Improved method for determining the experimental tooth friction coefficient of cylindrical worm gears

Abstract Cylindrical worm gears with a shaft crossing angle of 90° are crucial in industrial applications where drive systems require high gear ratios within a compact installation space. For the design of worm gears, the friction behavior in the tooth contact is essential for estimating the operating behavior in terms of efficiency and self-locking. A commonly used method for determining the tooth friction coefficient is based on experimental tests using a worm gear test rig. This coefficient can be derived from the total measured power losses. To accomplish this, the load-dependent gear loss is determined by considering the loss of components of the bearings and sealings. However, a standardized procedure for worm gears does not exist yet. This paper introduces an improved method for accurately determining the tooth friction coefficient of cylindrical worm gears using data from test rigs. The method’s applicability is demonstrated through a calculation study with a standard reference worm gear (ISO/TS 14521:2020) under injection lubrication involving a quenched and tempered worm paired with a nodular graphite cast iron worm wheel. The study’s results are compared with current standards, revealing discrepancies between standardized approaches and experimental results. The presented method offers a more accurate and reliable determination of tooth friction coefficients, enhancing prediction accuracy in worm gear drive design.