Abstract:
A bicycle frame includes front and rear parts, which are pivotally connected to each other by upper and bottom links, and a shock absorber. The bicycle frame is designed so that compression in the shock absorber isolates the bicycle rider from track noise. Additionally, energy loss caused by the shock absorber compression during positive acceleration is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
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     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
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     STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR 
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     BACKGROUND 
     This invention relates to mountain bicycles rear wheel suspension systems. A mountain bicycle may include a rear wheel suspension system to provide a smoother ride for its rider by implementing a shock absorber and a pivoting mechanism. 
     Shock absorbers are used to make riding over a rough terrain smoother, but they can cause loss of energy during positive acceleration. Some prior designs lack necessary features to address this problem and there is a need for a design to solve it. 
     SUMMARY 
     The present invention is directed to a bicycle frame that can be used as a mountain bike rear wheel suspension system. This invention has necessary features to reduce energy loss during positive acceleration. A bicycle frame having features of the present invention comprises a front part having a bottom bracket, a rear part, an upper link, a bottom link, and a shock absorber. 
     The front part and the rear part are attached to each other with the upper link, the bottom link, and the shock absorber. The upper link has a top pivot point and a bottom pivot point. The top pivot point pivotally connects the upper link to the front part and the bottom pivot point pivotally connects the upper link to the rear part. The bottom link has a front pivot point and a rear pivot point. The front pivot point pivotally connects the bottom link to the rear part and the rear pivot point pivotally connects the bottom link to the front part. The shock absorber includes a front connecting point and a rear connecting point. The front connecting point pivotally connects the shock absorber to the front part and the rear connecting point pivotally connects the shock absorber to the rear part. In the present invention the instant center of rotation of the rear part relative to the front part is located in front of the bottom bracket, and during the shock absorber change of length, which can be because of compression or extension of the shock absorber, the instant center of rotation of the rear part relative to the front part stays in front of the bottom bracket. 
     In certain embodiments of the present invention, the upper link and the shock absorber are pivotally connected to the rear part about a common pivot axis. 
     In certain embodiments of the present invention, the rear part includes two rear dropouts and a rear wheel is rotatably connected to the rear part at the rear dropouts. 
     In certain embodiments of the present invention, the front part has a top tube having a left end and a right end, a seat tube having a top end and a bottom end, and a down tube having a top-right end and a bottom-left end. These tubes are fixed to each other, giving a generally triangular configuration to the front part. 
     In certain embodiments of the present invention, during compression of the shock absorber the instant center of rotation of the rear part relative to the front part moves upwards. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  is a three dimensional view of a bicycle frame in accordance with an embodiment of the present invention; 
         FIG. 2  is a side view of the bicycle frame of  FIG. 1 ; 
         FIG. 3  is a side view of a bicycle frame in accordance with another embodiment of the present invention; 
         FIG. 4  is a diagrammatic side view of the bicycle frame of  FIG. 2 , with a shock absorber in a completely uncompressed state; and 
         FIG. 5  is a diagrammatic side view of the bicycle frame of  FIG. 2 , with the shock absorber compressed from approximately 0% to 100%. 
     
    
    
     DETAILED DESCRIPTION 
     In the following disclosure spacial direction terms such as, front, back, rear, lower, upwards, counterclockwise, and the like are used according to the shown bicycle frame, and they should be interpreted based on how the bicycle frame is drawn in the figures. 
       FIGS. 1 and 2  show a bicycle frame  10  according to certain embodiments of the present disclosure. The bicycle frame  10  comprises a front part  12 , a rear part  14 , an upper link  16 , a bottom link  18 , and a shock absorber  20 . 
     In the illustrated embodiment in  FIGS. 1 and 2 , the front part  12  includes a bottom bracket  22 , a top linkage support  24 , a shock absorber connection support  26 , a top tube  28 , a seat tube  30 , and a down tube  32 . The top tube  28  has a left end  34  and a right end  36 , which are located at the rear and front of the top tube  28  respectively. The seat tube  30  includes a top end  38  and a bottom end  40  (not indicated in  FIG. 1 ), wherein the left end  34  of the top tube  28  is fixed to the top end  38  of the seat tube  30 . The down tube  32  comprises a top-right end  42  and a bottom-left end  44 , wherein the top-right end  42  of the down tube  32  is fixed to the right end  36  of the top tube  28 , and the bottom-left end  44  of the down tube  32  is fixed to the bottom end  40  of the seat tube  30 , giving a generally triangular configuration to the front part  12 . The bottom bracket  22  is mounted in the connection location of the seat tube  30  and down tube  32 . The top linkage support  24  is connected to the front part  12  at a corner where the top tube  28  is fixed to the seat tube  30 , and the shock absorber connection support  26  is connected to the down tube  32 . Both top linkage  24  and shock absorber connection  26  supports can be made from a pair of parallel plates, as illustrated in  FIG. 1 . 
