GB2611347A

GB2611347A - Bicycle transmission

Info

Publication number: GB2611347A
Application number: GB2114104.9A
Authority: GB
Inventors: Perrott Jonathan
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-10-01
Filing date: 2021-10-01
Publication date: 2023-04-05
Anticipated expiration: 2041-10-01
Also published as: GB2611347B; WO2023052793A1; GB202114104D0

Abstract

A bicycle transmission includes a hub 10 that is switchable between a free wheel state and a fixed wheel state during use. The hub 10 comprises: a hub body 20; a sprocket carrier connected to the hub via a freewheel mechanism; a clutch mechanism comprising at least one fixed clutch plate 61 that is rotationally fixed with the hub body and at least one rotatable clutch plate 62 that is rotationally fixed with the sprocket carrier. When engaged the clutch locks the sprocket carrier with respect to the hub. Also disclosed is a tensioner (101 figure 9) separate from a rear gear shifting mechanism (8, figure 9) the tensioner being fixable in position when the hub is in a fixed-wheel state. A controller (135, figure 8) is described which synchronises operation of the hub 10 and the tensioner 101.

Description

BICYCLE TRANSMISSION

FIELD OF THE INVENTION

The present invention relates to a bicycle transmission, and in particular to a bicycle transmission including a hub that is switchable between a free wheel state and a fixed wheel state during use.

BACKGROUND OF THE INVENTION

Early bicycles used fixed wheel transmissions with no freewheel mechanism. In transmissions of this type the chainset or crankset is required to rotate continuously together with the driven wheel while the bicycle is in motion. In contrast, most modern bicycle transmissions include a freewheel mechanism that allows the chainset or crankset to drive the driven wheel of the bicycle in a forward direction but also allows the chainset or crankset to stop rotating while the bicycle is in motion such that the rider is not required to keep pedalling at all times during a ride.

Modern free wheel transmissions generally provide improved riding comfort and safety compared to fixed wheel transmissions. However, fixed wheel transmissions also provide various advantages over free wheel transmissions, including improved pedalling efficiency due to a "flywheel effect" and the ability to apply a reverse torque to the driven wheel via the transmission to aid deceleration, and remain popular with some riders.

Bicycle wheels that are capable of both fixed wheel and free wheel operation are available, including a fixed sprocket mounted on one side of the hub and a further sprocket mounted to the opposite side of the hub via a freewheel mechanism. However, wheels of this type must be removed from the bicycle frame, rotated to face the opposite direction, and then reattached to the frame in order for the transmission to be switched between its fixed wheel and free wheel states, and only allow a single gear ratio for each mode of operation.

The present invention aims to address disadvantages of such known bicycle transmissions.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a hub for a bicycle transmission that is configured to be selectively switched between fixed and free wheel states in use. The hub may comprise a hub body that is configured to have a plurality of spokes of a bicycle wheel coupled thereto; and a sprocket carrier that is configured to have at least one sprocket mounted thereto, the sprocket carrier being connected to the hub body via a freewheel mechanism that is configured to rotate the hub body together with the sprocket carrier when the sprocket carrier is rotated in a first direction or main drive direction about a central axis of the hub, and to allow the sprocket carrier to rotate relative to the hub body in a second direction or reverse direction opposed to the first direction. The hub may further comprise a clutch mechanism comprising at least one fixed clutch plate that is rotationally fixed with respect to the hub body and at least one rotatable clutch plate that is rotationally fixed with respect to the sprocket carrier, the clutch mechanism being switchable between a disengaged configuration in which the sprocket carrier is permitted to rotate in the second direction relative to the hub body, and an engaged configuration in which relative rotation between the sprocket carrier and the hub body is at least substantially prevented; and an actuation mechanism for selectively engaging and disengaging the clutch mechanism.

The hub of the present invention advantageously allows a rider of a bicycle that is fitted with a rear wheel including the hub to readily switch the bicycle between a fixed wheel state and a free wheel state while riding the bicycle, thereby enabling the rider to enjoy the advantages of both transmission types at will.

The freewheel mechanism may comprise a unidirectional ratchet mechanism.

The sprocket carrier may comprise a cylindrical body with a splined outer surface that is configured to receive the one or more sprockets thereon. However, in other embodiments the sprocket(s) may be connected to the sprocket carrier by one or more bolts, or even integrally formed with the sprocket carrier, especially in embodiments in which the hub forms part of a single speed transmission including only one rear sprocket.

The sprocket carrier may be connected to the hub body via a connection part, with the freewheel mechanism being provided between the sprocket carrier and the connection part and the connection part being coupled to the hub body via a non-rotating interface that prevents relative rotation between the connection part and the hub body in the first and second directions.

The connection part may optionally be integrated with the sprocket carrier and the freewheel mechanism as part of a stand-alone or self-contained freehub. However, in other embodiments the sprocket carrier and the freewheel mechanism may form part of a separate freewheel body that is configured to be coupled to the connection part, for example by engagement with a threaded outer surface of the connection part. In other embodiments the freewheel mechanism may be provided separately to the sprocket carrier as part of another component or assembly.

The rotatable clutch plate(s) may be coupled to the sprocket carrier by a clutch basket. The clutch basket may comprise a mounting portion that is mounted to and rotationally fixed with respect to the sprocket carrier, and a clutch plate engaging portion that extends outwardly from the mounting portion and is connected to the rotatable clutch plate(s) in order to prevent relative rotational movement between the rotatable clutch plate(s) and the sprocket carrier.

The mounting portion of the clutch basket may comprise a splined hole that is engaged with a splined outer surface of the sprocket carrier to thereby prevent relative rotational movement between the clutch basket and the sprocket carrier. In this case the mounting portion of the clutch basket may be configured to be axially retained on the sprocket carrier between a flange provided at an inner end of the sprocket carrier and a sprocket or cassette mounted to the sprocket carrier. In other embodiments the mounting portion of the clutch basket may be mounted to the sprocket carrier by one or more bolts.

The clutch plate engaging portion of the clutch basket may be coupled to the rotatable clutch plate(s) at or adjacent to the outer edge(s) of the rotatable clutch plate(s) outboard of the outer edge(s) of the fixed clutch plate(s).

The clutch plate engaging portion of the clutch basket may comprise a plurality of elongate plate engaging elements that are received within a corresponding plurality of apertures provided in the rotatable clutch plate(s). The plate engaging elements of the clutch basket may, for example, comprise cylindrical rods with a circular cross-section, although other cross-sectional shapes are also possible for the plate engaging elements.

The apertures within which the plate engaging elements are received may comprise through holes extending through the rotatable clutch plates and/or notches provided in the circumferentially outer surface(s) of the rotatable clutch plate(s). The apertures are preferably shaped to correspond to the cross-sectional shapes of the plate engaging elements.

At least one of the rotatable clutch plate(s) may be axially movable along the clutch plate engaging portion of the clutch basket in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly.

