Design Of Series Hydrostatic Power Split Continuously Variable Transmission For Tractor

Hydrostatic power split continuously variable transmission is a kind of double-flow transmission system with mechanical transmission and hydraulic transmission in parallel.It has the advantages of variable transmission ratio and high transmission efficiency.It can not only significantly improve the safety and controllability of the vehicle,but also make the vehicle obtain good power performance and fuel economy.Although this kind of transmission has a good application prospect,it is currently mainly equipped with large and medium power tractors.Chinese arable land resources are limited,and there are many mountains and hills,complex agricultural environment is very suitable for small power tractors and agricultural machinery operations.Therefore,it is an urgent problem to develop low-cost and low-energy hydrostatic power split continuously variable transmission and apply it to low-power tractors or agricultural machinery.In order to achieve stepless speed regulation on low-power tractors and agricultural machinery,this paper designs a series of hydrostatic power split continuously variable transmission based on the analysis of the research status of the domestic and foreign hydrostatic power split continuously variable transmission.The main research contents are as follows:(1)The shunt and confluence mechanism of hydrostatic power split continuously variable transmission is analyzed systematically,and it is concluded that the torque split and confluence mechanism is more suitable for transmission scheme of hydrostatic power split CVT.Then,combined with the actual working requirements of the tractor,a transmission scheme of the hydrostatic power split CVT is designed,and after the basic parameter calculation was completed,its speed regulation characteristics,torque characteristics and power characteristics are analyzed.(2)Based on the transmission scheme of the hydrostatic power split CVT,the structural design of the transmission is carried out,including the design of the transmission gear,transmission shaft,lubrication and cooling structure and box structure.The drawing of the whole set of product drawings is completed,and the processing of the experimental prototype of the hydrostatic power split CVT is finally completed.(3)The load test was carried out of the pump-controlled hydraulic motor on the load test bench,and the test data such as the speed,torque,mechanical efficiency and volumetric efficiency of each shaft were obtained,and the inlet and outlet oil circuits of the variable pump were obtained by the least squares method.The relationship equation between the pressure difference and its volumetric efficiency and mechanical efficiency provides important data support for subsequent analysis of transmission characteristics of gearboxes and tractors.(4)Based on the pump-controlled hydraulic motor parameters and relational equations obtained from the loading test,the efficiency calculation model of the hydraulic power split CVT and the hydrostatic CVT was constructed,the transmission efficiency and speed regulation characteristics of the two CVTs are compared and analyzed.The research results show that the designed CVT has better efficiency characteristics than the HST.On this basis,the mathematical model of the HMCVT tractor and the HST tractor was further constructed,and the traction characteristics of the two CVT tractors were analyzed and compared.The research results show that: the HMCVT tractor has lower fuel consumption than the HST tractor.The hydraulic power split continuously variable transmission designed in this research has the characteristics of simple structure,controllable cost,easy operation and excellent performance.The research work can provide basic theoretical and method support for the development of low-power CVT tractors and agricultural operation machinery in China.