WO2025176830A1

WO2025176830A1 - An assembly for coupling a drive unit and a wheel of a bicycle

Info

Publication number: WO2025176830A1
Application number: PCT/EP2025/054697
Authority: WO
Inventors: Alastair Rupert Joseph DARWOOD; Oliver Thomas Joyce; Andrew John DURNAN; Mareks ZEVALDS; Michael James Douglas
Original assignee: Blue Sky Ip Ltd
Current assignee: Blue Sky Ip Ltd
Priority date: 2024-02-23
Filing date: 2025-02-21
Publication date: 2025-08-28
Anticipated expiration: 2026-08-23
Also published as: GB202402634D0; TW202545775A; GB2638952A

Abstract

An assembly for coupling between a drive unit and a wheel of a bicycle, for transmission of torque from the drive unit to the wheel. The assembly comprises a drive element (16; 116) and a mounting assembly. The drive element comprises a pinion gear (16a; 116a) coupled to a drive member (10) for driving rotation of the wheel about a wheel rotation axis, such that rotation of the drive element about a drive element rotation axis drives rotation of the drive member and thereby the rotation of the wheel. The mounting assembly is attached to the drive member (10) and is non-rotatable therewith about the wheel rotation axis. The mounting assembly includes first and second bearing assemblies (50, 52; 150, 154) arranged to retain the drive element.

Description

AN ASSEMBLY FOR COUPLING A DRIVE UNIT AND A WHEEL OF A BICYCLE

Field of the Invention

The invention relates to an assembly for coupling a drive unit and a wheel of a bicycle, for transmission of torque from the drive unit to the wheel.

Background

Patent publication number W02022038207 discloses apparatus for connecting a drive unit to a wheel, where the apparatus is mounted on a hub of the wheel, extending radially from the hub between spokes and an end of the hub. The apparatus thereby occupies a thin space. The hub may be configured for a rim-brake bicycle or for mounting of a disc rotor of a disc braking system. The apparatus enables releasable engagement of a drive shaft of the drive unit to a drive element in the form of a pinion gear. The pinion gear is meshed with a drive member that includes an internal gear. The drive member is fixedly coupled to the hub. Where the hub is configured for mounting of a disc brake rotor, the drive member is fixed to the disc rotor mount in place of a conventional disc rotor. The pinion gear is mounted on a mounting member, which is attached to the drive member and non-rotatable relative to drive member. The publication discloses that the pinion gear may be supported by a single annular bearing on a side of the pinion gear nearer an engaged drive unit. It has been found that long term use of the apparatus with the pinion gear supported in this way results in wear of parts and occasional breakage. An object of the present invention is to address this problem. Particular difficulty arises due to need to mount the apparatus in a thin space such that the drive member can rotate between spokes and a chainstay when mounted on a rear wheel or between spokes and a fork when mounted on a front wheel.

Summary of the Invention

According to the present invention, there is provided an assembly for coupling between a drive unit and a wheel, preferably but not exclusively of a bicycle, for transmission of torque from the drive unit to the wheel, comprising: a drive element coupled to a drive member, for example comprising a pinion gear coupled to the drive member, for driving rotation of the wheel about a wheel rotation axis, such that rotation of the drive element about a drive element rotation axis drives rotation of the drive member and thereby the rotation of the wheel; and a mounting assembly attached to, for example mounted on, the drive member and non-rotatable therewith about the wheel rotation axis, wherein the mounting assembly includes first and second bearing assemblies arranged to retain the drive element. Thus, the first bearing assembly is on a side nearer a fork tine or a chain stay, and the second bearing assembly is on a side nearer the spokes.

Inclusion of the first and second bearing assemblies improves durability of parts, particularly of the drive element and the mounting assembly. Both can be included in the available space.

The drive element may be arranged to be driven by a coaxial drive shaft of the drive unit.

The drive element rotation axis and the wheel rotation axis may be parallel.

The pinion gear may be non- disengageable from the drive member.

The first and second bearing assemblies may be at different positions along the drive element rotation axis. The mounting assembly may retain the first and second bearing assemblies each on or at a respectively opposite axial side of the drive element.

The drive element may include an end portion, for example on a side of the drive element along the drive element rotation axis remote from spokes.

The first bearing assembly may comprise an annular bearing assembly fixed to the mounting assembly and around the end portion, to retain the end portion and to permit rotation about the drive element rotation axis.

