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A test was developed to determine the effect of licensed DEXRON®-III service fluids on the performance of the Electronically Controlled Capacity Clutch (EC3). Some fluids can cause shudder and/or hunting of the clutch and are unsuitable for use in EC3-equipped vehicles. The test uses a 1997 Riviera with a 3800 SC engine and a 4T65E transmission to evaluate fluids under a variety of driving conditions. The responses to both the reference and candidate fluids are statistically compared with each other and with pooled data from previous reference tests to identify and reject unsuitable fluids. The DEXRON®-III specification has been modified to include this test to ensure the elimination of unsuitable DEXRON®-III fluids from the marketplace.

This paper discusses four methods for measuring the resistance of transmission fluids to permanent viscosity loss through shear. The four methods include the Fuel Injector Shear Stability test, the Sonic shear test, the DEXRON®-III Cycling test and the KRL test. Each of these methods and their advantages are discussed and data provided for many OEM fluids and the effects of these methods on the final viscosity. The data indicates the KRL generates the maximum shear stress on the fluids compared to the other methods. The data also indicates the sonic shear method results are similar to those of the KRL test. The fuel injector test imparts the least stress to the fluid. Data is presented to show the correlation between viscosity changes obtained using these methods and viscosity changes observed with mileage accumulation in vehicle transmissions.

As part of the International Lubricant Standardization and Approval Committee's (ILSAC) goal of developing a global automatic transmission fluid (ATF) specification, members have been evaluating test methods that are currently used by various automotive manufacturers for qualifying ATF for use in their respective transmissions. This report deals with comparing test methods used for determining torque capacity in friction systems (shifting clutches). Three test methods were compared, the Plate Friction Test from the General Motors DEXRON®-III Specification, the Friction Durability Test from the Ford MERCON® Specification, and the Japanese Automotive Manufacturers Association Friction Test - JASO Method 348-95. Eight different fluids were evaluated. Friction parameters used in the comparison were breakaway friction, dynamic friction torque at midpoint and the end of engagement, and the ratio of end torque to midpoint torque.

General Motors (GM) currently uses about 1000 different seals for manufacturing all of its automatic transmissions worldwide. In order to assure that these seals function correctly in service, a method of measuring seal performance with service fill automatic transmission fluids (ATFs) has to be specified. Along with this measure, a pass/fail criterion for the evaluation of seal performance is implemented. Due to the large number of seals that are utilized, it would be impractical to test each one with every fluid that is submitted for GM DEXRON®-III and/or Allison C4 certification. It is also very difficult to use production seals in testing, due to the irregular shapes and material combinations, which make measurement of the seal material properties difficult. Therefore, a revised test will be included in the DEXRON®-III and Allison C4 service fill specifications to evaluate the compatibility of service fill ATFs with a representative sample of seal materials used in production.

The International Lubricant Standardization and Approval Committee (ILSAC) ATF subcommittee members have compared the two oxidation bench test methods, Aluminum Beaker Oxidation Test (ABOT) and Indiana Stirring Oxidation Stability Test (ISOT), using a number of factory-fill and service-fill ATFs obtained in Japan and in the US. In many cases, the ATFs were more severely oxidized after the ABOT procedure than after the same duration of the ISOT procedure. The relative severity of these two tests was influenced by the composition of the ATFs. The bench test oxidation data were compared with the transmission and the vehicle oxidation test data.

The rheological behavior of automatic transmission fluids (ATF) ranges from moderately shear-thinning to Newtonian. However, no commercially available ATFs are known to display shear-thickening behavior. A theoretical investigation was performed to determine if any advantages could be derived from the use of shear-thickening ATF in automatic transmission components and subsystems. A series of theoretical shear-thickening, shear-thinning, and Newtonian fluids were modeled by a power law function and compared to a reference shear-thinning ATF in simplified representations of transmission components and subsystem geometries. The results indicate that a shear-thickening ATF with zero shear viscosity, infinite shear viscosity, and power of 417 mPa-s, 6.23 mPa-s, and 1.03(dimensionless), respectively, displays optimized behavior with respect to the reference shear-thinning ATF.

Frictional characteristics of several automatic transmission fluids (ATF's) were evaluated in an SAE No. 2 Friction Machine adapted to the band clutch from a front-wheel-drive, three-speed automatic transaxle. The bench test apparatus subjects the band clutch to repeated engagements (24 000 in a 100-hour test period) at elevated temperature with representative clutch energy dissipation and lockup time, and with forced aeration of the fluid. Fluid frictional performance is judged from the level and stability of friction torque during the 24 000 clutch engagements. The test is repeatable and readily distinguishes fluids having different frictional characteristics. Fluid frictional behavior in the band machine is shown to reflect fluid effects on shift performance in an engine dynamometer, transaxle cycling test. Also, fluid effects determined in the cycling test are shown to match those obtained in a vehicle.

