Intersecting Shaft

Bevel Gears

Bevel gears are primarily used to transfer power between intersecting shafts. The teeth of these gears are formed on a conical surface. Standard bevel gears have teeth which are cut straight and are all parallel to the line pointing the apex of the cone on which the teeth are based as shown in Figure 15.21. Spiral bevel gears are also available with teeth form arcs. Hypocycloid bevel gears are a special type of spiral gear that will allow non-intersecting, non-parallel shafts to mesh. Straight tool bevel gears are generally considered the best choice for systems with lower speeds. They become noisy above this point. One of the most common applications of bevel gears is the differential in automobiles.

Figure 15.21 Bevel Gears

Limitations: It cannot be used for parallel shafts and becomes noisy at high speeds.

Advantages: It is an excellent choice for intersecting shaft systems.

Hypoid Gears

Hypoid gears resemble spiral bevels, but the axes of the pinion shaft and gear shaft do not intersect (Figure 15.22). This configuration allows both shafts to be supported at both ends. In hypoid gears, the meshing point of the pinion with the driven gear is about midway between the central position of a pinion in a spiral bevel and the extreme top or bottom position of a worm. This geometry allows the driving and driven shafts to continue past each other so that end-support bearings can be mounted. These bearings provide greater rigidity than the support provided by the cantilever mounting used in some bevel gearing.

Figure 15.22 Hypoid Gear

Figure 15.23 Worm Gear

Worm Gears

If a tooth of a helical gear makes complete revolutions on the pitch cylinder, the resulting gear is known as worm. The mating gear is called worm wheel as shown in Figure 15.23. Worm may be single start, double start, or triple start.