GB2458108A

GB2458108A - Swingarm motorcycle drive trains

Info

Publication number: GB2458108A
Application number: GB0803918A
Authority: GB
Inventors: Robert Ian Sykes
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-03-03
Filing date: 2008-03-03
Publication date: 2009-09-09
Also published as: WO2009109774A1; GB0803918D0

Abstract

Drive train apparatus for a motorcycle having an engine mounted on a frame or chassis and a driven wheel. The apparatus comprises a swingarm 4 having a first end for pivotal connection at a pivot point 3 to the engine or frame or chassis 1, and a second end for connection to an axle 10 of the driven wheel 5, which has a wheel gear or sprocket 7'. The apparatus further comprises a pivot point gear or sprocket 7''' at the first end of the swingarm 4 coaxial with the pivot point 3, first means 8' for transferring rotational motion from a gearbox output shaft 2 of the engine to the pivot point gear or sprocket, and second means 8 for transferring rotational motion from the pivot point gear or sprocket 7''' to the wheel gear or sprocket 7'. The pivot point gear or sprocket 7''' is coaxial with the pivot point 3 but not coaxial with the gearbox output shaft 2 when the swingarm 4 is connected to the motorcycle. Gears, sprockets, belts and/or chains may be used in varying arrangements to transfer the drive from the engine to the rear wheel. This arrangements allows a tight fitting chain/belt/gear guard 12 to be fitted.

Description

I

IMPROVEMENTS RELATING TO MOTORCYCLE DRIVE TRAINS

The present invention relates to drive trains for motorcycles, and in particular but not exclusively to rear wheel suspension and drive arrangements which help to eliminate or at least reduce changes in drive chain or belt or other drive lengths due to suspension movements.

BACKGROUND

In motorcycles, it is generally the case that the rear wheel is driven. Most motorcycles use a chain or a belt to transfer power from the engine to the rear wheel. Some motorcycles use a shaft drive, which needs less maintenance, but can create a gyroscopic force to one side which some riders find unsettling. Reference will now be made generally to chain or belt driven motorcycles when discussing prior art approaches.

The rear wheel is typically connected to the frame or engine of the motorcycle by a swingarm which has a rear end coupled to the rear wheel axle, and a front end coupled to the frame or engine at a pivot point. The location of the swingarm pivot is a key factor in the performance and handling characteristics of a motorcycle.

Typically, the swingarm pivot is located just behind the drive output from the engine transmission, such that the pivot is located within the perimeter of the chain or belt. A particular problem with this arrangement is that the tension in the chain or belt will change significantly when the swingarm pivots up or down around its pivot point. In some cases, an additional chain or belt tensioner is required so as to compensate for this change. A further problem is that it is difficult to provide a close-filling guard for the chain or belt, since the chain or belt does not pivot about the same point as the swingarm.

A particular disadvantage of chain drive motorcycles is that the chain needs to be regularly cleaned and lubricated, otherwise dirt from the road or other surface on which the motorcycle is ridden will build up in the chain and contribute significantly to wear.

Provision of a chain guard can help to ameliorate this problem, as well as to reduce noise from the chain, but the chain guard needs to be reasonably close-filling for best effect. If the swingarm and the chain do not pivot together with each other, this can be difficult to achieve, because the swingarm and/or the chain is likely to foul the chain guard due to the different relative movements of the swingarm and the chain.

One possible solution to the problem, for example as disclosed in US 2005/0139407 and WO 2006/060026, is to provide a coaxial arrangement in which the swingarm pivot point is coaxial with the drive output from the engine transmission. However, this requires changes to the overall geometry of the motorcycle frame and can lead to disadvantageous changes to handling and performance characteristics.

