GB2279050A - Varying the effective cranking length of a pedal crank for a cycle - Google Patents

Abstract

The apparatus comprises a drive crank, 10, eg for supporting a pedal, coupled to a shaft 12 for driving a drive member, eg a chain sprocket. The shaft 12 is rotatably supported in a bearing unit, 42, 44, which is rotatably supported in a housing. Preferably by a planetry gear arrangement, 28, 30, 32, the rotation of the shaft 12 causes rotation of the bearing unit 42, 44, which varies the position of the driven member with respect to the crank, so varying the effective cranking length. The apparatus is preferably arranged so the pedal follows on elliptical path, with its major axis parallel to the longitudinal axis of the cycle (fig 2). <IMAGE>

Description

VARIABLE CRANKING LENGTH This invention relates to apparatus for obtaining a variable cranking length in a drive employing a crank shaft.

The invention finds particular application to bicycles but may be applicable elsewhere.

Conventional bicycles are normally provided with the well-known drive mechanism comprising a pedal and crank.

Torque is applied to the drive wheel and is a function of well known characteristics including the ratio of the gears, power provided by the rider and by the length of the crank. Space considerations are also a factor. Gears require their own space and equally if the crank is lengthened consideration must be given to the locus of the rider's knees whilst pedaling, which is a matter of serious concern. As a result, a need has been identified for an improved drive mechanism providing a higher torque output and/or less dependence on the space considerations mentioned above.

In the case of a bicycle, it would be desirable to provide means whereby the torque generated by the rider during pedaling could be increased without the directly attendant increase in the travel of the rider's foot and knee which would be produced simply be increasing the length or throw of the crank itself.

An object of the present invention is to provide improvements in relation to apparatus for varying the effective length of a crank, including improvements in relation to one or more of the matters mentioned above, or generally.

According to the invention there is provided apparatus adapted for varying the effective length of a crank together with a combination of same with a bicycle crank and the use of same in a bicycle, as claimed in the accompanying claims.

In an embodiment of the invention there is provided apparatus adapted for varying the effective cranking length of a crank in which there is provided a bearing of eccentric construction, of which the advantages will be discussed below.

However, we mention here that by the term "bearing" as used in this specification, it is intended that the term will have an interpretation taking account of the following. The term is chosen taking account of the use of a bearing in a conventional bicycle pedal construction where, conventionally, there is provided a central shaft fixed to the bicycle crank and a pair of ball or the like bearings are provided at spaced positions on the shaft so that the pedal is freely journaled thereon. The "bearing" of the present invention serves to provide a function corresponding to such a bearing in the sense that the pedal mounted on the bearing is capable of executing the same motion with respect to the crank as in the conventional bicycle pedal bearing arrangement, but, at least in the described embodiment, there is the difference that the "bearing" does not permit free rotation of the pedal with respect to its non-rotatable shaft.

The use of the term "eccentric" in relation to the bearing of the invention refers to the mechanical construction of the bearing whereby relative rotation of the parts connected by it results in relative movement therebetween.

As a result of the eccentric construction of the bearing, the advantages provide that the effective cranking length of the crank can be varied, and by judicious choice of the relationship of the eccentric bearing with respect to the crank, the crank length can be made a maximum at the point of its cycle of movement at which the maximum torque is to be generated. Likewise, the cranking length can be arranged to be a minimum where, in the case of a bicycle for example, the rider's knees are at their highest position.

In an embodiment, a housing is eccentrically journaled on a crank shaft and drive means couples the housing to the shaft. The drive means is a sun and planet gear train and by this arrangement the attitude of the housing, and hence of the pedal which may be mounted thereon, is maintained at precisely that which is needed for maximum application of force by the rider.

It is envisaged that alternative eccentric bearing arrangements might be provided which could offer some at least of the above-identified advantages, including alternative drive arrangements between the housing and the crank shaft, or indeed much simplified arrangements in which a simple eccentric journal bearing causes the pedal to be raised and lowered with respect to the central axis of the normal shaft of the pedal, as that shaft rotates with the crank.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which Fig 1 shows a partially sectioned view of the end portion of a bicycle crank assembly with an eccentric bearing mounted thereon in place of the conventional journal bearings for a conventional pedal; Fig 2 shows the locus of movement of a pedal (shown in full lines) of a conventional bicycle crank arrangement, and the modified locus for the pedal of a crank assembly in accordance with the invention, shown in broken lines; and Fig 3 shows a section through a bearing, corresponding generally to the bearing seen in Fig 1, but shown on a somewhat larger scale and in more detail.

