Research On System Dynamics Analysis And Continuously Variable Speed Of Tractor

The tractor is the main power machinery in agricultural production.Vertical,lateral and longitudinal kinetic analyses constitute the key to correct assessments and improvements of tractors' performance.Currently,the studies on the key parameters identification,estimation accuracy improvement and model application of vibration,steering and supportingtrafficability characteristics of tractors have some defects.In addition,power and economic performance of tractors depends on characteristics of power and transmission systems.Hydro-mechanical continuously variable transmission(HMCVT)is the main device to realize continuously variable transmission of tractor at present.However,HMCVT is rarely used in tractors in China,and its research of efficiency characteristic analysis and improvement,optimization design,variable speed control still need to be further improved.In this case,the paper researches systems dynamics related to the tractor performance.In the aspects of vibration,steering and supporting-trafficability performance,the paper mainly studies dynamics model establishment,estimation accuracy improvement,key parameters identification and model application.In the aspects of power and economic performance,the paper studies characteristic analysis,performance improvement,optimization design and variable speed control of HMCVT.At the same time,the research work of the paper uses improved SA(Simulated Annealing)algorithm,improved PSO(Particle Swarm Optimization)algorithm,improved AFSA(Artificial Fish-swarm Algorithm),improved GA(Genetic Algorithm),feature dimensionality reduction method,PLS(Partial Least Squares),stepwise regression,RBF-NN(Radial Basis Function-Neural Network),interpolation method,response surface method and other methods.The paper's research work and results are as follows:(1)The research on the vertical vibration and road roughness of tractor.The research builds tractor 2 inputs 3-dof and 3 inputs 4-dof vibration models using the Lagrange equation of the second kind respectively,and vibration models' accuracy are verified by comparison.The research proposes a method to build models with unknown parameters of tractor vibration and error compensation.The method proposed uses the improved SA algorithm to identify relevant parameters of vibration,considers the vertical dynamics response in partial working conditions and compensates the models' errors using the regression analysis and the RBF-NN,respectively.The vertical vibration characteristics of the tractor under random excitation and pulse excitation are analyzed by using 3-dof model and virtual prototype model respectively.Research results show that the stiffness and damping of the seat system should be as small as possible within its desirable range;after the tractor experiences the pulsed excitation,the driver seat's vertical vibration frequency is concentrated in the range of 3?5 Hz,and the maximum vibration value should not exceed 34.59 m/s2;the 3-dof model has better estimation effect,and the internal excitation can be ignored when modeling;after the parameters identification,the vibration model has good simulation results and further improves estimation accuracy after the compensation.Based on the research on improvement of two road roughness acquisition methods,the paper proposes a compressed sensing collection method for road roughness which reconstructs road roughness signals using an improved SA-SP algorithm;the paper proposes a novel feature dimensionality reduction method combined with the sampling survey method and the improved AFSA for the dimension reduction selection of vertical dynamic response features in the road roughness time-domain estimation.Research results show that road roughness signals are sparse,and the improved reconstruction algorithm has low dependency on the number and sparseness of observed signals with the mean accuracy verified of 0.9837;a road roughness time-domain estimation can be completed with high accuracy when choosing 4 specified vertical dynamic responses.This research provides a basis and reference not only for obtaining the effective road roughness,but also for estimating and improving the vibration performance of the tractor.(2)The research on the establishment and application of tractor steering model.The paper proposes a full-vehicle relative parameters measurement method based on the tractor lateral dynamics response.Combined with the lateral dynamics response of some working conditions,the research adopts an GA to measure the distance from the center of mass to the front axle,the yaw rotational inertia and the full-vehicle weight.The parameter measurement results were compared with those measured by a HYCF-20 tractor static roll-over stability test bed.The paper proposes a MDOF nonlinear steering model equivalent substitution method combined with the trail-and-error method,the improved SA and the Hermite interpolation method to build an equivalent substitution transfer function model.The research explores the application of steering model.Research results show that parameters,such as the total mass and the location of center of mass of tractor,can be estimated with high accuracy according to the yaw velocity,and the model after estimation can be applied to the prediction of lateral dynamics response in other working conditions;the transfer function of second-order denominator is consistent with the steering response,and the transfer function can substitute for the original complex steering model effectively;the steering model can be used to get the SBW system's ideal angular transmission ratios and calculate the additional driving resistance in the steering.(3)The research on the supporting-trafficability performance under tire-soil interaction.The supporting-trafficability parameters were measured and analyzed by the contact test between tire and soil.Results show that the sinkage increases with the increase of vertical load and slip rate,and the average relative increase rate is 68.67%and 15.20%respectively.The vertical load has a greater effect on the sinkage.The research proposes two parameter identification methods for Magic Formula tire's longitudinal force model.The first method,combined with the interpolation method and GA,requires only 9 data points to complete the identification of parameters effectively;the second method,based on the nonlinear analysis of Magic Formula,needs only 4 data points to complete the identification effectively,and thus solves the non-unique solution problem existing in the lack of observed values.The longitudinal driving force of tire-soil contact and the traction force of tractor in the field were established by using the method in this paper.Results show that only 4 measurements are needed to effectively complete the establishment of the above supporting-trafficability model;the tractor should work in the range of 13.00%?39.24%slip rate or around 20.81%slip rate to improve its supporting-trafficability performance.