WO1992017365A1

WO1992017365A1 - Cycle gear cover

Info

Publication number: WO1992017365A1
Application number: PCT/GB1992/000606
Authority: WO
Inventors: Martin Lawrence Jelfs
Original assignee: Martin Lawrence Jelfs
Priority date: 1991-04-05
Filing date: 1992-04-03
Publication date: 1992-10-15
Also published as: AU1532892A; GB9107139D0

Abstract

A cover for sealing the derailleur (17) and rear sprockets (9) of a bicycle from the elements is described. In order to prevent road grime and foreign bodies from damaging the transmission components of a bicycle, these components are enclosed in a housing (23) which is so shaped as to allow movement of the derailleur (17) in order to permit gear changing. Where parts of the housing (23) move against each other, they may be provided with low-friction seals.

Description

CYCLE GEAR COVER

This invention relates to a cover for bicycle gearing systems, and particularly to a cover for derailleur gears.

It is long-established that pedal cycles are most efficiently propelled by a chain drive system, in which a chainwheel is connected to a rear sprocket by a roller chain. In order to allow for variation of the gearing, either derailleur or in-hub gearing systems may be used. With a derailleur system, the ability to select one of a plurality of rear sprockets of differing diameters is provided. This is enabled by the use of a derailleur, a device which physically moves the chain off the driven sprocket and into engagement with a larger or smaller one, according to the cyclist's desire. This system eliminates many of the drawbacks of alternative in-hub gear systems, which typically use planetary gear mechanisms in order to provide variable gearing of limited range.

It is known for cycles to be additionally provided with a plurality of chainwheels, and a front derailleur to enable selection of any one of these by physically pushing the chain into engagement with it.

Derailleur gearing, once the province of racing cycles due to its capricious nature in operation, has in recent years become more common on cycles designed for leisure use. The advent of indexed derailleur systems, which enable the rider to move the derailleur through a fixed preselected distance in order to engage the desired sprocket, has eliminated 'gear hunting' and made derailleur systems operable by even the most inexperienced riders.

Derailleur systems have been popularised to a large extent by the advent of the Mountain Bike, a rugged lightweight cycle designed for all-terrain use. Such machines have need of extremely wide gear ranges, which are best provided by derailleur systems. Typically a Mountain Bike will possess three chainwheels and between five and seven rear sprockets, giving a choice of between 15 and 21 gear ratios.

This technology has its price, and it is now considered acceptable to spend several hundreds of pounds on a Mountain Bike for leisure use. A basic machine can cost from £250 to £600. A major part of this cost is represented by the derailleurs, and especially the rear derailleur.

The rear derailleur is vulnerable to damage in a number of ways. These include physical impacts sustained in an accident or fall, particularly in off-road applications; the ensnarement of string, wire, thin branches or other detritus into the gear mechanism; and erosion of the moving parts of the mechanism by dust and grit, with which they become clogged after extensive use. This last problem also has the effect of dramatically reducing gear efficiency through friction, to a level at which a dirty derailleur system is less efficient than a hub (planetary) gear system.

Furthermore, being totally exposed, the derailleur is a source of aerodynamic drag on a bicycle. Great efforts have been made in recent years to increase the aerodynamic efficiency of the bicycle, including the adoption of teardrop or oval section frame tubes, disc wheels and aerodynamically shaped components. The derailleur, however, is a complex structure comprising a parallelogram and a chain tensioning cage, and is very difficult to make aerodynamic.

It is therefore the object of the invention to provide a cover for a derailleur gear.

According to a first aspect of the invention, there is provided a protective cover for a derailleur gear which substantially encloses the derailleur and is adapted for fixing to a bicycle. Substantial^" enclosure of the derailleur ensures protection from both large and small foreign bodies. It is an added advantage that the aerodynamic performance of the derailleur may be improved, as the cover can be so fashioned as to have a smooth and aerodynamically efficient profile. Both of these advantageous aspects of the invention could be further exploited by extending the cover to enclose the chainwheels and the chain, thus protecting the entire transmission system.

A problem incumbent with any cover enclosing the derailleur is that the derailleur in operation moves through considerable distances in two planes, both perpendicular to the chain as it shifts from one sprocket to another and parallel to the chain. In the latter plane it moves both to allow engagement of large sprockets and to maintain tension on the chain by the action of a sprung hinged lever arm mechanism. This mechanism, known as the cage, is particularly large on Mountain Bikes in order to maintain chain tension whichever of the sprockets of widely differing sizes present in the gear range is selected. It is therefore preferred that the derailleur cover be so shaped as to allow full movement of the derailleur in all required planes.

In a preferred aspect of the invention, it is envisaged that the derailleur cover is formed of at least two separate parts. These comprise a disc part, located adjacent the wheel and which rotates with the wheel; and a static moulded cover part, which is fitted so as substantially to enclose the derailleur between itself and the disc part. It is envisaged that the disc part may be vacuum formed, possibly from styrene, while the cover part may be injection moulded, possibly from ABS. The radius of the disc part is at least equal to the distance between the wheel spindle and the bottom of the derailleur cage. Optionally, the disc part may comprise a disc wheel. It is preferred that the clearance between the two parts be kept to a minimum, around 2 mm, in order to ensure protection of the derailleur from smaller foreign bodies.

