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The electric range of plug-in hybrids as well as the installed electric power has steadily increased. With an electric power share of more than half of the overall system power, concepts of hybrid electric vehicles with at least two electric machines come into focus. Especially the concept of adding an individual electric axle to a state-of-the-art parallel hybrid, such as a P2-hybrid, is promising. However, the system complexity of a so-called P24-hybird increases significantly because the number of possible system states rises. This leads to an increased development and calibration effort for an online energy management. Especially a transfer from an optimized operating strategy to a rule-based energy management is challenging. Thus, a development framework for the calibration of an online energy management system (EMS) which is as fuel efficient as possible is needed.

In order to adhere with future automotive legislation and incentives, the electric range of plug-in hybrids has steadily increased. At the same time, the installed electric power has risen as well leading to future hybrid vehicles with an electric power share of more than half of overall system power and hybrid configurations with at least two electrical machines come into focus. The concept of adding a separate electrical axle to a P2-hybrid - a so called P24-hybrid, is of special interest. The system complexity of a such a system increases significantly as the number of possible system states increases. Thus, this paper analyzes the efficiencies and benefits of the different system states within the fuel-optimal operating strategy derived by global optimization. By varying the electrical power distribution between the two axles, the impact on fuel efficiency and the changes within the operating strategy are investigated.