Drive Shafts
A drive shaft 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 drive shafts 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. The most common use of drive shafts is in automobiles. They 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 drive shafts are often used and are connected with a universal joint. Drive shafts 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. Drive shafts 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.
Drive shafts 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 drive shafts, although this material is very heavy. Aluminum/steel alloys are being experimented with because they are a strong and lightweight alternative. New advancements in composite technology are developing alternatives to drive shaft 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 RPM's 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.