Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BICYCLE SUSPENSION SYSTEM WITH AN IDLER PULLEY
FIELD OF THE INVENTION
[001] The invention relates generally to bicycles, and more specifically, to
bicycle
suspension systems.
BACKGROUND
[002] Bicycle suspension systems with an idler pulley are known in the art.
Bicycles
equipped with these suspension systems are known as high-pivot bicycles. This
name is
due to idler pulleys being commonly used in suspension systems having a
significantly
rearward axle path (which is typically achieved with an elevated or "high"
main suspension
pivot point). When used in such suspension systems, the idler pulley serves to
reroute the
upper portion of the drive chain (i.e. the portion of the drive chain that is
tensioned from
pedaling forces) so as to prevent the drive chain from excessively interfering
with the
functioning of the suspension.
[003] Idler pulleys can have an additional purpose, which was introduced by
the bicycle
drivetrain disclosed in Canadian Patent Application No. 3,080,960, filed on
May 14, 2020.
This additional purpose is to reroute the upper portion of the drive chain for
enabling a
certain motion of a tensioner chain guide, which is part of a chain tensioner.
In an
exemplary embodiment in Canadian Patent Application No. 3,080,960, the
tensioner chain
guide pivots around a bottom bracket shell axis for tensioning a drive chain.
The tensioner
chain guide is biased for rotation in a clockwise direction when viewed
laterally outwardly
from the drivetrain (i.e. when viewed laterally from an outward viewing
position from the
drivetrain). As discussed in Canadian Patent Application No. 3,080,960, the
range of
motion of the tensioner chain guide that is enabled by the idler pulley
depends on the idler
pulley's position. An idler pulley in a more elevated and forward position
will enable a
larger range of motion of the tensioner chain guide.
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[004] With regard to their potential employment with the bicycle drivetrain
disclosed in
Canadian Patent Application No. 3,080,960, previous suspension systems with an
idler
pulley are limited in their practicability for simultaneously achieving the
two objectives of:
(1) idler pulley placement for enabling a large range of motion of the
tensioner chain guide,
and (2) advantageous suspension kinematics. An exception to this may be the
type of
bicycle suspension system with an idler pulley disclosed in European Patent
No. 2,420,435,
which issued to Wuthrich on October 30, 2013. The illustrated embodiment in
European
Patent No. 2,420,435 is a bicycle with a linkage mechanism dedicated to
actuating a shock
absorber (such linkage mechanisms are conventional), and an additional linkage
mechanism
dedicated to controlling the position of an idler pulley. The linkage
mechanism for
controlling the position of the idler pulley can be arranged for achieving the
aforementioned
objective of idler pulley placement. However, this additional linkage
mechanism increases
the complexity of the bicycle. The additional linkage mechanism introduces
additional
moving parts and pivot bearings, which can increase the cost and maintenance
of a bicycle.
SUMMARY
[005] The present invention provides a suspension system for a bicycle. The
bicycle has a
rear wheel, a drive chain configured to transmit power to the rear wheel, and
a frame with
a front frame portion. The suspension system comprises:
1. a swing arm pivotably connected to the front frame portion;
2. a rocker arm pivotably connected to the front frame portion;
3. a link pivotably connected to the swing arm and pivotably connected to the
rocker
arm;
4. a shock absorber pivotably connected to the rocker arm; and
5. an idler pulley rotatably connected to the rocker arm for rotation around
an axis that
is eccentric with the pivot axis of the rocker arm with the front frame
portion;
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6. wherein the rear wheel is rotatably connected to the swingarm and movable a
distance relative to the front frame portion which defines a suspension
travel, and
wherein the idler pulley is configured to engage the drive chain and to move
along a
path as a function of the suspension travel.
BRIEF DESCRIPTION OF THE DRAWINGS
[006] In the drawings:
[007] FIG. 1 is an isometric view of the suspension system and the drivetrain
of the
bicycle in accordance with a first embodiment;
[008] FIG. 2 is a side elevational view of the suspension system and the
drivetrain of the
bicycle in accordance with the first embodiment;
[009] FIG. 3 is a side elevational view of the bicycle in accordance with the
first
embodiment;
[010] FIG. 4 is a side elevational schematic functional view of the suspension
system at
0% travel, in accordance with the first embodiment;
[011] FIG. 5 is a side elevational schematic functional view of the suspension
system at
50% travel, in accordance with the first embodiment;
[012] FIG. 6 is a side elevational schematic functional view of the suspension
system at
100% travel, in accordance with the first embodiment;
[013] FIG. 7 is a graph of the leverage ratio curve of the suspension system
in
accordance with the first embodiment;
[014] FIG. 8 is a graph of the anti-squat curves of the suspension system for
the cassette
sprocket sizes of 10, 18, and 45 teeth, with an assumed vertical position of
the center of
mass of 650 mm above the bottom bracket shell axis, in accordance with the
first
embodiment;
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[015] FIG. 9 is a side elevational schematic functional view of the suspension
system at
0% travel, with the idler pulley arranged to be concentric with the first link
pivot, in
accordance with a second embodiment;
[016] FIG. 10 is a side elevational schematic functional view of the
suspension system at
0% travel, with the idler pulley arranged to be concentric with the first
shock pivot, in
accordance with a third embodiment;
[017] FIG. 11 is a side elevational schematic functional view of the
suspension system at
0% travel, with the rocker arm rotating in the opposite direction of the
rocker arm of the
other embodiments shown in the figures, in accordance with a fourth
embodiment; and
[018] FIG. 12 is a side elevational schematic functional view of the
suspension system at
0% travel, with the shock absorber arranged to be pivotably connected to the
swingarm, in
accordance with a fifth embodiment.
