Study On The Method Of Constructing Diesel Engine Body Plan Model Based On Stiffness Evaluation

Vehicle engines are extremely complex power machinery equipment and are assembled from a combination of components and bodies.Its body is the overall skeleton of the engine and the basis for the normal operation of other parts and components systems.The durability and reliability of the airframe have a crucial influence on the normal high-speed operation of the engine.Therefore,it is very important for the structural design of the engine body in the early stage.Generally it can be divided into two stages.The first stage is the scheme design stage.The main task is to plan the overall structure of the engine and determine the design parameters of the engine components.The second stage is the detailed design stage,the local parts are optimized under the basic framework of the overall structure in this stage.From the perspective of the design cycle of the entire engine,the overall design phase is the key point in the entire engine design cycle.When determining the overall structural design characteristic parameters of an engine,the subsequent optimization only needs to be performed within the scope of the local structure.In view of the uncoordinated body deformation and uneven distribution of structural stress that may occur during the design phase of the engine,it is necessary to study the model establishment method that can reflect the stiffness of the body at the design stage and evaluate the stiffness.Firstly,extract the main characteristic structural parameters of the organism,establish a three-dimensional model of the organism and gradually refine the body model by using the method from simple to multiplicative features.Abaqus software was used to define the unit material properties,meshing,and loading boundary conditions for the progressively refined body program,in order to calculate the free modal analysis results.The calculated results are compared with the results of the airframe test modal tests obtained by the hammering method.When the calculated mode and the experimental mode are consistent with each other and the modal frequency error range of each modal remains within 10%,the correctness of the body plan model would be verified.Using the bodies of other types of engines to establish a solution model in accordance with the method for establishing the above scenario model,and compare the modal analysis results with the experimental data to further confirm the accuracy of the modeling method for the organism model,it could lay the theoretical foundation for the model subsequent parameterization.The parametric modeling of the body consists of two parts: common characteristic parameters and personality characteristic parameters.Its common characteristic is that all such parts meet basic functional characteristics while personality characteristics refer to features specific to individual parts.Through parameterized clustering of these characteristic parameters,the body's characteristic parameters are provided for the secondary development of the Abaqus software.Using the GUI plug-in integration method to realize the interface design of the finite element parametric modeling function,the graphical interface interaction method can realize rapid modeling of different types of aircraft bodies and shorten the poduct development cycle.According to the diesel engine structural assembly guidelines,five types of components such as cylinder heads,bearings,transmission boxes,oil pans,and flywheel housings are assembled on the body to establish a three-dimensional assembly model of the combined structure.The Abaqus modal analysis was performed based on the six-class,five-class,four-class,and three-class body-component combination structures.The frequency coverage method and the step-by-step inverse method of the vibration mode were used to study the stiffness matching of the frequency and vibration modes of each composite structure.It shows that the oil sump has the greatest influence on the modal frequency of the diesel engine.In the assembly structure of the five parts after the body is fitted with the oil pan,the first-order torsional modal frequency of the composite structure is reduced by 30.7%,and the torsional frequency of the other four components before and after being assembled separately to the body is only about 5%.Therefore,by using the law of mode variation,the stiffness matching of different components can be achieved,which is of significance for improving the NVH response characteristic of the automobile powertrain and improving the design efficiency of the diesel engine structure.