Mission Profile Effects on Automotive Drivetrain Electronics Reliability: Modeling and Mitigation

The reliability of electronic devices is dependent upon the conditions to which they are subject. Temperature variations coupled with differences in thermal expansion between bonded materials results in thermomechanical stresses to build up, which can instigate failure in the interconnects or other critical regions. With the move towards electrification in the automotive industry, there is the increasingly important consideration of powertrain electronics reliability, the pertinent conditions being governed by the drive cycle or mission profile of the vehicle. The mission profile determines the power dissipated by the electronic devices, which determines the peak and mean temperature, temperature swing and the resultant stress range, as well the effective thermal cycling frequency. This thesis, submitted in partial completion of the requirements for the Master of Science in Mechanical Engineering, herein investigates the relationship between predicted lifetime of electronic components in the drivetrain of an electric or hybrid electric vehicle and the mission profile it is operated at. The primary datasets are taken from the Environment Protection Agency (EPA) fuel economy test cycles, which lists various standard mission profiles for different driving conditions. The thermal profiles resulting from each mission profile are used to extract damage parameters and used to estimate time to failure. As the lifetimes are dependent on the thermal transients, ways are explored to minimize the temperature swings. One such way is to use phase change materials as thermal reservoirs that can be very effective thermal management option under the right conditions. Phase change materials absorb thermal energy as latent heat, which allows them to absorb a very large amount of heat per unit volume, but they are limited by low thermal conduction and long regeneration times. An affordable and widely available phase change material, paraffin, is used as a case study. A model is developed to mimic a widely available commercial power module, and detailed parametric studies are done to understand the effectiveness and best practices in using paraffin as a phase change material in cooling. The results show that PCMs hold great potential in automotive electronics cooling, but there is a delicate trade-off between the latent heat, thermal conductivity, and dissipated power that can be handled. As coefficient of heat transfer of secondary cooling mechanism gets larger, using PCMs become less advantageous