LIST OF REFERENCE NUMERALS
20 ___ suspension system 34 __ rear wheel
21 __ bicycle 35 __ rear wheel axis
22 ___ frame 36 __ tensioner chain guide
23 ___ drivetrain 37 __ swing arm
24 ___ front frame portion 38 __ rocker arm
25 ___ front wheel 39 __ link
26 ___ pedal crank 40 __ active sprocket
27 ___ drive chain 41 __ swing arm pivot
28 ___ idler pulley 42 __ rocker arm pivot
29 ___ cassette 43 __ first link pivot
30 ___ rear derailleur 44 __ second link pivot
31 ___ chain tensioner 45 __ shock absorber
32 ___ bottom bracket shell axis 46 __ first shock pivot
33 ___ chainring sprocket 47 __ second shock pivot
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48 ___ drive-side part 51 __ leverage ratio curve
49 ___ non-drive-side part 52 __ anti-squat curves
50 ___ rear wheel axis path
DETAILED DESCRIPTION OF EMBODIMENTS
[019] In the figures, an embodiment of a suspension system of the present
disclosure is
referred to in general as 20.
[020] FIG. 3 illustrates a bicycle 21 equipped with the suspension system 20
in
accordance with the exemplary embodiment. While the bicycle 21 is illustrated
as a
mountain bike, the suspension system 20 can be applied to any type of bicycle.
The
bicycle 21 can take many different configurations and can have a different
configuration of
components than that shown in the figures. The bicycle 21 can be entirely
driven by pedal
power, or it can be partially or entirely driven by a motive force supplied by
an electric
motor.
[021] The bicycle 21 includes a frame 22 and a drivetrain 23. A front frame
portion 24
forms the front of the frame 22 and can include a seat tube, down tube, top
tube, head
tube, etc. The front frame portion 24 is preferably equipped with a front
wheel fork to
which is attached at its most forward end a front wheel 25 which rotates about
a front
wheel axis. The bicycle 21 can be further equipped with a handlebar, a saddle,
brakes, etc.
Indeed, the bicycle 21 can be equipped with many other components, depending
on its
configuration and intended use, among other possible factors.
[022] Reference is now made to FIG. 1, which is an enlarged view of the
suspension
system 20 and the drivetrain 23. The drivetrain 23 includes at least a pedal
crank 26, a
drive chain 27, and an idler pulley 28, and it can also include a cassette 29,
a rear
derailleur 30, and a chain tensioner 31, all of which are described below.
[023] The pedal crank 26 is rotatably mounted to the frame 22 about a bottom
bracket
shell axis 32 and is adapted to receive pedaling actuation, or an input of
force, from a rider
Date Recue/Date Received 2021-03-29
of the bicycle 21. The pedal crank 26 includes a chainring sprocket 33 (or
front sprocket)
which engages the drive chain 27. The drive chain 27 forms the mechanical
linkage
between the pedal crank 26, specifically the chainring sprocket 33, and a
cassette 29
which is preferably provided on a rear wheel 34 for transmission of drive
torque to the rear
wheel 34. The cassette 29 is an arrangement of sprockets that are coaxial with
reference to
a rear wheel axis 35. Furthermore, the drive chain 27 has a drive chain upper
portion
27U, which is the portion of the drive chain 27 that is tensioned from
pedaling forces.
[024] As shown in FIG. 1, the drive chain upper portion 27U passes over an
idler
pulley 28 on its way from the pedal crank 26 to the cassette 29. The idler
pulley 28 is
rotatably connected to the bicycle 21 for rotation around an axis that is
substantially
parallel with the rear wheel axis 35. The idler pulley 28 is integrated with
the suspension
system 20 in a manner that is described later in the present disclosure. In
the example
shown, the idler pulley 28 is a sprocket with 20 teeth. However, the number of
teeth of the
idler pulley 28 can be different from 20. Also, the idler pulley 28 is shown
as a sprocket,
although it can instead be a roller, and the roller can have flanges for
preventing
disengagement of the drive chain 27 with the roller. Other configurations of
the idler
pulley 28 are within the scope of the present disclosure.
[025] The rear derailleur 30 is configured to control the shifting of gears of
the
bicycle 21 by selectively changing which sprocket of the cassette 29 is
engaged with the
drive chain 27. The bicycle 21 preferably includes a shifter (not shown) via
which the rear
derailleur 30 is operated by the rider for changing which sprocket of the
cassette 29 is
engaged with the drive chain 27.
[026] The chain tensioner 31 is configured for maintaining the drive chain 27
in a
tensioned state or restoring a tensioned state after an antecedent state of
insufficient
tension. The chain tensioner 31 includes a tensioner chain guide 36 which, in
the
exemplary embodiment shown in FIG. 1, is rotatably connected to the front
frame
portion 24 for rotation around the bottom bracket shell axis 32.
[027] The drivetrain 23 can take many different configurations than that which
is
described above and shown in FIG. 1. For example, the chain tensioner 31 can
be
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integrated with the rear derailleur 30, as is the case for the type of rear
derailleur that is
commonly used on bicycles. Instead of a cassette 29, the drivetrain 23 can
have a single
rear sprocket. The drivetrain 23 can include a gearbox which, for example, can
be mounted
to the frame 22 near the pedal crank 26. The drive chain 27 can instead be a
belt, with
the idler pulley 28, chainring sprocket 33, and other sprockets or pulleys
configured to
engage the belt. For the purposes of this disclosure, such a belt is
considered equivalent to
a chain. Also, there can be a chain guiding mechanism, which can include one
or more
pulleys, and which is disposed to engage the portion of the drive chain 27
between the
chainring sprocket 33 and the idler pulley 28. This chain guiding mechanism
can be part
of an electric drive system. Indeed, the drivetrain 23 can be configured in
many ways.
Suspension system
[028] Reference is now made to FIG. 2, which is a left elevational view of the
suspension
system 20, and reference is also made to FIG. 4, which is a right elevational
schematic
functional view of the suspension system 20. The suspension system 20 includes
a linkage
mechanism with parts connected by pivots. Compared to FIG. 1, FIG. 2 is a view
from
the opposite of the bicycle 21 to better show the parts of the suspension
system 20.
FIG. 4 is a simplified view of the suspension system 20 and its
interconnections. The
pivots are substantially parallel with the rear wheel axis 35, and in this
disclosure, they are
named after a component to which they are connected.