Using standard industry tests, the oxidation stability of General Motors current factory-fill automatic transmission fluid (ATF) was compared to that of a proposed factory-fill ATF to be introduced for the 1995 Model Year. Full-scale transmission tests and Aluminum Beaker Oxidation Tests run at various temperatures showed that a proposed factory-fill fluid is substantially more resistant to oxidation than the current factory-fill ATF. Using Total Acid Number increase (Δ-TAN) as the measure of oxidation, a minimum of 35% improvement was obtained with a proposed factory fill. This improvement at least doubles the time to “perceived fluid failure” (Δ-TAN = 2.5).

The friction characteristics of several DEXRON®-III automatic transmission fluids were examined in a variety of friction tests. These evaluations included tests with SAE No. 2 Friction Machines using either Band or Plate heads, breakaway friction tests, and low-sliding speed friction tests. The effect of bulk fluid temperature on friction performance was examined in band tests and in breakaway tests using the plate clutch apparatus. The DEXRON®-III fluids were compared to the previous generation automatic transmission fluids. Results showed that the DEXRON®-III fluids exhibited more desirable friction characteristics; for example, with the DEXRON®-III fluids in the band machine, dynamic friction remained stable during sustained operation at high temperature, whereas with DEXRON®-IIE fluids, dynamic friction decreased as much as 25%.

An integrated approach to modeling end of useful life of an automatic transmission fluid (ATF) has been developed. The flexible fluid life model allows either predictive or real-time calculations of the end of useful fluid life under different transmission design strategies and customer driver behaviors as reflected in operating temperatures, shift characteristics, fluid volume and fluid distribution throughout the transmission. An estimation of remaining useful fluid life is monitored using two metrics, namely bulk oxidation, as a general indicator of fluid quality, and frictional degradation, as an indicator of shift quality. As operating conditions increase in severity, ATF is subjected to conditions that may shorten its life. Using the developed technique, ATF useful life can be better predicted.

A viscous damper is used as part of the automatic transaxle torque converter in some new passenger cars for improved driveability and fuel economy. A viscous silicone fluid is a critical component of the damper. Fluid viscosity-shear rate characteristics were determined in the laboratory for temperatures of 25 to 150 °C at shear rates from 400 to over 6000 reciprocal seconds. Using these data, and the dimensions of the viscous damper, a mathematical model was developed which predicts viscous damper output torque. Correlation between model predictions and actual measured torques from dynamometer tests was excellent. As a result, the mathematical model is useful for predicting viscous damper performance from measured fluid viscosity-shear rate characteristics. Also, since the model includes the critical viscous damper dimensions, it can be used for determining effects of damper design modifications on damper performance.

The effects of automatic transmission fluid viscosity on the low-temperature performance of a front-wheel-drive transaxle were determined in a cold room maintained at a temperature of -20°F (-28.9°C), using both a cranking apparatus and a vehicle. Cranking and vehicle tests were conducted to determine the effects of fluid viscosity on the power required to crank a transaxle and on transaxle performance under low-temperature transient operation, respectively. Four automatic transmission fluids were tested, ranging in viscosity from 2 800 to 16 000 cP at -20°F. All test fluids contained the same additive package and were blended using the same types of base oils. Reducing fluid viscosity from 6 000 cP (current factory-fill) to 3 900 cP at -20°F reduced shift times by 10 percent, forward clutch engagement time by 25 percent, apply pressure rise times by 40 percent, and cranking loads by almost 40 percent.

In recent years, the slip lock-up mechanism has been adopted widely, because of its fuel efficiency and its ability to improve NVH. This necessitates that the automatic transmission fluid (ATF) used in automatic transmissions with slip lock-up clutches requires anti-shudder performance characteristics. The test methods used to evaluate the anti-shudder performance of an ATF can be classified roughly into two types. One is specified to measure whether a μ-V slope of the ATF is positive or negative, the other is the evaluation of the shudder occurrence in the practical vehicle. The former are μ-V property tests from MERCON® V, ATF+4®, and JASO M349-98, the latter is the vehicle test from DEXRON®-III. Additionally, in the evaluation of the μ-V property, there are two tests using the modified SAE No.2 friction machine and the modified low velocity friction apparatus (LVFA).

Twenty-two physical and chemical properties of a typical automatic transmission fluid were determined. In most cases the properties were determined over a range of temperatures. In general, air solubility, volumetric thermal expansion, and specific heat increase with increasing temperature; whereas, surface tension, specific gravity, viscosity, bulk modulus, density, thermal conductivity, and electrical resistivity decrease with increasing temperature.