Note: Descriptions are shown in the official language in which they were submitted.
CA 02357598 2001-09-20
TITLE OF THE INVENTION
AERODYNAMIC BICYCLE FRAME
FIELD OF THE INVENTION
The invention relates to a bicycle frame comprising a partially curved seat
S tube, which has a constant width at the trailing edge when viewed from the
rear, and
which covers a substantial portion of the front and upper portion of the rear
wheel, for
the purpose of aerodynamically shielding the rear wheel.
In conjunction with this, the invention also incorporates an improved rear
brake area that integrates the seat stays into the frame in such a manner to
improve
the aerodynamics of this area and includes a brake plate to which the rear
brake is
attached prior to its mounting to the frame. This plate permits attachment of
the brake
to the frame without compromising the aerodynamics, stiffness, or strength of
the
frame. The present invention further improves the aerodynamics by integrating
the
rear wheel with the frame through rearward facing adjustable dropouts that
allow
proper wheel to seat tube spacing, and a recessed concave trailing edge to the
lower
curved seat tube. Finally, the invention enhances the stability of the bike by
moving
the center of pressure rearward.
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BACKGROUND OF THE INVENTION
Prior art seat tubes are either straight or only have a recessed curved
section and, as such, do not fully shield the rear wheel. Additionally, prior
art seat
tubes with a curved section cut iryto a predominantly straight seat tube (as
shown in
figure 1 (a) and 'I (b)) do not have a trailing edge with a constant width as
viewed from
the rear (see figure 2): the middle is wider, and the top and bottom narrower.
As well, the prior art seat tube does not extend much over the upper
portion of the rear wheel. Further, it is the upper portion of the rear wheel
where
aerodynamic shielding is the most useful. By not covering as much of the upper
portion of the rear wheel, current bicycle frames do not achieve optimal
aerodynamic
shielding in this area.
Conventional bicycle frames, as illustrated for example 1n Fig. 12
generally have a one-piece straight seat tube. Bicycle frames with a one-piece
seat
tube having a curved portion are also known in the art, as 111ustrated for
example in
United States patents No. 5,957,473 to Lawwill and No. 4,900,050 to Bishop et
al.
If has been found advantageous to establish an aerodynamic shielding
on the rear wheel of a bicycle, especially on the upper portion. Attempts to
achieve
this goal have been made by constructing bicycle .frames with a straight seat
tube
having a recessed curved section. Unfortunately, this design does not allow
for a full
shielding of the upper porkion of the rear wheel.
Trimble in United States patent Nos. Re. 33,295; 4,941,674; and
4,982,975 discloses a bicycle frame made of comp4site material. The frame
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2a
comprises a seat tube having a curved section which is cut into a one-piece
straight
seat tube. ~ Such seat tubs is also illustrated in Figs. 1(a) and 1(b). The
resulted
design of the bicycle frame according to Trimble is that of a traditional
'double
diamond" frame, which has two open triangles with a common side. Typically,
the
curved section of such designs of seat tube does not allow for a full coverage
of the
upper portion of the rear wheel and thus an optimal aerodynamic shi8lding is
not
achieved.
Therefore, there remains a need fnr a bicycle frame allowing for a
maaomum aerodynamic shielding and reduced aerodynamic drag. There is also a
need for an aerodynamic frame having a brake which is temovably attached
therefrom
without reducing the aerodynamic efficiency of the frame, or its strength or
stiffness.
Indeed, in frames with recessed curved cutouts it becomes very difficult to
attach a
brake of conventional design because access to the rear of the brake is
required to
affix it. A large gap must therefore be left around the back of the brake for
access to
attach and tighten the brake to the frame. This large gap reduces the
aerodynamic
efficiency of the frame. In outer designs, access holes are provided in the
frame for
attachment of the brake thereto. This n3sults in adding weight as well as
costs, and
the stiffness and structural Integrity of the frame are reduced.
SUMMARY OF THE INVENTION
t3y using a seat tube of constant width at the trailing edge of the curved
section, greater aerodynamic efficiency is achieved through more effective
aero-
dynamic shielding. As well, by employing a larger curve in the seat tube, a
greater
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2b
portion of the rearwheel is aerodynamically shielded. This includes the upper
portion
of the rear wheel, where the greatest aerodynamic benefits are achieved.
It is an object of the present invention to provide a bicycle frame allowing
for an optional aerodynamic shielding on the upper portion of the rear wheel.
It is also an object of the invention to provide an aerodynamic bicycle
frame allowing for a reduced aerodynamic drag.
It is yet another object ofthe invention to provide an aerodynamic bicycle
frame which integrates a brake, without reducing the aerodynamic efficiency of
the
frame.
In accordance with the invention, there is provided a bicycle frame
comprising a bicycle frame comprising: a first tube; a second tube extending
transversely from an upper region of the first tube, in a direction; a third
tube extending
transversely and downwardly from a lower region of the first tube, and towards
the
same direction as the second tube; and a two-part tube joining the respective
ends of
the second and third tubes, the two-part tube having a straight upper part and
a
curved lower part, the straight upper part being substantially verkical and
the curved
lower part being curved longitudinally towards the first tube such as to
confomn to the
curvature of a bicycle wheel.
