Screw gears (crossed helical gears) | hyperboloid gears | hypoid gears

In this video, we take a closer look at screw gears. Screw gears, also known as hyperboloid gears, are a special variant of helical gears. In contrast to conventional helical gears, the gear axes of screw gears can be arranged at any angle to each other. The transmission ratio of screw gears depends not only on the number of teeth, but also on the helix angles.

The meshing of the screw gears is a screw movement with constant sliding of the flanks. Lubrication is crucial, as high lateral forces and flank loads occur. Screw gears are suitable for medium forces and speeds.

The basic bodies of screw gears are so-called rotational hyperboloids. A hyperboloid is obtained by rotating a skewed straight line around an axis of rotation. This straight line is then used to create the flank profile of the mating gear by rotating the straight line around the axis of rotation of the mating gear. The flanks of the gears then touch on this straight line.

It is also possible to use the upper part of the hyperboloid for the design of the flanks. In this case, the screw gears are conical. This is referred to as a screw bevel gear, also known as a hypoid gear. In contrast to conventional bevel gears, in which the axes of the ring gear and pinion intersect at a common point, a shaft offset can also be realized with screw bevel gears. Such a gearbox is then also referred to as a hypoid gearbox.

Due to the stronger helix of the teeth with a positive offset, several teeth are in mesh at the same time (large overlap ratio). As a result, not only can higher torques be transmitted than with normal bevel gears, but noise levels are also significantly lower. Hypoid gears are used, for example, in differentials.

00:00 Hyperboloid gears (cylindrical screw gears)
01:26 Properties of screw gears
02:35 Hypoid gears (screw bevel gears)
04:05 Advantages of hypoid gears