Pressure sensitive circuit breaker

The pressure sensitive circuit breaker comprises a metallic battery lid having a hole, an insulator formed with a cylindrical portion having a bore which cylindrical portion is inserted into the hole, a metallic rivet inserted through the cylindrical portion of the insulator, an insulating holder having a through hole for insertion therein of the rivet, and an electrically conductive connecting portion formed around an outer surface of the through hole of the holder and having an exposed surface with a space present on the back side thereof, the rivet having a tongue portion on the side opposite to a caulking portion thereof, with a terminal portion being bonded to the tongue portion by welding.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a pressure sensitive circuit breaker
 (hereinafter referred to as "PSCB") to be used for ensuring the safety of
 a storage battery such as a secondary battery capable of being regenerated
 by re-charging. Particularly, the invention is concerned with a PSCB
 having a rectangular lid.
 2. Description of the Related Art
 If a storage battery (a secondary battery) of this type is continued to be
 charged even after completion of charging or if it is charged with an
 electric current larger than a predetermined current, there may arise a
 problem such that some trouble occurs in the battery, with evolution of
 gas therein, increase of pressure and temperature in the battery, swelling
 of the battery, oozing of electrolyte caused by cracking, and adverse
 effect on devices installed in the battery. Even if the result is not to
 such an extent, if the battery is continued to be used in such a state,
 swelling of the battery will proceed and may cause cracking or burst.
 Thus, as to a storage battery which has undergone some trouble, it is
 necessary to stop the use thereof immediately.
 Among the devices for which the reduction of size has been required
 recently, there are many devices which are characterized by their small
 wall thickness. With this tendency, square or rectangular batteries have
 come to be used. Also in this case, reduction of thickness remains to be
 solved. On the other hand, in reply to a keen demand for safety, it is
 necessary to incorporate a safety valve and a current cut-off mechanism in
 such devices.
 In a conventional PSCB referred to above, when the internal pressure of a
 storage battery increases due to some abnormal chemical change of a power
 generating element, the increased pressure acts on a cut-off diaphragm, so
 that the diaphragm is lifted and an electric conduction passage which
 connects a central projection and a lead through a lead stripper plate is
 stripped or broken. As the pressure further increases and reaches a
 predetermined level, a thin-walled portion of the safety valve is broken
 and a gas present in a battery case and having the increased pressure is
 released to the exterior through a hole formed in the lid.
 In many of circular batteries, a single member is used for both diaphragm
 and safety valve.
 In such a secondary battery, members incorporating the above mechanisms are
 laminated together and a junction and a conductive portion for connection
 between the interior and the exterior are rendered integral and sealed
 hermetically by caulking with use of a rivet for example.
 According to the prior art described above, rivet caulking or
 fusion-bonding with laser or ultrasonic wave has been used for making
 integral and seal hermetically such a member as a lid. In this case,
 however, a strong force is exerted on a flat head of the rivet, resulting
 in that the head surface of the rivet, which is brought into pressure
 contact with the lid or a gasket, is flawed or crushed and hence
 deteriorates the sealability.
 Another problem has been encountered such that the member caulked by the
 rivet creeps due to a change with the lapse of time and thus the
 sealability and a long-term stability of an electrically contacted state
 are poor.
 Moreover, aluminum material is usually employed on the positive electrode
 side, so if the rivet used is also made of aluminum, it follows that the
 aluminum rivet and an internal terminal made of aluminum are connected
 together and hence the connected state becomes unstable. More
 particularly, since the gasket is formed of a synthetic resin such as PP,
 the rivet caulked portion is apt to become loose with the lapse of time,
 so if the connection is made by rivet caulking, there occurs a gap between
 the rivet and the internal terminal. As a result, not only the connected
 state becomes unstable, but also an aluminum oxide film is formed on the
 interface, resulting in increase of the resistance value and giving rise
 to a more stable condition.
 If welding is adopted for fixation, a damage is done thermally to the
 caulking portion and it is necessary to ensure a certain degree of
 thickness. Besides, it is difficult to ensure a receptacle portion for the
 bonding, and deformation is apt to occur.
