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Hybrid drivetrain hardware combines an electric motor and a transmission, gear box, or hydraulic unit. With many hybrid electric vehicle (HEV) hardware designs the transmission fluid is in contact with the electric motor. Some OEMs and tier suppliers have concerns about the electrical properties of automatic transmission fluids (ATFs). Lubrizol has conducted a fundamental research project to better understand the electrical conductivity of ATFs. In this paper, we will present conductivity data as a function of temperature for a range of commercially available ATFs. All fluids had conductivities ranging from 0.9 to 8x10-9 S/cm at 100 °C and can be considered insulators with the ability to dissipate static charge. Next we will deconstruct one ATF to show the relative impact of the various classes of lubricant additives. We find that more polar additives have a larger effect on conductivity on a normalized (per weight %) basis.

Analytical ferrography of used oils is most often associated with machine maintenance programs where it is used as a predictive tool to avoid catastrophic failures. The technique is not widely used in driveline fluid evaluations, likely due to both its expense and a general unfamiliarity of the technique among engineers and scientists involved in driveline fluid analysis. However, this technique can provide data essential to understanding the degraded performance of the friction interface. In this paper we briefly describe analytical ferrography. We then show three circumstances where the use of this technique is appropriate for the evaluation of used driveline fluids. First we illustrate how analytical ferrography can be used to detect the past presence of water in oil that is currently dry. Next we show how the technique can help identify contaminant particles that would normally remain undetected due to size and low abundance.

One of the most common failure modes for a friction interface is the accumulation of glaze on the friction material surface. Until recently, our analysis of glaze chemistry has always been consistent with the degradation of detergent, antiwear and extreme pressure additives in the oil. These additive degradation products are readily identified by the presence of Ca, P, S and Zn in an EDS analysis. In these cases the loss of friction performance, characterized by a gradual fade in friction coefficient and the concomitant development of a negative friction-speed gradient, is directly related to the loss of surface porosity due to the accumulation of glaze on the friction material surface. Over the past few years, the drive for better fuel economy in passenger cars has led to the introduction of lower viscosity oils possessing high viscosity index and shear stability. We have observed that these fluids also can lead to glaze accumulation on the friction surface.

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.

Friction plates are often described as ‘glazed’ when they become smoother, or take on a darkened or shiny appearance. Several mechanisms may lead to this type of appearance; hence, within the industry, the term ‘glazed’ is not universally defined. The term has been used to describe damage of the friction material due to excessive heat, deposition of fluid degradation products, the contamination of the friction material by fine particles or even the inclusion of used oil. We promote the use of the term ‘glazed’ to describe damage to friction plates resulting only from the deposition of fluid degradation products on the friction material surface. In this paper, we offer a methodology to evaluate friction material plates such that the nature of the damage is well understood. Some of the techniques described use advanced analytical equipment to provide direct information regarding the chemical nature of the glaze.

Several new generation friction materials with high energy, high coefficient of friction; good μ-v characteristics and durability were presented. These new generation materials were developed based on fundamental tribological friction interface phenomena understanding through various predictive models as well as chemical and physical characterization methods for friction materials / fluid interface interactions. Such new generation materials include desired characteristics for various wet clutch applications, e.g., wet start clutches, shifting clutches, and continuous slip clutches.

Wet clutch interfaces that operate in high-energy environments experience significant frictional heating. Under such conditions, thermoelastic or thermoplastic instabilities may lead to a transition from evenly distributed surface contacts to unevenly distributed regions that manifest themselves as hot spots on the separator plate. The critical power at which these instabilities occur depend on the thermal conductivity, thermal expansion, and stiffness of the components. Modeling has shown that for wet clutch interfaces the stiffness of the friction material has a dominant influence on the critical power. We have found that the lubricant additive package also plays a significant role in the onset of hot spots. In this paper, we report the influence of antiwear systems on the occurrence of hot spots.

A new successful friction material was developed to operate in the severe high-energy environment of the slipping clutch, including wet start clutch, continuous slip and limited slip applications. The new slipping material was based on the understanding of the interfacial phenomena occurring during the slipping operations. The resulting friction interface (friction material and lubricant combination) possesses the necessary heat dissipation, good shudder resistance and good launch feel. Bench, dynamometer and vehicle test results are presented and the underlying interfacial phenomena are discussed.