15-06-2012, 12:19 PM
Advanced, Lightweight Materials Development
and Technology for Increasing Vehicle Efficiency
Advanced, Lightweight Materials Development.pdf (Size: 1.78 MB / Downloads: 117)
Introduction
As Amory Lovins, Chief Scientist at the Rocky Mountain Institute wrote, “The
automotive industry is arguably the largest and most complex undertaking in industrial
history. Its highly evolved production methods satisfy the conflicting demands of price,
safety, performance, reliability, emissions, and market appeal.” (2004)
However, ever-increasing government regulations on vehicle safety and pressure
from consumers concerned with fuel economy and environmentalists concerned with
emissions, car and truck manufacturers, and their suppliers, must turn to new
technologies to help them achieve their goals of making vehicles stronger, lighter and
more efficient.
Energy Transfer In A Vehicle
Vehicles require only a small fraction of their maximum power output to maintain
their speed during steady-state cruising. Peak power is needed during high-load driving
conditions and hard acceleration, such as towing, passing, or climbing steep inclines. The
power required for a given level of acceleration can be simplified (not taking into account
such other factors as aerodynamic drag, rolling resistance, and motor efficiency) by the
vehicle’s rate of change of kinetic energy.
Vehicle Mass Distribution
Several studies have examined the distribution of mass within typical vehicles.
Stodolsky (1995) showed a mass distribution in a passenger car (according to component
groups) with the body, about 43% of the total vehicle mass, is the single heaviest group;
followed by the powertrain and chassis, in almost equal proportions, at 27% and 26%,
respectively. More recently, Bandivadekar et al (2008) found that within the body group,
the unit-body, or body-in-white (BIW), is the single largest component, with about 28%
of the total vehicle mass (Figure 5).
Mass Decompounding Concept
Intuitively, vehicle design engineers know that an unplanned mass increase in a
component during vehicle design has a ripple effect throughout the vehicle; other
components need to be made larger, which increases vehicle mass even more.
Vehicle Structural Materials: Conventional
A number of different materials are used in manufacturing passenger cars. Some
are selected to perform highly specialized functions, while others, like steel, cast iron and
aluminum, usually perform a more general “structural” function. The estimated material
content in a typical American-made passenger car is shown in Table 1.
Nearly three-quarters of an average vehicle’s weight is incorporated in its
powertrain, chassis, and body; the bulk of this is made of ferrous metals (Stodolsky,
1995). Other structural materials found in an average automobile, used to a much smaller
extent, include aluminum, plastics or composites. Figure 7 shows how the use of
aluminum and high-strength steel (HSS) as a percentage of total vehicle mass has been
increasing over the past two decades, while the use of iron and mild steel has been
declining.
Aluminum Alloys
Aluminum (Al) alloys have several properties that are attractive to auto designers.
Its density is one-third that of steel, certain Al alloys exist with excellent strength, and
other alloys exhibit excellent formability. It is easy to machine, cast and fabricate, and is
fairly corrosion-resistant. However, Al alloys perform poorly in fatigue, and are more
difficult to weld than conventional steel alloys.
Summary
Advanced engineering materials can play an important role in improving the
efficiency of transportation engines and vehicles. Weight reduction targets are frequently
set as a means to increase the fuel economy of vehicles, thereby reducing exhaust
emissions. By reducing mass of the vehicle’s main body and chassis structure, secondary
weight and cost savings can be realized by downsizing subsystems through the massdecompounding
effect. In addition, weight reduction has many significant secondary
benefits, improving performance and handling dynamics.