Development of Hydrogen-Free Diamond-Like Carbon Coating for Piston Rings
The first-ever application of a hydrogen-free diamond-like carbon (H free DLC) coating to a mass-production gasoline engine reduces friction between the cylinder bore and piston by 18%. It is explained the reducing friction effect of H free DLC by oil film thickness of piston ring. When H-free DLC is applied to top ring, friction is over 10% reduced. Because low friction coating is effective in a thin oil film at a large area near top dead center (TDC). It is also found that the friction reduction effect is enhanced when low viscosity engine oil is used. DLC as a low friction coating is more effective in a thinner oil film. In this study, the adhesion strength of H-free DLC coating on piston rings is improved because of providing a smooth substrate, the new washing process and the optimized coating characteristics. Adhesion strength is verified by test results using actual parts considered to contribute to piston ring load.