Connecting Rod Durability and Big End Distortion Study 2020-01-0184
The prediction of the connecting rod behaviour is one of the most important aspects of the engine design to estimate the engine life and its NVH behaviour. Connecting rod is usually simulated as a stand-alone component replacing the connected members with boundary conditions. These kinds of simulation usually underestimate the life of the connecting rod and overestimate the crankpin distortion. This unreal behaviour of simulation can result in over design of the crankshaft and wrong crankpin bearing selection, which can result in a noisy engine. The current Finite Element Analysis (FEA) is modelled by considering crankshaft, bearings and crankcase substructure along with the connecting rod to predict the fatigue life and bearing distortion. A multibody dynamics (MBD) simulation of the Cranktrain has been carried out to predict the forces and accelerations on the connecting rod by including the combustion force with a constant crankshaft speed for different conditions. Journal bearing crushing and bolt preload are the initial steps to the simulation. The extracted loads from MBD simulation at different conditions are imported into the FEA model, to predict stresses at maximum combustion and maximum inertia stages. The predicted stresses from FEA has been considered as input for the fatigue life prediction following the engine endurance cycle including the residual stresses. The big end distortion has been Fourier transformed to extract the bounds which give insight into clearance limit in the operating conditions. Fatigue life prediction and the big end distortion from the regular stand-alone connecting rod model and FEA assembly method has been compared and discussed. The wear pattern on the big end bearing in testing emulated the contact pressure pattern on the assembly method, which emphasises the importance of modelling the connecting rod fatigue life as an assembly model.
Nabeel Thekke Kolayath, Sreenivasulu T, Rod Giles