Optimum design and 3D CAD/CAE simulation of spiroid and worm gears.

摘要

This thesis describes research conducted by the author on the optimum design and 3D CAD/CAE virtual simulation of spiroid and worm gear drives. Three major contributions have been made: (1) an innovative approach to obtain favourable localised tooth contact, (2) a novel 3D parametric modelling methodology - virtual gear manufacturing (VGM), and (3) a feasible procedure for loaded multi-tooth contact analysis using an advanced finite element method. These techniques developed are illustrated using two types of spiroid gears including a conventional spiroid gear drive (whose pinion is a conical worm) and a helicon gear drive (whose pinion is a cylindrical worm), and three types of cylindrical worm gears including ZA, ZN and ZI. Favourable localised tooth contact is achieved by modifying the worm tooth surface. With this approach, only the worm cutter's geometrical angles and mounting position need to be adjusted. This approach is simpler and more economical than existing gear tooth modification methods because it can be implemented in standard gear bobbing machines without any modification to the hob geometry. Numerical simulations of the localised tooth contact have been conducted. The results confirm that the proposed gear modifying method can provide substantially improved localised bearing contact and is largely insensitive to misalignments, hi addition, the modified spiroid and worm gears have significant advantages over conventional designs such as better lubrication conditions, higher load capacity, longer working life and lower manufacturing costs. The VGM methodology developed includes virtual manufacturing of worm and gears within a computer software environment, creation of 3D parametric and adaptable gear models, and utilisation of the VGM models to simulate gear mesh, to analyse the contact pattern, and to detect tooth interference. Unlike conventional 3D modelling methods, the VGM method does not require complicated mathematical modelling and therefore the difficulties associated with the solution of nonlinear meshing equations can be avoided. In contrast to the existing modem computerised gear theory that can only numerically simulate the meshing of gearing in point or line contact, the VGM method has the capability to visually simulate the general regional contact problems. Consequently, the VGM method can help to significantly reduce the manufacturing cost in the design stage. The 3D gear models, created in Pro/Engineer using the VGM method, are imported into ANSYS via the IGES interface for the loaded multi-tooth contact analysis. Evaluation of solid and contact elements for nonlinear gear contact analysis has been conducted. Advanced techniques have been developed for 3D gear model geometry cleanup, 3D gear geometry data transferring via the IGES interface and 3D finite element model meshing. 14 full multi-teeth contact finite element models of spiroid and worm gears have been created. The loaded tooth contact stresses and deformations of spiroid and worm gear drives under different operating positions have been analysed. The results of the tooth stresses and tooth load shares successfully simulate the real gear operation. The FE models enable the loaded tooth contact pattern, stress distribution, contact force distribution and load share to be fully examined for the first time. This is impossible for conventional theoretical methods and experimental methods. Using the procedures and techniques developed in this research, researchers and engineers will be able to conduct and gain substantial benefits from the loaded gear tooth contact analysis.