SOUTHFIELD, Mich.—Federal-Mogul Corporation recently announced that it has expanded the performance capabilities of engine bearings by developing an innovative polymer-coated bearing shell that can reduce fuel consumption and CO2 emissions by withstanding mechanical loads produced by heavily boosted engines. Called IROX™, the new technology reportedly addresses lubrication challenges associated with frequent engine re-starts found in hybrid and other future stop-start engines by protecting both the crankshaft and the bearing shells from damage where metal-to-metal contact would otherwise occur. Federal-Mogul estimates that the IROX bearing overlay can help increase the life of crankshafts and bearing shells by more than five times in more extreme applications, such as direct-injected engines and engines with stop-start systems.
“The drive for increased engine efficiency is placing demands on crankshaft bearings that require new designs and materials applications,” said Michel Prefot, Federal-Mogul’s vice president, technology and innovation, bearings, in a statement. “Satisfactory lubrication requires an adequate oil film between the bearing shell and the crankshaft to keep the surfaces apart. Efforts to reduce fuel consumption and CO2 output are pushing engine design towards reducing oil film thickness and significantly increasing the number of starts, which is where bearings are most vulnerable. Federal-Mogul’s new IROX bearing overlay technology overcomes many of the most challenging wear-related issues that will be faced by a majority of new generation engines.”
As engines are downsized but maintain their output through turbo-charging, the specific loads on the bearings increase. When hybrids operate in electric mode or when drivetrains using stop-start strategies switch off the engine, the crankshaft speed drops to zero. Without rotation, the crankshaft settles into contact with the bearing shells and the oil pump stops providing lubrication, allowing metal-to-metal contact and causing wear when the engine restarts.
Although solid lubricants or dry bearing materials are effective at preventing metal-to-metal contact at low running speeds, these conventional solutions are not suited to higher speeds, which require journal bearings with a generous lubricant supply. Federal-Mogul’s new system is said to combine the best features of both of these established technologies by introducing a polymer coating for traditional metallic bearing shells, integrated with solid lubricants and wear inhibitors to produce what the company calls “a cost-effective, robust, and production-ready solution.”
Extensive development has led Federal-Mogul to identify and optimize a number of key parameters, such as layer thicknesses, substrate material specification, resin binder properties, curing conditions, and functional additive specifications. The IROX bearings have an overlay consisting of a PAI (PolyAmideImide) polymer resin binder that contains a number of additives dispersed throughout the matrix. These additives reportedly provide a variety of properties, such as wear resistance, mechanical strength, thermal conductivity, and embeddability (the ability to safely envelop loose, abrasive particles), to the finished coating.
According to the company, test results have shown a dramatic improvement in life compared to both conventional shell materials and state-of-the-art competitors. “Typical bearings with aluminum overlays show significant wear after 100,000 stop-start cycles,” said Prefot. “However, the new generation of engine systems require 250,000 to 300,000 cycles, so the durability challenge has been raised. Bearings with the IROX overlay can meet the demands of repeated starting; in comparison tests where conventional aluminum overlays showed 100 microns of wear and lead-free bronze showed up to 50 microns, our shells still looked like new with a measurable wear of just a few microns.”
Federal-Mogul (www.federalmogul.com) says that pilot manufacture of the new shells has been underway since 2005, and full-scale production is scheduled for next year.
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