K u rzfassu n g sb an d - Graz University of Technology

Energieinnovation 2006 91
4.3.2 „Energy saving potential of cars with an optimised powertrain
compared to conventional cars“
Andreas Jörg, Dierk Schröder (TU-München/Lehrstuhl für Elektrische
Antriebssysteme) 1
The optimised powertrain of the Technical University of Munich
At the Technical University of Munich a new powertrain is under development. It consists of a
conventional combustion engine (CE), a continuous variable transmission (CVT), an electrical motor
and a stack of double layer capacitors (UltraCap).
Why using an UltraCap instead of a battery
Former hybrid car solutions included large and heavy weight batteries to drive certain distances like
e.g. in cities without the usage of the CE. Today smaller batteries with less capacity and less weight or
UltraCaps are used as electrical energy storage devices (EESD). These solutions only provide energy
for very short distances like a few stop and go cycles. Former hybrid solutions had the target to drive
longer distances like e.g. within a city without emissions. Because of an improved exhaust
aftertreatment, emission problems are mitigated and recently fuel saving requirements and
acceptance by the customer are important. So a small weight of EESD is aspired. The advantages of
UltraCaps are the small equivalent series resistor (ESR) and the high power density resulting from
this. This means there are fewer losses while storing or delivering power to or from the UltraCap thus
higher efficiency of the whole powertrain can be achieved. Besides the costs for UltraCaps are less
than for high power batteries.
Operating strategy for hybrid cars
For a conventional car with manual gear the operating strategy for detecting the fuel consumption for
standard cycles are strictly defined, whereas with automated gears the inbuilt operating strategy is
used. The operating strategy of a hybrid car has a great influence on the fuel consumption, and there
are different methods and approaches to do this.
On the one hand there are offline optimisation methods like linear or nonlinear programming. These
methods take the whole cycle information or terrain information into consideration and calculate the
minimal possible fuel consumption. These methods can only be used, if the whole driving cycle is
known, but in real time operation the future is unknown. Nevertheless offline methods can be used to
detect the theoretical minimum and to get a reference for comparison with an online method.
On the other hand there are various approaches for real time operation of a hybrid car, e.g. loss
minimization, fuzzy logic, neural networks or knowledge based methods are employed. The target of
an optimized operation of a hybrid car should be minimal fuel consumption of course. But also driving
pleasure and customer friendly requirements have to be taken into account. The main problem, that
has to be solved within an online optimization, is the energy management of the EESD. By using as
much information as available, like GPS, terrain and traffic information the energy management and
therewith also the efficiency can be improved, so the target to reach the over all efficiency of the offline
optimisation can be converged.
1 Institute of Elektrical Drive Systems, Technical University of Munich;
Arcisstr. 21, 80333 München, Germany, Tel: +49 89 289 28451;
e-mail: andreas.joerg@tum.de, Url: http://www.eat.ei.tum.de;