AU2005201807B1

AU2005201807B1 - A Bicycle Crankshaft and Chain Wheel Assembly

Info

Publication number: AU2005201807B1
Application number: AU2005201807A
Authority: AU
Inventors: A.E. Gorza
Original assignee: GORZA A
Current assignee: GORZA A
Priority date: 2004-11-01
Filing date: 2005-04-29
Publication date: 2005-10-13
Anticipated expiration: 2025-04-29
Also published as: MY137825A; AU2005201807C1

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE PATENT SPECIFICATION A BICYCLE CRANK AND CHAIN WHEEL ASSEMBLY The invention is described in the following statement: SA BICYCLE CRANK AND CHAIN WHEEL ASSEMBLY 0

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FIELD OF THE INVENTION The present invention relates to a bicycle crank and chain wheel assembly. More particularly, the present invention relates to a bicycle crank and chain wheel assembly arranged so that the distance from the pedal to the axis of the chain wheel varies with the rotation of the chain wheel.

0 (0 BACKGROUND TO THE INVENTION The most common type of bicycle transmission includes a front chain wheel that orotates on an axle which traverses a sleeve formed through the bicycle frame. In such an arrangement the centre of the chain wheel is concentric with the axle.

Cranks at 1800 to each other extend from, and are rotationally fixed to, the axle. The crank on the chain wheel side of the bicycle terminate is fixed to the chain wheel.

Each of the cranks terminates in a threaded bore to which a pedal is attached.

Applying force to the pedals consequently applies torque to the chain wheel so that it rotates thereby driving a cog on the rear wheel of the bicycle by means of a chain.

It will be realised that the leverage that may be applied to the chain wheel by means of the pedals is constant throughout a full revolution of the chain wheel.

However, it would be desirable if the leverage that might be applied to the chain wheel were maximised at the point of rotation of the chain wheel at which a bicycle rider applies his or her downward power stroke to the pedal.

It is an object of the present invention to provide a bicycle transmission wherein the leverage afforded by the bicycle's cranks against the chain wheel is greatest at the point in the cycle at which the power stroke is applied.

SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a bicycle crank and chain wheel assembly including: a ring shaped chain wheel arranged to rotate about a first axis of rotation; a slotted guide extending outwardly from the chain wheel; a pair of opposed cranks arranged to rotate about an axle having a second axis of rotation; and a projection extending from one of the opposed cranks to move along the

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oslotted guide.

In a preferred embodiment of the invention the chain wheel rotates about a C) mounting disk that is fixed to a frame of the bicycle.

Preferably a ball bearing race is located between the mounting disk and an inner wall of the ring shaped chain wheel.

The projection may comprise a wheel rotatable about a pin that extends from o the crank on the chain wheel side of the frame.

00 N referablyceives the whe slotted guide comprises a lug in which is formed an axial slotl Nthat receives the wheel.

OAccording to a further aspect of the invention there is provided a bicycle that N includes a crank and chain wheel assembly as described above.

Preferably the crank and chain wheel assembly is mounted to the bicycle so that when the first axis, the second axis and the pedal end of the crank are collinear the crank makes an acute angle with vertical.

Further preferred features of the present invention will be described in the following detailed description which will refer to a number of figures as follows.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a bicycle crank and chain wheel assembly according to a first embodiment of the present invention.

Figure 2 is a first exploded view of the right side of a bicycle crank and chain wheel assembly of Figure 1.

Figure 3 is a second exploded view of the left side of the bicycle crank and chain wheel assembly of Figure 2.

Figures 4A-4H depict the bicycle crank and chain wheel assembly of Figures 1 to 3 at 450 intervals as the chain wheel is driven through a single rotation.

Figure 5 is a side view of a chain wheel and cam follower according to a second embodiment of the present invention which shows the relative location of these parts at the beginning of a downward power stroke.

Figure 6 depicts a bicycle crank and chain wheel assembly which includes the chain wheel and cam follower of Figure Figure 7 depicts the bicycle crank and chain wheel assembly of Figure 6 at 450 intervals as the chain wheel is driven through a single rotation.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT Referring now to Figure 1, there is depicted a plan view of a bicycle crank and chain C) wheel assembly according to a first embodiment of the present invention. Chain wheel 2 is ring-shaped and rotates about a disk 4 that is fast with bicycle frame 6.

