Research On Static And Dynamic Characteristics Of Conical And Curved Spool Of Direct Counterbalance Valve

As a key element in the balance circuit,the hydraulic counterbalance valve is widely used in construction machinery,especially hoisting machinery.When the crane boom is luffed,the cylinder is stretched and the weight is lowered,there will be an overriding load in the same direction as the direction of the load and its movement speed.It is necessary to install a counterbalance valve on the oil return line of the system to control the smooth movement of the load.Therefore,the performance of the counterbalance valve has an important influence on the overall safety,stability and work efficiency of the hydraulic system.This paper takes a certain type of direct-acting counterbalance valve as the research object,and adopts the research method combining theoretical analysis,numerical simulation and experimental test.The dynamic characteristics and internal flow field were compared and analyzed.The influence of the structure of the valve core on the performance of the counterbalance valve is studied,which provides theoretical guidance for the design and application of the valve core of the direct-acting counterbalance valve.The main research contents of this paper are as follows:The mathematical model of the balance circuit of the direct-acting counterbalance valve is established,and the influence of the key structural parameters of the counterbalance valve on the system stability is analyzed.The results show that:increasing the spring stiffness of the counterbalance valve,reducing the gradient of the valve port area,reducing the pilot force area of the spool,and reducing the diameter of the orifice d₂ of the pilot oil circuit can reduce the open-loop gain of the system to a higher level.Improve the stability of the system,but will reduce the response speed of the system.The AMEsim simulation model of the direct-acting counterbalance valve is built,and its dynamic characteristics are simulated and analyzed.The results show that the control oil first passes through the orifice d₁ of the pilot oil circuit and then builds up pressure in the control chamber,and then performs secondary filtering through the orifice d₂.When d₁>d₂,the stability of the system can be improved,and the response speed will not be greatly affected.Therefore,when designing the counterbalance valve pilot damping network,the design method of the damping hole diameter d₁≥d₂should be followed.In order to reduce the pressure fluctuation and load jitter during the opening adjustment process of the counterbalance valve,this paper designs three curved spools by changing the gradient of the valve port area of the counterbalance valve.A comparative analysis was carried out.The results show that the curved spool of the counterbalance valve can achieve the characteristics of"small opening with small gain,large opening with large flow".When the valve port is opened,the fluctuation of the load pressure can be effectively suppressed,so that the load starts to move smoothly;When the load moves smoothly,the flow rate rises rapidly to improve work efficiency.Compared with the double cone spool,the dynamic characteristics of the counterbalance valve are as follows:The overshoot of the cylinder speed when the load drops is reduced from 28.6%to 10.6%;When the load vibrates,the vibration amplitude of the valve port flow decreases,and the amplitude ratio L（f）at small flow rate is reduced from 10.7 to below 5;When controlling the pressure step response,the pressure fluctuation in the load chamber is significantly reduced.In terms of static characteristics,the test results show that the pressure loss is reduced by 0.5 Mpa when the valve port passes the rated flow.