Abstract:
A switch having closed and open positions moves from one position to the other in response to either an elevated temperature or an excessive pressure. A switch member of bimetal material or shape memory alloy operates in response to an elevated temperature, and a foil diaphragm that cooperates with a bumper operates the switch member in response to elevated pressure. The diaphragm may rupture to vent excessive pressure in the event pressure continues to rise despite operation of the switch member or due to failure of the switch member to operate.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to the art of switches and, more particularly, to switches that automatically move from either a normally open or a normally closed position to the opposite position in response to a change in pressure or temperature. The invention is particularly applicable for use with rechargeable batteries and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used with other devices where it is desired to open or close a circuit in response to an elevated pressure or temperature. The invention also will be described with reference to a switch assembly that responds to either pressure or temperature. However, it will be appreciated that the pressure and temperature responsive features do not necessarily have to be used together and that each feature is capable of independent use. 
     Circuit devices that respond to temperature and/or pressure are used with batteries to interrupt charging or discharging of the battery in the event of thermal runaway that may raise the battery internal pressure and/or temperature to undesirable levels. The circuit devices are intended to interrupt battery charging or discharging before undesirable temperature and/or pressure levels are reached. Arrangements also are used for venting the battery case responsive to an excessive internal pressure. Existing arrangements of this type are relatively complicated and/or have a relatively high resistance that reduces the efficiency of battery discharge and recharge. 
     SUMMARY OF THE INVENTION 
     A pressure and temperature responsive switch assembly includes a movable switch member that is in either a normally open or a normally closed position under normal temperature and/or pressure conditions. The switch member is of a bimetal material or of a shape memory alloy that responds to an elevated temperature by moving from the one normal position to the opposite position. A force transfer member such as a bumper is positioned between the switch member and a snap-acting foil diaphragm that responds to a predetermined pressure for moving the switch member from one position to the other in response to an elevated pressure acting on the opposite side of the diaphragm from the bumper. The foil diaphragm itself may rupture in response to excessive pressure for relieving same in the event increasing pressure is not interrupted by operation of the switch. 
     In a preferred arrangement, the temperature responsive switch member is of shape memory alloy that has a deformed shape at normal temperatures and a recovered shape at an elevated temperature. The switch member of shape memory alloy may have either a normally open or a normally closed position when it is in its deformed shape at normal temperatures, and automatically moves to the opposite position at an elevated temperature by changing to its recovered shape. 
     In other arrangements, the temperature responsive switch member is a bimetal that may have either a normally open or a normally closed position at normal temperatures, and automatically moves to the opposite position at an elevated temperature. 
     In one arrangement, a movable bumper integral with an insulator that supports a base portion of the switch member cooperates with a pressure responsive snap-acting foil diaphragm to impart movement to the movable switch member. An attachment ring secured to a housing member holds the support insulator in position. 
     A switch assembly that uses the bimetal or shape memory switch member may be attached to a housing member such as the lid of a battery case or a battery case itself, or to a housing for another device that may produce an excessive temperature and/or internal pressure. A switch assembly in accordance with the present application responds to an elevated pressure or temperature by interrupting the charging or discharging state of the battery before the pressure or temperature become excessive. 
     In one arrangement, a housing member has a fixed contact attached thereto and a snap-acting foil diaphragm normally closes a pressure port in the housing member adjacent the fixed contact. In its deformed shape at normal temperatures, a switch blade of shape memory metal has an end portion engaging the fixed contact and moves to an open position out of engagement with the fixed contact in response to an elevated temperature by assuming its recovered shape. 
     A movable dielectric force transfer member such as a bumper is located between the pressure responsive snap-acting foil diaphragm and the switch blade, and the blade is movable with the diaphragm and bumper in response to an elevated pressure for placing the switch blade in an open position. In one arrangement, the switch blade is on a switch blade member that has a base portion supported by an annular support insulator attached to the housing member by an attachment ring. A metal terminal plate is held to the support insulator against the base portion of the switch blade member, and an electrical lead is attachable to the terminal plate. 
     In one arrangement, the fixed contact may be a conductive foil located on the housing member outwardly of the pressure port that normally is closed by the snap-acting foil diaphragm. 
