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Technical Paper

A Non-Averaging Method of Determining the Rheological Properties of Traction Fluids

Traction machines have been frequently used to study the rheological properties of lubricants in elasto-hydrodynamic lubrication (EHL) contacts. Fundamental properties are inferred from EHL traction measurements based on the average pressures and temperatures in the contact. This average approach leads to uncertainty in the accuracy of the results due to the highly nonlinear response of fluid rheological behavior to both pressure and temperature. A non-averaging method is developed in this paper to determine the elastic and plastic properties of traction fluids operating in EHL contacts at small slide-to-roll ratios. A precision line-contact traction rig is used to measure the EHL traction at a given oil temperature and Hertz pressure. By choosing a sensible pressure-property expression, the parameters of the expression can be determined through the initial slope and peak traction coefficient of the traction measurements.
Technical Paper

An Internal Line-Contact EHL and Traction Test Rig

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.
Technical Paper

Changes in Particulate Composition and Morphology When Using of Vegetable Oil Lubricant in a Low Heat Rejection Engine

Thermal barrier coatings have been shown to be effective at reducing particulate emissions from diesel engines. Prior work by the authors has demonstrated a significant decrease in particulate emissions from a thermal barrier coated, single-cylinder, indirect injection (IDI) diesel engine, primarily through reduction of the volatile (VOF) and soluble (SOF) fraction of the particulate. Most of this prior work relied on conventional, commercially available, petroleum-based lubricants. Recently, the authors demonstrated additional particulate emissions reductions when a high oleic sunflower-based lubricant was used instead of a conventional petroleum-based lubricant. This paper concerns the manner in which the particulate was reduced, and reports on the changes in particulate composition and morphology between the two lubricants. Composition was examined quantitatively through thermal analysis of the particulate from a single-cylinder IDI diesel engine.
Technical Paper

Four-Ball Wear Studies of Steel-on-Steel, Steel-on-Ceramic and Ceramic-on-Ceramic Bearing Systems

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.
Technical Paper

Predicting Viscosity-Shear Relationships of VI Improved Lubricants

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).