Sectioned model of a motor car steering gear

Marles steering gear for cars, with spiral cam, sectioned model

This is an example of the steering gear for motor vehicles patented by Mr. H. Marles in 1914. In it spiral cams, fixed to the lower end of the steering pillar, bear on a pair of rollers which are mounted on a crank connected with the drop arm.

The rollers are mounted on an axis normally parallel with the steering pillar, and the cams are set opposite in phase so that, when the wheel is turned, one roller approaches the pillar, while the other recedes from it, but both remain in contact with the cams. In one example, used for light vehicles, single turn cams are used which have a variable pitch and permit the wheel to turn through about 300 degrees. For 40 degrees on each side of the central position the gear ratio is low and constant, but beyond this angle the ratio is constantly increasing, so that sharp turns may be made without excessive motion of the wheel. For heavy vehicles, a double-turn constant ratio cam is used, which permits the wheel to turn through about 1.75 revs.

In this system friction is reduced to a minimum, as the cam and the rollers have a purely rolling motion; ball or roller bearings may, however, be fitted. It is stated that the steering is very light, that wear does not take place, and that no backlash develops.