Spur Gears with Curved Directrix: Diversity and Methods of Generation. A Patent Study

Gear wheels and mechanisms deploying spur gears have been known since antiquity.Leonardo da Vinci's studies on gears are also exciting.Although there is no explicit information about how gears were cut in the ancient and medieval world, it is unanimously accepted that tooth profiles were not generated kinematically.The modern period is characterized by machines and movement, and gears are practically ubiquitous.Among the cylindrical gears, the most frequently used ones are those with straight directrix and those with helical cylindrical gears (cylindrical gears with inclined teeth), both types being rectifiable.Monographs or specialized treatises are rare that even mention that cylindrical gears can also have curved teeth, i.e. curved directrix to the associated reference rack.In the last five decades, and only sporadically before, explicit interests in and achievements emerged related to cylindrical gears with curved directrices, relevant in this sense being patents and doctoral theses.Most of the works mainly concern cylindrical teeth with involute and circular directrix, as well as methods and machines for their machining.At the limit, cambered teeth can also be considered cylindrical teeth with curved directrix.Cylindrical gears with poly-hypocycloid directrix and corresponding machining methods are a subject initiated by Professor Emil Botez and addressed exclusively by researchers from the Politehnica University of Bucharest.Romanian researchers are actively contributing to furthering knowledge about various cylindrical gear with curved directrices and their manufacturing methods.