Patent ID: 8678129

Claim:
A method for charging an accumulator of a vehicle steering system, the vehicle steering system including a hydraulic pump, the accumulator, an accumulator charging circuit, a bypass circuit, and a steering control unit, the hydraulic pump supplying hydraulic fluid to the accumulator charging circuit and the bypass circuit, the method of charging an accumulator comprising: opening a charging valve of the accumulator charging circuit to allow hydraulic fluid to flow from the hydraulic pump to the accumulator; closing a hysteresis valve of the accumulator charging circuit when the hydraulic fluid in the accumulator reaches a first fluid pressure, wherein before the hysteresis valve is closed, hydraulic fluid flowing through the hysteresis valve applies a pressure via a first pilot of the charging valve; closing the charging valve after the hysteresis valve is closed, wherein the charging valve is closed when a combined pressure applied by the first pilot and a spring drops below a pressure applied by a second pilot of the charging valve; and opening the charging valve to allow hydraulic fluid to flow from the hydraulic pump to the accumulator when the pressure applied by the second pilot of the charging valve decreases below the combined pressure applied by the first pilot and the spring, wherein the accumulator is charged only when the bypass circuit detects a loss of hydraulic fluid pressure.