Driverless cars give engineers a fuel economy headache

Judging from General Motors Co.’s test cars and Elon Musk’s predictions, the world is headed toward a future that’s both driverless and all-electric. In reality, autonomy and battery power could end up being at odds.

That’s because self-driving technology is a huge power drain. Some of today’s prototypes for fully autonomous systems consume two to four kilowatts of electricity -- the equivalent of having 50 to 100 laptops continuously running in the trunk, according to BorgWarner Inc. The supplier of vehicle propulsion systems expects the first autonomous cars -- likely robotaxis that are constantly on the road -- will be too energy-hungry to run on battery power alone.

In an industry where the number of LEDs in a brake light are scrutinized for their impact on gas mileage, processing data from laser, radar and camera sensors will be an enormous challenge -- not just for coders working on machine learning, but for engineers trying to power vehicles efficiently. As major markets from California to China ratchet up pressure to curb pollution, automakers and their suppliers will have to find creative new ways to offset emissions produced by feeding the car’s increasingly intelligent brain.

“We’ve been battling all the time because the governments are always pushing for a few percent improvement every year,” Scott Gallett, vice president of marketing at BorgWarner, said of fuel-economy standards. “This just amplifies that challenge.”

Driverless Rides

The autonomous features on a Level 4 or 5 vehicle, which can operate without human intervention, devour so much power that it makes meeting fuel economy and carbon emissions targets five to 10 percent harder, according to Chris Thomas, BorgWarner’s chief technology officer.

To be sure, those calculations are based on prototype cars with sensors rigged on the roof, and the power demands of electronics inside the car will inevitably fall as the technology improves. But even if chipmakers pull off promises to reduce power consumption by as much as 90 percent, automakers will still need to make fuel efficiency gains elsewhere in the vehicles to compensate for all that computing, Thomas said.

“They’re worried about one watt, and now you’re adding a couple thousand,” Thomas said. “It’s not trivial.” A fully autonomous subcompact car like a Honda Fit, for example, will get 54.6 miles to the gallon in 2025 in the best-case scenario, more than 5 miles below the U.S. emissions target, according to Borg Warner. A small pickup or SUV would be at 45.8 mpg, versus a target of 50.