US Patent 7000580 Control valves with integrated check valves

A spool valve for variable cam timing phaser comprising a spool, a plurality of check valves and passages from the advance chamber and the retard chamber to a port in the spool valve. The spool having at least two lands separated by a central spindle, slidably mounted within a bore. When the spool is in the first position, fluid from the advance chamber flows through the passage and the port to the bore surrounding the central spindle of the spool valve and through a check valve and port to the passage to the retard chamber. When the spool is in the second position, fluid from the retard chamber flows through the passage and the port to the bore surrounding the central spindle of the spool valve and through a check valve and port to the passage to the advance chamber.