In accordance with a preferred embodiment, the two-part tube can be
aerodynamic shaped and its upper part can be adapted to receive therein a post
member.
The bicycle frame according to the invention may comprise a first set of
tubes extending from the two-part tube at a junction between the upper and the
lower
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~C
parts. The first set of tubes are attached at their other ends to dropout
means located
at the center of the wheel. in addition, the frame may also comprise a second
set of
tubes extending from a lower end of the two-part tube and attached at their
other ends
to dropout means located at the center of the wheel. Preferably, the second
set of
tubes may be attached at a junction between the upper and the lower parts.
In accordance with a preferred embodiment, the lower part can be
curved in both horizontal and Vertical planes in arderto conform to the
curvature ofthe
bicycle wheel.
A prefer-ed embodiment of the bicycle frame can include brake means
which is removably attached to the two-part tube at a junction between the
upper and
the lower parts. More preferably, the brake means can include a brake mounted
to a
plate.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other advantages of the invention will become apparent upon
reading the following detailed description and upon referring to the drawings
In which:
FIGURE 1 (a ~ b) is a side view of a prior art aerodynamic bicycle frames;
FIGURE 2 is a rear view of the seat tube of a prior art aerodynamic
bicycle frame;
FIGURE 3 is a rear view of the seat tube of the aerodynamic bicycle frame
according to the invention;
FIGURE 4 is a cross section of the lower section df the seat tube of the
aerodynamic bicycle frame according to the invention;
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FIGURE 5 is a side view of the aerodynamic bicycle frame according to
the invention, showing the seat post - seat stay junction;
FIGURES 6 and 7 are opposite side views of the aerodynamic bicycle
frame according to the invention;
FIGURE 8 is a front view of the aerodynamic bicycle frame according to
the invention;
FIGURE 9 is a rear view of the aerodynamic bicycle frame according to
invention;
FIGURE 10 is a top view of the aerodynamic bicyde frame according to
invention;
FIGURE 11 is a bottom view of the aerodynamic bicycle frame according
to invention;
FIGURE 12 is a side view of a prior art bicycle showing the various parts
of the whale bicycle; and
FIGURE 13 is partial side view of the bicyde according to the invention,
showing the dose proximity of the tire to the trailing edge of the lower
curved portion
of the seat tube.
While the invention will be described in conjunction with illustrated
embodiments, it will be 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 inGuded urithin the spirit and scope of the
invention as
defined by the appended claims.
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4
DETAILED DESCRIPTION aF THE PREFERRED EMBODIMENTS
In the following description, similar features in the drawings have been
given similar reference numerals.
Features of the bicycle frame according to this invention are illustrated in
Figs. 3 through 11 and 13. Referring to Fig. 6, the bicycle frame 9 0
comprises a head
tube 20, a top tube 30, a down tube 40 and a seat tube 50. The head tube 20
extends
obliquely between its upper end 21 and its lower end 22, and forms an angle of
about
0 to 30 degrees with the vertical. In a preferred .embodiment of the
invention, this
angle is about 20 degrees. The top tube 30 is attached to the upper part 21 of
the
head tube at its first end 31 and extends substantially horizontaAy therefrom.
The top
tube may form an angle of about 0 to 15 degrees with the horizontal and can be
sloped either upwardly or downwardly, in a preferred embodiment of the
invention,
this angle is 0 degree. The down tube 40 is attached at its first end 41 to
the lower
part of the head tube 22. The down tube extends transversely and downwardiy,
toward the same direction as the top tube. The seat tube 50 joins the second
end of
the top tube 32 and the second end of the down tube 42.
The seat tube 50 of the invention is composed of two pacts: upper part 52
and a lower part 56. The upper part of the seat tube 52, is a substantially
stratghttube
extending downwardly and substantially vertically from its upper end 51 to its
lower
end 53. Upper seat tube 52 forms an angle of about 0 to 20 degrees with 'the
vertical.
in a preferred embodiment of the invention, this angle is about 5 degrees. The
lower
part of the seat tube 56 is curved both iong'~tudinaliy and transversely as
illustrated in
Fig. 4, and extends from its upper end 55 between its lower end 57. The seat
tube 50
can be made of two pieces (upper part 62 and lower part 66) welded together or
can
be made in one piece in the shape according to the invention_
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4a
In a preferred embodiment, the two-part seat tube 50 is aero shaped and
its interior is adapted to receive therein a seat post 73 (Fig. '13). The seat
past 73 may
also be aerodynamically shaped and adapted to slide inside the aero shaped
upper
seat tube 52, matching its interior shape. The terms "aero" and "aerodynamic"
refer to
tubes which depart from the traditional tubular shape, but which have an
elongated
radius in a direction parallel to the direction of travel ofthe bicycle. Such
members are
generally wing-shape or oval in section. Aftematively, the aero.shaped seat
post 73
may not matched the interior of tube 52. The aenxiynamic shape of the seat
post
reduces the aerodynamic drag of the frame and improves its performance. It
should
be noted that the two-part seat tube 50 as well as the seat post 73 may also,
each
separately have any other suitable shape. The cross section of the two parts
of the
seat tube may also be different.
