Research On Characteristics Of Variable Hydraulic Transformer And Its Flow Distribution

Under the requirements of energy conservation in the world,researchers present a new hydraulic technology called hydrostatic transmission system with secondary regulation that is based on the constant pressure network.In addition to finishing the prescribed missions,this technology is used to recover excess potential energy and kinetic energy of the system.Hydraulic transformer is one of the core components of the technology.Now,it has fewer specifications and other three problems.First,it has only one tunable parameter.So,it cannot control load pressure and load flow simultaneously.Second,it is not applied widely because its overall efficiency and pressure ratio is very low.Now more and more researchers are interested in its structure innovation.Its pressure ratio and the working range of its variable pressure angle are improved continually by the researches.Last,its noise is much louder than pump.In view of the existing problems of the hydraulic transformer,this dissertation presents a new hydraulic transformer,that is,variable hydraulic transformer(abbrev.VHT).The mathematical models of the VHT are built.These models can express the structure of the VHT’s port plate.The VHT’s flow,pressure,and power characteristics are also analyzed.The defintions of the pulsation absolute strength and the pulsation relative strength of the VHT’s characteristics can well depict the pulsation of the VHT’s characteristics.The VHT’s overall efficiency is defined as the ratio between the VHT’s real pressure ratio and the VHT’s ideal pressure ratio.Considering the impact of the variable displacement angle on friction,the power loss can be depicted in greater detail.Based on the consideration,a new mathematical model of the VHT’s pressure ratio is presented.The impacts of the variation of the variable displacement angle on the VHT’s characteristics are analyzed.Although the analyses indicate that the relationship between the variable displacement angle and the most of the VHT’s characteristics is approximately linear,the variable displacement angle has a weak impact on the VHT’s pressure ratio and overall efficiency.The key to turn the VHT from pressure regulator to power regulator is the introduction of the variable displacement angle.The coupling characteristics of the VHT is described through the mathematical model and the graph.Although the VHT can control the load pressure and the load flow simultaneously,the couplings between the operation variables and the output variables need to be decoupled.A decoupling scheme that uses the compensation principle is presented for the coupling characteristics of the VHT.The decoupling scheme can remove the impact of the variable pressure angle on the load flow.Mechanical model of the VHT’s port plate friction pair is built.Pressing force and torques on the VHT’s barrel by oil in the piston chamber are analyzed.The pressing torques are researched by way of the analyses of their arms,angles and action point paths.Reverse thrust and reverse thrust torques on the VHT’s barrel by oil film on the port plate are analyzed in the same manner.The residual pressing force coefficient and residual pressing torque coefficient are analyzed.The results show that the parameters of the VHT’s port plate pair are reasonable.The experiments indicate also that the parameters can improve the VHT’s pressure ratio.An optimization scheme of the complex buffer structure in which the amount of oil in piston chamber is adaptive is presented.The VHT’s noise by the flow distribution is suppressed by the buffer structure on the port plate through reducing hydraulic impact in the scheme.Based on the analysis of the optimal ratio between the oil volume that goes through buffer hole or groove and the overall pressing oil volume that the preloading and pre-releasing of the piston chamber need,the parameters of the buffer structure are obtained.The pressure equation and pressure gradient equation of the piston chamber are built when the piston chamber passes by the buffer structure.According to the scheme,two type port plates that have different buffer structures are designed,emulated and tested.The results present that the scheme can suppress the noise well.The structure of the VHT is designed.A flow distribution scheme is presented.The port shell of the scheme is connected to the blade shaft by using a full circular port groove,making the working range of the variable pressure angle unlimited.The scheme can prevent leakage effectively and improve the VHT’s pressure ratio.The experiments show that the pressure ratio of the prototype could reach 4.8.The experiments are performed through building an experimental table for the VHT.The correctness of the theoretical research about the characteristics and the buffer structure is confirmed by the experimental results.