     In another arrangement for a normally closed switch, the switch member may be a bimetal that is a bowed strip or a disc having a central portion cooperable with a movable force transfer member such as a bumper. The peripheral edge of the disc or the end edges of the strip switch member engage a metal terminal plate, and a conductive foil attached to the housing member provides a fixed contact that is positioned in engagement with the central portion of the switch member between the switch member and the bumper. The switch member may be a curved bimetal strip or a dished disc that opens a circuit by snapping to a reversed curvature in response to an elevated temperature so that the central portion of the bimetal engages the metal plate and its peripheral edge or end edges engage an electrical insulator positioned on the conductive foil fixed contact and the housing member. Movement of the snap-acting foil diaphragm and bumper responsive to an elevated pressure also causes the normally closed switch member to move to a reversed position for opening a circuit. 
     In a modified arrangement for a normally open switch, an insulator may be positioned between the disc or bowed strip bimetal switch member and the bumper to provide a normally open circuit. Upon reverse bowing of the switch member, its central portion opposite from the bumper engages a metal terminal plate and its peripheral edge or end edges engage a conductive foil fixed contact located outwardly from the insulator and the bumper to provide a closed circuit position at an elevated temperature or pressure. 
     In still another arrangement, a disc or bowed strip temperature responsive switch member that may be of shape memory metal or a bimetal has its peripheral edge or end edges engaging a metal plate and a central portion engaging a fixed contact to complete a circuit. The switch member automatically changes shape to move out of engagement with the fixed contact in response to an elevated temperature. Pressure responsive snap-acting foil diaphragms cooperate with a movable force transfer member surrounding the fixed contact to separate the switch member from the fixed contact in response to an elevated pressure. 
     The improved sensing switch of the present application for sensing elevated temperature and/or temperature conditions may be used in a multi-cell package for such applications as electric vehicles. A sensing switch is associated with each individual cell and disables an individual cell that may experience an elevated pressure or temperature while leaving the remaining cells in operation. 
     In all of the arrangements, the snap-acting foil diaphragm may be rupturable in response to excessive pressure for relieving same. Thus, even if the switch does not operate responsive to an elevated pressure or temperature, or if the pressure continues to build despite operation of the switch, rupturing of the diaphragm would vent the excessive pressure. 
     Although the switch may be designed to revert to its original position upon dissipation of an elevated temperature or pressure, it preferably is designed as a one-shot fuse and remains in the position to which it is moved by an elevated temperature or pressure following dissipation of the elevated temperature or pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross-sectional side elevational view of a switch assembly constructed in accordance with the present application; 
     FIG. 2 is a top plan view thereof; 
     FIG. 3 is a cross-sectional elevational view of an attachment ring used in the switch assembly of FIGS. 1 and 2; 
     FIG. 4 is a top plan view thereof; 
     FIG. 5 is a cross-sectional elevational view of an insulator ring used with the switch assembly of FIGS. 1 and 2; 
     FIG. 6 is a top plan view thereof; 
     FIG. 7 is a cross-sectional side elevational view of an insulating washer used in the switch assembly of FIG. 1 and 2; 
     FIG. 8 is a top plan view thereof; 
     FIG. 9 is a top plan view of a switch blade member used in the switch assembly of FIGS. 1 and 2; 
     FIG. 10 is a side elevational view thereof; 
     FIG. 11 is a view similar to FIG. 1 showing the switch blade in an open position as a result of an elevated temperature; 
     FIG. 12 is a view similar to FIG. 1 showing the switch blade in an open position as a result of an elevated pressure; 
     FIG. 13 is a cross-sectional elevational view of another embodiment; 
     FIG. 14 is a view similar to FIG.  13  and showing the switch member in an open position responsive to an elevated pressure; 
     FIG. 15 is a view similar to FIG.  13  and showing the switch member in an open position responsive to an elevated temperature; 
     FIG. 16 is a cross-sectional elevational view similar to FIG. 13 but showing a switch arrangement having a normally open configuration; 
     FIG. 17 is a view similar to FIG.  16  and showing the switch member in a closed position responsive to an elevated pressure; 
     FIG. 18 is a view similar to FIG.  16  and showing the switch member in a closed position responsive to an elevated temperature; 
