GB2338216A

GB2338216A - Bicycle with articulating rear wheel

Info

Publication number: GB2338216A
Application number: GB9811189A
Authority: GB
Inventors: Robert Arthur Buck
Original assignee: BIKE TECHNOLOGY DEV Ltd
Current assignee: BIKE TECHNOLOGY DEV Ltd
Priority date: 1998-05-22
Filing date: 1998-05-22
Publication date: 1999-12-15
Also published as: GB9811189D0

Abstract

The bicycle has a frame 1, a steerable front wheel 7 and the driven rear wheel 70 mounted by a suspension assembly 30 for articulation with respect to the frame 1. Drive to rear wheel sprockets 71 is performed by chain wheels 14 - 16 through the intermediary of an endless chain 75 having a lower path length 91 and an upper path length 92; to provide a substantially constant upper path length 92, an idler wheel 100 is located above an outer periphery of the chain wheels 14 - 16 and a pivot point 45 of the suspension is, preferably, substantially in a horizontal plane of the upper path length 92. The idler wheel 100 is moved on a support axle to move the chain 75 between the wheels 14-16.

Description

f 2338216 BICYCLE This invention relates to a bicycle and in particular,

although not exclusively, to a bicycle including least rear suspension.

It is known for a bicycle to have a frame and wheels that are all generally in a common vertical plane. A front end of the frame has a top bracket in which is located a bearing and through which at least one fork, usually a pair of forks, are rotatably mounted for steering a front wheel, the wheel having a pivotal axle located at a lower end of the front fork (s). The fork(s) mounting the front wheel is steered by handlebars. A further part of the frame includes a seat pillar upon which is mounted a saddle and a bottom end of the frame has a bottom bracket in which is located a bearing rotatably supporting a chain wheel. The chain wheel is secured to a pair of opposed cranks, one on each side of the frame, which normally mount pivotable pedals upon which a user positions their feet and drives the chain wheel in a circular motion. In a bicycle having rear suspension, a spring biassed damper has one end connected to a portion of the frame and an opposite end of the damper is pivotally connected to one limb of a framework, the opposite end of which rotatably locates a rear wheel. The framework has at least one further limb which is pivotally connected to a portion of the frame which lies within the diameter of the chain wheel and which is located forward of the axis of the chain wheel. By such connections, the rear wheel is suspended such that it is capable of articulation in the plane of the frame.

An axle of the rear wheel is secured to a plurality, for example eight, sprocket wheels each having a different circumference from one another, and an endless chain 1 'i interconnects the sprocket wheels with the chain wheel so that drive from the chain wheel is transferred to the sprocket wheel and, hence, the rear wheel. The sprocket wheels share a common axis and are associated with a Derailleur gear change mechanism known per se for changing the position of the chain from one sprocket wheel to another to effect a change in mechanical advantage.

With all terrain bicycles (ATB's), mountain bicycles and racing bicycles, there is usually provided more than one chain wheel and, for example, three chain wheels each having a different circumference from one another may be provided. To effect a change in chain position from one chain wheel to another, it is known to provide a spring biassed cable operated mechanism that comprises a pair of elongate plates located in close proximity to the chain wheels but rearward of the axis of the chain wheels. The pair of plates are elongate in the direction of travel of the chain and are located about an upper path of travel of the chain, it being understood that as the chain passes about the chain wheels and sprocket wheels there is defined a chain upper path and a chain lower path.

In one direction of motion of the plates to change gear from an outer chain wheel to an inner chain wheel, the cable mechanism is placed under tension to pull the plates against the bias of the spring. To move the chain from an inner chain to an outer chain wheel the tension on the cable mechanism is reduced and the plates move under spring bias to re-locate the chain on an outer one of the chain wheels; the terms inner and outer being with respect to the frame.

A bicycle of the foregoing type is marketed by a company named Marin.

