Electromagnetic switching-valve position detection system

A system that detects a position of a valve spool of an electromagnetic switching-valve in which a moving core that is attracted and moved to a fixed core by an excitation of an energized solenoid displaces the valve spool to switch a passage of a hydraulic circuit, the system comprising:

• an electric current control circuit including
• a bridge diode into which an electric current from a power supply flows,
• a primary smoothing capacitor configured to smooth a direct current from the bridge diode,
• a switching transformer configured to transform a pulse wave alternating current which being converted from the direct current smoothed at the primary smoothing capacitor by switching between turning on and off of a switching element in a period based on a pulse signal generated by a pulse signal generator, into a predetermined alternating current voltage and transmit the predetermined alternating current voltage to a secondary side,
• a secondary diode configured to rectify the alternating current transmitted to the secondary side, and
• a secondary smoothing capacitor configured to further smooth and output the rectified direct current to the solenoid side;
• a control unit configured to control switching between turning on and off the switching element by adjusting a pulse duration of the pulse signal by the pulse signal generator based on an electric current command based on a command signal and based on a detected result on an outputted side of the electric current control circuit;
• a carrier wave generator configured to superimpose a high frequency carrier wave for position detection on a signal wave of the electric current command;
• and
• a detecting circuit configured to extract a frequency component of the carrier wave for the position detection from a voltage feedback signal of the solenoid, detect a voltage amplitude from the frequency component, and obtain an amplitude signal based on the voltage amplitude, wherein the control unit further has
• a position determining circuit configured to determine a position of the valve spool based on the amplitude signal and pre-set determination reference values corresponding to valve spool positions, and
• a determination circuit configured to output a valve position signal based on the determination signal of the position determining circuit.