Patent ID: 7968502

Claim:
A system having diamond-like carbon (DLC) contact surfaces, comprising: relatively movable, facing contact surfaces at least one of which is coated with DLC, and a lubricant for a system having DLC contact surfaces interposed between said contact surfaces, said lubricant fulfilling following conditions (a), (b), (c), and (d): (a) wherein said lubricant for a system having DLC contact surfaces comprises a lubricant base oil (A) containing, as a main component, a base oil (X) selected from the group consisting of a hydrocracked mineral oil, a wax-isomerized mineral oil, a poly-α-olefin base oil, and mixtures thereof, wherein said base oil (X) has a kinematic viscosity of 3.5 to 5 mm 2 /s at 100° C., a total aromatic content of 0 to 2 mass %, and a sulfur content of not higher than 0.002 mass %; (b) wherein said lubricant for a system having DLC contact surfaces has a sulfur content of not higher than 0.2 mass %; (c) wherein said lubricant comprises 0.5 to 1.4 mass % friction modifier comprising glycerin monooleate, and at least two of a 0.05 to 0.2 mass % alkali metal or alkaline earth metal salicylate in terms of metal element as sulfur-free metal detergent (B), a 0.01 to 0.1 mass % zinc dialkylphosphate in terms of phosphorus elements as a sulfur-free phosphorus compound (C), and a 0.5 to 2 mass % sulfur-free ashless anti-oxidant (D); and (d) wherein said lubricant is free of sulfur-containing additives selected from the group consisting of zinc dithiophosphate, sulfur-containing metal detergents, and mixtures thereof.