The hub may further comprise central shaft that is connected to and rotationally fixed with respect to the hub body, the central shaft extending outwardly from a base of the hub body and through a housing of the hub body in which the fixed and rotatable clutch plates are located.

The sprocket carrier may be mounted to a distal end of the central shaft, that is the end furthest from the base of the hub body. The connection between the sprocket carrier and the central shaft may be provided via the connection part, which may be coupled to the distal end of the central shaft via a non-rotating interface.

The fixed clutch plate(s) may be mounted to and rotationally fixed with respect to the central shaft, and the rotatable clutch plate(s) may be freely rotatable around the central shaft when the clutch mechanism is in the disengaged configuration.

At least one of the fixed clutch plates may be mounted to the central shaft via a clutch plate carrier. The clutch plate carrier may comprise a splined bore that is engaged with a splined outer surface of the central shaft and configured to allow the clutch plate carrier to move along the central shaft in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly. In this case the at least one fixed clutch plate may comprise a splined aperture that is engaged with a splined outer surface of the clutch plate carrier and configured to allow the fixed clutch plate to move along the clutch plate carrier in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly.

The clutch mechanism may comprise first and second end plates that are configured to be moved relative to each other by the actuation mechanism in order to bring the fixed and rotatable clutch plates into engagement with each other to thereby engage the clutch mechanism. The first end plate may be rigidly connected to the central shaft. The second end plate may be mounted to and rotationally fixed with respect to the central shaft but movable along the central shaft in a direction aligned with the central axis of the hub. The second end plate may optionally be mounted to the central shaft via the clutch plate carrier, if present. In this case the second end plate may be provided by a flange, which may be integrally formed with or otherwise attached to a main body of the clutch plate carrier The first and second end plates may each act as fixed clutch plates of the clutch mechanism. There may also be one or more additional fixed clutch plates provided between the first and second end plates. However, it will be appreciated that the first and second end plates may form the only fixed clutch plates of the clutch mechanism, in which case it is only necessary for there to be a single rotatable clutch plate located between the first and second end plates.

The actuation mechanism may comprise a static portion and a movable portion, the static portion of the actuation mechanism including an anti-rotation arm that is configured to engage a frame of a bicycle with which the hub may be used in order to prevent the static portion of the actuation mechanism from rotating relative to the bicycle frame, and the movable portion of the mounting mechanism including an attachment point for attachment of an actuation cable for effecting relative movement between the static portion and the movable portion in order to control engagement of the clutch mechanism.

The actuation mechanism may comprise a guide, for example a jockey wheel, for guiding the actuation cable towards the movable portion of the actuation mechanism. The guide may be mounted to the static portion of the actuation mechanism. The guide may, for example, be mounted to the anti-rotation arm of the static portion of the actuation mechanism, or alternatively to a separate supporting arm that extends outwardly from a main body of the static portion of the actuation mechanism.

The actuation cable may be configured to rotate the movable portion of the actuation mechanism with respect to the static portion of the actuation mechanism. The actuation mechanism may be provided with a rotary-to-linear coupling, for example a ball drive mechanism, that is configured to generate relative axial movement between the static and movable portions of the actuation mechanism in response to relative rotational movement between the static and movable portions of the actuation mechanism in order to control engagement and disengagement of the clutch mechanism.

The movable portion of the actuation mechanism may be configured to engage and apply an axial force to the second end plate of the clutch mechanism and/or the clutch plate carrier in order to control engagement and disengagement of the clutch mechanism.

The actuation mechanism may define a housing, and the fixed and rotatable clutch plates may be located within the housing. The housing defined by the actuation mechanism may be an inner housing, and may be located inside an outer housing defined by the hub body. The housings defined by the actuation mechanism and the hub body may be open ended in order to facilitate assembly of the clutch mechanism. The mounting portion of the clutch basket may be arranged to close the open ends of the housings defined by the actuation mechanism and the hub body.

According to a further aspect of the present invention there is provided a bicycle wheel comprising a hub according to the first aspect of the invention.

According to a further aspect of the present invention there is provided a bicycle including a wheel comprising a hub according to the first aspect of the invention.

In some embodiments the hub of the present invention may form part of a single speed transmission, in which case the sprocket carrier may only carry a single sprocket. However, in one preferred embodiment the hub forms part of a multi-speed transmission, in which case the sprocket carrier may have a cassette including multiple sprockets mounted thereon.

Where the hub forms part of a multi-speed transmission, the transmission preferably includes a rear derailleur that does not include any chain tensioning mechanism, a chain tensioning system separate to the rear derailleur, and an actuation system that is operable to selectively increase the tension in the chain loop in order to remove slack from the chain loop for example to enable a reverse torque to be applied to the hub via the bicycle transmission (that is a torque in an direction opposed to the normal forward direction in which torque is applied to move the bicycle forwards). The rear derailleur preferably includes a laterally-movable housing through which the chain passes, but without including any sprockets or jockey wheels.

The rear derailleur is preferably mounted to a chain stay of the bicycle frame. The rear derailleur may be mounted to the chain stay at an intermediate location between a trailing end to which the hub is mounted and a leading end that is connected to a bottom bracket shell of the bicycle frame, optionally via a common bracket that is also engaged by the mounting part of the actuation mechanism. However, in other embodiments the rear derailleur may alternatively be mounted to a derailleur hanger provided at a trailing end of the chain stay, for example to a conventional integrated drop out and derailleur hanger.

According to a further aspect of the present invention, there is provided a transmission for a bicycle, the transmission comprising: a crankset including a front chainring; a chain that is configured to be driven by the crankset; a cassette comprising multiple sprockets that is configured to be driven by the chain; a derailleur that is configured to switch the chain between the sprockets of the cassette, and a chain tensioning system provided separately to the derailleur.

The chain tensioning system may comprise: an arm that is mounted to and movable with respect to a frame of the bicycle; a tensioning jockey wheel that is mounted to the movable arm and engaged with the chain, and a biasing mechanism that is configured to bias the arm in a first direction in order to impart tension to the chain via the jockey wheel.

The chain tensioning system may further comprise an actuation system that is operable to further bias the arm in the first direction in order to further increase the tension applied to the chain by the chain tensioning system.

The cassette may be mounted to a hub that is configured to be selectively switchable between a fixed wheel state and a free wheel state during use of the bicycle. However, it will be appreciated that the chain tensioning system may also be used in bicycle transmissions that include a standard rear wheel fitted with a continuously active freehub or freewheel body.

The derailleur may comprise a housing or stirrup through which the chain passes, and a linkage mechanism that is configured to move the stirrup in a lateral direction with respect to the cassette in order to move the chain between the sprockets of the cassette. However, the derailleur preferably does not include any chain tensioning system of its own.

The chain tensioning system may further comprise a second jockey wheel mounted to the bicycle frame that is also engaged with the chain. The second jockey wheel may have a fixed axis of rotation with respect to the bicycle frame, and may be mounted to a drive side chainstay of the bicycle frame, optionally via a mounting bracket.