A problem associated with a bicycle having rear suspension is that as the rear wheel articulates up and down so tension on the chain varies. This results in the top e length of chain between the rear sprocket wheels and the chain wheel varying in length and, as a result, the chain may, in a worst case, jump off the sprockets but, in any event, causes a jerking movement to a user's legs. Additionally, when a user accelerates the suspension compresses ("winds up") which results in loss of power to the driven rear wheel, i.e. the frame dips in relation to the pivot axes of the front and rear wheels. If a user is sitting on a saddle and, unless the seat pillar for the saddle is connected by a mechanical connection to the bottom bracket, so there will be a change in length from the seat to the pedals when the rear wheel articulates resulting in user discomfort.

A further difficulty exists in that if the rear wheel is articulated upwards and the rear brake is applied, the top length of chain between the sprocket wheels and the chain wheels lock the suspension preventing it from lowering which, at least, can be uncomfortable for a user and, at worst, dangerous.

It is an object of the present invention to at least mitigate the foregoing disadvantages.

According to a first aspect of this invention there is provided an apparatus for securement to a frame of a bicycle having a suspended rear wheel which is capable of articulating in the plane of, and with respect to, the frame, said apparatus comprising idler wheel means rotatably mounted in a member securable in a predetermined location on said frame at a location above, in use, an outer periphery of a chain wheel means of said bicycle, the position and arrangement of said idler wheel means being such that an upper path of a chain interconnecting the idler wheel means with sprocket wheel means driving the bicycle rear wheel has a substantially constant length throughout articulation of the rear wheel in use, and said idler wheel has an axle about which said idler wheel means rotates, and said idler wheel means being slidably mounted along a longitudinal axis of said axle for shifting said chain from one crank wheel to another.

According to a second aspect of this invention there is provided a bicycle having frame means to which is connected a front wheel and a driven rear wheel, plural chain wheels having a common axis and connected to the frame for rotation by a user; suspension means attaching said rear wheel to said frame so that said rear wheel may articulate in the plane of, and with respect to, said frame; drive wheel means rotatably mounted to said suspension means for driving said rear wheel by a chain interconnecting respective chain wheels with respective drive wheel means; idler wheel means rotatably mounted on said frame at a location above, in use, an outer periphery of said chain wheels such that an upper length of chain extending between the idler wheel means and the drive wheel means has a substantially constant length throughout articulation of the rear wheel in use, said idler wheel means having an axle about which said idler wheel means rotates, and said idler wheel means being slidably mounted along a longitudinal axis of said axle for shifting said chain from one chain wheel to another.

In a currently preferred embodiment, the idler wheel means is located between a pivotal axis of the chain wheels and a pivotal axis of the chain wheels.

Preferably, said suspension means includes stay means interconnecting:

(a) said drive wheel means to suspension pivot means located on said frame means about which said pivot means said rear wheel means is able to articulate, and (b) spring loaded damper means, whereby said spring loaded damper means controls the amount of articulation of said rear wheel.

Advantageously, an axis of said suspension pivot means is located, in use, above an axis of said idler wheel means, and preferably, substantially in a horizontal plane of said chain in the chain path length from said drive wheel means to said 5 idler wheel means.

Conveniently, said suspension pivot means and said idler wheel means are rotatably mounted in mounting plate means which is fixedly secured to a portion of the frame means adjacent a bottom end of the frame means, and seat pillar means is mounted on said mounting plate means.

Conveniently, said stay means comprises a generally triangular array of elongate members located substantially in a vertical plane of the frame means,' said elongate members being formed from a pair of side members generally forming an apex and at opposed ends of said side members from said apex there being a base member, said apex being formed substantially at, and locating, an axis of said rear wheel, said base member being connected to said axis of suspension pivot means, and said base member being pivotally connected to said side members.

Advantageously, the base member is shorter in length than the side members.

Preferably, said spring loaded damper means is connected between said frame means and an uppermost side member.

Advantageously, each side member is formed of a pair of side members, one on each side of said wheel.

Preferably, said chain wheels have a pair of opposed cranks secured thereto for rotating said chain wheels, said drive wheel means includes at least one sprocket wheel, and said idler wheel means is an idler sprocket wheel.

