US Patent 7364511 Torsional vibration damper

A torsional vibration damper includes: a primary mass adapted to be coupled to an engine crankshaft and defining a substantially ring-shaped chamber that is divided into at least two portions; a secondary mass relatively rotatably connected to the primary mass and connectable with a clutch; and a damping unit for coupling the primary and secondary masses to each other in a rotationally elastic manner. The damping unit includes a plurality of coil springs, a pair of end guides, and a friction guide that is disposed between neighboring coil springs and provided with an outer circumferential surface configured to be rubbed against an outer wall of the ring-shaped chamber. An oil groove is formed on the outer circumferential surface of the friction guide and at least a portion of the oil groove is formed to be slanted with respect to a circumferential direction of the ring-shaped chamber.