Crossed helical gears have been known for about two centuries, but unlike parallel helical gears, their applications are limited to low load-carrying capacity gear drives. A reason is their point contact in the meshing zone which results in high Hertzian contact stresses that diminish the tooth flank endurance.
The paper demonstrates the possibility of elevating the load-carrying capacity of crossed-axis helical gears by utilizing an enveloping tooth shape on one member of the gear pair, thus allowing the increase of the tooth lengthwise radius of curvature in the contact point and resulting in significantly reduced contact stresses. The enveloping helical gear is similar to a worm gear engaged with an involute helical gear instead of a worm.
The tooth contact analysis of enveloping helical gears is performed using Hertz’ equations for the general case of two bodies in contact, and the loaded tooth contact analysis (LTCA) is executed with the BECAL software modified for the enveloping crossed helical gears.
The results of the Hertz analysis and BECAL’s LTCA of the enveloping crossed helical gear pair indicate a severalfold increase in load-carrying capacity compared to conventional crossed helical gears. This would make it possible to consider their application in moderate to highly loaded gear transmissions.
The paper also describes the possible manufacturing technologies for enveloping helical gears, including conventional and CNC hobbing, CNC machining, and others.