Variable phase drive coupling

A variable phase drive coupling for providing drive from an engine crankshaft to two sets of cams, the drive coupling comprising a drive member connectable for rotation with the engine crankshaft and two driven members each connectable with a respective one of the two sets of cams, wherein the angular relationship of each of the driven members is independently variable relative to the drive member under the action of camshaft torque reversals, the driven members are hydraulically coupled for rotation with the drive member, the phase of the driven members is controlled by selectively enabling the flow of hydraulic fluid through one-way valves, and the flow of the hydraulic fluid is controlled by two concentrically mounted spool valves.