| Hydraulic excavator is the major construction machine in the earth moving, excavation and engineering field, and it is widely used in the mechanized construction of energy, transportation, water conservancy, urban construction and modernized military engineering field. Working mechanism is the main part for earth excavation, so the performance and reliability of working mechanism become the important symbol of machine.The work of the mechanism is completed by compound action of three fuel tanks and the interaction of earth moving, of which the movement and force analysis is quite complex. As domestic manufacture of hydraulic excavator is lagged behind and lack of design theory as a guide, traditional way is still used for the design of working mechanism. In practical application, arm crack, unreasonable excavation region, machine intervene and early failures of hinge often occur, which result in tremendous loss and directly influence the development of domestic excavator filed. Compared with other engineering machine, domestic hydraulic excavator is lack of competitiveness and has the lowest share in domestic market.Combining scientific research project from enterprise, aiming at the key common problems of working mechanism design, the paper makes systematic study on key technology of the finite analysis for working mechanism, the design for hinge bearing and the integrated optimization for mechanism kinematics and dynamics. The design theory is enhanced and the paper provides theory reference and practical method for working mechanism design and is of great significance for domestic excavator development.The main research work and innovate achievements are as follows:(1) Working mechanism is the main component of hydraulic excavator and its performance directly determines the performance of the whole hydraulic excavator, which brings high demands for working mechanism design. First a comprehensive analysis is performed for hydraulic working conditions. On the basis of work characters, the design of working mechanism is studied to meet the requirements for geometry, dynamic characteristics, structure strength, economic and other aspects of hydraulic excavator. And design principle is discussed. All of the research work has important guiding significance.(2) By comparing the current development of hydraulic excavator working mechanism from both domestic and foreign, the paper presents an integrated and refined 3D finite element analysis for working mechanism. Take excavator as an example, the 3D model of working mechanism is established. Based on assessment of preliminary finite element, the way of establishing finite element model is determined. Selected five typical working statuses, the paper makes stiffness, strength and modal analysis for assembled working mechanism, and takes test for actual product. The results show that stress distribution of work mechanism can clearly explain failure cause and the result can be applied for the guide of working mechanism design. In the paper, the excavator design method is improved and a new approach is provided for similar product design and analysis.(3) There are many hinge points in hydraulic working mechanism. There is relative rotation between hinge shaft and bushings, and the transfer load is high. The fit clearance between the hinge shaft and bushings directly affects the reliability. If the clearance is too small, it is difficult to form a stable lubricant film, and can easily cause friction, wear and fracture damage. If the clearance is too large, the fatigue life of the hinge shaft and bushings is affected. Therefore, a reasonable clearance between shaft and bushings is so important for the design of excavator working mechanism design. We obtain the following achievement for such key technical issues: 1) The fit clearance between hinge shaft and bushings of excavator working mechanism should guarantee to form the stable lubricant film required. The factors that should be fully considered when determine the smallest fit clearance are: the minimum security value of lubricant film thickness, the comparative deformation of the shaft, the surface roughness between the shaft and bushings, the linearity of the shaft, the circularity of the bushings inner circle, the shrinkage of bushings endpore after assembled and the reduction of the clearance due to the temperature raising. 2) The relationship between the change of the fit clearance and contact pressure of hinge shaft and bushings is close to a line. As the clearance increasing, the contact pressure become larger, and it can affect the contact fatigue life of shaft and bushings. Therefore, after the clearance between hinge shaft and bushings is primarily identified, Hertz formula is used for the calculation amendment of contact stress. 3) Adopt the 200kN excavator working mechanism as a study subject. Through the calculation and analysis of the clearance and the comparison between domestic and international clearance design, we find that the calculation theory and method of clearance in the paper is feasible, which is of great value and significance for determining the clearance of shaft and bushings and improving the design of excavator working mechanism.(4) According to the design requirements for excavator working design, based on the kinematic and dynamic analysis of working mechanism movement, the paper brings up the nephogram concept of breakout force for visual description of the excavation performance in certain field. And a kind of visualized and professional software for performance analysis of excavator working mechanism is developed. The software is object-oriented and can quickly and accurately analyze the reasonability of the working mechanism and its structure design, including movement characteristics, mechanical properties, and the distribution of breakout force etc. The software is visualized and its operation is simple. It can significantly shorten the design cycles, reduce the cost of product development and improve the design quality. In addition, the software can not only calculate for a large number of models but also collect data for optimization and provide simple reference.(5) Optimization of working mechanism is vital to the design of a hydraulic excavator, which is able to improve the whole machine'working efficiency and property. Optimization of working mechanism can't find the optimal solution by the common optimal algorithm, which is a multiobject, multivariable and multiextremum constrained nonlinear problem. The genetic algorithm have the capability of global optimization, which can solve a lot of complicated optimization problems. It is able to solve the antiprotrusion and antisuccessive optimization problems ,which is widely applied in structure fields. This paper optimized the kinematics and dynamics of the working mechanism by genetic algorithm. Base on parameters of the working mechanism, the mathematical model of optimal parameters design is built, which use in genetic algorithm. Through optimizing parameters of working mechanism, digging property improve evidently, under the premise of the kinematics and dynamics to be able to meet the requirements. Optimization project is widely applied in enterpriseThe innovative work is summarized as:(1) The method of finite element analysis is present. The finite model of hinge is established by using beam element and entity element. So the systematic modeling and load analysis for frame, boom, arm, bucket, tank and connecting hinge shaft can be achieved. The nonlinear finite element analysis and model analysis for working mechanism are performed, and its result is validated by on-site strength test. The results show that this overall integrating analysis method of working mechanism can significantly reduce the calculation error causing by simplifying and excellently guide the hydraulic excavator working mechanism design.(2) Analyzing the excavator working mechanism hinge failure mechanism, integrating a great deal failures of the working mechanism hinge with enterprise's key problem. According to hydrodynamic pressure lubrication theory, bring forward calculating formula of smallest gap and the biggest gap restrictions between the hinge axis and bushing. The applying in engineering practice of this method shows the calculation theory and the methods of hinge axis and bushings in this paper is feasible and have high application value and guiding significance to improve the design level of the working mechanism of the excavator.(3) Bringing forward performance visualization prediction method of the hydraulic excavator working device. According to the working mechanism performance visualization prediction method, a practical software is developed and a new method—excavating force nephogram is proposed which can intuitively describe the excavating performance in a area.(4) The optimum design model is established, which chooses the excavating performance in particular areas as the optimizing goal and uses the movement and mechanical properties of building up the constraint conditions. Using the genetic algorithm to optimizing the working mechanism of the excavator, the results show that the defects of the original design are avoided and the excavating performance is improved. Optimization approach has been adopted by the enterprise.
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