one of the generator  40  and the motor  50  according to the method according to the embodiment of the present invention, a rotational position P M  of the motor  50  is synchronized with the rotational position P P  of the generator  40 . That is, the rotational position P P  of the generator  40  is used as a reference value and the rotational position P M  of the motor  50  is used as a feedback value. 
     By the driving control for the generator  40  and the motor  50 , the rotational position of the driving wheel and the rotational position of the pedal may be synchronized, and, as a result, a pedaling feeling that an occupant of the electric bicycle feels may become similar to that of a real bicycle. 
       FIG. 9  is a control flowchart illustrating a device for driving an electric bicycle according to an embodiment of the present invention. 
     Referring to  FIG. 9 , a controller  20  may detect a position of the pedal  42  using a generator position sensor  31  (S 500 ). 
     The controller  20  may detect a position of the motor  50  using a motor position sensor  37  (S 502 ). 
     The controller  20  may determine a position difference between the detected position of the pedal and the detected position of the motor (S 504 ). 
     The controller  20  may determine a target pedal torque on the basis of the position difference between the position of the pedal and the position of the motor (S 504 ). The target pedal torque may be a torque that is preset to correspond to the position difference between the position of the pedal and the position of the motor. 
     The controller  20  may detect a current of the generator  40  using a generator current sensor  33  (S 508 ). 
     The controller  20  may determine a pedal torque according to a generator current (S 510 ). The pedal torque may be a torque that is preset to correspond to the current of the generator  40 . 
     The controller  20  may determine whether a current pedal torque reaches the target pedal torque (S 512 ). 
     As a result of the determination in operation S 512 , when it is determined that the current pedal torque reaches the target pedal torque, the controller  20  allows a current generator current to be maintained (S 514 ). 
     Meanwhile, as the result of the determination in operation S 512 , when it is determined that the current pedal torque does not reach the target pedal torque, the controller  20  may adjust the current generator current (S 516 ). Thereafter, the flow of the method may be moved to operation S 508  to perform the subsequent operations. 
     Meanwhile, after the target pedal torque is determined in operation S 506 , the controller  20  may determine a target motor acceleration according to the target pedal torque (S 518 ). The target motor acceleration may be a speed that is preset to correspond to the target pedal torque. 
     The controller  20  may detect a motor acceleration on the basis of the rotational position of the motor  50  which is detected using the motor position sensor  37  (S 520 ). The controller  20  may determine a motor speed using a change in the rotational position of the motor which is detected using the motor position sensor  37  and may determine the motor acceleration using the motor speed. 
     The controller  20  may determine whether a current motor acceleration reaches a target motor acceleration (S 522 ). 
     As a result of the determination in operation S 522 , when it is determined that the current motor acceleration reaches the target motor acceleration, the controller  20  allows a current motor current to be maintained (S 524 ). 
     Meanwhile, as the result of the determination in operation S 522 , when it is determined that the current motor acceleration does not reach the target motor acceleration, the controller  20  may adjust the current motor current (S 526 ). Thereafter, the flow of the method may be moved to operation S 520  to perform the subsequent operations. 
     As described above, in an embodiment of the present invention, it is possible to more effectively improve a pedaling feeling and a driving feeling as if there is a real chain on the electric bicycle. 
     A device for driving an electric bicycle according to still another embodiment of the present invention may include a first motor driver and a second motor driver. 
     A controller may determine a target pedal torque on the basis of a position difference between an average position of a position of a first motor and a position of a second motor and a position of a pedal. 
     The controller may determine a target motor acceleration according to the target pedal torque and may adjust a current of the first motor using the first motor driver and adjust a current of the second motor using the second motor driver so that the motor acceleration reaches the target motor acceleration. In addition, the controller may adjust the current of the generator so that the pedal torque according to the generator current reaches the target pedal torque. 
     The same motor acceleration command may be used for motor control for the first motor and the second motor. Therefore, speed control of the first motor and the second motor may be performed at the same motor acceleration. 
     As described above, in another embodiment of the present invention, it is possible to more effectively improve the feeling of having a chain on the electric bicycle regardless of the driving road surface, and it is possible to perform the speed control at the same speed even when there is a difference in road surface condition between wheels on which the motor is mounted. 
     The scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the scope of the present invention cannot be limited due to obvious changes or substitutions in the art to which the present invention pertains.