Experimental Research Of NVH For New Generation Xiali Passenger Car

This paper introduces the definition of NVH, noise and vibration creation, the method of vibration & noise reduction and development of NVH technology at home and overseas. To improve whole car NVH in the development of new generation Xiali car, some work has been engaged, such as target model determination and NVH analysis; engineering plan for enhancing NVH characteristics of the developed model; HyperMesh module analysis of key parts; the trial control of the whole vehicle and final assessment, a complete test program is provided in NVH performance test at the same time.The key technology of this project is to carry out module analysis for each part, do head measurement and evaluate the professional skills of test technicians, it directly affects the project improvement and improvement effects. The test included three stages. First, carrying out the first test assessment. The assessment group made comparison with test results after the test report was provided; Second, finding out the existing problems from the first test assessment, meanwhile laying down plan improvement and countermeasures after the second test assessment has been finished; Third, carrying out the third test assessment after the plan has been implemented. Finally, the specification of the developed model has satisfied the target model requirements.The method of NVH improvement of the whole vehicle described in this paper filled in the gaps in the development of the domestic-made passenger car, we have gained lots of test results, built a development team of talented persons and developed the new generation car. Improving NVH performance in the whole vehicle development and quality improvement has great influence for our company and auto industry.Automotive riding comfort means his satisfaction level about comfort feeling when a driver is driving a car or a passenger is riding in a car, comfort concept is engaged in many fields, such as the level of noise and vibration, interior temperature and humidity and the vehicle riding characteristics, so the comfort level is determined by people's feeling. NVH improvement is issued due to studying NVH reduction technology in this paper, NVH is one of the important factors in automotive riding comfort. From till now, updated high and middle-level sedans can easily satisfy the national compulsory standards of NVH, but they are hard to meet the consumers'requirements, in other words, the issue of NVH has greatly aroused the consumers'concern. The first impression of a car, its reputation and sales on the market is influenced directly by NVH characteristics, meanwhile NVH characteristics is also a key factor whether the new model is accepted on the market.There isn't any compulsory evaluation method in NVH performance analysis because NVH characteristics study is complicated and involved in many fields. At present, NVH is divided into 10 grades (higher grade has better comfort), NVH performance evaluation is only made by the feeling of the experts when they are riding in a car, the noise level is measured by the apparatus.The method of noise and vibration reduction has two ways. First, eliminating or reducing the noise source, improving the structure design for the purpose of noise and vibration reduction; Second, controlling the noise source radiation, by damping the vibration and absorbing the noise to reduce the level of the noise. Our company pays much attention on NVH during the development of the new model. The improvement of NVH performance already has been made at the end of car structure design stage, the work flow included 5 steps described as following, first, determining the target model and measuring its NVH parameters to obtain a design reference compared with the other brand same level model; second, analyzing design structure of the developed model, adopting some structures of the target model, at the same time finding out the difference between the target model and developed model, and resolving these problems; third, determining structure design plan by CAE analysis, and making optimization with the test result; forth, making final evaluation plan; finally, implementing the design of the developed model based on test and CAE analysis, meanwhile NVH performance of the developed model must be satisfied the requirements of target model.We selected a model whose level is higher than the developed model as a target, analyzed some parts which influence the characteristics of NVH such as body, roof, dash board and engine hood in the structure design. The method of NV reduction for the target model is decided by analyzing the 10th order vibration frequency for the roof with HyperMesh, at the same time the mounting position and dimension of vibration insulator is determined to be measured by analyzing the 15th order vibration frequency for the front and rear door respectively. For some parts which can't be analyzed with CAE, by making the head measurement and installing the accelerating speed sensor at the key points to acquire the data is accomplished.With the different types of the engine, it is found that low frequency continuous noise is created in the engine compartment at idle during the first phase test, the noise must be eliminated. The engineers found that the outlet is placed in the engine, the filter at the end of the car is linked with the tank, both make the flow amount of inlet and outlet unstable during the injection, in addition, inlet and outlet are rigidly conjoined with the floor, as a result, the noise is created and directly comes into the engine compartment. The engineers decided to make the modifications, they provided three modification programs, first, the conjunction between the outlet and the floor is changed to be conjoined flexibly; second, fuel pressure releaser is installed in the distribution pipe; third, the filter is removed into the engine compartment. Finally, they decided to install the fuel pressure releaser, even though the cost is increased.The second problem is to reduce the rear noise. It's proved that the rear noise level is higher than the target model through the test evaluation. With several tests, the engineers found that the noise is created when the oil pump connected with the tank is working. Finally, they selected a best method to solve this problem.To ensure the better NVH performance, the key process for this project is to control the welding of body in-white, PVC painting, and to stick the insulating materials on some parts in car assembly.The key technology of this project is to carry out module analysis for each part, do head measurement and evaluate the professional skills of test technicians, it directly affects the project improvement and improvement effects. The test included three stages. First, carrying out the first test assessment. The assessment group made comparison with test results after the test report was provided; Second, finding out the existing problems from the first test assessment, meanwhile laying down plan improvement and countermeasures after the second test assessment has been finished; Third, carrying out the third test assessment after the plan has been implemented. Finally, the specification of the developed model has satisfied the target model requirements.Determining the comparative model, using CAE to simulate the parts and components. From the beginning process of trial body panel, we adopted subjective assessment method and road test to verify the design program, and try to solve the existing problems, in order to improve NVH performance. This project has a complete work flow process which can provide some experience for the next design development, meanwhile we have acquired a lots of test specifications from it and have possessed of capability to improve the whole car NVH performance in the car design development.