GB2288156A

GB2288156A - Cycle drive mechanism

Info

Publication number: GB2288156A
Application number: GB9507071A
Authority: GB
Inventors: Paul John Butterworth
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-04-05
Filing date: 1995-04-05
Publication date: 1995-10-11
Anticipated expiration: 2015-04-05
Also published as: GB9406607D0; GB9507071D0; GB2288156B

Abstract

A cycle drive mechanism includes a cam 2 which rotates with a crank arm 8 and a cam follower 3 urged into engagement with the cam 2 by a spring 10 which acts as an energy storage means. The drive mechanism enables the cycle to be ridden by a disabled person having only one effective leg. During a downward movement by the effective leg, rotation of the cam 2 results in the transfer of energy to the spring 10, which then replaces energy during the subsequent rotation to ensure completion of a cycle of rotary movement of the cam 2 and crank arm 8. <IMAGE>

Description

CYCLE DRIVE MECHANISMS Field of the Invention This invention relates to cycle drive mechanisms.

Bicycles and tricycles are the most common types of human-powered vehicles. In one basic forms power i8 transmitted through a pedal and crank arm with sprocket attached via a chain to a final drive sprocket fixed to the rear wheel. This is known as a fixed wheel drive, where the pedal and crank arm are in constant rotation when the cycle is in motion.

More sophisticated forms of drive train use two or three sprockets at the front of the drive train and six or seven sprockets fixed to a freewheel at the rear. The chain is derailed at the front or rears thus obtaining the required drive ratio, using a system of deraileur mechanisms. The freewheel sprockets mounted on the rear wheel allow the cycle to continue moving forwardly without pedalling.

At present, a disabled person, who has the loss or restricted use of either leg, can only use a fixed wheel drive arrangement as described above. An obvious disadvantage of the fixed wheel drive i8 that no gears are available and the drive ratio is fixed.

It is accordingly an object of the present invention to provide an improved cycle drive mechanism which can be used by a disabled person and is such that a gear change facility can be obtained.

It is a further object of the present invention to provide a method of adapting a cycle so that it can be used by a disabled person.

Summary of the Invention According to a first aspect of the present invention there is provided a cycle drive mechanism which includes a crank arm, a cam having a profiled cam surface and arranged for rotation with the crank arm, a cam follower arranged in engagement with the cam surface and energy storage means acting on the cam follower urging it into engagement with the cam surface, with the arrangement such that, during a part of the rotary travel of the cam under torque applied by means of the crank arm, energy is stored in said energy storage means whereas, during another part of the rotary travel of the cam, the energy required to effect such rotary movement is supplied by the energy storage means.

The energy storage means is preferably a spring which acts, either directly or indirectly, to urge the cam follower into engagement with the cam surface. The arrangement is preferably such that, during movement of the crank arm from a tOp dead centre position to a bottom dead centre position, the cam follower is urged progressively radially outwardly away from the axis of the cam to increase the amount of energy stored in the spring. The cam and crank arm preferably continue rotating beyond the bottom dead centre position initially under their own momentum and then with the added impetus of the energy supplied by the spring.

The spring may be, for example, a leaf spring one end of which is fixed to the cycle frame and the other end of which is connected to the cam follower. Alternatively, the spring may act between an anchor point on the frame and a cam follower arm on which the cam follower is mounted, the cam follower arm being pivotally mounted on the frame at a position spaced from the spring anchor point. As a further alternative the spring may be a compression spring arranged to act radially of the axis of rotation of the cam, the spring being contained within a housing fixed to a part of the cycle frame. The direction of action of the spring may be arranged to coincide substantially with either the axis of the seat tube of the cycle frame or the axis of the down tube of the cycle frame.

According to a second aspect of the present invention there is provided a method of adapting a cycle to render it suitable for use by a disabled person, said method including the fitment to the cycle of a drive mechanism as defined above.

Brief Description of the Drawings Figure 1 is a diagrammatic illustration of a first form of cycle drive mechanism showing the positions occupied by the components of the drive mechanism in an initial position, Figures 2, 3 and 4 show the drive mechanism of Figure 1 in positions turned 90 , 180 and 270 from the initial position, Figure 5 shows the principles of operation of a second form of drive mechanism, Figure 6 shows some of the components of the mechanism of Figure 5, Figure 7 shows the principles of operation of a third form of drive mechanism, Figure 8 shows some of the components of the mechanism of Figure 5, Figure 9 shows the principles of operation of a fourth form of drive mechanism, Figure 10 shows some of the components of the mechanism of Figure 9, Figure 11 shows a free crank arm for use with any of the drive mechanisms of Figures 1 to 10, and Figure 12 shows the drive mechanism of Figures 1 to 4 mounted on a cycle.

