Unveiling the impact of start-stop on passenger cars: A comprehensive wear assessment of ultralow viscosity lubricant formulations based on an elastohydrodynamic simulation

Abstract

Contemporary trends in passenger car development are increasingly focused on implementing CO2 reduction technologies as a response to stringent greenhouse gas emissions limitations established by influential organizations such as the International Energy Agency (IEA), International Council on Clean Transportation (ICCT), and the European Commission (EC). To mitigate penalties and decrease harmful gas emissions, original equipment manufacturers (OEMs) incorporate innovative features in passenger cars. To curtail investment in new technologies, OEMs limit experimental campaigns until they reach a high technology readiness level (TRL). Consequently, research and development departments emphasize numerical simulation tools for cost-effective solutions. The advent of start-stop systems, introduced in the last decade to reduce emissions, offers substantial benefits in fuel efficiency and emissions reduction. However, it has also been associated with premature wear in ICE components, attributed to challenges during engine startup events. This research investigates early wear on passenger car connecting rod bearings using an elastohydrodynamic (EHD) simulation model. Elastic deformation is incorporated through the rod finite element (FE) model. The study also presents a novel wear algorithm to predict wear depth over time during transient start-stop conditions. Notably, the algorithm accounts for surface roughness changes during wear. Four ultralow viscosity lubricants, characterized by their rheological and tribological properties, are evaluated with the simulation framework for improved bearing performance. A wear assessment is conducted to identify the most suitable lubricant among the four candidates. The results include analysis of transient start-stop cycles, wear depth predictions, and the evolution of surface roughness parameters. This process provides a comprehensive assessment to support lubricant selection for passenger cars with start-stop systems, highlighting the importance of non-Newtonian behavior.