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

Theodossiades, S, De la Cruz, M, Littlefair, B, Mills, R, Howell-Smith, S, Rahnejat, Homer orcid iconORCID: 0000-0003-2257-7102 and Dwyer-Joyce, RS (2014) Transient Tribo-Dynamics of Thermo-Elastic Compliant High-Performance Piston Skirts. Tribology Letters, 53 (1). pp. 51-70. ISSN 1023-8883

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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 non-invasive 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.

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