It is known from US 4,735,277 to provide a drive train having a swingarm assembly made up of at least two, and preferably three, individual swingarms pivotally connected in series, each swingarm having its own chain drive. This somewhat complicated arrangement allows the rear wheel to move in any direction relative to the frame within a plane defined by the rotation of the wheel. However, this does not make it easier to provide a close-fitting chain guard -indeed, because of the multiple swingarms, provision of a chain guard is made even more difficult.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the present invention, there is provided a drive train apparatus for a motorcycle having an engine mounted on a frame or chassis and a driven wheel, the apparatus comprising a swingarm having a first end for pivotal connection at a pivot point to the engine or frame or chassis, and a second end for connection to an axle of the driven wheel, the driven wheel having a wheel gear or sprocket, the apparatus further comprising a pivot point gear or sprocket at the first end of the swingarm coaxial with the pivot point, first means for transferring rotational motion from a gearbox output shaft of the engine to the pivot point gear or sprocket, and second means for transferring rotational motion from the pivot point gear or sprocket to the wheel gear or sprocket, wherein the pivot point gear or sprocket is coaxial with the pivot point but not coaxial with the gearbox output shaft when the swingarm is connected to the motorcycle.

It will be understood that a sprocket is a toothed wheel that drives or is driven by a chain or belt, while a gear is a toothed wheel designed to mesh with the teeth of another toothed wheel.

In preferred embodiments, the swingarm is of substantially rigid construction. In particular, the swing arm of embodiments of the invention does not have any elbows or pivot linkages between its first and second ends. The swingarm may be of unitary construction, or may comprise a pair of (or several) components that, when connected together, form a substantially rigid construction.

The first means (for transferring rotational motion from the gearbox output shaft of the engine to the pivot point gear or sprocket) may comprise at least one endless chain or belt, or at least one gear, or a plurality of endless chains or belts with appropriate connecting sprockets.

The second means (for transferring rotational motion from the pivot point gear or sprocket to the wheel gear or sprocket) may likewise comprise at least one endless chain or belt, or a plurality of gears, or a plurality of endless chains or belts with appropriate connecting sprockets intermediate the first and second ends of the swing arm.

By making the pivot point gear or sprocket coaxial with the pivot point of the swingarm, movement of the swingarm about the pivot point does not change the distance between the pivot point gear or sprocket and the wheel gear or sprocket. Moreover, because the location of the pivot point is fixed in relation to gearbox output shaft of the engine, there is no change in distance between the gearbox output shaft and the pivot point gear or sprocket when the swingarm pivots. Accordingly, when (for example) a chain or belt is used for connecting the pivot point sprocket to the wheel sprocket, pivoting of the swingarm does not cause a change in tension of the chain or belt, and therefore no pretensioning devices are required. Moreover, because the pivot point sprocket is coaxial with the pivot point, pivoting of the swingarm does not cause any change in shape of the chain or belt. This means that a chain guard, preferably in the form of a close-fitting chain case, can be provided so as to protect the chain or belt from dirt and water arid, optionally, to provide an oil or other lubricant bath through or in which the chain and sprockets or gears can run. Where the chain case is configured to provide an oil or lubricant bath, it is advantageous to provide oil or lubricant seals where the chain passes into and our of the chain case so as to help retain the oil or lubricant within the bath.

Accordingly, preferred embodiments of the present invention further comprise an enclosure for the second means for transferring rotational motion from the pivot point gear or sprocket to the wheel gear or sprocket, the enclosure preferably being close-fitting. The enclosure may provide a sealed housing for the first means, preventing ingress of dirt or water. In some embodiments, the enclosure is adapted to contain oil or other lubricant so as to provide an oil or lubricant bath for moving parts of the second means. In these embodiments, the enclosure preferably includes oil seals where parts of the drive train (such as axles and shafts) extend from the inside to the outside of the enclosure. It will be appreciated that such an enclosure may be used with embodiments in which the first and/or second means comprise a series of meshing gears as well as embodiments in which chains and sprockets are provided.

This is in stark contrast to conventional swingarm arrangements in which movement of the swingarm about its pivot point changes the tension and shape of a chain or belt that connects the sprocket shaft to the wheel sprocket. Because of this change in tension and shape, it is impossible to provide a close-fitting chain case, since the chain case must accommodate all shapes that the chain or belt may take. Moreover, because of the changes in tension as the swingarm pivots, there is a high likelihood that the chain or belt will foul a chain guard and cause rattles and other unwanted noise, as well as excessive wear and tear.

A similar enclosure may additionally or alternatively be provided for the first means for transferring rotational motion from the gearbox output shaft to the pivot point gear or sprocket.

