Traditionally, using any material other than metal in the engine compartment was unthinkable. But, that old rule of thumb is changing as many automakers and suppliers use plastic to reduce vehicle weight.
Automotive suppliers and material formulators continue to find new uses for plastic under the hood, including applications that were unimaginable just a few years ago. For example, Mann + Hummel GmbH (Ludwigsburg, Germany) recently started to mass-produce a plastic oil pan. The all-plastic component cuts weight by 60 percent compared to a traditional all-aluminum part, or 30 percent compared to hybrid aluminum and plastic subassemblies.
“Further benefits with regard to cost, weight, installation space and assembly can be achieved by integrating additional components,” says Dieter Seipler, the company’s CEO. “For instance, with plastic, additional functions can be integrated to the same extent as in air-intake systems.
“Integration of such components as oil tubes, pick-up pipes, strainers, separate oil reservoirs and baffles may be considered,” adds Seipler. “Installation of a complete oil module consisting of oil filter and oil cooler also offers considerable potential, both from a technical and an economic point of view.”
“Plastic oil pans can be molded into difficult shapes to optimize scarce space in the engine compartment,” says Richard Schultz, a consultant at Ducker Worldwide (Troy, MI). “As a result, you can create a more intricate part.”
In the past, oil pans were either steel or aluminum. In the future, plastic may dominate. That’s what happened with fuel tanks. “They were all made out of steel 20 years ago,” says Schultz. “Today, 81 percent of fuel tanks are plastic.”
During the past two decades, intake manifolds have also slowly been evolving from metal-to-plastic designs. “Back in the mid-1980s, 80 percent of intake manifolds were aluminum,” Schultz recalls. “Today, aluminum accounts for 58 percent of the market, and that will eventually drop to 50 percent as plastic continues to make inroads.”
Although there’s more plastic in engine compartments today, Schultz believes steel will continue to play an important role. “New high-strength steels can save 15 percent to 20 percent weight over mild steel, because parts can be made thinner,” he points out. “That makes it competitive with plastic and other lightweight materials.”
In addition, many engine components, such as exhaust manifolds and turbochargers, cannot be made out of plastic and require the physical properties of metal.
“By definition, plastics will always strain under a load and creep when stressed,” says Holt. “These properties can be ameliorated, but never fully eliminated. However, who would have guessed 40 years ago that plastic intake manifolds would become commonplace in today’s market? Many [assembly] advances have allowed the use of plastic parts to not only survive the production line, but also long-term environmental exposure to underhood stresses.”
“If you look at the historical development of thermoplastic engineered materials used under the hood, they have progressed closer to the actual combustion process, beginning with low-risk, external pieces and migrating internal to the engine itself,” adds DSM’s Conley. “The actual cylinder where the combustion event takes place is unlikely, but a plastic engine block has been tried in the past.”
Indeed, in the mid-1980s, Ford engineers developed a 2.3-liter engine that featured a plastic block, rods and piston skirts. Although the experimental engine was never mass-produced, the Polimotor project proved that plastic could be used as a lightweight alternative to aluminum, cast-iron and steel.
“[Ongoing] efforts to improve quality and engine performance will lead to continued advancements in plastic materials,” predicts Branson Ultrasonics’ Heatherwick. “There are several new applications that are currently in development that will take the use of plastics in powertrain to the next generation.”
Due to confidentiality agreements, he can’t reveal any details. But, several resin suppliers provide a glimpse of how plastic will be used under the hood of future vehicles.
According to BASF’s Morgan, the next big application will be connecting rods and crankshafts, followed by engine blocks. DuPont’s Molteni claim there is a lot of R&D work currently being done on resonators and exhaust systems. He also predicts there will be more applications in the future involving cylinder head covers. A
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