ELECTROMAGNETIC TRIP DEVICE AND CIRCUIT BREAKER
BACKGROUND

The present invention relates to an electromagnetic trip device and a circuit breaker.

A circuit breaker is used to interrupt a circuit by opening contacts when a circuit connecting a power supply and a load is in a predetermined circuit condition (refer to, for example, Japanese Laid-Open Patent Publication No. 2000-231869) . The circuit breaker may be, for example, a molded case circuit breaker, an earth leakage circuit breaker, an overvoltage circuit breaker, an undervoltage circuit breaker, or the like. The molded case circuit breaker interrupts a circuit when detecting a fault current caused by a short circuit or an overload. The earth leakage circuit breaker interrupts a circuit when detecting current leakage. The overvoltage circuit breaker interrupts a circuit when the voltage of the circuit becomes higher than a predetermined upper limit voltage. The undervoltage circuit breaker interrupts a circuit when the voltage of the circuit becomes lower than a predetermined lower limit voltage. A multifunction circuit breaker that combines different types of circuit breakers is also known.

A typical circuit breaker includes a switch mechanism, which closes and opens contacts, a lever, which is used to manually close and open the contacts, and an electromagnetic trip device, which opens the contacts with the switch mechanism.

The circuit breaker of the '869 publication includes an electromagnetic trip device. A connecting rod projects from a housing of the electromagnetic trip device. The connecting rod is fitted into a housing of the circuit breaker, which is coupled to the electromagnetic trip device. When a fault voltage is generated, the electromagnetic trip device moves the connection rod and trips an interruption mechanism of the circuit breaker. The electromagnetic trip device includes an electromagnetic unit. The electromagnetic unit includes an electromagnetic coil, which is wound around a bobbin, a first core, which extends through a hole of the bobbin, a second core, which is attracted to the magnetic pole of the first core when current flows through the magnetic coil, and a coil spring, which urges the second core away from the magnetic pole of the first core.

In the electromagnetic trip device, the first core is fitted in the coil spring. A relatively large clearance is provided between the first core and the coil spring. When the coil spring is compressed, the coil spring buckles and/or bows due to the clearance. Thus, sufficient urging force may not be obtained.

SUMMARY

It is an object of the present invention to provide a magnetic trip device and a circuit breaker that stabilizes the urging force of the coil spring.

One aspect of the present invention is an electromagnetic trip device including a coil spring, a first core fitted into the coil spring, a second core urged away from the first core by the coil spring. The first core and the second core are configured to come into contact with each'other and move away from each other in accordance with an urging force of the coil spring and an electromagnetic force generated by the first core. The electromagnetic trip device includes a clearance reducing portion that reduces a clearance between an outer surface of the first core and an inner contour of the coil spring.

According to the foregoing arrangement, buckling and bowing of the coil spring may be prevented or limited. This allows for the coil spring to generate a sufficient urging force.

In an embodiment, the clearance reducing portion is a part of or formed integrally with the first core.

In an embodiment, the clearance reducing portion is a discrete component arranged between the coil spring and the first core to prevent or limit buckling and bowing of the coil spring.

In an embodiment, the clearance reducing portion includes one or more elongated pieces extending in an axial direction of the coil spring and arranged between the coil spring and the first core.

In an embodiment, the first core is U-shaped and includes a first arm, which holds the coil spring such that a clearance is formed between the first arm and the coil spring, and a second arm, which holds an electromagnetic coil. The one or more elongated pieces of the clearance reducing portion are arranged in the clearance between the coil spring and the first arm.

In an embodiment, the first core includes an arm having a tetragonal cross-section as viewed from the axial direction of the coil spring. The coil spring is cylindrical and surrounds the arm of the first core. The one or more elongated pieces of the clearance reducing portion are arranged between the arm of the first core and the cylindrical coil spring.

It is preferable that the one or more elongated pieces of the clearance reducing portion include a plurality of parallel plates sandwiching the arm.

