Speed up of the diesel injector is an urgent issue for improving tail pipe emission. One of the authors has developed a proportional injector controlled by a tandem arrayed giant-magnetostrictive actuator(GMA). Because the extension of giant-magnetostrictive material depends on pre-stress, it is important for a GMA to keep pre-stress constant. In this paper, the influence and compensation of pre-stress change caused by thermal expansion on the discharge characteristics of a diesel injector are investigated. Both issues of injection rate reduction and valve seat pressure change in high temperature are solved by using the low thermal expansion material of invar.

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H infinity control theory was applied to control of a variable displacement piston pump. Angle of the pump's swash plate was detected by means of a position sensor attached on a control piston. The position signal was fed back to a controller and a control input signal was added to a proportional flow control valve so that the control piston position follows the demanded signal. A control system for pump displacement was designed by applying H infinity control theory considering changes in pump speed and load pressure. The control system was examined experimentally on a test bench. Results demonstrated that the system shows stable and quick responses under different pump operating conditions.

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In order to reduce energy consumption, secondary control systems have been applied to many types of equipments. In lifting equipment and press machines using hydraulic cylinders, a hydraulic transformer is used, instead of a valve as a control component for motion control and for recovering potential energy of load. The transformer is a combination of a variable displacement pump/motor, which is a secondary controlled element, and a fixed displacement pump/motor. In this paper the energy-saving effect of the transformer is studied. Multiple closed loop controllers, consisting of displacement feedback of variable pump/motor, speed feedback of the cylinder and position feedback of the cylinder are used. The efficiency and energy consumption when the cylinder is driven up and down is calculated by simulation. Simulation results show that considerable energy saving is achieved by accurately choosing load ratio, circuit type and supply pressure.

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