AN INVESTIGATION IN LUBRICATION, CAGE DESIGN AND ELECTRIC DISCHARGE IN ROLLING ELEMENT BEARINGS FOR ELECTRIC VEHICLES

<p dir="ltr">Rolling element bearings (REBs) in electric vehicles (EVs) face difficulties from high rotational speeds and damage caused by stray electric currents. These factors affect lubrication performance and increase the risk of bearing failure due to electrically induced surface damage, limiting efficient bearing operation and life. These challenges have been comprehensively investigated in this work.</p><p dir="ltr">This study first investigates lubrication and cage design for these REBs using a combination of experimental and computational approaches. A custom test apparatus, designed to control the rotation of a single rolling element within a transparent cage segment, enabled examination of lubricant flow patterns within the cage pocket. High-speed camera was used to captured the formation of lubricant striations within the cage at varied operating speeds and cage positions. A two-phase computational fluid dynamics (CFD) model was developed to gain further understanding of cage lubrication, highlighting the role of lubricant surface tension in striation formation and supporting the experimental trends. The apparatus was adapted to an oil bath environment with custom transparent cage pockets of varying conformalities to visualize in-situ lubricant behavior and record pocket friction via a precise six axis load cell. The CFD model accurately predicted lubricant distribution and friction trends, showing that higher pocket conformality increases friction due to greater lubricant content.</p><p dir="ltr">In order to address lubrication challenges at elevated bearing speeds, the test setup was modified with a high-speed electrical motor. New grooved pocket designs were tested which exhibited substantial friction reduction for a wide range of roller speeds. The CFD model was extended to analyze lubrication in a complete bearing chamber, incorporating cage and raceway motion across various geometries, with grooved pockets consistently shown to reduce friction. Bearing cages for high-speed applications are often made from polymeric materials that deform under low loads due to their viscoelastic nature. To model the deformation at a lubricated roller-cage pocket contact, a Reynolds-based visco-elasto-hydrodynamic (VEHL) solver and a fluid-structure interaction (FSI) model were developed. Both methods showed strong agreement across varying degrees of material viscoelasticity.</p><p dir="ltr">In addition to bearing lubrication studies, this work also investigates electrically induced damage in isolated bearing contacts. A novel test setup was developed to examine electric discharge behavior between conductive bearing surfaces under controlled variation of voltage, current, and surface separation. Tests were performed using both direct current (DC) and alternating current (AC) power, with and without lubrication, to assess the influence of a combination of electrical and mechanical factors on discharge occurrence and surface damage. The resulting damage was characterized using optical surface profilometry, establishing correlations between the damage size and the applied conditions. A modified version of the setup incorporating a transparent conductive glass surface and high-speed imaging established in situ visualization of the discharge events for a range of test conditions. The high-speed videos revealed distinct differences in the nature of electric discharges between DC and AC signals.</p>