Abstract:
A bicycle frame is provided in which the head tube, top tube and down tube are constructed as a single structural unit with the ends of the top tube and down tube left open to allow for ease of molding.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to a bicycle frame and more particularly to a bicycle frame made with a unified front end. More particularly, the invention relates to a bicycle where the head tube, down tube and top tube are molded as a single piece. Furthermore, the end of the top tube and down tube are open to provide access to the inside of the tube during molding. 
   BACKGROUND OF THE INVENTION 
   Bicycle frames typically include a number of tubes joined together at their ends to form for example a main frame loop of a head, down, top and seat tubes with tubes for chainstays and seatstays extending rearwardly from the seat tube. Many known constructions provide lug type junction members at each point of connection between the tubes such that the junction member and ends of the tubes overlap. This has the disadvantage of increasing the weight of the frame and giving rise to localized concentration of forces. 
   Other known constructions mold the entire bike frame as a monocoque construction in a single molding process. Further, other known constructions mold only parts of the frame in a semi-monocoque construction. Monocoque construction and the prior semi-monocoque constructions have the disadvantages of difficulty in execution and high costs. 
   SUMMARY OF THE INVENTION 
   To at least partially overcome these disadvantages of previously known devices, the present invention provides a bike frame wherein the down tube, head tube and top tube are constructed as a unitary element. 
   An object of the present invention is to provide a bicycle frame with improved strength and reduced weight particularly where the top tube and down tube connect to the head tube. 
   Another object of the invention is to reduce point stresses at the connection points of the top tube and down tube with the head tube. 
   Another object of the invention is to provide a bicycle frame of a construction that is designed for ease of construction. 
   In accordance with the present invention, a bicycle frame is provided in which the head tube, top tube and down tube are constructed as a single structural unit with the ends of the top tube and down tube left open to allow for ease of molding. Furthermore, the bicycle may be made of a fibre reinforced composite material. 
   The inventors of the present invention have appreciated that in use of a bicycle some of the greatest forces applied to the bicycle frame are applied where forces from the front wheel, such as jarring forces from the front wheel engaging a hole in a road way, are transferred from the fork to the head tube and hence to the top tube and down tube. To provide a separate head tube, top tube and down tube which can adequately sustain the forces applied in use requires excessive reinforcement of junctions between separately formed head, top and down tubes. By making the front sub-assembly as a unitary, integrally molded element, the strength of the sub-assembly, especially at the junction of the head tube with the top tube and the down tube can be optimized having regard to its weight and the amount of material used. Providing the front sub-assembly with each of the ends of the top tube and down tube which are spaced from the head tubes open, convenient separate access into the top tube and the down tube is provided which affords ease of access through these tubes to the interior of the head tube as is advantageous for consistent, easy, quality molding of the head tube and junction regions between the head tube and the top tube or down tube. Each of the top tube and down tube is preferably straight or substantially straight to facilitate insertion of the removable cores. 
   In one aspect, the present invention provides a bicycle frame comprising: a top tube with a front end and a rear end, a head tube with a top end and a lower end, a down tube with a front end and a rear end, a seat tube with a top end and lower end, the front end of the top tube connected to the top end of the head tube, the front end of the down tube connected to the lower end of the head tube, the top tube and down tube diverging away from each another as they extend rearwardly from the head tube, the rear end of the down tube coupled to the lower end of the seat tube, the rear end of the top tube top connected to the top end of the seat tube, the top tube, head tube, down tube and seat tube substantially forming a closed main frame loop, the frame comprises a sub assembly molded simultaneously as a single piece comprising the top tube, the head tube and the down tube with the rear end of the top tube open providing access through the top tube to the top end of the head tube and with the rear end of the down tube open providing access through the down tube to the lower end of the head tube. Such a bicycle frame may have: a pair of chainstays each with a front end and rear end, and a pair of seatstays each with a front end and rear end, the pair of chainstays includes a left chainstay and a right chainstay being on opposite sides of the central plane, and the pair of seatstays include a left seatstay and a right seatstay being on opposite sides of the central plane, the front end of the right chainstay connected to the main frame loop proximate the junction of the seat tube and the bottom tube on a right side of the central plane, the front end of each of the right seatstays connected to the seat tube on a right side sides of the central plane spaced upwardly from the front ends of the chainstays, the rear end of the right chainstay connected to the rear end of the right seat stay on the right side of the central plane rearward of the seat tube, the front end of the left chainstay connected to the main frame loop proximate the junction of the seat tube and the bottom tube on a left side of the central plane, the front end of each of the left seatstays connected to the seat tube on a left side sides of the central plane spaced upwardly from the front ends of the chainstays, the rear end of the left chainstay connected to the rear end of the left seat stay on the left side of the central plane rearward of the seat tube, the right chainstay, the right seatstay, and the seat tube substantially form a closed right rear frame loop, the left chainstay, the left seatstay, and the seat tube substantially form a closed left rear frame loop, the rear ends of the pair of chainstays adapted to support a rear wheel journalled on an axle extending therebetween normal to the central plane. 
