When driverless cars call for backup

How do you design a fail-safe driverless car? That's a trick question, of course, because you can't.

So engineers are doing the next best thing: developing backup systems for the brakes, steering, sensors and computer chips that guide a self-driving vehicle.

The idea is to give vehicles secondary systems that will allow them to safely pull over in case of a catastrophic equipment failure. But to keep a lid on redundant costs, suppliers are developing components that can be programmed to handle more than one function.

Ideally, such dual-use components simply will need extra software to handle their emergency tasks.

One example is the electro-mechanical brake boost, dubbed iBooster, being marketed by Robert Bosch GmbH.

Its main function is to replace hydraulic brake boosts on electric and hybrid vehicles. But iBooster also can be programmed to actuate the brakes in the event that a self-driving car's stability-control system fails.

A driverless car "must allow you a certain reaction time to take over," said Christian Sobottka, president of Bosch's steering division. "For this period -- say, 10 seconds -- the car has to be able to brake."

It's not always possible to create backup systems simply by adding software.

For backup steering, Bosch this year unveiled an electric power steering boost that requires two actuators rather than one.

Each actuator provides half the boost needed during normal operation of the steering system. "If the first actuator fails, you still get 50 percent of the steering pressure," Sobottka said. "That's safe enough to bring the vehicle" to the side of the road.

Sobottka estimates the new steering actuator will cost about 10 percent more than a conventional unit. Since the actuators are small, the canister that houses them fits easily onto existing steering racks.

But how will automakers back up the brains of a self-driving car -- the electronic control unit that chooses the vehicle's course?

An airbag control unit could do double duty as a backup to guide the vehicle, says Frank Jourdan, president of Continental AG's chassis division. All it would take is some extra software.

System suppliers could reduce the risk of total failure by using separate teams to write the software programs for the main controller and its backup, Jourdan says.

"A potential software failure wouldn't cause a problem because the same bug would not be in both software packages," Jourdan said. "That would be one way to deal with the complexity."

Jourdan also believes vehicles should have a backup power source in case the main battery fails.

That shouldn't be a major problem for vehicles equipped with stop-start systems. A battery that stores electricity from regenerative brakes also could provide emergency backup power, Jourdan said.

Sensors are another technology that will require backup systems. Collision-avoidance systems currently use a mix of radar and cameras to detect obstacles in the road.

Over the next five years or so, automakers will add lidar to their arrays of sensors -- a belt-and-suspenders strategy to ensure obstacle detection in bad weather.

In January, Continental announced plans to launch commercial lidar production in 2018.

Efforts by Continental, Bosch and other suppliers to design backup safety systems have gotten a lift from the U.S. Transportation Department's Federal Automated Vehicles policy, which calls for such systems in self-driving cars.

At some point, it would make sense to create industry standards for backup safety systems, Jourdan said. But that's not likely to happen while automakers still are experimenting with different approaches.

"For safety and cost, it makes sense to develop standards," Jourdan said. "But it will take awhile. The strong systems will survive, and the weak ones will die out."