In today's vehicles, mechanical energy is transformed by means of lossy conversion-processes into hydraulic, electric, and thermal energy to ensure the operation of all vehicle functions. With its EfficientDynamics strategy, the BMW Group has developed technologies which are integrated as a series product in order to optimize the energy fluxes in the vehicle. This leads to a maximum in CO2 reduction by maintaining the typical driving performance of a premium segment vehicle. The degree of electrification in vehicles is continuously rising. This can be seen by using e.g. an electric water pump, steering system, air-flap controls, etc. However, a strong focus needs to be put on the provision of electric energy for the on-board electrical system. Besides the brake energy regeneration, the conversion of thermal waste energy (e.g. from the exhaust) into electrical energy by means of a thermoelectric generator (TEG) is a highly attractive technology. This technology, which is based on the Seebeck effect, can provide electricity to the on-board electrical system without the use of fuel, as - depending on the driving mode - around 2/3 of the chemical energy stored in the fuel is converted into unused thermal energy by the internal combustion engine. In order to utilize this energy, thermoelectric materials (e.g. Bi2Te3 or PbTe) can be applied which are placed in between the temperature gradient of the hot exhaust gases and the significantly colder coolant in the vehicle. The voltage generated by the TEG depends on the driving condition and, hence, on the thermal boundary conditions (e.g. mass flow and temperature of the exhaust gas and the coolant). In order to feed this electricity into the 12V electrical system of a vehicle, a coupling device is required. For this coupling device, a diode or a DC/DC-converter with a control strategy for maximum power point tracking can be applied. For the evaluation of the most effective device (cost- and efficiency wise) simulations as well as hardware tests are conducted. Last but not least the interference of the TEG with the overall vehicle electric system has to be evaluated and adjusted in order to optimize all parameters.
Waste-heat recovery in highly efficient powertrains - a key to further CO2 reductions
2009
12 Seiten, 14 Bilder, 3 Quellen
Aufsatz (Konferenz)
Englisch
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