GB2482159A

GB2482159A - Bicycle rear suspension

Info

Publication number: GB2482159A
Application number: GB201012279A
Authority: GB
Inventors: Patrick James Alexander; Ian Christopher Andrew Alexander
Original assignee: ATB Sales Ltd
Current assignee: ATB Sales Ltd
Priority date: 2010-07-21
Filing date: 2010-07-21
Publication date: 2012-01-25
Also published as: GB201012279D0

Abstract

A bicycle 10 comprises a frame 11 with a seat tube 12 and a down tube 14 connected with the seat tube at a junction, and a rear wheel suspension 15 comprising a triangular swing arm 16 carrying a rear wheel 19 at one of the three corners of the arm and two pivot links 17, 18 which are each pivotably connected with the arm 16 at or in the vicinity of a respective each of the other two corners of the arm. The links 17, 18 couple the arm 16 to the frame 11 to form a four-bar linkage therewith. A first or upper one 17 of the links is pivotably connected with the frame 11 at the seat tube 12. The second or lower one 18 of the links is pivotably connected with the frame 11 at the junction of the seat and down tubes 12, 14, where it is able to share the mounting location of part of a chain-and-sprocket drive transmission 21, 22, 24 for the rear wheel, in particular the location of an axle 24 of the transmission.

Description

BICYCLE REAR SUSPENSIN

The present invention relates to a bicycle and has particular reference to a rear wheel suspension in a bicycle.

Bicycles intended for off-road and other rough terrain uses commonly have rear suspension systems permitting sprung movement of the rear wheel relative to the bicycle frame. * A basic system is represented by a rearwardly extending swing arm carrying the rear wheel and pivotably connected to a seat tube or down tube of the bicycle frame. A spring and damper unit is coupled between the swing arm and the frame to control pivot movement of the arm under suspension travel. The swing arm is usually a sturdy cast or fabricated member which is suitably stiff in bending and which can incorporate robustly formed journals for pivot connection to the frame and the spring and damper unit. The sturdiness of the swing arm is highly desirable for acceptance of the shock loads acting on the suspension during off-road use, but the simple arc executed by the swing arm during suspension travel imposes a compromise with respect to the suspension behaviour. In particular, the drive force transmitted to the rear wheel by the usual chain-and-sprocket transmission during a power stroke applied by a rider tends to pivot up the swing arm and wheel independently of bump response of the suspension. The arm is then able to pivot down again in the interval until the next power stroke, which results in a bobbing effect or at least some degree of feedback from the foot pedal cranks which usually feed the drive force to the transmission.

These disadvantageous effects can be counteracted by more complex multi-element suspension linkages, of which the four-bar linkage is particularly effective from the viewpoint of controlling rear wheel movement in the course of suspension travel. Such a linkage can, depending on the position of its pivot centre, generate a counterbalancing force tending to pull the rear wheel down in opposition to the tendency of the wheel to move up during the power stroke of the rider. Whilst the dynamic characteristics of such a four-bar linkage, of which the swing arm is one element and the frame another, confer major advantages in terms of suspension travel control, a significant penalty is represented by the complexity and consequent cost of such suspension systems. A cast or fabricated swing arm is a strong, but relatively heavy and expensive component. An alternative form of swing arm offering comparable stiffness, but lighter weight, is represented by a triangular swing arm fabricated from, for example, tubes, in effect a triangular whe& carrier frame, and coupled by an upper pivot link and a lower pivot link to the bicycle frame. Cost and weight are, however, easily added to the equation by the disposition, length and pivot connections of the pivot links, all of which require careful consideration if the suspension is to retain its dynamic qualities with respect to an optirnised locus of the instantaneous pivot centre of the linkage during suspension movement, and yet remain light, economic in construction while employing, as far as may be possible, proprietary components.

It is therefore the principal object of the present invention to provide, on a bicycle, a rear wheel suspension embodying the four-bar linkage principal and combining strength, lightness and simple construction.

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 with a seat tube and with a down tube connected with the seat tube at a junction, and a rear wheel suspension comprising a substantially triangular swing arm carrying a rear wheel at one of the three corners of the arm and two pivot links which are each pivotably connected with the arm at or in the region of a respective one of the other two corners thereof and which couple the arm with the frame to form therewith a four-bar linkage, a first one of the pivot links being pivotably connected with the frame at the seat tube and the second one of the pivot links being pivotably connected with the frame at the junction of the seat and down tubes.

