Modeling and Simulation of Elastohydrodynamic Lubrication of Piston Skirts Considering Elastic Deformation in the Initial Engine Start-Up

Abstract

The presence of Elasto-hydrodynamic Lubrication (EHL) film between opposing piston and liner surfaces prevents possible solid-to-solid contact and wear. This enhances engine life manifold as compared to when the EHL film is non-existent in the initial engine startup or breaks down during normal engine operation. Forced dry sliding of piston during engine cranking followed by partial lubrication in the initial engine startup leads to adhesive wear. This research investigates the possibility of an EHL film on such an occasion by considering elastic deformation of opposing piston skirt and liner surfaces due to Elasto-hydrodynamic (EHD) pressures. The geometry of piston skirts is defined and governing equations are applied to determine hydrodynamic pressures. The EHL film thickness profile generated by inverse solution technique and its expression is defined by incorporating contact geometry and EHD pressures in the piezoviscous regime. A computer code is developed and used to simulate the performance parameters and their behavior during initial engine startup. Due to critical factors such as engine speed, redial clearance between piston skirts and liner and lubricant viscosity, a time dependent 2-D EHL film profile is generated. The simulated results indicate that, despite piston eccentricities due to secondary oscillatory motion, EHL film established between the opposing piston skirts and liner surfaces prevented possible solid-to-solid contact in the entire duration of 720-degree crankshaft rotation, which corresponds to four piston strokes.