An internal DPCS feeds (13) engine oil pressure (32) to one side
(19) of the spool and a solenoid controlled pressure (14) to a piston
(12) that has twice the area as that side (19) of the spool. The
spool end (21) that is fed control pressure is preferably twice the area
of the spool end (19) that is fed with engine oil pressure. A spring (18)
mounted in the phaser pushes the spool (25) to the default position in case
of solenoid failure. A PWM solenoid valve (15) or a proportional solenoid
valve controls the oil flow to the large area end (21) of the spool (25).
In a preferred embodiment of the invention, a position sensor (34) further
controls the position of the spool valve (28).
