How Drive-by-wire Technology Works

Concept Cars Image Gallery Is drive-by-wire the way of the future for automobiles? See more pictures of concept cars.
AP Photo/Greg Baker

So there you are, settled into your seat as you take hold of the joystick. Pushing the control up moves your vehicle forward, while pushing it side to side steers the car left or right. Ready to go, you jam the throttle forward, gaining speed. Your car accelerates faster and faster -- that is, until you reach the nearest stoplight, where you slow to a stop.

What is this, some kind of boring video game where the rules are to follow the speed limit and normal, everyday laws? Nope. In fact, this situation, one where the driver uses a video game-like joystick or controller, could soon become a reality in the cars that appear on the showroom floor.

A technology known as drive-by-wire, also called "x-by-wire" or simply "by-wire," could change the way people drive. A car with this type of system would rely mainly on electronics to control a wide range of vehicle operations, including acceleration, braking and, as mentioned in our earlier example, steering. Conventional cars mainly use hydraulic and mechanical technology to conduct these same basic vehicle operations, and although the systems are powerful, they can be overly complex, inefficient and conducive to wear and tear over the years.

But over the years, manufacturers and outside researchers and inventors have been integrating computers and electronics into modern cars. If drivers could simply get accustomed to the idea, drive-by-wire systems have the potential to increase comfort, functionality and safety during the drive. Computers and sensors would analyze commands and instruct vehicles on exactly what to do. And by-wire systems have an environmental angle, too, since the technology could improve fuel economy and reduce or improve engine emissions.

The term also might be familiar to aviation enthusiasts, since airplanes have used systems called "fly-by-wire" since the 1990s. That technology, just like drive-by-wire, uses electrical wires to control the normal operations of a plane. How does drive-by-wire in a car work? How can drivers speed up, slow down and steer with just a network of wires? Is it safe, or are there concerns over drive-by-wire systems?

Types of Drive-by-wire Systems

Drive-by-wire systems for accelerating, braking and steering have the biggest potential for reducing mechanical linkage under the hood.
Drive-by-wire systems for accelerating, braking and steering have the biggest potential for reducing mechanical linkage under the hood.
AP Photo/Keystone/Laurent Gillieron

In a typical hydraulic and mechanical system, there's a big tangle of parts that control different aspects of the vehicle's operation. Connected throughout the car is the brake booster, master cylinder, steering column, steering shaft, rack-and-pinion gear, hydraulic lines and various cables and links. These components work together and independently to give us a smooth driving experience. However, they also add weight to the vehicle and a potential for degradation over time.

In a drive-by-wire system, most or all of this would be replaced by electrical wires. In any type of by-wire system, sensors record information and pass data to a computer or a series of computers, which transfer the electrical energy into mechanical motion. There are several different types of drive-by-wire systems, which is why it's sometimes referred to generally as x-by-wire. Here are a few of the main by-wire systems:

  • Throttle-by-wire -- Throttle-by-wire, or accelerate-by-wire, was the first type of drive-by-wire system introduced. These systems use a pedal unit and an engine management system. The pedal uses sensors that measure how much or how little the driver moves the accelerator, and the sensors send that information to the engine management system. The engine management system is a computer that, among other tasks, determines how much fuel is required, and it provides this input to an actuator -- a device that converts energy into mechanical motion. The pedal could be the same pedal drivers have become accustomed to using today, an easy-to-reach pad placed near the foot that's pressed down in order to accelerate the car. The same operation could also be incorporated into a joystick or videogame-like controller, which would get rid of the need for a foot pedal completely. Of course, this would require drivers to use their hands for acceleration, braking and steering.
  • Brake-by-wire -- There are actually two types of brake-by-wire systems. Hydraulic, or "wet," brake-by-wire uses additional hydraulic parts to create pressure on the brakes. Electric, or "dry," brake-by-wire, on the other hand, simply uses an electric motor and no hydraulic brake fluid.
  • Steer-by-wire -- Sensors detect the movements of the steering wheel and send information to a microprocessor. The computer then sends commands to actuators on the axles, which turn according to the driver's directions.

This all sounds pretty good, right? Well, head on over to the next page where we discuss the benefits and the drawbacks of a drive-by-wire system.

Benefits and Drawbacks of Drive-by-wire Systems

Although drive-by-wire offers many benefits to car systems, concerns over reliability have stalled its full acceptance.
Although drive-by-wire offers many benefits to car systems, concerns over reliability have stalled its full acceptance.
AP Photo/Andree-Noelle Pot

Some people are excited about the prospect of more drive-by-wire systems in cars. By replacing conventional throttle systems, drive-by-wire systems can significantly reduce the number of moving parts in a vehicle. This reduces weight, increases operational accuracy and stretches out the time between service visits for things like mechanical maintenance and other adjustments. Some by-wire systems wouldn't even require service at all. Less weight and better accuracy would equal better fuel efficiency and fewer emissions, too.

Sounds great, right? Well, although it's well-established in the airline industry, drive-by-wire has been slow in its introduction to the car. The problem for some car manufacturers is in convincing drivers that the systems are safe. Because of the complexity of drive-by-wire systems, some people worry about potential electronic malfunctions in sensors and computers, leading to vehicle damage or even car accidents and passenger injury.

One argument against drive-by-wire is that any system using software has the ability to fail regardless of how many times that software has been tested. In a worst-case scenario, for example, the sensors on a brake-by-wire system could make an error in calculation, causing the brake caliper and pads to apply an incorrect amount of pressure -- either too light or too strong -- to the rotor. Unaware of any internal system problems, the driver using the brake-by-wire system could potentially get into an accident, even though he or she thought the correct amount of pressure was being placed on the brake pedal.

In any case, most people refer to the saying that any software is only as good as the programmers and manufacturers who built and designed it. Because of the reliability of fly-by-wire in airplanes, it's likely that experience and product testing could bring more drive-by-wire systems safely to everyday cars. Several car companies are already using (or have used) various drive-by-wire systems in use their vehicles, including BMW, Mercedes-Benz, Land Rover, Toyota, GM, Volkswagen and Nissan.

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