Piston Clearance Optimization using Thermo-elasto Hydrodynamic Simulation to Reduce Piston Slap Excitation and Friction Loss 2012-01-1530

The reduction of acoustic excitation due to piston slap as well as friction loss power and seizure are main issues when simulating the oil film lubricated piston - cylinder contacts of internal combustion engines. For a correct representation of the contact conditions between a piston skirt and a cylinder liner surface both the dynamics of the contacting flexible bodies, the shape of the contacting surfaces, the amount of available oil and the properties of the lubricant itself play important roles. Besides an appropriate representation of the hydrodynamic load carrying capacity using an averaged Reynolds equation with laminar flow conditions, the simulation has to use an appropriate asperity model to consider the mixed lubrication condition.

The lubricant properties are in particular influenced by its thermal conditions. In this work a thermo-elastic-hydrodynamic contact model is presented by the averaged Reynolds equation considering local and time variable dynamic viscosity in a mixed lubrication regime. The 2D temperature approach is derived from the 3D energy equation considering partly filled clearance gaps and mixed lubrication conditions. This advanced contact model is embedded in the multi-body software AVL-EXCITE, [8], which contributes the 3D dynamics of the flexible bodies of the cylinder kit.

An application of the method shows a typical engineering task of an optimization of piston skirt design parameters like nominal clearance, oval and ball shape with regard to the interfering criteria of piston slap induced noise on one hand and friction loss and seizure on the other hand.