GB2352212A - Rear wheel mounting in a bicycle - Google Patents

Abstract

The bicycle comprises a frame (10), a chain drive (14, 15a,b,c) mounted on the frame to be rotatable about an axis (14a), and mounting means either fixed or forming a rear suspension swing arm (19) carrying a rear wheel (18) rotatable about an axis (18a) and comprises a pivot member (21) which has rearwardly diverging limbs embracing the rear wheel and which extends from the region of the rear wheel axis (18a) to the region of the chain drive axis (14a) in the latter region being spaced below a centre line (L) interconnecting the axes. Due to the lower position of the member (21), its limbs can diverge a short distance behind the chain drive axis (14a) so as to accommodate a relatively wide rear wheel rim and tyre. The swing arm (19) can also comprise a further pivot member (22) connected to and extending upwardly and forwardly from the member (21) and a connecting piece (23) connecting the two members (21, 22) together at their forward ends. The chain drive can include several chain wheels (15a to 15c) selectably engaged by a chain (16) displaceable between the chain wheels by a chain displacing device (17), these drive components being accommodated by the swing arm (19) without constraint on its range of travel.

Description

2352212 REAR WHEEL MOUNTING IN A BICYCLE The present invention relates to

a bicycle and has particular reference to the mounting of the rear wheel of the bicycle.

The rear wheel of a bicycle is normally carried by a system of stays rigidly connected to the bicycle frame or, in the case of specialised bicycles such as those for off-road or rough terrain use, by a movable rear suspension based on a swing arm pivotably connected to one or other part of the frame. The frame itself conventionally consists of a down tube extending down from the region of the bicycle handlebars, a seat tube extending up from the lower end of the down tube and carrying the rider's seat, and a top tube or crossbar interconnecting the down tube and seat tube. A rear wheel drive system in the form of a pedal-operated chain wheel engaged by a drive chain is generally provided at the junction of the down tube and seat tube, which is the lowest part of the frame. Virtually all bicycles include a gear system which is commonly realised by several coaxial chain wheels of different diameter and a chain-displacing device, known as a derailleur mechanism, for displacing the chain between the chain wheels to step down or step up the ratio of drive transmission to the rear wheel. Chain tension is usually maintained by a depending jockey wheel at the rear wheel, which produces a considerable spacing between the drive and return runs of the chain.

In the case of a rigid stay system, lower stays of the system are invariably oriented along a straight centre line between the rear wheel axis and the axis of the chain wheels, which minimises the length of the resulting lever arm and thereby the bending load, but which imposes constraints on the shaping of the stays to provide space for the chain wheels on the one hand and clearance for the nearby wheel rim and tyre on the other hand. Since the trend for specialised categories of bicycle is for tyres of increasing width, it becomes problematic to accommodate both the tyre width and multiple chain wheels. Similarly, in the case of a movable rear suspension, the configuration of the swing arm not only has to provide appropriate geometry for rear wheel bump and rebound travel, but also must avoid conflict with the drive system, especially the chain and, if present, additional chain wheels and chain displacing device. In one known form of swing arm, an arched single arm extends from the rear wheel axle entirely above the chain and chain wheels and curves down to a pivot mounting point on the down tube. Such an arm represents an overhung cantilever construction and has to have sufficient solidity and strength to accept the 2 anticipated bending loads. The construction inevitably carries a weight penalty. In another known form of swing arm, a lighter but inherently strong triangular construction is employed, in which a lower member extends approximately along the centre line connecting the axes of rotation of the rear wheel and chain wheel and is kinked to pass over an axle carrying the chain wheel and to extend between the chain wheel and the frame. This has the disadvantage of being unable to clear standard arrangements of multiple chain wheels and derailleur mechanism, which consequently imposes constraints on the use of available gearing systems. In addition, as a matter of principle it is difficult or impossible to satisfactorily site a swing arm member along the mentioned centre line without clearance problems in relation to a derailleur mechanism and chain wheels during travel of the swing arm.

