Abstract:
A seal type storage battery has a battery case which has a sealing assembly for sealing an opened portion of an outer case, which holds an electricity generating element. The sealing assembly includes a pressure-sensitive conductive rubber member in the battery case. The pressure-sensitive conductive rubber member has a resistance that changes continuously depending on a rise of inner pressure in the battery case. A lead connecting with the, pressure-sensitive conductive rubber extends outside of the battery case, and the lead is capable of outputting a pressure detecting signal to outside.

Description:
This application is based on applications No. 94296 filed in Japan on Mar. 30, 2000 and No. 68336 filed in Japan on Mar. 12, 2001, the content of which incorporated hereinto by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a seal type storage battery such as a nickel-cadmium storage battery, a nickel metal hydride type storage battery or the like, in particular, an improve seal type storage battery having a pressure detector for detecting inner pressure of the battery. 
     A seal type storage battery such as a nickel-cadmium seal type storage battery, a nickel metal hydride storage battery or the like produces oxygen gas at a positive electrode when close to charge up, and in some cases hydrogen gas is produced at a negative electrode, thereby increasing the inner pressure of the battery. For this reason, this kind of battery has a relief valve, which exhausts the gas out of the battery when the inner pressure exceeds a predetermined pressure, and the valve closes when the inner pressure is lower than the predetermined pressure. 
     In this case, a decrease of battery capacity occurs due to a decrease of electrolyte in accordance with the process of charge-discharge cycles. Therefore, various charging methods for preventing overcharge are employed. For example, a so-called—delta-V method is employed to control the charge by detecting decreased voltage delta-V from a peak point in accordance with a phenomenon in which charged voltage shows the peak point at the end of charging. A method has also been employed that controls the charge by detecting surface temperature of the battery in accordance with the phenomenon that the surface temperature increases with the process of the charge. 
     However the charged voltage depends on charging current or ambient temperature, so that the—delta-V method described above has a problem in that dispersion of the detected delta-V value occurs at overcharge. On the other hand, the method that controls the charge by detecting the surface temperature of the battery, described above, can detect the difference of the temperature comparatively with accuracy when the charging current is small, but the temperature in short time charging increases quickly so that the method has the problem that an overcharge can occur due to a delay in detecting the increasing temperature. 
     Therefore, a method was proposed that controls the charge by detecting a rise of inner pressure of the battery due to the charge, for example in Japanese Laid-Open Patent Publication No. TOKU-KAI-HEI 5-153,734 (1993), Japanese Laid-Open Patent Publication No. TOKU-KAI-HEI 5-36,442 (1993) etc. However, in the method proposed in Japanese Laid-Open Patent Publication No. TOKU-KAI-HEI 5-153,734 (1993), a strain gauge is attached to the battery with adhesive to detect the inner pressure, and then deformation of the battery case is converted into variation of resistance so that charging is controlled by detecting the variation of resistance. In this case, it has a problem in that it cannot sufficiently prevent overcharge, since it cannot detect the inner pressure directly so that detection of the inner pressure is delayed, and sensitivity of the detection depends on the condition of the attachment of the strain gauge so that it cannot detect the inner pressure with certainty. 
     On the other hand, in the method proposed in Japanese Patent Application HEI 5-3644, 1993, it has a problem in that it cannot be used repeatedly when it cuts the charging current directly when charging with a huge amount of charging current, since a detection signal detected by a pressure detector controls a switching device, disposed in a charging circuit, to cut the charging current directly so that the switching device is susceptible to being broken. In addition, it is difficult to ensure that the pressure detector disposed in the trough will operate stably for a long time, so that it makes it difficult to detect its inner pressure with accuracy to protect the battery effectively. The detector is disposed under very extreme circumstances such as large variations of pressure or temperature, so that the detector is susceptible to aging. Further, the detector is exposed to electrolyte, which causes leakage. 
     Therefore, in order to solve the problems mentioned above, the object of the present invention is to provide a seal type storage battery that can detect the inner pressure of the battery caused by direct charging to prevent the occurrence of an overcharge. 
