Cam phaser having a torsional bias spring to offset retarding force of camshaft friction

摘要

A vane-type camshaft phaser wherein a coil spring under torsional compression or extension is disposed coaxially within an annular cavity formed in either the cover plate or back plate. A first end of the spring is connected to the cover plate or back plate, and a second end extends from the cavity and is connected to the phaser rotor. The spring constant is selected such that a biasing torque is exerted on the rotor in the valve-opening-advancing direction which counters the inherent valve-opening-retarding torque bias of the camshaft during operation. The bias spring permits more rapid response to a demand on the cam phaser for advancing valve timing, and is also useful in orienting the camshaft advantageously, especially an exhaust valve camshaft, in a timing-advanced position when the engine is shut off or operating at low engine speed.