WO2000010866A1

WO2000010866A1 - Suspension system for bicycle

Info

Publication number: WO2000010866A1
Application number: PCT/CA1999/000768
Authority: WO
Inventors: Paul Muser
Original assignee: Supima Holdings Inc.
Priority date: 1998-08-18
Filing date: 1999-08-18
Publication date: 2000-03-02

Abstract

Suspension system (52) for a bicycle (10) has a damper assembly (54) coupled to a first portion (12) of the bicycle and includes a hydraulic damper (74) made of polyurethane material. The damper assembly (54) has an outer casing (76) from which extends an arm (56) for applying a torque to the damper. Preferably the arm is segmented so that the effective length of the arm and the torque applied to the damper can be adjusted to suit the rider's requirements. A link (58) couples the arm (56) to a second portion (14) of the bicycle and the link is adjustable in length so that the bicycle geometry can be adjusted.

Description

SUSPENSION SYSTEM FOR BICYCLE

Technical Field

The invention relates to a suspension system for a bicycle

and is intended for incorporation into the frame of the bicycle to

improve comfort, safety and performance. As will be apparent from

the description which follows, the suspension system will find

application in other wheeled structures, such as motorized cycles

and wheelchairs.

Background Art

In order to incorporate a suspension system into a bicycle,

the bicycle frame must have two relatively movable frame

components. Normally, a first component is associated with a front

wheel or forward portion of the cycle and a second component is

associated with a rear wheel or rearward portion of the cycle. The

suspension system is installed between the frame components and

includes a shock absorber, whereby impacts to the frame are

absorbed or directed in some way to minimize impacts to the rider.

A common form of shock absorption in a bicycle

comprises a coiled compression spring mounted to a shaft coupling

the components of the frame and bearing against a piston. The

nature of the spring can be selected to provide lesser or greater

resistance to impacts and the piston may optionally be associated

with a hydraulic or pneumatic device, or an actuator to prestress the spring or modify the spring rate of travel. There is however a very

limited range of travel for the spring and little flexibility for

adjusting the sensitivity of the assembly in accordance with the

weight of the rider and the nature of the terrain over which the

rider anticipates riding the bicycle.

The disadvantages of a shock absorber incorporating a

coiled compression spring with limited axial displacement as

described above have been recognized in the motorcycle industry.

US 2,596,411 to Jordan provides a suspension system in which a

torsion bar couples the front steering forks of a motorcycle and

includes a shaft mounted to arms extending from the front wheel

axis. A rubber-like member is secured to the shaft and is adapted to

isolate the steering forks from the front wheel. A hydraulic,

adjustable link couples one end of the arms remote from the torsion

bar to the steering fork to supplement the resiliency in the torsion

bar.

Similarly, in US 5,487,443 to Therm, a torsion bar extends

between frame struts on the mainframe. The torsion bar is fixed to

the main frame at one end and is rotatably connected to the main

frame at the other end on a "floating nut" or bushing. A torsion

bar arm and turnbuckle link couple the torsion bar to a rear frame

or swing arm for mounting a rear wheel. Preferably, an auxiliary

damper to absorb linear shock is disposed between the mainframe

and the rear frame. Such torsion bars cannot be readily accommodated into a

bicycle frame without substantial modification to the frame.

Further, they exhibit limited sensitivity and cannot be adjusted to

suit a rider's requirements and individual preferences for a firm

suspension or a softer suspension.

US 4,913,255 to Takayanagi et al provides a shock

absorber for a motorcycle incorporating a rotary-type hydraulic

damper and a turnbuckle linking an arm coupled to the shaft or to

the casing of the hydraulic damper and to a swing arm or rear frame

for supporting a rear wheel.

The patent provides for varying the speed of rotation of

the rotary-type hydraulic damper by changing the length of the

turnbuckle link and thereby adjusting the damping power

characteristic of the damper. However, the rotary hydraulic damper

is costly and complex to produce. The suspension system is also

undesirably cumbersome and adds significant weight to the cycle.

Applicant's invention is intended to overcome the

aforementioned disadvantages in a simple and effective manner.

