A working pressure angle was defined as a function of an rotation angle of noncircular gears

called the Working-Pressure-Angle （WPA） function. A new method for generating noncircular gear pairs was developed. This method

called the Direct-Profile-Design （DPD） method

is to use WPA functions to obtain the desired profiles of generated pairs. The length of a tooth profile normal between the tooth profile and pitch curve was defined as the normal length of a tooth profile. This length is related to WPA by a first order differential equation. The differential equation ensures one tooth profile to be engaged with the other profile. A formula of the curvature radius of a tooth profile was given. This formula can be used to calculate the curvature radius of a tooth profile directly

when a WPA function for a tooth profile is given. As demonstrated

this new method is applicable to any type of gear pairs including circular or noncircular. In addition

by using this method

it is relatively easier to generate new tooth profiles

to investigate the geometrical and mechanical properties of gear pairs

and to realize the desired geometrical and mechanical properties into the design.