Automatic temperature control of a hydraulic system via stepped pressure modulation, a dual stage valve optimization

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Bacchiega, G.
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The AW 609 will be the world’s first civilian tiltrotor aircraft, and the full triplex redundant FBW hydraulic system is a key technology that will make this unique aircraft possible. The majority of aircraft actuation systems rely on constant pressure hydraulic power generated by variable displacement, mechanically actuated and pressure controlled hydraulic pumps. One of the possible failure modes of the hydraulic systems is associated to pump pressure regulator hardover, where the delivery pressure and flow of the pump reach the highest possible value due to inability of the regulator to correctly close the mechanical loop and reduce displacement. The state of the art of aerospace hydraulic circuit technology during this failure scenario does not grant pressure preservation and a proper control of temperature excess; therefore it is an objective of this design to provide a hydraulic system in which solenoid operated shut off valves and oversized heat exchangers are not required to manage such condition. Results evaluation shows that unloading of nominal pressure will reduce the energy transferred to the fluid converted in heat, placing the system within the safe temperature operating envelope and permitting a temperature limiting control of the circuit with the pump failed. In case of temperature decrease or recovery of pump functionality, the system can return to its normal functions. This paper reviews the AW 609 automatic temperature control requirements, design, and development test results.