Bearing down on emissions reduction

  • 12-Jun-2009 11:24 EDT
SKF cutout.jpg
SKF's energy-efficient hybrid pinion unit (shown in red) can be used on the pinion shaft of a front differential.

A portfolio of customized bearings can improve powertrain efficiency by reducing friction up to 30% and in the process cut CO2 emissions.

Energy-efficiency benefits of the bearings from SKF Automotive Division have their origin in the digital domain. "Our Vehicle Environmental Performance (VEP) simulator software enables us to analyze precisely what is happening inside the bearing in its operation. Depending on the application requirements, the bearings respond to the external loading conditions in a specific way. The final goal is to load each rolling element as little as possible," explained Thomas Wolf, the company's Senior Application Engineer for Powertrain and Steering.

SKF's proprietary VEP software provides engineers with the framework for evaluating how to reduce bearing friction. "By knowing the number of loaded rolling elements and the associated stress profiles in contact with the bearing raceways, we can change the internal geometry to meet a target," said Wolf. Primary variables include contact angle, number of rolling elements, and raceway topography.

In final drive scenarios, CO2 emissions can be cut up to 6 g/mi (3.7 g/km). In power takeoff applications, emissions can be reduced up to 5 g/mi (3.1 g/km). And in manual gearboxes, the reduction can be up to 2 g/mi (1.2 g/km).

"There have been a lot of testing activities to verify the efficiency rate improvement gained by these bearings. Having started with internal component testing on test rigs, the power loss improvement has been tested and confirmed by endurance testing. Additionally, a lot of internal testing was performed to verify the correlation with the results of our VEP software," noted Wolf.

SKF's energy-efficiency portfolio includes tapered roller bearings, driveline angular contact ball bearings, pinion units based on double-row ball-bearing units, and hybrid units based on double-row bearing units with balls and tapered rollers. "At first glance, powertrain components seem to be—because of loading conditions—the most promising area for energy-efficient concepts. However, other application areas such as the engine—i.e., replacing plain bearings on the crankshaft and piston rod by roller bearings—and wheel ends are in our focus as well," said Wolf.

SKF has been supplying ZF in Germany with energy-efficient hybrid pinion units to support the pinion shaft of six- and eight-speed automatic gearboxes for an all-wheel-drive application. This spring, SKF launched its energy-efficient bearings in the U.S. market. Vital bearing functions remain unscathed, said Wolf. "The main engineering challenge [was] to reduce the bearing's friction level without sacrificing bearing stiffness and bearing life in an unacceptable way."

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