[029] A pivot may be fixed or floating. A fixed pivot maintains its position
relative to
the front frame portion 24 when the suspension is compressed. A floating pivot
changes its
position relative to the front frame portion 24 when the suspension is
compressed. In the
schematic figures of the suspension system 20, such as FIG. 4, fixed pivots
are represented
by solid dots, and floating pivots are represented by circles of the same size
as the solid
dots.
[030] The suspension system 20 includes a swing arm 37, a rocker arm 38, and a
link 39. In the exemplary embodiment, the swing arm 37, rocker arm 38, and
link 39 are
considered part of the frame 22 of the bicycle 21, in addition to being part
of the
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suspension system 20.
[031] The swing arm 37 forms the rearmost portion of the frame 22, and is
attached at
its rearmost end to the rear wheel 34. In FIG. 4, the rear wheel 34 ______
while not shown is
concentric with an active sprocket 40 of the cassette 29. The swing arm 37 is
pivotably
connected to the front frame portion 24 via a swing arm pivot 41. This type of
arrangement is known as a "single-pivot" arrangement because the swing arm 37
pivots
about a single pivot axis that is fixed relative to the front frame portion
24. In the
exemplary embodiment shown in FIG. 1, FIG. 2, and FIG. 3, the swing arm 37 is
asymmetric across the center plane of the bicycle 21. This is to achieve
certain objectives,
such as strength, stiffness, and low weight, along with drivetrain
integration. However, the
swing arm 37 could instead be symmetric across the center plane of the bicycle
21, or
configured in any other way.
[032] The rocker arm 38 is pivotably connected to the front frame portion 24
via a
rocker arm pivot 42 and to the link 39 via a first link pivot 43. The link 39,
while
pivotably connected to the rocker arm 38, is also pivotably connected to the
swing arm 37
via a second link pivot 44. The rocker arm 38 and the link 39 are movable
relative to both
the front frame portion 24 and the swing arm 37.
[033] The suspension system 20 includes a shock absorber 45 with a spring and
damper.
The shock absorber 45 isolates and controls the movement of the rear wheel 34
relative to
the front frame portion 24. The shock absorber 45 is pivotably connected to
the rocker
arm 38 via a first shock pivot 46, and pivotably connected to another part of
the
bicycle 21 via a second shock pivot 47. In the exemplary embodiment, this
other part of
the bicycle 21 is the front frame portion 24; in other words, the shock
absorber 45 is
pivotably connected to the front frame portion 24 via the second shock pivot
47. The
schematic representation of the shock absorber 45 in FIG. 4 is the generic
symbols for a
spring and damper. These symbols should not be seen as constraining the type
of spring or
damper. For instance, although the symbol for the spring resembles a coil
spring, the
spring could instead be an air spring or any other type of spring. The damper
could
include a component that is fixed relative to the front frame portion 24 and
that is
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Date Recue/Date Received 2021-03-29
connected to the rest of the shock absorber 45 by a hose. Also, the shock
absorber 45
could be a pull shock instead of the push shock shown in the exemplary
embodiment.
Many configurations of the shock absorber 45 are possible.
[034] As can be seen in FIG. 4 based on whether the pivots are represented by
a dot or a
circle, the fixed pivots are the swing arm pivot 41, rocker arm pivot 42, and
second shock
pivot 47; and the floating pivots are the first link pivot 43, second link
pivot 44, and first
shock pivot 46. The distinction between fixed and floating pivots is useful
later in this
disclosure where the operation of the suspension system 20 is further
described.
[035] For the purposes of this disclosure, the idler pulley 28 is considered
part of the
suspension system 20 (in addition to being part of the drivetrain 23). The
idler pulley 28
is rotatably mounted to the rocker arm 38 for rotation about an axis that is
eccentric (or
non-coaxial) with the rocker arm pivot 42. As a result, the linkage mechanism
of the
suspension system 20 governs the movement of the idler pulley 28 during
suspension
travel. In other words, the idler pulley 28 is displaced when the suspension
system 20 is
actuated through its travel. In the exemplary embodiment, the idler pulley 28
is displaced
generally upward and forward when the suspension is compressed. The idler
pulley 28 (like
the active sprocket 40) can be considered to float like the aforementioned
floating pivots;
however, the rotation axis of the idler pulley 28 is not a suspension pivot
and is therefore
not illustrated as such in FIG. 4.
[036] In the exemplary embodiment, the rocker arm 38 has a drive-side part 48
and a
non-drive-side part 49. These two parts of the rocker arm 38 are indicated in
FIG. 1 and
FIG. 2. The drive-side part 48 of the rocker arm 38 is on the same side of the
bicycle 21
as the drivetrain 23. The idler pulley 28 is mounted to the drive-side part 48
and not to
the non-drive-side part 49. However, the idler pulley 28 could instead be
mounted to both
parts of the rocker arm 38, or there could not be a drive-side part 48 and non-
drive-side
part 49 of the rocker arm 38 (for example, the rocker arm 38 could be on one
side only of
the bicycle 21).
[037] In the exemplary embodiment, the pivots of the rocker arm 38 are
constructed
such that its drive-side part 48 and non-drive-side part 49 are each pivotably
connected to
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the front frame portion 24. This is such that if the link 39 and shock
absorber 45 were to
be disconnected from the rocker arm 38, the drive-side part 48 and non-drive-
side part 49
could pivot separately from one another, relative to the front frame portion
24.
[038] A focus of this disclosure is the two-dimensional, geometrical
arrangement of the
suspension system 20 and its pivots (illustrated in FIG. 4, FIG. 5, and FIG.
