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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).

The Cannon High Temperature High Shear (HTHS) capillary viscometer is currently used in the ASTM D4624 procedure to measure the viscosity of polymer containing lubricants at 150°C and shear rate of 106 sec-1. An expansion of the utility of this Cannon instrument is described in this paper to cover the temperature range of lubricants from 35 to 175°C and shear rates of up to 106 sec-1. A finite difference model is used to solve the transport equations for capillary flow at each temperature. The solution accounted for temperature, pressure, non-Newtonian and kinetic energy effects on viscosity. Fitting these data to a double truncated power law model provides the incipient non-Newtonian shear rate γ̇1, the power law index n, and the incipient second Newtonian shear rate γ̇2. All these parameters can be measured at temperatures of around 100°C or less. The n and γ̇2 were found to be regular functions of temperature while γ̇i is always in the measured range.

Capillary viscometers provide a convenient method of measuring the viscosity of polymer containing lubricants at 150°C and 106 sec-1 shear rate as specified in ASTM D4624 Procedure. The commercial Cannon HTHS viscometer and the Penn State HTHS viscometer were used in this study. Improved calibration of the capillaries in the commercial viscometer provided an order of magnitude improvement of the HTHS repeatable values from 4.47% to 0.39% for a typical polymer containing lubricant. The viscosities of seven polymer containing lubricants at 106 sec-1 and 150°C gave an absolute mean percentage difference of 0.62% from measurements made with both capillary viscometers used in this study. The data suggests that substantial improvements can be made in the repeatability of ASTM D4624 HTHS viscosity measurements without changing the design of the current commercial viscometer.

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.

Delivery of a lubricant as a vapor mixed with a carrier gas provides a method of controlling the delivery rate of the lubricant. Temperatures in the range of 370 to 800 C are high enough to produce a lubricating film from tricresyl phosphate [TCP] vapor delivered in nitrogen as a carrier gas. The solid film lubricant formed by this delivery system provides excellent lubrication for a four-ball wear tester run at 370 °C. Deposit rates are compared for TCP vapor delivered lubrication over a temperature range using stainless steel and quartz surfaces. The deposit rate is sensitive to TCP concentration in the carrier gas. The deposit rates of the TCP decomposition products versus time are reported. Having been demonstrated in laboratory tests, the Vapor Phase [VP] concept is being pursued for hot section lubrication of the advanced (low heat rejection) diesel engines.

THE PENN STATE MICROOXIDATION TEST has been shown to be useful for the study of the influence of non-volatile compounds such as metal salts on the oxidative behavior of lubricants. A pressurized microoxidation test has been developed to evaluate the effects of water, NOx, and blow-by products on the stability of fully formulated motor oils. In this evaluation, H2O, N2O and metal salts of organic acids have been evaluated as single contaminants and in various combinations at test temperatures of 150°C and 175°C. In general, these studies show that water alone and in combination with the other contaminating products produces a substantial deposit under mild oxidation conditions such as oxidation at 175°C for less than ten hours. Under somewhat more severe conditions (175°C, time > 15 hours), relatively large amounts of soluble iron salts appear to dominate the deposition process.

The low temperature rheological behavior of a number of lubricants was examined in the range of −12 to −37°C over a shear rate range of one to 1000 sec−1. Results are presented for the following fluids: a waxy mineral oil, a synthetic hydrocarbon oil (poly-alpha olefin) and four oils each containing an olefin copol ymer (OCP) viscosity index improver with different additive packages. All samples were subjected to the same cooling history consisting of a 0.56°C/min cooling rate, followed by a one hour soak period before data was collected. These data demonstrate that waxy oils without VI improvers can show non-Newtonian and viscoelastic behavior similar to data at low temperatures for polymer-thickened oils in a non-waxy solvent. Combinations of wax and VI improver can show both shear thinning and shear thickening, as well as viscoelastic properties.