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This paper presents a numerical model of the rotational and lateral dynamics of the piston (secondary motion) and piston slap in mixed lubrication. Piston dynamic behavior, frictional and impact forces are predicted as functions of crank angle. The model considers piston skirt surface waviness, roughness, skirt profile, thermal and mechanical deformations. The model considers partially-flooded skirt and calculates the pressure distributions and friction in the piston skirt region for both hydrodynamic and boundary lubrication. Model predictions are compared with measurements of piston position using gap sensors in a single-cylinder engine and the comparison between theory and measurement shows remarkable agreement.

Experiments were done to quantify the dynamic motion of the piston and oil-film during piston impact on the cylinder bore, commonly known as “piston slap.” Parameters measured include engine block vibration, piston-skirt to liner separation, oil-film thickness between the piston and liner, and other engine operating conditions. Experimental parametric studies were performed covering the following: engine operating parameters - spark timing, liner temperature, oil-film thickness, oil type, and engine speed; and engine design parameters - piston-skirt surface waviness, piston-skirt/cylinder-liner clearance, and wrist-pin offset. Two dynamic modes of piston-motion-induced vibration were observed, and effects of changes in engine operating and design parameters were investigated for both types of slap. It was evident that engine design parameters have stronger effects on piston slap intensity, with piston-skirt/liner clearance and wrist-pin offset being the dominant parameters.