There are a number of items of machinery in which a crank is used. Common examples are the pedals of bicycles, winches, and reciprocating steam or internal combustion engines. During the use of a crank, there will be one portion of its rotation where the force acting upon the crank is a push, often assisted by the force of gravity, while during another portion of the rotation, force acting on the crank will be pulling it, often against the force of gravity.

This is particularly the case with pedal cycles and winches. There is, therefore, a need to provide a crank by means of which a greaterforce may be exerted during one portion of its rotation than during another.

The effect of this becomes particularly apparent when the action involved in riding a bicycle is considered. A major portion of the impulse to drive the bicycle comes from a downwardly exerted force, exerted by the leading leg of the cyclist when pedalling, so that the right and left legs of the cyclist alternately produce a downthrust while the leg not producing the downthrust is largely occupied in controlling the respective pedal while it completes its rotation to reach the position in which it, in its turn, can exert a propulsive downthrust. In principle, the total propulsive force could be increased by increasing the length of the crank bearing the pedal, but this has disadvantages with bicycles, in that the chain wheel would have to be raised higher to provide adequate ground clearance, while the cyclist must have

additional leg movement, with each of the cyclist's feet performing a motion in a circle of greater radius than would be the case with cranks of conventional length.

The present invention provides means for the conversion of a reciprocating force into rotary motion of a rotatable member about a rotary bearing, wherein said rotatable member has force-imparting means, located at a distance from said rotary bearing, by which the reciprocating force is applied to said rotatable member, the distance between said rotary bearing and said force- imparting means being variable within the course of one rotation, wherebythe moment of said reciprocating force may be varied while said rotatable member is rotating.

According to one embodiment, the rotatable member comprises a slot directed away from said bearing, and force-imparting means, is adapted to slide freely within said slot.

Another embodiment provides a crank comprising an elongated memberwith a rotary bearing at a first end, and with said slot extending longitudinally of said member towards a second end.

According to one embodiment, the elongated member and slot are essentially linear, whereby the slot effectively extends radially from the rotary bearing.

In an alternative embodiment, the elongated member and its slot may be curved over at least the outer section remote from the rotary bearing. In another embodiment, the above-mentioned curve may be a simple curve, or a more complex curve, such as one having an ogival form.

In another embodiment, a radially-symmetrical member, such as a disc, is provided with a slot having a first end and a second end, said first end being

nearer said rotary bearing than said second end. The slot may be linear or curved, as in the above-described crank.

According to further embodiments of the invention, the force-imparting member may be fixed, and the rotary bearing may be movable within a slot.

Alternatively, both the force-imparting means and the rotary bearing may be movable within respective slots.

In further embodiments, the crank may be a telescoping member, with elastic means forcing the ends together.

Afurther embodiment comprises means comprising a drive wheel for driving a chain or belt drive, and having rotary bearing at its centre, a cam surrounding said rotary bearing and fixed with respect to the support of the rotary bearing, and a crank rod extending radially of said drive wheel and having a longitudinal slit at its end remote from said rotary bearing, said cam and crank rod being rotatable with said drive, a movable transverse member for applying said reciprocating force, movable lengthways of said slit, and a push rod extending longitudinally of said crank, and bearing at one end on said cam, and on the other end on the transverse member.

Another embodiment comprises means comprising a drive wheel for driving a chain or belt drive, and having a rotary bearing at its centre, a cam surrounding the rotary bearing and fixed with respect to the support of the rotary bearing, a crank rod extending radially of said drive wheel, and bearing on said cam, a sleeve surrounding the inward portion of the crank rod and having a first stop member at its outer end and a second stop member closer to said rotary bearing than the first, and spring means between said first and second stop members, said cam, crank rod and sleeve being rotatable with said drive wheel.

To propel a bicycle, the main chain wheel may be provided with a pair of cranks according to the invention, or with a pair of radially symmetrical members. In each instance, pedals will be freely movable in the slots, the slots in the respective cranks or radially-symmetrical members being diametrically opposed to one another.

There are disclosed in GB 462,113 (Warren) and GB 2050971 (Parry) crank mechanisms intended for use in bicycles in which the effective crank length available to the user is varied as the bicycle cranks rotate.

