Drive by wire: Safe at any speed?

September 11, 2014 // By Blaine Bateman
Drive by wire sub-systems in passenger vehicles have been in the news for some time. You might remember Toyota’s recalls for sticking accelerator pedals that seemed to have a mind of their own. The vast number of media reports (mostly with frightening overtone) raises the question about the safety of this technology.

There was plenty of news coverage of the various recalls related to the defective accelerator pedal system, creating speculation that a software glitch, or “ghost in the machine” as Popular Mechanics (PM) called it , was responsible for doing things the driver did not intend. In the same article, PM noted that in fact no software issue was found, even after NASA reviewed the source code provided by Toyota.

Wired Magazine reported in October 2012 that Nissan was developing an electronic system that would eliminate the mechanical link between the steering wheel and the actual turning of the wheels. They characterized the system as both a relatively small step from power assisted steering, as well as a logical step towards autonomous vehicles. Nissan did roll the system out in the 2014 Infiniti Q50 Sedan, under the moniker “ Direct Adaptive Steering ”.

Figure 1 The Infiniti 2014 Q50S includes a system which replaces the direct mechanical connection between the steering wheel and the steering gear with an electronic system that converts driver input into electronic control of the steering. (source: infinitinews.com)

The system includes modes that could be correctly called steer by wire; and Nissan promoted benefits such as eliminating unneeded feedback on rough roads: “Direct Adaptive Steering moderates the need for constant, subtle adjustment, imparting a commanding feeling while helping shield the driver from excessive road vibrations.” As you can see in Figure 2 , the system includes redundant electronic control modules; it also includes a clutch that, in normal use, disengages the mechanical link from the steering column to the steering rack.

Figure 2 The Infiniti Direct Adaptive Steering System translates steering input from the driver into electronic signals that are processed and used by the electronics to determine movement of the steering rack. Similarly, actual movement of the wheels and steering gear is processed and used to provide feedback to the driver through the steering wheel.

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