Non-uniform torque transmitting mechanisms such as bicycle chain

Details Non-uniform torque transmitting mechanisms such as bicycle chain Non-uniform torque transmitting mechanisms such as bicycle chain

1993-01-22

1994-06-28

Bui, Thuy M.

Endless belt power transmission systems or components

Positive drive pulley or guide roll

474160, F16H 900

Patent

active

053242386

DESCRIPTION:

BRIEF SUMMARY
This invention relates to mechanisms not capable to transmit uniform torque due to restriction imposed by the kinematic systems employed.
A classical example of such a system is the chainwheel of a bicycle with its left and right cranks and their pedals.
Each pedal subjected to a vertical downwards force applies a torque at the centre of rotation of the crank which varies in magnitude from a maximum value when the crank is horizontal to ZERO when the crank is vertical.
Conventional transfer of this non-uniform torque from the crank to the rear bicycle wheel is via a chainwheel to the rear bicycle wheel. This latter chainwheel has the ability of transmitting the received torque only clockwise and is thus called a freewheel as it does not transmit torque in the anti-clockwise direction.
This non-uniform torque is transmitted to the chainwheel twice for every complete rotation of cranks. The right crank during the first 180.degree. or last half a turn.
This invention minimises the torque non-uniformity by receiving and temporarily storing circumferential elastic energy in the chainwheel when each crank delivers significant torque, energy which is almost immediately given back to the chainwheel rim at the time when the cranks deliver the least torque.
According to the invention a torque transmitting wheel comprising an inner ring and an outer ring and a plurality of angular spaced elastically deformable ribs, each rib being arranged such that one end is connected to the inner ring and the other end is connected to the outer ring, only said ribs providing support between said rings, said ribs allowing the outer ring to rotate relative to the inner ring when torque is transmitted by the wheel.
Such embodiment receives and temporarily stores a circumferential deformation hence energy, when cranks deliver large torque and give back most of the same energy as torque to the chainwheel rim when cranks deliver small torque.
Extending the use of the selected polymer to almost the entire chainwheel adds advantages such as: load is shared by more chainwheel teeth than in the case of metal chainwheels; a significant weight saving; no corrosion protection; no lubrication required; kinder to the chain; built in chainguards; generous choice of colours hence aesthetically pleasant yet remaining technically and commercially competitive.
The invention will now be described in more details by way of example with reference to the drawings, in which:
FIG. 1 is a front view of the chainwheel showing only few teeth 10, and radial ribs 12, 12a and 12b, of the chainwheel (standard engineering drawing practice).
FIG. 2 is a side view of FIG. 1 with the upper half in section (Section X--X).
FIG. 3 is part side view of a three chainwheel set in which the chainwheel teeth 10, are attachable permanently or temporarily to the chainwheel rim 22, via chainwheel rings 32, 34, and 36, directly or indirectly. It also shows the chainguard 38 attachable permanently or temporarily to the largest chainwheel ring.
In FIG. 1 crank 14, is shown in the position where it can deliver the maximum torque to chain 16 via central metal plate 18, chainwheel boss 20, radial ribs 12, 12a, and 12b, chainwheel rim 22, and chainwheel teeth 10. The choice of radial ribs geometry 12, 12a, and 12b, will depend upon loading of chainwheels, materials and processes of manufacturing available and user preference, to some extent.
Chainwheel rim 22, may have the chainwheel teeth 10, integral with itself as in FIG. 1 and FIG. 2, where a single chainwheel without chainwheel guard is shown or attachable to itself as shown in FIG. 3 that refers to multi-chainwheel embodiments.
Dotted lines 24 and 26, show grossly exaggerated the positions the teeth 10, and ribs 12, 12a, and 12b, would take respectively during riding of the bicycle.
This position is well within the elastic limit of the material hence by the time the crank 14 reaches the vertical position A, the elastically displaced chain teeth 10 and radial ribs 12, 12a and 12b would have returned to their unloaded normal posit

REFERENCES:
patent: 4044621 (1977-08-01), McGregor, Sr. et al.
patent: 4475894 (1984-10-01), Sugino
patent: 5194051 (1993-03-01), Nagano

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