Thermo-Mechanical Coupling Parametric Finite Element Analysis On Drum Brake

The brake is one of important part in vehicle safety. Drum brakes have many advantages, such as simple structure, low-cost and high brake performance. Considering theses advantages, the brakes of front-and rear-wheels are drum brakes in large-passenger cars and heavy-goods vehicles. Samely, the brakes of rear-wheels are drum brakes in middle-and-low car based on economic and practical aspects. To simulate the whole working process of drum brakes through the finite element simulation skill is a multi-field problem related to the thermal field and the stress-strain field. In order to condider the interaction between the stress-strain field and temperature field simultaneously, the thermo-mechanical coupling method must be applied. In the aspect of drum brake design, traditional design method extended the product development cycle and can not accurately predict the braking performance. So, in this paper, on the basis of three-dimensional parametric modeling, the thermo-mechanical coupling parametric finite element analysis platform was built. Using this platform, the whole braking process of light truck rear drum brake was dynamically simulated. Comparing the simulation results with the test results which were got from the drum brake bench test, the comparison result showed that these two results matched well. Facts showed that, this parametric finite element simulation platform can effectively decrease the product design and development cycles, as far as cost-reduction and quality-improvement is concerned, it has a lot of significance.The major work involves the following aspects:(1) Establishment of thermo-mechanical coupling finite element model of drum brake In the stiuation of maintaining stiffness and mechanical properties of the brake parts basically unchanged, the structure of the real brake was simplified. The three-dimensional finite element model of drum brake including brake drum, brake shoes and friction plate was built by the big general finite software ABAQUS. Then all the boundary conditions in simulation process were initially identified by theory analysis and calculation. The Thermo-mechanical coupling finite element model was set based on the these work.(2) Simulation analysis of drum brake Thermo-mechanical coupling Simulation of the drum brake used in experiment was taken in emergency brake situation. The results shown the maximum equivalent stress of brake shoes was near the end of the rotation of the leading shoe. And the force of two side brake shoe was on the location where the equivalent stress was relatively large. The equivalent stress was relatively large in the lower part of friction lining of leading shoe. While the equivalent stress was relatively large in the upper part of friction lining of trailing shoe. The equivalent stress of the two friction linings was approximately centrosymmetric distributed. In the brake drum, the maximum equivalent stress was always in the bolt connection. The results of three-dimentional stress in axial node of braking surface shown axial stress and circumferential stress were both lager than radial stress. This was the reason why the main crack was generated in the axial direction of brake drum inner surface though the whole brake drum. The result of three-dimensional stress of flange root node showed that in the radial and axial directions node was subjected to alternating stress, and the stress cycle was short. In the radial direction, the effect of the alternating stress was stronger. In this case, the brake drum was prone to generate fatigue failure. That the reason why the brake drum generated cracking in the circumferential direction at flange root generally. As a result of moving heat source and convective heat transfer, the temperature of nodes of brake drum inner surface was increased by periodically "jagged" law. The maximum temperature was not in the end of braking, but in the braking process. The temperature of radial notes of stiffener had been on the rise in the braking process due to thermal conduction. Contact pressure between friction lining and brake surface was mainly in the central part of the friction lining. To improve the distribution of contact pressure between the two, stiffeners should be properly added on the two wings of brake shoe web to increase the stiffness of both side of brake shoe. The contact area between two side of friction lining and the brake surface of brake drum should be increased in order to make the contact pressure distrubuted equably in wide direction of friction lining. At the same time, stiffeners of brake drum outer surface in contact field between friction lining and brake surface should bias "open end" of brake drum a little. So the stiffnesses in the contact field are basiclly the same. Stiffener can increase the heat dissipation area, the temperature of the brake drum can be as much as possible toward the radial ribs and near the brake drum " open end" side of the axial direction of conduction. So the heat is lost by convection with air. Then the heat is away from the bolt connections as possible to improve temperature distribution of the brake drum surface.(3) Drum Brake Bench Test Bench test of drum brake was taken by QC/T 479-1999 truck and bus brake bench test method in accordance with China auto industry standards. The results showed that the simplified structure of brake drum and brake shoes had little effect on the simulation results. And the simulation results agreeed well with the experimental results.(4) Establishment of parametic finite element analysis platform of drum brakes related to Thermo-mechanical coupling Python language was used to take secondary development on Abaqus software. At the same time, a appropriate graphical user interface (GUI) was created. So a complete set of parametric finite element analysis platform was obtained to built the drum brake model and simulate. This platform includes two parts, the pre-processing module and post-processing module. The pre-processing module can be achieved in the parametic three-dimentional model of drum brake, parametic boundary conditions and parametic meshing and so on. According to the demand, users can modify these definition parameters to get their own Thermo-mechanical coupling finite element model. After the simulation, post-processing module can view the distribution of stress and thermal fields, as well as angular velocity, angular deceleration and braking torque curve. This platform provide an effective method to shorten product development cycle, reduce the cost of product development and improve product design quality. Also, the research in this thesis has laid a good foundation for the optimization work of future drum brakes.(5) Analysis of brake preformance factors According to orthogonal experimental design method which studied the impact on brake performance from promote power, friction coefficient and friction lining, the order of three factors is:the friction coefficient> promote power> friction lining corners. Braking torque increased with the friction coefficient and promote power increasing. And with the increase of the friction coefficient and promote power, the sensitivity of brake was greater, the brake stability was worse. Increasing the wrap angle of friction linings, brake torque increase is not significant, suggesting that, when the the wrap angle of friction lining in a certain range, the increase or decrease the angle value of braking torque is not too great. Excessive increase of wrap angle of the friction linings will increase the cost and quality of brake.