This example will compare a traditional planetary bevel gearbox (left) with a hypoid gearbox (right), in a 5:1 gear reduction ratio.
Planetary Bevel Gearbox
By construction, a planetary bevel gearbox is the combination of an input bevel gear stage and an output planetary gear stage. In order to achieve any gear reduction ratio, this type of gearbox always requires two or three gear stages. In this example, the first stage is a 1:1 bevel gear ratio and the second stage is a 5:1 planetary gear ratio. For a 3,000 RPM application, the motor speed is continued throughout the entire first gear stage, which means the input bearings and seals, gears, and output bearings and seals are all rotating at 3,000 RPM. The actual reduction doesn't occur until the planetary gear stage. Higher speeds throughout the gearbox means higher heat and can also result in a 50% service life de-rating for continuous applications.
A hypoid gearbox on the other hand can achieve up to a 15:1 ratio with only a single gear stage. In this 3,000 RPM application, the motor speed is immediately reduced to the final reduction speed of 600 RPM which is ideal for the gears, seals, bearings, and shaft. A lower speed means less heat, which is important to maximizing the life and load carrying capabilities of the output bearings in a gearbox. GAM’s Dyna Series hypoid gearbox has a 30,000 hour service life rating which is 50% more than a comparable planetary bevel gearbox. In addition to the performance advantages of using a hypoid gearbox, as mentioned in a previous post there is also a substantial space saving benefit. In the example above, GAM’s hypoid gearbox is 46% more compact than the planetary bevel gearbox.