     FIG. 19 is a cross-sectional elevational view of another embodiment shown in a normally closed position; 
     FIG. 20 is a view similar to FIG.  19  and showing the switch blade in an open position as a result of an elevated temperature; 
     FIG. 21 is a cross-sectional elevational view similar to FIG.  19  and showing the switch blade in an open position as a result of an elevated temperature; 
     FIG. 22 is a cross-sectional elevational view of another embodiment of a switch assembly having a normally open position; 
     FIG. 23 is a cross-sectional side elevational view similar to FIG.  22  and showing the switch blade in a closed position as a result of an elevated temperature; 
     FIG. 24 is a cross-sectional side elevational view similar to FIG.  22  and showing the switch blade in a closed position as a result of an elevated temperature; 
     FIG. 25 is a cross-sectional side elevational view of another normally closed embodiment; 
     FIG. 26 is a cross-sectional side elevational view similar to FIG.  25  and showing a switch member in an open position as a result of an elevated temperature; 
     FIG. 27 is a cross-sectional side elevational view similar to FIG.  25  and showing the switch blade member in an open position as a result of an elevated pressure; 
     FIG. 28 is a cross-sectional elevational view showing the switch assembly of FIG. 1 attached to the case of a battery or electrochemical cell; 
     FIG. 29 is a cross-sectional elevational view of the switch assembly of FIGS. 22-24 in combination with a charging circuit to illustrate an example of one application for a normally open switch in accordance with the present application; 
     FIG. 30 is a partial cross-sectional elevational view showing how a snap-acting diaphragm is positioned for forming by fluid pressure; and 
     FIG. 31 is a view similar to FIG.  30  and showing pressure applied to a foil disc for forming a smoothly curved snap-acting dimple or bubble therein. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawing, wherein the showings are for purposes of illustrating certain preferred embodiments of the invention only and not for purposes of limiting same, FIGS. 1 and 2 show a metal housing member A in the form of an end cap, lid or cover for a battery case. It will be recognized that the switch assemblies of the present application can be used with batteries by attaching the switch assembly thereto in ways other than by attachment to the battery case or end cap. It also will be recognized that the switch assembly may be attached to a housing member other than a battery cover or case where protection is desired against excessive temperature or pressure conditions internally of the housing. 
     A suitable hole is provided in housing member A for receiving a metal rivet  10  that is then deformed for attaching same to housing member A. Metal rivet A defines a fixed electrical contact, and electrical insulation  12  is interposed between the periphery of fixed contact  10  and housing A. 
     A circular pressure port defined by hole  14  in housing member A is normally closed by a snap-acting flexible metal foil diaphragm  16 . The peripheral undersurface of diaphragm  16  is welded or otherwise sealingly attached to the surface of housing member A surrounding hole  14 . The central portion of diaphragm  16  is formed to the shape of a smoothly curved dome, dimple or bubble that is shown in a concave configuration extending downwardly into hole  14  in FIG. 1, and that snaps to an opposite upwardly domed convex configuration above hole  14  in response to a predetermined elevated pressure acting thereon. Under normal conditions, the curved bubble is convex in a direction toward the source of possible elevated pressure, and snaps to a reverse curvature in which it is convex in a direction away from the source of elevated pressure. 
     An insulator attachment ring B has an inwardly extending bottom flange  20  welded or otherwise secured to housing member A in outwardly-spaced surrounding relationship to fixed contact  10  and pressure port  14 . A support ring C of electrical insulating material is received in attachment ring B and has a central opening  22  therethrough with an opening periphery located in outwardly-spaced surrounding relationship to fixed contact  10  and hole  14 . 
     An upper peripheral notch or recess  24  in support ring C is stepped outwardly from opening  22  for supporting an annular base portion  26  of a switch blade member D. A metal terminal plate  30  is positioned on base portion  26  of switch blade member D within recess  24 . An electrical insulating washer  32  is positioned against the outer peripheral portion of metal plate  30  and the top surface of insulator C, and attachment ring B is inwardly deformed to provide an inwardly extending top flange  36  that secures switch blade member D and metal plate  30  within insulator recess  24 . The flange  36  is deformed such that the peripheral underside of terminal plate  30  preferably is in compressive engagement with base portion  26  of switch blade member D for minimizing resistance and providing optimum conductivity. 