It is therefore the principal object of the invention to provide a bicycle with a rear wheel mounting configuration able to avoid the abovementioned problems associated with the described known arrangements, in particular a configuration giving improved clearance for components of a chain drive system as well as space, if needed, for wider versions of tyre and wheel rim. Other objects and advantages of the invention will be apparent from the following description.

According to the present invention there is provided a bicycle comprising a frame, chain drive means mounted on the frame to be rotatable about an axis, and mounting means mounting the rear wheel and comprising a member which has rearwardly diverging limbs embracing the rear wheel and which extends from the region of the axis of the rear wheel to the region of the axis of rotation of the chain drive means in such a direction that in the latter region it is spaced below a centre line interconnecting the two axes.

In this configuration of rear wheel mounting means, the underslung member can provide sufficient clearance for drive system components such as, for example, multiple chain wheels and any associated chain displacing mechanism, irrespective of whether the mounting means is movable or fixed relative to the frame and yet the limbs can begin to diverge at a shallow angle as soon as the circumference of any smaller or smallest chain wheel has been passed. The point at which this circumference is passed is located ahead of the intersection - viewed in the direction of the drive means axis of rotation - of the circumference with the centre line, this intersection being the earliest point at which the limbs could otherwise diverge if the member followed that line. The low level of the 3 member, by comparison with members passing along or above the centre line, also allows greater space for accumulations of mud ahead of the rear wheel and enables use of larger diameter chain wheels. At the same time, however, the length of the member in the direction of the centre line can be kept relatively small, so that the bending load to be accepted is not unduly increased. In this connection, it is desirable for the centre line itself to be kept to a minimum length, both to aid the responsiveness of the handling of the bicycle and to achieve optimum placement of the rider weight over the rear wheel for enhanced traction, especially in climbing.

The chain drive means can, as usual, include a chain wheel rotatable about the axis of rotation of the drive means at one side of the frame and the member can intersect - viewed in the direction of that axis - the circumference of the chain wheel. The normal spacing of the chain wheel from the plane of the frame and the rear wheel is sufficient for the member to, in effect, remain above the lowermost point of the circumference of the chain wheel and yet be disposed symmetrically with respect to the plane. The ground clearance of the bicycle in this region is thus determined by the circumference of the chain wheel or throw of associated pedal cranks and not by the member.

For preference, the drive means further comprises at least one further chain wheel, which is rotatable about the axis of rotation at the same side of the frame and which is smaller in diameter than the firstmentioned chain wheel and disposed between that chain wheel and the frame, and the member also intersects the circumference of the at least one further chain wheel. In the case of chain drive means with a typical stack of three concentric chain wheels of progressively increasing diameter in direction away from the frame, the stack can be readily accommodated outwardly of the member. Equally, if the rear wheel drive system includes a drive chain selectably displaceable between the chain wheels by displacing means acting on the chain in an upper region of the chain wheels, the member can be arranged, without compromising its configuration, at a spacing from the displacing means. A maximum clearance can thus be available for the displacing means.

Preferably, the limb of the member at the same side of the frame as the chain wheels includes a length portion extending substantially parallel and adjacent to a notional cone surface connecting the circumferences of the chain wheels. In the case of a stack of three chain wheels as mentioned above, the member can thus follow a path close to the chain wheels and begin to widen as soon as it has cleared the circumference of the smallest 4 diameter chain wheel. For preference, the limb of the member at the other side of the frame includes a length portion substantially symmetrical to said length portion of the firstmentioned limb with respect to a central plane of the frame and rear wheel. The mentioned length portions of the limbs preferably adjoin substantially parallel length portions thereof, so that the limbs diverge in a distinct step, or steps if further non- parallel length portions are included. The transverse dimension of the member can thus be kept small in the vicinity of chain drive components, as already mentioned, but enlarge to an appropriate extent in the immediate vicinity of the rear wheel rim and tyre. The particular shape of the member can be selected with additional regard to the clearances required for, for example, a chain of the drive system.