The drive element (for example the end portion) may be configured to enable releasable engagement with a correspondingly configured drive shaft end of the drive shaft of the drive unit, such that rotation of the drive shaft causes rotation of the drive element about the drive element rotation axis.

Where the first bearing assembly comprises an annular bearing assembly fixed to the mounting assembly and around the end portion, the drive element may be configured to include an opening in the end portion and to receive the drive shaft end through the opening with the drive shaft extending through the first bearing assembly.

The assembly may further comprise the drive member, the drive member being configured for fixing to or formed with a hub of the wheel. The drive member may comprise a drive member gear fixedly mounted for rotation about the wheel rotation axis, wherein the pinion gear is mated with the drive member gear such that rotation of the pinion gear drives rotation of the drive member gear about the rotation axis.

The drive member gear may be an internal gear or a spur gear, for example.

The assembly may further comprise an annular bearing assembly, wherein the mounting assembly and the drive member are fixed to the annular bearing assembly to enable the rotation of the drive member without rotation of the mounting member.

The mounting assembly may comprise a first part (e.g. a mounting member) and a second part (e.g. a bearing housing), fixed together to together retain the first and second bearing assemblies.

The mounting assembly may further comprise fixing means fixing the first and second parts together. The fixing means may comprise at least one dowel pin, wherein the at least one dowel pin is engaged in opposing recesses on each of the first and second parts to impede or prevent relative movement of the first and second parts radially with respect to the wheel rotation axis. Use of the at least one dowel pin facilitates maintenance of concentricity of the first and second bearing assemblies and the drive element, versus use of bolts in the same places.

The fixing means may further comprise at least one bolt fixing the first and second parts together.

One of the first and second parts may include a projection and the other of the first and second parts may include a retaining recess for receiving the projection. This supports alignment of the first and second parts and consequently concentricity of the first and second bearing assemblies and the drive element, and also alignment of the drive element and drive member.

The drive element may further comprise another end portion, nearer the spokes than the end portion, wherein the second bearing assembly is fixed to the mounting assembly and to the other end portion, thereby to retain the other end portion and to permit rotation of the other end portion about the drive element rotation axis. The second bearing assembly may be annular and fixed around the other end portion, thereby to retain the other end portion and to permit rotation of the other end portion about the drive element rotation axis.

The second bearing assembly may include an outwardly projecting annular flange. In this case the second part is shaped to provide a surface, preferably a recessed surface, against which the flange abuts. This avoids need for the mounting assembly to provide a lip, plate or other feature for the second bearing assembly to abut at a side thereof nearer the spokes, permitting the assembly to be thinner.

Alternatively, rather than the second bearing assembly being fixed around the other end portion, the drive element may include a cylindrical recess coaxial with the drive element, having an opening at the other end portion of the drive element, wherein the second bearing assembly is a needle roller bearing assembly and wherein the mounting assembly further comprises a pin retained by the mounting assembly, wherein the pin is arranged to extend into the cylindrical recess, and wherein the needle roller bearing assembly is fixed to a wall of the recess and the pin so that the drive element can rotate independently of the pin.

The assembly may be for mounting on a mount of a hub of the wheel. Preferably, the mount is integrally formed with an outer shell of the hub. The mount may be a disc brake rotor mount and the assembly may be for mounting on the disc brake rotor mount when a disc brake rotor is absent.

The drive member preferably provides a recessed region in which the drive element is at least partially located and in which the drive element is coupled with the drive member.

The drive member may be for location (or mounting) between spokes and a frame portion supporting the wheel. For example, where the transmission assembly is mounted on a rear wheel, the drive member is located between the spokes and a nearer of the dropouts. Where the transmission assembly is mounted on a front wheel, the drive member is located between the spokes and a nearer of the tines of a fork. At least some of the mounting means is preferably mounted in the same way. Thus, depth (in a direction of the wheel rotation axis) is constrained.

The drive element rotation axis may be parallel to a rotation axis (or axle) of the hub. The drive element and the first and second bearing assemblies may be located on the drive element rotation axis spaced from the axle orthogonally with respect to the rotation axis of the hub. That is, the drive element and the first and second bearing assemblies do not extend in space on the drive element rotation axis beyond a position thereon orthogonal to the end of the hub.

