Investigation of the Influence of Different Asperity Contact Models on the Elastohydrodynamic Analysis of a Conrod Small-End/Piston Pin Coupling

Bearings represent one of the main responsible of friction losses in internal combustion engines and their lubrication performance has a crucial influence on the operating condition of the engine. In particular, the conrod small-end bearing is one of the most critical engine parts from a tribological point of view since limited contact surfaces have to sustain high inertial and combustion forces. In this contribution an analysis is performed of the tribological behaviour of the lubricated contact between the piston pin and the conrod small-end of a high performance motorbike engine. An algorithm is employed based on a complementarity formulation of the cavitation problem. A comparison between two different approaches to simulate the asperity contact problem is performed, the former based on the standard Greenwood-Tripp theory and the latter based on a complementarity formulation of the asperity contact problem. A model validation is performed by comparing the results with those obtained adopting the commercial software AVL Excite Power Unit. Similar results are obtained from both the approaches, if a proper calibration of the model input data is performed. However, a remarkable sensitivity is highlighted of the results obtained using the Greenwood/Tripp model to the adjustment parameters. The realistic (engineering) difficulty in defining and identifying the roughness data and their purely statistical nature returns results that may be afflicted by a dose of uncertainty. Considering that results of such simulations usually offer guidelines for a correct design of the coupling, further investigations are suggested to identify a relationship between simply available roughness data and model input, starting from a direct experimental measurements of real roughness profiles.