In a preferred embodiment applicable to a movable rear suspension, the mounting means comprises a swing arm pivotably mounted on the frame, the member being part of the swing arm. The swing arm is preferably pivotably mounted on a down tube of the frame, but the pivot mounting can be differently located depending on the shape of the swing arm and disposition and shape of the elements making up the frame. The limbs of the member can continue to a forward end thereof and be connected together by a cross brace forwardly of the rear wheel, the low position of the member offering scope to freely site such a brace without conflict with a seat tube of the frame and consequent limitation of the swing arm movement. Alternatively, the two limbs can project rearwardly from a nondivided forward end portion of the member, so that this member is effectively a single solid element ahead of the rear wheel. In either configuration, the member can be arranged to pass below and forwardly of the axis of rotation of the chain drive means. The spacing from this axis can be selected with reference to the desired range of travel of the swing arm.

For preference, the swing arm comprises a further member connected to the firstmentioned member and extending divergently therefrom in upward and forward directions. By analogy with a bicycle construction without a movable rear suspension, the firstmentioned member equates with chain stays and the further member with seat stays, the former being low and the latter high to impart lateral stiffness to the rear wheel mounting means. The further member preferably comprises two limbs extending one on each side of the rear wheel and continuing so as to pass either side of a seat tube of the frame. The two members are preferably connected together at or in the region of the axis of the rear wheel, such as by gusset plates, lugs or similar. The swing arm itself can additionally comprise a connecting piece connected with forward ends of the members to form a closed frame structure, such a structure being, for example, substantially triangular. A triangular form of construction provides beam bending and can thus be lighter, yet stiffer, than a single member swing arm with cantilever bending.

The connecting piece, when present, can be utilised for the pivot mounting of the swing arm on the frame, such as the down tube, and the connecting piece can be conveniently disposed forwardly of the seat tube. The connecting piece can, if desired, be formed integrally with the firstmentioned member and may comprise two limbs disposed one on each side of the frame in the region of and extending upwardly from the down tube. The entire swing arm can then be fifted in place by sliding over the frame starting from in front of the down tube.

The rear suspension can be completed by spring and damping means acting between the frame and the swing arm, for example the frame top tube and an uppermost part of the swing arm.

In another preferred embodiment, applicable to a fixed rear wheel mounting, the member is rigidly secured to a down tube or seat tube of the frame. Similarly to the embodiment with a movable suspension, the mounting means can comprise a further member connected to the first- mentioned member and extending divergently therefrom in upward and forward directions. For preference, the further member comprises two limbs extending one on each side of the rear wheel and rigidly secured to the seat tube of the frame. The low siting of the first-mentioned member, in effect chain stays, resolves the contradictory requirements of compact dimensions in the vicinity of the chain wheel or wheels and adequate spacing of the limbs of the member to accept a wider wheel rim and tyre, the outer circumference of the latter generally being closely adjacent to the outer circumference of a chain wheel stack and thus causing space to be at a premium.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic side elevation of the rear half of a first bicycle embodying the invention; 6 Fig. 2 is a schematic inverted plan view, in the direction A in Fig. 1, of part of a rear suspension of the bicycle of Fig. 1 -. and Fig. 3 is a schematic side elevation of the rear half of a second bicycle embodying the invention- Referring now to the drawings, there is shown in Figs. 1 and 2 part of a bicycle comprising a frame 10 formed by a down tube 11 extending at an angle downwardly from the region of a handlebars and front fork assembly (not shown) at the front of a bicycle, a seat tube 12 joined to the lower end of the down tube and extending upwardly therefrom at such an angle as to be inclined rearwardly, and a top tube 13 connected with the seat tube 12 and with either the down tube or a head tube attached thereto. The seat tube 12 carries a seat for the rider of the bicycle.