Brief Description of Figures

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 is a perspective view of a bicycle wheel including a transmission assembly, and a drive shaft of a drive unit;

Figure 2 is a perspective view of parts of the bicycle wheel shown in Figure 1 , viewed from a cassette side of the wheel;

Figure 3 is an exploded perspective view of parts of the transmission assembly and drive shaft shown in Figure 1 ;

Figure 4 is another exploded perspective view of parts of the transmission assembly and drive shaft;

Figure 5 is an exploded view from the same perspective as the view of Figure 4, with a central annular bearing being shown within a central aperture of a mounting member;

Figure 6 is a close up view of some of the parts;

Figure 7 is another close up view of some of the parts;

Figure 8 is a view of some of the parts, with amounting member absent; and

Figure 9 is a schematic view of parts of a transmission assembly in accordance with an alternative embodiment of the invention.

Detailed Description of Embodiments

Embodiments of the invention relate to a transmission assembly for coupling a drive unit to a wheel, particularly to a hub of a wheel and particularly a wheel of a bicycle, and to a drive system comprising such a transmission assembly and drive unit. The transmission assembly is mountable on the hub and configured to enable engagement of the drive unit such that operation of an engaged drive unit can drive rotation of the wheel.

The drive unit includes a drive shaft and is operable to drive rotation of the drive shaft. In the embodiments to be described, the transmission assembly is mounted on the hub of a wheel of a bicycle. The drive unit may be operable to drive rotation of the drive shaft independently of pedals of the bicycle, or operable to assist in cycling when a rider is turning the pedals. The drive unit may include an electric motor to drive rotation of the drive shaft, but embodiments are also not limited to including an electric motor. Embodiments may be implemented with any drive unit configured to produce torque that can be transferred to a drive element in the transmission assembly. For example, embodiments of the transmission assembly may be driven by a drive shaft of a drive unit in the form of an internal combustion engine.

The wheel has an axis about which the wheel rotates and the term “central axis” shall be construed accordingly. The terms “hub axis” and “rotation axis” are to be construed as the same central axis. The terms “radial”, “outer”, “inner”, “external” and “internal” are to be construed in relation to the hub axis unless otherwise indicated by context.

Herein “spokes” are to be construed as covering any arrangement that functions as spokes, including arrangements where elongate members spanning between a rim and a hub are integrally formed with the rim and/or the hub and also where the spokes are replaced by a disc spanning between a rim and a hub.

Referring to Figures 1 to 8, the transmission assembly is mounted onto a hub 22 of a rear wheel 20 of a bicycle. As well as the hub 22, the wheel 20 includes a cassette 24 and spokes. An axle 25 extends through the hub 22 and the cassette 24 about which the hub 22 rotates. The transmission assembly may alternatively be mounted on a front wheel of a bicycle.

In an embodiment a transmission assembly includes a drive member 10, a mounting assembly, an annular central bearing 14 and a drive element 16. A drive shaft of the drive unit is indicated at 11.

The drive member 12 is arranged to fix to the hub 22 for synchronous rotation therewith. The mounting assembly is for retaining the drive element 16 in a position engaged with the drive member 12, such that a drive shaft of the drive unit can engage with the drive element 16 to drive rotation of the drive element 16 and thus the drive member 10. The drive member 12 is located and rotates between spokes of the wheel and a frame portion of the bicycle.

The drive member 10 has a first side that faces outwardly away from spokes of the wheel and a second side that faces the spokes. The drive member 10 includes a mounting portion, an annular back plate 10c, an internal gear 10d, a second cylindrical wall 10e and an annular braking rotor portion 10f. The mounting portion includes a first cylindrical wall 10b having a cylindrical outer circumferential surface. The first and second cylindrical walls 10b, 10e are coaxially mounted with respect to the hub 22. The first cylindrical wall 10b extends from the annular back plate 10c away from the spokes of the wheel 20. The annular back plate 10c extends radially outwardly with respect to the hub axis, from an end of the first cylindrical wall 10b. The second cylindrical wall 10e also extends from the annular back plate 10c away from spokes of the wheel 20. The internal gear 10d is mounted on an internal surface of the second cylindrical wall 10e, facing the outer surface of the first cylindrical wall 10b. The first and second cylindrical walls 10b, 10e are spaced to provide an annular recessed region 26 between them, in part of which the internal gear 10d is located.

