| Hydro-mechanical variable transmission(HMT)is a kind of double power flows transmission with characteristics of high transmission efficiency and stepless speed variation,which is compounded by hydraulic and mechanical transmissions,HMT is an ideal transmission for high-power vehicles.In order to solve the problems of rotation speed fluctuation of hydraulic components and power interruption during the power shift process of HMT,the power transfer mechanism of HMT in full power shift process and the displacement regulating law of the variable displacement hydraulic component during the shift process are studied,based on the five-stage full power shift method by overlapping the two clutches’ engagement.The main research contents include:(1)In this paper,an arithmetic two-range HMT is taken as the research object,and the characteristics of torque and power transfer of HMT in full power shift process are analyzed,the relationship between torque,power and hydraulic circuit pressure are obtained,the formula of torque transfer mechanism is obtained.(2)The closed hydraulic circuit is composed of the variable displacement hydraulic component,the fixed displacement hydraulic component and oil circuit,which is equivalent to the chamber model.Considering the influence of the volumetric efficiency of the hydraulic transmission unit,the chamber model for the closed hydraulic circuit of the HMT full power shift process is established.And the mathematical model of the displacement ratio adjustment of the variable displacement hydraulic component is derived.The step and slope displacement ratio adjustment rules are adopted respectively,and the corresponding response of hydraulic circuit pressure is obtained by simulation.The results show that the displacement ratio adjustment law has a great influence on the period of pressure build-up,and also has influence on the pressure fluctuation during high-and low-pressure circuits interchange.The step adjustment law can effectively reduce the period of pressure build-up,and there is no obvious increase of pressure fluctuation in the high-pressure circuit compared with the slope adjustment.In order to effectively reduce the shifting time,the displacement ratio step adjustment law can be adopted.(3)Through the displacement adjustment characteristic test of the HMT full power shift process,with the change of displacement ratio,the dynamic response process of the hydraulic circuit is obtained from the current range to the target range.The results show that the simulation results of displacement ratio change are in accordance with the test results,and the maximum deviation is about 9% under the same working conditions.Based on the parameters of current range state and target range pressure,the mathematical model of displacement ratio adjustment proposed in this paper can predict the displacement value of the target range and accurately describe the pressure interchange between the high-and low-pressure circuits.During the overlap process of the two clutches,the displacement ratio of the variable displacement hydraulic component is adjusted to the target value.And the pressure interchange between the high-and low-pressure circuits can be stably completed in the shift process,so that the torque is quickly transferred between the clutches.HMT output speed is unchanged,torque is basically continuous,and power is continuous and smooth.And the problems such as the speed fluctuation and power interruption in the shift process is solved.This study provides a reference for the realization of HMT full power shift control and subsequent research. |
