Abstract:
A tandem adapter frame that attaches to the back of a single-rider bicycle, transforming the bicycle into a tandem bicycle. The rear wheel of the single-rider bicycle is removed from the bicycle and installed on the back end of the adapter frame. The adapter frame is attached to the single-rider bicycle at the seat post and the rear dropouts, resulting in a rigid 3-point connection. This transforms the single-rider bicycle into a rigid frame, two wheel, tandem bicycle with a rider in front and a rider in back. Both riders have pedals. An adapter axle assembly with sprockets on the lower front of the adapter frame serves two functions. It easily attaches between the rear dropouts of the single-rider bicycle using a standard axle and quick-release, and it transmits drive power to the rear crank without modifying the drive chain of the single-rider bicycle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of provisional patent application No. 60/324,326, filed Sep. 24, 2002.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to devices for converting a standard bicycle into a tandem bicycle.  
           [0004]    2. Description of Prior Art  
           [0005]    Tandem bicycles provide bonding between the captain (front rider) and the stoker (back rider), and are an enjoyable alternative to riding separate bicycles or children riding in bicycle seats. Also, a tandem bicycle safely teaches children how to ride a bicycle while an older rider maintains control. However, tandem bicycles are hard to store and transport and expensive, so attempts have been made to provide conversion kits for standard bicycles, or specialized frames that convert between single and dual rider bicycles.  
           [0006]    However, existing products that adapt single-rider bicycles into tandem bicycle have one or more of the following problems:  
           [0007]    a. The conversion frame pivots on the bicycle. This makes the combined frames unstable and difficult to steer. It is usually not strong enough to support an adult in the rear position.  
           [0008]    b. Two bicycles are attached yielding a three or four-wheel tandem bicycle that is cumbersome, inefficient, and hard to maneuver.  
           [0009]    c. The attached device acts more as a trailer.  
           [0010]    d. The stoker is not required to pedal which means less participation/interaction between captain and stoker.  
           [0011]    e. The stoker device only attaches at a single point, such as the seat post, yielding an unstable tandem bicycle that will yaw.  
           [0012]    f. The whole frame is fully specialized for conversion to and from a single rider configuration, rather than using a standard bicycle. This is expensive.  
         SUMMARY OF THE INVENTION  
         [0013]    The objectives of the present invention are to solve the above problems as follows:  
           [0014]    1. Versatility. Provide a tandem adapter that attaches to a standard bicycle for a tandem ride, or left off for a solo ride.  
           [0015]    2. Adjustability. Provide a tandem adapter that easily adjusts to fit a variety of bicycle frame sizes.  
           [0016]    3. Ease of attachment and detachment. Provide a tandem adapter that can be setup by a person skilled in the art of bicycles, and then is easy to attach and detach by persons not skilled in the art.  
           [0017]    4. Cost. Provide a tandem adapter that is a comparatively inexpensive alternative to owning both a single-rider bicycle and a tandem bicycle.  
           [0018]    5. Storage. Provide a tandem adapter that requires less space than owning a single bicycle and a tandem bicycle.  
           [0019]    6. Transportation. Provide a tandem adapter that allows single rider bicycles to be transported via standard bicycle racks. Attachment of tandem adapter takes place at destination.  
           [0020]    These objectives are achieved by providing a tandem adapter frame that attaches to the back of a single-rider bicycle, transforming the bicycle into a tandem bicycle. The rear wheel of the single-rider bicycle is removed and the tandem adapter is attached to the single-rider bicycle at the seat post and the rear drop-outs, resulting in a highly rigid 3-point connection. The rear wheel is then mounted on the rear of the tandem adapter, transforming the single-rider bicycle into a rigid frame, two wheel, tandem bicycle with a rider in front (captain) and a rider in back (stoker). Both riders have pedals. An adapter axle assembly with sprockets on the lower front of the adapter frame serves two functions. It easily attaches between the rear dropouts of the single-rider bicycle using a standard axle and quick-release, and it transmits drive power to the rear crank without modifying the drive chain of the single-rider bicycle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a side view of a preferred embodiment of the tandem adapter frame.  
         [0022]    [0022]FIG. 2 is a side sectional view of FIG. 1.  
         [0023]    [0023]FIG. 3 is a side view of a tandem adapter attached to a bicycle to create a rigid tandem bicycle.  
         [0024]    [0024]FIG. 4 is an exploded view of the adapter axle assembly  
         [0025]    [0025]FIG. 5 is a front sectional view of the adapter axle assembly connected between the dropouts of a standard bicycle.  
         [0026]    [0026]FIG. 6 is perspective transparent view of an eccentric bottom bracket holder for the tandem adapter crankset.  
         [0027]    [0027]FIG. 7 is a side view of a second embodiment of the tandem adapter frame. 