The drive member 10 may be formed of a single piece of material. In variant embodiments the drive member 10 may be formed of more than one piece of material. In some variants, the internal gear 10d may be formed separately and fixed to a rest of the drive member 10 by welding or by any suitable manner of affixing, or in some variant embodiments by locking of corresponding portions (not shown) in the internal gear 10d and the drive member 10. In some variants, the braking rotor portion 10f may be formed separately and fixed to the rest of the drive member 10 by welding or any suitable manner of affixing, or in some embodiments by locking of portions suitably adapted for locking. The drive member 10 may be otherwise formed of different parts that are fixed together in other variant embodiments. Making the drive member 10 of multiple parts facilitates different parts being made of different materials.

The hub 10 is of a conventional type and includes a conventional disc rotor mount (not shown) configured to enable mounting of a matching conventional disc rotor. The mount is configured according to a conventional centre lock design. A conventional disc rotor configured for the centre lock design may be secured to the mount and used in a conventional disc braking system using the lock ring 23. When the conventional disc rotor is mounted on the mount, relative rotation of the disc rotor and the hub 10 is thus prevented so the disc rotor and the hub 10 rotate synchronously and calliper action on the disc rotor by a calliper mechanism brakes rotation of the wheel.

In the drive member 10, an interior surface of the first cylindrical wall 10 is configured to engage with the mount. A conventional disc rotor must be removed from the mount of the hub, if attached, to enable this and to permit the drive member 10 to be located on the hub 22. The drive member 10 may also be removed from the mounting plate and replaced if it wears out. The drive member 10 is locked in place with the lock ring 23. The engagement of the drive member 10 to the mount prevents relative rotation of the drive member 10 and the hub such that the drive member 10 and the hub 10 rotate synchronously. Hubs of other types are known that do not include a mount with a centre lock design for mounting of a disc rotor on the hub, but instead include alternative disc rotor mounts. The drive member 10 may in variant embodiments be configured to attach to such mounts. In particular, disc brake rotor mounts may use a well known six bolt design enabling attaching of a corresponding configured disc rotor having six holes equally angularly spaced around the rotation axis. In variant embodiments, the annular plate 10c includes holes enabling bolting to a mount in accordance with the six bolt design and can thus be securely bolted to the mounting plate in place of the conventional disc rotor.

In alternative embodiments, the transmission assembly may be mounted on a hub specifically designed to provide a mount for the transmission assembly that is not suitable for mounting of a conventional disc rotor. Embodiments are not limited to any particular configuration enabling secure attachment of the drive member 10 and the hub 22.

The transmission assembly may be mounted to a hub of a wheel that uses conventional rim brakes. The mount may be in accordance with a six bolt design or a centre lock design or other design used with conventional disc rotors, and thus be identical to a mount for mounting of conventional disc rotors. Alternatively, the mount may be to a different design not known for use with conventional disc rotors and the mounting portion may be configured correspondingly. In such embodiments, the annular braking rotor portion 10f may be absent. The mount is positioned, and parts (that is, the drive member 12, the central annular bearing assembly 14 and the mounting member 12 described below) of the transmission assembly shaped, to enable fitment of those parts of the transmission assembly between spokes of the wheel and the frame of the bicycle, particularly the relevant portion of the frame providing dropouts for the wheel (for example a chainstay for the rear wheel and a fork portion for the front wheel). Dropouts of a bicycle on which the wheel is mounted are usually spaced one or more standard distances apart, meaning that a minimum and maximum available space for mount and transmission assembly are known.

Herein it should be understood that the mount is part of the hub. Notably, mounts for disc brakes are made as integral parts of hubs by major manufacturers such as Shimano ®. Such mounts are typically in accordance with six bolt and centre lock designs. The hub 22, spokes and rim of the wheel 20 are functionally distinct parts common to all wheels. This is true regardless of whether two or all of these parts are formed together.

The first and second cylindrical walls 10b, 10e and the annular back plate 10c provide the annular recessed region 26 extending around the central axis of the hub 10. When mounted on a wheel, an open side of the recess 26 formed in the drive member 10 faces away from the wheel. The annular recessed region 26 is sufficiently wide radially as to accommodate the drive element 16 and the internal gear 10d in engagement, but not so wide as to interfere with operation of the braking rotor portion 10f where the braking rotor portion 10f enters the calliper. The drive member 10 may have a maximum depth of no greater than 14mm or no greater than 12mm, which is sufficient to accommodate the drive element 16 and the internal gear 10d. The drive member 10 may in variant embodiments provide a very shallow recessed region 26, for example of only 2mm to 5mm, and the drive element 16 be configured correspondingly.