6). However,
the mounting of the idler pulley 28 to the rocker arm 38 introduces certain
considerations
with regard to the three-dimensional configuration of the pivots of the rocker
arm 38. For
the exemplary embodiment shown in FIG. 1, when the drive chain 27 is engaged
with
either the smaller or larger sprockets of the cassette 29, the portion of the
drive chain 27
between the idler pulley 28 and cassette 29 is on an angle relative to the
center plane of
the bicycle 21. Therefore, a component of the force that the drive chain 27
exerts on the
idler pulley 28 will be in a direction normal to the center plane of the
bicycle 21. Practice
has shown that this force can be sufficient to displace the drive-side part 48
of the rocker
arm 38 in a twisting manner such that its rearmost end (near the idler pulley
28) and
foremost end (at the first shock pivot 46) are displaced in opposite
directions normal to
the center plane of the bicycle 21. For example, if the drive chain 27 is
engaged with the
largest sprocket of the cassette 29, the force from the drive chain 27 on the
idler pulley 28
will have a component directed toward the bicycle 21 and normal to the center
plane of
the bicycle 21. If the construction of the pivots of the drive-side part 48 of
the rocker
arm 38 allows it, this member may twist such that its rearmost end is
displaced toward the
bicycle 21 while its foremost end is displaced away from the bicycle 21. This
potential
issue is prevented by constructing the pivots of the drive-side part 48 such
that it is fixed
along the length of its pivots (namely, the second link pivot 44, rocker arm
pivot 42, and
first shock pivot 46). For example, known pivot bearing retention measures may
be used,
such as flanges or shoulders, retaining rings, interference fit, the
application of a retaining
compound (e.g. a methacrylate ester acrylic liquid, such as Loctite 680TM)
during assembly,
or a combination of these. However, the drive-side part 48 need not be fixed
along the
length of its pivots for successful operation of the suspension system 20. For
example, the
drive-side part 48 could be configured to float along the length of its pivots
or to do this in
combination with pivoting about an axis that is perpendicular to the rocker
arm pivot 42.
Date Recue/Date Received 2021-03-29
This could reduce the angle of the portion of the drive chain 27 between the
idler
pulley 28 and the cassette 29 relative to the center plane of the bicycle 21,
so as to reduce
friction and noise in the drivetrain 23. Many pivot constructions could be
described that
fall within the purview of this disclosure.
Operation of the suspension system
[039] The suspension system 20 acts to isolate the front frame portion 24 from
the
movement of the rear wheel 34 via the linkage mechanism. The suspension system
20 has
suspension travel with a beginning point of displacement where the suspension
is
completely uncompressed (0% travel) and an ending point of displacement where
the
suspension is completely compressed (100% travel). Suspension travel
translates into rear
wheel travel and shock absorber travel. Rear wheel travel is measured
vertically and
increases as the rear wheel 34 moves upward. Shock absorber travel is measured
between
the mounting points or pivot axes of the shock absorber 45 and increases with
increasing
force output of the spring of the shock absorber 45.
[040] For the following description of functional configurations of the
suspension
system 20 according to the exemplary embodiment, reference is made to FIG. 4,
FIG. 5,
and FIG. 6.
[041] FIG. 5 and FIG. 6 are schematic representations of the suspension system
20 and
are similar to FIG. 4 except that they show the suspension at 50% and 100%
travel,
respectively, whereas FIG. 4 shows the suspension at 0% travel. A rear wheel
axis path 50
is indicated, which is the path of rear wheel axis 35 (not shown) throughout
the range of
suspension travel. The amount of suspension compression can be seen from the
position of
the active sprocket 40 along the rear wheel axis path 50.
[042] As discussed previously, the floating pivots (i.e. the pivots that are
movable
relative to the front frame portion 24) are represented by circles whereas the
fixed pivots
(i.e. the pivots that are fixed relative to the front frame portion 24) are
represented by
solid dots. By comparing FIG. 4, FIG. 5, and FIG. 6, the floating pivots can
be seen to
change position, unlike the fixed pivots which are stationary. For instance,
the second
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shock pivot 47 is fixed whereas the first shock pivot 46 moves generally
downward for
increasing suspension travel (e.g. from FIG. 4 to FIG. 5), signifying
compression of the
shock absorber 45.
[043] In the schematic figures, the drive chain upper portion 27U is shown as
a line that
passes over the idler pulley 28 and that is tangential with the chainring
sprocket 33 and
active sprocket 40 of the cassette 29. The drive chain upper portion 27U is
the portion of
the drive chain 27 that is tensioned from pedaling forces. The portion of the
drive
chain 27 that is not tensioned from pedaling forces is not shown because it's
irrelevant to
this description of the operation of the suspension system 20.
[044] The idler pulley 28 is rotatably connected to the rocker arm 38 and is
eccentric
with the rocker arm pivot 42. Since the shock absorber 45 is pivotably
connected to the
rocker arm 38 via the first shock pivot 46 that is also eccentric with the
rocker arm
pivot 42, both the travel of the shock absorber 45 and the position of the
idler pulley 28
directly depend on the rotational position of the rocker arm 38. The idler
pulley 28 moves
along a path in function of suspension travel, similarly to how the shock
absorber 45 is
compressed in function of suspension travel. As is discussed later, the
pedaling
performance characteristics of the suspension system 20 depend on the movement
of the
idler pulley 28 along this path.
[045] This description now turns to what are known as suspension kinematics.
Suspension kinematics are characteristics of a suspension system that describe
its behavior
in quantitative terms. The focus here is on the suspension kinematics of
leverage ratio and
anti-squat. Below, these concepts are defined and discussed in relation to the
suspension
system 20.
[046] As a suspension system is compressed, the force at the rear wheel
depends on both
the force produced by the shock absorber and the leverage ratio of the
suspension system.
The leverage ratio of a suspension system varies throughout suspension travel,
and it is
defined as the ratio of rear wheel travel to shock absorber travel over an
identical given
rear wheel travel. A leverage ratio can be thought of in terms of the amount
of force at the
rear wheel for a given amount of force from the shock absorber. A lower
leverage ratio
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means that, for a given amount of force from the shock absorber, there is more
force at the
rear wheel. Conversely, a higher leverage ratio means that, for a given amount
of force
from the shock absorber, there is less force at the rear wheel.