(4)The research on HMCVT efficiency characteristics of tractor.Firstly,the efficiency characteristics of stepless speed regulation system is studied.Combining three theoretical models of variable pump efficiency and the efficiency test data of HPV-02 variable pump,the research makes an analysis on influencing factors,and uses the improved SA algorithm to match the parameters of three efficiency models and compares the consistency between three models and test data.On the basis,the research proposes an improved 7-parameter variable pump semi-empirical efficiency model using the trail-and-error method and the correlation coefficient method.Results show that the pump displacement is always positively correlated to the pump efficiency,and the rise of pump revolving speed and stress makes the pump efficiency first rise and then decline;the 3-parameter pump efficiency model has the highest mean accuracy(which of calibration is 95.39%,and of prediction is 96.93%),and can be used to describe the variation characteristics of pump efficiency accurately with low identification difficulty;pump stress,revolving speed,the sinusoidal variation of stress,and the product of stress and displacement have significant influences on the error of 3-parameter model,but the improved 7-parameter model further improves prediction accuracy and practicability.Secondly,the total efficiency of HMCVT is studied.The research builds the efficiency models of single-planetary-row working and multiple-planetary-row joint working HMCVT using the engaging power method and the applied transmission ratio method and analyzes influencing factors.Results show that reducing pump revolving speed and circulation power properly and increasing the mechanical route's revolving speed before confluence and planetary row's characteristic parameter can improve CVT's efficiency effectively.The research proposes a method to build the efficiency model of HMCVT with limited test data,and the method makes a calibration based on the SA algorithm and a relational model fitting by the least square method for hydraulic system's efficiency and gear efficiency,overcomes the defect of classical method setting the gear efficiency and hydraulic system efficiency as fixed values,and thus improves model accuracy(with the mean accuracy of 96.38%)while reducing test cost.The research provides a direct basis for HMCVT optimization design,CVT control and performance improvement.(5)The research on HMCVT optimization design of tractor.The paper researches the key content(the determination of speed regulation characteristics,the comparison of transmission schemes,and the design of minimum transmission ratio)needed before the optimization design.The research proposes three methods to build speed regulation characteristic model(a purely theoretical model,a virtual prototype,and a physical model based on Simscape)and makes a contrastive validation with test data.The research proposes the variable speed potential index,builds a transmission scheme evaluation method combined with the improved PSO algorithm for the contrastive analysis of three HMCVTs.According to tractor's longitudinal dynamics characteristics on the soil surface,the research determines the minimum design value of transmission ratio by drawing a driving-force-resistance equilibrium diagram.Results show that the virtual prototype and the Simscape model proposed have high consistency with test data and thus can avoid the errors in artificially theoretical analysis in the early period of design;the selection of transmission scheme should take the number of design variables,variable speed potential,variable speed range and structural complexity into consideration;the determination of minimum transmission ratio value should fit the driving resistance and the characteristics of diesel engine,to overcome the problem of invalid minimum transmission ratio appearing in the case of only considering engine speed and vehicle speed requirements.The research explores the optimization design of key mechanical parts(the gear,the planetary row and the wet clutch)and proposes two optimization design methods for transmission parameters.The first method makes the twolevel optimization of parameters for the purpose of light weight,maximum efficiency and continuous transmission.The second method,basing on the one-level optimization of parameters,introduces a joint point position rationalization goal and matches the working speed requirement of tractor.The research proposes a structural optimization design method for wet clutch,combined with the central composite design,the PLS,the stepwise regression,the RBF-NN and the improved SA algorithm,to optimize the shell structure on the basis of 81 groups of ANSYS finite element test results.Results show that after the optimization of transmission parameters,the volume reduces by 7.28%and the mean efficiency rises by 5%,and the two-level optimization can be realized easily and thus reduces computation complexity;the determination of position of joint point of every HMCVT's stage should meet the requirements of transmission efficiency and vehicle speed of tractor,and the optimization algorithm has a great influence on the optimization result;the clutch housing' maximum outer diameter and axial width have significant influences on the light weight,and the axial width has a great influence on maximum strain;it's better to use the RBF-NN and the stepwise regression to build the clutch light weight model and the maximum strain estimation model respectively.The research provides a systematic optimal design scheme for HMCVT used in tractor.(6)The research on HMCVT variable speed control of tractor.The paper proposes two methods to develop variable speed control strategy.The first method,combined with the Spline interpolation method,makes the optimal dynamic performance control strategy matching the diesel engine's speed regulation characteristics and transmission efficiency,and uses the acceleration dynamic performance on the soft-soil road and the dynamic factor double integral obtained by simulation for a verification.The method overcomes the accuracy defect of conventional stepped transmission which adopting the root extraction method of quadratic equation,and the MAP chart should reduce the interval of vehicle speed value and increase the interval of accelerator opening value.The second method,considering the dynamic performance requirements on the soft&hard road,the additional driving resistance during steering and the tractive load,makes the optimally economical unary five-parameter and binary four-parameter control strategies using the graphical method and the improved SA,respectively.The simulation test results show that the synergistic engine speed control has a better full-vehicle economical effect compared with the unary control effect depending on the driver's experience.The paper researches the continuously variable speed control(variable-pump control constant-displacement-motor)system's response characteristics.The research uses the dynamic equation to derive the variable speed control system's transfer function and proposes an imitated manual setting PID parameters method and then compares it with two classical methods for the simulation comparison verification.Then,according to the bench test,the research identifies the actual continuously variable speed control system,verifies the theory and derives the model,and makes a contrastive analysis on the identification results of the area method and the improved SA,and then carry out the PID control test.Results show that the denominator order of continuously variable speed control system is 4;the imitated manual setting PID parameters method is time-consuming but it improves the speed and accuracy of system response;the area method is easy to use but has a high requirement for sampling time and frequency;the improve SA algorithm has better identification accuracy and is independent of sampling time and frequency;the established PID control system can effectively realize the closed-loop adjustment of output speed under the circumstance of load fluctuation.The research lays the foundation for the development and design of HMCVT controller.