Note: Descriptions are shown in the official language in which they were submitted.
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BICYCLE FRAME CONSTRUCTION
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
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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
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reinforcement ofjunctions 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
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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
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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 therinal
expansion than
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materials used in the construction of the mold, such as silicon or rubber, or
self expanding
materials such as expanding foam.
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, 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 further 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.
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:.
In a further aspect, the present invention provides
Figure 1 is a side view of a prior art bicycle;
Figure 2 is a perspective right side view of a bicycle frame in accordance
with a first
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embodiment of the invention;
Figure 3 is a right side view of the bicycle frame of Figure 2;
Figure 4 is a front end view of the bicycle frame of Figure 2;
Figure 5 is an exploded side view of the bicycle frame of Figure 2; -
Figure 6 is a cross-sectional view of the front sub-assembly shown in Figure 5
along a
central plane;
Figure 7 is a cross-section view of the bicycle frame of Figure 2 similar to
that in Figure 6
but showing the front sub-assembly as received in a mold during a molding
process;
Figure 8 is a cross-section view of the bicycle frame of Figure 2 similar to
that in Figure 6
but showing the front sub-assembly as received in a mold during a second
molding process
. Figure 9 is a cross-section view of the bicycle frame of Figure 2 similar to
that in Figure 6
but showing the front sub-assembly as received in a mold during a third
molding process
Figure 10 is a cross-section view of the bicycle frame of Figure 2 similar to
that in Figure
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6 but showing the front sub-assembly as received in a mold during a fourth
molding process
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 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 Figure 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
Figures 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.
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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 of the
right chainstay 67 is connected to the lower end 57 of the seat tube 50 on a
right side thereo~ 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
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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 Figure 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 Figure 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 Figure 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.
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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.
Figure 5 is an exploded view of the bicycle frame of Figure 2 notably showing
that the
head tube 20, top tube 30 and down tube 40 comprise a unitary element on front
sub-assemblv 13.
The other components of the frame show a pedal crank junction member 29and 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 fonned
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 anvone
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.
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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 Figure 5 or
otherwise than
the front sub-assembly 13 may be made as sub-assemblies or be assembled in
advance.
Figure 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 Figure 1, but these openings are not necessary.
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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.
Figure 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 Figure 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
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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.
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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.
Figure 8 illustrates an alternate molding method where the mold 300 has a mold
cavitv
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 Figure 8, one core 310 is
located inside the
head tube 20 extending from open end I 10 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.
Figure 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 Figure 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.
Figure 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
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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 Figure 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.
