GB2474830A

GB2474830A - Gearing arrangement with planet gears having different relative sizes

Info

Publication number: GB2474830A
Application number: GB0914244A
Authority: GB
Inventors: Edward Bolam
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-08-14
Filing date: 2009-08-14
Publication date: 2011-05-04
Also published as: GB0914244D0

Abstract

A gearing arrangement, e.g. for a downhill bicycle, comprises a central sun gear 20, nine planetary gearing devices 30 which are circumferentially arranged around the sun gear 20, and an annular ring gear 40. One gearing device 30 has different size planet gears 32, 34 when compared to another gearing device 30 so that each gearing device 30 provides a different gear ratio than another gearing device 30. An idler gear 38 bridges a gap between the planet gear 34 and the ring gear 40 and also reverses a direction of rotation so that the ring gear 40 rotates in same direction as the sun gear 20. A clutch 50 selectively locks each planet gear 34 to each shaft 36 so that the planet gear 34 rotates with planet gear 32 which is fixed to the shaft 36 and rotated by sun gear 20. The clutch 50 comprises spring urged plates 52, 54 having saw tooth profiles which engage to select one of the gearing devices 50.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GBO9 14244.9 RTM Date:9 December 2009 The following terms are registered trademarks and should be read as such wherever they occur in this document: Nordlock Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk Gearing Apparatus The present invention relates to gearing apparatus. In particular, but not exclusively, the invention relates to internal gearboxes for bicycles such as downhill bicycles.

Downhill cycling is an increasingly popular sport which involves racing downhill while negotiating a variety of challenging terrains such as highly undulating ground comprising rocks and tree roots. It is known to provide bicycles which are specifically adapted for downhill racing, such as having a longer travel front suspension, a rear suspension and hydraulic disc brakes. However, such bicycles still have a conventional drive train, with conventional derailleur and cassette systems still being the most common gearing found on downhill bicycles due to the gear ratios that they offer. For downhill bicycles, a cassette consisting of nine gears is provided at the rear wheel and a rear derailleur moves the chain up and down the cassette. It is therefore identical to the drive train of a conventional bicycle except that only a single chainring is provided at the cranks, since the nine gears of the cassette provide sufficient variation in gear ratios for a downhill bicycle. However, the extreme environment of downhill racing results in frequent maintenance to the gearing being required. In particular, these conventional systems are exposed to the environment and are easily damaged by rocks or during a crash. It is common for the rear derailleur to be bent into the rear wheel leading to further damage. * * * ** I * *1S

It is desirable to provide a gearing apparatus for a downhill bicycle which is * ** protected from the environment. Internal gearboxes are known in the form of hub gears but these are generally not suitable for downhill racing. Many hub gear systems are not sufficiently robust for downhill riding or are not available in the correct sizes to fit downhill frames. They are also relatively heavy and offset the *: . .o weight balance of the bicycle (towards the drive side) considerably more than a conventional drive train. A few frame manufacturers have provided an internal hub gear at the centre of the frame and connected the input drive from the cranks using a short length chain and the output drive to a single cog on the rear wheel using a much longer chain. However, due to the movement of the rear wheel as it progresses through the suspension travel, the length of the chain varies and means for accommodating this is required.

Planetary gearboxes comprise an input gear (sun gear) provided at a central axis and with a number of identical planet gears rotating around the circumference of the sun gear which in turn drive an internal or ring gear. However, it is only possible to obtain a relatively small number of different gear ratios, which is achieved by locking either the ring gear, planet carrier or planet gears. A compound planetary gearbox is similar to the standard planetary gearbox except it utilises two sets of identical planet gears and two sun gears.

Typically, bicycle gearing systems require the rider to be pedalling in order to change gear. However, for downhill racing, the ability to change gear while not pedalling is far more important. It is desirable to provide a gearing apparatus for a downhill bicycle which allows changing gear while not pedalling.

