David L. Alexander

Change of high-shear-rate viscosity of engine oils during use: A review

It has long been known that the kinematic viscosities of multigrade engine oils change with use, the typical pattern being an initial decrease followed by a gradual increase. Recent work has shown that the patterns of change of the high-temperature, high-shear (HTHS) viscosity are different than those of the kinematic viscosity. These results, coupled with recent bearing oil film thickness results, suggest that kinematic viscosity changes are less significant in the operation of the bearings of engines than has been assumed. The pattern of HTHS viscosity change has been found to depend on both viscosity index (VI) improver type and engine test. Oil-thickening effects tend to be more prominent in the HTHS viscosity patterns than in the kinematic viscosity patterns.

Development of a High Shear Rate Capillary Viscometer for Engine Oils

A high shear rate capillary viscometer is described for measuring the viscosity of engine oils at shear rates and temperatures within the range experienced by automotive engine oils. Although the use of multigrade engine oils is well-established, the lack of commercial viscometers to measure engine oil viscosity at appropriately high temperatures and shear rates has led many laboratories to build their own viscometers. The simplicity of the capillary viscometer is enhanced since the device is used as a relative viscometer rather than as an absolute one. Viscosity is determined from calibration with Newtonian oils instead of calculation from capillary dimensions. Flow properties of the multigrade oil being tested are equated to viscosities of a series of single-grade reference oils. Principal elements of the capillary viscometer are a glass capillary, a pump-activated pressurization system, a glass timing column for flow rate measurements, and necessary temperature and pressure instrumentation. Procedures for using the viscometer are detailed, and the devices usefulness is demonstrated for a group of commercial engine oils. The viscometer can also be used for interpreting the results of a laboratory engine friction test.

Investigations of Engine Oil Shear Stability in Laboratory Tests and Road Tests

The relationship of shear stability in laboratory tests to shear stability in service was investigated in a diesel injector test, in the L-38 single-cylinder engine, in a multi-cylinder engine equipped for bearing film thickness measurement, and in road testing in an automobile and in trucks. All of the laboratory and road tests differed in severity of shearing and also showed that major VI improver types differed in the time needed for their kinematic viscosity to approach a fully-sheared value. Shear stability comparisons based on kinematic viscosities measured during the transition to the fully sheared condition did not accurately represent the relative shear stability of VI improvers in the fully-sheared condition. In the road tests, most of the oils were at their fully-sheared viscosity for the major part of their service life. The decrease of HTHS viscosity due to shearing in the road test and laboratory engines was usually less than half the kinematic viscosity decrease. Bearing oil film thicknesses showed little or no change with test duration in the multicylinder lab engine and correlate well with HTHS viscosity.

Propagation of Surface Disturbances on Radially-Loaded Disks

An analysis is presented showing the manner in which an initial point disturbance on the surface of one disk of a pair of radially loaded disks rolling and sliding in contact will grow and propagate other surface disturbances on both disks. In the analysis it is assumed that an area becoming disturbed will be able to cause disturbances on surfaces which come into contact with it. The patterns of the disturbances formed have been compared with scuff patterns on pairs of failed disks, and significant similarities are shown. The number of disturbances and the spacing of the leading edges of the disturbances are similar to the number and spacing of the scuff marks. The analysis gives lengths of the disturbances somewhat longer than the scuff marks. It is concluded that the analysis is helpful in understanding failures on disks, and it can be extended to scuff propagation on gears. Presented as an American Society of Lubrication Engineers paper ASLE/ASME Lubrication Conference held in Chicago, Illinois, Octobe...