WHAT IS DRIVE-BY-WIRE?
Drive-by-Wire is a developing technology based on replacing mechanical or hydraulic control systems with electronic control systems. It's a design philosophy which has been exploited by the aviation industry over the past 20 years.

Currently there are many manufacturers offering throttle systems that use drive-by-wire technology. These Throttle-by-Wire systems replace the traditional cable system between the throttle pedal and the engine's throttle body.

A sophisticated position sensor monitors the pedal position and sends the information to an electronic control unit. The control unit then opens the throttle as required by using an electronic actuator.

A throttle-by-wire system has a number of advantages over the traditional system: fewer moving parts in the system allow the potential for better mechanical reliability.

Benefits also include better engine efficiency due to the fact that the throttle actuation is more closely linked to the engine control systems and other electronic sensors. This also simplifies the process of combining the throttle position with other electronic systems on the car such as ESC, traction control and semi-automatic transmissions.

Other systems can be controlled by wire: Any interface between the driver and car has the potential to benefit from drive-by-wire technology.

Gear-by-wire
Gear selection by wire is already quite common. Several cars have what is commonly referred to as semi-automatic transmission. In a similar way to throttle-by-wire, semi-automatic systems do away with the traditional mechanical linkages.

Gearchanges can be initiated by push buttons, paddles or micro-switched gear levers. The signals are interpreted by the control unit, and gear changes and clutch engagement are made by actuators at the gearbox.

Brake-by-wire
One of the newest technologies of this type is Brake-by-Wire. Several car manufacturers and automotive electronic companies have being developing brake-by-wire systems over the last few years.

The hydraulic lines between the brake master cylinder and the brake calipers are substituted by wires carrying electronic signals. Sensors at the brake pedal determine the force and speed at which the brakes are applied.

A pressure accumulator stores maximum braking pressure at each wheel and depending on the information calculated by the control unit this is applied to the brakes in the safest and most efficient way.

Advantages of drive-by-wire tech
The systems are very complex but offer several advantages. Packaging and build complexity issues are reduced because the lack of physical connection between the components allows many freedoms in their final location.

Many safety benefits are offered from such a system. For example, the electronic systems can predict when heavy braking may be needed by closely monitoring driver inputs. ABS, EBD and ESC become more efficient because they are no longer parallel systems, and features such as applying small amounts of pressure to the brake discs to dry them in wet weather are more easily implemented via the control systems.

By-wire: how safe is it?
Perhaps the biggest issue for the manufacturers to overcome is proving to customers that drive-by-wire technology is safe.

Knowing that the technology has been in operation in aircraft for several years may put some minds at rest, however, the difference between cars and aircraft is the amount of maintenance that they undergo -- manufacturers cannot force customers to have their cars maintained. Thus any critical components such as brakes or steering must be ultra reliable.

Steer-by-wire is under investigation by many automotive companies (Selected BMW and Lexus models currently have 'active' steering functionality though there is still a mechanical connection between driver and steering mechanism) but for obvious reasons is not as easy to implement. The technology to make such a system is available, however, the system must be reliable -- and to allow for poorly maintained cars that means for the life of the vehicle.

'TAKE HOME' FACTS

• Electronic technology which replaces mechanical and hydraulic control systems
• Offers improved mechanical reliability and better integration of electronic systems
• Must be completely reliable for vehicle's useable life

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