Abstract: Giant magnetostrictive actuator used on high-pressure-common-rail injector is designed to control the bullet valve opening and closing. The axial magnetic field on giant magnetostrictive rod is not so uniform that the magnetic field value is the function of not only the current input but the axial coordinate. And the actuator displacement’s multiple degrees of freedom model is established based on J-A model, quadratic domain-transfer model and vibration theory, and the degree value of freedom is given appropriately. Steady step response and state space format of the model are presented and solved through Matlab software. The responses of direct and sinusoidal current in low frequency input calculated by the model are contrasted with test results to verify the model’s accuracy. Actuator’s behavior putting on the injector is forecasted through this model with the assumption of oil’s equivalent load being seen as elastic damping load. The results show that the direct current steady responses achieved by multi-degree of freedom model have little errors contrast with test results, and displacement-current curves under sinusoidal signals calculated through this model are similar to the test results. So the model’s precision is validated. With the injector, the actuator has large displacement and short responding time and can satisfy the driving requirement.

Key words: giant magnetostrictive actuator used on high-pressure-common-rail injector, multiple degrees of freedom model, oil’s equivalent load, responses of direct current, responses of sinusoidal current in low frequency