Research On Falling Controllability And Lifting Impact Resistance Of Pressurized Luffing System About Truck Crane

Truck crane is a kind of important engineering machines being widely used in construction projects.It has four main motions,winding,telescope,luffing and rotation.The telescope motion is not allowed when truck crane is performing lifting task in China.That means luffing is the only motion that can change the working radius.The performance of luffing motion directly impact the working quality and efficient of truck crane.Therefore,it has important practical significance and engineering value to research the luffing system.The traditional luffing system can be divided two kinds based on the manner of falling boom,gravity luffing system and dynamic luffing system.The falling speed of gravity luffing system is too slow at large angle range or light load condition which reduces work efficiency.The falling speed is too high at small angle range or overload condition which reduces the falling controllability and even causes an accident.The dynamic luffing system is great influenced by load pressure fluctuation.And its falling stability is bad which reduces work efficiency and safety.In addition,traditional truck crane basing on LUDV system always exists impact when lowing winch motion joins lifting boom motion.Which reduces the work efficiency and safety.To improve the falling controllability and lifting impact resistance of truck crane,further improve the work efficiency and safety,the main researches are as follows:1.For the problem that the falling controllability of traditional luffing system are bad,the pressurized luffing system is proposed.The mathematic models of luffing system are built.The load characteristics and falling angular velocity of luffing hydraulic system are obtained.The evaluation indexes of falling controllability are proposed.The influence of main components and parameters of luffing hydraulic system on falling controllability is analyzed.The results of MATLAB numerical analysis show that the falling uniformity of pressurized luffing system is obviously improved in different conditions.The results of AMESim simulation show that the falling uniformity is improved and the falling stability is not reduced obviously.2.Aim at the problem that falling speed is too high at small angle range or overload condition,the flow saturation characteristic of counterbalance valve is researched.The influence rule of counterbalance valve on falling speed is obtained.The numerical simulation and bench test result show that,the saturation flow increases as the control pressure,but the pressure difference firstly decreases and then increases.Decreasing the number of notch orifice will reduce the saturation flow and increase the pressure difference of counterbalance valve.Under the premise of the same spool stroke,the saturation flow will decrease with the decrease of spring stiffness and the pressure difference will also reduce.By improving the structure of counterbalance valve,the falling speed is limited and the falling uniformity is improved.3.A numerical algorithm for the characteristic parameters of counterbalance valve is proposed.Basing on three-dimensional model of counterbalance valve,different spool displacement intervals according to certain rules are selected to calculate the parameters of valve port.Then the continuous parameters are obtained by cubic spline difference method.The parameters are used to study the flow saturation characteristic of counterbalance valve.The simulation and experiment results are basically same.Thus the feasibility of the numerical algorithm is verified.4.The lifting impact resistance of luffing system at combined action condition is studied.The evaluation indexes of impact resistance are proposed.The response characteristics of the LUDV system under combined action and the reason why impact occurs are analyzed.The technical measure to improve the abrupt flow change of lifting boom is proposed.The AMESim simulation results show that the measure can effectively eliminate the abrupt flow change and the lifting impact resistance of truck crane is improved under the combined action.5.The falling controllability is test on prototype.The results show that the flow exist the largest value and falling speed exist a reduced trend which means the falling angular speed can be limited to improve the falling uniformity.The results also show that the pressure and flow at different conditions are both stable and the boom angle changes are small which means the falling stability of pressurized luffing system is well.The combined action test of truck crane before and after the improvement is carried out.The results show that the flow mutations of lifting boom are significantly weakened and the accelerations of turntable are reduced greatly.