Mounted at the junction of the down tube 11 and seat tube 12, thus at the lowermost part of the frame, is a chain drive in the form of an axle 14 rotatable about an axis 14a by crank arms (not shown) carrying pedals, and three coaxial chain wheels 15a, 15b and 15c arranged at short axial spacings on the axle 14 to be rotatable therewith, the chain wheels being disposed on the same side of the frame and having progressively smaller diameters in direction towards the frame. A chain 16 is engaged with a selectable one of the chain wheels 15a to 15c and displaceable from one to the other by a chain displacing device or derailleur mechanism 17. The chain wheels, chain and derailleur mechanism together provide a drive system with three ratios of drive transmission.

The bicycle further compdses a rear wheel 18 mounted on mounting means, in particular a rear suspension system, to be rotatable about an axis 18a. The rear suspension is formed by swing arm 19, which is pivotably mounted on the down tube 11, and a spring and damper unit 20 pivotably connected to and acting between the swing arm and the top tube 13. The swing arm is capable of pivot movement to enable upward and downward movement of the wheel 18 through a defined range of travel in response to bump deflection against the force of a spring of the unit 20 and rebound under relaxation of the spring. The swing arm 19 is composed of a lower pivot member 21 extending close to a centre line L connecting the axis 14a of the drive axle 14 and the axis 18a of the rear wheel 18, but inclined downwardly in the direction of its forward end so as to be spaced below the line L in the region of the axis 14a, an upper pivot member 22 connected at its 7 rearward end to the rearward end of the lower pivot member 21 in the region of the axis 18a of the rear wheel 18 and inclined upwardly in the direction of its forward end to extend beyond the seat tube 12, and a connecting piece 23 located forwardly of the seat tube 12 and connected with the forward ends of the lower and upper pivot members 21 and 22 to form therewith a rigid frame structure of generally triangular shape. The pivot mounting of the swing arm 19 on the down tube 11 is by way of the connecting piece 23, the mounting point being adjacent to the axle 14 of the chain drive.

In detail, the lower pivot member 21 consists of two limbs 21 a and 21 b Which extend either side of the rear wheel 18 and which diverge in stages, in particular by relatively angled length portions interconnecting parallel length portions as shown in Fig. 2, in rearward direction. The limbs 21 a and 21 b are thus close together in the region below the axle 14, so as to have a small dimension transversely of the central plane of the frame 10 and rear wheel 18 and thereby provide maximum space for the chain wheels 15a to 15c and chain 16, and relatively widely spaced in the region of the axis 18a of the wheel 18 so as to accommodate the wheel hub and a sprocket drivingly engaged - or more usually several sprockets selectably drivingly engaged - by the chain 16. The angle of divergence of the limbs 21 a and 21 b is such that the former, which is located on the same side of the bicycle as the chain wheels 15a to 15c and chain 16, passes through the closed loop defined by the chain. The chain is additionally engaged by a tensioning jockey wheel depending from the swing arm 19, with the result that the driving and return runs of the chain are relatively widely spaced and provide sufficient clearance for the pivot movement of the lower pivot member 21. In the case of multiple sprockets, a chain displacing device or derailleur mechanism similar in purpose to the mechanism 17 is carried by the swing arm in a depending position above the jockey wheel. The lower pivot member 21 is completed by a cross brace 21c located forwardly of the rear wheel 18. The option exists for the member 21 to consist of a single solid piece forwardly of the region of the cross brace.

The upper pivot member 22 similarly consists of two limbs, which pass either side of the seat tube 12, and the connecting piece 23 again of two limbs, which pass either side of and extend upwardly from the down tube 11. Below the down tube, the connecting piece could consist of a single solid piece. As depicted in Fig. 1, the connecting piece 23 is formed integrally with the lower pivot member 21. The swing arm 19 can, however, be constructed in various ways, including fabricated entirely from separately produced components defining the individual parts of the swing arm elements or fabricated from 8 components with integrally formed combinations of limbs and/or arm elements. The method of assembly of the swing arm 19 to the frame 10 may depend on the construction, but typically the arm is fitted to the frame by being slid into position from the front of the down tube 11.

