GB2055077A

GB2055077A - Bicycle crank assembly

Info

Publication number: GB2055077A
Application number: GB8023924A
Authority: GB
Original assignee: Collet Bernard Gaston
Current assignee: Collet Bernard Gaston
Priority date: 1979-07-27
Filing date: 1980-07-22
Publication date: 1981-02-25
Also published as: NL8004284A; IT8012601A0; FR2462331A1; IT1133460B

Abstract

A bicycle crank assembly has a pedal crank arm (1) at the end of which a disc (5a) or ring is freely rotatably mounted, e.g. by a ball or needle bearing, on an axis (5) parallel to the crank axis (2). A pedal (7) is mounted on the disc or ring on an axis (6) spaced from and parallel to the axis (5). The path of the pedal axis (b) is thus centred ahead of the crank axis (2) during rotation of the crank arm increasing the pedal leverage during the driving part of the path. The disc or ring can be replaced by an arm pivoted to the crank arm at one end and carrying the pedal at its other end. <IMAGE>

Description

SPECIFICATION Crank assembly The present invention concerns a bicycle crank assembly comprising two crank arms which are non-rotatably fixed to a spindle carrying one or more toothed wheels co-operating with a chain or transmission means acting on the drive wheel of the bicycle, the end of each crank arm of the assembly carrying a pedal which is freely rotatable about an axis parallel to the axis of the crank assembly.

In a conventional crank assembly, the length of the crank arms, that is to say, the distance between the axis of the crank pin or shaft of a pedal and the axis of the spindle is determined by the physical characteristics of the average cyclist.

Generaily, it is difficult, if not impossible, mathematically to analyse the drive power produced by the cyclist in each pedal stroke, that is to say, during each turn of the pedal.

This study depends on the variation in the force applied during a turn of the pedal. This force depends on the physiological characteristics of the cyclist.

However, and surprisingly, when bicycle tests are performed by different cyclists over identical and relatively long routes, there is a general tendency which emerges clearly from the opinion of the users (more or less rapid fatigue, difficulties...). Taking such tests as the basic starting point, on a large scale and in relation to a substantial number of people, it has been possible to determine the ideal position of the lever arm of the crank assembly.

Contrary to what might appear to be evident, it is not possible to increase the length of the lever arms in order to increase the torque that a cyclist can produce by applying the same force as with a shorter lever arm.

Indeed, this would result in very substantial fatigue without finally an increase in the power produced. Indeed, the gain in power which results from an increase in the lever arm results in more rapid fatigue on the part of the cyclist, since each foot travels over a circular path which is increased in the same proportion as the length of the lever arms.

By way of example, an increase in the length of the lever arms of only of the order of 10% (which corresponds to a length of 1 5 to 20mm) is not possible without a considerable increase in fatigue.

The present invention provides a crank assembly characterised in that each arm includes a connecting means connecting its end to the shaft of the pedal, for modifying the effective length of the lever arm of the pedal between the axis of the crank assembly about which the arm rotates and the axis of the pedal shaft.

In an advantageous embodiment of the invention, the connecting means is a member having two offset parallel axes, one of the axes being rotatably mounted at the end of the arm of the crank assembly and the other axis constituting the shaft of the pedal, said two axes themselves being parallel to the axis of the crank assembly, to axis of the pedal being attached to a disc freely rotatably mounted in a corresponding housing at the end of the arm of the crank assembly, the pedal axis being at an out-of-centre position relative to the disc.

By virtue of the invention, the torque produced by the cyclist is increased without thereby increasing the length of the path covered by the foot of the cyclist.

As indicated above, mathematical analysis of the work supplied by the cyclist is virtually impossible. Nonetheless, secret tests carried out in developing the present invention have shown that it was much less tiring to cover a certain bicycle route (on the flat, long hill, steep hill) with a bicycle provided with a crank assembly according to the invention, in comparison with a conventional bicycle, or conversely, for the same fatigue effect, it was possible to cycle much faster with a bicycle according to the invention.

