Dr. Quan Wang, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Dr. Zhiwei Wang, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Prof. Jiliang Mo, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Research and /or Engineering Questions/Objective: The disc friction brake which consumes the kinetic energy of the high-speed train through disc-pad friction is one of the important approaches to brake or decelerate the train as well as the safety and performance assurance. However, the friction between the brake pad and the disc may lead to the vibration of the brake components in the braking process. And when the friction-induced vibration of the disc brake system is transmitted through the suspension system to the bogie, it not only reduces the stability of the train operation and the ride comfort for the passengers, but also causes damage to the brake device and reduces the service life of such system. what’s worse, the vibration may provoke noise problems. Therefore, the mechanism of friction-induced vibration of the disc brake system and the method to eliminate the unstable vibration require in-depth research.

Methodology: The experimental research, finite element method and numerical simulation are widely used in the analysis of the disc brake system and a great deal of meaningful research achievements have been obtained. In this article, to reflect the vibration response of the disc brake system more realistic in the braking process, a three-degree-of-freedom dynamic model of the disc brake system for the China Railways High-Speed train CRH5 is established by considering the effect of the wheel/rail adhesive characteristics and the number of brake units (the powered wheelsets installs two brake units and the non-powered wheelsets installs three on CRH5). Then, the model is applied to analysis the nonlinear dynamic response under different brake conditions to investigate the stability of the disc brake system using the numerical integration method. And diagrams of bifurcation, phase plane, Poincaré map and time domain response are used to discuss the vibration characteristics of the disc brake system in details.

Innovation: The nonlinear friction between the brake disc and pad, and the nonlinear interactions between the wheel and rail are considered in this three-degree-of-freedom model. And it can be applied to investigate the effect of wheel/rail adhesive characteristics, parameters and the number of brake units on the disc brake system.

Results: Results show that with the increasing of the brake force, the brake pad occurs periodic motion and chaotic motion alternately, and the region of chaotic vibrations is growing while the region of periodic vibrations is decreasing. In addition, the stick-slip vibration of the brake pad and the torsional vibration between the brake disc and the wheelset are more complicated and violent with a larger brake force. It also shows that the chaos phenomenon of the disc brake system only occurs when the vehicle speed is less than the critical speed, and after that the system maintains stable periodic vibrations. Moreover, the results obtained with different number of brake units reveal that the chaotic region of the disc brake system with three brake units is narrower than the system with two brake units. It indicates that the high-speed train adopted three brake units to undertake the decelerating or braking task is more stable.

Conclusion: The research result can provide useful references for the design of the brake conditions and the vibration control of the disc brake system. The dynamic model proposed can also be applied to discuss the effect of parameters on the stability of the system further.

Dr. Qiang Liu, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Prof. Jiliang Mo, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Dr. Zaiyu Xiang, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Dr. Anyu Wang, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Mr. Wei Chen, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Mr. Honghua Qian, Tribology Research Institute Southwest Jiaotong University Chengdu 610031, P. R. China, CHINA

Research and /or Engineering Questions/Objective: Friction-induced vibration is a common phenomenon on the frictional contact interface between two solids in relative motion, which can be observed in many mechanical applications, especially for the brake system. The friction-induced vibration originated from the friction interface can transmit through the rigid connection structure of mechanical system and forms a vibration transmission path. The vibration transmission path, mainly reflected by the natural frequency and the damping ratio, influences the friction-induced vibration of system, even under the same friction interface. However, there is limited report on the friction-induced vibration of mechanical system under different vibration transmission paths. Therefore, the effect of structural stiffness in vibration transmission path on friction-induced vibration is investigated and discussed.

Methodology: The friction tests are carried out on a small-scale tribometer, which achieves a frictional contact between the balls and disc samples. The structural stiffness of vibration transmission paths is reflected by different fixtures of samples, whose dynamic characteristics are tested by the hammer method. In addition, a detailed three-dimensional finite element model based on different structural stiffness in vibration transmission paths is established to simulate the experimental process. At last, a four-degree-of-freedom friction-induced vibration model, including the interaction between the structure characteristics and the friction interface, is established to investigate the influence of the vibration transmission paths on the system stability.

Results: The instability of the friction system decreases with the increasing structural stiffness in vibration transmission path. However, when the structural stiffness exceeds the critical value, the instability of friction system is excited again, accompanied by severe friction-induced vibration and high frequency squeal noise. Similarly, the wear morphology is also influenced by vibration transmission paths. The higher structural stiffness is, the better tribological behavior of the contact interface is displayed. Once the critical stiffness is exceeded, more complicated tribological behavior of the contact interface is shown.

Limitations of this study: Applying the findings to practice system is still under studied since a real friction system is much more complex comparing to the customized small-scale tribometer.

What does the paper offer that is new in the field in comparison to other works of the author: The effect of structural stiffness in vibration transmission path on friction-induced vibration is investigated. The conclusions obtained by experimentally and numerically are beneficial for understanding the effect of structural stiffness in vibration transmission path on stability, vibration response and tribological behavior of the friction system.

Conclusion: The results show that the stability and vibration response of the friction system is significantly affected by vibration transmission paths. Evaluating and eliminating the influence of vibration transmission path on the friction-induced vibration is extremely crucial and meaningful for investigating the generation mechanism of the friction-induced vibration more precisely.