Efficiency of worm gear drives

Due to a wide range of properties, worm gears are an indispensable element on the current transmission market. Next to a huge gear ratio field in one gear stage of i = 5 to i = 80, operation with low noise and vibration is realizable. Furthermore, worm gears provide the opportunity of self-locking, respectively selfbraking. Despite these benefits, as a result of greater energy awareness, the efficiency of worm gears is in the focus. Because of high sliding velocities, especially at high gear ratios, gearing losses are a main topic of interest. Other gearbox concepts with combined spur and bevel gear sets show smaller gear ratio fields, and therefore the realization of high gear ratios in only one stage is not possible. Consequently, fewer components are necessary for worm gearboxes, which allows savings of assembly and maintenance costs. In the scope of recent research projects, the efficiency and the load-carrying capacity of worm gears is examined. Therefore, experimental investigations on different worm gears were conducted on several test rigs. Generally the pairing of bronze worm wheel with case-hardened worm is used in center distances between a = 65 and 315 mm. Additionally, the influence of different gear ratios, worm wheel materials, lubricants, and contact pattern on efficiency and load-carrying capacity are considered. In the course of these investigations, overall worm gearbox efficiencies of up to η = 96% are reached. The paper describes the conducted tests in detail and shows basic examples of experimental test results. On the basis of the experimental investigations and theoretical examinations, recommendations for an increase in efficiency are given.