System that maintains the last commanded position of device controlled by a two-stage, four-way electrohydraulic servo valve upon power interruption

A system, comprising:

• a fail-fixed valve body including a first inlet port, a second inlet port, a third inlet port, a first outlet port, and a second outlet port;
• a fail-fixed valve element disposed within the fail-fixed valve body and moveable therein between a first position, in which the first inlet port is in fluid communication with the first outlet port and the second inlet port is in fluid communication with the second outlet port, and a second position, in which the first inlet port is not in fluid communication with the first outlet port and the second inlet port is not in fluid communication with the second outlet port;
• and
• a two-stage, four-way electrohydraulic servo valve (EHSV) including:
• a servo valve body including a supply pressure port, a return pressure port, a head pressure port, a rod pressure port, and a fail-fixed control pressure port, the head pressure port in fluid communication with the first inlet port, the rod pressure port in fluid communication with the second inlet port, the fail-fixed control pressure port in fluid communication with the third inlet port and in fluid communication with the rod pressure port via a flow path, the flow path having a bleed orifice disposed therein,
• a first flow restriction formed in the head pressure port,
• a second flow restriction formed in the rod pressure port,
• a servo valve element disposed within the servo valve body and moveable therein between a centered control position and a plurality of non-centered control positions, and further moveable to an electrical null bias fail-fixed position, and
• a dual-channel torque motor coupled to the servo valve body,
• wherein:
• in the centered control position, the supply pressure port and the return pressure port are both fluidly isolated from the head pressure port, the rod pressure port, and the fail-fixed control pressure port,
• in the plurality of non-centered control positions, the supply pressure port and the return pressure port are both fluidly isolated from the fail-fixed control pressure port, and either (i) the supply pressure port is in fluid communication with the head pressure port and the return pressure port is in fluid communication with the rod pressure port or (ii) the supply pressure port is in fluid communication with the rod pressure port and the return pressure port is in fluid communication with the head pressure port, and
• in the electrical null bias fail-fixed position, the supply pressure port is in fluid communication with the fail-fixed control pressure port and the head pressure port, and the return pressure port is in fluid communication with the rod pressure port, whereby the fail-fixed valve element is moved from the first position to the second position.