Compound steering system for endless-track vehicles

Claim 1

A vehicular steering system comprising: a pair of driven shafts coupled with respective traction elements on opposite sides of a vehicle body; a hydraulic torque converter with an input side and an output side; an engine coupled to said input side; reversible transmission means linking said output side with said driven shafts, said transmission means having two branches including respective differential-gear sets each having a driving input and a steering input; a continuously adjustable hydraulic power train coupled with said input side; a supplemental mechanical power train coupled with said output side; additive gear means provided with a first input shaft drivable from said engine via said hydraulic power train, a second input shaft drivable from said torque converter via said mechanical power train, and an output shaft; and link means forming two relatively reversed driving connections from said output shaft to said steering inputs for translating any rotation of said output shaft into mutually opposite torque components applied to said driven shafts; said transmission means further including a main shaft powered by said torque converter and a first pair of clutches for alternately connecting said main shaft with both driving inputs to reverse the sense of rotation of said driven shafts; said mechanical power train including a second pair of clutches for alternately connecting said main shaft with said second input shaft for rotating said output shaft in either of two directions; said additive gear means including a first and a second planetary-gear set in cascade with each other, each of said planetary-gear sets having two inputs, said hydraulic power train including pump means drivable by said engine and a pair of hydrostatic motors fluidically linked with said pump means, said motors being connected with respective inputs of said first planetary-gear set, said mechanical power train being connected with one input of said second planetary-gear set, the other input of said second planetary-gear set being connected with the output of said first planetary-gear set.