CA3155940A1 - Adjustable bicycle suspension system - Google Patents

Abstract

Adjustable Bicycle Suspension System April 5, 2022 Inventor: D'Arcy O'Connor Assignee: D'Arcy O'Connor and Ursa Bikes Abstract: A bicycle rear wheel suspension system includes an upper link and a lower link both pivotally attached to the frame and to a rear stay member. An instantaneous center of rotation of the rear stay member is defined at an intersection between an upper axis extending through first and second pivots of the upper link and a lower axis extending through third and fourth pivots of the lower link. The attachment point of the lower link onto the front triangle dictates whether the rear suspension is a "high pivot" or a "low pivot" suspension. A high pivot suspension requires the use of an idler pulley above the crankset chainring, which the tension side of the drive chain routes over top of the pulley and then around the crankset chainring to towards the rear of the bike. A "low pivot" suspension does not require a pulley since the rearward wheel trajectory is predominantly vertical or slightly forward of vertical, and thus does not pull on the chain enough to require an idler pulley. This suspension accommodates for both a "high pivot" suspension design layout that utilizes an idler pulley as well as a "low pivot" suspension design which does not require an idler pulley on the same frame. Such an adjustable suspension would allow for a bike to transform between a suspension layout that would be ideal for Downhill Mountain Bike riding and a suspension layout that is better suited for more level-ground riding. Claims: The invention as claimed is: 1. Claim 1 - A bicycle frame set comprising: a main frame including at least a seat tube, a top tube, a head tube, a down tube, and a bottom bracket; and a rear wheel suspension system pivotally attached to the main frame, the rear wheel suspension system comprising: an upper link pivotally attached to the main frame at a first pivot point; a rear stay member having an upper end pivotally attached to the upper link at a second pivot point and a lower end having a dropout receiving a rear wheel axle of the bicycle, the rear wheel axle defining an axle axis about which the rear wheel rotates when mounted to the dropout; a lower link pivotally attached to the main frame at a third pivot point, called the Main Pivot ("MP"), located on said main frame at a lower vertical elevation than the first-pivot point, and the lower link being pivotally attached to the rear stay member at a fourth pivot point located on said rear stay member below said upper end thereof; and a shock absorber having a first end pivotally connected to the upper link and a second end pivotally connected to the main frame; wherein an instantaneous center of rotation is defined at an intersection between an upper axis extending through the first and second pivots and a lower axis extending through the third and fourth pivots. Said intersection, or ICR, translates as the rear wheel compresses. 1 Date Recue/Date Received 2022-04-20

Description

BACKGROUND ART
Rear wheel suspension systems have been used on a variety of two-wheeled vehicles, including motorcycles, scooters and bicycles, for providing improved rider comfort and increased performance.
Rear wheel suspensions on bicycles have become increasingly popular, and generally provide a rider with the benefits of a more comfortable ride and better control over the bicycle.
Such bicycle suspension systems improve ride quality by absorbing the energy incurred from encountering ground obstacles, rather than transmitting them through the frame to the rider. By maintaining greater contact between the tire and the ground, the suspension also provides the rider with better control for accelerating, braking, and cornering.
For a suspension to be suitable for use on a bicycle, it must be efficient.
Ideally, a perfect rear wheel suspension would compress only in reaction to ground forces but not to drive-train or braking forces.
Unwanted suspension movement resulting from drive train forces wastes rider energy.
Accordingly, there exists a need for an improved bicycle rear wheel suspension which reacts principally to ground forces and limits the action of drive-train and braking forces thereon. These kinematic qualities differ for downhill and cross-country riding applications and the intent of the present invention to accommodate for both riding conditions with the one bicycle frame.
SUMMARY OF THE INVENTION
It is therefore the aim of the present invention to provide an improved rear wheel suspension system for a bicycle.
Therefore, in accordance with the present invention, there is provided a bicycle frame set comprising: a main frame including at least a seat tube, a top tube, a head tube, a down tube, and a bottom bracket;
and a rear wheel suspension system pivotally attached to the main frame, the rear wheel suspension system comprising: an upper link pivotally attached to the main frame at a first pivot point; a rear stay member having an upper end pivotally attached to the upper link at a second pivot point and a lower end having a dropout receiving a rear wheel axle of the bicycle, the rear wheel axle defining an axle axis about which the rear wheel rotates when mounted to the dropout; a lower link pivotally attached to the main frame at a third pivot point located on said main frame, henceforward called the "Main Pivot (MP)", at a lower vertical elevation than the first pivot point, and the lower link being pivotally attached to the rear stay member at a fourth pivot point located on said rear stay member below said upper end thereof; and a shock absorber having a first end pivotally connected to the upper link and a second end pivotally connected to the main frame; wherein an instantaneous center of rotation (ICR), or Virtual Pivot Point (VPP), is defined at an intersection between an upper axis extending through the first and second pivots and a lower axis extending through the third and fourth pivots.
It is the precise location of the ICR in relation to the tension side of the chain that precisely determines the amount of Anti-squat and resultant pedal kickback (crankset counter-rotation) that the suspension will exhibit.

