Steer-by-wire

Steer-by-wire, in the context of the automotive industry, is a technology or system that allows steering some or all of a vehicle's wheels without a steering column connected to the wheel axles. It is different from electric power steering or power-assist, as those systems still rely on the steering column to transfer some steering torque to the wheels. It is often associated with other drive by wire technologies.

A vehicle with a steer-by-wire system may be manually controlled by a driver through a steering wheel, a yoke, or any other steering apparatus which is connected to one or more electronic control units, which uses the input to control steering actuators that turn the wheels side-to-side, steering the vehicle. The steering wheel or yoke may be equipped with haptic feedback to simulate road feel and wheel resistance, and change depending on the vehicle speed or customizable settings.

The safety of drive-by-wire systems is often ensured through redundancy, for example through redundant input sensors, redundant vehicle communication networks and power grids, redundant steering actuators per wheel, and fail-operational steering. If steering fails for one or even two wheels, the system can compensate with torque vectoring using the other available wheels.

Concept vehicles and race cars 

Several concept vehicles included steer-by-wire, such as ThyssenKrupp Presta Steering's Mercedes-Benz Unimog, General Motors' Hy-wire and Sequel, Saabs Prometheus and the Mazda Ryuga. Schaeffler Paravan Technologie has provided steer-by-wire systems for racing vehicles: a steer-by-wire Porsche Cayman GT4 raced the 2020 24 Hours of Nürburgring and finished 2nd place in its class and 29th overall; a steer-by-wire Mercedes-AMG GT3 raced the following year using the same system and finished 16th overall.

Production vehicles

Coupled with traditional steering 

Rear-axle-only steer-by-wire may be coupled with traditional front wheel steering for conditional four-wheel steering, reducing turning radius at low speeds and increasing stability at high speeds. Purely mechanical four-wheel steering systems have been available in production cars since the 1980s, with computer-controlled electronically-actuated rear-axle steering becoming available shortly after. Car manufacturers that have offered rear-axle steering in the 2020s include Acura, Audi, Bentley, BMW, Cadillac, Ferrari, General Motors, Genesis, Lamborghini, Lexus, Mercedes-Benz, Porsche, and Rolls-Royce.

One such rear-axle-only steer-by-wire system couple with traditional front steering was Quadrasteer. It was developed by Delphi and was offered starting 2002 on some General Motors trucks. Despite favorable reception the system was discontinued in 2005 due to poor market penetration of only 17 percent of sales of the same model, partially due to lack of familiarity with the system and partially due to its $1000 mark-up.

Rolls-Royce vehicles based on the Architecture of Luxury platform, such as the Cullinan, Spectre, Ghost, and Phantom, have computer-controlled four-wheel steering. The front wheel steering uses electric power assist while an electronic system controls the rear wheel steering and turns them in the opposite direction of the front wheels when turning at lower speeds, and slightly in the same direction as the front wheels at higher speeds in order to increase stability.

Without traditional steering 
Steer-by-wire without the use of a steering column was first offered in a production car with the Nissan Infiniti Q50 in 2013. The system has a backup steering column separated from the steering wheel with a clutch. The clutch connects the steering wheel to the steering rack in case of failure of the electronic steering sensors or actuators. After negative reception the model was retrofitted with traditional hydraulic steering. Steer-by-wire continued to be offered with the QX50 and QX55, and as of 2022 is being offered with the Infiniti Q60 coupe.

Electric vehicles 
Production battery electric vehicles (BEVs) with rear-axle SbW coupled with traditional front-wheel steering include the Rolls-Royce Spectre and Lotus Eletre.

Planned production BEVs as of 2023 that will offer steer-by-wire with no steering column include: Lexus RZ 450e, Toyota bZ4X, Canoo Lifestyle Vehicle, REE Automotive P7-module-based vehicles, and Geely Super Van. As of 2023 Lotus, Mercedes-Benz, Nio, Peugeot, and purportedly Tesla plan to offer no-steering-column steer-by-wire cars in the mid to late 2020s.

References

Advanced driver assistance systems