The gain in speed (or in respect of fatigue) represents an improvement of the order of 5 to 10%, under the experimental conditions defined above.

It is preferable for the axis member carrying the pedal to be mounted on a circular plate with possibly a ball or needle type bearing.

This provides a very rigid structure, without increasing frictional forces.

A simpler arrangement comprises, as indicated above, freely rotatably mounting the connecting means at the end of the crank assembly and connecting it by a connecting member to the bearing member which carries the pedal.

The present invention will be described in greater detail with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side view of a crank assembly with two crank arms, according to the invention, Figure 2 is a plan view from above in partial section of the assembly shown in Fig.

1, Figures 3 to 6 show another embodiment of the invention, Figures 3 and 4 show the arm of the crank assembly in the active position, Figures 5 and 6 show the arm of the crank assembly in the non-active position, and Figure 7 shows a modified form of the crank assembly of Figs. 1 and 2.

Referring to Figs. 1 and 2, the crank assembly comprises two similar crank arms 1 and 1' which are fixed to a spindle 2 carrying the toothed wheel or wheels co-operating with the chain or other transmission means of the bicycle. Such known parts do not require a detailed description.

The arms 1 and 1' are fixed to the spindle 2 by wedge-shaped keys in bores 3.

The description hereinafter will be limited primarily to description of the arm 1 and the members which carry it, it being appreciated that the reference numerals provided with a prime show the arm in its rearward horizontal position, the numerals without the prime showing the arm in its forward horizontal position.

The forward end 4 of the arm 1 carries a freely rotatable member 5a which contains an axis at a fixed distance parallel to its own axis 5. The axis 6 is that of the crank pin or shaft carrying the pedal 7, which is in this embodiment provided with an optional toe clip 8. In order to facilitate this description, in particular in respect of the mode of operation of the assembly according to the invention, it is advantageous to reference or denote the respective geometrical axes X-X, Y-Y and Z-Z of the axes 2, 5 and 6 which are parallel. The axis Y-Y is spaced from the axis X-X by a distance R and the axis Y-Y is spaced from the axis Z-Z by the distance a.Under these conditions, when the axes X-X, Y-Y and Z-Z follow each other in that order, in the same plane (right-hand part in Figs. 1 and 2), the axis Z-Z is spaced by the distance (R + a) from the axis X-X, whereas if the axes are in the same plane and follow each other in the order X-X, Z-Z, Y-Y (left-hand part in Figs. 1 and 2), the distance between the axes Z-Z and X-X is equal to (R - a).

In the preferred embodiment shown in Figs.

1 and 2, the member 5a is a disc which is mounted in a housing 1 a of corresponding shape in the end of the crank assembly. Thus, each arm of the crank assembly is roughly in the shape of a tennis racket. In order to reduce friction between the disc 5a and the housing 1 a in the end of the arm 1, it is possible to provide a ball bearing assembly or, better, a needle bearing assembly.

It is within the scope of the invention for the disc to be hollow or annular, for the purposes of saving weight.

Figs. 3 to 6 show a second embodiment which is simpler and less expensive than the first embodiment. In this case, the disc 5a is replaced by a connecting member 9 which is in the form of an arm rotatably mounted on the arm 1 and carrying the two axes 5 and 6.

The axis 5 projects from one side of the member 9 and the crank pin or shaft axis 6 projects on the other side of the member 9.

Figs. 3 and 4 respectively show in a side view and in a plan view, a pedal in which the shaft 6 of the pedal 7 is at a distance (R + a) from the geometrical axis X-X of rotation of the crank assembly.

In contrast, in Figs. 5 and 6 which are respectively a side view and a plan view, the axis 6 of the shaft of the pedal is disposed inwardly and is at a distance (R - a) from axis X-X of rotation of the crank assembly.

Figs. 1 and 2 on the one hand and Figs. 3 and 4 on the other hand show the extreme positions which may be occupied by the axis 6 or the pedal 7 with respect to the geometric axis X-X.

