Patent Publication Number: US-2005122681-A1

Title: Heat dissipating apparatus for a bicycle electronic component

Description:
BACKGROUND OF THE INVENTION  
      The present invention is directed to bicycles and, more particularly, to a heat dissipating apparatus for a bicycle electronic component.  
      In recent years, bicycles have been equipped with many electronic components in order to provide various desirable functions. Such components are disclosed in Japanese Kokai Publication Nos. 9-213852 and 2002-83912. For example, bicycles may be equipped with motor drive circuits structured to operate a gearshift motor for a bicycle transmission and/or structured to operate a suspension control motor for a bicycle suspension. Bicycles also frequently are equipped with control circuits used to control the operation of headlights mounted to the bicycle. Circuits used to control such devices may include one or more high speed CPU&#39;s mounted to a control substrate. Some control circuits may include overvoltage protection circuits that stabilize voltage applied to the various circuits and devices from a power supply such as a battery or an alternating current generator that converts the rotation of a wheel to electrical energy. Overvoltage protection circuits are particularly useful to protect against excessive voltage that may be generated by an alternating current generator during high speed riding.  
      Many electronic components provided for bicycles comprise elements such as diodes, transistors, etc. that generate significant amounts of heat during operation. For example, voltage prevention circuits use Zener diodes and transistors to absorb a portion of the load placed on a headlight, and such electronic components generate large amounts of heat. In conventional bicycles, no measures are taken for dissipating the heat generated by such heat-generating elements. Thus, there is the danger that excessive heat generated by the heat-generating elements will alter the operating characteristics of the electronic components or destroy the electronic components altogether, thereby creating electronic component malfunctions and the like.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to various features of a bicycle electronic component. In one embodiment, a heat dissipating apparatus for a bicycle electronic component comprises an electronic component that generates heat; a case having a thermally conductive portion, wherein the electronic component is supported by the case and the case includes a structure for mounting the case to a bicycle; and a thermally conductive member disposed between the electronic component and the case. Additional inventive features will become apparent from the description below, and such features alone or in combination with the above features may form the basis of further inventions as recited in the claims and their equivalents. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of a particular embodiment of a bicycle;  
       FIG. 2  is a schematic block diagram of a portion of an overall bicycle control device;  
       FIG. 3 (A) is a side view of a particular embodiment of a control box;  
       FIG. 3 (B) is a plan view of the control box;  
       FIG. 4  is a detailed view of a particular embodiment of a heat dissipating structure;  
       FIG. 5 (A) is a schematic block diagram of a particular embodiment of an overvoltage prevention circuit;  
       FIG. 5 (B) is a schematic block diagram of a particular embodiment of a motor driver circuit; and  
       FIG. 5 (C) is a schematic block diagram of a particular embodiment of a CPU mounted to a control substrate. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       FIG. 1  is a side view of a particular embodiment of a bicycle  1 . In this embodiment, bicycle  1  is a trekking bicycle that comprises a frame body  2  constructed by welding together tubing having different shapes. A front fork  3  is mounted to the front of frame body  2  for rotation around an inclined axis, and a handlebar assembly  4  is mounted to the top of front fork  3 . Handlebar assembly  4  comprises a handlebar stem  14  and a handlebar  15 , wherein handlebar stem  14  is mounted to the upper portion of fork  3 , and handlebar  15  is mounted to the upper portion of handlebar stem  14 . Brake lever assemblies and grips are mounted on opposite sides of handlebar  15 , wherein a shift control device (not shown) is integrated with the right side brake lever assembly. A headlight  18  is mounted to a central portion of handlebar  15 .  
      A saddle  16  is mounted to the upper middle part of frame body  2 , a drive mechanism  5  is mounted to the lower part of frame body  2 , a front wheel  6  having a hub dynamo  10  and possibly a roller brake is rotatably mounted to the bottom of front fork  3 , and a rear wheel  7  is rotatably mounted to the rear of frame body  2 . Hub dynamo  10  houses an alternating current generating dynamo  19  ( FIG. 2 ) for generating electricity through rotation of front wheel  6 . A front transmission  8  including a front derailleur  26   f  is mounted to the lower middle part of frame body  2 , and a rear transmission  9  including a rear derailleur  26   r  is mounted to the rear of frame body  2 . A front suspension  13   f  is mounted to front fork  3 , and a rear suspension  13   r  is mounted between stationary and articulated portions of frame body  2 .  
      Drive mechanism  5  comprises a crank  27  rotatably mounted at the bottom bracket of frame body  2 , front and rear transmissions  8  and  9 , and a chain  29 . Front transmission  8  comprises, for example, three front sprockets F 1 -F 3  and front derailleur  26   f . Front sprockets F 1 -F 3  are mounted to crank  27 , and front derailleur  26   f  is mounted on frame body  2 . Rear transmission  9  comprises, for example, a multiple sprocket assembly  25  having eight rear sprockets R 1 -R 8  and rear derailleur  26   r . Multiple sprocket assembly  25  is mounted to rear wheel  7 , and rear derailleur  26   r  is mounted at the back of frame body  2 . Crank  27  comprises a right crank arm  27   a  and a left crank arm  27   b , wherein front sprockets F 1 -F 3  are mounted to right crank arm  27   a . Chain  29  engages one of the front sprockets F 1 -F 3  and one of the rear sprockets R 1 -R 8 .  
