Hydraulic control system for a hydrostatic-mechanical transmission

摘要

A hydraulic circuit adjusts an infinitely variable drive ratio hydro-mechanical transmission in response to movements of operators speed and torque controls to enable precise selection of the wheel torque of a vehicle and selective variation of ground speed by changing drive ratio while the driving engine operates at a constant engine speed. Control fluid from a pump driven by the engine is used to generate a displacement signal for the hydrostatic section of the transmission. The displacement signal is limited to a value determined by an operators maximum speed selector while being modulated within that limit by means which compare actual output torque with a selected torque signal from the operators controls and which vary the displacement signal to conform output torque with that called for by the operator. The displacement signal is further modified when necessary by engine underspeed and overspeed sensing means responsive to variations in control fluid flow from the pump. Additional means sense extremes of hydrostatic section displacement and automatically shift drive range in the mechanical section of the transmission when necessary to enable continued ground speed variation by drive ratio adjustment.