This further-developed prototype vehicle was tested in several months of scheduled service at VAG Nuremberg in 2005. This enables a direct comparison between the improvement achieved in the optimised drive system and the current status. While in conventional buses/coaches with mechanical brakes the kinetic energy goes unused during braking, the "ultracap bus" developed by MAN can be decelerated electrically. The braking energy regained by this is stored in high-performance capacitors and reused when the bus moves off again. This markedly lowers the vehicle's fuel consumption, moving-off noises and emissions.
Ultracaps fundamentally differ from other energy accumulators such as batteries or flywheel storage systems by their particularly high power density, high power take-up capacity, reliability, high efficiency, the absence of moving parts and their maintenance-freeness. The storage capacity is designed so that the energy from one braking operation from 60 km/h can be stored complete. The newly developed ultracap storage system distinguishes itself mainly by a drastic reduction in storage losses as well as by a marked extension of its service life up to that of the vehicle itself thanks to improved cooling.
MAN Nutzfahrzeuge AG is continuing its systematic development of hybrid drive systems with diesel engines for the city bus sector in cooperation with its supplier, Siemens. At the beginning of 2007, two vehicles based on the MAN Lion’s City are planned for completion. The entire investment volume for the IDEAS project (IDEAS stands for “innovative diesel-electric hybrid drive for city buses”) is about four million Euros; € 1.4 million of this comes from subsidies from the Federal Ministry for Education and Research (BMBF). The project is part of the ministry’s research programme for mobility and transport planned from 2000 to 2005.
The research projects to date have revealed a considerable potential for fuel saving with hybrid-drive systems for city buses, in which the familiar diesel-electric drive is combined with a suitable energy accumulator. In MAN’s view, two drive systems are effective and forward-looking. The first variant, which is designed to achieve minimum fuel consumption, is a hybrid system with an ultracap storage system. This system makes it possible to leave bus stops by means of electricity and thus without any emissions (noise, exhaust gas). This has the additional advantage that it reduces the annoyance caused to passengers and to the people who live near to the bus stop.
The emphasis of the second version is on the reduction of emissions. This design consists of a combination with a high-performance battery system which, compared with the ultracap storage system, provides a considerably larger energy content. At the same time this permits emission-free, pure electric operation in core zones. Owing to the measures necessary to comply with the federal immission protection regulation this design could become more interesting in future.