Steer-by-wire systems do not have a mechanical connection between the steering wheel and the wheels. This steering system is the solution and prerequisite for the future of electric and autonomous cars. That's how far the technology has come.
Steer-by-Wire-System by Bosch
Bosch
Steer-by-wire systems do not require a physical connection between the steering wheel and the wheels. The driver's steering commands are transmitted to the steering system completely electronically and without mechanical or hydraulic components. More precisely: the steering command is transmitted electrically from a steering wheel via a control unit to an actuator that executes the steering command at the wheels.
In principle, steer-by-wire is a further development of electric power steering. "At the beginning of automotive engineering, steering systems used to be mechanical only, later on they had hydraulic, nowadays mostly electromechanical, power-assisted steering. [...] A rigid mechanical connection of steering wheel and road wheel is not always desirable. One steering system without this connection is Steer-by-Wire (SbW)", explains the South Korean chassis specialist Mando in the article Technical Approaches and the Feeling of Safety with Steer-by-Wire from ATZworldwide 2-2021.
An SbW system usually consists of two systems, the Steering Feedback Actuator (SFA) and the Road Wheel Actuator (RWA), as Mando explains. "The latter maps the driving situation based on the road feedback and steers the road wheels according to the driver's wish", says the suspension specialist. Algorithms evaluate the data from various RWA sensors or other vehicle systems and calculate changes in the tie rod and rack forces resulting from the road wheels. These estimated forces are transferred to the SFA as a key input variable, which then generates a steering feel on the steering wheel that correlates with the vehicle's driving situation.
Advances in Steer-by-Wire
X-by-wire is used today in various technical areas. In the 1970s, the first (analog) fly-by-wire system in civil aircraft construction was used in the Concorde. In the automotive industry, drive-by-wire (electronic accelerator pedal) as a mass-produced x-by-wire system causes the engine to respond more quickly to accelerator pedal commands depending on the change in pedal angle. It also enables targeted intervention in the traction control system in the event of excessive traction slip. Steer-by-wire and brake-by-wire are now also becoming more relevant.
Steer-by-wire technologies have been in development for years. Around ten years ago, the Nissan-Subsidiary Infiniti, was one of the pioneers of the technology, using steer-by-wire in the Q50 notchback saloon, although a mechanical connection was provided for emergencies. Before that, Daimler-Benz installed a prototype of a steer-by-wire system in an E-Class Mercedes in 1998. US steering system specialist Nexteer developed a prototype system for BMW in 2003.
Since then, steer-by-wire systems have become increasingly popular. They will soon be found in vehicles from Toyota, Lexus and Nio, for example. The Toyota bZ4X, for example, is to be equipped with a steer-by-wire system. Toyota's premium brand Lexus also relies on steer-by-wire. Steer-by-wire with the new yoke steering wheel is available as an option in the Lexus SUV RZ 450e. And the steer-by-wire technology developed by ZF will be part of the new Nio vehicle platform. In addition, the new Ultium platform from GM, which is also used by the Lyriq, is already set to enable steer-by-wire. Hella, meanwhile, wants to bring a steer-by-wire system to series production readiness together with the Lotus Tech Innovation Centre (LTIC), the research and development center of car manufacturer Geely. The system will then be rolled out to other customers within and outside the Geely Group.
New Design and Development Freedoms
Steer-by-wire offers numerous advantages. These include:
- Greater precision: The electronics implement the driver's directional request transmitted via the steering wheel much faster and more directly than mechanical systems.
- More comfort: Driver comfort is increased as the mechanical decoupling of the steering wheel and wheels means that vibrations are no longer transmitted. Modern steer-by-wire systems can convey a realistic steering feel through haptic feedback – any setting is possible, from sporty-direct to comfortable-relaxed, in one and the same car. This allows different steering modes to be set up for different driving conditions or styles.
- Adaptability: The steering wheel angle to the wheel steering angle can be adapted dynamically, continuously and without discontinuities to different driving situations. For example, fully adjustable steering reduces the steering wheel steering angle when parking or during slow driving maneuvers.
- More driving safety: Steer-by-wire enables new safety features in the area of driving dynamics control, while the elimination of the steering column increases crash safety.
- Compatibility with automated driving: Steer-by-wire systems can implement fully autonomous vehicle control for shuttles and robotaxis, among other things.
- More space and design options: Freedoms in the design of car interiors are made possible by retractable steering wheels for fully automated driving modes. The space freed up could also be used for larger dashboards or head-up displays.
Functional safety and reliability aspects as well as cybersecurity, on the other hand, are sticking points in steer-by-wire systems: It is important to realize these requirements with acceptable effort. A basic distinction can be made between two redundancy concepts, "fail-operational" and "fail-safe", as Springer author Ferit Küçükay explains in the German book chapter Steering, Steering Kinematics, Steering Power Assistance, Friction, Steer-by-Wire. The requirements for the redundancy of steer-by-wire systems in turn increase the costs, weight and complexity of the systems. According to Küçükay, this will be partially relativized in the course of the introduction of automated driving, as a fail-safe steering system will be required in the vehicle anyway.
Paving the Way for the Software-based Vehicle
Steer-by-wire is considered crucial, especially for electrified and automated driving. Steer-by-wire is one of the key technologies on the road to automated, software-defined vehicles. Bosch wants to bring steer-by-wire steering systems to the market in large-scale production by the middle of the decade. The supplier is working together with the start-up Arnold NextG. Hella's steer-by-wire system could be in use from 2026. Competitor ZF expects a significant expansion of the steer-by-wire market share by 2030.
According to data and analysis company Globaldata, the market for automotive steering systems in the Asia-Pacific region is expected to record a compound annual growth rate of 2.7 % between 2023 and 2028 – from an estimated 48.1 million units in 2023 to 54.9 million units in 2028. Demand for steer-by-wire steering systems and electric power steering systems is being driven by the steady electrification of mechanical systems, the emergence of electric vehicles and the increasing use of driver assistance systems.
