DuPont™ Zytel® nylon used for first polymer oil pan module adopted for serial-production cars

For the first time in automotive history, an oil pan module made from a thermoplastic polymer is now used for serial-production cars. Working in close cooperation with the automotive supplier Bruss and DuPont (www.dupont.com), Daimler has achieved a genuine breakthrough by developing a modular design for its new 4-cylinder diesel engines (model OM651), which consists of a die-cast aluminium upper shell and a multifunctional lower shell, made of DuPont™ Zytel® 70G35 HSLR. The implemented design assures the part’s stiffness, and, at the same time, achieves a significant weight reduction of 1.1 kg versus an entirely aluminium design. Moreover, production efficiency is increased due to the high flow of the heat-stabilised, glass-fibre reinforced nylon, enabling long flow distances, short injection times and the reliable moulding of thin-walled sections. The material’s high compatibility with vibration welding further benefits productivity. The new oil pan design will be first used in the Mercedes-Benz C Class.

The rear section of the oil pan, which forms the sump for approximately 6 litres of oil, is very rigid due to its shape. The front section is of a flatter design due to chassis and steering gear space requirements. As a consequence, this section’s resistance to bending and stiffness is relatively low, requiring additional design measures to minimise warpage and deformation, and to eliminate the potential for leakages at the joint with the aluminium upper shell.

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The solution was to create a sandwich design with a second injection-moulded part: A separately-produced oil deflector, welded onto the flat section of the pan, helps calm the oil, churned by the crankshaft and balance shaft, and directs it back into the oil pan. Between them, the pan and the deflector, as well as further refinements to the overall design, help ensure stability under all operating conditions. In the oil sump section, warm-embedded brass inserts accommodate the oil discharge screw and oil level switch. The high ribs in the sump act as baffles, helping to calm the oil and direct it towards the sump.

Before producing the first tool, Bruss requested technical support from DuPont in addition to their own, comprehensive simulation software. Finite element analysis (FEA) was used to refine the positioning of ribbing at the edge of the pan (outside of the area covered by the oil deflector) to significantly improve the overall stiffness of the critical, flat section, yet with minimal effect on the overall height of the design. Flow studies, also based on FEA modelling, were used by DuPont to gauge the impact of wall thickness, the number of gates, and their positioning, on weld line formation and warpage behaviour, and to optimise the respective processing parameters. Indeed, due to the high melt flow of Zytel® 70G35 HSLR, one single, central gate was enough to completely fill the mould cavity, while permitting short moulding cycles. In comparison to multi-point gating (which would potentially be necessary for other nylon grades), tool costs are reduced and process control is simplified, while the number of weld lines and the risk of air entrapments are also minimised.

Finally, at the DuPont European Technical Centre in Geneva, the structure’s properties were further analysed by simulating the combined engine and transmission being dropped forcefully by a fork-lift truck. Real-life testing at Bruss, using prototype components, confirmed the success of the adopted design: Even after 1000 hours of aging in hot oil at 150 °C, the pan is able to withstand these severe test conditions without incurring critical damage.

Overall, the use of thermoplastic polymers for oil pans creates a significant opportunity for further functional integration. Already, in its current form, the oil deflector has been integrated – used to encourage a calmer flow of oil back to the sump. Additional functions, envisaged for integration in future oil pan models, could include the oil pick-up pipe, oil level switch, oil filter, other oil return components or oil pumps.

FAKUMA 2008, Friedrichshafen, 14.-18. October 2008, Hall B4, Stand 4201

DuPont de Nemours (Deutschland) GmbH, Neu-Isenburg

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