GB2280002A - Hub assembly for bicycle wheel comprises floating sprocket carrier - Google Patents

Abstract

The hub assembly comprises a tubular body part 12 having two axially spaced flanges 14, 16 for connection to the spokes of the wheel, a tubular support 20 extending from one end of the body part, and a sprocket carrier 22 rotatable on the support, the sprocket carrier carrying a number of axially spaced sprockets 30. The sprockets 30 are mounted on the sprocket carrier 22 so as to be capable of free axial sliding movement, so that when a selected sprocket 30 is being driven by the drive chain, any sideways force applied to the sprocket by misalignment with the drive chain displaces the sprocket axially on the sprocket carrier 22 to correct the misalignment. The sprocket carrier is preferably mounted on bearings 38 and is acted on by springs. <IMAGE>

Description

Improvements in or Relating to Hub Assemblies The present invention relates to hub assemblies, and particularly to hub assemblies for bicycle wheels.

In particular, the invention relates to a hub assembly for a bicycle wheel of the kind comprising an elongate generally tubular body part having two axially spaced external peripheral flanges for connection to the spokes of the wheel, a generally tubular sprocket carrier support extending from one end of the body part, a generally tubular sprocket carrier surrounding the sprocket carrier support so as to be concentric therewith, the sprocket carrier having external locating means to locate on the carrier, so as to be nonrotatable relatively thereto, a plurality of axially spaced toothed sprockets, and bearing means between the sprocket carrier and the sprocket carrier support to permit rotation of the carrier relatively to the support.

In use, as is well known, the hub assembly is driven by an endless drive chain which extends between a pedal-driven chain ring on the bicycle and one of the sprockets on the hub assembly. The rider may engage the chain selectively with any one of the sprockets on the hub assembly by operation of a gear change mechanism.

There may be provided as many as eight axially spaced sprockets of different diameters on the hub assembly and the rear end of the chain must be displaced axially of the hub assembly, by the gear change mechanism, for engagement with the selected sprocket.

Normally, in conventional hub assemblies, the axial positions of the sprockets are fixed so that only one of the sprockets is in accurate alignment with the chain ring. Accordingly, when any of the other sprockets is selected and engaged by the drive chain there will be a degree of misalignment between the chain and the sprocket. That is to say, the general plane in which the chain lies will not extend exactly at right angles to the axis of rotation of the sprocket. When using the outer sprockets the extent of such misalignment may be up to 2.9 .

This misalignment means that a proportion of the work exerted by the rider is wasted in applying a sideways force to the sprocket, and the misalignment increases frictional loses and the risk of distortion of the bicycle frame. The sideways component of the force applied through the chain also causes wear of the chain and sprockets as the side plates of the chain are pulled against the sprocket gear teeth. Further energy loses are generated in overcoming friction between the side plates of the chain and the teeth.

In order to overcome this problem, hub assemblies have been designed where, during the gear change, the sprockets are positively moved axially to a position where the selected sprocket is correctly aligned with the drive chain, the sprocket being positively maintained in that position. For example, such an arrangement is shown in British Patent Specification No. 2240825. Such arrangements have the disadvantage that, in practice, a fairly complex mechanism has to be provided to move the selected sprocket to the appropriate axial position and locate it in that position. This has resulted in hub assemblies which are too bulky and heavy for general acceptance. Furthermore, a conventional type of gear change mechanism, such as a derailleur gear, cannot be used. For example, in the arrangement of Specification No. 2240825 the rear end of the drive chain remains in the same axial position during the gear change, which is effected solely by movement of the sprockets, whereas a conventional derailleur mechanism necessarily involves axial displacement in the rear end of the drive chain for engagement with the selected sprocket.

The present invention sets out to provide an improved arrangement for overcoming the above-mentioned problems while avoiding the deficiencies of known systems.

According to the invention, a hub assembly of the kind first referred to is characterised in that said toothed sprockets are mounted on the sprocket carrier for axial sliding movement relatively thereto, said axial sliding movement being free of restraint whereby, when a selected sprocket is being driven by the drive chain, any sideways force applied to the sprocket by misalignment with the drive chain will displace the sprocket axially on the sprocket carrier to correct the misalignment.

Thus, according to the invention, instead of the sprocket being positively moved to, and fixed in, a position where it is in alignment with the drive chain, the sprocket freely floats axially. When a product is selected the tension in the drive chain applies a sideways force to the sprocket so as automatically to keep it at all times in the aligned position.

The sprocket carrier may comprise two parts: an inner part which is mounted on the sprocket carrier support for rotation relatively thereto, and an outer part on which one or more sprockets are non-rotatably mounted, the outer part being mounted on the inner part for axial sliding, but non-rotatable, movement relatively thereto.

Preferably all of the sprockets are mounted in axially spaced relation on said outer part of the sprocket carrier. However, the invention does not exclude arrangements in which there are provided two or more separate outer parts each carrying one or more sprockets.

