Shaft Couplings/
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.
