| As the key agricultural machinery and equipment commonly used in grain harvesting,grain combine harvesters play a vital role in the process of agricultural mechanization.However,the complex system composition of the combine leads to a large number of excitation sources for the whole machine,and the transmission and coupling between the excitation sources leads to a complex vibration environment.Therefore,it is urgent to carry out research on vibration response mechanism and damping optimization scheme for the vibration response and excitation force transmission of grain combine system.This paper mainly classified and simplified each device of the combine harvester according to the different structure composition and working mode,and studied the vibration transmission and response characteristics of the main working devices under multiple working conditions.The research work of this paper mainly consists of the following four parts.（1）The main working devices of the combine were taken as the research object.The vibration transmission characteristics of each device were analyzed under the time domain distribution by carrying out the vibration experiment of the whole machine under multiple working conditions,and the three main research devices of header,conveying trough and threshing drum were determined.Analyze the movement mode and structure composition of the main devices,establish the motion model of each device,and derive the device balance equation and excitation force equation.The combine was divided into crawler walking system,chassis frame system,threshing frame system and header conveying system.The connection mode between working device systems was analyzed and simplified.The nine-degree-of-freedom dynamic model of the whole machine was gradually established.The dynamic environment simulation of the dynamic model was carried out using the Simulink simulation module in MATLAB,and the vibration response characteristics of the whole machine under different excitation were analyzed.（2）Through the vibration experiment of threshing drum test bench under different feed rates,the impact of variable load and unbalanced force of each working device under the disturbance of feed rates were explored.According to the acceleration signal analysis,when the grain feeding disturbs the threshing drum,it changes the mass and damping coefficient of the system at the same time.When the damping characteristic of grain was more obvious,the disturbance of grain feeding to threshing drum became weaker.The variable amplitude vibration experiment of combine under field conditions shown that the change of feed quantity has damping effect on the vibration of all devices of combine,especially in threshing drum device.By enveloping the RMS value of the root mean square in Matlab,the effective excitation signal of the channel under the sudden disturbance of the feed quantity was obtained,and the shock condition of the vibration signal was judged by the kurtosis,margin factor and pulse factor.（3）Compare and improve several classical transfer path analysis methods,combine the OTPA method with the discrete time matrix method to obtain the transfer matrix,and analyze the transfer path of the combine.The motion parameters and spatial inertia coordinates of the nonlinear system of the whole machine were linearized,and the transfer equation and transfer matrix in a unified format were derived according to the input and output of components.The signal analysis function of Signal Analyzer in Matlab was used for data processing,the modified periodogram algorithm was selected to calculate the power spectrum,and the power spectrum density function and power spectrum analysis of each working device were obtained.The vibration energy at the conveying trough and threshing drum was concentrated,and the contribution sound pressure level was the strongest,reaching about 20 d B.（4）The three-dimensional model of the combine frame was established in Creo and imported into WORKBENCH for simulation analysis of excitation force transmission.Set the load and constraint according to the combine frame function and stress,solve the change of the model vector principal stress,identify the vector path by displaying the isometric vector,distinguish the key stress areas,and then display the vector length and vector direction to obtain the vector force transfer direction.Based on the analysis of the experiment results of the main vibration sources of the frame,the vibration transmission law of each working device and the static simulation results of the frame,the problem path of the whole machine was selected,and the damping optimization scheme selects the constrained damping vibration reduction method,and the damping optimization was carried out for the selected problem path area.Conduct combine vibration experiment under different working conditions,and compare the vibration characteristics of each working device of the combine before and after optimization.After optimization,the acceleration of the cab console was reduced by 11.233 m·s-2.Excluding the measurement point data at the location where the damping material is installed,the average variation of the measurement points is 6.56%.It verified the reliability of the damping optimization design of the appropriate transmission path in this paper,thus verifying the effectiveness of the damping optimization of the grain combine.The dynamics and vibration characteristics of combine harvester multi-body system were explored from the numerical,experimental and analytical perspectives.Based on the vibration environment of combine harvester with multi-source excitation,the vibration source of main working device was identified through vibration response experiment,and the vibration transmission response characteristics under time-frequency environment were compared and analyzed.Based on the motion mode and structural composition of the device,established a motion model of the device and derived a balance equation to analyze the vibration excitation force.Simplified the dynamics of the working device,established a multi-degree of freedom dynamic model for the entire machine space,and studied the influence of different system parameters on the vibration characteristics of the device.In view of the disturbance of the feeding amount to the system parameters during field work,the vibration characteristics of each working device of the combine harvester under different feeding amounts were analyzed quantitatively,and the effective excitation signals and effective signal intervals under the sudden disturbance of the feeding amount were obtained.Based on the basic time-domain characteristic parameters,calculated the waveform characteristics of the vibration signal and clarified the dynamic variation law of the vibration mode.For the time-varying nonlinear vibration transmission of multiple devices,established a transfer matrix for the main working devices,and combined power spectrum and energy spectrum analysis to identify the main transmission path of the entire system based on the transmission contribution.On this basis,the simulation analysis was carried out for the transmission of multi vibration source excitation force of combine harvester.Combined with the excitation response experiment,transmission contribution identification and excitation force simulation analysis,the problem area and optimization area of vibration transmission were identified and selected,and a set of damping optimization scheme suitable for suppressing the vibration of the whole combine harvester under dynamic load was determined.Based on the optimization scheme,the damping optimization design of the main working device was carried out,and the vibration characteristics before and after the damping optimization were verified by comparing with the actual experiments. |
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