Research On Independent Metering And Active-passive Combined Control Hydraulic Excavator Swing System

Hydraulic excavator is a kind of multi-functional and multi-purpose construction machinery,which is widely used in construction,mining,water conservancy,municipal,transportation and civil engineering,underground and tunnel engineering.Therefore,it is of great significance to research the energysaving technology and smoothness of hydraulic excavator.There are several actuators integrated on the hydraulic excavator.Swing is a typical excavator action,there are twice swing during a complete working cycle of excavator,the swing motion accounts for long working time of an excavator,and it is a frequently accelerating and decelerating motion.In the traditional hydraulic excavator,the swing system is controlled by an open-loop valve-controlled hydraulic motor system.The control valve is multiple-way directional control spool valve with a single degree of freedom,which will result in large throttling loss.In addition,among all the actuators of the hydraulic excavator,the swing system has the largest moment of inertia,as a result,there is large overflow loss during the starting process.Based on the above reasons,the swing system of the hydraulic excavator has poor stability,low controllability,low positioning accuracy and high energy consumption.To solve the above problems,taking the hydraulic excavator swing system as the object,a series of studies have been carried out.Firstly,flow matching with pump and valves combined control for independent metering swing system is proposed.The pressure and flow of the hydraulic motor are controlled independently,and the output flow of the hydraulic pump is adjusted in real time to match the rotational speed,so as to reduce the throttle loss and start-up overflow loss.Compared with LUDV,the pressure loss of the new system is reduced by 50%;the average power of the system is reduced by 35.6% when it rotates with the minimum radius of gyration,and 25.5% when it rotates with the maximum radius of gyration;pressure oscillations and swing vibrations of the upper structure are suppressed during braking.Secondly,a velocity and position combined control method based on S curves is proposed.In the rotational process,a S-curve of velocity is generated according to the desired position of rotation for the velocity feedforward control.At this time,the velocity feedforward control plays a major role in reducing position tracking error,and pressure difference feedback and speed feedback are added to improve system dynamics characteristics.In the vicinity of the desired position,the position feedback control plays the key role,and the control valve is converted from independent metering control to symmetrical control,which improves the positioning accuracy and speed.The experimental results show that the system can achieve high positioning accuracy with different rotating speed,and the positioning error is only 0.5°.Based on above work,in order to apply the traditional hydraulic excavators operation habits,the original handle operation mode does not need to be changed,while high positioning accuracy is obtained,a control method is proposed.The desired position control signal is obtained by integrating the signal of the handle,which is applied to the proposed velocity and position combined control strategy.High positioning accuracy will be achieved when the required rotary angle is random in each swing process.As a result,the practicability of this method is improved.By using the principle of energy balance,the displacement overshoot and oscillation caused by the integral delay of the handle are reduced,and the dynamic characteristics of the system are improved.The experimental results show that he positioning error is 0.5°,and the displacement overshoot is suppressed。Finally,an active-passive combined control method with dual hydraulic motor for hydraulic excavator swing system is proposed.While recovering the braking kinetic energy and eliminating the braking overflow loss,the passive system assists the active system to drive the upper structure,which can fully reuse the recovered energy,and the energy efficiency is improved greatly.The research results show that the energy consumption of the system during accelerating process can be reduced by 46.8% compared with the existing system.