 SUMMARY OF THE INVENTION
 It is the first object of the present invention to provide a PSCB wherein a
 rivet has a tongue portion on the side opposite to a caulking portion
 thereof, with an internal terminal being connected to the tongue portion,
 thus reducing damage to the caulking portion and improving sealability and
 a long-term stability of an electrically contacted state.
 It is the second object of the present invention to provide a PSCB wherein
 the tongue portion projects in a direction parallel to a lid, thus
 permitting the reduction in thickness of the connected portion and the
 reduction of space.
 It is the third object of the present invention to provide a PSCB wherein
 an annular projection of a flange portion of the rivet bites into a member
 to be caulked, whereby sealing is effected positively.
 It is the fourth object of the present invention to provide a PSCB wherein
 an exposed surface of an electrically conductive connecting portion is
 deformed by caulking toward a space formed on the back side thereof, the
 connecting portion being formed around an outer surface of a through hole
 of the holder, so that a force is imposed on the caulked portion at all
 times to eliminate the fear of loosening of the rivet even if there occurs
 a change with the lapse of time.
 The above first object is attained by a first means comprising a metallic
 battery lid having a hole, an insulator having a cylindrical portion to be
 inserted into the hole, the cylindrical portion having a bore, a metallic
 rivet to be inserted through the cylindrical portion of the insulator, an
 insulating holder having a through hole for insertion therein of the
 rivet, and an electrically conductive connecting portion formed around an
 outer surface of the through hole of the holder and having an exposed
 surface with a space present on the back side thereof, the rivet having a
 tongue portion on the side opposite to a caulking portion, with an
 internal terminal being connected to the tongue portion.
 The above second object is attained by a second means in combination with
 the first means wherein the tongue portion projects in a direction
 parallel to the lid.
 The above third object is attained by a third means in combination with the
 first means wherein the surface of a flange portion of the rivet which
 surface comes into contact with a member to be caulked is formed with an
 annular projection.
 The above fourth object is attained by a fourth means in combination with
 the first means, wherein the exposed surface of the connecting portion is
 deformed toward the back-side space thereof by caulking.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
 FIG. 1 is a transverse sectional view of a PSCB according to an embodiment
 of the present invention, FIG. 2 is a longitudinal sectional view of the
 PSCB, FIG. 3 is a transverse sectional view of the PSCB, FIG. 4 is an
 exploded perspective view of the PSCB, FIG. 5 is a side view of the PSCB,
 FIG. 6 is a longitudinal sectional view taken along line 6--6 in FIG. 1,
 FIG. 7 is a longitudinal sectional view taken along line 7--7 in FIG. 1,
 FIG. 8 is a longitudinal sectional view taken along line 8--8 in FIG. 1,
 FIG. 9 is a bottom view of a holder, FIG. 10 is a longitudinal sectional
 view of the holder, FIG. 11 is a plan view of the holder, FIGS. 12A, 12B,
 12C and 12D are longitudinal sectional views taken along lines 12A--12A,
 12B--12B, 12C--12C and 12D--12D, respectively, in FIG. 9, FIGS. 13A, 13B
 and 13C are a plan view, a front view and a right side view, respectively,
 of the holder, FIGS. 14A, 14B, 14C and 14D are a plan view, a right side
 view, a longitudinal sectional view and a bottom view, respectively, of a
 lid, FIG. 15 is an explanatory view showing a diaphragm portion of the lid
 on a larger scale, FIG. 16 is an explanatory view showing a safety vale
 portion of the lid on a larger scale, FIGS. 17A, 17B and 17C are a plan
 view, a front view and a right side view, respectively, showing a
 connected state of a rivet and a terminal portion, and FIGS. 18A and 18B
 are a plan view and a longitudinal sectional view, respectively, of the
 rivet.
 In these figures, the numeral 1 denotes the PSCB embodying the present
 invention. The PSCB 1, which is generally rectangular as a whole, mainly
 comprises a terminal portion 2, an insulator (gasket) 3, a lid (negative
 case) 4, a holder 5, an external electrode 6, a cut-off element 7, and a
 rivet 8.