   In a further aspect, the present invention provides a bicycle frame comprising: a top tube with a front end and a rear end, a head tube with a top end and a lower end, a down tube with a front end and a rear end, the front end of the top tube connected to the top end of the head tube, the front end of the down tube connected to the lower end of the head tube, the top tube and down tube diverging away from each another as they extend rearwardly from the head tube, a seat support member on the frame coupled to the rear end of the top tube. a pedal crank journal housing on the frame adapted to receive a pedal axle, the journal housing coupled to the rear end of the down tube, the head tube adapted to be coupled to a pivotable front fork which carries a front wheel and handlebars, the frame comprises a sub assembly molded simultaneously as a single piece comprising the top tube, the head tube and the down tube with the rear end of the top tube open providing access through the top tube to the top end of the head tube and with the rear end of the down tube open providing access through the down tube to the lower end of the head tube. 
   In still a further aspect, the present invention provides a method of manufacture of a bicycle frame outlined above comprising: molding the sub assembly, manufacturing the remainder of the elements of the frame, and assembling the sub assembly and the remainder of the elements. Such a method may contain steps: wherein the step of molding includes placing a pre-formed hollow element formed of uncured fibre reinforced composite material to form the top tube, head tube and down tube in the mold cavity, placing cores into the hollow element, constraining the hollow element between interior surface of the mold cavity and exterior surfaces of the cores. The cores placed in the hollow element maybe inflatable cores such as an air bladder, solid core with a higher coefficient of thermal expansion than materials used in the construction of the mold, such as silicon or rubber, or self expanding materials such as expanding foam. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages of the invention will become apparent upon reading the following description together with the accompanying drawings in which: 
       FIG. 1  is a side view of a prior art bicycle; 
       FIG. 2  is a perspective right side view of a bicycle frame in accordance with a first embodiment of the invention; 
       FIG. 3  is a right side view of the bicycle frame of  FIG. 2 ; 
       FIG. 4  is a front end view of the bicycle frame of  FIG. 2 ; 
       FIG. 5  is an exploded side view of the bicycle frame of  FIG. 2 ; 
       FIG. 6  is a cross-sectional view of the front sub-assembly shown in  FIG. 5  along a central plane; 
       FIG. 7  is a cross-section view of the bicycle frame of  FIG. 2  similar to that in  FIG. 6  but showing the front sub-assembly as received in a mold during a molding process; 
       FIG. 8  is a cross-section view of the bicycle frame of  FIG. 2  similar to that in  FIG. 6  but showing the front subassembly as received in a mold during a second molding process 
       FIG. 9  is a cross-section view of the bicycle frame of  FIG. 2  similar to that in  FIG. 6  but showing the front sub-assembly as received in a mold during a third molding process 
       FIG. 10  is a cross-section view of the bicycle frame of  FIG. 2  similar to that in FIG.  6  but showing the front sub-assembly as received in a mold during a fourth molding process 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a side view of a prior art bicycle  12 . The bicycle  12  has a frame  10  comprising a head tube  20 , a top tube  30 , a down tube  40  and a seat tube  50 . Each of these tubes is connected end-to-end to one another and form substantially a closed main frame loop  14 . A seat post  73  is supported by an upper end  51  of the seat tube  50  carrying a seat  75 . 