[047] The leverage ratio of a suspension system varies in function of
suspension travel. It
is therefore useful to graph leverage ratio as a function of suspension travel
(with leverage
ratio on the vertical axis and suspension travel on the horizontal axis). This
graph is
referred to as a leverage ratio curve. For a given geometrical arrangement of
suspension
pivots, there is a single leverage ratio curve.
[048] It can be advantageous for the leverage ratio of a suspension system to
substantially decrease as the suspension approaches full compression. Such a
decrease in
leverage ratio may result in more force being needed to compress the
suspension as it
approaches full compression than if, for example, the leverage ratio were
constant. That
way, when the suspension reaches full compression, such as during a big
impact, the
variation in force that the rider experiences is less sudden (thus increasing
rider control
and comfort). A decrease in leverage ratio for increasing suspension travel,
or a negative
slope of the leverage ratio curve, is called leverage ratio progression.
[049] In this disclosure, the leverage ratio progression of a suspension
system is
quantified by calculating the difference between the maximum leverage ratio in
the first
half of suspension travel and the minimum leverage ratio in the second half of
suspension
travel, divided by the maximum leverage ratio in the first half of suspension
travel.
Leverage ratio progression is expressed as a percentage.
[050] The amount of leverage ratio progression that is deemed advantageous
depends on
many factors, including the rider's preferences and the configuration of the
shock absorber.
However, it's generally recognized that an advantageous amount of leverage
ratio
progression is typically between 10 and 40%. This statement assumes the use of
a
conventional or commercially-available shock absorber.
[051] A leverage ratio curve 51 of the suspension system 20 is shown in FIG.
7,
according to the exemplary embodiment. As can be determined from the variation
in
leverage ratio in the leverage ratio curve 51, the leverage ratio progression
is
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Date Recue/Date Received 2021-03-29
approximately 23% (100%. (3.1 ¨ 2.3)/3.1 23%). In general, this can be an
advantageous
amount of leverage ratio progression. If the leverage ratio progression were
significantly
less, or even negative (i.e. leverage ratio digression) or near zero, the
rider would
experience more sudden variation in force when the suspension reaches full
compression.
Additionally, the leverage ratio curve 51 has a fairly consistent slope, so
that a rider may
experience consistent behavior of the suspension across the range of
suspension travel (this
depends also on the shock absorber 45 and other possible factors).
[052] The leverage ratio curve 51 of the suspension system 20 can be different
than what
is shown in FIG. 7. For example, the leverage ratio curve 51 could have a
different amount
of progression, it could have a positive slope (increasing leverage ratio), it
could be flat
(constant leverage ratio), or the leverage ratio could vary in a more complex
manner with,
for example, one or more turning points (where the slope changes from positive
to
negative, or vice versa). Although the graph of FIG. 7 is specific, it should
not be
construed as limiting the scope of this disclosure but merely as providing
description of the
exemplary embodiment.
[053] When a bicycle accelerates, there is an increase in force between the
rear wheel and
the ground (i.e. there is weight transfer to the rear wheel). This increase in
force can cause
compression of a bicycle's rear suspension system. This compression is known
as "squat"
and its opposite is known as "rise".
[054] When a suspended bicycle undergoes powered acceleration, power is
transmitted
through the vehicle's drivetrain from the power source to the rear wheel, and
forces are
applied to the movable elements of the suspension system. The drivetrain
forces can affect
the overall behavior of the suspension system. More specifically, the
drivetrain forces can
generate an extension or compression force on the suspension system which
affects the
amount of squat. If the drivetrain forces reduce the amount of squat of a
suspension
system under powered acceleration, the suspension system is said to have anti-
squat.
[055] Anti-squat is expressed as a percentage. At 0% anti-squat, the
drivetrain generates
no extension or compression force on the suspension system ________________ in
other words, the drivetrain
does not influence the suspension system and therefore, the suspension
system
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Date Recue/Date Received 2021-03-29
compresses during powered acceleration. At 100% anti-squat, the drivetrain
generates an
extension force on the suspension system that exactly balances the compressive
weight
transfer force __ therefore, the suspension system neither compresses nor
extends during
powered acceleration.
[056] The meaning of anti-squat percentages other than 0 and 100% can be
deduced
from its meaning at these two values. Between 0 and 100% anti-squat, the
drivetrain's
extension force is less than the compressive weight transfer force, so there
will be some
squat. Above 100% anti-squat, the drivetrain's extension force is more than
the
compressive weight transfer force, so there will be rise. And below 0% anti-
squat, the
drivetrain generates a compression force instead of an extension force, and
this
compression force adds to the compressive weight transfer force to produce a
lot of squat.
Negative anti-squat can be called pro-squat.
[057] Anti-squat varies as a function of suspension travel. It is therefore
useful to graph
anti-squat as a function of suspension travel (with anti-squat on the vertical
axis and
suspension travel on the horizontal axis). This graph is referred to as an
anti-squat curve.
There are known methods in the art for calculating anti-squat, and any
suitable method
may be applied.
[058] The size of the chainring sprocket and active cassette sprocket affects
the amount
of extension or compression force from the drivetrain. The size of these
sprockets is
frequently varied to produce desired gear ratios. Therefore, it's beneficial
for anti-squat
curves to be accompanied by information on the size of the chainring and
cassette
sprockets that are assumed in the calculation of the anti-squat. Also, it's
common for
anti-squat curves for multiple cassette sprocket sizes to be provided on a
single graph.
[059] The vertical position of the center of suspended mass affects the amount
of
compressive weight transfer force (the suspended mass includes the rider and
the front
frame portion). A higher center of suspended mass will produce more
compressive weight
transfer force, and a lower center of suspended mass will produce less
compressive weight
transfer force. Since anti-squat is defined in relation to the amount of
compressive weight
transfer force, it's beneficial for anti-squat curves to be accompanied by
information on the
Date Recue/Date Received 2021-03-29
vertical position of the center of suspended mass that is assumed in the
calculation of the
anti-squat. Providing the assumed vertical position of the center of suspended
mass allows
for useful comparisons of anti-squat between different suspension systems.