The second jockey wheel may be located above the tensioning jockey wheel, and may be either in front of or behind the tensioning jockey wheel with respect to a forward direction of the bicycle. The tensioning jockey wheel and the second jockey wheel may be arranged such that the chain extends upwardly from the chainring of the crankset towards the second jockey wheel, around the second jockey wheel, downwardly from the second jockey wheel towards the tensioning jockey wheel, around the tensioning jockey wheel, and rearwardly and upwardly from the tensioning jockey wheel towards the rear cassette. In a preferred embodiment the chain may extend upwardly and rearwardly from the chainring of the crankset towards the second jockey wheel, and downwardly and forwardly from the second jockey wheel towards the tensioning jockey wheel.

The actuation system may comprise an actuation cable that is connected to a user-operable lever, which may be mounted at any suitable location on the bicycle, for example on the handlebars of the bicycle.

The lever may be a first lever, and may form part of a lever assembly that further comprises a second user-operable lever. The second lever may, for example, be connected to a further actuation system that is configured to switch the hub between the fixed state and the free wheel state. The first lever may be located in front of the second lever such that the first lever is engaged before the second lever when a user pulls on both levers.

The movable arm may be a swing arm that is pivotable with respect to the bicycle frame.

The movable arm may be mounted to a bottom bracket shell of the bicycle frame. The movable arm may, for example, be mounted to a flange or tab that extends radially outwardly from the bottom bracket shell. In other embodiments the movable arm may be mounted to the bottom bracket shell via a bottom bracket that is fitted to the bottom bracket shell.

The movable arm may be mounted to the bottom bracket shell via a mounting bracket. The mounting bracket may be fixed with respect to the bottom bracket shell, and the movable arm may be pivotally mounted to mounting bracket.

The movable arm may be pivotable with respect to the bicycle frame about an axis that is aligned with a central axis of the crankset such that the jockey wheel is capable of tracing an arc that is centred on the central axis of the crankset.

The biasing mechanism may be mounted to the bottom bracket shell of the bicycle frame, optionally via the same flange or tab as the movable arm.

The biasing mechanism may comprise a rotationally biased gear that is engaged with a toothed rack provided on the movable arm. The toothed rack may, for example, be provided on a mounting portion of the movable arm via which the movable arm is connected to the mounting bracket. The toothed rack may follow a curved arc, which may be centred on the central axis of the crankset.

Alternatively, the biasing mechanism my comprise a spring that acts directly on the arm, for example a coil spring arranged between the mounting portion of the movable arm and the mounting bracket via which the arm is mounted to the bicycle frame.

The actuation system may be connected to the biasing mechanism and configured to act on the biasing mechanism in order to further bias the arm in the first direction. The actuation system may, for example, comprise an actuation cable that is connected to the rotationally biased gear and configured to rotate the gear in order to further bias the arm in the first direction. The actuation cable may be connected to the gear via a lever, which may be configured to increase the rotational movement of the gear for a given longitudinal movement of the actuation cable compared to an alternative arrangement in which the cable is attached directly to the gear.

Alternatively, the actuation system may be connected to the arm and configured to act directly on the arm in parallel with the biasing mechanism, for example via an actuation cable that is connected directly to the movable arm.

According to a further aspect of the present invention, there is provided a bicycle comprising a transmission as described above.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described by way of non-limiting example only and with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a bicycle 1 according to one possible embodiment of the present invention, Figures 2 to 5 schematically illustrate cross section views through the hub of the rear wheel of the bicycle of Figure 1; Figure 6 schematically illustrates an end on view of the hub of Figures 2 to 5; Figure 7 schematically illustrates a plan view of the hub of Figures 2 to 5; Figure 8 schematically illustrates the handlebars of the bicycle of Figure 1; Figure 9 schematically illustrates the transmission of the bicycle of Figure 1; Figure 10 schematically illustrates the chain tensioning system of the transmission shown in Figure 9; Figures 11, 12a and 12b schematically illustrate components of the chain tensioning system shown in Figure 10, and Figures 13 and 14 schematically illustrate an alternative hub according to another possible embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 schematically illustrates a bicycle 1 according to one possible embodiment of the present invention. As shown in Figure 1, the bicycle 1 includes a frame 2 having front and rear wheels 3, 4 mounted thereto. The rear wheel 4 is configured to be driven by a transmission 5 including a chainset or crankset 6 that is configured to drive a chain 7 in order to rotate a hub 10 that is integrated with the driven rear wheel 4. The hub 10 includes a clutch mechanism that is configured enable the hub 10 to be selectively switched between a fixed wheel state and a free wheel state during use, as described in more detail below. The transmission 5 also includes a rear derailleur 8 for moving the chain 7 between sprockets on the rear hub 10, and a chain tensioning system 100 for removing slack from the chain 7, as described in more detail below.

The hub 10 is illustrated in more detail in cross section in Figures 2 to 5, from the side of the bicycle 1 in Figure 6, and in plan view in Figure 7. The cross section view of Figure 5 shows the hub 10 in its entirety, but various components are omitted in Figures 2 to 4 in order to provide a clearer view of other components.

As shown in Figure 2, the hub 10 includes a hub body 20 comprising an annular or cylindrical outer wall 21 that extends outwardly from a generally planar base 22 and is aligned with a central axis A of the hub 10. The outer wall 21 and the base 22 together define an outer housing 23 of the hub 10 that is closed at one end 24 by the base 22 of the hub body 20 and open at the other end 25. A pair of circumferential flanges 26 including apertures for receiving spokes of the rear wheel 4 extend radially outwardly from the outer wall 21 at the opposed ends 24, 25 of the housing 23.

The base 22 of the hub body 20 includes a central aperture 22a for receiving an axle 29 (shown in Figure 5) that is used to mount the hub 10 to the frame 2 of the bicycle 1. An aperture 27 for receiving a bearing for mounting the hub 10 to the axle 29 is provided on an outer side of the base 22, and a further aperture 28 for receiving a fixed central shaft (describe in more detail below) is provided on an inner side of the base 22.

As also shown in Figure 2, a central shaft 30 extends through the housing 23 defined by the hub body 20 along the central axis A. The central shaft 30 has a proximal end 31 that is received in the aperture 28 provided on the inner side of the base 22 of the hub body 20 and rigidly connected to the base 22 of the hub body 20. The proximal end 31 of the central shaft 30 may have a threaded outer surface that is configured to engage a threaded internal surface of the aperture 28, and may also be fixed to the base 22 of the hub body 20 by one or more bolts that extend through the base 22 and into threaded bore(s) provided in the central shaft 30. The central shaft 30 extends outwardly from the base 22 of the hub body 20 towards a distal end 32 that is located adjacent to the open end 25 of the housing 23. The central shaft 30 includes a through hole 33 for receiving the above-mentioned axle, and a splined outer surface 34 along a portion of its length.

