A high capacity electromagnetic clutch was developed by means of Si-containing diamond-like carbon (DLC-Si) coating. The dependency of the friction coefficient on sliding velocity for the DLC-Si film under oil lubricated condition was studied under a wide range of contact pressures. Automatic transmission fluid (ATF) with 35 sq mm/sec at 313K was used. The DLC-Si film showed a very small dependency of friction coefficient on sliding viscosity under a wide range of contact pressures in ATF. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).