| Along with the development of automobile industry and transportation, automatic transmission is widely used in America, Japan and Europe. There will be more and more automatic transmissions in China. The hydraulic mechanical automatic transmission, AT for short, is in common use, and the torque converter is one of the most important parts. The torque converter has great effect on the economy and power of vehicle. In recent years, there are many projects about torque converters are made by the overseas automotive companies and research centers. But the progress is slow in China. This paper has made some research on the modern design strategy of torque converter deeply and systematically. Take W305 torque converter as the prototype, the internal flow is modeled and simulated, the design method of blade is studied, and the modern design system is established at last. Numerical simulation of internal flow field For the incompressible viscous flow, the continuity equation and momentum equation are called as Navier-Stokes equations, short for N-S equations. Reynolds averaging are the most used method for simulating the turbulence. But in the Reynolds averaging equations, Reynolds stress made the equations unclosed, because of which the turbulent viscosity method is introduced. Many turbulence models are established to make the equations closed. Among them the k ?εtwo-equation model is used widely, and then the control equations include time averaging N-S equations and k ?εturbulent equations. These equations can be expressed as a uniform equation, which is called convection and diffusion equation. After comparison to different methods such as FEM, FDM and FAM, Finite Volume Method is chosen to solve the equation. Up wind method is the way to accomplish the space discretion. SIMPLE and PISO are two strategies for coupling the pressure between continuity equation and momentum equation. For this paper, the former is more favorable. The internal flow of torque converter is very complex, so some simplification is made before numerical simulation. When the geometry model and mesh are completed, the flow field is calculated by CFD software STAR-CD. Based on the simulation result, the performance curve of torque converter can be calculated. Comparison between test data and simulation result shows that the numerical simulation is precise. Analysis of flow field This paper analysis the character of flow field in pump, turbine and stator in detail. At the same time, some statistical parameters are studied in depth. Through the analysis, several valuable conclusions are educed. There is jet/wake flow structure on the outlet of pump, and Coriolis force and inertial force affect the distribution. The pressure distribution in the pitch plane is becoming more proportional to the radius with the rising speed ratio. There are strong secondary flow field in pump, and the direction is switched from the mid-chord plane to outlet. The hydraulic loss of pump is most happen in the first half part of the flow field. It means that the shock loss of pump is high. When the speed ratio is low, a large region with low velocity is found in the first half part of turbine flow field. Along with speed ratio is rising, the low velocity region is vanished. The field around turbine outlet has a uniform and consistent velocity distribution. When the fluid flow out of turbine, its direction keeps good with the blade angle. The secondary flow in turbine field is uniform in different speed ratios, and no vortex is found. Under different working condition, the incidence angle of stator changes in a wide range. The fluid rushes at the pressure side of stator blade when the speed ratio is low, and a high-pressure region with low velocity is produced at the same position. When speed ratio is high, the fluid rushes to the suction side of blade, and a wake region with low velocity appears at the pressure side. In stator, the flow is approximately developed in the span plane. There is no strong secondary flow on spanwise direction. Except for shock loss is high, the hydraulic loss has a uniform distribution from middle to outlet. Analysis of internal flow helps us have a deep understand about the working mechanism of torque converter. The statistical parameters can express the relationbetween flow character and performance. These are important for the modern design strategy. Blade design According to traditional momentum equally distribution method, unequally distribution method of blade design is put forward in this paper. How the distribution affect the performance of torque converter is studied. For the aim of high efficiency, the momentum can be designed to change less in former part for pump, and change more in former part for turbine and stator. For reducing the pump capacity factor, the momentum can be designed to be equally distributed, and change less in former part for turbine and stator. To boost the torque ration of speed ratio zero, the momentum can be designed to change more in former part for pump, and change less in former part for turbine and stator. Besides this, the three dimensional designing method for blade is brought forward. Based on the basic geometry relation, the blade angle and thickness are used to describe the blade shape. Comparison between three kinds of blades with specific angle law gave us some directive results. The angle law has little effect on the efficiency of torque converter. The more effective method to achieve different efficiency is changing the angle of blade inlet and outlet. The angle law of stator has a great impact on the pump capacity factor, but it is not true for pump and turbine. The pump capacity factor can be adjusted in a wide range through changing the angle law of stator blade. To improve torque ratio of speed ratio zero, the angle law should be moderate in middle but vary sharply near leading edge and trailing edge for pump, and moderate near leading edge and trailing edge but moderate in middle for turbine and stator. Research on blade design is necessary for the modern producing technology, and the conclusions are important for the optimal design of torque converter. Modern design strategy According to different judge method, two kind of modern design strategy are put forward in this paper. One is based on torque converter itself and the other is based on the vehicle performance. The analysis and conclusions mentioned before is used in the modern design system. In the beforehand designing process, a performance predicting method based on amending head loss is established. By means of it, the quickly prediction for performance is more precisely.
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