Abstract

A variable cam timing phaser mounted to a camshaft and including a housing assembly having an outer circumference for accepting a drive force; a rotor assembly received by the housing assembly defining a chamber separated into an advance chamber and retard chamber by a vane; a control valve in fluid communication with the advance chamber and the retard chamber, a source of fluid, and a sump through at least one exhaust line connected to at least one exhaust port; and at least one check valve in the at least one exhaust line between the control valve and the sump. The at least one check valve prevents air from the sump connected to the at least one exhaust port from being sucked into the variable cam timing phaser through the at least one exhaust port during a torque reversal of the camshaft.