The present invention relates to a circuit breaker having a thermal tripping device for tripping an open/close mechanism portion by driving a trip bar by a bimetal which bends when overcurrent occurs on an electric path.

A conventional circuit breaker adapted to an electric path containing a harmonic component employs a thermal tripping device. Generally, the thermal tripping device is configured to drive a trip bar by a bimetal which bends and deforms when overcurrent occurs on an electric path, thereby tripping an open/close mechanism portion.

For enhancing the breaking capacity of such a circuit breaker, particularly in a product with low rating (for example, 30A or lower) which needs to satisfy operation within two minutes prescribed in Electrical Appliance and Material Safety Act, current is directly applied to the bimetal so that the operation within two minutes is satisfied (for example, see Patent Document 1).

However, there are such problems that, when short-circuit current upon short circuit passes through the bimetal, the bimetal is fused or the bimetal is permanently deformed.

For preventing this, a circuit breaker is known which has an extended plate provided at a head end of a bimetal (for example, see Patent Document 2).

• Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-153072
• Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-218765

In the case of further enhancing the breaking capacity in the conventional circuit breaker configured as described above, increase in the current passing upon breaking has a great influence on tripping operation time delay after the breaking due to permanent deformation of the bimetal.

The reason is as follows. The trip bar connecting the open/close mechanism portion and the thermal tripping device has a stopper position spaced by a certain stroke after tripping of the open/close mechanism portion, and therefore the bimetal upon breaking is held at the stopper position, thereby causing permanent deformation.

Therefore, after the breaking, the distance between the trip bar and the bimetal increases due to the permanent deformation, leading to tripping operation time delay.

In the case of attempting to solve the above problem by means other than a thermal tripping device, for the purpose of extending the arc length on an arc extinguishing device side, expansion of the outer shape, expansion of a contact separation distance, and reduction of a contact opening start time and an opening time may be conducted, or a measure such as current limiting performance improvement by, for example, narrowing the arc diameter by pressure increase, or employment of a tripping device that does not pass current through the bimetal upon large current breaking, may be taken. However, in such cases, it becomes difficult to maintain the present outer dimension or realize size reduction. In addition, needless to say, there is disadvantage in terms of cost.

In addition, in the configuration in which the extended plate is provided as shown in Patent Document 2, in order to satisfy an initial stable thermal tripping characteristic, generally, bending of the extended plate corresponding to a tripping load needs to be suppressed to be equal to or smaller than 0.5 mm.

Therefore, in order to cause a load corresponding to the tripping load by using this extended plate within the bending amount of 0.5 mm, the extended plate needs to be formed by a plate material having a considerably high spring constant.

As a result, this extended plate needs a plate material having a rigidity equal to that of the bimetal, and a bending amount of the bimetal upon breaking is directly transmitted to the bimetal. Therefore, it is difficult to prevent permanent deformation.

An object of the present invention is to, without great modification of the conventional outer shape and structure, provide a circuit breaker having a thermal tripping device which can realize stable operation without change in tripping time between before and after breaking.

The present invention is a circuit breaker including: an open/close mechanism portion for driving open/close contacts to open or close an electric path; an electromagnetic tripping device for driving a trip bar to trip the open/close mechanism portion, when overcurrent flows on the electric path; and a thermal tripping device for driving the trip bar by a bimetal which bends when overcurrent flows on the electric path, to trip the open/close mechanism portion. The thermal tripping device includes: a bimetal upper base fixed on a head end of the bimetal; a bimetal upper rotatably provided on the bimetal upper base and fixed to an overcurrent characteristic adjustment member opposing to the trip bar via a predetermined gap therebetween; and a bimetal upper spring held by the bimetal upper base and constantly energizing the bimetal upper by a load equal to or greater than a tripping load of the open/close mechanism portion. When overcurrent flows on the electric path, the bimetal upper is rotated against the bimetal upper spring by bending of the bimetal, and thereby the trip bar is driven via the overcurrent characteristic adjustment member.

The present invention makes it possible to, without great modification of the conventional outer shape and structure and with the minimum number of additional components, realize a thermal tripping device which can perform stable operation without change in tripping time between before and after breaking, and easily obtain a small-size circuit breaker that is adaptable to harmonic and has a high breaking capacity.

• [FIG. 1] FIG. 1 is a vertical sectional view showing the entirety of a circuit breaker according to embodiment 1 of the present invention.
• [FIG. 2] FIG. 2 is an enlarged side view showing a tripping device in FIG. 1.
• [FIG. 3] FIG. 3 is an enlarged perspective view showing a major part of a thermal tripping device in FIG. 2.
• [FIG. 4] FIG. 4 is a vertical sectional view showing the entirety of the circuit breaker upon breaking, according to embodiment 1.
• [FIG. 5] FIG. 5 is an enlarged side view showing the tripping device in FIG. 4.
• [FIG. 6] FIG. 6 is an enlarged side view showing a bent state of a bimetal in the thermal tripping device in FIG. 4.
• [FIG. 7] FIG. 7 is an explanation diagram showing a load characteristic of a bimetal upper of the thermal tripping device according to embodiment 1 as compared to that in a conventional structure.
• [FIG. 8] FIG. 8 is an enlarged perspective view showing a major part of a thermal tripping device according to embodiment 2 of the present invention.
• [FIG. 9] FIG. 9 is an enlarged side view showing a tripping device at the maximum trip position according to embodiment 2.

