US3373057A - Battery having an automatic circuit breaker therein - Google Patents

Description

E. mqJos-r ET AL 3,373,057

March 12, 1968 BATTERY HAVING AN AUTOMATIC CIRCUIT BREAKER THEREIN Filed Oct. 24, 1965 United States Patent 3,373,057 BATTERY HAVING AN AUTOMATIC CIRCUIT BREAKER THEREIN Ernest M. Jost, Attleboro, and Pieter J. Nicuwkoop, Norton, Mass., assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Oct. 24', 1965, Ser. No. 504,359 Claims. (Cl. 136-6) ABSTRACT OF THE DISCLOSURE The cover of a sealed rechargeable-battery casing is provided centrally with an inwardly concave contact button. A dished (which is to say concavoconvex) snap-acting spring disc of the automatic reset type is marginally sealed to the inside of the cover. Its concave side faces the cover. An automatic reset disc after snapping in one direction in response to pressure on its convex side will return with snap action when the pressure is relieved. The disc is provided centrally with a sealed movable contact for engagement and disengagement with an internal fixed contact when the disc snaps to and fro. The arrangement is such that when the contacts are engaged the disc is slightly sprung toward the cover but short of causing snap action. This maintains good electrical contact pressure under safe internal gas pressures. The fixed contact is electrically connected with one set of battery plates and the other set of plates is electrically connected with the casing.

In a first form of the invention the cover is insulated from the casing but the seal between it and the disc is electrically conductive. Thus the disc carries current.

In a second form the cover, casing and disc are conductively connected but the button is insulated from the cover and the disc is insulated from the movable contact which it carries. Hence the disc carries no current. In this case a conductive spring reacts between the button and movable contact to bias the disc in the direction of contact closure.

In a modification of the second form, a conductor leads from the fixed contact through the cover to a second ex ternal contact. The conductor and second contact are insulated from the cover and casing. This provides for application of an external discharge circuit.

The concave contact button may or may not have an external vent. If not, :the compressed gas trapped in it under snap action of the disc supplies some bias on the disc toward automatic reset contact-closing action.

Among the several objects of the invention may be noted the provision of a rechargeable battery in which dangerous overpressurizing during charging is obviated without damage thereto; the provision of a battery of the class described which is automatically disconnected under charging current in response to any tendency to become overpressurized; and the provision of a battery of this class in which delay may be avoided in reconnecting it after disconnection. Other objects and features will be in part apparent and'in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a schematic view illustrating one form of the invention;

FIG. 2 is a view similar to FIG. 1, showing a second form of the invention;

FIG. 3 is a view similar to FIG. 1, showing a third form of the invention; and

31,373,057 Patented Mar. 12, 1968 FIG. 4 is an enlarged view of certain details of the form of the invention shown in FIGS. 2 and 3.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawmgs.

Certain sealed batteries, such as, for example, nickelcadmium batteries, produce oxygen at the cathode and consume oxygen at the anode. The rates of production are such that under normal conditions the battery will operate under pressure at equilibrium, as for example under about p.s.i., which is a, safe limit. However, under certain charging conditions, and particularly at high charging rates (greater than a five-hour rate, for example), the pressure may increase beyond such a safe limit. Therefore, such batteries require a safety mechanism. Heretofore this has been accomplished by puncturing a safety diaphragm in response to excess pressure. This is not desirable because it renders the battery inoperative after puncture. The use of a pressure switch which will turn off the charging current when the safe pressure limit is approached is more desirable. According to the present invention, such a switch is located and sealed within the battery.

Referring now particularly to FIG. 1, there is shown at 1 a container in the form of a metal cylinder or can having a metal cover 3 centrally shaped to form a contact button 5. The peripheral margin of the cover 3 is supported in a rolled portion 7 of the top of the container 1. Insulating material 9 is interposed between the margin of the cover 3 and the rolled portion 7.

Within the container 1 is located the usual electrically positive and negative plate assembly shown schematically and generally at 11. This may be of any type known to the art, as for example but without: limitation, a socalled coiled or jelly-roll form wherein the positive plates, the negative plates and the separators therebetween are coiled in forming the plate assembly 11. One set of plates 13 (negative, for example) is electrically connected to the metal container 1 making it of negative polarity, as indicated. The other set of plates 15 (positive, for example) is connected to a central current collector 17, making it of positive polarity, as indicated. The plates 13 and 15 form the assembly 11- At numeral 19 is illustrated a dished sheet-metal snapacting spring disc carrying a central metal contact 21 normally engaging with the current collector 17. The disc is of the automatic reset type, which is to say that upon application of a certain critical pressure thereto it will snap from its original shape to another shape. The circular margin 23 of disc 19 is metallurgically bonded to the conductive cover 3. The bond is electrically conductive. The shape of the dished disc 19 is such that upon assembly it is slightly sprung, so that: the contact 21 presses on the current collector 17 as long as the pressure in the container 1 does not exceed approximately 100 p.s.i., for example. However, it will snap in the upward direction to snap the contact 21 from the collector 17 under a pressure in container 1 in excess of about 100 p.s.i., for example. The snap-acting character of the separation minimizes contact arcing. Thus if a charging circuit is connected between the container 1 and the button 5, as indicated by the dotted lines 25, and the charging rate is such as to bring about an unsafe pressure, the disc 19 will under excess pressure on its underside snap the contact 21 away from the collector 17, thus opening the charging circuit. Then before charging can be reinstated, the pressure must drop below the safe value, at which time the contact 21 will reclose. The pressure in the battery will diminish in time without release to the outside atmosphere. Thus the battery, even if fully charged when the contact 21 opens, cannot be discharged for such a period, and this may be several hours. This is a disadvantage in some although not all installations and is obviated by the third form of the invention to be decribed below. It will be noted that any external pressure on the contact button will not influence the snapping performance of the disc 19.

