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There are a few general types of gearboxes, including planetary, spur/helical gear and worm gear. Each has advantages and applications for which they are best suited. The most common type for mobile and off-highway machinery is the planetary drive. These consist of a center “sun” gear with three or more circumferential “planet” gears, which in turn are surrounded by a ring gear. Planetary gearboxes are robust and capable of holding high radial loads, especially when the load is correctly centered. This is why they’re often found in wheel drive applications. Spur- or helical-gear style gearboxes use two or more gears meshed side by side, and are often used in industrial applications, such as a rolling mill. Their size and possible gear ratios vary widely, with the upper end of torque capacity only limited by the size of gears able to be manufactured. These types of gearboxes can have input and output shafts on either the same or opposing sides. Also quite popular are worm gear style gearboxes. They employ a helical axial input shaft, which directs force across a perpendicular gear ring that is attached to the output shaft. Operation is always with input and output 90° from each other. Worm gear units are generally light to medium duty. Gearboxes are applied to either increase torque or increase speed, and it should be clear that increasing one decreases the other. When used to increase torque, they can achieve this at ratios anywhere from 2:1 relative to input torque, to 10,000:1 or more … which of course would slow the output speed drastically. When used to increase speed, sometimes planetary or helical/ spur gearboxes can be used in reverse. A common use for overdriven gearboxes is for pump drives. A 1,000-rpm PTO speed doesn’t take advantage of a hydraulic pump capable of 3,000 rpm, so a speedincreasing gearbox/pump mount would allow for the use of a smaller pump. Please note, worm gear reducers do not allow input energy at their output shaft.



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Fluid Power Handbook 2016  

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Fluid Power World Handbook 2016

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