Date Recue/Date Received 2022-04-20 Bump absorption and suspension sensitivity is increased by elevating the tension side of the chain, and correspondingly raising the ICR relative to the ground such that there is an increase in rearward movement of the rear axle as the suspension compresses. A higher tension side chain, used in conjunction with an idler pulley is called a "high pivot" suspension. This increase in rearward axle movement, or "-x" rear axle trajectory (referring to the Cartesian coordinate system located in "Figure 3", below) better matches the trajectory of the front axle (moved rearward by a telescoping fork and a slack head tube axis angle relative to the horizon). As a result a more constant distance between the rear and front wheel axes is maintained (called "Wheelbase, WB") throughout all points in front and rear suspension travel. When the change in Wheelbase length is minimized throughout the course of suspension travel, the rear suspension can move more freely and independently, particularly when both front and rear brakes are applied. Also, when there is an increase in "-x"
wheel trajectory, the rear suspension is better able to absorb square edge ground obstacles, moving the rear wheel out of the way of the bump, instead of being rotated into the bump edge.
One disadvantage of a "high pivot" suspension is that the addition of an idler pulley introduces a degree of friction to the drivetrain, and there exists a perceivable disadvantage when pedalling uphill, for example. This suspension system is able to convert to a "low pivot" suspension design, by moving the point of fixation to the main frame to a location that is more proximate to the Bottom Bracket Axis, as well as removing the idler pulley allowing the tension side of chain to wrap only over the crankset chainring. Additional to a moving main pivot fixation point, there are two additional pivot points that require adjustment in order to maintain a similar suspension kinematic and bicycle frame geometry. The two additional kinematic adjustment points are located at either end of the shock absorber. By moving these three suspension pivot points from locations set "A", or the "high pivot" suspension, to locations set "B", or the "low pivot" suspension layout, a higher pedaling efficiency suspension is created. The disadvantage to the "low pivot" suspension is the fact that the rear wheel trajectory is more vertical, and less effective towards absorbing the impact forces of a square edged ground obstacle.
This suspension system then describes two sets of pivot points, located on the same frameset that allows the bike to convert between a "high pivot" and a "low pivot suspension layout. It is the intention for both suspension layouts to perform adequately and similarly, and to represent a distinct added value to the owner of a frameset that utilizes this suspension layout design.
A BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made to the accompanying drawings, showing by way of illustration a particular embodiment of the present invention and in which:
Figure 1 is a schematic right side view of a bicycle frame including a rear suspension system according to the "high pivot", pivot point set "A" embodiment of the present invention;
Figure 2 is a schematic right side view of a bicycle frame including a rear suspension system according to the "low pivot", pivot point set "B" embodiment of the present invention;