     As it is shown in  FIG. 1 , the rear part  14  comprises of two subframes  50 , two rear dropouts  52 , and a connecting link  54 . Each subframe  50  is mounted on either side of a median plane passing through the bicycle. The subframe  50  includes a chain stay  58 , a seat stay  60 , and a bracing profile  62  which are fixed to each other giving a generally triangular configuration to the subframe  50 . Each bracing profile  62  close to its lower end has a protrusion  64 , where the bottom link  18  is pivotally connected to the rear part  14 . Ends of the connecting link  54  are fixed to the seat stays  60 . The rear dropout  52  is fixed to the subframe  50  at a location where the chain stay  58  and the seat stay  60  are attached to each other, and a rear wheel (not shown here) is rotatably connected to the rear part  14  at the rear dropouts  52 . 
     Within the scope of this disclosure, mentioned configurations of the front and rear parts  12 ,  14  are not exclusive. As a nonlimiting example, the front part instead of having a top tube, seat tube, and down tube fixed to each other in a triangular configuration, can be made of a single member which passes through the vertices of a triangle and three tubes that extends from the center of the triangle to its vertices. 
     The front part  12  is moveably attached to the rear part  14  with the upper link  16 , the bottom link  18 , and the shock absorber  20 . 
     As it is shown in  FIG. 2 , the upper link  16  includes a top pivot point  70  and a bottom pivot point  72 . The top pivot point  70  pivotally connects the upper link  16  to the top linkage support  24  of the front part  12 . For its part, the bottom pivot point  72  pivotally connects the upper link  16  to the rear part  14 , at or close to the location where the seat stays  60  join the bracing profiles  62 . As it is illustrated in  FIG. 1 , the upper link  16  can be of a U-shape configuration close to the bottom pivot point  72 . The top  70  and bottom  72  pivot points may or may not employ bearings and/or bushings. 
     As it is shown in  FIG. 2 , the bottom link  18  includes a front pivot point  80  and a rear pivot point  82 . The front pivot point  80  pivotally connects the bottom link  18  to the protrusions  64  of the rear part  14 , and the rear pivot point  82  pivotally connects the bottom link  18  to the front part  12 . The front  80  and rear  82  pivot points may or may not employ bearings and/or bushings. 
       FIG. 3  shows another embodiment of the present invention, as it is shown the shock absorber  20  includes a front connecting point  90  and a rear connecting point  92 . The front connecting point  90  pivotally links the shock absorber  20  to the shock absorber connection support  26  of the front part  12 , and the rear connecting point  92  pivotally links the shock absorber to the rear part  14 . In the preferred embodiment illustrated in  FIGS. 1 and 2 , the rear connecting point and the bottom pivot point have a common pivot axis, which means the same pivot shaft connects both the upper link  16  and the shock absorber  20  to the rear part  14 . The front  90  and rear  92  connecting points may or may not employ bearings and/or bushings. Further description of the shock absorber  20  is not necessary because it is a well known component in the bicycle design art. 
       FIG. 4  shows the bicycle frame  10  of  FIG. 2  via a diagrammatical side view. A rear wheel  100  is rotatably attached to the rear part  14  at the rear dropouts  52 . Bicycle cranks (not shown here) and one or more chainrings  108  are rotatably connected to the bottom bracket  22 , and one or more cogs  110  are fixed to the rear wheel  100  at the rear dropouts  52 . A bicycle chain  112  extends from the chainrings  108  to the cogs  110 , transmitting energy of pedaling to the rear wheel  100 . As it is well known to the people skilled in the art of bicycle design, the instant center of rotation (ICR) of the rear part  14  relative to the front part  12  is located at the intersection of two straight lines (L 1 ) and (L 2 ). The line (L 1 ) passes through the top  70  and bottom  72  pivot points, and the line (L 2 ) passes through the front  80  and rear  82  pivot points. In the art of bicycle design there is a reasonably well known graphical method that uses the instant center of rotation (ICR) to calculate anti-squat percentage of a bicycle. The anti-squat will be described hereinafter without going into details of using the graphical method. 
     During positive acceleration of the bicycle, the center of gravity of the bicycle and its rider shifts towards the back of the bicycle, causing the rear wheel  100  to carry more force (F 1 ) compared to the time when the speed is constant. This extra force (F 1 ) tends to compress the shock absorber  20 , which means extra loss of energy during positive acceleration. If the bicycle has the necessary features, it is possible to use tension force (F 2 ) in the bicycle chain  112  to balance the extra force (F 1 ) and reduce the loss of energy. This property of balancing is called anti-squat in the bicycle design art. 
     As it is shown in  FIG. 4  the extra force (F 1 ) and the chain tension (F 2 ) create opposite momentums around the top  70  and bottom  72  pivot points, and in this way they balance each other and give anti-squat property to the bicycle frame of the present invention. 
       FIG. 5  shows how different elements of the bicycle frame move when the rear wheel hits a bump and shock is transferred to the rear wheel. Because of the bump, the rear dropouts move upwards, the upper and bottom links rotate counterclockwise, the shock absorber (not shown here) gets compressed and the instant center of rotation of the rear part relative to the front part moves upwards. The compression in the shock absorber acts to absorb the shock and provides a smoother ride for the rider. 
     Although the present description has been described in a considerable detail with reference to certain examples, it should be clear to those skilled in the art that within the scope of the present invention other embodiments are possible to be made.