A two-stage servovalve comprising:
- a motor having a stator and a rotor having a rotor null position and configured and arranged to rotate about a motor axis under the effect of a magnetic field generated by said stator;
- a first bias mechanism configured and arranged to bias said rotor to said rotor null position;
- a first stage valve having a first valve member movably mounted in a first chamber along a first valve axis, and adapted to be moved from a first null position to a first off-null position along said first chamber axis to selectively meter fluid flow from at least one port defined between said first valve member and said first chamber;
- a second stage valve in fluid communication with said port of said first stage valve and having a second valve member movably mounted in a second chamber along a second valve axis, and adapted to be moved from a first position to a second position along said second valve axis as a function of movement of said first valve member, to selectively meter the flow of fluid from at least one control port and at least one reference port between said second valve member and said second chamber;
- said first stage valve and said second stage valve configured and arranged such that said second stage valve member is at a pressure equilibrium and does not move when said first stage valve member is in said null position;
- a reference stage element in fluid communication with said reference port of said second stage valve and having a separate reference member movably mounted in a reference chamber along a reference axis, and adapted to be moved from a first position to a second position along said reference axis as a function of a pressure differential on said reference member;
- a second bias mechanism configured and arranged to bias said reference member along said reference axis;
- a transfer link acting between said first valve member and said reference member;
- an eccentric drive member acting between said rotor and said transfer link and having a first eccentric axis that is off-set a distance from said motor axis and arranged such that selective rotation of said rotor about said motor axis causes said transfer link to move;
- said transfer link and said drive member configured and arranged such that selective movement of said rotor from said rotor null position to a second rotor position causes said drive member and said transfer link to move said first valve member from said first null position to said first off-null position;
- movement of said first valve member from said first null position to said first off-null position causes said second valve member to move from said first position to said second position;
- and
- said movement of said second valve member to said second position applies on said reference member a pressure differential from a load;
- said pressure differential on said reference member causes movement of said reference member;
- and
- said movement of said reference member causes said transfer link to move said first valve member from said first off-null position back to said null position.