The National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) have chosen to "provide an incentive to use lightweight materials and structures," rather than "reductions in size," by adopting a footprint approach to emission reductions, according to the ACC comments, which also support the agencies' approach to consider only vehicle mass reduction that will not adversely affect overall fleet safety.
In addition to lightweighting, plastics and related materials will also contribute to fuel efficiency and emission reductions through more aerodynamic shaping and parts integration according to the ACC. "About 60 percent of engine power at highway cruising speed is used to overcome air resistance. As a result, improved aerodynamics translates into substantial improvements in fuel efficiency and emissions, even with vehicle size held constant," notes the ACC comments. "Injection-molded plastics allow for aerodynamic styling and parts integration not possible with metal or glass. Drag coefficients for present-day vehicles range between 0.30 and 0.35, but an additional 25 percent reduction in drag has been predicted in coming years."
The ACC submission also emphasize that the increasing supply and production capacity of high-tech composites and hybrid materials should be factored into agency cost estimates on an ongoing basis. "Advanced composites such as carbon fiber reinforced thermoplastics will assume a greater role in both body and structural components in the MY 2017-2025 time frame. Recent data suggest that the supply of plastic composite materials will continue to accelerate with an attendant decrease in costs as production processes are refined and economies of scale are realized. There is also the potential for a game-changing breakthrough that will advance commercialization." This might be in the form of a lower cost process for manufacturing carbon fiber, or successful commercialization of more efficient composite processing technologies.
The ACC also emphasized that the final rule should extend the proposed off-cycle credit for thermal control to recognize the benefits of glazing materials with superior insulation performance. Credits are awarded to automakers whenever a manufacturer's sales-weighted fuel economy beats the CAFE (corporate average fuel economy) standard for the year and can be used to towards meeting any future standards for five years afterwards
In addition to weight reduction and improved aerodynamic performance, polycarbonate glazing better insulates the cabin during operation of the vehicle compared with glass, reducing both the demand for air conditioning and the associated tailpipe emissions. However, standard test drive "cycles" used to measure mileage and emissions are not designed to capture this latter benefit.
"We applaud the agencies for proposing an off-cycle credit that recognizes the thermal control benefits of glazing," said Greg Adams, vice president, automotive and polycarbonate, SABIC Innovative Plastics (Pittsfield, MA). "We believe such a credit also should apply to market-ready advanced polycarbonate glazing solutions with superior insulation properties."
"Recognizing the benefits of polycarbonate glazing through expanded technology credits would provide OEMs with greater flexibility in meeting proposed mileage and emission targets," agreed Bruce Benda, vice president, automotive and transportation, Bayer MaterialScience (Pittsburgh, PA).-[email protected]