A test procedure to investigate lubricant-surface combination for high performance racing transmissions

Compact light weight and dry sump (significantly reduced volume of lubricant) are the desired attributes for high performance racing transmissions, whilst improving upon efficiency and reliability remain paramount objectives. The complex multi-objective nature of this task points to an integrated approach to lubricant-mechanical system optimisation. The extreme operating conditions in racing transmissions, such as contact kinematics and thermal loading present significant tribological challenges. Thin lubricant films in non-Newtonian shear are subjected to mixed thermo-elastohydrodynamic regime of lubrication. Under these conditions boundary active lubricant species often determine the contact tribological performance rather than the bulk rheological properties of the lubricant itself. Therefore, the interaction of lubricant additive package with the contacting solid surfaces is the key to an optimised solution. The paper investigates the lubricant-surface interfacial effect upon frictional characteristics in contact conditions which are representative of gear teeth meshing conditions in high performance transmissions. The study uses pin-on-disc tribometry. As the contact conditions are mainly governed by the formation of surface-adhered tribo-films, their effect upon frictional characteristics is further investigated through use of atomic force microscopy (AFM) in lateral force mode (LFM). A test procedure is presented to benchmark lubricant additive package-surface combinations for improved tribological performance. The investigation takes into account surface material, surface topography and lubricant additive package, all of which affect the tribo-chemical absorption or bonding of a thin film to the contacting surfaces. The test protocol also includes surface chemical spectrometry and Scanning Electron Microscopy (SEM). The presented methodology has not hitherto been reported in literature.