Development of High-Speed Giant-Magnetostrictive Actuator with a Stroke-Amplifier and Its Application to Diesel Fuel Injectors

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Electro-hydraulic switching-valves are used in the pulse-flow control system of automotive transmission or construction manipulator. The control qualities, precision and quietness are improved by quickening the switching speed. The giant-magnetstrictive material actuator (Te_<0.3>Dy_<0.7>Fe_<1.9>) stretches its length in proportion to the magnitude of magnetic field with a natural angular frequency of over 1.2kHz. It has the mechanical properties of maximum strain of 1500-2000*10^<-6>. The displacement of 35mm is provided by using 70mm in length of the device at the strain of 500*10^<-6> in usual magnetization. This displacement is not so sufficient to control the usual switching-valve of flow capacity of 8l/min at 7MPa. For applying this device to control the valve, two types of hydraulic stroke-amplifiers based on the Pascal's principle are designed and tested. One is a combination of large and small pistons, the other is a set of metal-bellows. The both mechanisms amplify the stroke through the fluid enclosed in the primary and secondly chambers. This research presents the comparison of performance of both types in the points of response, stiffness, amplifying-ratio and adaptability to the electro-hydraulic switching-valve. The test result is that the piston-type actuator can control the pressure of 3-port-switching-valve at the PWM carrier frequency of 300Hz. Furthermore, its application to diesel fuel injection valves is discussed and a basic design of the injector using the giant-magnetostrictive actuator is presented.