Variable pitch screw drives

Abstract The propulsion of vehicles by a variable pitch screw parallel to the track has been proved in the past to be safe and efficient, but entailed a large and expensive screw shaft. Distributing the contact between the vehicle and the shaft amongst a series of roller followers mounted on a development of a Sarrus mechanism, reduces the problems causing the size and expense. In particular lateral reactions on the vehicle and the shaft can be balanced and gaps in the screw shaft, required for support bearings, can be crossed.