Abstract:
A rear suspension road bicycle frame uses an integrated rear shock absorbing assembly installed in a typical diamond bicycle frame with a head tube, down tube, top tube, seat tube, tubular chainstays, tubular seat stays, brake bridge at the top of said seat stays connecting them, the shock absorbing assembly having an elastomer shock absorbing spring member with a slide affixed to the brake bridge, and a sliding bearing in the upper wishbone so that the preloaded spring member absorbs shock and the frame absorbs flexing tending to unload the spring member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention is a rear suspension design which can be incorporated into light weight racing frames such as are used by professional racing teams.  
           [0003]    2. Summary of the Invention  
           [0004]    Professional racing teams race some extremely rough courses including many sections paved with cobblestones. These can be extremely fatiguing and dangerous to the riders, causing many instances of loss of control of the bike and resultant crashes. For example, one race that is famous for the amount of rough surface conditions is the Paris-Roubaix.  
           [0005]    These races can be very damaging to the riders and their equipment. They will sometimes use larger diameter tires than on normal courses in order to provide a little more cushion and more resistance to flatting on the harsh bumps. The drawback is that additional mass on the bike degrades its performance in several ways and the larger tires typically add additional weight to the bike. In addition, the road racing bike frames are typically made so as to be very close to the narrow racing tires. So it is usually possible to only put a slightly larger tire on. There usually is not clearance for a substantially larger tire. The side pull type brakes that road racing bikes use also preclude a much larger tire. They do not have adequate reach adjustment or tire clearance to fit larger road tires. So even if you designed more tire clearance into a frame, it would not be able to use this type of brake.  
           [0006]    It is possible to use a different type of bike called a cyclo-cross type which does allow the use of significantly larger tires. These bikes are intended for off road use and utilize a different type of braking system called cantilevers which allow for a larger tire. So on these bikes the frame and the brakes have more clearance for larger tires.  
           [0007]    But most of the road racing teams like to stay on their road racing bikes, even for the rougher road conditions. They are used to the fit and handling of their personal bike and don&#39;t like to change the type of bike.  
           [0008]    In addition to the fatigue, the rough courses cause substantial loss of energy to the bumps and result in significantly lower bike speeds than the similar amount of effort on a smooth course would achieve. The vertical up and down motion which is beating up the rider and causing loss of wheel traction comes out of the pedaling energy supplied by the rider.  
           [0009]    Some road racing teams have used front suspension forks on these rougher courses. These forks are typically add at least 1 kilogram of mass to the bike. This is a large amount of weight to add and a considerable detriment to the bikes performance on a moderate to smooth road. As they have a significant amount of stiction, the static friction resulting from the sliding seals and bearings which must be overcome before the suspension can begin to move, they are only partially effective at attenuating the front wheel shocks. They provide noticeable cushioning of the hands of the rider, but not much for the saddle or feet, where most of the riders weight is. Most of the weight of the cyclist, and the all of the cyclists forward driving force is located at the rear wheel. So suspension and better traction is likely to be at least, if not more useful on the rear than on the front wheel. In addition, the sliding type front forks have a tendency to move up and down with each pedal stroke, unless the stiction is high enough to prevent it. This motion wastes the rider&#39;s energy. But higher stiction reduces the amount of road shock that the front fork attenuates.  
           [0010]    This is especially evident in a sprint, when the pedaling forces are larger, so the weight shift from front wheel to rear wheel with each pedal stroke is greater, and more of the riders weight is moved forward to the front wheel as he leans forward or stands up. As a result, the use of front suspension forks in these types of events has had very limited success.  
           [0011]    The invention is intended to attenuate the amplitude of deflections that the rider feels, both in the feet and seat. This will reduce fatigue in the rider, especially over a longer course. The invention is further intended to improve the adhesion of the tires to the pavement, by reducing the amount of time they are not in contact with the road surface and reducing the variation or amplitude of forces between the tire and the ground.  
           [0012]    The invention provides a limited amount of very supple rear wheel suspension travel, about 1 to 1.8 cm in the preferred configuration, while retaining the light weight of the some of the lightest professional level bicycle racing frames, and retaining sufficient structural rigidity to control the out-of-plane deflection of the overall frame and the rear wheel of the bike which lead to loss of efficiency and control of the bike.  