As shown in Figure 4, a freehub 40 including a main body or sprocket carrier 41 and a connection portion 42 is mounted to the hub body 20 via the central shaft 30. The sprocket carrier 41 of the freehub 40 is generally cylindrical, and is provided with a splined outer surface 43 that is configured to receive a cassette 50 including a plurality of sprockets 51 thereon, as shown in Figure 5. The sprocket carrier 41 includes a flange 44 towards its inner end (that is the end of the sprocket carrier 41 that faces inwardly towards the hub 10 in use) for assisting with axial location of the cassette 50 on the sprocket carrier 41.

The sprocket carrier 41 is connected to the connection portion 42 of the freehub 40 by a freewheel mechanism 46 that is configured to rotate the connection portion 42 together with the sprocket carrier 41 when the sprocket carrier 41 is rotated in a first direction or main drive direction about the central axis A of the hub 10, but to allow the sprocket carrier 41 to rotate relative to the connection portion 42 in a second direction or reverse direction opposed to the first direction in order to enable the hub 10 to be used in a free wheel state.

The freehub 40 is axially retained with respect to the hub body 20 by a hollow retaining pin 45 that extends from the sprocket carrier 41 of the freehub 40, through a central aperture in the connection portion 42 of the freehub 40 and into engagement with a threaded portion of the through hole 33 in the central shaft 30. In addition, the connection portion 42 of the freehub 40 is rotationally fixed with respect to the hub body 20 at a non-rotating interface formed by a plurality of locating pins 35 that extend outwardly from the distal end 32 of the central shaft 30 into engagement with a splined protrusion or splined bore provided on the connection portion 42 of the freehub 40. However, it will be appreciated that many other mounting mechanisms are also possible for axially retaining the freehub 40 with respect to the hub body 20 and preventing relative rotation between the connection portion 42 of the freehub 40 and the hub body 20 depending on the shape and design of the freehub that is used. For example, in another embodiment the connection portion 42 of the freehub 40 may instead include an engagement formation with external or internal threading that is configured to engage a corresponding formation with internal or external threading provided at the distal end 31 of the central shaft 30 or on another intermediate component provided between the central shaft 30 and the freehub 40.

As shown in Figure 5, the entire hub assembly 10 is mounted to the frame 2 of the bicycle 1 via an axle 29 that extends between the left and right portions of the rear triangle of the bicycle frame 2. The axle 29 is supported by the bearing 27a provided in the aperture 27 on the outer side of the base 22 of the hub housing 20 on a first side of the hub assembly 10, and by a further bearing 47a that is seated against a seating formation 47 provided in the sprocket carrier 41 of the freehub 40 on the other side of the hub assembly 10.

The clutch mechanism 60 is located inside the housing 23 defined by the hub body 20 between the base 22 of the hub body 20 and the freehub 40, as shown in Figure 5. The clutch mechanism 60 comprises a plurality of fixed clutch plates 61 that are configured to remain rotationally fixed with respect to the hub body 20, and a plurality of rotatable clutch plates 62 that are configured to remain rotationally fixed with respect to the sprocket carrier 41 of the freehub 40. The fixed clutch plates 61 and the rotatable clutch plates 62 are generally annular in shape, and extend around the central shaft 30 of the hub 10. Each of the fixed clutch plates 61 is provided with a high friction surface or coating on each of its major surfaces, although the high friction surfaces could alternatively (or additionally) be provided on the rotatable clutch plates 62.

The fixed clutch plates 61 are mounted to the central shaft 30 via a clutch plate carrier component 70, which is shown most clearly in Figure 4 in which the fixed and rotatable clutch plates 61, 62 are omitted for clarity. The clutch plate carrier 70 has a hollow cylindrical body 71 that surrounds the central shaft 30, the cylindrical body having a splined inner bore 72 that engages the splined portion 34 of the central shaft 30 in order to prevent the clutch plate carrier 70 from rotating with respect to the hub body 20 while permitting axial movement of the clutch plate carrier 70 in a direction aligned with the central axis A of the hub 10. The body 71 of the clutch plate carrier 70 also includes a splined outer surface 73 that engages splined apertures of the fixed clutch plates 61 in order to prevent the fixed clutch plates 61 from rotating with respect to the clutch plate carrier 70 and the hub body 20 while permitting axial movement of the fixed clutch plates 61 along the body 71 of the clutch plate carrier 70. An annular flange 75 extends outwardly from the body 71 of the clutch plate carrier 70 at its end closest to the base 22 of the hub housing 23.

The rotatable clutch plates 62 are coupled to the sprocket carrier 41 of the freehub 40 on which the cassette 50 is mounted by a clutch basket component 80, shown in Figure 5. The clutch basket 80 includes a mounting portion 81 comprising an annular retaining plate 82 with a splined central aperture that is received on the sprocket carrier 41 of the freehub 40. The retaining plate 82 is sandwiched between the cassette 50 and the flange 44 at the inner and of the sprocket carrier 41 in order to axially retain the clutch basket 80 with respect to the freehub 40, and interaction between the splined hole of the retaining plate 82 and the splined outer surface 43 of the sprocket carrier 41 prevents the clutch basket 80 from rotating with respect to the sprocket carrier 41 of the freehub 40.

The clutch basket 80 further comprises a plate engaging portion 83 including a plurality of plate engaging elements 84 in the form of elongate rods with a circular cross section that extend outwardly from the mounting portion 81 of the clutch basket 80 and into the hub housing 23 in a direction towards the base 22 of the hub body 20. The rods 84 are each received within apertures provided adjacent to the outer edges of the rotatable clutch plates 62 outboard of the outer edges of the fixed clutch plates 61. The rotatable clutch plates 62 are slidable along the rods 84 in a direction aligned with the central axis A of the hub 10, but are rotationally fixed with respect to the clutch basket 80, and therefore also the sprocket carrier 41 of the freehub 40, by their interaction with the rods 84.

An annular end plate 65 is rigidly mounted at the distal end 32 of the central shaft 30 between the end face of the central shaft 30 and the connection portion 42 of the freehub 40, as shown in Figure 4. (Figure 4 shows the end plate 65 mounted to the distal end 32 of the central shaft 30 without the fixed and rotatable clutch plates 61, 62 being present, but it will be appreciated that the fixed and rotatable clutch plates 61, 62 will be placed around the central shaft 30 before the end plate 65 is connected thereto during assembly of the hub 10.) The end plate 65 includes a central aperture that allows the retaining pin 45 of the freehub 40 to pass therethrough, and a plurality of smaller apertures located around the central aperture for allowing the locating pins 35 to pass therethrough.

