Single Cylinder 25kW Range Extender as Alternative to a Rotary Engine Maintaining High Compactness and NVH Performance 2013-32-9132

Due to the restricted capacity of today's battery systems and therefore limited operating range of electric vehicles (EV), several solutions for recharging the energy storage during driving already have been published and still are the subject of extensive development programs. One example is the Range Extender (RE), which is a combination of an internal combustion engine (ICE) with a generator unit, which serves the purpose of a power back-up in case of a battery with low state of charge (SOC), without any direct connection to the drivetrain.

For this kind of RE-application, different boundary conditions are very important. Especially in EVs topics like packaging space and NVH behavior play a main role. To fulfill these important characteristics, AVL has developed a Wankel-RE unit in which the generator is driven directly from the eccentric shaft of the rotary-piston ICE. With such an arrangement and the correct balancing of the power unit directly on the rotor of the generator, a very small packaging size in combination with smooth and silent running can be achieved and fulfills the most important characteristics for an electric vehicle. Besides these outstanding attributes, and although RE rotary engine concepts have proven to have acceptable fuel efficiency even under stringent emission challenges, the main drawback of rotary engines can be seen in non-availability of large scale manufacturing devices for specific rotary engine components. Therefore, the industry would prefer and is demanding solutions based on conventional piston engines.

Following this request, AVL has developed an alternative concept which shows the potential of substituting the Wankel engine by a common single-cylinder piston engine within the same tight packaging boundaries. By means of a tailor made balancing system, the mass forces and torsional vibration have been brought to a level which is competitive to the excellent NVH behavior of the Wankel engine.

This paper shows the development of this concept, the resulting design and packaging in combination with simulation results confirming the NVH behavior of the single cylinder RE.