     A flexible switch blade  40  extending into the opening within annular base portion  26  of switch member D is bent downwardly from base portion  26  and has a free end portion normally engaging fixed contact  10  that is electrically connectable with a battery electrode. An electrical lead may be soldered, welded or otherwise attached to the outer surface of metal terminal plate  30  for connection to a device that is to be powered by the battery. Thus, switch blade  40  is in the battery circuit in this example and completes a circuit between fixed contact  10  and metal terminal plate  30 . A movable force transfer member such as a bumper  42  of electrical insulating material is interposed between snap-acting flexible foil diaphragm  16  and switch blade  40 . 
     With reference to FIGS. 5 and 6, dielectric support C has top and bottom surfaces  44 ,  46 , and peripheral recess  24  is located adjacent top surface  44 . Bumper  42  is molded integrally in one-piece with insulator C and extends into insulator opening  22  from one end thereof Bumper  42  is connected with the main body portion of insulator C by flexible arms  48 ,  50 . In the arrangements shown and described, attachment ring B and insulator C are oval, although it will be recognized that other shapes also are possible. When the shape is oval, rectangular or otherwise elongated, flexible arms  48 ,  50  preferably are attached to the body portion of insulator C at one of the ends of the elongated configuration. 
     With reference to FIGS. 9 and 10, switch blade member D preferably is of shape memory alloy such as a nickel-titanium shape memory alloy. However, it will be appreciated that it may be possible to use other shape memory alloys such as copper-based ternaries including copper-zinc-aluminum and copper-nickel-aluminum. The transition temperature range at which the alloy changes from its deformed shape to its recovered shape can be varied by selecting different shape memory alloy compositions and by varying the heat treatment process. 
     In manufacturing switch blade member D of shape memory alloy, the entire switch blade member is heated to the austenitic transformation temperature of the shape memory metal. After cooling to its martensitic state, switch blade  40  is bent relative to base portion  26  to the desired configuration generally shown in FIG.  10 . When switch blade  40  again is heated to its austenitic transformation temperature, it reverts back to the general configuration that it had before it was bent. The bent configuration of FIGS. 1 and 10 is commonly known as the deformed shape that the shape memory metal has at normal temperatures. The configuration that the switch blade assumes at its austenitic transformation temperature is shown in FIG.  11  and is known as its recovered shape. 
     The configuration of the switch components normally would be as shown in FIG. 1 to provide for discharge and recharge of a battery. In response to an elevated temperature condition and/or in response to I 2 R heating of switch blade  40 , the switch blade moves from its closed position to the open position shown in FIG. 11 by assuming its recovered shape at the predetermined austenitic transformation temperature of the alloy. Switch blade  40  can be treated and processed to remain permanently in the open position or to return to the closed position upon cooling. In batteries, the preferred arrangement is to have the device remain open and function as a one-shot fuse so that the battery circuit will not reclose once a problem condition has been sensed. 
     In response to an elevated pressure acting on diaphragm  16  on the opposite side thereof from bumper  42 , diaphragm  16  snaps to its opposite domed or bubble configuration as shown in FIG. 12 to move bumper  42  and lift switch blade  40  from engagement with fixed contact  10 . In the event of excessive pressure, foil diaphragm  16  may rupture for allowing relief of pressure through hole  14 . One or more vent openings may be provided through terminal plate  30  or support C and attachment ring B to vent the cavity or chamber within which switch blade  40  is situated. 
     The pressure responsive snap-acting diaphragm preferably is bistable and remains in the position of FIG. 12 even though the elevated pressure dissipates. The biasing force of switch blade  40  is insufficient to collapse the bubble so that the bubble holds the blade in its open position. This also is the preferred arrangement for other embodiments in which the diaphragm bubble holds the switch member in either its open or its closed position. However, it is possible to make the switch blade with sufficient biasing force to collapse the bubble or to provide a supplemental spring to collapse the bubble and reclose the switch when the pressure dissipates if so desired. 
