Kurzfassung:
The amount of electric consumers in modern automobiles, especially in hybrid and electric cars, is growing more and more in the recent years, whereas the available space remains the same or even decreases. Closely related is the increase of connecting structures like cables, cable bundles, current bars and current distribution boxes. As all these devices and their connections generate heat by the Joule effect, thermal loads often represent a bottleneck in the dimensioning of components. On the one hand, manufacturers would like to reduce cable diameters and the amount of electric conducting material to save costs, weight and space and to decrease CO2 emission. On the other hand, they must not design them too small due to the danger of overheating and hotspot generation as well as the rise of thermal losses.
For these reasons, car industry and automotive suppliers are faced with numerous changes at the moment. Old norms used for the layout of components for many years are called into doubt due to the recent developments. The question of how to correctly dimension cables and other connecting structures has mostly been answered with the help of past experience and very elaborative measurements. Experience can hardly help in many cases concerning new developments; measurements are extremely expensive and offer only a limited spectrum of investigation opportunities. Finite element simulations are used in some companies, but due to the great effort involved, their application is often not sufficiently profitable. Moreover, there often exists, especially in the cable industry, a lack of necessary knowledge for adequate modelling and of the decisive or negligible influences.
The goal of the present work is to develop new specific methods for the computation of thermal loads in electric connecting structures. Although the simulation with finite elements constitutes an important part of this thesis, calculation methods that allow a simplified thermal analysis and excel by an enormous decrease of computational efforts thanks to qualified reduction of input data and smart discretization strategies represent the core issue. Problem specific modelling and computational approaches for insulated single-core cables, shielded cables of the automotive high voltage technology, cable bundles, current bars and fuses are derived. To obtain estimations for the accuracy respectively for possible weaknesses of the approaches, they are compared to finite element simulations. In order to ensure practical applicability, external measurements for each considered connection type are provided and accordance respectively discrepancies of those to simulations are analysed.
In addition, we demonstrate on a large number of examples how manufacturers can apply the developed methods in a profitable way and thus may reduce the amount of time and material. Optimization of cable cross sections, thickness of current bars and configuration of single cables in cable bundles are the main subjects of this thesis. Moreover, a design improvement of fuses that results in a more accurate and reliable blowing mechanism is proposed. We answer questions on thermal interaction between different components like current bars and wires or wires and fuses as well as on convergence and mathematical plausibility of our methods. It turns out that there is a close relation between the existence of solutions to the specific problems and the convergence of applied iterative methods.