The end plate 65 defines an outer end of the clutch mechanism 60. The opposed, inner end of the clutch mechanism 60 is defined by the flange 75 of the clutch plate carrier 70. The end plate 65 and the flange 75 of the clutch plate carrier 70 each include a high friction surface that faces inwardly into the clutch mechanism 60, and each serve as additional fixed clutch plates of the clutch mechanism 60 in addition to the fixed plates 61 that are slidably mounted to the main body 71 of the clutch plate carrier 70.

A spring 66 is provided between the inwardly facing surface of the end plate 65 and the outer end face of the clutch plate carrier 70. The spring 66 acts to bias the clutch plate carrier 70 and its flange 75 in an axial direction away from the end plate 65, thereby holding the clutch mechanism 60 in a disengaged configuration.

The hub 10 further comprises an actuation mechanism 90 for controlling actuation of the clutch mechanism 60, as shown in Figures 3 to 7. As shown in Figure 3, the actuation mechanism 90 includes a static shell 91 including a part cylindrical outer wall 91a that extends outwardly from an annular base 91b. The base 91b of the static shell 91 is mounted to the central shaft 30 via a bearing that sits between the splined portion 34 of the central shaft 30 and the base 22 of the hub body 20, and sits within the outer housing 23 defined by the hub body 20 adjacent to the base 22 of the hub body 20.

The outer wall 91a of the static shell 91 extends outwardly from the base 91b towards the open end 25 of the hub body 20, and extends around a majority of the circumference of the hub 10 but includes a side opening, as shown in Figure 6.

An anti-rotation arm or torque bar 92 extends radially outwardly from an outer end of the outer wall 91a of the static shell 91 at a location outboard of the open end 25 of the hub body 20. The distal end of the anti-rotation arm 92 includes an engagement formation 92a including an aperture that engages a bracket 2b provided on the drive-side chain stay 2a of the frame 2 of the bicycle 1, as shown in Figures 6 and 7, in order to prevent the static shell 91 of the actuation mechanism 90 from rotating relative to the bicycle frame 2 as the rear wheel 4 rotates during use of the bicycle 1.

As also shown in Figure 3, the actuation mechanism 90 further includes a movable shell 93 including a part cylindrical outer wall 93a that extends outwardly from an annular base 93b. The outer wall 93a of the movable shell 93 extends outwardly from the base 93b towards the open end 25 of the hub body 20, and fills a portion of the opening left in the outer wall 91a of the static shell 91. The outer walls 91a, 93a of the static and movable shells 91, 93 together define an inner housing 94 located inside the outer housing 23 defined by the hub body 20 within which the clutch mechanism 60 is located.

The base 93b of the movable shell 93 is sandwiched between the base 91b of the static shell 91 and the flange 75 of the clutch plate carrier 70. The base 93b of the movable shell 93 is separated from the flange 75 of the clutch plate carrier 70 by a thrust bearing 98 that is configured to allow the clutch plate carrier 70 and the fixed clutch plates 61 mounted thereon to rotate together with the hub body 20 relative to the actuation mechanism 90 as the rear wheel 4 turns.

A rotary-to-linear coupling in the form of a ball drive mechanism 95 is provided between the base 93b of the movable shell 93 and the base 91b of the static shell 91. The ball drive mechanism 95 comprises a plurality of balls 95a that are sandwiched between the bases 91b, 93b of the static and movable shells 91, 93, as shown in Figure 3. As shown in the side on view of Figure 6 (in which the end plate 65, clutch plate carrier 70 and clutch plates 61, 62 have been omitted in order to reveal the base of the actuation mechanism 90), the balls 95a of the ball drive mechanism 95 are located in tapered recesses 95b provided in the bases 91b, 93b of the static and movable shells 91, 93 such that relative rotation between the static and movable shells 91, 93 around the main axis A of the hub 10 can vary the axial position of the movable shell 93 within the hub body 20.

Since the base 93b of the movable shell 93 is sandwiched between the flange 75 of the clutch plate carrier 70 and the base 91b of the static shell 91 and biased in a direction towards the base 91b of the static shell 91 by the spring 66 located between the end plate 65 and the outer end of the clutch plate carrier 70, the movable shell 93 is naturally rotationally biased towards a position that allows the movable shell 93 to sit as close to the closed end 24 of the hub body 20 and as far away from the clutch mechanism 60 as possible. However, the movable shell 93 is also provided with an attachment point 96 located outboard of the open end 25 of the hub body 20, which is connected to an actuation cable 97 that is configured to rotate the movable shell 93 relative to the static shell 91 about the central axis A of the hub 10. The actuation cable 97 has a distal end (furthest from the hub 10) that is connected to a user-operable lever 134 forming part of a lever assembly 132 that is mounted to the handlebars 130 of the bicycle 1, as shown in Figure 8 and described in more detail below. The actuation cable 97 is guided towards the attachment point 96 of the movable shell 93 via a pulley or jockey wheel 99 mounted on the anti-rotation arm 92 of the static shell 91, as shown in Figures 6 and 7. (The arm 92 and the attachment point 96 are shown on opposite sides of the actuation mechanism in Figure 5 for ease of viewing in two dimensions, but are in fact both provided towards a front side of the actuation mechanism, as best shown in Figure 6.) During use of the bicycle 1, when the crankset 6 is rotated in a forward direction, the chain 7 drives the cassette 50 in a forward direction thereby causing the freehub 40 to drive the hub body 20 and therefore the rear wheel 4 forwards. However, since the sprocket carrier 41 of the freehub 40 is permitted to rotate relative to the hub body 20 in a reverse direction opposed to the main drive direction, it is also possible for a rider of the bicycle 1 to stop pedalling while the bicycle 1 is moving forwards, in which case the hub body 20 will continue to rotate together with the rear wheel 4 in the forward direction but the sprocket carrier 41, cassette 50, chain 7 and crankset 6 are not required to continue rotating in the forward direction.

If a rider of the bicycle 1 wants to switch the bicycle transmission 5 from the above-described free wheel state to a fixed wheel state then he may do so by operating the user-operable lever 134 to pull on the actuation cable 97 in order to rotate the movable shell 93 of the actuation mechanism 90 relative to the static shell 91. As the movable shell 93 is rotated relative to the static shell 91, the ball drive mechanism 95 moves the movable shell 93 in an axial direction away from the base 91b of the static shell 91. This movement in turn moves the flange 75 of the clutch plate carrier 70 in an axial direction towards the end plate 65 of the clutch mechanism 60 until the fixed and rotatable clutch plates 61, 62 are brought into mutual engagement with each other. When the clutch mechanism 60 has been engaged in this way, interaction between the fixed and rotatable clutch plates 61, 62 prevents relative rotation between the sprocket carrier 41 of the freehub 40 and the hub body 20, thereby bypassing the freewheel mechanism 46 of the freehub 40 and switching the transmission 5 into a fixed wheel state.

