Land vehicles – Wheeled – Occupant propelled type
Patent
1986-11-19
1988-05-24
Pekar, John A.
Land vehicles
Wheeled
Occupant propelled type
B62K 1912, B62K 1902
Patent
active
047461365
DESCRIPTION:
BRIEF SUMMARY
This invention relates to bicycle frames.
A conventional bicycle frame is basically of steel or alloy tubing and consists of a saddle tube or stem and a head which are joined by a lower bar and an upper bar. The upper bar may be generally horizontal, as in a man's bicycle, in which case it is known as a cross bar, or it may be oblique and generally parallel with the lower bar, as in a lady's bicycle. The head carries a bearing for an assembly of front forks and handlebar, while rear forks are carried by the saddle stem.
My published United Kingdom patent application No. 2136745 relates to bicycle frames cast in a lightweight metal or alloy, such as magnesium or an alloy thereof.
In accordance with the invention of the above-mentioned published application, the frame has parts cast, particularly in open section, from a lightweight metal or alloy, and the open section upper and lower bars are joined by a structural bridge linking them at a location between the head and the saddle stem.
The bridge, which may be of I section, has the effect of considerably increasing the torsional stiffness of the frame, which enables the use of cast magnesium, which has comparatively low torsional stiffness when compared with the steels used for bicycle frames, for the upper and lower bars. The greatest torsional stresses are applied to the lower bar, which connects the saddle stem to the head, and therefore has to react the effort applied to the pedals and to the handlebar.
I have discovered that while the use of I or other open section for the cast frame parts, is satisfactory for most of the components, considerable advantages accrue from using a two part casting, especially for the highly stressed lower bar, so as to enable the closure of the section. Closure of the section is also advantageous for the saddle stem.
In accordance with a first aspect of the present invention, there is provided a bicycle frame including a saddle stem and a head interconnected by upper and lower bars, in which at least the saddle stem and the upper and lower bars are integrally cast in a lightweight metal or alloy, in which at least the lower bar is cast in an open section which is closed by means of a second casting secured to the open section.
As in the above-mentioned published application, the upper and lower bars are preferably joined by an integrally cast structural bridge, which may be of I section, linking them at a location between the head and the saddle stem.
The second casting is preferably secured to the open section by means of an ultra-strong adhesive, which may be stoved to complete the hardening.
In a preferred form the lower bar is cast originally in a C section, and the second casting is a complementary C section received within the original casting.
In the above mentioned published application, the saddle stem is described as being of V section, and this may also be closed by an additional casting, e.g. of a C section, to enter the wide end of the V.
In a further United Kingdom application, which is to be published under No. GB-A-2164300, the lower bar may join the saddle tube or stem at an intermediate point so that the axis of the lower bar passes substantially through the axis of the rear wheel, thus transmitting the stresses in the most satisfactory manner.
In use, a bicycle frame is subject to cyclic flexing as effort is applied to the pedals, and different sets of stresses, and their accompanying strains, occur during cornering. In order to absorb these stresses the adhesive used to join the two castings together has to meet exacting requirements, and it has been found that by providing some mechanical interlocking between the castings, the requirements of the adhesive may be reduced.
Accordingly, in accordance with a preferred form of the invention, the second casting is mechanically interlocked with the open section casting and is also secured by adhesive.
Preferably, the mechanical interlocking is provided by interengaging elements, conveniently cast-in projections and recesses on the castings, arranged at an angl
REFERENCES:
patent: 594136 (1897-11-01), Hill
patent: 4550927 (1985-11-01), Resele
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