GB2522461A

GB2522461A - Bicycle rear suspension

Info

Publication number: GB2522461A
Application number: GB1401260.3A
Authority: GB
Inventors: Robert James Barr
Original assignee: ARBR Ltd
Current assignee: ARBR Ltd
Priority date: 2014-01-25
Filing date: 2014-01-25
Publication date: 2015-07-29
Anticipated expiration: 2034-01-25
Also published as: GB201401260D0; GB2522461B

Abstract

The rear suspension of a bicycle, particularly suitable for off road use, comprises a swing arm 1, mounted to main frame 16 by a pivot 5, above and to the rear of a bottom bracket location. A droplink 2 pivots to the swing arm 1 at pivot 7 and extends forwardly and above the bottom bracket to rocker 3, said rocker driving a rear shock unit 4.

Description

BICYCLE REAR SUSPENSION

DESCRIPTION

The invention relates to a rear suspension system for a bicycle that offers a rearward wheel path, low centre of gravity and tuneable wheel rate.

BAC KG RO U N D

Front and rear bicycle suspension help isolate the rider from rough trail conditions, resulting in improved comfort and speed. A bicycle may be human powered) or with assistance from an additional power source such as an electric motor, or with full power from an additional power source. Bicycles may be have a rigid connection between the frame and wheels, be fitted with front suspension, or fitted with both front and rear suspension.

A crank assembly is typically fitted to the bicycle frame which rotates about the bottom bracket. The crank assembly can be fitted with a single chain ring or multiple chain rings. At the rear wheel, concentric with the rear axle and connected to the wheel hub, there typically exists multiple cogs. A chain connects between a selected chain ring and a selected cog. Selection of the chain ring is made using a front derailleur. Selection of the cog is made using a rear derailleur. A crank assembly contains crank arms each side of the bottom bracket to which pedals are fitted, allowing the rider to generate torque to drive the bicycle forward. The crank assembly turns rotary motion from the rider's legs to the rear wheel generating forward motion. Chain ring and cog selection is controlled by the rider to achieve the desired mechanical advantage between the crank assembly and rear wheel.

A bicycle may be fitted with a gearbox, located in the main frame or in the rear wheel hub. Drive from such units is typically transmitted to the rear wheels either by belt drives or chain drives.

Front suspension commonly forms part of the front fork assembly, pivoting around the head tube axis and connected to a handle bar above the head tube.

Bicycles that benefit from rear suspension are typically for off road use and are required to negotiate bumpy terrain, isolating the rider from bumps and undulations.

Rear suspension systems control the translation of the rear wheel when a load is applied. As the wheel is moved through its travel the majority of travel is vertical and a portion is longitudinal.

Suspension travel is measured and quoted by the vertical travel of the rear wheel axle relative to the frame. Energy from forces that displace the wheel are absorbed and controlled through a spring and damper unit known as a shock absorber. Vertical wheel travel can be referred to as bump travel.

Rear suspension solutions range from simple single pivot designs to more complex multi-link designs. Multilink designs generate virtual pivot points defined by the intersection of certain link members. Single pivot designs typically place a compromise on wheel path and anti-squat characteristics due to design constraints. Multi-link designs offer less of a dynamic compromise but with increased complexity, weight and cost.

Single pivot designs are commonly operated with linkage arrangements to the shock absorber that allow more design freedom when it comes to setting wheel rate (Shock absorber spring rate seen at the wheel). Commonly used designs activate shock absorbers that are positioned high up in the frame or adjacent to the rear wheel. Such systems have the disadvantage of either increasing the centre of gravity of the bicycle) or locating the shock absorber in such a position that it gets coated in road and trail debris, reducing performance and increasing wear and component damage.

The desirable attributes of a rear suspension design can be defined as: Rearward rear wheel axle path, simple single pivot swing arm installation, ability to tune rear wheel rate and rear wheel travel, elimination of feedback from chain growth, low centre of gravity, anti-squat characteristic to minimise energy loss from drive torque, protection of shock absorber and mechanism from damage and wear from road and trail debris.

It is desirable for the longitudinal part of the rear wheel travel to be rearward so as to move more easily out of the way when running over obstacles. This becomes more challenging to achieve when wheel diameter is increased, the rear axle height increasing relative to the bottom bracket and swing arm pivot location, or virtual pivot location. To achieve a rearward axle path the swing arm pivot or virtual pivot must be increased in height, in line with the increase in rear axle height.

