Design And Control Of Tractor Hydrostatic Power Split CVT With Single Planetary Gear Set And Multiple Ranges

Tractor is the most important agricultural power machinery.In addition to road transportation,it also perform light-load operations such as sowing and fertilization,as well as heavy-load operations such as ploughing and harvesting.In order to meet the requirements of running speed and load intensity under different working conditions,tractors are generally equipped with more working gears.Although the increase of working gear can better meet the different operation requirements,it also makes the structure of gearbox complex and the cost high,and also brings difficulties to shift operation and gear selection.Therefore,stepless speed regulation has become a technological development trend of tractors.In our country,the research on the hydraulic power split continuously variable transmission started late and adopted the multi-planetary row and multi-section transmission scheme.The overall structure of CVT is complex,and its industrial application has not yet been realized.Therefore,the research on the hydraulic power split CVT of single-planetary row and multi-section tractors is particularly urgent.In this paper,based on the analysis of the research status of the domestic and foreign hydraulic power CVT technology,a single-planetary row and multi-section hydraulic power split CVT is designed,and the optimal design theory and the shift control strategy of the CVT are studied.The specific research contents of this paper are as follows:(1)Transmission scheme design.In this scheme,a single planetary row can be used to complete the whole tractor stepless speed regulation.By setting the gear in the motor shaft,the problem of equal difference restriction of speed ratio in each section of the single-planetary row hydraulic power split CVT is solved,thus the acceleration performance of this kind of transmission is optimized.(2)Transmission parameter design.According to the tractor's operation requirements,its typical operation conditions are analyzed,and the speed range of each section is determined.In this paper,the transmission efficiency calculation model of the hydraulic power split CVT tractor is constructed under SimulationX,and the simulation research is carried out.On this basis,the relationship between transmission parameters and internal energy consumption of the transmission is revealed,and the transmission parameters are optimized.And a suitable integrated pump-controlled hydraulic motor is selected,so that it has lower energy consumption and higher transmission efficiency under the main working conditions.(3)Transmission structure design.This chapter covers the design and assembly of gears,shafting,clutches and boxes.Specifically,based on the calculation results of the aforementioned parameters,the gear matching calculation including differential planetary gear and the strength check calculation of gear and shaft are further completed,and the installation structure of gear and clutch of each shaft is determined.The design of the box fully considers its structural technology,which not only meets the requirements of high-precision assembly of each component,but also facilitates the subsequent disassembly and maintenance.In addition,the modal analysis of gearbox case,is carried out by using ANSYS Workbench software.Combined with the calculated meshing frequency characteristics of the gearbox,it is found that the variation range of the gear pair meshing frequency of this kind of gearbox is large during operation,and it is difficult to completely eliminate the resonance phenomenon in theory.Therefore,the resonance proximity calculation was performed on the natural frequency of the transmission case and the meshing frequency of the gear pair of the hydraulic circuit where resonance may occur,and a corresponding control strategy is formulated to avoid the resonance phenomenon.(4)Development of the test-bed for the shift hydraulic system.In order to complete the shift test,this paper designs the structure of the working oil circuit,lubricating and cooling oil circuit,pump station and valve block of the shift hydraulic system.The test-bed control system is built with the industrial computer as the upper computer and the PLC as the lower computer.On the basis of industrial computer,NI data acquisition card and pressure sensor,flow sensor,temperature sensor,etc.,the test-bed test system is constructed.In addition,a PLC program is compiled,and a host computer software is developed based on Labview to achieve the integration of test and control systems.(5)Construction of dynamics model of shift.Based on the Simulation X,the mathematical models of the wet clutch and the proportional pressure reducing valve are constructed and verified by experiments.On this basis,the dynamic models of the CVT and the whole machine of the tractor are established.(6)Research on the shift quality.Different from the traditional hydraulic power split CVT,the gearbox designed in this paper has only a single planetary row.Although the structure is simple,it requires the cooperative control between the clutch and the pump-controlled hydraulic motor when shift.Based on the aforementioned dynamic model of shift,the influence of clutch control parameters on the quality of CVT tractors and its mechanism are systematically studied.In this study,a high-dimensional visualization method is proposed for the first time,that is,a solution domain analysis method used to find the macro-control laws.Based on this method,the optimal matching strategy between the control parameters of the segment change is obtained.The work of this project provides a new design idea and research method for the research and development of tractor hydraulic power split CVT,which has a certain theoretical significance for promoting the localization process of hydraulic power split CVT tractor in China.