Single Cylinder 25kW Range Extender: Development for Lowest Vibrations and Compact Design Based on Existing Production Parts
Authors: Hubmann Christian , Friedl Hubert , Gruber Stefan , Foxhall Nigel 
Published: November 2023

<div class="section abstract"><div class="htmlview paragraph">The automotive trend towards increased levels of electrification is showing a clear direction for hybrid technologies. Nowadays Mild- and plug-in-hybrids open a very wide area of future developments whereas battery electric vehicles (BEV) are still evident but still perceived as niche products with limited production volumes. Nevertheless, major OEMs are working on these kinds of vehicles and have also brought such EV concepts into series production.</div><div class="htmlview paragraph">All of these designs show a clear trend that, beside the topic of electric traction motor and energy storage systems, the internal combustion engine (ICE) is also coming into focus again. In many of these vehicles the range extender (RE) unit is foreseen as an emergency unit to recharge the batteries if the state of charge (SOC) is too low.</div><div class="htmlview paragraph">One of the major advantages of a BEV over other designs is the very good acoustic behavior, so the NVH performance becomes the most challenging topic for RE development.</div><div class="htmlview paragraph">AVL has already investigated, published and partially also developed different types of RE units:
<ul class="list disc"><li class="list-item"><div class="htmlview paragraph">single rotor Wankel [<span class="xref">1</span>]</div></li><li class="list-item"><div class="htmlview paragraph">2 cylinder inline [<span class="xref">2</span>]</div></li><li class="list-item"><div class="htmlview paragraph">single cylinder [<span class="xref">3</span>]</div></li></ul></div><div class="htmlview paragraph">Amongst others, a significant benefit of the single cylinder RE is the possible usage of parts from already existing powersports applications providing technology which typically is needed to fulfill the requirements of a BEV, such as:
<ul class="list disc"><li class="list-item"><div class="htmlview paragraph">compact design</div></li><li class="list-item"><div class="htmlview paragraph">good power to weight ratio</div></li><li class="list-item"><div class="htmlview paragraph">high specific power</div></li><li class="list-item"><div class="htmlview paragraph">good NVH behavior</div></li><li class="list-item"><div class="htmlview paragraph">affordable production cost</div></li><li class="list-item"><div class="htmlview paragraph">available industry (niche volume)</div></li></ul></div><div class="htmlview paragraph">Rotax Engines of BRP-Powertrain GmbH &amp; Co KG (BRP) fulfill the above mentioned aspects and therefore have been chosen to collaborate with the RE design.</div><div class="htmlview paragraph">This paper describes the general design features of the RE unit, how and which parts and systems could be taken over out of the existing BRP series product pallet. In addition first test bed results are shown in comparison with the simulations carried out in a previous development program.</div><div class="htmlview paragraph">The 3D CAD/simulations have shown that the desired power as well as the necessary small package requirements could be achieved whilst taking as many parts out of the ROTAX engine line-up as possible. Following these virtual studies, the engine was manufactured and tested on the dyno. These tests have confirmed the simulation results and especially the vibration investigations have shown an excellent engine mount excitation behavior compared to other RE concepts and standard 1 cylinder solutions.</div></div>