Advantageously, said idler sprocket wheel is biassed by bias means toward one end of said axle and is moved in one direction between respective chain wheels against the bias of said bias means by a user-operated mechanism, and said idler sprocket wheel is moved in an opposite direction between respective chain wheels by the bias of said bias means.

Conveniently, said bias means is spring means which may 5 be a leaf spring.

Preferably, said drive wheel means comprises plural sprocket wheels, each having a different circumferential size, but all sharing a common axis, said sprocket wheels being associated with a Derailleur gear change mechanism known per se for changing the position of the chain from one sprocket wheel to another so as to effect a change in mechanical advantage.

Preferably, said frame means includes said seat pillar means and at least one steerable front fork having an extremity to which the front wheel is pivotally mounted.

Conveniently, two front forks are provided, one on each side of the front wheel.

Normally, the axes of rotation of the wheels, the chain wheels, the sprocket wheels and the idler sprocket wheel all lie in parallel planes.

By the present invention the forementioned disadvantages are overcome and the idler wheel facilitates movement of the chain from one chain wheel to another, thereby providing a dual function.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 shows a schematic side view of a bicycle in accordance with this invention, Figure 2 shows a partial side view of the bicycle shown in Figure 1 in which the drive train and suspension are shown to an enlarged scale, and Figure 3 shows a mechanism for shifting location of the chain over differently sized chain wheels.

In the Figures like reference numerals denote like parts. The bicycle shown in Figure 1 has a frame 1 formed from, for example, lightweight metal tubing, for example chrome alloy, and has a main frame member 2 secured to a top bracket 3 which houses a bearing (not shown) into an upper end of which is rotatably mounted a handlebar assembly 4. Mounted into the lower end of the top bracket 3 to be rotated by the handlebars 4 is a front fork assembly 5 having a lower extremity 6 locating a front wheel 7. The forks may comprise a single fork, although usually a pair of forks are provided extending one on each side of the front wheel 7.

At a lower end of the member 2 is a bottom bracket 13 which houses a bearing for supporting, in rotatable fashion, a triple chain wheels 14, 15, 16, each chain wheel having respectively different circumferences to provide differing mechanical advantages but sharing a common axis of rotation. The chain wheels 14 - 16 are connected to a pair of opposed cranks 17 (only one being shown in the Figures), one on each side of the frame, and an outer end of each crank rotatably mounting a pedal 18.

The frame 1 further includes a seat pillar 22 to which, at an upper end is connected a tube 23 for locating a shaft 24 (shown in broken lines) of a saddle 25. An upper end of the seat pillar 22 is fixedly secured to a seat stay 26 which extends to a lug 27 welded to the member 2. The lower end of the seat pillar 22 is connected to a mounting plate 80, the mounting plate being fixedly secured to a lower end of the member 2.

A suspension assembly 30 has a spring loaded damper 31 formed from a cylinder 32 and a pneumatic or hydraulically driven piston 33, the piston being biassed by a compression spring 34. The cylinder 32 has a control valve mechanism 35 for controlling the fluid or gas pressure within the cylinder.

The cylinder is connected by a pivot 36 to a bracket 37 that is fixedly secured to the member 2. The piston 33 is connected by a pivot 38 to one corner of a triangular array of elongate members formed by a pair of side members 41, 42 and a base member 43. The side members 42 generally form an apex at which an axle bearing 60 for a rear wheel 70 is secured. The triangular array of side members 41, 42 and base member 43 are fixedly secured together by, for example, bolting or welding. It is to be understood that there are, preferably, two side members 41 and two side members 42, each on a respective side of the rear wheel 70. There is, however, only one base member 43, although two may be provided if found convenient. The base member 43 is fixedly secured to a bracket 44 that is mounted on a pivot bearing 45 located in the mounting plate 80.

