Patent Abstract:
Bicycle brake shoes are provided for a bicycle braking device. The brake shoes are pressed into contact with a bicycle wheel rim to apply a braking force thereto. The brake shoes are coupled to the bicycle braking device by brake shoe holders. Each brake shoe includes an attachment portion coupled to the brake shoe holder and a rim contacting portion for contacting the side braking surface of the rim. The brake shoes are formed from a polymer that is obtained by cross-linking Nitrile Buna Rubber, Styrene-butadiene rubber with sulfur. The brake shoe is elongated in the rotation direction of the wheel rim and has a braking surface opposite to the braked surface of the rim.

Full Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to brake shoes are formed from a polymer that is obtained by cross-linking Nitrile Buna Rubber, Styrene-butadiene rubber with sulfur, and the polymer is further added with predetermined superaddition, so that said bicycle brake shoe does not excessively wear the rim while maintaining good performance in wet conditions.  
         [0003]     2. Description of the Prior Arts  
         [0004]     There are several types of bicycle braking devices on the current market. The types of bicycle braking devices include rim brakes and caliper brake, and the caliper brakes generally includes: a cantilever type, a side pull type, a center pull type.  
         [0005]     All these prior art bicycle brakes are equipped with brake shoes typically molded from a rubber that is cross-linked with sulfur. The braking surfaces of the bicycle rim maybe hard and shiny surfaces that have been anodized, or the braking surface can be been ground and then polished to form a bicycle rim with softer braking surfaces. In the case of the anodized rim, the braking surfaces are hard and shiny which provides good braking performance in dry conditions, but poor braking performance in wet conditions. In the case of ground and polished braking surfaces, the conventional rubber brake shoes provide good braking performance in dry conditions, and better braking performance in wet conditions than hard and shiny braking surfaces with an anodized finish.  
         [0006]     Attempts have been made to improve braking performance, especially in wet conditions, by manufacturing rubber brake shoes with refractory fillers. For example, rubber brake shoes have been manufactured with alumina (Al 2 O 3 ). While such improved rubber brake shoes provide good wet and dry performance, such brake shoes with alumina cause too much wear of soft braking surfaces in the ground and polished types of rims. The trend in the bicycle industry is to produce more and more rims that have ground and polished braking surfaces. Since these braking surfaces are softer than the braking surfaces of the anodized rim, the alumina-improved brake shoes should not be used because of the excessive amount of wear on these types of rims.  
         [0007]     The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.  
       SUMMARY OF THE INVENTION  
       [0008]     One object of the present invention is to provide bicycle brake shoes that have improved braking performance in wet conditions.  
         [0009]     Another object of the present invention is to provide bicycle brake shoes that do not excessively wear the rim during deceleration or stopping of the rim by the bicycle brake shoes braking while maintaining good performance in wet conditions.  
         [0010]     The foregoing objects can be attained by providing a bicycle brake shoe comprising a rim contacting portion with a braking surface formed from a polymer that is obtained by cross-linking Nitrile Buna Rubber with sulfur, and the polymer is further added with predetermined superaddition.  
         [0011]     The foregoing objects can be further attained by providing a bicycle brake shoe comprising a rim contacting portion with a braking surface formed from a polymer that is obtained by cross-linking Styrene-butadiene rubber with sulfur, and the polymer is further added with predetermined superaddition.  
         [0012]     The foregoing objects can be further attained by providing a bicycle brake shoe comprising a rim contacting portion with a braking surface formed from a polymer that is obtained by cross-linking Polybutadiene Rubber with sulfur, and the polymer is further added with predetermined superaddition.  
