Optimization of Hybrid Strategies with Heuristic Algorithms to Minimize Exhaust Emissions and Fuel Consumption

The hybrid powertrain is a promising concept to contribute to achieve future CO2-targets. This paper describes a method to improve future automotive powertrains efficiently in real world driving conditions. Beside the optimization of the internal combustion engine and the electric components, the operating strategy of the hybrid powertrain is of particular importance to minimize the vehicles fuel consumption. A combination of start/stop operation, downspeeding, load-point shifting and pure electric driving can provide substantial fuel savings compared to conventional powertrains. However, in addition to the fuel consumption the more and more stringent future emission legislation must be taken into the account when optimizing the operating strategy. A fast light-off of the catalytic converters and a control of the converter temperatures during pure electric driving must be achieved. Therefore, numerous parameters have to be optimized simultaneously to realize the best solution for the hybrid powertrain. A numerical optimization approach was used to define the operating strategies efficiently for the mentioned goals. The results of this optimization were compared to the fuel consumption and the exhaust emissions of the conventional powertrain. The potential of a further strategy optimisation could be evaluated. Generally, it could be shown that long phases of electric driving combined with aggressive load point shifting to balance the battery’s state of charge are most favorable in terms of efficiency. The phases of electric driving are additionally limited by the temperature drop of the catalysts and the lack of pollutant conversion after restart. This is a new and innovative approach to develop electrified powertrains efficiently. Finally it can be stated, that the numerical optimization method proved to be a powerful tool to support the development process of hybrid powertrains with numerous degrees of freedom.