A low centre of gravity is desirable as it increases the stability of the bicycle, improving rider control and confidence. An increase in the centre of gravity will reduce rider confidence. As the swing arm pivot height is increased to achieve a desirable rear wheel path the centre of gravity increases.

An undesirable effect of rearward wheel paths is chain growth, caused by an increasing length between the bottom bracket and rear axle. If the chain is connected directly between the front chain ring and rear cog the chain length must increase as the wheel moves through its travel creating chain tension and torque over the chain ring, which feed backs to the rider in a disconcerting manner. It is desirable to design out this characteristic.

It is desirable for rear suspension systems to exhibit anti squat tendencies. Suspension squat causes the suspension to compress when power is applied through the cranks. Cranks turn rotary motion from the rider's legs to the rear wheel generating forward motion. On a bicycle where the power comes from a human suspension squat wastes noticeable energy that would otherwise be used to drive the bicycle and rider forward.

It is desirable that the force required to move a rear wheel through its travel is variable, to increase rider control and adapt the response of the bicycle to the requirements of the terrain and rider. This is achieved by varying the motion ratio between the rear wheel and shock absorber to change the wheel rate. It is also desirable that such adjustability be achievable independently of the main bicycle frame structure.

To optimise bicycle rear suspension performance typically design focus centres on rear wheel path, wheel rate and anti-squat characteristics during forward motion. A need exists for a suspension system that allows fine tuning and versatility of wheel rate combined with a high mounted swing arm pivot to achieve a rearward rear wheel axle path and desired anti squat characteristic, which does not compromise shock absorber location with regard to a high centre of gravity and protection from trail debris.

STATEMENT OF INVENTION

The rear suspension system of this invention consists of a bicycle assembly containing a swing arm with a shock absorber actuated via a droplink and rocker mechanism. Embodiments of the invention are detailed in the attached figures. The figures in the attachments are for illustrative purposes to describe the content of the invention, the scope of the invention is not limited by the schemes in the figures.

Figure lisa view on the right hand side of a bicycle detailing an embodiment of the invention with the suspension in an uncompressed state.

Figure 2 is a view on the right hand side of a bicycle detailing an embodiment of the invention, as in Figure 1, with the suspension in a compressed state.

Figure 3 is a view of a droplink and rocker mechanism according to certain embodiments of the current invention. The rear suspension is shown in an uncompressed state.

Figure 4 is a view of a droplink and rocker mechanism according to certain embodiments of the current invention. The rear suspension is shown in an uncompressed state.

FigureS is a view of a droplink and rocker mechanism according to certain embodiments of the current invention. The rear suspension is shown in an uncompressed state.

Figure 6 is a view of a droplink and rocker mechanism according to certain embodiments of the current invention. The rear suspension is shown in an uncompressed state.

Figure 7 is a view of a concentric idler option. For simplicity many components of the bicycle assembly are not shown in this figure.

Figure 8 is a view of an eccentric idler option. For simplicity many components of the bicycle assembly are not shown in this figure.

Descriptions of the components in the figures are as follows: Swing arm (1), droplink (2), rocker (3), shock absorber (4), swing arm pivot (5), rocker pivot (6), droplink swing arm pivot (7), droplink rocker pivot (8), shock rocker pivot (9), shock frame pivot (10), rear wheel axle (11), rear wheel (12), front wheel (13), down tube (14), top tube (15), seat tube (16), head tube (17), bottom bracket (18), front chain ring (19), rear cassette (20), idler (21), rear derailleur (22), chain line (23), rear wheel axle path (24), idler bearing (25), swing arm pivot axis (26), idler bearing axis (27), eccentric chain line option (28), idler bearing support (29), frame (30), ground line (31). The bicycle frame (30) consists of the down tube (14), top tube (15), seat tube (16), head tube (17) and bottom bracket (18) and any additional structures linking these components.

The horizontal axis is parallel to the ground line (31). Forward direction passes from the rear wheel (12) to the front wheel (13). The vertical axis is perpendicular to the horizontal axis. The upward direction passes from the ground line (31) through the frame (30) components. The illustrations in the figures are a view on the right hand side.

The swing arm pivot (5), rocker pivot (6) and shock frame pivot (10) remain fixed in position relative to the frame (30). The rear wheel axle (11), droplink swing arm pivot (7), droplink rocker pivot (8) and shock rocker pivot (9) are pivots that float, their position relative to the frame (30) depending on the amount of rear suspension compression and the displacement of the component to which they are attached.