Disclosure of the Invention

In its simplest embodiment, the invention provides a

hydraulic damper comprising a cylinder of polyurethane material

mounted to a toothed shaft which is adapted to be fixed to a first

portion of a cycle frame. The polyurethane damper is confined by a casing bearing on an outer cylindrical surface of the damper, and by

transverse bearings bearing on opposite ends of the damper and

adapted to prevent axial displacement and flow of the damper.

Advantage is being taken of the unique properties of polyurethane

when placed under hydrostatic pressure.

Preferably, the casing has an arm extending in a radial

direction to the axis of the shaft and the arm may be segmented into

two portions, whereby the effective length of the arm can be

adjusted. Advantageously, the resulting torque applied to the

damper for a predetermined force can be varied to change the

damping characteristics of the damper.

A link which couples the arm to a second portion of the

cycle frame may be adjustable in length so as to maintain the cycle

geometry, if desired, in any selected configuration of the arm

portions. Alternatively, a bracket for supporting the shaft and

slidable on the cycle frame is provided to compensate for changes in

cycle geometry.

Description of Drawings

A preferred embodiment of the invention and variations

thereof are described below, with reference to the accompanying

drawings, in which:

FIG. 1 is a side elevation view of a bicycle incorporating a

prior art suspension system incorporated into a first style of bicycle

frame: FIG. 2 is a similar view to Fig. 1 showing a suspension

system in accordance with a first embodiment of the invention and

incorporated into a second style of bicycle frame;

FIG. 3 is a similar view to Fig. 1 showing a second

embodiment of the invention incorporated into a bicycle frame of

the style shown in Fig. 1;

FIG. 4 (drawn to a larger scale) is a partly-sectioned view

showing the components of the suspension system drawn in Fig. 3,

with an alternative configuration drawn in ghost outline;

FIG. 5 is a top plan view of the components shown in Fig.

4 drawn in association with a mounting bracket and with a

turnbuckle link fully extended;

FIG. 6 is a similar view to Fig. 5 showing an alternative

embodiment of a rotary damper at one end of the suspension

system;

FIG. 7 is a side elevational view of a third embodiment of

the invention having a fixed length link;

FIG. 8 is a side elevation view of the suspension system

drawn in Fig. 4 and showing, in ghost outline, the dynamic change

in position of a casing for the rotary damper forming part of the

suspension system;

FIG. 9 is a cross-sectional view through the rotary damper

drawn on line 9-9 of Fig. 8;

FIG. 10 is a schematic side elevation of a portion of a cycle incorporating a damper assembly forming part of a suspension

system in accordance with the invention;

FIG. 11 is a cross-sectional view through the damper

assembly of Fig. 10;

FIG. 12 (drawn adjacent Fig. 11) is an assembly drawing

showing the damper assembly of Fig. 11; and

FIG. 13 (drawn adjacent Fig. 12) is a side view of a

mounting bracket forming part of the suspension system of Fig. 10.

Best Mode for Carrying Out the Invention

A typical bicycle frame for a suspension bicycle is

indicated by reference numeral 10 in the prior art drawing of Fig. 1.

The frame 10 comprises a forward portion 12 independently

movable from a rear portion 14 respectively supporting a front

wheel 16 and a rear wheel 18.

The forward portion 12 of the bicycle frame 10 comprises

a mainframe 20 to which is attached the head tube 22 at the front, a

rearwardly extending cross-bar 24, and an upwardly-extending seat

tube 26. The rear portion 14 of the bicycle frame 10 comprises a

pair of upwardly extending seat stays 28 (only one of which may be

seen in Fig. 1 ), a pair of rearwardly extending chain stays 30

pivotally connected to the bottom of the seat tube 26 and the

mainframe 20, and a pair of generally vertically-extending stabilizers

32 connecting seat stays 28 to chain stays 30. A chain sprocket 34 is mounted in conventional fashion so as to be driven by pedals 36, at

the junction between the seat tube 26 and mainframe 20.

In the prior art suspension device illustrated, a coiled

compression spring 38 is mounted to a shaft extending between a

forward end of the seat stays 28 and a bracket 40 which joins the

cross-bar 24 to the mainframe 20. In the embodiment illustrated,

the compression spring 38 has been prestressed and only occupies a

portion of the length of the shaft. The maximum displacement of

the compression spring 38 is indicated by arrow 42 and is

commensurate with the length of the shaft.

