Vehicle manufacturers are facing increasing pressure by legislation and economics to reduce vehicle emissions and deliver improved fuel economy. Over the coming years, significant reductions in carbon dioxide (CO2) emissions need to be achieved to meet fleet targets, whilst at the same time satisfying the more stringent forthcoming Euro7 emissions regulations. This focus on techniques to reduce the tailpipe CO2 is increasing the interest in hybrid and electric vehicle technologies. Pure electric vehicles require bulky and expensive battery packs, with a high embedded CO2 content, to enable an acceptable driving range. Range Extended Electric Vehicles (REEVs) partly overcome the limitations of current battery technology by having a range extender (REx) unit that allows a reduction of the traction battery storage capacity, whilst still maintaining an acceptable vehicle driving range. Building on previous research projects, focused on Rex and heavily downsized internal combustion engines, MAHLE have designed a plug-in hybrid driveline in which the systems have been fully integrated and optimised. The hybrid drive-line features a cost effective and high-efficiency, Miller-cycle, turbocharged, two-cylinder gasoline engine, with external exhaust gas re-circulation (EGR) and a pre-chamber combustion system, achieving over 40% brake thermal efficiency from a very low-cost architecture. This compact engine is combined with an electric traction system which can satisfy the full-dynamic requirements of the vehicle, even during pure-electric operation. The internal combustion engine can be operated in either series hybrid, or direct drive modes, via a compact multi-speed transmission. The paper will present the key features of the hybrid drivetrain and will describe the various modes of operation in the vehicle. Results of testing to validate the pre-chamber combustion system, coupled with a very high geometric compression ratio (CR) and external cooled EGR, will also be presented to support the efficiency claims made in the paper. Drive-cycle analysis, based on the engine test results, will also be used to show the efficiency of the entire system. Finally, the paper will present the scalability of the concept across a range of vehicle classes and performance levels.

Dr. Michael Bassett, MAHLE Powertrain Limited, UNITED KINGDOM Mr. Ian Reynolds, MAHLE Powertrain Limited, UNITED KINGDOM Mr. Adrian Cooper, MAHLE Powertrain Limited, UNITED KINGDOM Mr. Simon Reader, MAHLE Powertrain Limited, UNITED KINGDOM Dr. Martin Berger, MAHLE Powertrain GmbH, GERMANY