In both of these prior-disclosed mechanisms the construction of the crank length adjustment mechanism leaves much to be desired in the sense that a substantial additional mechanism is provided in order to achieve the potential advantages of a varying crank length. Moreover, the adoption of the design approach of controlling the crank length by permanent internal sliding/meshing engagement of cooperating mechanical devices as disclosed in these prior patents has consequences not only in terms of unacceptable levels of frictional loss and/or unacceptable levels of routine maintenance (for a manually powered mechanism), but there is also (I have discovered) the associated loss of operational freedom, in terms of the non-availability of selective variation of crank length, which is a feature of certain embodiments of my invention.

An object of the present invention is to provide a method and apparatus applicable to pedal bicycles and like mechanisms in which improvements in relation to one or more aspects of the shortcomings of the prior art as discussed above are provided, or improvements generally.

In an embodiment of the invention described below, means is provided to allow the crank mechanism to permit more than one effective crank length at

least at some locations in the locus of travel of the crank, whereby the user is provided with, in some embodiments, an extremely simple user-controlled means for varying the crank length and with a minimum of frictional losses.

In other embodiments, means is provided to assist the user to adopt an optimum crank length at various positions in the locus of travel of the crank.

Such means comprises in some embodiments, spring means adapted to exert a spring effect tending to cause the adoption of at least an approximation to the optimal crank length at at least some positions in the locus of travel of the crank.

In other embodiments, profiled slot means is utilised to permit not only the varying of crank length but also (bythe adoption of an appropriate slot profile) there is also provided the means to promote adoption of the optimal (or an approximation thereto) crank length at at least certain positions in the locus of travel of the crank.

In yet other embodiments, alternative means for promoting the adoption of the appropriate crank length is provided including pneumatic, hydraulic, mechanical, electrical, or magnetic means, or combination of these.

In all embodiments of the invention where there is provided means to permit more than one effective crank length at at least certain positions in the locus of travel of the crank, the arrangement is such that the effect in the embodiment is at least equivalent to the provision of a slot in the crank permitting variation of the crank length whereby the user, whether with or without assistance is able at least partially to vary the crank length according to need or inclination or skill. Thus, in the simplest embodiments, which are intended for the more skilful and serious cyclists, the user is able to adopt a

pedaling regime which is particularly and skilfully adapted to the user's particular requirements.

A further aspect of the construction of the described embodiments relates to the fact that the extent of extension of the cranks of the mechanism may be under user control so that the user can exercise a degree of selection in relation to the length of the crank used at any given moment. Moreover, the embodiments allow for the degree of freedom of selection to be controlled in accordance with user needs.

In the embodiments, the maximum freedom of control of crank length is provided in those embodiments where the pedal or other device for applying thrust to the crank is freely slidable in a slot in the crank (or else the other end of the crank is likewise slidable in a slot). In this way the user can select with complete freedom the degree of variation of the crank length from its minimum length.

To assist the user to select correctly (or at least somewhat appropriately) the relevant length of crank for any given point in the locus of the crank travel, various means may be provided, these including the provision of non-linear slots with appropriate slot profile and attitude with respect to the direction of application of thrust by the user.

Alternatively there is provided resilient means tending to return the pedal or other thrust application device to a reference position (such as minimum crank length). Typically, the arrangement is such that the user's thrust applied to the crank causes resilient flexure of the resilient device as the point of application of thrust moves lengthwise of the crank so as to increase the effective length of the crank.

By means of such arrangements, the embodiments of the invention allow the user varying degrees of control of the crank length and thus of the torque applied to the bicycle chain wheel or related device.

The disclosure in the GB 2050971A (Parry) shows the provision of a cam track and follower facility for controlling crank length which has some merit in terms of its relative simplicity of construction as compared with the GB 462113 (Warren) specification's eccentric roller bearing race mechanism, but both share the limitation of providing operational characteristics which are unduly prescriptive in the sense that no option for variability of the crank length arises since the mechanism defines the exact degree of crank extension at any given point on the locus of crank travel.

Accordingly, it can be seen that there are significant difficulties in providing, for a variable-length crank mechanism of this kind, the degree of versatility of operation which modern practice in such areas requires.

