Breaker, safety circuit and secondary battery pack

1. A breaker provided with:

a fixed contact;

a movable piece, which has an elastic portion formed in a plate shape and elastically deformable, and a movable contact formed in one end portion of the elastic portion, and which is for pressing the movable contact against the fixed contact;

a thermally-actuated element deforming with a change in temperature so as to shift the movable piece from a conduction state in which the movable contact contacts with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact;

a first resin case having an opening for housing the movable piece and the thermally-actuated element;

a second resin case mounted on the first resin case in order to close the opening; and

a plate-shaped cover piece embedded in the second resin case,

wherein

the first resin case is provided with a first fixing surface fixed to the second resin case, and formed continuously around the opening,

the second resin case is provided with a second fixing surface fixed to the first resin case, and formed continuously facing the first fixing surface,

the second fixing surface is provided with a protruding portion protruding toward the first fixing surface, and

the protruding portion and the plate-shaped cover piece are at least partially overlapped with each other in a plan view of the plate-shaped cover piece viewed in its thickness direction,

wherein

the opening includes a rectangular area which is formed in a rectangular shape in said plan view, and

the protruding portion and the plate-shaped cover piece are overlapped with each other in regions which are adjacent to four corners of the rectangular area on outer sides thereof in the plan view,

wherein

the second resin case is formed in a rectangular shape which is longer in a longitudinal direction of the movable piece in the plan view, and

the protruding portion includes:

first portions extending linearly along the opening in parallel with long sides of the second resin case,

second portions continued from the first portions, and bent inward in a short direction of the movable piece in the above-said adjacent regions, and

third portions continued from the second portions, and disposed inward in the short direction than the first portions, and extending linearly in parallel with the first portions.

2. The breaker as set forth in claim 1 , wherein

the second portions and the plate-shaped cover piece are overlapped with each other in the plan view.

3. A safety circuit for electrical equipment, which comprises the breaker as set forth in claim 1 .

4. A secondary battery pack, which comprises the breaker as set forth in claim 1 .

5. A breaker provided with:

a fixed contact;

a movable piece, which has an elastic portion formed in a plate shape and elastically deformable, and a movable contact formed in one end portion of the elastic portion, and which is for pressing the movable contact against the fixed contact;

a thermally-actuated element deforming with a change in temperature so as to shift the movable piece from a conduction state in which the movable contact contacts with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact;

a first resin case having an opening for housing the movable piece and the thermally-actuated element;

a second resin case mounted on the first resin case in order to close the opening; and

a plate-shaped cover piece embedded in the second resin case,

wherein

the first resin case is provided with a first fixing surface fixed to the second resin case, and formed continuously around the opening,

the second resin case is provided with a second fixing surface fixed to the first resin case, and formed continuously facing the first fixing surface,

the first fixing surface is provided with a protruding portion protruding toward the second fixing surface, and

the protruding portion and the plate-shaped cover piece are at least partially overlapped with each other in a plan view of the plate-shaped cover piece viewed in its thickness direction,

wherein

the opening includes a rectangular area which is formed in a rectangular shape in said plan view, and

the protruding portion and the plate-shaped cover piece are overlapped with each other in regions which are adjacent to four corners of the rectangular area on outer sides thereof in the plan view,

wherein

the second resin case is formed in a rectangular shape which is longer in a longitudinal direction of the movable piece in the plan view, and

the protruding portion includes:

first portions extending linearly along the opening in parallel with long sides of the second resin case,

second portions continued from the first portions, and bent inward in a short direction of the movable piece in the above-said adjacent regions, and

third portions continued from the second portions, and disposed inward in the short direction than the first portions, and extending linearly in parallel with the first portions.

6. The breaker as set forth in claim 5 , wherein

the second portions and the plate-shaped cover piece are overlapped with each other in the plan view.

7. A safety circuit for electrical equipment, which comprises the breaker as set forth in claim 5 .

8. A secondary battery pack, which comprises the breaker as set forth in claim 2 .