Hydraulic servo system for power steering

Claim 1

IN A HYDRAULIC SERVO SYSTEM FOR A POWER STEERING ASSEMBLY INCLUDING A FLUID RESERVOIR, AN ENGINE DRIVEN PUMP, A MANUALLY OPERATED CONTROL PUMP CONNECTED TO A STEERING WHEEL TO ACTUATE SAID CONTROL PUMP, A REVERSIBLE HYDRAULIC STEERING CYLINDER CONNECTED TO THE WHEELS OF A VEHICLE TO BE STEERED, AND AN OPEN CENTER SPOOL VALVE TO CONTROL THE FLOW OF FLUID TO SAID HYDRAULIC CYLINDER FROM SAID PUMPS, SAID VALVE PROVIDING A FLUID CIRCUIT WHEREBY FLUID FROM SAID ENGINE DRIVEN PUMP IS DIRECTED THROUGH SAID CONTROL PUMP BEFORE BEING DIRECTED TO SAID STEERING CYLINDER, SAID VALVE INCLUDING MEANS PROVIDING FIRST AND SECOND FLUID CHAMBERS, SAID FIRST FLUID CHAMBER CONTAINING CONTROL PUMP FLUID ON ITS WAY TO SAID STEERING CYLINDER, SAID CONTROL PUMP FLUID BEING AT A RELATIVELY GREATER PRESSURE THAN SAID ENGINE DRIVEN PUMP FLUID, SAID VALVE SECOND FLUID CHAMBER CONTAINING FLUID DISPLACED FROM SAID STEERING CYLINDER, SAID FLUID BEING AT A RELATIVELY LOWER PRESSURE THAN SAID ENGINE DRIVEN PUMP FLUID, THE IMPROVEMENT COMPRISING: MEANS PROVIDING A THIRD FLUID CHAMBER CONTAINING FLUID FROM SAID ENGINE DRIVEN PUMP, SAID THIRD FLUID CHAMBER BEING POSITIONED IN SAID VALVE BETWEEN SAID FIRST AND SECOND FLUID CHAMBERS PRESENTING A BUFFERING ZONE OF INTERMEDIATE PRESSURE FLUID RESTRICTING LEAKAGE OF FLUID FROM SAID FIRST FLUID CHAMBER TENDING TO RESULT IN STEERING WHEEL SLIP.