Elevator Gearbox: Worm Gear Self-Locking vs Helical, PMSM Replacement, Oil Maintenance and Noise Levels

Geared traction machines use a gearbox to reduce the motor speed (typically 750–1500 rpm) to traction sheave speed (typically 30–90 rpm). Gear types: (1) Worm gear — the most common type historically; a worm (helical screw) meshes with a worm wheel (bronze or cast iron); high reduction ratio in one stage (40:1 to 100:1); self-locking property (the worm cannot be back-driven by the load) provides additional safety; efficiency ~40–60% (lower than helical); (2) Helical gear — involute gear tooth profile; higher efficiency (85–95%); lower reduction ratio per stage, may need two stages; not self-locking; used in higher-speed geared machines; (3) Combination (worm + helical) — some designs use a combination for efficiency and reduction ratio. In modern elevators, gearless PMSM machines (MRL) have largely replaced geared machines for new installations. Geared machines remain in service in existing installations and are used where machine room space allows and speed ≤1.0 m/s. Maintenance requirements: (a) Oil level check — the gear case is oil-lubricated; oil must be checked and replaced at intervals defined by EN 13015/manufacturer (typically every 2–4 years); (b) Worm wear — the bronze worm wheel is a wear item; regular inspection of wear patterns; (c) Bearing condition — drive end and output end bearings. Noise: geared machines produce more noise than gearless; typically 70–90 dB(A) in the machine room.

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