(Only a portion of frame 6 is visible in the figures.) The axis of rotation of chain wheel 4 is indicated by 8. Cranks 10 and 12 are disposed at 1800 to each other and O rotationally fixed to axle 15 which traverses a sleeve through frame 6 in the 00 Sconventional manner. Fixed to chain wheel 2 and extending radially away from axis 0 N of rotation 8 is a slotted cam follower 14 which serves as a slotted guide. Cam o follower 14 receives a cam 16 that is mounted to a pin which projects from, and is 0 N fixed to, the inner side of crank The distance between the axis of rotation 8 of chain wheel 2 and the axis of axle 15 is indicated as in Figure 1. It will be noted that in the configuration shown in Figure 1, wherein crank 10 is angled to receive a downward powerstroke from a rider of the bicycle, the distance between the end of crank 10 and axis of rotation 8 of chain wheel 2 is at a maximum because axis 8, axle 15 and the pedal end of crank 10 are collinear. As will be shown later with reference to Figures 4A-4H distance varies throughout a revolution of the chain wheel.

The structure of the crank and chain wheel assembly can be seen in more detail in the exploded views of Figures 2 and 3. The inner wall of chain wheel 2 is welded to a ball bearing race 20. Ball bearing race 20 fits snugly over a circular flange 24 that projects from circular mounting plate 22. Mounting plate 22 is welded or otherwise secured to bicycle frame 6. Cap 26 is located on the outside of chain ring 2. Screws 9 and 11, seen in Figure 1, are inserted through holes 26 and 27 of the cap and secured into threaded holes 25 and 23 of mounting plate 22. Mounting plate 22 has a hole 21 which axle 15 traverses. Axle 21 passes through ball race and thence through hole 30 of cap 4. Axle 15 is received into square bores 32 and 34 formed at the ends of cranks 10 and 12 respectively and secured in place by bolts at either end in the conventional manner.

Figures 4A to 4H depict a single revolution of chain wheel 2 at 450 intervals. It will be realised that in the interests of clarity, pedals have not been shown fixed to the free ends of cranks 10 and 12. The position in which a downward power stroke is applied to crank 10 is shown in Figure 4A which is the same position shown in Figure i1. In this position the distance between the free end of crank 10 and the axis of 0 o rotation of chain wheel 2 is at its maximum as indicated by distance Force ci 0^ 00 ci Vlr0 0 0 o applied to the free end of crank 10 is applied to chain wheel 2 by contact of cam 16

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owith the inside of slotted cam follower 14 thereby causing chain wheel 2 to rotate about fixed disk 4. It will be noted that as crank 10 is forced down and around axle the distance D diminishes. Distance D reaches a minimum as the chain wheel rotates through 1800 from the starting position to the position shown in Figure 4E.

oHowever, it will be realised that at that point shown in Figure 4E the free end of crank 12 is in position to receive the next downstroke from the rider and furthermore the o distance between the free end of the crank and the axis of rotation of chain wheel 2 00 is at a maximum.

0 It will be realised that a crank and chain wheel assembly according to the opresent invention is desirable because the leverage of the crank against the N chainwheel is at a maximum at the point in the rotation of the chainwheel where the power stroke is applied to the pedals. Consequently, power can be readily transferred from the rider to the chain wheel and thence to the rear wheel of the bicycle.

In the first embodiment of Figure 1, the cam follower 14 extended outwardly from the chain wheel 2 such that the elongate slot in which the cam 16 moved along was aligned with a cam movement axis co-incident with the centre of the chain wheel 2. That is, the cam movement axis formed a normal to the circular perimeter of the chain wheel 2. Hence, the cam follower 14 constrained the cam 16 to move linearly along the rotating cam movement axis as the chain wheel 2 performed a revolution.

