Study On Axial Force In Hydrodynamic Torque Converter Based On Numerical Solution Of Three-Dimensional Flow Field

Hydrodynamic torque converter is a kind of automatic continuously variable speed device which uses liquid as its work medium. It has excellent automatic adaptability to external load and can change speed and moment automatically with the change of working condition of vehicle or working machinery, improve stability of low-speed in transmission, the starting characteristic and the overload protection performance. As hydrodynamic torque converter uses liquid as its working medium, it can absorb or eliminate the twist vibration from engine and the shock from machinery. So it can prolong the service life of the engine and components of the transmission. Besides, hydrodynamic torque converter also has performance that can improve passability and travelling comfort of vehicle, makes vehicle operate simply, start smoothly and avoid engine miss.Because the working medium is liquid, there is no mechanical friction in hydrodynamic elements themselves. But mechanical friction still exists in some other parts such as bearings and oil seals, which makes these parts be wearing parts and decrease the service life of hydrodynamic torque converter.When a torque converter is designed, the axial force must be taken into account and it should be reduced as far as possible. Because of the complexity of the internal flow, there was no good method to calculate axial force of hydrodynamic torque converter accurately in the past years. Traditional method based on one-dimensional flow theory has many defects. The calculation method of axial force based on similarity theory is limited by geometric similarity and model experimental data .The axial force can be got also by experiment, and there were some experiments about axial force of torque converter both domestic and foreign. But the axial force has direct relation with the shape of impeller and vane and the structure of torque converter, so it is uneconomical and difficult to get axial force all by experiment. And the choice of bearing at the design stage asks for a better calculation method of axial force.With the development of CFD and computer technology, three-dimensionalflow field in torque converter can be calculated accurately. Basic computational methods of flow field by CFD are briefly introduced in this paper. 3-D circumfluence geometric model of flow passage in torque converter is built in UG. Then mesh model is built in Gambit. Boundary conditions are set on the basis of the real working situation of torque converter. Flow field in torque converter is calculated under different work conditions. Flow field in pump, turbine and stator are analyzed respectively under starting condition, middle speed ratio condition and high speed ratio condition, which provide theoretical foundation for further study of axial force. Based on the result of numerical simulation of flow field, axial force on each impeller is calculated. Compared with traditional results based on one-dimensional flow theory, the computational method on axial force in hydrodynamic torque converter based on numerical solution of three-dimensional flow field has higher precision and more practical value in engineering. Factors that influence axial force size are analyzed briefly and the general method of how to decrease axial force is introduced. These fruits settled the foundation for the further study.Some conclusions drew from this paper are as followings:①Due to approximate calculation of the axial force caused by interior flow in flow passage, the calculated results based on one-dimensional flow theory are smaller than practical case. The calculated results based on numerical solution of three-dimensional flow field have higher precision and the calculation method can be used for engineering purposes.②Axial force caused by interior flow in turbine is positive, and the value of axial force in high speed ratio condition is larger than in low speed ratio. Axial force caused by interior flow in pump and stator are negative. The value of axial force caused by interior flow in pump shows the gradually decreasing trend. While axial force caused by interior flow in stator is comparatively stable and negative.③Overall axial force on pump is positive, it made pump to approach turbine; Overall axial force on turbine is negative, it made turbine to approach pump; Overall axial force on stator was negative, it made stator to approach pump; Overall axial force on stator has the same direction with the axial force caused by interior flow; But the overall axial force on pump and turbine are contrary to theaxial force caused by interior flow in their flow passage.④Axial force on pump is bigger than on turbine and on stator, and it is descending slowly; Axial force both on pump and on turbine have the maximum under the state of starting condition; Axial force on stator is small all and has a downward trend while i swells.⑤Axial force on stator mainly comes from the interior flow in its flow passage, and axial force caused by no equilibrium area is small and has little effect on stator. But both pump and turbine are influenced by the flow in cavity of ab, cd, ef, gh greatly, both the direction and the magnitude of the axial force of them changed greatly.⑥Axial force in DT265 torque converter changes smoothly while speed ratio i swells, and all the axial force keeps their direction. This will be beneficial to its bearings.