The present invention relates to a drive mechanism particularly for use in rotary drive systems.

Technical Field

The invention is to be applied to rotary drive systems in which a driven member such as for example a wheel, a propeller, a rotatable blade and other forms of apparatus are intended to be driven for rotatory movement from a remote remote manual driving means. The driving means may consist for instance of a handle or handles or pedals which are linked by transmission means to the driven member so that rotation of the driving means will result in rotation of the driven member. A specific application of the rotary drive system is in relation to a pedal driven conveyance such as a pedal bicycle or tricycle.

The driven member is generally arranged to be driven from a remote location by a transmission means such as a drive belt or a chain which passes over a belt pulley or sprocket attached to the driven member and over a driving pulley or sprocket so journalled that the drive pulley sprocket can be manually turned by pressure exerted by the legs or arms of the operator. In many instances it is desirable to vary the ratio of the speed of rotation of the driven member to that of the drive pulley or sprocket for the purpose either or increasing the speed of rotation of the driven member in relation to the drive pulley or sprocket or of decreasing the speed and thereby allowing an increased torque to be applied to the driven member. Various means as are known in the art are employed for this purpose. One such means comprises a series of stepped pulleys of varying diameters where the transmission means is in the form of a flexible belt or a series of stepped sprockets of varying diameters where the transmission means is in the form of a chain.

In the case of a pedal conveyance such as a bicycle, the speed varying means generally consists of a series of sprockets of varying diameters fixed to the driven wheel and a series of drive sprockets of varying diameters so that the link means which is generally a chain, can be moved to mesh with a selected pair of sprockets to obtain the

1 -

optimum speed of rotation of the driven wheel in relation to the drive sprocket.

While it is possible to improve the torque applied to the driven member by means such as that hereinbefore described, nevertheless it is highly desirable that means be provided so that the amount of torque can be increased to an optimum value by means other than the known gear multiplication ratios.

Object of the Invention

It is therefore an object of this invention to provide an improved drive mechanism for a rotary drive system of the kind described.

Disclosure of the Invention

Accordingly, one form of the invention comprises a drive mechanism for a rotary drive system of the type described including a driven member having a hub and a rim substantially coaxial with and supported by said hub, said hub being adapted to be journalled to a frame to allow rotation of the driven member in relation to the said frame, characterised in that the driven member includes:

a transmission hub co-axial with said hub.

at least two transmission cables each having one end anchored to said transmission hub to extend radially from said transmission hub at a position approximately 180° opposite each other,

a pulley block fixed to said rim substantially opposite the point of connection of the each said transmission cable to the said transmission hub,

a guiding sheave journalled within each said pulley block,

a guide attached to said rim at a position substantially equidistant between each said pulley block, and

wherein each transmission cable extends from its point of connection to the transmission hub, over the guiding sheave within the said pulley block radially opposite the said point of connection, the said transmission cable extending from the said pulley block towards the next contiguous pulley block in a direction opposite that in which the driven member is to be rotated and wherein the distal end of the transmission cable is anchored to said contiguous pulley block,

means being provided to pre-tension the said transmission cable.

Brief Description of Drawings

Fig. 1 is a side view in a partly diagrammatic form of a driven wheel which includes the preferred form of drive mechanism;

Fig. 2 is a diagrammatic partially sectional view along the line 2 - 2 of Fig. 1;

Fig. 3 is a diagrammatic view of a detail, and

Figs. 4a and 4b are diagrammatic views of further details.

Best Mode of Carrying out the Invention

A typical wheel such as the rear wheel of a pedal bicycle is indicated in Fig. 1 and comprises a rim 2 mounting a pneumatic tyre 3 and having spokes (not shown in the drawings) which may be of a conventional construction and which radiate from a central hub 5 which is journalled for rotation about an axle 4. When the wheel is for use with a pedal bicycle the axle 4 will be mounted on a suitable bicycle frame (not shown in the drawings) as is known in the art. Drive sprockets 6 which may be single or multiple sprockets as indicated in the drawings are also journalled to the axle 4. Since the hub 5 is free to rotate on the axle 4 then the whole wheel with the drive sprockets 6 may also freely rotate on the said axle.

