Root Cause Test Diagnosis And Improvement Measures For NVH Performance Of An Electric Bus

As the global environmental pollution problem is becoming increasingly prominent and the resources such as oil is getting scarce,the pollution-free and energy-saving electric vehicle is constantly getting people’s attention.Compared with traditional Internal combustion engine automobile,electric vehicle has obvious advantages in vibration and noise,but there are still some problems that need to be solved urgently.Electric vehicle uses motor to provide power,It has no internal combustion noise,instead,the motor produces high frequency noise.Without the noise of the internal combustion engine,there is no masking effect,this makes noise from air,suspension and tires more easily heard.electric vehicle still has vibration and noise problems.Designers also need to study the NVH problem of electric vehicle.In this paper,an electric vehicle modified from a light bus was studied.The current vibration and noise performance of the electric vehicle was analyzed,and was compared with the traditional vehicle,and some NVH performance problems of the electric vehicle were found,and the corresponding optimization suggestions and improvement measures were given.Firstly,the current vibration and noise performance of the electric vehicle was analyzed through the LMS.TEST.LAB system and the corresponding equipments.And the vibration and noise data of each excitation source and response point of the vehicle was measured.This test contains vehicle vibration and noise test,vehicle ride comfort test,vehicle acceleration driving outside noise test,etc.Through the analysis of the data,some problems of the vibration and noise of the vehicle were found,and the corresponding improvement and optimization plan was put forward.Secondly,according to the principle of the finite element modeling,the finite element model of the electric vehicle frame and body-in-white was established and their modal characteristics were analyzed.The finite element model was based on the original established three-dimensional model which was established based on appropriate simplification and geometry cleaning.Through the modal analysis,the natural frequency and the corresponding formation of the frame and the body were calculated.And then compared with the vibration peak frequency measured by the test,the cause of vibration and noise was found.it can provide a reference for the reasonable distribution of the natural frequency of the motor mount system.It was also prepared for further optimization.Thirdly,on the basis of measuring the structural parameters of the motor mount system,its simulation model was established in MATLAB and ADAMS software.And then the natural frequency,formation and energy decoupling rate of the motor mount system were solved through simulation.The performance of the vehicle was evaluated by the data,and the improvement program was presented.Finally,the energy decoupling rate of the motor mount system was optimized by Isight and MATLAB software.The energy decoupling rate of motor mount system was optimized with multi-island genetic algorithm.The natural frequency distribution of the mount system was optimized by changing the position and stiffness of the mount.Through the optimization of the motor mount system,the NVH performance of the electric vehicle was improved.