Hydraulic system for responsive splitting of engine power

Claim 1

A hydraulic system for a vehicle having an engine developing peak torque at a given speed, the engine arranged to power a motive drive train, a first fixed displacement pump, a variable displacement pump and a charge pump disposed to supply the entire fluid requirement of said variable displacement pump, comprising: an orifice positioned between said charge pump and said variable displacement pump, said orifice accepting substantially the entire discharge from said charge pump; control ram means operatively connected to said variable displacement pump to vary the displacement of said variable pump upon the application of fluid pressure to said control ram means; a conduit extending from the output of one of said fixed and variable displacement pumps to said control ram means; a speed valve disposed in said conduit, said speed valve being operatively associated with said orifice to shift between positions providing full flow and no flow in said conduit in response to the pressure drop across said orifice, the position of said speed valve being independent of the output pressure of said variable displacement pump; said hydraulic system being disposed to condition said variable pump for minimum displacement when said engine speed is below said given speed and for conditioning said variable pump for maximum displacement when said engine speed is above said given speed.