[060] For the total range of travel of a suspension system, the anti-squat
values of
greatest significance are those for the suspension travel positions when a
rider pedals. The
suspension travel positions when a rider pedals are primarily within a range
known as
suspension sag. When a rider is immobile on a bicycle on flat ground, the
suspension will
be compressed by a certain, fixed amount, called static sag. When the rider
pedals the
bicycle, the drivetrain forces and the motion of the rider will cause
actuation of the
suspension system, and the suspension will be compressed by a varying amount,
called
dynamic sag. The suspension travel of a bicycle that is being pedaled is
usually in the
range of dynamic sag. Furthermore, suspension sag is typically given as a
percentage of
total suspension travel.
[061] Three anti-squat curves 52 of the suspension system 20 are shown in FIG.
8,
according to the exemplary embodiment. For all three anti-squat curves 52, the
size of the
chainring sprocket 33 is 30 teeth. Each curve is for a different size of the
active
sprocket 40 of the cassette 29: the dashed line is for a sprocket size of 10
teeth, the solid
line is for a sprocket size of 18 teeth, and the dotted line is for a sprocket
size of 45 teeth.
In the calculation of anti-squat, the assumed vertical position of the center
of suspended
mass is 650 mm above the bottom bracket shell axis. An arbitrary range of
dynamic sag is
illustrated as being between 25 and 50 mm of rear wheel travel (20-40% of
travel).
[062] The anti-squat curves 52 in FIG. 8 convey certain pedaling performance
characteristics of the suspension system 20. In the illustrated range of
dynamic sag, the
anti-squat is around 110-130%. Practice has shown that, for commonly assumed
vertical
positions of the center of suspended mass, such as 650 mm, 110-130% can be an
advantageous amount of anti-squat for achieving a reasonable amount of
pedaling efficiency
while balancing other performance considerations (such as pedal kickback,
which isn't
discussed in this disclosure).
[063] The three anti-squat curves 52 are seen to intersect in the range of
dynamic sag;
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Date Recue/Date Received 2021-03-29
more specifically, they intersect at a rear wheel travel of 33 mm or 26%
travel. While a rider
pedals, if the suspension system 20 were to not actuate (or bob) and the
static sag were to
be 26% (i.e. the suspension travel were to be constant at 33mm), the amount of
anti-squat
would be approximately constant at 122% for the range of gears of the
exemplary
embodiment. This means that the rider could change gears and the drivetrain 23
would
produce approximately the same amount of extension force on the suspension
system 20.
This can be an advantage when comparing with other suspension systems where
anti-squat
may considerably vary between gears. For this advantage to be captured, the
anti-squat
curves 52 needn't intersect; what matters is that the anti-squat be
substantially constant
between gears in the range of dynamic sag and especially near the static sag.
[064] The aforementioned intersection of the anti-squat curves occurs at a
slightly
smaller amount of travel if the size of the chainring sprocket 33 is increased
from 30 teeth
to, for example, 32 teeth, and it occurs at a slightly greater amount of
travel if the size of
the chainring sprocket 33 is decreased from 30 teeth to, for example, 28
teeth. However,
for these and other chainring sprocket 33 sizes, the anti-squat of the
suspension system 20
will in general remain substantially constant between gears in the range of
dynamic sag.
[065] For the exemplary embodiment, the anti-squat curves 52 of the suspension
system 20 have a generally negative slope. This can be advantageous because it
compensates for the increasing amount of force produced by the shock absorber
45 as the
suspension is compressed. Also, anti-squat has less significance in scenarios
when
suspension approaches full compression, so there are little to no drawbacks to
low
anti-squat or inconsistent anti-squat deep in suspension travel (toward 100%
travel).
[066] A purpose of showing the anti-squat curves 52 is to describe the
exemplary
embodiment of the suspension system 20; however, these curves are not to be
interpreted
as narrowing the scope of this disclosure. The suspension system 20 can be
configured with
different anti-squat curves 52 than those shown in FIG. 8. For example, there
could be an
overall greater or smaller amount of anti-squat in the range of dynamic sag in
any gear,
and the anti-squat curves 52 could have a generally positive slope (increasing
anti-squat),
they could be flat (constant anti-squat), or they could vary in a more complex
manner
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Date Recue/Date Received 2021-03-29
with, for example, two or more turning points (where the slope changes from
positive to
negative, or vice versa). The anti-squat curves 52 can differ from those shown
in FIG. 8
and can have advantages of their own without departing from the scope of this
disclosure.
[067] As discussed previously, the idler pulley 28 is mounted to the rocker
arm 38 and
pivots around the rocker arm pivot 42. This makes the idler pulley 28 move
along a path
as the suspension is actuated. Anti-squat can be tuned by controlling the path
of the idler
pulley 28 and the speed of its movement along this path, and this can be done
by making
certain changes to the geometrical arrangement of the suspension system 20. As
a result,
the suspension system 20 affords flexibility with regard to tuning anti-squat
and the
dynamic behavior of the bicycle 21 under pedaling power.
[068] A consequence of both the idler pulley 28 and a pivot of the shock
absorber 45
being mounted to the rocker arm 38 is that certain changes to the geometrical
arrangement of the suspension system 20 will affect both its anti-squat curves
52 and its
leverage ratio curve 51. However, other changes may affect the anti-squat
curves 52 and
not the leverage ratio curve 51, or vice versa. Specifically, both the anti-
squat curves 52
and leverage ratio curve 51 are affected by changes to the locations of the
rocker arm
pivot 42, first link pivot 43, second link pivot 44, and swing arm pivot 41.
On the other
hand, changes to the location and size (tooth count) of the idler pulley 28
will affect the
anti-squat curves 52 and not the leverage ratio curve 51, and changes to the
location of
the first shock pivot 46 or second shock pivot 47 will affect the leverage
ratio curve 51 and
not the anti-squat curves 52. When changing or designing a geometrical
arrangement of
the suspension system 20, one should take into account which variables affect
both the
anti-squat curves 52 and the leverage ratio curve 51 or affect one or the
other.