First, with reference to the drawings, the schematic structure of a circuit breaker according to embodiment 1 of the present invention will be described.

In FIG. 1, a circuit breaker 100 is formed using a housing 1 composed of a base 2 and a cover 3 which are formed by an insulation material.

On the base 2, circuit breaking units for respective phases whose number is equal to a pole number (for example, in the case of three phases, three circuit breaking units) are disposed in parallel with each other. Above the center circuit breaking unit, an open/close mechanism portion 20 having a known toggle link mechanism is disposed.

The cover 3 covers the circuit breaking units for respective phases on the base 2, and the open/close mechanism portion 20. An operation handle 21 of the open/close mechanism portion 20 protrudes from the cover 3.

The circuit breaking units for respective phases have the same configuration. A cross bar 10 is disposed on the base 2 so as to cross the circuit breaking units for respective phases and be perpendicular to the circuit breaking units for respective phases,

The circuit breaking units for respective phases each have: a power-supply-side terminal 7 provided on the base 2; a fixed contact 4 provided so as to extend from the power-supply-side terminal 7; a movable contact 5 to contact with or be separated from the fixed contact 4; a movable contactor 6 rotatably held by the cross bar 10, with the movable contact 5 being provided at one end of the movable contactor 6; a tripping device 30 connected to the movable contactor 6 via a movable element holder 9; and a load-side terminal 8 connected to the tripping device 30 and provided on the base 2. The fixed contact 4 and the movable contact 5 compose open/close contacts for opening or closing an electric path.

When the movable contact 5 contacts with the fixed contact 4, an electric circuit between the power-supply-side terminal 7 and the load-side terminal 8 is turned on. When the movable contact 5 is separated from the fixed contact 4, the electric circuit between the power-supply-side terminal 7 and the load-side terminal 8 is turned off.

The cross bar 10 is disposed at a bottom portion of the base 2, and extends perpendicularly to the drawing surface of FIG. 1. The cross bar 10 is rotated about the axis thereof by the open/close mechanism portion 20. The movable contactors 6 of the circuit breaking units for respective phases are attached to the cross bar 10.

When the cross bar 10 is rotated about the axis thereof, the movable contactors 6 of the circuit breaking units for respective phases are simultaneously rotated, and the rotation of the movable contactor 6 causes the movable contact 5 to contact with or to be separated from the fixed contact 4.

The open/close mechanism portion 20 is formed by a known toggle link mechanism, and has a known trip bar 22 which is driven by the tripping device 30, and a trip bar stopper 23 which locks the trip bar 22 at the maximum trip position.

An arc extinguishing chamber 11 is disposed near the movable contactor 6, and extinguishes an arc caused between the movable contact 5 and the fixed contact 4 upon operation of the open/close mechanism portion 20.

The tripping device 30 is composed of an electromagnetic tripping device 40 and a thermal tripping device 50 as shown in FIG. 2.

The electromagnetic tripping device 40 has: a fixed iron core 41; a movable iron core 42 which is to be adhered to the fixed iron core 41 upon instantaneous breaking, to drive the trip bar 22; a return spring 43 energizing the movable iron core 42; and a shaft 44 pivotably supporting the movable iron core 42.

FIG. 3(a) and FIG. 3(b) are enlarged perspective views of a major part of the thermal tripping device 50 as seen from respective directions opposite to each other. The thermal tripping device 50 has: a bimetal 51 having a lower end fixedly connected to the movable element holder 9; a bimetal upper base 52 fixed on a head end of the bimetal 51; a bimetal upper 54 pivotably supported by the bimetal upper base 52 with a rotary shaft 53 used as a pivot, with an overcurrent characteristic adjustment screw 57 being screwed into the bimetal upper 54; and a bimetal upper spring 56 held by the bimetal upper base 52 and energizing the bimetal upper 54 toward the trip bar 22, for giving a movable load.

The bimetal upper 54 is constantly energized by the bimetal upper spring 56 while contacting with a bimetal upper stopper 55 provided on the bimetal upper base 52. A spring load on the bimetal upper 54 is set to be greater than a tripping load, at an abutting position of the trip bar 22.

An electric conduction connection member 58 is fixed at an upper end of the bimetal 51 by a rivet 60. The bimetal 51 is connected to the load-side terminal 8 via the electric conduction connection member 58 and a flexible conductor 59 so that current of the electric path can flow therethrough.

In FIG. 3, an example where the bimetal upper base 52 is integrally formed with the electric conduction connection member 58, has been shown. However, the bimetal upper base 52 and the electric conduction connection member 58 may be separately formed and then may be fixed with each other by welding or the like.

Next, a breaking operation of the circuit breaker 100 will be described.

