Patent ID: 8555918

Claim:
A flow rate control valve comprising: a spool having a plurality of valve members and slidably accommodated in a sleeve having a plurality of ports, said flow rate control valve performing flow rate control by linearly moving the spool with an actuator; a generally straight target probe formed of a magnetically-responsive substance and mounted to one end of the spool, the sleeve having an opening formed at one end thereof to permit passage there through of said target probe; a sensor housing mounted to the one end of the sleeve for detecting a linear position of said target probe, said sensor housing having a cylinder section formed of a non-magnetic substance and defining an inner space to permit entry therein of said target probe, the inner space communicating with the opening formed in the one end of the sleeve; first and second coils disposed around the cylinder section within said sensor housing and axially spaced from each other by a predetermined distance; and a ring-shaped magnetically-responsive shield member inside said second coil, wherein said first coil is disposed so as to respond to said target probe, wherein said target probe has a tapered section that is elongated in an axial direction thereof so that its volume gradually decreases toward a distal end thereof so that magnetic response of said first coil gradually varies in one direction in response to a linear position of said target probe, wherein said second coil is configured to not respond to linear displacement of said target probe at least within a predetermined linear displacement range of said target probe, wherein a linear position of said target probe, and hence a position of the spool, is detected through differential synthesis performed between outputs of the first and second coils, wherein said first coil is located nearer to said target probe than said second coil, and wherein the distal end of said target probe is extendable into a sensitive region of said second coil.