Patent Publication Number: US-2022212750-A1

Title: Electric power assist device for bicycles and bicycle

Description:
TECHNICAL FIELD 
     The present invention relates to an electric power assist device for bicycles, and a bicycle. In particular, the present invention relates to an electric power assist device for bicycles capable of calibrating a rotational angle sensor for detecting crank rotational angles used for power assist control, and a bicycle fitted with the electric power assist device. 
     BACKGROUND ART 
     Known power assisted bicycles include those configured to detect a pedaling force with a torque sensor, and control an electric motor for assisting the rider&#39;s pedaling based on the detected pedaling force (See Patent Documents 1 and 2). 
     PRIOR ART DOCUMENT(S) 
     Patent Document(s) 
     
         
         Patent Document 1: JP2000-053069A 
         Patent Document 2: JP2008-260400A 
       
    
     SUMMARY OF THE INVENTION 
     Task to be Accomplished by the Invention 
     Known technologies for power assisted bicycles include using an electric power assist device which can be attached to a frame structure of a bicycle and perform power assist control without using a torque sensor, where the electric power assist device includes: an electric motor connected to a crankshaft or crankarm in a torque transmitting relationship; a rotational angle sensor for detecting a crank rotational angle of the crankshaft; and a control unit for controlling operation of the electric motor, and is configured to determine a drive torque of the electric motor based on a difference or a ratio between motor currents, angular velocities, or angular acceleration values measured at a first crank rotational angle and a second crank rotational angle in each cycle of the rotation of the crankshaft. 
     Such an electric power assist device for power assisted bicycles needs to detect the absolute angle of a crank rotational angle in order to determine a first crank rotational angle and a second crank rotational angle. Thus, when the electric power assist device can be mounted on bicycles at different angles, the variation of the angle at which the electric power assist device is mounted on a bicycle produces errors in the crank rotational angles (absolute angles) detected by the rotational angle sensor provided therein, resulting in the inability to achieve a proper power assist control. 
     The present invention has been made in view of the problem of the prior art, and a primary object of the present invention is to provide an electric power assist device which can achieve proper power assist control regardless of the angle at which the electric power assist device mounted on a bicycle. 
     Means to Accomplish the Task 
     One aspect of the present invention provides an electric power assist device which can achieve proper power assist control regardless of the angle at which the electric power assist device mounted on a bicycle. An electric power assist device for bicycles of the present invention comprises: a housing ( 52 ) which can be attached to a frame structure ( 18 ) of a bicycle ( 10 ); an electric motor ( 58 ) provided in the housing; a rotating member ( 64 ,  72 ) rotatably supported by the housing, rotationally driven by the electric motor, and connected to a crankshaft ( 24 ) or crankarm ( 26 ) of the bicycle in a torque transmitting relationship; a rotational angle sensor ( 124 ) provided in the housing and configured to detect a rotational angle of the electric motor or the rotating member; and a control unit ( 120 ) for controlling operation of the electric motor ( 58 ) based on the rotational angle detected by the rotational angle sensor, wherein the electric power assist device further comprises a tilt angle detector ( 128 ) for detecting a tilt angle with respect to a direction of gravity, and wherein the control unit comprises a calibrator ( 148 ) for determining an absolute angle of the rotational angle detected by the rotational angle sensor based on an output signal from the tilt angle detector. 
     This configuration enables proper power assist control regardless of the angle at which the electric power assist device mounted on a bicycle. 
     In this electric power assist device, preferably, the tilt angle detector includes a gyro sensor ( 128 ). 
     According to this configuration, the tilt angle detector can accurately detect the tilt angle with respect to the direction of gravity without being bulky. 
     In this electric power assist device, preferably, the housing and the rotating member are provided with respective marks ( 154 ,  156 ) which are externally visible, wherein alignment of the marks indicates that the rotating member is rotated to a predetermined rotational position with respect to the housing, and wherein the calibrator determines the absolute angle of the rotational angle sensor when the marks are aligned. 
     In this configuration, the calibration can be easily performed by aligning the marks to thereby adjust the rotational position of the rotating member. 
     In this electric power assist device, preferably, the calibrator determines the absolute angle of the rotational angle sensor when the rotating member is maintained at the predetermined rotational position for a predetermined period of time. 
     In this configuration, the calibration can be properly performed by aligning the marks to thereby adjust the rotational position of the rotating member. 
     In this electric power assist device, preferably, the electric power assist device further comprises a check switch ( 152 ) which can be toggled by a user&#39;s manual operation, and wherein the calibrator determines the absolute angle of the rotational angle sensor when the check switch is toggled. 
     In this configuration, the calibration can be properly performed by aligning the marks to thereby adjust the rotational position of the rotating member. 
     In this electric power assist device, preferably, the electric power assist device further comprises a position sensor ( 158 ,  160 ) for detecting that the rotating member is positioned at a predetermined rotational position, wherein the calibrator determines the absolute angle of the rotational angle sensor when the position sensor detects that the rotating member is positioned at the predetermined rotational position. 
     In this configuration, the adjustment of the rotational position of the rotating member can be automatically confirmed, which enables the calibration to be properly performed. 
     In this electric power assist device, preferably, the predetermined rotational position of the rotating member is set as any rotational position within a predetermined rotational position range of the rotating member. 
     In this configuration, a user can set the absolute angles of the first and second crank rotational angles as desired, which enables the response time of power assist control to be customized for the user. 
     In this electric power assist device, preferably, the control unit allows power assist control to be started when the rotating member is sequentially positioned at a plurality of predetermined rotational positions in a predetermined sequence. 
     In this configuration, the electric power assist device serves as a dial-lock-type lock mechanism, providing an anti-theft feature. 
     In this electric power assist device, preferably, the control unit determines a drive torque of the electric motor based on a difference or a ratio between motor currents, angular velocities, or angular acceleration values measured at a first crank rotational angle and a second crank rotational angle in each cycle of the rotation of the crankshaft. 
     In this configuration, a pedaling force put on the pedals of the bicycle ( 10 ) can be estimated based on a difference or a ratio between motor currents, angular velocities, or angular acceleration values measured at a first crank rotational angle and a second crank rotational angle, and power assist control can be performed based on the estimated pedaling force. 
     In this electric power assist device, preferably, a rotational phase difference between the first crank rotational angle and the second crank rotational angle is 90 degrees. 
