A drive shaft, also known as a propeller shaft or Cardan shaft, is a mechanical part that translates the torque generated by a vehicle's engine into usable motive force to propel the vehicle. Physically, it is tubular in design, with an outside metal housing that protects an interior metal cylinder, which spins at a frequency governed by engine output. Depending on the engine and drive configuration of a vehicle, be it automobile, boat, or motorcycle, one or more drive shafts may work cooperatively to turn engine power into motion.
In modern front-engine, rear-wheel drive (RWD) automobiles, a system known as Hotchkiss drive incorporates a long drive shaft running the length of the car, and a differential — connected by universal joints at both ends — to direct engine torque to the powered wheels at the back. Two short metal tubes called half-shafts then connect the wheels to the differential. By way of differentiation, the longitudinal shaft that runs from the transmission is sometimes called the propeller, or prop shaft. The use of universal or 'U' joints is unique to the Hotchkiss design, and allows much greater flexibility of the drive shaft, and more room by the rear axle for suspension parts.
In a front-wheel drive (FWD) vehicle, two drive shafts emanate from the transmission, connecting to each front wheel. As opposed to U-joints, drive shafts on FWD cars usually have constant-velocity or CV joints that allow for articulation of the wheels. CV joints are generally more flexible and require less frequent maintenance than U-joints, making them more suitable for FWD applications, where the wheels that receive power are also the ones responsible for steering.
Drive shaft configurations for all wheel drive (AWD) vehicles vary depending on the make and model of car. Some base their AWD systems on RWD designs, while others build upon FWD. It is common to see heavier AWD vehicles, such as trucks and sport-utility vehicles (SUVs), use RWD-based configurations, while AWD cars and wagons use FWD-based configurations. RWD-based AWD systems typically incorporate a transfer case at some point behind the transmission, which serves as a junction to distribute power to the wheels through multiple drive shafts. FWD-based AWD systems are housed up front, near the transmission, with a single shaft running down to the back wheels.
In other kinds of vehicles, the principles of using this part remain much the same as in cars. In terms of design, they are markedly simpler on motorcycles, and serve as a more robust but less efficient alternative to chain drives. In powered boats, the prop shaft operates in much the same way as in cars, save the obvious difference of connecting the transmission to a propeller instead of wheels.