Effects of profile shifted factor and pressure angle on the ZK-type dual-lead worm gear drives

In the light of a mathematical model of the ZK-type dual-lead worm gear set proposed in the authors’ recent work, this study adopts tooth contact analysis to compute the kinematic errors, instantaneous contact teeth (ICT) and average contact ratios (ACR). An elastic deformation of 3 μm is allowed while calculating ICT and ACR. In addition, increasing the ICT from three to four or from four to five reduces the root stress of the gear set due to its multiple contact teeth. Although a worm gear driven with a small pressure angle can increase the ICT, a worm gear with a small pressure angle incurs a more serious undercutting phenomena. Undercutting can also be averted by applying a positive-shifted modification of the hob cutter during the worm gear generation. Moreover, the boundary of conjugate and non-conjugate surface regions appears on the worm gear tooth surface when the worm gear has a low pressure angle. The non-conjugate region also influences the transmission efficiency, operational life time and noise of the worm gear drive. Furthermore, worm gear generation with a negative-shifted modification can decrease the unfavorable non-conjugate region.