TransForum Vol. 9, No. 1

Drivetrain Electrification Components also 'Drive' Price

The concept of hybrid and electric automobiles is now old news, but these alternative fuel vehicles are still in the minority on American roads.

The most significant factor limiting the commercial success of these next-generation vehicles is not a technological barrier; it’s the price tag.

“The technology for electric drives accomplishes the performance needs for electrically driven vehicles, but not the cost targets to make them competitive with conventional vehicles,” said Ted Bohn, an electrical engineer in Argonne’s Transportation Technology R&D Center.

That’s where Argonne’s component technology development program comes into play. Bohn and other researchers In Argonne’s Advanced Powertrain Research Facility are currently looking at the electric drivetrain components to improve efficiency and lower manufacturing costs, so that hybrid and electric vehicles can become more affordable to the general public.

Through-the-road (TTR) parallel hybrid showing placement of component technologies

Energy storage systems, power electronics, electric machines and gearboxes and control systems are the four main components used in drivetrain electrification. Here are a few of the projects Argonne is currently working on to increase performance and reduce costs:

Through-the-Road Parallel Hybrid (TTR). This in-house plug-in electric hybrid vehicle (PHEV) development platform was created so that high-level vehicle control strategies can be evaluated. In addition to the features shown in the diagram above, the TTR test vehicle has axle torque sensors in the front and rear to measure power “through-the-road.”

Energy Storage System (ESS) Components. Argonne has partnered with Maxwell Technologies to investigate the benefits of combining high-power density ultracapacitors with high- energy density lithium-ion batteries. This combination potentially reduces the net ESS cost and provides full acceleration and braking power at low temperatures or high battery state of charge.

Electric Machine/Gearbox Components. A 55 kilowatt peak/30 kilowatt continuous hybrid electric prototype machine has been designed that meets the performance and cost targets established by DOE’s Office of Vehicle Technologies by minimizing high frequency losses in the motor. This machine focuses on low material cost, low rotor losses, 95% efficiency at 20% load, and constant power from 2,800-14,000 rpm, with 105°C coolant. Bohn pointed out that the Department of Energy’s FreedomCAR and Fuel Partnership’s cost targets could also help lower the price tag of hybrid and electric vehicles. By 2015, FreedomCAR sets an electric drive system cost goal of $12/kW for a 55kW peak rated motor.

Another factor that could contribute to reducing manufacturing costs is gas prices. “If fuel prices rise again as the economy recovers, the incentive to reduce fuel consumption, driven by fuel cost, will also enable higher volumes of hybrid vehicles to be sold which, via economies of scale, will reduce the cost of hybrid vehicle components,” Bohn said.

“If this goal could be met, it would bring the cost of building a hybrid vehicle much closer to that of a conventional engine,” Bohn said.

This research was funded by the Department of Energy’s Office of Vehicle Technologies under Lee Slezak.

May 2009