Lubrication Condition Monitoring of Practical Ball Bearings by Electrical Impedance Method

Abstract

In this study, the electrical impedance method was developed to monitor the thickness and breakdown ratio of oil films in elliptical elastohydrodynamic (EHD) contacts of practical ball bearings. First, it is theoretically shown that the oil film thickness and breakdown ratio can be simultaneously measured from the complex impedance generated when a sinusoidal voltage is applied to elliptical contacts. Subsequently, lubrication conditions of practical ball bearings were monitored at an ambient temperature to verify the measurement accuracy of the developed method. The oil film thickness in the low-speed range was consistent with the theoretical value calculated by Hamrock-Dowson equation. However, in the high-speed range, the oil film was thinner than the theoretical value considered an ambient temperature. In this high-speed range, the results of both the outer ring temperature and bearing torque revealed that the viscous shear heating and starvation were occurring simultaneously, thus supporting that the measured thickness would be thinner than the theoretical value. Besides, the developed method can also measure the breakdown ratio, confirming that it increases in the lowspeed range where the bearing torque increases. That is, it indicates that not only the oil film thickness but also the breakdown ratio can be evaluated quantitatively.

Intrinsic Friction Behaviour Originating from Molecular Structure of Lubricant in Nanoscale Gap Fabricated by Microelectromechanical Systems

“…The oil film thickness is one of the most important factors in this friction test. The capacitance of oil films is often used to calculate the oil film thickness [46,47]. The capacitance of oil films was measured to obtain the oil film thickness.…”

Review of Tribological Failure Analysis and Lubrication Technology Research of Wind Power Bearings

“…This method reflects the oxidation of the lubricant by the change in the charging signal resulting from the contact (separation) of the oil-impregnated cellulose and polymer phases, i.e., when the potential is reduced, the lubricant is oxidized. Maruyama et al [ 213 ] developed an electrical impedance method for monitoring the lubrication status of deep groove ball bearings. The methodology was primarily for monitoring the oil film thickness and breakdown rate in elliptical elastomeric flow (EHD) contacts of bearings.…”

Comparison of analytic and numeric methods to calculate ball bearing capacitance

“…Different authors, i.e. [11,12,17,21,[24][25][26], used a semi-analytical method, Equation 3, to compute the capacitance of these areas as a function of a varying lubrication gap height ℎ( , ):…”

“…On the other hand, electrical bearing characteristics can be used sensorially, since they depend on the lubricant film thickness and thus on the load condition [9], which in turn requires a precise electrical modeling of the bearing. Therefore electrical models have been improved and utilized for sensorial applications [10][11][12]. In addition, capacitance measurements are used for lubrication film investigations as they have certain advantages compared to tactile or optical measurements [13].…”