Gear couplings offer efficient torque transmission in a compact mechanism and permit a high degree of axial movement. However, gear couplings require piloting and may malfunction at very high or very low torques. Crowned tooth flanks allow angular displacement to occur between each gear. Two coaxial shafts can also be connected by a single joint gear coupling, known as a gear-type flexible or flexible coupling. Slight misalignments of 0.5° to 5° are tolerated by this type of gear coupling.
Gear couplings and universal joints are used in similar applications, most predominantly in the automobile industry. While gear couplings have higher torque density, universal joints induce lower vibration than gear couplings. The gear teeth in a gear coupling have high backlash, which can contribute to vibration, to allow for angular misalignment. Gear couplings are found in all rear-wheel and four-wheel driven passenger cars.
In a gear coupling, the two shafts being joined meet in the third shaft which contains gears. The teeth interlock with each other to rotate and, in doing so, they transfer torque, power and energy. Every gear coupling has differing stall speeds, which is the highest speed that the gears can turn when maximum input power is applied. Flexible shaft couplings such as gear couplings are necessary because during operation, some types of shafts tend to shift, causing misalignment.
Shaft movement is caused by bumps or vibration and it results in parallel, angular or skewed shaft misalignment. Flexible shaft couplings provide efficient accommodation for moderate shaft misalignment that occurs when the shafts’ axes of rotation become skewed. There are many different kinds of shaft couplings. 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. The Oldham coupling consists of three components: two hubs and a central plastic disk. It accommodates slight parallel misalignment, while providing almost zero backlash.