     This configuration enables more accurate estimation of a pedaling force based on a difference or a ratio between motor currents, angular velocities, or angular acceleration values measured at a first crank rotational angle and a second crank rotational angle. 
     In this electric power assist device, preferably, when the bicycle is travelling on a uphill road which slopes upward at an upward-inclined angle, the control unit corrects the first and second crank rotational angles so as to advance the angles by an amount corresponding to the upward-inclined angle, and wherein, when the bicycle is travelling on a downhill road which slopes downward at a downward-inclined angle, the control unit corrects the first and second crank rotational angles so as to delay the angles by an amount corresponding to the downward-inclined angle. 
     This configuration enables accurate estimation of a pedaling force even when the bicycle is traveling on a slope road. 
     In this electric power assist device, preferably, the control unit determines whether the crankshaft rotates in a forward direction or in a reverse direction based on crank rotational angles detected by the rotational angle sensor, and wherein, when determining that the crankshaft rotates in the reverse direction, the control unit causes the electric motor to stop operating. 
     This configuration prevents the electric power assist device from performing unnecessary power assist when the crankshaft rotates in the reverse direction. 
     In this electric power assist device, preferably, the control unit corrects a drive torque of the electric motor based on the tilt angle with respect to the direction of gravity detected by the tilt angle detector. 
     This configuration enables proper power assist control when the bicycle is traveling on a slope road. 
     In this electric power assist device, preferably, the electric power assist device further comprises: a battery ( 122 ) which serves as a power source for the electric motor; and a voltage sensor ( 132 ) for detecting a voltage of the battery, wherein the control unit reduces a rotational output of the electric motor in response to a voltage drop detected by the voltage sensor. 
     This configuration prevents over-discharging of the battery. 
     Another aspect of the present invention provides a bicycle fitted with the above-described electric power assist device. 
     This configuration enables proper power assist control regardless of the angle at which the electric power assist device mounted on the bicycle. 
     Effect of the Invention 
     In an electric power assist device and a bicycle according to the present invention, proper power assist control can be performed regardless of the angle at which the electric power assist device mounted on the bicycle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an electric power assist device according to a first embodiment of the present invention and a bicycle fitted with the electric power assist device; 
         FIG. 2  is a fragmentary perspective view of the electric power assist device and the bicycle of the first embodiment; 
         FIG. 3  is a fragmentary exploded perspective view of the electric power assist device and the bicycle of the first embodiment; 
         FIG. 4  is a block diagram of a power assist control system for the electric power assist device and a bicycle fitted with the electric power assist device of the first embodiment; 
         FIG. 5  is an explanatory diagram showing a crank rotational angle when the bicycle is traveling on a flat road; 
         FIG. 6A  is an explanatory diagram showing a crank rotational angle when the bicycle is traveling on an uphill road; 
         FIG. 6B  is an explanatory diagram showing a crank rotational angle when the bicycle is traveling on a downhill road; 
         FIG. 7  is a graph showing the relationship between the crank rotational angle and the motor current in the bicycle; 
         FIG. 8  is a flowchart of power assist control of the electric power assist device of the first embodiment; 
         FIG. 9  is a flowchart of calibration of the rotational angle sensor for detecting crank rotational angles of the electric power assist device of the first embodiment; 
         FIG. 10  is a flowchart of calibration of the rotational angle sensor for detecting crank rotational angles of the electric power assist device of a variation of the first embodiment; 
         FIG. 11  is a side view of an electric power assist device according to a second embodiment of the present invention and a bicycle fitted with the electric power assist device; 
         FIG. 12  is a flowchart of calibration of the rotational angle sensor for detecting crank rotational angles of the electric power assist device of the second embodiment; 
         FIG. 13  is a side view of an electric power assist device according to a third embodiment of the present invention and a bicycle fitted with the electric power assist device; 
         FIG. 14  is a side view of an electric power assist device according to a fourth embodiment of the present invention and a bicycle fitted with the electric power assist device; and 
         FIG. 15  is a flowchart of calibration of the rotational angle sensor for detecting crank rotational angles of the electric power assist device of the fourth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     An electric power assist device and a bicycle according to a first embodiment of the present invention will be described with reference to  FIGS. 1 to 9 . 
     As shown in  FIGS. 1 to 3 , a bicycle  10  is provided with a frame structure  18  that includes a seat tube  12  extending substantially in the vertical direction and having a saddle (not shown in the drawings) attached to the upper end thereof, a down tube  14  extending substantially in the fore and aft direction, and left and right chain stays  16 . The lower end of the seat tube  12 , the rear end of the down tube  14 , and the front ends of the chain stays  16  are connected to one another by a bearing tube  20  for supporting a crankshaft and also serving as a pipe joint. 
     The bearing tube  20  rotatably supports a crankshaft  24  extending substantially horizontally in the lateral direction. The left and right shaft ends of the crankshaft  24  project out of the bearing tube  20 , and the base ends of the left and right crankarms  26  and  28  are fixed to the respective shaft ends of the crankshaft  24  with a rotational phase difference of 180 degrees. The crankshaft  24  forms the rotational center of the crankarms  26  and  28 , and the rotational center axis of the crankshaft  24  and the rotational center axis of the crankarms  26  and  28  coincide with each other. 
     A spline shaft portion  24 A is formed on the outer circumferential surface of the shaft end of the crankshaft  24 . A spline hole  26 A is formed at the base end of the crankarm  26 . The spline shaft portion  24 A and the spline hole  26 A are engaged with each other so that the crankshaft  24  and the crankarm  26  are connected to each other in a torque transmitting relationship. 
     The outer end of the crankshaft  24  is formed with a screw hole  24 B opened at the end surface thereof. The base end of the crankarm  26  is formed with a screw hole  26 B coaxially communicating with the spline hole  26 A and having an inner diameter larger than that of the spline hole  26 A. The screw hole  24 B threadably engages a crankarm mounting screw  27  provided with a flange portion that abuts against the annular shoulder surface defined between the spline hole  26 A and the screw hole  24 B. As a result, the crankarm  26  is prevented from being dislodged from the crankshaft  24 . 
     The connection between the crankshaft  24  and the crankarm  28  on the other side is made in the same manner as the above discussed connection between the crankshaft  24  and the crankarm  26 . 
     A pedal  30  is attached to the free end of each crankarm  26 ,  28 . A drive sprocket  32  (chain wheel) is positioned between the crankarm  28  on the right side and the bearing tube  20 . The drive sprocket  32  is coaxially connected (fixed) to the crankshaft  24 . 