A bicycle with a rear wheel suspension having the above-described features employs a swing arm of substantially triangular construction, which constitutes a structural element of recognised strength with capability of manufacture from relatively inexpensive and lightweight materials such as tubing. The pivot links, which are essential components of the four-bar linkage, are located at or close to two of the three corners of the swing arm so that they can be widely spaced in order to minimise or avoid lateral flexing of the arm relative to the frame and are connected with the frame at, respectively, the seat tube and the junction of the seat and down tubes, as a result of which the links can be kept short and overlap of the swing arm with the seat tube kept small. Because the second one of the pivot links, namely a lower link in the use (upright) orientation of the bicycle, is connected with the frame at the seatldown tube junction the possibility is then given of combining the link pivot point with or integrating the link pivot point in the rear wheel drive transmission conventionally located at that junction. As a result there is scope to avoid the need for a completely separate and dedicated pivot mount for that link, such as a forged bracket and a pivot pin on the seat or down tube above the junction. This not only offers cost-saving potential, but also provides opportunity to make greater use of proprietary components, i.e. components of the transmission.

Consequently, in a preferred embodiment the bicycle comprises drive transmission means for transmitting drive to the rear wheel, the drive transmission means being rotatable about an axis of rotation at the junction of the seat and down tubes and the second one of the pivot links being pivotable about the axis. The second pivot link can thus utilise, for a pivot axis at the frame, an axis of rotation of a typical bicycle drive transmission, which conventionally comprises a pedal-driven sprocket of a chain-and-sprocket rear wheel drive system. The drive transmission means in that case preferably includes an axle defining the axis of rotation, the second one of the pivot links then being pivotably connected with the frame by connecting means concentric with the axle.

The connecting means can comprise, for example, a sleeve rotatable relative to both the axle and the frame. Such a sleeve can rotatably receive the axle, optionally by way of bearings, and in turn be journalled in a transverse tube provided at the junction of seat and down tubes. For preference, the second one of the pivot links has two spaced-apart end portions each connected with the sleeve at a respective end thereof, in which case the end portions can define eyes receiving the sleeve. The end portions can be formed by, for example, a bifurcated end of a single component such as a forging or casting or by the ends of two separately constructed bars making up the link. In order to facilitate assembly, and disassembly if required, securing means can be provided to releasably secure the sleeve in the eyes, for example, locking screws or similar extending through the link end portions and into the sleeve.

The second pivot link can, however, be connected with the frame in other ways, for example, by connecting means in the form of two spaced-apart bearings mounted on the axle. In that case, the second link can have two end portions, whether the bifurcated end of a single component or the ends of two separately constructed components, each with a respective bearing in which the axle is received.

The first one of the pivot links preferably comprises two para'lel arid spaced-apart bars receiving the seat tube therebetween. The bars are in fixed relationship, which can be achieved simply by the pivot connections of the bars to the swing arm and the frame. The bars of the first link are, for preference, pivotably connected with the frame by a single continuous pivot pin, which provides a particularly stable, but cost-effective, means of connecting the components.

In order to minimise overlap of the swing arm and frame each of the pivot links preferably extends from the frame in a direction away from the rear wheel. With this configuration of the pivot links and taking account of the usual rearward slope -in direction from bottom to top -of a bicycle seat tube in the use position of the bicycle, overlap of the swing arm and frame can be eliminated or, at least, reduced to a small amount in the region of the upper corner of the arm.

For preference the arm is movable between a first end setting in an unloaded state of the suspension and a second end setting in a loaded state of the suspension, the first one of the pivot links being oriented in a use position of the bicycle downwardly in a direction away from the arm. Preferably, also, the second one of the pivot links in that position of the bicycle is oriented upwardly in a direction away from the arm. This orientation of each pivot link contributes to a compact form of the four-bar linkage geometry and creates a precondition for swing arm movement counteracting the afore-mentioned bobbing effect that can arise with swing arms due to movement induced not by suspension reaction to uneven surfaces, but by pulsations in transmission of drive to the rear wheel. Accordingly, in the case of an arm movable between first and second end settings as described above the pivot links are preferably so arranged that on movement of the arm from the first to the second end setting an instantaneous pivot centre defined by the intersection of two axes each containing the pivot points or fulcra of a respective one of the links moves downwardly and rearwardly with respect to a fore and aft direction of the bicycle. This locus of the instantaneous pivot centre, in which its rate of movement will diminish as the swing arm approaches its second end setting, provides a preferred behaviour of the four-bar linkage with respect to control of the direction of wheel movement to counteract the bobbing effect occurring due to tensioning and relaxation of the chain of a chain-and-sprocket drive under the pulsed input of drive power into the transmission, in particular by the power strokes Of rider-operated drive pedals.

