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This paper provides an overview of driveline fluids, in particular automatic transmission fluids (ATFs), and is intended to be a general reference for those working with such fluids. Included are an introduction to driveline fluids, highlighting what sets them apart from other lubricants, a history of ATF development, a description of key physical ATF properties and a comparison of ATF fluid specifications. Also included are descriptions of the chemical composition of such fluids and the commonly used basestocks. A section is included on how to evaluate used driveline oils, describing common test methods and some comments on interpreting the test results. Finally the future direction of driveline fluid development is discussed. A glossary of terms is included at the end.

Multiple plate disc clutches are used extensively for shifting gears in automatic transmissions. In the active clutches that engage or disengage during a shift the automatic transmission fluid (ATF) and friction material experience large changes in pressure, P, sliding speed, v, and temperature, T. The coefficient of friction, μ, of the ATF and friction material is a function of these variables so μ = μ(P,v,T) also changes during clutch engagement. These changes in friction coefficient can lead to noise or vibration if the ATF properties and clutch friction material are improperly matched. A theoretical understanding of what causes noise, vibration and harshness (NVH) in shifting clutches is valuable for the development of an ATF suitable for a particular friction material. Here we present a theoretical model that identifies the slope, ∂μ/∂T, of the coefficient of friction with respect to temperature as a major contributor to the damping in a clutch during engagement.

This laboratory presents a new step-automatic transmission fluid with enhanced friction durability and robustness for the Asian marketplace. This mineral-oil-based fluid also meets JASO M315-1A performance requirements on torque capacity, anti-oxidation, anti-wear, extreme pressure (EP), anti-aeration/foam control, copper corrosion and anti-rust performance. The fluid offers a JASO M349 low velocity friction apparatus (LVFA) durability lifetime of over 1100 hours. Moreover, this fluid maintains stable torque capacity during its entire LVFA durability lifetime, across the temperature range of 40 to 120 °C. Similarly, friction level changes with sliding speed are smaller than experienced by other commercial factory-fill ATFs. These critical performance features are due to a new fluid friction system approach, which may enable new types of transmission hardware or calibration.

This report focuses on an extended investigation of the durability of Dual Clutch Transmission (DCT) fluids. The performance requirements of DCT fluids differ from those of traditional step automatic transmission fluids. For that reason, key performance lab tests are discussed in this paper. Friction durability is measured with a modified version of the JASO M348 SAE#2 friction plate test. In addition, results from a vehicle chassis dynamometer test are discussed. This test involves running a 2008 Volkswagen GTI for 60,000 dynamometer miles (42,000 cycles) of severe acceleration and high speed conditions. Finally, a new DCT fluid, which performs well in these tests, offers friction stability and superior wear protection of transmission hardware, when compared to the commercial reference fluid.

An automatic transmission planetary gear fatigue test is used to screen lubricant performance of various automatic transmission fluids. The key use of this test is to assess the ability of a lubricant to extend or limit planetary gear system fatigue life. We study the fatigue behavior in this test and find the major failure modes are tooth macropitting, and macropitting-related tooth fracture of the sun and planetary gears (short and long pinion gears). Micropitting appears to be responsible for these gear failure modes. Macropitting is also seen on the shafts and needle rollers of the bearings. Gear tooth fracture appears to have originated from the surface as a secondary failure mode following macropitting. Bearing macropitting is initiated by geometric stress concentration. Bending fatigue failure on the sun and planetary gears also occurs but it is not a micropitting-initiated failure mode.

To develop an automatic transmission fluid (ATF) that meets DEXRON® III-H specifications, the ATF must pass two critical tests, the GM oxidation test (GMOT) and the GM cycling test (GMCT), in addition to many other performance tests. The specification on the GMOT is that delta TAN (difference in total acid number compared with the fresh oil) at the end of the test does not exceed 3.25 while the specifications on GMCT are that delta TAN cannot exceed 2.0 and the 1-2 shift time must stay between 0.30 and 0.75 seconds throughout the test. For this work, we analyze oil oxidation and changes in oils' surface tension, drum and band surface degradation and deposit formation. We have found that with respect to the delta TAN limits of the DEXRON® III-H specification, the GMCT is more severe than the GMOT. The effect of base oil chemistry on oxidation in these tests has been quantified. Oil oxidation is not responsible for the GMCT 1-2 shift time increase.

This paper presents data on the effect of ATF additives on lead corrosion as measured in a simple bench test and the MERCON® ABOT. The correlation between the bench test and the ABOT test will be discussed. The effect of base oil, carboxylic acids, and oxidation products on lead corrosion will also be discussed. Two types of additives used in automatic transmission fluids can reduce lead corrosion. Each additive has shown a statistically significant linear correlation to lead loss. There is also a statistically significant detrimental interaction between the additives when both are present in the fluid simultaneously. A mechanism to explain this interaction will be presented along with analyses of the lead surfaces after ABOT testing.

Different mechanical components in a vehicle can be made from different steel alloys with various surface treatments or coatings. Lubricant technology is needed to prevent wear and control friction on all of these different surfaces. Phosphorus compounds are the key additives that are used to control wear and they do this by forming tribofilms on surfaces. It has been shown that different operating conditions (pressures and sliding conditions) can influence the formation of tribofilms formed by different anti-wear additives. The effect of surface metallurgy and morphology on tribofilm formation is described in this paper. Our results show that additive technology can form proper tribofilms on various surfaces and the right combination of additives can be found for current and future surfaces.

Deposit formation is an issue of great significance in a broad range of applications where lubricants are exposed to high temperatures. Lube varnish causes valve-sticking, bearing failure and filter blockage which can lead to considerable equipment downtime and high maintenance costs. Recently this has become a pressing issue in the stationary power generation industry. In order to investigate the chemistry leading to varnish, three samples of varnish-coated components from the lube/hydraulic systems of gas turbines from the field were obtained, along with information on the commercially available formulated oils which were used. Samples of these three fresh oils were analysed by a variety of chromatographic and spectroscopic techniques, which confirmed chemical identity of aminic and/or phenolic antioxidants, corrosion inhibitors and antiwear components. The varnish-coated turbine components were also investigated by these methods.