Cam phasing system with mid-range engine shutdown

A camshaft phaser system includes an oil control spool valve having two opposing springs to center the spool at a rest position to lock the phaser rotor by blocking supply/vent to both the C 1 and C 2 chambers, obviating a conventional locking pin mechanism. A double-acting solenoid actuator moves the spool to first and second positions, supplying or venting C 1 and C 2, respectively. The rotor may be locked hydraulically at any position between full advance and full retard. A system for monitoring the rotational positions of the crankshaft and camshaft includes magnets disposed on opposite sides of the shaft axis. A magnetic sensing element senses the rotational direction of the magnetic field for each position of the shaft. An engine control module uses the position signal and an algorithm to lock the rotor at a desired position.