Note: Descriptions are shown in the official language in which they were submitted.
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REAR SUSPENSION SYSTEM FOR BICYCLES
Technical Field
[0001] This application relates to an improved rear suspension
system for bicycles.
Backgro
[0002] High-end mountain bikes typically have both rear and front
suspension systems to assist in traversing uneven terrain. This is
particularly the case for freeride, downhill and trail bikes which are
designed to descend steep and uneven mountain terrain, often at high
speeds. Many rear suspension systems designed for freeriding and other
biking applications are known in the prior art. Such systems generally
include a rear suspension permitting a limited degree of travel of the rear
wheel relative to the bicycle frame and a rear shock absorber for absorbing
suspension forces. The range of rear wheel travel that is permitted by
existing suspension systems varies, but is typically within the range of
about 5 to 12 inches measured vertically (although some designs permit
travel outside this range).
[0003] While many mid and long rear wheel travel bicycle designs
are known, most designs have rear suspension systems which compromise
overall bike performance and versatility. Two primary problems caused
by existing designs are (a) undesirable contact between the rear tire or
suspension linkages and the bicycle seat or seat tube when the rear
suspension system is under full compression; and (b) a restricted range of
adjustability of the seat position.
[0004] United States patent Nos. 5,509,679, 5,678,837 and 5,899,480
owned by Specialized Bicycle Components, Inc. of Morgan Hill, California
describe two primary types of four bar linkage rear suspension systems,
commonly referred to as the walking beam and low linkage designs. The
above-noted patents are incorporated herein by reference in their entireties.
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The walking beam design is illustrated in Figure 1 and includes a rocker
arm Iink extending in a near horizontal orientation and a rear shock
absorber having a travel axis extending in a near vertical orientation. The
rocker arm link pivots on the seat tube portion of the bicycle frame and
extends between an upper end of the rear shock absorber and an upper end
of the seat stays. The main manufacturing advantages of the walking beam
design are that the frame of the bike can be built out of a typical "triangle"
shape, common in the bicycle industry, the pivot point for the rockex arm
link can be conveniently arranged to mount to the seat tube, and the rear
shock can be conveniently pivotally connected to the top of the bottom
bracket area. The main performance advantage of the walking beam design
is that the seat tube is straight and continuous and allows for a full
adjustment range of the seat (i.e. saddle) height. This is important because
the seat needs to be raised to the correct biomechanical position to allow for
effective pedaling performance when climbing up hills and crossing
non-technical terrain and the seat needs to be lowered substantially
(typically by 4 to 8 inches or more depending upon the rider's height and
body proportions) so that the rider can safely and effectively traverse
difficult or challenging terrain and obstacles.
[0005] T'he walking beam design is suitable for bicycle suspension
frames with up to approximately 6 inches of vertical rear wheel travel.
However, as the rear travel gets longer than about 6 inches, several
problems arise with the walking beam design. As the rear wheel travel
path starts to come forwards, towards the front of the bike, this movement
combined with the generally rearward sloping seat tube causes the rear
wheel and the seat tube to collide before the rear wheel has finished its
travel. Further, the relatively high linkage arrangement (when compared
to the low linkage four bar design described below) causes the rocker arm
link (when the rear suspension is under substantial or full compression) to
interfere with the low rearward position of the rider's "bottom" (a position
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needed to ride challenging terrain) and also the rear seat when the seat is
lowered.
