COIL SPRING

摘要

Disclosed is a coil spring wherein the hysteresis loss due to the friction resistance with an object member can be reduced, and the resistance to the contacts between coiled wires can be improved. An arc spring (41) is disposed in a clutch unit (1). In order to reduce the hysteresis loss, a wear-resistant layer having a friction coefficient (µ) of less than 0.15 and a hardness of Hv1000 or more is formed on the surface of the arc spring (41). The wear-resistant layer is a MoS2 layer (molybdenum disulfide layer), an electroless NiP layer (electroless nickel-phosphorus layer), a DLC layer (diamond like carbon layer), or a TiN layer (titanium nitride layer). The wear resistance can be improved in the wear resistant layer excluding the MoS2 layer. Regarding, specifically, the DLC layer, it is preferable that the DLC layer is formed on the surface of the coil spring shown in FIG. 2 which requires a high wear resistance, because the hardness of the DLC layer is approximately Hv3000.