Hydrostatic transmission dual pressure charge-servo system

Claim 1

IN A HYDROSTATIC TRANSMISSION SYSTEM HAVING A VARIABLE DISPLACEMENT PUMP AND A VARIABLE DISPLACEMENT MOTOR HYDRAULICALLY INTERCONNECTED TO FORM A CLOSED CIRCUIT UNIT, AN OIL-COOLER FOR COOLING EXCESS HEATED FLUID DISCHARGED FROM SAID PUMP AND MOTOR UNIT, AND HYDRAULIC SERVO-MECHANISMS OPERATIVE FOR SELECTIVELY CONTROLLING DISPLACEMENT OF THE PUMP AND MOTOR ELEMENTS OF SAID UNIT, THE COMBINATION THEREWITH OF A RESERVOIR SOURCE OF FLUID, A DUAL PRESSURE OUTPUT FLUID SUPPLY PUMP, A PLURALITY OF CONTROL VALVES, CONDUITS COMMUNICATIVELY INTERCONNECTING SAID SUPPLY PUMP WITH SAID SOURCE OF FLUID AND WITH SAID PUMP AND MOTOR UNIT AND SERVO-MECHANISMS AND WITH SAID PLURALITY OF CONTROL VALVES, SAID SUPPLY PUMP BEING OPERATIVE FOR SUPPLYING MAKE-UP FLUID TO SAID PUMP AND MOTOR UNIT AT ONE PRESSURE AND AT A HIGHER PRESSURE TO SAID SERVO-MECHANISMS FOR OPERATION THEREOF, SAID PLURALITY OF CONTROL VALVES BEING OPERATIVE ONE VALVE FOR LIMITING PRESSURE OF MAKE-UP FLUID SUPPLIED SAID PUMP AND MOTOR UNIT FROM SAID SUPPLY PUMP, ONE VALVE FOR LIMITING PRESSURE OF FLUID SUPPLIED SAID SERVO-MECHANISMS FROM SAID SUPPLY PUMP AND ONE VALVE FOR MAINTAINING MINIMUM PRESSURE OF THE FLUID SUPPLIED SAID OIL-COOLER, BY-PASS VALVE MEANS, ADDITIONAL CONDUIT MEANS COMMUNICATIVELY INTERCONNECTING SAID BY-PASS VALVE, SAID OIL-COOLER, A SELECTED ONE OF SAID PLURALITY OF VALVES, SAID PUMP AND MOTOR UNIT AND SAID RESERVOIR SOURCE OF FLUID, AND HAVING SAID BY-PASS VALVE MEANS OPERATIVE FOR BY-PASSING FLUID AROUND SAID OIL-COILER.