[0006] Longer travel suspension frames work better with rear shock
absorber stroke length ratios that match their travel. If the ratio of rear
wheel travel versus shock stroke length increases beyond a favourable
ratio, then the relatively short stroke shock absorber will be less effective
in
its ability to control the movement of the rear suspension and will be
potentially more prone to failure. Additionally, higher rear shock absorber
spring rates are required, which reduces the "suppleness" of the rear
suspension's feel. As the rear wheel's travel increases, the rocker arm link
pivot must also be moved up "higher" along the seat tube, to accommodate
the longer stroke rear shock absorber (which is fixed near the bottom
bracket of the front triangular frame as shown in Figure 1). Additionally,
the rocker arm link needs to be longer to accommodate the greater length
of the shock absorber stroke. This exacerbates the problems discussed
above concerning the interference of the rear wheel and rocker arm link
with the frame's seat tube, seat, and the rider's bottom. These effects are
increased even more in the case of smaller frame sizes designed for smaller
riders, because there is less room for the suspension elements to move due
to a seat that is in an overall lower position (because the rider is smaller).
[0007] Low linkage four bar rear suspensions as exemplified by the
Specialized FSR design shown in Figure 2 also exhibit several limitations.
On the one hand, such low linkage designs do not suffer from rear wheel
and rocker arm link interference issues as described above in connection
with the walking beam configuration. This is because the rocker arm link
is typically mounted in a lower, diagonal to near vertical position, and the
rear shock absorber is mounted in a diagonal to near horizontal position
(Figure 2). Additionally, the seat tube position can be arbitrary, as it is
typically mounted to the end of a cantilevered "beam", instead of being
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welded in line with the bottom bracket axis. However, on the other hand
the low linkage design requires that the rear shock "interrupt" the seat tube
and hence causes the seat tube to be cut off at the shock absorber location:
This severely limits the range of seat and seat post adjustability. This is a
major problem on bikes designed for technical riding where the seat needs
to be substantially lowered so that it is out of the way of the rider's body
movement, such as when traversing uneven downhill terrain. To get the
seat low enough, technical riders typically cut their seat post to a shorter
length. However, this leaves the seat post too short and the seat cannot be
raised enough to provide a biomechanically correct pedaling position for
the rider; particularly when climbing hills. A full range of adjustable seat
post positions is desirable for the reasons specified above.
[0008] Other existing rear suspension systems designed for technical
riding, such as single pivot swing arm and virtual pivot point designs, also
suffer from various drawbacks. For example, rear suspensions having long
swing arms typically have lower overall lateral rigidity than other designs.
Some long travel virtual pivot point designs include interrupted seat tubes,
or have full length seat tubes which are bent to provide sufficient rear
wheel clearance, but such designs restrict the range of seat height adjust-
ability. Other four bar virtual pivot point designs have elongated seat stays
which extend past the seat tube to allow for a full length seat tube.
However, increasing the length of the seat stays also sacrifices the overall
lateral stability of the rear suspension system which is not desirable.
[0009] The need has theref ore arisen for an improved rear suspension
system for bicycles which maintains the advantages of prior art designs
while eliminating or substantially reducing their disadvantages.
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Summar,~f Invention
[0010] In accordance with the invention, a rear suspension system for
a bicycle having a rear wheel and a frame is provided. The frame includes
a seat tube having a longitudinal axis. The system includes a rear suspen-
sion pivotally coupling the wheel to the frame; a rear shock absorber
disposed entirely forwardly of the seat tube; and a linkage coupling the rear
suspension to the shock absorber for transferring forces therebetween;
wherein the linkage extends in an orientation intersecting a plane passing
through the seat tube parallel to the longitudinal axis.
[0011] The linkage is configured to transmit the suspension forces
around the seat tube. In one embodiment the linkage may straddle the seat
tube. For example, the linkage may comprise first and second linkage
elements disposed on opposite sides of the seat tube. The linkage
preferably has a length exceeding the diameter of the seat tube and is
pivotably coupled to both the rear suspension and the shock absorber. In
one embodiment the rear suspension may include one or more pivot points,
where the most forward one of the pivot points is located rearwardly of the
longitudinal axis.
[0012] Preferably the seat tube of the bicycle frame is continuous and
the shock absorber has first and second ends coupled to the frame
forwardly of the seat tube. In one embodiment the first end of the shock
absorber is pivotably coupled to the frame and the second end of the shock
absorber is pivotably coupled to the linkage. In one particular configura-
tion, the frame comprises a top tube, a head tube and a down tube in
addition to the seat tube, and the first and second ends of the shock
absorber are coupled to the down tube.
