Bus Body Modal Analysis And Optimization

In recent years, with the improvement of people’s living standards, government regulations on noise limits more and more strict, people also put forward higher and higher requirements for the comfort of passenger cars. Bus body structure is a space truss, mainly profiles based, Natural frequency is low, the low order modal frequency is easy to be excited by the power system and the road surface to produce structural resonance, so that the vehicle noise and vibration value exceeds the standard, Reasonable body mode is very important to the bus performance of the NVH, At present, the research on the NVH of the car body mode is becoming more and more mature, But for the full load truss structure of the bus, there is no detailed report, Therefore, it is necessary to study the problem of the vibration caused by the vehicle body mode.Firstly, this paper introduces the research status of the vibration and noise of passenger car, mainly from two aspects of technology and mode analysis. Then the mechanism of the noise and vibration in the passenger car is introduced, and some measures are summarized. Then, the test method of the vibration and noise of the passenger car is described. The problem of excessive vibration of wheel and floor in the idle mode, and the noise in the vehicle is studied. Firstly, using the method of LMS modal test to carry on the modal test, The analysis of the data that the steering system modal frequency and the engine ignition frequency coupling and The lack of the steering system’s stiffness is the cause of the excessive vibration of the steer wheel. Because the steering system is fixed on the body, the vehicle needs to be modeled. The model of a school bus is modeled in HyperMesh. The Optistruct solver is used to carry out the modal analysis. According to the results of the analysis: Front rail structure stiffness is not good and the body of the first bending mode near the engine idling excitation frequency is the main reason causing the floor vibration. At the same time, the vehicle stiffness is not good, when the car traveling on rough road or by the impact, the body deformation is large, some parts of the low frequency range of resonance, resulting in the vehicle noise value will exceed. The vehicle body structure and steering system structure are modified. the modified passenger car for vibration testing, found that the steering system idle vibration qualified and body floor Y to vibration. Then the modal test of a passenger car is carried out. The finite element model is modified by the results of the test. Rational design of the body structure, sensitivity analysis of key parts, Through the analysis and optimization of the body mode, the vibration of the car’s steering wheel is reduced by 79%, the floor vibration value is below 0.2 m/s2, the noise value of the car is decreased by 5-6dB.this paper takes a bus body vibration as an example, discusses the use of diesel engine and the engine front, Transfer path analysis of steering system vibration and floor vibration, for vehicle body mode research and get the basic method and thought of vibration control of the bus, and through the optimization of its body structure to get good results. With CAE for the body to carry out modal analysis and sensitivity analysis of key components, can accurately identify the impact of the sensitive components, and then improve the overall modal frequency by modifying the structure and increasing the thickness of the plate. Saving the cost of automobile development, shortening the development cycle, the method can also be used for the optimization of other NVH performance of the whole vehicle, which has a good prospect of engineering application.