Abstract:
A crank assembly formed as a unitary composite structure, the crank arms and crank shaft being hollow to provide maximum weight reduction, the crank arms being over-sized to provide the necessary stiffness and strength. The unitary composite crank assembly may further include a crank claw integrally formed with the crank assembly. Additionally, a spider may be integrally formed with the crank assembly reducing the amount of parts for the assembly, increasing stiffness and reducing overall weight.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a composite crank assembly and more specifically to a single-piece unitary structure crank assembly formed from a composite material. 
       BACKGROUND OF THE INVENTION 
       [0002]    Crank arm assemblies have been in use for many years and typically include a crank shaft, bearings for facilitating rotation of the crank shaft in a bottom bracket of a bicycle, and opposing crank arms affixed to ends of the crank shaft. A chain sprocket is typically coupled to one side of the crank shaft to rotate with the crank shaft and thereby drive a chain coupled to a rear wheel of the bicycle. 
         [0003]    The crank arm assembly and crank shaft are subject to considerable forces applied by a rider as they pedal the bicycle. As such, most know system have provided crank arms and crank shafts made of metal or a metal composite to afford the necessary strength characteristics. Additionally, systems have provided an integrally formed crank arm and spider that couples to the chain sprocket. However, many of these designs resulted in a rather large, heavy crank assembly. 
         [0004]    To combat these problems, crank arms have been provided with hollow interiors such as, for example, U.S. Pat. Nos. 5,493,937; 5,988,016; 6,314,834 and U.S. Patent Application Publication No. 2004/0149076. While providing hollow crank arms does reduce the weight of the assembly to an extent, the crank assembly is still quite heavy, which during competitive racing is a severe disadvantage to the rider. Other systems have provided crank arms with integrally formed spiders to couple to the chain ring, including U.S. Pat. No. 5,893,299 and U.S. Patent Application Publication Nos. 2004/0162172 and 2004/0177717. However, these systems, while attempting to reduce the overall weight of the crank assembly are quite heavy due to the metal fabrication material. 
         [0005]    Still other systems have attempted to provide portions of the crank assembly as a composite material, such as a carbon fiber or pre-impregnated resin fiber. While composite materials do reduce the overall weight of the system, composite materials typically do not have the same strength characteristics of metal. For example, U.S. Pat. No. 4,811,626 discloses use of a multi-sectional crank arm assembly that uses a metal hub for the crank. This system is complicated to fabricate being formed from so many pieces, which weaken the overall design and is a combination of composite material and metal disadvantageously increasing the overall weight of the device. 
         [0006]    U.S. Pat. No. 5,632,940 is directed toward a crank arm constructed from a composite material. However, this system comprises a plurality of composite material structures encased in a polymer composite material. Again, while this system does reduce the overall weight of the system to an extent, due to the solid construction technique, it is still too heavy and has strength issues where the crank arms couple to the crank shaft. 
         [0007]    European Patent No. 1,378,433 provides still another crank arm configuration utilizing a composite material. This system provides a hollow interior that reduces overall weight, however, the patent still teaches use of a metal bottom bracket axle fitting that couples to the composite crank arm. (See, Col. 5, Ins. 24-31.) Due to the tremendous stresses applied to the crank arm assembly, especially in competition, this configuration will no provide the necessary strength characteristics required and is still unnecessarily heavy. 
         [0008]    Still further, U.S. Patent Application Publication No. 2004/0182197 discloses a crank arm formed of a composite material and having an integrally formed spider to couple to the chain ring. While this system does provide for reduced weight and increased coupling strength, the system is still unnecessarily heavy and due to the coupling arrangement with the crank shaft, has strength issues. 
         [0009]    Additionally, U.S. Patent Application Publication No. 2006/0103106 discloses a system where both the right crank arm and the left crank arm are each integrally connected to the crank axle. However, this system fails to provide for a system that includes an integral feature for coupling to the spider. In addition, this system further teaches that a continuous septum that extends through crank axle and bent regions and through at least a portion of right crank arm and left crank arm. 
       SUMMARY OF THE INVENTION 
       [0010]    What is desired is a system and method that reduces to an absolute minimum, the overall weight of the crank assembly (e.g. the crank arms and the crank shaft) without having any supporting members running therethrough. 
         [0011]    It is further desired to provide a system and method that increases the overall strength of the crank assembly while at the same time, keeps the weight of the crank assembly to a minimum. 
         [0012]    It is still further desired to provide a system and method that is quick and easy to install reducing the overall number of pieces and parts that require assembly. 
         [0013]    It is yet further desired to provide a system and method that increases the overall strength of the crank arm assembly coupling to the chain ring. 