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[0013] In one embodiment, the bicycle frame is orientable in a vertical
plane and the shock absorber may be supported so that its longitudinal axis
extends in a plane at an angle of between about 45 - 90° relative to
the
vertical plane. In one embodiment the shock absorber may extend in a
horizontal or near-horizontal orientation to maximize its stroke length. In
a particular embodiment the shock absorber may extend beneath and
parallel to a top tube of the bicycle frame.
[0014] In one particular embodiment, the rear suspension may
comprise a four bar suspension design including a chain stay link and a seat
stay link coupled to the rear wheel and a rocker arm link coupled to the seat
stay link and extending forwardly therefrom. In one embodiment the
linkage is coupled to the rocker arm. In alternative embodiments the
linkage is alternatively coupled to the seat stay link or the chain stay link.
[0015] The suspension system is particularly useful to mid to long
rear wheel travel bicycle designs where the range of vertical travel of the
suspension system exceeds approximately 5 inches.
[0016] The application also relates to a bicycle having a rear wheel
and a frame orientable in a vertical plane, the frame comprising a seat tube
having a longitudinal axis. The bicycle further includes a rear suspension
for pivotally coupling the rear wheel to the frame, wherein the rear wheel
is movable within a range of travel between a most rearward position and
a most forward position. The bicycle further includes a rear shock absorber
disposed entirely forwardly of the seat tube and a linkage coupling the rear
suspension to the rear shock absorber, wherein the linkage extends in an
orientation intersecting a plane passing through the seat tube parallel to the
longitudinal axis.
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[0017] Preferably the rear wheel and the rear suspension system are
spaced apart from the seat tube in the most forward position and the
longitudinal axis of the seat tube extends at an angle substantially
tangential to the most forward position of the rear wheel. In one
embodiment the longitudinal axis of the seat tube extends at an angle
between about 50 - 75° degrees relative to a horizontal plane passing
through the seat tube and extending perpendicular to the vertical plane.
More preferably, the longitudinal axis of the seat tube extends at an angle
of between about 55 - 65° degrees relative to the aforesaid horizontal
plane.
[0018] The seat tube of the frame is preferably continuous. The frame
may also include a down tube and a bottom bracket mounted at a lower
end of said down tube for receiving a crank assembly of the bicycle. The
bottom end of the seat tube is offset forwardly as compared to conventional
frame designs such that the longitudinal axis of said seat tube intersects the
down tube at a location forward of the bottom bracket.
[0019] The invention may also relate to a kit for coupling a rear
suspension to a shock absorber using the linkage of the applicant's
invention.
Brief Descrit~tion of Drawings
[0020] In drawings which illustrate embodiments of the invention, but
which should not be construed as restricting the spirit or scope of the
invention in any way,
[0021] Figures 1 is a side elevational view of a rear suspension system
of the prior art configured in a walking beam four bar subassembly.
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[0022] Figures 2 is a side elevational view of a rear suspension system
of the prior art configured in a low linkage four bar subassembly.
[0023] Figure 3 is a side elevational view of a bicycle having the rear
suspension system of the invention.
[0024] Figuxe 4 is an enlarged side elevational view of the applicant's
rear suspension system of Figure 3.
[0025] Figure 5(a) is an enlarged rear isometric view of the applicant's
rear suspension system of Figure 3 in an uncompressed configuration.
[0026] Figure 5(b) is an enlarged isometric view of the applicant's rear
suspension system of Figure 3 under full compression.
[0027] Figure 6 is a schematic view showing the relative orientation
of the bicycle subframe and rear suspension system of Figures 3 - 5 when
the suspension system in a fully compressed configuration.
[0028] Figure 7 is a schematic view showing the bicycle subframe and
rear suspension of Figures 3 - 5 when the suspension system is in an
uncompressed configuration.
