Electromagnetic actuator for controlling fluid flow

Claim 1

An electromagnetic actuator for controlling fluid flow comprising: a housing having a fluid passage therein and a valve seat portion provided around the fluid passage; a substantially rigid valve body positioned within the housing in such a manner that the valve body shuts the fluid passage when the valve body is seated on the valve seat and opens the fluid passage when the valve body is unseated from the valve seat; a solenoid coil for generating a magnetic force when it is energized; a moveable core arranged to move along an axis thereof when the magnetic force is applied, the valve body being connected with the moveable core in such a manner that the valve body can slide along the axis of the core; a first elastic member biasing the moveable core in a direction opposite to that of the magnetic force by a first biasing force; a second elastic member biasing the valve body toward the valve seat by a predetermined second biasing force; a limiting piece fixed on the moveable core for limiting movement of the valve body caused by the second biasing force when the valve body is unseated from the valve seat; a controlling device for controlling a duty ratio of an energizing period of the solenoid coil to an unenergizing period of the solenoid coil in order to control an amount of the fluid passing between the valve body and the valve seat; a third elastic member abutting the limiting piece for biasing the moveable core in a direction opposite to that of the second elastic member by a third biasing force; an adjusting means holding the third elastic member for adjusting the third biasing force so that the first biasing force, the second biasing force and the third biasing force are functionally modulated by the adjusting means.