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A new, low cost, simple and compact bench type machine has been developed for investigating automatic transmission clutch plate lubrication. The energy absorbed per unit of clutch facing area during clutch engagement is comparable to that absorbed by the clutch during a full-throttle upshift in a car. The machine uses full-size clutch plates and requires a 13-ounce sample of fluid. Condition of the clutch plates after running under cycling conditions correlates with that found in an engine-transmission-dynamometer cycling test.

Automatic transmission clutch failures and rapid oxidation of the transmission fluid have sometimes been attributed to high temperatures in the clutch pack. For the purpose of estimating these temperatures, an analysis was made of the clutch system, and a solution was developed from the partial differential equations of heat conduction with appropriate boundary conditions. The solution thus obtained was verified experimentally. There were several important conclusions to this study. The maximum temperature rise occurs somewhat earlier than the end of the lockup time. The interface temperature rise increases as the lockup time decreases for a fixed amount of energy input. The ratio of heat flux entering the reaction plate to that entering the composite plate is not constant, as has been assumed by others. The heat absorbed by the fluid outside the clutch pack is negligible during the short lockup time. Temperature rises for some typical cases are computed.

The importance of controlling band/drum interface temperature to maintain friction system durability in an automatic transmission clutch is investigated in this paper. Frictional durability is extremely important to assure smooth, consistent shifts and long transmission life. A statistically designed series of experiments was run in a SAE No. 2 band test machine to determine the parameters which impact interface temperature. Sump level, sump temperature, engagement speed, system inertia, direct lubrication of the drum surface, and engagement time were all examined. The analysis reveals each of these parameters, with the exception of engagement time, directly influences interface temperature under the tested conditions. Interface temperature was then linked to frictional system stability. This was accomplished through a second series of experiments where interface temperature was varied by changing only one of the previously identified parameters.

Automatic transmission clutches are complex tribological systems. Frictional performance is controlled by the interaction of base fluids, additive components, composition clutches, and steel reaction plates with varying energy inputs and thermal stresses in an oxidizing environment. This paper, rather than addressing fully formulated fluid performance in such a system, takes a more fundamental approach where the number of system variables is reduced and the relative effects of formulation variables on system performance can be better examined. Relationships among observed friction performance, system oxidation, friction member condition, and representative performance additives are explored using a synthetic base fluid and a conventionally refined mineral base fluid.

Torque Hole Filling (THF) is a model based approach for controlling the automatic transmission clutches and input torque during a part-pedal upshift or zero-pedal downshift. A desired transmission output torque is first calculated and then the clutches and input torque are controlled to achieve that output torque. This is a system design approach with drivability as one of the direct design objectives. This paper presents the control design and implementation of Torque Hole Filling. First, the paper introduces the topic, defines the terms, and explains the basic operation and intended result. Next, it describes how it works with one instance of implementation and its corresponding dynamics equations, for both torque transfer and ratio change phases. Lastly but most importantly, it covers the various robustness considerations for real-world applications.

The influence of lubricant breakdown and additives on the frictional performance of wet automatic transmission clutch linings was studied with a low velocity friction apparatus. Base oil degradation products were shown to reduce static friction. Type A fluids were degraded in the friction machine to evaluate initial effects and in a bench oxidizing apparatus to evaluate extensive degradation effects. These methods rated the fluids in the same order and showed they varied widely in sludge formation, frictional and chemical stability. On frictional degradation, the friction level of two fluids increased with paper-based linings and decreased with sintered copper powder linings. The copper linings accelerated lubricant degradation and caused a different type of degradation.

A Finite Element Analysis technique was used to predict the clutch lining load distribution in automatic transmissions. This technique is explained and demonstrated on several clutch designs. The analysis shows the importance of rigid backing plates and optimum piston apply points. The benefit of tapered apply plates is also discussed. The importance of having a uniform clutch lining load distribution is described as it relates to clutch torque and energy capacity. THE PURPOSE of this paper is to discuss the importance of clutch lining load distribution for automatic transmissions as it relates to torque and clutch energy capacity. The design variables that affect these will be presented. Clutch pack compliance versus rigidity will also be addressed. A finite element technique for calculating the clutch lining load distribution will be discussed. This technique will be demonstrated on several clutch designs.

With the object of improving the technique of testing and specifying friction materials, a new type of friction material test fixture has been developed by the SAE Friction Subcommittee. This is a completely self-contained machine especially designed for cyclic testing and quality control work. This does not replace, but rather supplements, the steady state type friction test fixture (SAE No. 1) previously developed by the committee. This fixture, known as the SAE No. 2 test fixture, is designed to test clutch packs in an environment which is as close as possible to that of the friction elements in an automatic transmission. Both friction material manufacturers and users are employing this machine for quality control, component selection, and evaluation of friction materials and lubricants.

Open clutch spin loss computation is of interest for new clutch designs. It is desirable to minimize open clutch spin loss. Spin loss in automatic transmission clutches is mainly due to the viscous shear of the transmission fluid. Depending on the relative rotational speed of the plates the spin loss varies. At low rotational speeds the gap between the plates is filled with ATF (Automatic Transmission Fluid) and spin loss increases linearly with the rotational speed. At higher speeds the ATF layer, which is held together primarily by surface tension, begins to breakdown due to higher centrifugal forces and air pockets form at outward radial locations of the clutch plates. This results in a decrease in spin loss for the open clutch. CFD (computational fluid dynamics) modeling is an attractive option in calculating the spin loss for an open clutch.

The automatic transmission clutch represents a complex system involving critical interactions between the separator plates, fluid, operating conditions and friction material. This paper focuses on the effect of separator plate flatness on the performance and durability of two friction materials on an SAE #2 machine. The data from this study shows that flat separator plates yield higher dynamic coefficients and lower wear when compared to non-flat plates. These effects were obtained for separator plates with peak-to-peak departure from flatness values between approximately .08mm and .25mm. In addition, other variables such as material elastic modulus, separator plate thickness, and material operating pressure were studied. The use of soft friction materials to improve performance with non-flat reaction plates was quantified.

A bench scale apparatus and accelerated test protocol were developed to evaluate the effect of contamination of automatic transmsission fluid by mg/kg levels of water on cellulose frictional clutch surfaces. The testing indicated that water added at levels as low as 600 mg/kg migrated to the surface of untreated paper frictionals and contributed to loss of the paper coating and erratic torque transfer properties. Treated, “high performance” paper frictional surfaces showed less physical damage but the same torque transfer effects from water contaminated ATF. A mechanism of the water coating, swelling and weakening the hydrophillic cellulose fibers, with subsequent destruction due to hydrodynamic shear was proposed.