The interest in electric propulsion of vehicles has increased in recent years and is being discussed extensively by experts as well as the public. Up to now the driving range and the utilization of pure electric vehicles are still limited in comparison to conventional vehicles due to the limited capacity and the long charging times of today's batteries. This is a challenge to customer acceptance of a pure electric vehicle, even for a city car application. A Range Extender concept could achieve the desired customer acceptance, but should not impact the “electric driving” experience, and should not cause further significant increases in the manufacturing and purchasing cost. The V2 engine concept presented in this paper is particularly suited to a low cost, modular vehicle concept. Advantages regarding packaging can be realized with the use of two generators in combination with the V2 engine.
Compared to other engine applications there is one decisive attribute of a range extender - the NVH behavior. The operation of a range extender must be completely unnoticeable in order to realize the desired “electric driving” experience, particularly during engine start and stop. This requirement might seem easily achievable, but represents one of the biggest challenges for a combustion engine. With a new technology concept, called “FEVcom,” the vibration excitations due to torque fluctuations are completely eliminated. This leads to the desired unnoticeable noise impression in the vehicle interior in combination with the engine concept presented here.
The lack of a mechanical connection of the range extender was evaluated using vehicle simulation analysis with respect to CO2 emissions. Particularly for a city car, the results show that the transfer of mechanical power does not realize a noticeable fuel economy benefit. In contrast, a mechanically disconnected range extender offers additional advantages, for example, with respect to packaging, modularization and cost. Considering all characteristics, the range extender module for electric city cars presented in this paper represents a beneficial addition which improves the utilization of the vehicle. Based on simulation results, a range extender module was developed by FEV in cooperation with KSPG targeting a production-intent prototype.