Abstract:
A power transmission and pedal force sensing system for an electric motor includes an electric motor, a gear reduction train, a pedal force sensing system, and a power combination mechanism. These four mechanisms are concentrically, closely mounted in a single casing. The pedal force sensing system includes a pedal force transmitting sleeve having an elastic device mounted therein, and a pedal force sensing sleeve mounted outside the pedal force transmission path for converting the pedal force into an axial displacement. A proximity sensor is used to detect the axial displacement and outputs a voltage signal representing the magnitude of the pedal force. The power transmission path is shortened and only one casing is required to house all of the elements to thereby obtain a structure of a higher transmission efficiency and reduced volume and weight.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric bicycle, and more particularly to a power transmission and pedal force sensing system for an electric bicycle. 
     2. Description of the Related Art 
     A conventional electric bicycle generally comprises a high speed electric motor used as an auxiliary power source, a gear reduction mechanism for reducing speed of the motor and increasing the output torque, and a power combining mechanism for combining the power from the motor after speed reduction and the pedaling power from the cyclist for subsequent transmission to a chain wheel for driving the electric bicycle at a labor-saving mode. A pedal force sensor is provided on a pedal force transmission path to detect the magnitude of the pedal force to thereby control auxiliary output power from the electric motor. 
     A transmission mechanism for the above conventional electric bicycle includes a frame mounted adjacent to a crankshaft of a bicycle and including a main casing and an auxiliary casing arranged in a direction perpendicular to the main casing. The power combining mechanism and the pedal force sensing mechanism are mounted in the main casing, while the electric motor and the gear reduction mechanism are mounted in the auxiliary casing. Bevel gears are used for transmission. Such a transmission mechanism has a low transmission efficiency as there are too many stages for gear reduction and the transmission path is too long. In addition, the electric motor is not mounted inside the main casing such that additional supporting casing and transmission elements are required, and this results in a bulky structure. Further, the sensing system adopts a bolt and nut or plane cam to convert relative angular displacement into axial displacement, which, in turn, is detected by a proximity sensor for outputting a signal corresponding to a magnitude of the pedal force. Yet, the elements of the pedal sensing system are located on the pedal force transmission path and are thus liable to wear. 
     The present invention is intended to provide a power transmission and pedal force sensing system that mitigates and/or obviates the drawbacks of the above conventional electric bicycle. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a power transmission and pedal force sensing system for an electric bicycle, in which the power transmission path is shortened and the transmission efficiency is improved. 
     It is a further object of the present invention to provide a power transmission and pedal force sensing system for an electric bicycle that has a smaller volume and a lower weight. 
     It is another object of the present invention to provide a power transmission and pedal force sensing system for an electric bicycle to reduce friction between elements. 
     In order to effectively solve the drawbacks of the conventional transmission design and to achieve the above-mentioned objects, the present invention provides a power transmission system and a pedal sensing system. In accordance with the present invention, a casing is mounted to the crankshaft for housing an electric motor, a gear reduction train, a pedal force sensing system, and a power combination mechanism. These four mechanisms are concentrically, closely mounted in the single casing. 
     The power transmission system for an electric motor of the present invention comprises a casing, a crankshaft for pedals extended through the casing, a hollow axle mounted around the crankshaft, and a motor hollow shaft mounted around the hollow axle. A left part of the motor hollow axle is connected to an electric motor, and a right part of the motor hollow axle is connected to an input gear of a gear reduction train. The gear reduction train is preferably a Ferguson&#39;s mechanical paradox gear that has a high gear reduction ratio. An output gear of the gear reduction ratio is connected to an outer periphery of an enlarged hollow end of the hollow axle via a first single direction clutch of the power combination mechanism. An inner periphery of the enlarged end of the hollow axle and the crankshaft together define a space therebetween for receiving a pedal force sensing system. The pedal force sensing system includes a pedal force transmitting sleeve that has an inner ring securely mounted around the crankshaft to rotate therewith and an outer ring connected to the inner periphery of the enlarged end of the hollow axle via a second single direction clutch of the power combination mechanism. The first single direction clutch and the second single direction clutch are mounted to the outer periphery and inner periphery of the enlarged end of the hollow axle along a radial direction. The other end of the hollow axle is securely connected to a chain wheel to rotate therewith. Thus, the pedal force is transmitted to the hollow axle via the crankshaft, the pedal force transmitting force of the pedal force sensing system, and the second single direction clutch to thereby drive the chain wheel and the bicycle frame. The power from the electric motor is transmitted to the hollow axle via the motor hollow shaft, the gear reduction train, and the first single direction clutch to thereby drive the chain wheel and the bicycle frame. By such an arrangement, the power transmission path is shortened and thus has a higher transmission efficiency. In addition, the electric motor is housed in the casing such that the overall volume and the overall weight are both reduced. 
