New Daimler Diesel Engines Go with Nylon for Oil Pans
Doug Smock, Contributing Editor -- Design News, November 5, 2008
Nylon 6/6 replaces aluminum for the oil pan module in the new Daimler C-Class four-cylinder diesel engine, saving up to 25 percent in production costs, boosting horsepower and reducing weight by 2.2 lbs. It's the first-ever use of plastic for oil pans in commercial production cars.
Injection molding allows designers to incorporate a windage tray (oil deflector) into the modules, reducing oil vapor around the crankshaft for an estimated 5-percent increase in horsepower. "We can put in functionality where we need to, taking advantage of plastics," says Patrick Granowicz, DuPont Automotive engine covers segment manager.
The rear section of the oil pan, which forms the sump for six liters of oil, is very rigid because of its shape. The front section is flatter due to chassis and steering gear space requirements. As a result, 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 upper shell.
Engineers designed a sandwich using a second injection-molded part: A separately produced oil deflector, which is vibration-welded onto the flat section of the pan, helps to calm the oil churned by the crankshaft and balance shaft. The combination of the pan, the deflector and other refinements to the overall design enhance the component's stability. In the oil sump section, embedded brass inserts accommodate the oil discharge screw and oil level switch. The high ribs in the sump act as baffles and also help to calm the oil and direct it toward the sump.
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 modeling, were used by DuPont to gauge the impact of wall thickness, the number of gates and their positioning, on weld line formation and warpage behavior and to optimize the respective processing parameters. One single, central gate was enough to completely fill the mold cavity while permitting short molding cycles.
Even after 1,000 hours of aging in hot oil at 150C, the pan is able to withstand drop tests conducted by Bruss, the manufacturer of the modules. Other functions that could be included in future module designs are the oil pick-up pipe, oil level switch, oil filter, other oil return components or oil pumps.
The part was nominated for the Society of Plastics Engineers' Most Innovative Use of Plastics Award in the powertrain category.
