A VW Golf was retrofitted to serve as a development/demo car with Nexteer's Steering on Demand, Quiet Wheel Steering and Stowable Steering Column technologies. (Nexteer)
Nexteer readies steering technologies for autonomous and mixed-mode driving
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Steering-technology engineers continue to consider different solutions to the issue of whether a driver will be prepared to instantly take control from an autonomously-driven vehicle—and in a nod to driver’s-training school, drivers assuming steering control from an SAE Level 3-5 autonomously driven vehicle might need to pass a hands-on test before the handover.
“We want a safe transition and a driver ‘training session’ might be a potential way to pre-address that transition,” Patrik Ryne, Nexteer’s Manager for Steer-by-Wire, said in an Automotive Engineering interview.
That training session might unfold with the driver performing various steering tasks such as turning the wheel 90 degrees to the right, then 90 degrees to the left—all while the vehicle is still in the automated-driving mode.
“These steering wheel movements will not affect the road wheels at all,” Ryne said, underscoring the de-coupling that’s possible with a steer-by-wire system. “It’s just a training exercise to prepare and confirm that the driver is ready for the transition.”
Close attention to human factors
Human-factors studies vary on the predicted time a driver needs to competently take control from an autonomously-driven vehicle. However, industry experts agree that it’s imperative the driver’s attention is focused on driving tasks before the handover. In-vehicle sensors and cameras for monitoring the driver’s head and eye movements as well—as vehicle CAN bus messages to confirm a foot is on the accelerator pedal—already are part of the human-factors solution package, Nexteer said.
“An automated driving system will keep doing what it’s doing until there is a handover to the driver. We just want that handover to be a safe and intuitive transition,” Ryne stressed. The actual handover could be handled via Nexteer’s Steering on Demand, an in-development system that transitions steering control between manual and automated driving.
Nexteer’s steer-by-wire system is the key technology enabler to Steering on Demand, as well as the company’s Quiet Wheel Steering, and Stowable Steering Column innovations.
By-wire technology foundation
Nexteer’s steer-by-wire system features variable steering ratios and performance settings, according to Michael Hales, Nexteer’s Engineering Lead for Steer-by-Wire Development.
“Our goal with this technology is to give the driver an emulated feel of the road after the transition from automated to manual driving. That’s really important,” Hales said, “as most drivers don’t realize how many cues they take from how the steering ‘feels’ on different surfaces, such as the feel of a dry road versus an icy road.”
A Nexteer development/demonstration vehicle—retrofitted with steer-by-wire technology to replace an electric power steering system—is being used by engineers in Saginaw, Michigan to develop an evasive-emergency maneuver system. “We want the system to provide an extra steering nudge to the driver’s main steering input if that’s needed for obstacle avoidance,” Hales said.
Another Nexteer development/demonstration car leverages steer-by-wire technology for the refinement of Steering on Demand, Quiet Wheel Steering (QWS) and Stowable Steering Column technologies.
QWS can be programmed to have either minimal steering wheel movement or zero steering wheel movement. “If you’re in automated mode and a 90-degree turn is occurring, the steering wheel is spinning very fast and that could be a safety hazard,” said Ryne.
The trio of Steering on Demand, QWS and Stowable Steering Column technologies are designed to work in unison for a driver handover. QWS holds the steering wheel still via a proportional-integral-derivative (PID) control loop in the steering-column controller that ignores the torque command from the steering gear while the steering column from its potential retracted position. The ‘unstow’ column position is measured via a digital position sensor, which sends the signal by a private CAN bus message to the steering column controller.
“As the driver starts steering the vehicle, the system will verify the driver’s intent,” said Ryne, noting that intent-confirmation will likely include camera, CAN bus message and algorithms that detect hands on the steering wheel among other inputs. “All of these sensor signals are fused together for an intent decision. If the intent is correct, the steering will be handed over the driver.”
Nexteer currently has 12 advanced steering development programs with OEM partners. Those programs are applicable to SAE Level 3-5 automated driving.
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