| As a phenomenon of energy dissipation accompanying the braking process,automobile braking noise seriously affects the hearing experience of automobile users.Braking noise is often caused by a variety of factors such as materials,environment,and structure.Studying the influencing factors of braking noise has important theoretical significance and engineering value for finding out the causes of braking noise,formulating noise reduction and vibration reduction improvement measures,and eliminating the adverse effects of braking noise.The main research work of the thesis is as follows:Firstly,the bench test of a disc brake is carried out.According to the SAE J2521 test procedure,the sound pressure level,frequency and noise occurrence degree of braking noise were measured.The results show that braking noise covering multiple frequency bands is generated under the lag condition.The loudest pressure level noise of 105.71 d B(A)appears at 12200 Hz,and absolute noise occurrence degree of 4.96% is the highest at30 bar braking pressure。Then,the braking noise analysis finite element model of a disc brake is established and verified.Given the parts after the material properties to calculate the free modal of disc,pad,caliper and bracket,and compared with LMS test results,show that the simulation results and experimental results are in good consistency and brake noise analysis model of each component material properties such as setting reasonable.Then,the influence of various factors on braking noise is analyzed by complex modal analysis.According to the requirements of SAE J2521 test procedures,braking pressure was applied to the braking noise analysis model under the condition of drag section,and the complex modal simulation results under the condition of multiple braking pressures were obtained.The results are in good agreement with the indirect comparison of bench test results,and reduce the "owe forecast" degree of results of the single brake pressure,proves that the braking noise analysis model of the complex modal analysis of accuracy.A seven degrees of brake system was established.Using the braking noise analysis model,the effects of seven factors on the complex modal analysis results of braking noise were analyzed,including friction coefficient of disc,friction coefficient between other contacts,elastic modulus of brake disc and brake block,damping coefficient of damping plate,braking pressure and braking speed.The simulation results show that the contact friction coefficient of the disc and pad,the friction coefficient of other contacts and the braking pressure have obvious effects on the results.Increasing the damping coefficient of the damping piece and the elastic modulus of the pad can reduce the number of unstable modes and change the real part of the complex eigenvalue.Considering the significance of the influencing factors and the feasibility of the project,the damping piece with high damping coefficient rubber layer was selected as the initial improved noise reduction scheme.Finally,the feasibility of improving the structure of damping plate and brake disc is studied.The adaptability of the four types of damping pieces was analyzed.The bench test results show that the A-type damping piece has the best noise reduction effect,but it still fails to completely suppress the braking noise near 12300 Hz.Combined with modal analysis and strain energy analysis found that the No.9 out-of-plate mode of disc is not stable and the strain energy of disc is highest,put forward a structural improvement scheme of decreasing the thickness of the outer plate of the disc by 0.5mm along the axial direction.The modal test results show that the modal natural frequency of No.9 of disc increase by 4.52% than before improvement,and bench test results of brake noise are qualified.Then the low-frequency creeping noise performance of the improved brake was tested by the real vehicle,and the results show that the brake doesn,t produce noise with the sound pressure level over 70 d B(A)in the tested frequency band. |
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