OEM & Lieferant Ausgabe 2/2019 - OEM & Supplier 2/2019 by VEK Publishing

157 BorgWarner www.borgwarner.com Website low coolant pressures. CFD simulations were necessary in order to finalize the optimiza- tions of the designs. The aim was to avoid hot spots inside the EGR cooler and realize a high coolant velocity in all parts of the com- ponent, Figure 2. Thermal robustness as one of the main challenges Designing a solution that withstands thermal fatigue is a very important and challenging aim of EGR systems for commercial vehicles. Component failure is usually caused by load variations, but thermal transient phenomena can cause additional thermal stress. Commer- cial applications in particular are very demand- ing with regard to thermal fatigue due to their high loads and high design life requirements. Flexibility is another important factor besides robustness here. Some of the principal reasons for thermal stress are the different thermal expansions of the EGR cooler components shell, the in- ner tubes and the gas entry side header and cone. If the conditions of the components and their materials differ too strongly in their characteristics, the resulting thermal inertia differences bring about transient stress peaks. For this reason, it is important to use components with a similar thickness and thermal inertia to enable a high reliabil- ity. In comparison with the solutions cur- rently available on the market, the floating core goes a different way. Its design layout provides for the decoupling of the inner tubes from the outer shell, meaning they can expand and contract independently of each other. The concept typically includes O-rings which work as a seal between the inner core and the shell. In addition, they al- low longitudinal displacement between the two components. The thermal damper is located at the gas inlet and has no temperature limitation, Figure 3. With its reaction force of only 1000 N for a compression displacement of 0.3 mm (a re- duction of 50 % in comparison with previous floating core solutions featuring O-rings), the CFC EGR cooler family provides a high degree of flexibility and is outstandingly resistant to harsh thermal fatigue cycles. Summary Time and cost considerations play a major role in the development of new vehicles. The cost-efficient floating core technology reduces development complexity and of- fers robust EGR cooling performance even under the harshest conditions. In addition, it avoids boiling issues, limits the skin metal temperature of the inner core and makes the system more robust against thermal fatigue when used in both parallel and counterflow arrangements. Figure 3: Design of the CFC cooler with thermal damper | Integration of design, simulation and performance engineering | Deep understanding of legal and customer requirements | Team of more than 500 safety experts | Testing facilities in Germany and Spain Frankfurt | Ingolstadt | München Stuttgart | Wolfsburg T +49 (841) 88 53 8-0 idiada_germany@idiada.com www.idiada.de