[0029] Figure 8 is a schematic view showing the relative orientation
of the bicycle, subframe and rear suspension system in an alternative
embodiment of the invention.
[0030] Figure 9 is a schematic view showing the relative orientation
of the bicycle subframe and rear suspension system in a further alternative
embodiment of the invention.
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[0031] Figure 10 is a schematic view showing the relative orientation
of the bicycle subframe and rear suspension system in a further alternative
embodiment of the invention.
Description
[0032] Throughout the following description, specific details are set
forth in order to provide a more thorough understanding of the invention.
However, the invention may be practiced without these particulars. In
other instances, well known elements have not been shown or described in
detail to avoid unnecessarily obscuring the invention. Accordingly, the
specification and drawings are to be regarded in an illustrative, rather than
a restrictive, sense.
[0033] This application relates to a bicycle 10 having an improved rear
suspension system 12 (Figure 3). Bicycle 10 includes a rear wheel 14, a front
wheel 16 and a frame 18 coupled to wheels 14,16 for supporting a rider. As
described in detail below, rear suspension system 12 pivotably couples rear
wheel 24 to frame 18. Front wheel 16 is coupled to frame 18 by means of
front forks 20. Forks 20 may optionally include front shock absorbers 21.
[0034] As used in this patent application, the terms "front", "forward",
and forwardly" mean toward the front end of bicycle 10 and the terms "rear,
"rearward", and rearwardly mean toward the rear end .of bicycle 10.
Similarly, the words "top", "upper", "upward" and "upwardly" mean toward
the upper portion of bicycle 10 when it is in an ordinary riding orientation
with wheels 14,16 resting on a support surface, as shown in Figure 3. The
words "bottom", "lower", "toward" and "lowardly" refer to the lower portion
of bicycle 10 when it is in the ordinary riding orientation
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[0035] In the illustrated embodiment, bicycle frame 18 has a generally
triangular configuration and comprises a top tube 22, a down tube 24 and
a seat tube 26. Frame 18 also includes a head tube 28 for receiving forks 20
and handlebars 30 at the front end of bicycle 10. A seat post 32 supporting
a seat 34 is slidably coupled to seat tube 26. The position of seat post 32 is
adjustable to alter the height of seat 34. Although the present invention is
described with reference to the triangular-shaped frame 18 of Figure 3, the
invention is equally applicable to other frame designs, including
monocoque frames (such as is shown in Figure 2).
[0036] Bicycle frame 18 further includes a bottom bracket 35 located
at the bottom end of down tube 24 for receiving a pedal assembly (not
shown) including a crank arm and bottom bracket axle. Most conventional
bicycle frames having a triangular configuration have a seat tube which is
coiilcident with the bottom bracket as shown in Figure 1 (i.e. the longitudi-
nal axis of the seat tube intersects the bottom bracket). However, in the
Applicant's invention, the position of seat tube 26 is shifted forwardly so
that the axis of seat tube 26 intersects down tube 24 at a location spaced:
forwardly and upwardly from bottom bracket 35. This feature is described
in further detail below. The Applicant's frame 18 may further include a
bottom bracket block 37 for supporting bottom bracket 35 and elements of
rear suspension system 12 at a location rearwardly of seat tube 26.
[0037] Rear suspension system 12 is illustrated in detail in Figures 4
and 5. System 12 may include a rear suspension 40, a rear shock absorber
42 arid a linkage 44 for coupling rear suspension 40 to shock absorber 42.
Linkage 44 enables transfer of forces around seat tube 26 between
suspension 40 and shock absorber 42 as discussed in detail below.