           [0013]    The invention is adaptable to be used in a variety of bicycle frames including molded fiber reinforced plastic frame such as FIGS.  1 -___ or a metal frame, such as the welded and heat treated aluminum type of frame as shown in FIGS. __-___. One of ordinary skill in the art will understand that the invention can be adapted regardless of the particular frame material, whether fiber reinforced plastic, metal such as steel, aluminum or Titanium, or a combination of materials. Similarly, one of ordinary skill will be able to adapt component mounting such as the brake fixing nut which also retains the shock.  
           [0014]    3. Description of Related Art  
           [0015]    Some of the prior art suspension designs used curved seatstays. The bend(s) destabilize the seat stay tubes, and cause it to flex more when an axial load is applied, either by the riders weight or by a momentary bump impact. Unfortunately, the bends also greatly reduce the capability of a given tube to support an axial load. Thus, the bent seat stays must be made heavier than normal to provide adequate frame structure. One design uses a single large radius bend in the seatstays, but the amount of flex under compression is limited by a layer of polymer and a stainless steel strap under tension. This of course adds considerable weight to the overall structure, while providing less benefit than the current invention.  
           [0016]    Prior art devices either used mechanical pivots to allow the rear wheel to move vertically with respect to the rest of the frame and the rider, or they utilized very vertically flexible members for the chainstays, for example, in order to allow a large amount of deflection from their resting position. Some of these have metal chainstays but which have been reinforced and flattened horizontally so they are not stiff in the vertical direction, but still torsionally and laterally rigid. Or they have had sections of the chainstay where the metal is replaced by a flat fiberglass spring, for example.  
           [0017]    U.S. Pat. No. 6,406,048 issued to Castellano on Jun. 18, 2002. This patent is entitled “Pivotless Rear Suspension System For Bicycles”. According to Castellano, utilization of tubular type chainstays precludes a useful amount of suspension travel. Castellano further states that the alignment between the upper and lower portions of the wishbone must be free to move angularly in order to allow operation of the particular shock arrangement of the &#39;048 patent. This patent is incorporated by reference.  
           [0018]    Adding pivots or reinforcing and substantially reshaping the chainstays, or adding flat springs to the chainstays all typically add weight to the bike. And since the resultant structure is not very rigid vertically, in order to take a large deflection in one direction for many cycles without fatigue, the compressive spring must be designed to take most of the compressive loads, making it heavier. There also needs to be a negative spring and mechanism for activating it included in these designs, which again adds weight and complexity. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a side elevation of the bicycle frame of the invention.  
         [0020]    [0020]FIG. 2 is a exploded view of the seat stay and shock absorber assembly of the invention.  
         [0021]    [0021]FIG. 3 is a bottom plan view of the chain stay and bottom bracket assembly of the invention.  
         [0022]    [0022]FIG. 4 is an enlarged exploded view of a portion of the seat stay yoke and shock absorber assembly of the invention.  
         [0023]    [0023]FIG. 5 is a exploded perspective view of the seat stay and shock absorber assembly of the invention.  
         [0024]    [0024]FIG. 6 is a perspective view of the brake bridge.  
         [0025]    [0025]FIG. 7 is a perspective view of the frame with an exploded view of the shock absorber assembly.  
         [0026]    [0026]FIG. 8 is a fragmentary perspective view of the seat lug portion of the frame and the seatstay assembly with the shock absorber assembly in place.  
         [0027]    [0027]FIG. 9 is a fragmentary perspective view of the upper monostay portion of the frame and the seatstay assembly with the shock absorber assembly in place.  
         [0028]    [0028]FIG. 10 is a sectional view of the frame with the shock absorber assembly in place. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    A bicycle frame  10  of the well known diamond configuration has head tube, down tube, top tube, and a rear triangle  12  generally made up of a seat tube  14 , a chainstay assembly  16  and a seatstay assembly  18 . A shock absorber assembly  20  operates in conjunction with the other elements of the rear triangle  12  to provide an ultra lightweight, high efficiency bicycle suspension. The shock absorber assembly is generally identified by reference number  20 , while its components are separately described below.  
         [0030]    The invention is adaptable to various tubular section chainstay assemblies. Thus, in an aluminum frame, the lateral width of a cross section of the chainstays is approximately equal to or slightly greater than the vertical height of a cross section of the chainstays. While in a carbon fiber reinforced plastic frame, the height appears to be significantly greater than the width.  
         [0031]    The shock absorber assembly  20  is incorporated into the wishbone  22  of the seat stay assembly  18  as part of the bicycle frame  10 . The shock absorber assembly  20  is mounted between a upper wishbone tube  24  connected to the seat tube  14 , and a lower wishbone tube  26 .  
