Study On Load Sharing And Fatigue Life Of Planetary Gear Sets

Load sharing of planetary gear sets is an important issue in the field of gearmanufacturing. The load sharing of planetary gear sets has a major impact on thestability also closely relationship to the service life of the entire wheel system. Underideal conditions, for a planetary gear sets with n planets, each path will carry an1/n ofthe input torque. However, such equal sharing of the input torque between the parallelpaths is not realized in practical applications due to the presence of manufacturingerrors, assembly errors, temperature increase, and so on. The load sharing of planetarygear sets are affected by many factors. Currently, the research focuses on planet holeposition errors, gear rim thickness, planet pin stiffness factors to impact the loadsharing. Beyond that, the impact caused by the mesh misalignment to the gear train’sload sharing can’t be neglected. Mesh misalignment can be divided into three types:parallel misalignment (center distance change), angular misalignment parallel to theplane of action, angular misalignment perpendicular to the plane of action. A part ofresearch in this paper is supported by the National Natural Science Foundation ofChina (NO:51075179), Angular misalignment parallel to the plane of action isselected to study the impact on load sharing of planetary gear sets. The main resultsand conclusions:(1) Introduced the causes and the forms of mesh misalignment, calculate the relativedisplacement of two point of line of action use the space coordinate transformationprinciple before and after misalignment. Two calculation methods of load sharing areintroduced. Use Hypermesh software to meshing planetary gear sets. Two teeth in theengagement at a certain thickness of the tooth surface to carry a separate gridencryption partition, others were rough partition, add constraints through ABAQUS.(2) Carry the stress analysis with different forms of misalignment. Obtain the angularmisalignment parallel to the plane of action will cause backlash changes, and impactthe load sharing of planetary gear sets. (3) Conduct finite element analysis by ABAQUS software. Because of the values ofload sharing are changing with time, a simulation cycle is set from into engagement toexit engagement, and this cycle is divided into nine time points(some key points suchas highest point of single tooth contact, lowest point of single tooth contact, pitchpoint are found), and calculate the radius of the engagement of each contact pointrespectively. Thus, the amount of floating of the sun gear in each contact point isobtained. According to these data, the finite model in Hypermesh is modified. Ninepositions which contain misalignment errors are analyzed by finite element software(error angular of0.02°,0.04°,0.06°,0.08°,0.1°). The study shows that misalignmenterrors have great influence on the distribution of the tooth surface load and the speedof the Max Unit surface load increase gradually reduced when the errors increased toa certain extent; the load sharing of planetary gear sets changes along with the contactposition, while at the same contact position and the different misalignment angular,the load sharing of planetary gear sets is two the same generally.(4) The effects of misalignment errors and planet hole position errors are combined toinvestigate the change law of the load sharing factors. The results show that themaximum load percentage of planet1and4reduces with increase of the planet holeposition errors while the maximum load percentage of planet2and3increase whenboth of two types of errors work.(5) A predictive model of planetary gear sets is built by Romax software and thebending fatigue life of planetary gear sets under different misalignment angular anddifferent loads level is predicted. The results show that, the misalignment errors havea great influence on gear bending fatigue. With increasing of misalignment angular,the reduction speed of life of sun gear faster than the life of the planet.This paper perfects the study of load sharing of planetary gear sets and thevariation of load sharing obtained in the paper can provide some data reference valueof the planetary gear design.