Drive by wire

Drive by wire or DbW technology in the automotive industry is the use of electronic or electro-mechanical systems in place of mechanical linkages that control driving functions. The concept is similar to fly-by-wire in the aviation industry.[2] Drive-by-wire may refer to just the propulsion of the vehicle through electronic throttle control,[3] or it may refer to electronic control over propulsion as well as steering and braking, which separately are known as steer by wire and brake by wire, along with electronic control over other vehicle driving functions.[4]

SpeedE, an academic concept car developed for studying drive-by-wire technologies[1]

Driver input is traditionally transferred mechanically to the motor and wheels through a steering wheel and steering column, throttle, hydraulic brakes, brake pull handles and so on. In drive-by-wire systems, driver input is processed by an electronic control system which controls the vehicle using electromechanical actuators. The human–machine interface, such as a steering wheel, yoke, accelerator pedal, brake pedal, and so on, may include haptic feedback that simulates the resistance of hydraulic and mechanical pedals and steering, including steering kickback. Components such as the steering column, intermediate shafts, pumps, hoses, belts, coolers, vacuum servos and master cylinders are eliminated from the vehicle. Safety standards for drive-by-wire are specified by the ISO 26262 standard level D.

Properties
Simplified diagram of a corner module for an electric vehicle.
REE Automotive electric vehicle corner module diagram. The module implements drive, steer, brake, and park-brake by-wire, collectively called x-by-wire.[3]

Dispensing with mechanical linkages has several advantages: it reduces complexity and simplifies assembly; simplifies service and tuning; reduces the force required to engage inputs and allows it to be customized with haptic technology; allows for more interior design freedom in the placement of input mechanisms; allows for automation of driving functions; reduces cabin noise by eliminating the acoustic linkage to the drive systems; and by reducing floor openings it improves the crash behavior of the vehicle.[5] Because driver inputs can be overridden, safety can be improved by providing computer controlled intervention of vehicle controls with systems such as electronic stability control (ESC), adaptive cruise control and lane assist systems.[2]

Each drive-by-wire system leads to more actuator in the vehicle and therefore greater energy consumption. For instance, the drive-by-wire technology adds actuator motors to create the torque needed to turn the wheels, and a feedback transducer to create the "road feel" on the steering wheel.

Safety considerations require redundancy of driver input sensors, vehicle communication networks, actuators,[5] and other systems. Automotive safety standards such as ISO 26262 require drive-by-wire fail-operational and fail-safe behaviors.[6]

Safety and security

Failures in drive by wire systems can lead to potential hazardous situations where safety depends entirely on the vehicle's failure mode. The Aachen University Institute for Motor Vehicles (ika – Institut für Kraftfahrzeuge), in collaboration with Mercedes-AMG and others, studies the operation, risks, and safety mechanisms of drive-by-wire systems through its drive-by-wire concept vehicle, SpeedE. Studied scenarios include loss of control over acceleration, brakes, or steering.[1]

Early by-wire systems had mechanical backup systems in case the by-wire systems failed.[3] The modern drive by wire paradigm dispenses with mechanical backups, and relies on redundancy, fail-operational systems, and other safety and security measures: computational redundancy through lockstep CPUs; functional redundancy through modular design where the failure of one module is compensated by an identical module, for example by torque vectoring to compensate for a failed steering or braking module; multi-sensor fault detection; self-isolation of damaged systems; and fault-tolerant communication. Such fail-safes are specified by the ISO 26262 standard level D.[6]

Assessment and standardization of drive-by-wire computer security has also taken place. Researchers demonstrated in 2011[7] and 2013[8][9] that some systems in commercially-available vehicles are susceptible to hacking, allowing for external control of the vehicle. Hacking demonstrations included remote activation of systems like the horn, windshield wipers, accelerator, brakes, and transmission.[9] Modern standards such as the ISO/SAE 21434 standard and UNCE regulations 155, 156, and 157 require dedicated cryptographic modules that encrypt all communication between the ECUs and the drive system components.[3]

Systems

Brake by wire
Main article: Brake-by-wire

A brake-by-wire system eliminates the need for a mechanical connection that transfers force between the brakes and a driver input apparatus such as a pedal or lever. The three main types of brake-by-wire systems are: electronic parking brakes which have, since the turn of the 21st century, become more common; electro-hydraulic brakes (EHB) which can be implemented alongside legacy hydraulic brakes and as of 2020 have found small-scale usage in the automotive industry; and electro-mechanical brakes (EMB) that use no hydraulic fluid, which as of 2020 have yet to be successfully introduced in production vehicles due to their novel actuation methods.[10]