Another aspect of the present invention is a circuit breaker including a lever pivotal between an ON position and an OFF position, an interruption mechanism directly or indirectly connected to the lever, wherein the interruption mechanism engages and disengages a movable contact with and from a fixed contact in accordance with the pivoting of the lever, and the electromagnetic trip device set forth above connected to the interruption mechanism so that the interruption mechanism trips the contacts and interrupts the circuit when a circuit connected to the circuit breaker is in a predetermined circuit condition.

In an embodiment, the electromagnetic trip device is configured to interrupt the circuit when voltage at the circuit becomes less than or equal to a predetermined voltage by tripping the contacts with the interruption mechanism. Attraction force between the first core and the second core is set to be smaller than an urging force of the coil spring when the voltage at the circuit is less than or equal to the predetermined voltage. When the voltage at the circuit becomes less than or equal to the predetermined voltage, the first core is disengaged from the second core.

In an embodiment, the electromagnetic trip device includes a link linked to the interruption mechanism. The link functions to interrupt the circuit when voltage at the circuit becomes greater than or equal to a predetermined voltage by tripping the contacts with the interruption mechanism. Attraction force between the first core and the second core is set to be greater than an urging force of the coil spring when the voltage at the circuit is greater than or equal the predetermined voltage. When the circuit becomes greater than or equal to the predetermined voltage, the first core and the second core are attracted to each other thereby opening the fixed contact and the movable contact.

As will be appreciated, other aspects, embodiments, and/or configurations of the disclosure are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a perspective view of a circuit breaker;

Fig. 2 is a left view of the circuit breaker in an OFF state;

Fig. 3 is a right view of the circuit breaker in the OFF state,-

Fig. 4 is a perspective view of an electromagnetic trip device;

Fig. 5 is an exploded perspective view of the electromagnetic trip device;

Fig. 6 is a side view of the electromagnetic trip device;

Fig. 7 is a cross-sectional view of the electromagnetic trip device;

Fig. 8 is a cross-sectional view of the electromagnetic trip device taken along line 8-8 in

Fig. 6;

Fig. 9 is a left view of the circuit breaker in an ON state;

Fig. 10 is a left view of the circuit breaker at the moment of an undervoltage trip;

Fig. 11 is a left side view of the circuit breaker in an undervoltage trip state;

Fig. 12 is a perspective view showing a further example of an electromagnetic trip
device;

Fig. 13 is a cross-sectional view of the electromagnetic trip device shown in Fig. 12;

Fig. 14 is a left view showing another example of an electromagnetic trip device in an
ON state; and

Fig. 15 is a left view of the electromagnetic trip device shown in Fig. 14 in an OFF state.

DESCRIPTION OF EMBODIMENTS

One embodiment of an electromagnetic trip device and a circuit breaker including the electromagnetic trip device will now be described. The circuit breaker shown in Figs. 1 to 11 is an example of an undervoltage circuit breaker that interrupts a circuit when the voltage of the circuit becomes lower than a predetermined lower limit voltage. The undervoltage circuit breaker may be used with a different type of circuit breaker, such as a molded case circuit As shown in Fig. 1, the undervoltage circuit breaker includes a terminal unit 11 that is connected to an external power supply. The terminal unit 11 may be arranged in a housing 10 of the undervoltage circuit breaker, which includes a first cover 14 and a second cover 15. The first cover 14 and the second cover 15 may be formed from an insulative synthetic resin. An open end 14a of the first cover 14 is joined with an open end 15a of the second cover 15 to define an interior compartment in the housing 10. A lever 20, an indicator 30, an interruption mechanism 40, and an electromagnetic trip device 90 are arranged in the interior compartment of the housing 10. A lever gate 16 and an indicator window 17 are formed in an upper surface of the housing 10 of the undervoltage circuit breaker.

As shown in Figs. 2 and 3, the interruption mechanism 40 includes a cooperative piece 41, a driver 50, a thrust bar 60, a latch 70, an electromagnetic trip device 90, and a circuit board 13. The housing 10 accommodates the indicator 30, which indicates the operational condition of the undervoltage circuit breaker in the indicator window 17, and an indicator latch 80.

