| Drum brakes are the common brake equipments for the large and medium-sized buses and trucks for their compact structure, reliable performance, large brake power, and easy to install mount devices. However, during the running on the city's streets, there are often appearing avoiding cars, emergency stops etc. Such emergency braking conditions often lead to the complex of braking anomalies. The abnormal phenomena mainly include uneven wear phenomenon, self-locking phenomenon, low frequency vibration such as braking judder phenomenon etc and high frequency vibration such as brake squeal phenomenon etc. While uneven wear phenomenon and self-locking phenomenon also directly induce the low frequency vibration and high frequency vibration phenomenon, therefore, it is can be said to a large extent that the abnormal brake phenomena can be considered as the NVH (noise,vibration and harshness) problems, which also called the braking and vibration noise problems.For the brake anomalies mentioned above, there are no clear explantions from the existing theories and numerical models. Therefore, the academic purpose of this paper would be to explore some modeling methods to characterize such issues of brake anomalies based on the existing research achievments. The key points and difficulties of the technology exploration route are the realization of the cam drive model, the multi-point-plane contact model between flexible drum and brake linings with the algorithm of separation of static friction force and dynamic friction force. Focused on the phenomena of uneven contact and friction between the drum and linings during the braking process, analyzed the brake vibration and noise problems on the base of the interpretation of such relative phenomena, and explained the relative phenomena about brake vibration and noise.This paper explored the following discussions according to the technology exploration route.First of all, this paper built the flexible multi-body dynamic simulation model of the S-shape cam drum brake according to the technical requirement. Corresponding the key points and difficulties mentioned in the technology route, this model has the following features: (1) the drum is introduced as flexible body, so that it could be observed the deformations and its variations of the drum during the brake process, therefore, the brake problems concerning the drum's deformations could be discussed. (2) To establish and improve the cam drive model to realize the process of braking under the given drive manner. (3) Considering the stiffness between the drum brake and the axle in order to consider the possible influence of the stiffness. (4) The realization of multi-point-plane contact model between flexible drum and brake linings with the algorithm of separation of static friction force and dynamic friction force between the drum and brake linings in order to observe the distribution and variations of static friction state. The accordance between the simulation results and the existing reference shows that the model built in this paper meets the technical requirements mentioned before, and the model could be the basement for the further relative study.Secondly, this paper discussed the related issues of low-frequency brake vibration and noise problems. In generally, it is believed that the variability of the friction torque is the main factor which induces the brake vibration and noise. However, there are little existing literatures on discussing the cause of the time-varying friction torque. Because of the concerning of the multi-point-plane contact model and taking into account the deformation of the drum in the simulation model, through the study of the pressure and its variation of the linings, the contact conditions between the drum and linings, as well as the deformation with its variation of the drum during the brake process, this paper argues that, the time-varying friction torque which induced by the non-synchronization contact between the brake linings assembly and drum was the reason of causing the low-frequency brake vibration and brake noise, especially the phenomena of non-synchronization contact between the leaking shoe linings and drum as well as the elliptic deformation and its variation.In addition, the elliptical deformation easily leads to the emergence of the phenomenon of wedge-shaped effect, which induces the self-locking and braking judder phenomenon during the process. From the process of the development and changes of the drum's deformation, the brake judder is mainly related to the top of the leaking shoe linings and the bottom of the trailing shoe linings. For the principles of elimination or relieve brake noises'phenomenon (including its frequency shift phenomenon), according to the analysis of this article, the essence of this work is to improve the contact condition between the linings and drum, reduce the sensitivity of the pressure distribution as well as its variation of the linings about the relevant factors such as brake pressure and brake pressure's rate etc. at the same time, the elliptical deformation of the drum is the other factor to be considered.Thirdly, this paper discussed the related issues of high-frequency brake vibration and noise problems. Because of the concerning of the multi-point-plane contact model as well as taking into accounts the algorithm of separation of static friction force and dynamic friction force between the drum and brake linings, the analysis found that, during the brake process, there are circumferential and axial reciprocating sliding phenomena between the linings (especially the leaking shoe linings) and drum, at the same time, there is the switching phenomenon between static friction state and dynamic friction state. Modal analysis results showed that the change of the drum's frequency characteristics with the switching of static friction state and dynamic friction state. On this basis, this paper purposed that the reciprocating sliding between the drum and brake linings (especially the leaking shoe linings) could provide the resource of the vibration, and under the variation friction boundary conditions, the diversity of the drum's inherent characteristic could match the frequency of the resource frequency, the resonance between the two leads to the brake squeal. Through the simulation analysis, from the reverse confirmed the rationality of the speculation about the mechanism of brake squealsBased on the conclusions mentioned above, this paper explained some phenomena about brake squeals during the braking process. At the same time, this paper discussed some principles to eliminate or relieve brake squeals'phenomenon (including its frequency shift phenomenon). The essence of such work is to improve the friction contact conditions between the linings (especially the leaking shoe linings) and drum, and reduce the occurrence of reciprocating sliding phenomena, as well as avoid the phenomena of non-synchronization contact between the linings and drum.Finally, based on the exiting experimental conditions, this paper selected the road test and from the perspective of road test made the related study of the brake vibration and noise problems. By excluding the impact of road environment, and the other negative factors of sound resources, many bus brake tests considering different braking pressures and different speeds had been done. Through the analysis of the frequency distribution and variation of the noise signal, the author found that the contact situation between the linings and the drum was the major factor in making vibration and noise. At the same time, braking pressure, especially the rate of change of braking pressure had large impact on brake vibration and noise. This also confirms the related conclusions of the simulation analysis part. In addition, the test showed that elimination or relief the brake vibration and noise significantly by installing new brake device and the replacement of new linings and drum which could improve contact situation between the linings and drum. It also could be seen, that the discussion about elimination or relief the brake vibration and noise during the related simulation part was consistent with the experimental results. To sum up, this paper exploered the technology in accordance with the technology exploration route mentioned before, using the existing theoretical methods and simulation conditions, and built the flexible muti-body dynamic simulation model of the drum brake. From the dynamic simulation point of view, not only could explain the phenomena of uneven contact and friction between the drum and linings during the braking process during the brake process, but also give the reason of the brake vibration and noise. Tests showed that the results of this study about elimination or relieve brake noises'phenomenon could be used the guide the design and manufacture of drum brakes.
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