Date Recue/Date Received 2022-04-20 Figure 3 is a schematic side view of part of the frame and suspension system of Figure 1, showing the suspension system in fully compressed and fully extended positions;
Figure 4 is a schematic side view of part of the frame and suspension system of Figure 2, showing the suspension system in fully compressed and fully extended positions;
Figure 5 is a graphical representation of a rear wheel trajectory of an example of both suspension systems such as shown in Figure 1 and Figure 2;
Figure 6 is a graphical representation of the suspension rate curves of an example of both suspension systems such as shown in Figure 1 and Figure 2;
Figure 7 is a graphical representation of the first derivative of the curves shown in Figure 6.
Figure 8 is a graphical representation of the Kickback curves of an example of the suspension systems such as the ones shown in Figure 1 and Figure 2.
A DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
Referring to Figure 1, a bicycle frame assembly according to a "high pivot", pivot point set "A"
embodiment of the present invention is generally shown at 12, and comprises a rear suspension system linkage assembly 14 and a main frame 20. In a particular embodiment, the main frame 20 is manufactured out of aluminum, steel, carbon-fiber, or any other suitable material.
The main frame 20 comprises a seat tube 13, a down tube 15, a top tube 17, a head tube 19 and a bottom bracket 22. The bottom bracket 22 defines a crank axis 21 extending normal to the view orientation, about which the bicycle's pedal cranks rotate.
In an alternate embodiment, the main frame 20 is a single large structure rather than the previously described assembly of distinct tubes, such as a monocoque-type frame section which can be made, for example, of carbon fiber or sheet metal.
A springing and damping mechanism, or shock absorbing member, such as a shock absorber 24, is pivotally attached to the main frame 20, by a shock mounting bracket 57. In the embodiment shown, the forward shock mounting bracket 57 is secured within the main frame 20 to a mount that is connected to the top tube 17, such as by welding or bolting in place. The shock absorber 24 provides a compression resistance force against which the rear suspension system linkage assembly 14 operates. In an alternate embodiment, the shock absorber 24 can alternately be mounted with equal effect elsewhere within the main frame 20 by attaching it to one or more of the other tubes, or outside the main frame 20, such as to the down tube 15, for example.
The shock absorber 24 acts to counter any forces that may be applied to the rear suspension linkage assembly 14 by the rear wheel as it encounters ground obstacles so as to tend to maintain the relative Date Recue/Date Received 2022-04-20 positions of the main frame 20, the sprung mass, relative to the ground. Doing so thereby also tends to attempt to keep the rear wheel in substantially continuous contact with the ground thereby affording the rider greater control of the vehicle than would occur if the rear wheel is permitted to leave contact with the ground for significant periods of time. Having the rear wheel out of contact with the ground results in a significant decrease in the rider's ability to exert control over the vehicle, caused by a loss in traction with the ground. By doing so, the shock absorber 24 absorbs much of the energy which enters the vehicle through the rear wheel rather than having that energy transferred through the main frame 20 to the rider. As a result, the rider experiences a more comfortable ride and is able to maintain better control over the vehicle. This is of particular significance when the vehicle is operated over highly uneven terrain such as what commonly takes place in the operation of mountain bicycles.
The linkage assembly 14 includes an upper link member 50, a pair of lower link members 40, and a pair of rear stay members 30. The rear wheel of the bicycle is mounted between the pair of rear stay members 30 at dropouts 35 provided at the lower ends thereof. Hence, the rear wheel's axle, and, therefore, the rear wheel's central axis 33, is mounted within the dropouts 35.
The rear ends of the lower link members 40 are pivotally connected to the rear stay members 30 at a rear pivot point 43, and the front ends of the lower link members 40 are pivotally connected to the main frame 20 at a front pivot point 41. The front pivot point 41 is located substantially above, not proximate to the crank axis 21, and the rear pivot point 43 is located proximate the rear wheel's axis 33. The lower link members 40 are located such that their primary axis (i.e. the axis extending through the pivots 41 and 43) is below the rear wheel axis 33 (i.e. the transverse axis extending through the axle of the rear wheel) throughout the travel of the rear wheel from fully extended to fully compressed positions.
One end of the upper link member 50 is pivotally connected to the top of the rear stay members 30 at a pivot point 31. The top link member 50 is further pivotally connected at pivot point 51 that is connected to the top tube 17. The intermediate pivot point 51 is substantially higher on the main frame 20 than is the front pivot point 41 of the lower link member 40. Additionally, the opposite end of the top link member 50 is pivotally connected to the shock absorber 24 at a shock pivot point 53.
In the embodiment shown, two rear stay members 30 and two stay members 40 are provided, one of each type of member being located on a respective side of the vehicle's rear wheel and being generally symmetrical with the other.
Referring to Figure 2, a bicycle frame assembly according to a "low pivot", pivot point set "B"
embodiment of the present invention is generally shown at 12, and comprises the same rear suspension system linkage assembly 14 and main frame 20 found in Figure 1.

