The efficiency potential of internal combustion engines (IECs) is widely exhausted, right? Think twice: if operated constantly at the sweet spot of their characteristic curve, there is still headroom for better efficiency - which translates into lower fuel consumption and lower emissions. At its optimum efficiency point, the efficiency of an IEC is significantly better than in other speed ranges.
This does not necessarily mean that the vehicle has to be driven at a singular, constant speed. Along with commercial companies Meta Motoren und Energie-Technik and Centre for Concepts on Mechatronics (CCM), a group of researchers at the Technische Hochschule Cologne university has developed a powertrain that uncouples the engine rpm from the vehicle speed.
The core of the drive topology is what the developers call a “double rotating electrical machine”, or DREM. It is located between the front-axle differential and the combustion engine. Thus, the IEC can be used much like a range extender – independently of the rotation speed of the wheels, it runs at its optimum speed range which lies between 2.000 and 3.400 rpm. “In urban driving according to the New European Driving Cycle (NEDC), we achieved fuel savings of 25 percent, compared to a series vehicle of the same type”, explains Andreas Lohner, the head of the research team.
The IEC drives the front axle whereas the battery is charged or discharged, depending on the operation point. The rear wheels, in contrast are equipped with a near-wheel electric motor each. Both motors can be controlled independent of each other. “Thus, we increase driving stability and driving dynamics at the same time”, says research associate Magnus Böh. The vehicle can drive solely on electric power over distances of up to 25 km. In combined mode, the DREM makes the vehicle function like a normal plug-in hybrid,