Abstract: In the same injection molding machine, the theoretical analysis and experimental study on energy efficiency are done by using five different electro-hydraulic control strategies to process the same products, which five different control strategies are respectively induction motor driven constant pump, variable speed induction motor driven constant pump, induction motor driven variable displacement pump, variable speed induction motor driven variable displacement pump and AC servo motor driven constant pump. At first the power transmission mathematical models of motor and pump are established and the energy curves are drawn in the different control circuit. The power consumptions of the hydraulic system and the motor drive system are compared and analyzed, when the injection molding machine works in the packing and cooling conditions. The research results confirm that: In the part-load and no-load conditions the large overflow and throttle losses and low efficiency exist in induction motor driven constant pump system. On this basis variable speed control is introduced and implemented by enveloping the system required flow, so the motor power consumption is reduced and the efficiency is improved and the energy efficiency nearly equals by comparing with the induction motor driven variable displacement pump system. In the induction motor driven variable displacement pump system, the overflow losses are completely eliminated, however the big motor idling loss still exits. On this basis variable speed control is introduced to the motor output power and the hydraulic load matching, and to further improve the energy efficiency of 26.5%. The research also shows that the energy efficiency of the AC servo motor driven constant pump system is the highest, and can save energy 88% by comparing with induction motor driven constant pump, and the system has simple structure and good dynamic performance.

Key words: AC servo motor, Energy efficiency, Energy saving, Variable frequency, Injection molding machine