Transmission Main Reduction Gear Finite Element Analysis

Transmission is an important part of vehicle and main reduction gears which are often in the meshing state, as one of the important transmission parts, will be beared all the torque from the vehicle. At the same time, lift of the main reduction gears will be shorten because of the vehicle frequent shift and unstatic speed. Because of main reduction gear is expensive, cannot exchange optional, manufacturing precision is very high, and the bearing capacity of the gear is mainly restricted by the contaction strength and bending strength. Therefore, it is necessary to do scientific analyze to main reduction gears'contaction strength and bending strength.This article based on the structure and the mechanical performance parameters of the manual transmission's main reduction gears, achieve the main deceleration helical gear 3d parametric precise modeling. Although many researchers have achieve "parametric" inclined gear modeling by using CAD/CAM/CAE software, but this "parametric" is achieved after people operate, not totally parameter modeling. In addition, a lot of research literature ignore the accurate gear root modeling, and this is the important premise to finite element calculation for gear's the bending strength. This article established the complete and useful mathematical model of the helical gear, the so-called "complete" no only include the involute tooth profile, but also include transition curve tooth profile; the so-called "useful", refers to establish mathematical modeling base on the symmetric axis of gear thickness centerline, it is useful to establish 3d CAD modeling. And the article realize inclined gear 3d parametric precise modeling based on the APDL language。This paper analyze the gear pair's load and constraint conditions when engine output maximum torque (transmission maximum input torque). And emphatically introduce the definition of helical gear meshing most evil loading line, and according to the definition of it, the main reduction gear's most evil loading line are calculated, and load the loading to the gears base on the most evil load line. After solving, the activing and driven gears'bending stress distribution are studied respectively, obtain the most dangerous position for gear bending stress. This can as a reference to actual gear design, and can as a reference to do the special process at the position of the biggest bending stress by the manufacture and heat treatment process for increase life and reliability of gear. Compare with traditional calculation and finite element method, the result obtain by the calculation formula will be less than finite element method, and it prove that the design and check by finite element method is safe in the real work. Using finite element analysis results to check bending strength, the maximum allowable stress is less than material elastic stress, it is concluded that gear bending strength is enough. This is consistent to the fact that main reduction gear seldom occur bending broken. In order to up the speed for the nonlinear contact analysis of the gear meshing modeling and up the accuracy of the result, this paper simplify the gear meshing modeling, and take four big gear tooth and three of the small gear tooth to do the finite element analysis. Establish contact pairs (design contact and target face, create target face and contact elements, adjust contact initial conditions), calculation the stress with influence behind load and constraint, obtain the contact stress change map. Analyze the map, we can know that the max contact stress is 929.6 MPa, The contact stress of gear tooth surface become linear distribution, the biggest contact stress appear in the gear root. Obtain the most dangerous position of gear contact stress, it can as a reference to actual gear design, and can as a reference to do the special process at the position of the biggest bending stress by the manufacture and heat treatment process for increase the life and reliability of gear. Similar with bending analyze, compare with traditional calculation and finite element method, the result obtain by the calculation formula will be less than finite element method, and it prove that the design and check by finite element method is safe in the real work. Use the finite element method to check the contact strength, its result get cooperation enterprise recognition, have higher precision.To sum up, this paper analyze the bending strength and contact strength for the MT21 transmission's main reduction gear pair, master the stress distribution of the gear, check the strength, the analysis results obtain certification by the enterprise, have higher precision. The study of the article is the foundation for gear tooth repair analysis. Because of the complexity of the gear strength calculation, the study of the article is still the foundational work. It will be conveniently further study the structure optimization, gear teeth gear repair form, multi-physical evil close analysis, probability design (reliability design) base on this article.