Involutprofil

Involutprofil, or involute profile, is the tooth geometry used on most spur and helical gears. It is based on the involute of a circle, a curve traced when a taut string is unwound from a base circle. The involute profile has the key property that when two gears with such teeth mesh, the contact point lies on a common line of action that is tangent to both base circles. This yields favorable transmission characteristics and enables consistent tooth engagement during rotation.

In gear design terms, each gear has a pitch circle, with radius rp, and a base circle, with radius rb = rp cos φ, where φ is the pressure angle. For involute teeth, the line of action follows a fixed direction relative to the gear axes, so the instantaneous center of rotation moves along this line as the gears rotate. The resulting gear ratio, determined by the pitch radii, remains essentially constant over the contact path, which is a primary reason for the widespread use of the involute form in mechanical transmissions.

Manufacturing and standards: The involute profile can be generated by rack-cutting or by using hob cutters designed to produce the involute shape. Standard gear specifications (ISO/DIN) define parameters such as pressure angle (commonly 20°), module or diametral pitch, addendum, and dedendum. The involute form allows straightforward cutting and mating of gears with constant velocity ratios and is compatible with a variety of mounting arrangements and center distances.

Applications and limitations: Involute gears are used in automotive, industrial, and precision machinery due to smooth meshing and reliable performance. Limitations include potential undercut for gears with few teeth and sensitivity to manufacturing tolerances, misalignment, and excessive backlash, which can affect contact quality and efficiency.