On the surface, it could seem that gears are being “reduced” in quantity or size, which is partially true. When a rotary machine such as an engine or electric motor needs the output speed decreased and/or torque improved, gears are commonly used to accomplish the required result. Gear “reduction” specifically refers to the rate of the rotary machine; the rotational quickness of the rotary machine is “reduced” by dividing it by a gear ratio higher than 1:1. A gear ratio greater than 1:1 can be achieved whenever a smaller gear (reduced size) with fewer quantity of teeth meshes and drives a more substantial gear with greater number of teeth.
Gear reduction gets the opposite influence on torque. The rotary machine’s output torque is improved by multiplying the torque by the gear ratio, less some efficiency losses.
While in many applications gear reduction reduces speed and boosts torque, in other applications gear reduction is used to improve rate and reduce torque. Generators in wind generators use gear reduction in this manner to convert a relatively slow turbine blade rate to a higher speed capable of generating electricity. These applications make use of gearboxes that are assembled reverse of these in applications that reduce rate and increase torque.
How is gear decrease 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 certain number of teeth meshes and drives a more substantial gear with a greater number of teeth. The “reduction” or equipment ratio is calculated by dividing the number of tooth on the large gear by the number of teeth on the small gear. For instance, if an electric motor drives a 13-tooth pinion equipment that meshes with a 65-tooth equipment, a reduction of 5:1 is achieved (65 / 13 = 5). If the electric motor speed is usually 3,450 rpm, the gearbox reduces this speed by five occasions to 690 rpm. If the engine torque is usually 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 models thereby increasing the apparatus reduction. The total gear decrease (ratio) is determined by multiplying each individual equipment ratio from each gear arranged stage. If a gearbox contains 3:1, 4:1 and 5:1 gear sets, the total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric engine would have its quickness decreased to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric electric motor torque would be risen to 600 lb-in (before performance losses).
If a pinion gear and its mating gear have the same amount of teeth, no decrease occurs and the apparatus ratio is 1:1. The gear is called an idler and its own principal function is to improve the path of rotation rather than decrease the speed or raise the torque.
Calculating the apparatus ratio in a planetary equipment reducer is much less intuitive as it is dependent upon the number of teeth of the sun and ring gears. The earth gears act as idlers and do not affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on the sun and ring equipment 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 equipment ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear models can achieve ratios from about 3:1 to about 11:1. If more equipment reduction is necessary, additional planetary stages may 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 amount of teeth on the mating worm wheel. If the worm has two starts and the mating worm wheel has 50 tooth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Whenever a rotary machine such as an engine or electric motor cannot supply the desired output acceleration or torque, a equipment reducer may provide a good solution. Parallel shaft, planetary, right-position worm drives are normal gearbox types for achieving gear reduction.