         [0014]    These and other objects are achieved, in one advantageous embodiment, by the provision of a single unitary crank arm assembly formed of a composite material. For example, the crank arms are provided as a single unitary structure with the crank shaft to form a single composite structure. Advantageously, the crank arms are provided as hollow tubes to still further reduce the overall weight of the apparatus. The crank shaft is provided with bearings positioned thereon to allow the crank shaft to rotate within the bottom bracket assembly. The single unitary structure provides superior strength characteristics as there are not couplings between the crank arms and the crank shaft. To further increase the strength of the assembly, the crank arms may be fabricated over-sized. 
         [0015]    In alternative embodiments, the single unitary crank assembly may further include an integrally formed spider to couple to the chain ring(s). The spider may be formed from the composite material such that the entire assembly is preformed reducing the weight of the structure and increasing the overall strength. 
         [0016]    Still further, it is contemplated that the crank assembly may be formed integral with a spider providing superior strength and reduction in weight of the assembly. The spider may be provided with a chain ring provided on a circumference thereof. The chain ring may be provided as a metal cap or attachment that extends beyond the diameter of the spider to engage with the chain. The spider may further be provided having multiple chain rings attachable thereto having differing circumferences to accommodate different riding conditions. 
         [0017]    In one advantageous embodiment, a crank assembly for attaching to a bottom bracket of a bicycle is provided comprising a substantially cylindrical crank shaft portion extending longitudinally through the bottom bracket, the crank shaft portion being formed of a composite material. The assembly further comprises a first crank arm portion having a proximal end extending from a first end of the crank shaft portion, the first crank arm portion integrally form of a composite material with the crank shaft portion. The assembly still further comprises a second crank arm portion having a proximal end extending from a second end of the crank shaft portion opposite the first end, the second crank arm portion integrally form of a composite material with the crank shaft portion. The assembly is provided such that the crank shaft, the first crank arm and the second crank arm are all integrally formed of a composite material to form a single unitary crank assembly. The assembly is further provided such that the substantially cylindrical crank shaft portion has an integrally formed splined surface provided at the first end for engaging with a spider. 
         [0018]    In another advantageous embodiment, a crank assembly for attaching to a bottom bracket of a bicycle is provided comprising a substantially cylindrical crank shaft portion extending longitudinally through the bottom bracket, the crank shaft portion being formed of a composite material. The assembly further comprises a first crank arm portion having a proximal end extending from a first end of the crank shaft portion, the first crank arm portion integrally form of a composite material with the crank shaft portion. The assembly still further comprises a second crank arm portion having a proximal end extending from a second end of the crank shaft portion opposite the first end, the second crank arm portion integrally form of a composite material with the crank shaft portion. The assembly is provided such that the crank shaft, the first crank arm and the second crank arm are all integrally formed of a composite material to form a single unitary crank assembly. The assembly also comprises a spider, comprising a composite material, the spider integrally formed with the crank shaft and crank arms. 
         [0019]    In another advantageous embodiment, a method for making a single unitary crank assembly from a composite material to be positioned in a bottom bracket assembly of a bicycle is provided comprising the steps of defining a substantially cylindrical crank shaft portion of a composite material, the crank shaft having first and second ends, defining a hollow elongated first crank arm portion of a composite material having a proximal end and defining a hollow elongated second crank arm portion of a composite material having a proximal end. The method further comprises the steps of forming a composite unitary crank assembly by affixing the first crank arm to a first end of the crank shaft and affixing the second crank arm to the second end of the crank shaft. The method still further comprises the step of integrally forming a splined surface on the substantially cylindrical crank shaft portion for engaging with a spider. The method also comprises the steps of positioning a first bearing around the first end of the crank shaft portion, positioning a second bearing around the second end of the crank shaft portion and positioning the crank assembly into the bottom bracket of a bicycle. 
         [0020]    In another advantageous embodiment, a method for making a single unitary crank assembly from a composite material to be positioned in a bottom bracket assembly of a bicycle is provided comprising the steps of defining a substantially cylindrical crank shaft portion of a composite material, the crank shaft having first and second ends, defining a hollow elongated first crank arm portion of a composite material having a proximal end and defining a hollow elongated second crank arm portion of a composite material having a proximal end. The method further comprises the steps of forming a composite unitary crank assembly by affixing the first crank arm to a first end of the crank shaft and affixing the second crank arm to the second end of the crank shaft. The method still further comprises the step of integrally forming a spider of a composite material with the crank shaft and crank arms. The method also comprises the steps of positioning a first bearing around the first end of the crank shaft portion, positioning a second bearing around the second end of the crank shaft portion and positioning the crank assembly into the bottom bracket of a bicycle. 
         [0021]    Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an illustration of a single-piece composite crank assembly. 