The inner part of the sprocket carrier may include one or more axial grooves in which engage bearing members which are movable axially with the outer part of the sprocket carrier. For example, the bearing members may comprise ball bearings housed in the inner surface of the outer part of the sprocket carrier.

Preferably an axially extensible, generally tubular, sealing sleeve encircles the inner part of the sprocket carrier at each end of the outer part, each sleeve being sealingly connected at one end to the inner part of the sprocket carrier, or an element rotatable therewith, and at the other end to the outer part of the sprocket carrier, or an element rotatable therewith.

The invention includes within its scope a sprocket assembly, for use in bicycle hub assembly, comprising a generally tubular sprocket carrier having external locating means to locate on the carrier, so as to be non-rotatable relatively thereto, a plurality of axially spaced tooth sprockets, and bearing means for rotatable engagement between the sprocket carrier and a sprocket carrier support, the assembly being characterised in that said toothed sprockets are mounted on the sprocket carrier for axial sliding movement relatively thereto, said axial sliding movement being free of restraint whereby, when a selected sprocket is being driven by the drive chain, any sideways force applied to the sprocket by misalignment with the drive chain will displace the sprocket axially on the sprocket carrier to correct the misalignment.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawing which is a longitudinal section through one form of bicycle hub assembly according to the invention.

The hub assembly 10 comprises an elongate generally tubular body part 12 integrally formed with two axially spaced external peripheral flanges 14, 16 for connecting the assembly to the spokes (not shown) of the rear wheel of a bicycle. The body part has a central cylindrical passage 18 extending longitudinally through it.

A sprocket carrier support 20 is integrally formed with the body part 12 and projects from one end thereof. The sprocket carrier support 20 is concentric with the body part 12 and its interior forms a continuation of the central passage 18 in the body part 12.

Surrounding the sprocket carrier support 20 is a generally cylindrical sprocket carrier 22 comprising an inner part 24 and an outer part 26. The external surface of the sprocket carrier support 20 constitute a cylindrical plain bearing surface which is in close rotatable sliding engagement with the corresponding internal cylindrical plain bearing surface on the inner part 24 of the sprocket carrier 22.

The outer part 26 of the sprocket carrier 22 is formed with circumferentially spaced axial splines 28 which engage in corresponding recesses around the inner periphery of toothed sprockets 30 so as to locate the sprockets non-rotatably on the outer part 26 of the carrier. Axial spacing rings 32 are disposed between adjacent sprockets 30 in conventional manner. A clamping ring 34 is in screw threaded engagement with one end of the outer part 26 of the sprocket carrier and serves to clamp the sprockets 30 and spaces 32 against an abutment flange 36 on the opposite end of the outer part 26.

Three sets of axially aligned ball bearings 38 are spaced 1200 apart around the inner periphery of the outer part 26 of the sprocket carrier. Each set comprises four axially aligned spaced ball bearings received in generally hemispherical recesses in the inner cylindrical surface of the outer part 26 of the sprocket carrier. The four aligned ball bearings in each set engage in a corresponding axial groove 40 formed in the outer cylindrical surface of the inner part 24 of the sprocket carrier. This bearing arrangement allows the outer part 26 of the sprocket carrier, with the sprockets 30, to slide axially in relation to the inner part 24 of the carrier while the two parts remain coupled together for rotation as a unit.

In order to ensure that the sprocket carrier 22 can only rotate in one direction relative to the body part 12 and sprocket carrier support 20, and thus provide a free-wheel arrangement, a pawl and ratchet device 42 (which may be of any known kind) or other suitable uni-directional device, is provided between an end flange 44 of the inner part 24 of the sprocket carrier and an annular cavity 46 in one end of the body part 12 which overlaps the end portion 44 on the part 24.

The passageway 18 extending along the length of the body part 12 and into the sprocket carrier support 20 receives an axle 48 the ends of which, in use, are clamped to the rear forks of the bicycle frame (not shown) in well known manner. The axle 48 is held in place within the hub by means of a ball bearing set 50 and a needle bearing set 52. The ball bearing set 50 is a force fit within an annular recess in a thickened portion of the body part 12 adjacent one end thereof.

The needle bearing set 52 is similarly a force fit within the sprocket carrier support 20. The bearing set 50 is located adjacent an annular shoulder on the axle 48 and the bearing set 52 is similarly located adjacent an annular flange 56 on the axle. Nuts are secured to threaded end portions of the axle 48, in known manner, to mount the hub assembly on the bicycle frame.

An end cap 58 closes off the open end of the sprocket carrier support 20, and a generally tubular flexible seal is connected between the outer periphery of the end cap 58 and the clamping ring 34 on one end of the outer sprocket carrier part 26. A similar seal 62 is connected between the end 36 of the outer carrier part 26 and the adjacent end 44 of the inner carrier part 24. The purpose of the seal 60, 62 is to prevent dirt and grit fouling the grooves 40 and ball bearings 38.

