Drive-by-wire is a catch-all term that refers to a number of electronic systems that either augment or replace traditional mechanical controls. Instead of using cables or hydraulic pressure to control a vehicle, drive-by-wire technology uses electronic systems to activate brakes, control steering, and fuel the engine.
There are three main driving components that drive-by-wire systems typically replace with electronic controls: throttle, brakes, and steering. These systems are typically referred to as:Electronic Throttle ControlBrake-By-WireSteer-By-Wire
Electronic Throttle Control
The most common form of drive-by-wire technology and the easiest to find in the wild is electronic throttle control. Unlike traditional throttle controls that couple the gas pedal and throttle with a mechanical cable, these systems use a series of electronic sensors and actuators.
Vehicles with computerized fuel controls have used throttle sensors for decades. These sensors tell the computer the position of the throttle, but the throttle itself is still activated by a physical cable. In vehicles that use true electronic throttle control (ETC), there is no physical connection between the gas pedal and the throttle. Instead, the gas pedal sends a signal that causes an electromechanical actuator to open the throttle.
This is often seen as the safest type of drive-by-wire technology, as it is exceedingly easy to implement this kind of system with a fool-proof, fail-safe design. In the same way that the throttle will simply close if a mechanical throttle cable brakes, electronic throttle control systems can be designed so that the throttle closes if it is no longer receiving a signal from the pedal sensor.
Brake-by-wire technology is seen by some as more dangerous than electronic throttle control because it involves removing the physical connection between the driver and the brakes. However, brake-by-wire is actually a spectrum of technologies that range from electro-hydraulic to electromechanical systems, and both can be designed with fail-safes in mind.
Traditional hydraulic brakes make use of a master cylinder, as well as several slave cylinders. When the driver pushes down on the brake pedal, it applies physical pressure to the master cylinder. In most cases, that pressure is amplified by a vacuum or hydraulic brake booster. The pressure is then transmitted via brake lines to the brake calipers or wheel cylinders.
Anti-lock brake systems were early precursors of modern brake-by-wire technologies, in that they allowed the brakes of a vehicle to be pulled automatically with no driver input. This is accomplished by an electronic actuator that activates the existing hydraulic brakes. A number of other safety technologies have also been built on this foundation. Electronic stability control, traction control, and automatic braking systems all depend on ABS and are peripherally related to brake-by-wire technology.
In vehicles that use electro-hydraulic brake-by-wire technology, the calipers located in each wheel are still hydraulically activated. However, they are not directly coupled to a master cylinder that is activated by pushing on the brake pedal. Instead, pushing on the brake pedal activates a series of sensors. The control unit then determines how much braking force is required at each wheel and activates the hydraulic calipers as needed.
In electromechanical brake systems, there is no hydraulic component at all. These true brake-by-wire systems still use sensors to determine how much brake force is required, but that force is not transmitted via hydraulics. Instead, electromechanical actuators are used to activate the brakes located in each wheel.
Most vehicles use a rack-and-pinion unit or worm-and-sector steering gear that is physically connected to the steering wheel. When the steering wheel is rotated, the rack-and-pinion unit or steering box also turns. A rack-and-pinion unit can then apply torque to the ball joints via tie rods, and a steering box will typically move the steering linkage via a pitman's arm.
In vehicles that are equipped with steer-by-wire technology, there is no physical connection between the steering wheel and the tires. In fact, steer-by-wire systems don't technically need to use steering wheels at all. When a steering wheel is used, some type of steering feel emulator is typically used to provide the driver with feedback.
What Vehicles Already Have Drive-By-Wire Technology?
Tesla has vehicles that come very close to full drive by wire and they clearly are pushing the envelope as hard as they can to get them approved for autonomous use.
There are no fully drive-by-wire production vehicles, but a number of manufacturers have built concept vehicles that fit the description. General Motors demonstrated a drive-by-wire system in 2003 with its Hy-Wire concept, and Mazda's Ryuga concept also used the technology in 2007. Drive-by-wire can be found in equipment like tractors and forklifts, but even cars and trucks that feature electronic power steering still have physical steering linkages.
Electronic throttle control is far more prevalent, and a variety of makes and models make use of the technology. Brake-by-wire can also be found in production models. Two examples of the technology are Toyota's Electronic Controlled Brake and Mercedes Benz's Sensotronic.
Exploring the Future of Drive-by-Wire
Safety concerns have slowed the adoption of drive-by-wire technologies. Mechanical systems can and do fail, but regulatory authorities still see them as being more reliable than electronic systems. Drive-by-wire systems are also more expensive than mechanical controls due to the fact that they are significantly more complex.
However, the future of drive-by-wire technology could lead to a number of interesting developments. The removal of mechanical controls could allow automakers to design vehicles that are radically different from the cars and trucks that are on the road today. Concept cars like the Hy-Wire have even allowed the seating configuration to be moved around since there are no mechanical controls that dictate the position of the driver.
Drive-by-wire technology could also be integrated with driverless car technology, which allows vehicles to be operated remotely or by a computer. Current driverless car projects use electromechanical actuators to control steering, braking, and acceleration, which could be simplified by connecting directly to drive-by-wire technology.