Electrified EHL line contact with dielectric breakdown of lubricant -- a numerical model

TL;DR

This work addresses electrically induced bearing damage (EIBD) by developing a numerical framework that couples an isothermal EHL line-contact solver with a discharge model formulated as a linear complementarity problem (LCP). The approach integrates interfacial resistance and capacitance to predict how discharge zones form and expand, how current density $J^*(x^*)$ and voltage $V^*(x^*)$ distribute under current- and voltage-driven loads, and how roughness modulates these electrical responses. Validation against established EHL scaling and a test of the parallel-plate capacitor assumption support the model’s key findings: discharge initiates near the minimum film thickness and broadens with increasing current, while roughness intensifies localized discharges and creates multiple sub-regions. While the framework offers a path toward mitigating EIBD, it also highlights limitations such as a uniform dielectric, DC loading, and the need for full RC network integration and density-dependent dielectric effects for future realism and applicability to AC operation.

Abstract

With the rapid growth of the electric vehicles with drive systems with higher voltages, power outputs, frequencies, and speeds, mitigating electrically induced bearing damage (EIBD) in electric motors has become critical. In this study, a novel numerical model characterizing discharge-induced current density and voltage drop at the elastohydrodynamic lubrication line contact interface is presented. The current density and voltage drop constitute a linear complimentarily problem, which is efficiently solved using the conjugate gradient method. This paper sheds light on electrical characteristics at the inaccessible lubrication interface during discharge, highlighting the significance of roughness radius of curvature on current density. This numerical model lays the groundwork for future research on mitigating or even permanently solving EIBD problems in electric motor bearings.

Figures (10)

• Figure 1: Schematic of a typical EHL line contact
• Figure 2: Schematic of electrified EHL line contact interface and discharge zone
• Figure 3: Schematic of the lubricant film thickness at the inlet, Hertzian contact region, and outlet
• Figure 4: (a) Dimensionless pressure and (b) dimensionless film thickness distributions with various Moe's parameters: $M = W(2U)^{-1/2} \in [2, 100]$ and $L = G (2U)^{1/4}= 10$. Other essential parameters are given in Table \ref{['tab:Table_1']}.
• Figure 5: Dimensionless current density ($J^*$) and voltage drop ($V^*$) distributions with four different values of $I^*$: (a) 0.001, (b) 0.01, (c) 0.1, (d) 1. $M = 20$, $L = 10$. The dashed line corresponds to the dimensionless breakdown voltage, which is the same as $h^*$. Other essential parameters are given in Table \ref{['tab:Table_1']}.