Modal Analysis And Optimization Of The Diesel Coverage

With the progress of human society and the continuous improvement of the standard vehicle, vibration and noise of the engine are problems that have become increasingly prominent. According to a survey, 70 percent of the urban noise is from traffic noise which comes mainly from motor vehicles. Furthermore, 71 percent of the motor vehicles is from the automobile engine noise. Therefore, people studied the vibration and noise of the engine in depth and do everything possible to reduce the vibration and noise and control them, which is a major task for contemporary engine workers.According to the way of radiation, the noise occurred by the engine can be divided into aerodynamic noise and surface radiated noise. Aerodynamic noise includes inlet noise, exhaust noise and fan noise. Surface radiated noise can be divided into combustion noise and vibration noise by the mechanism of noise. Because the aerodynamic noise, particularly the exhaust noise, can be greatly reduced by the silencer . Therefore reducing the surface noise that accounts for a large portion of the engine noise has an extremely important meaning for the noise control of the engine noise and the vehicle. Vibration is the source of the surface noise. Practice has shown that one can effectively control engine vibration by improving the structure and increasing the stiffness and damping. Therefore the surface radiation noise of the engine can be significantly reduced at the same time. Currently, the use of modal analysis technique is the most effective method of optimizing the structure.Because of the characteristic that diesel coverage has a big event thin surface and is the major source of the surface radiation noise. Therefore this paper uses the modal analysis and optimization technique to reduce vibration and noise.Currently, modal analysis technology is the most advanced method and mean for dynamic analysis of the automobile and other technical fields. The ultimate goal of modal analysis is to identify the modal parameters, which can provide parameters for structure vibration analysis and dynamic properties of the optimal design. The application of modal analysis for structural optimization of product design can significantly increase the scientific and enhance the efficiency of design, lower costs of design.In this paper, using a combinational method consists of the simulation of the finite element and the modal test to analysis the modal of the diesel coverage and optimizate the design.The finite element method is a continuous discrete numerical calculation. It hypothesis to be classified as a limited number of elements, which are among the nodes interconnected by a certain degree of freedom.Thus, the original continuous reason became a separated structure that is assembled by the limited number. The infinite degrees of freedom for the original problem becomes into discrete structure of the limited number of degrees of freedom. Building the finite element model is a prerequisite for calculation of finite element. Firstly, this paper selects Pro/E software to establish the geometric models of Diesel coverage, including the oil pan, Valve Cover, Gear Cover.There is a great impact on the structural components of the grid next step when establishes the geometric model. More complex of the structure, more numbers of the grid units. Therefore, the time and workload of analysis will be more, which is likely to result in modular form is not satisfactory. So the accumulated error is going on increasing and the computing precision is lowering.Depending on the above problems, this paper uses a new method to simplify the model, which is to delete holes, to simplify fillet at right angles and to shield certain structural characteristics that are unrelated to complex structure. Therefore the time of establishing the model and the workload of mesh model and calculation of finite element will be reduced. This method can efficiently increase computational speed and accuracy of the computation.Built model, it is required to carry out structural discrete mesh generation for the boundary conditions, which prepares for the boundary condition and applied load. Before meshing, one firstly needs to define the characteristics of units, including the element type, real constant definition and material attributes. Thinking of account elements of this test, the more complex the structure, workload and other factors, this paper chooses HyperMesh software to mesh grid ofFinally, using the finite element software to calculate modals of oil pan, valve cover room, gear room.Firstly put grid meshed by HyperMesh software into Ansys, based on the finite element model has been completed to set component properties and identify the parameters, and calculate the natural frequencies and mode shapes of the components. Some parameters of the components have been set forth in HyperMesh.Experimental modal analysis is a corresponding modal analysis method to finite element modal analysis. In accordance with the excitation signal types, modal test methods can be divided into nine kinds ,such as pure random, pseudo-random, periodic random, random burst, burst quickly, impact (hammer excitation), scanning sine and step sine.Although the Hammer excitation method has the weak ,for instants, signal-to-noise ratio is poor, controllable low sensitivity, high overload shortcomings, also have a very high demand on percussion test the skills and experience of its staff.However, according to its simple, rapid, low test conditions and equipment requirements, such as minimum leakage characteristics. The experiments were more exciting to use single-point pick hammer excitation experimental modal test for free. Applying LMS TEST LAB experimental modal analysis system of test equipment companies LMS, multi-channel data acquisition front-end, together LC series can impact hammer and acceleration sensors. Hammer excitation test items includes flags, incentives, site selection response, modeling, determine exciting,data collection and processing. Because of the basically same experimental methods, just use the example of gear Cover step to explain the experimental.By comparing experimental modal analysis and finite element modal calculation, know the natural frequency of the experimental and calculated the maximum error is only 7.09% less than 10%, and modal is basically identified. Therefore, a result is concluded by the experiment that is finite element model of Diesel coverage has a sufficient accuracy in a certain frequency range and can be used to model the dynamic characteristics of its expression. Dynamic optimization can also be carried out in accordance with its design.The dynamic design that is based on the results of experimental modal analysis is an improved dynamic design. Its basic tenets are described as below, based on the data obtained from the natural frequency, damping ratio, as well as local vibration frequency response function and other important information.And structuring engineering judgments have resonance; whether the structure of some important local amplitude has obvious weak links. Then, using changes in local damping, stiffness or quality to improve dynamic performance.Integrating modal analysis results of oil pan, valve cover room, gear room, this paper decides on optimizing the design of oil pan. The goal of design is to improve the stability of the Oil vibration and increase the sound insulation. With the analysis of Oil function and the forces of the Oil vibration, this paper uses dynamic stiffness ways to complete requirements of the design of oil pan. Through the simulation of the improved Oil pan one can find that the rigidity has increased and the change of the modal shape has reduced, which means that each node displacement reduces and basicly meets the design of the desired effect.