When overcurrent equal to or greater than predetermined current flows in the bimetal 51, the bimetal 51 itself generates heat, and the bimetal 51 is deformed to be bent by the heat generation.

Since the overcurrent characteristic adjustment screw 57 is fixed to the bimetal 51 via the bimetal upper 54 and the bimetal upper base 52, when the bimetal 51 has been bent, the overcurrent characteristic adjustment screw 57 pushes the trip bar 22, whereby the open/close mechanism portion 20 is driven to rotate the movable contactor 6. By the rotation of the movable contactor 6, the movable contact 5 is separated from the fixed contact 4, whereby the operation of current breaking is completed (see FIGS. 4 to 6).

It is noted that FIG. 4 shows the state where the thermal tripping device 50 has just operated, and in this state, the movable contact 5 is still in contact with the fixed contact 4.

When the above-described overcurrent characteristic adjustment screw 57 pushes the trip bar 22, the bimetal upper 54 is constantly energized toward the trip bar 22 by the bimetal upper spring 56 while contacting with the bimetal upper stopper 55 provided on the bimetal upper base 52.

In this case, since a spring load on the bimetal upper 54 is set to be greater than a tripping load at the abutting position of the trip bar 22, the bimetal upper 54 can push the trip bar 22 without rotating.

FIG. 7 is an explanation diagram showing a load characteristic of the bimetal upper 54 of the thermal tripping device 50 as compared to that in the conventional structure. The spring load on the bimetal upper 54 is set to be greater than the tripping load, at the abutting position of the trip bar 22, and also, is set to be smaller than a spring load on the extended plate in the conventional structure, at the lock position of the trip bar 22.

Therefore, at the abutting position of the trip bar 22, the bimetal upper 54 can push the trip bar 22 without rotating, and also, in the state where the trip bar 22 is driven and thereby the open/close mechanism portion 20 is tripped, the bimetal upper spring 56 bends in accordance with a load applied to the bimetal upper 54.

When overcurrent such as short-circuit current flows, the movable iron core 42 is adhered to the fixed iron core 41 owing to magnetic force generated in the fixed iron core 41 of the electromagnetic tripping device 40, whereby the movable iron core 42 rotates about the shaft 44 as a pivot against energizing force of the return spring 43.

The rotation causes the movable iron core 42 to push the trip bar 22, whereby the open/close mechanism portion 20 is driven to rotate the movable contactor 6.

The rotation of the movable contactor 6 causes the movable contact 5 to be separated from the fixed contact 4, whereby the overcurrent is interrupted and the trip operation is completed.

However, also when overcurrent such as short-circuit current flows, the bimetal 51 is bent. The bending stroke is equal to or greater than a stroke for the trip bar 22 to abut the trip bar stopper 23 of the open/close mechanism portion 20.

Therefore, the bimetal upper 54 rotates. Since a load equal to or greater than the spring load characteristic of the bimetal upper spring 56 is applied to the bimetal upper 54, the bimetal upper spring 56 is bent, so that the bimetal upper 54 rotates.

Thus, since the bimetal upper 54 rotates, a load equal to or greater than the spring load characteristic of the bimetal upper spring 56 is eventually not applied to the bimetal 51.

In conventional case, the bending stroke of the bimetal 51 is forcibly fixed by the trip bar stopper 23 of the open/close mechanism portion 20 and thereby permanently deformed. However, in the present embodiment, when a load applied to the bimetal 51 becomes equal to or greater than the spring load characteristic of the bimetal upper spring 56, the bimetal upper spring 56 is bent and the bimetal upper 54 rotates, whereby permanent deformation of the bimetal 51 can be prevented.

Thus, it becomes possible to obtain a circuit breaker capable of stable tripping without change in a tripping time between before and after breaking.

FIG. 8(a) and FIG. 8(b) are enlarged perspective views of a major part of the thermal tripping device 50 as seen from respective directions opposite to each other. FIG. 9 is an enlarged side view showing a tripping device at the maximum trip position, according to embodiment 2.

Embodiment 2 uses a bimetal upper spring 61 formed by a compression spring instead of the bimetal upper spring 56 formed by a torsion spring in embodiment 1. The other configuration is the same as in embodiment 1, so the description thereof is omitted.

It is noted that although embodiment 2 uses a compression spring as the bimetal upper spring, a tension spring or the like may be used, which can obtain the same effect.

100

circuit breaker

1

housing

2

base

3

cover

4

fixed contact

5

movable contact

6

movable contactor, movable element

7

power-supply-side terminal

8

load-side terminal

9

movable element holder

10

cross bar

11

arc extinguishing chamber

20

open/close mechanism portion

21

operation handle

22

trip bar

23

trip bar stopper

30

tripping device

40

electromagnetic tripping device

41

fixed iron core

42

movable iron core

43

return spring

44

shaft

50

thermal tripping device

51

bimetal

52

bimetal upper base

53

rotary shaft

54

bimetal upper

55

bimetal upper stopper

56

bimetal upper spring

57

overcurrent characteristic adjustment screw

58

electric conduction connection member

59

flexible conductor

60

rivet

61

bimetal upper spring