Research On Flywheel-based Boom Energy Recovery System For Hydraulic Excavator

Hydraulic excavator is one of the most widely used types of construction machinery.It has the characteristics of large sales,large installed power and low energy efficiency.These brings great pressure to environmental protection.With the proposal of carbon peak and neutrality goals,energy conservation and consumption reduction has become an important goal for the development of the excavator industry.In order to improve the energy efficiency of excavators,energy recovery technology has attracted the attention of many researchers.According to the specific form,energy recovery technologies can be divided into three types: electrical,hydraulic and mechanical.At present,the first two energy recovery technologies are common in excavators.Currently,flywheel-based mechanical energy recovery technology is mainly used in the field of vehicle technology for the recovery of braking energy.Inspired by this idea,in order to realize the recovery and reuse of the potential energy of the excavator boom,a noval flywheelbased energy recovery system for hydraulic excavator boom is proposed.In this system,a flywheel is used as the energy storage element and a hydraulic pump motor(hydraulic secondary unit)as the energy conversion element.Its theoretical analysis and experimental research are carried out in this dissertation.The main research contents of this dissertation are as follows:(1)A flywheel-based energy recovery system for excavator boom is proposed,and its feasibility is demonstrated.The typical working conditions of excavator and the recoverable energy of boom are analyzed.Aiming at the problem of boom potential energy waste,a new mechanical boom energy recovery hydraulic system is proposed based on the principle of flywheel energy storage.The system uses flywheel as energy storage element and hydraulic pump motor as energy conversion element.When the boom falls,the system can recover the potential energy of the boom and avoid energy waste;When the boom is lifted,the system can reuse the recovered energy and reduce the energy consumption of the system.Then,this dissertation demonstrates the feasibility of flywheel-based energy recovery technology for recovering the potential energy of excavator boom from three aspects: working conditions,number of energy conversions and the characteristics of energy storage elements.Finally,since using a flywheel as the energy storage element,combined with the working conditions of the excavator,this dissertation puts forward the double optimization objectives of improving the mass energy storage density and reducing the occupied space,and the NSGA-Ⅱ algorithm is used to optimize the shape of the flywheel.(2)An improved Drosophila algorithm for optimizing PID controller parameters of energy recovery system is proposed.Firstly,the mathematical models of conventional boom system and energy recovery system are established,and the characteristics of energy recovery system are analyzed.In order to obtain better control performance,an improved Drosophila algorithm is proposed to optimize the parameters of PID controller.The effects of PID controller optimized by the improved Drosophila algorithm,a conventional Drosophila algorithm and genetic algorithm are compared and analyzed to verify the effectiveness of the proposed algorithm.The results show that the PID controller using the improved Drosophila algorithm has the advantages of fast response and no overshoot.Finally,the influence of hydraulic pump motor displacement and flywheel inertia on the system performance is studied.The research shows that the smaller the displacement of the hydraulic pump motor,the higher the energy efficiency of the system.For the moment of inertia of the flywheel,the greater the value,the higher the energy efficiency of the system.(3)Taking the conventional load sensing system widely used in excavators as a reference,the energy recovery and reuse efficiency of the flywheel-based energy recovery system is studied.The conventional load sensing system and the new system are simulated under no-load and full load conditions respectively,and the energy recovery efficiency and reuse efficiency are analyzed.According to the energy consumption,the energy flow diagrams of the two systems under different working conditions are drawn.The simulation results show that the new system can save 45.7%and 27.6% energy compared with the conventional load sensing system under no-load and full load conditions.Considering the fuel consumption of the engine,the new system can achieve fuel saving rates of 30.4% and 22.2% under no-load and full load conditions.(4)To better reuse the recovered energy,a control strategy based on fuzzy allocation is proposed.This strategy can make a adjustment according to the load of the boom and the energy storage in the flywheel,and determine the energy allocation coefficient between the engine and the flywheel.The results show that the optimized new system can save 51.9% and 30.3% energy compared with the conventional load sensing system under no-load and full load conditions.Compared with that before optimization,the energy-saving efficiency under no-load and full load conditions is increased by 11.5% and 3.8% respectively.As for the engine,the optimized new system can achieve 32.6% and 22.2% fuel saving rate compared with the conventional load sensing system under no-load and full load conditions,and the fuel saving rate is increased by 3.1% and 2.3% respectively compared with that before optimization.(5)Based on the above theoretical analysis,a 4-T hydraulic excavator is reformed,and the hydraulic system,energy recovery unit and measurement and control system are added as the test bench.The flywheel-based energy recovery system and control strategy proposed in this dissertation are experimentally verified,and the energy-saving effect and controllablity of the system are evaluated.The experimental results show that the controllability of the new system is equivalent to that of the conventional load sensing system,and the energy of the pump is decreased by 13.7% at the same time.The flywheel-based energy recovery system proposed in this dissertation provides a new idea for the energy recovery of construction machinery represented by hydraulic excavator.There are 160 figures,31 tables and 217 references in this dissertation.