     FIG. 13 shows another arrangement wherein a battery terminal  50  extends through a suitable hole in housing member A 1  and is electrically isolated therefrom by electrical insulation  52 . A pressure port defined by circular hole  54  in housing member A 1  is normally closed by a snap-acting flexible foil diaphragm  56  that supports a bumper  58  having a central vent hole  60  therethrough and a central stem  62 . An electrically conductive metal foil  64  that defines a fixed contact is positioned on housing member A and is normally engaged by the undersurface of the central portion of a snap-acting bimetal bowed disc or bowed strip switch member E. The central portion of switch member E has a guide hole loosely receiving bumper stem  62 . The periphery or peripheral end edges  66 ,  68  of bimetal bowed disc or bowed strip switch member E engage the undersurface of a metal terminal plate  70  supported on an insulator support ring  76  attached to housing member A as by rivets  78 ,  80 . An electrical insulating member or dielectric foil  82  is positioned on conductive foil  64  outwardly of bumper  58  and the central portion of switch member E. 
     FIG. 13 shows the closed position of the switch with a circuit being completed from conductive foil  64  to the central portion of switch member E and then through switch member E to its periphery and to metal terminal plate  70 . In response to an elevated pressure, switch member E assumes the configuration shown in FIG. 14 with the periphery or peripheral end edges  66 ,  68  of the bimetal bowed disc or bowed strip engaging insulator foil  82  to provide an open circuit. Conductive foil  64  may have a plurality of radial score lines extending in a direction away from bumper  58  so that the foil will rupture along the score lines to facilitate movement of bumper  58  therethrough to the position of FIG.  14 . 
     FIG. 15 shows the open position of the switch in response to an elevated temperature. Snap-acting bimetal switch member E separates from bumper  58  and assumes the inverted bowed configuration with its central portion engaging or located adjacent to metal terminal plate  70 , and with peripheral edges  66 ,  68  engaging insulator foil  82 . Any condition that generates an elevated pressure also will cause an elevated temperature. An elevated temperature softens the bimetal so that it will snap to a reversed configuration with the boost provided by the bumper even though the elevated temperature itself may not be quite adequate to cause reverse snapping. 
     FIG. 16 shows an arrangement similar to FIG. 13 except that the switch is normally open rather than normally closed as in FIG.  13 . In FIG. 16, insulator foil  82   a  is interposed between the central portion of switch member E and conductive foil  64  so that there is no circuit from conductive foil  64  through switch member E to metal terminal plate  70 . In response to an elevated pressure condition, snap-acting bimetal switch member E assumes the configuration shown in FIG. 17 with the disc periphery or strip peripheral end edges  66 ,  68  of a bowed snap-acting bimetal switch member E engaging conductive foil  64  outwardly of insulator  82   a.  The upper central portion of switch member E engages the underside of metal terminal plate  70  to complete a circuit through switch member E from conductive foil  64  to metal plate  70 . Conductive foil  64  may have a plurality of radial score lines adjacent bumper  58  so that the foil will rupture when the diaphragm moves to the position of FIG.  17 . 
     FIG. 18 shows the arrangement of FIG. 16 in a closed position in response to an elevated temperature. When bimetal E is heated to a predetermined temperature, it snaps to the inverted position shown in FIG. 18 with its central portion engaging the underside of metal terminal plate  70  and with its peripheral edge or end edges  66 ,  68  engaging conductive foil  64 . When bimetal E snaps inverted in response to temperature, it separates from bumper  58  as shown in FIG.  18 . 
     FIG. 19 shows another arrangement similar to FIG. 13 but with a different kind of switch member. In the arrangement of FIG. 19, the periphery  89  of an annular base portion on switch member F is supported on insulator support ring  76  beneath metal plate  70 . A switch blade member  90  of shape memory metal normally projects inwardly from annular or ring base portion  89  and engages electrically conductive foil  64  to complete a circuit between foil  64  and metal plate  70 . Switch blade  90  is movable to an open position as shown in FIG. 20 upon assuming its recovered shape at an elevated temperature. In the alternative, switch blade member  90  assumes its open position in response to an elevated pressure as shown in FIG.  21 . Flexible foil diaphragm  56   a  snaps in a direction toward switch blade  90  carrying bumper  58   a  therewith to place switch blade  90  in its open position. Hole  60   a  in bumper  58   a  allows venting of pressure therethrough upon rupture of diaphragm  56   a  in response to excessive pressure. 
