Electromagnetic relay

1. An electromagnetic relay comprising:

an exciting coil configured to form a magnetic field on energization;

a stationary core placed in a coil center hole formed in an inner diameter portion of the exciting coil and configured to form a magnetic circuit;

a yoke placed to cover an outer periphery of the exciting coil and an end of the exciting coil in an axial direction to form a magnetic circuit, the yoke having an opening portion formed in its one side in the axial direction correspondingly to a position of the stationary core;

a movable core facing the stationary core through the opening portion and configured to be attracted toward the stationary core on energization of the exciting coil; and

a return spring configured to urge the movable core in a direction opposite to a direction of attraction, wherein

a first gap is formed between the stationary core and the movable core on deenergization of the exciting coil,

a second gap is formed between the yoke and the movable core on deenergization of the exciting coil, the second gap allowing the yoke and the movable core to generate an attractive force therebetween in a direction to attract the movable core toward the stationary core on energization of the exciting coil, and

the return spring is made of a magnetic material and is placed to magnetically bridge the first gap or the second gap.

2. The electromagnetic relay according to claim 1 , wherein

the return spring is placed to magnetically bridge the first gap, and

the return spring is in part positioned between the stationary core and a periphery of the opening portion at a start of energization.

3. The electromagnetic relay according to claim 1 , wherein

the return spring is placed to magnetically bridge the first gap, and

the return spring is in part placed to pass between the stationary core and a periphery of the opening portion during a period from a start of energization to a completion of attraction.

4. The electromagnetic relay according to claim 3 , wherein

a spring pitch in a region of the return spring passing between the stationary core and the periphery of the opening portion is set to be smaller than a spring pitch in an other region.

5. The electromagnetic relay according to claim 1 , wherein

the return spring is in contact with the stationary core and the movable core during a period from a start of energization to a completion of attraction.

6. The electromagnetic relay according to claim 5 , wherein

the return spring is placed between facing surfaces of the stationary core and the movable core which face each other.

7. The electromagnetic relay according to claim 6 , wherein

when the movable core is in an attractive state, a distance between the stationary core and the movable core is equal to a minimum length of the return spring.

8. The electromagnetic relay of claim 7 , wherein

the return spring is a conically wound conical spring.

9. The electromagnetic relay according to claim 1 , wherein

the return spring is in contact with the movable core and the yoke during a period from a start of energization to a completion of attraction.

10. An electromagnetic relay comprising:

an exciting coil configured to form a magnetic field on energization;

a stationary core placed in a center hole formed in an inner diameter portion of the exciting coil and configured to form a part of a magnetic circuit on energization of the exciting coil;

a yoke placed to cover an outer periphery of the exciting coil and an end of the exciting coil in the axial direction and configured to form a part of the magnetic circuit, the yoke having an opening portion correspondingly to a position of the stationary core in its one side in the axial direction;

a movable core facing the stationary core at a position corresponding to the opening portion and configured to be attracted toward the stationary core by a magnetic attraction force on energization of the exciting coil;

a movable contact having a movable contact element and movable to follow the movable core;

a plurality of fixed terminals having fixed contacts configured to make contact with the movable coil on energization of the exciting coil; and

a return spring configured to urge the movable core in a direction away from the stationary core, wherein

the return spring is formed of a plurality of springs, and

at least one of the plurality of springs is made of a magnetic material.

11. The electromagnetic relay according to claim 10 , wherein

the spring made of the magnetic material among the plurality of springs is a volute spring.

12. The electromagnetic relay according to claim 10 , wherein

at least one of the plurality of springs is made of a non-magnetic material.

13. The electromagnetic relay according to claim 12 , wherein

the spring made of the non-magnetic material among the plurality of springs is placed between respective windings of the spring made of the magnetic material.

14. The electromagnetic relay according to claim 10 , wherein

at least one of the plurality of springs is made of a non-magnetic material, and

the spring made of the magnetic material and the spring made of a non-magnetic material among the plurality of springs are volute springs formed of plywood in which the magnetic material and the non-magnetic material are combined together.

15. The electromagnetic relay according to claim 10 , wherein

at least one of the plurality of springs is configured to generate a spring force urging in an attraction direction to attract the movable core to the stationary core.

16. The electromagnetic relay according to claim 15 , wherein

one end of the spring, which is configured to generate the spring force urging in the attraction direction, is fixed to the movable coil, and

the other end is fixed to a non-movable portion including the stationary core, the exciting coil, and the yoke.