The lever 2 0 includes a pivot portion 21 and a lever projection 22. The pivot portion 21 includes a first pivot shaft 18 and is pivoted about the first pivot shaft 18. The first pivot shaft 18 is located in the first cover 14. When the lever projection 22 is operated, the lever 20 is pivoted about the first pivot shaft 18. A connecting rod 23 extends from the lever projection 22 parallel to the first pivot shaf"t 18.' The connecting rod 23 may be coupled to the lever of another circuit breaker. Thus, the connecting rod 23 pivots the lever 2 0 of the undervoltage circuit breaker together with the lever of another circuit breaker. In the illustrated example, the lever projection 22 is located at an ON position (close position) when moved away from the terminal unit 11 and located at an OFF position (open position) when moved close to the terminal unit 11. The lever 2 0 is constantly urged away from the ON position by, for example, a lever spring 2 5 wound around the first pivot shaft 18. In the description hereafter, the direction in which the lever 2 0 pivots from the OFF position shown in Fig. 2 to the ON position shown in Fig. 9 (clockwise direction in Figs. 2 and 9) is referred to as the ON direction, and the direction in which the lever 2 0 pivots from the ON position to the OFF position (counterclockwise direction in Figs. 2 and 9) is referred to as the OFF direction.

The cooperative piece 41 is pivotally supported by a third pivot shaft 43. The cooperative piece 41 holds one end of a metal cooperative rod 42 . The other end of the cooperative rod 42 projects out of the second cover 15 through a slit 15b and is coupled to a cooperative piece of another circuit breaker.

The driver 50, the latch 70, and the indicator 30 are pivoted about a second pivot shaft 19. The second pivot shaft 19 includes two ends supported by the housing 10. A recovery spring 55, which is a coil spring, and a recovery spring 56, which is a torsion spring, constantly urge the driver 50 in the OFF direction. The recovery springs 55 and 56 each have one end coupled to the first cover 14 and another end coupled to the driver 50. The lever spring 25 constantly urges the lever 2 0 in the OFF direction. An indicator latch spring 83, which is a torsion spring, constantly urges the indicator latch 80 in the ON direction.

The thrust bar 60 may be a metal round rod that is bent to be U-shaped. The thrust bar 60 includes an operation end 61, which is fitted into a connection hole 24 of the lever 20, and a transmission end 62, which is arranged in a link hole 54 formed by an engagement piece 51 and a latch piece 71 of the latch 70. Under this situation, the thrust bar 60 is latched by the latch 70 (latch state). In the latch state, the thrust bar 6 0 transmits the movement of the lever 20 to the driver 50.

When the driver 50 is driven by the electromagnetic trip device 90, the driver 50 and the latch 70 pivot relative to each other and opens the link hole 54. Then, the transmission end 62 of the thrust bar 6 0 moves out of the link hole 54. Under this situation, the thrust bar 60 is released from the latch 70 (unlatch state).

A fourth pivot shaft 82 pivotally supports the indicator latch 80. The indicator latch spring 83 constantly urges the indicator latch 8 0 in the OFF direction. The indicator latch 8 0 includes an upper end 81, and a lower side of the indicator 30 includes an engagement projection 32. When the upper end 81 of the indicator latch 80 contacts the engagement projection 32 of the indicator 30, further rotation of the indicator 3 0 in the OFF direction is restricted. The indicator 3 0 includes a distal end that defines an indication portion 31, which indicates the circuit condition. The indication portion 31 includes an upper surface divided into two regions. The side of the indication portion closer to the lever 2 0 defines a normal region 31a, and the side of the indication portion farther from the lever 2 0 defines a trip region 31b. One of the regions 31a and 31b is exposed from the indicator window 17.

The housing 10 accommodates the circuit board 13. The electromagnetic trip device 90 is mounted on the circuit board 13 to drive the latch 70 by supplying current to an electromagnetic coil 92. The circuit board 13 includes an excitation circuit that stops exciting the electromagnetic coil 92 of the electromagnetic trip device 90 when detecting a fault voltage.

