Michael P. Gahagan

Systematic formulation of efficient and durable axle lubricants for light trucks and sport utility vehicles

Consumer demand for size, weight and horsepower has dictated a prominent role for sport utility vehicles and light trucks in the product lines of major North American automobile manufacturers. Inherently less efficient than passenger cars, these vehicles will be facing more stringent light duty CAFE (Corporate Average Fuel Economy) standards beginning in 2005 when mileage targets will be elevated to 21 mpg; this figure will be further increased to 22.2 mpg by 2007. In order to accommodate both public demand and CAFE requirements, vehicle manufacturers are seeking ways to improve fuel economy through design and material modifications as well as through improvements in lubrication. The axle lubricant may have an important impact on fuel economy, and axle lubricants can be tailored to deliver higher levels of operating efficiency over a wide range of conditions. Improvements in city-highway axle efficiency can be gained through the lubricant when appropriate rheological properties are coupled with lighter (SAE 75W-90) viscosity grades to minimize frictional churning losses. Light trucks and sport utility vehicles (SUVs), often functioning under high duress and heavy loading, demand lubricants which are capable of controlling operating temperatures; historically, higher viscosities (SAE 75W-140) coupled with special rheological characteristics have served this purpose. The penalty for high load durability and longer vehicle life is often a loss in city-highway efficiency; at the same time, high city-highway efficiency ratings are not generally consistent with vehicle durability under highly stressful operation. The challenge is bridging the efficiency-durability gap. Laboratory test rigs which simulate the FTP-75 and various trailer-tow duty cycles, recently described by these authors, are valuable tools which enable the formulator to design versatile and balanced axle lubricating fluids. Both rigs operate with a high level of control over testing conditions and produce repeatable fluid rankings. Herein, we will describe a fluid development program utilizing key physical and chemical screening methods, efficiency and durability rig testing, bearing life testing, and field validation testing. Of particular interest, certain SAE 75W-140 grade candidate fluids emerging from this process have demonstrated traditional high torque durability (and bearing life) but also significantly improved operating efficiency.

Lubricant Technology for Hybrid Electric Vehicle Automatic Transmissions

Of the three main automatic transmission types, the stepped automatic (AT), the continuously variable transmission (CVT) and the dual clutch transmission (DCT), the high mechanical efficiency of DCT technology [1] makes it a preferred technology for many hybrid vehicles. The mechanical efficiency of the DCT means it saves on both battery and engine demand to drive the vehicle. It is selected for hybrids because it provides high energy transfer efficiency, which delivers vehicle fuel economy performance improvements. The DCT is efficient in terms of mechanical efficiency as there are no torque converter losses [2].

Performance and surface analysis of tapered bearings lubricated with a manual transmission fluid

The comparative tribological performance of a series of tapered bearings lubricated with a fully formulated manual transmission fluid (MTF) and its PAO base oil was obtained using a KRL thrust bearing tester. Bearing performance was based on the successful completion of an eight hour test procedure created for the KRL tester. Optical microscopy was used to conduct textural analyses on the body contact areas of tested rollers while X-ray photoelectron spectroscopy (XPS) depth profiles were used to collect surface film composition at the previously mentioned contact area. The KRL results indicated that the MTF operated at lower temperatures and performed better than the PAO. This difference was ascribed to the enhanced thermal stability of the additive packages used in the fluid. The optical analyses detected a series of dark bands at the body contact area of all tested rollers indicative of the presence of an EP/AW surface film. XPS depth profiles of the base oil indicated that it generated a mixture of organic carbon and iron oxide which proved ineffective under more severe test conditions. In contrast, the profile of the MTF included a mixture of carbonate, borate, sulfide, phosphates and oxide throughout the film. Finally, the combination of thermal stability and EP/AW film composition was attributed to the better performance of the MTF.