Plastic Oil Pans Present Major Integration Opportunity

The next big under-the-hood application for nylon may be oil pans, which are traditionally made from cast aluminum, stamped steel or metal-plastic-metal hybrid constructions.

New plastic versions cut weight 40 percent or more and also integrate functionality. German auto supplier ElringKlinger developed a design for pickup trucks that integrates significant components of the oil-circulation system. 

"Our selection of a particularly high-melt flow grade of Zytel nylon resin meant that we were able to manage the long flow distances at a comparably low injection pressure and despite some very low wall thicknesses," says Ralf Franz, development engineer at ElringKlinger. "This, in turn, reduces cycle times, helps preserve the tool and keeps energy costs low." 

The multifunctional design includes the pan (measuring approximately 550 mm long, 400 mm wide and 300 mm high), sections of the pipeline for suction of oil from the sump, the fastening flanges for the pressure pipelines to and from the oil filter and the oil filter flange with a directly encapsulated oil filter thread. 

Separate injection-molded parts include the two-piece cover of the suction pipe, the double pipe for connection with the oil filter and the cover for the oil filter flange. All of the individual parts, as well as the polymer-encapsulated metal sieve located in the oil intake, are connected to the pan with friction welding.

The nylon 66 from DuPont is reinforced with 35 percent (by weight) glass fibers, creating very stiff creep- and hydrolysis-resistant components. The compound combines high-impact resistance over a wide temperature range with a high resistance to lubricants, road salts and other media commonly present in vehicles. The additional heat stabilization enables the long-term usage of the material at temperatures of up to 150C and makes it particularly resistant to heat aging. And as in air intake manifolds, glass-fiber-reinforced nylon provides good mechanical and acoustic attenuation properties.

Franz says the low warpage behavior of the material is also important because it facilitates a durable and reliable seal along the circumference of the oil pan. 

"We had to design the new polymer oil pan in such a way that its connection to the engine was consistent with the metal construction previously used," says Franz. "We were thereby presented with relatively large distances between the connection points. Thanks to the high stiffness of the material and the purpose-made application of ribs, we managed to limit deformation under load to the required rate despite these unfavorable conditions, thus ensuring a constant surface pressure across the whole perimeter."

Whereas the ribbing located in the upper section of the oil pan principally contributes to dimensional stability in the seal area, the many high ridges in the lower section are designed to absorb external impacts caused, for example, by stones as they are thrown up from the road during normal driving. 

More significant impacts may also occur when the dismounted engine is placed heavily on the floor during transportation.

For the production of the seals between the pan and the engine, as well as for the connection of oil circuit elements, ElringKlinger uses a highly heat- and oil-resistant ethylene acrylic elastomer.

At the National Plastics Exposition held June 22-26 in Chicago, BASF also emphasized that oil pans are a major target of its development activities.

BASF has developed Ultramid B3ZG7 OSI, an "optimized for stone impact" grade that equals and exceeds the performance of cast aluminum in oil pans, says Phillip E.  Wilson, the new business development manager for engineering plastics at BASF.

The OSI material is a 35-percent glass-reinforced and impact-modified nylon 6. It has survived a battery of experimental data showing OSI initial cracking at 60 mph, whereas aluminum pans crack at an impact of around 50 mph under the BASF proprietary 'stone impact' simulation testing.

Wilson showed a nylon pan incorporating a windage tray, oil pickup tube and an integrated oil filter module. Additional benefits include weight and cost reduction.