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Reliable model of lubricant‐related friction in internal combustion engines
Author(s) -
Benchaita M. T.,
Lockwood F. E.
Publication year - 1993
Publication title -
lubrication science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.632
H-Index - 36
eISSN - 1557-6833
pISSN - 0954-0075
DOI - 10.1002/ls.3010050402
Subject(s) - lubricant , lubrication , materials science , internal combustion engine , friction loss , mechanics , mechanical engineering , boundary lubrication , crankcase , combustion , composite material , engineering , chemistry , physics , organic chemistry
Abstract A linear model of lubricant‐related engine friction was developed. Based on lubrication fundamentals, the technique is comprised of three simple bench tests that respectively operate under thick fluid‐film hydrodynamic lubrication, elastohydrodynamic lubrication, and boundary lubrication. With adequate configuration and appropriate test conditions, these bench tests are seen to simulate major friction losses in a typical internal combustion engine. Lubricant characteristics obtained in the bench tests were combined using SAS linear regression and correlated to ASTM Five‐Car and Sequence VI engine tests. The linear model gave an excellent prediction of engine data. It further showed that hydrodynamic friction losses dominate lubricant‐related engine friction, followed by boundary friction losses, and elastohydrodynamic or mixed friction losses. This simple, reliable, and inexpensive technique can be used as a research tool to study friction characteristics of crankcase lubricants and to develop superior fuel‐efficient engine oils. Major findings from this study can be summarised as follows: 1 The linear model predicts that 5 to 6% fuel economy improvement over the industry high reference oil HR‐4 is achievable with today's motor oil technology 2 Hydrodynamic friction losses in both ‘thick' and ’thin' fluid‐film lubrication account for 63% of total friction losses caused by the engine oil while boundary friction losses amount to 37%. 3 Friction losses in the elastohydrodynamic (EHD) engine are significant, up to 22% of total friction losses. This, combined with the fact that EHD film thickness is the most significant parameter in the linear model, suggests that pressure effects (ie, high‐temperature/high‐shear/high‐pressure viscosity, pressure‐viscosity coefficients) are important. 4 Increasing fuel economy improvement is in general in the order: SAE 10W–40 < SAE 10W–30 < SAE 5W–30, providing that base stock and additive systems are unchanged.