Technologies for Advanced Vehicles Performance and Cost Expectations

This chapter discusses the technical potential and probable costs of a range of advanced vehicle technologies that may be available for commercialization by 2005 and 2015 (or earlier). As noted, projections of performance and cost can be highly uncertain, especially for technologies that are substantially different from current vehicle technologies and for those that are in a fairly early stage of development. In addition, although substantial testing of some technologies has occurred- -for example, the Advanced Battery Consortium has undertaken extensive testing of new battery technologies through the Department of Energy’s national laboratories--the results are often confidential, and were unavailable to the Office of Technology Assessment (OTA). Nevertheless, there is sufficient available data to draw some preliminary conclusions, to identify problem areas, and to obtain a rough idea of what might be in store for the future automobile purchaser, if improving fuel economy were to become a key national goal.

The chapter discusses two groupings of technologies:

1. Technologies that reduce the tractive forces that a vehicle must overcome, from inertial forces associated with the mass of the vehicle and its occupants, the resistance of the air flowing by the vehicle, and rolling losses from the tires (and related components); and

2. Technologies that improve the efficiency with which the vehicle transforms fuel (or electricity) into motive power, such as by improving engine efficiency, shifting to electric drivetrains, reducing losses in transmissions, and so forth.

Technologies that reduce energy needs for accessories, such as for heating and cooling, can also play a role in overall fuel economy--especially for electric vehicles--but are not examined in depth here. Some important technologies include improved window glass to reduce or control solar heat input and heat rejection; technologies for spot heating and cooling; and improved heat pump air conditioning and heating.

Weight Reduction With Advanced Materials And Better Design

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.1 Future efforts to reduce vehicle weights will focus both 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.2 At the other extreme, some advocates claim that the use of strong, lightweight polymer composites such as those currently used in fighter aircraft, sporting goods, and race cars, coupled with other reductions in tractive loads and downsized powertrains, will soon allow total weight reductions of 65 percent to 75 percent.3 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:

· Time pressure. Automakers have found that, as with so many other industries, time to market is central to market competitiveness. While tooling acquisition and facilities planning are major obstacles to shortening the development cycle, they tend to be outside the direct control of the automaker. 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.

· 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). Furthermore, because the established component has a known performance history, the product liability risk and the warranty service risk is also much reduced.

· 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. Given this limitation, it is far more efficient to start with a past design that has proven to be successful, and to modify it to meet the geometric limitations of the new vehicle. The modified design can then be supported with prototyping and road testing.

This normative design process has been central to automobile design for decades. Although it , has generally served the automakers well, it also has some limitations. In particular, this strategy is unfriendly to innovations such as the introduction of new materials in a vehicle design. The advantages of a new material stem directly from the fact that it offers a different combination of performance characteristics than does a conventional material. If the design characteristics are specified in terms of a past material, however, that material will naturally emerge as the “best” future material for that design. In other words, if a designer says, “Find me a material that is at least as strong as steel, at least as stiff as steel, with the formability of steel, and costing no more than steel for this design that I derived from a past steel design,” the obvious materials choice is steel.