     In the pedal force sensing system, an elastic means is provided between the inner ring and the outer ring of the pedal force transmitting sleeve. A pedal force sensing sleeve is mounted adjacent to the pedal force transmitting sleeve and includes a square key groove so as to be securely mounted on the crankshaft. In addition, at leas tone plane cam is provided on one side of the pedal force sensing sleeve that faces the pedal force transmitting sleeve. When pedaling, the crankshaft drives the inner ring of the pedal force transmitting sleeve and thus exerts a force on the outer ring of the pedal force transmitting sleeve such that the elastic means between the inner ring and the outer ring deforms. As a result, a relative angular displacement occurs between the inner ring and the outer ring. Namely, the pedal force sensing sleeve and the outer ring of the pedal force transmitting sleeve have a relative angular displacement therebetween. This relative angular displacement causes axial displacement of the pedal force sensing sleeve, and a proximity sensor is used to detect the axial displacement and outputs a voltage signal representing the magnitude of the pedal force. Friction between the elements is eliminated, as the elements of the pedal force sensing system are not located on the pedal force transmission path. 
    
    
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a power transmission and pedal force sensing system in accordance with the present invention; 
     FIG. 2 is a schematic side view illustrating an electric bicycle equipped with the power transmission and pedal force sensing system of the present invention; 
     FIG. 3 is a sectional view of a pedal force transmitting sleeve of a pedal force transmitting mechanism of the present invention; 
     FIG. 4 is an exploded perspective view of the pedal force transmitting mechanism; 
     FIG. 5 is a schematic view of a bearing type single direction clutch; 
     FIG. 6 is a schematic view of a ratchet/pawl type single direction clutch; 
     FIG. 7 a  is a schematic view of the pedal force sensing sleeve and an analog type Hall element; 
     FIG. 7 b  is a view similar to FIG. 7 a,  wherein the Hall element is closer to the pedal force sensing sleeve; 
     FIG. 8 a  is a voltage/time diagram of an output of the analog type Hall element in FIG. 7 a;    
     FIG. 8 b  is a voltage/time diagram of an output of the analog type Hall element in FIG. 7 b;    
     FIGS. 9 a ,  9   b , and  9   c  are schematic views illustrating operation of the pedal force sensing sleeve and a digital type Hall element; 
     FIGS. 10 a ,  10   b , and  10   c  are voltage/time diagrams corresponding to outputs of the digital type Hall element in FIGS. 9 a  to  9   c,  respectively; and 
     FIG. 11 is a block diagram illustrating operation principle of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a power transmission and pedal force sensing system for an electric bicycle in accordance with the present invention generally includes a casing  15 , an electric motor  20 , a gear reduction train  30 , a power combination mechanism  40 , a pedal force sensing mechanism  50 , and a sensor means  60 . 