In use, upward displacement of the rear wheel 18 as

indicated by arrow 44 will manifest itself as a forward displacement

of the coil spring 38 and a corresponding change in the ground

clearance of the chain sprocket 34 as indicated by arrow 46.

An alternative embodiment of a bicycle frame 46 is drawn

in Fig. 2 and similar components are identified by like numerals. It

will be seen that, in this style of bicycle frame, the seat tube 26 has

its lower portion truncated so as to accommodate the rear portion

14 directly beneath the seat tube 26 and to allow for displacement of

the rear portion 14 of the bicycle frame without obstruction by the

seat tube 26. An alternative trigonal form of bracket 48 is welded to

the cross-bar 24 and mainframe 20 for supporting one end of a

suspension system 50. The suspension system 50 is made in

accordance with one embodiment of this invention which will be described in more detail further below.

A preferred embodiment of a suspension system made in

accordance with the invention is generally indicated by numeral 52

in Fig. 3 where it is incorporated into a bicycle frame 10 of the kind

drawn in Fig. 1. The suspension system 52 is drawn to a larger scale

in Figs. 4 and 5, to which reference will now be made to describe

the component parts. From left to right (as drawn), the components

comprise a damper assembly 54, a segmented arm 56, and a

turnbuckle link 58.

The damper assembly 54 comprises a central, hollow shaft

60 which extends across the width of the bicycle frame 10 and has

threaded apertures 62 adapted to receive fasteners 64 (Fig. 5) which

secure the shaft 60 to respective sides 66, 68 of a bifurcated bracket

70. The location of the bracket 70 may be seen in Fig. 3 where it is

shown welded to the mainframe 20 and extending upwardly towards

the cross-bar 24. It will be understood that the nature of the

bracket 70 can be varied as exemplified by bracket 40 (Fig. 1) and

bracket 48 (Fig. 2). For simplicity of illustration, the bracket 70 and

fasteners 64 have been omitted from Fig. 4.

The outer ends of the shaft 60 comprise a reduced diameter

portion, as can be seen more clearly from the cross-sectional view

drawn in Fig. 9. The larger diameter portion of the shaft 60 has a

toothed exterior surface indicated by numeral 72. The profile of the

surface 72 is carefully formed to avoid sharp wells which might cut or tear a hydraulic damper 74 of polyurethane material positioned

on the exterior of the shaft 60.

The hydraulic damper 74 is in the form of a hollow

cylinder having a longitudinally-extending opening which receives

the shaft 60 therein and is confined between the shaft 60 and an

outer casing 76. The casing 76 has a split 77 and is formed with a

pair of radially-extending lugs 78 disposed adjacent said split 77.

Apertures 79 are formed in the lugs 78 for receiving a bolt 80

whereby the lugs are urged together so as to clamp the outer casing

76 into engagement with the outer cylindrical surface of the

polyurethane hydraulic damper 74. The inner surface 82 of the

casing 76 is also toothed and, together with the toothed surface 72

of the shaft 60, is adapted to mold the polyurethane material in situ,

and form an intermediate gear between the casing and the shaft. It

will be noted that the interior surface of the casing 76 adjacent to

the lugs 78 is smooth so that the polyurethane material will not

extrude into the split 77 and between the lugs 78 and also to prevent

the polyurethane material from being pinched between the lugs.

The polyurethane material comprising the hydraulic

damper 74 is further confined by a pair of bearings 84, 86

transversely-disposed to the axis of the shaft 60 and bearing on

opposite ends of the hydraulic damper 74, the bearings 84, 86 being

adapted to prevent axial displacement and flow of the polyurethane

material out of the damper assembly 54. As can be seen most clearly in Fig. 9, the bearings 84, 86 each comprise an annular disc

with a central aperture which receives the reduced diameter portion

of the shaft 60 and locates against a shoulder formed between the

reduced diameter portion and the toothed large diameter portion of

the shaft 60. An annular lip 88 is formed on an inner surface of the

bearings 84, 86 and locates in a cooperating groove 90 formed in the

outer casing 76 so as to seal the assembly and prevent the

introduction of dirt and the like into the interior of the assembly.