      Front sprockets F 1 -F 3  are arranged in the order of an increasing number of teeth, wherein front sprocket F 1  is the laterally innermost front sprocket having the least number of teeth, and front sprocket F 3  is the laterally outermost front sprocket having the most number of teeth. Rear sprockets R 1 -R 8  are arranged in the order of a decreasing number of teeth, wherein rear sprocket R 1  is the laterally innermost rear sprocket having the most number of teeth, and rear sprocket R 8  is the laterally outermost rear sprocket having the least number of teeth.  
      A rotation sensor (not shown) is provided for sensing the rotation of crank  27 . The presence or absence of rotation of crank  27  ordinarily is used in part to control the operation of front and rear transmissions  8  and  9 . For example, derailleurs cannot shift properly when crank  27  is stationary, so any requested operation of a derailleur may be delayed until crank  27  is rotating. A rotation sensor typically comprises a reed switch (not shown) mounted to frame body  2  and a plurality of (e.g., four) magnets (not shown) concentrically mounted to one of the crank arms  27   a  and  27   b  so that reed switch  23  provides four pulses for each revolution of crank  27 .  
      A control box  11  containing various electronic components for controlling various components including front and rear transmissions  8  and  9 , front and rear suspensions  13   f  and  13   r  and headlight  18  is mounted to frame body  2  between fork  3  and drive mechanism  5 . More specifically, the components within control box  11  control front and rear transmissions  8  and  9  and front and rear suspensions  13   f  and  13   r  in response to the operation of gear switches and control switches (not shown) mounted to handlebar  15 . The components within control box  11  also automatically control the operation of front and rear transmissions  8  and  9  in response to bicycle velocity. Headlight  18  is turned off and on in response to ambient light.  
       FIG. 2  is a schematic block diagram of the components used to control the operation of headlight  18  and one of the front and rear transmissions  8  and  9 , for example. Heavy lines indicate lines carrying about 1 A of current, thin solid lines indicate lines carrying about 1 mA of current, and broken lines indicate signal lines. The main relevant components comprise dynamo  19 , a gearshift controller  23 , a motor unit  30  for controlling the one of the front and rear transmissions  8  and  9 , an overvoltage prevention circuit  52   a  connected between headlight  18  and dynamo  19 , and a motor driver  52   b.    
      An operating switch  28 , a liquid crystal display (LCD)  24  and an optical sensor  36  are connected to gearshift controller  23 . Operating switch  28  is used for requesting various operations of gearshift controller  23 , LCD  24  is used for displaying various operating information, and optical sensor  36  serves as an ambient light sensor for controlling the operation of headlight  18 .  
      A dynamo waveform shaping circuit  34  receives the alternating current signal from dynamo  19  and provides speed indicating signals to gearshift controller  23 . More specifically, dynamo waveform shaping circuit  34  may perform half-period sampling of the alternating current sine wave signals, pass the sampled signals through an appropriate waveform shaping circuit such as a Schmitt circuit, and generate a pulsed signal corresponding to the speed of the bicycle.  
      A charging and rectifying circuit  33  also receives the alternating current signal from dynamo  19 , coverts the alternating current signal to a direct current signal, and provides the direct current signal to an electricity storing device  32 . Charging and rectifying circuit  33  may comprise a half-wave rectifying circuit that rectifies the alternating current from dynamo  19  into direct current and supplies the direct current to the electricity-storing device  32 .  
      Electricity storing device  32  provides operating power to gearshift controller  23 , charging and rectifying circuit  33 , overvoltage prevention circuit  52   a  and motor driver  52   b . Approximately 1 mA of electric current is supplied to gearshift controller  23 , motor driver  52   b  and charging and rectifying circuit  33 . Approximately 1 A of electric current is supplied directly to motor driver  52   b . Electricity storing device  32  may comprise, for example, a high capacity capacitor. Electricity-storing device  32  also may comprise a secondary battery, such as a nickel-cadmium battery, lithium-ion battery, nickel-hydride battery, etc., instead of a capacitor.  
      Overvoltage prevention circuit  52   a  is used to prevent excessive voltage generated by dynamo  19  from being applied to headlight  18 . Overvoltage prevention circuit  52   a  accomplishes this by converting a portion of a high voltage generated by dynamo  19  to thermal energy while bicycle  1  is traveling at high speed. Overvoltage prevention circuit  52   a  comprises a Zener diode and various transistors. As shown in  FIG. 5 ( a ), overvoltage prevention circuit  52   a  is connected in parallel with dynamo  19  and headlight  18 . Headlight  18  is turned on by electrical energy that dynamo  19  generates when front wheel  6  rotates. When bicycle  1  travels at high speed, the electrical energy generated by dynamo  19  increases, thus increasing the load placed on headlight  18  and significantly shortening the life of headlight  18 . The Zener diode in overvoltage protection circuit  52   a  stabilizes the voltage to a proper lever, thus preventing damage to headlight  18 . However, undesirably large amounts of heat are generated by the Zener diode and other heat-generating elements in overvoltage prevention circuit  52   a  to accomplish such protection. A solution to this problem is discussed below.  