         [0032]    The limited amount of suspension travel is effected by in-plane flexure of the bicycle frame  10  itself and compression and extension of a bumper  30  preferably formed of a lightweight high energy storage cellular polyurethane elastomer. The preferred material is called Elastocell and is produced by BASF.  
         [0033]    The out-of-plane deflection of the bicycle frame  10  is controlled by a light weight sliding shaft  32  rigidly attached to the wishbone tube  26 . Shaft  32  slides in anti-friction bearing assembly  34 .  
         [0034]    Wishbone  22  further has a lower portion  36  which has two projecting tubes  38  projecting downwardly from brake bridge  42 . Tubes  38  in turn directly connect to seat stays  54  and  56 . Variations on these components can exist consistent with the invention. For example, brake bridge  42 , tubes  38 , lower portion  26  could all be molded from a fiber reinforced plastic. Alternatively, a cast metal brake bridge could have tubes  26 ,  38  formed as a unitary portion or could have separate tubes. As another example, all or a portion of lower portion  36  could be fabricated from metal such as by welding tubes.  
         [0035]    In practice, adapting in one embodiment of brake components, for example, the brake will have a short 6 mm threaded stud protruding from the back of the brake (towards the front of the bike in the case of the rear brake) for mounting purposes. In standard frames, with straight seat stays and a small diameter brake bridge connecting the two seat stays, a short allen head recessed nut is used to engage and secure the 6 mm threaded stud. In the case of the wishbone style of seat stays, the brake bridge has additional thickness, and a longer recessed nut is needed to secure the brake. This nut is additionally used to secure the sliding shaft member  32  in the invention.  
         [0036]    The invention is preferably closely coupled to the brake bridge. While the drawings show an extension of the wishbone above the brake bridge, this could be substantially eliminated because the invention is that it can be made quite short. This is particularly desirable where the suspension is to be used in smaller frames where the upper portion of the wishbone is very short, and places where there is not room for a conventional shock.  
         [0037]    Shaft  32  passes through the center of the elastomeric bumper  30  and then shaft  32  slides in a suitable anti-friction bearing assembly  34  located in the upper wishbone tube  24 .  
         [0038]    The shaft  32  is hollow in the preferred configuration, and the bearing assembly  34  is elongated along the axis of the upper wishbone tube  24 .  
         [0039]    Bearing assembly  34  has a central cylinder  43  on which is formed, at a top end, a top flange  44  and at a bottom end, a bottom flange  46 . Bottom flange  46  further has a small circumferential lip  48  which traps one or more edges of the elastomer bumper  30  of shock absorber assembly  20 .  
         [0040]    Anti-friction bearing assembly  34  is formed or mounted in cylinder  24 . Preferably a top and bottom sleeve bearings  50 ,  52  inside cylinder  42  enable maximum stability for shaft  32  while minimizing weight and complexity in assembly  34 . Thus, a pair of bearings  50 ,  52  maintains the most effective axial alignment of the upper wishbone section with the lower seat stays and brake bridge.  
         [0041]    The anti-friction bearings  50 ,  52  are held in plane by means of a relatively large diameter but thin wall and thus light weight tube  24 . This provides adequate lateral rigidity to keep the bicycle wheel in vertical alignment with the front of the frame  10  in conjunction with the aforementioned sliding shaft  32  and bearings  50 ,  52  and with adequate fore-aft rigidity to resist excessive deflection and vibration of the lower seat stays  54 ,  56  and brake bridge  42  when the rear brake is applied in order to decelerate the bike.  
         [0042]    There is sufficient angular flexibility in the combination of the seat tube  14 , the seat stay assembly  18 , and the chainstay assembly  16  to allow the bearings  50  and  52  to slide on shaft  32  without binding. The greatest angular flexibility is in the seatstay assembly  18  as the tubes  54  and  56  are smaller diameter and lighter weight than the tubes in the other assemblies.  
         [0043]    The elastomeric bumper  30  is held in position radially by the sliding shaft  32  going through its hollow center, and in the preferred configuration, additionally by the circumferential lip  48  which traps one or more edges of the elastomeric bumper  30 . Bumper  30  has its top stepped to fit into the space defined by lip  48 , a small cylindrical center portion, and two conical segment portions reducing the diameter to the diameter of tube  26 . Alternatively, the elastomeric bumper  30  can be retained in position by a matching pattern such as V grooves or channels in the frame and in the elastomeric bumper  30 .  
         [0044]    The chainstays  58 ,  60  of the bike are also of relatively large diameter construction in order to provide good torsional and lateral rigidity to the frame while allowing sufficient movement for the suspension to operate effectively.  