As can be seen in Figs. 1 and 2, the spacing of the lower pivot member 21 from the axle 14 is such that the limbs 21a and 21b pass below the axle, but above the levels of the lowermost points of the circumferences of both the largest diameter chain wheel 15a and the intermediate diameter chain wheel 15b. The spacing of the member 21 downwardly from the axis 14a of the axle 14 is thus relatively small, so that rearwardly of this axis there is no undue increase in length of the member in relation to the length of the centre line L. The shape of the limbs 21 a and 21 b is such that the graduated diameter chain wheels 15a to 15c can nest in the space alongside the narrowed forward end portion of the pivot member 2 1, for which purpose the limbs 21 a and 21 b each diverge from the central plane of the frame 10 and rear wheel 18 at an angle which, in the view of Fig. 2, approximately corresponds with the angle of a notional cone tangential to the circumferences of the chain wheels. Since the limb 21 a in side elevation of the bicycle intersects and thus clears the circumferences of the chain wheels 15a and 15b significantly ahead of the points of intersection of these circumferences with the centre line L, it can depart from parallelism with the central plane earlier than would be the case if it followed the line L. In conjunction with the symmetrically arranged other limb 21b, a wide space is formed to accept wider sizes of rim and tyre of the rear wheel 18.

In use, the configuration of the swing arm 19 allows a substantial range of bump and rebound movement of the rear wheel without risk of contact of components of the suspension with any part of the chain drive system. Siting of the lower pivot member 21 partly below the axis of the chain drive allows use of a light, but stiff triangulated format of swing arm while providing sufficient space not only for a usual arrangement of multiple chain wheels of different diameters and a derailleur mechanism, but also for the rear wheel rim and tyre.

A further embodiment of bicycle, in which the rear wheel is carried by non-movable mounting means, is illustrated in Fig. 3. The same reference symbols employed in connection with the embodiment of Figs. 1 and 2 are used for the embodiment of Fig. 3 except for the mounting means. In the latter embodiment, the rear wheel 18 is mounted in 9 a rigid stay structure 19' to again be rotatable about the axis 18a. The stay structure is composed of a lower fixed member 21' extending close to the centre line L, but inclined downwardly in direction of its forward end so as to be spaced below the line L in the region of the axis 14a, and an upper fixed member 22' connected at its rearward end to the rearward end of the lower member 21' in the region of the axis 18a and inclined upwardly in the direction of its forward end to extend up to the seat tube 12. Each of the members 21' and 22' consists of two limbs extending either side of the rear wheel 18, those of the lower member 21' being rigidly secured, such as by welding, to a downward prolongation of the down tube 11 and those of the upper member 22' being similarly secured to the seat tube 12. The stay structure, in conjunction with the frame tube sections interconnecting the forward ends of the members 21' and 22', forms an inherently stiff triangulated mount for the rear wheel.

The limbs of the lower member 21', which extends on substantially the same path as the member 21 of the embodiment of Figs. 1 and 2, but does not pass below and forwardly of the axle 14, can be shaped in substantially the same manner as the limbs 21 a and 21b shown in Fig. 2. The advantages attributed to the underslung pivot member 21, apart from those specifically associated with a movable rear suspension, are thus equally applicable to the fixed member 21'. The illustrated direct attachment of the limbs of the member 21' to the down tube I I is merely by way of example, The limbs could equally well be secured to a downward prolongation of the seat tube 12 or by lugs or brackets to either or both of these tubes or to a sleeve or other casing of the axle 14.

Claims (27)

1 A bicycle comprising a frame, chain drive means mounted on the frame to be rotatable about an axis, and mounting means mounting the rear wheel and comprising a member which has rearwardly diverging limbs embracing the rear wheel and which extends from the region of the axis of the rear wheel to the region of the axis of rotation of the chain drive means in such a direction that in the latter region it is spaced below a centre line interconnecting the two axes.

