Case Study: Low weight electric bus with multiple energy supply - Sweden

Website: www.uppsalabuss.se/OMUPPSALABUSS/elhybridbuss.html

Case Study (53 KB PDF)

Summary

The project aimed at showing a city bus design for the beginning of this century including an environmentally friendly technique. The aim must be expressed as follows: "public transport without noticeable negative impact on the environment". The project gives an opportunity to develop environmentally friendly prototype buses together with a bus manufacturer. Buses that further on may come into serial production. In the project a new type of bus with the following properties is demonstrated:

• Average energy savings and reduction of CO₂-emission of 30 % compared to present day city buses;
• Zero emission operation in limited restriction areas;
• Average reduction of the pollution to approximately half compared to conventional buses; comfortable, quiet low floor buses;
• Economically attractive as a series product.

Results

The intention was from the beginning that two experimental hybrid buses should be able to replace one standard bus. In Malmö only one hybrid bus was available. In Uppsala both hybrid buses were in normal operation, but with accessibility less than 50 %. The expectation that a hybrid bus could have an accessibility of 50 % was initially not fulfilled. All buses had several system faults and even "normal" mechanical faults in the conventional bus components. At this initial stage the accessibility was below 20 %. During the later part of the "monitoring phase" the accessibility has been increased considerably for the buses, both in Malmö and in Uppsala, and today it exceeds the stipulated 50 % level.

All innovative parts performed well in their mechanical parts, such as electric wheel motors, engine-generator and drive battery. The electronic management systems, however, had to be regarded as prototypes and functioned accordingly.

The Thermie Project cleared the way for technical and commercial knowledge about the electric drive. Since the electric drive is a basis for future development of emission free energy efficient vehicles, the project was both a test and an important milestone in the development of public transport vehicles.

From the first test results it was shown that the emissions were unusually high. This was, however, not representative for gas engines generally but should be seen as a result of an incorrectly tuned engine. Despite the lack of catalyst and incorrectly tuned engine, the emission figures were not higher than what is normal for a diesel engine. Furthermore, the engine was not completely adjusted to electric hybrid propulsion. The conclusion was that a correctly adjusted engine, optimized for a complete and total electric hybrid system gave considerably better results.

At hybrid mode with combined battery- and combustion engine drive it is possible to reach large decrease in the emissions from the engine. Measurements have shown:

• CO₂-emissions can be reduced with ca 30%,
• CO-emissions can be reduced with ca 60%,
• NOx-emissions can be reduced with ca 50%.

During two weekdays in March 2000, 119 passenger questionnaires were distributed and collected on board the Electric Hybrid buses. 80% of the respondents were frequent passengers, i.e. travel at least once a week or more. The overall impression can be summarized as follows: two thirds of the respondents graded the bus as good or very good. Most positive were the young and the +60 groups where 80% in both groups said the bus was good or very good. None of the respondents graded the bus as very bad. Only 2% totally thought the bus was bad.

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