According to a second embodiment of the present invention, there is provided a chain wheel and cam follower arrangement as shown in Figure 5 whereby the cam movement axis 50 is not co-incident with the centre of the chain wheel 2. That is, the cam follower 14 extends outwardly from the chain wheel 2 such that the cam movement axis 50 is not normal to the circular perimeter of the chain wheel 2. In this manner, the cam follower 14 is attached to the chain wheel 2 such that the cam movement axis 50 is substantially horizontal at the beginning of the downward power stroke in the location shown in Figure 6 shows a bicycle crank and chain wheel assembly which includes the chain wheel and cam follower of Figure 5. Like reference numerals refer to like features in the first embodiment described. The change of pitch of the cam movement axis 50 between the first and second embodiments amounts to three teeth a triplet) 45 on the distal side of chain wheel 2 from cam follower 14.

~fl Figures 7A-H show the relative movement of the chain wheel 2 and the left ocrank 12 at 450 intervals as the chain wheel is driven through a single rotation. The N relative speed of the same triplet of teeth 45 of the chain wheel 2 with respect to the ;Z left crank 12 is shown at various stages of rotation.

Between figures 7A and 7B, the speed of the triplet of teeth 45 decreases with o respect to the speed of the left crank 12 as the distance between the triplet of teeth and the left crank 12 increases.

o Between figures 7B and 7D, the speed of the triplet of teeth 45 increases with 00 respect to the speed of the left crank 12 as the distance between the triplet of teeth 0 N 45 and the left crank 12 increases.

o In figure 7D, the triplet of teeth 45 engage with the chain of the bicycle and Ni power applied to the left crank 12 is transferred to the chain and, in turn, to the rear wheel of the bicycle.

Between figures 7D and 7G, the speed of the triplet of teeth 45 and the speed of the left crank 12 are approximately the same as the distance between the triplet of teeth 45 and the left crank 12 remains approximately constant at each stage. That is, power applied to the left crank 12 is transferred to the chain and, in turn, to the rear wheel of the bicycle during the downward power stroke of the left crank 12.

In figure 7H, the triplet of teeth 45 disengage with the chain of the bicycle.

Between figures 7H and 713, the speed of the triplet of teeth 45 decreases with respect to the speed of the left crank 12 as the distance between the triplet of teeth and the left crank 12 increases.

Similarly, the peripheral speed of the chain wheel 2 at the cam follower 14 and the speed of the right crank 10 are approximately the same between figures 7H to when the cam movement axis 50 is approximately aligned with the right cam shaft 10. Hence, during the downward power stroke on a respective crank 10, 12, the speed of the teeth of the chain wheel 2 about that respective crank 10, 12 is the approximately the same as the speed of that respective crank 10, 12.

It will, of course, be realized that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as summarised herein.

Claims

3. An assembly as claimed in claim 2, wherein a ball bearing race is located between the mounting disk and an inner wall of the ring shaped chain wheel.
4. An assembly as claimed in claim 1, wherein the projection comprises a wheel rotatable about a pin that extends from the crank on the chain wheel side of the frame. An assembly as claimed in claim 4, wherein the guide comprises a lug in which is formed an axial slot that receives the wheel.
6. An assembly as claimed in claim 5, wherein the slot is elongate so as to constrain the projection to move linearly along a third axis as the chain wheel revolves.
7. An assembly as claimed in claim 6, wherein the guide extends outwardly from the chain wheel so that the third axis is co-incident with the centre of the chain wheel.
8. An assembly as claimed in claim 6, wherein the guide extends outwardly from the chain wheel so that the third axis is not co-incident with the centre of the chain wheel and the projection movement axis is substantially horizontal at the beginning of a downward power stroke. 0 O 0 ci
9. A bicycle including a crank and chain wheel assembly as claimed in claim 1. A bicycle as claimed in claim 9, wherein the crank and chain wheel assembly is mounted to the bicycle so that when the first axis, the second axis and the pedal end of the crank are collinear the crank makes an acute angle with vertical.
11. A bicycle crank and chain wheel assembly as claimed in any one of claims 1 to 8, and substantially as herein described with reference to the accompanying drawings.
12. A bicycle as claimed in claim 9 or claim 10, and substantially as herein described with reference to the accompanying drawings. Dated this 3rd Day of August 2005 A. E. Gorza By my attorneys Eagar Buck Patent and Trade Mark Attorneys