Research On The Hydraulic Hybrid Vehicle Systerti Based On Hydraulic Transformer

With the rapid development of auto industrialization process all over the world,the rising vehicle population led to the increasingly serious problem of energyshortage and environmental pollution and then the automobile manufacturers at homeand abroad urgently needs to research and development of energy-efficient andenvironment-friendly automobile. Hydraulic transformer (HT) is a new kind ofsecondary regulation component, when it used to be in the common pressure rail(CPR) system, it is not only no throttling loss to adjust the pressure ratio by adjustingthe control angular displacement of valve plate of HT in higher efficiency but also tomutually independent between the two loads. It is no doubt that the pressure and flowcoupling phenomenon can be avoided and flexibility and efficiency of the hydraulicsystem can be improved by using of HT in the hydraulic hybrid vehicle (HHV).Obviously, the hydraulic hybrid vehicle system based on hydraulic transformer isbuild to realize the braking energy recovery and secondary utilization at braking anddeceleration of vehicle. Using this hydraulic hybrid vehicle composition not onlythrottling losses caused by the throttle valve have be decreased compared with theconventional hybrid system but also the control performance, reliability and cost haveimproved. Therefore, the study of hydraulic hybrid vehicle based on the hydraulictransformer has been carried out by combining the national key projects of "863":"Application study of hybrid drive system and energy-efficient constructionmachinery technology".The main works of the thesis are as follows:1. The composition form and current research status of HHV are introducedbased on a lot of publications and conference papers. Moreover, the history andcurrent research status of HT are presented and the key technologies, energy-savingprinciple and engineering applications are described. Finally, the main research aimand content are proposed. 2. The conception of hydraulic hybrid vehicle system based on the HT waspresented and the the theory of limit cycles was applied to the HHV, which analysesdynamic characteristics of the HHV system. The phase diagrams of global topologicalstructure of HHV system were entirely described according to qualitative analysis ofthe singular points, the singular points at infinity and the inherent properties of closedtrajectory. At the same time, the analysis of equilibrium points showed that if theYoung's modulus of fluid is neglected, the equilibrium points of the system will bedistributed on both sides of the initial function Alx+Vt=0, and there is a uniqueequilibrium point according to the practical signification of the system parameters.The nonexistence analysis showed that there is no limit cycle for the system, nomatter how the viscosity coefficient B changes. The stability analysis of equilibriumpoints showed that the system is asymptotically stable about the equilibrium point atB≥0and the equilibrium point is the center point of the system at B=0.3. The relations curves between the control angle of HT port plate and thecharacteristic parameters of accumulator (i.e. valid volume, specific energy andefficiency) was done to selected the optimization parameters to improve theenergy-saving indicators of bladder accumulator. Moreover, the instantaneouspressure ratio function of HT was built to obtain the rational curve of HTinstantaneous pressure ratio and characteristic parameters to study the pulsationcharacteristic of HHV, which includes angular displacement of HT piston, controlangle of HT port valve and pressure of T kidney. Then, the mathematical model ofseries and parallel bladder accumulator was established by the lumped parametermethod, respectively. The analysis of dynamic characteristics of accumulator (i.e.instantaneous valid volume, instantaneous specific energy and instantaneousefficiency) was done after simulation was carried out. Finally, the braking energyregenerative efficiency of this HHV compared to traditional hybrid vehicle system inthe case of invariable braking torque was get, and the results show that theenergy-saving effect is obvious with pressure ratio effective regulation of HT.4. When the vehicle is braking and decelerating, the optimization energy-savingcontrol algorithm of HT based on the HHV working principle was presented, which istime to meet the energy-saving optimization conditions of accumulator in differentworking conditions of vehicle, which is control algorithm at the state of load as a major influencing factor and HT as major regulator factor. The relational curves ofoptimization energy-saving control algorithm and the various influencing parameterswere got after simulation was carried