Study boasts the uses of aluminum over steel

According to a new study at the Center for Automotive Research's (CAR) Business of Plugging In conference, opting for high-strength, low-weight aluminum over heavier steel structures for plug-in electric and hybrid vehicles can cut vehicle price overall by reducing the battery energy requirements and the associated costs. The study was jointly conducted by The Aluminum Association, Inc. with Ricardo, a leading technical research and strategic consultancy to the world's automotive, transport and energy industries.

According to the study, the driving range of the vehicles could be improved approximately equal to the mass saved. Reduce the mass of the vehicle 20 percent, go 20 percent father. One example vehicle had the range extended from 80 to 97 miles.

The heaviest vehicle in the study, at 1,822 kg, consumed about 300 Wh/mi, while the lightest at 627 kg consumed about 146 Wh/mi.

Regenerative braking could recover about 65 percent of the energy associated with the vehicle's momentum irrespective of the vehicle weight. But this is only about 15-20 percent of the total energy expended.

For the lightest vehicle, about 44 percent of the energy is lost to power train inefficiencies, with 33 percent of the energy used to overcome air resistance, and only 24 percent is used to move the vehicle. As with conventional vehicles, the lighter vehicles have faster accelerations.

The purpose of the Ricardo study was to evaluate the impact of vehicle weight reductions on electric vehicle performance, range and battery size. The majority of the vehicle simulations were done using the FTP75 drive cycle with a few highway drive cycles. In general, the relationships between vehicle mass, battery weight and energy, and range are linear up to the maximum range studied of 80 miles. At this range, the battery weight doesn't grow enough to start a significant "weight spiral."

The study also examined the role of vehicle mass on regenerative braking; specifically the question of whether strong regenerative braking might lessen the impact of weight reduction. This turns out not to be the case. All vehicles studied could recoup about 65 percent of energy associated with moving the vehicle. But the energy balance for each vehicle changes. As the vehicle gets lighter, less energy is required to move it, while the aerodynamic losses remain constant. For the lightest vehicle the aerodynamic losses are higher than the energy to accelerate the vehicle.