 The terminal portion 2 is made of aluminum. As shown in FIGS. 4 and 17A to
 17C, the terminal portion 2 is bent approximately at right angles and a
 tongue portion 2a to be welded to a tongue portion 8d of the rivet 8 is
 extended from one longitudinal end (the side opposite to a caulking
 portion) of the terminal portion 2 (the hatched area in FIG. 17 is the
 welded area). Numeral 2b denotes an aperture.
 The insulator 3, which is formed of an insulating synthetic resin,
 comprises a cylindrical portion 3a for insertion therethrough of the rivet
 8, the cylindrical portion 3a being formed at a position close to one end
 of the insulator 3, a recess 3b which permits a diaphragm portion 4c of
 the lid to swell inwards, vent holes 3c, 3c formed in the bottom of the
 recess 3b, a hole 3d for welding, generally rectangular apertures 3e, 3e
 for communication with a safety valve portion of the lid 4, and a
 positioning lug 3f.
 The lid 4 is formed by an electrically conductive metallic plate such as a
 stainless steel plate and, as shown in FIGS. 14A to 14D, an upwardly
 projecting annular projection 4a is formed on an outer peripheral portion
 of the lid 4. In the bottom of the lid 4 are formed a hole 4b at a
 position close to one end of the lid bottom for insertion therethrough of
 the cylindrical portion 3a with the rivet 8 inserted therethrough, the
 diaphragm portion 4c formed thin integrally by grinding, a safety valve
 portion 4d formed thin in an annular shape by press working, and a
 positioning lug 4e.
 After the diaphragm portion 4c is formed thin by grinding, it is bulged in
 a bowl shape inwards of the battery by press working. The diaphragm
 portion 4c is centrally provided with a breaking projection 4f for
 breaking a cut-off element 7 which is mounted above the diaphragm portion.
 Therefore, the diaphragm portion 4c is pressed outwards with an increase
 in internal pressure of a battery and performs a reversing motion as soon
 as the internal pressure exceeds a certain level.
 As shown in FIG. 16, the safety valve portion 4d has an annular thin-walled
 portion 4g so that the thin-walled portion 4g is broken upon generation of
 an excessive internal pressure of the battery.
 The holder 5 is formed of an insulating resin such as PPS and, as shown in
 FIG. 2, it is of a size capable of being fitted in the projection 4a of
 the lid 4. Near one end of the holder 5, as shown in FIGS. 9 to 11, are
 formed a through hole 5a for insertion therethrough of the cylindrical
 portion 3a with the rivet 8 inserted therethrough, a rivet connecting
 portion 9a for the rivet 8, the rivet connecting portion 9a being provided
 in a recess formed around the through hole 5a, apertures 5b, Sb with a
 pair of leads 9b, 9b projecting therein respectively, a pedestal portion
 5c which holds an external electrode 6, an external electrode connecting
 portion 9c for connection with a connecting portion of the external
 electrode 6, a fixing portion 9d to be welded to the lid 4, an aperture 5d
 formed in a position corresponding to the safety valve portion 4d, and a
 cutout portion 5e for fitting thereof of the positioning lug 4e of the lid
 4. In the lower surface of the holder 5 is formed a hole 5f for welding to
 which is exposed the lower surface of the external electrode connecting
 portion 9c. A welding tool is inserted into the hole 5f and is brought
 into contact with the lower surface of the external electrode connecting
 portion 9c of the holder 5, while a welding tool is brought from above
 into contact with the connecting portion 6c of the external electrode 6,
 to sandwich the external electrode connecting portion 9c and the
 connecting portion 6c. In this state, resistance welding is performed to
 fix the external electrode 6 to the holder 5 and make an electric
 connection to a lead 9b.
 A space is formed on the back side of an outer periphery of the through
 hole 5a of the holder 5 and the back side of the connecting portion 9a is
 also exposed to forman exposed surface. That is, a synthetic resin, which
 forms the body of the holder 5, is not applied to the peripheral edge of
 the hole of the connecting portion 9a through which a lead 9b is inserted.