In accordance with the present invention, in addition to the spokes, the drive from the sprockets 6 is transmitted to the rim 2 of the wheel by means of a transmission cable

12 and associated apparatus which together will provide a variable mechanical advantage through the force transmitted to the wheel according to the resistance to the rotation of the wheel which in the case of a bicycle would be provided by the load being carried on the bicycle, the gradient being climbed and so forth.

Preferably the drive mechanism utilizes four transmission cables 12 as indicated in Fig. 1 together with their associated apparatus and while this is the highly preferred number the invention encompasses any other desired number of combined transmission cable and associated apparatus.

As shown in the drawings, the transmission cables 12 lie in a notional radius of the wheel extending from around the central axis thereof to the rim 2. One end of each transmission cable 12 is suitably anchored to a transmission hub 15 which is connected to the sprockets 6 so that when the drive sprockets 6 are rotated then the transmission hub 15 will also rotate.

Each transmission cable 12 is adapted to cooperate with a pulley block 13, shown more particularly in Fig. 4a. Each pulley block 13 has arms 25 which when the mechanism is to be applied to a bicycle wheel is formed with an attachment means such as that indicated at 25a which will clamp over the rim 2 of the wheel to locate and fix the pulley block on the rim. Suitable means (not shown in the drawings) are provided to maintain the arms 25 of the pulley block 13 clamped to the rim 2. Each pulley block 13 includes a main sheave 20 (see Fig. 3), a guiding sheave 21 and an anchor point 22. Both the main sheave 20 and the guiding sheave 21 are journalled so they may freely rotate in the pulley block 13.

As can be seen from the drawings, the transmission cable 12 extends from the hub 15, around the main sheave 20 and over the guiding sheave 21 of a first pulley block 13 and has its distal end 12a anchored to the anchor 22 of a second anchor block 13. For this purpose a terminal hook 24 (see Fig. 3) may be attached to the anchor point 22 so that the distal end 12a of the transmission cable can be readily anchored so the pulley block 13. The transmission cable 12 passes through a suitable guide 29 which may also

be attached to the rim 2, the guide having arms 31 which support guide pins 30 so that the cable can pass between two guide pins in the guide block. As can be seen particularly from Fig. 2, the transmission cable 12 is attached to the hub 15 at a point approximately 90° from a notional line drawn between the axle 4 and the sheave 20 over which the transmission cable passes. If the wheel as shown in Fig. 1 is intended to rotate in an anticlockwise direction, then the point of attachment of the transmission cable 12 to the hub 15 is offset 90° in an anticlockwise direction.

Each transmission cable also includes a tensioning device 17 which will act to provide the desired degree of tension to the transmission cable 12. The tensioning device 17 can consist for instance of any suitable means as is known in the art which will be able to exert the desired static tension to the transmission cable 12. In a highly preferred form of the invention the tensioning device 17 may include suitable screw adjustment connectors such as those indicated at 18 in Fig. 1. The transmission cable 12 may consist of two parts, one part 12a extending between the transmission hub 15 and one end of the tensioning device 17 and the other end extending between the tensioning device and the termination at the distal end 12a.

When rotary force is applied to the drive sprocket, this is transmitted through the hub via the spokes to the rim 2 and also through the hub 15 via the transmission cables 12 to the rim 2 of the wheel. The turning moment of the hub 15 will introduce an additional tension on the transmission cables 12 which as before described are anchored at points offset from the axis of the drive sprocket 6. This particular arrangement will provide a mechanical advantage which will induce a further tension which is transmitted to the rim 2 of the wheel to cause rotary movement thereof. The wheel is thus pulled in the direction of rotation when the tension in the cable reaches a threshold level which is dependent on the load on the bicycle, the gradient of the hill being climbed and other factors as will be apparent.

By reason of the drive mechanism of this invention the rotary motion of the driving sprocket 6 is relatively efficiently transmitted by means of a generally tangential pull on the wheel rim 2. Furthermore, since the tension on the transmission cable will

result in slight extension of the cable this will provide a lag between the turning of the drive sprocket 6 and the turning of the wheel thereby effectively providing a variable ratio gearing of the bicycle.

For foregoing describes the invention including preferred forms thereof. Variations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof as defined in the appended claims.