In operation, a gear change mechanism (not shown) is associated with the hub assembly and serves to engage the drive chain (also not shown) selectively with one or other of the sprockets 30. Once the drive chain has been engaged with the selected sprocket, if there is any misalignment between the sprocket and chain the tension in the chain will apply a resultant sideways force to the sprocket and this force will slide the outer part 26, with the sprockets 30, axially with respect to the inner part 24 of the sprocket carrier until the engaged sprocket is correctly aligned with the chain. In this position there will be no resultant sideways force on the sprocket so that the sprocket will remain in this aligned position. When the chain is moved to another sprocket, as a result of a gear change, sprockets will again be moved axially to the appropriate position where the newly engaged sprocket is aligned with the chain.

A derailleur mechanism, of generally conventional type, may be used to effect the gear change. The mechanism will initially move the chain, and the sprocket which it is engaging, axially of the hub assembly until the outer moveable part 26 of the sprocket carrier reaches the limit of its axial movement whereupon the gear change will occur in the normal manner. Where there are three sprockets, as shown, the derailleur arm must be able to move the chain either one or two positions sideways and then return it to the central running position, pulling the sprocket carrier with it.

Alternatively, the gear change mechanism may be of a special design whereby the gear change is effected by a mechanism which positively displaces the sprockets axially while the chain is kept in a stationery position by a jockey wheel. Once the selected sprocket has been brought into alignment with the chain, the chain is engaged with the sprocket. The mechanism for moving the sprockets is disengaged therefrom during normal running, so that the sprockets are free to float axially, as previously described, thus minimising wear of the chain and sprockets, and waste of energy. It will be appreciated that such system has some similarity with the known systems referred to earlier, to the extent that the selected sprocket is positively moved to the desired position. According to the present invention, however, the mechanism has the important distinction that, during subsequent running, the sprocket is not positively held in a specific axial position but is free to float axially.

Claims (8)

1. A hub assembly for a bicycle wheel comprising an elongate generally tubular body part having two axially spaced external peripheral flanges for connection to the spokes of the wheel, a generally tubular sprocket carrier support extending from one end of the body part, a generally tubular sprocket carrier surrounding the sprocket carrier support so as to be concentric therewith, the sprocket carrier having external locating means to locate on the carrier, so as to be non-rotatable relatively thereto, a plurality of axially spaced toothed sprockets, and bearing means between the sprocket carrier and the sprocket carrier support to permit rotation of the carrier relatively to the support, said toothed sprockets being mounted on the sprocket carrier for axial sliding movement relatively thereto, said axial sliding movement being free of restraint whereby, when a selected sprocket is being driven by the drive chain, any sideways force applied to the sprocket by misalignment with the drive chain will displace the sprocket axially on the sprocket carrier to correct the misalignment.

2. A hub assembly according to Claim 1, wherein the sprocket carrier comprise two parts: an inner part which is mounted on the sprocket carrier support for rotation relatively thereto, and an outer part on which one or more sprockets are non-rotatably mounted, the outer part being mounted on the inner part for axial sliding, but non-rotatable, movement relatively thereto.

3. A hub assembly according to Claim 2, wherein all of the sprockets are mounted in axially spaced relation on said outer part of the sprocket carrier.

4. A hub assembly according to Claim 2 or Claim 3, wherein the inner part of the sprocket carrier includes one or more axial grooves in which engage bearing members which are movable axially with the outer part of the sprocket carrier.

5. A hub assembly according to Claim 4, wherein the bearing members comprise ball bearings housed in the inner surface of the outer part of the sprocket carrier.

6. A hub assembly according to any of Claims 2 to 5, wherein an axially extensible, generally tubular, sealing sleeve encircles the inner part of the sprocket carrier at each end of the outer part, each sleeve being sealingly connected at one end to the inner part of the sprocket carrier, or an element rotatable therewith, and at the other end to the outer part of the sprocket carrier, or an element rotatable therewith.

7. A sprocket assembly, for use in a bicycle hub assembly, comprising a generally tubular sprocket carrier having external locating means to locate on the carrier, so as to be non-rotatable relatively thereto, a plurality of axially spaced tooth sprockets, and bearing means for rotatable engagement between the sprocket carrier and a sprocket carrier support, said toothed sprockets being mounted on the sprocket carrier for axial sliding movement relatively thereto, said axial sliding movement being free of restraint whereby, when a selected sprocket is being driven by the drive chain, any sideways force applied to the sprocket by misalignment with the drive chain will displace the sprocket axially on the sprocket carrier to correct the misalignment.

8. A hub assembly for a bicycle wheel substantially as hereinbefore described with reference to the accompanying drawings.