Chester K. Murphy

Interactions Between a Zinc Dialkylphosphorodithioate and Lubricating Oil Dispersants

Direct infrared spectrophotometric evidence of interactions between lubricating oil dispersants and a zinc dialkylphosphorodithioate (ZDP) is presented. Increasing the concentration of the dispersants polyamino monoalkenylsuccinimide, barium thiophosphonate, and basic barium dinonylbenzene sulfonate in a mineral oil containing 1.2% by weight of a ZDP decreased the intensity of the phosphorus-oxygen-carbon and phosphorus-sulfur infrared bands, and caused the appearance of a new band at 668 cm−1. The dispersants barium dinonylnaphthalene sulfonate, calcium petroleum sulfonate, and alkaline petroleum sulfonate decreased the intensity of the phosphorus-sulfur bands only after the solutions had aged, and independently of dispersant concentration. It is speculated that chemical reactions cause these interactions between the ZDP and the dispersants, and that ionic metal phosphorodithioates are formed. The possibility of association, isomeric, and complexation effects is also explored. Regardless of the exact mec...

A Correlation Between Engine Oil Rheology and Oil Film Thickness in Engine Journal Bearings

Oil film thickness measurements made in the front main bearing of an operating 3.8 L, V-6 engine were compared with rheological measurements made on a series of commercial and experimental oil blends. High-temperature, high-shear-rate viscosity measurements correlated with the film thicknesses of all single-grade and many multigrade oils. However, the film thicknesses provided by some multigrade oils were larger than could be accounted for by their high-temperature, high-shear-rate viscosities alone. Although the pressure-viscosity coefficients of some of the oils were significantly different from those of the majority of oils tested, they were not oils which produced unusual film thicknesses. As a consequence, correcting oil viscosities for the estimated pressures acting within the bearing was unsuccessful in improving the correlations. The correlations were improved, however, by accounting for the elastic properties of the multigrade oils. Measurements of oil relaxation times at high temperatures and shear rates showed large differences in elastic properties among the test oils. A good correlation (R/sup 2/ = 0.73) was obtained from a multiple linear regression of film thickness as a function of both high-temperature, high-shear-rate viscosities and relaxation times.

A comparison of the total capacitance and total resistance techniques for measuring the thickness of journal bearing oil films in an operating engine

Bearing oil film thickness (BOFT) values were determined for the front main bearing of a four-cylinder engine at different engine speeds, loads, and oil temperatures using two different measurement techniques. The total resistance technique assumes the oil film can be modelled as a simple ohmic resistor. The total capacitance technique assumes the oil film can be described as a simple capacitor. A comparison of results determined using both methods for a set of single-grade oils demonstrated that, although the methods agree quantitatively for certain combinations of engine test conditions and oils, the level of precision with the total capacitance technique is greater than with the total resistance technique

Viscosity Effects on Engine Wear Under High-Temperature, High-Speed Conditions

Four multigrade engine oils, containing the same base oil plus SE additive package but polymeric viscosity-index improvers of differing shear stability, were evaluated in 80 000 km of high-speed, high-temperature vehicle service. Bearing, piston ring and valve guide wear, as well as oil consumption, oil filter plugging and engine cleanliness were all worse for the engines operated on the low-shear stability oils. The wear differences were traced to differences in high-shear-rate viscosity, while the cleanliness, filter plugging and oil consumption differences occurred because of excessive wear or polymer shear degradation. These results suggest that engine oil viscosity should be specified under high-shear-rate conditions.

Measuring the effect of oil viscosity on oil film thickness in engine journal bearings

The minimum oil-film thickness in the front main bearing of a 3.8 L, V-6 engine was measured at 3,000 r/min, and 140 N.m using an electrical resistance technique. For a series of seven Newtonian, single-grade oils, film thickness correlated with oil viscosity measured either in a kinematic or in a high-shear-rate viscometer. For a series of fifteen polymer-containing, non-Newtonian, multigrade oils, however, no single measure of viscosity adequately correlated with film thickness for all of the oils. By eliminating four multigrade oils from the combined single and multigrade data sets, it was possible to correlate film thickness to the viscosity (of the remaining multigrade and Newtonian oils) measured at 150 deg C and 500,000/s, conditions which are believed to be representative of temperatures and shear rates in bearing oil films. Possible explanations for the lack of correlation with the entire set of twenty-two oils are discussed.