 Therefore, the exposed surface of the connecting portion 9a can be
 elastically deflected downward as shown in FIG. 2. Once the rivet 8 is
 caulked as in FIG. 2, there is no fear of the rivet 8 becoming loose even
 if there occurs a change with the lapse of time, because a force is
 applied to the caulked portion continually by an elastic reverting force
 of the connecting portion 9a.
 As shown in FIGS. 13A to 13C, the rivet connecting portion 9a, the paired
 leads 9b, 9b, the external electrode connecting portion 9c and the fixing
 portion 9d are initially connected in a hoop shape to a frame (not shown)
 through a connecting portion 9e. The hoop is formed using an electrically
 conductive material such as nickel. In forming the hoop, the holder 5
 shown in FIGS. 9 to 11 is formed by insert molding with use of an
 insulating resin and thereafter the connecting portion 9e is cut at the
 position of dash-double dot lines. Thus, the rivet connecting portion 9a
 and one lead 9b are connected together. The lead is connected to the other
 lead 9b and the external electrode connecting portion 9c through a cut-off
 element 7. On the other hand, the fixing portion 9d is not electrically
 connected to any other component.
 The holder 5 is fixed by spot-welding the fixing portion 9d to the bottom
 portion of the lid 4 located on the underside of the fixing portion. A
 welding tool for the spot welding can be brought into abutment with the
 bottom portion of the lid 4 from the welding hole 3d of the insulator 3
 located on the lid bottom.
 The cut-off element 7, which is generally in the shape of a belt, comprises
 an insulating ceramic or resin base plate 7a and a cut-off circuit 7b
 formed on the upper surface side of the base plate 7a by printing or by
 lamination of a metallic foil. The leads 9b, 9b of the holder 5 are
 connected respectively to both longitudinal ends of the cut-off circuit
 7b.
 The cut-off element 7 is disposed above the diaphragm portion 4c, so upon
 reversal of the diaphragm portion 4c with an increase in internal pressure
 of the battery, the cut-off circuit 7b of the cut-of f element 7 can be
 cut off positively by the breaking projection 4f of the diaphragm portion.
 The external electrode 6 is formed from steel plated with nickel and it
 becomes a positive electrode of a storage battery (not shown) when the
 PSCB 1 is installed into the battery. The external electrode 6 comprises a
 generally rectangular body portion 6a, leg portions 6b, 6b bent from both
 side edges of the body portion 6a, and a connecting portion 6c to be
 welded to the connecting portion 9b of the holder 5. As shown in FIG. 6,
 the leg portions 6b are bent to fix the external electrode 6 to the holder
 5.
 The rivet 8 is formed of aluminum and, as shown in FIGS. 18A and 18B, it
 comprises a columnar portion 8a whose upper end portion is somewhat
 smaller in diameter, a flange portion 8b formed at the lower end, an
 annular projection 8c projecting along the outer periphery of the flange
 portion 8b, and a tongue portion 8d extending sideways from the outer
 peripheral surface of the flange portion 8b. To the tongue portion 8d is
 fusion-bonded the tongue portion 2a of the terminal portion 2, as noted
 previously. The insulator 3, lid 4 and holder 5 are made integral with one
 another by caulking of the rivet 8. The upper end of the columnar portion
 8a of the rivet 8 is caulked and connected to the rivet connecting portion
 9a of the holder 5. Consequently, the external electrode 6 is connected to
 the terminal portion 2 through the cut-off circuit 7b, etc.
 Therefore, when the insulator 3 is put on the rivet 8 and the rivet is
 inserted into the columnar portion 3a of the insulator and then caulked,
 the annular projection 8c of the flange portion 8b bites into the lower
 surface of the insulator 3 to ensure a hermetic seal.
 Although in the above embodiment the diaphragm portion is formed thin by
 grinding, it may be formed thin by press working.
 The following description is now provided about a method for installing the
 PSCB 1 into a storage battery (a secondary lithium ion battery).
 Before installation, by inserting the PSCB 1 from above into a battery case
 of the storage battery (not shown) and then caulking the lid 4 throughout
 the whole circumference of a caulking portion of the battery case, the
 PSCB 1 is surely installed and sealed into the storage battery.