The upper seat tube 52 of the bicycle frame according to a preferred
embodiment of the invention is very close to vertical (as opposed to mostly
oblique as
in the prior art). Therefore, the seat post 73 and upper seat tube 52 drop
substantially
vertically towards the wheel from the saddle and the lower curved part 56 thus
comes
further up and back on the wheel, resulting in a greater coverage of the upper
portion
ofthe rearwheef and the aerodynamic drag is reduced. In addition, given
thefiactthat
the seat post and upper seat tube 52 are farther back than on conventional
designs,
the center of pressure of the bicycle is moved rearward, resulting In better
stability.
The lower longitudinally curved part 56 of the seat tube is transversely
curved as shown in Fig. 4 and is designed to act as a fairing, and reduces the
aerodynamic drag of the rotating rear wheel and tire assembly. Fig. 4
illustrates a
cross section of the lower part 56 of the seat tube.
The bicycle frame according to the invention also comprises seat stays TO
which extend from the;unction between upper seat tube 52 and the lower curved
part
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56. The frame also comprises chain stays 71 which extend from the lower part
57 of
the currred lower part 5fi. Seat stays 70 and chain stays 71 meet indirectly
at the
center of the whe~I, as better explained below.
In a preferred embodiment of the bicycle frame according to the invention,
rearward facing horizontal dropout means 7~ is provided at the center of the
wheel.
As can be seen for example in Figs. 6 and 7, seat stay 70 and chain stay 71
are each
attached thereto. The dropouts~allow the wheel to be adjusted as close as
possible to
the transverse curved portion of the lower pact of the seat tube 56. This
results in an
optimal aerodynamic shielding and a reduced aerodynamic drag. The rearward
facing
horizontal dropouts also allow the user to use different sizes of tires and
still optimize
the aerodynamic pertormance of the bicycle.
it should be noted thatthe bicycle frame aCCOrding to the invention differs
significantly from the traditional "double diamond° frame shape, which
generally has
two open triangles with a common side. In contrast, the front portion of the
bicycle
frame of the invention has four sides and incorporates a curved member. The
rear
portion has only 3 sides and one is a curve. In addition, the seat stays 70 do
not
intersect at the vertex joining the seat tube 50 and the top tube 32 as in
most other
firaditional °double diamond" frame designs, but rather at the junction
between the
upper and lower seat tubes ~2 and 56, This dropped seat stay design improves
the
aerodynamic performance and stiffness of the frame.
The bicycle frame according to a preferred embodiment of the invention is
constructed from custom aluminum extrusions and meets the latest UCI
regulations. It
should be noted that any suitable material, such as mefiallic, composite or
the like
material can be used,
Referring to Figs. 6 and 13, the bicycle frame according to a preferred
embodiment of the invention is provided with brake means 60, which Is
integrated at
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the junction between the upper seat tube 52 and the seat stays 70. The brake
means
is constituted of a rear brake of conventional design that is bolted to a
small plate 7B,
and the plate is subsequently bolted to the rear of the frame. This brake and
brake
plate design provides the leanest aerodynamic solution by nat requiring a
large gap
between the tire and frame for access to the brake attachment, and it does not
degrade the frame stiffness or strength with access holes or other
compromises.
fn addition to the principal invention, the following inventions support the
principal invention:
1. The integration of the seat stays with the seat tubs which results in a
much
cleaner aerodynamic form.
2. The brake plate to which the rear brake must be attached before the plate
(with the attached brake) are then bolted to the frame. This design allows us
to attach the brake to the frame in its conventional orientation while
CA 02357598 2001-09-20
enhancing the aerodynamics, stiffness, or strength of the area. (see Figure
5).
3. The portion of the seat tube forward of the rear wheel has a trailing edge
of
constant width which protects the rear wheel by the same amount over its
5 complete length.
4. The long length and high curvature of the lower curved portion of the seat
tube protects and covers the forward edge of more of the rear wheel than is
possible with prior art designs.
5. The high curvature and long length of the lower curved section of the seat
tube results in improved rider comfort compared to prior art designs.
6. The use of horizontal dropouts to optimize the tire clearance to the curved
seat tube for use with different tire and wheel sizes.
7. A recessed concave area in the rear of the seat tube to further enhance the
rear wheel aerodynamics. Seat tube lower cross section is shaped as
shown in Figure 4.
8. The design of the seat tube also has the additional advantage of moving the
Aerodynamic Center of Pressure to the rear which further enhances stability.
Thus, it is apparent that there has been provided in accordance with the
invention an AERODYNAMIC BICYCLE FRAME that fully satisfies the objects,
aims and advantages set forth above. While the invention has been described in
conjunction with a specific embodiment thereof, it is evident that many
alternatives,
modifications and variations will be apparent to those skilled in the art in
light of the
foregoing description. Accordingly, it is intended to embrace all such
alternatives,
modifications and variations as fall within the spirit and broad scope of the
invention.