In a preferred construction the arm comprises two substantially triangular spaced apart frames connected together in fixed relationship and disposed on either side of the rear wheel. The swing arm is, in effect, composed of a double frame, each part of which can be made of, for example, relatively lightweight and slender tubes or a similarly lightweight casting with incorporated mounting and attachment points, so that strength is derived from a quasi-box construction. The frames of the arm are conveniently connected together at a hub of the rear wheel, whereby use can be made of a hub axle as a connecting element.

A further connection of the frames of the arms can be provided at the location of the second one of the pivot links, thus making use of a pivot connection of that link to the swing arm. In addition, the frames of the swing arm can be rigidly connected together into a unit by at least one bridge piece extending between parallel members of the frame, for example in the region of the seat tube.

For preference, the bicycle comprises a spring and damper unit acting between the suspension and a frame and arranged to urge the swing arm into an end setting and to damp movement of the arm out of that setting. In that case it is advantageous if the spring and damper unit is arranged in the frame in a space bounded at least in part by the seat tube, down tube and crossbar. The unit is thus accommodated within the bicycle frame and does not add to the overall bulk of the bicycle outside the frame. The unit is preferably directly coupled to the frame at one end, particularly in the region of the junction of the seat and down tubes, and indirectly at an opposite end, for example by a pulllpush rod connected with the swing arm at the point of connection with the first pivot link and optionally also by a further pivot arm connected with the seat tube. The above-described preferred locus of the instantaneous pivot centre of the four-bar linkage also has the desirable consequence of contributing to a rising rate in the action of the spring and damper unit in the course of movement of the swing arm from the first to the second end setting, thus under loading of the suspension.

A preferred embodiment of the present invention will now be more particular described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic side elevation of the rear part of a bicycle embodying the invention; and Fig. 2 is a schematic partly sectioned plan view, to an enlarged scale, of the junction of a seat tube and a down tube of a frame of the bicycle of Fig. 1, showing the connection of a lower pivot link of a rear wheel suspension of the bicycle to the frame.

Referring now to the drawings there is shown part of a bicycle 10 comprising a substantially triangular frame 11 composed of a seat tube 12 carrying a seat (not shown) at an upper end, a crossbar 13 connected at one end with the seat tube and at the other end with a short handlebars sleeve (not shown) for a handlebars shaft with front wheel forks, and a down tube 14 connected at one end with the seat tube 12 and at the other end with the handlebars sleeve.

The bicycle 10 further comprises a rear suspension 15 composed of a triangular swing arm 16 and first and second pivot links 17 and 18 connecting the swing arm 16 with the frame 11 to form therewith a four-bar linkage, the four elements of which are thus formed by the arm, the two pivot links and the frame. The swing arm 16 at one corner thereof carries a wheel 19 (shown only in part) by way of a wheel hub 20 and is composed of two triangular wheel carrier frames (only one visible in the drawing) arranged on either side of the wheel and connected together in fixed relationship. The wheel hub 20, more particularly an axle spindle of the hub, provides connection of the carrier frames at that corner of the arm 16.

Drive is transmitted to the rear wheel 19 by way of a chain-and-sprocket transmission comprising a chain 21 extending around and meshing with a rear sprocket (not shown) at the rear wheel hub 20 and with a front sprocket 22 mounted on the frame 11 to be rotatable about an axis 23 of rotation. The axis 23 is defined by an axle 24 which is fixed to the front sprocket 22 and rotatably received in a bore provided at the junction of the seat and down tubes, for example the bore of a short transverse tube 25 to which the seat and down tubes are both fixed. At its extremities, the axle 24 carries rider-operated pedal cranks (not shown) by which drive is introduced into the transmission and translated into rotation of the rear wheel. In this connection, the transmission can include, at the rear wheel hub 20, multiple different-diameter rear sprockets selectably engageable with the chain 21 in dependence on the desired transmission ratio of the transmission. Geared transmissions inclusive of pedal drive are conventional bicycle components and are generally supplied by specialist manufacturers as proprietary parts for use by bicycle constructors.

The first or upper pivot link 17 is pivotably connected with the frame 11 at the seat tube 12 and with the swing arm 16 at the upper one of its other two corners. The second or lower pivot link 18 is pivotably connected with the frame 11 at the junction of the seat and down tubes 12 and 14 and with the swing arm 16 at the lower one of its other two corners. The pivot links 17 and 18, which are able to be kept short in length, are then disposed one above the other at a relatively substantial spacing represented by the length of one side of the triangle defined by the arm.

