Curbing the urban emissions with a hybrid bus

The CAMBUS hybrid bus under construction at LUT is just about ready for research use. One can expect to see the bus in real urban traffic in a few years. The vehicle was built in co-operation with the Saimaa University of Applied Sciences and the Saimaa Vocational College Sampo.

The body of the bus is an old long-distance bus that has been decommissioned from traffic. The old power line, combustion engine, transmission and rear, as well as the majority of accessories have been removed from the bus to make room for the new 32kWh batteries and the new power line consisting of a 2.5-litre diesel engine, generator and electric engine. According to Teemu Sairanen, Project Engineer at LUT, it will be ready for the first test drives by September.

According to Sairanen, "The electric engine has already been run and so has the diesel engine, as well. In general, the technology is falling into place mechanically speaking. Now we're only missing the intercooler from the diesel engine and the additional cooler. In addition, the bus's propeller shaft is not in place for safety reasons. The electricity and interior work are also not entirely finished. On the electricity side, we're still working on fine-tuning and testing the automation."

Electricity in traffic

The new hybrid system installed in the bus is the most energy efficient on the market: a radically smaller combustion engine and more powerful battery capacity enable urban-traffic emissions to be reduced by up to fifty percent compared to current levels. In addition, the bus's cooling system is more advanced than the commercial versions.

"The bus has liquid cooling with three different circuits: the batteries, diesel engine, drive engine and inverters are cooled in their own closed systems. If necessary, the heat produced by the diesel engine can be transferred to the battery circuit with a heat exchanger. We aim to make the best use of secondary heat through advanced electric control," Sairanen explains.

After the modifications, the bus can be driven by an electric or combustion engine or a combination of the two. In the CAMBUS model, the diesel engine helps the electric engine and not vice-versa, which is how the current hybrid systems on the market work. Thanks to its large battery capacity, CAMBUS can run solely on electricity in the urban area, which is where the emissions are the highest.

We will still have to wait to see the bus in urban traffic: risk analyses and other safety tests will be performed on it before production begins. One of the risk factors is the bus batteries, located at the rear of the vehicle. The batteries weigh in at approximately a thousand kilograms.

"We must consider the results of the risk analyses in battery fixing. The fixings must withstand greater than average force, that is, what occurs in the case of an accident. However, it is still important to consider that this is a prototype. If a commercial version were to be built, many solutions would probably be different. For example, the batteries might be installed on the roof or under the floor, and many welded structures used in this CAMBUS prototype could be replaced with the commercial version cast parts."

The CAMBUS system can be modified for different types and brands of buses and machines. Work on the prototype will yield practical information on the behaviour of machine batteries in both the test environment and the Finnish urban environment.

CAMBUS is part of the Green Campus environment at LUT. The project is funded by the European Regional Development Fund (ERDF) and the City of Lappeenranta.

Additional information

Project engineer Teemu Sairanen,
tel. +358 50 5767568,
teemu.sairanen@lut.fi