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A linear solenoid comprising: linear solenoid portion, comprising: a coil; a cylindrical movable core which is attracted toward a fixed core when the coil is energized; and a cylindrical yoke which surrounds an outer circumference surface of the movable core, wherein the movable core has a shaft-les

A linear solenoid comprising: linear solenoid portion, comprising: a coil; a cylindrical movable core which is attracted toward a fixed core when the coil is energized; and a cylindrical yoke which surrounds an outer circumference surface of the movable core, wherein the movable core has a shaft-less structure, a first plain bearing and a second plain bearing for slidably supporting both ends of the movable core are provided respectively at both ends of a cylindrical yoke along its axis, and the first plain bearing and the second plain bearing are provided to be projected from the inner circumference surface of the cylindrical yoke by a predetermined length T toward the movable core.

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1. A linear solenoid comprising: linear solenoid portion which is provided in a housing, comprising: a coil;a cylindrical movable core which is attracted toward a fixed core when the coil is energized; anda cylindrical yoke which surrounds an outer circumference surface of the movable core,wherein s

1. A linear solenoid comprising: linear solenoid portion which is provided in a housing, comprising: a coil;a cylindrical movable core which is attracted toward a fixed core when the coil is energized; anda cylindrical yoke which surrounds an outer circumference surface of the movable core,wherein said cylindrical yoke and said fixed core are spaced apart from each other,wherein said cylindrical yoke and said housing constitute a single member, andwherein the movable core has a shaft-less structure, one or more bearings for slidably supporting the movable core are attached to one or more annular recesses formed in the cylindrical yoke, and the one or more bearings contact less than the entire surface of the movable core and project by a predetermined length from an inner circumference surface of the cylindrical yoke toward the movable core, such that the movable core slidingly contacts only said one or more bearings. 2. The linear solenoid according to claim 1, wherein the bearing comprises a plurality of bearings, and a plurality of annular recesses into which the bearing can be inserted along the axis of the cylindrical yoke are provided at both ends of the inner circumference surface of the cylindrical yoke. 3. The linear solenoid according to claim 1, wherein the housing comprises: a housing bottom surface which is provided at one end of the housing along an axis of the housing; a cylindrical projection which extends from the housing bottom surface; and a swaging portion which extends from the cylindrical projection,a disc member made of a nonmagnetic material which is provided at one end of the housing, and abuts on the cylindrical projection so as to be held by the swaging portion so that the disc member blocks an opening at one end of the housing. 4. The linear solenoid according to claim 3, wherein one end of the movable core which faces to the housing bottom surface is arranged so as to intersect a line which is approximately orthogonal to an axis of the movable core and passes through a thick central portion along an axis of the housing bottom surface. 5. The linear solenoid according to claim 4, wherein the bearing to support one end of the movable core is arranged so as to intersect a line which is approximately orthogonal to an axis of the movable core and passes through a thick central portion along an axis of the housing bottom surface. 6. The linear solenoid according to claim 1, wherein the bearing comprises a single bearing, and a single annular recess into which the bearing can be inserted from the fixed core along the axis of the cylindrical yoke is provided on the fixed core side of the inner circumference surface of the cylindrical yoke. 7. The linear solenoid according to claim 1, wherein the housing comprises a housing bottom surface which is provided at one end along an axis of the housing; a cylindrical projection which extends from the housing bottom surface; and a projecting bottom portion which extends from the cylindrical projection,a first stopper which is made of a nonmagnetic material and limits a displacement of the movable core in one direction is provided through the projecting bottom portion, and the first stopper is fixed to the projecting bottom portion by swaging a cylindrical portion passing through a through hole of the projecting bottom portion so as to plastically deform an inner wall of the projecting bottom portion. 8. The linear solenoid according to claim 7, wherein a recess to which the movable core faces is formed on the fixed core,a second stopper to limit a displacement of the movable core in another direction is pushed into a hole which continues to the recess, andthe second stopper is provided with a inserting hole through which a displacement transmission member to transmit the displacement of the movable core is inserted. 9. A linear solenoid comprising: linear solenoid portion which is provided in a housing, comprising: a coil;a movable core which is attracted toward a fixed core when the coil is energized; anda cylindrical yoke which surrounds an outer circumference surface of the movable core,wherein said cylindrical yoke and said fixed core are spaced apart from each other,wherein said cylindrical yoke and said housing constitute a single member, andwherein one or more bearings for slidably supporting the movable core are attached to one or more annular recesses formed in the cylindrical yoke, and the one or more bearings contact less than the entire surface of the movable core and project by a predetermined length from an inner circumference surface of the cylindrical yoke toward the movable core, such that the movable core slidingly contacts only said one or more bearings, anda hard layer which is harder than the inside of the movable core is provided at a contact region to the bearing on an outer surface of the movable core. 10. The linear solenoid according to claim 9, wherein the hard layer is formed with a NIP plating. 11. The linear solenoid according to claim 9, wherein the hard layer is formed with a nitrided film. 12. The linear solenoid according to claim 11, wherein the nitrided film is formed by high-frequency heating. 13. A valve operating mechanism comprising: a valve body having a plurality of ports through which a pressure fluid flows;the linear solenoid according to claim 1; anda valve element which is provided within the valve body and switches between a communication state and a discommunication state among the plurality of ports by displacement of the movable core.