Study On Starting And Shifting Control Method Of Power-cycling Continuously Variable Transmission

Construction machinery plays an important role in the development of national economy.Under the current background of energy conservation,emission reduction and industrial upgrading,higher requirements are put forward for the fuel economy,emission performance,adaptability to working conditions and intelligent control level of construction machinery.The transmission system is the key component of construction machinery.The working environment is complex and the working load changes dramatically.Because of the advantages of automatic adaptability,stable starting acceleration,buffer and shock absorption,the automatic transmission system has been widely used in construction machinery.However,the efficiency of hydraulic transmission is relatively low.Therefore,it is an urgent need for the development of domestic construction machinery to develop a new automatic transmission system and formulate relevant control strategies to improve the comprehensive performance of construction machinery.This paper is based on the "design theory and control method of a new type Power-cycling continuously variable transmission system"(Project No.51375505)and "construction and design theory and control method of reflux power variable transmission series"(Project No.51875055)of NSFC.In view of the complicated and changeable working conditions and special structural transmission characteristics of the power-cycling continuously variable transmission(PCVT),this paper uses the dynamic analysis method to improve the fuel economy and power performance,improve the work efficiency,and improve the starting shift quality.The shift strategies under different working conditions,starting and shifting process control method of PCVT loader are studied.The main contents of this paper are as follows:1.According to the transmission structure and mechanism of PCVT loader,the speed ratio and efficiency characteristics of the system are derived from the perspective of power transmission and kinematic analysis.In order to facilitate the later dynamic analysis,the model of each part the whole loader system are established,and in order to make the theoretical model consistent with the actual situation as much as possible,the resistance model of the loader including the digging resistance is introduced.2.The shift characteristics of PCVT system are analyzed.It is considered that the shifting is a combination of stepless speed regulation and step-by-step speed regulation.The "throttle opening,engine speed and working point of torque converter" are proposed as shift control parameters.Based on the steady-state experimental data of diesel engine,the three-parameter optimal power and optimal economy shift strategy is proposed.The loader usually runs under typical working conditions,and the basic shifting strategy is often used to switch repeatedly under the optimal power and economy mode,which is easy to increase the workload of the driver.Therefore,the dynamic programming algorithm is used here,and the penalty function is added to avoid frequent shifting,so the optimal shifting law of PCVT loader under V-type working conditions is obtained.3.When the loader works in the unsteady state(the mass of the whole loader and slope gradient often change),the shifting strategy based on the steady state is no longer applicable,so the double forgetting factor least square method is proposed to identify the mass of PCVT loader and slope gradient.The influence of loader's different loading mass on PCVT's shifting law and its changing law is studied in this paper.An adaptive modification shifting strategy based on the change of loading mass is proposed.The changing rule of PCVT's shifting point under different uphill gradients is studied.A modified method of shifting points under different uphill gradients is proposed.The simulation results show that the proposed uphill correction strategy can effectively avoid the cycle shifting phenomenon on the premise of ensuring the dynamic performance,and can ensure the torque converter to work in the high efficiency area and improve the fuel economy.Based on the braking characteristics of the engine,the change rule of downhill balanced speeds of the PCVT loader coasting with gear clutch engaged is studied.Based on the balance speed of downhill,the gearshift strategy of downhill is established.Finally,the simulation results show that the proposed strategy can make full use of engine braking and effectively ensure the safety of downhill driving.4.Based on the particularity of PCVT structure and the characteristics,two starting modes of pure throttle starting and clutch starting are proposed,and the starting dynamics model of PCVT is established.Based on the constant speed control of engine,the starting process of pure throttle and clutch is analyzed respectively,and the control strategies of engine throttle and clutch engagement speed are formulated respectively.Based on the two starting modes,the PID controller of engine throttle and clutch engagement speed is designed.The parameters of PID controller are optimized with impact degree,friction work,torque converter heat and starting time as the starting optimization indexes.The simulation results show that: compared with pure throttle starting mode,the heat of torque converter is less when PCVT loader starts with clutch,but it has more friction work of clutch.Through optimization,the two starting methods both can effectively reduce the impact and ensure a smooth start.5.The dynamic model of shifting process is established,and the shifting process of PCVT is analyzed in detail.In the torque phase,taking the impact degree and friction work as the optimization objective function,the change rate of clutch engagement torque is optimized by using the quadratic optimal control theory.In this stage,the engine adopts closed-loop PID control.In the phase of inertia,in order to ensure that the sudden change of the system speed ratio does not cause the great torque change of the PCVT system,the fuzzy control algorithm is used to design the clutch controller based on the input of the speed difference between the driving and driven discs of the clutch,the speed ratio difference between the actual and the target of torque converter and the efficiency change rate of PCVT system.Simulation results show that the proposed shift control strategy can achieve smooth shift and meet the control requirements well.6.The test bench of the torque converter and PCVT prototype driven by three-phase asynchronous motor is built.The basic performance experiment of the torque converter and PCVT prototype are conducted by using this test bench.Firstly,the feasibility of PCVT scheme is confirmed by the test,and the basic performance parameters are obtained through the test of torque converter and PCVT prototype.