| Hydro-mechanical continuously variable transmission(HMCVT)put hydraulic static transmission(HST)and mechanical drive system in parallel,through a fixed axis gear pair(planetary gears)carries out engine power distribution,through planetary gears(fixed axis gear pair)carries out the convergence of engine power,and carries out stepless regulation in the range of expected speed by using the stepless speed regulation characteristic of pump-motor.This type of transmission makes full use of the high efficiency of mechanical transmission and the stepless speed regulation characteristics of hydraulic transmission,has advantages of high transmission power,good operation comfort and fuel economy,especially meets complex requirements of high-power tractor' s working condition.So,it is an important development direction in the future of high-power tractor.This paper was supported by Jiangsu Science&Technology Support Plan(BE2014134)and Jiangsu Union Innovation Fund(BY2014128-04),did a comprehensive research on the hydraulic mechanical stepless transmission theory,and combined with the domestic and foreign typical design scheme and tractors specific requirements designed a new type of hydraulic mechanical stepless transmission(2 patents has applied),this paper mainly study the following several aspects:1.The theory of hydraulic-mechanical transmission.First of all,analyzed transmission ratio,torque and power characteristic of two types of transmission scheme in which the planets carried out power split and confluence,combined with the requirement of smooth shifting analyzed the feasibility of power split and confluence using single and double planetary line,and analyzed different kinds of transmission scheme on the basis of restrictions of key characteristic parameters and speed characteristics of equidifferent and geometric transmission.Then listed in detail mature designs at home and abroad,and carried on the analysis and contrast,with the consideration of the broad consensus of the international and tractor's design requirements,put forward a transmission scheme of HMCVT using HI four segments,dual planetary line realized power confluence.2.The design of the new transmission scheme.On the base of analysis to main parameters of typical hydraulic power split stepless transmission on abroad,put forward a new transmission scheme of HMCVT,this transmission with four segments and dual planetary line realized power confluence put intermediate typed mechanical transmission and HST in parallel.With highest total transmission efficiency as the goal to choose key characteristic parameters,and then determined the transmission ratio parameters of gear train,and completed the design of HST's hydraulic circuit and component selection.Comparing the transmission scheme designed with the original prototype,we can draw a conclusion that,the new scheme can easily control the power-output shaft through independently control double-acting clutch;using synchronizer to shift in instead of wet clutch,effectively decrease the size of the gearbox;At the same time,reducing the number of gear pair makes the structure more compact,and transmission efficiency higher.Further,the transmission characteristic of the gearbox was calculated,it shows that,the new scheme fully meet the requirements of stepless speed regulation,and the lowest stable speed is slightly lower the design requirement's,so it can provide greater output torque;tractor with this transmission scheme can have higher speed under the same load,to a certain extent to improve the working efficiency;when the tractor speed is the same as the original design,the engine can meet the job requirements with smaller torque output,thus can prolong the service life of the engine.Through the analysis of gearbox transmission efficiency,we can know in hydraulic speed regulation system,when the input speed of hydraulic pump reducing,the hydraulic motor load increasing,and the pressure difference getting bigger,all can improve the transmission efficiency of this transmission,it laid a theoretical basis for the development of the field experiment prototype.3.Through the introduction of the structure and working principle of various kinds of synchronizer,this paper chose the locking type synchronizer suitable for transmission designed,designed and calculated its structure parameters,and using CREO software rendered 3D model of it.This paper analyzed the process of gear's design,and completed parametric modeling of helical gear.This paper also analyzed the method for determining the dangerous journal and accomplished3D modeling of major parts of the transmission.4.The engine universal characteristic model,the dynamic load model,and the transmission system model of HMCVT were built based on AMEsim,the transmission characteristics and typical working condition of the proposed scheme were simulated.The simulation results of transmission characteristics showed that,the power split stepless transmission designed has the expected characteristics of stepless speed regulation,the torque ratio of the motor shaft and output shaft every segment approximately satisfies constant power transmission,and the highest hydraulic power split ratio is 44%.The simulation results of plough working condition showed that,using HM2 and HM1 for plough operation,and tractor speed and engine fuel consumption were respectively 8.5 km/h,6.1 km/h and 215 g/(kW-h),300 g/(kW·h).Under the same operating condition,higher segment and lower engine speed can improve the fuel economy of the tractor.The simulation results of planting condition showed that,when the load is a constant value,the engine would adjust the output speed according to the throttle opening,the fluctuation of speed is small when shifting,and when transmission's working state is HM3 with zero delivery,it can meet seeding condition's requirements for tractor speed and output torque,at the same time has high transmission efficiency.5.The experimental platform in view of the pump motor speed control system was set up,and it researched the relationship between excitation voltage controlling swash plate angle of the pump and pump motor transmission ratio.The experiment of pump motor speed regulation shows that,under the same engine speed,the pump motor transmission ratio with the same voltage value are different in the process of excitation voltage increasing and decreasing;when the swash of variable pump is positively biasing or negative biasing,excitation voltage and the transmission ratio of pump and motor showed linear relation.Further,making the transmission ratio of pump and motor and excitation voltage as the input and output,through system identification toolbox in Matlab to carry out system identification,the result showed that the identified model has high fitting rate,which provides convenience for accurate control on transmission ratio.Above research provides a theoretical reference and technical support for the design of later field experimental prototype,and is also significant to promote the application of HMCVT on high-power tractors and promote technological innovation of tractor manufacturing in our country. |
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