Study On The Theory And Characteristic Of Low Frequency Vibration For Drum Brake

The drum brake is commonly applied to the brake device of trucks and large-and-medium-scale passenger trains. It makes use of frictional force to slowdown or park the car, and is one of the important security parts on the automobile. In the processing of pursuing the brake strength, researchers have found some problems in the course of applying the brake too, such as friction and wear, thermal, squeal and scream, judder, etc.. Nowadays there is an increasing concern over the problems caused due to the brake. This kind of self-excited vibrations may have consequences, ranging from passengers'discomfort, reducing service life, to the loss of control and catastrophe, etc.. Many years ago, researchers had begun the study on relevant problems of the brake, but the explorations on the low frequency vibration of the brake, especially of the drum brake are seldom reported.This dissertation is intended to study the drum brake low frequency vibration, and furthermore its result is used to optimize the design of drum brake. The main results and major innovations of this dissertation are as follows:Through the analysis of low frequency vibration characteristic and operation principle of drum brake, a 2-DOF (Degree of Freedom) non-linear model was proposed to simulate the mechanism of drum brake low frequency vibration. The analysis proves that the low frequency vibration of drum brake in the course of applying brake is mainly caused because of structure parameter coupling, which has important influence on its vibration characteristic.Regarding the leading-trailing shoe drum brake as the prototype, a 5-DOF non-linear model was proposed to simulate the low frequency vibration of drum brake. By analyzing the stability, the effect of the structure parameter on the system stability was also studied and the system stable-unstable regions on the parameters plane were shown. These have offered the basis for improving the design of drum brake. Centre manifold theory was applied to reduce the 5-DOF non-linear model nearby the Hopf bifurcation point, and the norm form was calculated. Through the calculation of normal form of the reduced system at the Hopf bifurcation point, the limit cycle oscillations (LCOs) amplitude was obtained. In this way, the effect of the drum brake parameter on LCO amplitude was studied.On the basis of the rigid body model, the finite element model was set up to study the characteristic of drum brake low frequency vibration in the dissertation. Compared with the results of the rigid body model, their results are similar.The method of using gene algorithm to optimize to the drum brake structure was studied in the dissertation, and meanwhile the result of stability analyzing was applied in the optimization method. The Matlab program was programmed to optimize the structure parameters of drum brake, which improved obviously the efficiency of the brake.On the basis of theoretical study, through bench testing, the test characteristic of drum brake low frequency vibration was studied, and the result of the theoretical analysis was proved at the same time.