Special Coverage

SAE World Congress

DETROIT – Experts from industry and government ask how to measure the efficiency of electrified vehicles, especially compared with traditionally powered cars and trucks, and arrive at this consensus – it’s impossible.

“It is an astonishing challenge,” says Michael Tamor, executive technical leader-hybrid electric vehicles and fuel-cell vehicles at Ford Motor Co.

But it also is a challenge auto makers and the U.S. Environmental Protection Agency must undertake given today’s mainstream-brand vehicles will begin sharing the showroom floor with electrified models by the end of the year.

In fact, new corporate average fuel economy and emissions rules taking effect next year call for the EPA to remake window stickers by the ’12 model year, so consumers can easily understand the advantages of electrification.

Everyday consumers, however, are light years behind engineers and regulators in understanding complex notions such as miles-per-gallon equivalent, or MPGe, which attempts to express the efficiency of an electrified vehicle in terms of the fuel it would consume.

“I suspect no one buying a car today knows what an mpg-equivalent is,” submits Chris Grundler, deputy director-transportation and air quality at the EPA, during a technical session on the correct way to compare fuel economy at the annual SAE World Congress here.

Pete Savagian, engineering director-hybrid powertrain systems engineering at General Motor Co., goes a step further. “The miles-per-gallon equivalent is not realistic. There are no gallons.”

Another problem, Savagian says, is the efficiency of vehicles with a fully electric range, such as the Chevy Volt extended-range electric vehicle coming later this year, are adversely affected by any number of factors, such as driver aggressiveness, ambient temperature, HVAC system use and charging frequency.

“So an adjustment is in order between the (EPA) testing and the label,” he says.

Savagian, who also spearheaded development of GM’s EV1 electric car a decade ago, offers this solution: provide separate measurements for fuel consumption and electrical consumption.

He also suggests the EPA add the all-electric range of a vehicle to the label and perhaps a table for shoppers to estimate the efficiency of the vehicle based on their average daily commute.

“I think everyone here can say how far they commute every day,” he says.

But HEVs or plug-ins operate in potentially three different modes – electric, internal combustion and a combined cycle. Therefore, it’s nearly impossible to estimate electricity usage.

“We think all-electric range should be used for vehicles only with an all-electric range,” says Savagian, whose Volt is expected to travel an average 40 miles (64.4 km) exclusively under electric power.

Nonetheless, he says GM supports two proposed SAE rules for figuring EV efficiency. Doug Greenhaus, director-environment, health and safety at the National Automobile Dealers Assn., stresses the need for an ambitious consumer-education program whatever the outcome.

“I’m not sure there is a right metric,” he says, noting consumers “have no clue” right now how to compare electrified vehicles with traditional ones. “We have to get the public caught up.”

He also warns against estimating for consumers total cost savings of owning an EV compared with a traditional internal-combustion-engine vehicle, because most consumers shop with a monthly payment in mind and not a long-term goal.