Field of the Invention

The invention relates to bike frames, improvements to bike frames and components of bike frames; and its method of manufacture.

Background to the Invention and Prior Art known to the Applicant

The applicant's own prior bike frames are the closest known art. In a prior bike frame version the seat beam is split into two tubes along the entire portion between the top beam and the bottom bracket shell. The junction between the bottom bracket shell and the seat beam is provided on the uppermost portion of the bottom bracket shell only. Similarly, the diagonal down beam comprises two tubes which merge into a single tube towards the uppermost portion of the diagonal beam whilst splitting out into two distinct beams. The separation between the beams increases gradually until their junction with the bottom bracket shell which occurs adjacent to the lower portions of the seat beams on the uppermost portion of the bottom bracket shell. Furthermore, the various frame components are formed separately and then assembled in a subsequent bonding process.

A number of advances have been developed in order to improve the bike frame in at least some of the following areas: • resistance to twisting and bending in the diagonal down beam;

• improvements in distribution of concentrations of stress and strain in the bottom bracket shell region;

· improvements to the resistance to twisting, the overall strength and a reduction of stress and strains in the area between the seat beam and the bottom bracket shell;

• simplification of frame manufacture and assembly; and

• an achievable reduction in the weight of the bike frame.

Summary of the Invention

In a first broad independent aspect, the invention provides a bike frame comprising a top beam; a head beam; two diagonal down beams; a seat beam; and a bottom bracket shell; said top beam extending between the seat beam and the head beam; and said diagonal down beams extending between said head beam and said bottom bracket shell; said bike frame further comprising a pair of seat stays and a pair of chain stays; said pair of seat stays extending rearwardly from said seat beam and said pair of chain stays extending rearwardly from said bottom bracket shell; wherein said frame preferably comprises composite sheet material of fibre and resin; and wherein each one of said pair of diagonal down beams is preferably hollow and preferably incorporates an innermost wall of composite sheet material which is preferably substantially upright and parallel to an innermost wall of composite sheet material of its neighbouring beam.

Preferably, said pair of diagonal down beams are substantially parallel to each other along substantially their entire length between said head beam and said bottom bracket shell. This configuration is particularly advantageous in terms of improving the stiffness of the diagonal down beams. It also provides greater resistance to bending which allows the beams to be potentially reduced in size for particular bike frame applications. This dramatically increases the effective area of the bike frame in order to improve its mechanical properties. It also reduces unwanted distortions of the bike frame as a rider applies pedalling forces onto the individual pedals. In certain embodiments, the frame has reduced wind resistance and therefore improved aerodynamic properties.

Preferably, said frame is formed substantially entirely of carbon fibre sheets and resin material. Preferably, said carbon fibre sheets and said resin are bonded in a single bonding process to form an integral frame with all the components of the bike as defined in the first broad aspect joined together in a single bonding process.

In a further subsidiary aspect, each one of said diagonal down beams incorporates an outermost wall which is outwardly bowed. Preferably, said inner walls and said outermost walls are formed from a single sheet of fibre and resin composite. This configuration is also particularly advantageous in terms of the reduction of the concentration of stress and strains and consequential prevention of failure or fracture.

It also improves the resistance of the individual beams to unwarranted twisting.

In a further subsidiary aspect, each one of said diagonal down beams is substantially D- shaped in cross-section. Preferably, said D is formed from a single sheet of fibre and resin composite. This configuration is particularly advantageous in terms of improving the overall mechanical properties as parallel upright walls provide improvements to the toughness of the diagonal beams. Furthermore, these may act as a pair in order to counterbalance the effects of individual pedal actions. In a further subsidiary aspect, each one of said diagonal down beams incorporates an inner projecting ear with an upper attachment surface. Preferably, the uppermost surface of the ear is integral with the upper most surface of the diagonal down beams so that in a preferred embodiment, the carbon fibre matting provided in the uppermost surface of the diagonal down beam extends directly and without any break in the matting into the ear. This configuration is particularly advantageous in providing an upper location for attachment whilst maintaining the mechanical advantages of the overall structure of the diagonal down beams. In a further subsidiary aspect, said inner projecting ears are offset relative to one another. This allows the limited space to be used to maximum effect whilst providing the advantage of surfaces for attachment of various devices. In a further subsidiary aspect, said pair of chain stays engage said bottom bracket shell and surround said bracket shell and continue into said pair of beams; whereby the pair of chain stays, the bracket shell engagement and the pair of beams incorporate two portions disposed in parallel. This allows the dual aspect of the chain stays to be carried through to the bottom bracket shell region and into the diagonal down beams.

Optionally, a common sheet of composite material may be used which extends from the diagonal down beams to the chain stays via the bracket shell for each opposite parts of the frame. Preferably, the diagonal down beams, the bottom bracket shell region and the chain stays may be formed of an integral piece of material. This then improves the distribution of stress and strain throughout the frame.