Description of the Preferred Embodiments The drive mechanism shown in Figures 1 to 4 comprises a cam 2 with a central aperture so that it can be fitted over the drive axle 15 of a sprocket drove system of a cycle. The cam 2 is formed with five equi-angularly spaced holes 1 located at a uniform spacing from the axis of the drive axle 15 and the cam 2 i8 connected to the inner sprocket 22 of the sprocket drive system by means of spacers 14 so that the cam 2 rotates with the inner sprocket 22 which forms part of a gear-change mechanism and i8 arranged for cooperation with a chainset 21.

The spaced holes 1 may be replaced by equi-angularly spaced slots (not shown) so that timing adjustment may be obtained.

A crank arm 8 carrying a pedal (not shown) is fixed to the axle 15 so that rotation of the drive system can be obtained with the crank arm 8 moving through 360 during a cycle of operations from the top dead centre position shown in Figure 1 via the positions shown in Figures 2, 3 and 4 back to this top dead centre position.

The axis of rotation of the drive axle 15 is located at the junction between the centre line of the seat tube 12 of the cycle frame and the centre line of the inclined frame tube 11.

The centre line of the cycle chain stay 13 extends rearwardly from this axis, the direction of forward movement of the cycle being represented by the arrow 20 in Figure 1.

The cam 2 has an external profile which is engaged by a circular cam follower 3, which may be in the form of a disc rotatably mounted on a cam follower arm 4 which is pivotally mounted on the frame tube 11 for pivotal movement relative thereto about an axis 7. The cam follower 3 thus moves radially of the axis of the cam 2 in the direction indicated by the arrow 5 during rotation of the cam 2 as a result of pedalling movement of the crank arm 8 as it moves from its initial position shown in Figure 1 which is approximately the position at which a downward pedalling movement is commenced.

A helical spring 10 acts on the cam follower arm 4 to urge the cam follower 3 continuously into engagement with the cam profile of cam 2. The spring 10 is connected at its one end to a fixed anchor point located beneath the axis of the axle 15 and is connected at its other end to a movable anchor point 9 on the cam follower arm 4.

As the user of the cycle applies downward foot pressure on the pedal, the crank arm 8 is rotated about the axis of axle 15 to transmit drive to the cam 2 and to the sprocket assembly.

The cam 2 is thus turned into the position shown in Figure 2 displaced 90 from the position shown in Figure 1. As will be seen, the cam follower 3 has been displaced radially outwardly in the direction indicated by the arrow 5, the cam follower arm 4 has been pivoted in a clockwise direction about the pivot axis 7 and the spring 19 has been extended, placing it under tension and, in effect, storing energy in the spring 10.

As pedaling continues and the cam 2 is turned through a further 90 , the position shown in Figure 3 will be reached, in which the cam follower 3 is in substantially the same radial position as was shown in Figure 2. No additional energy will be stored in the spring 10 and the whole of the applied effort will be used for providing forward motion of the cycle.

At the completion of the downward stroke of the pedal, the crank arm 8 and the cam 2 will tend to continue to rotate under their own momentum. Once thé position shown in Figure 3 has been passed, the cam follower 3 is in engagement with a part of the cam profile which is of steadily reducing radial extent. The action of the spring 10 will thus assist continued rotary movement of the cam 2 and the crank arm 8.

The initial position shown in Figure 1 can be regarded as a top dead centre position, and the position shown in Figure 3, in which the cam 2 and the crank arm 8 have been turned through 180 , can be regarded as a bottom dead centre position.

The stored energy in the spring 10 will continue to be converted into rotary movement of the cam 2 and the crank arm 8 as the cam 2 completes a cycle of rotation and moves via the position shown in Figure 4 back into the position shown in Figure 1. In this position, the spring 10 is in a condition of minimum stored energy, i.e. the energy transferred to the spring 10 during the downward stoke of the pedal has now been utilised to effect rotary movement of the cam 2 and the crank arm 8 about the axis of the drive axle.

