Akademik Veri Yönetim Sistemi
Proceedings of the Annual Automotive Technology Development Contractors' Coordination Meeting, Dearborn, MI, USA, 28 - 31 Ekim 1991, ss.657-677
This paper describes a general, design-oriented 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. In order to accurately represent the effect of oil films, the model includes comprehensive treatments of hydrodynamic and boundary lubrication of the skirt and of wristpin bearings. The skirt lubrication submodel also allows representation of oil starvation at the cylinder end of the skirt. The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Oil and contact pressure and film thickness distributions in skirt-bore and wristpin interfaces are also solved for. 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. 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, skirt profile, roughness and lubricated area, bore distortion etc. are specifiable to the model as inputs. The integrated model was applied in a number of parametric studies, to conventional and articulated pistons. Effects of speed, load and piston configuration as well as viscosity, skirt design and profile were investigated. Results indicate that the skirt friction predictions of the model correspond to known levels and trends. Further, design parameters such as nominal clearance, skirt profile, circumferential lubrication extent as well as oil viscosity are shown to have key influences on the action of the oil films and thereby on piston motions and skirt friction.