Oil circuit and spool valve for selective control of variable valve lift systems

A spool valve assembly operable for an automatic control of an oil flow, the spool valve assembly comprising:

• an outer case comprising a first surface, a second surface on an opposite end of the first surface, and a lateral surface between the first surface and the second surface;
• a spool valve configured to slide axially between the first surface and the second surface within the outer case;
• a return spring adjacent to the first surface, the return spring being configured to cause the spool valve to return to a rest position;
• a first inlet port on the outer case configured for connecting with a first oil gallery, wherein the first oil gallery is operable as an outlet of a first oil control valve, and wherein the first inlet port is on the second surface of the outer case such that an oil flow through the first oil gallery into the first inlet port pressures the return spring to open to cause the spool valve to slide axially within the outer case to a non-rest position along a direction towards the first surface from the second surface;
• a second inlet port on the lateral surface of the outer case configured for connecting with a second oil gallery, wherein the second oil gallery is operable as an outlet of a second oil control valve;
• and
• a spool outlet on the outer case configured for connecting with a third oil gallery.