Vibration Mechanism And Response Of Crawler Combine Harvester Frame Under Multi-source Excitation

As one of the indispensable harvesting machines,the crawler combine harvester carries the important task of ensuring food safety in China.At present,the harvesting performance indicators of domestic combine harvesters have basically met the harvesting requirements,and some models have reached the international advanced level.However,when the domestic combine harvester is working,there are generally problems such as large vibration of the whole machine,easy damage of components,and low reliability of the whole machine.These problems have seriously affected the harvest efficiency and the driver's physical and mental health.Therefore,in this paper,the combination of theoretical calculation analysis,experimental analysis verification and numerical calculation simulation is adopted to solve the problem of severe vibration of the crawler combine harvester in the field.This paper systematically analyzes the structural characteristics,working characteristics and vibration characteristics of the crawler combine harvester frame and its various components,and obtain the vibration generation mechanism and response characteristics of the frame and various components.It provides theoretical basis and new ideas for vibration and noise reduction of crawler-type combine harvesters and structural design and development of new models.This article is of great significance for improving the comprehensive performance and reliability of domestic crawler combine harvesters.The research content of this paper includes the following points:(1)Based on the chassis frame and threshing frame structure of the existing domestic crawler combine harvester,three-dimensional modeling is carried out and its structural characteristics are analyzed through theory.Through the weighing test and formula calculation,the amplitude of the load applied on the frame is obtained.Perform static analysis on the chassis frame and threshing frame to check whether its strength and deformation meet the design requirements.(2)Taking a domestic crawler combine harvester as the research object,it conducts vibration test under multiple working conditions,and analyzes the vibration response characteristics of the complete machine and main frame under multi-source excitation.Tests have shown that the lateral vibration of the threshing cylinder,the reciprocating motion generated by the vibrating screen,the up and down swing of the conveyor and the up and downvibration generated by the engine are the main vibration sources of the combine in the X,Y,Z directions,and the incentive of the road to the whole machine can not be ignored.The excitation main frequency of the crawler combine harvester engine is the second-order ignition frequency,and the vibration amplitude at the engine bracket is the largest in the Y direction(transverse),followed by the Z direction(vertical).It may be that the engine is installed on the chassis frame at an angle,resulting in the decomposition of the vertical excitation force generated by the engine's combustion torque in the Y and Z directions.In addition,in order to reduce the vibration of the whole machine,the excitation of the whole machine by low-speed vibration sources such as cutting blades,the driving shaft of the conveyor and the vibrating screen can not be ignored.It is necessary to add a vibration damping device in the connection part with the main frame,so as to make the rotation speed between the various vibration sources stagger and avoid the natural frequency of the structure.(3)In order to study the relationship between the excitation frequency of multiple vibration sources on the crawler combine harvester and the inherent properties of the main frame structure,the calculation modal analysis and the experimental modal analysis are performed on the frame.The results show that the finite element modal calculation results of the threshing frame and the chassis frame are basically consistent with the modal test results.The first six natural frequencies of the threshing frame are between 14-60 Hz.The vibration deformation of whole frame was mainly composed of bending and twisting shapes.The first 6 natural frequencies of the chassis frame are between 23-51 Hz,and the vibration modes are mainly bending,torsion and local modal.The frequency of the bending shapes at the top of the threshing frame is 32.16 Hz,and the frequency of the bending shapes of the chassis frame is 39.11 Hz.The bending-torsion shapes constitutes the low-order vibration modal of the main frame.In addition,the front sixth-order natural frequencies of the frame were within the operating frequency range of multiple vibration sources of combine harvester,which could cause complex vibration coupling and resonance.As a result,the frame vibration of the harvester was intense while working,which could easily cause fatigue damage to key components.This serious vibration was greatly reducing the service life of combine harvester.(4)Theoretical analysis and experimental research on the vibration characteristics of the main vibration sources on the crawler combine harvester were carried out.According to thestructural characteristics and working characteristics of each vibration source,each dynamic model is established to further analyze its vibration mechanism and theoretical excitation characteristics,and list its excitation force expressions.On this basis,each vibration source is subjected to a separate vibration test,and the test data is compared with the theoretical analysis conclusion,so as to verify the excitation characteristics of each vibration source,and provide theoretical basis and data support for dynamic simulation.(5)On the basis of mastering the vibration characteristics of the whole machine and each vibration source,the dynamics model of 10 degrees of freedom of the whole machine was established by Newton's second kinematics law,and the road surface excitation model was established.Through MATLAB / Simulink,the dynamic simulation model and road excitation model of the whole machine were established,and the simulation parameters and excitation expressions of each vibration source were studied and calculated.The above parameters can be used as input to obtain the vibration response of the main frame under multi-source excitation.Based on the established simulation model,the effects of different road levels,vehicle speeds and target parameters on the vibration response of the main frame are studied,which can provide a reference for further research on the vibration response of the main frame under multi-source excitation.Studies have shown that changes in road surface conditions and changes in vehicle speed have a greater impact on the vibration response of the main frame of the crawler combine harvester,and the smooth running performance of the whole machine is also closely related to the changes of the two.On the other hand,it also shows the importance of optimizing the chassis structure and crawler vibration isolation performance of the crawler combine harvester.