out. Moreover, simulation analysis to controlperformance of optimization energy-saving algorithm was carried out using PID,Fuzzy logic controller (FLC) and Fuzzy-PID control strategy based on mathematicalmodel of valve controlling cylinder driving the valve plate of HT. The results showthat Fuzzy-PID controller is more suitable to the HHV in terms of basic controlperformance and robust performance. Finally, the PID, FLC and Fuzzy-PID controllerwas applied to the above mentioned energy-saving algorithm under two differentstates at vehicle braking and decelerating, respectively. The control performanceparameters of3rd kind of controller were got through comparative analysis.5. The general form of the friction item of the basic elements of hydraulictransmission line distribution parameters was obtained by the roots of hyperbolicfunction approximate equation, which is to substitute the distributed parameter basedelements by the finite sum approximations of partial fraction functions about the zeropoles. By this method, the approximate computation of distributed parameter basiselements for hydraulic transmission line was presents by the method of undeterminedcoefficients. The numerical examples results show that the effectiveness andaccurateness of this method in the low frequency region by comparing with modalapproximation of Zhao T. and Hullender, respectively. Moreover, the relevantmathematical models of instantaneous flow of HT were built and the theoreticanalysis of series and parallel accumulator were made with frequency method. Theflow pulsation characteristic simulation curve of HT and accumulator was done, andthe result shows that the effect of the damping of pulsation of HT by seriesaccumulator was much superior to that by the parallel accumulator, whether controlangle of HT port plate is zero. Finally, the pulsation characteristics of HHV system isanalyzed in considering the hydraulic transmission pipeline effect which was adoptedthe hydraulic transmission pipeline approximate model of Hullender, Zhao T. and thismethod in this paper, respectively.6. The test-rig of hydraulic hybrid vehicle system based on HT was built atHarbin Institute of Technology University. The test experiments were carried outunder the different conditions, which are mainly composed of the basic characteristic of the HT, the pulsation characteristics of HHV and control performances of HT servovalves applied to PID and Fuzzy-PID controller. The experiment results show that theexpatiated theoretical study is correct and the HHV system is successful via benchtest.7. The some conclusions are given and some opinions for research works are tutforward in the future, then the some innovations of this paper were summarized.The innovative achievements of the thesis are as follows:1. According to the working principle of the HHV system and its components,the theory of limit cycles was applied to the HHV, which analyses dynamiccharacteristics of the HHV system. And the phase diagrams of global topologicalstructure of the HHV system were entirely described via qualitative analysis of thesingular points, the singular points at infinity and the inherent properties of closedtrajectory.2. The relations curves between the control angle of HT port plate and thecharacteristic parameters of accumulator, and the HT instantaneous pressure ratio anddynamic characteristics parameters of the series and parallel bladder accumulatorwere done to selected the optimization parameters to improve the energy-savingindicators of bladder accumulator, respectively. The braking energy regenerativeefficiency of this HHV compared to traditional hybrid vehicle system in the case ofinvariable braking torque was get, and the results show that the energy-saving effectis obvious.3. When the vehicle is braking and decelerating, the optimization energy-savingcontrol algorithm of HHV system based on the optimized energy-saving condition ofaccumulator was presented. The basic control performance and robust performanceparameters of HT control device and various performance parameters of optimizationenergy-saving algorithm were got under the control response of the PID, Fuzzy logiccontroller (FLC) and Fuzzy-PID control strategy, respectively.4. A kind of the pipeline approximation algorithm by the roots of hyperbolicfunction approximate equation was presented. The pulsation characteristics of HHVsystem and the pulse characteristic of system in considering the hydraulictransmission pipeline effect were analyzed according to the mathematical model ofthe HHV system. The results show that the proposed pipeline approximation algorithm is reasonable and effective at the middle and low frequency, and the seriesaccumulator was much superior to that by the parallel accumulator in terms of theeffect of pulsation damping.