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This paper describes the design and construction of a dynamic flow apparatus for the measurement of air entrainment and release characteristics of lubricants, specifically automatic transmission fluids. Data are provided on test method development and correlation with transmission cycling tests. The results obtained using this apparatus and method are compared with those obtained from readily available, and newly developed, foaming and air entrainment tests. The existing tests give an inconsistent picture of fluid foaming and air entrainment characteristics. Foaming tests contained in the major ATF service fill specifications have been found incapable of identifying lubricants with poor fluid level control in an automatic transmission cycling test. The newly developed dynamic flow apparatus is capable of correctly ranking the fluid level control of tested lubricants as determined in the transmission cycling test.

We have compared five different, commercially produced, API Group III base oils in a next-generation, OEM automatic transmission fluid (ATF) formulation. One objective of this work is to understand the impact of base oil selection on the performance properties of finished ATF. This may help us to develop technically sound criteria for allowing interchange among premium Group III base oils in both factory-fill and service-fill ATFs. The performance data, measured from lab bench tests, include such properties as seal swell, low temperature viscometrics, oxidation life, and LVFA static and dynamic friction. Certain properties of the base oils, such as low temperature viscosity and oxidation stability, have a strong impact on the ATF performance. However, there are many chemical similarities between the Group III base oils, and this results in little to no differences observed in many performance areas.

Anti-shudder characteristics are an important part of automatic transmission fluid (ATF) performance. Anti-shudder performance has two aspects, initial friction aimed at the prevention of “green shudder” and anti-shudder durability which is the prevention of shudder at high vehicle mileage. Different methods of measuring anti-shudder durability give different results. We have found that some fluids give very acceptable performance when measured in a Low Velocity Friction Apparatus (LVFA) test, such as a JASO M349-2001 [1] , do not give good results when measured in a method that includes high energy engagements and oxidation. This apparent anomaly in test results is due to unexpected behavior of certain fluids after oxidation. The observation is a cause for concern relative to the widely accepted JASO method.