Pump output control system with high efficiency hydromechanical variable speed drive

A system for controlling the delivery rate of a liquid pump to a predetermined level, said pump including a source of substantially constant speed drive power and a pump exhibiting a non-linear power versus fluid delivery characteristic such that a predetermined reduction of said drive power effects a proportionally larger corresponding reduction of said delivery rate, the combination comprising:

• first means comprising a mechanical differential having a first shaft connected from said source of drive power, a second shaft connected to said pump and a third shaft providing an output at speed proportional to the difference between the speeds of said first and second shafts;
• second means comprising a fixed displacement hydraulic pump driven from said third shaft and a variable displacement hydraulic motor powered by pressurized hydraulic fluid from said fixed displacement hydraulic pump, said variable displacement hydraulic motor having an output shaft and displacement adjustment means controllable by an externally applied parameter;
• third means comprising a mechanical power reentry connection from said variable displacement hydraulic motor output shaft to a point in the power train between said source of drive power and said liquid pump;
• and fourth means responsive to the output pressure of said liquid pump as a parameter relating to said liquid pump delivery rate to control said displacement of said variable displacement hydraulic motor.