Ternary Regulation Control Strategy Of The Continuously Variable Transmission Tractor For Productivity-Economy Comprehensive Optimal

In recent years,with the continuous improvement of the level of industry and agriculture in China,agricultural production is gradually moving towards large-scale and modernization.Intelligent new generation tractors with high horsepower are more and more popular in the market.Hydro-Mechanical Continuous Variable Transmission（HMCVT）is widely used by more and more tractor manufacturers because of its high transmission efficiency and wide range of infinite speed regulation.It is of great practical significance to study the transmission law and control strategy of HMCVT and to improve the performance of HMCVT tractor.Taking a certain type of CVT tractor as an example,this dissertation studies the characteristics of the hydraulic mechanical CVT equipped by the tractor.In order to meet the requirements of economy and productivity in traction operation of CVT tractor,the comprehensive evaluation index IEP of productivity-economy is used to characterize the traction performance of the tractor.Aiming at the optimum productivity-economy combination,this paper analyses and formulates the corresponding variable speed regulation and control strategy.According to the influencing factors of tractor productivity and economy,IEP is expressed by the ratio of traction power to specific fuel consumption.In the tractor load characteristic field,when IEP is the largest,the productivity-economy synthesis is the best.The change characteristics of IEP in the process of adjusting engine speed and torque,transmission speed ratio and farm tool tillage depth were analyzed.Under the fixed speed and traction force,the maximum IEP value of the working point is solved,and the corresponding optimal engine speed and torque,the optimal transmission ratio and the optimal tillage depth of farm tools are determined.The optimal IEP distribution of all working points is obtained in the whole load characteristic field.Taking the actual working conditions of tractors as constraints,the corresponding working areas of tractors in the load characteristic field during ploughing operation are defined,the maximum I_EPmPm of the optimum IEP in the working areas and the corresponding optimum working points are determined,and the three-dimensional adjusting parameters of engine,transmission and ploughing depth are solved to form the three-dimensional adjusting variable speed law.The three-way control strategy is formulated to adjust the engine,transmission and hydraulic suspension system to work at the optimal engine speed and torque,the optimal transmission ratio and the best tillage depth of farm tools,so as to realize the optimal transmission law of productivity and economy.Compared with the traditional control strategy,adopting the comprehensive optimal control strategy of productivity-economy can reduce the average value of tractor fuel consumption by 4.5%,increase traction power by 6%,and improve tractor performance.In order to verify the feasibility of variable speed regulation,a dynamic model of tractor transmission system is established in Matlab/Simulink software based on dynamic theory,including engine model,multi-stage HMCVT dynamic model,central transmission system model and walking mechanism model.The vehicle control model is built according to the optimal transmission law and control strategy.The commonly used control theory is briefly described.According to the actual working conditions,the PID parameters are automatically adjusted by using fuzzy control,so that the multi-stage HMCVT tractor can work at the target speed and traction force,and the simulation experiment is carried out.Experiments show that,compared with ordinary PID control,the fuzzy adaptive PID control has the advantages of fast response time,small speed fluctuation and strong adaptive ability.The feasibility of variable speed regulation is verified,which provides a reference for practical engineering applications.