Drive for the rear wheel is performed by at least one sprocket wheel 71 and, typically for a mountain bike or allterrain bike, eight sprocket wheels may be provided each having differing respective circumferences from one another but sharing a common axis of rotation so as to provide varying ranges of mechanical advantage when used in combination with the differently sized chain wheels 14 - 16. An endless chain 75 interconnects the chain wheels 14 - 16 with the sprocket wheels 71 is shifted from one sprocket wheel to another by a Derailleur gear change mechanism 76 known per se that is operated by a Bowden type cable 77 - usually lever operated by a user. The Derailleur gear change mechanism 76 incorporates a pair of idling sprocket wheels 78 that are spring biassed to take up slack in the lower path length of travel of the chain 75. In this respect, the chain 75 has a lower path length 91 in which slack is taken up by the spring bias of the idling sprocket wheels 78 and an upper path length 92.

In the prior art there is no mechanism for taking up !I'- slack in the upper path length 92 of the chain and this invention provides an idler wheel 100 which, preferably, has sprocket teeth (not shown) and about which the chain travels. The idler wheel 100 is rotatably mounted in the mounting plate 80. The location of the idler wheel 100 is about the outer periphery of the largest chain wheel 14 and is, preferably, located rearwardly of the bottom bracket 13. The pivot bearing 45 is arranged to be above the axis of rotation of the idler wheel 100 and, preferably, substantially in a horizontal plane of the chain upper path length 92.

As the rear wheel articulates, with respect to the bottom bracket 13, as shown by broken line 110, in the vertical plane of the frame 1, so the suspension pivots about the pivot bearing 45 and the piston 33 reciprocates within cylinder 32.

Also, as the rear wheel articulates, an arcuate path, described by the axle bearing 60 of the rear wheel with respect to the axis of rotation of the idler wheel 100, moves as shown by the line 111. By virtue of the use and position of the idler wheel 100, the upper path length 92 of the chain for a sprocket wheel in use between the sprocket wheel and the idler wheel 100 remains substantially constant with the result that there are no undue shocks to a user's legs, the chain does not jump off the sprocket wheels, the suspension is not locked when the brakes are applied, and there is no rear wheel axle "windup" resulting in loss of traction.

Referring to Figure 3, the mounting plate 80 is, preferably, a pair of plates 81, 82, each located in a respective side of the member 2 (not shown in Figure 3) and supporting therebetween the pivot bearing 45. The plates 81, 82 are also separated by a spacer 83 through which is a bolt 84 that is threadably secured to an internal surface of a longitudinal bearing 85 having an outwardly extending flange 86. The bearing 85 supports a slider 87 which, in turn, supports a sealed ball race bearing 88, upon which the idler wheel 100 is mounted. The lateral location of the slider 87 is biassed outwardly from the frame by a leaf spring actuator 89. Movement of the slider 87 in an inwards direction, i.e. toward the frame, is accomplished by a Bowden type cable 177. The flange 86 terminates outward sliding movement of the slider 87. The locations of the chain wheels 14, 15 and 16 are shown by broken lines in Figure 3.

Thus, the idler wheel 100 also performs the function of changing the position of the chain on the chain wheels 14 16.

Although it is expected that bicycles will be manufactured with the idler wheel incorporated at the stage of original manufacture, it is possible that users having bicycles with rear wheel suspension may desire to retrofit an idler wheel 100, and such a retrofit apparatus is intended to be encompassed by this invention.

Claims

CLAIMS:

1. An apparatus for securement to a frame of a bicycle having a suspended rear wheel which is capable of articulating in the plane of, and with respect to, the frame, said apparatus comprising idler wheel means rotatably mounted in a member securable in a predetermined location on said frame at a location above, in use, an outer periphery of a chain wheel means of said bicycle, the position and arrangement of said idler wheel means being such that an upper path of a chain interconnecting the idler wheel means with sprocket wheel means driving the bicycle rear wheel has a substantially constant length throughout articulation of the rear wheel in use, and said idler wheel has an axle about which said idler wheel means rotates, and said idler wheel means being slidably mounted along a longitudinal axis of said axle for shifting said chain-from one crank wheel to another.

