Caterpillar Tractor Co.

Charles E Beals

Ronald L Satzler

Robert O Chambers

Edwin E Hanson

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.

Hydraulic control system for a hydrostatic-mechanical transmission

A drive apparatus for a rotary output member of a vehicle or the like includes a pair of orbiting members having outwardly-projecting teeth which engage with inwardly-projecting teeth of an output member. Hydraulically-actuated piston and cylinder means provide orbiting of the orbiting members, through a rotary valving element, to in turn rotate the rotary output member.

Valving for dual radial piston motor

A hydromechanical vehicle transmission system for an engine most efficiently operated at a single speed is disclosed providing an infinitely variable reduction ratio for a given constant input speed requiring minimum operator skill in operation of the vehicle speed control and the engine torque control in both full and part load operation. The transmission consists of a multi-speed hydrostatic mechanical arrangement using a variable displacement hydrostatic pump-motor in conjunction with a fixed displacement hydrostatic pump-motor providing two power paths through the transmission, one hydrostatic and one mechanical. The preferred embodiment discloses four gear ranges although three gear ranges are sufficient to fulfill the objects of the invention. A split torque recycling planetary unit is coupled with the hydrostatic units and two conventional planet trains, the low and reverse range being fully hydrostatic, the intermediate ranges a combination of hydrostatic and mechanical drive, the high range being hydrostatic and mechanical in the lower output speed portion and fully mechanical in the higher output speed area when the hydrostatic path is locked out and engine speed is increased. Control of the transmission is provided through a hydraulically operated automatic system allowing minimum override capability on the part of the operator. Automatic shifting of reduction ratio is accomplished by comparing actual engine speed to an operator commanded engine speed with resulting upshifting or downshifting of the variable displacement unit and if required a selection of a different gear range occuring without operator intervention except for a capability to limit the highest ratio selected to one of the four gear ratios. The fully hydrostatic low and reverse range may be fully controlled by the operator limiting the displacement of the variable displacement hydrostatic pump-motor to a selected level.

Growing community of inventors

Pekin, IL, United States of America

Charles E Beals