Second embodiment
[069] In the following description of alternate embodiments, a reference
numeral to be
assigned to a given member is the same as that assigned to its relevant member
of the
aforementioned exemplary embodiment. However, when a given member is
constructed
differently from its relevant member of the aforementioned exemplary
embodiment, a
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Date Recue/Date Received 2021-03-29
three-digit reference numeral is assigned to the given member. The three-digit
reference
numerals are produced by adding a digit to the reference numeral assigned to
the relevant
member of the aforementioned exemplary embodiment.
[070] FIG. 9 is a right elevational schematic functional view of a suspension
system 220
at 0% travel, in accordance with a second embodiment. Similarly to the first
embodiment,
a swing arm 237 is pivotably connected to the front frame portion 24 via a
swing arm
pivot 241. A rocker arm 238 is pivotably connected to the front frame portion
24 via a
rocker arm pivot 242 and to a link 239 via a first link pivot 243. The link
239, while
pivotably connected to the rocker arm 238, is also pivotably connected to the
swing
arm 237 via a second link pivot 244. The shock absorber 45 is pivotably
connected to the
rocker arm 238 via a first shock pivot 246, and pivotably connected to the
front frame
portion 24 via a second shock pivot 247.
[071] In the first embodiment, the idler pulley 28 is eccentric with all of
the pivots of the
rocker arm 38. However, the idler pulley 28 can be rotatably connected
anywhere on the
rocker arm 38, as long as it's eccentric with the rocker arm pivot 42, without
departing
from the scope of this disclosure. A differentiating aspect of the second
embodiment is that
the idler pulley 28 is concentric with the second link pivot 244, as can be
seen in FIG. 9.
[072] In the first embodiment, the link 39 is in tension between the first
link pivot 43
and the second link pivot 44 when force is applied at the rear wheel 34 to
compress the
suspension system 20. In the same scenario for the second embodiment, the link
239 is in
compression (instead of tension) between the first link pivot 243 and the
second link
pivot 244.
Third embodiment
[073] FIG. 10 is a right elevational schematic functional view of a suspension
system 320 at 0% travel, in accordance with a third embodiment. Similarly to
the first
embodiment, a swing arm 337 is pivotably connected to the front frame portion
24 via a
swing arm pivot 341. A rocker arm 338 is pivotably connected to the front
frame
portion 24 via a rocker arm pivot 342 and to a link 339 via a first link pivot
343. The
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Date Recue/Date Received 2021-03-29
link 339, while pivotably connected to the rocker arm 338, is also pivotably
connected to
the swing arm 337 via a second link pivot 344. The shock absorber 45 is
pivotably
connected to the rocker arm 338 via a first shock pivot 346, and pivotably
connected to
the front frame portion 24 via a second shock pivot 347.
[074] In the first embodiment, the idler pulley 28 is eccentric with all of
the pivots of the
rocker arm 38, and in the second embodiment, the idler pulley 28 is concentric
with the
second link pivot 344. A differentiating aspect of the third embodiment is
that the idler
pulley 28 is concentric with the first shock pivot 346, as can be seen in FIG.
10.
[075] In contrast with the other embodiments where the idler pulley 28 moves
generally
upward or generally upward and forward when the suspension is compressed, in
the third
embodiment, the idler pulley 28 moves generally forward when the suspension is
compressed. This and various other types of movement of the idler pulley 28
can produce
desired pedaling performance characteristics.
Fourth embodiment
[076] FIG. 11 is a right elevational schematic functional view of a suspension
system 420 at 0% travel, in accordance with a fourth embodiment. Similarly to
the first
embodiment, a swing arm 437 is pivotably connected to the front frame portion
24 via a
swing arm pivot 441. A rocker arm 438 is pivotably connected to the front
frame
portion 24 via a rocker arm pivot 442 and to a link 439 via a first link pivot
443. The
link 439, while pivotably connected to the rocker arm 438, is also pivotably
connected to
the swing arm 437 via a second link pivot 444. The shock absorber 45 is
pivotably
connected to the rocker arm 438 via a first shock pivot 446, and pivotably
connected to
the front frame portion 24 via a second shock pivot 447.
[077] In the previous embodiments, the rocker arm 38, 238, 338 rotates
clockwise when
the suspension is compressed (when viewed laterally outwardly from the
drivetrain 23). In
the fourth embodiment, the rocker arm 438 rotates counter-clockwise when the
suspension
is compressed. The rocker arm 38 and the link 39 are movable in various
possible ways
relative to the front frame portion 24 and the swing arm 37.
Date Recue/Date Received 2021-03-29
Fifth embodiment
[078] FIG. 12 is a right elevational schematic functional view of a suspension
system 520 at 0% travel, in accordance with a fifth embodiment. Similarly to
the first
embodiment, a swing arm 537 is pivotably connected to the front frame portion
24 via a
swing arm pivot 541. A rocker arm 538 is pivotably connected to the front
frame
portion 24 via a rocker arm pivot 542 and to a link 539 via a first link pivot
543. The
link 539, while pivotably connected to the rocker arm 538, is also pivotably
connected to
the swing arm 537 via a second link pivot 544. The shock absorber 45 is
pivotably
connected to the rocker arm 538 via a first shock pivot 546.
[079] In the previous embodiments, the shock absorber 45 is pivotably
connected to the
front frame portion 24 via the second shock pivot 47, 247, 347, 447. However,
the shock
absorber 45 can be pivotably connected via the second shock pivot 47 to any
other part of
the bicycle 21. In the fifth embodiment shown in FIG. 12, the shock absorber
45 is
pivotably connected to the swing arm 537 (rather than the front frame portion
24) via a
second shock pivot 547. This means that the shock absorber 45 is pivotably
connected to
both the rocker arm 538 and the swing arm 537. In the previous embodiments,
the second
shock pivot 47 is a fixed pivot, but in the fifth embodiment, the second shock
pivot 547 is
a floating pivot.
Advantages
[080] The reader will see that at least one embodiment of the invention
provides a
bicycle suspension system with advantageous suspension kinematics, such as a
progressive
leverage ratio curve and a substantial amount of anti-squat across a range of
gears.