[0038] In the illustrated embodiment, rear suspension 40 is config-
ured in a conventional low linkage four bar arrangement. Such an
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arrangement is described in detail in US Patent Nos. 5,509,679, 5,678,837
and 5,899,480 which are incorporated herein by reference, as indicated
above. In this arrangement, rear suspension 40 includes a chain stay link
46, a seat stay link 48 and a rocker arm link 50 which, together with frame
18, define a four bar linkage. More particularly, chain stay link 46 includes
spaced-apart first and second arms 47 which straddle rear wheel 14 when
bicycle 10 is assembled (Figure 3). A yolk-shaped first end 52 of chain stay
arms 47 is pivotably coupled to bottom bracket block 37 of frame 18 by
means of a pivot 56. A second end 58 of each chain stay arm 47 is pivotably
coupled to a drop-out bracket 60 by means of a pivot 62. Drop-out bracket
60 supports axle 64 and hub 65 of rear wheel 14 (Figures 5(a) and 5(b)). In
the embodiment of Figure 3 - 5 pivot 62 is therefore spaced a short distance
fowardly of the axis of axle 64 and hence the center of rear wheel 14 (in the
schematic views of Figures 6 -10 reference 64 denotes the center of wheel
14).
[0039] Seat stay link 48 includes spaced-apart arms 49 which also
straddle rear wheel 14 when bicycle 10 is assembled. A first end 66 of each
seat stay arm 49 is coupled to a corresponding drop-out bracket 60 and a
second end 68 of each seat stay arm 49 is coupled to rocker arm link 50 by
means of a pivot 70. In the illustrated embodiment rocker arm link 50
includes spaced-apart arm elements 51 which are connected together at a
first end 72 thereof by a seat stay arch 53. Seat stay arch 53 extends
transversely between arm elements 51 in the vicinity of pivots 70. Each
rocker element 51 also has a second end 74 pivotably coupled to bottom
block 37 of frame 18 by means of a pivot 76. As shown best in Figures 5(a)
and 5(b), pivot 76 is located proximate seat tube 26 and above a pivot 56.
[0040] Rear suspension 40 illustrated in Figures 3 - 5 thus includes
four separate pivot points, namely pivots 56, 62, 70 and 76. This arrange-
ment enables rear wheel 14 to pivot relative to bicycle frame 18 between a
rear position (Figure 5(a)) when traveling over flat terrain and a raised
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forward position (Figure 5(b)) to accommodate uneven terrain. The
maximum amount of travel of rear wheel 14 permitted by rear suspension
40 may vary, but is typically in the range of 5 - 10 inches measured
vertically. Unlike conventional single pivot suspension designs, rear
suspension 40 has multiple pivot points and is therefore not constrained to
follow a constant arc pivoting wheel path. Rather, as will be appreciated
by a person skilled in the art, suspension 40 exhibits the advantages of other
known four bar suspension geometries in terms of pedal-induced suspen-
sion movement, acceleration, pedal feedback and braking characteristics.
[0041] As will also be appreciated by a person skilled in the art, the
drawings illustrate only one example of a rear suspension 40, namely a low
linkage four bar configuration, and many other types of suspension systems
could be substituted without departing from the invention, including
walking beam four bar linkages, virtual pivot point designs and single
pivot swing arm designs.
[0042] As indicated above, rear suspension system 12 also includes a
rear shock absorber 42 for absorbing forces received from rear suspension
40 via linkage 44. In the Applicant's invention shock absorber 42 is
positioned entirely forwardly of seat tube 26. In the illustrated embodi-
ment, shock absorber 42 extends along an axis substantially parallel to top
tube 22. This orientation is sometimes referred to in the bicycle industry as
a "horizontal" orientation as opposed to a "vertical" orientation as exempli-
fied by the walking beam design shown in Figure 1. However, neither
orientation is precisely "horizontal" or "vertical" and many variations are
possible. One advantage of orientating shock absorber 42 parallel to top
tube 22 is that the length of shock absorber 42 may be maximized (i.e. there
is sufficient available space to accommodate relatively large, long stroke
length shock absorbers 42). There are also advantages to isolating shock
absorber 42 from the effects of side loading of rear suspension 40 and
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protecting shock absorber 42 from "tire roost" (i.e. protecting shock
absorber 40 from being exposed to soil and water flung upward by the
bicycle tires).