Due to the rough terrain a downhill bike is subjected to, a chaindevice is required in order to keep the chain from falling off the single front chainring. The chaindevice mounts to tabs on the frame via three M6 bolts, and there are two different patterns of these tabs known as ISCG and ISCGO5 with the ISCGO5 *.. : configuration being based upon a larger pitch circle diameter (PCD). * S.. * . ***.

*:*::* According to the present invention there is provided a gearing apparatus corn prisi ng: a central gear; a plurality of gearing devices circumferentially arranged around the central gear; and an annular gear which circumscribes the central gear and the plurality of gearing devices, wherein the plurality of gearing devices are configured to provide a plurality of gear ratios.

The central gear may be the input gear and the annular gear may be the output gear. Alternatively, the central gear may be the output gear and the annular gear may be the input gear.

The gearing apparatus may be configured such that only one of the plurality of gearing devices interconnects the central gear and the annular gear at a given time to provide the particular gear ratio associated with the interconnecting gearing device.

The gearing apparatus may include gear switching means adapted to switch between the plurality of gearing devices which interconnects the central gear and the annular gear and thus provide a plurality of gear ratios.

Each of the gearing devices may comprise a first gear. Each of the gearing devices may comprise a second gear.

The first and second gears of each gearing devices may be mounted on a common shaft. *.* * * * ** S

Each of the gearing devices may comprise a third gear interposing the annular gear and the first and second gears.

The gearing apparatus may be configured such that the central gear is constantly engaged with the first gear. *30

* S. 55 S S * The first gear may be fixedly mounted to the shaft. The second gear may be rotatably mounted to the shaft and selectively lockable to the shaft using a clutch member.

Alternatively, the second gear may be fixedly mounted to the shaft. The first gear may be rotatably mounted to the shaft and selectively lockable to the shaft using a clutch member.

The clutch member may comprise a first clutch plate and a second clutch plate.

The second clutch plate may be fixedly mounted to the shaft. The first clutch plate may be rotatably mounted to the shaft. The first clutch plate may be movable along the shaft from a first position in which it is disengaged to a second position in which it is engaged with the second clutch plate.

The gearing apparatus may include biasing means. The biasing means may be adapted to bias the first clutch plate towards the second position. Further biasing means may be provided to bias the first clutch plate towards the first position.

The contact face of the first clutch plate may have a saw tooth profile. The contact face of the second clutch plate may have a corresponding saw tooth profile.

One of the first or second gears may comprise a helical gear. The gearing S..' .. : apparatus may be configured such that the helical gear produces a force in the S...

axis of the shaft to assist engagement with the clutch member. * I.

The third gear may be constantly engaged with one or both of the second gear and the annular gear. * * S

::.::o In an alternative embodiment, at least one of the central gear, first gear, second gear, third gear or annular gear may be selectively movable from a first position in which the gear is disengaged to a second position in which the gear is engaged. The movable gear may be pivotable or linearly slidable between the first and second positions.

The gearing apparatus may include one or more bearings for substantially free rotation of one or more gears.

The gear switching means may be adapted to axially move one of the clutch member or a gear of a particular gearing device such that the gearing device interconnects the central gear and the annular gear. The gear switching means may be circumferentially movable around the central gear to selectively operate a particular gear. Further biasing means may be provided to bias the gear switching means in a circumferential direction.

The gearing apparatus may include a cable travel converting device for converting the travel of the gear shifter cable during a gear change to the desired travel of the gear switching means in the circumferential direction. The cable travel converting device may comprise an input pulley and an output pulley.

The gearing apparatus may be provided within a housing.

The gearing apparatus may be provided on a bicycle. The gearing apparatus may be provided on a downhill bicycle. * * * ** a

*.25 The gearing apparatus may be configured to provide a plurality of gear ratios * which substantially correspond to the gear ratios provided by derailleur and cassette gearing for a bicycle.

The gearing apparatus may be provided at the bottom bracket of a bicycle.

