| The transmission system of construction vehicle usually utilizes hydro-dynamic mechanical transmission to advance the adaptability of heavy load, but the transmission efficiency is too low, especially when the instantaneous heavy load was run into, the transmission efficiency will drop despite the transmission system need lager power. The effective method to solve the problem was to increase the shifts of gear-box and adopt automatic transmission technology, when the load changed, the hydrodynamic torque converter was held working at the high efficiency range through gear changes shift. It greatly enhanced the transmission efficiency of heavy load, and improved the work efficiency, the power performance and the economic performance of construction vehicle. In this scheme, the three-element hydrodynamic torque converter was selected. Moreover, the transmission efficiency of three-element hydrodynamic torque converter was relatively higher, the even transmission efficiency of construction vehicle would be further improved. Due to the superiority of this scheme, at home and abroad, the trend adopting this scheme had presented in the lately years, many scientific research persons engaged in the construction vehicle were dedicating to the research of this technology. With the automatic transmission technology development of construction vehicle, the hydrodynamic mechanical transmission system which equipped the three-element hydrodynamic torque converter will be widely applied. Because the hydrodynamic torque converter is the core device of hydrodynamic mechanical transmission system, its work performance will directly influence the quality of hydrodynamic mechanical transmission system. Moreover, it is necessary to research the design method and running mechanism of the hydrodynamic torque converter by the scientific, thorough and systemic means. The intention was to explore the scientific design method and design the three-element hydrodynamic torque converter which has the higher efficiency, it could improve not only the efficiency of hydrodynamic transmission, but the work efficiency, the power performance and the economic performance of construction vehicle. Therefore, it would have very important theoretical and practical significance to further develop research work of three-element hydrodynamic torque converter. This paper combines with the project (No.59705005) named "Study on Construction Vehicle Electronic Control for Saving Energy" and "Study on Electronic Control Method for Improving the Dynamical and Economic Performance of Construction Vehicle Hydrodynamic Mechanical Transmission System", which supported respectively by National Natural Sciences Foundation of China and Backbone Teacher Foundation of Ministry of Education, aiming at researching the methods of the design of 3-Dimension(3-D)geometric sculpting, the internal flow field numerical simulation and the performance prediction for hydraulic torque converter. The internal flow state of the hydrodynamic torque converter determines the external characteristic, the external characteristic is its external representation, and its internal flow state is ultimate inner reason. Therefore, in the paper, the advanced technique was utilized , such as the computer numerical simulation, Computational Fluid Dynamics(CFD)and Computer Aided Design( CAD). Firstly, the internal flow state was thorough researched, secondly, the relation between the outer characteristic and internal flow state was further studied. This paper includes the contents as below: 1. Introduction On the base of referring to a great deal of external and internal technique information, the various contents were summarized as below: (1)Trait, application and development of hydraulic transmission; (2)Application and development of every aspect of CFD field(such as mathematical model, numerical method, numerical solution of hydrodynamic equations and CFD soft etc.); (3)Application and development of CFD technique in hydro-machine field; (4) Application of CFD technique in hydro-component field was introduced. The existent problems at present were analyzed. For the hydrodynamic torque converter, its necessity and the feasibility of the research had been discussed by using the method, means and tools of modern scientific research. The main researching contents of the dissertation were outlined.2. 3-D Flow Numerical Simulation The multi-forms of the turbulent flow control mathematics model for the liquid were introduced, and knew that the New k-εModel due to Shih(NKE)turbulent flow model was fit for CFD analysis of the hydro-machine, which included hydrodynamic torque converter. The Finite Element Method of 3-D flow numerical simulation was researched and expatiated on. It included the discrete method for hydraulic control equations, constructing method for radix function of element, and the content of SIMPLEF and SIMPLEN arithmetic. The mathematical model which is the 3-Dimension incompressible viscosity turbulent flow Finite Element Method was established. It established the theoretic foundation to come true numerical simulation of turbulent flow for hydro-machine. 3. 3-D geometric sculpting Design of Hydrodynamic Torque Converter On the base of summarizing technique development actuality of hydro-machine CAD, the 3-D geometric sculpting method of flow parts were researched and developed. The Non-Uniform Rational B-Spline (NURBS) method, which was used to design of 3-D surface geometric sculpting for the impellers and the flow path of the hydrodynamic torque converter, was accurate and convenient. At the same time, the application of NURBS made for the design of graphics processing programs, either. And then, a set of 3-D graphics processing programs of all flow parts surface were programmed by VBA based on the software of the AutoCAD 2000. The program could accurately describe the surface of the impellers and the flow path and offer the accurate geometric boundary condition for CFD calculating and analyzing to the flow field inside the hydrodynamic torque converter. The geometry sculpting methods of the work impellers and its flow path for the hydrodynamic torque converter with Pro/E software were introduced, which has obtained the better effect by combining with the before-mentioned programs of hydrodynamic design. 4. The internal 3-D Flow Calculating of the Hydrodynamic Torque Converter Due to the hydrodynamic torque converter included rotational multi-impellers and inner mutual interfere, the flow inside the hydrodynamic torque converter is so complex that it is difficult to carry through the numerical simulation of internal flow. In this paper, the calculating model of the three-element centripetal hydrodynamic torque converter was established under the premise of the reasonable suppose, and the applied resolve scheme of internal flow field was for the first time put forward. Its core was firstly that assuming no interacting betweeneach impeller, and the impellers were separated and analyzed one by one with CFD, and then the influence between each impeller was thought over after the flow parameters of the upstream impeller exit were treated as the boundary condition of downstream impeller inlet, and the next round calculating was performed. Ultimately, the flow field of the work status was solved through calculating again and again. It accurately calculated the inner flow of hydrodynamic torque converter and opened out the pressure and velocity distributing of the flow field. Based on theory and CFD technique nowadays, the practically calculating indicated that the solving scheme was logical and applied, and it offered the practical criterion for the establishing of interferential flow theory and the forming of interferential flow numerical simulation method. The detailed process and concerned content of calculating on the impellers internal flow field were discussed and expatiated on, and the software used to calculate was ANSYS/FLOTRAN finite element analysis CFD software. At the same time, it indicates that hydromechanics problems could entirely be researched by the existing commercial software such as ANSYS/FLOTRAN in practice, and the research persons can utilize the tool to solve the concerned calculating problems. The trait of flow distributing could be further understood by observing the inner flow field simulation calculating results of hydrodynamic torque converter. The velocity field which was from the calculating indicates that the fluid between the pump impeller and torque impeller trends to flow along with the external ring side of the impellers. The fluid in the stator trends to flow along with internal ring side of stator, and the viscous flow or whirlpool could form at the external ring side of the stator exit. 5. Work Performances Prediction of the Hydrodynamic Torque Converter It is for the first time to put forward the method of predicting the performance of hydrodynamic torque converter according to the internal flow numerical simulation results, and the performance parameters of the hydrodynamic torque converter, such as the torque, the flow, the pressure, and the efficiency etc., were computed by the method. Due to circular influence between the each work impeller, the boundary condition was unable to be exactly ensured once. Therefore, to the each impeller, the boundary condition should be firstly destined, and then performed numerical simulation calculating, pictured the work performance curve and raveled the work characteristic and law of each impeller. Secondly, the...
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