Electromagnetic driving device and flow rate controlling apparatus employing the same driving device

An electromagnetic driving device comprising;

• a movable core,
• a stator having a housing portion for housing said movable core in such a manner as to move in a reciprocating fashion therein, and an attaching portion, a magnetic force being generated between said attracting portion and said movable core for attracting said movable core to move in one reciprocating movement direction and cooperating with said movable core to form a magnetic circuit,
• a coil for generating a magnetic force which attracts said movable core to said attracting portion side when energized, and
• a non-magnetic layer formed on at least one of sides where said housing portion and said movable core are situated, respectively, to diametrically face each other,
• wherein an eccentricity R defined as (d1/d0)×100 is set so as to satisfy 20%≦R≦60%, where d0 is a magnetic gap which is formed in a radial direction between the housing portion and the movable core, excluding the non-magnetic layer, and d1 is an air gap which is formed in a radial direction between the facing surfaces of the housing portion and the movable core, including the non-magnetic layer, when the movable core does not deviate from, but remains coaxial with, the housing portion,
• wherein a first non-magnetic layer is formed on an inner circumferential wall of the housing portion and a second non-magnetic layer is formed on an outer circumferential wall of the movable core, said air gap being formed in a radial direction between said first and second non-magnetic layers and said magnetic gap being formed between magnetic materials of the housing portion and the movable core.