Drive by wire

Drive by wire, DbW, by-wire, Steer-by-wire, or x-by-wire technology in the automotive industry is the use of electrical or electro-mechanical systems for performing vehicle functions traditionally achieved by mechanical linkages. This technology replaces the traditional mechanical control systems with electronic control systems using electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators. Components such as the steering column, intermediate shafts, pumps, hoses, belts, coolers and vacuum servos and master cylinders are eliminated from the vehicle. This is similar to the fly-by-wire systems used widely in the aviation industry.

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.

Eliminating mechanical linkages can provide savings in weight.

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. These systems will fall under the category of safety critical systems which are recommended to be developed under standards like ISO 26262 which require extensive changes in the development process generally taken for developing other traditional systems. Drive by wire systems can be "hacked," and their functions and control disabled or commandeered, by either wired or wireless connections.

Drive by wire systems also have increased response time versus their mechanical counterparts. The mechanical system offers direct manipulation of throttle linkage and throttle plates, whereas the drive by wire system must feed data into a controller and use an electromechanical actuator to provide throttle actuation.

Uses in passenger cars

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 cars because of the availability of high power electrical supplies required for the new electrical actuators.

Throttle by wire

Main article: Electronic throttle control

This system helps accomplish vehicle propulsion by means of an electronic throttle without any cables from the accelerator pedal to the throttle valve of the engine. In electric vehicles, this system controls the electric motors by sensing the accelerator pedal input and sending commands to the power inverter modules.

Brake by wire

Main article: Brake by wire

A pure brake by wire system eliminates the need for hydraulics completely by using motors to actuate calipers and lock the wheels in comparison to the currently existing technology where the system is designed to provide braking effort by building hydraulic pressure in the brake lines.

Shift by wire

Main article: Shift by wire

The direction of motion of the vehicle (Forward, Reverse) is set by commanding the actuators inside the transmission through electronic commands based on the current input from the driver (Park, Reverse, Neutral or Drive).

Steer by wire

This kind of system will provide steering control of a car with fewer mechanical components/linkages between the steering wheel and the wheels. The control of the wheels' direction will be established through electric motor(s) which are actuated by electronic control units monitoring the steering wheel inputs from the driver.

This is currently used in electric forklifts and stockpickers and some tractors. The first production vehicle to implement this was the Infiniti Q50. 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, Saabs Prometheus and the Mazda Ryuga. A rear wheel SbW system by Delphi called Quadrasteer is used on some pickup trucks but has had limited commercial success.

This is not to be confused with Electric Power Steering. Electric Power Steering can be considered as a stage of evolution from mechanical steering to steer by wire systems.

Park by wire

Main article: Park by wire

The parking pawl in a traditional transmission has a mechanical link to the gear lever and locks the transmission in the park position when the vehicle is set in Park. Not to be confused with the parking brake. A park by wire system uses electronic commands to actuate the parking pawl by a motor when the driver puts the vehicle in park.

Safety critical systems

Failures in electronic control units used to implement these drive by wire functionalists can lead to potential hazardous situations where the driver's ability to control the vehicle will depend on the vehicle operating scenario. For example, unintended acceleration, loss of braking, unintended steering, shift in the wrong direction and unintended roll away are some of the known hazards. Implementing drive by wire systems requires extensive testing and validation as is the case when any new technology is introduced.

Recently it has been demonstrated that some of these systems are susceptible to hacking, allowing for external control of the vehicle. While generally such hack demonstrations like remote activation of the horn or windshield wipers/washers fall into the "annoying or amusing" category, other hacks involving the accelerator, brakes, and transmission have a much more serious security and safety implications.

External links

• Missing data compensation for safety-critical components in a drive-by wire system
• Fusion of redundant information in brake-by-wire systems, using a fuzzy Voter
• Position sensing in by-wire brake callipers using resolvers
• GM skateboard drive by wire concept video