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Drive by wire
Drive-by-wire, DbW, by-wire, or x-by-wire technology in the automotive industry replaces the traditional mechanical control systems with electronic control systems using electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators. Hence, the traditional components such as the steering column, intermediate shafts, pumps, hoses, belts, coolers and vacuum servos and master cylinders are eliminated from the vehicle. Examples include electronic throttle control and brake-by-wire.
Advantages
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.
Ergonomics can be improved by the amount of force and range of movement required by the driver and by greater flexibility in the location of controls. This flexibility also significantly expands the number of options for the vehicle's design.
Parking can be made easier with reduced lock-to-lock steering wheel travel as with BMW's Active Steering System, or semi-automatic parallel parking which is available in some Toyota Prius in Japan, Lexus LS460 models worldwide and newer European Volkswagen models. Although neither of these are strictly Steer-by-Wire (SbW) because they retain mechanical linkages, they show the capabilities that are possible.
Disadvantages
The cost of DbW systems is often greater than conventional systems. The extra costs stem from greater complexity, development costs and the redundant elements needed to make the system safe. Failures in the control system could theoretically cause a runaway vehicle (although this is no different from the throttle return spring snapping on a traditional mechanical throttle vehicle). The vehicle could still be stopped by turning the ignition off if this occurred. Another disadvantage is that manufacturers often reduce throttle sensitivity in the low-mid throttle range to make the car easier or safer to control - or to protect the drivetrain (gearbox, clutch, etc.) from driver abuse. The feeling to the driver is that the throttle feels less responsive. There are aftermarket electronic kits to increase throttle sensitivity, to re-gain a more direct-feeling relationship between pedal position and throttle valve opening.
Steer by Wire
This is currently used in electric forklifts and stockpickers and some tractors [1]. Its implementation in road vehicles is limited by concerns over reliability although it has been demonstrated in several concept vehicles such as ThyssenKrupp Presta Steering's Mercedes-Benz Unimog, General Motors' Hy-wire and Sequel and the Mazda Ryuga Concept. A rear wheel SbW system by Delphi called Quadrasteer is used on some pickup trucks but has had limited commercial success.
Competitors in the DARPA Grand Challenge, an automated driving competition, relied on 100% DbW systems, in some cases including a SbW system provided by the manufacturer [2].
This is not to be confused with Electric Power Steering.
Passenger car state-of-the-art
Electronic fuel injection metering in diesel and gasoline engines is now widely used. Electronic throttle control is also in widespread use for gasoline engine control. Purely electronic brake and steering systems have yet to find widespread application in passenger cars. This is primarily because of the significant safety implications of steering or braking systems without a redundant mechanical backup in case of failure of the DbW system. Although it is technically feasible to address these concerns with multiple redundant electronic systems (as in fly-by-wire systems used by many airliners and military aircraft), the additional cost and service requirements have made these systems commercially uncompetitive to date. Hybrid electric vehicles employ limited electronically controlled regenerative braking, but the standard hydraulic braking system is retained. The growth in sales of hybrid and electric vehicles is likely to become an enabling factor for drive-by-wire systems in the future because of the availability of high power electrical supplies required for the new electrical actuators.
The future
Some fanciful theories and applications abound as to what the ultimate implications of DbW technology might be. It has been suggested that DbW might allow a car to become completely separate from its controls, meaning that a car of the future might theoretically be controlled by any number of different control systems: push buttons, joysticks, steering wheels, or even voice commands — whatever device that designers could come up with.