[081] An additional advantage of the suspension system 20 is that, if used
with the type
of drivetrain disclosed in Canadian Patent Application No. 3,080,960 and
illustrated in
FIG. 1, the suspension system 20 can enable a large range of motion of the
tensioner chain
guide 36. The suspension system 20 accomplishes this without the increased
cost and
complexity of the prior-art suspension system disclosed in European Patent No.
2,420,435
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Date Recue/Date Received 2021-03-29
and described in the Background section. This additional advantage is further
understood
as follows.
[082] The position of the portion of the drive chain 27 that extends between
the
chainring sprocket 33 and the idler pulley 28 generally determines how far
forward the
tensioner chain guide 36 can rotate. The position of this portion of the drive
chain 27
depends on the position of the idler pulley 28. Since the suspension system 20
enables the
idler pulley 28 to be in an elevated and forward position, it also enables the
tensioner
chain guide 36 to rotate far forward and to have a large range of motion. An
increased
range of motion of the tensioner chain guide 36 signifies an increased drive
chain 27
recuperation capacity of the chain tensioner 31. Therefore, increasing the
range of motion
of the tensioner chain guide 36 enables the use of a cassette 29 with a larger
difference in
the number of teeth between its smallest and largest sprockets (i.e. a larger
cassette 29
sprocket size range), or more rear suspension travel, or both.
Other exemplary embodiments
[083] (a) A slide mechanism can be configured to displace the idler pulley 28
relative to
the frame 22 in an axial direction that is substantially parallel with the
bottom bracket
shell axis 32. When the drivetrain 23 is configured with the drive chain 27
engaged with
any of the cassette 29 sprockets, the idler pulley 28 will be displaced to
reduce the
likelihood of the drive chain 27 being in an excessively oblique position.
With such a slide
mechanism, the idler pulley 28 can be considered self-aligning (or
"floating"). The slide
mechanism can reduce the torsional forces on the rocker arm 38. Additionally,
the slide
mechanism can reduce the friction and noise in the drivetrain 23.
[084] (b) In the exemplary embodiment, the link 39 is a single part that
connects the
swing arm 37 to the rocker arm 38. However, the link 39 could instead be
composed of
two or more parts. For example, the link 39 could be composed of one or two
parts that
connect the swing arm 37 to the drive-side part 48 of the rocker arm 38, and
an additional
one or two parts that connect the swing arm 37 to the non-drive-side part 49
of the rocker
arm 38.
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Date Recue/Date Received 2021-03-29
[085] (c) The drive-side part 48 and non-drive-side part 49 of the rocker arm
38 could
be fixedly connected such that they must pivot concurrently. This fixed
connection could
be through a pivot axle, or through some other means, such as fasteners that
fixedly
connect parts of the rocker arm 38 elsewhere than at a pivot. Also, the drive-
side part 48
and non-drive-side part 49 of the rocker arm 38 could be integral with one
another
(i.e. the rocker arm 38 could be manufactured as a single unit). Indeed, the
rocker arm 38
can be configured in many different ways.
[086] As can be seen from the preceding discussion, there are various possible
constructions of the pivots and the parts of the suspension system 20 such as
the link 39
and the rocker arm 38. These various possible constructions are conventional
and thus will
not be discussed in further detail.
Scope
[087] In understanding the scope of the present invention, the term
"comprising" and its
derivatives, as used herein, are intended to be open-ended terms that specify
the presence
of the stated features, elements, components, groups, integers, and/or steps,
but do not
exclude the presence of other unstated features, elements, components, groups,
integers,
and/or steps. The foregoing also applies to words having similar meanings,
such as the
terms "including", "having", and their derivatives. Also, the terms "part",
"section",
"portion", "member", or "element" when used in the singular can have the dual
meaning of
a single part or a plurality of parts unless otherwise stated.
[088] Also, it will be understood that although the terms "first" and "second"
may be
used herein to describe various components, these components should not be
limited by
these terms. These terms are only used to distinguish one component from
another. Thus,
for example, a first component discussed above could be termed a second
component and
vice versa without departing from the teachings of the present disclosure. The
term
"attached" or "attaching", as used herein, encompasses configurations in
which: (1) an
element is directly secured to another element by affixing the element
directly to the other
element; (2) configurations in which the element is indirectly secured to the
other element
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Date Recue/Date Received 2021-03-29
by affixing the element to the intermediate member(s) which in turn are
affixed to the
other element; and (3) configurations in which one element is integral with
another
element, i.e. one element is essentially part of the other element. This
definition also
applies to words of similar meaning, for example, "joined", "connected",
"coupled",
"mounted", "bonded", "fixed", and their derivatives. Finally, terms of degree
such as
"substantially", "about", and "approximately" as used herein mean an amount of
deviation
of the modified term such that the end result is not significantly changed.
[089] While only selected embodiments have been chosen to illustrate the
present
invention, it will be apparent to those skilled in the art that various
changes and
modifications can be made herein without departing from the scope of the
invention as
defined in the appended claims. For example, unless specifically stated
otherwise, the size,
shape, location, or orientation of the various components can be changed as
needed and/or
desired so long as the changes do not substantially affect their intended
function. Unless
specifically stated otherwise, components that are shown directly connected or
contacting
each other can have intermediate structures disposed between them so long as
the changes
do not substantially affect their intended function. The functions of one
element can be
performed by two, and vice versa, unless specifically stated otherwise. The
structures and
functions of one embodiment can be adopted in another embodiment. It is not
necessary
for all advantages to be present in a particular embodiment at the same time.
Every
feature which is unique from the prior art, alone or in combination with other
features, also
should be considered a separate description of further inventions by the
applicant,
including the structural and/or functional concepts embodied by such
feature(s). Thus, the
foregoing descriptions of the embodiments according to the present invention
are provided
for illustration only, and not for the purpose of limiting the invention as
defined by the
appended claims and their equivalents.
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Date Recue/Date Received 2021-03-29
