Hydromechanical mechanical continuously variable transmission

Abstract

An automatic continuously variable transmission having a power train with a dual path hydromechanical unit and a multistep ratio mechanical gear unit connected in series for overall continuously variable ratio change. The hydromechanical unit has planetary gearing and a variable displacement hydrostatic transmission connecting the reaction and output members to provide progressive and step ratio change. The controls have an automatic gear unit control responsive to output speed and torque demand for step shifting the gear unit to higher gear ratios at higher speeds, and a hydrostatic control responsive to input speed, output speed, and throttle position having hydrostatic power transfer pressure and displacement control of hydromechanical unit speed ratio in first gear from zero at stall through the mechanical speed ratio at zero reaction member speed to the stepup speed ratio and a cycle on each gear shift to step change to a step-down ratio to provide the same overall ratio and to progressively increase the speed ratio from the step-down speed ratio through the mechanical speed ratio to the next step-up speedratio in intermediate gear ratios and, in the highest gear ratio, only up to the mechanical speed ratio. The overall speed ratio is continuusly varied from zero with all power transmitted hydraulically at stall for starting drive to maximum speed ratio with all power transmitted mechanically to meet an engine speed and vehicle speed program varying with throttle for optimum engine and vehicle performance.