Spheroid Worm Gear

a variety of worm drive in which the rotating worm gear is spheroidal (concave). The working surface of the spheroid worm gear is formed by the rotation about its axis O₁O₂ (Figure 1)of an arc of circumference with diameter d, bounded by an angle of contact equal to 2β. In the USSR spheroid worm gears are standardized, with square worm gear threads and gear teeth. The profiles are farmed by straight lines tangent to the profiling circumference d₀

Figure 1. Spheroid worm gear

The spheroid worm gear is a tooth-and-thread drive that is becoming increasingly widespread in view of its high load capacity, which is determined by the simultaneous engagement of a large number of gear teeth (four to seven) and an advantageous positioning of lines of contact. Spheroid worm gears operate in a fluid or semifluid friction regime, in which the contact surfaces of the teeth of the wheel and the threads of the worm gear are completely or largely separated by a resistant layer of lubricant. Medium and large spheroid worm gears have three to five times the capacity of conventional worm gears of the same size, and conversely, the gears required to transmit the same power are considerably smaller and lighter.

The drawbacks of spheroid worm gears include more complicated manufacture and assembly than for conventional worm drives and their operation at high heat, with the consequent need for artificial cooling. Spheroid worm gears are most efficient with large loads in a stable mode of operation, as well as in cases where compact and light equipment is necessary (in transportation and mining equipment, airplanes, and so on).