Research on control strategy of electric forklift fork drop

TONG Shui-guang, GUAN Jian-yu, TONG Zhe-ming, CONG Fei-yun, SHAN Yu-shuang, HE Shun, YU Yue, TANG Ning
(College of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China)

Abstract: Aiming at the problem of throttling loss of the traditional electric forklift during the descent of the fork and the heating in the hydraulic system，the potential energy recovery technology  was applied to the speed control of forklift lowering. The relationship between the total load during the potential energy recovery process and the speed of the hydraulic motor, the speed of the generator, and the expansion and contraction speed of the hydraulic cylinder piston was studied. The method of controlling the descending speed of the fork during the potential energy recovery process of an electric forklift was summarized. A potential energy recovery scheme based on a variable hydraulic motor, a generator, and a super capacitor was proposed. The electromagnetic resistance of the generator during the potential energy recovery process was used to control the fork. The mathematical model of the potential energy recovery system was established, the governing equation of the descending speed of the fork was deduced, and the control strategy of the descending speed of the fork based on electromagnetic resistance was designed. The AMEsim software was used to simulate the descent process of the fork to verify the effectiveness of the proposed control strategy and energy recovery scheme. The simulation results indicate that the proposed control method can keep the fork at the rated descent speed of 0.2 m/s, and the potential energy recovery efficiency can reach 54% at a load of 2 000 kg.

Key words: electric forklift; potential energy recovery; fork drop; electromagnetic resistance; control strategy