The main vibration mode of a vehicle is its exhaust system. In daily operation, the engine has a certain excitation effect on the exhaust system of the car, and the unstable road surface can also cause vibration to the exhaust system of the car. The exhaust system of the car will generate a certain excitation force during use. Applying hooks to the car body can also affect the NVH performance of the system. At present, the research focus of domestic and foreign experts is gradually shifting towards how to solve the vibration problem of automotive muffler equipment. The use of CAE tools can effectively assist in the design verification of automotive products, including design verification, 3D design, vehicle modeling, and part processing, providing relevant data and experience for actual automotive research and development work.
1、 Practical functions of CAE and automotive exhaust systems.
1. The practicality of CAE technology.
The vehicle emission system is a very complex system, which is closely related to the analysis, calculation, and design of various parts of the exhaust system during the research and development process. The use of CAE technology can comprehensively reflect all the characteristics of the exhaust system, and thus select exhaust system products that are more compatible with the engine. The application of CAE technology in the actual automotive research and development process has the following practical effects: firstly, the application of CAE technology can effectively shorten the automotive development cycle. Applying CAE technology to parametric modeling and solid modeling in automotive modeling and analysis work greatly facilitates the modification of parameters and models, and further shortens the time required to determine reasonable structural parameters. Secondly, it can effectively reduce the cost of automotive research and development. The use of CAE tools can effectively analyze the role of various components in the automotive development process, and its development cost is much lower than indoor testing and actual road testing. By using CAE software, it is possible to effectively optimize automotive components during the automotive development process, thereby developing better performing components and automotive products for users.
Before applying CAET tools, two aspects should be noted: firstly, one should be proficient in the use of CAE technology. Secondly, provide basic databases and relevant experimental data. The experimental data includes various material properties, road characteristics, and other data. This database should include the data accumulated by automotive companies during the research and development process. At present, there are still many problems in the boundary conditions and model establishment process of CAE analysis of automotive exhaust systems, and the accuracy of the analysis will affect the simulation results, lacking corresponding verification. Therefore, when conducting simulation analysis on the exhaust system, comprehensive analysis should be taken into account the coupling factors, such as the coupling between the muffler and the engine, the impact and vibration of air on the exhaust system, etc. Fluid solid and acoustic solid coupling analysis can be carried out on the exhaust system, and simulation calculations can be performed on the exhaust system.
2. Analysis of Automotive Exhaust Systems.
A system for collecting and discharging exhaust gases is the automobile exhaust system. Car mufflers, exhaust pipes, temperature sensors, catalytic sensors, and other devices. Its main function is to emit exhaust gas during the operation of the engine, achieving the goal of reducing exhaust pollution and noise. Although the appearance of the exhaust system is relatively simple, in the development process, factors such as pipe diameter, pipe length, muffler size, and frame layout in the exhaust system need to be considered. At the same time, the flow of gas in the car exhaust system should also be fully considered to avoid the phenomenon of mutual influence between the two airflows when adjacent cylinders exhaust. In the exhaust manifold, an oxygen sensor for the electronic fuel injection engine is installed, which is affected by oxygen molecules in the car exhaust and feeds back to the electronic control unit to determine the proportion of mixed gas entering the engine.
2、 CAE analysis and optimization design method for automobile exhaust system.
1. System fatigue life analysis.
According to the car muffler factory, fatigue durability refers to the ability of the car exhaust system to withstand various forms of damage, including thermal fatigue and structural fatigue. In the exhaust system, structural fatigue affects its durability, which is related to factors such as the material, installation method, fixing method, and self structure of the car exhaust system. For the automobile exhaust system, an exhaust pipe is used at the front end of the system, connected to the engine, and the other end is connected to the vehicle body with a hook. When designing, the position of the hook should be determined and cannot be changed arbitrarily. In order to effectively improve the durability of its exhaust system, the optimization process should focus on the design of exhaust system related materials and structures. A stress analysis model for the exhaust system of a certain vehicle model was established using CAD modeling, and the Goodman mean stress correction method was used to transfer it to the MSC. Fatigue analysis software. The life and fatigue values of the exhaust system were effectively analyzed, and a numerical cloud map was obtained to visually observe the fatigue life data of each node in the exhaust system.
Therefore, it is necessary to identify the effective correspondence between the areas with higher stress and shorter lifespan, which are generally located in the front muffler section, pipe welding area, front muffler section, and rear flange connection area. Through analysis, the gap between the actual lifespan and the design lifespan can be understood, and the exhaust system structure can be optimized reasonably to make it more robust and durable.
2. Establish finite element model and automobile exhaust system model.
When establishing a finite element model, specific factors such as positioning parameters and characteristic parameters should be considered. The characteristic parameters include the thickness of the pipe body and cylinder metal material in the exhaust system, engine mass, rubber lifting ears, corrugated pipe stiffness and density, etc. The positioning parameters of automobile engines include the position of the exhaust system, suspension position, center of mass position, etc. When establishing a flow field analysis grid model, the calculation range of flow field analysis is the cavity of the automobile exhaust system. When dividing the model grid, it is necessary to scientifically and effectively simplify the internal structure of the automobile exhaust system to ensure the authenticity of the simulation results. The partitioning of mixed mesh models can be divided into prism tetrahedra, prism pentagons, and prism hexahedrons. Some relatively simple transducers, exhaust pipe components, and corrugated pipes mainly use structured hexahedral grids, while more complex front and rear mufflers use unstructured tetrahedral grids. This method not only effectively improves computational efficiency but also ensures computational accuracy. When dividing the grid, the quality of the grid should be effectively controlled.
3. Summary.
In the vibration of a car, the exhaust system is a sensitive part. For car models using diesel engines, attention should be paid to the design of the structural state and the reasonable selection of suspension forms and exhaust system suspension points in the design work. CAE analysis should be used for inspection and analysis work to reduce automotive development costs, prevent exhaust system failure, and improve the quality of automotive use.