      Motor unit  30  comprises a gear shifting motor  45  and an operating position sensor  47 . Motor  45  moves one of the front derailleur  26   f  or rear derailleur  26   r . Operating position sensor  47  senses the operating position of the relevant front derailleur  26   f  or rear derailleur  26   r , and this operating position information is provided to gearshift controller  23 . Of course, motor unit  30  could be used to operate one of front suspension  13   f  or  13   r , in which case motor  45  would be a suspension control motor.  
      Motor driver  52   b  performs positioning control for gear-shifting motor  45 . Motor driver  52   b  comprises various transistors, such as an FET and the like. As shown in  FIG. 5 ( b ), motor driver  52   b  is connected to electricity storing device  32  and gear-shifting motor  45 . Motor driver  52   b  operates on the approximately 1 mA of electric current supplied from electricity storing device  32  and directs the approximately 1 A of electric current supplied from electricity-storing device  32  to gear-shifting motor  45 . Since a relatively large current flows through motor driver  52   b , the voltage drops of the transistors and other heat-generating elements generate a substantial amount of heat. A solution to this problem also is discussed below.  
       FIG. 3 (A) is a side view of a particular embodiment of control box  11 ,  FIG. 3 (B) is a plan view of control box  11 , and  FIG. 4  is a detailed view of a particular embodiment of a heat dissipating structure  50 . Control box  11  (an example of a case) comprises a lid  11   a  and a main body  11   b , both of which are made of a lightweight material having a relatively high coefficient of thermal conductivity such as an aluminum alloy. Mounting bolts  17  mount control box  11  to bolt holes (not shown) formed in frame body  2  of bicycle  1 . Supported and housed within control box  11  are various electronic components  52 , such as a control substrate  51 , overvoltage prevention circuit  52   a , motor driver  52   b , and a high speed CPU  52   c  ( FIG. 5 (C)) that forms a part of gearshift controller  23 . CPU  52   c  also generates heat as it functions. Overvoltage prevention circuit  52   a , motor driver  52   b  and CPU  52   c  may be mounted on control substrate  51 . The heat generating elements within these circuits are designated generally as  53 , and they contact lid  11   a  of control box  11  through a thermally conductive member such as a thermally conductive sheet  60 . Lid  11   a  of case  11 , heat generating elements  53  and thermally conductive sheet  60  form a heat dissipating structure  50 .  
      In this embodiment, thermally conductive sheet  60  is a relatively soft, thin and flexible member formed using copper or aluminum to facilitate contact with heat generating elements  53  and lid  11   a  of control box  11  over a relatively large area. Since thermally conductive sheet  60  makes contact with both the heat-generating elements  53  comprising the electronic components  52  (i.e., the Zener diode of overvoltage prevention circuit  52   a , the transistors in motor driver  52   b  and CPU  52   c  , etc.) and lid  11   a  of control box  11  through a large area, the heat generated inside the electronic components  52  can be efficiently dissipated. As a result, fluctuations in operating characteristics of the electronic components or heat destruction of the electronic components can be avoided. Heat dissipation is further enhanced by the fact that control box  11  is mounted in a location on bicycle  1  as shown in  FIG. 1  where it will be subjected to wind during riding.  
      While the above is a description of various embodiments of inventive features, further modifications may be employed without departing from the spirit and scope of the present invention. For example, while electronic components  52  such as overvoltage prevention circuit  52   a , motor driver  52   b  and high speed CPU  52   c  shown in FIGS.  5 (A)- 5 (C) were provided as examples of electronic components that generate heat, the teachings herein could be applied to any heat generating components.  
      While control box  11  was mounted to frame body  2  of bicycle  1 , control box  11  could be mounted most anywhere on bicycle  1 . For example, control box  11  also could be mounted to handlebar  15  or to a basket mounted somewhere on bicycle  1 . While control box  11  was made of an aluminum alloy in the described embodiment, copper or some other metal with a high coefficient of thermal conductivity also could be used to form at least the heat dissipating part of control box  11 .  
      While bicycle  1  was described as a trekking bike, clearly the teachings herein could be applied to any type of bicycle, such as a mountain bike, sport bike or some other bicycle.  
      The size, shape, location or orientation of the various components may be changed as desired. Components that are shown directly connected or contacting each other may have intermediate structures disposed between them. The functions of one element may be performed by two, and vice versa. The structures and functions of one embodiment may be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the scope of the invention should not be limited by the specific structures disclosed or the apparent initial focus or emphasis on a particular structure or feature.