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June 7, 2013

News & Features

A first: Infiniti Q50's steering wheel has no mechanical connection to wheels

New York Times News Service

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The steering wheel in the 2014 Infiniti Q50 has no mechanical connection to the front wheels. It's the first production car to offer the system. (Nissan)

So long as their car moves when the pedal is pressed, there is little reason for drivers of newer cars to care whether electronics have replaced the physical connection between the accelerator and the engine.

But a new application of so-called drive-by-wire technology, to be available on the 2014 Infiniti Q50 sedan that goes on sale this summer, may attract more attention. Except during emergencies, that car's steering wheel will have no mechanical connection to the front wheels.

Bert Brooks, senior manager of product planning at Nissan's Infiniti brand, is quick to emphasize what steer-by-wire is not.

At least at Infiniti, he says, electronic steering is not a steppingstone toward self-driving, autonomous cars. Nor does it mean an end to physical feedback from the steering system.
"A common misconception is that it's going to feel kind of like a video game," Brooks says.
"It's completely the opposite."

While the Q50 will become the first production car to offer steer-by-wire — or Direct Adaptive Steering, as the company prefers — the concept is not new. TRW, a leading supplier of conventional steering systems, built its first steer-by-wire prototype car almost 11 years ago.

Early experiments by a variety of companies found that even if customers would accept the idea of effortless steering, it was virtually impossible to keep a car traveling in a straight line without physical feedback.

Creating an electronic steering system that simulates road feel while reassuring drivers that they will still be able to control their cars during emergencies led to a complex formula for steer-by-wire.

The steering wheel of the Infiniti is connected to an actuator, a kind of electric motor. Combined with sensors, it tells a computer what the driver is doing. More precisely, it informs three computers, which provide a safety factor.

The computers, in turn, move the wheels through two electric motors. Normally the motors share the workload, but each can do the job on its own in the event of a failure.
The tricky part of the system is giving the driver a sense of what the car is doing. "The tuning of this has probably been the biggest challenge," Brooks says.

The three computers analyze data from the wheels and decide how the actuator should recreate the feeling at the steering wheel. If, say, the car hits a pothole, the driver will feel it through the steering wheel. But unlike conventional steering, the steering wheel will not jerk out of the driver's hands.

The system also lets the Infiniti's computers vary the car's steering ratio — the proportion of turns at the steering wheel it takes to go around a corner — without restriction. That, according to the company, can make it possible to have very light steering for parking and very tight steering at higher speeds.

If the engine fails, the steering motors and the computers continue to operate as long as the car's battery has a charge. But if there's a complete electrical failure as well, a clutch immediately connects the steering wheel to the front wheels, enabling the driver to pull off the road. The clutch also engages whenever the engine is intentionally shut down.

Not everyone is enamored of steer-by-wire. Alexander Gaedke, director of research and development at ZF Lenksysteme, says his company abandoned the technology because it was "very expensive and we did not see big customer benefits." Gaedke's company instead sells a system to BMW and Audi that maintains a mechanical steering link but adds an actuator to the steering column.

There is one feature made possible in steer-by-wire systems that is not likely to appear in showrooms anytime soon. Brooks says that without the clutch backup system, Infiniti's designers would have been able to install the steering wheel anywhere in the Q50.

"But why would we want do that?" he adds.

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