Study On The Synchronous Ranges Shifting Stability Of Hydromechanical Continuously Variable Transmission

China is a large agricultural country.The modernization of agricultural machinery reflects the level of agricultural development.Tractors are the main agricultural machinery.The development of modern,high efficiency and high horsepower tractor has been listed as the national key construction projects.Because of its high efficiency,high power and wide range of transmission speed,the multi-range hydro-mechanical continuously variable transmission(HMCVT)has a good application value in agricultural tractors.The research on the change law of transmission has become the core of the research and application of tractor technology.In this paper,the multi-range HMCVT of a certain type of wheeled tractor is taken as the specific research object,and the working principle of the multi-range HMCVT is expounded.The transmission characteristics of multi-range HMCVT are analyzed from five aspects,the speed ratio,the characteristics of synchronous switching,the torque characteristics,the power split characteristics and the efficiency characteristics.Take HM2 range to HM3 range in the multi-range HMCVT as an example,according to the principle of dynamics,the mathematical models of shafting,pump motor system,planetary gear train,clutch,engine,main drive system,walking mechanism are established with modular method.Using Matlab/simulink and stateflow modeling tool,based on the principle of finite state machine,simulation model is established for the process by the engine module,HMCVT module,clutch module,state transition logic module,calculation module,main drive module and walking mechanism module seven modules of multi-range HMCVT according to the object-oriented method.The research results indicate that,the factor of efficiency difference-the volumetric efficiency of the pump-motor system is the important reason for the circularly shift range.It also affects the stability of tractor.The control principle of eliminating the segment change of the segment is put forward.Combined with tractor unit dynamics,engine dynamic characteristics and the multi-range HMCVT transmission characteristics,the dynamic three parameter dynamic ranges shifting law of the multi-range HMCVT is formulated.The throttle degree,vehicle speed and driving resistance are taken as control parameters.The driving speed calculated by different throttle opening and different driving resistance is regarded as the changing speed of adjacent two ranges.The simulation results indicate that,application of the proposed method can effectively eliminate the change of segment in the process ofrange shifting.Compared with the traditional synchronous ranges shifting law which is fixed throttle corresponding fixed ranges shifting speed,the velocity stability factor,jerk,sliding friction work and dynamic load coefficient of the multi-range HMCVT are respectively decreased by 57.14%,75.26%,55.38%,and 55.75% with applying the dynamic three parameter dynamic ranges shifting law.The dynamics,ranges shifting stability and durability of the multi-range HMCVT system are effectively improved.The simulation test of speed and displacement ratio based on dSPACE real-time simulation system is realized.This study lays a theoretical foundation for the development and application of automatic transmission.