     The crankshaft  24  can be rotationally driven by the left and right crankarms  26  and  28 . The rotation of the crankshaft  24  is transmitted to the drive sprocket  32 , and is transmitted from the drive sprocket  32  to the rear wheel (not shown in the drawings) by a chain transmission mechanism (not shown in the drawings). As a result, the electric power assisted bicycle  10  travels forward. 
     The electric power assisted bicycle  10  is provided with a unitized and retrofittable electric power assist device  50 . In the following description, the various directions such as up/down, front/rear, and right/left are based on the state where the electric power assist device  50  is attached to the frame structure  18  of the electric power assisted bicycle  10  as shown in  FIGS. 1 and 2 . 
     The electric power assist device  50  is provided with a housing  52  having a hollow structure. The housing  52  includes a ring portion  54  and a tongue shaped extension portion  56  extending radially outward from the ring portion  54 . An electric motor  58  for generating an assist force is attached to the right surface of the extension portion  56 . One end of the electric motor  58  is fixed to the extension portion  56  so that the rotational axis of the rotor output shaft (not shown in the drawings) is directed in the lateral direction. 
     As shown in  FIG. 3 , the ring portion  54  includes a cylindrical portion  62  centrally defining a central opening  60  that is open in the lateral direction, The cylindrical portion  62  rotatably supports an annular rotational output member  64  on the outer periphery thereof. The cylindrical portion  62 , together with the rotational output member  64 , is disposed between the frame structure  18  and the crankarm  26  in a coaxial relationship with the crankshaft  24  while the crankshaft  24  extends laterally through the central opening  60  in a loosely received state. The rotational output member  64  is connected to the electric motor  58  in a torque transmitting relationship via a gear train (not shown in the drawings) provided in the housing  52 , and is thereby rotationally driven by the electric motor  58  in a coaxial relationship with the crankshaft  24 . 
     The cylindrical portion  62  and the rotational output member  64  are installed between the frame structure  18  and the crankarm  26  by the following procedure. 
     First, the left pedal  30  which is on the side not fitted with the drive sprocket  32  is removed by using a common tool such as a spanner. Next, with the electric power assist device  50  tilted sideways (the posture in which the electric motor  58  faces upward), the free end side of the left crankarm  26  is inserted into the central opening  60 , and with the crankarm  26  passed into the central opening  60 , the electric power assist device  50  is moved toward the base end side (rotational center side) of the crankarm  26  along the extending direction of the crankarm  26 . 
     As a result, the crankarm  26  is passed through the cylindrical portion  62  and the rotational output member  64  until the cylindrical portion  62  and the rotational output member  64  are positioned near the base end of the crankarm  26 . The inner diameter of the central opening  60  is dimensioned so that the crankarm  26  may be passed through the central opening  60 . If the central opening  60  has a large enough inner diameter to allow the pedal  30  attached to the crankarm  26  to be pass through, the assembly work can be performed without requiring the pedal  30  to be removed. 
     Next, the electric power assist device  50  is oriented to the normal posture (the posture shown in  FIG. 2 ) in which the electric motor  58  faces sideways, and the crankshaft  24  is loosely passed into the central opening  60  in the axial direction. As a result, the cylindrical portion  62  and the rotational output member  64  can be positioned between the frame structure  18  and the crankarm  26  with the crankshaft  24  extending laterally and loosely received in the central opening  60  simply by removing the pedal  30  or without even requiring the pedal  30  to be removed. 
     The rotational output member  64  is connected to the crankshaft  24  and the crankarm  26  by a connecting mechanism  70 . The connecting mechanism  70  includes a connecting main member  72  and two clamp piece members  74  and  77 . 
     The screw hole  26 B of the crankarm  26  threadably receives a male screw portion  78 A of a flanged screw member  78  constituting a mount part for the crankarm  26  of the connecting main member  72 . The connecting main member  72  has a substantially circular disk shape, and is fixed to the rotational output member  64  at the peripheral edge thereof by a plurality of bolts  75  and to the screw member  78  at the central part thereof by a bolt  76 . As a result, the rotational output member  64  is coaxially positioned relative to the crankshaft  24  via the connecting main member  72  and the crankarm  26 . 
     The two clamp piece members  74 , each having a wedge shape, are positioned on either side of the base end part of the crankarm  26  with respect to the rotational direction thereof, such that each clamp piece member  74  is in contact with an angled edge  73  of a corresponding connecting main member  72 . A bolt  80  is provided for each clamp piece member  74 , and as the bolts  80  are tightened to connect the clamp piece members  74  to the connecting main member  72 , the clamp piece members  74  are caused to slide toward each other guided by the angled edges with interposing the crankarm  26  from both sides with respect to the rotational direction, so that the crankarm  26  and the connecting main member  72  are connected to each other in a torque transmitting relationship. 
     As a result, the rotational output member  64  is coaxially connected to the crankshaft  24  in a torque transmitting relationship, via the connecting main member  72  and the crankarm  26 , and thus the rotational output member  64  and the connecting main member  72  can rotate together with the crankshaft  24 . The rotational output member  64  and the connecting main member  72  are collectively referred to as a rotating member. 
     The clamp piece members  74  define bolt through-holes  81 , through which the bolts  80  are passed. The bolt through-holes  81  are each formed in an oval shape so that, as the bolts  80  are tightened to connect the clamp piece members  74  to the connecting main member  72 , the clamp piece members  74  can slide toward each other. 
     The extension portion  56  of the housing  52  is positioned under the down tube  14  while supporting the electric motor  58 . The extension portion  56  is supported by and suspended from the down tube  14  via a support mechanism  90 . 
     The support mechanism  90  includes a mount member  92 . The mount member  92  includes a support base member  98  fixed to the down tube  14  by a fastening band  94  and provided with a rectangular frame structure part  96  in a lower part thereof, and a support member  104 , the support member  104  having a rectangular plate-shaped part  100  fitted into the rectangular frame structure part  96  and fixed to the support base member  98 , and a depending piece  102  depending downward from the rectangular plate-shaped part  100  and extending in the fore and aft direction. 
     The depending piece  102  is a cantilever piece, and defines a through-hole  103  which extends in the axial direction of the crankshaft  24  (or in the lateral direction) and is provided with an annular shoulder. A cylindrical fixed bush  106  is fitted in (or fixed to) the through-hole  103  of the depending piece  102  in a rotationally fast manner. 
