Structural Optimization Design Of Crank Link Mechanism In Automotive Engine

Optimization problem exists in all the departments of national economy and all fields of engineering applications. Structural optimization design means to optimize the interface size of various component elements so that the overall structure can achieve the desired effect for example to reduce costs, improve stiffness and control the vibration, when given the type, materials, layout of the topology and geometry of the structure. Crank link mechanism is one of the two major components in the engine, which directly affects the size of the engine size and weight, so to design the lighter and all aspects of design performance meeting the requirements of the crank is an important work.At present the main methods for structural optimization design are multi-bodies dynamics simulation, finite element analysis, optimal design theory methods and structural optimization design of critical components in automotive. And structural optimization design of critical components is the central issue of the current virtual manufacturing and assembly areas. The subject in my study is crank link mechanism. Firstly I will establish the parameters of three-dimensional digital model of it, and then optimize its size which will use the finite element method in optimization algorithms.The shape of crank link mechanism is very complexly because there are many small fillet and small hole, if you consider all these factors when modeling will increase the solution error and decrease the precision. Therefore, the process of its geometric modeling should be as simple as possible, without affecting the solution precision. Firstly, we will introduce the design requirements of the engine piston, connecting rod, crankshaft and build their three-dimensional model using CATIA. And then fitting them together, doing thermal coupling analysis of the assembly to solve its stiffness and strength evaluation problems. Finally, through the simplification of the these parts we establish the theoretical model of piston, connecting rod and crankshaft based on its force and motion features and other aspects. Supposing the bore, cylinder spacing, trip is not mutative and the structural dimensions of the connecting rod, crankshaft is in a certain proportion, we get the optimization model of the piston, connecting rod and crankshaft. The objective function is volume, the constraints are the structure size and physical stress must be less than the maximum permissible value. Above all, finite element method will be built in the first Order algorithm or sub-problem approximation algorithm within ANSYS to get the optimal solution. The results mean that piston, connecting rod and crankshaft can meet their stiffness and strength requirements with smaller size when the agencies load and constraint conditions on the crank link mechanism unchanged.