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Sequential four-ball wear tests have been used to evaluate automotive crankcase oils for use as heavy-duty hydraulic fluids and automotive crankcase lubricants. This test technique has been adapted for use with steel-on-steel, steel-on-ceramic and ceramic-on-ceramic bearing systems. In addition to the conventional “run in” and “steady-state” wear studies, the data produced have been used to interpret bearing unit load levels for the various bearing systems involved. The data produced show that in many cases hybrid bearing systems (steel-on-ceramic) and ceramic-on-ceramic bearing systems may be useful at higher unit loadings than the conventional steel-on-steel systems. These studies focused on achieving low boundary lubricated wear rates. The bearing unit loadings were obtained from the unit bearing pressures after the “run in” of the specific bearing system.

The majority of crankcase lubricants are now formulated to contain polymeric additives to improve the viscosity temperature properties to provide a better lubricating film in the various bearing systems in an internal combustion engine. These VI (viscosity index) improved lubricants are non-Newtonian under the high shear conditions that exist in most automotive bearing systems. The conditions of interest range from starting the engine at temperatures of as low as -40°C to operating the engine at normal operating conditions including bearing temperatures of 150°C or higher. This paper presents a method for predicting the viscosity shear relationship for a series of SAE multigrade engine oils as a function of temperature and shear stress. The method is demonstrated using three types of polymeric VI improvers currently used in SAE multigrade engine oils. The polymer types include olefin copolymers (OCP), polymethacrylates (PMA), and styrene-isoprene copolymers (SI).

This paper presents a unique line-contact EHL test rig. One of the features of the rig is that the EHL junction is formed by a cylindrical roller in contact with the internal surface of a cylindrical ring. With this design configuration, only a very small amount of lubricant is needed even for high speed testing as the centrifugal force maintains a good oil supply to the contact region. The roller and the ring are driven separately by servomotors. The roller assembly is mounted on a platform supported by a hydrostatic air bearing to allow accurate traction measurement. With a coated sapphire ring, the EHL film thickness in the contact zone can be measured by means of optical interferometry. The control and data acquisition systems are integrated in a Labview environment, and the test sequence can be programmed and automatically carried out by the control program. The innovative design features and test parameters of the rig are presented along with a set of typical test results.