| Drum brake is mainly used in medium or heavy trucks or large buses, the braking process is implemented by the friction between the Pair-Parts. The frictional contact of the braking process is a three-dimensional frictional contact of which the conditions is extremely complex and mutable, therefore, the study of the drum brake involves kinds of theories such as multi-body dynamics, tribology, contact mechanics, heat transfer theory and so on. Friction contact, friction heat and the interrelated heat and thermodynamics phenomena have important influence on the frictional behaviours of the frictional pair. Yet at the present time, studies of the drum brake are mainly carried out by theoretical analysis from a single-physics field point, which is limited within the laboratory. Therefore the studies of the stress field, the temperature field and the coupled field of the frictional pair are the most important for designing and analysing drum brakes. Domestic Automobile Enterprises are still at the stage of analogical design or empirical design in the aspect of brakes'designing and analysing , the industrial standards adopted are definition of terms, methods of bench test and requirement of brake performance, not involving the methods of simulation and methods of designing, neither the key technology for designing the automotive brake based on the multi-physics model.Aiming at the problems mentioned above, it is imperative to carry out the research of the brake's key technology based on the multi-physics field coupling by the integrated application of the digital multi-disciplinary design theories and methods, in order to acquire intellectual property rights for key thchnologies, which have economic significance and social significance.The virtual prototype technology, tribology, multibody system dynamics, contact mechanics, contact mechanics and heat transfer theory are took as this paper's theoretical and technological basis. The software of MATLAB, multibody dynamics analysis and finite element analysis are used as this paper's research tools. To build the rigid-flexibel coupling virtual prototype of the brake, to accomplish dynamics performance analysis and multi-physical finite element analysis, to build a digital designing and analysing platform and to solve the practical problems of braking failure is this paper's purpose. Thus an indepth study was implemented in this paper, whose main work involvs the following aspects:(1) The domestic and foreign study status was analyzed combined with the practical need of the subject, thus the main content of the drum brake's study was determined, the technical route was proposed and the key points of the study was recognized clearly.(2) Digital multibody dynamics model of the drum brake was built and the simulation of the braking performance based on the regid-flexible coupling method was implemented. First the three-dimensional solid model was built using the three-dimensional geometric modeling software, then the drum brake's rigid-flexible coupling virtual prototype was generated in the environment of the multibody dynamics simulation by using the multibody dynamics simulation software and finite element analysis and the Interface Technology between the softwares. At last, boundary conditons was determined, constraint was applied on the kinematic pair, and the braking performance process under defferent working conditons of the drum brake was implemented. The checking of the braking performance simulation results by bench test proves that, the rigid-flexible coupling virtual prototype which was built can accurately pre-estimate the braking performance, friction torque, braking time and so on as the response indicators, the time-domain load output could be applied as the boundary conditons in the finite element analysis.(3) The finite element analysis model was built and contact analysis was implemented in order to examine the distribution of the drum brake's contact pressure, and study the static stress field and the strain field, Getting the conclusion that the distribution law of the contact perssure between the friction lining and the brake drum is non sinusoidal, the values of which are large in the two side and small in the middle, and the distribution difference between the simulation result and the theoretical analysing result was examined. The law of the stress distribution and the corresponding strain conditions was analyzed, on this basis, the failure cause of the first cracking form of the brake drum in the truck E260 was analyzed, the analyzed conclusion was verified by experiment of examining the material, the results demonstrate that the results of the contact analysis could be used to analyse the cracking failure of the brake drum.(4) In order to analyse the dynamic varing process of the temperature and stress of the drum brake under the combined influence of the multi-physics field, the digital multi-physics coupling model of the drum brake was built, thermal-structure coupling simulation analysis and thermal failure simulation analysis was implement. First the multi-physics coupling analysis model was built, then the boundary conditons of the dynamics simulation was imported and was applied on the finite element model; Secondly, the thermal-structure analysis was implemented based on the contact analysis. The frictional heat generation and dissipation analysis was accomplished by coupling analysis, getting the temperature field of the friction process of the friction pair; the stress field under the influences from several boudary conditions was analysed. Aiming at the problem of the cracking failure of the E260 truck, the eastablished thermal-structure coupling analysis model was used to implement a simulation analysis. The analysis indicated that, the first cracking form of the brake drum was caused by the concentration of the mechanical stress at the fillet of the flange, further proving the conclusion of the contact analysis. The second cracking form of the brake drum was caused by the thermal fatigue which was caused by the thermal stress. The bench test and the material inspecting test demonstrated that, the conclusion of the simulation analysis correspond to the results of the test, that is, the establish coupling analysis model is right.(5) The digital platform for desining and analysing was developed. After building the solid model, multi-flexible-body dynamics model, finite element contact analysis model and thermoelastic coupling model, the interface file among the calculation software, dynamics analysis software and finite element analysis software was established, through file management, the softwares could achieve collaboration, realizing the coordinating working between the multi-flexible-body dynamics simulation and the finite element thermoelastic coupling analysis. On this basis,the simulation model can be refined repeatedly through bench test, and man-machine interface can be set up using the refined model, kinds of brake's properties can be simulated on computer graphically, thus the digital platform for the brake's designing and analysing was developed.The innovative work of this paper are mainly listed as follows:(1) Through the method of theoretical calculating analysis and numerical simulation technology, combined with the brake's bench test and material examining test, a digital technique of designing and analysing the drum brake's virtual prototype was provided base on the multi-physics coupling, establishing a digital platform for brake's designing and analysing. (2) A comprehensive analysing technology including kinematics, dynamics, tribology and thermoelastic coupling was used in combination with digital technology and test technology to build the thermokinetics model of the brake, the problems of the pressure distribution, thermal analysis and the stucture strengh was unified as one coupling problem, in order to study the coupling effects among the stress field, temperature field and stress field.(3) The rigid-flexible coupling virtual prototype of the drum brake was established ,of which the brake drum, brake shoes and friction film are flexible body, brake cam, idler pulley are rigid body.
|
PDF Full Text Request