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 asteering column that turns the direction of those wheels mechanically. It is different fromelectric power steering or power-assist, as those systems still rely on the steering column to transfer some steering torque to the wheels.[3] It is often associated with otherdrive 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 othercontroller which is connected to one or moreelectronic 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 withhaptic feedback to simulate road feel and wheel resistance, and change depending on the vehicle speed or customizable settings.[3][4]
Thesafety of drive-by-wire systems is often ensured throughredundancy, for example through redundant input sensors, redundantvehicle 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 withtorque vectoring using the other available wheels.[5]
Severalone-off vehicles and concept vehicles implemented steer-by-wire, such as the early-1990sSaab Prometheus,[7] 1996Mercedes F200,[8] 2001SKF Filo based on theOpel Zafira,[9] 2003 General MotorsHy-wire,[10] 2005GM Sequel,[11] 2007Mazda Ryuga,[12] and others.
Schaeffler Paravan Technologie has provided steer-by-wire systems for one-off racing vehicles, for example: a steer-by-wirePorsche Cayman GT4 raced the2020 24 Hours of Nürburgring and finished 2nd place in its class and 29th overall; a steer-by-wireMercedes-AMG GT3 racedthe following year using the same system and finished 16th overall.[13][14]
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.[15] Purely mechanical four-wheel steering systems have been available in production cars since the mid 1980s, soon followed by computer-controlled systems in the late 1980s. Manufacturers implementing these systems includedCitroën,Honda,Isuzu,Mazda,Mitsubishi,Nissan,Porsche, andToyota. The popularity of four-wheel steering waned in the 1990s, with few models being offered in the early 2000s. Four-wheel steering systems reappeared in the late 2000s and 2010s in models by manufacturers includingAcura,BMW,Nissan,Porsche, andRenault.[16] Car manufacturers that have offered rear-axle steering in the 2020s includeAcura,Audi,Bentley,BMW,Cadillac,Ferrari,General Motors,Genesis,Lamborghini,Lexus,Mercedes-Benz,Porsche, andRolls-Royce.[17]
One such rear-axle-only steer-by-wire system couple with traditional front steering wasQuadrasteer. 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.[15]
Rolls-Royce vehicles based on the Architecture of Luxury platform, such as the Cullinan, Spectre, Ghost, and Phantom, have computer-controlled four-wheel steering.[18] The front wheel steering useselectric power assist[19] 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.[20]
Steer-by-wire without the use of a steering column was first offered in a production car with theInfiniti Q50 in 2013.[4] 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.[2] After negative reception the model was retrofitted with traditionalhydraulic steering.[21] Steer-by-wire continued to be offered with the QX50 and QX55, and as late as 2022 it was being offered with theInfiniti Q60 coupe,[22] which was discontinued that year.[23]
Productionbattery electric vehicles (BEVs) with rear-axle SbW coupled with traditional front-wheel steering include as of 2024 theRolls-Royce Spectre,[24]Lotus Eletre,[25]GMC Hummer EV, andChevrolet Silverado EV.[22]
Production BEVs with steer-by-wire with no steering column include as of 2024 theTesla Cybertruck[26] which is sold at retail, andREE Automotive P7-C[27] which is sold to fleet operators. Planned production vehicles with no-steering-column SbW as of 2023 include:Lexus RZ 450e,[28]Nio ET9,[29]Toyota bZ4X,[22] andGeely Super Van.[30] As of 2023Lotus,[25]Mercedes-Benz,[31] andPeugeot[32] plan to offer no-steering-column steer-by-wire cars in the mid to late 2020s.
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