Optimization Research On The Performance Of Hydro-Mechanical Continuously Variable Transmission

Hydro-Mechanical Continuously Variable Transmission (HMCVT) is a new kind of compound stepless transmission device,with the stepless speed regulation characteristics of hydraulic mechanism and the high-efficiency transmission characteristics of mechanical mechanism,which will become a new tendency of big-power tractor transmission system. In order to improve the overall performance of tractor transmission system,this paper carried out the researches on HMCVT from four aspects:design scheme,efficiency promotion,shift strategy and matching control,and introduced the hardware design and software development of the control system of HMCVT.On the base of existing research results of universities and research institutes at home and abroad,make further research for a multi-range HMCVT,with a single planetary gear and more clutches,which is one of the five indigenous design schemes.According to the design requirements,the dynamic analysis and kinematics analysis were performed for the tractor system. The parameters and the assembly schemes of main parts can be calculated. It shows the stepless speed regulation curves of HMCVT.Response characteristics and efficiency characteristics of pump controlled motor system (the hydraulic speed regulation mechanism of HMCVT),were studied according to the simulation and test. Input-output relationship and stability performance of pump controlled motor system were analyzed,and the various factors which have influence on the efficiency of pump controlled motor system were discussed,including rotational speed,displacement,and pressure.The results showed that displacement ratio is determined by input current of pump,motor rotational speed is controlled by input current of pump and pump rotational speed,and load torque have no obvious effect on motor rotational speed;the stability performance of pump controlled motor system was excellent,and the stability performance of closed-loop system based on PID control was better than that of open-loop system;the efficiency of pump controlled motor system can reach over 85% under the operating condition of higher speed,larger displacement,and medium pressure.Expounded the influence factors on the efficiency of HMCVT, especially the cycle power,and researched the efficiency improvement of HMCVT by efficiency definition method and meshing power method from the perspectives of structure parameters.The results showed that:the efficiency of HMCVT increased along with the increasement of planetary gear characteristic parameters,the product of input transmission ratio and output transmission ratio of hydraulic speed regulation mechanism,and the hydraulic system efficiency.The efficiency of HMCVT reached the peak when the displacement ratio of hydraulic speed regulation mechanism became 0. Researched the efficiency improvement of HMCVT by bench test from the perspectives of running environment.The results showed that:the higher the engine speed,the lower the transmission efficiency and the more obvious the vibration;the larger the input transmission ratio of hydraulic speed regulation mechanism,the higher the transmission efficiency;engine power and pressure of hydraulic speed regulation mechanism had no obvious effect on the transmission efficiency;the efficiency of hydro-mechanical ranges were higher than that of hydraulic range.Established the shift model of HMCVT based on the Simulation X.speed drop amplitude,dynamic load coefficient,maximum degree of shock,and shift time were regarded as the evaluation indexes of shift quality;mechanical parameters(engine rotational speed,load torque,pressure of main circuit,and flow of speed control valves) and shift time(switching time of clutches) were considered as the influencing factors of shift quality;parameters comparison method,range method,variance analysis method and experimental verification method were used as the research methods of shift quality,in order to analysis the continuous shift process of HMCVT. Shift strategy based on the mechanical parameters and shift time should be used to solve the shift quality problems of the two typical conditions by simulation study and experimental verification.The results showed that:the shift quality of typical conditions determine the shift quality of continuous shift process. In the shift process from negative transmission of hydro-mechanical ranges to the positive transmission of hydro-mechanical ranges,in order to get better shift quality,shift strategy based on mechanical parameters is the lower engine rotational speed,the smaller load torque,the lower pressure of main circuit,and the larger flow of speed control valves;shift strategy based on shift time is that switch the clutches of shift mechanism firstly,separate the clutches of planetary gear mechanism secondly,engage the clutches of planetary gear mechanism lastly. In the shift process from the hydraulic range to the hydro-mechanical range,in order to get better shift quality,shift strategy based on mechanical parameters is the lower engine rotational speed,the lower pressure of main circuit,and the larger load torque and flow of speed control valves;shift strategy based on shift time is that switch the clutches of hydraulic shift mechanism and planetary gear mechanism at first,then switch the clutches of shift mechanism.Established the matching model of man machine environment Integration based on the MATLAB.The optimal power performance and optimal fuel economy performance were regarded as main lines.Control strategy based on the driver’s Intentions and intelligent adjustment should be used to solve the matching quality problems by simulation study.Control strategy based on the driver’s Intentions is that HMCVT regulate the transmission ratio automatically to meet the optimal power and optimal fuel economy requirement from the points of the throttle variable quantity and the throttle variation rate. Control strategy based on the intelligent adjustment is that HMCVT regulate the transmission ratio automatically to ensure the optimal fuel economy of vehicle system requirement from the points of the resistance variable quantity and the speed variable quantity. The hardware design and software development of control system used for HMCVT were introduced, which will provide a theoretical basis for the engineering application of shift and matching control strategy.