In a further subsidiary aspect, said seat stays engage said seat beam at a location offset relative to the uppermost portion of said seat beam. This further optimises the construction of the frame. In a further subsidiary aspect, said seat stays are outwardly bowed. This configuration further improves the tensile strength resistance of the seat stays.

In a further subsidiary aspect, said seat stays increase in width along their length in the direction of the rear wheel location. This configuration improves the resistance to failure in the rear wheel engaging portion of the bike frame.

In a further subsidiary aspect, said top beam intersects said seat beam at the uppermost portion of said seat beam. This configuration allows the top beam to sit flush on the top of the uppermost portion of the seat beam.

In a further subsidiary aspect, the seat beam comprises, underneath said seat stays, a first portion which is formed by a single beam and a second portion which bifurcates into two substantially parallel beams prior to joining said bottom bracket shell. This configuration further reduces the concentration of stress and strain in the bracket shell area. It also allows the diagonal down beams, the bifurcated portions of the seat beam and the chain stays to be formed of two separate portions. This provides improved resistance to twisting, a reduction of stress and strains and a greater resistance to bending which may allow embodiments of the invention to be reduced in dimensions and therefore to reduce the effective weight of the bike frame.

In a further subsidiary aspect, the beams of said second portion incorporate inner walls which are substantially parallel to each other. Preferably, said inner walls are formed of a composite sheet of fibre and resin. Optionally, said inner walls are formed from a single sheet of composite material. This configuration is particularly advantageous in order to improve the strength of the oppositely disposed portions of the bike frame.

In a further subsidiary aspect, said beams of said second portion incorporate outer walls which diverge from one another from top to bottom; whereby said beams increase in width. Optionally, said outer walls are formed from a single sheet of composite material. This configuration is particularly advantageous in terms of strengthening the lowermost portion of the seat beams whilst at the same time joining the lower portions of the diagonal down beams and the chain stays in order to reinforce the dual configuration of the bike frame.

In a further subsidiary aspect, said second portion forms a recess which is bounded by a rounded portion at the uppermost region of said recess. Optionally, said inner walls and said rounded portion are formed from a single sheet of composite material. This reduces the concentration of stresses and strains which may otherwise arise in this region.

In a further broad independent aspect, the invention provides a bike frame comprising a top beam; a head beam; two diagonal down beams; a seat beam; and a bottom bracket shell; said top beam extending between the seat beam and the head beam; and said diagonal down beams extending between said head beam and said bottom bracket shell; said bike frame further comprising a pair of seat stays and a pair of chain stays; said pair of seat stays extending rearwardly from said seat beam and said pair of chain stays extending rearwardly from said bottom bracket shell; wherein said frame comprises preferably sheet material of fibre and resin; and wherein said seat beam comprises, underneath said seat stays, a first portion which is formed by a single beam and a second portion which bifurcates into two substantially parallel beams prior to joining said bottom bracket shell. Said parallel beams preferably incorporate inner walls of composite sheet material. This configuration is particularly advantageous in terms of providing a dual beam configuration in each direction away from the bottom bracket shell.

In a further broad independent aspect, the invention provides a bike frame comprising a top beam; a head beam; two diagonal down beams; a seat beam; and a bottom bracket shell; said top beam extending between the seat beam and the head beam; and said diagonal down beams extending between said head beam and said bottom bracket shell; said bike frame further comprising a pair of seat stays and a pair of chain stays; said pair of seat stays extending rearwardly from said seat beam and said pair of chain stays extending rearwardly from said bottom bracket shell; wherein each one of said pair of diagonal down beams incorporates an innermost wall of composite sheet material which is substantially upright and parallel to an innermost wall of its neighbouring beam; or wherein said seat beam comprises, underneath said seat stays, a first portion which is formed by a single beam and a second portion which bifurcates into two substantially parallel beams prior to joining said bottom bracket shell.

Brief Description of the Figures Figure 1 shows a perspective view of the bike frame from beneath the frame.

Figure 2 shows a perspective top view of the bike frame. Figure 3 shows a front elevation of the bike frame.

Figure 4 shows a rear elevation of the bike frame. Figure 5 shows a left-hand elevation of the bike frame. Figure 6 shows a right-hand elevation of the bike frame. Figure 7 shows a top view of the bike frame. Figure 8 shows a bottom view of the bike frame.

Figure 9 shows a cross-sectional view along line C - C. Figure 10 shows a cross-sectional view along line E - E.

Figure 1 1 shows a cross-sectional view along line D - D.

Detailed Description of the Figures

The figures show a bike frame generally referenced 1 with a top beam 2 and a head beam 3. The bike frame further comprises two diagonal down beams 5 and 6 extending between the head beam 3 and the bottom bracket shell 7. A seat beam 8 is provided between the top beam 2 and the bottom bracket shell 7. A pair of seat stays 9 and 10 extend rearwardly from the seat beam between the seat beam and a pair of chain stays 1 1 and 12.