*.. I.* S * The annular gear may be operatively connectable to the chainring of a bicycle.

The gearing apparatus may include a crankset.

The gearing apparatus may be mountable to the chaindevice tabs provided on the frame of a bicycle. The gearing apparatus may be adapted such that it is mountable to both ISCG and ISCGO5 tabs.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a side view of a conceptual diagram of a gearing apparatus; Figure 2 is an external side view of a first embodiment of a gearing apparatus mounted on a bicycle; Figure 3 is an internal side view of the gearing apparatus of Figure 2; Figure 4 is a perspective view of the gearing apparatus of Figure 2; Figure 5 is a detailed side view of the gearing apparatus of Figure 2; and Figure 6 is another perspective view of the gearing apparatus of Figure 2. * .** * S * S.

*.25 Figure 1 shows a conceptual diagram of a gearing apparatus 10 which comprises * a central sun gear 20, nine gearing devices 30 which are circumferentially arranged around the central gear 20, and an annular ring gear 40 which circumscribes the central gear 20 and the gearing devices 30. Each gearing *. device 30 is conceptually shown as comprising two planet gears 32, 34 which each differ in their relative sizes (although the combined diameters of the two S....) planet gears always corresponds to the radial distance between the central gear and the annular gear 40). In such an arrangement, each gearing device 30 provides a particular gear ratio and so the gearing apparatus 10 can provide a plurality of gear ratios if only one of the gearing devices 30 connects the central gear 20 to the annular gear 40 at a given time. Using different sizes of planet gears is one method of providing a variety of gear ratios although other methods can be envisaged.

Figure 2 shows the gearing apparatus 10 mounted to the bottom bracket 100 of a bicycle via bearing cups 102. The weight of the gearing apparatus 10 is therefore central on the bicycle. It is clear that the axial width available is limited (and the chaindevice 104 and chainring 106 must also be accommodated between the crank arms 108) and so a highly compact arrangement is required.

The diameter is also restricted due to clearance with the linkage on some bicycle frames and to maintain a good ground clearance.

The gearing apparatus 10 includes a housing 12. This protects the housed components from damage, such as from rocks, as well as the ingress of dirt.

In the embodiment of Figure 2, the central gear 20 is the input gear which is rotated with the bottom bracket shaft 110 during pedalling and the annular gear is the output gear. The annular gear 40 is connected to the chainring 106 which rotates the chain to drive the rear wheel of the bicycle.

b: As shown in Figure 3, each of the gearing devices 30 includes a first gear 32 and a second gear 34, both of which are mounted on a common shaft 36. The first * gear 32 is fixed to the shaft 36, while the second gear 34 can freely rotate relative totheshaft36.

The second gear 34 is engaged with a third or idler gear 38 which is itself * 3S engaged with the annular gear 40. The idler gear 38 bridges the gap between * the first and second gears and the annular gear 40 and also reverses the direction of rotation so that the annular gear 40 rotates in the same direction as the central gear 20.

A clutch 50 is provided at one end of the shaft 36, adjacent to the second gear 34. The clutch 50 comprises a first clutch plate 52 which is spaced from the second gear 34 and fixed to the shaft 36, and a second clutch plate 54 which is connected to the second gear 34 and rotatably mounted to the shaft 36. The first clutch plate 52 is movable along the shaft 36 from a first position (as shown in Figure 3) in which it is disengaged to a second position in which it is engaged with the second clutch plate 54.

The clutch 50 includes a spring for biasing the first clutch plate 52 towards the second position and a second spring to bias the first clutch plate 52 towards the first position.

The contact face of the first clutch plate 52 has a saw tooth profile and the contact face of the second clutch plate 54 has a corresponding saw tooth profile.

This allows the clutch 50 to engage and disengage the gears in a uniform and reliable manner without any rotation before engagement occurs, as could occur with a standard dog clutch.

