| With the development of the automobile industry, NVH has become one of the most important technical indicators. The internal combustion engine vibration is the main excitation of vehicle noise. Piston slap force is one of the engine vibration excitation sources, which induced noise is the biggest mechanical noise that is only smaller than combustion noise. The vibration generated by the impact of the piston and cylinder periodically is entirely in the internal cylinder, which is difficult to measure accurately by the test method. It is of great significance for reducing engine vibration-noise and vehicle noise pollution through software modeling and simulation which can research piston slap mechanism and realize the quantitative analysis during vibration-noise. The LD1110diesel engine is selected as the research object to carry out a in-depth research to slap vibration-noise of piston, which can be a theoretical reference for diesel engine noise reduction. The main contents of this paper are as follows:(1)Each stage of indicator diagram of diesel are researched to simulate an indicator diagram curve through MATLAB programming and related parameter settings. The results show that the software simulation is more efficient and economic than test to simulate indicator diagram. (2)A detailed analysis of the movement and the force of piston is executed, then the mathematical model is built by MATLAB programming. A rigid body model of the movement of piston system is established through ADAMS vibration module, which ignores the influence of piston rings and oil film for reducing the amount of computation and improving efficiency. Finally, the calculation of the mathematical model and the results of emulational model were compared to prove the accuracy of the simulation model.(3)The finite element model of engine block is created by ANSYS software on the basis of proper simplification of engine block. The free and constrained model analyses are executed, and then a preliminary understanding of the dynamic characteristics is achieved. The analysis result shows that the large deformation lies in the place where the simple and low stiffness structure appears. Therefore, the vibration can be reduced by increasing stiffness of the structure appropriately.(4)The engine block response is researched under the effect of slap load through transient dynamics calculation after applying the piston slap calculation results to the finite element model. Transient analysis shows that the steady-state response of the vibration of engine block is mainly caused by the y-axis direction vibration of nodes which lies in the plane of left、right and upper surface of engine block.(5)The acoustic finite element model is established in ACTRAN. Acoustic model is a sphere structure which wraps the engine block, but the part of engine block is hollowed out. Spherical internal surface is the noise excited surface of engine block. The part of sphere is composed by finite elements. The spherical outer surface is the interface of finite element and infinite element. Then the noise measurement points were set according to the results calculated by the vibration. The results show that noise peak will appear in two bands of exciting force, therefore, these bands of exciting force should eliminate as much as possible in order to reduce the noise.Finally, the vibration-noise analysis is implemented under the condition of reducing the stiffness of upper edge of strut and localization, which shows that the vibration-noise of piston slap can be controlled effectively by reducing stiffness properly. |
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