WO2008031135A1

WO2008031135A1 - Assembly to vary crank length

Info

Publication number: WO2008031135A1
Application number: PCT/AU2006/001626
Authority: WO
Inventors: Cornelis J. J. Scheepmaker; Lauren Patricia Hoy
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-09-13
Filing date: 2006-11-01
Publication date: 2008-03-20
Anticipated expiration: 2009-03-13

Abstract

The length of each pedal crank (2) of a bicycle varies so as to lengthen on the downstroke (so giving a rider greater mechanical advantage) and shorten on the upstroke. Extension/retraction of crank (2) results from reciprocation of pins (10) held in bores in crank (2). Changes in length of crank (2) occur automatically during its rotation due to cam follower (5) on crank (2) being constrained to follow a circular cam groove (4) which is offset forward and somewhat upward with respect to crankshaft (1) and fixed with respect to bicycle frame (7).

Description

ASSEMBLY TOVARY CRANKLENGTH

Title:

Description.

The innovation technology is applied to the drive train of a bicycle in place of a conventional crank and pedal arrangement, and will comprise of:

• Crank arms mounted to the crank shaft on a sliding mechanism so as to allow the radial length of the cranks to be alternately increased and decreased

• The sliding cranks will be each fitted with a follower, which runs in a cam fixed to, and is part of, the bicycle frame.

The cam causes the crank's length to extend beyond a 'standard' length on the down or power stroke and reduces the length of the cranks on the up or return stroke.

• The path of the bicycle pedal will be circular, about a point forward and slightly upward of the crankshaft.

Drawings:

• Drawing of the OFF-SIDE of the variocrank. Showing the variocrank arm fully extended

• Cross sectional drawing of the relevant component parts.

• Drawing of the NEAR-SIDE of the variocrank. Showing the variocrank arm fully retracted Design, Materials and Applications.

Design.

The design can be significantly improved when commercial production is realized.

The OFF-SIDE cam can be part of an aerodynamically streamlined design so as to offer minimal air resistance. This part can align and be locked to the NEAR-SIDE cam of similar streamlining.

The whole of the crankshaft housing can be integrated into a two part die- cast component.

Materials.

As the addition of the variocrank and its associated cam components will add weight to the bicycle, the choice of a suitably stable and strong material is necessary especially in the cam and gear-cover design. Some of the new and modern composite materials will perhaps qualify better for this design as a lightweight die cast metal.

This would require substantial engineering and manufacturing interest and financial investment.

Applications.

The racing bike industry would be very interested in any advantage over their competitors. As would pedal and gear manufacturers, envisaging a form of ' Pedal- Cam and Variocrank' kit.

The principle of a varying length crank outside the bicycle might provide equivalent advantage in many mechanisms utilizing a crank, such as piston engines, particularly the slower cathedral type engines as used in shipping, as these are less weight conscious applications. Drawing description

1/3 Fig. 1 Drawing of the OFF-SIDE of the variocrank,

Showing the variocrank arm fully extended.

2/3 Fig. 2 Cross sectional drawing of the relevant component parts.

3/3 Fig. 3 Drawing of the NEAR-SIDE of the variocrank

Showing the variocrank arm fully retracted

Additional notes:

F - Protective cover. (Not shown)

There is a potential pinch point between the sliding parts of the variocrank For this reason a protective cover is fitted into place on the fixed part ( or sliding part) of the variocrank so as to eliminate this pinchpoint As the protective cover would block the view and action of the variocrank over one revolution, it has been left off the drawings.

G - Gate. Removable part of the cam outer wall.

As shown on drawing 3/3 Fig.3 on the NEAR-SIDE

Part G, slides and clips into place.

When part G is removed, the opening in the cam wall allows the moveable pedal part (with the cam follower) of the variocrank to be removed for inspection

A similar gate can be placed in the OFF-SIDE cam.

Claims

The advantage of this invention is as follows:

The device will increase the mechanical advantage obtained from the crank of a bicycle drive train.

• The innovation provides the leverage arm of a longer crank through a sector of its orbit, without significantly increasing pedal travel or reducing ground clearance, relative to a crank of standard length.

• The additional mechanical advantage creates the equivalent of a lower gear ratio providing greater power or torque.

• Equivalent additional torque obtained by use of a lower geared chain sprocket would require a greater number of pedal revolutions.

• Equivalent torque obtained by use of a longer crank would produce an inconvenient long pedal and reduce the pedal to ground clearance.

• The innovation does not alter any of the existing gears and their associated gear change mechanisms.