The Strength Analysis Of Heavy Automobile Transmission Case Based On Multi-part Contact

Forecasting the strength of the transmission case exactly is very important along with the increasing of the automobile transmission carrying capacity and working reliability. There are mainly the case load and the neighbouring component rigidity to influence the case strength. And the contact pairs are defined to account of above-mentioned factors. The primary contact pairs include the gear to gear and the bearing to case. The gear-gear contact pairs give birth to the gear loads, and then the loads pass the shafts and the bearing-case contact pairs to the case. Finally, the case strength is gained. Before, when we calculated the case strength by FEA, we seldom took the effects of the other parts into account. There were two reasons. Firstly, the computer's operation capability was limited. Secondly, accounting the parts about can introduced the nonlinear calculation, so the convergence couldn't reach. With the increasing of the computer performance and the functions improving of the CAE software, it is to likely to analyse the case strength in the assembly. In the state of the assembly, we can simulate the displacement boundary and the load boundary very really and truly, and the case strength in the assembly is achieved rationally.The heavy automobile transmission was regarded as a research object in this thesis, and the first shift FEA model assembly of the transmission was built by the Hypermesh CAE software. ABAQUS was utilized to analyze the strength of the transmission case under 3 times rated load of the first shift, and the strength of the transmission case was researched by analyzing and testing.In chapter one, the purposes of the thesis were introduced, and the technical characters and developing trend of the transmission were also. After that, the usual accounting methods of the transmission case were introduced.In chapter two, the thesis introduced theoretic bases of the finite element method, including the contact interface's mechanics condition and solving methods, and also solving processes of the contact problems using the ABAQUS software. All of this provided a foundation for the case strength analysis.In chapter three, the finite element models of the first shift assembly were built. Firstly, the assembly structures were simplified. Then, the element types were chose, the material attributes were defined, the finite element mesh was generated, the contact pairs were established, the constraint and boundary conditions were applied. Finally, the assembly's FEA model was achieved, which made preparation for the next finite element analysis.In chapter four, the structural strength of the transmission case was analyzed by using the finite element method. Firstly, through detailedly analyzing the mechanics condition of the case, the relations of the gear force with the gear bending stress were found, and the relations of the gear force with the case strength were also. Secondly, because the mesh density had direct effect on the exact computation of the gear force and the exact analysis of the transmission case, the mesh density of the gears was confirmed based on the continuity of the contact line and the smoothness of the gear bending stress curve and also the economy of the computation time, all of which offered the technical basis for the case strength analysis, and we used the first meshing for the gear bending stress analysis, offering the technology basis. Thirdly, the gear bending stress was gained by the finite element analysis, making theory basis for the exact computation of the gear force and the exact analysis of the transmission case. Finally, the structural strength of the transmission case under the torsion of 1300Nm and 3900Nm was carried out based on the validity of the gear load. And the strength under 1300Nm was not 3 times under 3900Nm, and we could draw a conclusion that the strength result was nonlinear. Based on above, when we wanted to have the 3 times strength analysis according to the test-bed means for the automobile mechanism transmission and the assembly technical condition for the automobile transmission, we should apply the contact arithmetic in the case analysis under 3 times load, otherwise, the case strength design was conservative excessively. The case strength under the 3 times load was analyzed in term of the nation standard, the analysis results made clear that the case could reach to the strength need, and the case strength distributing was rational.In chapter five, the torsion test of the transmission assembly was finished. The test purpose was to validate the strength analysis of the transmission case. Firstly, in the state of the assembly, we successively parked the transmission to the first shift,the second shift and the third shift, and then to measure the bending stress of the middle shaft gear in the condition of 1 time rated load 1300Nm making use of the dynamic strain apparatus. Comparing analysis with test, we could conclude that the bending stress of the gear was right, and the gear finite element model could bring out the appropriate driving force, and then the computing strength of the transmission case was right, etc. Secondly, we compared the analysis strength under 3 times torsion with the test rupture of the same transmission case in the same condition, and we had some conclusions that the weak strength positions of the case were coincided with the rupture positions, which proved that the strength analysis of the transmission case was appropriate and rational.