Date Recue/Date Received 2022-04-20 A springing and damping mechanism, or shock absorbing member, such as a shock absorber 24, is pivotally attached to the main frame 20, by a shock mounting bracket 57'. In the embodiment shown, the shock mounting bracket 57' is secured within the main frame 20 to a mount that is connected to the top tube 17, such as by bolting in place. In the "low pivot", pivot point set "B" embodiment the shock mating point 57' is in a different Cartesian location then for the "high pivot" embodiment of the present invention.
The linkage assembly 14 includes an upper link member 50, a pair of lower link members 40, and a pair of rear stay members 30. The rear wheel of the bicycle is mounted between the pair of rear stay members 30 at dropouts 35 provided at the lower ends thereof. Hence, the rear wheel's axle, and, therefore, the rear wheel's central axis 33, is mounted within the dropouts 35.
The rear ends of the lower link members 40 are pivotally connected to the rear stay members 30 at a rear pivot point 43, and the front ends of the lower link members 40 are pivotally connected to the main frame 20 at a front pivot point 41. The front pivot point 41 is located above, and proximate to the crank axis 21, and the rear pivot point 43 is located proximate the rear wheel's axis 33. The lower link members 40 are located such that their primary axis (i.e. the axis extending through the pivots 41 and 43) is below the rear wheel axis 33 (i.e. the transverse axis extending through the axle of the rear wheel) throughout the travel of the rear wheel.
One end of the upper link member 50 is pivotally connected to the top of the rear stay members 30 at a pivot point 31. The top link member 50 is further pivotally connected at pivot point 51 that is connected to the top tube 17. The intermediate pivot point 51 is substantially higher on the main frame 20 than is the front pivot point 41 of the lower link member 40. Additionally, the front end of the top link member 50 is pivotally connected to the shock absorber 24 at a shock pivot point 53', which is in a different Cartesian location then for the "high pivot" embodiment of the present invention.
Referring to Figure 3, the "high pivot" suspension setting is shown. The instantaneous center of rotation (ICR) of the linkage assembly 14 is generally determined by the intersection of a first axis extending through the pivots 31, 51 of the upper link member 50 and of a second axis extending through the pivots 43,41 of the lower link member 40. In the Figure, points 31,43 are used to schematically indicate the position of the pivots 31' and 43' in the un-compressed position of the suspension system. Solid dark lines illustrate the various elements in the fully compressed position, that is, the position where the suspension system is located when maximum loads are being applied to the system. The grey dotted single lines show the position of the "skeleton" suspension in the fully extended position, when no load is applied to the system. In order to achieve the required suspension rate, anti-squat, anti-rise, rear wheel trajectory and resultant kickback curves, a virtual pivot suspension is used, such that the intersection point between said first and second axis generally translates from ICR to ICR' over the course of rear suspension compression travel.
Referring to Figure 4, the "low pivot" suspension setting is shown. The instantaneous center of rotation (ICR) of the linkage assembly 14 is generally determined by the intersection of a first axis extending through the pivots 31, 51 of the upper link member 50 and of a second axis extending through the Date Recue/Date Received 2022-04-20 pivots 43,41 of the lower link member 40. In the Figure, points 31, 43 are used to schematically indicate the position of the pivots 31' and 43' in the un-compressed position of the suspension system. Solid dark lines illustrate the various elements in the fully compressed position, that is, the position where the suspension system is located when maximum loads are being applied to the system. The grey dotted single lines show the position of the "skeleton" suspension in the fully extended position, when no load is applied to the system. In order to achieve the required suspension rate, anti-squat, anti-rise, rear wheel trajectory and resultant kickback curves, a virtual pivot suspension is used, such that the intersection point between said first and second axis generally translates from ICR to ICR' over the course of rear suspension compression travel.
Referring to Figure 5, a rear wheel trajectory 100 and 101 for an example of a High pivot and Low pivot suspension system respectively, such as was previously described and shown in Figures 1 through 4 are graphically shown. In a particular embodiment, the rear wheel axis 33' in the fully compressed position for the high pivot suspension system, trajectory 100, is located approximately between 1% and 4% of the vertical travel behind its location in the fully extended position 33. For example, 3 mm rearward of its location in the fully extended position for a vertical travel of 160 mm.