In currently preferred embodiments of the present invention, the second means (for transferring rotational motion from the pivot point sprocket to the wheel sprocket) comprises a single endless chain or belt, preferably provided with a close-fitting enclosure as described hereinbefore. This is a simple and relatively lightweight, yet robust, mechanism for transferring rotational motion. The first means (for transferring rotational motion from the gearbox output shaft of the engine to the pivot point sprocket) preferably also comprises a single endless chain or belt, connecting a sprocket on the gearbox output shaft to the pivot point sprocket, and optionally also provided with a close-fitting enclosure. Where both the first and second means are each provided with a close-fitting enclosure, such as a chain case, it will be appreciated that the two chain cases should be arranged so that they can pivot relative to each other about the pivot point.

Instead of the first means comprising an endless chain or belt, it may comprise at least one gear that is driven by a gear on the gearbox output shaft and in turn drives the pivot point gear or sprocket (either directly or by way of a coaxially-mounted gear). Where only one gear is provided between the gearbox output shaft gear and the pivot point gear, it will be appreciated that the engine needs to be configured so that the gearbox output shaft rotates in a reverse direction to embodiments in which the first means comprises a direct chain or belt drive. Alternatively, an additional, reversing or idler gear may be provided.

Furthermore, instead of the second means comprising an endless chain or belt drive, it may comprise a series of intermeshing gears. This is possible if the intermeshing gears are sufficiently strong and wear-resistant while still being sufficiently light-weight so as not to add unnecessarily to the overall weight of the motorcycle. Intermeshing gears are particularly low-maintenance in comparison to chain and sprocket arrangements, and may be the best option for small, relatively low-power motorcycles. There is no danger of chain stretching and wear, and no need to adjust the chain tension.

The swingarm may comprise a single arm on one side only of the motorcycle, or may comprise a pair of arms, one on each side of the driven wheel. The arm or arms of the swingarm may be solid or hollow, or may include through holes or apertures which can help to reduce weight.

Where a chain or belt is used in the second means for transferring rotational motion, the chain or belt and its associated sprockets may be located behind or inside the swingarm, in other words, between the swingarm and the driven wheel when viewed from a side of the motorcycle. Alternatively, the chain or belt and its associated sprockets may be located in front of or outside the swingarm. In this alternative arrangement, it may be possible to remove the chain or belt and associated components (for example the chain case and sprockets) for cleaning or maintenance without having to remove the swingarm or wheel beforehand.

Likewise, the gearbox output shaft sprocket may be located outside or inside the chain or belt of the second means for transferring rotational motion, as may the pivot point sprocket.

Embodiments of the present invention, because they do not require the gearbox output shaft to be coaxial with the swingarm pivot point, are particularly suited for fitting onto existing motorcycle designs, since no special changes to frame geometry are required.

In other words, a motorcycle production line facility in a factory can relatively easily be modified so that embodiments of the present invention can be fitted, since no significant changes to the motorcycle frame design or geometry are necessarily required.

Embodiments of the present invention can provide the advantages of conventional coaxial swingarm arrangements in a relatively cheap and simple manner without requiring changes to motorcycle frame designs, which is of particular attraction to users and manufacturers of existing motorcycles.

Moreover, by enabling the provision of a close-fitting chain case to protect the chain or belt, embodiments of the present invention can provide the low-maintenance advantages of shaft drive arrangements while avoiding the generation of gyroscopic forces that can cause problems for users.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made to the accompanying drawings, in which: FIGURE 1 is a side elevation of a conventional chain drive arrangement; FIGURE IA is a plan view of the arrangement of Figure 1; FIGURE 2 is a side elevation of a first embodiment of the present invention; FIGURE 2A is a plan view of the embodiment of Figure 2; FIGURE 3 is a side elevation of a second embodiment of the present invention; FIGURE 4 is a side elevation of a third embodiment of the present invention; FIGURE 5 is a side elevation of a fourth embodiment of the present invention; FIGURE 6 is a side elevation of a fifth embodiment of the present invention; FIGURE 7 is a side elevation of a sixth embodiment of the present invention; FIGURE 8 is a side elevation of a seventh embodiment of the present invention; FIGURE 9 is a side elevation of an eighth embodiment of the present invention; FIGURE 10 is a side elevation of a ninth embodiment of the present invention; FIGURE Ills a side elevation of a tenth embodiment of the present invention; FIGURE 12 is a side elevation of an eleventh embodiment of the present invention; FIGURE 13 is a side elevation of a twelfth embodiment of the present invention; and FIGURES 14 to 20 are schematic plan views of various sprocket, swingarm and frame configurations.