     The casing  15  is mounted between a seat tube  101  and a chain stay  102  of an electric bicycle (FIG.  2 ). The casing  15  includes a main casing part  151 , a left casing part  152 , and a right casing part  153 . As shown in FIG. 1, a crankshaft  11  of the bicycle extends through the casing  15  and is rotatably supported by a bearing  16  at the left casing part  152 . A hollow axle  13  of a chain wheel  14  is rotatably mounted around the crankshaft  11  by bearings  18  and  19 . The hollow axle  13  includes an enlarged disc-like hollow end  131  retained in the casing  15 , and the other end of the hollow axle  13  extends beyond the right casing part  153 , connects with the chain wheel  14 , and is supported by a bearing  17  in the right casing part  153 . A motor hollow shaft  21  is mounted around the hollow axle  13  via two bearings  43  and  44 , and the electric motor  20  and the gear reduction train  30  are mounted around the motor hollow shaft  21 . In a space (not labeled) inside the enlarged end  131  of the hollow axle  13 , the pedal force sensing mechanism  50  is mounted to the crankshaft  11 . In addition, the power combination mechanism  40  is mounted to an inner periphery and an outer periphery of the enlarged end  131  of the hollow axle  13 , which will be described in detail later. 
     The electric motor  20  includes the hollow motor shaft  21 , a stator comprising a silicon-steel plate  22  and a coil  23 , a rotor  25 , a permanent magnet  26 , and a sensor  27  for detecting angular position of the rotor  25 . The rotor  25  is rotatably mounted to a right portion of the motor hollow shaft  21 . The silicon-steel plate  22  is secured to an inner periphery of the main casing part  151  via a supporting block  24 . 
     The gear reduction train  30  includes a sun gear  31 , a planetary gear  32 , a planetary gear shaft  33 , a fixed ring gear  35 , and a rotatable ring gear  37 . Preferably, the gear reduction train  30  is a Ferguson&#39;s mechanical paradox gear, yet other kinds of gear reduction trains can be used. 
     The input sun gear  31  is mounted around the motor hollow shaft  21  and acts as an input gear. The planetary gear  32  supported by the planet gear shaft  33  and a supporting arm  31  meshes with and revolves round the sun gear  31 . The fixed ring gear  35  meshes with the planetary gear  32  and is secured to the inner periphery of the main casing part  151  by a supporting block  36 . The rotatable ring gear  37  meshes with the planetary gear  32  and acts as an output gear. The rotatable ring gear  37  is mounted adjacent to the fixed ring gear  35 , and the difference between the numbers of teeth respectively of the two ring gears  35  and  37  is relatively small. For example, if the fixed ring gear  35  has forty (40) teeth and the rotatable ring gear  37  has thirty-eight (38) teeth, when one of the teeth of one of the two ring gears  35  and  37  (e.g., the ring gear  35 ) aligns one of the teeth of the other of the two ring gears  35  and  37  (e.g., the ring gear  37 ), the two teeth respectively next to the above-mentioned two teeth of the ring gears  35  and  37  only have a deviation of one-twentieth of a pitch therebetween. Thus, when the planetary gears  32  meshed with the fixed ring gear  35  revolves round the sun gear  31 , the rotatable ring gear  37  is moved by one-twentieth of a pitch when the planetary gear  32  travels from one tooth to the next tooth of the fixed ring gear  35 . When the planetary gear  32  revolves through 180°, the rotatable ring gear  37  travels through one (1) pitch. Accordingly, the gear reduction ratio of the rotational speed of the planetary gear shaft  33  to the rotational speed of the rotatable ring gear  37  is twenty (20). As a result, a high gear reduction ratio can be obtained when further taking the gear reduction ratio between the sun gear  31  and the planetary gear shaft  33  into consideration. 