In a particular embodiment, the rear wheel axis 33' in the fully compressed position for the low pivot suspension system, trajectory 101, is located approximately between 6% and 10% of the vertical travel in front of its location in the fully extended position 33. For example, 13 mm horizontally forward of its location in the fully extended position for a vertical travel of 160 mm.
Referring to Figure 6, instantaneous suspension rates 102 and 103 for the high and low pivot suspension configurations respectively, as a function of rear wheel travel for the exemplary suspension systems are graphically shown. The instantaneous suspension rate shown is computed by dividing the instantaneous incremental shock stroke by the resultant instantaneous incremental rear wheel travel. Suspension rate is the first derivative of shock stroke with respect to the rear axle 33 position. As can be seen that in this particular embodiment, this suspension rate curve is progressive which means that the rear wheel travel becomes incrementally smaller the further the rear suspension is in its travel towards a fully compressed state. This is an important suspension quality that ensures maximum rear wheel grip near the extended position of suspension travel, while also aids in the prevention of using all of the rear suspension travel too quickly on larger rear wheel impacts. It is the intent of the present invention to create similar suspension rate characteristic between the high and low pivot suspension configurations so the least about of shock adjustment is required in order to maintain a similar ride feel between them.
Figure 7, curves 104 and 105 for the high and low pivot suspension configurations respectively, are the derivative of the rate curves 102 and 103, or the second derivative of shock stroke with respect to rear axle 33 position. As can be seen, curve 104 is always a positive value, which indicates an entirely progressive rate curve 102. As can be see, curve 105 starts as negative then moves to positive, indicating a progressive rate curve from the point of positive derivative values to the fully compressed state. Also, the majority of change in values of curve 104 and 105 happens in the first 50%
of suspension travel, from fully extended to mid stroke, while the second half of curve 104 remains at an approximately constant set of values. This means that most of the suspension progression happens in the second half Date Recue/Date Received 2022-04-20 of travel where the rate of change values are the highest, thus providing a "bottomless feel" to the suspension system, and provides some additional resistance to the suspension from reaching full travel too quickly. In the first 50% of travel where tire grip is required the most, lower rate of change values are present, allowing for more free-moving suspension that does not resist ground impact forces as much as is present towards the second half of suspension compression.
Figure 8, the kickback curve 106, 107, 108 and 109 for the high and low pivot suspension configurations respectively, are calculated using the Gergely Kovacs equations (found at www.bikechecker.com) and are verified using trigonometry. These particular curves show the amount of crank counter-rotation, in degrees, that occurs when the suspension is compressed whilst in a specific gear chosen for the purposes of the calculation. Curves 106 and 107 are calculated using an 18 tooth gear sprocket at rear axle 33, a 16T pinion gear 56 and a 34 tooth chainring at the crankset. Curves 108 and 109 are calculated using an 18 tooth gear sprocket at rear axle 33, and a 34 tooth chainring at the crankset. All curves are also calculated with 29 inch wheels front and rear. Curve 106, 107, 108 and 109 are calculated with respect to level ground or the horizon. The calculations used to generate curves 106 and 108 allow the rear wheel to rotate as the suspension compresses, as if the rear brake were applied. The calculations used to generate curves 107 and 109 do not allow the rear wheel to rotate as the suspension compresses, which is representative as a brakes off riding condition. What is important to the functioning of this suspension system is that the kickback curves remain below a pre-determined threshold, preventing the rider from experiencing any harsh forces on the feet at the pedals due to excessive pedal kickback when the suspension encounters a harsh square edged impact.
The embodiments of the invention described above are intended to be exemplary.
Those skilled in the art will therefore appreciate that the foregoing description is illustrative only, and that various alternate configurations and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present invention is intended to embrace all such alternate configurations, such as a non-virtual pivot suspension (a "single pivot" suspension), or modifications and variances which fall within the scope of the appended claims.