     
    
     REFERENCE NUMBERS  
       [0028]    [0028] 1 . Handle bar clamp  
         [0029]    [0029] 2 . Telescoping tube of handle bar stem  
         [0030]    [0030] 3 . Handle bar stem  
         [0031]    [0031] 4 . Top tube telescoping tube  
         [0032]    [0032] 5 . Captain&#39;s seat post clamp  
         [0033]    [0033] 6 . Seat post clamp pivot  
         [0034]    [0034] 7 . Pinch bolts  
         [0035]    [0035] 8 . Handle bar stem pivot  
         [0036]    [0036] 9 . Seat tube pivot  
         [0037]    [0037] 10 . Cable stops  
         [0038]    [0038] 11 . Bent top tube  
         [0039]    [0039] 12 . Seat tube  
         [0040]    [0040] 13 . Axle assembly  
         [0041]    [0041] 14 . Boom tube  
         [0042]    [0042] 15 . Bottom bracket shell  
         [0043]    [0043] 16 . Set screw  
         [0044]    [0044] 17 . Chain stay  
         [0045]    [0045] 18 . Rear drop out of adapter frame  
         [0046]    [0046] 19 . Brake boss  
         [0047]    [0047] 20 . Seat stays  
         [0048]    [0048] 21 . Captain&#39;s rear drop outs  
         [0049]    [0049] 22 . Top tube brace  
         [0050]    [0050] 23 . Braced top tube  
         [0051]    [0051] 25 . Bottom bracket top tube telescoping tube  
         [0052]    [0052] 26 . Top tube pivot  
         [0053]    [0053] 27 . Cable quick-connect coupling  
         [0054]    [0054] 28 . Tandem adapter brake cable  
         [0055]    [0055] 29 . Tandem adapter handle bar  
         [0056]    [0056] 30 . Tandem adapter brake  
         [0057]    [0057] 31 . Rear wheel  
         [0058]    [0058] 32 . Captain&#39;s rear brake cable  
         [0059]    [0059] 33 . Captain&#39;s seat post  
         [0060]    [0060] 34 . Captain&#39;s chain  
         [0061]    [0061] 35 . Captain&#39;s crank set  
         [0062]    [0062] 36 . Captain&#39;s rear derailleur  
         [0063]    [0063] 37 . Tandem adapter derailleur cable  
         [0064]    [0064] 38 . Axle assembly chain  
         [0065]    [0065] 39 . Tandem adapter crank set  
         [0066]    [0066] 40 . Tandem adapter chain  
         [0067]    [0067] 41 . Tandem adapter derailleur  
         [0068]    [0068] 42 . Axle assembly housing  
         [0069]    [0069] 43 . Exterior threaded hollow axle  
         [0070]    [0070] 44 . Sprocket hub  
         [0071]    [0071] 45 . Fixed sprocket  
         [0072]    [0072] 46 . Sprocket spacer  
         [0073]    [0073] 47 . Free wheel sprocket  
         [0074]    [0074] 48 . Threaded axle spacer  
         [0075]    [0075] 49 . Quick release skewer  
         [0076]    [0076] 50 . Eccentric bottom bracket holder  
         [0077]    [0077] 51 . Captain&#39;s rear derailleur cable  
         [0078]    [0078] 52 . Brace pivot  
         [0079]    [0079] 53 . Gear cluster  
         [0080]    [0080] 54 . Sprocket hub tightener  
         [0081]    [0081] 55 . Tandem adapter seat post  
         [0082]    [0082] 56 . Freewheel pawl mechanism  
         [0083]    [0083] 57 . Captain&#39;s top tube  
         [0084]    [0084] 58 . Captain&#39;s down tube  
         [0085]    [0085] 59 . Captain&#39;s chain stay  
         [0086]    [0086] 60 . Captain&#39;s seat stay  
         [0087]    [0087] 61 . Optional disk brake bracket  
       TERMINOLOGY  
       [0088]    Captain: The front rider on a tandem bicycle.  
         [0089]    Stoker: The back rider on a tandem bicycle.  
         [0090]    Drop-out: A wheel axle mounting plate with an open-ended slot to receive an axle.  