         [0045]    In order for a suspension to operate smoothly, it needs both a compression spring means to store energy from bumps and return it, and a negative spring which keeps the unit from topping out harshly when all of the load is released from the wheel, as in when the bike is airborne. These two spring means oppose each other, and achieve a balanced position when there is no weight on the suspension, and a different balanced position with weight applied.  
         [0046]    The invention uses the frame  10  of the bicycle as the negative spring when the bike is unloaded. Most of the spring action is due to flexure of the chainstays  58 ,  60  of the bike, but there is some deflection in some of the other tubes of the bike as well. With the normal rider&#39;s weight static on the bike, the frame is still providing a small amount of negative spring force. But when the rider hits a bump, and the chainstays  58 ,  60  travel further upward, the frame goes past its neutral position and begins to act as a positive spring, reinforcing the elastomeric bumper  30 .  
         [0047]    This is a key element of the invention. The preferred configuration is a frame made from high strength aluminum alloy or composite fiber (such as U.S. Pat. No. 6,270,104, incorporated by reference as if fully set forth herein) for light weight and high performance. While there are slight visual differences in drawings showing these alternatives, the operation of the shock absorber assembly  20  in conjunction with these tubular frames is the same in either tubular frame.  
         [0048]    Other frame designers have said that aluminum could not be used for this type of design, because of its poor fatigue strength. If the aluminum frame were made as laterally and torsionally stiff as a racer would like, and the total suspension travel was in one direction, upward, from the unloaded position of the frame, then the amount of travel which would not cause frame fatigue would probably be limited to a small, and possibly not as useful amount as the present invention. Further, the advantageous strength, stiffness and weight properties of hollow tubes can be utilized in the entire frame, including the bottom bracket and chainstay assembly  16 .  
         [0049]    By using essentially a standard, high quality racing frame as the basis, with the addition of the suspension parts described, the rear suspension can add as little as about 65 grams (2.3 oz) to the weight of the bike. Sample frames (not including the front fork or steering bearings) including the complete suspension weigh less than 3 pounds, or 1.5 kilograms. This was in primarily aluminum structure frames. The total weight would likely be even less in a carbon fiber composite frame. This is much lighter than prior art designs.  
         [0050]    The relative dimensions of such a standard frame adapted to receive the shock absorber  20  illustrate the efficiency of this shock absorber arrangement. A gap of about 25 mm separates tube  24  and tube  26  when the bicycle frame is fully assembled with all the tubes in the normal orientation and with the normal structure. Tube  24  is fully hollow and receives bearing assembly  34 . Tube  26  is closed with a disk  62  formed over its end. An aperture  64  receives shaft  32 .  
         [0051]    Installation of assembly  20  in frame  10  is temporarily aided by the use of bolt  66 . Bolt  66  fits a threaded end of shaft  32  to provide, effectively a handle and a guide so that assembly  20  can be fitted in tube  24  and shaft  32  can be aligned in portion  22 . Once assembled, a standard brake binder stud and nut pass through break bridge  42  and also through a transverse bore in the base of shaft  32 . Fixing the brake in place, therefore, fixes assembly  32  in place with no additional fasteners.  
         [0052]    An added structural advantage is the placement of a transverse bore in shaft  32  which receives a standard brake binder bolt, the transverse placement of which provides great strength utilizing a component that would be present in any bicycle frame, thereby further improving performance relative to strength and weight. This therefore provides a performance advantage when compared to a suspension placing a shaft on the top portion of the wishbone proximate the seat tube.  
         [0053]    The dimension of elastomeric bumper  30 , uninstalled, and at rest is about 30 mm. Assembly  20  is fit in the gap by flexing chainstays  58 ,  60  downward, to enable an increase in the gap. Upon fitting assembly  20  in place and bolting shaft  32  through brake bridge  42 , tension on chainstays  58 ,  60  is partially released and partial compression or preload is applied on bumper  30 . This has the effect of enabling the negative springing by chainstays  58 ,  60  as ride conditions impose a reduced load on bumper  30 —for example after a rider passes a bump in a road surface.  
         [0054]    While the present invention has been disclosed and described with reference to two alternative embodiments thereof, it will be apparent, as noted above that variations and modifications may be made therein. It is also noted that the present invention is independent of the specific tubular frame, and is not limited to the particular frame. It is, thus, intended in the following claims to cover each variation and modification that falls within the true spirit and scope of the present invention.