This paper describes a general model for the analysis of secondary motions in conventional and articulated piston assemblies. The model solves for the axial, lateral and rotational departures in positions and motions from the nominal kinematics, resulting from clearances within the piston assembly and also between the piston assembly components and the cylinder.
The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Motions of the piston, pin, rod and (for articulated pistons) skirt are separately calculated, by integrating equations of motion for individual components and dynamic degrees of freedom. Various configurations with respect to rigid attachment of the wristpin to other components can also be represented. In the equations of motions solved, all gas pressure, inertia, friction and oil or contact pressure forces are accounted for. Detailed submodels of skirt and wristpin lubrication are utilized to calculate the effect of these oil films. All pertinent operating parameters (engine speed and cyclic pressure variation) as well as design parameters, such as component masses, moments of inertia, mass centers, pin offsets etc. are specifiable to the model as inputs.
The model was applied, in conjunction with the skirt and wristpin lubrication submodels, to conventional and articulated pistons, in a number of parametric studies. Effects of speed, load and piston configuration were investigated.