Study On The Modification And Dynamic Contact Characteristics Of Involute Cylindrical Gears

Gear transmission is widely applied in machines, electronic, chemical, metallurgy, traffic and so on because of its high transmission efficiency and constant power. Along with the rapid development of modern industrial technology, the requirement of vibration and noise reduction is becoming even higher. The design method based on thermo-elastic contact analysis, gear modification, and impact dynamic simulation is widely used to improve the dynamic performance of gear transmission.The thesis subject is supported by National Project of Scientific and Technical Supporting Programs and Chongqing Natural Science Foundation. Combining with principle of gear engagement, theory of heatl transfer, contact mechanics, and structural dynamics, the thermo-elastic deformation and meshing impact characteristics in meshing process are studied.The research work presented in this thesis can be summarized as follows:1) Using the kinematics of gear engagement principle, the tooth profile equation of involute gear is derived, and contact finite element models of involute gear pair with different geometric parameters are established.2) Based on Hertz theory, the contact pressure on tooth surface is analyzed. The software of ANSYS is used to analyze the contact performance of gear transmission, and then the changes along the contact path of gear tooth contact force, contact deformation and engagement stiffness are obtained.3) The relative sliding velocity between the tooth flanks is analyzed, then the convection heat transfer coefficient and tooth surface heat flux are calculated. Using above results, the body temperature of gear is studied based on multi-tooth pair model. Coupled with the temperature field, displacement field and stress field, the thermo-elastic deformation of gear pair is obtained. The results indicate the value of gear thermo-elastic deformation is a little smaller than the value of deformation in the cold state and the contact stress is a little larger than the cold state.4) Based on finite element analysis of tooth contact problem, the gear modification is studied, and the curves of gear modification which without temperature effect and with temperature effect are obtained. The contact finite element analysis of standard involute gear pair and modified gear pair in the meshing in and meshing out position is compared by the software of ANSYS. It shows the contact stress of modification gear pair is significantly reduced.5) The dynamic contact finite element model of standard involute gear pair and modified gear pair are established. By using the software of ANSYS/LS-DYNA, the dynamic contact force and dynamic stress of gear pair in meshing process are calculated, the contact characteristics of modified gear pair are improved significantly.6) By the language of Visual Basic and ANSYS/APDL, a finite element anlysis program is compiled to analyze the thermo-elastic contact and dynamic contact problem of gears. Using this program, the finite element model of gear pair with different module, teeth number, helical angle and modification coefficient can be built quickly, and the static/dynamic contact analysis and body temperature calculation can be completed conveniently by the help of the secondary development of ANSYS.