Friction dissipation in reciprocating internal combustion engines: camshaft bearings

The increasing environmental awareness of the last decades has led to a huge tightening of the restrictions on vehicle pollutant and carbon dioxide emissions. Friction dissipation plays a strategic role as its reduction necessarily leads to a decrease in CO2 emissions. Valve timing system is responsible for a significant part of the overall friction losses and provides a relatively wide margin of improvement. This system regulates intake and exhaust flows in the combustion chamber. The camshaft allows the motion transmission between the crankshaft and the valves. The main goal of this research is the friction dissipation modeling in camshaft bearings of reciprocating internal combustion engines. The proposed model is aimed to investigate possible optimization strategies and to evaluate, with an appropriate precision to the design phase, different constructive solutions of the camshaft from the point of view of friction losses. An empiric model for the evaluation of the Stribeck curve was proposed. It allows to estimate friction coefficient explicitly through a continuous function. Then, this study showed that camshaft friction losses optimization is possible, through the careful adjustment of parameters such as number of bearings, camshaft diameter and bearings dimensions.