As shown in the drawing, the first pivot link 17 is oriented to extend forwardly and downwardly from the swing arm 16 and the second pivot link 18 forwardly and upwardly from the swing arm. The two links thus extend convergently in direction away from the swing arm and, in particular, at such angles relative thereto that the instantaneous pivot centre 26 of the swing arm -as defined by the intersection of two axes each containing the pivot points of a respective one of the links -on travel of the swing arm 16 from a first end setting in an unloaded state of the rear suspension 15 to a second end setting in a loaded state of the suspension moves downwardly and rearwardly with respect to the fore and aft direction of the bicycle 10, thus has the locus 27 shown in the drawing. The suspension setting shown in the drawing approximately represents a partly loaded state as adopted when the bicycle carries the weight of rider and is thus deflected from its first end setting.

This geometry of the rear suspension has the result that the rate of movement of the instantaneous pivot centre 26 reduces along its locus in the rearward and downward direction.

The first pivot link 17 consists of two parallel spaced-apart bars (only one visible in the drawing) and is connected with the frame 11 by way of a dedicated bracket 28 provided at a side of the seat tube 12 facing the front end of the bicycle. The two bars of the link 17 pass either side of the seat tube and are pivotably connected to the bracket 28 by a single continuous pivot pin 29. Pivot connection of the two bars with the swing arm 16 is preferably by way of two separate coaxial pivot joints 30 (only one visible in the drawing) each respective to one of the bars, but can be by way of a single continuous pivot pin if there is no overlap of the arm 16 -in particular the carrier frames constituting the arm -towards and in the upper end setting of the suspension 15.

The second pivot link 18 can similarly consist of two parallel spaced-apart bars or, since it does not have to. accommodate the seat tube 12, a single integral or assembled component, which has a bifurcated end remote from the wheel 19 to define two spaced-apart end portions. Each of these end portions of the component or each of two corresponding end portions of the bars is, for example, formed with an eye which fixedly receives a sleeve 31 extending between the two end portions and rotatably mounted in the transverse tube 25 at the junction of the seat and down tubes 12 and 14. The sleeve 31 in turn rotatably receives the axle 24, which carries the front sprocket 22 and pedal cranks (not shown) outboard of the end portions of the link. The second pivot link 18 is thus mounted on the bicycle frame 11 to be pivotable about the axis 23 defined by the axle 24 of the chain-and-sprocket transmission and effectively shares the mounting location of the sprocket 22 of the transmission. This eliminates the need for a dedicated mounting point such as the bracket 28 provided for the first link 17. The provision of eyes in the end portions of the second link 18 and engagement of the fixed connecting sleeve 31 in the eyes is merely by way of example; other forms of pivot connection are possible, including rotatable mounting of the link 18 directly on the axle 24 if an axle of suitable strength is provided or on protruding stubs of the transverse tube 25 if extended in length for that purpose. If so desired, plain, ball or roller bearings can be included in the pivot connection of the link. Removal of the link 18 from the frame -if there is a perceived need to provide for removal -can be carried out in various ways, for example, extraction of the axle and removal of the sleeve 31, if provided, after release of securing means securing the sleeve in the end portions of the link, or disassembly of the link if assembled from of several parts.

Fitting of the link can be carried out by a reverse procedure.

Finally, in order to provide sprung and damped movement of the rear suspension 15 the bicycle 10 includes a spring and damper unit 32 acting between the suspension and the bicycle frame 11 and arranged in a location optimising use of available space, in particular in the area bounded by the seat tube 12, crossbar 13 and down tube 14. The unit 32 is pivotably connected at its lower end with the frame 11 at a brace or gusset extending between the seat and down tubes and at its upper end with the swing arm 16 by way of a pull/push rod 33, which can be of double-bar construction similar to the first pivot link 17 and which shares the pivot joints 30 connecting the link 17 with the arm 16. Movement and location of the unit 32 are further assisted by a control arm 34 pivotably connected with the upper end of the unit 32 and with the bracket 28, the control arm sharing the pivot connection, in particular that provided by the pin 29, of the link 17 with the bracket. The spring and damper unit 32 advantageously has a rising rate, under movement of the swing arm from the first to the second end setting, as a result of the locus 27 of the instantaneous pivot centre 26 and the reducing rate of movement of that centre 26 in downward and rearward direction.

Other orientations and forms of mounting the spring and damper unit 32 are, however, possible, including attachment at one end to the crossbar 13 rather than to the brace or gusset between the seat and down tubes.

