Thermal pre-dimensioning methodology based on thermal impedance

The reduction of fuel consumption and the emergence of hybrid or electrical vehicles, and the improvement of in road car safety have introduced new embedded electronic functions in the automotive industry. Regarding hybrid or electrical vehicles the dissipated thermal power of these new functions can be significant. Therefore, the thermal analysis is now essential for peak and thermal cycle amplitudes prediction which are the main driving factors for equipment reliability. The use of Computational Fluid Dynamics (CFD) Software is becoming increasingly common to perform this kind of analysis. Unfortunately, when quick response is needed to trade off between several design solutions, when complex power profiles have to be addressed or when non linear effects of temperature have to be considered in power loss prediction (electro-thermal simulation), the CFD solution is sometimes of little help. The paper describes a methodology which allows to perform a thermal analysis in a reduced time. Simulation time reduction is based on simplification of the thermal model by focusing analysis on a reduced number of points (power injection points and observed temperatures). 3D model using millions of cells is converted into a “0D” or “mesh less” model using a few tens of points.