Internal Gears

Internal Gears

Internal Gears - Internal gears have teeth on their inner surface. This type may have spur, bevel or helical teeth. Fig shows external and internal gears. Whereas, meshed external teeth gears rotate in the opposite direction, in a combination of one external and one internal gear, they rotate in the same direction. Moreover, centre to centre distance in this case is also less.

Gears with External Teeth	Gears with internal Teeth
A - Axial Distance	B - Axial Distance

Other advantages in combining internal and external gears is their compactness. Since the centers of the gears are closer together, less space is required. They also possess increased operational efficiency: more teeth are in mesh the tooth lines curve in the same direction and friction is reduced.