A driveshaft is a steel shaft that transmits power in the form of torque from the transmission to the wheels on a vehicle. In an automobile, two driveshafts must be connected by a shaft coupling before power can be transmitted. Shaft couplings provide secure connections between shafts, wheels, and rotary equipment. In addition, flexible shaft couplings are used to prevent misalignment, which can be caused by an unbalanced or bent shaft.
Driveshafts range in length and diameter and consist of a shaft with an assembly on either end. They are most commonly used in automobiles to transfer the power from the transmission to the wheels either through a differential or directly to the wheels, depending on whether the car is front wheel drive, all wheel drive, or rear wheel drive. In a four wheel drive vehicle, two piece driveshafts are often used and are connected with a universal joint. Driveshafts are also used in motorcycles as an alternative to chain and belt drives; their function in motorized boats is to connect the transmission inside the vessel directly to the propeller. Driveshafts are also often components in semi-trucks, oil rigs, sewage treatment facilities, windmills, irrigation systems, paper mills, tractors, and other industrial and agricultural heavy machinery.
Driveshafts are usually hollow but large in diameter so that they are strong enough to bear torsion and shear stress, while avoiding too much additional weight. Typically, high carbon steel is used in the manufacturing of driveshafts, although this material is very heavy. Aluminum and steel alloys are being experimented with because they are a strong and lightweight alternative. New advancements in composite technology are developing alternatives to driveshaft materials. The most common polymer matrix composites are fiberglass, carbon fiber, and carbon fiberglass hybrids. Composites are preferable over steel because they can operate at higher rotations per minute than steel of the same dimensions. However, the strengths of some composites are weaker than steel, and therefore more research is needed to make composite drive shafts widely available. The most common construction methods for these important devices are similar to bellow couplings and include electroforming, chemical deposition, mechanical forming and welding. Electroformed drive shafts are made by adding layers of metal on a mandrel until the desired thickness is reached and the mandrel is melted away to leave behind the shaft. Chemical deposition is a similar method except that the materials are added by electrodeposition. Mechanical forming includes roll-forming or extrusion. Welded drive shafts are made by welding a series of rings or washers on both the inside and outside until smooth and seamless.