     FIG. 22 shows an arrangement similar to FIG. 1 except that the switch is normally open instead of normally closed as in FIG.  1 . In this arrangement, metal terminal plate  96  has fixed contact  10   a  attached thereto and isolated therefrom by electrical insulation  12   a.  Switch blade  40   a  of shape memory metal in FIG. 22 moves from an open position to a closed position as shown in FIG. 23 by changing to its recovered shape in response to an elevated temperature in the chamber within which it is situated and/or in response to self-induced I 2 R heating. In the alternative, switch blade  40   a  may be moved from its open position to its closed position by an elevated pressure acting through pressure port  14   a  on the opposite side of snap-acting diaphragm  16   a  from bumper  42   a  as shown in FIG.  24 . 
     FIG. 25 shows another arrangement wherein a metal housing member G such as a lid or end cap for a battery case or the like has a cylindrical guide sleeve  110  secured thereto. A disc  112  of electrical insulating material is attached to the interior of guide sleeve  110  and to a battery terminal  114  that is connected to a battery electrode. A movable force transfer member  116  of electrical insulating material has a central hole  118  therethrough freely receiving battery terminal  114 . A circular recess  120  in the underside of movable force transfer member  116  slidably receives guide sleeve  110 . Force transfer member  116  may be termed an actuator, and may be a disc or a generally rectangular bar with opposite end portions. A bowed strip or bowed disc switch member  122  of bimetal or shape memory material has a central portion normally engaging terminal  114 , and outer peripheral edge or edges  126 ,  128  normally engaging a metal terminal plate  130 . 
     An attachment ring H has an outwardly extending flange  140  welded or otherwise secured to housing member G. An electrical insulating support ring member  142  is received within attachment ring H on housing member G. Inwardly extending supports  144 ,  146  support the peripheral or end portions of switch member  122 , and the bottom of a recess  150  supports metal terminal plate  130 . An electrical insulating washer  152  is positioned on the top surface of insulating ring  142  and metal terminal plate  130 , and the upper peripheral portion of attachment ring H is deformed inwardly into a securing flange  154 . Recesses  160  and  162  are located outwardly of switch member ends  126 ,  128  between supports  144 ,  146  and metal terminal plate  130 . 
     Pressure ports provided by holes  164 ,  166  in housing member G normally are closed by snap-acting diaphragms  170 ,  172 . In response to an elevated temperature, shape memory switch member  122  moves from its deformed shape at normal temperatures as shown in FIG. 25 to its recovered shape at an elevated temperature as shown in FIG. 26 to open the switch. In response to an elevated pressure, diaphragms  170 ,  172  snap to the positions shown in FIG.  27  and cause movable force transfer member or actuator  116  to move upwardly for separating the central portion of switch member  122  from the upper end of fixed contact  114 . When actuator  116  is a disc, diaphragms  170 ,  172  are located at diametrically opposite positions adjacent the outer periphery of the disc. When actuator  116  is rectangular, diaphragms  170 ,  172  are located adjacent the opposite ends thereof. In the event of excessive pressure, diaphragms  170 ,  172  may rupture to vent the interior of the battery case. In the arrangement of FIGS. 25-27, switch member  122  preferably is of shape memory metal but it also may be a bimetal. 
     FIG. 28 shows the switch assembly of FIG. 1 attached to a battery or electrochemical cell I having a metal case  200  with lid or end cap A welded thereto. It will be recognized that the other embodiments may be attached to the case of a battery or electrochemical cell in a similar manner. Case  200  may have many different configurations including, but not necessarily limited to, cylindrical and rectangular. 
     Case  200  may contain a wrapped multi-layer assembly J that forms the battery electrodes, and a wire  210  is attached between the electrode and fixed contact  10 . One electrode of electrode assembly J is attached to fixed contact  10  as by wire  210  while the other electrode is connected to battery case  200 . In the arrangement shown in FIG. 26, fixed contact  10  is the positive battery terminal while the battery case and the lid are the negative terminal. However, it will be recognized that reverse arrangements also are possible and either the positive or negative battery electrode may be connected with the battery case while the opposite electrode is connected with the fixed contact. In the arrangements of FIGS. 13-21 either a positive or negative battery electrode may be connected with the battery case, of which housing member A 1  is a part, and the opposite electrode is connected with fixed contact  50 . In the arrangement of FIGS. 25-27, either the positive or negative battery electrode is connected with the battery case, of which housing member G is a part, and the opposite electrode is connected with fixed contact  114 . 