Nordlock washers are designed for securing nuts and bolts and feature two washers that must expand before the nut or bolt can loosen. It has been found that a clutch based on the same principle of the wedged shape teeth is well suited for transmitting drive. Nordlock washers have a slightly rounded profile and feature a small overlap which could not only lead to slip but also limit the magnitude of power that could be transmitted. However, a modified clutch plate in which these features are omitted provides efficient drive transmission. * *

If the central gear 20 is rotating (due to pedalling), this will drive the first gear 32 and therefore the shaft 36 and first clutch plate 52. At the first position of the first clutch plate 52, the second gear 34 will be unaffected by this rotation but, at the second position, the first clutch plate 52 will engage with the second clutch plate 54 to cause rotation of the second gear 34 which in turn drives the annular gear via the idler gear 38.

Gear switching means allows switching between individual gearing devices 30 to provide a plurality of gear ratios. This is achieved by moving the clutch 50 of a particular gearing device 30 so that the gearing device 30 interconnects the central gear 20 and annular gear 40.

In an alternative embodiment, the clutch 50 can be provided at the other end of the shaft 36 adjacent to the first gear 32. The second gear 34 could be fixed to the shaft 36 and the first gear 32 could be rotatably mounted to the shaft 36 and selectively lockable to the shaft using the clutch 50.

However, it is to be appreciated that the method of using constantly meshed gears and a clutch 50 is only one method of connecting the central gear 20 and annular gear 40 using a particular gearing device 30. For instance, any one of the central gear 20, first gear 32, second gear 34, idler gear 38 or annular gear 40 could be movable from a first position in which the gear is disengaged to a second position in which the gear is engaged. The movable gear could be pivotable or linearly slidable between the two positions. This has the advantage that a cable and lever mechanism can be located at the back of the gearing apparatus 10 and not take up space within the gearing apparatus 10. *..S * ** * *

The gearing apparatus 10 is configured to provide substantially the same gear * ratios as provided by conventional derailleur and cassette gearing for a bicycle.

The table below shows the gear ratios based upon a 36 tooth chainring and a standard downhill cassette. A 36 tooth chainring offers greater ground clearance :. 30 than a 38 tooth chainring. At the rear wheel the smallest cog possible is an 11 * tooth.

S.....

S S

Gear Chainring Cassette Cog Gear Ratio Ratio Change 9 36 11 3.273 109.09 8 36 12 3 108.33 7 36 13 2.769 107.69 6 36 14 2.571 107.14 36 15 2.41 13.33 4 36 17 2.118 111.76 3 36 19 1.895 110.53 2 36 21 1.714 109.52 1 36 23 1.565 The overall size of the gearing apparatus 10 is governed by maintaining the same ground clearance as that set down by a 36 tooth chainring. This limits the annular gear 40 to a maximum size of 160 mm.

The internal bore of the central gear 20 has to clear the outside of the bottom bracket cup 102. A 1 mod gear size allows for a 60 tooth central gear 20 and a tooth annular gear 40 to allow the gearing apparatus 10 to maintain the same ground clearance as a conventional 36 tooth chainring setup. The largest factors influencing the bending stress are the modulus and the face width of the gear and so a 1 mod over a 0.8 mod gear is preferable. The idler gear has no effect on the output gear ratio and its size is set to the minimum required gear size to bridge the second gear 34 to the annular gear 40. The table below shows . :25 the calculated gear sizes along with their overall gear ratio output based upon using a 36 tooth chainring and a 12 tooth cog. * S.