A preferred material of construction for the bearings is Delrin ™ or

Addiprene™ 750 D at 75 D Shore hardness plastic and the

polyurethane preferably is Addiprene™ L-100 or Vibrathane™ B60 2

having a durometer of between 80 A to 90 A on the Shore scale.

The outer casing 76 has a radially-extending arm 56 which

is angularly-staggered from the lugs 78. The arm 56 is segmented

into a first arm portion 92 integrally formed with the casing 76 (Fig.

5) and a second arm portion 94 rotatably coupled to the first arm

portion 92 on a releasable fastener 96. It will be seen that the

mating surfaces of the first arm portion 92 and the second arm

portion 94 are serrated for positive engagement with one another in

a range of angular positions. A change in angular position is

indicated by the chain-dotted outline in Fig. 4 and the range of

positions may extend between chain line 97 and chain line 99.

The outer, free end of the second arm portion 94 is

bifurcated to receive therebetween one end of the turnbuckle link 58. A pivot pin 98 which traverses the bifurcated end of the second

arm portion 94 and the turnbuckle link 58 is held in position with a

Circlip ™ 100. The turnbuckle link 58 and the segmented arm 56

are thus pivotally linked.

The turnbuckle link 58 is adjustable in length and

comprises an outer sleeve 102 and threaded rods 104, 106 which

mesh with internal threads of the sleeve 102 at opposite ends

thereof. Rotating the sleeve 102 using a friction grip 108 comprising

an annular disc of polyurethane material varies the length of the link

58. It will be understood that means other than the grip 108 may

be provided for rotating the sleeve 102. The threaded rod 106

remote from the damper assembly 54 is pivotally connected to the

seat stays 28 forming part of the rear portion 14 of the bicycle frame

10 by means of a bolt 110 having a threaded outer end and a

cooperating nut 112.

Industrial Applicability

The dynamic operation of the suspension system in

accordance with the invention will now be described with reference

being made particularly to Fig. 8. Any shocks transmitted to the

cycle, for example, as a result of the rear wheel 18 encountering an

obstacle, will manifest itself as a forward displacement of the

turnbuckle link 58 as indicated by arrow 114 to assume the position

drawn in ghost outline in Fig. 8. The axial movement indicated by arrow 114 is quite substantial for purposes of illustration but it will

be understood that, in practice, angular displacements of the outer

casing 76 and of the segmented arm 56 of 15 - 60 ° are expected.

Depending on wall thickness, the polyurethane material comprising

the hydraulic damper 74 inside the damper assembly 54 can be

displaced through a 90 ° arc before reaching the limit of its tensile

strength (about 8,000 p.s.i.). In practice, the maximum stress applied

to the polyurethane material will be approximately 600 p.s.i.

It will be noted that a small angular displacement of the

polyurethane material is associated with a significantly large travel

distance at the outer end of the segmented arm 56. This is an

important advantage for off-road cycling where it is necessary for

the wheel clearance indicated by arrow 116 in Fig. 3 to change

constantly to accommodate surface bumps and to allow the cycle to

track properly.

The nature of the polyurethane material is such that a

displacement indicated by arrow 114 may be in the opposite

direction from that drawn in Fig. 8 and the hydraulic damper 74

will operate equally well to absorb the resulting impact. Thus the

suspension system in accordance with the invention is adapted to

provide damping in response to upwardly directed forces indicated

by arrow 117 and downwardly directed forces indicated by arrow

119, (Fig. 3).

Polyurethane, being substantially incompressible, has a relatively constant volume and therefore behaves differently under

torsional load than rubber. When the bolt 80 is tightened to close

the lugs 78 on outer casing 76, the polyurethane hydraulic damper

74 becomes confined between the bearings 84 and 86 and is then

placed under an initial hydrostatic pressure completely filling the

cavity inside the casing 76 which determines the adherence between

the polyurethane material and the associated components, the shaft

60 and the outer casing 76. With a torsional load applied to the

casing 76, the adherence of the polyurethane to the adjacent surfaces

of the shaft and the casing increases, particularly where the

components have a toothed or irregular surface, as illustrated. As a

result, the shock resistance of the polyurethane actually increases

with increasing loads being applied. Conveniently, the polyurethane

hydraulic damper is discrete and can be removed and replaced or

reshaped, as required. While the polyurethane will not delaminate

from the surrounding structure, if the forces applied exceed its

tensile strength, damage may manifest itself in the form of a tear or

separation of the polyurethane material. Such damage does

temporarily weaken the hydraulic damper 74, but the damper

continues to perform adequately because the material adjoining the

tear coalesces to form a bond and effectively repairs itself if the

hydrostatic load is maintained.

