Evaluation And Optimization Of Vibration And Noise Of Diesel Outboard Engine

As the most widely used power device,internal combustion engine is determined to generate vibration due to its unique form of motion and structure.With the development of engine to the direction of faster speed,stronger power and higher efficiency,noise and vibration has gradually become an important parameter to judge the performance of engine.For ships,the engine becomes the most important source of noise and vibration.Outboard engine is widely used in boats near the beach.Due to the different engine layout and working environment from vehicle,the more complicated vibration and noise problems are caused than vehicle.In addition,the outboard engine body is directly exposed to the environment.All of these factors lead to very severe vibration and noise problems.Therefore,it is necessary to carry out vibration and noise research on outboard engine,discuss the vibration and noise problems generated by the engine,and optimize them.This research project is funded by the school-enterprise cooperation project.It uses both simulation and experiment method to evaluate the vibration and noise of a threecylinder outboard diesel engine,and optimizes it in effective ways.The main contents of this paper are as follows:First of all,based on the three-dimensional model of engine parts in Pro/Engineer,the assembly modeling of the whole engine is built up,the assembly interference of the model is checked,and the correctness and rationality of the geometric parameter of engine model are verified.Then the finite element model of outboard engine is established,including the finite element model of engine block,valve cover shell,oil pan and other main components.The modal analysis is carried out to find out its natural frequency and formation.At the same time,the dynamic model of the crankshaft piston connecting rod system is established then by defining the constrain and the motion relationship,the response of the power system and the force received at the main bearing of the body are obtained.It provides the basic data for the calculation of the structure acoustics response and noise of the whole engine.Secondly,the acoustic mesh of the whole machine is established based on the finite element model of engine.The boundary element method and the modal-based acoustic transfer vector method are used to calculate the acoustic and vibration response,and the characteristic points are selected to monitor the radiated noise in the external acoustic field,which provides data support for the next optimization of structure.Finally,the whole machine is optimized by adding a single balance shaft to the dynamic system and optimizing the structure on the surface of the engine.At last,according to the structural characteristics of the outboard engine,a series of performance experiments on the prototype engine after improvement were carried out on a special experimental bench,including vibration test,noise test and noise source identification test.The experimental results and simulation results are compared to verify the correctness of the model simulation results.The test results show that the improved outboard engine meets the development goals set in the plan,and the optimized acoustics power of the whole engine is less than 2d B(A)at low frequency.