Claus Doll. August 2008.

The current debate on climate gas emission targets and on CO2 emission limits of motor vehicles call for advanced technical as well as non-technical concepts. Among the latter traffic demand management, pricing and regulatory measures, including speed limits and infrastructure access control, provide possible solutions. Technical solutions constitute an important component in solving future climate and environmental problems caused by transport. Technological and political solutions do not exclude, but complement each other.

One of the intensively discussed technical solutions are combined fossil fuel and battery powered acceleration systems. These hybrid  electric vehicles (HEVs) allow driving quietly and locally emission-free because the internal combustion engine is run in a more favorable load range, while the highly efficient electric motor supports at low speeds and in acceleration phases. Further reductions in fuel consumption are achieved by down sizing the combustion engine and by recuperating brake energy back into the battery

Electric motors are constantly energy efficient across a wide range of engine speeds while combustion engines are less efficient at low speeds. Electric motors  can thus either support the internal combustion engine  while starting or accelerating the vehicle or may fully take over vehicle propulsion in certain situations.

Electric energy storage on board is one of the key issues for designing hybrid vehicles. Due to safety reasons contemporary models use nickel-metal hybrid (NMH) batteries. But advances in the safety and durability of lithium-ion batteries promise an extended range of the electric power train and thus more efficient hybrid or pure battery powered vehicles. The plug-in hybrid concept uses the electric motor for driving purposes only and fuels the battery via the electricity grid network.

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