The maximum torque which may be applied to the

hydraulic damper 74 occurs in the configuration illustrated in Fig. 8 where the effective length of the segmented arm 56 is at a maximum

and the turnbuckle link 58 is disposed at a right angle to the

segmented arm 56. Such a configuration would be adopted where

maximum damping is required, for example, for a lightweight rider

or for riding over a particularly hard surface.

It will also be understood that the same configuration of

the segmented arm 56 and relative position to the turnbuckle link 58

can be maintained while changing the angular disposition of the

outer casing 76 relative to the shaft 60. This is illustrated in part, by

the ghost outline position of the lugs 78 drawn in Fig. 4.

It will be appreciated that a maximum mechanical

advantage is achieved in the solid outline (5 o'clock) position drawn

in Fig. 8, and that the suspension will become harder or less reactive

as an increasing load is applied to move the outer casing 76 from the

solid line position drawn in Fig. 8 to the ghost outline position

drawn (6 o'clock).

Conversely, if the initial position of the outer casing 76

and segmented arm 56 is in a 4 o'clock position, the continued

application of force will progressively be resisted much less and the

suspension will feel softer and more forgiving.

Returning now to Fig. 4, it will be seen that the effective

length of the arm 56 may be adjusted by changing the relative angle

between the first and second arm portions 92, 94. The range of

positions of the second arm portion 94 is limited at one end by a lockout position indicated by chain line 97 and at the other end

indicated by chain line 99 or by abutting on the bicycle frame 20.

It will be understood that the maximum effective length for the arm

56 is in the ghost position drawn in Fig. 4 (6 o'clock) and that the

effective length of the arm 56 is reduced in other radial positions of

the second arm portion 94.

The relative arm positions would therefore be adjusted in

accordance with the anticipated terrain and the body weight of the

rider. For example, a lightweight rider would be inclined to require

a softer suspension and would therefore increase the effective length

of the arm 56 by approaching the 6 o'clock position where both

arm positions are aligned to subtend an angle of 180 °. However, if

the terrain over which the rider is expecting to use the cycle is very

hard or very bumpy, a certain minimum stiffness may be

appreciated and therefore the rider may choose to set up the

suspension system for a medium responsiveness corresponding to a

relative angle between the first and second arm portions of about 4

o'clock.

From Fig. 4, it will clearly be seen that the two

configurations illustrated show an increase in the separation between

the second arm portion 94 and the seat stays 28 when the arm

portion 94 is moved into the ghost line position. If the rider

requires the frame of the cycle to be static, it becomes necessary to

adjust the length of the turnbuckle link 58. If the length of the turnbuckle 58 is not adjusted, the relative positions of the front

portion 12 and rear portion 14 of the bicycle frame 10 will change

and this change in geometry will have a commensurate change in

the ground clearance indicated by arrow 116 of Fig. 3 and

consequently, also shift the centre of gravity for the cycle.

In Fig. 3, a bicycle including the suspension system 52 of

Fig. 4 and having a short length turnbuckle link 58, is drawn in

solid outline while the same cycle with a longer turnbuckle length is

drawn in ghost outline. This shows that merely manipulating the

turnbuckle 58 to change its length can have a profound effect on the

geometry of the cycle. As cycling enthusiasts will appreciate, such

versatility in adjustment allows the cyclist to approach various

terrains with confidence and with less fear of compromising rider

safety because the center of gravity of the cycle can be raised or

lowered, as required.