When it is desired to return the bicycle transmission 5 to its free wheel state, the user-operable lever 134 may be released, thereby allowing the movable shell 93 of the actuation mechanism 90 to return to its de-activated position and allowing the fixed and rotatable clutch plates 61, 62 to disengage from each other. Once the hub assembly 10 has returned to this state the fixed and rotatable clutch plates 61, 62 are once again permitted to rotate relative to each other, thereby enabling the sprocket carrier 41 of the freehub 40 to rotate relative to the hub body 20 in the reverse direction when a rider of the bicycle 1 stops pedalling.

The transmission 5 is required to include slack in the chain 7 in order to enable the chain 7 to be switched between the sprockets 51 of the cassette 50. However, it is also desirable to be able to remove the slack from the chain 7 when the transmission 5 is being operated in the fixed wheel state in order to benefit from the flywheel effect and in some cases also enable a reverse torque to be applied to the rear wheel via the transmission 5. To this end the transmission 5 includes a specially designed rear derailleur 8 that does not include any chain tensioning mechanism, and a chain tensioning system 100 for removing slack from the chain 7 that is provided separately to the rear derailleur 8.

As shown in Figure 7, the rear derailleur 8 comprises a housing or stirrup 8a that is configured to allow the chain 7 to pass therethrough. The housing 8a is mounted to the bicycle frame 2 via a slant parallelogram type linkage mechanism 8b that is configured to move the housing 8a in a lateral direction with respect to the bicycle frame 2 in order to move the chain 7 between the different sprockets 51 of the cassette 50. The linkage mechanism 8b is mounted to the drive-side chain stay 2a of the rear triangle of the bicycle frame 2 via the same bracket 2b that is engaged by the anti-rotation arm 92 of the hub's actuation mechanism 90, and extends rearwardly from the frame 2 in a direction towards the cassette 50. The linkage mechanism 8b is also connected to a push/pull type cable 8c including an internal wire that is connected to a gear shifting device such as a shifting lever or a twist-type gear shifter 131 provided on the handlebars 130 of the bicycle 1 (as shown in Figure 8). The cable 8c is configured to move the linkage mechanism 8b and housing 8a of the rear derailleur 8 in order to enable a rider of the bicycle 1 to shift the chain 7 between the sprockets 51 of the cassette 50 as desired.

As shown in Figure 9, the chain tensioning system 100 comprises a chain tensioning swing arm 101. The swing arm 101 comprises an annular mounting portion 102 via which the swing arm 101 is mounted to the bottom bracket shell 2c of the bicycle frame 2, and an elongate arm portion 104 that extends radially outwardly from the mounting portion 102 towards a distal end 105 remote from the mounting portion 102. A movable jockey wheel 106 is mounted to the arm portion 104 towards its distal end 105. The movable jockey wheel 106 is arranged in the same plane as the single chainring 6a of the crankset 6, and is located below and to the rear of the axis of rotation of the crankset 6.

As shown in Figure 10, in which the various components of the chain tensioning system 100 are shown in cross section and in an exploded state with respect to the bicycle frame 2, the mounting portion 102 of the swing arm 101 is mounted to the bottom bracket shell 2c via an annular mounting bracket 107, the mounting portion 102 of the swing arm 101 being pivotally coupled to the mounting bracket 107 via a bearing 108, and the mounting bracket 107 being fixed to an annular flange 2d that extends radially outwardly from the bottom bracket shell 2c by a plurality of bolts. The swing arm 101 is pivotable relative to the bottom bracket shell 2c within a limited range of motion around an axis that is aligned with the central axis of the bottom bracket shell 2c and crankset 6 of the bicycle 1 such that the movable jockey wheel 106 is capable of tracing an arc that is centred on the central axis of the bottom bracket shell 2c and the crankset 6.

As shown in Figure 9, the chain tensioning system 100 further comprises a second jockey wheel 110 with a fixed axis of rotation that is mounted on the outer side of the drive-side chain stay 2a of the bicycle frame 2. This fixed jockey wheel 110 is also arranged in the same plane as the chainring 6a of the crankset 6 and the movable jockey wheel 106, and is located above the movable jockey wheel 106 such that the chain 7 extends around a portion of the chainring 6a of the crankeset 6, rearwardly and upwardly from the underside of the chainring 6a towards the fixed jockey wheel 110, around the fixed jockey wheel 110, downwardly and forwardly from the fixed jockey wheel 110 towards the movable jockey wheel 106, around the movable jockey wheel 106, and rearwardly and upwardly from the movable jockey wheel 106 towards the rear cassette 50 via the rear derailleur 8.

As also shown in Figure 9, the chain tensioning system 100 further comprises a biasing mechanism 120 including a rotationally biased spur gear 121 that is configured to bias the swing arm 101 in a rotational direction about its axis that is opposed to the main drive direction of the crankset 6, that is an anti-clockwise direction when the bicycle 1 is viewed from the drive-side. The spur gear 121 is mounted to the bicycle frame 2 by a mounting bracket 122 that is in turn mounted to the same mounting flange 2d as the swing arm mounting bracket 107 by a plurality of bolts, as shown in Figure 10.

The spur gear 121 is rotatable with respect to the spur gear mounting bracket 122, and is biased in a clockwise direction when viewed from the drive-side of the bicycle 1 by a spring 123 provided between the spur gear 121 and the mounting bracket 122. The spur gear 121 is engaged with a curved toothed rack 103 provided on the mounting portion 102 of the swing arm 101 (shown in Figure 11) in order to impart the required biasing force to the swing arm 101 and bias the swing arm 101 in the anticlockwise direction about its axis.

As shown in Figures 12a and 12b, the chain tensioning system 100 further comprises an actuation system 126 for increasing the biasing force that is applied to the swing arm 101 by the biasing mechanism 120. The actuation system 126 comprises an actuation cable 127 that is connected to a lever 125 that is fixed with respect to and extends outwardly from a rear plate 124 of the spur gear 121. The actuation cable 127 is connected to a user-operable lever 133 of the lever assembly 132, and is configured to further bias the spur gear 121 in the clockwise direction, thereby further biasing the swing arm 101 in the anti-clockwise direction, when the lever 133 is operated by a user of the bicycle 1. The lever 125 via which the actuation cable 127 is mounted to the rear plate 124 of the spur gear 121 acts to increase the rotational movement of the spur gear 121 for a given longitudinal movement of the actuation cable 127 compared to an alternative arrangement in which the actuation cable 127 is attached directly to the spur gear 121.

As shown in Figure 8, the user-operable lever 133 to which the actuation cable 127 of the chain tensioning system 100 is connected is a first lever of a handlebar-mounted dual lever assembly 132 that also includes a second user-operable lever 134. As mentioned above, the second user-operable lever 134 is connected to the actuation cable 97 that controls activation of the clutch mechanism 60 of the hub 10. The first lever 133 of the dual lever assembly 132 (to which the actuation cable 127 of the chain tensioning system 100 is connected) is longer than the second lever 134 (to which the actuation cable 97 of the hub 10 is connected) and is located in front of the second lever 134 such that the first lever 133 is engaged before the second lever 134 when a user of the bicycle 1 pulls on both levers 133, 134.

