On the surface, it may appear that gears are being “reduced” in quantity or size, which is partially true. Whenever a rotary machine such as an engine or electric motor needs the result speed reduced and/or torque improved, gears are commonly utilized to accomplish the desired result. Gear “reduction” specifically refers to the rate of the rotary machine; the rotational speed of the rotary machine is usually “decreased” by dividing it by a gear 
ratio higher than 1:1. A gear ratio greater than 1:1 can be achieved when a smaller equipment (reduced size) with fewer amount of tooth meshes and drives a larger gear with greater number of teeth.
Gear reduction has the opposite effect on torque. The rotary machine’s result torque is improved by multiplying the torque by the gear ratio, less some efficiency losses.
While in many applications gear reduction reduces speed and improves torque, in various other applications gear reduction is used to increase speed and reduce torque. Generators in wind turbines use gear decrease in this fashion to convert a comparatively slow turbine blade speed to a high speed capable of generating electricity. These applications use gearboxes that are assembled opposite of these in applications that decrease speed and increase torque.
How is gear reduction achieved? Many reducer types can handle attaining gear decrease including, but not limited to, parallel shaft, planetary and right-angle worm gearboxes. In parallel shaft gearboxes (or reducers), a pinion gear with a specific number of tooth meshes and drives a more substantial gear with a lot more teeth. The “reduction” or gear ratio is certainly calculated by dividing the number of teeth on the large equipment by the number of teeth on the small gear. For example, if an electric motor drives a 13-tooth pinion equipment that meshes with a 65-tooth equipment, a reduction of 5:1 is definitely achieved (65 / 13 = 5). If the electrical motor speed is usually 3,450 rpm, the gearbox reduces this swiftness by five occasions to 690 rpm. If the electric motor torque is 10 lb-in, the gearbox raises this torque by a factor of five to 50 lb-in (before subtracting out gearbox efficiency losses).
Parallel shaft gearboxes often contain multiple gear units thereby increasing the gear reduction. The full total gear reduction (ratio) depends upon multiplying each individual equipment ratio from each equipment established stage. If a gearbox contains 3:1, 4:1 and 5:1 gear sets, the full total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric electric motor would have its velocity decreased to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric electric motor torque would be increased to 600 lb-in (before effectiveness losses).
If a pinion equipment and its mating gear have the same amount of teeth, no reduction occurs and the gear ratio is 1:1. The gear is called an idler and its primary function is to improve the direction of rotation instead of decrease the speed or raise the torque.
Calculating the gear ratio in a planetary gear reducer is less intuitive as it is dependent upon the number of teeth of sunlight and band gears. The planet gears act as idlers and don’t affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on sunlight and ring gear divided by the number of teeth on the sun gear. For instance, a planetary arranged with a 12-tooth sun gear and 72-tooth ring gear includes a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear units can achieve ratios from about 3:1 to about 11:1. If more gear reduction is needed, additional planetary stages can be used.
The gear decrease in a right-angle worm drive is dependent on the number of threads or “starts” on the worm and the number of teeth on the mating worm wheel. If the worm has two begins and the mating worm wheel offers 50 the teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Whenever a rotary machine such as for example an engine or electric electric motor cannot provide the desired output velocity or torque, a gear reducer may provide a great choice. Parallel shaft, planetary, right-position worm drives are common gearbox types for achieving gear reduction.