In the FIG. 1 form, the disc 19 carries current, which in some cases it is desirable to avoid. In such case the form of the invention shown in FIG. 2 is employed in which like numerals designate like parts, other numerals being employed to describe differences, these being as follows. The cover, which is numbered 29, is welded to the container 1 as shown at 31. This cover has a central opening 2 (shown better in FIG. 4) covered by a central conductive button 33 which is sealed to the cover 29 around the opening 2. Sealing is effected through a ring of insulating material 4, such as for example glass 35. Glass-to-metal seals are known in the art.

At numeral 37 is shown a dished disc, the margins of which are bonded to the cover 29. In this case the bond is not required to be conductive and needs not to be metallurgical. For example it may be an epoxy bond. In the center of the disc 37 is an opening 6 through which extends a downwardly headed conductive contact 41. This is connected with the disc 37 through a glass-to-metal insulating seal 43. A spring 45 connects the contact 41 with the button 33. Operation of the form of the invention shown in FIGS. 2 and 4 is like that described in connection with FIG. 1, its advantage being that current is carried from the collector 17 to the external contact button 33 through the spring 45, rather than through the snap acting disc 37 and the cover 29.

In FIG. 3 is shown the third form of the invention, in which like numerals designate parts like those in FIGS. 2 and 4. In this case, however, the collector 17 is provided with a conductive side arm 47 which passes through a glass-to-metal seal 49 in the cover, numbered 39, terminating in an external contact button 51. This provides for application of an additional discharging circuit 53 (shown in dotted lines) which may be established between the positive button 51 and the negative container 1 after the disc 37 has snapped open the contact 41. Circuit 53 is included to allow discharge without requiring resetting of contact 41 due to pressure decrease in the cell. Such pressure decreases may require several hours and thus discharge of the cell would be prevented if circuit is used both for charging and discharging said cell. In short, the form of th invention shown in FIG. 3 provides for saparate charging and discharging circuits.

It will be seen that in each form of the invention the contact button on the cover is of hollow form, with the central portion of the snap-acting disc beneath it and normally concavely disposed toward it. This arrangement provides for the required upward snap-acting movement of the disc, space for a spring such as 45 and a pocket of gas which when the disc snaps is somewhat compressed to aid in return movement of the disc upon reset, especially in the FIG. 1 form in which, unlike FIGS. 24, no return spring is employed. If desired, this gas pocket may be opened to atmosphere by providing a small hole through the external contact button. This will not admit air to the plate assembly in the container because such air is in any event sealed off by the seal at the margin of the disc and its central seal around the movable contact carried thereby. In the event that such a hole is used, the disc in the case of FIG. 1 will be of the type which requires no return pressure for reset but simply a relaxation of pressure on its convex bottom side. It will be appreciated that dished snap-acting discs to meet these requirements are conventional per se.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A rechargeable battery subject to internal gas pressure rise upon recharging, comprising a casing, a sealed cover on the casing, said casing containing two sets of plates, a sealed contact button on the cover, a snap-acting normally concave-convex spring disc having its margin sealed to the inside of the cover with its concave side facing the cover, said disc being subject to unsafe gas pressures on its convex side to cause the snap action of its central portion toward the cover, said disc being of the automatic reset type to effect snap action away from the cover under sate gas pressure in the casing, a fixed contact in the casing on the convex side of the disc and electrically connected to one set of plates therein, the other set of plates being electrically connected to the casing, an inside contact sealed to and carried substantially centrally by the disc for snap-acting movement into engagement with the fixed contact under said safe gas pressures on the disc and for snap-acting disengagement from said fixed contact upon snap action of the disc under said unsafe gas pressures on the disc, the assembled arrangement between the casing and the cover which carries the dis-c being such as to engage the contacts and somewhat to spring the disc to maintain good electrical contact pressure without causing snap action under safe gas pressure.

2. A battery according to claim 1 wherein said button has a hollow inside portion facing the central portion of the disc.

3. A battery according to claim 2 including resilient means in said hollow portion between the movable contact and said button for biasing the movable contact toward engagement with the fixed contact.

4. A battery according to claim 3 wherein the seal between the button and the cover is composed of electrical insulation, wherein the seal between said movable contact and the disc is also composed of electrical insulation, and wherein said resilient means is an electrically conductive spring.

5. A battery according to claim 4 including a second exterior contact button having an internal connection with said fixed contact, said second button and its connection being electrically insulated from said cover and the casing.

References Cited UNITED STATES PATENTS 2,578,027 12/ 1951 Tichenor. 3,037,066 5/1962 Grieger et al 136-6 3,081,366 3/1963 Belove 1366 ALLEN B. CURTIS, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

D. L. WALTON, Assistant Examiner.

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