Modification Method For Helical Gears Based On Contact Analysis

Helical cylindrical gear transmission has meshing of smoothness and stability,high bearing capacity and other advantages. Planetary gear transmission has manyadvantages, such as compact structure, light weight, big transmission ratio. Helicalplanetary gear transmission is often used as transmission structure in automaticgearbox in cars. It can also be used together with hydraulic coupling implement andhydraulic moment-ranged implement, so it has a wide application in automobileindustry.Manufacturing error and installation error of gears, as well as tooth deformationin mesh process, can cause mesh impact together with noise and vibration. Bendingdeformation and torsional deformation of gear shaft can cause load distributionnonuniformity of teeth, and bearing capacity of teeth is also decreased. Normally, themethod for improvement is profile modification and axial modification. Researchesindicate that tooth modification can effectively mitigate mesh impact, and eliminateedge contact and axial bias load. Therefore, making research on tooth modificationhas significant meaning in reducing vibration and noise, and improving bearingcapacity and service life of gear, so it’s valuable in engineering application.Focusing on requirement of automobile industry for tooth modification, thispaper takes one stage helical planetary transmission device in an automobileautomatic transmission as research object, and a method to establish parametric finiteelement model quickly is proposed. Profile and axial modification, meshcharacteristics and analysis of dynamic contact of the gear pair consisting of ring gearand planet gear are deeply investigated. Main research achievements are as follows:1. Based on ANSYS APDL, which is a parametric design language, a method toestablish the parametric model of helical planetary gear transmission devicequickly is proposed. The method has advantages such as accuracy, convenience,parameter changing with easiness, which establishes the foundation for design ofmodification and analysis of mesh characteristics.2. Based on finite element analysis, the max magnitude of profile modification isdetermined through extraction of displacement of teeth in direction of mesh line. Microgeometry modification in profile is realized through parametric language.Moreover, mesh stress and contact pressure before and after profile modificationare compared and analyzed.3. The magnitudes of drum-shaped modification and helix angle modification aredetermined through the extraction of bending and torsional deformation of planetgear, and contact pressure before and after modification are compared andanalyzed, which indicates that helical angle modification is more suitable thandrum-shaped modification for axial modification.4. Mesh period is equally devided and models of gear segments before and aftercomprehensive modification in each mesh position are established. The variationof max mesh stress and max contact pressure is deeply analyzed with the changeof mesh position.5. Finite element models at recess position in different modification conditions areestablished, and law of influence of modification factors on mesh characteristicsis determined based on orthogonal experiment, and the best combination ofmodification factors is given.6. Transmission process is simulated through the use of ANSYS/LS-DYNA, anddynamic mesh characteristics are analyzed. Research indicates that modificationcan eliminate mesh impact, and influence of rotational speed on the fluctuation ofdynamic contact force and vibration of gear pair is clear.