     Referring to FIG. 4, the pedal force transmitting mechanism  50  includes a pedal force transmitting sleeve  51  and a pedal force sensing sleeve  52 . As shown in FIG. 1, the pedal force transmitting mechanism  50  is mounted in a space encircled by the enlarged end  131  of the hollow axle  13  and the left casing part  152 , in which the pedal force transmitting sleeve  51  is securely mounted on the crankshaft  11 . As shown in FIG. 3, the pedal force transmitting sleeve  51  includes a rigid inner ring  511 , a rigid outer ring  513 , and an elastic means (e.g., four elastic members  512 ) sandwiched between the inner ring  511  and the outer ring  513 . Each elastic member  512  is preferably a W-shaped spring steel plate, yet elastic members of other material and shapes can be used. The elastic members  512  are deformed when the inner ring  511  and the outer ring  513  are respectively subjected to torque in opposite directions such that relative angular displacement between the inner ring  511  and the outer ring  513  occurs. In addition, restraining grooves  514  are provided in the outer ring  513  to avoid excessive relative angular displacement to thereby prevent from damage to the elastic members  512  due to excessive deformation resulting from a relatively large pedal force. The pedal force sensing sleeve  52  is securely mounted on the crankshaft  11  by a square key groove  55  defined in a center thereof A side of the pedal force sensing sleeve  52  is biased by a return spring  54  (FIG.  1 ), while the other side of the pedal force sensing sleeve  52  contacts with the outer ring  513  of the pedal force transmitting sleeve  51 . In this embodiment, plane cams  53  are provided on the other side of the pedal force sensing sleeve  52  that faces the pedal force transmitting sleeve  51 , as shown in FIG.  4 . The angular position of the pedal force sensing sleeve  52  is the same as that of the inner ring  511  of the pedal force transmitting sleeve  51 . As a result, the relative angular displacement between the inner ring  511  and the outer ring  513  is identical to that between the pedal force sensing sleeve  52  and the outer ring  513  of the pedal force transmitting sleeve  51 . When there is a relative angular displacement between the two sleeves  51  and  52 , the pedal force sensing sleeve  52  is moved axially under the action of the plane cams  53 . The relative angular displacement is detected by the sensor means  60  (preferably of a proximity type), and a voltage signal representing the magnitude of the pedal force is sent out. 
     The power combination mechanism  40  includes a first single direction clutch  41 , a second single direction clutch  42 , and the hollow axle  13  for the chain wheel  14 . As shown in FIG. 5, the first clutch  41  may be of a single direction bearing type that includes an inner disc  411 , an outer disc  412 , and a number of rollers  413 . The inner disc  411  includes spaced grooves each of which cooperates with the outer disc  412  to define a wedge-like chamber  414  for receiving a roller  413  therein. When the outer disc  412  rotates clockwise relative to the inner disc  411 , each roller  413  moves toward the relatively wide area of the associated chamber  414  and thus cannot connect the inner disc  411  with the outer disc  412 . Namely, the first clutch  41  is in a disengaged status. To the contrary, when the outer disc  412  rotates counterclockwise relative to the inner disc  411 , each roller  413  moves toward the relatively narrow area of the associated chamber  414  and thus connects the inner disc  411  with the outer disc  412 . Namely, the first clutch  41  is in an engaged status as the inner disc  411  and the outer disc  412  move together. The first single direction clutch  41  is mounted to the outer periphery of the enlarged end  131  of the hollow axle  13 , wherein the inner disc  411  of the clutch is secured to the enlarged end  131  of the hollow axle  13 . In addition, the rotatable ring gear  37  of the gear reduction train  30  is securely mounted around the outer disc  412  via a lateral connecting block  38  (FIG.  1 ). 
     FIG. 6 illustrates an embodiment of the second single direction clutch  42 . The second single direction clutch  42  includes an inner disc  421  and an outer disc  422 . A ratchet wheel  424  is provided on an inner periphery of the outer disc  422 . A number of grooves (not labeled) are defined in an outer periphery of the inner disc  421  and each include therein a pawl  423  biased by a spring  425  for releasably engaging with the ratchet wheel  424  of the outer disc  422 . When the outer disc  422  rotates counterclockwise relative to the inner disc  421 , each pawl  423  is moved inwardly by the outer disc  422  and thus cannot connect the inner disc  421  with the outer disc  422 . Namely, the second clutch  42  is in a disengaged status. To the contrary, when the outer disc  422  rotates clockwise relative to the inner disc  421 , each pawl  423  is engaged with the ratchet wheel  424  of the outer disc  422  and thus connects the inner disc  421  with the outer disc  422 . Namely, the second clutch  42  is in an engaged status as the inner disc  421  and the outer disc  422  move together. 
