Research On Finite Element Analysis Of Automotive Drum-Brake Thermal Properties

As traffic development and automotive amount increase, traffic accidents occur frequency and harm has become even more serious. Traffic accidents include various factors, for example persons, vehicle road, environment, and so on. Surveying traffic accidents, we find that brake system thermal decay of vehicle is typical cause. Especially for heavy vehicle, their bad working condition and heavy load result in thermal decay easy. Investigating raise of temperature of heavy vehicle's drum brake is more important.The paper introduces the raise of temperature and dissipating heat about drum brake. In braking process, brake drum inner surface rubs with friction lining, and quantity of heat comes from it. The quantity of heat contains two parts. One part is friction heat which from the two friction surfaces, the other is friction lining thermal degradation. The latter occupies 2% of all heat. So the most heat comes from friction surface. One part of friction heat in the process of braking is absorbed by brake, also part of the heat in out, that is heat dissipation. It is three manners for thermal transfer, thermal conductivity radiation and convection. Convection is uppermost manner. It occupies 80% of all dissipating heat. The three manners concur in the process of braking. The paper emphasizes convection,including the factors of affecting convection film coefficient, the measures of calculating convection film coefficient and calculation formulae.As development of finite element (FE) technique, FE software is applied extensive. ANSYS is FEA software about structural thermal fluid electromagnetic and sound field. The paper using ANSYS10.0 analyses drum brake. According to the analytic approach, the paper analyses drum brake from several aspects like below: Firstly according to the brake actual model,simplify mechanical model. Secondly establish three-dimension FE solid model. When protracting model, predigesting some parts of drum brake for the quality of latter mesh, and it affects analytical results little. Selecting elements mesh the model. Meshing is the process creating nodes and elements. When calculating, all loads and boundary condition transfer to nodes and elements. The shape of mesh direct affects calculation precision and calculation time. Because of stress and slipping between drum and friction lining, contact pair is established between drum inner surface and friction lining outer surfaces.The paper analyses the structure of drum brake. According to three phases about drum brake, structural analysis contains two load steps. First load steps putting on force. Put on rotational displacement in second load step. Analyse the results of the two load steps. After analyzing stress distribution and displacement of drum, brake shoes and friction linings, comparing the results of two load steps. In the first load steps, stress and displacement of all parts of drum brake distribute symmetrical. They distribute unsymmetrical in second load step. The differences can be seen obviously in the von Mises stress plots, displacement plots and vector plots of FEA results.Brake moment can be directly attained. The results of FEA are validated by comparison of the calculation moment with measured experimental data.Basing on the structural analysis, thermal analysis is studied. The postulate of thermal analysis of ANSYS is dealing with analytical object mesh finite elements (every element contains some nodes), and then according to conversation of energy extracting every node's thermal balance equation to a certain boundary condition and initial condition, calculating every node's temperature value, last extracting other correlative variable.In the process of braking, potential energy and kinetic energy of vehicle change to heat. From a great lot tests elicit that tyre occurs 8%~12% slip rate when it decelerate. It indicates braking energy is absorbed by two parts. One is ground and type (occupying 8%~12% of all braking energy).The other is drum brake (occupying 88%~92% of all braking energy).The drum absorbs 95%of the energy occupying by drum brake. So this paper investigates the raise of drum's temperature. Using ANSYS establish thermal FEA model. Boundary and initial conditions are put on the thermal model. The results of FEA indicate the temperature of brake drum having been broken in different speeds.The paper also tests thermal properties of drum brakes. The test contains rising temperature tests and dispelling heat tests. The tests indicate raise of brake drum's temperature and convection film coefficients of drum brake in different speeds.The results of FEA are validated by comparison of the calculation data with testing data.The research in the design and manufacture of brakes improves their dynamic performance and reliability of its work, extends their service life, and provides a theoretical basis to further optimize brake design.