       DETAILED DESCRIPTION  
       [0091]    [0091]FIG. 1 is a side view of the drive train side of the tandem adapter frame constructed in accordance with the invention. The rear triangle, like that of a regular bicycle, is constructed of a seat tube  12 , chain stays  17 , rear drop outs  18 , seat stays  20 , brake bosses  19 , a bottom bracket shell  15 , and cable stops  10 . A telescoping top tube assembly extends upward and forward from the bottom bracket shell. The top tube assembly preferably comprises a top tube pivot  26 , a bottom bracket top tube telescoping tube  25 , a braced top tube  23  with pinch bolts  7  on both ends, a top tube telescoping tube  4 , a seat post clamp pivot  6 , and a captain&#39;s seat post clamp  5 , and a top tube brace  22 . The top tube brace spans between the seat tube  12  and the braced top tube  23 , with pivots  9 ,  52  at both ends of the top tube brace. Other tube configurations may be used for the top tube assembly. A boom tube  14  extends forward from the bottom bracket shell. An adapter axle assembly housing  42  is attached to the front end of the boom tube. An eccentric bottom bracket holder  50  is mounted rotatably in the bottom bracket shell, and is locked in place by a set screw  16 . A handle bar stem  3  is attached to the top tube telescoping tube via a handle bar stem pivot  8  that allows the handle bar stem to adjust rotationally. The handle bar stem accepts a telescoping tube section  2  that terminates in a handle bar clamp  1 .  
         [0092]    [0092]FIG. 3 is a view of the drive train side of the tandem adapter attached to a standard bicycle. The points of connection are the seat post of the standard bicycle and the two rear drop-outs of the standard bicycle. This  3 -point connection provides both lateral and vertical rigidity to the resulting tandem bicycle frame. Both degrees of rigidity are needed for stable efficient tandem pedaling and steering. The standard bicycle frame becomes the forward, or captain&#39;s section of a tandem bicycle. A seat post clamp  5  on the front end of the tandem adapter top tube  4  clamps onto the captain&#39;s seat post  33 . An adapter axle assembly  13  on the lower front end of the adapter frame attaches to the captain&#39;s rear drop outs  21  by means of a standard bicycle axle  43  and a standard quick-release axle fastener  49 .  
         [0093]    [0093]FIG. 4 is an exploded view of the axle assembly  13 , and FIG. 5 is a front sectional view of it as installed. An axle assembly housing  42  is attached to the front end of boom tube  14 . The axle assembly housing holds a standard hollow bicycle axle horizontally transversely to the boom tube. The axle is attached between the rear drop-outs of the bicycle using a standard quick-release axle fastener  49 . The axle assembly housing has interior threads to receive a sprocket hub tightener  54 . This tightener attaches a sprocket hub  44  to the axle assembly housing. The sprocket hub rotates about the axle. A fixed sprocket  45  and a sprocket spacer  46  slide onto an external spline on the sprocket hub, and thus rotate with the sprocket hub. A freewheel sprocket  47  threads onto the hub against the sprocket spacer, retaining the fixed sprocket. The freewheel sprocket has a freewheel device  56  as known in the art. This allows the freewheel sprocket to rotate independently of the sprocket hub in one direction of relative rotation between the freewheel sprocket and the hub, and otherwise causes the freewheel sprocket to co-rotate with the hub, driving the hub. This allows the captain to stop pedaling at any time, whether the stoker continues pedaling or not. However, when the captain pedals, the stoker must also pedal.  
         [0094]    A standard hollow axle  43  passes through this entire hub assembly. A threaded axle spacer  48  is threaded onto the axle to fill the space between standard dropouts. A quick-release axle fastener  49  has a control rod passing through the hollow axle with a cam lever on one end and an adjustment nut on the other end, as is well known in the art. This quickly and securely connects and disconnects the axle assembly between the dropouts of the bicycle.  
         [0095]    The two sprockets  45 ,  47  on the axle assembly provide transmission of power to the rear crank set  39  and thence to the rear wheel without modifying the captain&#39;s drive chain. Transmission of power to the rear wheel  31  from the captain&#39;s crank  35  set is achieved via the captain&#39;s chain spanning between a sprocket on the captain&#39;s crank set and the freewheel sprocket  47  of the axle assembly. The freewheel sprocket thence drives the fixed sprocket  45  via the sprocket hub  44 . An axle assembly chain  38  spans between the fixed sprocket of the axle assembly and a first sprocket on the tandem adapter crank set  39 . Finally, a tandem adapter chain spans between a second sprocket on the tandem adapter crank set and a final sprocket on the gear cluster  53  of the rear wheel hub.  
         [0096]    Control of the tandem adapter brake  30  is maintained by the captain via a tandem adapter brake cable  28  which attaches to the captain&#39;s rear brake cable  32  with a cable quick connect  27 . Control of the tandem adapter derailleur  41  is maintained by the captain via a tandem adapter derailleur cable  37  which attaches to the captain&#39;s rear derailleur cable  51  with another cable quick connect  27 .  
         [0097]    Figure six is an eccentric bottom bracket holder  50 . This is a cylinder that fits into the bottom bracket shell  15  of the adapter frame, and is tightened in place by a set screw  16 . The eccentric bottom bracket holder is traversed by an off-center hole with threads at both ends. This threaded hole accepts the tandem adapter crank set  39 . The eccentric mounting of the crank set provides fine tension adjustment of the axle assembly chain  38  between the axle assembly  13  and the tandem adapter crank set  39 . The eccentric bottom bracket holder is turned until a desired chain tension is achieved, then the setscrew is tightened.  