     A female screw  108  is formed on the inner circumferential surface of the fixed bush  106 . A male screw  109  formed on the outer circumferential surface of a movable bush  110  is threaded with the female screw  108  so that the movable bush  110  can be threaded into and out of the large diameter portion  106 B in the axial direction of the crankshaft  24  (i.e., in the lateral direction). 
     The movable bush  110  is provided with a flange part  112  on the side remote from the fixed bush  106 . The outer circumference of the flange part  112  is provided with an uneven shape similar to flower petals so that the movable bush  110  can be turned by hand. The flange surface  112 A of the flange part  112  is in direct contact with the laterally inwardly facing end surface  66 A of a boss part (connecting part)  66  formed on an upper part of the extension portion  56  of the housing  52 . 
     The mount member  92  fixedly supports the housing  52  with a fastening bolt  114  which is centrally passed through the fixed bush  106  and the movable bush  110  in the axial direction of the crankshaft  24 , and threaded into a screw hole  68  (not shown) of the boss part  66 . 
     In this way, the fixed bush  106  and the movable bush  110  are provided with a screw mechanism formed by the female screw  108  and the male screw  109  extending in the axial direction of the crankshaft  24  between the housing  52  and the frame structure  18 , the screw mechanism forms an adjustment mechanism capable of adjusting (increasing or decreasing) the distance between the mount member  92  and the housing  52  along the axial direction of the crankshaft  24 . 
     By suitably adjusting the distance along the axial direction, the tilting of the rotational output member  64  with respect to the central axis (crankshaft line) of the crankshaft  24  can be corrected, and the posture of the rotational output member  64  can be adjusted so that the rotational output member  64  extends along a plane orthogonal to the crankshaft axial line. 
     Triangular marks  154  and  156  that are externally visible are printed on the outer surfaces of the extension portion  56  and the connecting main member  72  of the housing  52 , respectively, and alignment of the marks indicates that the connecting main member  72 , (i.e., the rotational output member  64  integrated with the connecting main member  72 ) is rotated to a predetermined rotational position with respect to the housing  52 . As shown in  FIG. 1 , the marks  154  and  156  are aligned when the angle β formed by the straight line (unit center line) C and the straight line (crankarm line) E is 90 degrees, where the unit center line C passes through the rotation center point A of the crankshaft  24  (that of the rotational output member  64 ) and the rotation center point B of the electric motor  58 , and the crankarm line E passes through the rotation center point A of the crankshaft  24  and the rotation center point D of the pedal  30 . 
     The mounting angle of the housing  52  with respect to the frame structure  18  determines the angle γ formed by the vertical line V along the direction of gravity and the unit center line C, which is detected based on an output signal of the gyro sensor  128  described later. When the marks  154  and  156  are aligned; that is, when the crankarm  26  is rotated to the rotational angle β, the angle α formed by the vertical line V and the crankarm line E is β−γ (i.e, α=90−γ), and the rotational angle sensor  124  is calibrated based on the angle α as described later. 
     The extension portion  56  of the housing  52  is provided with a push-button check switch  152  which can be operated by a user of the bicycle  10  (see  FIG. 2 ). When the push button  152 A of the check switch  152  is pressed and the check switch  152  is toggled, the control unit  120  performs calibration of the rotational angle sensor  124  as will be described later. 
     The extension portion  56  of the housing  52  contains the control unit  120  for electric power assist therein. A battery  122  consisting of a secondary battery that serves as a power source for the electric motor  58  and the control unit  120  is attached to the seat tube  12  by a fastening band (not shown) or any other fastening means. 
     Next, the control system of the electric power assist device  50  will be described with reference to  FIG. 4 . 
     A rotational angle sensor  124 , a pulse sensor  126 , a gyro sensor  128 , a current sensor  130 , and a voltage sensor  132  are attached to the electric power assist device  50 . 
     The rotational angle sensor  124  is provided on the electric motor  58  or the housing  52 , and configured to detect the motor rotational angle or the rotational angle (absolute angle) of the rotational output member  64 . When the housing  52  of the electric power assist device  50  is attached to the frame structure  18  of the bicycle  10  and the rotational output member  64  is connected to the crankshaft  24  by the connecting mechanism  70 , the rotational angle sensor  124  detects the crank rotational angle (absolute angle) of the crankshaft  24 . As shown in  FIG. 5 , the zero point (origin) of the absolute angle that is detected by the rotational angle sensor  124  is set to the crank rotational angle of the crankshaft  24  when the pedal  30  of the crankarm  26  is located at the highest position. 
     In the following description, based on the premise that the electric power assist device  50  is attached to the frame structure  18  for the sake of simplicity, the rotational angle sensor  124  is sometimes described as being configured to detect the crank rotational angle of the crankshaft  24 , which is equivalent to the motor rotational angle or the rotational angle of the rotational output member  64 . 
     The pulse sensor  126  is provided in the housing  52  and detects the rotation of the rotational output member  64 . 
     The gyro sensor  128  is provided in the housing  52  and detects the angular velocity of the rotational output member  64  (crankshaft  24 ). The gyro sensor  128  forms part of the tilt angle detector. Specifically, based on the output signal of the gyro sensor  128 , the tilt angle detector detects the tilt angle of the electric power assist device  50  in the left-right direction and the fore and aft direction with respect to the direction of gravity; that is, the vertical line V. 
     The current sensor  130  detects the motor current value i of the electric motor  58 . 
     The motor current value i changes in a 360-degree cycle according to the rotational angle of the rotational output member  64 , which corresponds to the crank rotational angle, and the motor current value i also has a correlation with the rotational angular velocity of the crankshaft  24 ; that is, the pedaling force. 
     The voltage sensor  132  detects the voltage of the battery  122 . 
     The control unit  120  is an electronically controlled device including a microcomputer and other components. The control unit includes a pedaling force estimator  140 , a crank rotational direction determiner  142 , a pedaling force presence determiner  144 , a motor drive controller  146 , and a calibrator  148 . 
     The pedaling force estimator  140  receives information on the crank rotational angle from the rotational angle sensor  124 , information on the rotational movement of the crankshaft  24  from the pulse sensor  126 , information on the motor current value i from the current sensor  130 , and estimates the pedaling force of the bicycle  10  from the difference or the ratio between the motor current value i 1  at a preset first crank rotational angle and the motor current value i 2  at a preset second crank rotational angle which is different from the first crank rotational angle. 