 Reference will now be made to the operation of the PSCB 1 as used in the
 above secondary lithium ion battery.
 In the PSCB 1, while the battery is charged, an electric current flows
 successively from the external electrode (positive electrode) 6 to lead
 9b, cut-off circuit 7b of the cut-off element 7, lead 7a, rivet 8 and
 terminal portion 2.
 In this case, if the electric current is continued to flow even after
 completion of the charging, with consequent overcharging, or if the
 charging is performed with an electric current larger than the
 predetermined level of current, there will occur an abnormal condition in
 the storage battery (not shown) and the internal pressure and temperature
 of the battery will increase.
 The increased internal pressure of the storage battery will be transmitted
 as an external pressure to the PSCB 1. As a result, as shown in FIG. 3,
 this external pressure acts to deflect the diaphragm portion 4c of the lid
 4 upward through the vent holes 3c, 3c of the insulator 3. Then, when the
 increased internal pressure of the storage battery, not shown, has reached
 a certain level, the diaphragm portion 4c of the lid 4 reverses upward
 quickly and its central breaking, projection 4f pushes a nearly central
 part of the cut-off element 7 upward, whereby the base plate 7a of the
 cut-off element 7 is broken.
 This breakage of the cut-off element 7 causes breakage of the cut-off
 circuit 7b of the cut-off element 7 and the leads 9b, 9b cease to conduct,
 so that the PSCB 1 cuts off the electric current flowing between the
 external electrode 6 and a power generating portion of the storage
 battery, whereby a further charging is stopped and the secondary lithium
 ion battery is made incapable of functioning as a storage battery.
 With a further increase in internal pressure of the storage battery, the
 thin-walled portion 4g of the safety valve portion 4d in the lid 4 is
 broken, with the result that the gas present within the battery flows from
 the broken part of the thin-walled portion 4g of the safety valve portion
 4d, passes through the PSCB 1 and is discharged from the aperture 5d. For
 example, the operating pressure of the PSCB 1 is set to a pressure in the
 range of 4 to 10 atmospheres and that of the safety valve is set to a
 pressure in the range of 10 to 20 atmospheres.
 Thus, the PSCB of the above embodiment comprises the metallic battery lid 4
 having the hole 4b, the insulator 31 formed with the cylindrical portion
 3a having a bore which portion 3a is inserted into the hole 4b, the
 metallic rivet 8 which is inserted through the cylindrical portion 3a of
 the insulator 3, the insulating holder 5 having the through hole 5a into
 which the rivet 8 is inserted, and the electrically conductive connecting
 portion 9a formed around an outer surface of the through hole 5a of the
 holder 5 and having an exposed surface with a space formed on the backside
 thereof. The rivet 8 has the tongue portion 8d on the side opposite to the
 caulking portion and the terminal portion 2 is bonded to the tongue
 portion 8d. Accordingly, there is less damage to the caulking portion and
 improvement can be made not only in sealability but also in a long-term
 stability of an electrically contacted state.
 In the above embodiment, moreover, since the tongue portion 8d projects in
 a direction parallel to the lid 4, a small thickness of the bonded portion
 will do and hence it is possible to save the required space.
 In the above embodiment, since the flange portion 8b of the rivet 8 is
 formed with the annular projection 8c on its side which comes into contact
 with the insulator 3 as a to-be-caulked member, the annular projection 8c
 bites into the to-be-caulked member 3 to afford a positively sealed
 condition.
 Further, in the above embodiment, the PSCB has the electrically conductive
 rivet connecting portion 9a formed around the outer surface of the through
 hole 5a of the holder 5 and having an exposed surface with a space present
 on the back side thereof, the exposed surface of the rivet connecting
 portion 9a being deformed toward the back-side space by caulking. Thus, a
 force is exerted continually on the caulked portion and hence there is no
 fear of loosening of the rivet even if there occurs a change with the
 lapse of time.
 Many widely different embodiments of the invention may be constructed
 without departing from the spirit and the scope of'the present invention.
 It should be understood that the present invention is not limited to the
 specific embodiments described in the specification, except as defined in
 the appended claims.