Pure Electric Power System Based On Displacement Adaptive And Variable Speed Control For Electric Excavators

With the increasing severity of environmental pollution and climate warming,and the increasingly strict emission regulations,construction machinery is facing tremendous pressure on energy conservation and emission reduction.Pure electric-driven technology has become one of the most ideal driving methods for construction machinery due to its low noise,zero emissions and high efficiency.As the most typical construction machinery,hydraulic excavators have high energy consumption and poor emissions.The current research on pure electric-driven excavator has remained on simply replacing diesel engine with electric motor,so that the excellent characteristics of pure electric drive system are not fully utilized.Hence,the research of pure electric drive excavator power assembly has great practical significance and profound social significance.Therefore,it is of great practical significance and far-reaching social significance to conduct research on the power assembly of pure electric-driven excavator.Firstly,by analyzing the working characteristics of the hydraulic excavator,the basic structure of the pure electric-driven power assembly is determined.Lithium iron phosphate battery is used as the energy storage unit.The permanent magnet synchronous motor is employed the power source.Besides,the load sensing system is applied.Aiming at the shortcomings of load-sensing system,a new load sensing system based on displacement adaptive-variable speed control is proposed,which has the advantages of large flow adjustment range,variable pressure difference control,and flexible control.The parameters of the pure electric-driven power assembly of the 8-ton excavator were matched to form a complete scheme.Secondly,in order to exert the advantages of dual variable regulation and make the power source operate efficiently,a displacement adaptive variable speed control strategy based on stepped differential pressure control is proposed.By classifying the differential pressure of variable displacement and variable speed control,the variable pump and the motor can adjust the load sensing differential pressure instages without interfering with each other.The flow matching of the full variable range of the power source is realized,and at the same time,the variable pump is guaranteed to work in an efficient high displacement range.The simulation model was established in AMESim and the feasibility of this control strategy was verified.Thirdly,in order to overcome the shortcoming of large differential pressure loss of traditional load sensing system,combined with the advantages of the variable differential pressure control and the electronic pilot control of the new system,a composite control strategy for pumps and valves based on the minimum differential pressure is proposed.In the stage of variable speed regulation of stepped differential pressure control,the target differential pressure of variable speed controller and the pilot pressure of the multi-way valve are controlled synchronously based on the flow rate estimation based on pilot joystick signals.Minimizing the differential pressure at the orifice can be achieved without affecting the controllability.The simulation model was established in AMESim and the feasibility of this control strategy was verified.Last,an 8-ton pure electric-driven excavator prototype was built,and the proposed displacement adaptive variable speed control strategy based on stepped differential pressure control was experimentally studied.The results show that the control strategy can significantly reduce system energy consumption under the premise of fast differential pressure response and better flow following.The proposed composite control strategy for pumps and valves based on the minimum differential pressure is experimentally tested.The experimental results show that the control strategy further improves the energy saving of the system without affecting the working performance.