     The pedaling force estimator  140  estimates the pedaling force to be greater with an increasing difference (i 1 −i 2 ) or ratio (i 1 /i 2 ) between the motor current value i 1  at the first crank rotational angle and the motor current value i 2  at the second crank rotational angle. 
     The first crank rotational angle is within an angular range of 0 to 90 degrees inclusive from the position where the pedal  30  of the crankarm  26  is located above the crankshaft  24  on the vertical line V (see  FIGS. 5 and 6 ) which passes through the rotation center point A of the crankshaft  24 . The second crank rotational angle is within an angular range of 90 to 180 degrees inclusive from the position where the pedal  30  of the crankarm  26  is located above the crankshaft  24  on the vertical line V (see  FIGS. 5 and 6 ) which passes through the rotation center point A of the crankshaft  24 . Preferably, a rotational phase difference between the first crank rotation angle and the second crank rotation angle is 90 degrees. 
     When the calibration of the rotational angle sensor  124  by setting the reference absolute angle is performed on a flat ground (ground with no gradient), and the reference absolute angle (zero point angular position) detected by the rotational angle sensor  124  is set as an angle where the pedal  30  of the crankarm  26  is located above the crankshaft  24  on the vertical line F extending perpendicular to the road surface and passing through the rotation center point A of the crankshaft  24 , the vertical line F overlaps the vertical line V as shown in  FIG. 5 . Thus, when the calibration of the rotational angle sensor  124  is performed on a flat ground (ground with no gradient), the first crank rotational angle may be within an angular range in which the absolute angle detected by the rotational angle sensor  124  is within 0 to 90 degrees inclusive and the second crank rotational angle may be within an angular range in which the absolute angle detected by the rotational angle sensor  124  is within 90 to 180 degrees inclusive. A reference symbol X denotes the position of the pedal  30  when the absolute angle detected by the rotational angle sensor  124  is 0 degree. 
     Each of the motor current values i 1  and i 2  may be a motor current value i at at least one point within a corresponding above-mentioned angular range. Alternatively, the motor current value i 1  may be an average value or an integrated value of the motor current value i in a first angular range θ 1  in which the absolute angle detected by the rotational angle sensor  124  is about 0 to 15 degrees, and the motor current value i 2  may be an average value or an integrated value of the motor current value i in a second angular range θ 2  in which the absolute angle detected by the rotational angle sensor  124  is about 90 to 15 degrees. 
     When the bicycle is on an uphill road where the road surface slopes upward at a certain angle, the vertical line F tilts with respect to the vertical line V according to the slope angle of the uphill road, as shown in  FIG. 6(A) , and thus the zero point position of the rotational angle sensor  124  deviates to the delay angle side in the crank rotational direction with respect to the vertical line V. In this situation, the first and second angular ranges θ 1  and θ 2 , which are to be set with reference to the vertical line V, need to be corrected to θ 1   a  and θ 2   a  on the advance angle side, respectively. 
     When the bicycle is on a downhill road where the road surface slopes downward at a certain angle, the vertical line F tilts with respect to the vertical line V according to the slope angle of the downhill road, as shown in  FIG. 6(B) , and thus the zero point position of the rotational angle sensor  124  deviates to the advance angle side in the crank rotational direction with respect to the vertical line V. In this situation, the first and second angular ranges θ 1  and θ 2 , which are to be set with reference to the vertical line V, need to be corrected to θ 1   b  and θ 2   b  on the delay angle side, respectively. 
     Accordingly, on the uphill road, the pedaling force estimator  140  corrects the first and second crank rotational angles to the advance angle side in the crank rotational direction by an amount corresponding to the slope angle of the road surface, and on a downhill road, the pedaling force estimator  140  corrects the first and second crank rotational angles and the second crank to the delay angle side in the crank rotational direction by an amount corresponding to the slope angle of the road surface. 
     As a result, even when the bicycle is traveling on an uphill road or a downhill road, the pedaling force estimator  140  can properly estimate the pedaling force put on the bicycle  10  as in the case of on a flat road (road with no gradient). 
     As can be seen from the motor current waveform shown in  FIG. 7 , the average value or integrated value of the motor current value i 1  in the first angular range θ 1  is greater than the average value or integrated value of the motor current value i 2  in the second angular range θ 2 , and the difference (i 1 −i 2 ) or the ratio (i 1 /i 2 ) is roughly proportional to the pedaling force, which correlates with the crank angular velocity. 
     The motor drive controller  146  outputs a control command to a motor drive circuit  150  so as to operate the electric motor  58  with an electric power (current or voltage) according primarily to the pedaling force estimated by the pedaling force estimator  140 . 
     The motor drive controller  146  also receives information on the crank rotational angle from the rotational angle sensor  124 , and based on the received information, the motor drive controller  146  calculates the angular velocity ω 1  of the crankshaft  24  at the first crank rotational angle or in the first angular range θ 1 , and the angular velocity ω 2  of the crankshaft  24  at the second crank rotational angle or in the second angular range θ 2 , and then outputs a drive torque control command determined based on the difference between the angular velocities θ 1  and ω 2 , to the motor drive circuit  150 . 
     The motor drive circuit  150  quantitatively sets the electric power to be supplied from the battery  122  to the electric motor  58 . As a result, the electric motor  58  assists the pedaling with the drive torque determined according to the estimated value of the pedaling force. In this way, the electric motor can assist the pedaling according to the pedaling force without the need for any complicated feature for detecting pedaling force and any modification made to the bicycle  10 . 
     The crank rotational direction determiner  142  determines whether the crankshaft  24  is rotating in a forward direction or in a reverse direction based on the crank rotational angles detected by the rotational angle sensor  124 . When the crank rotational direction determiner  142  determines that the crankshaft  24  rotates in the reverse direction, the motor drive controller  146  performs control to cause the electric motor  58  to stop operating. This prevents unnecessary power assist from being applied when the crankshaft  24  rotates in the reverse direction. 
     The pedaling force presence determiner  144  determines whether or not a pedaling force is put on the pedal  30  from the rotational movement of the crankshaft  24  detected by the rotational angle sensor  124 . When the pedaling force presence determiner  144  determines there is no pedaling force on the pedal, the motor drive controller  146  performs control to cause the electric motor  58  to stop operating. This prevents unnecessary power assist from being applied when there is no pedaling force on the pedal. 
