Engine optimal operation lines for power-split hybrid electric vehicles

The powertrain of a hybrid electric vehicle (HEV) can be operated in either a power-boosting or an energy-saving mode. The first mode is used for responding to the driver's full-load demand and the second for achieving high fuel efficiency given an increased number of degrees of freedom in energy management. Optimization problems for the two operation modes are formulated, and the design spaces are analysed for general power-split architectures. Optimization results are presented and analysed for input-split and compound-split architectures. The analysis leads to the definition of a new concept of HEV optimal operation that improves the conventional idea of engine optimal operation line.