Marles steering gear

Marles steering gear was an hour-glass-and-roller steering gear for mechanically propelled vehicles invented by British inventor and businessman Henry Marles (1871-1955) who also gave his name to his joint-venture Ransome & Marles a major British ball-bearing manufacturer. Aside from ease of use Marles' steering's great appeal to drivers was its lack of backlash.

Invented in 1913 it became common from the 1920s until the mid 1950s. In USA when power-steering becoming popular in the 1950s it was mainly replaced by worm and recirculating-ball nut steering —which incorporated ball-bearings. In Europe Marles' design was replaced by a general move to rack-and-pinion steering gear.

A pair of opposed cams or cam surfaces connected to the steering column operate a transverse rocker shaft carrying the vehicle's steering arm. The point of difference was the use of purely rolling contact and not sliding contact in the meshing elements of a worm-and-follower steering gear.

Ultimately its most popular form was an hour-glass shaped worm which engages with a double-toothed roller follower on the rocker shaft for the steering arm. The result is that substantially the same leverage is provided from one steering lock to the other.

Marles Variomatic is the trademark name of an automotive power steering system of the 1960s and 70s, which was characterised by its variable steering ratio. It was developed in 1961 by the Adwest Engineering Co Ltd of Reading, England, in conjunction with the Bendix Corporation. The Adwest product was fitted to several British luxury automobiles of the era, including; the Aston Martin V8, Daimler Sovereign, Jaguar 420 and Rover P6B 3500S.

The Variomatic is essentially a refinement of the power assisted "cam and roller" type of steering, being referred to instead as "hour glass and roller". The steering box contains an "hour glass" cam machined with a varying helix angle to provide the variable steering ratio. In common with other power steering systems, control of power assistance in response to steering inputs is via a hydraulic control valve in the input shaft of the cam. Pressurised hydraulic fluid is supplied to the system by a separate hydraulic pump.

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