Challenges of an electronically distributed all wheel drive on basis of a “retrofit” full hybrid 4WD solution

One important task of electrification of vehicle powertrain is the functional integration of all new systems in respect of the performance, comfort and emission restrictions. In this particular case, starting from a mass produced vehicle platform in the small vehicle segment, the requirement was to keep the originally installed powertrain largely unchanged, but on the other hand enabling hybrid operating functions such as boosting and recuperating and additionally providing some torque vectoring features, under all relevant driving situations. The paper describes and explains the possibilities and limitations of an electrically supported four wheel drive system: first in simulation by use of a mathematical model and then, the experiences gained in the actual development of a prototype car, will be reported. A special focus will be put on the methodology of the development of a model based hybrid controller.