Powertrain Mounted Exhaust System Failure Correlation and Methodology Development in CAE 2017-26-0267

Exhaust system is one of the complex automotive systems in terms of performance and strength prediction due to combination of transient mechanical and thermal loads acting on it simultaneously. Traditionally, most of automotive vehicles have exhaust systems with hot end mounted on engine and cold end mounted on chassis or BIW through hangers. A new powertrain mounted exhaust system was developed in-house. This exhaust system underwent validation and evaluation during development phase. Durability concerns were observed on exhaust system in Track test and gear shift durability test.

This paper focuses on identifying the root cause of these concerns based on the failures observed during evaluation in Accelerated Durability (ADT) and gear shift durability (GSD) tests. Based on the architecture and packaging space challenges in vehicle, engine is mounted on two mounts and a roll restrictor. Muffler, which has higher inertia, is mounted at higher offset with respect to engine rolling axis. A new transient loadcase representative of gear shift durability test was developed. The misalignments due to tolerance stacking and process variability were measured on physical assembly at catalytic converter and muffler mountings and imposed in the analysis through appropriate enforced displacement constraints. These assembly preloads act as mean load for the exhaust system. Fatigue analysis was carried out for transient loadcase with assembly preloads and the results were correlated with failure data. A new design was proposed and evaluated based on this loadcase and it has cleared validation and evaluation phase without any concern.

All new powertrain mounted exhaust systems will be evaluated and verified using this loadcase in early phase of program. The overall exercise has helped to improve the prediction and robustness of exhaust system analysis.