Bevel and Hypoid gear terminology
Cone and tooth height parameters
See figure below for geometry parameters related to the tooth height, face width, the different cones (pitch, face and root) and the pitch cone apex distance relative to the crossing point. Please note that all cone apexes are located at the same point - at the pitch cone apex. Hence, the face and root angles can be calculated from pitch cone angle, mean cone distance, mean addendum and mean dedendum values.
Spiral Angle
An (ideal) logarithmic tooth shape function is used which gives constant spiral angle throughout the lengthwise tooth direction, see below. that is, the inner, mean and outer spiral angle values are the same. Hence, the user specifies only one value - the mean spiral angle.
Tooth section profile
An involute tooth profile function is used where the user specifies a mean normal pressure angle (αn) at the pitch radius, which is used both on drive and coast flank side. Below the mean transverse pressure angle (αt) is shown,
Hand of spiral angle and hypoid offset
The sign of the hypoid offset and the hand of the spiral angle of the gears have to match each other in order to properly assemble the pair. When viewing a hypoid gear pair in such way that the pinion gear is located at the right and the wheel gear cone is pointing out from picture, the following applies:
■If the pinion axis is located below the wheel axis as in the left case (the hypoid offset is a positive value), the wheel gear spiral angle has to be right hand sided while the pinion gear has to be left hand sided.
■If the pinion axis is located above the wheel axis as in the right case (the hypoid offset is a negative value), the wheel gear spiral angle has to be left hand sided while the pinion gear has to be right hand sided.
