Lubrication of a flexible piston skirt conjunction subjected to thermo-elastic deformation: A combined numerical and experimental investigation

Abstract

The piston-cylinder conjunction accounts for nearly 50% of all the parasitic frictional losses in an IC engine of which the piston skirt accounts for nearly half of these losses. Consequently, part-circumferential short skirted compliant pistons have become a development trend, particularly for high-performance engines. Another trend has been the use of light weight moving parts to reduce inertial imbalance. This has led to the use of shorter lighter pistons constructed from lower density materials, such as aluminium. These higher power density pistons typically operate at elevated temperatures and undergo significant mechanical and thermal distortions due to the relatively high thermal expansion coefficients. As a result thermo-mechanical distortion of the skirt plays an important role in controlling the clearance gap between the skirt and the liner and makes the analysis, particularly skirt deformation, a computationally intensive procedure. This paper presents a semi-automatic methodology for the prediction of piston skirt thermo-mechanical deflection, which incorporates skirt deformation as well as piston crown compliant contribution to the skirt-liner clearance. This procedure is based on the creation of a compliance matrix and its intricate manipulation, significantly reducing the simulation run times. Integration of this approach with the numerical solution of Reynolds equation leads to an accurate prediction of film thickness. In addition, an array of ultrasonic sensors is used to directly measure the conjunctional lubricant film thickness in a non-invasive manner. The predictions and measurements show good conformance, an approach not hitherto reported in literature.

A transient tribodynamic approach for the calculation of internal combustion engine piston slap noise

“…They have all combined the oil film behaviour with piston dynamics (tribo-dynamics), forming a multi-physics study of the piston's secondary motion. Further studies have been reported with the variations in the lubrication regime during the full engine cycle taken into account, together with the piston-profile and the connecting rod effects [6,8,[23][24][25]. The above mentioned piston-liner contact tribo-dynamic models are employed to identify piston slap events, irrespective of the structural excitation, engine block response and sound quality (dB levels and frequency) perceived by the receiver [26].…”

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

“…These are particularly important practical features of low rotational inertia high-performance race engines, subject of the current paper. After some manipulation and accounting for the effect of engine order vibrations [2,33] and Littlefair et al [19], the kinematic displacement, velocity and acceleration are obtained as (''Appendix 1'' for A and B coefficients):…”

“…The methodology used for the estimation of the piston's deflection is the same as that presented by Littlefair et al [19]. However, for completeness, a brief summary is provided here.…”

“…They also included a simple model for pin-bore interactions. They employed a compliance matrix in a similar manner to that of Littlefair et al [19]. The work of McClure was developed further by Bai [1] to include a more accurate description of contact surface, using the average flow solution of Reynolds equation with limited oil availability.…”

On the Transient Three-Dimensional Tribodynamics of Internal Combustion Engine Top Compression Ring

“…The deformation of the bore and ring can originate from thermal and mechanical loading, cylinder head bolt tightening and abrasion [10][11][12]. In practice, the bore is not a right circular cylinder, which affects the ring-bore conjunctional friction and gas flow [13].…”