Weight reduction has been a primary component of efforts to improve automobile fuel economy during the past two decades. Between 1976 and 1982, in response to federal Corporate Average Fuel Economy (CAFE) regulations, automakers managed to reduce the weight of the steel portions of the average auto from 2,279 to 1,753 pounds by downsizing the fleet and shifting from body-on-frame to unibody designs.
Future efforts to reduce vehicle weights will focus both l Peter T. Peterson, “Steel, Not Plastic, Reduces Auto Weight–A Myth Dispelled, “Metal Forming, November 1991. p. 2. 60 on material substitution–the use of aluminum, magnesium, plastics, and possibly composites in place of steel–and on optimization of vehicle structures using more efficient designs.
Although there is widespread agreement that improved designs will play a significant role in weight reduction, there are several views about the role of new materials. On the one hand, a recent Delphi study based on interviews with auto manufacturers and their suppliers projects that the vehicle of 2010 will be composed of materials remarkably similar to today’s vehicles.
The factors that influence the choices of vehicle materials and design are discussed below. Vehicle Design Constraints The most important element in engineering design of a vehicle is past experience. Vehicle designs almost always start with a consideration of past designs that have similar requirements. Designers rarely start from “blank paper,” because it is inefficient for several reasons:
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Time pressure.
Automakers have found that, as with so many other industries, time to market is central to market competitiveness. Design time, however, is directly under the control of the automaker, and reduction of design time has, therefore, been a major goal of vehicle development.
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Cost pressures.
The reuse of past designs also saves money. In addition to the obvious time savings above, the use of a proven design means that the automaker has already developed the necessary manufacturing capability (either in-house or through purchasing channels).
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Knowledge limitations.
Automakers use a various analytical methods (e.g., finite element codes) to calculate the stresses in a structure under specified loading. They have only a rough idea, however, of what the loads are that the structure will experience in service. Thus, they cannot use their analytical tools to design the structure to handle a calculated limiting load.
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