2. A bicycle as claimed in claim 1, wherein the chain drive means comprises a chain wheel rotatable about the axis of rotation of the drive means at one side of the frame and the member intersects the circumference of the chain wheel as seen in the direction of that axis.

3. A bicycle as claimed in claim 2, wherein the drive means comprises at least one further chain wheel, which is rotatable about the axis of rotation of the drive means at the same side of the frame and which is smaller in diameter than the first-mentioned chain wheel and disposed between that chain wheel and the frame, and wherein the member intersects the circumference of the at least one further chain wheel as seen in the direction of that axis.

4. A bicycle as claimed in claim 3, comprising a drive chain selectably displaceable between the chain wheels by displacing means acting on the chain in an upper region of the chain wheels, the member being disposed at a spacing from the displacing means.

5. A bicycle as claimed in claim 3 or claim 4, wherein the limb of the member at the same side of the frame as the chain wheels includes a length portion extending substantially parallel and adjacent to a notional cone surface connecting the circumferences of the chain wheels.

6. A bicycle as claimed in claim 5, wherein the limb of the member at the other side of the frame includes a length portion substantially symmetrical to said length portion of the first-mentioned limb with respect to a central plane of the frame and rear wheel.

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7. A bicycle as claimed in claim 6, wherein said length portions of the limbs adjoin substantially parallel length portions thereof.

8. A bicycle as claimed in any one of the preceding claims, wherein the mounting means comprises a swing arm pivotably mounted on the frame, the member being part of the swing arm.

9. A bicycle as claimed in claim 8, wherein the swing arm is pivotably mounted on a down tube of the frame.

10. A bicycle as claimed in claim 8 or claim 9, wherein the limbs of the member continue to a forward end thereof and are connected together by a cross brace forwardly of the rear wheel.

11. A bicycle as claimed in claim 8 or claim 9, wherein the limbs of the member project rearwardly from a non-divided forward end portion of the member.

12. A bicycle as claimed in any one of claims 8 to 11, wherein the member passes below and forwardly of the axis of rotation of the chain drive means.

13. A bicycle as claimed in any one of claims 8 to 12, wherein the swing arm comprises a further member connected to the first-mentioned member and extending divergently therefrom in upward and forward directions.

14. A bicycle as claimed in claim 13, wherein the further member comprises two limbs extending one on each side of the rear wheel and passing either side of a seat tube of the frame.

15. A bicycle as claimed in claim 13 or 14, wherein the pivot members are connected together at or in the region of the axis of the rear wheel.

16. A bicycle as claimed in of claims 13 to 15, wherein the arm further comprises a connecting piece connected with forward ends of the members to form a closed frame structure.

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17. A bicycle as claimed in claim 16, wherein the structure is substantially triangular.

18. A bicycle as claimed in claim 16 or claim 17, wherein the swing arm is pivotably mounted on the frame by the connecting piece.

19. A bicycle as claimed in any one of claims 16 to 18, wherein the connecting piece is disposed forwardly of a seat tube of the frame.

20. A bicycle as claimed in any one of claims 16 to 19, wherein the connecting piece is formed integrally with the first-mentioned member.

21. A bicycle as claimed in any one of claims 16 to 20, wherein the connecting piece comprises two limbs disposed one on each side of the frame in the region of and extending upwardly from a down tube of the frame.

22. A bicycle as claimed in any one of claims 8 to 21, comprising spring and damping means acting between the frame and the swing arm.

23. A bicycle as claimed in any one of claims 1 to 7, wherein the member is rigidly secured to a down tube or seat tube of the frame.

24. A bicycle as claimed in claim 23, wherein the mounting means comprises a further member connected to the first-mentioned member and extending divergently therefrom in upward and forward directions.

25. A bicycle as claimed in claim 24, wherein the further member comprises two limbs extending one on each side of the rear wheel and rigidly secured to the seat tube of the frame.

26. A bicycle substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

27. A bicycle substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.