Toyota's Problem Was Unforeseeable

As systems grow in complexity, experts say designing for failure may be the best course of action for managing it

Charles J. Murray, senior technical editor, electronics -- Design News, January 28, 2010

Toyota's sticking gas pedal was an almost-unforeseeable problem, experts say, and the best course of action now is for engineers to ensure that drivers can handle the failure if it happens again.

"This is one of those horrifying nightmare problems that will occasionally occur, no matter how hard you try," said David Cole, chairman of the Center for Automotive Research.

Automotive experts said this week that predicting the problem would have been nearly impossible during design and test, especially given the kind of accelerated testing that is typically used to evaluate components which may have to last from 10 to 15 years. Making it even more difficult was the fact that the gas pedals didn't appear to fail by themselves, but rather, by interaction with other components, such as heaters or floor mats.

"It's not that they didn't design a good accelerator pedal or linkage or floor mat or heater," said Steven D. Eppinger, professor of Management Science and Engineering Systems at Massachusetts Institute of Technology (MIT). "They designed them each quite well. But the most difficult problems always relate to interactions between components and other systems."

Although Toyota now appears to be coming close to a repair for the gas pedal problem, many questions still remain about its genesis. The giant automaker has gone through a succession of theories about the problem's cause, including interaction with floor mats, materials in the accelerator's friction lever, and condensation and corrosion from heaters. During the two-year course of problems, Toyota has examined its floor mats, shortened its pedals, lengthened the friction lever and changed its linkage materials. This morning, the company reportedly said it will add a "spacer" that will increase the tension in a spring that would keep the pedal from sticking.

Still, experts say that one of the best fixes is one that helps drivers deal with the problem when it happens. "The takeaway is that it's less about durability testing and accelerated testing, and more about designing for failure," said Jake Fisher, senior automotive engineer for Consumer Reports.

Software Fix

The key to empowering drivers lies in software, the experts said.

Toyota's throttle-by-wire systems, already in place on most or all of the affected vehicles, will soon contain additional software commands that will interrupt the flow of gasoline to the engine if a driver hits the brake pedal. Such software could go a long way toward preventing fatalities, since most drivers instinctively step on the brake pedal when the gas pedal sticks. Many competing automakers already incorporate those software commands in their electronic throttle bodies.

Affected vehicles include the Toyota RAV4, Corolla, Matrix, Avalon, Tundra, Sequoia, some Camrys, and non-hybrid Highlanders. Recent news reports have also said that millions of Toyota vehicles in Europe and China will also be included in the recall. Most of the vehicles are believed to incorporate throttle-by-wire systems, which will be able to cut off fuel flow based on the driver's actions. Throttle-by-wire, which has grown enormously popular in recent years, uses a sensor to monitor position and a tiny electric motor to open and close the throttle. The electric motor is driven to its required position through communication with the engine's ECU. By adding software code to the ECU, engineers will enable braking action to override the throttle when the gas pedal is stuck. Toyota has said it will incorporate the new software algorithms in its production by the end of 2010.

"With the software fix, if the throttle is depressed and you step on the brake, the electronics will say, "The driver wants to stop more than he wants to go ahead, so we'll cut off the engine,'" Cole said.

Up to now, Toyota's ECUs haven't contained such override commands, even though some other manufacturer's vehicles have, says Consumer Reports. "Most German vehicles and Toyotas have electronic throttle bodies," Fisher said. "In the German vehicles, if you push down on the gas pedal, it overrides the brake pedal. Toyota never implemented that logic when it went to electronic throttle bodies."

Without a "smart" throttle, drivers have little chance of dealing with a stuck pedal, especially by engaging the brakes. "When you have a 250-horsepower engine at wide-open throttle, you can stop it with the brakes — but only temporarily," Cole said. "And then the brakes get hot. They fade and deteriorate, and you're in trouble again."

 

Finding the Source

For Toyota, as well as for engineers around the world, the stuck-gas-pedal story has served as a painful lesson in how difficult it is to get everything right in the design of a machine with tens of thousands of parts.

"You can't design a part and test it through its real lifetime," Cole said. "There's not enough time for that. You have to use accelerated testing. The problem is this is not the type of problem that you would notice in accelerated test. It's a very tough issue for engineers to deal with: How do you simulate something that will only occur over a lengthy aging process and, even then, only very rarely?"

Cole credits Toyota for publicly taking responsibility for the problem, saying that in the long term it will work to the company's advantage. When Audi experienced a similar problem more than two decades ago, company executives refused to accept blame, largely because no mechanical or electrical faults were observed. The ultimate cause (the gas pedal and brake were too close together) was eliminated with a redesign, but Audi's reputation was severely damaged. "Audi's response was, ‘It was the driver's fault,'" Cole said. "And that's what really hurt them."

Experts wonder if Toyota will ever pin down the real reason for the gas pedal problem. "It's a culmination of a lot of factors," Fisher said. "It's difficult to get a real handle on it."

Even if the "spacer" and the smart throttle help Toyota deal with the problem, experts aren't convinced Toyota will ultimately find the smoking gun. Nor do they blame engineers for not being able to foresee it during the design and test stages. "Can you test all the parts in an integrated way? I don't think that can be done with accelerated testing," Eppinger said. "No test can catch everything."