Flexible Shaft Couplings
A flexible shaft coupling is a device that connects two shafts that can transmit torque even if misaligned. In ideal circumstances, shafts are connected by a coupling to form a straight line. However, two shafts can become out of line as the result of poor installation, thermal growth or shrinkage, foundation movement or component wear.
A flexible shaft coupling is needed to connect shafts that are slightly misaligned. In parallel misalignment, two shafts are virtually parallel but slightly offset. In angular misalignment, the shafts intersect at angles to each other. Axial misalignment is a combination of both parallel and angular misalignment. The degree of misalignment a coupling can tolerate depends on its material and its application, but in general, up to 5° of misalignment can be tolerated.
The most common materials for flexible shaft couplings in automobiles are stainless steel, which protects against corrosion and increases torque capacity and strength, and aluminum, which is a lighter and less expensive option. Certain types of flexible shaft couplings contain a central disk comprised of plastic or rubber that transmits torque. Flexible shaft couplings are cylindrical in shape, and vary depending on the different types and their functions.
Flexible shaft couplings are used to connect drive shafts in automobiles; they isolate driveline vibration, propeller pulse, and gear chatter in motorized boats. Other industrial applications include use in printing machines, paper making machines, roll forming machines, hydraulic pumps, and wind turbines.
There are many different kinds of flexible shaft couplings. The Oldham coupling consists of three components: two hubs and a central plastic disk. It accommodates slight parallel misalignment, while providing almost zero backlash. Backlash is the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established. The bellows coupling has two hubs and a thin walled metallic bellows and can accommodate all three types of misalignment.
Single beam couplings are usually made of a single piece of aluminum and have a system of spiral cuts that allow it to bend in order to accommodate angular misalignment. Multiple beam couplings consist of two to three overlapping beams that address problems of torsional rigidity. Jaw, or spider, couplings consist of two metallic hubs, each with a set of interlocking teeth, and a flexible rubber or plastic piece (the spider), in the shape of a star which fits between them.
Jaw couplings have zero backlash and function well at high speeds but do not tolerate a great deal of misalignment. A single disc coupling is composed of two hubs that bend to accommodate angular misalignment. The double disc coupling has two hubs that are connected by an additional center spacer that allows them to bend in opposite directions to manage offset shafts.