DETAILED DESCRIPTION

Figures 1 and IA show a conventional rear wheel chain drive arrangement on a motorcycle. There is shown a part of a motorcycle frame I to which is attached a first end of a swingarm 4 at a pivot point 3. As best shown in Figure 1A, the swingarm 4 comprises a pair of generally parallel arms, but it may equally comprise a single arm on one side only. A second end of the swingarm 4 is attached to an axle 10 of the rear wheel 5, which is provided with a tyre 6 and a brake disc II. An engine (not shown) is mounted on the frame I and has a gearbox output shaft 2 on which is mounted a sprocket 7. A chain 8 runs from the gearbox output shaft sprocket 7 to a sprocket 7' mounted on the axle 10. A simple chain guard 9 is provided above the chain 8. The chain guard 9 serves primarily to prevent mud and water from being thrown towards the rider of the motorcycle, but does not provide any protection for the chain 8 itself.

Because the gearbox output shaft 2 and the swingarm pivot point 3 are not coaxial, it can be seen that when the swingarm 4 pivots about the pivot point 3, the distance between the gearbox output shaft 2 and the axle 10 will change, leading to changes in the tension and shape of the chain 8.

Figures 2 and 2A show a first embodiment of the present invention, with like parts being labelled as in Figures 1 and IA. In this embodiment, the first end of the swingarm 4 is attached to the frame I at a pivot point 3 as before. However, instead of the chain 8 running directly between the sprocket 7' on the axle 10 of the rear wheel 5 and the sprocket 7 on the gearbox output shaft 2, there is provided an additional drive link from the sprocket 7 on the gearbox output shaft 2 to a sprocket 7" on a pivot point shaft 3 by way of a chain 8'. A second sprocket 7" on the pivot point shaft 3 is then connected by way of the chain 8 to the sprocket 7' on the axle 10. It can be seen that the shape and tension in the chain 8 will not change as the swingarm 4 pivots about the pivot point shaft 3. Moreover, the shape and tension in the chain 8' will not change either, since the gearbox output shaft 2 and the pivot point shaft 3 are in fixed relation to each other.

Because the chains 8 and 8' are of constant shape and tension, it is possible to encase the chains 8 and 8' in respective close-fitting chain cases 12 and 12' without risk of the chains 8, 8' rattling or unduly wearing through contact with the chain cases 12, 12'.

Where oil seals or the like (not shown) are provided where the axle 10, pivot point shaft 3 and gearbox output shaft 2 extend from the respective chain cases 12, 12', the chain cases can be partially or completely filled with oil or other appropriate lubricant so as to provide a lubricant bath in which the chains 8, 8' can run. The chain cases 12, 12' also serve to prevent the accumulation of dirt and grit in the chains 8, 8', thereby helping to reduce wear.

Figure 3 shows an embodiment similar to that of Figures 2 and 2A, with like parts being labelled as in Figures 2 and 2A, but without the chain cases 12, 12'.

Figure 4 shows an alternative embodiment in which a gear 101 is mounted on the gearbox output shaft 2. The gear 101 meshes with an idler or reversing gear 102 which in turn meshes with a gear 103 provided on the pivot point shaft 3 coaxially with the sprocket 7". The chain case 12 is omitted for clarity. In this way, the same advantages as for the Figure 2 embodiment can be realised, but with the first means for transferring rotational motion comprising a direct gear drives rather than a chain and sprocket drive.

The idler or reversing gear 102 means that the gearbox output shaft 2 can be configured to rotate in the same direction as in a conventional motorcycle.

Figure 5 shows a variation of the Figure 4 embodiment but without the idler or reversing gear 102. In this embodiment, the gearbox output shaft 2 must rotate in a reverse direction to a conventional motorcycle.

Figure 6 shows a variation of the Figure 2 embodiment, with the chain cases 12, 12' omitted for clarity, in which the chains 8, 8' are replaced by flat belts 15, 15'. The sprockets 7, 7', 7" and 7" are replaced by flat belt pulleys 14, 14', 14" and 14".

