Martin Kober

Upgrading hybrid-vehicles with a Thermoelectric Generator

To meet the future development in vehicle drivetrains, the Institute of Vehicle Concepts of the German Aerospace Center (DLR) aims to prove, that exhaust heat recovery using a Thermoelectric Generator (TEG) is, even with more electrification, still a promising concept to increase efficiency. Together with material researches at the Fraunhofer Institute of Physical Measurement Techniques (IPM) in Freiburg, the DLRs next generation of TEG is adapted to the special boundary conditions in hybrid vehicles. After investigating and measuring these boundary conditions, a first potential analysis is made. In test cycles a potential reduction of fuel consumption of about 3 % is calculated. It has been shown, that under exemplary driving conditions the possible electric power output of a TEG can be increased, compared to conventional vehicle, despite the increased efficiency of the drivetrain in a hybrid.

Development of a Thermoelectric Module Suitable for Vehicles and Based on CoSb3 Manufactured Close to Production

Despite the ongoing electrification of vehicle propulsion systems, vehicles with combustion engines will continue to bear the brunt of passenger services worldwide for the next few decades. As a result, the German Aerospace Center Institute of Vehicle Concepts, the Institute of Materials Research and the Institute of Technical Thermodynamics have focused on utilising the exhaust heat of internal combustion engines by means of thermoelectric generators (TEGs). Their primary goal is the development of cost-efficient TEGs with long-term stability and maximised energy yield. In addition to the overall TEG system design, the development of long-term stable, efficient thermoelectric modules (TEMs) for high-temperature applications is a great challenge. This paper presents the results of internal development work and reveals an expedient module design for use in TEGs suitable for vehicles. The TEM requirements identified, which were obtained by means of experiments on the test vehicle and test bench, are described first. Doped semiconductor materials were produced and characterised by production methods capable of being scaled up in order to represent series application. The results in terms of thermoelectric properties (Seebeck coefficient, electrical conductivity and thermal conductivity) were used for the simulative design of a thermoelectric module using a constant-property model and with the aid of FEM calculations. Thermomechanical calculations of material stability were carried out in addition to the TEM’s thermodynamic and thermoelectric design. The film sequence within the module represented a special challenge. Multilayer films facilitated adaptation of the thermal and mechanical properties of plasma-sprayed films. A joint which dispenses with solder additives was also possible using multilayer films. The research resulted in a functionally-optimised module design, which was enhanced for use in motor vehicles using process flexibility and close-to-production manufacturing methods.