US Patent 7815028 Clutch plate, friction clutch, and coupling device

A friction clutch includes an iron inner clutch plate and two iron outer clutch plates. Each clutch plate has a sliding surface that friction-engages with the other clutch plates. A diamond-like carbon film containing silicon, which functions as a solid lubricant, is formed on the sliding surface of each outer clutch plate through a conventional method such as plasma chemical vapor deposition. The diamond-like carbon film contains 1 wt % to 80 wt % of silicon. A coupling device includes a pilot clutch mechanism that has the friction clutch and an electromagnetic actuator. As a result, the friction clutch has an improved resistance to wear, and the coupling device is durable.