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

Types of Drive-by-wire Systems

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.