A Newly Designed Lift System Of The Forklift And The Energy Efficiency Analysis Of It

The forklift is one of the lifting and carrying machines,they serve at the ports and warehouses.Since that the hydraulic system has the high power density,high load capacity,good stability and high reliability,hydraulic lift system is still installed on the forklift as main stream.Considering the efficiency of the energy transforming between mechanical energy and hydraulic energy,and the energy lose in the tubes and valves as the liquid floating through,the energy efficiency of the hydraulic lifting system is low.According to the data gathered in its working stage,the efficiency rate of forklift CPD30(one type of forklift)is between 30% and 40%.In another words,between 60% and 70% of the energy used was wasted.Presently,many advanced technology were used to improve the energy using efficiency,such as the energy recovery technology and the hybrid technology.No matter what kind of the advanced technology is used,an efficient transmission system insures that it works.A transmission system with high efficiency can not only improve the energy using rate directly,it also makes sure that the advanced technology is worthy and achieve high energy efficiency.To improve the efficiency of the transmission system,this article focused on a newly invented lifting system of the forklift.In place of the hydraulic cylinder,the new system used the rolling screw pair to reduce the energy lose.The transmission efficiency of the rolling screw pair is between 90% and 98%,no matter it is working at the forward transmission state or reverse transmission state.In the rolling screw pair,since the nut can drive screw,energy can be generated and recovered in the reverse transmission state.Since the stiffness of the rolling screw pair is high and its transmit accuracy is good,this kind of lifting system provide quick response and accurate stop.To test the dynamic performance and energy consumption,it is necessary to build the dynamic model for it.Based on the power bond theory,the dynamic model of the transmission mechanism was built and demonstrated as a state-space expression.The new system chose the brushless DC machine to provide driving torque,and the model of it was selected from the MATLAB/Simscape.The brushless DC machine used the double closedloop controller,which consist of the velocity loop and the current loop.The self-adaptive PID controller was designed for the brushless DC machine in the current loop depend on the fuzzy logic theory.Combining the models of the motor controller,the brushless DC machine,the battery and the dynamic model of the transmission system,the total system was simulated on MATLAB/Simulink,The performance of the rolling screw lift system was evaluated by the energy efficiency and the fork's velocity trajectory.According to the simulation,the rolling screw system satisfied the requirement of fork's velocity and acceleration.When it is full loaded(3000kg),the efficiency rate is 56.23%.When the load is 1170 kg,the efficiency rate is 49.91%.And when the load is 620 kg,the efficiency rate is 29.19%.To certify that the new system provides a higher energy efficiency than the hydraulic system,the experiments were executed between the hydraulic system and the rolling screw system on the CPD30.The result turned out to be satisfied.The rolling screw system enhanced the energy efficiency by 2.01% and 7.45% with 620 kg load and 1170 kg load respectively,and the new value were 31.56% and 45.79%.As to the dynamic performance,the average velocity of the rolling screw system was faster than the hydraulic system by 0.018m/s and 0.003m/s with 620 kg load and 1170 kg load respectively.This article calculated the efficiency rate of the rolling screw system by simulation,and certified the dynamic performance and energy efficiency of the rolling screw system by experiments,compared with the hydraulic system.The results proved that there is potential in developing this new system.This article also provide good mechanical platform for the advanced technology,and good reference for the similar engineering machinery.