Research On Flat Hydrodynamic Torque Converter For Passenger Car

The hydrodynamic torque converter is a kind of turbo machine which is widely used in today's automatic transmissions for passenger cars. Its functions include damping of engine torque fluctuation, damping of noise and vibration in the drive line, and automatic amplification of torque according to the difference in rotational speed between the input and output shafts without requiring any external control. It also has great impact on the dynamical and fuel economy of passenger cars. Although the torque converter has existed for a century, there have been tremendous changes in the most recent decade. It has undergone continuous refinement through the years that have paralleled the development of the automobile, and these improvements continue. Most passenger cars with small and medium displacement engines have adopted a front-wheel-drive layout in recent years. Torque converters accordingly have been designed with an increasingly narrower profile for the purpose of achieving a smaller axial size, which also translates into weight savings. The research on the flat torque converter for the passenger car has been carried out early in abroad, but related research is in the blank in domestic. In this paper, the modern design method of the flat torque converter has been carried out for the purpose of developing better performance flat torque converter which could meet or exceed similar foreign products.1. Design of the flat torque converterThe shell is first determined in tradition design method of circulatory circle, and then, core and middle flow line are found out by means of flow section area. Using tradition design method often need modify several times to obtain satisfactory results. Tradition flatness ratio of the circulatory circle is defined as the ratio of the width to effective diameter that causes the change of the flatness ratio can't completely reflect the change of the whole circulatory circle. To dissolve above two problems, considering the development of the CNC machining technology, the bran-new flat circulatory circle design method is put forward, and the shape is ellipse. Flatness ratio is defined as the ratio of short axial to length axial. So the better flat circulatory circle can be designed. By compared result of the new method with actual result, both of them have close magnitude and well agreement with. It shows that the new method is more correct and effective. The new method can be used in design of the flat circulatory circle. The three circulatory circles with different flatness ratio are designed by using new method.The blades of the torque converter are designed by momentum distribution method. The rules of momentum distribution decide blade shape, finally influence the performances of the torque converter. To find out the reasonable rule of the momentum distribution and get good blades, how the distribution affects the performances of torque converter is researched. The design method of the flat torque converter blade based on quadratic function distribution of momentum is put forward. Quadratic functions for each impeller are different to design better blades.2. Numerical simulation of the flow field and performances predictionWith the development of computer technology and Computational Fluid Dynamic (CFD) theory, numerical simulation of the torque converter flow field has been used in engineering practice. So the internal flow performances of the flat torque converters are investigated by numerical analysis using CFD software. Based on the numerical solution, the performances of the flat torque converter are predicted. As soon as figuring out the performances, the prediction results can be analyzed and compared with the test results. Then the correctness of numerical simulation of the flow field and performances prediction can be testify.Coupling algorithms for the multi-flow regions, which mainly include Multi Rotating Reference Frames model, Mixing Planes model, and Sliding Meshes model, its specific application in the hydrodynamic components are discussed. Sliding Meshes model is used in the numerical simulation of the unsteady flow field and which is transient method. Published available literature at home and abroad show that the transient calculation of unsteady flow field appears is first time.The control equations of the fluid mechanics are explained. For the incompressible viscous flow, the continuity equation and momentum equation are called as Navier-Stokes equations, short for N-S equations. Many turbulence models are established to make the equations closed. Among them, the RNG k ?εtwo-equation model is more precise, and the control equations include N-S equations and RNG k ?εturbulent equations. After comparison to different methods, such as, Finite Difference Method (FDM), Finite Element Method (FEM), Finite Volume Method (FVM), FVM is chosen to solve the equation. Up wind method is the way to accomplish the space discretion. SIMPLE method is used for coupling the pressure between continuity equation and momentum equation. The boundary conditions are such as'grid interfaces'for interactive faces and'wall'for others. The rotational velocity of each impeller is defined as same as the test to facilitate the performances comparison. The performances prediction method based on the numerical solution is also find out .The torque in each impeller of the torque converter D245 is figured out, then the performances is predicted. The results of performances prediction are analyzed and compared with the experimental results, both of them have close magnitude and well agreement. Then it comes to the conclusion the numerical simulation method and performances prediction for the flow field of the flat torque converter is correct and effective.3. Analysis of the transient flow fieldThe transient flow field of the flat torque converters which have different flatness ratio under speed ratio 0 and 0.81 conditions is investigated and analyzed for the purpose of learning the distribution rules of the pressure and velocity. The character of the flow field in pump, turbine and stator is analyzed in detail. At the same time, some statistical parameters are studied in depth. Through the analysis, several valuable conclusions are educed.4. Research on influence of the flatness ratio of the torque converter on hydrodynamic performanceBased on the analysis of internal flow field and numerical solution, the performances of the flat torque converters which are designed by both new and traditional torus design method are predicted. Then firstly, by comparing with the performances of the same flatness ratio torque converters designed by both new and traditional torus design method, it comes to the conclusion former is better. Next, by comparing with the performances of different flatness ratio torque converters designed by same method, the influence of the flatness ratio of torque converter on hydrodynamic performance is found out. Finally, the performances of the flat torque converter are advanced by changing the structure parameters, the results of characteristics prediction are compared with that of original torque converter. It shows that the performances of optimization torque converter are significantly improved.