The main vibration mode of the vehicle is its exhaust system. In the daily operation of the vehicle, the engine plays a certain excitation role on the vehicle exhaust system, and the unstable driving road will also vibrate the vehicle exhaust system. The vehicle exhaust system will produce a certain excitation force in the process of use. Acting on the vehicle body through the suspension hook will also affect the NVH performance of the system. At present, the research focus of relevant experts at home and abroad gradually focuses on how to solve the vibration problem of automobile muffler equipment. The use of CAE tools can effectively assist the design verification of automotive products, including design verification, three-dimensional design, vehicle modeling, parts processing and other links, and can provide relevant data and experience for the actual automotive R & D work.

一、 CAE and practical functions of automobile exhaust system.

1. The practicability of CAE technology.

The vehicle emission system is a very complex system. In the process of R & D, it is closely related to the analysis, calculation and design of each part of the exhaust system. The use of CAE technology can comprehensively reflect all the characteristics of the exhaust system, so as to select the exhaust system products that better match the engine. The application of CAE technology has the following practical functions in the actual automobile R & D process: first, the application of CAE technology can effectively shorten the automobile development cycle. The application of CAE technology to parametric modeling and solid modeling in automobile modeling and analysis greatly facilitates the modification of parameters and models, and further shortens the time required to determine reasonable structural parameters. Second, it can effectively reduce the cost of automobile R & D. The use of CAE tools can effectively analyze the role of automobile components in the process of automobile R & D, and its R & D cost is much lower than that of indoor test and road actual test. Using CAE software, auto parts can be effectively optimized in the process of auto R & D, so as to develop better parts and auto products for users.

Before applying caet tools, we should pay attention to two aspects: first, we should master the use of CAE technology. Secondly, the basic database and relevant experimental data are provided. Relevant test data include various material characteristics, road characteristics and other data. The database should contain the data accumulated by automobile enterprises in the R & D process. At present, in the CAE analysis of automobile exhaust system, there are still many problems in the process of boundary conditions and model establishment. The accuracy of its analysis will affect the simulation results and lack of corresponding verification. Therefore, in the simulation analysis of the exhaust system, the coupling factors, such as the coupling between muffler and engine, the impact and vibration of air on the exhaust system, should be comprehensively analyzed and considered. The fluid solid and sound solid coupling analysis of the exhaust system can be carried out, and the simulation calculation of the exhaust system can be carried out.

2. Analysis of automobile exhaust system.

A system for collecting exhaust gas and discharging it is an automobile exhaust system. Automobile silencer, exhaust pipe, temperature sensor, catalytic sensor and other devices. Its main function is to exhaust the exhaust gas during engine operation, so as to reduce exhaust pollution and noise. Although the shape of the exhaust system is relatively simple, in the development process, it is necessary to consider the pipe diameter, pipe length, muffler size, frame layout and other factors in the exhaust system. At the same time, it is also necessary to fully consider the flow of gas in the automobile exhaust system to avoid the interaction between the two air flows during the exhaust of adjacent cylinders. In the exhaust manifold, the oxygen sensor of the EFI engine is installed, which is affected by the oxygen molecules in the vehicle exhaust and fed back to the electronic control unit to make it enter the mixed gas proportion of the engine.

CAE analysis and optimization of automobile exhaust system

二、 CAE analysis and optimization design method of automobile exhaust system.

1. System fatigue life analysis.

According to the automobile muffler factory, fatigue durability refers to the bearing capacity of the automobile exhaust system to withstand various damage modes, including thermal fatigue and structural fatigue. In the exhaust system, structural fatigue affects its durability, which is related to automobile exhaust system materials, installation methods, fixing methods, self structure and so on. For the automobile exhaust system, the exhaust pipe is used at the front end of the system to connect with the engine, and the other end is connected with the vehicle body with a hook. During the design, the position of the hook shall be determined and can not be changed at will. In order to effectively improve the durability of the exhaust system, the optimization process should focus on the design of relevant materials and structures of the exhaust system. Aiming at the CAD model of exhaust system of a certain vehicle model, the stress analysis model of automobile exhaust system is established, and it is transferred to MSC. Fatigue analysis software by Goodman average stress correction method. The life and fatigue value of automobile exhaust system are effectively analyzed, and the cloud diagram is obtained, which can intuitively observe the fatigue life data of each node in automobile exhaust system.

Therefore, find out the effective correspondence between the position with high stress and the position with short service life, which is generally located at the front muffler section, pipe welding, front muffler section, rear section flange, etc. Through the analysis, we can understand the gap between the actual life and the design life, and reasonably optimize the structure of the exhaust system to make it more durable.

2. The finite element model and automobile exhaust system model are established.

When establishing the finite element model, the specific conditions such as positioning parameters and characteristic parameters should be considered. The characteristic parameters include the thickness of pipe body and cylinder metal material in the exhaust system, engine mass, rubber lifting lug, bellows stiffness and density, etc. The positioning parameters of automobile engine include the position of exhaust system, mounting position, centroid position and so on. When establishing the grid model of flow field analysis, the calculation scope of flow field analysis is the cavity of automobile exhaust system. When dividing the model grid, we should scientifically and effectively simplify the internal structure of the automobile exhaust system, so as to ensure the authenticity of the simulation results. The hybrid mesh model can be divided into prismatic tetrahedron, prismatic pentahedron and prismatic hexahedron. Some relatively simple buzzers, exhaust pipe components and bellows mainly use structured hexahedral grid, while the more complex front muffler and rear muffler use unstructured tetrahedral grid. This method can not only effectively improve the calculation efficiency, but also ensure the calculation accuracy. When meshing, the mesh quality should be effectively controlled.

CAE analysis and optimization of automobile exhaust system.

三. Summary.

In the vibration of the vehicle, the exhaust system is a sensitive part. For the vehicle model using diesel engine, attention should be paid to the design of structural state in the design work, and the suspension form and suspension point of the exhaust system should be reasonably selected. CAE analysis should be used for inspection and analysis to reduce vehicle R & D cost, prevent exhaust system failure and improve vehicle service quality.