The mounting assembly includes a first part in the form of a mounting member 12. The mounting member 12 is mounted on the drive member 10 such that it is rotatably independent of the drive member, that is, it does not rotate with the drive member. Preferably, the mounting member 12 is fixed in place so that it remains stationary relative to the frame of the bicycle or is able to rotate about the wheel rotation axis to only a small angular extent by a rotation prevention means, such as with an arm (not shown) that clamps to the frame or a strap. However, preferably the mounting member 12 is fixed in place via rotation prevention means attached to an engaged drive unit.

The mounting member 12 includes a wall 12a providing a cylindrical interior surface defining a space in which the central bearing assembly 14 is located, an outer race of the central bearing assembly 14 being located against the cylindrical interior surface. The mounting member 12 also includes an inwardly projecting rim 12b at an outer side of the mounting member 12 against which the outer race of the central bearing assembly 14 abuts. The mounting member 12 also includes bolt holes 17 at equal, angularly spaced intervals with respect to the central axis in a plane around the cylindrical interior surface. A fixing ring 19 having corresponding bolt holes 20 is fixed to an inner side of the mounting member 12, to retain the outer race of central bearing assembly 14 against the cylindrical interior surface and the rim 12b. This arrangement ensures that the bearing assembly 14 is securely affixed to the mounting member 12; embodiments are not however limited to this and alternative mounting methods may be employed.

The mounting member 12 is shaped to provide an aperture 64 through which an end of a drive shaft 11 may extend, and also features enabling securing of the drive unit to the mounting member 12. Such features include first and second drive unit engagement recesses 72a, 72b and a curved bayonet engagement recess 73. As can be seen in Figure 4, the mounting member 12 includes first and second engagement recess walls 76a, 76b. Although not shown in the Figures, the drive unit includes projections that project each into a respective recesses 76a, 76b when the drive shaft is engaged through the aperture 64. Also not shown in the Figures, the drive unit includes a bayonet-type twist attachment feature that engages in the bayonet engagement recess 73 and enables the drive unit to be releasably mounted on the mounting member 12. Embodiments of the invention are not limited to any particular mechanism for attachment and release of the drive unit to the mounting member 12.

The drive element 16 has a pinion portion 16a and first and second end portions 16b, 16c. The pinion portion has circumferential pinion teeth and a central drive element axis. The first and second end portions 16b, 16c extend from the pinion portion 16a in opposite directions and each have a cylindrical exterior surface arranged to rotate about the drive element axis. The pinion portion 16a and the first and second ends 16b, 16c are formed of a single piece of durable material, for example steel, titanium or aluminium. A diameter of each of the cylindrical exterior surfaces is less than a diameter of the pinion body portion 16a, although this is not essential in variant embodiments provided space is available for first and second annular bearing assemblies, described below. The pinion portion 16a is engaged with the internal gear 10d, such that rotation of the pinion portion 16a about the central drive element axis drives rotation of the internal gear 10d and thus the drive member 10. The pinion portion 16a is not disengageable from the internal gear 10d.

The mounting assembly further comprises an annular first bearing assembly 50, an annular second bearing assembly 52, a second part in the form of a bearing housing 54, bolts 56 and first and second dowel pins. The bearing housing 54 includes a bearing mounting portion 58, first bolt holes 60, first dowel recesses 61 and provides a retention recess 79.

The first and second bearing assemblies 50, 52 are arranged to retain the drive element 16, to facilitate rotation of the drive element 16 about the drive element axis. Embodiments are not limited to any particular design for the first and second bearing assemblies, provided they enable the drive element 16 to rotate relative to the other parts of the mounting assembly. Such annular bearing assemblies are widely available.

An inner race of the first bearing assembly 50 is fixed around the cylindrical exterior surface of the first end 16b of the drive element 16. The mounting member 12, at a side facing the spokes, is shaped to provide a cylindrical surface. An outer race of the first bearing assembly 50 is fixed to this cylindrical surface.