     The motor drive controller  146  further performs control to increase or decrease the drive torque of the electric motor  58  according to the tilt angle with respect to the direction of gravity detected based on the output signal from the gyro sensor  128 ; that is, according to the tilts of the bicycle  10  in the left-right direction and the fore and aft direction with respect to the direction of gravity. This feature enables the power assist to be performed as needed by the rider, and improves the safety. For example, when the bicycle  10  is tilted to the left or right during turning, the motor drive controller decreases the assist force, and when the bicycle  10  is tilted in the fore and aft direction on an uphill road, the motor drive controller increases the assist force. 
     The motor drive controller  146  further performs control to reduce the rotational output of the electric motor  58  in response to the decrease in the battery voltage detected by the voltage sensor  132 . This feature prevents over-discharging of the battery  122 , thereby extending the life of the battery  122 . This feature can also reduce the power consumption of the battery  122 , thereby extending the power assist available distance (duration time) on one charge of the battery  122 . 
     The calibrator  148  calibrates the rotational angle sensor  124 , setting the reference absolute angle measured by the rotational angle sensor  124  on a flat ground based on the direction of gravity detected based on the output signal from the gyro sensor  128 . 
     When the rotational angle sensor  124  is calibrated by setting the reference absolute angle of the rotational angle sensor  124  (detecting the origin angular position) based on the angle α calculated by α=90−γ, where γ is determined by the mounting angle of the housing  52  with respect to the frame structure  18  when the marks  154  and  156  are aligned; that is, when the rotational angle β of the crankarm  26  is 90 degrees. 
     A user can align the mark  154  with the mark  156  by turning the crankarm  26  in the reverse direction, or turning the crankarm  26  with the rear wheel (not shown) of the bicycle  10  away from the road surface. When the marks  154  and  156  are aligned and the user presses the push button  152 A of the check switch  152 , the calibrator  148  recognizes that the marks  154  and  156  are aligned and thus the angle β is 90 degrees, and then performs the calibration of the rotational angle sensor  124 . 
     By performing the calibration, the first and second crank rotational angles determined from the motor current values i 1  and i 2  detected (measured) by the current sensor  130  are prevented from varying according to the mounting angle (i.e., the angle γ) of the electric power assist device  50  with respect to the frame structure  18 . 
     As a result, even when the mounting angle of the electric power assist device  50  with respect to the bicycle  10  varies, the electric power assist device can perform proper power assist control through the proper detection of the crank rotational angles (absolute angles). 
     Next, a power assist control routine executed by the control unit  120  will be described with reference to the flowchart shown in  FIG. 8 . 
     This control routine is started when the electric power assist device  50  is turned on. First, the calibration of the rotational angle sensor  124  is performed (step S 1 ). In the present embodiment, the calibration of the rotational angle sensor  124  is performed every time the electric power assist device  50  is turned on. However, the calibration may be performed when the electric power assist device  50  is attached to the bicycle  10  or when a calibration request is made by an external signal. 
     When the calibration is completed, the control unit  120  performs a standby state entry process, causing the electric power assist device  50  to enter a standby state (step S 10 ). In the standby state entry process, the control unit  120  activates the rotational angle sensor  124 , the pulse sensor  126 , the gyro sensor  128 , the current sensor  130 , and the voltage sensor  132  by feeding power, and causes the electric motor  58  to stop operating. 
     Next, the control unit  120  determines whether or not the power supplied to the electric power assist device  50  is turned off (step S 11 ). When the power is turned off, the control unit  120  performs a power-off process (step S 12 ). The power-off process involves stopping the power supplied to each of the sensors  124 ,  126 ,  128 ,  130  and  132 . 
     When the power is not turned off, the control unit  120  determines whether or not the crankshaft  24  rotates in the reverse direction (step S 13 ). When the crankshaft  24  is rotating in the reverse direction, the process returns to the standby state entry process (step S 10 ). 
     When the crankshaft  24  is not rotating in the reverse direction, the control unit  120  confirms that the crankshaft  24  has made one rotation (step S 14 ), and then starts the electric motor  58  (step S 15 ). 
     Next, the control unit  120  performs a road gradient correction according to the slope angle of the road surface (step S 16 ). As shown in  FIGS. 5 and 6 , the control unit  120  performs the road gradient correction based on the slope angle of the road surface determined based on the output signal from the gyro sensor  128 , by shifting the first and second angular ranges θ 1  and θ 2  to the advance angle side (uphill road) or the delay angle side (downhill road) of the crank rotational angle so as to correspond to the respective angular ranges in the case of on a flat road. As a result, even when the bicycle is traveling on the uphill road or the downhill road, the first angle range θ 1  and the second angle range θ 2  are properly set in response to the change in pedaling force as in the case of traveling on a flat road. 
     Next, the control unit  120  determines whether or not the waveform of the motor current value i is constant during one rotational movement of the crankshaft  24  (step S 17 ). When the waveform of the motor current value i is constant during one rotation, the control unit  120  estimates that the pedaling force is substantially zero and determines that the bicycle is coasting without requiring power assist, and the process returns to the standby state entry process (step S 10 ). 
     When the waveform of the motor current value i is not constant during one rotation, the control unit  120  determines whether or not the change (difference) in the motor current value i is equal to or greater than a predetermined threshold value (step S 18 ). Specifically, the control unit  120  calculates the change (difference value) between the average value or the integrated value of the motor current value i in the first angular range θ 1  and that in the second angular range θ 2 , and determines whether or not the change (difference value) is equal to or greater than the predetermined threshold value. 
     When the change in the motor current value i is equal to or greater than the predetermined threshold value, as the pedaling force is roughly proportional to the difference value between the average value or integral value of the motor current value i in the first angular range θ 1  and that in the second angular range θ 2 , the control unit  120  estimates the pedaling force based on the difference value, and calculates the motor drive output according to the estimated pedaling force (step S 19 ). 
     Next, the control unit  120  performs a motor drive process based on the calculated motor drive output (step S 20 ). The motor drive process involves energizing the electric motor  58  with electric power (voltage or current) corresponding to the calculated motor drive output (drive torque). As a result, the electric motor can assist the pedaling according to the pedaling force. 
