Drive by wire (DBW) in theautomotive industry is thetechnology that useselectronics orelectro-mechanical systems in place ofmechanical linkages to control driving functions. The concept is similar tofly-by-wire in the aviation industry.[2] Drive-by-wire may refer to just thepropulsion of the vehicle throughelectronic throttle control,[3] or it may refer to electronic control over propulsion as well assteering andbraking, which separately are known assteer by wire andbrake by wire, along with electronic control over other vehicledriving functions.[4]
Driver input is traditionally transferred to the motor, wheels, and brakes through amechanical linkage attached to controls such as asteering wheel,throttle pedal,hydraulic brake pedal,brake pull handle, and so on, which apply mechanical forces. In drive-by-wire systems, driver input does not directly adjust a mechanical linkage, instead the input is processed by anelectronic control unit which controls the vehicle usingelectromechanicalactuators. Thehuman–machine interface, such as a steering wheel, yoke, accelerator pedal, brake pedal, and so on, may includehaptic feedback that simulates the resistance of hydraulic and mechanical pedals and steering, includingsteering 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 theISO 26262 standardlevel D.
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 withhaptic technology; allows for moreinterior 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 thecrash behavior of the vehicle.[6] Because driver inputs can be overridden, safety can be improved by providing computer controlled intervention of vehicle controls with systems such aselectronic stability control (ESC),adaptive cruise control andlane assist systems.[2]
Each drive-by-wire system leads to more actuators 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 requireredundancy of driver input sensors,vehicle communication networks, actuators,[6] and other systems. Automotive safety standards such asISO 26262 require drive-by-wirefail-operational and fail-safe behaviors.[7]
Failures in drive by wire systems can lead to potential hazardous situations where safety depends entirely on the vehicle'sfailure mode. TheAachen University Institute for Motor Vehicles (ika –Institut für Kraftfahrzeuge Aachen), in collaboration withMercedes-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 onredundancy,fail-operational systems, and other safety and security measures: computational redundancy throughlockstep CPUs; functional redundancy through modular design where the failure of one module is compensated by an identical module, for example bytorque 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 theISO 26262 standardlevel D.[7]
Assessment and standardization of drive-by-wirecomputer security has also taken place. Researchers demonstrated in 2011[9] and 2013[10][11] that some systems in commercially available vehicles are susceptible tohacking, allowing for external control of the vehicle. Hacking demonstrations included remote activation of systems like the horn, windshield wipers, accelerator, brakes, and transmission.[11] Modern standards such as theISO/SAE 21434 standard andUNCE regulations 155, 156, and 157 require dedicatedcryptographic modules that encrypt all communication between the ECUs and the drive system components.[3]
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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 apedal orlever. 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 legacyhydraulic brakes and as of 2020 have found small-scale usage in the automotive industry; andelectro-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.[14]
Shift-by-wire employs electrical or electronic connections that replace themechanical connection between the driver'sgearshift mechanism and thetransmission. Since becoming commercially available in 1996, shift-by-wire has been commonly used inautomated manual transmission, and has later been implemented insemi-automatic transmission andautomatic transmission.[6]
Park by wire may be considered a form of shift-by-wire.[6] Not to be confused withpark-brake by wire which engages aparking brake, park-by-wire engages theparking pawl. A parking pawl in a traditional automatic transmission has a mechanical link to thegear 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.
A vehicle equipped with a steer-by-wire system is able to steer some or all of its wheels without asteering column connected to the wheel axles. It is different fromelectric power steering or power-assist, as those systems still rely on the steering column to mechanically transfer some steering torque to the wheels.[15]
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 moreelectronic 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 withhaptic feedback to simulate road feel and wheel resistance, and change depending on the vehicle speed or customizable settings.[15][16]
Accelerate-by-wire or throttle-by-wire,[17] more commonly known aselectronic 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 otherpropulsion systems. In electric vehicles, this system controls the electric motors by sensing the accelerator pedal input and sending commands to the power inverter modules.