     Electrode assembly J may be of many types including stacked, plate and spirally wound, and is generally shown as a spirally wound or jelly roll type. In such a construction, strips of anode and cathode material with a separator strip between them are wound into a shape for reception in the open top portion of the battery case that has integral peripheral and bottom walls. The anode material is a consumable metal and the cathode material is reducible by electrochemical action. The separator may be a porous electrical insulator material that is ionically conductive. The electrode assembly is inserted into the container forming the battery case, and an electrolyte of solvent containing a conductive solute is added to the container. The cover or end cap then is attached sealingly to the open top of the container to seal the electrode assembly and electrolyte within the battery case. 
     With reference to FIG. 29, electrical leads  250 ,  252  for a signal circuit are soldered, welded or otherwise attached to metal plate  96  and fixed contact  10   a  of the normally open switch assembly described with reference to FIGS. 22-24, and are connected with a controller K. Leads  254 ,  256  connect controller K with a charging circuit M that in turn is connected by leads  258 ,  260  with terminals  262 ,  264  of an electrochemical cell N. 
     By way of example, the arrangement of FIG. 29 may be used in a system that has a plurality of individual cells that are constantly charging, such as in an electrochemical cell package that includes a plurality of individual cells for an electric vehicle. Each individual cell would have a sensing switch in accordance with the present application associated with the cell housing to sense an excessive pressure or temperature condition. When such a condition is sensed, the switch closes to send a signal to controller K for cutting off charging current to that particular cell while leaving the remaining cells in service. Other normally open embodiments may be used in the same manner. 
     When items are referred to as being plated, it will be recognized that this includes, but is not necessarily limited to, coating by electroplating, sputtering or vapor deposition. Materials and platings will be identified by way of example with reference to FIG.  1 . Lid A and attachment ring B are nickel plated cold rolled steel. Fixed contact  10  is aluminum. Shape memory actuator D is nickel-titanium provided with a gold strike covered by silver plating on all surfaces, including peripheral surfaces. This provides current flow from precious metal on one surface to the other surface through the peripheral precious metal. Terminal or contact plate  30  is silver plated brass, including opposite surfaces and the peripheral surface. Diaphragm  16  is of aluminum. Similar parts in other embodiments are of similar materials and platings. In the embodiments of FIGS. 13-19, foil contact  64  is of a precious metal such as silver or gold or a metal foil plated with a precious metal. However, it will be recognized that the improvements of the present application are not necessarily limited to these particular materials and platings. 
     The resistance of the switch assembly is less than 20 milliohms, more preferably less than 12 milliohms, and most preferably not greater than 6 milliohms. In the embodiment of FIG. 1, this resistance is measured across the outer surfaces of metal terminal plate  30  and fixed contact  10 . When closed, the movable switch member or blade has sufficient stiffness and bending strength to engage the fixed contact with a force of at least 150 grams. The extremely low resistance is achieved by plating the parts as indicated, by placing the terminal plate in compression against the periphery of the switch member and by providing high force of engagement between the switch member and the fixed contact. The other embodiments have a corresponding low resistance. 
     FIGS. 30 and 31 show an aluminum foil diaphragm  270  peripherally clamped in sealed relationship between cylindrical dies  272 ,  274  having central cylindrical passages  276 ,  278  therethrough. Passage  276  in die  272  is connected through a suitable control with a source of high fluid pressure that preferably is air but could be a liquid. When fluid pressure is admitted to passage  276  as indicated by arrow  277 , the pressure acts uniformly on foil  270  to deform same into cylindrical passage  278  in die  274  and provide a smoothly curved bubble or dome  280  therein. Thus, the bubble is formed by a substantially uniform pressure acting on the entire area of the bubble. 
     By way of example, the fluid pressure used to produce bubble  280  in an 1100 or 3003 series aluminum foil having a thickness between {fraction (2/1000)}-{fraction (6/1000)} inch may be around 300 p.s.i.g. The pressure required to reverse the direction of the bubble usually is slightly greater, such as around 320 p.s.i.g. The bubble collapses and reverses with snap action when the pressure acting on it is at least equal to, and usually slightly greater than, the pressure that formed it. Many different materials may be used for the foil diaphragm, including nickel plated steel, as long as the material is compatible with the electrolyte used in the cell. 