An inner race of the second bearing assembly 52 is fixed around the cylindrical exterior surface of the second end 16c of the drive element 16 more distant from an engaged drive unit than the first bearing assembly 50. The bearing housing 54 is shaped to retain the second annular bearing assembly 54 in the bearing mounting portion 58 and an outer race thereof is fixed to the bearing housing 54 at the bearing mounting portion 58. The second bearing assembly is flanged, that is, has an outwardly projecting annular flange 52a of the second annular bearing assembly 52 abuts the bearing housing 54. The bearing housing 54 provides an annular recessed surface 54a, the flange 52 and the recessed surface 54a being shaped so that the flange 52a abuts the recessed surface 54a and so that lateral radial movement relative to the drive element axis is impeded or prevented. The flange 52a usefully avoids need for a lip, plate or other feature in the bearing housing 54 to be provided for the second bearing assembly 52 to abut when it is inserted.

The mounting member 12 includes bolt holes 70a-c and second dowel recesses 71a, 71 b. The mounting member 12 also includes a projection 80. The bearing housing 54 is fixed to the mounting member 12 with the bolts 56 through the holes 70a-c

The projection 80 shaped to engage in the retaining recess 79 to prevent relative radial movement of the mounting member 12 and the bearing housing 54. The projection 80 and the retaining recess 79 are cylindrical. In variant embodiments, the projection 80 may be otherwise shaped and the retaining recess 79 correspondingly shaped to recess the projection 80.

First and second dowel pins (not shown) locate in each in opposing ones of the first and second dowel recesses 61 , 71a, 71 b. These impede any lateral movement or support lateral alignment of the drive member 10 and the drive element 162.

The first end 16b of the drive element 16 has an opening in the form of a keyway 65. The keyway 65 is configured to receive an end of the drive shaft 11 . The drive shaft end is shaped to engage in the keyway 65 such that rotation of the drive shaft causes corresponding rotation of the drive element 16, the rotation of both being about the drive element rotation axis. The end of the drive shaft 11 is male splined and the keyway is correspondingly female splined. Embodiments are not limited to any particular way in which the drive shaft end and the keyway engage such that rotation of the drive shaft causes corresponding rotation of the drive element 16.

As already mentioned, the drive system includes rotation prevention means to prevent unwanted rotation of the mounting member 12 and the drive unit. This may be in the form of a strap from the drive unit attaching to a frame of the bicycle, or an arm mounted on the mounting member 12 attached or abutting the frame of the bicycle. The drive unit may be fixed rigidly in place with respect to the frame of the bicycle, for example using a releasable clamping arm.

In use, the drive unit is releasably mounted on the mounting member 12, which includes the drive shaft end being located into the keyway 65. Operation of the drive unit then drives rotation of the drive shaft 11. Due to the engagement of the drive shaft end and the drive element 16, the rotation of the drive shaft 11 drives rotation of the drive element 16. The drive element 16 is retained between the first and second bearing assemblies 50, 52. The drive element 16 causes rotation of the internal gear and thus the drive member 10 and the hub 22.

In variant embodiments, instead of an internal gear, the transmission assembly may be modified to include a spur gear. In this case, the pinion portion of the drive element 16 mates with the spur gear. Embodiments are not limited to the drive member or the drive element being a specific type of gear, provided they can each perform their function together.

In a variant embodiment, the first end of the drive shaft may be modified to be longer and be retained by the first annular bearing assembly and additionally at least one further annular bearing assembly extending around the first end. The first end projects away from the spokes and the mounting assembly is modified to retain the further annular bearing assembly. As a result of the modifications, the mounting assembly may, if it were permitted to rotate, project sufficiently to abut a seat stay. In this embodiment, the second annular bearing 16c may be present as described above, or may be absent with the mounting assembly modified accordingly. Sufficient support may be provided by the first annular bearing assembly and the at least one further annular bearing assembly so that the second annular bearing assembly is not required.