Referring to Figs. 4 and 5, the electromagnetic trip device 90 includes a coil spring 98, a fixed core 93, which is fitted into the coil spring 98, a movable core 97, which is separated from the fixed core 93 by the coil spring 98, and a spacer 100, which is arranged between the fixed core 93 and the coil spring 98. The spacer 100 serves to reduce the clearance between the outer surface of the fixed core 93 and the inner contour of the coil spring 98. In the illustrated example, the electromagnetic coil 92 is wound around a bobbin 91, which is formed from a synthetic resin. A holder 96 holds the movable core 97 so that the movable core 97 moves relative to the fixed core 93 . The movable core 97 functions as a second core. The spacer 100 functions as a clearance reducing portion. The holder 96 functions as a link that links the electromagnetic trip device 90 and the interruption mechanism 40.

The fixed core 93 is formed by a plate of a magnetic material (iron). Further, the fixed core 93 is U-shaped and includes 'a first arm, or upper arm 94, and a second arm, or lower arm 95. The lower arm 95 is fitted into a hole of the bobbin 91. One end of the bobbin 91 includes an inlet flange 91a and the other end of the bobbin 91 includes an outlet flange 91b. The lower arm 95 of the fixed core 93 includes a distal end that is exposed from the outlet flange 91b of the bobbin 91. The coil spring 98 is held on the upper arm 94 of the fixed core 93. In the illustrated example, the coil spring 98 is cylindrical.

Referring to Figs. 4 to 7, the holder 96 incudes a holder pivot shaft 96a, which is pivotally supported by the outlet flange 91b of the bobbin 91. A projection 96b projects from a distal end of the holder 96. When the holder 96 pivots, the projection 96b pushes and rotates the driver 50 in the ON direction. The movable core 97, which is formed by a magnetic plate, is held by the holder 96. Further, when the holder 96 pivots about the holder pivot shaft 96a, the movable core 97 pivots between a position where the movable core 97 contacts distal end surfaces (magnetic pole surfaces) of the two arms 94 and 95 of the fixed core 93 and a position where the movable core is separated from the distal ends surfaces (magnetic pole surfaces) of the two arms 94 and 95 of the fixed core 93.

Referring to Figs. 4 and 5, the spacer 100 is coupled to the fixed core 93. As shown in Fig. 8, the spacer 100 reduces the clearance between the outer surface of the fixed core 93 and the inner contour of the coil spring 98. The spacer 100 includes a plurality of elongated pieces extending in the axial direction of the coil spring 98. In the illustrated example, the elongated pieces are two plates 101 and 102 facing each other and extending along the upper arm 94 of' the fixed core 93. A bridging piece 103 connects the plates 101 and 102. Contact of the bridging piece 103 with a back surface 93a of the fixed core 93 positions the spacer 100 relative to the fixed core 93 in the axial direction. The shape and size of the spacer 100 is set so as not to generate frictional force that impedes the expansion and contraction of the coil spring 98. The arrangement of the spacer 100 in the clearance between the outer surface of the fixed core 93 and the inner contour of the coil spring 98 prevents or limits buckling and bowing of the coil spring 98 . This stabilizes the urging force of the coil spring 98a and stabilizes the properties or magnetic field of the electromagnetic trip device.

The operation of the undervoltage circuit breaker will now be described with reference to Figs. 2, 3, and 9 to 11.

The operation of the undervoltage circuit breaker when switching from the OFF state of Fig. 2 to the ON state of Fig. 9 will first be described.

When the lever 20 is pivoted from the OFF position (Fig. 2) to the ON position (Fig. 9) in the ON direction, the thrust bar 6 0 pushes the engagement piece 51 of the driver 50 and pivots the driver 50 in the ON direction.