Particularly in the case of bicycle manufacturers, there is a need to be able to offer controllable drive characteristics in a manner analogous to those offered by the ubiquitous gear change mechanisms for bicycle chain wheel drives. It will be readily appreciated that the provision of a variable crank system complementing a standard gear change mechanism would provide an attractive drive package but there is a need, at least for manufacturers, to be able to offer such with characteristics matching those of the bicycle type or category for which they are provided, whether racing or mountain or recreational etc, and such provides a technical challenge which has hitherto not been able to be met.

In certain embodiments of the present invention this need is met by the provision of interchangeable cam means offering at least two differing cam

profiles corresponding to crank extension and retraction profiles adapted to suit differing user requirements.

In the embodiments, the provision of resilient means adapted to cause cam profile-following for crank length control offers operating characteristics well adapted to the energy availability and other characteristics of non-motorised cycle usage.

By using the external surface of a rotary cam as the control means for crank extension and retraction, as opposed to the provision of a cam follower located in a profiled cam track, the embodiments offer the ability to provide the required degree of crank control without the energy consumption implications of a cam track system, and such is offered in combination with the facility (if required) to allow some degree of user-controlled departure from the predetermined cam-controlled operating characteristics (depending upon the spring characteristics used for maintaining cam and follower contact), if so desired.

The present invention will be further described with reference to the accompanying Drawings in which: Fig 1 shows a side elevation of one form of crank, Fig 2 shows a side elevation of an alternative form of crank, Fig 3 shows a side elevation of another alternative form of crank.

Fig 4 shows a plan view of a crank, Fig 5 represents a plan view of a crank with a pedal attached to it,

Fig 7 shows a view of a crank attached a chain wheel of a bicycle, Fig 7 shows the track of one foot of a cyclist while completing a rotation of the pedal and crank, Fig 8 shows a side elevation of another form of crank wherein the rotary bearing is movable within a slot, Fig 9 shows a side elevation of yet another form of crank wherein both the force-imparting means and the rotary bearing are movable within respective slots, Fig 10 shows a view of a crank of the embodiment of Fig 9, Fig 11 shows a further embodiment of the invention, Fig 12 shows a further embodiment of the invention, Fig 13 shows another embodiment of the invention with a disc-shaped rotatable member, Fig 14 shows another embodiment of the invention with a disc-shaped rotatable member and both the rotary baring and the force-imparting means being movable within slots, and Figs 15 and 16 show further embodiments where the distance apart of the rotary bearing and force-imparting means are controlled by means of a cam, located around the rotary bearing.

Figs 17 to 24 show a further embodiment illustrating the interchangeability of cam means provided for controlling cam length, Fig 17 showing a plan or elevation view of a bicycle crank mechanism including twin cranks connected by a shaft and each including means for varying the effective crank length in a manner similar to that of Figs 15 and 16; Fig 18 shows a side elevation view of one of the cam means of Fig 17, the direction of viewing being shown by arrow XVII in Fig 17; Fig 19 shows a corresponding view of one of the cranks and its associated cam means, the direction of viewing being indicated by arrow XIX in Fig 17; and Figs 20 to 25 show, in views similar to that of Fig 18, six variations in the profile of the cam means providing corresponding variations in the profile of the crank lengths produced during use of the mechanisms.

Referring now to the Drawings, Fig 1 shows one embodiment of a crank according to the invention. This crank [1] is provided with a rotary bearing [2] at one end and has a slot [3] extending towards the further end. A stop member [4] is provided at the end of the slot furthest from the rotary member [2]. The stop member is preferably provided with an impact absorbing means, comprising, for example, a spring, an elastic polymer such as rubber, or a hydraulic device.

Fig 2 shows an alternative embodiment of the crank according to the invention, in which the elongated member [1 a] and the slot [3] are curved over at least the outer portion of the crank.

Fig 3 shows another alternative embodiment of the crank, in which both the crank [1 b] and the slot are in the form of a complex curve.

Fig 4 shows a plan view of the crank [1] with the slot [3] and stop member [4], and a bore [5] adapted to fit the rotary member [2].