[0043] In the illustrated embodiment a first end 80 of shock absorber
42 is coupled by means of a pivot 82 to a first support bracket 84 mounted
on an upper; forward portion of frame down tube 24 . A second end 86 of
shock absorber 42 is coupled by means of a pivoting swing link 88 to a
second support bracket 90 mounted on an upper lower portion of frame
down tube 24. More particularly, pivoting swing link 88 has one end
coupled to second support bracket 90 by means of a pivot 92 and another
end coupled to second end 86 of shock absorber 42.
[0044] Linkage 44 couples rear suspension 40 to shock absorber 42.
In the embodiment illustrated in Figures 3 - 5, linkage 44 couples second
end 86 of shock absorber 42 to a central portion of rocker arm 50. However,
many other arrangements for operatively coupling rear suspension 40 and
shock absorber 42 may be envisioned, as described below: In the embodi-
ment of Figures 3 - 5, linkage 44 includes a pair of spaced-apart push
linkages 96 which straddle seat tube 26. A first end of 98 of each push
linkage 96 is pivotably connected to second end 86 of shock absorber 42 by
means of a pivot 101 and a second end 100 of each push linkage 96 is
pivotably connected to a midportion of a corresponding rocker arm
element 51 by means of a pivot 102. In operation, forward pivoting motion
of rocker arm 50 toward seat tube 26 causes a transfer of forces through
push linkages 96 to shock absorber 42 (Figure 5(b)). Thus linkage 44
transfers suspension forces received by rear suspension 40 at a location
rearward of seat tube 26 to shock absorber 42 located forward of seat tube
26. In order to accomplish this function linkage 44 extends in a plane
intersecting the longitudinal axis of seat tube 26.
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[0045] In an alternative embodiment of the invention linkage 44 may
include a single push linkage 96 (i.e. it is not a requirement of the
invention
that two separate push linkages 96 straddle seat tube 26).
[0046] Linkage 44 is sometimes referred to herein as Four X 4TM or 4
X 4TM linkage. This is because each push linkage 96 includes four separate
pivots to transfer forces from rear suspension 40 around seat tube 26 to
shock absorber 42, namely pivots 76, 92,101 and 102. As described above,
rear suspension 40 also employs four different pivot points, namely pivots
56, 62, 70 and 76. Thus rear suspension system 12 may be considered do be
a "dual four bar" suspension system. As a result of the relative positions
and spacing of the aforesaid pivots, the spacial relationship between the
various linkages of rear suspension system 12 changes significantly
between the uncompressed riding configuration of Figure 5(a) and the
compressed configuration of Figure 5(b). For example, as rocker arm link
50 moves forwardly to a more upright orientation extending generally
parallel to seat tube 26 as shown in Figure 5(b), swing link 88 is also
caused,
via push linkages 96, to pivot to a more upright orientation, thereby causing
compression of shock absorber 42.
[0047] One notable difference between the present invention and
some prior art configurations is that in the applicant's design the most
forward pivot point of rear suspension 40 is located rearward of the
longitudinal axis of seat tube 26 rather than on or in front of seat tube 26.
One advantage of this design is that the length of chain stay link 46, seat
stay link 48 and rocker arm link 50 can be maintained at a normal length
(i.e. the length of one or more of such linkages does not need to be
increased in order to connect directly to shock absorber 42 or to support
structures located forwardly of seat tube 26). By contrast, some prior art
designs have comparatively long linkages or swing arms which results in
a sacrifice of lateral rigidity.