Shift by wire
Main article: Shift by wire

Shift-by-wire employs electrical or electronic connections that replace the mechanical connection between the driver's gearshift mechanism and the transmission. Since becoming commercially available in 1996, shift-by-wire has been commonly used in automated manual transmission, and has later been implemented in semi-automatic transmission and automatic transmission.[5]

Park by wire may be considered a form of shift-by-wire.[5] Not to be confused with park-brake by wire which engages a parking brake, park-by-wire engages the parking pawl. A parking pawl in a traditional automatic transmission has a mechanical link to the gear stick and locks the transmission in the park position when the gear-shift handle is set in "park". A park-by-wire system uses electronic commands sent to an actuator that engages the parking pawl.

Steer by wire
Main article: Steer-by-wire

A vehicle equipped with a steer-by-wire system is able to steer some or all of its 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 mechanically transfer some steering torque to the wheels.[12]

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 and steer 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.[12][13]

Throttle by wire
Main article: Electronic throttle control

Accelerate-by-wire or throttle-by-wire,[14] more commonly known as electronic throttle control, is a system that actuates vehicle propulsion without any mechanical connections, such as cables, from the accelerator pedal to the throttle valve of the engine or other propulsion systems. In electric vehicles, this system controls the electric motors by sensing the accelerator pedal input and sending commands to the power inverter modules.

References
  1. SpeedE – Forschungsplattform, ika – Institute for Motor Vehicles of RWTH Aachen University, 2016
  2. Austin Weber (March 26, 2010), "Wire Processing: Drive-by-Wire", Assembly Magazine
  3. Scheibert, Klaus; Kostarigka, Artemis; Dannebaum, Udo; Ambekar, Abhijit; Cai, Wenlin; Heidt, Laurent (2023). "Challenges with the Introduction of X-By-Wire Technologies to Passenger Vehicles and Light Trucks in regards to Functional Safety, Cybersecurity and Availability". SAE Technical Paper Series. Vol. 1. doi:10.4271/2023-01-0581. S2CID 258033364.
  4. Pillai, Arjun V.; Manojkumar, B. (2022). "Overview of drive by wire technologies in automobiles". INTERNATIONAL CONFERENCE ON TRENDS IN CHEMICAL ENGINEERING 2021 (ICoTRiCE2021). AIP Conference Proceedings. Vol. 2452. p. 030001. Bibcode:2022AIPC.2452c0001P. doi:10.1063/5.0113232. S2CID 253697706.
  5. Harald Naunheimer; et al. (2011), "9.1.3 Shift-by-Wire", Automotive Transmissions: Fundamentals, Selection, Design and Application (Second ed.), Springer, doi:10.1007/978-3-642-16214-5, ISBN 978-3-642-16213-8
  6. Arunkumar Sampath, "Toward functional safety in drive by wire vehicles" (PDF), Mobility Engineering (December 2020)
  7. Checkoway, Stephen. "Comprehensive Experimental Analyses of Automotive Attack Surfaces". YouTube. Archived from the original on May 31, 2017. Retrieved August 23, 2018.
  8. Greenberg, Andy. "Hackers Reveal Nasty New Car Attacks—With Me Behind The Wheel (Video)". Forbes. Archived from the original on August 25, 2017. Retrieved August 26, 2017.
  9. Greenberg, Andy. "Hackers Remotely Kill a Jeep on the Highway—With Me in It". Wired. Archived from the original on January 19, 2017. Retrieved March 6, 2017.
  10. Dieter Schramm; et al. (2020), "5 Braking systems", Vehicle Technology: Technical foundations of current and future motor vehicles, De Gruyter Oldenbourg, doi:10.1515/9783110595703, ISBN 9783110595703, S2CID 216374738
  11. Lydia Saß (July 26, 2023), "25 Jahre PARAVAN", barrierefrei-magazin.de
  12. Chris Perkins (March 17, 2023), "How Toyota Is Making the Case for Steer-By-Wire", Road & Track
  13. Jancer, Matt. "Take a Look Inside the First Steer-by-Wire Car". Wired. Archived from the original on March 16, 2014. Retrieved March 6, 2017.
  14. John Fuller (April 28, 2009), "How Drive-by-wire Technology Works", HowStuffWorks
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