Plastics push into powertrains

  • 24-Oct-2008 03:04 EDT

Mercedes-Benz's new 2.2-L diesel for the C-Class gets an oil-pan module made of thermoplastic polymer.

Claims of "firsts" come thick and fast in the auto industry, and now there is a new one for series production cars: a weight-saving oil-pan module made from a thermoplastic polymer—"for the first time in automotive history," according to DuPont.

Mercedes-Benz is fitting the polymer oil pan to its new 2.2-L diesel engine. Initially, the unit will power the C-Class, but it will be extended to other models. The oil pan has been developed by the automaker together with DuPont and automotive supplier Bruss. It comprises a die-cast aluminum upper shell and "multifunctional" lower shell made of DuPont Zytel 70G35 HSLR.

"The implemented design assures the part’s stiffness and achieves a significant weight reduction of 1.1 kg vs. an entirely aluminum design," stated DuPont press information from Fakuma 2008, the international trade fair for plastics processing in Friedrichshafen, Germany.

Production efficiency is said to be increased thanks to the high flow of the heat-stabilized, glass-fiber-reinforced nylon, which enables long flow distances, short injection times, and the reliable molding of thin-walled sections. The material is compatible with vibration welding.

At Fakuma 2008, DuPont stated that the shape of the oil pan’s rear section contributed to its high rigidity. Because of constraints caused by chassis and steering-gear space requirements, the front section is flatter: "As a consequence, this section’s resistance to bending and stiffness is relatively low, requiring additional design measures to minimize warpage and deformation and to eliminate the potential for leakages at the joint with the aluminum shell."

To meet this need, a sandwich design with a second injection-molded part was created—a separately produced oil deflector welded onto the flat section of the oil pan. DuPont explained that this helped "calm" the oil churned by the crankshaft and engine’s balance shaft, and directed it back to the oil pan.

FEA was used to refine positioning of ribbing at the edge of the pan (outside the area covered by the oil deflector) to improve overall stiffness of the critical flat section but with minimal effect on height of the design.

At DuPont’s Technical Center in Geneva, the structure’s properties were analyzed by simulating the combined engine and transmission being dropped "forcefully" by a forklift truck. Real-life testing using prototype components was carried out successfully by Bruss. "Even after 1000 h of aging in hot oil (150ºC), the pan is able to withstand these severe test conditions without incurring critical damage," stated DuPont, adding that additional functions envisaged for integration in future oil-pan models could include the oil pickup pipe, oil level switch, oil filter, and other oil return components or pumps.

DuPont also detailed at the Friedrichshafen event the integration of a sealing and baffle function in General Motors' new 6T40 and 6T45 transversely mounted six-speed automatic transmissions. The integrated baffle and seal lip assembly are made of DuPont Hytrel thermoplastic polyester elastomer and are positioned in the torque transfer case with the task of reducing oil aeration, providing a seal that limits fluid from flooding the chain while "ultimately enabling transmission fluid fill for life," explained the company.

The integrated component is described by DuPont as "significantly" reducing overall cost because it obviates the need for multistep production and assembly processes, which were typically metal stampings or plastic carriers with a rubber bead. And it contributes to packaging solutions and clutch and transmission durability.

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