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[0048] One other important advantage of the present invention is that
a continuous seat tube 26 may be employed. This ensures that seat post has
a sufficient height adjustment range. As used in this patent application a
"continuous" seat tube 26 refers to a seat tube that extends upwardly from
a lower portion of frame 18, such as down tube 24, and is straight and
uninterrupted between frame 18 and its upper end. By way of contrasting
example, Figure 2 shows an arrangement of the prior art where the seat
tube is discontinuous (i.e. it is interrupted at its lower end to accommodate
a rear shock absorber underneath the seat tube). As explained above, such
an arrangement restricts the adjustabilify of the seat post slidable within
the
seat tube and hence the available range of seat positions. By way of
another example, a seat tube having a lower portion which is bent to avoid
contact with the rear suspension would also considered to be "interrupted"
and not continuous since the bend in the tube would impede a full range
of adjustment of the seat post slidable therein.
[0049] Further, as shown best in Figure 6, in the applicant's invention
the position and angle of continuous seat tube 26 has been engineered to
ensure that a rider seated on seat 34 is in an optimum biomechancial
position. In the following discussion seat tube 26 is assumed to extend in
the same plane as the remainder of bicycle frame 18 (i.e. in a substantially
vertical plane when bicycle 10 is in a normal riding orientation). The
position and angle of seat tube 26 is determined by two primary con-
straints. First, seat tube 26 is positioned so that its longitudinal axis
extends
tangentially relative to the most forwardly intrusive position of rear wheel
14 and rear suspension 40 (Figures 5(b) and 6). As used herein "forwardly
intrusive" refers to the most forward position of rear wheel 14 and/or rear
suspension 40 when rear suspension system 12 is under full compression.
In this case, rear wheel 14 is in a raised and forward position and seat stay
link 48 and rocker arm link 50 are pivoted forwarded (Figure 5(b)). For
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example, comparing Figures 5(a) and 5(b), seat stay arch 53 and pivots 70
have moved forwardly and upwardly to a position closely proximate to seat
tube 26.
[0050] Secondly, the longitudinal axis of seat tube 26 is such that
when seat 34 is raised or lowered to the desired height the rider is
positioned in a biomechanically efficient position. As discussed above, seat
34 ordinarily needs to be raised to allow for effective pedaling performance
when climbing hills and traversing non-technical terrain. Seat 34 also needs
to be lowered substantially (usually by 4 - 8 inches or more depending on
the rider's height and body proportions) so that the rider can safely and
effectively traverse difficult or challenging terrain and obstacles, for
example during aggressive freeriding. In particular, it is desirable to move
seat 34 to a lower forward position so that it does not interfere with
preferred downhill riding positions (when traversing steep downhill slopes
or other challenging terrain, it is often desirable for the rider's "bottom"
to
be lowered and moved rearwardly to alter the rider's center of gravity).
[0051] As shown in Figure 6, a "region of biomechanical efficiency" is
shown in hatched lines which denotes a preferred range of positions of seat
tube 26 (and hence seat 34). In this example, the bottom boundary of the
region is the longitudinal axis of frame top tube 22; the front boundary of
the region is a line that is 5° from a vertical plane passing through
the axis
of bottom bracket 35 and 85° from a horizontal plane centered on the
bottom bracket axis; the rear boundary is of the region is a line that is
30°
from a vertical plane passing through the axis of bottom bracket 35°
and
60° from a horizontal plane centered on the bottom bracket axis; and
the top
boundary is a line formed by the intersection of the plane of the bicycle
front frame and a horizontal plane which includes a point defined by the
intersection of the longitudinal axes of top tube 22 and head tube 28.
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[0052] As should be apparent from Figure 6, it is important that the
longitudinal axis of seat tube 26 extend within the region of biomechanical
efficiency at a location that does not interfere with rear wheel 14 or rear
suspension 40 when such components are in their most forward position
(i.e. when rear shock absorber 42 is under full compression). As explained
above, the position of seat 34 is largely determined by the angle of seat tube
26 (although seat 34 may be adjustable forwardly and rearwardly to a
limited extent on rails (not shown) mounted on the top of seat post 32).
