Method to reduce rotational oscillation of a vane style phaser with a center mounted spool valve

A phaser for limiting leakage across a plurality of chambers for an internal combustion engine having at least one camshaft comprising:

• a housing having 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 the plurality of chambers, the vane being capable of rotation to shift the relative angular position of the housing and the rotor, wherein when the housing and the rotor are fixed relative to each other they maintain a phase angle;
• a spool valve comprising a spool having a plurality of lands slidably mounted within in a bore in the rotor, the spool slidable to route operating fluid from a supply of pressurized fluid to the chambers, wherein at least two of the plurality of lands prevent operating fluid from the supply to the chambers when the housing and rotor are fixed relative to each other;
• and
• at least one passage from the supply to the chambers for providing makeup fluid, wherein the passage contains a check valve and a restrictor.

A method of operating a phaser for limiting leakage across a plurality of chambers for an internal combustion engine having at least one camshaft a housing having 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 plurality of chambers, the vane being capable of rotation to shift the relative angular position of the housing and the rotor, a spool valve comprising a spool with a plurality of lands slidably mounted within in a bore in the rotor, the spool slidable to route operating fluid from a supply of pressurized fluid to the chambers, the steps comprising:
• moving the phaser to a first null position by fixing the housing relative to a rotor to maintain a phase angle, such that the spool with the plurality of lands prevents operating fluid from entering the plurality of chambers, limiting leakage from chamber to chamber such that oscillation of the phaser is limited;
• and
• moving the phaser to a second non-null position by moving the housing relative to the rotor, such that the spool with the plurality of lands allows operating fluid to enter the plurality of chambers through at least one passage from the supply line to the chambers for providing makeup fluid, wherein the passage contains a check valve and a restrictor, such that the restrictor restricts the loss of operating fluid from the phaser when the phaser is the non-null position.