         [0013]     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  shows bicycle brake shoes in accordance with the present invention is installed on the front fork of a bicycle;  
         [0015]      FIG. 2  is perspective view of the bicycle brake shoes in accordance with the present invention;  
         [0016]      FIG. 3  shows the brake arm of bicycle braking device in accordance with the present invention;  
         [0017]      FIG. 4  is an operational view of the bicycle brake shoes in accordance with the present invention;  
         [0018]      FIG. 5  is a perspective view of the bicycle brake shoes in accordance with the present invention;  
         [0019]      FIG. 6  is an exploded view of the bicycle brake shoes in accordance with the present invention;  
         [0020]      FIG. 7  is a perspective view of a bicycle brake shoe in accordance with another embodiment of the present invention;  
         [0021]      FIG. 8  is a perspective view of a bicycle brake shoe in accordance with yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Referring initially to  FIGS. 1 and 2 , a front portion of a bicycle  10  is illustrated having a bicycle braking device  11  with a pair of brake shoes  20  according to the present invention. Bicycles and their various components are well-known in the prior art, and thus, bicycle  10  and its various components will not be discussed or illustrated in detail herein, except for the components of bicycle  10  which relate to the braking device  11  in accordance with the present invention. In other words, only bicycle braking device  11  will be discussed and illustrated in detail herein.  
         [0023]     As seen in  FIG. 1 , the front braking device  11  is illustrated as being coupled to front fork  12  of bicycle  10  in a relatively conventional manner. Of course, it will be apparent to those skilled in the art from this disclosure that another braking device  11  is preferably coupled to the rear fork of bicycle  10  in a conventional manner.  
         [0024]     As shown in  FIGS. 2 and 3 , the front braking device  11  is a “cantilever type” of braking device. Of course, it will also be apparent to those skilled in the art from this disclosure that other types of bicycle braking devices that can utilize the brake shoes  20  of the present invention, as needed and/or desired.  
         [0025]     Basically, braking device  11  is coupled to the front fork  12  of the bicycle  10  such that it can move between a release position and a brake position.  
         [0026]     In the release position, the brake shoes  20  of the braking device  11  do not engage the rim  20  so that the wheel  13  is free to rotate.  
         [0027]     In the brake position, the brake shoes  20  of the braking device  11  are pivoted such that the bicycle brake shoes  20  grip the braking surfaces  132  of the rim  131  to decelerate or stop rotation of the wheel  13 .  
         [0028]     In particular, the rider will operate the brake operating device  14  which in turn will pull cable  141  to cause the brake shoes  20  of the braking device  11  to engage the braking surfaces  132  of the rim  131  of the wheel  13 . Since most braking devices are well known to those skilled in the art, the braking device  11  will only be briefly discussed and illustrated herein to the extent needed to understand the present invention.  
         [0029]     Basically, each braking device  11  has a pair of brake mechanisms  15  that are pivotally coupled to front fork  12 . Each of the braking mechanisms  15  have a brake arm  151 , and a pair of brake shoe holders  152  to which the brake shoes  20  are secured in a conventional manner. A link  142  and one end of cable  141  interconnect the upper ends of brake arms  151  such that the brake mechanisms  15  pivot together in a conventional manner.  
         [0030]     The brake shoe holders  152  are coupled to the brake arms  151  by a center post  16  and a nut  161 . In operation, when the rider operates the brake lever of the brake operating device  14 , the inner wire of the cable  141  is pulled within the outer casing of the cable  141  so that the upper portions of the brake arms  151  are pulled inwardly. Thereafter, the friction pads  20  on the brake shoe holders  152  and pad supports  162  are pressed against the side surfaces of the rim  131 , thus causing a braking action to be performed.  
         [0031]     Once the rider releases the brake lever of the brake operating device  14 , the brake wire of the cable  141  is relaxed so that the coil springs within the brake arm cause the brake arms  151  to pivot in the opening direction. As a result, the tip ends of the brake shoes  20  (or so-called friction pads) on the brake shoe holders  152  are withdrawn from the side surfaces of rim  131  so that the braking action is released.  
         [0032]     As best seen in  FIGS. 4-6 , each of the bicycle brake shoes  20  has an attachment portion  21  and a rim contacting portion  22  with a braking surface A. The attachment portion  21  and the rim contacting portion  22  are integrally formed as a one-piece, unitary member, and the attachment portion  21  is disposed in the metal housing  30 , to a rear end of the housing  30  is connected the center post  16 , and then the brake shoe holders  152  are coupled to the brake arms  151  by the center post  16  and the nut  161  in such a manner that the center post  16  inserts the pad supports  162 . Thereby, the brake shoes  20  can be replaced directly from the metal housing  30  after being worn out (the brake shoes  20  and the metal housing  30  are attached together through track engagement).  
