Coupled Computational Prediction of Efficiency, Thermal State and Wear Evolution in Worm Gear Drives

ABSTRACT

Efficiency, oil temperature and wear of worm gear drives are coupled through the lubricant film: heat lowers viscosity, a thinner film transfers load to asperities, and the resulting friction and wear feed back into heat generation and contact geometry. A reduced‐order model of this loop was built for steel/bronze worm gears with involute helicoid (ZI) worms. The contact line is represented by equivalent rollers with local sliding velocity and curvature; the film thickness follows the regime‐covering Moes line‐contact formula with inlet heating, viscosity follows the Roelands relation, and friction combines an asperity load share with non‐Newtonian Ree–Eyring shear. Over 6000 designs, coupling changed efficiency by more than 1 percentage point in 67% of thermally admissible designs relative to a one‐pass isothermal calculation, because the actual oil temperature sets the film parameter. In the mixed regime, friction rises with temperature; the friction–temperature derivative changes sign near Λ  ≈ 1.71–2.13, and the thermal limit appears as a steep, locally bistable rise of the oil temperature. Sobol analysis ranked the entrainment factor c _e first for wear‐life uncertainty (total index 0.57), whereas the wear coefficient contributed 0.09. Against eight independent FZG efficiency measurements, the mean absolute error was 1.41 percentage points, but efficiency was predicted to fall with torque, whereas it rose. A model‐free two‐torque decomposition traced this to load‐independent losses 7–62 times larger than the component models predict, a deficit that plausible bearing, seal and immersion configurations did not close.