Transient Tribo-Dynamics of Thermo-Elastic Compliant High-Performance Piston Skirts

Abstract

Advanced piston technology for motorsport applications is driven through development of lightweight pistons with preferentially compliant short partial skirts. The preferential compliance is achieved through structural stiffening, such that a greater entrainment wedge is achieved at the skirt's bottom edge through thermo-elastic deformation, whilst better conforming contact geometry at the top of the skirt. In practice, the combination of some of these conditions is intended to improve the load-carrying capacity and reduce friction. The approach is fundamental to the underlying ethos of race and high-performance engine technology. Contact loads of the order of 5 kN and contact kinematics in the range 0-35 m/s result in harsh transient tribological conditions. Therefore, piston design requires detailed transient analysis, which integrates piston dynamics, thermo-elastic distortion and transient elastohydrodynamics. The paper provides such a detailed analysis as well as verification of the same using noninvasive ultrasonic-assisted lubricant film thickness measurement from a fired engine under normal operating conditions, an approach not hitherto reported in literature. Good agreement is noted between measured film thickness and predictions.

Analysis of piston-pin lubrication considering the effects of structure deformation and cavitation

“…The mechanical distortion is determined by the method used by Littlefair et al (2014). The loads applied for the estimation of the piston's mechanical distortion are as follows: (1) gas load applied on the piston crown; (2) piston inertial force due to the primary accelerative motion; and (3) piston side force acting orthogonal to the skirt surface.…”

“…The loads applied for the estimation of the piston's mechanical distortion are as follows: (1) gas load applied on the piston crown; (2) piston inertial force due to the primary accelerative motion; and (3) piston side force acting orthogonal to the skirt surface. As shown in (Littlefair et al, 2014), these loads actually cause the skirt to deform, which in turn affect the pin boss. In this study, the multi-body dynamic motion model is established with the solid model.…”

The Analysis of Secondary Motion and Lubrication Performance of Piston considering the Piston Skirt Profile

“…Hence, the study of the effects of the piston skirt profile on the secondary motion and piston dynamics is essential. Littlefair et al [16] analyzed the piston dynamics, thermoelastic distortion, and transient elastohydrodynamics of the lightweight piston with preferentially compliant short partial skirt. The greater entrainment wedge at bottom skirt and better conforming contact geometry at top skirt were achieved, and therefore, the load-carrying capacity was improved and the friction was reduced.…”

Passive Control of Piston Secondary Motion Using Nonlinear Energy Absorbers

“…VIB-16-1462 -Theodossiades is the piston rotation about its pin and it can be defined in terms of piston eccentricities ( and ) [19]. Newmark integration and predictor-corrector techniques are exploited to numerically solve equations (6).…”

“…The parameters of these elements are evaluated either experimentally [15,16] or theoretically [13]. Models combining tribology and dynamics take into account jointly the effects of piston dynamics, structural deformability and hydrodynamics of the lubricant film (Elasto-hydrodynamic lubrication) [17][18][19]. Thus, tribodynamics models are largely exploited to predict and identify piston-cylinder interactions [20,21].…”