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 output speed decreased and/or torque increased, gears are commonly utilized to accomplish the desired result. Gear “reduction” particularly refers to the velocity of the rotary machine; the rotational swiftness of the rotary machine is certainly “decreased” by dividing it by a gear ratio higher than 1:1. A gear ratio greater than 1:1 is achieved when a smaller gear (reduced size) with fewer quantity of the teeth 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 effectiveness losses.
While in many applications gear reduction reduces speed and boosts torque, in various other applications gear reduction is used to increase speed and reduce torque. Generators in wind turbines use gear decrease in this manner to convert a comparatively slow turbine blade quickness to a high speed capable of generating electricity. These applications make use of gearboxes that are assembled opposing of those in applications that decrease speed and increase torque.
How is gear decrease achieved? Many reducer types are capable of attaining gear decrease including, but not limited by, parallel shaft, planetary and right-angle worm gearboxes. In parallel shaft gearboxes (or reducers), a pinion gear with a specific number of teeth meshes and drives a larger gear with a lot more teeth. The “reduction” or gear ratio is calculated by dividing the number of the teeth on the large equipment by the number of teeth on the tiny gear. For instance, if an electric motor drives a 13-tooth pinion equipment that meshes with a 65-tooth gear, a reduced amount of 5:1 is achieved (65 / 13 = 5). If the electric motor speed is 3,450 rpm, the gearbox reduces this speed by five situations to 690 rpm. If the motor torque is usually 10 lb-in, the gearbox boosts this torque by a factor of five to 50 lb-in (before subtracting out gearbox effectiveness losses).
Parallel shaft gearboxes often contain multiple gear models thereby increasing the apparatus reduction. The total gear reduction (ratio) depends upon multiplying each individual equipment ratio from each equipment set stage. If a gearbox includes 3:1, 4:1 and 5:1 gear units, the full 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 reduced to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric engine torque would be increased to 600 lb-in (before effectiveness losses).
If a pinion gear and its mating gear have the same number of teeth, no decrease occurs and the gear ratio is 1:1. The apparatus is called an idler and its own primary function is to change the direction of rotation rather than reduce the speed or increase the torque.
Calculating the apparatus ratio in a planetary equipment reducer is less intuitive as it is dependent upon the number of teeth of the sun and band gears. The earth gears act as idlers and don’t affect the gear ratio. The planetary equipment ratio equals the sum of the number of teeth on sunlight and ring gear divided by the number of teeth on sunlight gear. For example, a planetary set with a 12-tooth sun gear and 72-tooth ring gear has a equipment 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 necessary, additional planetary stages may be used.
The gear decrease in a right-angle worm drive is dependent on the amount of threads or “starts” on the worm and the amount of teeth on the mating worm wheel. If the worm has two begins and the mating worm wheel has 50 teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Whenever a rotary machine such as for example an engine or electric motor cannot provide the desired output velocity or torque, a equipment reducer may provide a good solution. Parallel shaft, planetary, right-angle worm drives are normal gearbox types for achieving gear reduction.