     As shown in FIG. 1, the second single direction clutch  42  is engaged with the inner periphery of the enlarged end  131  of the hollow axle  13 , in which the outer disc  422  is connected to the inner periphery of the enlarged end  131  of the hollow axle  13 . The outer ring  513  of the pedal force transmitting sleeve  51  of the pedal force sensing mechanism  50  is connected to the inner ring  421  of the second clutch  42 . Still referring to FIG. 1, again, the first single direction clutch  41  and the second single direction clutch  42  are disposed to the outer periphery and the inner periphery of the enlarged end  131  of the hollow axle  13 , respectively, and are located on the same line in radial direction. 
     When cycling, if the rotational speed of the crankshaft  11  is higher than that of the motor after gear reduction (i.e., the speed of the rotatable ring gear  37 ), the pedal force transmitting sleeve  51  drives the hollow axle  13  of the chain wheel  13  under the action of the second single direction clutch  42 , yet the hollow axle  13  does not drive the rotatable ring gear  37  and the connecting block  38  under the action of the first single direction clutch  41 . At this time, the pedal force solely drives the chain wheel  14  and the bicycle frame. In the mean time, the inertia of the elements of the electric motor  20  shall not become a burden to pedaling. 
     If the rotational speed of the crankshaft  11  is lower than that of the rotatable ring gear  37 , the hollow axle  13  drives the rotatable ring gear  37  under the action of the first single direction clutch  41 , yet the hollow axle  13  of the chain wheel  13  does not drive the pedal force transmitting sleeve  51  and the crankshaft  11  under the action of the second single direction clutch  42 . At this time, the power of the electric motor  20  solely drives the chain wheel  14  and the bicycle frame. In the mean time, the inertia of the crankshaft  11  shall not become a burden to the power of the electric motor  20 , and the pedals of the bicycle shall not be forcibly driven by the electric motor  20 . 
     If the rotational speed of the crankshaft  11  is equal to that of the rotatable ring gear  37 , the pedal force transmitting sleeve  51  and the rotatable ring gear  37  together drive the hollow axle  13  under the action of the first and second single direction clutches  41  and  42 . At this time, the pedal force and the power of the electric motor  20  are combined at the hollow axle  13  and together drive the chain wheel  14  and the bicycle frame. 
     The sensor means  60  may include an analog output type Hall element  61  (FIGS. 7 a  and  7   b ) for sensing pedal force, a digital output type Hall element  62  (FIGS. 9 a ,  9   b , and  9   c ) for sensing rotational speed of the pedals, and a Hall element  63  (FIGS. 9 a ,  9   b , and  9   c ) for sensing rotational speed of the electric motor  20 , each Hall element  61 ,  62 ,  63  having a biased permanent magnet  64 ,  65 ,  66  mounted to a rear side thereof As shown in FIG. 7 a , the Hall element  61  for sensing pedal force faces the pedal force sensing sleeve  52 . When the pedal force is small, the magnetic-flux-density of the magnetic lines of the magnet  64  that pass through the Hall element  61  is small such that the Hall element  61  outputs a voltage signal of a low value (e.g., 1 volt, see FIG. 8 a ). When the pedal force is larger, the pedal force sensing sleeve  52  is moved to a location closer to the Hall element  61 . As a result, the magnetic-flux-density of the magnetic lines of the magnet  64  that pass through the Hall element  61  is larger such that the Hall element  61  outputs a voltage signal of a high value (e.g., 5 volt, see FIG. 8 b ). 
     Referring to FIG. 9 a , the Hall element  62  for sensing rotational speed of the pedals faces outer teeth  521  (for sensing rotational speed of pedals) formed on an outer periphery of the pedal force sensing sleeve  52 . When the tooth root passes through the Hall element  62  (FIG. 9 a ), the magnetic-flux-density of the magnetic lines of the magnet  65  that pass through the Hall element  62  is small such that the output voltage signal of the Hall element  62  is low (the logical output is ‘0’, see FIG. 10 a ). When the tooth crest passes through the Hall element  62  (FIG. 9 b ), the magnetic-flux-density of the magnetic lines of the magnet  65  that pass through the Hall element  62  is greater such that the output voltage signal of the Hall element  62  is high (the logical output is ‘1’, see FIG. 10 b ). The resultant output voltage signal of the Hall element  62  corresponding to rotational movement of the pedal force sensing sleeve  52  (FIG. 9 c ) is shown in FIG. 10 c . The higher the rotational speed of the pedals, the higher the frequency of the impulse signals in FIG. 10 c.    
