Elastohydrodynamically lubricated finite line contacts operating under transient conditions

The effect of greenhouse gas emissions contributing to the global warming is today becoming an increasingly important problem worldwide and has led to increased efforts being made on improving tribological performance of interacting surfaces in mechanical systems. Due to increasingly stringent CO2regulations, a reduced fuel consumption has become a key area of interest for the automotive industry where low cost, low emission solutions are continuously developed and where low friction alternatives to machine elements currently in use are evaluated. Crankshaft roller bearings have been shown to reduce the mechanical friction in internal combustion engines compared to the plain (sliding) bearings used today, further leading to a reduced fuel consumption and thereby reduced CO2emissions. However, the transition from plain (sliding) bearings into crankshaft roller bearings means new challenges with e.g. increased noise, vibration and harshness (NVH) levels and reduced durability of the bearings. Therefore, in order to optimise the crankshaft roller bearings that operate under the highly transient conditions in the engine, an increased understanding of the tribological system is required. Research related to elastohydrodynamic lubrication (EHL) has led to the possibility to improve friction performance and durability of machine elements where lubricated non-conformal contact geometries interact. Traditionally, simplifications of the contacting geometries and the assumption of steady-state conditions have often been applied to the EHL analysis. The purpose of this work has thus been to develop a simulation model based on previous work done in the field and further utilise the model to simulate the contact on a detailed level, incorporating transient effects and the influence of oil behaviour using state-of-the-art modelling. The influence of the piezoviscous response and the compressibility-pressure behaviour of the lubricant on the sub-surface stress field were studied, showing that stiff lubricants may lead to increased stress concentrations in the vicinity of the surface, which may further influence the durability of the bearing. It was also seen that highly transient loading conditions applied to the contact initiate oscillations in the lubricated system, affecting pressure, film thickness and sub-surface stresses over time. These findings further elucidate the importance of including non-steady behaviour while analysing highly transient lubricating conditions of EHL contacts. By considering and optimising the aforementioned effects during design of crankshaft roller bearings, an improved NVH performance and an increased durability of the crankshaft roller bearing may be achieved