Fig 5 shows a crank in partial plan view with a pedal attached. From this, it will be seen that a transverse member [6] bearing a portion [7] such as a pedal adapted to provide driving force when the cycle is used, extends orthogonally of the crank and is retained within the limits [3a, 3b] of the slot by means of appropriate retaining members [8]. This transverse member [6] may, for example, be provided with an appropriate ball bearing or roller bearing in order to provide a smoother and easier movement along the extent of the slot from limit [3a] to limit [3b]. By means of this, when the pedal and its transverse member are in the forward position, extending to the limit [3b] of the slot, a greater force tangential to the crank, thereby producing a rotation about the bearing, will be exerted than would be if the pedal and its transverse member were at the rear end [3a] of the slot.

Fig 6 shows a schematic view of a crank attached to a chain wheel [9] of a bicycle. This wheel is shown only schematically since the teeth of the wheel, and the chain, will be of conventional type.

Fig 7 shows a plot of the orbit of a pedal sliding within the slot relative to the rotary bearing [2]. The orbit of a pedal of conventional fixed type [10] will be seen to be substantially a circle. The orbit [11] followed by a crank according to the invention, however, is very different since it deviates from the circle during the portion corresponding to an upward movement of the pedal, which and therebyfollows a shorter distance. Correspondingly, the cyclist will have to exert considerably less leg movement during each pedal stroke.

In its simplest form, e. g. when used in connection with a bicycle, it may be possible to have the transverse member and driving force e. g. bicycle pedals, movable with respect to the slotwithout specific means for moving the pedals other than the feet of a cyclist.

Fig 8 shows a straight crank [12] with a rotary bearing [14] provided with an adaptor [15] movable longitudinally of the slot [13]. An elastic means [16], comprising a spring, or pneumatic or hydraulic means is provided to control the sliding of the bearing within the slot. A fixed bore [17] is provided to take a pedal.

Fig 9 shows a variation of this embodiment in which the crank [12a] is curved and both the rotary bearing [14] and the pedal are movable within respective slots [13,3].

Fig 10 shows the orbit [18] for the embodiment of Fig 9.

It may be desirable to provide some alternative means of providing relative movement between the driving force and the crank. Such alternative means may include mechanical, electrical, magnetic, hydraulic or pneumatic mechanisms, as such or in combination.

Alternative embodiments of the invention are shown in Figs 11 and 12. In both, the cranks [19] are made of two sub-cranks telescoping one within the other. In the embodiment of Fig 11, the telescoping is controlled by the central arms [20] journalled to the ends of the crank and to one another, with spring means [21], or an equivalent thereof, forcing the link between the control arms away from the crank.

Alternatively as shown in Fig 12, the telescoping crank may be provided with an internal piston [22], with a spring [21] urging the ends of the crank together.

Figs 13 and 14 show alternative embodiments of the invention wherein the rotatable member is a disc [23,24] in which the slot [3a] is curved. It may, however, be a straight slot, radially directed from the bearing [2], as in the case of the above-described crank. In Fig 13, this is a fixed rotary bearing [2].

In Fig 14, the bearing [14] is movablewithin slot] 13], as described abovewith reference to Fig 9.

Figs 15 and 16 show constructions in which a drive wheel [28], for instance one adapted for a belt or chain drive, or which may be provided with teeth as members of a gear train, surround the rotary bearing. A cam [27] is also provided surrounding the bearing. In the construction of Fig 15, a crank having a slot at its outer end, extends radially from the wheel. The slot has a bearing [25] movable longitudinally within it for transmission of the reciprocating force to the crank. The bearing [25] can, for instance, form part of a pedal assembly, as shown in Fig 5. A push rod [26] extends longitudinally of the crank, which may for instance be in the form of a sleeve surrounding the push rod. One end of the push rod bears on the bearing [27], and the other end bears on the cam [27]. The cam is fixed with respect to the supports of the bearing, for instance, the frame in the case of a bicycle pedal assembly.

Consequently as the wheel [28], the crank and the push rod rotate with respect to the bearing support, the rod [27] and bearing [25] are able to follow the contour of the cam, the bearing [25] moving along the slot.