Gear change operations can be effected in the normal way and are not affected by the provision of the cam 2 adjacent the inner sprocket 22.

In the arrangement shown in Figures 1 to 4, the cam follower 3 moves substantially horizontally between its radically innermost and radially outermost positions and the spring means is a torsion spring. In the first alternative arrangement shown in Figures 5 and 6, the cam follower 3 is in the form of a wheel mounted on a shaft 24 which projects from a housing 25 connected by means of a bracket (not shown) to the seat tube 12. The housing 25 contains a compression spring 10 or an elastomer and/or a hydraulic damper so that, as the cam follower 3 is displaced upwardly during the downward 9 toke of the pedal, energy is stored in ths spring 10 or its equivalent and thus stored energy is then applied, as described above in relation to Figures 1 to 4, to effect continued rotary movement of the cam 2 and the crank arm 8.

Figures 7 and 8 show a further arrangement which includes a follower wheel 3 urged upwardly into engagement with the profiled surface of the cam 2. The spring means is, in this case, a leaf spring 10, one end of which carries the cam follower 3 and the other end of which is attached by mesons of an attachment bracket 26 to the chain stay frame member 13. The mode of operation of the mechanism will again be as described above in relation to Figures 1 to 4.

Figures 9 and 10 show a still further arrangement in which the cam follower 3 is in the form of a wheel carried on a shaft 28 which is acted upon by spring means 10 (again in the form of a compression spring, an elastomer or a hydraulic damper) contained within a housing 27 fixed by means of a bracket (not shown) to ehe inclined down tube 11 of the cycle frame. The mode of operation of the mechanism will again be as described above in relation to Figures 1 to 4.

A standard crank arm 8 is mounted at the end of the drive axle 15 corresponding to the effective leg of the user of the cycle and a free wheel crank ars 30 (as shown in Figure 11) is mounted on the other end of the drive axle. The free wheel crank arm 30 includes a portion 31 to which a pedal is attached and a portion 32 which contains a bearing for fitment on the drive axle so that, in use, the free wheel crank arm 30 will not rotate with the drive axle 15 but will extend downwardly from the axle 15 so as to provide support for the non-effective leg of the user.

It will thus be seen that the present invention provides a cycle drive system which can be used by a person with one disabled leg and that the amount of modification to an existing cycle is minimal.

Claims

Claims: 1. A cycle drive mechanism which includes a crank arm, a cam having a profiled cam surface and arranged for rotation with the crank arm, a cam follower arranged in engagement with the cam surface and energy storage means acting on the cam follower urging it into engagement with the cam surface, with the arrangement such that, during a part of the rotary travel of the cam under torque applied by the crank arm, energy is stored in said energy storage means whereas, during another part of the rotary travel of the cam, the energy required tO effect such rotary movement is supplied by the energy storage means.
2. A drive mechanism as claimed in Claim 1, in which the energy storage means is a spring.
3. A drive mechanism as claimed in Claim 2, in which the arrangement is such that, during movement of the crank arm from a top dead centre position to a bottom dead centre position, the cam follower is urged progressively radically outwardly away from the axis of the cam to increase the amount of energy stored in the spring.
4. A drive mechanism as claimed in Claim 2 or Claim 3, in which the spring is a leaf spring, one end of which is fixed to the cycle frame and the other end of which is connected to the cam follower.
5. A drive mechanism as claimed in Claim 2 or Claim 3, in which the spring acts between an anchor point on the frame and a cam follower arm on which the cam follower is mounted.
6. A drive mechanism as claimed in Claim S, in which the cam follower arm is pivotally mounted on the frame at a position spaced from the spring anchor point.
7. A drive mechanism as claimed in Claim 2 or Claim 3, in which the spring i8 a compression spring arranged to act radially of the axis of rotation of the cam.
8. A drive mechanism as claimed in Claim 7, in which the spring is contained within a housing fixed to a part of the cycle frame.
9. A cycle drive mechanism substantially as hereinbefore described with reference to and as shown in Figures 1 to 4 and 12 of the accompanying drawings.
10. A cycle drive mechanism substantially as hereinbefore described with reference to and as shown in Figures 5 and 6, or Figures 7 and 8, or Figures 9 and 10 of the accompanying drawings.
11. A method of adapting a cycle to render it suitable for use by a disabled person, said method including the fitment to the cycle of a drive mechanism as claimed in any one of the preceding claims.