         [0098]    A seat post clamp  5  is attached to the front end of the top tube  4  of the tandem adapter frame by a pivot connection  6 . It preferably has a quick-release cam lever or other quick clamping mechanism as known in the art for fast, secure attachment to the captain&#39;s seat post  33 . However, it can be simply a piece of tubing with a slit cut in one side that allows the tubing to compress onto the captain&#39;s seat post  33  via pinch bolts on tension bands.  
         [0099]    A standard bicycle is initially configured by a bicycle mechanic for use with the tandem adapter. This includes installing quick connectors on the rear brake cable and derailleur cable. Also a dummy derailleur cable is installed on the captain&#39;s bike to hold the captain&#39;s derailleur over the freewheel sprocket of the axle assembly when the captain&#39;s derailleur cable is connected to the tandem adapter derailleur cable. After these modifications are made, subsequent conversions to and from a tandem bicycle are easily done by a user without tools.  
         [0100]    Operation  
         [0101]    1. User removes rear wheel  31  of single-rider bicycle.  
         [0102]    2. User installs rear wheel  31  of the captain&#39;s bicycle in the rear dropouts  18  of the tandem adapter.  
         [0103]    3. The axle assembly  13  of the tandem adapter fits into the captain&#39;s rear dropouts  21  from which the rear wheel  31  was removed. The user secures this connection by compression achieved by an industry standard quick release axle fastener  49 .  
         [0104]    4. User attaches the captain&#39;s seat post clamp  5  to the captain&#39;s seat post  33 .  
         [0105]    5. The top tube assembly telescopes and pivots to fit a variety of frames. It is adjusted so that the captain&#39;s crank set  35 , the captain&#39;s rear drop outs  21 , the axle assembly  13 , and the tandem adapter crank set  39  are all in a straight line parallel to the ground. Then pinch bolts  7  on the top tube assembly are tightened to lock the adjusted frame geometry.  
         [0106]    6. The tension of the chain between the tandem adapter crank set  39  and the axle assembly  13  is adjusted by rotating the eccentric bottom bracket holder  50  in the bottom bracket shell  15 . Once the desired tension is achieved, the eccentric bottom bracket holder  50  is locked in place with a setscrew  16 .  
         [0107]    7. Transmission of power to the rear wheel  31  from the captain&#39;s crank set  35  is achieved by placing the captain&#39;s chain  34  on the free wheel sprocket  47  of the axle assembly  13 . The free wheel sprocket  47  drives the fixed sprocket  45  via the sprocket hub  44 . This drives the axle assembly chain  38 , which drives the tandem adapter crank set  39 , which drives the tandem adapter chain  40 , which drives the gear cluster  53 .  
         [0108]    8. The captain maintains control of the tandem adapter brake  30 . A cable quick-connect coupling  27  is installed on the captain&#39;s rear brake cable  32  in front of the captain&#39;s seat tube  12 . The captain&#39;s rear brake cable  32  is separated at this coupling, and re-coupled to the tandem adapter brake cable  28 . The tandem adapter brake cable is routed along the top tube assembly and the seat stays  20  through cable stops  10  and attaches to the tandem adapter brake  30 .  
         [0109]    9. Control of the rear derailleur on the tandem adapter and the ability to change gears is maintained by the captain. A cable quick-connect coupling  27  is installed in the captain&#39;s derailleur cable  51 . The captain&#39;s rear derailleur cable  51  is separated at this coupling and re-coupled to the tandem adapter derailleur cable  37 . If the captain&#39;s rear derailleur cable  51  is routed along the top tube  57  of the captain&#39;s bike, it continues along the top tube assembly of the tandem adapter and down the seat stays  20  of the adapter frame to the tandem adapter derailleur  41 . If the captain&#39;s rear derailleur cable is routed along the down tube  58  and chain stay  59  of the captain&#39;s bike, it continues along the boom tube  14  and chain stay  17  of the tandem adapter to the tandem adapter derailleur  41  through cable stops  10 .  
         [0110]    10. The Captain&#39;s derailleur  36  is held in place over the free wheel sprocket  47  by connecting the end of the captain&#39;s derailleur cable to the dummy cable that was installed on the bike in the set-up process.  
         [0111]    11. The riding position of the stoker is adjusted by moving the telescoping handle bar stem  2  in or out, pivoting the handlebar stem  3 , and by adjusting the tandem adapter seat post  55  up or down.  
         [0112]    Although the present invention has been described herein with respect to preferred embodiments, it will be understood that the foregoing description is intended to be illustrative, not restrictive. Modifications of the present invention will occur to those skilled in the art. All such modifications that fall within the scope of the appended claims are intended to be within the scope and spirit of the present invention.