Spool position indicator
AssigneeMoog Controls, Inc.
InventorThomas R. Frederick
Life of this patent
Estimating the term…
Abstract
An electro hydraulic servo valve has a pair of oppositely polarized magnets mounted in the surface of the spool of the valve to be controlled. A Hall effect sensor is mounted in the housing adjacent the magnets to precisely measure the position of the spool relative to the housing. The magnets and transducer are mounted on the longitudinal centerline of the spool to eliminate the spurious signals, due to temperature, vibrations, shock, hydraulic supply pressure and back pressure. The strength and spacing of the magnets and air gap are chosen to provide a linear output signal over the range of displacement desired and to provide the accuracy of location necessary for the particular configuration.
Claims22
A fluid servo valve comprising:
- an outer housing;
- a first valve member mounted in said outer housing forming a first stage of a servo valve;
- actuating means connected to said first valve member, said actuating means being connected to receive a command signal;
- a second valve member mounted in said outer housing forming a second stage of the servo valve, having a body portion with an axially displaceable spool element therein;
- said displaceable spool element being movable in said second valve member body portion under control of said first valve member;
- magnet means symmetrically mounted about an axial center of said displaceable spool element formed a magnetic null at said center;
- a Hall effect transducer fixed in said second valve member body portion centered on the magnetic null of said magnetic means on said spool element;
- and
- circuit means coupled to said Hall effect transducer for producing an analog output signal proportional to the axial displacement of said spool element, relative to said second valve member body portion.
In a hydraulic servo valve having a valve body, a spool displaceably mounted in the valve body and means for selectively positioning the spool in the valve body, the method of controlling the position of a movable spool element in a valve body which comprises the steps of:
- determining a hydraulic null position of a spool element in a valve body;
- determining a magnetic null of a magnetic field means;
- mounting said magnetic field means on said spool element centered at an axial center thereof so that the hydraulic null position and magnetic null position coincide;
- determining the signal output null of a Hall effect transducer;
- mounting said Hall effect transducer at a position in said valve body corresponding to the spool element axial center and adjacent said magnetic field means so that the Hall effect signal null and the hydraulic null positions coincide;
- displacing said movable spool element to generate a signal in said Hall effect transducer;
- deriving a linear signal from said Hall effect transducer signal proportional to the movement of said spool element;
- and
- using said Hall effect transducer signal to control the position of said spool element;
- whereby the extraneous effect of temperature, supply pressure, acceleration and back pressure on the Hall effect transducer signal are eliminated.
Apparatus for accurately determining the location of a movable fluid control element which includes:
- a moveable spool means in a valve body;
- magnet means fixed at a predetermined location on said movable spool means, said magnet means being centered about an axial center point on said movable spool means;
- Hall effect transducer means fixed in said valve body at a position corresponding to said magnet means;
- said magnet means and said Hall effect transducer means being selected and spaced apart to provide a generally linear magnetic field strength versus displacement function so that axial movement of said movable spool means relative to said center point on said movable spool means produces an output signal in said Hall effect transducer, within the range of said field strength versus displacement function, that is directly proportional to said spool displacement.
Dependencies are inferred from the claim text.