Fig. 9 shows a switching boundary line L, which is a straight line connecting the first pivot shaft 18 of the lever 20 and the transmission end 62 of the thrust bar 60. As the lever 20 pivots in the ON direction, when the operation end 61 of the thrust bar 60 goes beyond the switching boundary line L, the transmission end 62 of the thrust bar 6 0 stops when pushed against the engagement piece 51. Here) the lever 2 0 and the thrust bar 6 0 are held at the ON position, and the undervoltage circuit breaker goes ON. The latch 70, which is pivoted by the latch spring 34, is pivoted to a position where the latch 70 contacts the transmission end 62 of the thrust bar 60. The driver 50 pushes an engagement portion 33 of the indicator 30. This pivots and moves the indicator 3 0 in the ON direction to an indication reset position. Under this situation, the indicator latch spring 8 3 urges and moves the indicator latch 80 to a position where the indicator latch 30 latches the indicator 30. Further, the cooperative piece 41 pivots in the ON direction as the driver 50 pivots, and moves the cooperative piece of the other circuit breaker with the cooperative rod 42. If the voltage is normal in the ON state, the excitation circuit supplies current to the electromagnetic coil 92 of the electromagnetic trip device 90. This attracts the movable core 97 to the fixed core 93. The holder 96 is pivoted to the ON position against the urging force of the coil spring 98. 'Here, the projection 96b at the distal end of the holder 96 is separated from the driver 50.

The operation of the undervoltage circuit breaker when switching from the ON state to the OFF state will now be described.

When the lever 20 is pivoted from the ON position (Fig. 9) to the OFF position (Fig. 2) in the OFF direction, the thrust bar 60 pulls the latch 70. This pivots the latch 70 against the urging force of the latch spring 34 and opens the link hole 54 toward the upper side. The driver 50 is urged by the recovery springs 55 and 56 and pivoted in the OFF direction until stopped when contacting a stopper piece 14b "of th'e first cover 14. The projection 52 of the driver 50 pushes and pivots the cooperative piece 41 against the urging force in the OFF direction. The latch spring 34 urges and pivots the indicator 3 0 in the OFF direction. The indicator 3 0 stops when the engagement projection 32 contacts the upper end 81 of the indicator latch 80. Here, the normal region 31a of the indication portion 31 is exposed from the indicator window 17. The projection 96b at the distal end of the holder 96 is pushed by the engagement projection 53 of the driver 50. This pivots the holder 96 in the OFF direction and holds the movable core 9 7 at a position where the movable core 97 contacts the magnetic pole surface of the fixed core 93.
The operation when the electromagnetic trip device 9 0 functions and switches the undervoltage circuit breaker from an ON state (Fig. 9) to a trip state (Fig. 11) will now be described. Fig. 10 shows the moment undervoltage tripping occurs.

In the ON state, when the excitation circuit detects that the voltage is lower than a predetermined set value, which is lower than a rating voltage (undervoltage state), the excitation circuit turns off a switch that is series-connected to the electromagnetic coil 92 to trip the undervoltage circuit breaker. This stops the supply of current to the electromagnetic coil 92 and cancels the electromagnetic attraction force between the fixed core 93 and the movable core 97. Consequently, as shown in Fig. 10, the urging force of the coil spring 98 pivots the holder 96 in the ON direction (clockwise direction), and the distal end of the holder 96 pushes the engagement projection 53 of the driver 50. The latch member 70 pivots in the OFF direction' (counterclockwise direction). Further, the transmission end 62 of the thrust bar 6 0 moves away from the latch piece 71 and out of the link hole 54.

Since the transmission end 62 of the thrust bar 60 moves out of the link hole 54, as shown in Fig. 11, the driver 50, which is no longer supported by the thrust bar 6 0 is urged by the recovery springs 55 and 56 and pivoted in the OFF direction to the OFF position. Further, the projection 52 of the driver 50 pushes the cooperative piece 41 toward the upper side, and the cooperative rod 42 drives the interruption mechanism of the other circuit breaker so that the interruption circuit opens the contacts. This stops the supply of current to the load connected to the other circuit breaker and thereby protects the load.

