Scott & Phillott's British Patent No. 860 of 1878
Scott and Phillott's seems to have been the first practicable patent for an epicyclic change-speed gear for cycles. These notes summarise key points from the patent. They were prepared by Tony Hadland in 1997 for Pryor Dodge when Pryor was working on the exhibition Bike: Cycles - A tour of bicycle design from 1825 to 2000, staged at London's Design Museum from 30 October 1997 to 22 March 1998.
The Inventors
George Dennistoun Scott was an engineer from Derby, an industrial town in the English Midlands which is next door to Raleigh's home town, Nottingham - not that Raleigh existed at this time. Scott's middle name is also spelled Dennistown in the patent but that is probably just a typo.
George Henry Phillott was an architect from Cheltenham, an altogether more elegant and genteel Georgian spa town in Gloucestershire, in the west of England.
Basic Configuration
Scott & Phillott's gear as illustrated in the patent is fitted into the hub of a front-driving cycle. It employs a variant of the simple epicyclic principle, whereby two equal-sized co-axial bevel gears take the place of the sun and annulus. Meshing with both were another pair of bevel gears, taking the place of planet pinions. These planet bevels were mounted on a cross-head, taking the place of a planet cage.
Because the sun and annulus equivalents were of equal size, the gear changes were very widely spaced - 100% increase or 50% decrease (doubled or halved).
Two Arrangements
Two arrangements were described. The first was a two-speed, offering direct drive, a 'neutral' (non-automatic freewheeling) position, and 100% increase in wheel speed relative to the crank. In this version gear change was solely by sliding the cranks sideways.
With the cranks slid to the left, the crank shaft was clutched to one of the bevel wheels which was rigid with the road wheel - hence direct drive.
With the cranks in the middle they were not locked to anything, hence the machine was freewheeling.
With the cranks to the right, the crankshaft was clutched to the cross-head on which the planet bevels were mounted. The other bevel wheel was locked to the fork, hence an increased speed was obtained, the road wheel rotating twice as fast as the crankshaft. (Just as a three-speed hub rotates faster in high gear when the input is fed to the planet cage and output taken from the annulus.)
The second version was a three-speed, which offered additionally the 50% decrease. Thus it was necessary to be able to declutch the first bevel wheel from the driving wheel and instead clutch the cross-head to the driving wheel - and also to clutch the crankshaft to the first bevel wheel. (Like low gear in a three-speed, where the power input is to the annulus and the output is taken from the planet cage.)
The second bevel wheel, instead of being permanently locked to the fork, was held by a friction clutch operated by a cord or other linkage to a lever.
With this version of the gear, moving the cranks to the right engaged high gear, the central position again gave freewheeling, and the left position gave low gear.
To change from high or low gear to direct drive, the rider released the cord-operated friction clutch, thus freeing the second bevel wheel. This was the equivalent of unlocking the sun wheel, and a bit like the situation with the older Sturmey-Archer five-speed hubs, where changing from high to extra high, or from low to extra low, required a separate lever which selected one sun or the other.
