Chapter: Mechanical : Maintenance Engineering : Repair Methods For Basic Machine Elements
Gears or cogwheel
Gears
• A gear
or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh
with another toothed part in order to transmit torque, in most cases with teeth
on the one gear being of identical shape, and often also with that shape on the
other gear. Two or more gears working in tandem are called a transmission and
can produce a mechanical advantage through a gear ratio and thus may be
considered a simple machine. Geared devices can change the speed, torque, and
direction of a power source. The most common situation is for a gear to mesh
with another gear; however, a gear can also mesh with a non-rotating toothed
part, called a rack, thereby producing translation instead of rotation.
• The
gears in a transmission are analogous to the wheels in a crossed belt pulley
system. An advantage of gears is that the teeth of a gear prevent slippage.
• When
two gears mesh, and one gear is bigger than the other (even though the size of
the teeth must match), a mechanical advantage is produced, with the rotational
speeds and the torques of the two gears differing in an inverse relationship.
• In transmissions which offer multiple gear ratios, such as bicycles, motorcycles, and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when the gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission
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