As the name implies, all-wheel-drive systems power both the front and rear wheels all the time. But in practice, there are actually two types of drivetrains that are called AWD. One does, in fact, drive all the wheels continuously, and some manufacturers refer to this as full-time AWD. The second, often called part-time AWD or automatic AWD, operates most of the time in two-wheel-drive mode, with power delivered to all four corners only when additional traction control is needed.
How Does All-Wheel Drive Work?
AWD systems, both full-time and part-time, generally operate with no input from the driver, although some offer selectable modes that allow a degree of control over how much power goes where. All the wheels get torque through a series of differentials, viscous couplings and/or multiplate clutches, which help distribute power to the wheels so that the car’s traction is optimized. The vehicle still operates smoothly under normal conditions.