     When the change in the motor current value i is less than the predetermined threshold value, the control unit  120  calculates the angular velocity ω 1  of the crankshaft  24  in the first angle range θ 1  and the angular velocity ω 2  of the crankshaft  24  in the second angle range θ 2 , and determines whether or not (ω 1 /ω 2 ) is equal to or greater than one (step S 21 ). When (ω 1 /ω 2 ) is equal to or greater than one, the process returns to the standby state entry process (step S 10 ). When (ω 1 /ω 2 ) is less than one, the control unit  120  then determines whether (ω 1 /ω 2 ) is less than a predetermined threshold value ωS (step S 22 ). 
     When (ω 1 /ω 2 ) is equal to or less than the predetermined threshold value ωS, as the pedaling force is estimated to increase with a decreasing value of (ω 1 /ω 2 ), the control unit  120  calculates the motor drive output according to (ω 1 /ω 2 ) (step S 19 ), and performs the motor drive process based on the calculated motor drive output (step S 20 ). As a result, the electric motor can assist the pedaling according to the pedaling force. 
     When (ω 1 /ω 2 ) is greater than the predetermined threshold value (DS, the control unit  120  sets the motor drive output to a predetermined low output (“weak” motor drive output) (step S 23 ), and performs the motor drive process based on the “weak” motor drive output (step S 20 ). 
     As a result, the electric motor can assist the pedaling according to the pedaling force, and can perform the power assist as needed by the rider. 
     Next, the calibration of the rotational angle sensor  124  will be described with reference to the flowchart shown in  FIG. 9 . 
     First, the control unit  120  determines whether or not the tilt of the bicycle  10  in the left-right direction with respect to the road surface is equal to or less than a predetermined threshold value (step S 30 ). When the tilt in the left-right direction is greater than the predetermined threshold value, the control unit  120  does not perform the calibration. 
     When the tilt in the left-right direction is equal to or less than the predetermined threshold value, the control unit  120  automatically sets a direction of gravity detected based on the output signal from the gyro sensor  128  (step S 31 ). Thereby, the control unit  120  sets the mounting angle γ. 
     Next, a user manually rotates the connecting main member  72  (rotational output member  64 ) so as to align the mark  156  with the mark  154  (step S 32 ). 
     Then, the control unit  120  determines whether or not a user presses the push button  152 A so that the check switch  152  is turned on in order to confirm that the alignment is completed (step S 33 ). 
     When the check switch  152  is in the ON state, the control unit  120  calibrates the rotational angle sensor  124  (step S 34 ). 
     As a result, the rotational angle sensor is calibrated to eliminate errors in the detected crank rotational angle (absolute angle) caused due to variation of the angle at which the electric power assist device is attached to the bicycle  10 . 
     In the above embodiment, the calibrator  148  can perform the calibration when the connecting main member  72  is confirmed to be at the rotational position where the marks  154  and  156  are aligned. However, in other embodiments, the calibrator  148  may perform the calibration when the connecting main member  72  is maintained at the rotational position where the marks  154  and  156  are aligned for a predetermined period of time (e.g., about one second). In this case, the check switch  152  can be omitted. 
     The calibration of the rotational angle sensor  124  according to this embodiment, in which the check switch  152  is not used, will be described with reference to the flowchart shown in  FIG. 10 . 
     First, the control unit  120  determines whether or not the tilt of the bicycle  10  in the left-right direction with respect to the road surface is equal to or less than a predetermined threshold value (step S 40 ). When the tilt in the left-right direction is greater than the predetermined threshold value, the control unit  120  does not perform the calibration. 
     When the tilt in the left-right direction is equal to or less than the predetermined threshold value, the control unit  120  automatically sets a direction of gravity detected based on the output signal from the gyro sensor  128  (step S 41 ). Thereby, the control unit  120  sets the mounting angle γ. 
     Next, a user manually rotates the connecting main member  72  (rotational output member  64 ) so as to align the mark  156  with the mark  154  (step S 42 ). 
     When the state in which the alignment is completed is maintained for a predetermined period of time (step S 43 ), the control unit  120  causes the electric power assist device to produce a confirmation sound or causes a confirmation lamp to emit light, thereby notifying the user of the start of the calibration (step S 44 ). Then, the control unit  120  calibrates the rotational angle sensor  124  (step S 45 ). 
     Next, an electric power assist device  50  according to a second embodiment of the present invention will be described with reference to  FIG. 11 . In  FIG. 11 , the parts corresponding to those in  FIGS. 1 to 3  are denoted with like reference numerals without necessarily repeating the description of such parts. 
     In the second embodiment, the electric power assist device  50  includes a position (rotational position) sensor (pulse sensor)  162 , which is comprised primarily of a magnetic sensor  158  attached to the extension portion  56  of the housing  52  and a magnet piece  160  attached to the connecting main member  72  at a predetermined circumferential position thereof. The position sensor  162  can detect that the connecting main member  72  is positioned at a predetermined rotational position as the magnetic sensor  158  senses the magnet piece  160  when the connecting main member  72  is at that position. In other words, the position sensor  162  in the second embodiment replaces the marks  154  and  156  in the first embodiment with electrical signals. The position sensor  162  outputs a pulse signal when the connecting main member  72  is positioned at the predetermined rotational position, and may be the part of the pulse sensor  126  in the first embodiment. 
     When the position sensor  162  detects that the connecting main member  72  is located at the predetermined rotational position, the calibrator  148  automatically starts the calibration in order to set the reference absolute angle of the rotational angle sensor  124 . 
     In the second embodiment, it is ensued that the electric power assist device  50  can calibrate the rotational angle sensor  124  when the connecting main member  72  at the predetermined rotational position. 
     The calibration of the rotational angle sensor  124  will be described with reference to the flowchart shown in  FIG. 12 . 
     First, the control unit  120  determines whether or not the tilt of the bicycle  10  in the left-right direction with respect to the road surface is equal to or less than a predetermined threshold value (step S 50 ). When the tilt in the left-right direction is greater than the predetermined threshold value, the control unit  120  does not perform the calibration. 
     When the tilt in the left-right direction is equal to or less than the predetermined threshold value, the control unit  120  automatically sets a direction of gravity detected based on the output signal from the gyro sensor  128  (step S 51 ). Thereby, the control unit  120  sets the mounting angle γ. 
     Next, while a user manually rotates the connecting main member  72  (rotational output member  64 ), the control unit  120  monitors for a pulse signal from the position sensor  162  (step S 52 ). When detecting the pulse signal from the position sensor, the control unit  120  calibrates the rotational angle sensor  124  (step S 53 ). 