Sun Gear 1st gear 2nd gear Idler gear Annular gear Gear Speed Teeth Speed Teeth Speed Teeth Speed Teeth Speed Teeth Ratio 9 1 60 6 10 6 22 9.43 14 1.10 120 3.300 : 8 1 60 6 10 6 20 8.00 15 1.00 120 3.000 *I**.*

S

7 1 60 5 12 5 22 8.46 13 0.92 120 2.750 6 1 60 6 10 6 17 6.38 16 0.85 120 2.550 1 60 6 10 6 16 5.65 17 0.80 120 2.400 4 1 60 5 12 5 17 5.31 16 0.71 120 2.125 3 1 60 5 12 5 15 4.41 17 0.63 120 1.875 2 1 60 5 12 5 14 4.12 17 0.58 120 1.750 1 1 60 5 12 5 13 3.61 18 0.54 120 1.625 The gearing apparatus 10 includes a number of bearings for substantially free rotation of gears. The second gear 34 of each gearing device 30 rotates freely on the shaft and so requires a bearing. Bearings are also located at each end of the shaft 36.

As shown in Figures 4 and 5, one end of each shaft 36 is mounted within an insert 62 provided at an aluminium backplate 60. Rather than having the bearings rotating within the backplate, the inserts provide a harder wearing surface and strengthens the supports for the shafts 36. At the opposing end of the shafts 36 a support ring 64 fits over all nine shafts.

Further bearings are provided for the fixing of the idler gear 38 to the shaft 36, for the shaft supports and for mounting behind the first clutch plate 52. The clutch plate bearing allows the first clutch plate 52 to retract fully against the back plate and still spin with little resistance and also to provide a low resistance surface when in contact with the raised section of the gear changer. Due to the small size :25 of some gears, bushings are preferable rather than standard ball bearings. * *

* The gear switching means comprises a gear changer. As the cable pull is uniform for each shift, the nine gears are equally spaced with a 40° separation around the central gear 20. This allows the gear changer to move a consistent :. 30 rotation per gear change. Figure 6 shows the gear changer and its groove 66 * within the back plate 60. A raised section 68 pushes the first clutch plate 52.

****** * S The cable 70 enters from the back of the apparatus 10 before passing through a milled out area on the back of the raised section 68. A crimp positioned along the cable 70 within the milled out section causes the gear changer to move with the cable 70. The remaining cable 70 wraps around the perimeter of the gear changer before exiting into the wider groove on the outside of the idler gears 38.

This contains a spring 72 which is compressed as lower gears are selected.

Currently, in downhill racing, there is approximately a 50% split between riders using Sram or Shimano shifters. Both are similar operation but the amount of cable pull per index shift is different. The present invention can be configured to be compatible with both types. The amount of cable travel per index shift has been determined and is 34.925 mm for Sram shifters and 21.209 mm for Shimano shifters.

The gear changer has a diameter of 90mm. With the gear cable diameter wrapping around the outside of the gear changer and being 1mm thick the effective diameter becomes that to the centre of the cable and thus 91mm. The 9 gears are each separated by 40°. Therefore the gear changer must travel 320° in order to move through the entire gear range.

The gearing apparatus 10 includes a cable travel converting device for converting the travel of the gear shifter cable to the desired travel of the gear switching means in the circumferential direction. The cable travel converting device :25 comprises an input pulley and an output pulley with dimensions set to achieve *...

the required conversion. * **

The gearing apparatus 10 can be mounted to the chaindevice tabs provided on the frame of a bicycle. It is adapted such that it is mountable to both ISCG and *.*30 lSCGO5tabs. *

*** S*. * S

The frame tabs are M6 threaded and the bolt patterns are so close on their PCD it is not possible to allow for countersunk slotted holes in the back plate for both standards. Unfortunately the use of standard head bolts is also not an option due to clearance issues with the gears. Furthermore, the use of three fixing bolts as required by both mounting standards is not possible, again due to clearance issues with the gears.

The gearing apparatus 10 is mounted behind the bottom bracket cup and clamped up against the bottom bracket shell of the frame. Apart from the friction generated by the bottom bracket being tightened, nothing would prevent the apparatus 10 from rotating but this is solved by using M6 grub screws screwed through the back plate, and engaging into the frame tabs.