When the cyclist bears alternately on the pedal (right or left) which, in each revolution of the crank assembly, is at the front in the direction of movement, the axis 6 comes into its most forward position, that is to say, naturally, the axis 6 and the pedal 7 occupy a position close to or adjoining that shown in Figs. 1 and 2. Indeed, as the force applied to the pedal 7 is directed downwardly and forwardly, along the vector/A (Fig. 1), the angle formed between the arm 1 and a line between the axes 5 and 6 tends to open and to be close to 180 . Depending on the position of the rotating assembly over the path of movement, the abovementioned angle opens to a greater or lesser degree, but always remains close to 180 over the forward half of the path of movement.

In contrast, in the rearward position, that is to say, substantially over the rearward half of the path of movement of the pedal (being the part of the path of movement which is disposed substantially rearwardly of a vertical line passing through the geometrical axis X-X), as the foot of the cyclist is not applying any force but is returned by the movement of the other arm of the crank assembly, which is in the active part of its movement, the connecting member containing the axes 5 and 6 occupy a position similar to that shown in Figs. 3 and 4, that is to say, the axis 6 or Z-Z is between the geometrical axes X-X and Y-Y.

In a first approximation, the foot of the cyclist occupies a constant position over its path of movement, so that the axis 6 describes a substantially circular path which is eccentric to the circular path of movement of the axis 5 which is centered on the geometrical axis X-X, in accordance with a translatory movement corresponding to the distance between the axes Y-Y/Z-Z, depending on the inclination of the foot of the cyclist.

As, in practice, there are nonetheless slight variations in the inclination of the foot of the cyclist, the path of movement is not perfectly circular. However, these deviations are sufficiently small as to be negligible in most cases.

In conclusion, the foot of the cyclist covers a circular path of the same radius R as the radius of the path of movement of the axis 5 about the geometrical axis X-X, which means that the movement of the foot is similar to that performed with a known crank assembly, but the lever arm varies in a substantial manner since, in the active part of the path of movement (forward half of the path move ment), the length of the lever arm is greater than the length R and is equal in the main part of the path of movement (R + a). In the passive part (rearward half of the path of movement) of the path of movement, the length is less than the length R and is close to the length (R - a).

Fig. 7 is a diagrammatic view of a practical construction of an arm 1 which is in the shape of a racket and which is reduced in weight by an opening 1 b and whose housing 1 a receives a ring 5a provided with a housing 5b for receiving the crank pin or shaft (not shown) of the pedal 7.

In practice, the length a is of the order of 10 to 40mm.

Claims

1. A bicycle crank assembly comprising two arms each of which is fixed to a spindle carrying one or more toothed wheels co-operating with a chain or other transmission means acting on the drive wheel of the bicycle, the end of each arm of the crank assembly carrying a pedal freely rotatable about an axis parallel to the axis of the crank assembly, each arm comprises a connecting means connecting its end to the shaft of the pedal so as to vary the distance between the axes of the pedal and the crank assembly during each rotation of the assembly.

2. A crank assembly according to claim 1 wherein the connecting means is a member having two offset parallel axes, one of the axes passing through the arm of the crank assembly adjacent its end and the other axis being that of the shaft of the pedal, said two axes being parallel to the axis of the crank assembly.

3. A crank assembly according to claim 2 wherein the connecting member is a disc freely rotatably mounted in a housing at the end of the arm of the crank assembly and carrying at an out-of-centre position the second axis of the shaft of the pedal.

4. A crank assembly according to claim 3 wherein the disc is recessed or hollowed and is in the form of a ring.

5. A crank assembly according to claim 2 characterised in that the connecting member is a straight member rotatably mounted at one end on the arm and having the pedal shaft rotatably mounted thereon at its other end.

6. A bicycle crank assembly constructed and arranged substantially as hereinbefore described and shown in Figs. 1 and 2, or 3-6, or 7 of the accompanying drawings.