In order to fix the moulded cover to the cycle, it is envisaged that the cover should have a hole appropriately positioned to allow it to be bolted to a bush fitted to the wheel spindle. Advantageously, the fixing mechanism could be combined with quick-release wheel fixing means so as to allow rapid removal of the cover.

It is envisaged that the moulded cover may or may not enclose the entire transmission. In a preferred aspect, the cover encloses only the derailleur and the rear sprockets. In this case, provision must be made for the chain to enter and/or exit the cover while engaging the derailleur and sprockets in a number of chainwheel and sprocket combinations. This could be achieved by the provision of slots in the derailleur cover.

In an alternative case, the quadrant between the chain stay and the seat stay could be left open, so as to allow visual inspection of the gear ratios and adequate scope for chain movement.

Advantageously, a low friction seal, preferably a brush seal, is fitted between the moulded cover and the disc part to exclude dirt and smaller foreign bodies. A seal may also be fitted to the slots which may be provided for entry and/or exit of the chain from the derailleur cover. Preferably, this seal is a long brush seal.

It is important that the seal should be of low frictional resistance while being effective to exclude dirt. The distance between the moulded cover and the disc is therefore of importance, and it is envisaged that the cover fixing mechanism could allow for adjustment of the clearance between the cover and disc parts. Optionally, such an adjustment could be provided by the use of a double-threaded adjuster.

Further adjustment facility could be incorporated by the provision of an enlarged or slotted fixing hole in the cover and double washers to hold the cover in the desired position when the fixing is tightened.

In certain applications, it is envisaged for luggage carriers or mudguards to be fitted to the cycle. This may require the formation of an aperture in the cover to allow access of the mudguard or carrier stays to fixing points on a rear dropout of the bicycle.

A further advantage of the invention is that it prevents the soiling and damaging of clothing and the like by the gear mechanism. It is envisaged for the derailleur cover of the invention to be of an attractive design, which can be fashioned so as to appeal to the serious cyclist as well as for the teenage and leisure markets.

Optionally, the derailleur cover of the invention may be produced in a coloured design, possibly with a manufacturer's logo printed on it. Alternatively, it may be formed in a transparent material, such as PVC, to allow ready inspection of the gear mechanism.

A derailleur cover according to the invention is now described, by way of example only, with reference to the accompanying drawings, in which:-

Fig. I is a side view of the rear of a bicycle, showing the derailleur cover in place.

Fig. II is a part sectional rear view of the derailleur cover and wheel, with part of the wheel broken away. Referring to the drawings, the rear of the bicycle has a rear wheel 1 fixed by its wheel spindle 2 in a rear dropout 3 located in known manner, at the junction of a chainstay 5 and seatstay 7. Sprockets 9 are threaded onto rear wheel hub 11 which rotates around the spindle. The hub is provided with a flange 13 into which spokes 15 are located. A derailleur 17 is bolted onto the rear dropout 3.

The derailleur cover comprises a disc part 19 which rotates with the rear wheel when the bicycle is in motion. The part 19 is af ixed to the rear wheel and its inner periphery is located between the spokes 15 and the sprockets 9, with its outer periphery at least affixed to the spokes by clips 21. The derailleur cover further comprises a moulded cover part 23 which is held in a stationary position by a fixing bolt 25 which cooperates with a bush 26 fixed to the wheel spindle. The moulded cover part and the disc part enclose the derailleur 17 and sprockets 9 between them.

It is evident that the two parts of the derailleur cover substantially enclose the derailleur and sprockets to protect them from dirt and debris. Close cooperation between the disc part and the moulded cover part ensures that ingress of debris is kept to a minimum.

In order to allow passage of a bicycle chain to the derailleur and sprockets, two openings are provided in the derailleur cover. A lower run 27 of the bicycle chain passes through one opening in the form of a slot 29 which is sealed by brush seal 31. The upper run 33 of the bicycle chain passes through a second opening in the form of an open quadrant 35 formed between the chainstay 5 and the seatstay 7.

It will be understood that the invention is described herein by way of example only and that a number of modifications may be made to the described embodiment by the man skilled in the art within the scope of the invention.

Claims

1. A protective cover for a derailleur gear which substantially encloses the derailleur and is adapted for fixing to a bicycle.

2. A protective cover according to claim 1 which substantially encloses the rear derailleur and rear sprockets of a bicycle transmission.

3. A protective cover according to claim 1 or claim 2 which is so shaped as to allow full movement of the derailleur in all required planes.

4. A protective cover according to any preceding claim which comprises a disc part, located adjacent the wheel and which rotates therewith and a static cover part, which is fitted so as substantially to enclose the derailleur between itself and the disc part.

5. A protective cover according to claim 4 wherein the disc part comprises a disc wheel.

6. A protective cover according to claim 4 or claim 5 wherein provision is made for the chain to enter and/or exit the cover while engaging the derailleur and sprockets in any selected chain wheel and sprocket combination.

7. A protective cover according to anyone of claims 4 to 6 wherein a low friction seal is disposed between the disc part and the cover part.

8. A protective cover according to claim 6 or claim 7 wherein the provision to allow entry and/or exit of the chain comprises a low friction seal.

9. A protective cover according to claim 7 or claim 8 wherein the low friction seal is a brush seal.

10. A protective cover according to anyone of claims 4 to 9 wherein the cover part is adapted to be adjustably fixed to a bush fitted to the rear wheel spindle.

11. A protective cover substantially as hereinbefore described with reference to the drawings.