Figure 7 shows a further variation, in which rotational motion is transferred from the gearbox output shaft 2 to the wheel 5 by way of a series of directly intermeshing gears 101, 103, 104, 105, 106, 107 and 108. The gears may be made of a plastics material with metal or metallised teeth, or may be made entirely of appropnate metal or alloy materials. Preferably, the gears are contained within casings (not shown for clarity) similar to the chain cases 12, 12' of the Figure 2 embodiment. While seven gears are shown, comprising four intermediate gears 104, 105, 106 and 107 between a pivot point gear 103 and a rear axle gear 108, it will be understood that any appropriate number of intermediate gears may be employed according to design requirements.

Figure 8 shows the embodiment of Figure 2 with an integrated, one-piece swingarm and chain case 16. The axis location of the gearbox output shaft 2 is shown at 17, and the swingarm pivot point shaft 3 axis location is shown at 18, and the axle 10 axis location is shown at 19. In this embodiment, oil seals are provided at axis locations 17, 18 and 19 so as to retain oil or lubricant within the chain cases 16, 12'.

Figure 9 shows a variation of the Figure 8 embodiment in which the integrated swingarm and chain case unit 16 is configured with a central cut-out or aperture 110.

This can help to reduce weight.

Figure 10 shows a variation of the Figure 5 embodiment having a gear 101 mounted on the gearbox output shaft 2 and configured to drive a gear 103 mounted on the pivot point shaft 3. An integrated swingarm and chain case 16 with a central aperture or cut-out 110 is shown.

Figure 11 shows the embodiment of Figure 2 with the chain cases 12, 12' shown in full.

The axis location of the gearbox output shaft 2 is shown at 17, and the swingarm pivot point shaft 3 axis location is shown at 18, and the axle 10 axis location is shown at 19.

In this embodiment, oil seals are provided at axis locations 17, 18 and 19 so as to retain oil or lubricant within the chain cases 12, 12'. The swingarm 4 is located outside the chain case 12.

Figure 12 shows a variation of the Figure 11 embodiment, this time with an aperture or cut-out 110 provided in the chain case 12.

Figure 13 shows a variation of the Figure 8 or 9 embodiments in which an integrated swingarm and chain case 16 is configured as a one-sided swingarm. In other words, the integrated swingarm and chain case 16 supports the rear wheel 5 on one side only.

Structural reinforcements 111 may be provided to add strength and rigidity to the swingarm..

Figures 14 to 20 show, in schematic plan view, various ways in which the frame 1, swingarm 4, axes 17, 18, 19 and sprockets may be arranged. In the Figures, the following designations are used: gearbox output shaft sprocket 20, rear wheel sprocket 21, pivot point shaft sprockets 22, and the overall configuration is similar to the Figure 2 embodiment described above. The chains 8, 8' and chain cases 12, 12' are not shown for the sake of clarity. In Figures 15 to 20, the first means for transferring rotational motion comprise the sprocket pair 20, 22 and associated chain 8' (not shown); and the second means for transferring rotational motion comprise the sprocket pair 22, 21 and associated chain 8 (not shown). P1

Figure 14 shows the arrangement on a conventional motorcycle.

Figures 15 and 16 show arrangements in which all of the sprockets 20, 21, 22 are inside the frame I and swingarm 4.

Figure 17 shows an arrangement in which the first means is located inside the frame I and swingarm 4, and the second means is located inside the swingarm 4 but outside the frame 1. It will be noted that the swingarm 4 is outside the frame 1.

Figure 18 shows an arrangement in which the first means is located inside the frame 1 and swingarm 4, and the second means is located outside the swingarm 4 but inside the frame 1. It will be noted that the swingarm 4 is inside the frame 1.

Figure 19 shows an arrangement in which the first and second means are both located between the frame 1 and the swingarm 4, with the swirigarm 4 inside the frame 1. It will be appreciated that the swingarm 4 may alternatively be located outside the frame 1.

Figure 20 shows an arrangement in which the first means is located inside the frame I and swingarm 4, and the second means is located outside the frame I and the swingarm 4. It will be noted that the swingarm 4 is outside the frame 1, but it could equally be located inside the frame 1. This arrangement has the particular advantage that the second means can easily be removed for cleaning and maintenance without having to detach the swingarm 4 from the frame 1.

