Unsteady Piston Skirts EHL at a Small and a Large Radial Clearances in the Initial Engine Start Up

摘要

In the low speed initial engine start up, the transient transverse displacements of the piston are generated in the absence of an elastohydrodynamic lubricating (EHL) film. Such transient affect the lubrication of the piston skirts and contribute towards adhesive wear. The large piston to bore radial clearance at the time of cold engine start up affects the skirts lubrication differently as compared to a hot engine re-start up at a small clearance. This study models the 2-D transient piston skirts hydrodynamic and EHL at both the large and the small radial clearances. The 2-D transient Reynolds equation is solved to generate the hydrodynamic pressures under the unsteady state conditions. The simulation results show the piston eccentricities, secondary velocities, film thicknesses and the rising pressures as the functions of 720 - degree crank rotation cycles. The outcomes suggest that the cold and hot engine start up conditions affect the hydrodynamic and EHL adversely.