If you've been surfing the Web today, you've probably already seen this morning's reports from the mainstream media detailing Toyota's show-and-tell rebuttal of the high-profile claims made by Dr. David Gilbert of Southern Illinois University-Carbondale. If you haven't, the bullet points are that today a panel of technology experts, including Dr. Chris Gerdes, associate professor from Stanford University's Center for Automotive Research (full disclosure -- which Toyota helps to fund) along with Matthew Schaw, Subodh Medhekar, and Shukri Souri of Exponent, an independent engineering analysis outfit hired by Toyota, and Kristen Tabar (actually of Toyota) demonstrated with Xacto knifes, resistors, and jump wires how Dr. Gilbert achieved his proposed simulation of the alleged Toyota pedal/unintended acceleration phenomenon.
Their point was to demonstrate that the Gilbert effect doesn't just happen. It requires some extreme and deliberate fooling with the electronics, and while always being polite to their fellow engineer, they didn't hesitate to deride Gilbert for effectively reengineering the pedal and then failing to explain how this situation could ever possibly be duplicated in the real world. To my eyes, Dr. Gilbert's hypothesis looked well and truly filleted. And putting a knife through its heart, the Exponent people performed Gilbert's manipulation on the pedals of a Ford Fusion, a Subaru Outback and a BMW, right before our very eyes. And when the proper contacts were made -- guess what? -- each car's revs similarly raced out of control. There was also an analysis of footage shown during a recent ABC News segment on the Toyota brouhaha (made with the aid of the good Dr. Gilbert) that was obviously doctored for dramatic effect (it's since been re-edited on the ABC Web site). And oh, did the Toyota team happen to note that Dr. Gilbert also receives funding from trial lawyers. Um, yes they did. I didn't know Toyota also builds steam rollers.
But argument-flattening aside, I found it illuminating was to see exactly what the heck Dr. Gilbert actually did.
Basically, these pedals contain twin, independent circuits for measuring pedal angle. Each one employs three wires, each its own voltage supply, ground, and a third wire that carries a signal voltage associated with the pedal's angle. Six wires in total. The two signal voltages vary linearly with throttle angle, but are intentionally different from each other (offset) with one ranging from 0.8 volt at closed throttle to about 4 volts at open throttle, the other going from 1.8 volts to about 5 volts. Each signal is monitored such that if either stays outside a certain (tight) voltage relationship to each other the system falls into limp-mode, letting you drive out of any dangerous traffic situations and registering an error code.
What Dr. Gilbert did was to first place a 200-ohm resistor between the two signal voltage wires (that's exactly what's needed to replicate their signal wire's engineered-in voltage difference) and then short the supplied 5 volts to the signal voltage wire that, when working normally, isn't surprised to see 5 volts at wide-open throttle. Voila - with the masking effect of the 200-ohm resistor added, the signals from both circuits appear to be requesting full power. And the engine revs like mad.