Study On Impact Of Stator Structures On Performances Of Flat Hydrodynamic Torque Converter

The torque converter is an important component of an automatic transmission. Its shape and performance has important effects on the fuel economy and dynamical of the passenger car. For the front-wheel-drive passenger car, the torque converter has been designed with a flat shape for the purpose of reducing axial size. The stator shape has important effects on changing axial length, also it can affect the hydraulic performance of the torque converter. The goal of this study is to investigate effects of the stator shape and find a suitable stator shape for the torque converter with a flatness ratio of 0.8.Two flat torque converters are designed, including the circulatory circles and the blades. The models of passage and models of passage mesh of the two torque converters are built. Computational analysis with three dimensional CFD software shows the internal flow field of the torque converters, also the performance. The effects of the stator shape on inner flow field are got by analyzing the CFD results. By comparing with the performance of torque converters with different stator shapes, the influence rules of the stator shapes are found out. According to the results of the computational analysis, a new torque converter is designed to optimize the hydraulic performance of the flat torque converter. The main contents are as follows:(1) Design of the two torque converters with the flatness ratio of 0.8. First, the circulatory circles are designed. Use a new design method to design the circulatory circle and its shape is an ellipse. The flatness ratio of 0.8 equals to the ratio of the short axial to length axial. The circulatory circle of the pump and turbine of the two torque converters are designed without any differences. One of the stator is called straight line stator and the other is circular stator.Second, blades of the two torque converters are designed. All blades are designed by momentum distribution method. Quadratic functions for pump, turbine and stator are different. Blades of the two pumps are designed with the same rule of momentum, so are the blades of the two turbines and stators.Third, build the models of passage of torque converters and analyze with the Computational Fluid Dynamic (CFD) software. Using the CFD software we can get the models of passage mesh from models of passage. Then the computational analysis is done by the CFD software. The coupling algorithm is the sliding meshes model and the boundary conditions are defined as grid interface and wall. The control equation is standardκ-εturbulent equation. Use the SIMPLE method to couple the pressure between the momentum equation and the continuity equation.(2) Analysis of the transient flow field of the torque converters.Compare with the internal flow field of the torque converters to investigate the distribution rules of the velocity and pressure.The distribution rules of the velocity field and pressure field of the two torque converters are similar under speed ratio 0 and 0.81 conditions. At a stall point, the circulating flow rate is large, the rotational speed of the turbine is zero, the pressure and velocity of the oulet of the pump is higher than of the inlet, but they decrease in turbine field, they change little in stator field, the pressure and velocity of the shell is higher than the core due to the centrifugal force and Coriolis. At 0.8 speed ratio, the pressure and velocity discrepancy is small, this is because the rotational speed of the pump and turbine is close, the changes of the energy decrease.The centrifugal force is large so the pressure and velocity of the shell is much higher than the core.There are some differences between the pressure and velocity of the torque converters because of the change of stator shape. The pressure of the torque converter with the circular stator is higher than the other, the velocity of the outlet of the pump is lower, but the velocity of the flow of the stator is higher at a stall point. The pressure and velocity of the torque converter with the circular stator is higher at the 0.8 speed ratio.(3) Compare with the performance of the torque converters to find out the influence rules of the stator shape.The efficiency and the torque ratio of the torque converter with the circular stator is higher than the other when the speed ratio i<0.8.They are nearly equal when the speed ratio i≥0.8 The torque converter with the circular stator has a smaller circulating flow rate and higher torque capacity.(4) Optimize the performance of the torque converter.A new torque converter is defined based on the torque converter with the circular stator. The blades length is cut in half, the number is doubled and the blade thickness is reduced. The effects of the performance are got by analyzing the CFD results. The circulating flow rate increases and the torque capacity decreases. The performances of the third torque converter improve.