Importance

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Abstract

A hydraulic control valve for a continuously-variable-ratio transmission (CVT), particularly one of the toroidal race rolling traction type. The transmission includes hydraulically-operated clutches (25,26) whose capacity to transmit torque varies with the operating pressure supplied to them. The transmitted ratio is related to the position of a hydraulic ram (35), which when it overshoots its normal stroke creates a pressure rise upstream of it in the circuit. This pressure rise first resists further overshoot, and then causes a reduction in the clutch operating pressure. Ram position is controlled by valves (56,57) which are located downstream of the ram, and which are themselves sensitive (via 58) to feedback from upstream circuit pressure: when that pressure rises, the valves open so as to depress the downstream circuit pressure by which the clutches are operated (via 68). A double-acting ram is shown, controlled by a circuit comprising two parallel hydraulic lines (42,54: 43,55) associated respectively with the opposite ends (36,37) of the ram, each line being controlled by a separate downstream control valve. The pressure feedback to the control valves and the operating pressure for the clutches are taken from cross-connections (48,60) between the two lines, so that each such pressure always has the higher of the values existing in the two lines at each end of the cross-connection.

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First Claim