Study On Working Stage Identification And Staged Energy-saving Control Of Hydraulic Excavator

The hydraulic excavators are widely applied in the construction of earthwork projects.Under the background of the international energy crisis and the increasingly prominent environmental problems,the energy-saving level of excavators has become an important indicator to measure its core competitiveness.Under the typical working cycle conditions,the action law of the excavator’s actuator and the corresponding external load appears with obvious periodicity.The engine power control mode of "working mode + gear" is difficult to guarantee the working point stable at the fuel economy zone,which results in the high fuel consumption and serious emission.Considering that the earthmoving work of excavator is a dynamic process,the action of actuator has certain randomness and it is difficult to conduct repeatable experiments.It brings great difficulties to obtain the external load characteristics as well as the response of hydraulic system during the typical operation cycle.It further hinders the fine identification of working stage based on multi-sensor information fusion and the study of staged energy-saving control.To improve the fuel economy of hydraulic excavator,the approaches of theoretical method,numerical simulation and experiment are combined to study the dynamic external load characteristics as well as the corresponding hydraulic system energy consumption distribution.The working stage identification method of hydraulic excavator is proposed and the engine operating point adjustment strategy matching with the working stage is formulated to realize staged energy-saving control and reduce the fuel consumption of the whole machine.The specific contents of this paper are as follows:(1)Based on the principle of equivalence,a simplified model of bucket external load in excavation stage is proposed.Then a simulation model of soil excavating process based on the arbitrary Lagrangian-Euler(ALE)method is established and the time-varying characteristics of the excavation resistance system are obtained.The dynamic model of excavator converts the digging resistance system into the output force of the hydraulic cylinder,where the maximum error is verified as 14.56% by the actual vehicle test.By investigating the influence of excavation parameters and methods on the dynamic external load,the optimal compound excavating trajectory is determined with the evaluating indicators of excavation resistance amplitude and specific energy consumption.(2)Based on the platform of ADAMS and AMESim,a co-simulation model of hydraulic excavator machine-hydraulic system is established,where the accuracy of the model is verified through three aspects of components,subsystems,and complete system.The research on the energy consumption distribution of the hydraulic system driven by real-time dynamic external loa is carried out combined with the solving method of dynamic external load of bucket.The quantitative results of the energy consumption distribution of the ZE215E-10 hydraulic system and the response characteristics of key parameters under the typical working cycle are obtained.The results show that,during the single process of 90°loading without load,the useful power of the system is 22.18 k W,accounting for 45.08%.The throttling loss is the largest,accounting for45.51%.During the single process of 90° loading with load,the proportion of the system’s useful work increases to 50.08%.The inlet throttling loss is significantly increased,and the oil return throttling loss is reduced.Moreover,the comparison between different response characteristics of key parameters under each working stage is analyzed,which could provide the researching foundation for the recognition technology of excavator working cycle stages.(3)According to the mechanism action and the varying characteristics of external load in each working stage,the LIBSVM identification model of work cycle stage is established with the waveform of each working stage under stable main pump pressure as the segment symbol.Besides,an intelligent verification is introduced to correct some misunderstood results caused by human factors and signal fluctuations.The overall identification accuracy of model is found the highest as91.93% at the time window width of 0.4 s and the signal sampling frequency of 20 Hz.Aiming at the excessive lag misrecognizing rate derived from the omitting of the hydraulic system response delay,the control signal waveform that can directly reflect the action information of actuator is selected as the identification mark.By applying the deep learning method,the LSTM identification model for the working stage is established,which effectively reduces the lagging misidentification rate by 31.86%.Finally,the influence mechanism of model parameters on the performance of two working stage identification methods is compared.(4)Considering that the power controlling mode of the engine power with fixed gear is difficult to satisfy the energy saving requirement of the excavator,a staged energy-saving strategy for excavators is proposed based on the operating point regulation.With the application of statistical method,the target speed range is determined for each working stage.Besides,in order to meet the operating requirement at the transition between working stages as well as the energy saving requirement within each working stage,a speed adjustment strategy based on the principle of maximum acceleration and a torque stabilization strategy optimized by genetic algorithm are proposed.Considering the torque requirement of the auxiliary equipment,based on the recursive thinking,the optimal target torque fuzzy controller is designed with the input determined as the engine torque bias and bias varying rate and the output determined as the outlet pressure variation of secondary pressure reducing valve.Conducting the rear car test under the typical working cycle,the results show that the load appears stable during the standby and pre-digging stage where the distribution of working points almost remain unchanged.During the stage of lifting,unloading and digging,the operating point is found moving towards the economical fuel area with high torque and low speed.Besides,the work point area appears concentrated during the swinging stage.Under the staged energy-saving control of excavator based on working point adjustment,the average fuel consumption rate of the whole machine is 197.2369 g/k W·h and the fuel economy is improved by 1.27%.116 figures,34 tables and 229 references are included.