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Aluminum-tin (Al-Sn) and aluminum-tin-silicon (Al-Sn-Si) alloy lined bimetals have traditionally been utilized in rod and main bearing applications in light duty gasoline engines due to their combination of strength and soft-phase properties, such as embeddability and conformabilty. The load carrying capability of Al-Sn-Si alloys can be further increased by applying a polymer overlay, but recent advances in engine design, to improve efficiency and reduce CO2 emissions, have resulted in maximum specific load requirements beyond the performance limits of current Al-Sn-Si-Cu products. In these instances, the usual option would be to specify a lead-free bronze-based bearing solution, which has increased strength, but necessitates greater weight and brings a significant cost disadvantage over aluminum products.

On urban and emission homologation cycles, engines operate predominantly at low speeds and part loads where engine friction losses represent around 10% of the consumed fuel energy but would account for 25% of the fuel consumption once combustion efficiency is taken into account. Under such mild conditions, engine and engine oil temperatures are also lower than ideal. The influence of oil viscosity on friction losses are significant. By reducing lubricant viscosity, engine friction, fuel consumption and emissions are reduced. Tribological and machine learning models were investigated to predict the effect of oil viscosity on fuel consumption during the FTP75 emission cycle with the use of detailed actual emission test measurements. Oil viscosity was calculated with the measured oil temperature. As the same vehicle transient is followed in the cold and hot phases, the models were evaluated by comparing their prediction of fuel consumption in the hot phase versus the measured value.

Low viscosity combined with appropriated additive technology is one of the main paths to reduce friction on Internal Combustion Engines. Japan is on the cutting edge of low viscosity oils, having already available SAE 0W-8 in the market. On the other hands, in emergent countries like Brazil, SAE 15W-40 is still used in some passenger cars while the Japanese origin car brands use SAE 0W-20. Lubricant friction additives type also differs depending on the original equipment manufacturer (OEM) origin, and the Japanese ones usually containing high amounts of the Molybdenum type. In this paper, some of the advantages and challenges of using low viscosity oils are discussed and emphasis is given in the friction reduction obtained with the synergic effects of the right choice of additives components type and the material/coating used in the engine parts. Ring-liner rig and floating liner engine tests comparing different oils will be presented.