Modelling the Rough Piston Skirts EHL at a Small and a Large Radial Clearance in the Initial Engine Start Up

摘要

At initial engine start-up, the low speeds take time to develop considerable film thickness between piston and liner surfaces. Factors like radial clearance, oil viscosity and roughness of interacting surfaces play an important role in this regard. A two dimensional model is presented for hydrodynamic lubrication and EHL of rough piston skirt under isothermal conditions. Flow factors method is used to incorporate the deterministic isotropic roughness effects in Reynolds’ equation and Greenwood-Tripp asperity contact model is used for involving the corresponding asperity contact forces and moments. The numerical model is used to get simulation results including piston eccentric displacements, hydrodynamic and EHL film thickness and rising pressures for 10 micron and 100 micron radial clearance between piston and liner. All results are plotted against 720 degree crank rotation cycle. The results show considerable change in each parameter by changing radial clearance from small value to large.