Patent ID: 7137371

Claim:
A variable cam timing phaser for an internal combustion engine having at least one camshaft comprising: a housing having an outer circumference for accepting drive force; a rotor for connection to a camshaft coaxially located within the housing, the housing and the rotor defining at least one vane separating a plurality of chambers, at least one chamber being an advance chamber and another chamber being a retard chamber, the vane being capable of rotation to shift the relative angular position of the housing and the rotor; a spool valve comprising a spool having a plurality of lands slidably mounted within a bore in the rotor, the spool slidable from an advance position through a holding position to a retard position; an advance passage extending from the advance chamber to the spool valve; a retard passage extending from the retard chamber to the spool valve; an advance exhaust passage extending from the spool valve to a return passage, for routing fluid back to the advance chamber and the retard chamber through the spool valve; a retard exhaust passage extending from the spool valve to the return passage for routing fluid back to the advance chamber and the retard chamber through the spool valve; a single recirculation check valve in the return passage allowing fluid to flow in a first direction and preventing fluid flow in an opposite direction; a supply passage coupled to the return passage for supplying operating fluid to the advance chamber and the retard chamber through the single recirculation check valve for makeup only; wherein the single recirculation check valve in the return passage is between the supply passage and the spool valve; wherein when the spool is in the retard position, fluid flows from the advance chamber through the advance passage, the spool and the advance exhaust passage and into the return passage through the single recirculation check valve to the retard chamber; wherein when the spool is in the advance position fluid flows from the retard chamber through the retard passage, the spool and the retard exhaust passage and into the return passage through the single recirculation check valve to the advance chamber.