Hybrid Vehicle Case Study
The Design Challenge
The development and production of electric and hybrid vehicles has beenon the rise over the last 2 decades and this trend is likely to increaseexponentially over the next 20 years. As automotive manufacturers lookto utilize cleaner, cheaper energy and meet CO2 regulations worldwideby 2020, electric and hybrid vehicles will become a much larger part ofthe market.
However, the power needed to run a vehicle combined with design needsfor compact, lightweight inverters has made thermal management animportant stumbling-block for automotive engineers and manufacturers.Thermal solutions for these power modules must be lightweight, smallenough to fit within the powertrain, powerful enough to cool extremelyhot components, and cost efficient enough not to raise the price pointson these vehicles.
To overcome these challenges, Infineon Technologies came to Aavid,Thermal division of Boyd Corporation, for help in developing a coolingsolution for their latest power module family, HybridPACK™ DoubleSided Cooling (DSC) for hybrid and electric vehicles. Their dimensionsand characteristics allow these modules to be more flexible with acompact design of the overall application and can dissipate heat onboth sides of the module. Infineon and our European Design Centerstudied a concept for a liquid cooling solution able to provide thespecific performance level.
The Aavid Solution
The specifications for this application: power to be dissipated by each of the threeDSC modules, electronic connections and integration, and boundary conditions.Starting from the characteristics of DSC modules and the requested thermalresistance and pressure drop, Aavid began the analysis of possible concepts ofLiquid Cold Plates (LCPs); the basic idea was to put one LCP on top and one LCPon the bottom, in order to cool the two active sides of each module.
Different key points have been considered: overall geometry, internal coolerstructure, wall thicknesses, inlet and outlet position, top-bottom connection,mounting technique and target cost. The geometry has been defined by the mainmechanical constraints: dimensions of the active area of DSC modules, availablespace around the modules and integration with the overall system.
The internal structure has been defined according to the requested performancelevel (thermal resistance and pressure drop), and the key was to add anaccurately optimized turbulator in order to increase the exchange surface andthe convection heat exchange coefficient, while keeping pressure drop under theestablished limit; CFD simulations have been made. The material thickness hasbeen properly evaluated in order to withstand the requested operating andtesting pressure. Further analysis was focused on the connection between topand bottom Liquid Cold Plate (LCP) and the position of inlet and outlet; at thisstage, the connection between top and bottom has been considered external tothe LCP itself, made by means of flexible tubes and clamps (each LCP has one inletand one outlet port). In this way, a parallel connection between the top andbottom LCP has been obtained, with the advantage of having two equal parallelflows and consequently the same performance level on the two LCPs.
Finally, the mechanical clamping between top and bottom has been studied:considering the minimum clearance and creepage distances to be guaranteed,eight fixing point have been added, externally to the active exchange surfacearea. The mechanical connection between top and bottom can be done eitherwith fast features such as rivets or with screws. Prototypes of this concept havebeen made in order to validate the thermal and mechanical analysis and theresults of the experimental tests confirmed that it is suitable to withstand therequested pressure and to guarantee both the indicated thermal resistance andpressure drop. For the first prototypes, rivets have been used to clamp top andbottom Liquid Cold Plates.
The concept developed by Aavid and the availability of prototypes enable theautomotive industry to quickly design efficient inverters for hybrid and electricvehicles using Infineon HybridPACK DSC modules.