DuPont Engineering Design Electronic Magazine
First polymer oil pan module
for use in serial-production cars
By Dirk Winnemann
DuPont Engineering Polymers, Germany
Oil pans for cars were one of the last great strongholds of metal. Now, for the first time, an oil pan module made of polymer has gone into serial production. The joint development, between Daimler, the supplier Bruss and DuPont, saves manufacturing cost as well as weight, and – in the long term – offers the potential for greater functional integration.
To date, thermoplastics have successfully replaced metal in applications such as air intake manifolds, slide and tensioning rails, cylinder head covers and, most recently, oil filter modules. Now, with the first oil pan module to be made of a thermoplastic polymer for serial-production cars, Daimler has broken new ground. Since the end of 2008, it is part of the new 4 cylinder diesel engine (model OM651), used initially in cars belonging to the C Class range. Various additional ranges are set to follow.
A complex set of requirements
Vehicle oil pans are exposed to a combination of stresses as a result of lubricant-use, temperature changes and static and dynamic loads. Even so, their seal performance must be maintained in all conditions. Additionally, the pan is required to withstand the rough handling by a forklift truck of the combined engine and gearbox unit.
Its specifications are correspondingly diverse and complex. It was for this reason that the development team decided from the outset to use DuPont™ Zytel® 70G35 HSLR A4, a glass-fiber reinforced, heat-stabilized and hydrolysis-resistant grade of nylon 66, which is tried and trusted for engine components. Its high melt flow enables long flow distances, short injection times and the molding of thin partition walls and ribbing.
Integrated oil deflector as reinforcement
Fundamental to the design of the oil pan was the need to achieve sufficient stiffness within the flat section ahead of the oil sump, thereby minimizing sealing area deformation. The adoption of any internal ribbing should not interrupt oil flow, while the use of external, reinforcement ribbing was almost impossible due to the lack of available space.
The solution was to create a sandwich design with two injection-molded parts. A separately-produced oil deflector is welded onto the flat section of the pan, and is used to calm the oil churned by the crankshaft and balance shaft, and direct it back into the oil pan.
Moreover, the deflector significantly improves the vibration behavior of the overall design. The high reinforcement ribbing in the sump simultaneously acts as a baffle, also helping to calm the oil. A die-cast aluminum upper shell is used to attach the oil pan to the engine block. The overall construction achieves a significant weight reduction of 1.1 kg compared to an entirely aluminum design.
Simulation shortens development time
Before producing the first tool, Bruss requested technical support from DuPont in addition to its own, comprehensive simulation software. Finite element analysis (FEA) was used to refine the positioning of the ribbing at the edge of the pan, thereby contributing significantly to the overall stiffness of the critical flat section despite its minimal height. Flow studies, also based on FEA modeling, were used by DuPont to gauge and optimize the impact of wall thickness, the number of gates, and their positioning, on weld line formation and warpage behavior. Indeed, due to the high melt flow of Zytel® 70G35 HSLR A4, a single, central gate was enough to completely fill the mould cavity, while permitting short molding cycles.
Finally, at the DuPont European Technical Centre in Geneva, the structure’s properties were further analyzed by simulating the combined engine and gearbox unit being dropped heavily by a fork-lift truck. This allowed critical parts – particularly the external ribbing designated for the contact area – to be identified and dealt with. Real-life testing of prototype parts at Bruss confirmed the success of the simulated design – even after 1000 hours of aging in hot oil at 150 °C (302 °F)
Welding of the oil deflector to the oil pan module was optimized by a team comprising Bruss, DuPont and the joining product manufacturer, Branson. All tolerances were defined with regard to process control and the material used, in order to ensure reliable joints, even in unfavorable conditions. Subsequent pull-off tests revealed pull-off forces of around 1300 N, a higher value than required.
In its current form, the component meets all requirements. The seal area remains leak free during hot oil testing at 150 °C, at minimum sealing force (smallest seal in largest groove) and during alternating climate testing.
Wide scope for integration
Increased integration means lower manufacturing costs. In its current form, and as described in this article, an oil deflector has already been integrated. Additional functions, envisaged for integration in future oil pan models, could include the oil pick-up pipe, oil level switch, oil filter and other oil return components or oil pumps.