As shown in Fig 1, a bicycle crank assembly 10 has mounted at its outer end, in the conventional manner, a crank shaft 12 which is rigidly fixed to the remainder of the crank assembly 10 for rotation under the action of the rider's feet about an axis of rotation of a bicycle main chain wheel (not shown). Shaft 12 and its mounting on the bicycle chain wheel is generally conventional and could have a conventional pedal mounted thereon through journal bearings in the usual way.

In place of the conventional pedal bearing arrangement there is provided the bearing 14 which is of eccentric construction and arranged so that when the rider applies a load L to bearing 14 (for example through a pedal, not shown,) to rotate the crank assembly 10 in the conventional way, as the crank assembly rotates the eccentric bearing 14 varies the position of the application of load L with respect to the axis 16 of the crank shaft 12 itself. The arrangement is such that the cranking length of the crank shaft assembly 12 is a maximum at the 9 o'clock and 3 o'clock positions seen in Fig 2 at 18 and 20, and a minimum at the 12 and 6 o'clock positions seen at positions 22 and 24.

Fig 2 shows how the throw of the eccentric bearing assembly 14 is superimposed upon the otherwise circular locus of movement of shaft 12. The locus of shaft 12 is identified at 26 in a full line and the somewhat ivoid locus of movement of a point such as that seen in Fig 1 where load L is applied to bearing 14, is seen in a broken line in Fig 2 at 27.

Thus, it can be seen that the cranking length of crank assembly 10 is a maximum at the 9 o'clock position identified at 18, whereby the rider's torque generating capability is maximised.

In Fig 1 it can be seen that bearing 14 comprises two shafts and two spur gears and an associated toothed housing, and these will be more fully described in relation to Fig 3.

In Fig 3, parts corresponding to Fig 1 are numbered accordingly, though there may be some differences of detail perceptible.

As shown in Fig 3, crank shaft 12 carries a first spur gear 28 meshing with a second spur gear 30. First spur gear 28 meshes with and drives a peripheral gear track 32 formed on the inner surface of a housing 34 of bearing 14. Shaft 12 is journaled in a ball race 36 at one end and a needle bearing 38 at the other. Shaft 40 on which second spur gear 30 is mounted, is mounted between an inner disc 42 at one end of housing 34 and an outer disc 44 at the other, which is itself journaled in a ball race 46. In use first pinion 28 rolls around internal gear track 32 and second spur gear 30 rolls around the periphery of first spur gear 28. This rotary motion produces the "throw" of the eccentric bearing discussed above and illustrated in Fig 2. Typically, the throw of the eccentric bearing assembly may be from 5 to 20 millimetres, and will usually be in the range of 7.5 to 12.5 millimetres.

Claims (8)

1 Apparatus adapted to vary the effective cranking length of a crank comprising a) a bearing permitting rotation with respect to a crank of a driving or driven element connected to said crank through said bearing; characterised by b) said bearing being of eccentric construction whereby said driving or driven element varies in position with respect to said crank as the crank rotates.

2 Apparatus adapted to vary the effective cranking length of a crank characterised by an eccentric bearing which varies the position of a driving or driven element as the crank rotates.

3 Apparatus according to claim 1 or claim 2 characterised by said bearing comprising a housing eccentrically journaled on a crank shaft and drive means coupling said housing to said crank shaft.

4 Apparatus according to claim 3 characterised by said drive means comprising a sun and planet gear train.

5 Apparatus according to claim 3 or claim 4 characterised by said drive means having a drive ratio such as to maintain said housing in a constant attitude as said crank rotates.

6 Apparatus adapted to vary the effective cranking length of a crank substantially as described herein with reference to the accompanying drawings.

7 Apparatus according to any one of claims 1 to 6 in combination with a bicycle crank characterised by said bearing being adapted to have a bicycle pedal mounted thereon and the arrangement being such that the cranking length is a maximum at the 9 and 3 o'clock positions of said crank and a minimum at the 12 and 6 o'clock positions.

8 A bicycle comprising two sets of apparatus according to claim 7.