| Braking vibration and noise problems have been one of the concerns of consumers for many years.Up to now,there are no ideal mathematical and simulation models at home and abroad to describe the mechanism and control method of vibration and noise during braking.The simulation analysis mostly focuses on the brake assembly or single component model,but the brake NVH bench test contains many factors such as suspension,shock absorber,bushing and so on,which leads to a great difference between the simulation analysis and the experimental results.In addition,indirect comparisons are more often used in NVH simulation analysis and experimental research of brakes in the past.Therefore,in view of these shortcomings,this paper establishes a multi-body system dynamics model based on test bench to carry out NVH research on the brake.The main work of the thesis is as follows:Firstly,the existing brake road NVH test and bench NVH test methods are analyzed and compared,and it is found that the brake bench NVH test method is more superior in analyzing the NVH problem of brake parts and components level.For this reason,the bench noise test of a drum brake is carried out according to bench test specifications,and the results show that the noise of the brake bench test exceeds the standard and exceeds the requirements of customers.Then,the reason of the low frequency judder and the noise exceeding the standard during NVH test results of drum brake bench is analyzed in order to guide the improvement design of brake.From the perspective of multi-body dynamics,the physical model of each component under the bench test conditions,boundary and analysis load are established in ADAMS,and the virtual prototype model based on the experimental environment is obtained: multi-rigid dynamic model and multi-flexible dynamic model.The results show that the simulation results of the multi-rigid virtual prototype model and the experimental results are quite different.The simulation results of the multi-flexible model considering the brake assembly and the rear torsion beam suspension as flexible bodies are close to the experimental results.The multi-flexible virtual prototype model is more in line with the actual situation.Finally,based on the multi-flexible virtual prototype technology,the causes of the low frequency judder of a drum brake in bench NVH test are studied.From the stress of theshoe drum brake,the low frequency dithering factors of vibration source and vibration transmission path are analyzed.The results of vibration source analysis show that the braking judder phenomenon is related to the fluctuation of braking moment,and the fluctuation of braking moment is related to the asynchronism of the contact between friction lining and brake drum during braking,and the pre-tightening force and stiffness of reset spring and braking pressure have influence on the amplitude of braking judder,while the coefficient of braking friction and speed have influence on the frequency of braking judder.The results of transmission path analysis show that the vibration of the lower end of the helical spring of the suspension is the largest,and the vibration of the lower end of the shock absorber and the outer end of the bushing at the connection between the suspension and the workpiece is the same.Both the shock absorber and the bushing play a role of vibration attenuation. |
