| Hydraulic excavator is a kind of important engineering machinery joint with mechanical,electrical and hydraulic and always works in complex working conditions.Traditional hydraulic excavator driven by the engine.Because of greatly influenced by the load fluctuation,the engine’s working point is often in low efficiency area and in addition,there is much energy consumption in the process of energy transfer.There are so many fruitful research in power matching between engine and hydraulic pump,hybrid excavator and energy recovery technology,valve control system of energy saving,had carried on.The inherent low energy conversion rate,the noise,the vibration and pollution of engine still restrict the promotion of overall efficiency of hydraulic excavator.With the development of the society,the new requirements are proposed,such as zero emissions and low noise in mine laneway or interior space of large building.Traditional hydraulic excavator can’t adapt to these situations.It is an important research direction to combine variable speed motor with high energy density of the hydraulic system into an excavator.This paper made systematic research on Variable speed-variable displacement hydraulic power source applied in hydraulic excavator and made beneficial exploration in the movement and energy efficiency characteristics of electric drive hydraulic excavator system,supported by the National Natural Science Foundation of China under Grant No.U1510206 and No.51575374.In this paper the following researches have been completed:Firstly,paper summarizes the evolution process of power source of excavator and electric shovel,the technologies status in quo of power matching,hybrid power and energy saving at home and abroad.In order to get new type hydraulic excavator power supply system with higher efficiency and better energy saving characteristic,combined with the current social demands for excavator zero pollution and low noise,cost-effective electric variable speed motor with good shock resistance is proposed to replace the original engine.At the same time,this paper expounds research status in quo of Independent Metering Circuit(IMC),a pump and valve coordinate flow matching control strategy is proposed to decrease the energy consumption and improve the stability when hydraulic cylinder drives large inertia loads at startup stage.Secondly,the two-phase motor mathematical model and vector control algorithm mathematical model are established in rotating coordinate system.After analyzing the mathematical model,a simulation model of three-phase asynchronous motor controlled by vector control system is built with simulationX.Through simulation and test in rig,the Static characteristic of speed and torque,and dynamic characteristics of startup and load disturbance are studied.To solve the slow startup problem of three-phase asynchronous motor,a hydraulic power source structure of variable speed ? variable displacement is proposed.Using this hydraulic power source,the dynamic response and energy efficiency characteristic are improved by two methods: one is using the swivel control of electrohydraulic proportional pump to control the flow response at dynamic state;another is matching the energy consumption with motor speed at steady state.Thirdly,the energy consumption of the three-phase asynchronous motor and hydraulic pump is researched by theory analysis,simulation and experimental.Based on the data of research,the high efficient working points are established and the power matching strategy is designed for hydraulic power source of variable speed ? variable displacement.Combined with the patent technology of low energy consumption at low velocity of hydraulic power source,the automatic idle speed control strategy is put forward,compared to the status of light load at power frequency speed,the total input power consumption can reduce from 4.141 kW to 0.727 k W and energy-saving rate can reach to 82.4%.Furthermore,a pump and valve coordinate flow matching control strategy with IMC is applied when hydraulic cylinder drives large inertia loads at startup stage under a power extension mode,such as hydraulic excavator boom’s lifting.A control strategy is designed in which pressure control is superposed on the basis of flow matching control in IMC system.When boom retracts under over-running load,another strategy in which the meter-out flow rate control and flow regeneration control are used to reduce energy consumption.Based on the multibody dynamics software named simulationX,a simulation model joint mechanical,electrical and hydraulic is established.The working performs and energy-saving features of electric hydraulic excavator with IMC is researched.Excavator experiment platform is built and d SPACE is applied as the main controller.The experimental results show that the energy consumption of the boom system falls 15% compared to the load sensing system.Fanally,the paper summarizes the paper’s main work and innovation points,and the future research direction is discussed. |
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