Diagonal down beams 5 and 6 as seen for example in Figure 1 are substantially parallel to each other along substantially their entire length between the head beam 3 and the bottom bracket shell 7. Whilst this is not apparent from the figures, the various beams of the bike frame are preferably hollow. These are also preferably primarily of composite fibre and resin material. These may be formed by moulding plastics material in order to form the bike frame shown in the figures as a single piece. Each one of the diagonal down beams incorporates an innermost wall such as wall 13 which is substantially upright provided the bike frame is in the upright position. The innermost wall may also be parallel to the innermost wall of a neighbouring beam. Inner wall 13 consists preferably of a sheet of carbon fibre and resin. The carbon fibres are preferably woven as shown in magnified view 2A. The fibres are preferably disposed in a criss-cross pattern with a first number of fibres extending along the length of the diagonal down beams and a second number of fibres being substantially orthogonal to the first number. This configuration is particularly advantageous in various modes of operation. Optionally, a single sheet of carbon fibre and resin extends along the entire lengths of the down beam and the single sheet is closed or bonded to define the entire circumference of the down beam which is of D shape in cross-section. Figure 2 shows for example the inter-relationship between innermost walls 13 and 14. A gap is formed between the beams in order to accommodate some degree of movement as individual beams become more or less loaded during the various loading conditions during the stages of a cycle. Both internal walls of respective down beam are preferably of carbon fibre and resin composite material. The composite includes preferably a matting of criss-crossing fibres.

Figure 9 shows the D-shaped diagonal down beams in cross-section. As can be seen the innermost walls 13 and 14 are substantially parallel yet spaced apart. The upper portion 15 of the beam slopes only very gradually downwards until it reaches a rounded corner 16. After rounded corner 16 there is provided a downwardly extending portion 17 with a rounded lower corner 18 located relatively inwards when compared to the upper corner 16. Lower rounded corner 18 joins the lower portion of wall 14 with a rounded edge. Rounded corners 16 and 18 are preferably formed by a continuous (junction free) portion of carbon fibre matting in order to reduce stresses and strain concentrations in these components.

Each one of the diagonal down beams 13 and 14 incorporates an inner projecting ear 19 and 20 which are integrally formed with their respective beam. These in effect extend the upper surface 15 of the diagonal down beams. In preferred embodiments, the upper surface of the ears and upper surface of down beam 6 is formed by a single continuous (junction free) portion of carbon fibre matting in order to reduce stresses and strain concentrations in these components. Ears 19 and 20 incorporate a recess such as recesses 21 and 22 which allow the attachment of an object such as a water bottle holder. Recesses 21 and 22 may incorporate a threaded member to facilitate the attachment. The projecting ear is tapered downwards so as to decrease in width. The downward portions of the ears are formed from a junction free and continuous matting member which is integral with or simply a continuation of the inner walls 13 and 14. The inner projecting ears 19 and 20 are preferably offset relative to one another.

As shown in Figure 1 the pair of chain stays 11 and 12 engage the bottom bracket shell and tend to surround the bracket shell. This configuration particularly strengthens the junction between the bracket shell and the other components of the bike frame. The pair of chain stays form in effect a continuation of the diagonal down beams 5 and 6. This is particularly advantageous in embodiments where a common portion of carbon fibre sheet and resin is employed for the combination of the down beam, the bracket shell's circular lips and the chain stays of a particular side of the dual aspect bike frame. As seen in Figure 4 the chain stays 1 1 and 12 protrude from bottom bracket shell 7. Circular lips 23 and 24 protrude around the bottom bracket shell 7.

Seat beam 8 extends below seat stays 9 and 10 as a single beam in a first portion. In a second portion the seat beam bifurcates into two substantially parallel beams 25 and 26. Beams 25 and 26 engage the lower portions of their respective parts of the dual arrangement of diagonal down beams and the dual arrangement of chain stays. Inner walls 27 and 28 of the beams 26 and 25 are substantially parallel to each other and join together towards an upper portion in a rounded portion. Preferably, the inner walls 27 and 28 form part of a common sheet of carbon fibre/resin matting. The outer walls

29 and 30 progressively diverge from one another from top to bottom in order to increase the beams' width. Figure 10 shows the cross-section of the bifurcated beams 25 and 26. As can be seen the inner walls 27 and 28 are substantially parallel.

Furthermore, each one of the outer walls is bowed with a first surface 31 extending towards a rounded corner, followed by a substantially flat surface 32 before reaching a second rounded corner 33 and a further tapered portion 34.

Figure 1 1 shows a view of the bifurcated beam along axis D - D. This view illustrates the substantially parallel surfaces 27 and 28 in conjunction with the diverging outer surfaces 29 and 30. The protruding portions 23 and 24 which surround the bottom bracket shell 7 are also apparent. In preferred embodiments, the bike frame is formed as a single piece in a single curing step in order to avoid having to separately bond various components of the frame together in a subsequent assembly stage.