Referring to Figure 9, in another embodiment the drive element 16 and mounting assembly may be modified relative those in the transmission assembly described with reference to Figures 1 to 8. A drive element 116 has a cylindrical recess coaxial with the drive element rotation axis extending from an opening thereto in the second end 116c of the drive element 116. The mounting assembly includes a pin 190 located in the recess. In place of the annular second bearing assembly 52, a second bearing assembly in the form of a needle roller bearing assembly 152 is provided, located between the pin 190 and a cylindrical interior surface of the recess. An inner race of the needle roller bearing assembly is fixed to the outer surface of the pin. An outer race of the needle roller bearing assembly is fixed to the drive element 16, at the cylindrical interior surface of the recess. The drive element 116 is freely rotatable about the drive element rotation axis with respect to the pin 190. The pin 190 is formed with a base 192 that is located on a modified bearing housing. Thus, the drive element is retained by the pin 190 and the second bearing assembly 152, as well as by the first annular bearing assembly 150 which is configured in the same way to the first annular bearing assembly 50. In use, the drive system operates as described for previous embodiments, except the drive element 116 is supported by and rotates about the pin 190, as well as a first annular bearing assembly 150, configured like the first annular bearing assembly 50 of Figures 1 to 8.

In variant embodiments, the pin 190, cylindrical recess in which the pin is located and the second annular bearing assembly 152 need not be cylindrical in nature. For example, the pin may instead be conical and the pin and the second annular bearing assembly adapted correspondingly.

In the embodiments described above, the mounting member 12 is mounted on the drive member 10 and is rotatably independent of the drive member 10. In alternative embodiments, an alternative mounting member is mounted on a frame of a bicycle, for example on a chain stay using a clamp. The alternative mounting member is configured to support the drive element mounting assembly and the drive element mounted in the assembly, with the drive element being coupled to the drive member 10. In this alternative embodiment, the alternative mounting member may also be configured for supporting and releasable securing of the drive unit or an additional or separate mounting member provided for this purpose.

Embodiments are not limited to the specific designs of the mounting assembly described herein. In particular, embodiments are not limited to the specific designs of bearing housing 54 and/or the mounting member 12, provided they retain the drive element 16, 116 with the first and second bearings 50, 52, 152 supporting the drive element 16, 116 at axially opposing ends of the drive element and/or such that the retaining of the first and second bearings is performed at axially opposing ends of the drive element.

Maintenance of concentricity of the first and second bearing assemblies and the drive element is desirable in all embodiments for durability of the transmission assembly. Inclusion of two bearing assemblies improves concentricity, as well as other features that prevent lateral movement in a plane orthogonal to the wheel rotation axis. Embodiments are not limited to any particular way in which concentricity of the drive element and the first and second bearing assemblies is maintained. Notably, in all embodiments, engagement of the end of the drive shaft into the keyway in the drive element can be considered to be “loose”, so that the drive shaft end can be easily inserted and removed by a user. Thus, the drive shaft does little to assist with maintaining of concentricity.

In alternative embodiments, instead of the curved bayonet recess being provided in the mounting member 12, the recess may be provided in the bearing housing and a curved aperture provided in the mounting member enabling a bayonet element to be projected through the curved aperture into the bayonet recess in the bearing housing for engagement.

Embodiments are not limited to any way in which the drive unit is releasably secured to the mounting member described in relation to any embodiment or variant or alternative embodiment. The drive unit being releasable provides advantages in that the drive unit can be removed for security against theft, for convenience of battery charging, and so that the bicycle may be used without the drive system. However, the drive unit need not be releasable from the transmission assembly and may be fixedly secured thereto.

Parts of the transmission assemblies described above may be made with conventional materials, typical durable, rigid metals such as steel, aluminium or titanium. Parts may alternatively be made of hard plastics material.

In variant embodiments, the drive member described above may be integrally formed with the hub.

Embodiments are not limited to transmission systems for mounting on hubs of wheels of bicycles. Transmission systems in accordance with embodiments may be mounted on hubs of wheels of other vehicles, including, without limitation, trolleys, carts, tricycles, other vehicles not having an integrated motor.

Unless otherwise indicated, all individual features and/or steps of all embodiments described herein are disclosed in isolation and any combination of two or more such features is also disclosed, to the extent that such features or steps or combinations of features and/or steps are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art. This is regardless of whether such features or steps or combinations of features and/or steps solve any problems disclosed herein.

Claims

1 . An assembly for mounting on a hub of a wheel, for coupling between a drive unit and a wheel of a bicycle, for transmission of torque from the drive unit to the wheel, comprising: a drive element comprising a pinion gear coupled to a drive member for driving rotation of the wheel about a wheel rotation axis, such that rotation of the drive element about a drive element rotation axis drives rotation of the drive member and thereby the rotation of the wheel; and a mounting assembly attached to the drive member and non-rotatable therewith about the wheel rotation axis, wherein the mounting assembly includes first and second bearing assemblies arranged to retain the drive element each on a respectively opposite axial side of the drive element, and to facilitate rotation thereof.

