A geared elevator drive using a worm-and-wheel gear reduction to increase torque from an AC or DC motor, common in low-to-mid-speed installations up to 1.6 m/s.
Full Definition
A hardened worm shaft driven by the motor meshes with a bronze worm wheel keyed to the drive sheave shaft, achieving a gear ratio of 10:1 to 40:1. This allows use of a compact, faster-running motor. The shallow helix angle creates inherent self-locking — the worm cannot be back-driven by sheave load — providing a secondary mechanical braking layer. Efficiency losses in the gear mesh reach 15–30 %, generating heat requiring oil-bath lubrication with periodic oil changes. Worm gear machines are quiet, relatively low-cost, and adequate for speeds up to about 1.0 m/s but are increasingly replaced by gearless PMSM machines in new installations due to energy costs. EN 81-50 governs traction machine type examination.
