More than three-quarters of all passenger cars produced today have automatic transmissions, and almost all of those have torque converters. The advantages of a torque converter are well documented, if somewhat misunderstood.
Torque converters allow a car to start and stop without user intervention. It is this feature that makes an automatic truly "automatic," and the main reason that torque converters are used.
In the moments before full engagement, torque converters act as a sort of continuously variable transmission. This torque multiplication means that a vehicle so equipped can accelerate faster and smoother than one with a clutch.
Because torque converters are very heavy, they tend to act as a sort of inertial flywheel. This flywheel effect means that vehicles with torque converters have a steadier idle and smoother operation than clutch cars.
To a point, a torque converter can slip almost indefinitely without damage. This compares sharply with a manual transmission's tendency to burn clutches if allowed to slip too much.
Torque converters hold several quarts of transmission fluid, and can help to decrease transmission overheating by providing a source of cool fluid when required.
