Patent ID: 8561583

Claim:
A variable cam timing phaser for adjusting phase between a first shaft and a second shaft using oil pressure from an oil pressure source, comprising: a housing assembly having an outer circumference to accept a drive force; and a rotor assembly having a plurality of vanes coaxially located within the housing assembly for connection to the first shaft, the housing assembly and the rotor assembly defining a plurality of segments, each segment divided into two chambers by one of the plurality of vanes, the plurality of segments comprising: at least one operating segment comprising an advance chamber and a retard chamber, the advance chamber and the retard chamber being oppositely switchable between at least a source of oil pressure and a drain, the vane being movable by oil pressure from the oil source applied to either the advance chamber or the retard chamber with the other of the advance chamber and the retard chamber being coupled to the drain, the moving of the vane acting to shift the relative angular phase of the rotor assembly and the housing assembly; and at least one assist segment comprising an assist chamber and a vent chamber, the vent chamber being vented to atmosphere; such that oil supplied to the assist chamber assists the motion of the vane in a direction.