     SUMMARY OF INVENTION 
     To achieve the objects mentioned above, the seal type storage battery of this invention has a pressure-sensitive conductive rubber whose resistance changes continuously depending on a rise of inner pressure in the battery case. The conductive rubber is disposed in the battery case, and a lead connecting with the pressure-sensitive conductive rubber is extended to outside of the battery case. The lead which is extended to outside of the battery case, outputs a pressure detecting signal. 
     Since the seal type storage battery has the pressure-sensitive conductive rubber whose resistance is changed continuously depending on the rise of inner pressure of a battery case so that the detection does not delay because the inner pressure can be immediately output as the detecting signal. In addition, the pressure-sensitive conductive rubber detecting the pressure has superior resistance for transmutation of pressure and temperature so that the structure can prevent its aging. Further, as shown in FIG. 4, the pressure-sensitive conductive rubber has a characteristic that its resistivity changes in accordance with load (pressure) so that it can detect a rise of the inner pressure with accuracy. Especially, the resistitvity is extremely sensitive in the early stage at which load operates, so that the increasing inner pressure can be detected more precisely. Further, the pressure-sensitive conductive rubber shows a superior water-proof quality such that it can effectively prevent the degradation caused by the electrolyte. Accordingly, the seal type storage battery according to the present invention can detect the inner pressure of the battery with accuracy and immediacy using the pressure-sensitive conductive rubber. Thus, overcharging can be prevented for this type of battery over a long period of time with certainty. Furthermore, the seal type storage battery has a lead connected with the pressure-sensitive conductive rubber. The lead is disposed in the battery case and extended to the outside, so that simply connecting the extended lead with the control circuit of the charging circuit can cut the charging current, thus facilitating the connecting work between the seal type storage battery and charging circuit. 
     In this case, the seal type storage battery according to the present invention has a sealing equipment or assembly which has a sealing sheet having an opened hole in the center. The sealing assembly seals an open hole of the outer case via an insulative gasket and an electrode cap fixed on the outer surface of the sealing sheet. An alkali-resisting rubber sheet is disposed between the sealing sheet and the electrode cap, wherein the pressure-sensitive conductive rubber is disposed at the position of the opened hole of the sealing sheet and is sandwiched between the alkali-resisting rubber sheet and the electrode cap, so that the pressure due to gas produced in the battery can be transmitted to the pressure-sensitive conductive rubber via the alkali-resisting rubber. Therefore the gas pressure produced in the battery can be instantly transmitted to the pressure-sensitive conductive rubber immediately, and then output to the outside as an electrical signal via the lead connected to the pressure-sensitive conductive rubber. 
     Thereby, the seal type storage battery connected with the charging circuit can prevent overcharge, since the lead connected to the pressure-sensitive conductive rubber connects with the control circuit of the charging circuit so that the charging current can be cut immediately when the inner pressure of the battery exceeds a predetermined pressure value. In addition, even the sealing sheet has an open hole in the center of it, and the alkali-resisting rubber seals the open hole so that the internal battery is maintained in an airtight condition, and therefore the pressure-sensitive conductive rubber is not exposed to the alkali-condition of the internal battery. 
     In addition, the seal type storage battery may have a pressure-regulating valve assembly disposed between the sealing sheet, which is a component of the sealing equipment, and the electrode cap. The pressure-regulating valve equipment comprises a valve sealing the open hole portion of the sealing sheet and an elastic body biasing the valve to the open hole. In the valve, the pressure-sensitive conductive rubber is disposed in a position facing the open hole portion of the sheet via an alkali-resisting rubber. The seal type storage battery can cut the charge current immediately by detecting a rise of the inner pressure of the battery with the pressure-sensitive conductive rubber disposed inside of the valve. Further, in the seal type storage battery, the pressure-regulating valve can exhaust the gas in the battery case to the outside by opening the valve instantly, even if the charge current cannot be cut immediately in response to an increase of the inner pressure because of an error at the pressure-sensitive conductive rubber. 
     Furthermore, the seal type storage battery may seal the open portion of the outer case with the sealing sheet via a insulative gasket. 
    
    
     The above and further objects and features of the invention will more fully be apparent from the following detailed description in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross sectional view of the process for producing the sealing equipment of the present invention, which has the pressure-sensitive conductive rubber 
     FIG. 2 shows a cross sectional view of the finished sealing equipment of the present invention, which has having the pressure-sensitive conductive rubber. 
