Study On Modelling And Analysis Methods Of A New Closed-loop Coupling Model Of Disc Brake

Brake noise has been one of the most intractable issues in the automotive industry for decades. So study on brake noise is not only valuable for engineering practice, but also for academic researches. Closed-loop coupling model is one of the most effective and wildely used analysis models for brake noise. The contact between substructures in traditional closed-loop coupling models is modeled by assumed springs. But the physical meaning of coupling spring was seldom discussed and there’s no systematic method to determine the value of spring stiffness.In this paper, a new closed-loop coupling disc brake squeal model based on new modelling assumptions and modal synthesis technique is developed. The equation of dynamics of the system are derived through dynamic force analysis. The system characteristic equation is obtained through repeated nodal coordinates reduction and coordinate transformation to substructure modal space. Then, the complex eigenvalue decomposition is applied to find the unstable modes of the system. Then, negative friction slope is taken into account and leads to negative damping items in dynamic equation of system and increases the degree of the instability of the system. Different from the traditional models, where the interface nodes are coupled through assumed springs, they are connected directly in the presented model. So the complexity of modelling and uncertainty of results caused by model parameters are largely reduced.The structural instability caused by the improper matching of the structural parameters of the brake is the fundamental cause of brake squeal. Based on the new closed-loop coupling disc brake squeal model, analysis methods including substructure modal composition analysis and substructure modal parameters sensitivity analysis are derived. Those analysis methods can be used to evaluate the influence of substructure modal parameters on squeal and help to find the key substructure structure factors and determine the direction of structure modification in eliminating brake squeal.The presented model and analysis methods are applied to a typical squealing disc brake. The model prediction results are compared with those from brake squeal test. The comparision shows good consistency and the presented model is proved to be valid and effective. Then, the effect of friction character and brake pressure on the stability of system is preliminarily studied. Finally, the presented analysis methods are applied to analyse a high frequency squeal problem of the disc brake and the key structural factors that affect the squeal occurrence are found. The analysis results consist qualitatively with those from literatures and the modified direction indicated by the analysis results is qualitatively correlated with the result of the noise suppression of engineering practice, which proves the validity of the analysis methods.Through the presented work, the modelling and analysis methods form a systematic method which can be used to analyze the problem of disc brake squeal. It will provide a solid base to adopt noise suppressing solutions effectively.