YJSW340Dual-Turbine Torque Converter Turbine Torque Distribution Regularity And Optimization Research

Dual-turbine torque converter is widely used in construction vehicles because of its advantages such as high efficiency in low speed region, big starting torque ratio and wide high efficiency region, etc, which can improve vehicle power performance and fuel economy. When automatically shifting with the change of external load, dual-turbine torque converter itself is equivalent to two speeds respectively so as to reduce the gearbox planetary, so that the structure and manipulation of the gearbox can be simplified. One dual-turbine torque converter is designed and analyzed by the CFD software to investigate the turbine torque distribution regularity and the inner flow field. By comparing the CFD result with the test result, the three dimensional CFD software is proved to be reliable. Rules of the turbine torque distribution is got by analyzing the CFD results of the dual-turbine torque with different output gear of the first turbine., so as the influence to the efficiency of the dual-turbine torque and the vehicle. According to the results of the computational analysis, a new dual-turbine torque converter is designed to optimize the performance. The main contents are as follows:(1) Numerical simulation of the dual-turbine torque converter and analysis of the flow field.By using three-dimensional modeling software and meshing tools, models of the passage of dual-turbine torque converter are established as well as the working flow passage models. The coupling algorithm is the sliding meshes model, and the boundary conditions are defined as grid interface and wall. PISO method is used to couple the pressure between continuity equation and momentum equation. Up wind method is the way to accomplish the space discretion. Large eddy simulation model is used to carry out numerical simulation of turbulence. Analysis of the flow field characteristics under speed ratio0,0.5and1.0is implemented based on numerical calculated results of the three-dimensional flow field in the CFD.(2) the Comparison between CFD predicted performance and experimental performance According to impeller speed tested in the experiment of YJSW340dual-turbine torque converter, the speed in the flow field is set up so as to obtain simulation results and make a comparison between numerical data and tested data. Based on the impeller torque extracted from CFD results, stall torque ratio and efficiency are acquired as well as torque coefficient of pump, the compared results show that the simulated results have a good agreement with tested data, which also indicate that the CFD method selected in this paper is a effective way to calculate the internal flow field of dual-turbine torque converter.(3) Analysis of the impact of the first turbine’s output gear ratio on turbine torque distribution regularityBased on the CFD simulation results, the impact of the first turbine’s output gear ratio on the turbine torque distribution is analyzed as well as the distribution of the internal flow field. When output gear ratio of the first turbine is on the increase, the idling conversion point moves forward gradually, meanwhile, torque of the first turbine is on the decrease, but torque of the second turbine increases gradually under all conditions.Velocity and pressure distribution of the flow field under high efficiency condition of low speed ratio and high efficiency condition of high speed ratio are analyzed and compared, the results illustrate that the out put gear has a small effect on the flow field of dual-turbine torque converter.(4)Analysis of the impact of the first turbine’s output gear on performances of dual-turbine torque converterWhen output gear ratio of the first turbine is on the increase, efficiency under high efficiency condition of low speed ratio reduces slowly, at the same time, the efficiency and stall torque ratio under high efficiency condition of high speed ratio increase gradually as well as capacity factor of pump, after matching with the same engine, the maximum speed is on the decrease, but the maximum traction force is on the opposite direction with different stalls.(5) Optimization design of Twin-turbine torque converteroutlet angle of pump blade is on the increase for the purpose of optimizing overall performance of Twin-turbine torque converter with the first turbine’s output gear ratio50/22and increasing flow areas of the first turbine and stator, then optimized flow passage model and numerical model are established, CFD software is used to calculate the flow field of optimized Twin-turbine torque converter, the calculation results show that stall torque ratio and pump’s torque coefficient of optimized Twin-turbine torque converter increases moderately, efficiency of high speed ratio zone decreases slightly, starting performance of Twin-turbine torque converter is improved too. after matching with the same engine, the maximum speed of all stalls changes slightly, but the maximum traction force increases significantly, dynamic performance is improved, and the goal of optimizing performance of Twin-turbine torque converter is realized too.Based on the contents discussed above, the internal flow field of YJSW340dual-turbine torque converter is simulated, the feasibility of CFD method is verified by making a comparison between simulation results and experimental results, through changing output gear ratio of the first turbine, the impact of changing trends on turbine torque distribution regularity is analyzed and obtained, at the same time, by optimizing structure of this type dual-turbine torque converter, starting performance and dynamic performance of vehicles have got improved too.