Further, the actual position of seat 34 may be above the above-defined
region of biomechanical efficiency, especially when seat 34 is in the most
raised position for hill climbing, but the longitudinal axis of seat tube 26
preferably extends through this region. In the illustrated embodiment the
longitudinal axis of seat tube 26 extends at an angle of about 58°
relative to
a horizontal plane (as defined above). Since the longitudinal axis of seat
tube 26 is not coincident with the axis of bottom bracket 35, but is instead
offset forwardly as described above, this corresponds to an effective seat
tube angle of about 72° relative to the horizontal plane. as measured
from
bottom bracket 35 (which support's the bicycle pedals). In one embodi-
ment of the invention, the preferred actual angular range of seat tube 26 as
measured above is between about 50 - 70° which corresponds to a
preferred
effective angular range of between about 60 - 85° as measured above. If
the
longitudinal axis of seat tube 26 is too sharply inclined (e.g. having an
actual angle less than about 45° relative to a horizontal plane), this
may
result in rear suspension 40 contacting seat tube 26, seat post 32 or seat 34
when rear suspension 40 is in its most forwardly intrusive position,
particularly in the case of long travel rear suspension systems. Further,
such a sharply inclined seat tube 26 would restrict the amount of space
available forward of seat tube 26 to accommodate rear shock absorber 42.
Conversely, if the orientation is overly upright (e.g. if the longitudinal
axis
of seat tube 26 extends at an actual angle more than about 75° degrees
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relative to a horizontal plane), then the rider will not be an optimum
biomechanical position for uphill pedaling.
[0053] As explained above, the principles of the present invention
may apply to many alternative bicycle configurations, including bicycles
having different frame 18 and/ or rear suspension 40 configurations. Some
examples of alternative arrangements are shown schematically in Figures
6 -10. Figure 6 - 7 illustrates schematically the embodiment of Figures 3 -
5 where linkage 44 is driven by rocker arm link 50 (Figure 6 showing this
configuration in a compressed configuration and Figure 7 showing the
same configuration in an uncompressed configuration).
[0054] Figure 8 illustrates an alternative arrangement where linkage
44 is driven by chain stay link 46. In particular, instead of coupling linkage
44 to rocker arm 50, pivot 102 is located rearwardly of rocker arm 50 and is
coupled by means of linkages 110 and 112 to pivots 56 and 62 located on
opposite ends of chain stay link
[0055] Figure 9 illustrates a further alternative arrangement where
linkage 44 is driven by a single pivot suspension system employing a longer
swing arm (i.e. chain stay link 46). In this arrangement rear wheel 14 is
mounted at a fixed location on chain stay link 46 which is in turn connected
directly to pivot 54. In this embodiment pivot 62 is positioned at one end
of seat stay link 48 and linkage 44 is driven by a combination of rocker link
50 and seat stay link 48.
[0056] Figure 10 illustrates a walking beam four bar linkage utilizing
the invention. In this case a modified walking beam linkage 114 extends
between an upper end of seat stay link 48 and a pivot 116 mounted on seat
tube 26. Linkage 44 employs a push linkage 96 having one end pivotably
coupled to walking beam linkage 114 by means of a pivot 115 and another
CA 02453046 2005-03-11
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end coupled to triangular a A-links 116 fixed to frame 18. At least one
segment of A-links 116 intersects a plane parallel to the longitudinal axis of
seat tube 26 to couple push linkage 96 to shock absorber 42. As in other
embodiments of the invention, linkage 44 functions as an intermediate
coupling for transferring rear suspension forces around seat tube 26 to
shock absorber 42 located at a position forwardly of seat tube 26.
[0057] As will be appreciated by a person skilled in the art, many
other alternative variations of linkage 44 may be envisioned for use in
association with different rear suspension designs.
[0058] As will be apparent to those skilled in the art in the light of the
foregoing disclosure, many alterations and modifications are possible in the
practice of this invention without departing from the spirit or scope thereof
.
Accordingly, the scope of the invention is to be construed in accordance
with the substance defined by the following claims.
