ANALYSIS OF FAILSAFE HYDRAULIC ACTUATION SYSTEM USING PASSIVE RELIEF VALVES; APPLICATION FOR POWER ASSISTING DEVICES

This paper presents a hydraulic circuit to ensure safety actuation mechanically. The system includes passive valves for safety operation. When the actuation system moves toward intended direction discharged hydraulic fluid from pump goes through the proposed passive valves and flows into the actuator cylinder to assist movement of the actuator. Consequently, supplied pressure from the pump is correctly loaded to the cylinder. On the other hand, when the actuation system moves for unintended direction, relief port to relieve pressure of the actuator is formed and at the same time bypass channel from higher pressure side of the pump to lower pressure side of the pump is formed by the proposed passive valve. As a result, the supplied flow is bypassed by the valve and pressure of the cylinder is kept on lower than the discharged pressure of the pump. Simulations are carried out to evaluate the effectiveness of the circuit.