   A fork  77  is rotatably coupled to the head tube  20  to extend through the head tube carrying at an upper end the handlebars. The fork  77  splits into a pair of arms supporting the front wheel  78 . A seatstay  65  and a chainstay  67  extend rearwardly from the seat tube  50  and support a rear wheel  79  journalled on a rear axle  83  extending between the rear ends  84  of the chainstays  67 . Two pedals  80  are carried on respective pedal crank arms  45  secured to a pedal axle  46  journalled in a pedal crank journal housing (not shown in  FIG. 1 ) secured proximate the junction of seat tube  50  and down tube  40 . 
   Through all of the drawings the same reference numbers are used to refer to similar elements. 
   The bicycle frame  10  in accordance with a first embodiment of the invention is shown in  FIGS. 2 to 5  and includes a head tube  20 , a top tube  30 , a down tube  40 , a seat tube  30 , a right hand chainstay  67 , a left hand chainstay  68 , a right hand seat stay  65  and a left hand seatstay  66 . The head tube  20  has an upper end  21  and a lower end  22 . The top tube  30  has a front end  31  and a rear end  32 . The down tube has a front end  41  and a rear end  42 . The seat tube  50  has an upper end  51  and a lower end  57 . The seat tube has an upper tubular portion  52  which has the upper end  51  and a lower end  53 ; and a lower tubular portion  56  which has an upper end  55  and the lower end  57 . 
   The front end  31  of the top tube  30  is the top end  21  of the head tube  20 . The front end  41  of the down tube  40  is connected to the lower end  22  of the head tube  20 . The top tube  30  and down tube  40  diverge away from each other as they extend rearwardly from the head tube  20 . The rear end  42  of the down tube  40  is coupled to the lower end  57  of the seat tube  50 . The rear end  32  of the top tube  30  is connected to the top end  51  of the seat tube  51 . 
   The right hand chainstay  67  has a front end  85  and a rear end  84 . The left hand chainstay  68  has a front end  87  and a rear end  86 . The right hand seatstay has an upper end  61  and a lower end  62 . The left hand seatstay  66  has an upper end  63  and a lower end  62 . The front end  85  ofthe right chainstay  67  is connected to the lower end  57  of the seat tube  50  on a right side thereof. The upper end  61  of the right seatstay  65  is connected to the seat stay  50  spaced upwardly from the front end  85  of the right chainstay  67 . The rear end  84  of the right chainstay  67  is connected to the lower end  62  of the right seatstay  65 . 
   The front end  87  of the left chainstay  68  is connected to the lower end  57  of the seat tube  50  on a left side thereof. The upper end  63  of the left seatstay  66  is connected to the seat stay  50  spaced upwardly from the front end  87  of the left chainstay  68 . The rear end  86  of the left chainstay  68  is connected to the lower end  64  of the left seatstay  66 . 
   Proximate the juncture between the lower end  57  of the seat tube  50  and the rear end  42  of the down tube  40 , a pedal crank journal housing  27  is provided adapted to journal an axle such as the axle  46  for the pedals shown in  FIG. 1 . 
   The rear ends  84  and  86  of the chainstays  67  and  68  each carry an axle slotway  71  and  72  adapted to receive a rear axle such as the axle  83  for the rear wheel  79  shown in  FIG. 1 . 