The coil spring 98 urges and pivots the holder 96 in the ON direction to the position of Fig. 10 where the projection 96b contacts the engagement projection 53. The urging force of the recovery springs 55 and 56 is set to be greater than the urging force of the coil spring 98. Thus, the holder 96 cannot be further pivoted in the ON direction from the position of Fig. 10. Referring to Fig. 11, when the driver 50 receives the urging force of the recovery springs 55 and 56 and pivots in the OFF direction, the engagement projection 53 of the driver 50 pushes the projection 96b of the holder 96. This pivots the holder 96 in the OFF direction to a position where the movable core 97 contacts the magnetic pole surface of the fixed core 93.

A projection 96c of the holder 96 pushes and pivots the indicator latch 80 (refer to Fig. 3) in the OFF direction to unlatch the indicator 30. When the indicator 3 0 is unlatched, the indicator 30 receives the urging force of the latch spring 34 and pivots in the OFF direction. The trip region 31b of the indication portion 31 is exposed from the indicator window 17. Then, the lever 20 receives the urging force of the lever spring 2 5 and pivots in the OFF direction. When the lever reaches the OFF position, the transmission end 62 of the thrust bar 60 is fitted into the link hole 54 and moved to a position where the transmission end 62 engages with the latch piece 71. Here, the transmission end 62 of the thrust bar 60 is fitted into the link hole 54, which is surrounded by the driver 50 and the latch 70. Thus, when pivoting the lever 20 in the ON direction to the ON position, the state shown in Fig. 9 is obtained.

The present embodiment has the advantages described below.

(1) The electromagnetic trip device 90 includes the spacer 10 0 that reduces the clearance between the outer surface of the fixed core 93 (for example, the outer surface of the upper arm 94) and the inner contour of the coil spring 98. Thus, buckling and bowing of the coil spring 98 may be prevented or limited. This allows for the coil spring 98 to generate a sufficient urging force.

(2) The circuit breaker is provided with the electromagnetic trip device 90 that includes the spacer 100, which at least partially occupies the clearance between the outer surface of the fixed core 93 and the inner contour of the coil spring 98. This prevents or limits buckling and bowing of the coil spring 98 and allows the circuit breaker to open a circuit with further stability.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.
In the described and illustrated embodiment, the plates 101 and 102 of the spacer 100 are flat. However, the plates 101 and 102 may be arcuate and extend along the inner contour of the coil spring 98. In this case, the spacer 100 reduces the clearance at the inner side of the coil spring 98 . This prevents or limits buckling or bowing of the coil spring 98.
In the electromagnetic trip device 90 of the described and illustrated embodiment, the spacer 100 is a dedicated component that is discrete from the fixed core 93. However, the fixed core 93 may be formed integrally with a clearance reducing portion so that a portion of the fixed core 93 functions as the clearance reducing portion. For example, referring to Fig. 12, a fixed core 193, which may be cylindrical and bent to be U-shaped, includes an upper arm 194 having an outer diameter that is equal to or slightly smaller than the inner diameter of the coil spring 98. As shown in Fig. 13, when viewed in the axial direction of the coil spring 98, the cross-sectional shape and size of the upper arm 194 of the fixed core 193 is in correspondence with the shape and diameter of the coil spring 98. This allows for buckling and bowing of the coil spring 98 to be prevented or limited. Further, the number of components may be reduced, and the burden for coupling the spacer to 100 to the fixed! core 93 may be eliminated.