On conventional drivetrains, the chainring attaches directly to the driveside crank arm. The most common mounting pattern is based upon 4 bolts on a 104mm PCD. As such the internal gear must allow for fitment to the 36 tooth chainring on a 104mm PCD in order to be compatible with current standards. The sun gear must also attach to the cranks in a similar fashion. The fixing holes on the internal gear are based upon using standard chainring bolts. The sun gear must be attached to a plate which in turn can attach to the spider of the crank arm. This is achieved by mounting the sun gear to a 2mm thick plate via 8 Stainless Steel 304 pins pressed in place. The pins are located on a radius on 27mm and have a 3mm diameter. *S..

25 The chain device secures the chain in place on the chainring and must also be capable of providing a constant tension for a variable chain length. Normally the * rear derailleur provides this tension and allows for chain growth as the bike moves through its travel. However with the rear derailleur removed, a spring loaded device is required at the gearbox. This is provided where the chain exits from the chainring due to the extra room around the bike frame at this point. *

S S* **I * S A spring loaded double roller arrangement is in place at the bottom. As the chain effectively shortens during suspension movement the bottom device moves up. It is preferable for this direction of movement as it allows the unit to move out of the way should contact be made with any obstacle. The top part of the chain device acts purely as a guide.

The present invention provides many advantages. The gearing apparatus 10 replaces the gears at the rear wheel of a bicycle with an enclosed set of gears at the crankset while still maintaining full compatibility with all current standards for bicycle frames. The enclosed arrangement prevents foreign objects from entering the drivetrain and so extends the life of the apparatus 10. For each gear, the optimum chainline is maintained which provides greater efficiency.

Since there is no derailleur, there is no risk of bending the derailleur hanger or derailleur. Since, the drivetrain weight is moved forward and is in a central position relative to the length of the bicycle, there is better weight distribution which improved handling. Furthermore, the apparatus provides the ability to change gear while not pedalling. Also, the apparatus 10 is fully compatible with bicycle shifters such as rapidfire shifters and utilises a fast engagement speed.

Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. * S ** **** * * **S. * ** * * * * ** * S * S.. *

*. ..*

Claims

Claims A gearing apparatus comprising: a central gear; a plurality of gearing devices circumfereritially arranged around the central gear; and an annular gear which circumscribes the central gear and the plurality of gearing devices, wherein the plurality of gearing devices are configured to provide a plurality of gear ratios.
2. A gearing apparatus as claimed in Claim 1, wherein the central gear is the input gear and the annular gear is the output gear.
3. A gearing apparatus as claimed in Claim 1 or 2, wherein the gearing apparatus is configured such that only one of the plurality of gearing devices interconnects the central gear and the annular gear at a given time to provide the particular gear ratio associated with the interconnecting gearing device.
4. A gearing apparatus as claimed in Claim 3, including gear switching means adapted to switch between the plurality of gearing devices which interconnects the central gear and the annular gear and thus provide a plurality of gear ratios.

.. :25
5. A gearing apparatus as claimed in any preceding claim, wherein each of S...the gearing devices comprises a first gear and a second gear. * ..
6. A gearing apparatus as claimed in Claim 5, wherein the first and second gears of each gearing devices are mounted on a common shaft. * * * *.S

* *5 SI S * *
7. A gearing apparatus as claimed in Claim 5 or 6, wherein each of the gearing devices comprises a third gear interposing the annular gear and the first and second gears.
8. A gearing apparatus as claimed in any preceding claim, wherein the gearing apparatus is configured such that the central gear is constantly engaged with the first gear.
9. A gearing apparatus as claimed in Claim 6, wherein the first gear is fixedly mounted to the shaft.
10. A gearing apparatus as claimed in Claim 6 or 9, wherein the second gear is rotatably mounted to the shaft and selectively lockable to the shaft using a clutch member.
11. A gearing apparatus as claimed in Claim 6, wherein the second gear is fixedly mounted to the shaft and the first gear is rotatably mounted to the shaft and selectively lockable to the shaft using a clutch member.
12. A gearing apparatus as claimed in Claim 10 or 11, wherein the clutch member comprises a first clutch plate and a second clutch plate.
13. A gearing apparatus as claimed in Claim 12, wherein the second clutch plate is fixedly mounted to the shaft and the first clutch plate is rotatably mounted .. :25 to the shaft. *... * S S...* **
14. A gearing apparatus as claimed in Claim 13, wherein the first clutch plate is movable along the shaft from a first position in which it is disengaged to a second position in which it is engaged with the second clutch plate.S **.*.

