MODIFIED SURFACE TOPOLOGY OF INVOLUTE HELICAL GEARS DEVELOPED FOR IMPROVEMENT OF BEARING CONTACT AND REDUCTION OF TRANSMISSION ERRORS

摘要

A modified surface topology of involute helical gears is proposed. The proposed new topology provides an involute zone in the central area of gear tooth surface smoothly connected to crowned zones at the top, bottom, front, and back sides. The involute zone allows line contact in case of aligned gear drives while the crowned zones provide a localized bearing contact and low levels of transmission errors in case of misaligned gear drives. In many cases, non-standard cutting hobs are required to provide chamfers to gear tooth surfaces for avoiding of edge contact when misalignments are presented, but the chamfers are not connected smoothly, the magnitude of required chamfers is not determined analytically, and consequently, severe contact and linear functions of transmission errors may appear. The new topology is based on generation of gear tooth surfaces by an involute grinding worm. Modified roll is applied to the involved motions of generation in order to provide profile and longitudinal crowned zones with smooth connections to the involute zone. Tooth contact analysis and stress analysis by the finite element method has allowed the advantages of the proposed topologv to be verified. Finite element models with three pairs of contacting teeth are considered. A function of transmission errors with a low level is obtained as a precondition of reduction of noise and vibration. An uniform transition of load is guaranteed between the adjacent pairs of teeth avoiding areas of severe contact stresses.