This invention defines the rear suspension mechanism and layout for a bicycle, the primary features of which are described.

Figure 1 illustrates a bicycle that includes an embodiment of a preferred rear suspension assembly.

The swing arm pivot (5) position is located above the bottom bracket (18) and rearward of a vertical line drawn from the centre of the bottom bracket (18) axis. The swing arm pivot(s) is positioned high on the frame (30) such that it generates an initially rearward rear wheel axle path (24) as the suspension moves into bump. The arc travelled by the rear wheel axle (11) through its travel creates a vertical tangent before the end of its travel, this limits chain stay extension. A pivot in this

elevated location can be observed in prior art.

The high swing arm pivot (5) has been utilised to generate space above the bottom bracket (18) so a forward running droplink (2) can run below the swing arm pivot (5), above the bottom bracket (18) and connecting to a rocker (3) whose rocker pivot (6) sits in front of the bottom bracket (18). The droplink swing arm pivot (7) is situated below the swing arm pivot (5), the rearward end of the droplink (2) connects to the droplink swing arm pivot (7). In a preferred embodiment the droplink swing arm pivot (7) is situated forward of a vertical line passing through the swing arm pivot (5). The forward end of the droplink (2) connects to a rocker (3) at the droplink rocker pivot (8), the rocker (3) drives the shock absorber (4) which connects to the shock rocker pivot (9). The shock absorber connects to the frame (30) at the shock frame pivot (10).

The droplink (2) works in tension as the wheel moves into bump. The shock absorber (4) works in compression to support rider weight and absorb wheel impacts. The mechanism allows precise control of the shock absorber (4) motion ratio and gives design control over the shock absorber (4) location. Figure 2 illustrates the rear suspension embodiment of Figure 1 in a compressed state, the shock absorber (4) being fully compressed and the rear wheel (12) being at its extreme of vertical travel.

The forward direction of the droplink (2) allows the rocker (3) to be placed away from the rear wheel (12) and low in the frame, between the top tube (15) and down tube (14). The rocker axis sits forward of the bottom bracket (18). A low centre of gravity is maintained which improves rider control. The frame structure may be designed such that it protects the rocker (3) and shock absorber (4) from debris flicked up by the rear wheel (12).

The droplink (2) which runs between the droplink swing arm pivot (7) and the droplink rocker pivot (8), points predominantly forward. In certain embodiments this line may be angled to enable and adjustment of the rocker (3) location. Embodiments of this suspension require the droplink (2) to run predominantly forward from the droplink swing arm pivot (7). The line drawn between the droplink swing arm pivot (7) and the droplink rocker pivot (8) should sit in an angular range of plus and minus 45 degrees from horizontal when the rear suspension is in an uncompressed state.

In certain embodiments of the design the droplink swing arm pivot (7) may be positioned rearward of a vertical line passing through the main swing arm pivot (5) axis. As illustrated in Figure 2 the droplink swing arm pivot (7) moves rearward of the swing arm pivot (5) as the rear suspension compresses. Rearward positioning of the droplink swing arm pivot (7) with the rear suspension in an uncompressed state is unlikely to extend more than 20 degrees when considering the angle between a vertical line and a line passing between the swing arm pivot (5) and the droplink swing arm pivot (7). The droplink swing arm pivot (7) is positioned in front of the rear wheel (12). In certain embodiments the droplink swing arm pivot (7) may be required to sit further forward than depicted in the figures. In certain embodiments the droplink swing arm pivot (7) may be required to sit further rearward than depicted in the figures. In certain embodiments the droplink swing arm pivot (7) may be required to sit higher than depicted in the figures. In certain embodiments the droplink swing arm pivot (7) may be required to sit lower than depicted in the figures.

In the preferred embodiment illustrated in Figure 1 the upper chain line (23) is routed over an idler (21). The idler (21) can be mounted concentric with the swing arm pivot (5) as can be observed in prior art. A more detailed illustration of the chain line (23) and idler (21) assembly of this embodiment is shown in Figure 7. The chain line (23) route over an idler (21) eliminates chain growth along the upper portion of the chain line (23), removing pedal feedback to the rider. With an idler (21) positioned close to the swing arm pivot (5) an optimal anti squat characteristic is achieved when the bike is at its weighted ride height) increasing drive efficiency. The position of the swing arm pivot (5) and idler (21) location maintains chain wrap around the front chain ring (19) for the purpose of chain retention while negotiating bumpy terrain.