The electromagnetic trip device may be used in a breaker other than an undervoltage circuit breaker. For example, as shown in Figs. 14 and 15, an electromagnetic trip device 290 is used in an overvoltage circuit breaker. The overvoltage circuit breaker interrupts a circuit when the voltage of the circuit becomes higher than a predetermined upper limit voltage. The overvoltage circuit breaker is provided with a driver 50 that includes a movable contact plate 201. When a movable contact 202 of the movable contact plate 201 is separated from a fixed contact 203, the overvoltage breaker interrupts a circuit. In the electromagnetic trip device 290, the positional relationship of a bobbin 291 (electromagnetic coil 292) relative to a fixed core 293 is reversed from that of the described and illustrated embodiment. A holder 296 is pivoted about a holder pivot shaft 2 96a, which is located in an upper portion of the bobbin 291. The electromagnetic trip device 290 includes a movable core 297 separated from the fixed core 293 under a normal condition. The movable core 2 97 contacts the fixed core 293 when overvoltage occurs. A distal end of the holder 296 contacts the latch 70 and moves the driver 50 to separate the movable core 297 from the fixed core 293. A lower arm 295 of the fixed core 293 is coupled upside down to the spacer 100, which is similar to that of the described and illustrated embodiment. In this manner, the electromagnetic trip device 290 according to the present invention may also be used for an overvoltage circuit breaker.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

CLAIMS

1. An electromagnetic trip device comprising:
a coil spring;
a first core fitted into the coil spring;
a second core urged away from the first core by the coil spring, wherein the first core and the second core are configured to come into contact with each other and move away from each other in accordance with an urging force of the coil spring and an electromagnetic force generated by the first core; and
a clearance reducing portion that reduces a clearance between an outer surface of the first core and an inner contour of the coil spring.

2. The electromagnetic trip device according to claim 1, wherein the clearance reducing portion is a part of or formed integrally with the first core.

3. The electromagnetic trip device according to claim 1, wherein the clearance reducing portion is a discrete component arranged between the coil spring and the first core to prevent or limit buckling and bowing of the coil spring.

4. The electromagnetic trip device according to claim 3, wherein the clearance reducing portion includes one or more elongated pieces extending in an axial direction of the coil spring and arranged between the coil spring and the first core.

5. The electromagnetic trip device according to claim 4, wherein the first core is U-shaped and includes a first arm, which holds the coil spring such that a clearance is formed between the first arm and the coil spring, and a second arm, which holds an electromagnetic coil; and the one or more elongated pieces of the clearance reducing portion are arranged in the clearance between the coil spring and the first arm.

6. The electromagnetic trip device according to claim 4 or 5, wherein the first core includes an arm having a tetragonal cross-section as viewed from the axial direction of the coil spring, the coil spring is cylindrical and surrounds the arm of the first core, and the one or more elongated pieces of the clearance reducing portion are arranged between the arm of the first core and the cylindrical coil spring.

7. The electromagnetic trip device according to any one of claims 4 to 6, wherein the one or more elongated pieces of the clearance reducing portion include a plurality of parallel plates sandwiching the arm.

8. A circuit breaker comprising:
a lever pivotal between an ON position and an OFF position;
an interruption mechanism directly or indirectly connected to the lever, wherein the interruption mechanism engages and disengages a movable contact with and from a fixed contact in accordance with the pivoting of the lever; and the electromagnetic trip device according to any one of claims 1to 7 connected to the interruption mechanism so that the interruption mechanism trips the contacts and interrupts the circuit when a circuit connected to the circuit breaker is in a predetermined circuit condition.

9. The circuit breaker according to claim 8, wherein the electromagnetic trip device interrupts the circuit when voltage at the circuit becomes less than or equal to a predetermined voltage by tripping the contacts with the interruption mechanism,- attraction force between the first core and the second core is set to be smaller than an urging force of the coil spring when the voltage at the circuit is less than or equal to the predetermined voltage; and
when the voltage at the circuit becomes less than or equal to the predetermined voltage, the first core is disengaged from the second core.

10. The circuit breaker according to claim 8 or 9,
Wherein the electromagnetic trip device includes a link linked to the interruption mechanism; the link functions to interrupt the circuit when voltage at the circuit becomes greater than or equal to a predetermined voltage by tripping the contacts with the interruption mechanism;
attraction force between the first core and the second core is set to be greater than an urging force of the coil spring when the voltage at the circuit is greater than or equal the predetermined voltage; and
when the circuit becomes greater than or equal to the predetermined voltage, the first core and the second core are attracted to each other thereby opening the fixed contact And the movable contact.