ABSTRACT
Internal involute gearings are used to transmit a rotation from a driving shaft to the driven shaft when the axes of the rotations are parallel to one another. The vector diagram of an internal gear pair is illustrated in this chapter. An internal gear pair is composed of an external pinion and internal gear. Internal parallel-axes gear pairs composed of helical involute gears are extensively used in the industry. For special applications, internal parallel-axes gear pair composed of herringbone involute gears are designed. The chapter provides examples for internal spur involute gear and application of internal gears. The set of three conditions to fulfill in order to transmit a uniform rotation by means of internal parallel-axes gears is identical to that of external gearings; that is: the condition of contact; the condition of conjugacy; the equality of base pitches of a gear and a mating pinion to the operating base pitch of the gear pair.
