Measurement of EHL temperature by thin film sensors - Thermal insulation effects

The temperature of elastohydrodynamically lubricated (EHL) contacts strongly influences fluid friction. The higher the EHL temperature, the lower is the effective lubricant viscosity and hence shear stress. EHL contacts with Diamond-like Carbon (DLC) coatings have shown lower fluid friction than EHL contacts without DLC coatings. A strong thermal insulation effect resulting in higher EHL temperatures is indicated. This has been confirmed by theoretical investigations, but rarely validated experimentally. Hence, EHL temperatures were measured using thin film sensors for different bulk and coating materials on a twin-disk test rig. The measurements were analyzed by a thermal EHL (TEHL) simulation model. Simulated and measured EHL temperatures are in very good accordance and confirm the significance of thermal insulation effects.