A June recall of Toyota's vehicles has sparked debate over how far engineers should go in designing for misuse of products. The recall urged Toyota to fix 154,000 vehicles to prevent problems that might occur when improper floor mats are used by owners. "The accelerator pedal can get stuck in the wide open position due to its being trapped by an unsecured or incompatible driver's floor mat," said a statement from the National Highway Traffic Safety Administration (NHTSA).
The latest recall, which involves the 2010 Lexus RX 350 and Lexus RX 450h, raises questions about the role of design engineers with its citing of "unsecured or incompatible floor mats."
"Sometimes, owners use floor mats from another vehicle," Toyota spokesman Mike Michels told us. "Sometimes, they use aftermarket mats. We've even found carpet remnants stacked on the floor. The record was eight -- in that case, you couldn't even see the accelerator pedal."
Use of unsecured floor mats can be a problem when they get caught on the accelerator pedal. It's not known if the mats caused any of Toyota's incidences of unintended acceleration that dominated the media two years ago. To prevent such problems in the future, however, Toyota has had to recall hundreds of thousands of vehicles. In some cases, the company's engineers re-shaped the bottom of the accelerator pedal to create more clearance. In others, they modified the plastic pad on the floor and even altered the vehicle floor pan to make more room.
Automotive experts told Design News that Toyota engineers might have been able to prevent the floor mat issues. Even though the mats may have been inappropriate for the Toyota and Lexus vehicles, they said, the problem involved interaction between just two components -- floor mat and pedal. As such, engineers probably could have imagined the potential failure modes, tested for them, and taken preventative measures.
"They should have been able to test for most of the conditions -- when the mats slide around, when they are mispositioned, when they are upside down, and even when the driver and passenger floor mats are swapped," Steven Eppinger, professor of engineering systems at Massachusetts Institute of Technology (MIT), said in an interview. "It's impossible to test for everything, but if you make your design more robust for the 50 things you can think of, then it's likely to be robust for the 20 things you didn't think of."
Although the number and severity of the owner complaints have not yet been made public, some observers believe that use of aftermarket floor mats by American consumers may have posed an unforeseen problem for Japanese designers. David Champion, senior director of Consumer Reports Automotive Test Center, told us:
They don't consider aftermarket floor mats, especially in Japan where everything is neat and tidy. There were also other issues -- like people putting rubber floor mats on top of existing floor mats. These are forms of misuse that can happen. And any misuse that would be considered normal in the US car market should have been taken into consideration.
Toyota typically designs its floor mats with grommets that slip over hooks on the floor to prevent them from sliding. On the bottom side, the mats employ a rubber surface with "nibs" that create friction and further prevent them from moving. The company argues that when properly anchored, compatible floor mats are used, problems don't occur. "It's a challenge for engineers to imagine every way that people might misuse their product," said Michels of Toyota.
Two years ago, when Design News talked to experts about the Toyota situation, most were in agreement that the automaker's problems were unforeseeable. At the time, however, the company's engineers were considering multiple culprits, including the accelerator's friction lever, heater condensation, corrosion, electronics, and floor mats. Toyota has since examined the mats, shortened the pedals, lengthened the friction lever, added a spacer, and changed the linkage materials. NHTSA has also definitively announced that the electronics were not the problem.How much to consider?
Still, experts now say that the simple interactions between floor mat and pedal should have been easier to catch. "To be fair, there are only so many conditions that an engineer can think of," Eppinger said. "So while you can't fault them for not considering every circumstance, you can fault them for not considering enough."
An engineer's responsibility in such situations is essentially set by the legal system, experts said. "What it comes down to is that if you design something, you have to contemplate how people will misuse it," said David Cole, chairman emeritus of the Center for Automotive Research. "It's a fundamental area of law, but it's also a deterrent to innovation."
To be sure, vehicle manufacturers are complying with all measures designed to prevent future cases of unintended acceleration. In April, NHTSA proposed inclusion of a mandatory brake-throttle override system that would shut down the throttle if the brake and accelerator pedals are pressed simultaneously. Toyota already has the technology on its vehicles and the Alliance of Automobile Manufacturers has said they stand behind it, as well.
"The truth is, there's probably a very low risk that anything will happen," Champion said, referring to the floor mat problem. "It's one of those times when, yes, it could happen, so they're saying, 'Let's get the recall out anyway, just to be safe.'"