It will be noted that the turnbuckle link 58 may be

extended by a distance sufficient for the turnbuckle link to reach the

seat tube 26. In the style of cycle drawn in Fig. 3, the seat tube 26

extends downwardly from the seat to the chain sprocket 34 and the

seat stays 28 extend forwardly of the seat tube 26 where they are

joined by the bolt 110. Continued rotation of the grip 108 to

extend the turnbuckle link 58 will result in the seat stays 28 bearing

against the seat post, as drawn. This prestresses the rotary damper

54 by moving the arm 56 away from the seat tube 26 to assume a forward position illustrated by the ghost outline position drawn in Fig. 8.

Alternative Embodiments

Simple variations of the invention will now be described

with reference to the remaining drawings. The suspension system

indicated by numeral 50 in Fig. 2 comprises a damper assembly 54

and adjustable turnbuckle link 58 but has an arm 56 which is not

segmented. In this embodiment of the invention, the effective

length of the arm through which torque is applied to the hydraulic

damper 74 remains constant and therefore the force required to

obtain a desired damping effect cannot be adjusted as easily.

However, as explained above with reference to Fig. 8, the radial

position of the outer casing 76 relative to the shaft 60 can be

adjusted and therefore the rate of damping desired may be selected

so that it begins relatively hard and becomes softer (falling rate) or

begins softer and becomes relatively harder (rising rate). In selecting

the initial position of the outer casing 76 relative to the shaft 50, the

user will have to consider that there will be an initial radial

displacement or sag caused by the weight of the rider being

transferred to the frame when the rider sits upon the cycle seat.

In another variation of the invention drawn in Fig. 10, a

suspension system designated generally by reference numeral 140 is

incorporated into a cycle frame having a forward portion 142 and a rear portion 144 relatively movable to each other. The forward

portion 142 includes an upwardly-extending seat tube 146, a cross¬

bar 148, and a main frame portion 150 to which is attached a head

tube (not shown) for supporting handle bars and a front wheel. The

rear portion 144 of the cycle frame comprises a pair of upwardly

extending seat stays 152 (only one of which is shown) and a pair of

rearwardly extending chain stays 154 (only one of which is shown)

pivotally connected to the bottom of the seat tube 146 at one end

and joined to respective seat stays 152 at the other end.

The seat stays 152 and chain stays 154 may be discrete

elements each rotatably coupled to a hub (not shown) for a rear

wheel 156 or a unitary body, as drawn.

The suspension system 140 couples a forward end of the

seat stays 152 to the forward portion 142 of the cycle frame and

includes a mounting bracket 158 secured to the seat tube 146 for

example, by welding, and a damper assembly 160. Because the

bracket 158 extends rearwardly from the seat tube 146, no separate

links are required to connect the damper assembly 160 to the rear

portion 144 of the cycle frame although the seat stays 152 could

themselves be considered links to the rear portion 144 of the cycle

frame.

In accordance with the invention, the damper assembly

160, shown in detail in Fig. 11, comprises an outer casing 162 having

an integrally formed arm 164 which extends outwardly from the casing 162 on one side thereof. The arm 164 is transverse to an axis

of rotation defined by a shaft 166 rotatably coupled to the outer

casing 162 and fixed to the bracket 158 with fasteners 163. A free

end of the arm 164 is bifurcated (see Fig. 12) to receive a tongue

extending from the seat stays 152 and apertures 170, 172 are formed

in the bifurcated ends of arm 164 to receive a pivot pin 168 which is

coupled to the seat stays 152. The pivot pin 168 has an annular

groove at one end which receive a Circlip ™ 174 and a head 176 at

the other end whereby the pivot pin 168 is secured to the arm 164.

A hydraulic damper 178 comprising a sleeve of

polyurethane material having a Shore hardness ranging from 80 A to

90 A and chemically adjusted to suit the intended application is

received between the outer casing 162 and the shaft 166.

Unlike the damper assembly of Fig. 4, the outer casing 162

is not split and it cannot be adjusted to clamp the polyurethane. In

order to confine the polyurethane damper 178 and apply the

necessary force to the polyurethane for the desired hydrostatic

pressure, the components are carefully dimensioned and assembled

with a press. The damper 178 is oversized to exceed the radial

separation between the shaft 166 and an inner cavity formed in the

outer casing 162 and is first placed into the outer casing 162. The

shaft 166 is then driven inside a longitudinally extending opening

formed in the polyurethane sleeve which causes the polyurethane

material to come into intimate contact with the outer casing 162 and the shaft 166 and to bulge out under the pressure applied so as to

protrude from a little beyond the toothed surfaces on the inside of

the outer casing 162 and the toothed surfaces on shaft 166. Since

penetration of the shaft 166 into the damper 178 is difficult, a

lubricant of 5-10% volume dishwashing soap to water maybe

applied.

