Effect of driving electric machine type on the system efficiency of an industrial forklift

Electric drives offer effective means of directly controlling working machine hydraulic movements instead of using traditional valve control. This paper takes a step further and investigates the effect of the electric machine type applied in a direct electro hydraulic drive on the system efficiency of the electric energy recovery system of a hydraulic forklift. The control of the system is implemented directly with an electric motor drive without any control valves. A theoretical model is made and the model is verified by practical results. Permanent magnet motor and squirrel cage induction motor drives are compared. Finally, possible improvements of the efficiency in the suggested system are estimated.