On the surface, it may seem 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 output speed reduced and/or torque improved, gears are commonly used to accomplish the required result. Gear “reduction” specifically refers to the quickness of the rotary machine; the rotational velocity of the rotary machine is certainly “reduced” by dividing it by a gear ratio greater than 1:1. A gear ratio greater than 1:1 is usually achieved whenever a smaller equipment (reduced size) with fewer number of tooth meshes and drives a more substantial gear with greater amount of teeth.
Gear reduction gets the opposite effect on torque. The rotary machine’s output torque is increased by multiplying the torque by the gear ratio, less some effectiveness losses.
While in lots of applications gear decrease reduces speed and increases torque, in other applications gear reduction is used to increase speed and reduce torque. Generators in wind generators use gear decrease in this manner to convert a relatively slow turbine blade quickness to a higher speed capable of generating electricity. These applications use gearboxes that are assembled opposite of these in applications that reduce speed and increase torque.
How is gear decrease achieved? Many reducer types can handle attaining gear reduction including, but not limited by, parallel shaft, planetary and right-angle worm gearboxes. In parallel shaft gearboxes (or reducers), a pinion gear with a certain number of teeth meshes and drives a larger gear with a greater number of teeth. The “reduction” or equipment ratio is certainly calculated by dividing the number of tooth on the large equipment by the number of teeth on the tiny gear. For example, if a power motor drives a 13-tooth pinion gear that meshes with a 65-tooth gear, a reduction of 5:1 is achieved (65 / 13 = 5). If the electrical motor speed is usually 3,450 rpm, the gearbox reduces this velocity by five moments to 690 rpm. If the engine torque can be 10 lb-in, the gearbox boosts this torque by one factor of five to 50 lb-in (before subtracting out gearbox performance losses).
Parallel shaft gearboxes many times contain multiple gear sets thereby increasing the apparatus reduction. The full total gear decrease (ratio) is determined by multiplying each individual equipment ratio from each equipment established stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear models, the full total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric electric motor would have its rate reduced to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric engine torque would be increased to 600 lb-in (before efficiency losses).
If a pinion gear 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 main function is to improve the direction of rotation instead of reduce the speed or boost the torque.
Calculating the gear ratio in a planetary equipment reducer is much less intuitive as it is dependent upon the amount of teeth of the sun and ring gears. The planet gears become idlers and don’t affect the apparatus ratio. The planetary gear ratio equals the sum of the number of teeth on the sun 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 has a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear models can perform ratios from about 3:1 to about 11:1. If more gear reduction is needed, additional planetary stages may be used.
The gear reduction in a right-angle worm drive would depend 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 provides 50 the teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).
When a rotary machine such as an engine or electric electric motor cannot provide the desired output rate or torque, a equipment reducer may provide a good solution. Parallel shaft, planetary, right-angle worm drives are normal gearbox types for attaining gear reduction.