The polyurethane damper 178 is then confined inside the

outer casing 162 by means of a pair of transverse bearings 180 in the

form of an annular disc dimensioned to bridge the radial separation

between the shaft 166 and the inner cavity of the outer casing 162.

A central aperture 182 formed in the bearings 180 receives the shaft

166 and the bearings 180 are disposed on opposite ends of the shaft.

The bearings 180 may be made of Delrin ™, as previously described,

or be made from a harder polyurethane material such as Addiprene™

LF 750 D having a Shore hardness of 75 D, for example.

Optionally, a second pair of annular bearings 184 disposed on the

first pair of bearings 180 between said bearings 180 and the

mounting bracket 158 are provided to minimize friction between the

damper assembly 160 and the mounting bracket 158.

The fasteners 163 are received through apertures 186

formed in the mounting bracket 158 and are threaded at one end to

secure to threaded holes 188 formed in the shaft 166. In this way,

pressure is applied to confine the polyurethane damper 178 inside

the outer casing 162 so as to prevent axial displacement and flow of the polyurethane material.

In the embodiment of the suspension system 118 drawn in

Fig. 6, like parts are identified by similar numerals as in Fig. 5. The

only change appears in the damper assembly 54 which includes a

second pair of bearings 120, 122 disposed between the respective

sides 66, 68 of the bracket 70 and the bearings 84, 86 disposed

adjacent to the outer casing 76. The second pair of bearings 120,

122 preferably made from a different material than bearings 84, 86,

isolates the outer casing 76 from the bracket 70 so that there will be

no friction hindering movement of the outer casing 76 about the

internal shaft 60. In addition, a plurality of bearing disc pairs (84,

86) and (120, 122) provides flexibility to allow the components of

the suspension system to be fitted to brackets where the separation

between the sides 66, 68 may change in accordance with the width

of the associated cycle frame.

As discussed with reference to Fig. 4, the relative angle

between the first and second arm portions 92, 94 can be adjusted to

change the force required to apply a predetermined torque to the

hydraulic damper 74. In so doing, if the separation between the end

of the second arm portion 94 remote from the rotary damper 54 and

the seat stays 28 is fixed, the relative position of the front portion 12

and rear portion 14 of the bicycle frame 10 will change.

In an alternative embodiment of the invention, drawn in

Fig. 7, with like components identified by like numerals, a link 130 of fixed length couples the second arm portion 94 to the seat stay

28. Where it is not desirable to change the geometry of the cycle

frame resulting from different angular positions selected for the

portions 92, 94, the damper assembly 54 is mounted to a bracket 132

which is slidably mounted on to cross-bar 24 as indicated by

directional arrow 134. The bracket 132 comprises an upper portion

134 and a lower portion 136 adapted to receive the cross-bar 24

therebetween and having cooperating flanges secured by suitable

fasteners 138 for securing the bracket 132 at selected locations on the

cross-bar 24. Thus, rotation of the first arm portion 92 on fastener

96, as indicated by arrow 136, will cause the unsecured bracket 132

to slide on the cross-bar 24 and the relative position of the link 130

to the seat stays 28 can be maintained when the bracket is secured in

place.

It will be understood that several variations may be made

to the above-described embodiments of the invention without

departure from the inventive concept defined in the appended

claims. The invention provides a simple structure for suspending

relatively movable parts which is easily adjustable and which does

not unduly add any weight to the associated structure. The

components require no lubrication and are relatively maintenance-

free. While the embodiments have been described with reference to

a bicycle, it will be understood that there has been no dimensional

limitations placed on the components and that a polyurethane torsion spring having a 20mm thickness suitable for a bicycle, could

easily be scaled to a thickness of 12-15cm so that it can safely be

used with a heavier- weight cycle such as a motorcycle.

Commensurate changes in the associated components would be

required as will be apparent to those skilled in the art and will be

understood to be within the scope of the appended claims.

