Publication

Rolling bearings used in sliding parts of various machines are required to reduce torque, thus decreasing the effects of global warming. To further contribute to this goal, it is necessary to reduce the viscosity, or the amount of the lubricant. However, this may result in oil film collapse in EHD (elastohydrodynamic) contacts. Therefore, it can be said that the monitoring technique of lubrication condition is necessary to achieve both lower torque and longer life of rolling bearings. Conventionally, the optical interferometry has been mainly used as a visualization technique of the lubrication condition in EHD contacts. Although the optical method can accurately measure the oil film thickness and its distribution, it cannot be applied to practical bearings. Normally, when monitoring the lubrication condition in steel/steel contacts, electrical methods have been applied. In recent years, the electrical impedance method has been developed, which can simultaneously monitor the thickness and breakdown ratio of oil film by applying the sinusoidal voltage. In this report, the conventional electrical methods are introduced, and the electrical impedance method developed in recent years will be especially described in detail.