Design Article
Steer-by-wire technology approaches production vehicles
Charles Murray
12/4/2012 8:43 PM EST
The decision to bring steer-by-wire to a production vehicle is a major one for the automobile industry because it lays the foundation for eventual elimination of the mechanical components that now connect the driver to a vehicle's tires.
"There are a lot of advantages to this," Infiniti spokesman Kyle
Bazemore told Design News. "It enhances the driving experience.
And in the future, after consumer acceptance of the technology, we
could theoretically do away with the mechanicals and save the
weight."
The next-generation steering system, as Nissan calls it, works by endowing the steering wheel with sensors that read the desired steering angle. Data from the sensors is sent to one of three electronic control units (ECUs), which activate electric motors on the vehicle's steering rack. In contrast, conventional steering uses a direct mechanical connection to the rack-and-pinion.
In truth, the new Nissan system won't eliminate the mechanical connection to the driver. Instead, it will use the mechanical connection as a redundant system, only in cases of extreme emergency. If, for example, a power supply conks out or all of the ECUs fail, it will employ a back-up clutch to mechanically connect the steering wheel to the tires. "The clutch is disengaged 999,999 times out of a million," Bazemore told us. "But the steering shaft is still there, just in case."
Nissan said steer-by-wire will enhance the driving experience. When it reaches the market late next year, it will eliminate some of the vibration from rough road surfaces and it will minutely adjust tire angles to compensate for crosswinds and sloped surfaces. At the same time, it will enable drivers to "feel" the road. Grip information, such as slipperiness, will be transferred back to a steering force actuator that will allow the steering wheel to retain some of its original feel.
"Theoretically, you could have no steering feel at all, but that would not be good for drivers," Bazemore said. "That's why we dialed some -- but not all -- of the steering feel back into the system."
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Ian McMillan
12/6/2012 12:04 PM EST
I like the idea of compensating for cross-winds; but experience in the aircraft industry (which uses triple-redundancy) has shown that unless fly-by-wire has some means of being very quickly by-passed when the voting circuit makes a mistake, you can find yourself in real trouble real quick. Split-second timing can be vital, can be life-and-death... I still feel the butterflies there
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docdivakar
12/10/2012 1:25 PM EST
I am sure the Nissan engineers have figured out the response characteristics of the wired steering systems vs. the mechanical one so the driver will notice little change when the backup / redundant system takes over. But the situation described by @Ian McMillan above does bring up an important issue. It would be nice to know more about this.
MP Divaar
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