Patent Publication Number: US-2021163092-A1

Title: Bicycle with compliant seat post interface

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 15/947,584, filed Apr. 6, 2018, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates generally to bicycles and specifically to bicycle frames having features for reducing the amount of road shock transmitted to the rider. 
     Bicycles designed for paved roads commonly have a rigidly mounted rear wheel, which is light weight and provides rear end stiffness that is desired by most serious road cyclists. In some riding conditions, such as when riding long distances or over rough roads, it would be desirable to reduce the amount of shock or vibration transmitted from the road to the rider. One way to accomplish this is to make the rear end of the bicycle compliant, which facilitates absorbing of the shock and vibration. However, such attempts to make the rear end of a road bike compliant have commonly resulted in an increase in weight or loss of rear end lateral stiffness, both of which are undesired. 
     SUMMARY 
     The present invention provides a bicycle comprising front and rear wheels, a frame supported on the front and rear wheels, a seat post supported by the frame, and a damping member. An upper portion of the seat post is movable relative to the frame between a static first position and a stressed second position. The damping member (e.g., a hydraulic damper) couples the seat post to the frame to dampen movement of the upper portion of the seat post between the first and second positions. A collar can be used to secure the damping member to the seat post. The damping member can be positioned at least partially in a tube of the frame, such as the top tube. Preferably, a lower portion of the seat post is substantially rigidly secured to the frame, and the seat post flexes when the upper portion of the seat post moves from the first position to the second position. 
     In one embodiment, the frame includes a seat tube having a length between a crank axis and an upper end of the seat tube, and the frame further includes a securing location for securing the seat post. In this embodiment, the securing location can be a distance from the upper end that is at least 30% (preferably at least 45% and more preferably at least 55%) of the length of the seat tube. 
     In another embodiment, the seat post has a front-to-rear width, and the frame includes a seat tube having a rear wall spaced from the seat post by a gap that is at least 25% (preferably at least 35% and more preferably at least 45%) of the front-to-rear width of the seat post. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a bicycle embodying the present invention. 
         FIG. 2  is a front perspective view of a frame and seat post assembly from the bicycle of  FIG. 1 . 
         FIG. 3  is a rear perspective view of the frame and seat post assembly of  FIG. 2 . 
         FIG. 4  is an enlarged exploded view of the frame and seat post assembly of  FIG. 3 . 
         FIG. 5  is a section view of the frame and seat post assembly taken along line  5 - 5  in  FIG. 2  with the seat post in an unflexed position. 
         FIG. 6  is the section view of  FIG. 5  with the seat post in a flexed position. 
         FIG. 7  is an enlarged view of a seat post binder clamp from the bicycle of  FIG. 1 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a bicycle  10  having two wheels  12 , a frame  14  supported on the wheels  12 , handlebars  16  for steering the bicycle  10 , and a seat  18  for supporting the rider. The illustrated frame  14  includes a top tube  20 , a down tube  22 , a seat tube  24 , two chainstays  26 , and two seatstays  28 , as is known in the art. A crankset  30  defines a crank axis  32  and supports two pedals  33 . A seat post  34  is partially positioned inside the seat tube  24  and protrudes upwardly from the seat tube  24  to support the seat  18 . 
     Referring to  FIGS. 2-6 , the seat post  34  is secured to the seat tube  24  by clamping at a clamping location  38  spaced from the upper end  36  of the seat tube  24  by a distance D that is about 60% of the length L of the seat tube (measured from the top of the seat tube to the crank axis  32 ). For example, for a frame having a seat tube length L of 560 mm, the distance D would be about 336 mm. The upper end  36  of the seat tube  24  includes a flared portion  44  that defines a gap G between a rear wall  46  of the flared portion  44  and the seat post  34 . The illustrated gap is about 50% of the front/rear width W of the seat post  34 . For example, for a seat post having a width of 27.2 mm, the gap would be about 13.6 mm. The opposing side walls  48  and front wall  50  of the flared portion  44  are substantially parallel to each other and define a much smaller gap between the walls  48 , 50  and the seat post  34 . 
     By virtue of the above-described flared portion  44  and gap G, the upper end of the seat post  34  can move (e.g., flex) rearwardly and downwardly to facilitate the absorption of shock and vibration travelling from the rear wheel  12  and through the seatstays  28 . The rearward and downward flexing of the seat post is best shown in  FIG. 5-6 . It should be appreciated that instead of flexing the seat post could be designed to pivot or hinge relative to the frame. In such an embodiment, a biasing member would need to be used to bias the seat post toward the raised or unstressed position. 
     The illustrated arrangement further includes a damping member  52  operatively positioned between the seat post  34  and the frame  14 . More specifically, the damping member  52  is secured between the top tube  20  and a collar  54  secured to the seat post  34 , and is chosen to dampen movement of the seat post  34  between the unflexed and flexed positions. The illustrated damping member  52  is an oil-filled through shaft damper with a low speed rebound adjuster. It has bushings at each end of the outer tube so it can take side load from the seat post and it has a clevis mounting. Due to the close fit of the end bushings, the damper provides lateral stability to the seat post. 
     The illustrated arrangement further includes a resilient boot  56  positioned to cover the top opening of the seat tube  24 , and particularly the gap G between the seat post  34  and the flared portion  44  of the seat tube  24 . The boot  54  is made from a suitable elastomeric material, such as silicone. The boot  54  substantially fills the space between the seat post and the upper end of the seat tube  24 , thereby prevent intrusion of unwanted substances, such as water or dirt. 
     It is envisioned that different riders might want different stiffnesses for the seat post (e.g., due to rider weight, riding style, or other preference). In this regard, the present invention allows the seat post to be customized to the rider&#39;s preference by changing the material, thickness, shape, or other relevant characteristic to achieve a seat post with the desired dynamic performance. In addition, in an alternative embodiment, the gap G between the seat post  34  and the flared portion  44  could be filled with a resilient bushing (not shown) to provide extra support to the seat post and resistance to flexing. In this embodiment, in the event that a rider perceives that the seat post  34  is flexing too little or too much, the bushing can be replaced with a softer or stiffer bushing to achieve the desired amount of flexing of the seat post  34 . 
     Referring to  FIG. 7 , clamping the seat post  34  to the seat tube  24  is accomplished with a binder clamp including two ears  60  on opposing sides of a slot  62  in the seat tube  24 . A fastener  64  can be inserted through one of the ears and threaded into the other to provide binding force to clamp the lower end of the seat post  34 . 
     Various features and advantages of the invention are set forth in the following claims.