In the embodiment of Fig 16, the crank [29] is provided with a bore for a transverse member, for instance a pedal assembly. The inner end of the crank has a wheel [32] contacting the cam [28]. A sleeve surrounds the crank [29]

and is provided with two retaining members, each provided with an appropriately shaped bore permitting axial movement of the crank. The sleeve is attached to and rotates with the drive wheel [28]. The crank [29] also rotates with the drive wheel [28]. Aspring [30], bearing on a collar [31] and the outer of the stop members, ensures thatthe wheel [32] remains in contact with the outer surface of the cam [27], as the drive wheel rotates with respect to the support of the rotary bearing. This permits the moment exerted by the reciprocating force to vary during the course of revolution of the drive wheel.

When the invention is used in connection with a bicycle, some re-design of the bicycle frame may be required so that the pedals and saddle may occupy a slightly different position from the conventional.

Turning now to the embodiments of Figs 17 to 25, these illustrate, as indeed do the preceding embodiments, a method of driving a pedal cycle (not shown) or other (not shown, but which might comprise a winch or the like) crank- operated mechanism 100 in which a user (not shown) applies a force to a rotatable crank 102,104, the method comprising providing means 106 for varying the effective length of the rotatable crank during rotation of same.

In this embodiment, as in the preceding embodiments, there is provided means 108 to permitthe userto exercise a degree of control overthe effective length of the cranks 102,104 at at least one given location in the locus of travel of the cranks. In use the cranks are caused to adopt an effective length at the said at least one location during their loci of travel, which is at least partially under user control.

In these embodiments, the means to permit the user to exercise a degree of control over the effective length of the cranks comprises slot or the like means 110 provided in the crank means 102,104 in relation to either or both

ends of the cranks. Specifically in this embodiment, the structure corresponds more to that of the embodiment of Fig 16 than to that of Fig 15, and the slot or the like means 110 is thus in the form of a telescoping assembly of crank elements 112,114 which permit the cranks 102,104 to vary in length.

Resilient means 116 is provided in relation to each of the cranks to permit resilient yielding to the force applied to the crank by a user, thereby changing the effective length of the crankwhile exerting a corresponding resilientthrust on the means 118 in the form of pedals 120 whereby a user applies the said force to the cranks so as to urge same towards adoption of a suitable crank length. Although in these embodiments, the crank means 102,104 are provided in the form of the telescoping elements 112,114, in corresponding embodiments in which slot means is provided as described previously, such slot means may be provided having a profile as disclosed for example in Figs 13 and 14 disposed so as to promote the adoption by the user of a suitable crank length as the crank rotates.

In this embodiment, the means to permit the user to exercise a degree of control over the effective length of the crank comprises cam means 122 having a profile adapted to provide adoption of a suitable crank length as the cranks rotate, in accordance with torque and energy conservation requirements. Having thus described the general features of the construction of the embodiments of Figs 17 to 25, we will now describe in more detail some of the significant other features thereof. It is to be understood that where in the present embodiments, a generic term is used in relation to structures having counterparts in the preceding embodiments, the corresponding terminology is to be understood to be applicable to those preceding embodiments likewise.

As shown in Fig 17, cranks 102,104 are rotatably mounted on a common shaft 124 for rotation about an axis 126. Shaft 124 is journalled in bearings (not shown) in a bicycle bottom bracket 128 forming part of the bicycle frame (not shown) and having cam means 122 removably secured thereto by bolts 130, with chain wheel 132 mounted on shaft 124 for rotation with the cranks and coupled by a chain (not shown) to the bicycle rearwheel in the usual way. The telescopic construction of cranks 102,104 is generally as described above in relation to Fig 16. Resilient means 116 in the form of a coiled compression springs acts on a cam follower arm 134 having a rotary cam engaging wheel 136 running on the external surface of the generally elliptical. external surface 138 of each of the cam means 122, which have apertures 140 for bolts 130.

The differing cam profiles for the cam means 122 of Figs 21 to 25 provide for varying operational characteristic according to desired bicycle usage, the profiles shown corresponding to the following general designations of usage; Figs 18 and 25: basic profile for general usage; Fig 20: mountain bike; Fig 21: touring bike; Fig 22: for hill climbing; Fig 23: for racing; Fig 24: for sprinting.

It will be seen from Fig 17 to 25 that all of the cam means 22 provide external outwardly facing cam surfaces 138 against which the cam follower provided by cam engaging wheel 136 and cam follower arm 134 are resiliently urged, but from which contact can be disengaged by user loading, depending on the spring force exerted by compression spring 116.