As also shown in Figure 8, the handlebars 130 of the bicycle 1 are further fitted with a second dual lever assembly 135 also comprising a first lever 136 and a second lever 137. The first lever 136 of the second dual lever assembly 135 is connected to an actuation cable for a front brake of the bicycle 1 (not shown), and the second lever 137 of the second dual lever assembly 135 is connected to an actuation cable for a rear brake of the bicycle 1 (not shown). As with the first dual lever assembly 132, the first lever 136 of the second dual lever assembly 135 is also longer than the second lever 137 and is located in front of the second lever 137 such that the first lever 136 is engaged before the second lever 137 when a user of the bicycle 1 pulls on both levers 136, 137.

In use, the movable jockey wheel 106 at the distal end 105 of the swing arm 101 imparts sufficient tension to the chain loop to prevent the chain 7 from accidentally switching between the sprockets 51 of the rear cassette 50 while still allowing the chain 7 to be switched between the sprockets 51 of the cassette 50 using the rear derailleur 8. When the chain 7 moves between the sprockets 51 of the cassette 50 during use of the bicycle 1, the swing arm 101 rotates slightly with respect to the bicycle frame 2 in order to accommodate chainrings of different sizes within the chain loop while maintaining an approximately constant tension in the chain 7. However, when it is desired to operate the bicycle 1 in its fixed gear state, a user of the bicycle 1 may pull on the first and second levers 133, 134 of the first dual lever assembly 132. As the user pulls on the first lever 133, the actuation cable 127 of the chain tensioning system 100 pulls on the lever 125 connected to the spur gear 121 of the biasing mechanism 120, thereby further biasing the swing arm 101 in the anti-clockwise direction. This enables the chain tensioning system 100 to further increase the chain tension and removes slack from the chain loop. Pulling simultaneously on the second lever 134 also causes the clutch mechanism 60 of the hub 10 to be engaged in the manner already described above, thereby bypassing the freewheel mechanism 46 of the freehub 40 and enabling the transmission 5 to be operated in its fixed wheel state.

It will be appreciated that the above description relates to a non-limiting exemplary embodiment of the present invention, and that many modifications and variations may be made within the scope of the present invention as defined in the accompanying claims.

For example, in another embodiment the spur gear type biasing mechanism 120 may be replaced by a spring that acts directly on the swing arm 101, and the actuation cable 127 of the chain tensioning system 100 may be connected to the swing arm 101 directly, that is to say independently of the biasing mechanism.

In addition, in the above-described embodiment the hub 10 forms part of a multi-speed transmission, and is fitted with a multi sprocket cassette 50 that is received on a splined outer surface 43 of a self-contained freehub component 40. However, Figures 13 and 14 schematically illustrate an alternative embodiment of the present invention in which a similar hub 10 is fitted with a screw-on freewheel body 140 that carries a single rear sprocket 151.

The hub 10 shown in Figures 13 and 14 is generally similar to the hub 10 shown in Figures 2 to 5, and the same reference numbers have been used to identify identical or equivalent components for ease of reference. However, in place of the freehub 40 that is directly connected to the central shaft 30 via the integrated connection portion 42 in the embodiment of Figures 2 to 5, the hub 10 of Figures 13 and 14 is instead provided with a separate connection part 142 that is secured to the distal end of the central shaft 30 and rotationally fixed with respect to the central shaft 30 by the retaining pin 45 and locating pins 35, and a freewheel body 140 that is screwed onto a threaded outer surface of the connection part 142. A locking ring 147 is also screwed onto the threaded outer surface of the connection part 142 on the outer side of the freewheel body 140, which acts to prevent the freewheel body 140 from unscrewing itself from the connection part 142 when a reverse torque is applied to the sprocket 151 via the bicycle transmission.

The freewheel body 140 includes an inner race 143 with a threaded inner surface that is engaged with the threaded outer surface of the connection part 142, an outer race 144 to which the rear sprocket 151 is connected, and a unidirectional freewheel mechanism 146 located between the inner and outer races 143, 144. The outer race 144 includes an integral flange 145. The rear sprocket 151 and clutch basket 80 are both mounted to the outer race 144 by a plurality of bolts that extend from the rear sprocket 151, through the flange 145 and into a modified mounting portion 81 of the clutch basket 80.

Where the freewheel body 140 is a standard component, the flange 145 may be an integral sprocket of the freewheel body 140 that has been repurposed for mounting the rear sprocket 151 and the clutch basket 80 to the outer race 144 of the freewheel body 140. In this case the bolts used to mount the rear sprocket 151 and the clutch basket 80 to the outer race 144 of the freewheel body 140 may pass through holes provided in the integral sprocket or between teeth of the integral sprocket. However, in other embodiments in which the freewheel body 140 is a custom component, the flange 145 may be a dedicated mounting flange instead of a repurposed integral sprocket, or the rear sprocket 151 that is engaged by the chain 7 may itself be integrally formed with the outer race 144 of the freewheel body 140.

In addition, the actuation mechanism 90 of the hub 10 shown in Figures 13 and 14 also has a slightly modified design compared to the actuation mechanism 90 shown in Figures 3 and 6. In particular, in place of the forwardly extending anti-rotation arm 92 that is configured to engage a bracket that is fixed to the drive-side chainstay as shown in Figure 6, the static shell 91 of the actuation mechanism 90 of the hub 10 shown in Figures 13 and 14 instead comprises an anti-rotation arm 192a that extends axially outwardly from the main body of the static shell 91 from a location towards the rear end of the static shell 91 before extending radially inwardly towards the central axis A of the hub 10. The distal end of the modified anti-rotation arm 192a is configured to be received within a standard rear-facing drop out as commonly found on single speed bicycle frames, and to interact with the rear facing drop out to prevent the static shell 91 of the actuation mechanism 90 from rotating with respect to the bicycle frame 2. In this embodiment the jockey wheel 99 that guides the actuation cable 97 towards the attachment point 96 of the static shell 93 of the actuation mechanism 90 is mounted to a separate mounting arm 192b that extends radially outwardly from a forward portion of the static shell 91.

It will be appreciated that no rear derailleur or chain tensioning mechanism is required in the single speed embodiment shown in Figures 13 and 14 since the chain loop in this embodiment is not required to include slack for enabling gear changes.

