WO2000059770A2

WO2000059770A2 - Bicycle suspension system

Info

Publication number: WO2000059770A2
Application number: PCT/GB2000/001106
Authority: WO
Inventors: Iain Lawson
Original assignee: Sharpworth Limited
Priority date: 1999-04-01
Filing date: 2000-03-31
Publication date: 2000-10-12
Also published as: AU3564900A; WO2000059770A3; GB9907615D0

Abstract

A bicycle suspension system located between the cyclist's feet and the bicycle frame (2) and associated with the crank assembly. This suspension system is only active when the cyclist's weight acts in a direction opposite to the drive direction on one pedal, counter balancing the weight on the other pedal. Thus in travel over rough terrain where the cyclist adopts a stance on the bicycle such that both feet are equally weighted with the crank arms (5) in an approximately horizontal orientation the system will be active. Whilst pedalling the system is inactive and does not compromise the rigidity of the drive transmission.

Description

BICYCLE SUSPENSION SYSTEM

The present invention relates to a bicycle suspension system.

Bicycle suspension systems are known which are used to isolate the rider from shocks resulting from travel over uneven terrain. The two main types are front and rear wheel suspension.

Front suspension systems can be fitted to existing bicycles by replacing the front forks with ones incorporating a suspension system that generally consists of a spring/damping arrangement. The front wheel is therefore able to move, in a controlled manner relative to the frame.

Rear suspension systems are generally made by replacing the rear end of a conventional bicycle with a swing arm arrangement that pivots about some point in the general location of the crankshaft. The rear wheel being thus isolated from the frame is then free to have its movement controlled via a spring/damping arrangement as above. It is common for bicycles to be provided with either, both or indeed no suspension. There are advantages and disadvantages of each arrangement.

Problems associated with rear suspension systems are that the bicycle geometry becomes far more complex and as a result undesirable weight is added. On a vehicle where motive power is provided by the rider excess weight is particular undesirable. Furthermore, the motive force exerted by the chain can tend to pull the suspension into compression with a resultant loss of power. As a result of these points, rear suspension systems are not fitted to the majority of bicycles as the benefits gained on the downhill sections are outweighed by the penalties on the uphill sections. Racing bicycles in particular cannot afford to carry excess weight or have power wasting drive arrangements.

The first aim of the present invention therefore is to provide a bicycle suspension system which provides useful suspension characteristics but minimises the loss of power and weight penalty associated with prior art rear suspension systems.

Front suspension systems also have disadvantages that they provide a weight penalty and although the suspension movement reduces jarring to the rider's hands there may be a penalty in a loss of directness in the steering.

The shocks resulting from travel over uneven terrain are also absorbed through the cyclists legs, in the case of down hill travel over rough terrain, this is usually achieved by adopting a stance on the bicycle such that both feet are equally weighted with the crank arms in a approximately horizontal orientation.

Of course adopting this stance inevitably has a fatiguing effect on the rider. Therefore it is a further aim of the present invention to provide a suspension system which meets the first aim while taking into account this typical riding posture.

According to the present invention, there is provided a bicycle suspension system comprising a resilient biasing means associated with the crank mechanism such that relative movement occurs between the crank mechanism and the associated drive when force, greater than the biasing force, is applied to a drive pedal in a direction opposite to the drive direction of that pedal.

Preferably, the resilient biasing means acts between each pedal and the respective crank arm.

Alternatively the resilient biasing means acts between the crank arm and the crankshaft.

Preferably the resilient biasing means comprises a tracked ball bearing arrangement biased by a spring mechanism.

More preferably the ball bearing arrangement transmits drive in one direction and allows relative movement, against the resilient biasing means, in the opposite direction.

Preferably also the resilient biasing means is adjustable. In order to provide a better understanding of the present invention an example will now be described by way of example only, and with reference to the accompanying Figures, in which :

Figure 1 illustrates shows a general view of a bicycle with an exploded view of the crank shaft & arms;

Figure 2 shows an isometric sketch of a first specific embodiment of the invention; and

Figure 3 shows a cross section of an alternative embodiment of the invention.