Fig. 2 shows, in half section, a plan view of the junction of the seat tube 12 and down tube 14 of the frame 11, inclusive of the transverse tube 25 and the sleeve 31 rotatably mounted therein, in this instance by way of two spaced-apart ball bearings 35. The sleeve 31 is connected, in a manner secure against relative rotation, with the lower pivot link 18, here in the form of two bars provided at their ends remote from the sleeve with eyes accommodating bearings (not shown) in which a pivot pin (denoted by axis 36) connecting the bars with the swing arm 16 is received. The bars are partly recessed in the tube 25 and emerge through cut-outs therein each extending over an arc at the side of the tube facing the swing arm. The sleeve 31 has at each end an internal thread threadedly engaged with a conventional plug 37 which houses a bearing 38 rotatably mounting the axle 24. The sleeve 31 is usable with a proprietary assembly of plugs 37 and axle 24, which confers significant cost benefits in the manufacture of the bicycle.

A bicycle embodying the present invention combines the advantages of a four-bar linkage rear suspension with a suspension construction which can be relatively light and economic, in particular by use of a triangular form of swing arm in conjunction with pivot links which in part share the mounting location of elements of the rear wheel drive transmission.

Claims

CLAIMS1. A bicycle comprising a frame with a seat tube and with a down tube connected with the seat tube at a junction, and a rear wheel suspension comprising a substantially triangular swing arm carrying a rear wheel at one of the three corners of the arm and two pivot links which are each pivotably connected with the arm at or in the region of a respective one of the other two corners thereof and which couple the arm with the frame to form therewith a four-bar linkage, a first one of the pivot links being pivotably connected with the frame at the seat tube and the second one of the pivot links being pivotably connected with the frame at the junction of the seat and down tubes.
2. A bicycle as claimed in claim 1, comprising drive transmission means for transmitting drive to the rear wheel, the drive transmission means being rotatable about an axis of rotation at the junction of the seat and down tubes and the second one of the pivot links being pivotable about the axis.
3. A bicycle as claimed in claim 2, wherein the drive transmission means comprises an axle defining the axis of rotation and the second one of the pivot links is pivotably connected with the frame by connecting means concentric with the axle.
4. A bicycle as claimed in claim 3, wherein the connecting means comprises a sleeve rotatable relative to both the axle and the frame.
5. A bicycle as claimed in claim 4, wherein the second one of the pivot links has two spaced-apart end portions each connected with the sleeve at a respective end thereof.
6. A bicycle as claimed in claim 5, wherein the end portions define eyes receiving the sleeve.
7. A bicycle as claimed in claim 6, comprising securing means releasably securing the sleeve in the eyes.
8. A bicycle as claimed in claim 3, wherein the connecting means comprises two spaced-part bearings mounted on the axle.
9. A bicyde as claimed in any one of the preceding claims, wherein the first one of the pivot links comprises two parallel spaced-apart bars receiving the seat tube therebetween.
10. A bicycle as claimed in claim 8, wherein the bars are connected with the frame by a single continuous pivot pin.
11. A bicycle as claimed in any one of the preceding claims, wherein each of the pivot links extends tram the arm in a direction away from the rear wheel:
12. A bicycle as claimed in any one of the preceding claims, wherein the arm is movable between a first end setting in an unloaded state of the suspension and a second end setting in a loaded state of the suspension, the first one of the pivot links being oriented in a use position of the bicycle downwardly in a direction away from the arm.
13. A bicycle as claimed in any one of the preceding claims, wherein the arm is movable between a first end setting in an unloaded state of the suspension and a second end setting in a loaded state of the suspension, the second one of the pivot links being oriented in a use position of the bicycle upwardly in a direction away from the arm.
14. A bicycle as claimed in any one of the preceding claims, wherein the arm is movable between a first end setting in an unloaded state of the suspension and a second end setting in a loaded state of the suspension, the pivot links being so arranged that on movement of the arm from the first to the second end setting an instantaneous pivot centre defined by the intersection of two axes each containing the pivot fulcra of a respective one of the links moves downwardly and rearwardly with respect to a fore and aft direction of the bicycle.
15. A bicycle is claimed in any one of the preceding claims, wherein the arm comprises two substantially triangular spaced apart frames connected together in fixed relationship and disposed on either side of the rear wheel.
16. A bicycle as claimed in claim 15, wherein the frames of the arm are connected together at a hub of the rear wheel.
17. A bicycle as claimed in claim 15 or claim 16, wherein the frames of the arm are connected together at the location of the second one of the pivot links.
18. A bicycle as claimed in any one of the preceding claims, comprising a spring and damper unit acting between the suspension and a frame and arranged to urge the swing arm into an end setting and to damp movement of the arm out of that setting.
19. A bicycle as claimed in claim 18, wherein the spring and damper unit is arranged in the frame in a space bounded at least in part by the seat tube, the down tube and the crossbar.