           [0023]      FIG. 2  is an illustration of drive side the single-piece composite crank assembly according to  FIG. 1  installed in the bottom bracket of a bicycle with an attached chain ring. 
           [0024]      FIG. 3  is an illustration of an opposite side of the single-piece composite crank assembly according to  FIG. 2  installed in the bottom bracket of a bicycle with an attached chain ring. 
           [0025]      FIG. 4  is front view of the single-piece composite crank assembly according to  FIG. 1  with an integrally formed spider coupled to a chain ring(s). 
           [0026]      FIG. 5  is side view of the single-piece composite crank assembly according to  FIG. 4 . 
           [0027]      FIGS. 6-9  are cut-away drawings that illustrate a series of steps for forming the single-piece composite crank assembly according to  FIG. 1  integrally with a spider to for a unitary structure. 
           [0028]      FIG. 10  is an exterior view of the integrally formed single-piece composite crank assembly according to  FIG. 1  with the spider. 
           [0029]      FIG. 11  is a partial view of the exterior of the spider according to  FIG. 10 . 
           [0030]      FIG. 12  is a view of a first side of the spider according to  FIG. 11  with a chain ring affixed to the spider. 
           [0031]      FIG. 13  is a view of a second side of the spider according to  FIG. 12  with multiple chain rings affixed to the spider. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views. 
         [0033]      FIG. 1  is a perspective view of the composite crank assembly  100 . The composite crank assembly  100  generally includes a crank shaft  102 , a first crank arm  104  and a second crank arm  106 . The crank assembly  100  is formed as a single, unitary composite structure such that no couplings or joints are provided between the crank arms  104 ,  106  and the crank shaft  102 . The unitary structure increases stiffness and strength in part, by eliminating stress concentrations, and slight movement, loosening and wear in joints. In addition, the fabrication as a composite structure reduces the overall weight of the device and eliminates creaking by reducing the number of overall parts. 
         [0034]    The crank arms  104 ,  106  are provided with pedal bores  108 ,  110  provided in distal ends  112 ,  114  respectively. The pedal bores  108 ,  110  are provided for coupling pedals (not shown) to the crank assembly  100 . 
         [0035]    The crank arms  104 ,  106  are provided in this embodiment, as over-sized elongated arms. While conventional crank arms are provided having a relatively small diameter (e.g. typically 24 mm), crank arms  104 ,  106  are provided having a width of approximately 35-40 mm. The crank arms  104 ,  106  are provided as hollow structures to further lighten the crank assembly  100 . However, the crank arms  104 ,  106  are provided as over-sized arms ensuring strength and stiffness. 
         [0036]    Also shown in  FIG. 1  are bearings  116 ,  118  positioned at first end  120  and second end  122  of crank shaft  102 . The bearings  116 ,  118  are provided surrounding crank shaft  102  and engage with an inner surface (not shown) of a bottom bracket  124  ( FIG. 3 ) allowing the crank assembly  100  to rotate relative to the bottom bracket  124 . Bearings  116 ,  118  are fitted over the end  112  of crank arm  104  and slid into position on crank shaft  102 . It is further contemplated that a sleeve  103 , such as for example, comprising an alloy such as aluminum, may be fitted over crank shaft  102 . In this embodiment, bearings  116 ,  118  are positioned on the outside of the aluminum sleeve  103 , which may be used to reduce wear of the crank shaft  102 . The bearings  116 ,  118  may further be held in place by protrusions or rings (not shown), for example, positioned in bottom bracket  124 . One example of a bottom bracket assembly that may effectively be used with the crank assembly  100  is disclosed in U.S. patent application Ser. No. 11/735,212 filed on Apr. 13, 2007 entitled “Split Bottom Bracket” and is incorporated herein by reference. 
         [0037]    Splined surface  126  and collar  128  are provided at one end of crank shaft  102  for engaging with a spider  130  ( FIGS. 2 &amp; 3 ). It is contemplated that splined surface  126  and collar  128 , in one embodiment, are integrally formed with crank shaft  102  reducing the number of parts and increasing stiffness of the structure. 
         [0038]    Referring now to  FIGS. 2 and 3 , the crank assembly  100  is illustrated mounted in the bottom bracket  124  with the spider  130  attached to crank shaft  102 . In this embodiment, the spider  130  is detachably connectable to crank shaft  102  and may comprise a light weight metal or alloy. The spider  130  is provided, in this embodiment, with five spokes  132  that extend radially outward relative to crank shaft  102 . While five spokes  132  are provided, it is contemplated that a greater or fewer number of spokes may be provided, the number typically ranging from three to six, but more may be used if desired. 
