Optimal control of the transient emissions and the fuel efficiency of a diesel hybrid electric vehicle

As an important technical innovation which has emerged in the automotive industry, powertrain hybridization has been considered as one of the most effective ways for addressing transportation energy consumption and environmental concerns. However, owing to the complex physical and chemical nature of the engine combustion process, and the dynamic interactions between the engine and the alternative power source, it is difficult to optimize simultaneously and precisely both the engine fuel consumption and the emissions, especially during transient operations. Targeted at achieving both global energy optimization and reduction in the transient emissions, a control-oriented diesel engine emission model is first investigated and identified using a large number of experimental data. On this basis, a two-mode hybrid energy management strategy is proposed. In the fuel-efficiency-improving' mode, a dynamic programming algorithm is used to seek global optimization of the fuel economy and to ensure sustainability of the battery's state of charge over any given driving cycle while, in the emission-reducing' mode, the management strategy utilizes a linear quadratic regulator to optimize locally the surging emissions due to undesired engine torque transients. At the end of each emission-reducing mode, the locally optimized engine operation is driven back to match the globally optimized trajectory, i.e. the initial states of the next fuel-efficiency-improving mode. This seamless integration of the two modes will realize a reduction in the local transient emissions without losing optimality of the global fuel efficiency and sustainability of the battery's state of charge. Experimental results demonstrate that the proposed modeling and control strategy can considerably reduce the local soot emissions of a power-split diesel hybrid electric vehicle but can still maintain a high fuel efficiency and a high state of charge of the battery.