Editing Involute gear (section)

==Types of involute gears==
Most common stock gears are spur gears with straight teeth. Most gears used in higher-strength applications are helical involute gears where the spirals of the teeth are of different handedness, and the gears rotate in opposite directions. Studies have also been performed on gears having teeth with a non-involute curve profile.<ref>{{Cite journal |last=Liu |first=Lei |last2=Meng |first2=Fei |last3=Ni |first3=Jiale |date=2019-10-01 |title=A novel non-involute gear designed based on control of relative curvature |url=https://www.sciencedirect.com/science/article/pii/S0094114X19306664 |journal=Mechanism and Machine Theory |language=en |volume=140 |pages=144–158 |doi=10.1016/j.mechmachtheory.2019.05.022 |issn=0094-114X|url-access=subscription }}</ref><ref>{{Cite web |title=Non-Involute Gearing, Function and Manufacturing Compared to Established Gear Designs {{!}} Gear Technology Magazine |url=https://www.geartechnology.com/articles/22109-non-involute-gearing-function-and-manufacturing-compared-to-established-gear-designs |access-date=2023-02-01 |website=www.geartechnology.com |language=en}}</ref><ref>{{Cite patent|number=US5271289A|title=Non-involute gear|gdate=1993-12-21|invent1=Jr|inventor1-first=Meriwether L. Baxter|url=https://patents.google.com/patent/US5271289A/en}}</ref>

Helical involute gears are typically only used in limited situations where the spirals of the teeth are of the same handedness, the spirals of the two involutes are of different handedness, and the line of action is the external tangents to the base circles (analogous to a normal belt drive, whereas normal gears are analogous to a crossed-belt drive), and the gears rotate in the same direction,<ref>Professor Jacques Maurel, "Paradoxical Gears", http://www.jacquesmaurel.com/gears</ref> such as can be used in [[limited-slip differential]]s {{clarify|date=March 2017}}<ref>Jacques Mercier, Daniel Valentin US Patent 4831890</ref><ref>Arthur J. Fahy, Neil Gillies US Patent 5071395</ref> because of their low efficiencies, and in locking differentials when the efficiencies are less than zero.