Design Enhancement of EGR System for Improved Vibration Performance on Truck Diesel Engine

In the diesel engine Exhaust Gas Recirculation (EGR) components, valve and connecting pipes are the critical components and fails often during new engine development. These components are important for meeting NOx emissions norms. Therefore design of these components should remain robust. But the challenge in design is compact packaging of complete EGR components on the engine consequently vibration related failure plays a major role. Normally in pneumatic EGR valve, shaft spring stiffness plays a major role for shaft opening and closing. But in this layout during emission testing, shaft is self-opened without feedback signal from sensor this is due to resonance and this problem is solved by increasing the spring stiffness. The next key components is the EGR pipes, the flexible bellows on these pipes are useful for thermal expansion during hot conditions. In this case the bellow crack failure is observed due to vibration. Therefore design improvements were made by proper design of bellow geometry and bracket support for these pipes facilitated prevention of EGR pipe failure. Overall this paper describes the methodology to conduct proper failure investigation to identify the root cause for vibration related failures of EGR system during new product development.