CFD Analysis of Transient Heat Conduction in the Electronic Control Circuitry of Steering Wheel Column Adjustment System

Abstract

Abstract Automotive grade 3 electronic components are expected to meet their functional, performance and thermal safety requirements within the ambient temperature range from −40-degree C to +85-degree C. In this study, CFD and thermal analysis of electronic control circuitry of a power steering wheel column adjustment system is performed. It consists of 6 MOSFETs (Metal Oxide Semi-Conductor Field Effect Transistor) packaged in 3 Dual package MOSFET casings (Q6, Q7 and Q8) that are arranged in two H-bridge configurations for dependent control of the two motors. Two of these MOSFETs cause thermal power dissipation during the normal operation of the system. There are also other thermally significant devices such as a reverse polarity protection MOSFET (Q1), two inductors used in a low pass filter and one current sense resistor. Because of cost and packaging limitations, there are no external heat sinks to enhance heat transfer. The components will rely on the Printed Circuit Board (PCB) and plated-through-holes/thermal vias for heat transfer to maintain operation within the thermal safety limits. The inherent transient nature of operation of the power steering wheel column adjustment system causes the circuit to draw high current for a short duration of time. This necessitates temperature dependent heat source formulation. In this study, an initial CFD study was performed to assess the thermal safety of all the electronic components in the control circuitry. It was found that the electronic components such as MOSFETs and inductors were below the maximum operating junction temperature under the hot limit condition (+85degree C) for the entire duration of operation. However, under the cold limit condition (−40-degree C), both the MOSFETs and the inductors were significantly hotter than the maximum junction temperature. Based on CFD results, the sizing and placement of thermal vias may be optimized. Further, a comparative analysis was performed to assess the different levels of fidelity offered by lumped PCB model, multi-layer PCB model and explicit modeling of thermal vias in PCB.