Theoretical And Experimental Research On Double Rotor Hydraulic Transformer

Faced with the powerful challanges of the power system,the concept of the Common Pressure Rail(CPR)system indicates a bright direction for building an efficient,modular,and highly reliable hydraulic system.The hydraulic transformer studied here is the core hydraulic component in the CPR system.The hydraulic transformer is functionally a new type of hydraulic component used to regulate the direction,pressure and flow of fluid in the fluid transmission circuit.This requires that the flow,pressure and control characteristics must meet certain requirements.In the hydraulic transformer,the instantaneous driving torque and the load torque generated by the pistons fluctuate drastically and interact with each other,causing fluctuations in flow rate and pressure.In addition,the inertia of the valve plate and the cylinder block are small,and the dynamic response of the hydraulic transformer itself is fast,which makes its anti-interference ability very poor.A slight change in the position of the valve plate will immediately change the balance of the rotor torque and thus the rotational speed of the transformer,so that the flow transmitted by the hydraulic transformer also changes rapidly,and the vibration and noise problems also come afterwards.At present,hydraulic transformers still have problems such as large output fluctuations,torque fluctuations,unstable operation at low speeds,and high noise.Therefore,there is an urgent need to conduct a systematic research on the core component of the hydraulic transformer to solve the key problems that limit the performance of the hydraulic transformer.This dissertation proposes a novel double rotor hydraulic transformer(DRHT).The extra rotor helps break through the limitation of the cylinder strength and double the number of plungers,thus alleviating the fluctuation problem of the hydraulic transformer.The mathematical models related to the displacement,flow rate,and pressure ratio of the DRHT are established.Through the simulation study of the C program of the model,the change rules of the displacement,flow rate and pressure ratio of the DRHT are obtained.The results show that the discontinuity of the theoretical instantaneous flow is the main reason for the large fluctuation of the hydraulic transformer,and by increasing the number of plungers,the flow pulsation rate of each distribution slot can be significantly reduced.In order to improve the performance of the DRHT,a method of adjusting the relative angles of the distribution slots on the valve plate is proposed.And the influences of the structural parameters such as the wrap angle of the distribution slot,the number of plungers,and the operating parameters such as the control angle and the CPR pressure on the characteristics of the DRHT are discussed.A double rotor flow distribution mechanism is proposed by following the principle of hydraulic rotary joint,solving the throttling problem existing in the traditional valve plate rotating hydraulic transformer.The leakage characteristics of the distribution mechanism are analyzed,and the mathematical model of the swing spindle of the distribution mechanism is obtained.Through the analysis of the force characteristics of the distribution mechanism,the models of pressing and supporting force are obtained,which can make the dynamics model more accurate.The experimental prototype of the double rotor flow distribution mechanism is designed and manufactured.The test bench is built and the experimental data of the leakage characteristics and torque characteristics of the flow distribution mechanism is obtained.And the correctness of the principle of the double rotor flow distribution mechanism is verified.The mathematical model of the pressure and rotating speed of the DRHT are established,in which the instantaneous torque generated by the plunger,the frictional resistance torque and the instantaneous angular velocity of the rotor are obtained by the dynamic model of the rotor,and the output pressure and the instantaneous pressure in the plunger chamber are solved by the fluid pressure model.At the same time,the model also established the pipeline model through the 1D mass conservation equation and the momentum equation.By means of combining rotor dynamic characteristics with fluid flow di stribution characteristics,the coupling calculation of the pressure and speed of the DRHT can be realized and the pressure characteristics of the DRHT under different working conditions can be obtained.Through the simulation study of the model,the effects of structural parameters and working parameters on the instantaneous pressure inside the plunger chamber are studied,as well as the output pressure and the pressure ratio under different working conditions can be studied,and the change l aw of the transient and average pressure characteristics are obtained.Furthermore,the experimental prototype is designed and manufactured and the theoretical model is verified.The CFD study is carried out for the pressure reduction process of the DRHT.The precise 3D fluid domain model is first established and high quality meshing is then completed.The CFD model is based on dynamic mesh method,which also considers the effects of turbulence and cavitation,and is calculated by FLUENT's AMG solver.During the calculation,the user-defined function(UDF)written by C program is called in each discrete time and iteration cycle to control the shape and position change of the fluid domain mesh,communicate between each compute nodes,and complete numerical integration calculation and data post-processing based on each field quantity.Through the multi thread parallel calculation,the variation law of the transient pressure in the plunger cavity with the parameters such as rotational speed and control angle is obtained.The results show that with the increase of the rotating speed,the pressure drop inside the plunger chamber is the most obvious under the condition of ? = 30o,and is likely to cause suction phenomenon.Damping grooves can alleviate this problem,but they will bring volume loss.Through the parameterization research on the dimensions of the damping groove,an optimized scheme is obtained,which can prevent excessively low transient pressure in a large speed range,and it can also ensure a low volume loss rate.The rotor supporting scheme using direct support rotor structure is developed,which applies non-through rotors,so that the central axis only acts to transmit torque and does not withstand radial forces.The central axis connecting the two rotors is also relatively shorter,which improves the stress state during the working process of the DRHT.A prototype of the DRHT based on this rotor supporting scheme is manufactured,and the test bench is also set up.By comparing the experimental results of "double rotor" and "single rotor",it can be concluded that "double rotor" can effectively suppress the violent pressure fluctuation,and the noise level is also lower.Compared with the ideal pressure ratio,the experimental results are generally lagging behind,while the curves of the pressure ratio from "double rotor" and "single rotor" are basically the same.In addition,the experimental results also verify the correctness of the theoretical research.