Abstract: The research, for an innovative electro-hydraulic servo system that a differential cylinder is controlled closed loop with two speed variable pumps, specially used to control a clamping unit of plastic injection moulding machine, is carried out. On the base of summer pressure and chamber pressure controller, further a new idea that control the inlet and outlet of cylinder separately is put forward. With this principle the back pressure keeps a constant low value, that make the pressure of system always keeping adaptive with load automatically. The capability of each motor can be used sufficiently, the energy consumption of system and electric motors be reduced greatly, and the heat of pumps also be reduced without any influence of dynamic and static performance of system. The researching work is approved by simulation and test. The results have important significance for developing new type of plastic injection moulding machine with high efficiency and low energy consumption.

Key words: Differential cylinder, Efficiency, Electro-hydraulic servo control, Speed variable pump