   The head tube  20 , top tube  30 , down tube  40  and seat tube  50  form a closed main frame loop indicated as  14  which are disposed to lie with each of its tubes in a flat central plane  90  as seen in  FIG. 4 . Each of the head tube  20 , top tube  30 , down tube  40  and seat tube  50  are elongate members disposed about their own longitudinal axis. The longitudinal axis of each of the head tube  20 , top tube  30 , down tube  40  and seat tube  50  lie in the same flat central plane  90 . The right chainstay  67 , right seatstay  65  and the seat tube  50  between the front end of the right chainstay  67  and the upper end of the right seatstay  65  form a closed right rear frame loop indicated as  15 . The left chainstay  68 , left seatstay  66  and the seat tube  50  between the front end of the left chainstay  68  and the upper end of the left seatstay  66  form a closed left rear frame loop indicated as  16 . The pair of seatstays is symmetrical of each other about the central plane  92 . The pair of chainstays is also symmetrical about each other about the central plane  92 . 
   In a further alternate construction, the seatstays are not symmetrical about the central plane  92  but are on opposite sides of the central plane  92 . Furthermore, the chainstays are not symmetrical about the central plane  92  but are on opposite sides of the central plane. 
     FIG. 5  is an exploded view of the bicycle frame of  FIG. 2  notably showing that the head tube  20 , top tube  30  and down tube  40  comprise a unitary element on front sub-assembly  13 . The other components of the frame show a pedal crank junction member  29  and the chainstays  67 ,  68  formed in a unitary construction. The pedal crank junction member  29  carries the pedal crank journal housing  27  and two tenons  204  and  205  adapted to receive the free ends of each of the down tube and seat tube which are to couple thereto. As shown the top tube and seatstays are adapted to connect with the seat tube and are held in place by a wrap construction. 
   In an alternate embodiment, the pedal crank junction member  29  is not formed in a unitary construction and has tenons adapted to receive the free ends of each of the down tube, seat tube and chainstays. Furthermore, pedal crank junction member  29  could be adapted to receive the free ends of each of the down tube, seat tube and chainstays where each can be connected by anyone of tenons, lugs or wrap construction. 
   In an alternate embodiment, the seat junction member has three sockets adapted to receive the free ends of each of the top tube, seat tube and seatstays which are to couple thereto. The seat junction member may also be adapted to receive each of the top tube, seat tube and seatstays to be connected by use of tenons, lugs or a wrap construction. 
   The bicycle frame  10  is made by first manufacturing the front sub-assembly  13  as a unitary element and then coupling the sub-assembly  13  to the remainder of the components of the frame. 
   The front sub-assembly  13  may be connected to the remainder of the components of the bicycle frame by any construction desired including lug construction with the ends of the tubes fitted over or inside the lugs, in a wrap construction in which ends of the tubes are abutted and are wrapped with reinforcing materials or by use of tenons. 
   Any two or more of the other components whether as shown in  FIG. 5  or otherwise than the front sub-assembly  13  may be made as sub-assemblies or be assembled in advance. 
     FIG. 6  is a cross section along the central plane through the front sub-assembly  13 , that is, through the top tube, head tube and down tube. Each of the tubes comprise a hollow tubular member extending about their own longitudinal axis with the longitudinal axis of  93 ,  92  and  94 , respectively, each of the top tube  30 , head tube  20  and down tube  40  lying in the flat longitudinal central plane  90 . Each of these tubular members has a circumferential wall  103 ,  102  and  104 , respectively, about their longitudinal axis which circumferential wall is preferably generally symmetrical about the central plane  90 . The head tube  20  is shown as having openings  110  and  112  at each of its end about its axis  92  as may be useful with many arrangements for coupling to a fork  77  such as in  FIG. 1 , but these openings are not necessary. 
   In the sub-assembly  13 , the top tube  30  is open at its rear end  32  as an opening  114  and the down tube  40  is open at its rear end  42  as an opening  116 . 
     FIG. 7  shows the front sub-assembly  13  in the process of being molded. The sub-assembly  13  is molded in a mold  300  from uncured fibre reinforced composite material such as graphite epoxy by curing the resin by the application of heat when constraining the resin and fibre in the mold. The mold  300  has a mold cavity with an interior surface  301  to engage the outside surfaces of the sub-assembly  13  and with inflatable cores  304 ,  305  removably located inside the hollow interior of the sub-assembly  13  to engage the inside surfaces of the sub-assembly  13 . 