Referring to Figure 1 a bicycle is illustrated having a front fork arrangement 1 affixed to a frame 2 to which a rear fork arrangement 3 is in turn fixed. The bicycle has an axle 4 to which cranks 5 are affixed.

In the present invention one or both of the standard crank arms (5) are replaced with the arrangement of Figure 2 consisting of a modified crank arm (6) attached to the bicycle as per the standard crank arm (5) but in place of the pedal is a guide surface to guide the movement. A spring (7) is mounted such that a pre-load or biasing force exists holding it in place against the modified crank arm (6) until a force is exerted on it, acting in a direction opposite to the drive direction, that exceeds a predetermined amount, (nominally the static force exerted by the cyclist.) A pedal is mounted through the spring (7) to a retaining piece such that the guide surface of the crank arm (6) is straddled by the spring (7) and the retaining piece (8). The suspension thus provided is active when the cyclist is standing on the pedals with the crank arms in an approximately horizontal orientation. The suspension is thus below the foot to the rear of the bicycle, however the foot to the front is also incorporated as the two crank arms maintain their 180-degree relative orientation.

The bicycle is therefore able to move, in a controlled manner relative to the cyclist.

In a second arrangement, illustrated in Figure 3, the standard crankshaft arrangement is modified by splitting it into two pieces (10,11) with the torque being transmitted through the shaft via a number of ball bearings (12). This assembly is held together by an Allan type bolt (13) reacting against a stiff spring (14) and cir-clip (15). The bolt is accessed via the tapered hole in the crankshaft (as exists on standard crankshafts for attachment of crank arms) and locked in place with a grub screw (16) accessed similarly from the other side. Relative motion between the two pieces (10,11) is limited by both the pre-load in the spring (14) and the geometry of the retaining grooves shown in section X-X and Y-Y (Yl-Yl shows the pedalling configuration and Y2-Y2 shows the loaded or fully sprung configuration) . In use the modified crank shaft will behave as a solid shaft when transmitting drive forces, but will allow a limited amount of radial movement of (10) relative to (11) when the forces through it are such that all of the following criteria are satisfied:

a) the force exceeds a predetermined amount. b) the forces on each half of the crank shaft (10 & 11) act in opposite directions. c) the force on the half of the crankshaft that does not contain the chain sprocket is acting in a direction opposite to the drive direction.

The pre-load in the spring (14) and the geometry of the retaining grooves return the assembly to its original condition as the loading conditions dictate. One of the existing bearings is to be modified to allow for the small amounts of axial movement required as the ball bearings move up the ramped groove.

Pre-load can be adjusted to suit the individual cyclists weight by adjusting the bolt (13) and the systems stiffness altered to provide greater resistance at the end of the stroke by altering the geometry of the ramped groove.

Further modifications may be made within the scope of the invention herein intended.

Claims

1. A bicycle suspension system comprising a resilient biasing means associated with the crank mechanism such that relative movement occurs between the crank mechanism and the associated drive when force, greater than the biasing force, is applied to a drive pedal in a direction opposite to the drive direction of that pedal.

2. A bicycle suspension system as claimed in Claim 1 wherein the resilient biasing means acts between each pedal and the respective crank arm.

3. A bicycle suspension system as claimed in Claim 1 wherein the resilient biasing means acts between the crank arm and the crankshaft.

4. A bicycle suspension system as claimed in Claim 3 wherein the resilient biasing means comprises a tracked ball bearing arrangement biased by a spring mechanism.

5 A bicycle suspension system as claimed in Claim 4 wherein the ball bearing arrangement transmits drive in one direction and allows relative movement, against the resilient biasing means, in the opposite direction.

6. A bicycle suspension system as claimed in any of the preceding Claims wherein the resilient biasing means is adjustable. A bicycle suspension system substantially as hereinbefore described, with reference to and as shown in the accompanying drawings .