This presentation was held at the 2020 NAFEMS UK Conference "Inspiring Innovation through Engineering Simulation". The conference covered topics ranging from traditional FEA and CFD, to new and emerging areas including artificial intelligence, machine learning and EDA.

Resource Abstract

Roller bearings are critical components in hybrid and electric vehicle powertrains. They are often performance limiting, and introduce NVH (Noise, Vibration and Harshness), tribological and wear challenges. The high-speed and varying load conditions of modern electric powertrains necessitates accurate modelling of the bearings to ensure satisfactory system performance and durability. Furthermore, with a push towards achieving zero-prototype development, the use of advanced simulation tools to accurately predict their behaviour at both component and system level is becoming more prevalent.

For numerical analysis of high-speed bearings, the critical role of the elastohydrodynamic (EHL) film cannot be ignored. This, therefore, necessitates a tribodynamic (i.e. the combination of dynamics and contact mechanics) analysis.

This work presents numerical tribodynamic analysis of elements in a cylindrical roller bearing under test on an experimental rig. The need for a full dynamic model is circumvented using novel experimental methodology for measuring insitu bearing displacement.

The roller bearing undergoes a speed sweep from 0-15,000rpm with radial load applied to the shaft. The relative vertical displacement between the rigid inner and outer race is found using instrumentation on the shaft and bearing bore. A stepwise solution is performed on an individual roller as it passes through each angular position, with the displacement data used as a boundary condition to calculate 1-dimensional deflection within an explicit tribological model. At each angular position, lubricant film thickness and loading on the roller can be found. The change in film thickness over the speed sweep is observed, as well as the change in lubrication regime as the roller passes through loaded and unloaded regions. Using contact load values at specific time periods found from the explicit tribological model, a 1-dimensional numerical EHL solution based on Reynolds equation is then used to calculate the contact pressure profile in the loaded region of the roller.

Results reveal that the EHL film thickness increases from 0.2 to 2 microns across the speed sweep, with peaks of 5 microns as loading conditions change due to system resonance. Calculation of lubricant film thickness in these bearing models allows for the analysis of asperity interaction and frictional power loss which is not achievable using a dry contact analysis.