Claims

CLAIMS: 1. A drive train apparatus for a motorcycle having an engine mounted on a frame or chassis and a driven wheel, the apparatus comprising a swingarm having a first end for pivotal connection at a pivot point to the engine or frame or chassis, and a second end for connection to an axle of the driven wheel, the driven wheel having a wheel gear or sprocket, the apparatus further comprising a pivot point gear or sprocket at the first end of the swingarm coaxial with the pivot point, first means for transferring rotational motion from a gearbox output shaft of the engine to the pivot point gear or sprocket, and second means for transferring rotational motion from the pivot point gear or sprocket to the wheel gear or sprocket, wherein the pivot point gear or sprocket is coaxial with the pivot point but not coaxial with the gearbox output shaft when the swingarm is connected to the motorcycle.
2. An apparatus as claimed in claim 1, wherein the second means is provided with an enclosure.
3. An apparatus as claimed in claim I or 2, wherein the first means is provided with an enclosure.
4. An apparatus as claimed in claim 3 depending from claim 2, comprising first and second enclosures that are arranged to be pivotable relative to each other about the pivot point.
5. An apparatus as claimed in any one of claims 2 to 4, wherein the or each enclosure is adapted as an oil or lubricant bath for the means for transferring rotational motion.
6. An apparatus as claimed in claim 5, wherein the or each enclosure includes seals at locations where shafts pass therethrough.
7. An apparatus as claimed in any preceding claim, wherein the swingarm is of substantially rigid construction.
8. An apparatus as claimed in claim 7, wherein the swingarm does not include any linkages or pivots between its first and second ends.
9. An apparatus as claimed in claim 3 or any one of claims 4 to 8 depending from claim 3, wherein the enclosure is integral with the swingarm.
10. An apparatus as claimed in any preceding claim, wherein the first means comprises at least one endless chain or belt and at least two sprockets.
11. An apparatus as claimed in any one of claims 1 to 9, wherein the first means comprises at least one pair of intermeshing gears.
12. An apparatus as claimed in any preceding claim, wherein the second means comprises at least one endless chain or belt and at least two sprockets.
13. An apparatus as claimed in any one of claims I to 11, wherein the second means comprises at least one pair of intermeshing gears.
14. An apparatus as claimed in claim 2 or 3 or any one of claims 4 to 13 depending from claim 2 or 3, wherein the enclosure is a close-filling enclosure.
15. An apparatus as claimed in claim 14, wherein the enclosure is a close-filling chain case.
16. An apparatus as claimed in claim 1, wherein the second means comprises a pivot point sprocket, a wheel sprocket and a single endless chain or belt, the second means being further provided with a close-filling chain case.
17. An apparatus as claimed in claim 1, wherein the second means comprises a pivot point sprocket, a wheel sprocket and a single endless chain or belt, the second means being further provided with a close-filling chain case.
18. An apparatus as claimed in claim 17, wherein the first means comprises a gearbox output shaft sprocket, a pivot point sprocket, and a single endless chain or belt, the first means being further provided with a close-filling chain case.
19. An apparatus as claimed in claim 17, wherein the first means comprises a gearbox output shaft gear and a pivot point gear, the first means optionally being provided with an enclosure.
20. An apparatus as claimed in claim 19, wherein a reversing or idler gear is provided between the gearbox output shaft gear and the pivot point gear.
21. An apparatus as claimed in claim 18, 19 or 20, wherein the chain case or enclosure is adapted as an oil or lubricant bath for the means for transferring rotational motion.
22. An apparatus as claimed in any preceding claim, wherein the swingarm comprises a single arm on one side only of the motorcycle.
23. An apparatus as claimed in any one of claims 1 to 21, wherein the swingarm comprises a pair of arms, one on each side of the driven wheel.
24. An apparatus as claimed in claim 12 or any claim depending from claim 12, wherein the chain or belt and its associated sprockets is located behind or inside the swingarm.
25. An apparatus as claimed in claim 12 or any claim depending from claim 12, wherein the chain or belt and its associated sprockets is located between the swingarm and the driven wheel when viewed from a side of the motorcycle.
26. An apparatus as claimed in claim 12 or any claim depending from claim 12, wherein the chain or belt and its associated sprockets is located in front of or outside the swingarm.
27. An apparatus substantially as hereinbefore described with reference to or as shown in Figures 2 to 13 and 15 to 20 of the accompanying drawings.