Research Of Electro-Hydraulic Recovery And Utilization System For Braking Energy Of Large-Inertia Rotary Mechanism

As a kind of machinery widely used in engineering work,hydraulic excavator has the characteristics of high power,complicated working environment and large working range.Engine is generally used to drive hydraulic pumps to provide hydraulic system with high pressure oil,which is distributed to the hydraulic actuators through control valves.Due to the diversification of working environment and the variety of operation functions,the loading of excavator fluctuates greatly and changes frequently,which gives rise to the low energy utilization ratio and high emissions of excavator,resulting in a large amount of waste and serious pollution sequentially.With the working time of the swing system of the excavator accounting for about50%of the total working cycle of the excavator,the heat generation accounts for 30%⁴0%of the total heat generated by the hydraulic system of excavator according to statistics.Therefore,the recovery and regeneration of braking energy of the swing system of hydraulic excavator is of great significance to improve the overall energy efficiency of hydraulic excavator and reduce the system heat and emission.To solve the problems above,scholars and research institutions at home and abroad did a lot of researches.At present,the energy-saving hydraulic swing system mainly includes secondary regulation system,closed pump-controlled system and meter-in and meter-out method system.Besides,hydraulic recovery method（accumulator is used as energy storage unit）and electrical recovery method（battery or supercapacitor is used as energy storage unit）are wildly taken to recuperate the braking energy of swing system of hydraulic excavator.Some achievements have been made by taking those means above into practice.However,there are still a few problems.On one hand,accumulator is limited by the non-linear pressure characteristics of the accumulator when recovering and releasing the braking energy.Accumulator can only drive the loads which with lower pressure than accumulator during energy releasing process.On the other hand,in the electrical recovery method,owe to the long path and the complicated conversion link transferring energy,the energy recovery efficiency is low,meanwhile,the response of the hydraulic motor-generator unit is relatively slow,affecting the stability of the excavator swing system.In view of the above problems,the research of electro-hydraulic recovery and utilization system for braking energy of large-inertia rotary mechanism（abbreviated as electro-hydraulic recovery system in the following context）is presented in this paper.The hydraulic accumulator and supercapacitor are used to store the energy at the same time,and the real-time pressure of the accumulator is coupled to the torque of the generator.The recovery ratio of the system recovering the braking energy of the swing can be maximized,and the braking stability can be ensured at the same time.The specific work is as follows:In Chapter 1,the significance of energy saving of swing system of hydraulic excavator is presented from the aspects of working time and heat ratio.The research status and main methods of energy saving in the swing system of hydraulic excavator at home and abroad are summarized,and the electro-hydraulic recovery system of swing braking of hydraulic excavator is proposed in view of the shortcomings of the existing research.In chapter 2,the working principle of traditional hydraulic excavator swing system is analyzed,the theoretical analyses of the swing acceleration and deceleration braking are carried out respectively,the mathematical models are established,and the forms of energy loss are analyzed.Based on the analyses above,the feasibility of energy recovery is analyzed,the design principle of recovery system is determined,and the recovery scheme is carried out,providing a theoretical basis for the next simulation work.In Chapter 3,the existing swing system model and electro-hydraulic recovery system model of 20 t hydraulic excavator are constructed in the simulation software SimulationX,respectively.Under the typical rotation angle of 90°,120°and 180°,the no-loading swing system of the excavator is simulated and studied.The feasibility of the proposed electro-hydraulic recovery system is verified by simulation,and the influence of the inlet pressure of the recovery hydraulic motor is analyzed,where p_inset is defined as the setting value of inlet pressure of the recovery hydraulic motor of the recovery system.The simulation results show that the smaller the set pressure value p_inset is,the more energy can be recovered by the recovery system,meanwhile increasing the braking time of the swing system.When the nominal volume,maximum working pressure and minimum working pressure of the hydraulic accumulator are constant,the characteristics of energy recovery and utilization of the system are greatly affected by the pre-charging pressure of the hydraulic accumulator.The energy recovery efficiency of the accumulator decreases with the increase of the pre-charging pressure,and the energy recovery efficiency of the supercapacitor increases with the increase of the pre-charging pressure.when the hydraulic accumulator and punching force,maximum working pressure and minimum working pressure are fixed,the characteristics of energy recovery and utilization of the system are greatly affected by the rated volume of the hydraulic accumulator.The energy recovery efficiency of the accumulator decreases with the increase of the rated volume,and the energy recovery efficiency of the supercapacitor increases with the increase of the rated volume.The energy recovery efficiency of the system is inversely proportional to the rated volume of the accumulator.In Chapter 4,the traditional swing system model and electro-hydraulic recovery system model of 6 t hydraulic excavator are built in the simulation software SimulationX.Compared with the swing system of 20 t excavator,the applicability of the electro-hydraulic recovery system on small excavator is studied.The simulation results show that the system also has good recovery effect on 6 t hydraulic excavator.In Chapter 5,the main conclusions and deficiencies are summarized and the further research work is put forward.