   As seen in  FIG. 7 , one inflatable core  304  is located inside the top tube  30  extending longitudinally inside the top tube  30  from its open end  114  to opening  112 . With the top tube  30  being generally straight insertion, position and removal of the core  304  is readily permitted which is particularly advantageous to provide for ease of and advantageous location of the core  304  in the junction between the top tube and the head tube. One inflatable core  305  in located inside the down tube  40  extending longitudinally inside the down tube  40  from its open end  116  to opening  110 . With the down tube  40  being generally straight insertion, positioning and removal of the core  305  is readily permitted which is particularly advantageous to provide for ease of and advantageous location of the core  305  in the junction between the down tube and the head tube. 
   The bicycle frame may be made by molding the front sub-assembly  13  as a unitary element, manufacturing the remainder of the components of the frame, and assembling the front sub-assembly  13  and the remainder of the elements. The sub-assembly  13  is preferably made by placing a preformed hollow element formed of uncured fibre reinforced composite material such as graphite epoxy to form the top tube, head tube and down tube in the mold cavity, placing the inflatable cores into the hollow element, constraining the hollow element between the interior surface of the wall cavity and the exterior surface of the inflatable cores while curing the resin by application of heat. 
   In an alternative configuration, a solid core may be used instead of the inflatable core The solid core is manufactured from a material with a higher coefficient of thermal expansion than the materials used in construction of the mold. Examples of such are silicon and rubber. 
   In another configuration, a core manufactured from a material which self expands, such as expanding foam, is used instead of the inflatable cores. 
   The cores themselves are designed to compact the frame material in the mold. Through the expansion of the cores, the cores compact the uncured fibre reinforced composite material against the interior surface of the cavity of the mold. 
   By manufacturing the sub-assembly with two open ends at the open ends of the top tube and down tube, increased compaction and increased control of the position of the layers of material can be obtained. The open ends provide better access for easier and more simplified routing of cores which further creates a stronger frame sub-assembly. 
   The open ends further reduce the associated costs of manufacturing by not only creating a simplified process but by also reducing the size and costs of the associated tools. 
     FIG. 8  illustrates an alternate molding method where the mold  300  has a mold cavity with an interior surface  301  to engage the outside surfaces of the sub-assembly  13  and three cores  310 ,  312  and  314  removably located inside the hollow interior of the sub-assembly  13  to engage the inside surfaces of the sub-assembly. As seen in  FIG. 8 , one core  310  is located inside the head tube  20  extending from open end  110  to open end  112 . In this embodiment the core  310  is substantially straight. One core  312  is located in the top tube and core  314  is located in the down tube. 
     FIG. 9  illustrates an alternate molding method where the mold  300  has a mold cavity with an interior surface  301  to engage the outside surfaces of the sub-assembly  13  and two cores  322  and  324  removably located inside the hollow interior of the sub-assembly  13  to engage the inside surfaces of the sub-assembly. Further, as seen in  FIG. 9 , one core  320  is located inside the head tube  20  extending from open end  110  to open end  112 . In this embodiment the core  320  extends into the front end  31  of the top tube  30  and into the front end  41  of the down tube  40 . One core  312  is located in the top tube and core  314  is located in the down tube. 
     FIG. 9  illustrates an alternate molding method where the mold  300  has a mold cavity with an interior surface  301  to engage the outside surfaces of the sub-assembly  13  and three cores  330 ,  332  and  334  removably located inside the hollow interior of the sub-assembly  13  to engage the inside surfaces of the sub-assembly. As seen in  FIG. 9 , one core  320  is located inside the head tube  20  extending from open end  110  to open end  112 . In this embodiment the core  320  extends into the front end  31  of the top tube  30  and into the front end  41  of the down tube  40 . One core  312  is located in the top tube and core  314  is located in the down tube. 
   While the invention will be described in conjunction with the illustrated embodiments, it is understood that it is not intended to limit the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the following claims.