A variable cam timing system for an internal combustion engine having at least one camshaft comprising:
- a housing with 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 chamber in the housing into an advance chamber and a retard chamber, the vane being capable of rotation to shift the relative angular position of the housing and the rotor;
- a locking pin slidably located in a bore in one of the rotor or the housing, comprising a body having a diameter adapted to a fluid-tight fit in the bore, and an inner end with a portion adapted to fit in a recess in the other of the rotor or the housing, the locking pin being moveable in the bore from a locked position to an unlocked position;
- a spool valve comprising a spool slidably located within a bore comprising an open outer end, an inner surface and an inner end and arranged along the bore, an advance port in fluid communication with the advance chamber, a retard check valve port in fluid communication with the retard chamber, a supply port, an advance check valve port in fluid communication with the advance chamber, a retard port in fluid communication with the retard chamber and the locking pin, and a vent port;
- the spool comprising, in order from an outer end to an inner end, a first land, a first groove, a second land, a second groove, a third land, a third groove, a fourth land, a fourth groove, and a fifth land,
- wherein when the spool is in the a retard position, closest to the end of the bore, the advance port is in fluid communication with the advance chamber and the retard check valve port, the retard check valve port is in fluid communication with the supply, the advance port, the retard chamber, and the lock pin, such that the locking pin is in an unlocked position, the advance check valve port is blocked by the third and fourth spool lands, the retard port is blocked by the fourth and fifth lands, and the vent port is blocked by the fifth land;
- wherein when the spool is in the null position, the advance port is blocked by the first land, the retard check valve port is in fluid communication with the supply, the retard chamber, the advance check valve port, the retard port, and the locking pin, such that the locking pin is in an unlocked position, the advance check valve port is in fluid communication with the supply, the retard check valve port, the advance chamber, and the retard port, the retard port is in fluid communication with supply, the retard check valve port, the advance check valve port, and the locking pin, the vent port is blocked by the fifth spool land;
- wherein when the spool is in the advanced position, the advance port is blocked by the first spool land, the retard check valve port is blocked by the first and second spool lands, the advance check valve port is in fluid communication with the advance chamber, the supply, and the retard port, the retard port is in fluid communication with the retard chamber, the advance check valve port and the locking pin, such that the locking pin is in an unlocked position, and the vent port is blocked by the fifth land;
- wherein when the spool is in the innermost advanced position, the advance port is blocked by the first land, the retard check valve port is blocked by the first and second lands, the advance check valve port is in fluid communication with the advance chamber and the supply, the retard port is in fluid communication with the retard chamber, the vent, and the locking pin, such that the locking pin is in a locked position, the vent port is in fluid communication with the retard port.