Fuel injection valve

1. A fuel injection valve comprising:

a valve seat and a valve body that cooperatively open and close a fuel passage;

a movable element including the valve body provided at one end part thereof and a movable iron core provided at another end part thereof;

a fixed iron core disposed to face the movable iron core and to attract the movable iron core by applying a magnetic attraction force to the movable iron core; and

a cylindrical member including thereinside the fixed iron core and the movable iron core,

wherein the cylindrical member is formed of magnetic material and provided with a non-magnetic part or a part having weaker magnetism than the magnetic material at an outer circumferential part of a facing part at which a facing end surface of the fixed iron core and a facing end surface of the movable iron core face each other,

wherein the fixed iron core includes a reduced-diameter part on an outer circumferential surface at a side facing the movable iron core,

wherein the movable iron core includes a reduced-diameter part on an outer circumferential surface at a side facing the fixed iron core,

wherein an end part, on a side opposite the side facing the movable iron core, of the reduced-diameter part of the fixed iron core is located closer to the side opposite the side facing the movable iron core than an end part on a side opposite the side facing the movable iron core of the non-magnetic part or the part having weaker magnetism, and

wherein when the valve is opened, an end part on a side opposite the side facing the fixed iron core of the reduced-diameter part of the movable iron core is located closer to the side opposite the side facing the fixed iron core than an end part on a side opposite the side facing the fixed iron core of the non-magnetic part or the part having weaker magnetism.

2. The fuel injection valve according to claim 1 , wherein an outer diameter of the facing end surface of the fixed iron core, facing the movable iron core is equal to an outer diameter of the facing end surface of the movable iron core facing the fixed iron core.

3. The fuel injection valve according to claim 1 , wherein the reduced-diameter part of the fixed iron core is formed in a tapered shape such that an outer diameter of the fixed iron core is gradually reduced toward the movable iron core.

4. The fuel injection valve according to claim 1 , wherein the reduced-diameter part of the fixed iron core is formed by a cylindrical surface parallel to an inner circumferential surface of the cylindrical member.

5. The fuel injection valve according to claim 4 , wherein a tapered surface in which an outer diameter of the fixed iron core is reduced so as to taper from a first diameter part formed on the anti-movable iron core side of the reduced-diameter part of the fixed iron core toward the cylindrical surface is formed between the first diameter part and the cylindrical surface.

6. The fuel injection valve according to claim 1 , wherein the reduced-diameter part of the movable iron core is formed in a tapered shape such that an outer diameter of the movable iron core is gradually reduced toward the fixed iron core.

7. The fuel injection valve according to claim 1 , wherein the reduced-diameter part of the movable iron core is formed by a cylindrical surface parallel to an inner circumferential surface of the cylindrical member.

8. The fuel injection valve according to claim 7 , wherein a tapered surface in which an outer diameter of the movable iron core is reduced so as to taper from a first diameter part formed on the anti-fixed iron core side of the reduced-diameter part of the movable iron core toward the cylindrical surface is formed between the first diameter part and the cylindrical surface.

9. The fuel injection valve according to claim 1 , wherein:

the fixed iron core includes a chamfer at an inner circumferential edge of the facing end surface thereof which faces the movable iron core,

the movable iron core includes a chamfer at an inner circumferential edge of the facing end surface thereof which faces the fixed iron core, and

a length of the reduced-diameter part of the fixed iron core in a direction along a central axis of the fuel injection valve is larger than each of a length of the chamfer formed in the fixed iron core and a length of the chamfer formed in the movable iron core in the direction along the central axis.

10. The fuel injection valve according to claim 9 , wherein:

the reduced-diameter part of the movable iron core is formed such that a length of the reduced-diameter part in a direction along a central axis of the movable element is larger than each of the length of the chamfer formed in the fixed iron core and the length of the chamfer formed in the movable iron core in the direction along the central axis, and

in a valve closing state in which the valve body comes into contact with the valve seat, a length of the a space between the end part on an anti-movable iron core side of the reduced-diameter part of the fixed iron core and the end part on the anti-fixed iron core side of the reduced-diameter part of the movable iron core is larger than a length of the non-magnetic part or the part having weaker magnetism in the direction along the central axis of the fuel injection valve.

11. The fuel injection valve according to claim 1 , wherein:

the fixed iron core includes a chamfer at an inner circumferential edge of the facing end surface thereof which faces the movable iron core,

the movable iron core includes a chamfer at an inner circumferential edge of a facing end surface thereof which faces the fixed iron core, and

a length of the reduced-diameter part of the movable iron core in a direction along a central axis of the movable element is larger than each of a length of the chamfer formed in the fixed iron core and a length of the chamfer formed in the movable iron core in the direction along the central axis.

12. The fuel injection valve according to claim 11 , wherein:

the reduced-diameter part of the fixed iron core is formed such that a length of the reduced-diameter part in a direction along a central axis of the fuel injection valve is larger than each of the length of the chamfer formed in the fixed iron core and the length of the chamfer formed in the movable iron core in the direction along the central axis, and

in a valve closing state in which the valve body comes into contact with the valve seat, a length a space between the end part on the anti-movable iron core side of the reduced-diameter part of the fixed iron core and the end part on the anti-fixed iron core side of the reduced-diameter part of the movable iron core is larger than a length of the non-magnetic part or the part having weaker magnetism in the direction along the central axis of the fuel injection valve.

13. The fuel injection valve according to claim 10 , wherein the non-magnetic part or the part having weaker magnetism of the cylindrical member is formed of a member different from that of the cylindrical member which is formed of the magnetic material.

14. The fuel injection valve according to claim 12 , wherein the non-magnetic part or the part having weaker magnetism of the cylindrical member is formed of a member different from that of the cylindrical member which is formed of the magnetic material.

15. The fuel injection valve according to claim 1 , wherein the movable element comprises a valve assembly, and the cylindrical member comprises a cylindrical metallic body.