The Effect of Crankshaft Flexibility on the EHL of Connecting Rod Bearings

With the continuous demand to squeeze more performance from critical engine components such as crankshaft bearings, design analysis and calculations methods are also required to become more comprehensive. With the advent of Elasto Hydrodynamic Lubrication (EHL) methods, for example, designers could investigate theoretically the effects of housing geometry or stiffness on bearing performance; which was previously not possible with rigid bearing (mobility method) calculations.

Traditional methods for EHL analyses of crankshaft bearings normally incorporate the elasticity of the connecting rod or housing but assume that the crankpin is rigid. This paper demonstrates the effects of including the flexibility of the crankshaft journal (up to the adjacent main bearing) for three examples of connecting rod bearings. The examples cover a typical Formula 1 (F1) racing engine at 16000rpm, an automotive gasoline engine at 5500rpm and a 120mm journal diameter diesel engine at 2000rpm.