Chemistry: electrical current producing apparatus – product – and – With control means responsive to battery condition sensing...
Reexamination Certificate
1999-09-08
2001-10-02
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With control means responsive to battery condition sensing...
C429S007000, C429S057000, C429S090000
Reexamination Certificate
active
06296965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cell electrical path breaking mechanism, and, more particularly, to a cell electrical path breaking mechanism which makes a storage cell, renewable by recharging, safe to use.
2. Description of the Related Art
For example, chargeable lithium ion secondary cells are widely used as electrical power sources in portable devices such as portable telephones or personal computers. In such secondary cells, organic solvent type electrolyte is injected into a cell case, which is hermetically sealed.
However, when such secondary cells are overcharged when they are recharged, or when an amount of electrical current larger than a specified amount is passed through them, an abnormality occurs in the cell, causing gas to be produced in the cell case. The production of gas increases the pressure and the temperature in the cell case. When the pressure and the temperature increase, the cell case expands and cracks, causing the electrolyte in the cell case to leak out of it, which adversely affects devices incorporating such secondary cells.
Even if the abnormality occurring in such secondary cells is not as serious as that described above, it is still necessary to stop using any abnormal cells immediately. This is because continued use of abnormal cells causes them to expand more and more, which may cause cell cases incorporating abnormal cells to rupture.
To prevent a cell from rupturing, a cell electrical path breaking mechanism is used. A conventional cell electrical path breaking mechanism used with a circular cell is shown in
FIGS. 9 and 10
. A cell cover
3
and an actuator
4
are mounted to a cell case
1
. The cell cover
3
is mounted by welding or caulking through a gasket
2
in order to hermetically seal the cell case
1
. The actuator
4
which can be displaced upward is provided below the cell cover
3
.
Vent holes
3
a
are formed in the cell cover
3
in order to allow the portion of the air between the cell cover
3
and the actuator
4
to escape therefrom to the outside when the actuator
4
below the cell cover
3
is displaced upward and rupturing occurs.
The actuator
4
includes an annular safety valve portion
4
a
, which is formed by drawing or the like and which includes a protrusion
4
b
and grooves
4
c
. The protrusion
4
b
protrudes downward at the center portion of the actuator
4
. The grooves
4
c
are formed radially in the surface around the protrusion
4
b.
Below the actuator
4
is disposed an insulating plate
5
, which has a hole
5
a
and a vent hole
5
b
formed therethrough. The hole
5
a
is formed to receive the protrusion
4
b
of the safety valve portion
4
a.
Below a portion of the insulating plate
5
is disposed a lead fixing member
6
, which has a hole
6
a
and a vent hole
6
b
formed therein. The hole
6
a
connects to the hole
5
a
formed in the insulating plate
5
. The vent hole
6
b
connects to the vent hole
5
b
formed in the insulating plate
5
.
The protrusion
4
b
of the safety valve portion
4
a
is binserted into the hole
5
a
of the insulating plate
5
and the hole
6
a
of the lead fixing member
6
. A lead
7
formed of a thin metallic plate is mounted to the summit of the protrusion
4
b.
The lead
7
includes a connection portion
7
a
which is joined to the summit of the protrusion
4
b
by welding or the like. It allows electrical conduction between the actuator
4
and the lead
7
. The edge of the lead
7
not joined to the protrusion
4
b
is connected to a generating element
8
disposed below the lead
7
, whereby an electrical path is formed between the generating element
8
and the cell cover
3
.
The cell case
1
is filled with an electrolyte (not shown).
When an abnormality occurs in the cell, so that the pressure in the cell case
1
is increased, gas whose pressure has been increased flows from the vent holes
5
b
and
6
b
, as indicated by arrow A in FIG.
10
. When this takes place, a force which tries to push the back surface of the safety valve portion
4
a
upward is exerted thereto.
When the force exerted on the safety valve portion
4
a
causes stress to be concentrated at the connection portion
7
a
of the lead
7
, and this concentrated stress becomes larger that the shear stress of the connection portion
7
a
, the connection portion
7
a
breaks off or peels off from the lead
7
. This electrically disconnects the lead
7
and the actuator
4
from each other, thereby breaking the electrical path of the cell.
When the electrical path is broken, the flow of electrical current in the cell is interrupted. This suppresses pressure increase in the cell case
1
, making it possible to prevent the cell from rupturing.
The production of smaller portable telephones or any other types of portable device using such conventional cells has caused a stronger demand for smaller and thinner cells (so that they can be used in smaller portable devices).
However, in conventional cell electrical path breaking mechanisms such as that described above, when an abnormality occurs in the cell, flammable gas is sometimes produced in the electrolyte or the like. When the internal pressure in the cell increases to a value equal to or greater than a predetermined value, causing the connection portion
7
a
to break off from the lead
7
, an arc may be generated. The arc may ignite the flammable gas, and cause an explosion.
It is necessary to construct such conventional cell electrical path breaking mechanisms so that an arc is not produced when connection portion
7
a
breaks off from the lead
7
. However, constructing cell electrical path breaking mechanisms taking this into account limits the types of material that can be used to form the actuator
4
or the like, and the forms that the actuator
4
or the like can take, thereby limiting the freedom with which cell electrical path breaking mechanisms can be designed.
SUMMARY OF THE INVENTION
Accordingly, in order to overcome the above-described problems, it is an object of the present invention to provide a cell electrical path breaking mechanism which makes cells safe to use and which has a simple structure, wherein if the electrical path in the cell is broken, and an arc is produced, the arc does not ignite the gas in the cell.
To this end, according to an aspect of the present invention, there is provided a battery electrical path breaking mechanism comprising:
a cell case connected to a generating element accommodated in the cell case;
a cell cover for hermetically sealing the cell case;
a diaphragm formed at a portion of the cell cover so as to bulge towards the inner side of the battery case, the diaphragm being displaceable in accordance with changes in internal pressure in the battery case;
a connection member disposed above the diaphragm for connection to the diaphragm;
an external electrode electrically connected to the connection member; and
a holding member for holding the external electrode, with the connection member being joined to the diaphragm;
wherein an electrical path is formed between the cell case and the external electrode through the diaphragm and the connection member; and
wherein when the internal pressure in the cell case increases to a value equal to or greater than a predetermined value, causing the diaphragm to be displaced upward, the connection member is severed, causing the electrical path to be broken.
In the battery electrical path breaking mechanism of the aforementioned aspect of the present invention, the connection member may include hold portions formed on both sides thereof, and a connection portion formed between the hold portions for connecting the diaphragm thereto, with both hold portions being held by the holding member. Here, when the diaphragm is displaced upward, the connection portion and the hold portions are severed from each other, causing the electrical path to be broken.
In the battery electrical path breaking mechanism of the aforementioned aspect of the present invention, the connection member may include a hold porti
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Maples John S.
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