Figure 8 illustrates an embodiment of a rear suspension assembly that utilises and eccentric pivot.

The idler bearing axis (27) can be fitted eccentrically to the swing arm pivot axis (26). The idler bearing support (29) is mounted eccentrically to the swing arm pivot (5) and swing arm pivot axis (26). The idler bearing support (29) is rotationally timed to an axle that runs through the swing arm pivot (5) and is grounded to the frame (30). This embodiment of the invention enables the eccentric chain line option (28) to sit lower that the concentric idler chain line (23). Eccentric pivot options in relation to the swing arm pivot (5) allow force vectors and anti-squat characteristics to be tuned as will be understood by those skilled in the art.

In certain embodiments the idler (21) can be mechanically fixed to the swing arm (1) or a structure attached to the swing arm (1). In certain embodiments the idler (21) can be mechanically fixed to the main frame or a structure attached to the main frame. In certain embodiments the idler (21) may be mechanically attached to a linked structure that connects to both the swing arm (1) and the frame (30).

The chain line (23) runs over the top section of the swing arm (1) in certain embodiments of the invention. In other embodiments the chain line (23) may run through an opening in the swing arm (1), or a split swing arm. This option is required but not limited to an idler (21) that is lower than the swing arm pivot (5).

In the preferred embodiment of the rear suspension system the crank assembly if fitted with a single chain ring (19). It is common for crank assemblies to include multiple chain rings, typically up to three chain rings, and for the a front derailleur to be attached to the frame. In this instance an idler (21) assembly must be fitted that allows axial movement as a degree of freedom such that the plane of idler (21) rotation can translate to coincide with the plane of rotation of the selected chain ring on the crank assembly.

Although undesirable, due to the described pedal feedback from chain tension, the chain line (23) may be routed without the use of an idler (21). In this instance the right hand side of the swing arm (1) should be raised above the chain line, or split around the chain line so the chain can run through the swing arm (1).

In the embodiment of a preferred rear suspension illustrated in Figure 1 the swing arm (1) rotates clockwise about the swing arm pivot (5) as the rear wheel (12) travels into bump. The droplink swing arm pivot (7) rotates clockwise. The droplink (2) translates predominantly rearwards with the swing arm (1), the exact path being dependant on position of the swing arm pivot (5), droplink swing arm pivot (7), droplink rocker pivot (8) and rocker pivot (6).

The droplink rocker pivot (8) may be placed lower than the rocker pivot (6) generating a clockwise rotation of the rocker (3) as the rear wheel (12) moves into bump. The droplink rocker pivot (8) may be placed higher than the rocker pivot (6) generating an anticlockwise rotation of the rocker (3) as the rear wheel (12) moves into bump. The shock rocker pivot (9) may be located at any point on a diameter whose centre is concentric with the rocker pivot (6).

The embodiment detailed in Figure 3 has a rocker pivot (6) that sits higher than the droplink rocker pivot (8). In this instance as the rear wheel (12) moves into bump the rocker (3), driven by tension in the droplink (2), will rotate clockwise. The shock rocker pivot (9) sits rearward of the rocker pivot (6). The shock frame pivot (10) sits forward and above the shock rocker pivot (9).

The embodiment described in Figure 4 has a rocker pivot (6) that sits higher than the droplink rocker pivot (8). In this instance as the rear wheel (12) moves into bump the rocker (3), driven by tension in the droplink (2), will rotate clockwise. The shock rocker pivot (9) sits lower than the rocker pivot (6).

The shock frame pivot (10) sits lower and rearward of the shock rocker pivot (9).

The embodiment described in FigureS has a rocker pivot (6) that sits lower than the droplink rocker pivot (8). In this instance as the rear wheel (12) moves into bump the rocker (3), driven by tension in the droplink (2), will rotate anticlockwise. The shock rocker pivot (9) sits above the droplink rocker pivot (8). The shock frame pivot (10) sits rearward of the shock rocker pivot (9).

The embodiment described in Figure 6 has a rocker pivot (6) that sits lower than the droplink rocker pivot (8). In this instance as the rear wheel (12) moves into bump the rocker (3), driven by tension in the droplink (2), will rotate anticlockwise. The shock rocker pivot (9) sits forward of the droplink rocker pivot (8) and the rocker pivot (6). The shock frame pivot (10) sits above the shock rocker pivot (9).

