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29 "My perception is that in 2025 we're going to end up with hybrid structures," Elmoursi says. He provides an example: Eaton developed a lighter diferential casing made from steel and polyphenylene sulfde (PPS) with carbon fber. When development commenced, the initial goal was to determine where the maximum mechanical stresses were before determining where composite material could function efectively to save weight. To accomplish this, they used analysis software from Altair ( altair.com ). Elmoursi explains, "In this application we wanted the plastic to function as a mechanical support, but not as the primary carrier." Instead of making the entire piece from plastic, the metal frame would provide strength in critical areas. An initial model of the diferential case was 3D printed, Elmoursi says, but the prototype was compression molded, using the PPS material with long carbon fber. The current diferential case is made from diecast alumi- num and weighs 6.4 lb., while the prototype hybrid part weighs 3.8 lb.—a 40% weight savings. Eaton also developed a hybrid solution for its EGerodisc hydraulically operated, electronically controlled slip diferential. The current cast-aluminum product is found in the Jeep Grand Cherokee. The hybrid prototype part trims the part weight by 30% by using an injection molded glass-fber reinforced nylon, reducing the need for machining the entire part. One of the challenges that developing hybrid components presents is making sure the bond between the composite material and metal is robust: "Our big- gest challenge today is at the interface between the metal and the composite," he notes. To address the issue, Eaton is working with the University of Michigan to conduct cohesive zone modeling (CZM) to ensure the interfaces are sound prior to manufacturing physical parts. CZM is able to predict the behavior of structures to determine potential vulnerabilities in the material. Eaton is also exploring the use of composite parts in its superchargers to entirely replace metal in small, sub- liter engine applications. "When we look at polymers we already know we cannot achieve the same tolerances we can achieve with metal," Elmoursi says. Nevertheless, he argues the efciency losses can be made up for by making cost efective products and in some cases, reducing the number of parts. For small engines prevalent in India and China, Eaton developed prototype plastic timing gears for its superchargers that reduce weight, eliminate the need for machining, and minimize noise. The gears are made from polyether ether ketone (PEEK) material, a robust organic polymer, which tolerates high temperatures without compromising performance. "Metal gears are lubricated and require an oil seal," Elmoursi explains. "With plastic, you remove the oil all together by running plastic-on-plastic, and as long as you're not wearing them out, you're good, and they're quieter." Switching to plastic gears ofers a 30% weight reduction per part. The company has also developed a rotor made with carbon-fber weave that can handle the required 20,000-rpm rotor speed and 150°C continuous-use temperature. The composite rotor saves 40% of the weight compared to existing aluminum rotors. The process of developing these rotors wasn't an easy one, Elmoursi notes. It required some trial-and-error to get the shape right, a process that remains underway. First, they took the aluminum rotor and made it into what he describes as a "Christmas-tree shape" and overmolded that to attain 20% weight savings. By altering the shape incrementally by injection molding, they eventually reached a 40% weight savings. Right now, the rotor lobes are straight, but this year Elmoursi says his team is focused on making convoluted lobes to more closely resemble the existing aluminum rotors, while still saving signifcant weight. t This prototype diferential casing by Eaton is made from steel and polyphenylene sulfde (PPS) with carbon fber, reducing the weight compared to the existing aluminum casing by 40%. p Eaton's carbon fber weave rotor for superchargers for sub-liter engines can handle the required 20,000-rpm rotor speed and 150°C continuous use temperature, while shedding 40% of the weight compared to existing rotors. 0314ADP FEATURE Eaton.indd 29 2/18/2014 3:31:38 PM