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Federal-Mogul Corporation

Monosteel Piston

To meet tighter emissions standards without sacrificing fuel efficiency, medium-duty diesel engine manufacturers are designing for exhaust recirculation pressures of 230 bar and greater. This creates greater mechanical and thermal stresses on pistons, in an environment that is already both more corrosive and abrasive. Furthermore, fleet operators now demand engines able to provide a million miles of service, so a modern piston must have enormous durability. Designing cooling galleries that would work led to hard-to-manufacture architectures, but articulated pistons and other two-piece designs were too weak mechanically and insufficiently durable. In short, pistons were a significant bottleneck to developing the next generation of cleaner, more efficient diesel engines.

With its Monosteel piston, Federal Mogul overcame this challenge. Starting with a two-piece design, and using inertial welding to combine the crown and the sleeve into a structurally sound whole, meets the stress and durability requirements of the next-generation diesel engine. Two pieces allows the design of an effective cooling gallery without the need for machining. That in turn enables the sleeve to provide sufficient mechanical support. The Monosteel piston not only lasts longer, avoiding burnout and cracking, but performs better than previous designs, in terms of blow-through and other performance characteristics.

Federal Mogul's design capabilities included computer simulation of mechanical and thermal stress, analysis of the piston’s reciprocating motion, and modeling of oil flow cooling, to come close to a "virtual" design cycle. This allowed shortened engineering lead time, without extensive prototyping and testing. With the flexibility of the Monosteel approach, Federal Mogul is poised to make additional improvements in piston design, as it shifts from inertial to inductive welding, explores the use of different materials for crown and head, implements designs that eliminate pin bushings, and develops innovative coatings. Monosteel piston positions Federal Mogul to lead in the next generation of diesel engine designs, helping protect the environment while lessening fuel consumption. Strong market acceptance among major diesel engine manufacturers already demonstrates the success of this innovation.