         [0039]    The spokes  132  are provided with a first mounting surface  136  at the end  138  of each spoke  132 . The first mounting surface  136  is provided as a stepped portion  140  having an opening provided therein for receiving a mounting element  142 , such as, a bolt. A chain ring  144  is coupled to the spoke  132  by means of the mounting element  142 . The chain ring  144  is provided with a mounting portion  146  complementary to mounting surface  136  of spoke  132 . Chain ring  144  is provided having a splined circumference for engaging with a chain  148  to drive the bicycle as is well known in the art. 
         [0040]    Also provided on spoke  132  is a second mounting surface  150  provided at the end  138  of each spoke  132  and substantially opposite to first mounting surface  136 . It is contemplated that mounting element  142  may effectively be used to secure a second chain ring  152  to the second mounting surface  150 , the second chain ring having an outer circumference smaller than and offset from the outer circumference of chain ring  144 . In this particular embodiment, both chain ring  144  and second chain ring  152  may advantageously comprise a light-weight metal or alloy. 
         [0041]    Turning now to  FIGS. 4 and 5 , the crank assembly is similar to that illustrated and described in connection with  FIGS. 2 and 3 , however, in this embodiment; the spider  130  is integrally formed with crank assembly  100 . This again provides for fewer parts, which increases stiffness and strength in part, by eliminating stress concentrations, and slight movement, loosening and wear in joints. Integrating the spider  130  with the crank assembly  100  also reduces the overall weight of the device as the spider is fabricated from a composite material, and eliminates creaking by reducing the number of overall parts. 
         [0042]    Also illustrated in  FIGS. 4 and 5  are end caps  154 ,  156 , which include threaded portions  158 ,  160  that may in one advantageous embodiment, engage with threads on an interior surface of bottom bracket  124 . 
         [0043]    Again, crank assembly  100  is provided as a single, unitary composite structure including spider  130 , where crank arms  102 ,  104  are provided having a hollow core to further reduce overall weight. It is further contemplated that in one advantageous embodiment, crank shaft  102  is also provided having a hollow core to still further lighten the overall weight of the device. Alternatively, the core may be filled with a foam substance to provide further support for the device. While certain configuration of crank assembly  100  are described in connection with the embodiment of  FIGS. 4 and 5 , it is contemplated that they may equally apply to the embodiments described in connection with  FIGS. 1-3  and  FIGS. 6-13 . 
         [0044]    Referring now to  FIGS. 6-9 , a method of integrally manufacturing a composite spider  162  ( FIGS. 8-10 ) with the crank assembly  100  is illustrated in the cut-away drawings as a series of steps. For example,  FIG. 6  illustrated a first spider portion  164  including an opening  166  extending therethrough for receiving crank assembly  100 . The opening  166  further includes a coupling portion  168 .  FIG. 7  illustrates a second spider portion  170  having an opening  172  extending therethrough. The opening  172  further includes a coupling portion  174  that is complementary to coupling portion  168  of first spider portion  164 . 
         [0045]    As illustrated in  FIG. 8 , when first and second spider portions  164 ,  170  are positioned together, the openings  166 ,  172  form a channel  176  for receiving crank assembly  100 . In one advantageous embodiment, the pre-molded first and second spider portions  164 ,  170  are put in a final mold and the crank arm  106  is then bladder molded into the spider  162 . It should be noted that the spider  162  constrains the crank arm  106  where it passes through the channel  176  for form the molded unitary structure as illustrated in  FIG. 9 . 
         [0046]      FIG. 10  illustrates the molded unitary structure including the crank assembly  100  integrally molded with the spider  162 . As seen in  FIG. 9 , the molded spider  162  is provided with a hollow interior space  172  still further reducing the overall weight of the structure. 
         [0047]    Referring now to  FIG. 11 , a partial view of the spider  162  is illustrated including an outer surface  174  having an outer circumference  176  and a raised portion  178  having an inner circumference  180  that is smaller than outer circumference  176 . Pads  182  are variously positioned on raised portion  178  and may, in one embodiment, comprise aluminum pads. The aluminum pads  182  may be faced, drilled and tapped so that the attached chain rings  184 ,  186  ( FIG. 13 ) may run true without depending on perfect spider flatness out of the mold. 
         [0048]      FIGS. 12 and 13  show chain rings  184 ,  186  affixed to outer circumference  176  and inner circumference  180  respectively. In this embodiment it can be seen that the chain rings  184 ,  186  have been reduced to a minimum, which greatly reduces the over all weight of the device. In one embodiment, chain rings  184 ,  186  are affixed to spider  162  by bolts, such as for example, M3 Torx bolts to take advantage of the lateral stiffness of the spider  162 . 
         [0049]    Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.