         [0033]     The brake shoes  20  in this embodiment are formed from a polymer that is obtained by cross-linking Nitrile Buna Rubber, Styrene-butadiene rubber with sulfur, and the polymer is further added with predetermined superaddition. The braking distances for bicycle brake shoes  20  of the present invention in wet conditions are substantially equal to the braking distances for the prior art bicycle brake shoes. However, the amount of rim wear for bicycle brake shoes  20  of the present invention is substantially reduced as compared to prior art bicycle brake shoes, where a substantial amount of alumina is used.  
         [0034]     The aforementioned superaddition includes Stearic Acid, Zinc Stearate, Wax, ZnO, Barium Sulfate, Calcium Stearate, which can be added to the polymer that is obtained by cross-linking SBR with peroxide of adhesive or sulfur, as needed and/or desired, so as to adjust property of the brake shoes  20 .  
         [0035]     Referring now to  FIG. 7 , bicycle brake shoes  40  are illustrated in accordance with an alternative embodiment of the present invention. Specifically, the attachment portions  401  and the rim contacting portions  402  are formed of separate pieces that are integrally attached together by adhesive or the like. Thus, in this embodiment, the attachment portions  401  can be constructed of any other suitable material. Each of the attachment portions  401  is fixedly attached to one of the rim contacting portions  402  by a suitable means such as adhesive or the like. The attachment portions  401  are received in recesses of the brake shoe holders. Threaded fasteners or screws are utilized to fixedly secure the bicycle brake shoes to the brake shoe holders in a relatively conventional manner.  
         [0036]     Referring to  FIG. 8 , the center posts  53  are embedded in the brake shoes  50 , specifically, one end of each center post  53  is embedded within one of the attachment portions  51  during the molding process of the bicycle brake shoes  50 . The attachment portions  51  and the rim contacting portion  52  are integrally formed as a one-piece, unitary member. In other words, while only limited manufacturing techniques are disclosed herein for constructing bicycle brake shoes in accordance with the present invention, it will be apparent to those skilled in the art from this disclosure that numerous other manufacturing techniques may be utilized in constructing bicycle brake shoes in accordance with the present invention.  
         [0037]     In manufacturing the bicycle brake shoes, the various materials to be blended are first measured by weight to the appropriate weight percentage and then mixed together. Next, the mixture is processed in a conventional manner to form an extruded sheet of rubber. The sheet of rubber is then cut into individual sheets that are used in a conventional molding process to form a plurality of bicycle brake shoes with rim contacting portions composed of the rubber compound, as mentioned above.  
         [0038]     During the molding process, the attachment portion and the rim contacting portion are preferably integrally formed as a one-piece, unitary member. Alternatively, the attachment portion can be formed of separate piece that is integrally attached to the rim contacting portion by adhesive or the like after molding the rim contacting portion as mentioned above. Moreover, one end of the center post can be embedded within the attachment portion and/or the rim contacting portion during the molding process mentioned above.  
         [0039]     The bicycle brake shoes in accordance with the present invention are made from the polymer that is obtained by cross-linking Nitrile Buna Rubber, Styrene-butadiene rubber with sulfur. The wet braking distance for conventional bicycle brake shoes is very poor, while very little rim wear occurs. Accordingly, rubber brake shoes have been manufactured with alumina (Al 2 O 3  in order to improve the wet braking performance, while such improved rubber brake shoes with alumina cause too much wear of soft braking surfaces in the ground and polished types of rims. The braking distances for bicycle brake shoes  20  of the present invention in wet conditions are substantially equal to the braking distances for the prior art bicycle brake shoes with alumina. However, the amount of rim wear for bicycle brake shoes  20  of the present invention is substantially reduced as compared to prior art bicycle brake shoes, where a substantial amount of alumina is used.  
         [0040]     While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.

Technology Classification (CPC): 5