Three-piece oil control rings (TPOCR) are widely used in the majority of modern gasoline engines and they are critical for lubricant regulation and friction reduction. Despite their omnipresence, the TPOCRs’ motion and sealing mechanisms are not well studied. With stricter emission standards, gasoline engines are required to maintain lower oil consumption limits, since particulate emissions are strongly correlated with lubricant oil emissions. This piqued our interest in building a numerical model coupling TPOCR dynamics and oil transport to explain the physical mechanisms. In this work, a 2D dynamics model of all three pieces of the ring is built as the main frame. Oil transport in different zones are coupled into the dynamics model. Specifically, two mass-conserved fluid sub-models predict the oil movement between rail liner interface and rail groove clearance to capture the potential oil leakage through TPOCR.
The model is applied on a 2D laser induced fluorescence (2D-LIF) engine. A high-speed camera system is utilized to visualize the TPOCR rail motions as well as oil interactions with the ring. The TPOCR model produces simulation results consistent with the experimental observations in rail dynamics and is able to explain the mechanism behind these.
Using a parametric study based on this model, it was found that at high speed larger inertia opens up the rail groove clearance, while net oil leakage into the 3rd land through the rail groove interface is not likely to happen. This is due to the positive land pressure and oil motion in the non-contact regions. High speed and high engine load also lead to larger rail liner clearances and the rail liner sealing is dependent on the asymmetrical scraping ability of the rails. Due to the rail twist difference and 3rd land pressure effect between the up- and down-stroke, the symmetrical profile shows more scraping ability in up-stroke than down-stroke, thus as a net effect oil is up-scraped into the 3rd land. A complete picture of the oil transport mechanism around TPOCR will be discussed.