Date Recue/Date Received 2022-04-20

Claims (6)

1. A bicycle rear wheel suspension system includes an upper link and a lower link both pivotally attached to the frame and to a rear stay member. An instantaneous center of rotation of the rear stay member is defined at an intersection between an upper axis extending through first and second pivots of the upper link and a lower axis extending through third and fourth pivots of the lower link. The attachment point of the lower link onto the front triangle dictates whether the rear suspension is a "high pivot" or a "low pivot" suspension. A high pivot suspension requires the use of an idler pulley above the crankset chainring, which the tension side of the drive chain routes over top of the pulley and then around the crankset chainring to towards the rear of the bike. A "low pivot" suspension does not require a pulley since the rearward wheel trajectory is predominantly vertical or slightly forward of vertical, and thus does not pull on the chain enough to require an idler pulley. This suspension accommodates for both a "high pivot" suspension design layout that utilizes an idler pulley as well as a "low pivot" suspension design which does not require an idler pulley on the same frame. Such an adjustable suspension would allow for a bike to transform between a suspension layout that would be ideal for Downhill Mountain Bike riding and a suspension layout that is better suited for more level-ground riding.
2. 2. Claim 2 ¨ The suspension as described in claim 1, whereas said Main Pivot has two mounting locations located on said main frame. The one most proximate to the bb axis is the "low pivot"
   location. The MP mounting hole farthest from the BB axis is called the "high pivot" location.
3. 3. Claim 3 - The suspension as described in claim 2, wherein when the lower link is mounted in the "high pivot" MP location, the chain is routed over a pulley wheel fixed to the main frame in a location proximate to said "high pivot" axis, and then routed onto the BB
   Crankset chainring.
   When the lower link is attached to the "low pivot" MP position the chain pulley is removed, and the chain is routed directly over the BB Crankset chainring.
4. 4. Claim 4 ¨ A bicycle frame set comprising: a main frame including at least a seat tube, a top tube, a head tube, a down tube, and a bottom bracket; and a rear wheel suspension system pivotally attached to the main frame, the rear wheel suspension system comprising: an upper link pivotally attached to the main frame at a first pivot point; a rear stay member having an upper end pivotally attached to the upper link at a second pivot point and a lower end pivotally attached to a lower link. Said lower link at the rearward end has a dropout receiving a rear wheel axle of the bicycle, the rear wheel axle defining an axle axis about which the rear wheel rotates when mounted to the dropout. The forward end of the lower link is attached to the main frame at a third pivot point, called the Main Pivot ("MP"), located on said main frame at a lower vertical elevation than the first-pivot point, and the lower link being pivotally attached to the rear stay member at a fourth pivot point located on said lower link member proximate to said rear wheel axle axis; and a shock absorber having a first end pivotally connected to the upper link and a second end pivotally connected to the main frame; wherein an instantaneous center of rotation is defined as being stationary and coaxial with said MP axis.
5. 5. Claim 5 - the suspension as described in claim 4, including said Main Pivot has two mounting locations located on said main frame. The one most proximate to the bb axis is the "low pivot"
   location. The MP mounting hole farthest from the BB axis is called the "high pivot" location.
6. 6. Claim 6 - The suspension as described in claim 5, wherein when the lower link is mounted in the "high pivot" MP location, the chain is routed over a pulley wheel fixed to the main frame in a location proximate to said "high pivot" axis, and then routed onto the BB
   Crankset chainring.
   When the lower link is attached to the "low pivot" MP position the chain pulley is removed, and the chain is routed directly over the BB Crankset chainring.
   Description:
   TECHNICAL FIELD
   The present invention relates generally to two-wheeled vehicles, particularly bicycles both electric and non-electric, and more specifically to a rear wheel suspension and drivetrain for such bicycles.
   
   Date Recue/Date Received 2022-04-20