     Next, an electric power assist device  50  according to a third embodiment of the present invention will be described with reference to  FIG. 13 . In  FIG. 13 , the parts corresponding to those in  FIGS. 1 to 3  are denoted with like reference numerals without necessarily repeating the description of such parts. 
     In the third embodiment, the electric power assist device  50  is provided with a mark (quick)  156 A, a mark (slow)  156 B, and marks  156  between the mark (quick)  156 A and the mark (slow)  156 B such that adjoining marks  156  are separated from each other at predetermined intervals in the rotational direction of the connecting main member  72 , thereby forming a scale-like pattern. The marks  156  are provided for adjusting the rotational position of the connecting main member  72 . 
     In the third embodiment, a user can rotate the connecting main member  72  so as to change a selected one of the scale-like marks  156  (between the mark (quick)  156 A and the mark (slow)  156 B) to be aligned with a mark  145  on the housing  52 , thereby changing the crank rotational angle at which the calibration of the rotational angle sensor  124  is performed. 
     In this way, the absolute angle determined with respect to the crank rotational angle detected by the rotational angle sensor  124  can be changed, allowing a user to select the absolute angles of the first and second crank rotational angles as desired. As a result, the user can appropriately decide the response time of power assist control (the crank rotational angle at which power assist control starts for each rotation of the crankshaft) between a quick response time and a slow response time. 
     Next, an electric power assist device  50  according to a fourth embodiment of the present invention will be described with reference to  FIG. 14 . In  FIG. 14 , the parts corresponding to those in  FIGS. 1 to 3  are denoted with like reference numerals without necessarily repeating the description of such parts. 
     In the fourth embodiment, the electric power assist device  50  is provided with a plurality of marks  156  on the connecting main member  72  arranged along its rotational direction for adjusting the rotational position thereof. In the present embodiment, three marks  156  numbered 1, 2, and 3 are provided on the connecting main member  72 . 
     The calibrator  148  performs the calibration of the rotational angle sensor  124  only when the calibrator recognizes, based on the output signal from the rotational angle sensor  124 , that the connecting main member  72  is rotated and the respective marks  156  are sequentially aligned with the mark  154  on the housing  52  such that the numbers of the aligned marks are in a sequence of 1-3-1-2, for example. 
     When this sequence of numbers is kept secret by the user, the electric power assist device provided with these marks  156  serves as a dial-lock-type lock mechanism, providing an anti-theft feature. 
     The calibration of the rotational angle sensor  124  in the fourth embodiment will be described with reference to the flowchart shown in  FIG. 15 . 
     First, the control unit  120  determines whether or not the tilt of the bicycle  10  in the left-right direction with respect to the road surface is equal to or less than a predetermined threshold value (step S 60 ). When the tilt in the left-right direction is greater than the predetermined threshold value, the control unit  120  does not perform the calibration. 
     When the tilt in the left-right direction is equal to or less than the predetermined threshold value, the control unit  120  automatically sets a direction of gravity detected based on the output signal from the gyro sensor  128  (step S 61 ). Thereby, the control unit  120  sets the mounting angle γ. 
     Next, a user manually rotates the connecting main member  72  (rotational output member  64 ) so as to align the mark  156  numbered “1”, with the mark  154  (step S 62 ). 
     When the state in which the alignment is completed is maintained for a predetermined period of time (step S 63 ), the control unit  120  causes the electric power assist device to produce a confirmation sound or causes a confirmation lamp to emit light, thereby notifying the user that the alignment state is maintained for the predetermined period of time (step S 64 ). 
     Thereafter, when the user manually rotates the connecting main member  72  (rotational output member  64 ) to sequentially align the respective marks  156  with the mark  154  such that the numbers of the aligned marks are in a sequence of 3-1-2 (step S 65 ), the control unit  120  performs the calibration of the rotational angle sensor  124  (step S 66 ). 
     The present invention has been described in terms of specific embodiments, but is not limited by such embodiments, and can be modified in various ways without departing from the scope of the present invention. 
     For example, although, in the above-described embodiments, the rotational angular velocity of the crankshaft  24  is represented and detected as the motor current of the electric motor  58 , the rotational angular velocity of the crankshaft  24  may be directly detected as the rotational angular velocity of the crankshaft  24 . A sensor for implementing the tilt angle detector is not limited to a gyro sensor  128 , and may be an electronic level or any other type of tilt sensor. 
     A basis for the estimation of pedaling force is not limited to the difference or the ratio between motor currents at different crank rotational angles, and may be the difference or the ratio between angular velocities or angular acceleration values at different crank rotational angles. 
     The housing  52  may be arranged between the seat tube  12  and the down tube  14 , and indirectly supported by the frame structure  18  via the seat tube  12  or the down tube  14 . 
     In addition, all of the components shown in the above-described embodiments are not necessarily essential for the present invention, but can be appropriately omitted and substituted as long as such omission and substitution do not deviate from the gist of the present invention. 
     Glossary 
     
         
         
           
               10  bicycle 
               12  Seat tube 
               14  down tube 
               16  chain stay 
               18  frame structure 
               20  bearing tube 
               24  crankshaft 
               26  crankarm 
               26 A spline hole 
               27  crankarm mounting screw 
               28  crankarm 
               30  pedal 
               32  drive sprocket 
               50  electric power assist device 
               52  housing 
               54  ring portion 
               56  extension portion 
               58  electric motor 
               60  central opening 
               62  cylindrical portion 
               64  rotational output member 
               66  boss part 
               70  connecting mechanism 
               72  connecting main member 
               73  angled edge 
               74  clamp piece member 
               75  bolt 
               76  bolt 
               78  screw member 
               80  bolts 
               81  through-hole 
               90  support mechanism 
               92  mount member 
               94  fastening band 
               96  rectangular frame structure part 
               98  support base member 
               100  rectangular plate-shaped part 
               102  depending piece 
               103  through-hole 
               104  support member 
               106  fixed bush 
               106 B large diameter portion 
               108  female screw 
               109  male screw 
               110  movable bush 
               112  flange part 
               114  fastening bolt 
               120  control unit 
               126  pulse sensor 
               128  gyro sensor 
               130  current sensor 
               132  voltage sensor 
               140  pedaling force estimator 
               142  crank rotational direction determiner 
               144  pedaling force presence determiner 
               146  motor drive controller 
               148  calibrator 
               150  motor drive circuit 
               152  check switch 
               152  push button 
               154  mark 
               156  mark 
               158  magnetic sensor 
               160  magnet piece 
               162  position sensor