2. A bicycle having frame means to which is connected a front wheel and a driven rear wheel, plural chain wheels having a common axis and connected to the frame for rotation by a user; suspension means attaching said rear wheel to said frame so that said rear wheel may articulate in the plane of, and with respect to, said frame; drive wheel means rotatably mounted to said suspension means for driving said rear wheel by a chain interconnecting respective chain wheels with respective drive wheel means; idler wheel means rotatably mounted on said frame at a location above, in use, an outer periphery of said chain wheels such that an upper length of chain extending between the idler wheel means and the drive wheel means has a substantially constant length throughout articulation of the rear wheel in use, said idler wheel means having an axle about which said idler wheel means rotates, and said idler wheel means being slidably mounted along a longitudinal axis of said axle for shifting said chain from one chain wheel to another.

3. A bicycle as claimed in claim 2, wherein the idler wheel means is located between a pivotal axis of the chain wheels and a pivotal axis of the drive wheel means.

4. A bicycle as claimed in claim 2 or 3, wherein said suspension means includes stay means interconnecting:

5. A bicycle as claimed in claim 4, wherein an axis of said suspension pivot means is located, in use, above an axis of said idler wheel means.

6. A bicycle as claimed in claim 5, wherein said axis of said suspension pivot means is created substantially in a horizontal plane of said chain in the chain path length from said drive wheel means to said idler wheel means.

7. A bicycle as claimed in claim 4 or 5, wherein said suspension pivot means and said idler wheel means are rotatably mounted in mounting plate means which is fixedly secured to a portion of the frame means adjacent a bottom end of the frame means, and seat pillar means is mounted on said mounting plate means.

8. A bicycle as claimed in claims 4 to 7, wherein said stay means comprises a generally triangular array of elongate members located substantially in a vertical plane of the frame means, said elongate members being formed from a pair of side members generally forming an apex and at opposed ends of said side members from said apex there being a base member, said apex being formed substantially at, and locating, an axis of said rear wheel, said base member being connected to said axis of suspension pivot means, and said base member being pivotally connected to said side members.

9. A bicycle as claimed in claim 8, wherein the base member is shorter in length than the side members.

10. A bicycle as claimed in claims 4 to 9, wherein said spring loaded damper means is connected between said frame means and an uppermost side member.

A bicycle as claimed in claim 8, wherein each side 20 member is formed of a pair of side members, one on each side of said wheel.

12. A bicycle as claimed in any preceding claim, wherein said chain wheels have a pair of opposed cranks secured thereto for rotating said chain wheels, said drive wheel means includes at least one sprocket wheel, and said idler wheel means is an idler sprocket wheel.

13. A bicycle as claimed in claim 12, wherein said idler sprocket wheel is biased by bias means toward one end of said axle and is moved in one direction between respective chain wheels against the bias of said bias means by a user-operated mechanism, and said idler sprocket wheel is moved in an opposite direction between respective chain wheels by the bias of said bias means.

14. A bicycle as claimed in claim 13, wherein said bias 5 means is spring means which may be a leaf spring.

15. A bicycle as claimed in any preceding claim, wherein s'd drive wheel means comprises plural sprocket wheels, each al having a different circumferential size, but all sharing a common axis, said sprocket wheels being associated with a Derailleur gear change mechanism known per se for changing the position of the chain from one sprocket wheel to another so as to effect a change in mechanical advantage.

16. A bicycle as claimed in any preceding claim, wherein said frame means includes said seat pillar means and at least one steerable front fork having an extremity to which the front wheel is pivotally mounted.

17. A bicycle as claimed in claim 16, wherein two front forks are provided, one on each side of the front wheel.

18. A bicycle as claimed in claim 17, wherein the axes of rotation of the wheels, the chain wheels, the sprocket wheels and the idler sprocket wheel all lie in parallel planes.

19. An apparatus substantially as herein described with reference to, and as shown in, the accompanying drawings.

20. A bicycle substantially as herein described with reference to, and as shown in, the accompanying drawings.