Claims

1. Suspension system (52) for a bicycle (10) having first (12)

and second (14) relatively movable frame portions, the suspension

system including:

a damper assembly (54) having a shaft (60) defining an axis

of rotation and adapted to be coupled to said first frame portion

(12), a hydraulic damper (74) comprising a sleeve of polyurethane

material having a longitudinally extending opening receiving the

shaft (60) therethrough, an outer casing (76) rotatably coupled to the

shaft (60) with said sleeve of polyurethane material disposed

therebetween, the outer casing (76) bearing on an outer surface of

the sleeve of polyurethane so that the polyurethane material makes

intimate contact with said shaft (60) and said casing (76), and at least

one pair of bearings (84, 86) transversely disposed to said axis of

rotation and bearing on opposite ends of said sleeve of polyurethane

material, the bearings (84, 86) being adapted to confine the

polyurethane material and to prevent axial displacement and flow of

the polyurethane material so that the polyurethane is placed under

hydrostatic pressure;

a segmented arm (56) comprising a first arm portion (92)

extending outwardly from said outer casing (76) and transversely

disposed to said axis of rotation, and a second arm portion (94)

rotatably coupled to the first arm portion (92), said first and second

arm portions (92, 94) being adapted to subtend a selected angle which defines an effective arm length for torquing said hydraulic

damper (74); and

a link (58) having a first end rotatably coupled to said

second arm portion (94) and having a second end rotatably coupled

to said second frame portion (14).

2. Suspension system (52) according to claim 1 in which the

link (58) has length adjustment means (102, 104, 106) for changing

the length of the link.

3. Suspension system according to claim 1 having a mounting

bracket (70) for supporting said shaft (60) and coupled to said first

frame portion (12).

4. Suspension system according to claim 3 in which the

mounting bracket (132) is adapted to be slidably mounted to the

first frame portion (12).

5. Suspension system (140) for a bicycle having first (142) and

second (144) relatively movable frame portions, the suspension

system including:

a damper assembly (160) having a shaft (166) defining an

axis of rotation and adapted to be coupled to said first frame portion

(142), a hydraulic damper (178) comprising a sleeve of polyurethane material having a longitudinally extending opening receiving the

shaft (166) therethrough, an outer casing (162) rotatably coupled to

the shaft (166) with said sleeve of polyurethane material disposed

therebetween, the outer casing (162) bearing on an outer surface of

the sleeve of polyurethane so that the polyurethane material makes

intimate contact with said shaft (166) and said casing (162), and at

least one pair of bearings (180, 184) transversely disposed to said axis

of rotation and bearing on opposite ends of said sleeve of

polyurethane material, the bearings (180, 184) being adapted to

confine the polyurethane material and to prevent axial displacement

and flow of the polyurethane material so that the polyurethane is

placed under hydrostatic pressure; and

an arm (164) extending outwardly from said outer casing

(162) and transversely disposed to said axis of rotation, said arm

(164) having a free end which is coupled to said second frame

portion (144).

6. Suspension system (50) for a bicycle (46) having first (12)

and second (14) relatively movable frame portions, the suspension

system including:

a damper assembly (54) having a shaft (60) defining an axis

of rotation and adapted to be coupled to said first frame portion

(12), a hydraulic damper (74) comprising a sleeve of polyurethane

material having a longitudinally extending opening receiving the shaft (60) therethrough, an outer casing (76) rotatably coupled to the

shaft (60) with said sleeve of polyurethane material disposed

therebetween, the outer casing (76) bearing on an outer surface of

the sleeve of polyurethane so that the polyurethane material makes

intimate contact with said shaft (60) and said casing (76), and at least

one pair of bearings (84, 86), (120, 122) transversely disposed to said

axis of rotation and bearing on opposite ends of said sleeve of

polyurethane material, the bearings (84, 86), (120, 122) being adapted

to confine the polyurethane material and to prevent axial

displacement and flow of the polyurethane material so that the

polyurethane is placed under hydrostatic pressure;

an arm (56) extending outwardly from said outer casing

(76) and transversely disposed to said axis of rotation; and

a link (58) having a first end rotatably coupled to said arm

(56) and having a second end rotatably coupled to said second frame

portion (14).