The option exists to place multiple alternative eyelet positions on the rocker (3) for both the droplink (2) and shock rocker pivot (9) to adjust the motion ratio of the shock absorber (4) and allow varying levels of rear wheel (12) travel. This allows quick adjustment of performance parameters to meet the needs of the terrain and rider to maximise control and performance.

The examples given illustrate the design flexibility that the utilisation of the droplink (2) location opens up. The invention is not limited in scope by the by the specific embodiments described. The mechanisms are functionally equivalent. Modifications of the invention in addition to those described are possible and such modifications are intended to fall within the scope of the intended claims.

The droplink (2) and rocker (3) mechanism) and the associated freedom on shock absorber (4) location allow the structural top tube (15) to pass directly and uninterrupted from the head tube (17) to the swing arm pivot (5) axis.

In a preferred embodiment the down tube (14) that connects between the head tube (17) and the bottom bracket (18) bifurcates as it approaches the rocker pivot (6) to allow clearance for a centrally positioned droplink (2) and its attachment to a centrally positioned rocker (3). The down tube (14)is used to mount a detachable rock guard protector) which doubles as a mudguard) preventing contamination and debris entering into the rocker (3) area. A brace structure between the top tube (15) and down tube (14) doubles as the mounting for the forward shock frame pivot (10). The seat tube (16) runs vertically as a single member, supported with a forward brace down to the top tube (15)) above the swing arm pivot (5). Below the swing arm pivot (5) the seat tube (16) bifurcates so that a central droplink (2) may pass though and connect to the rocker (3).

In an alternative embodiment the down tube (14) remains as a single continuous member between the head tube (17) and bottom bracket (18). The seat tube (16) remains as a single continuous member between the swing arm pivot (5) and the bottom bracket (18). The droplink (2) is split into two components, one component passing each side of the seat tube (16), one on the left hand side and one on the right hand side. The rocker (3) is split into two components, sharing the same rocker pivot (6), mounted each side of the down tube (14)) one on the left hand side and one on the right hand side. The right hand side droplink (2) connects to the right hand side rocker (3). The left hand side droplink (2) connects to the left hand side rocker (3). The shock absorber (4) is connected between the two halves of the rocker (3) at the shock rocker pivot (9).

The rocker (3) and droplink (2) may be replaced with alternative components to change the travel and wheel rate of the suspension system to suit rider preference. The benefit of this invention is that travel and wheel rate can be controlled without the need for frame (30) and swing arm (1) changes.

The left had side of the swing arm (1) may be fitted with an attachment to mount a rear brake caliper as part of a disc brake assembly as can be seen in prior art. The swing arm (1) may be fitted with a floating brake caliper mount, as typically fitted to mountain bikes with disc brakes in prior art, to refine behaviour under braking.

The swing arm (1) may be fitted with an attachment to mount rim brakes as can be seen in prior art.

In certain embodiments the area around the bottom bracket (18) may contain a gearbox or electric motor unit. In these circumstances the swing arm pivot (5), droplink swing arm pivot (7) may be translated forward, rearward, upwards and downwards so that the droplink (2) clears such components. The droplink rocker pivot(s), rocker pivot (6)) shock rocker pivot (9) and shock frame pivot (10) may be repositioned to suit the available package space.

The invention has been described in its preferred embodiments, it will be understood by those skilled in the art that the scope of the invention extends beyond the specifically enclosed embodiments and alternative embodiments and modifications and equivalents thereof.

Claims

CLAIMS1. A swing arm (1) rear suspension having a swing arm pivot (5) above and rearward of the bottom bracket (18), with a droplink swing arm pivot (7) mounted on the swing arm (1) and below the swing arm pivot (5), a droplink (2) predominantly running forward and above the bottom bracket (18) and connecting to a rocker (3) with a rocker pivot (6) that is forward of the bottom bracket (18).
2. A suspension system according to claim 1, in which the rocker (3) rotates clockwise to compress the shock absorber (4) as the rear suspension compresses in bump, the rocker pivot (6) being positioned higher than the droplink rocker pivot (8).
3. A suspension system according to claim 1, in which the rocker (3) rotates anti clockwise to compress the shock absorber (4) as the rear suspension compresses in bump, the rocker pivot (6) being positioned lower than the droplink rocker pivot (8).