The three-speed cycle gear which became known as the TriVelox was patented by Alec Shuttleworth and William Hill in the early 1930s. It went into production in about 1932. Unlike other derailleur gears of the time and those of today, which move the chain to change gear, the TriVelox moved the sprockets instead. This ensured a perfect chain line for all three gears. (In those days an in-line chain was regarded by some cycling authorities as an essential requirement!)
The complete patent document may be viewed here.
There is no evidence to suggest that either Shuttleworth or Hill were familiar with Edmund Hodgkinson's much earlier, but short-lived, Gradient gear: the Gradient also employed sliding sprockets but functioned by lifting the chain clear of them while changing gear . It was exhibited at the 1899 Stanley Show in London . However the patent agents for the TriVelox probably studied the patent for the Gradient and recognised the similarities between the two gears. Hence the patent application for the TriVelox emphasised its advantage over the Gradient, real or imagined, when it came to changing gear:
In a previous arrangement the chain has been lifted off one of the coaxially mounted sprockets and then dropped on the selected newly-aligned one after they had been shifted axially, a rather cumbersome operation during which free-wheeling was advisable. The main object of the [TriVelox] invention is to provide an improved arrangement which will be efficient and simple.
The TriVelox gear was developed at Tanfield Garage in Keighley. It was subsequently manufactured, in turn, by three companies: the Triumph Company Limited in Coventry; TriVelox Gears Limited, a subsidiary of Coventry Bicycles Limited; and the TriVelox Gear Company in Spennymoor, County Durham, a subsidiary of Smart & Brown (Engineers) Limited.
1. For a history of the Gradient gear, see: Frank Berto. The Dancing Chain. 4th edition. San Francisco: Cycling Publishing, 2012, pages 54-55 and 57-58; and Ron Shepherd, 'The Origins of Derailleur Gears', The Boneshaker, Winter 1990, pages 5-10. (The Boneshaker is the magazine of the Veteran-Cycle Club.) Shepherd also describes, on pages 11-12, an in-line derailleur that was patented in 1909 by a Frenchman named Gabriel Hervier. This gear, a descendant of the Gradient, derailed the chain by merely pushing the cluster of sprockets from side to side with a metal finger and did not rely, as did the Gradient and most of its other descendants, on a device for lifting the chain. Hence the Hervier gear anticipated the TriVelox by more than twenty years, although unlike the TriVelox it required the use of two cables for its operation.