Development and Application of Elastohydrodynamic Lubrication Model for Piston Pin

Abstract

The piston pin, as the connection between the piston and the connecting rod, is a crucial component in the internal combustion engine. It transfers the cylinder pressure of combustion to the crankshaft and is subjected to high stress and harsh lubrication conditions. Pin seizure is a severe problem in new engine development and coatings could be a solution to this problem. However, by advancing the knowledge about the lubrication effect and the contact patterns on the pin’s surface, it is possible to find more cost-effective methods, such as modifying the profile or adding oil grooves.

A numerical model was developed in this study to investigate the lubrication and dynamics of the piston pin, taking into account the deformation of the structures and oil cavitation. The model employs multi-body dynamics and elasto-hydrodynamic lubrication. A routine for generating and processing compliance matrices was created and improved. Additionally, a simple built-in run-in model was utilized to modify the pin bore and small end’s profile based on asperity contact pressure. In order to adapt to various oil supply situations, a method for controlling the boundary oil flow on the piston pin’s surface was also implemented.

The model was then applied to a large bore gas engine to simulate the piston pin’s rotation and frictional forces under different operating conditions. The simulation results indicate that hydrodynamic lubrication plays a dominant role in supporting the normal load after break-in, and the direction and angular speed of the piston pin’s rotation are closely linked to the operating conditions. The experimental results were compared to the simulation, revealing the model’s reliability and accuracy.

The second part of the thesis examines the oil supply boundary conditions at the boundaries of the lubrication areas. A computational fluid dynamics (CFD) model was established to analyze the flow of lubricating oil at the vicinity of the pin joints, which reveals that the amount of lubricating oil supplied from different locations can vary. It was found that during high-speed reciprocating motion, lubricating oil may not be able to remain on the piston pin’s surface long enough, particularly at top and bottom. Lubricating oil flow, contact and friction patterns with different oil supply conditions were analyzed and compared in a heavy-duty diesel engine model.