A Complex Eigenvalue Analysis Of The Squeal Propensity Of A Railway Vehicle Disc Brake System Using The Finite Element Method

Brake squeal generated by a railway vehicle disc brake system pollutes life environments seriously. At the same time, it indicates that a strong self-excited vibration occurs on the brake system, which probably leads to invalidation or destroy of the brake system. So, it is significant to study brake squeal and self-excitation vibration characteristics of disc braking systems for developing high speed railway transportation.Research on brake squeal mechanisms to decrease or eliminate brake noise and vibration is an active subject for researchers and engineers. CAE simulation and analysis methods play an important role in understanding brake squeal mechanisms. The friction motion stability and brake squeal of a railway vehicle disc brake system was modeled and analyzed using the finite element method in this thesis. The method and technology for analyzing brake squeal of a disc brake system by means of the finite element complex eigenvalue method was developed. The efficiency of the finite element complex eigenvalue analyis of a brake system could be ehanced largerly by applying them.In this paper, the author established a 3D full scale finite element model of a railway vehicle disc brake system which includes a brake disc, 2 pads, 2 pad brackets and a caliper. In the model, the friction force leads to an asymmetric stiffness coupling. A commercial finite element software was applied to solve the complex eigenvalues of the motion equations of the model. If the real part of a complex eigenvalue is positive, the corresponding mode is unstable, which may result in squeal. The influences of the friction coefficient, the friction contact stiffness coefficient and the system constraints on system stability are discussed. Based on the numerical simulation result, the following conclusions can be drawn: 1. When brake squeal occurs, the modes of the disc brake system are characterized by mode coupling. Namely, some neighboring modes with close frequencies may merge when friction coefficient varies. In the merging points, the real parts of the corresponding complex eigenvalues are positive. In the case, the brake system has a propensity of squeal occurrence.2. The coefficient of friction has a heavy influence on occurrence of brake squeal. With the friction coefficient increasing, the real part values of the complex eigenvalues of coupling modes increase and more modes with positive real parts arise. That shows that the propensity of squeal occurrence will increase.3. The friction contact stiffness coefficient has a heavy influence on occurrence of brake squeal. The propensity of squeal occurrence can be suppressed by means of decreasing the contact stiffness between the disc and pads.4. The direction of disc rotation has an influence on generation of brake squeal. It is found that the stability area without squeal increases when the disc rotation direction is counter-clockwise.5. The constraints have a distinct influence on occurrence of brake squeal. It is found that the propensity of squeal occurrence increase with the number of constraints decreasing. It is feasible to promote motion stability of disc brake systems and to suppress squeal by designing appropriate constraints for disc brake systems.6. The analysis accuracy of the finite element model of brake squeal is mainly dependent on the meshing size of the model. The number of the simulation contact springs between the disc and pads on brake friction contact faces has little influence on complex eigenvalue analysis results of the finite element model.