Impacts of Friction-Modified Fully Formulated Engine Oils on Tribological Performance of Nitrided Piston Rings Sliding against Cast Iron Cylinder Bores

Abstract

The tribochemical interaction in a nitrided piston ring/cast iron cylinder bore sliding contact with two commercial fully formulated engine oils (ILSAC GF-2 and GF-3 category, referred to as modified GF-2 and modified GF-3, respectively) supplemented with molybdenum dithiocarbamate (MoDTC) friction modifier was investigated in a laboratory bench test. Test results indicated that the modified GF-2 oil could produce a rapid friction reduction while the modified GF-3 oil maintained a stable and lower coefficient of friction (μ = 0.03) for a longer testing time. The modified GF-3 oil also generated a lower wear rate compared with the modified GF-2 oil under the same tribotest conditions. Based on SEM/EDX analyses of wear tracks on the tested tribo-components, it appears that the better formed tribofilm on both the lower and upper specimens by the modified GF-3 oil made a significant contribution to its tribological performance compared with the modified GF-2 oil when sliding under the same test conditions.

Keywords:

• Tribochemical Interaction
• MoDTC
• Friction and Wear

ACKNOWLEDGMENTS

The authors thank Dr. Michael McMillan and Dr. James Spearot for their advice and valuable suggestions. In addition, the author appreciates Dr. Ben Zhou for 3-D surface and roughness analysis and the Surface Analysis Group of Tsinghua University for their valuable help on experimental analyses. The authors also thank Lubrizol Corporation for providing test lubricants.

Presented at the 58th STLE Annual Meeting in New York City, New York April 28-May 1, 2004

Final manuscript approved March 8, 2004

Review led by Elaine Yamaguchi

Notes

^a Rz: Average maximum height of the profile.

^b Rt: Maximum height of the profile.