Other modifications and variations will also be apparent to the skilled person

Claims

CLAIMS1. A hub for a bicycle transmission, the hub comprising: a hub body that is configured to have a plurality of spokes of a bicycle wheel coupled thereto; a sprocket carrier that is configured to have at least one sprocket mounted thereto, the sprocket carrier being connected to the hub body via a freewheel mechanism that is configured to rotate the hub body together with the sprocket carrier when the sprocket carrier is rotated in a first direction about a central axis of the hub, and to allow the sprocket carrier to rotate relative to the hub body in a second direction opposed to the first direction; a clutch mechanism comprising at least one fixed clutch plate that is rotationally fixed with respect to the hub body and at least one rotatable clutch plate that is rotationally fixed with respect to the sprocket carrier, the clutch mechanism being switchable between a disengaged configuration in which the sprocket carrier is permitted to rotate in the second direction relative to the hub body, and an engaged configuration in which relative rotation between the sprocket carrier and the hub body is at least substantially prevented; and an actuation mechanism for selectively engaging and disengaging the clutch mechanism.
2. A hub according to Claim 1, wherein the rotatable clutch plate(s) are coupled to the sprocket carrier by a clutch basket, the clutch basket comprising a mounting portion that is mounted to and rotationally fixed with respect to the sprocket carrier, and a clutch plate engaging portion that extends outwardly from the mounting portion and is connected to the rotatable clutch plate(s) in order to prevent relative rotational movement between the rotatable clutch plate(s) and the sprocket carrier.
3. A hub according to Claim 2, wherein the mounting portion of the clutch basket comprises a splined hole that is engaged with a splined outer surface of the sprocket carrier to thereby prevent relative rotational movement between the clutch basket and the sprocket carrier.
4. A hub according to Claim 2 or Claim 3, wherein the clutch plate engaging portion of the clutch basket comprises a plurality of elongate plate engaging elements that are received within a corresponding plurality of apertures provided at or adjacent to the outer edge(s) of the rotatable clutch plate(s) outboard of the outer edge(s) of the fixed clutch plate(s).
5. A hub according to any of Claims 2 to 4, wherein at least one of the rotatable clutch plate(s) is axially movable along the clutch plate engaging portion of the clutch basket in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly.
6. A hub according to any preceding claim, further comprising a central shaft that is connected to and rotationally fixed with respect to the hub body, the central shaft extending outwardly from a base of the hub body and through a housing of the hub body in which the fixed and rotatable clutch plates are located.
7. A hub according to Claim 6, wherein the sprocket carrier is mounted to a distal end of the central shaft.
8. A hub according to Claim 6 or Claim 7, wherein the fixed clutch plate(s) are mounted to and rotationally fixed with respect to the central shaft, and the rotatable clutch plate(s) are freely rotatable around the central shaft when the clutch mechanism is in the disengaged configuration.
9. A hub according to any of Claims 6 to 8, wherein at least one of the fixed clutch plates is mounted to the central shaft via a clutch plate carrier, the clutch plate carrier comprising a splined bore that is engaged with a splined outer surface of the central shaft and configured to allow the clutch plate carrier to move along the central shaft in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly.
10. A hub according to Claim 9, wherein the at least one fixed clutch plate comprises a splined aperture that is engaged with a splined outer surface of the clutch plate carrier and configured to allow the fixed clutch plate to move along the clutch plate carrier in a direction aligned with the central axis of the hub in order to facilitate engagement and disengagement of the clutch assembly.
11. A hub according to any of Claims 6 to 10, wherein the clutch mechanism comprises first and second end plates that are configured to be moved relative to each other by the actuation mechanism in order to bring the fixed and rotatable clutch plates into engagement with each other to thereby engage the clutch mechanism, the first end plate being rigidly connected to the central shaft, and the second end plate being mounted to and rotationally fixed with respect to the central shaft but movable along the central shaft in a direction aligned with the central axis of the hub.
12. A hub according to any preceding claim, wherein the actuation mechanism comprises a static portion and a movable portion, the static portion of the actuation mechanism including an anti-rotation arm that is configured to engage a frame of a bicycle with which the hub may be used in order to prevent the static portion of the actuation mechanism from rotating relative to the bicycle frame, and the movable portion of the mounting mechanism including an attachment point for attachment of an actuation cable for effecting relative movement between the static portion and the movable portion in order to control engagement of the clutch mechanism.
13. A hub according to Claim 12, wherein the actuation cable is configured to rotate the movable portion of the actuation mechanism with respect to the static portion of the actuation mechanism, and wherein the actuation mechanism is provided with a rotary-to-linear coupling, for example a ball drive mechanism, that is configured to generate relative axial movement between the static and movable portions of the actuation mechanism in response to relative rotational movement between the static and movable portions of the actuation mechanism in order to control engagement and disengagement of the clutch mechanism.
14. A hub according to any preceding claim, wherein the actuation mechanism defines a housing, the fixed and rotatable clutch plates being located within the housing.
15. A transmission for a bicycle, the transmission comprising: a crankset including a front chainring; a chain that is configured to be driven by the crankset; a cassette comprising multiple sprockets that is configured to be driven by the chain; a derailleur that is configured to switch the chain between the sprockets of the cassette, and a chain tensioning system provided separately to the derailleur, the chain tensioning system comprising: an arm that is mounted to and movable with respect to a frame of the bicycle; a tensioning jockey wheel that is mounted to the movable arm and engaged with the chain; a biasing mechanism that is configured to bias the arm in a first direction in order to impart tension to the chain via the jockey wheel, and an actuation system that is operable to further bias the arm in the first direction in order to further increase the tension applied to the chain by the chain tensioning system.
16. A transmission according to Claim 15, wherein the cassette is mounted to a hub that is configured to be selectively switchable between a fixed wheel state and a free wheel state during use of the bicycle.
17. A transmission according to Claim 15 or Claim 16, wherein the rear derailleur comprises a stirrup through which the chain passes, and a linkage mechanism that is configured to move the stirrup in a lateral direction with respect to the cassette in order to move the chain between the sprockets of the cassette, but does not include any chain tensioning system.
18. A transmission according to any of Claims 15 to 17, wherein the chain tensioning system further comprises a second jockey wheel mounted to the bicycle frame that is also engaged with the chain.
19. A transmission according to Claim 18, wherein the second jockey wheel is mounted to a drive side chainstay of the bicycle frame and is located above the tensioning jockey wheel.
20. A transmission according to any of Claims 15 to 19, wherein the actuation system comprises an actuation cable that is connected to a first user-operable lever, wherein the first lever forms part of a lever assembly that further comprises a second user-operable lever, wherein the first lever is located in front of the second lever such that the first lever is engaged before the second lever when a user pulls on both levers.
21. A transmission according to any of Claims 15 to 20, wherein the movable arm is a swing arm that is pivotable with respect to the bicycle frame.
22. A transmission according to any of Claims 15 to 21, wherein the movable arm is mounted to a bottom bracket shell of the bicycle frame.
23. A transmission according to any of Claims 15 to 22, wherein the biasing mechanism comprises a rotationally biased gear that is engaged with a toothed rack provided on the movable arm.
24. A transmission according to any of Claims 15 to 23, wherein the actuation system is connected to the biasing mechanism and configured to act on the biasing mechanism in order to further bias the arm in the first direction.
25. A bicycle comprising a hub according to any of Claims 1 to 14 and/or a transmission according to any of Claims 15 to 24.