2. The assembly of claim 1 , wherein the drive element is arranged to be driven by a coaxial drive shaft of the drive unit.

3. The assembly of claim 1 or claim 2, wherein the drive element rotation axis and the wheel rotation axis are parallel.

4. The assembly of any one of the preceding claims, wherein the drive element includes an end portion and wherein the first bearing assembly comprises an annular bearing assembly fixed to the mounting assembly and around the end portion, thereby to retain the end portion and to permit rotation of the end portion about the drive element rotation axis.

5. The assembly of any one of the preceding claims, wherein the drive element is configured to enable releasable engagement with a correspondingly configured drive shaft end of the drive shaft of the drive unit, such that rotation of the drive shaft causes rotation of the drive element about the drive element rotation axis.

6. The assembly of claim 5 when dependent on claim 4, wherein the drive element is configured to include an opening in the end portion and to receive the drive shaft end through the opening with the drive shaft extending through the first bearing assembly.

7. The assembly of claim 6, further comprising the drive member, the drive member being configured for fixing to or formed with a hub of the wheel.

8. The assembly of claim 7, wherein the drive member comprises a drive member gear fixedly mounted for rotation about the wheel rotation axis, wherein the pinion gear is mated with the drive member gear such that rotation of the pinion gear drives rotation of the drive member gear about the rotation axis.

9. The assembly of claim 8, wherein the drive member gear is an internal gear or a spur gear.

10. The assembly of any one of the preceding claims, further comprising an annular bearing assembly, wherein the mounting assembly and the drive member are fixed to the annular bearing assembly to enable the rotation of the drive member without rotation of the mounting member.

11. The assembly of any one of the preceding claims, wherein the mounting assembly comprises a first part and a second part, fixed together to together retain the first and second bearing assemblies.

12. The assembly of claim 11 , further comprising fixing means fixing the first and second parts together, the fixing means comprising at least one dowel pin, wherein the at least one dowel pin is engaged in opposing recesses on each of the first and second parts to impede or prevent relative movement of the first and second parts radially with respect to the wheel rotation axis.

13. The assembly of claim 12, wherein the fixing means further comprises at least one bolt fixing the first and second parts together.

14. The assembly of any one of claims 11 to 13, wherein one of the first and second parts includes a projection and the other of the first and second parts includes a retaining recess for receiving the projection.

15. The assembly of any one of the preceding claims, wherein the drive element includes another end portion and wherein the second bearing assembly is fixed to the mounting assembly and to the other end portion, thereby to retain the other end portion and to permit rotation of the other end portion about the drive element rotation axis.

16. The assembly of claim 15, wherein the second bearing assembly is annular and fixed around the other end portion, thereby to retain the other end portion and to permit rotation of the other end portion about the drive element rotation axis.

17. The assembly of claim 16, wherein the second bearing assembly includes an outwardly projecting annular flange, wherein the second part is shaped to provide a surface against which the flange abuts.

18. The assembly of any one of claims 1 to 16, wherein the drive element includes a cylindrical recess coaxial with the drive element, having an opening at another end portion of the drive element, wherein the second bearing assembly is a needle roller bearing assembly and wherein the mounting assembly further comprises a pin retained by the mounting assembly, wherein the pin is arranged to extend into the cylindrical recess, and wherein the needle roller bearing assembly is fixed to a wall of the recess and the pin so that the drive element can rotate independently of the pin

19. The assembly of any one of the preceding claims, wherein the assembly is for mounting on a mount of a hub of the wheel.

20. The assembly of claim 20, wherein the mount is a disc brake rotor mount and the assembly is for mounting on the disc brake rotor mount when a disc brake rotor is absent.

21 . The assembly of any one of the preceding claims, wherein the drive member provides a recessed region in which the drive element is at least partially located and in which the drive element is coupled with the drive member.

22. The assembly of any one of the preceding claims, wherein the drive member is for location between spokes and a frame portion supporting the wheel.

23. The assembly of any one of the preceding claims, wherein the drive element is not disengageable from the drive member.

24. The assembly of any one of the preceding claims, wherein the drive element and the first and second bearings, when mounted on a hub, are located in a space orthogonal to the rotation axis of the hub.