     Still referring to FIG. 9 a , the Hall element  63  for sensing rotational speed of the electric motor  20  faces peripheral teeth  381  (for sensing rotational speed of the electric motor  20 ) formed on a side of the connecting block  38  for the rotational ring gear  37 . When the tooth root passes through the Hall element  63  (FIG. 9 a ), the magnetic-flux-density of the magnetic lines of the magnet  66  that pass through the Hall element  63  is small such that the output voltage signal of the Hall element  63  is low (the logical output is ‘0’, see FIG. 10 a ). When the tooth crest passes through the Hall element  63  (FIG. 9 b ), the magnetic-flux-density of the magnetic lines of the magnet  66  that pass through the Hall element  66  is greater such that the output voltage signal of the Hall element  63  is high (the logical output is ‘1’, see FIG. 10 b ). The resultant output voltage signal of the Hall element  63  corresponding to rotational movement of the peripheral teeth  381  of the connecting block  38  (FIG. 9 c ) is shown in FIG. 10 c.  The higher the rotational speed of the electric motor  20 , the higher the frequency of the impulse signals in FIG. 10 c.    
     Operational principle of the present invention will be described in detail with reference to FIGS. 1 and 11. When cycling, the pedal force is transmitted to the hollow axle  13  via the crankshaft  11 , the pedal force transmitting sleeve  51 , and the second single direction clutch  42 , thereby driving the chain wheel  14  and the bicycle frame. In the mean time, the pedal force also causes axial displacement of the pedal force sensing sleeve  52  such that the sensor means  60  outputs an analog voltage signal representing the magnitude of the pedal force, a first digital logic signal representing rotational speed of the pedals, and a second digital logic signal representing rotational speed of the electric motor  20  to a controller  103  (FIG.  1 ). The controller  103  calculates proportion of the auxiliary power corresponding to the rotational speed of the pedals represented by the first digital logic signal. Then, the detected pedal force value is multiplied by the proportion value of the auxiliary power and thus obtains a command value for the auxiliary power. Thereafter, the voltage command for the electric motor  20  and relative pulse width modulating factor are calculated when taking the rotational speed of the electric motor  20  into consideration. A time ratio for controlling rapid opening/closing of power transistors can thus be controlled. The pulse width modulating signal decides electricity from the battery unit  104  (FIG. 1) to the electric motor  20 . Thus, the electric motor  20  may output a proper torque as an auxiliary power that is transmitted to the hollow axle  13  via the motor hollow shaft  21 , the gear reduction train  30 , and the first single direction clutch  41 . 
     Again, when the rotational speed of the pedals is higher than the rotational speed of the electric motor  20  after gear reduction, the first single direction clutch  41  is in a disengaged status while the second single direction clutch  42  is in an engaged status such that the pedal force solely drives the chain wheel  14  and the bicycle frame. When the rotational speed of the pedals is lower than the rotational speed of the electric motor  20  after gear reduction, the first single direction clutch  41  is in an engaged status while the second single direction clutch  42  is in a disengaged status such that the power of the electric motor  20  solely drives the chain wheel  14  and the bicycle frame. When the rotational speed of the pedals is equal to the rotational speed of the electric motor  20  after gear reduction, the first and second single direction clutches  41  and  42  are both in an engaged status such that the pedal force and the power of the electric motor  20  together drive the chain wheel  14  and the bicycle frame. 
     According to the above description, the power transmission and pedal force sensing device of the present invention includes the following advantages: 
     1. The power transmission path is shortened, and the transmission efficiency is improved. 
     2. Frictional wear to the pedal force sensing elements is eliminated, as the pedal force sensing elements are not located on the pedal force transmission path. 
     3. The overall volume is small and the overall weight is low as the electric motor is mounted in the casing. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.