Hydrostatic transmission assembly and method of increasing the torque and speed range thereof

摘要

A hydrostatic transmission assembly is disclosed in which a variable displacement hydraulic pump is coupled to drive a variable displacement hydraulic motor. The output shaft of the motor in turn is coupled to the input of a mechanical transmission having a gear change ratio substantially equal to the hydraulic motor displacement (stroke) ratio. Control of the shifting of the mechanical transmission and the stroking or destroking of the motor is provided. When the output shaft of the transmission reaches a predetermined sensed speed proximate the torque and speed limit of the pump and motor, the mechanical transmission is simultaneously shifted as the motor is fully stroked or destroked to enable pressure surge-free and torque peak-free extension of the torque and speed range of the transmission assembly. A method is also disclosed in which the torque and speed range of the hydrostatic transmission is substantially increased by coupling a mechanical transmission to a hydrostatic drive and simultaneously shifting the transmission while the hydraulic motor portion of the drive is either stroked or destroked.