S S
15. A gearing apparatus as claimed in any of Claims 12 to 14, including biasing means.
16. A gearing apparatus as claimed in Claim 15, wherein the biasing means is adapted to bias the first clutch plate towards the second position.
17. A gearing apparatus as claimed in Claim 15 or 16, wherein the biasing means is adapted to bias the first clutch plate towards the first position.
18. A gearing apparatus as claimed in any of Claims 12 to 17, wherein the contact face of the first clutch plate has a saw tooth profile and the contact face of the second clutch plate has a corresponding saw tooth profile.
19. A gearing apparatus as claimed in any of Claims 5 to 7, wherein one of the first or second gears comprises a helical gear.
20. A gearing apparatus as claimed in Claim 19, wherein the gearing apparatus is configured such that the helical gear produces a force in the axis of the shaft to assist engagement with the clutch member.
21. A gearing apparatus as claimed in Claim 7, wherein the third gear is constantly engaged with one or both of the second gear and the annular gear.
22. A gearing apparatus as claimed in Claim 7, wherein at least one of the S...*.. :25 central gear, first gear, second gear, third gear or annular gear is selectively movable from a first position in which the gear is disengaged to a second position in which the gear is engaged.
23. A gearing apparatus as claimed in Claim 4, wherein the gear switching means is adapted to axially move one of a clutch member ora gear of a *Sparticular gearing device such that the gearing device interconnects the central gear and the annular gear.
24. A gearing apparatus as claimed in Claim 23, wherein the gear switching means is circumferentially movable around the central gear to selectively operate a particular gear.
25. A gearing apparatus as claimed in Claim 24, including biasing means to bias the gear switching means in a circumferential direction.
26. A gearing apparatus as claimed in Claim 24 or 25, including a cable travel converting device for converting the travel of the gear shifter cable during a gear change to the desired travel of the gear switching means in the circumferential direction.
27. A gearing apparatus as claimed in Claim 26, wherein the cable travel converting device comprises an input pulley and an output pulley.
28. A gearing apparatus as claimed in any preceding claim, wherein the gearing apparatus is provided within a housing.
29. A gearing apparatus as claimed in any preceding claim, wherein the gearing apparatus is adapted to be provided on a bicycle.
30. A gearing apparatus as claimed in Claim 29, wherein the gearing * apparatus is adapted to be provided on a downhill bicycle. * S.
31. A gearing apparatus as claimed in Claim 29 or 30, wherein the gearing apparatus is configured to provide a plurality of gear ratios which substantially :. 30 correspond to the gear ratios provided by derailleur and cassette gearing for a * bicycle.S.....S
32. A gearing apparatus as claimed in any of Claims 29 to 31, wherein the gearing apparatus is provided at the bottom bracket of a bicycle.
33. A gearing apparatus as claimed in any of Claims 29 to 32, wherein the annular gear is operatively connectable to the chainring of a bicycle.
34. A gearing apparatus as claimed in any of Claims 29 to 33, including a crankset.
35. A gearing apparatus as claimed in any of Claims 29 to 34, wherein the gearing apparatus is adapted to be mountable to the chaindevice tabs provided on the frame of a bicycle.
36. A gearing apparatus as claimed in Claim 35, wherein the gearing apparatus is adapted such that it is mountable to both ISCG and ISCGO5 tabs. * * . ** * S... * . * S. * . S * *. ** * . * *S*SS..... * .