Operating strategy for optimized CO2 and NOx emissions of diesel-engine mild-hybrid vehicles

Abstract

Over the last decades the pollutant emissions of passenger-car diesel engines have been reduced significantly. Particulate emissions were cut back to a minimum with the introduction of diesel particulate filters. The upcoming EU6 exhaust regulation will further reduce the nitrogen-oxide emissions. In many cases an efficient nitrogenoxide exhaust-gas aftertreatment system will be installed. In the years to come, however, the requirements for passenger-car diesel engines will become even more demanding in various regards. On the one hand, current discussions are focusing on the registration of pollutant emissions produced during real driving (RDE, real driving emissions). Compared to the currently applicable European driving cycle for passenger cars future test cycles will include stricter requirements regarding output and transient operations. On the other hand, significant further reductions of CO₂ emissions must be achieved for all passenger cars. For this purpose, improvements on the diesel engine (e.g. reduced friction, further development of more efficient combustion methods, etc.) will be complemented by various approaches of hybridization. Robert Bosch GmbH is running comprehensive studies on the optimization of the operating behaviour of hybridized diesel-engine powertrains. The aim of these studies is to develop scalable engine-control functions resulting in the efficient and optimum matching of the diesel engine and the hybridization concept. The functions presented in this paper support the significant further reduction of the NO_x emissions of diesel passenger cars especially under real driving conditions while leading only to minor fuel consumption penalties.