     It will be recognized that the fluid pressure used to form the bubble may vary depending on the thickness and properties of the foil, and the application in which the diaphragm will be used. For use with electrochemical cells, the diaphragm preferably snaps in a reverse direction at a pressure of at least 250 p.s.i.g., and more preferably within 10% of at least 300 p.s.i.g. However, it will be recognized that snap action at other pressures can be used. Forming the snap-acting bubble with fluid pressure rather than mechanically such as by stamping provides more uniform stresses in the foil material rather than concentrated stresses that are produced by stamping. This enables formation of a snap-acting bubble that will snap in a reverse direction when subjected to a reverse fluid pressure that is within about 10% of the fluid pressure that formed it. The bubble undergoes very rapid buckling and reversal when the critical predetermined pressure is reached and, while it is not a true snap-acting movement, it is so rapid that for all intents and purposes it may be considered to be snap-acting. In all embodiments, one or more vent openings may be provided for the chamber in which the switch member is positioned in the event the diaphragm ruptures due to excessive pressure. 
     Shape memory alloys or bimetal materials may be selected to have a wide range of transformation or transition temperatures. The shape memory alloy or bimetal material selected is one that has a transformation or transition temperature approximating that of the over temperature condition to be protected against. For use in batteries, examples of transformation temperatures for shape memory materials, plus or minus 5°, include 62° C., 73° C. and 82° C. These examples would have transformation temperature ranges of approximately 57-67° C., 58-78° C. and 77-87° C. It will be recognized that a wide range of shape memory alloys or bimetal materials may be chosen depending upon the application for the thermal switch assembly. The switch can be fabricated to change from a normally closed or normally open position to the opposite position at an elevated temperature in the range of about 60-125° C. A preferred range is about 65-75° C. 
     The switch of the present application preferably functions as a one-shot fuse by remaining in the position it assumes in response to an elevated temperature or pressure even after the elevated temperature or pressure dissipates. For example, a normally closed switch that moves to an open position in response to an elevated temperature or pressure will remain open rather than reclosing upon dissipation of the elevated temperature or pressure that initially caused the movement. In the case of a bimetal switch member, this may be done by using a fuse disc or fuse strip bimetal material that snaps to a different position upon being heated to a predetermined temperature and does not revert to its original position when cooled. In the case of a shape memory switch member, this may be done by using a shape memory material that moves to a different position upon being heated to a predetermined temperature and changing from its deformed state to its recovered state, and does not revert to its deformed state or its original position upon cooling. 
     The snap-acting pressure responsive diaphragm preferably is bistable. Upon snapping to its opposite position under the influence of a predetermined pressure, the diaphragm remains in that opposite position even though the pressure dissipates. The force of the switch member acting on the diaphragm is insufficient to collapse the diaphragm so that it holds the switch member in the position that it is moved to in response to an elevated pressure even after the pressure dissipates. 
     Although a switch that functions as a one-shot fuse is a preferred arrangement as described above, it will be recognized that the improvements of the present application can be used in arrangements where the switch member reverts to its original position when the elevated temperature or pressure dissipates. The bimetal material may be one that snaps to a new position upon being heated to a predetermined elevated temperature and snaps back to its original position upon cooling. The shape memory material may be one that moves to a new position upon being heated to a predetermined temperature by changing from its deformed shape to its recovered shape, and reverts to both its original position and its deformed state upon cooling. The diaphragm may be one that is not bistable, or a supplemental biasing force may be provided to collapse the diaphragm bubble and allow movement of the switch member back to its original position upon dissipation of the elevated pressure. It also is possible to provide a manual reset button to reset the switch member back to its original position. 
     For purposes of description, the position of the diaphragm bubble when it extends toward the source of high pressure such as in FIG. 1 may be considered a passive position, and its opposite position holding the switch member in its alternative position such as in FIG. 12 may be considered an operational position. The same is true for all embodiments. The terminal plate and the fixed contact formed by the aluminum rivet or foil may be called conductors or metal members that are connected in a closed position of the switch member and are disconnected in the open position of the switch member. The foil fixed contact may be welded or otherwise attached to the housing member to provide low resistance. 
     Although the invention has been shown and described with reference to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.