| The rapid development of automobile industry puts forward higher requirements for the characteristics of NVH(Noise,Vibration and Harshness)of today’s automobiles.Brake,as an important component of automobile safety guarantee,has been regarded as one of the key quality problems in automobile industry because the Vibration and Noise of braking affect the driving comfort.The research methods of braking NVH characteristics mainly include numerical simulation analysis and experimental analysis.However,the research objects of the two methods are not consistent at present,which leads to the problem that the research results cannot be directly compared and there is a big difference.Therefore,this paper attempts to take an automobile disc brake as the research object,using the method of combining multi-body dynamics simulation and bench test,to establish a rigid-flexible coupling model of the brake based on the bench NVH test environment,to analyze the influencing factors of brake NVH characteristics,and to study the radiated noise.The main research contents of this paper are as follows:Firstly,the NVH bench test of a disc brake is carried out,and the test equipment,test scheme,test procedure,working condition and test results are analyzed in detail.The test results show that the braking noise appears near the five frequencies of 1569 Hz,1871Hz,2125 Hz,2663Hz and 2889 Hz.Secondly,the rigid-flexible coupling model of the brake is established based on the test environment,and the braking NVH characteristics are studied by using the multi-body dynamics method.According to characteristics of test apparatus,kinetic parameters calculation simulation model,the brake assembly(calliper,bracket,the piston and guide pin),Gong Jia,spindle and the flywheel parts for the rigid body model is set up,such as shock absorber damping characteristics,coil spring and bushing stiffness characteristics according to the load test curve,and the brake disc,brake block assembly and suspension set up into through modal test verified the rationality of the flexible body,a coupled dynamic model;According to the test conditions,the rigid-flexible coupling model is loaded and analyzed by simulation,and the simulation results are compared with the test results to verify the accuracy of the rigid-flexible coupling model.Then,the influencing factors of braking NVH characteristics are analyzed from three aspects: structure,excitation source and transfer path.The control variable method is used to analyze the structural factors,and the results show that changing the damping parameters of the brake disc and the friction lining can improve the braking NVH characteristics without affecting the braking performance.Through simulation,the influence of excitation and resonance sources,such as friction coefficient,brake fluid pressure,brake disc speed and other materials and working conditions,on the fluctuation of braking torque is analyzed.The results show that the larger the coefficient of dynamic friction,the lower the corresponding frequency of the peak friction,and the more obvious the vibration.The change of brake fluid pressure has no obvious effect on it.Different speed of brake disc will cause the change of the corresponding frequency and amplitude of the peak friction force,thus causing vibration and noise phenomenon.Modal test method is used to further clear source of resonance,the results show that the second order to fifth order brake disc axial modal(Y direction),support the second and third order axial modal and the brake pliers and connection plate axial mode such as the first order natural frequency of the modal and the bench test of noise frequency is relatively close to illustrate the above parts may cause resonance,braking noise phenomenon.The transmission path method is used to analyze the propagation process of braking vibration.The results show that the lower end of the suspension spiral spring has the largest vibration,and the shock absorber and bushing have significant damping effect on the vibration.Finally,the acoustic boundary element method(BEM)is used to establish the relation between braking vibration and noise,which is directly compared with the test results.Only research most likely caused by vibration and noise radiation of parts,brake disc,brake disc surface vibration results from the above as boundary conditions,the import to the boundary element model for radiation noise as a result,the results show that the simulation result of radiated noise and the result of bench test generally consistent,verified the coupled acoustic boundary element model and the feasibility of the model.Based on the NVH test environment of the brake bench,the rigid-flexible coupling model is established to conduct virtual tests,and the influencing factors of braking NVH characteristics and radiated noise analysis are studied,which has important theoretical significance and engineering application value for vibration and noise reduction design. |
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