     FIG. 3 shows a partial cross sectional view of the main part of a nickel-cadmium storage battery having the seal equipment of FIG.  2 . 
     FIG. 4 shows the relationship of the pressure-sensitive conductive rubber of the present invention between compression pressure (load stress) and resistivity. 
     FIG. 5 shows a block diagram of the charging circuit for the seal type storage battery according to the present invention. 
     FIG. 6 shows a cross sectional view of the finished sealing equipment of another embodiment having the pressure-sensitive conductive rubber. 
     FIG. 7 shows a cross sectional view of the completed sealing equipment having the pressure-sensitive conductive rubber in accordance with another embodiment of the present invention. 
     FIG. 8 shows an enlarged cross sectional view of a valve of the sealing equipment shown in FIG.  7 . 
     FIG. 9 shows a cross sectional view of the valve, shown in FIG. 8, under pressure. 
     FIG. 10 shows a cross sectional view of the completed sealing equipment having the pressure-sensitive conductive rubber in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention applied to a nickel-cadmium seal type storage battery, is described in conjunction with FIG.  1 -FIG. 3 below. FIG.1 shows a cross sectional view of the process to produce the sealing equipment of the present invention having the pressure-sensitive conductive rubber, FIG. 2 shows a cross sectional view of the finished sealing equipment of the present invention having the pressure-sensitive conductive rubber, and FIG. 3 shows a partial cross sectional view of the main part of the nickel-cadmium storage battery having the sealing equipment of FIG.  2 . 
     1. Producing the Sealing Equipment 
     A pressure sensor is produced by preparing a lead  12  having a pressure-sensitive conductive rubber  11 (for example, Inastmar manufactured by Inaba Rubber Inc.), covering one side of the pressure-sensitive conductive rubber  11 , joined to the lead  12 , with an insulative sheet  13 , attaching an alkali-resisting rubber (for example ethylene-propylene diethylene rubber (EPDM)) sheet  14  to the other side of the pressure-sensitive conductive rubber that is not joined to the lead  12 . The pressure-sensitive conductive rubber  11  is mainly made of a pressure-sensitive conductive material having the characteristics that its resistivity decreased in accordance with the increase of the pressure (load stress) as shown in FIG.  4 . Also, at one end of the lead  12 , a pair of core wires  12   a ,  12   b  is exposed. 
     The next steps include, preparing a sealing sheet  15  with an opened hole  15   a  in the center, and an electrode cap  16  having a projection  16   a  in the center with a pierced hole  16   b  at its bottom, then disposing the pressure-sensor described above between the sealing sheet  15  and the electrode cap  16 . In the battery of this embodiment, the electrode cap  16  is a positive electrode. In this case, after the lead  12  of pressure-sensor is inserted into the pierced hole  16   b  of the electrode cap  16 , the pressure-sensitive conductive rubber  11  is positioined at the opened hole  15   a  of the sealing sheet  15 . Subsequently, the pressure-sensitive conductive rubber  11  is sandwiched between the sealing sheet  15  via the alkali-resisting rubber sheet  14  and the electrode cap  16  by caulking the periphery  15   b  of the sealing sheet  15  by bending. As described above, the pressure-sensitive conductive rubber  11 , which is sandwiched between the sealing sheet  15  and the electrode cap  16 , has the advantage that it can be located at a predetermined position with certainty. Further, since the pressure-sensitive conductive rubber  11  is disposed such that the opposite side of the surface facing the opened hole  15   a  is in surface contact with the electrode cap  16 , the electrode cap  16  can firmly receive the load applied to the surface facing the opened hole  15   a  and detect the pressure with accuracy. Next, producing a sealing equipment or assembly  10  by attaching an insulative gasket  17  around the caulked portion of the sealing sheet  15 . 
     2. Producing the Nickel-Cadmium Storage Battery 
     The process includes applying positive activating material slurry having a positive activating material mainly made of nickel hydroxide and adhesive on both sides of a core plate made of a punching metal, after drying, producing a nickel positive electrode plate by cutting it into a predetermined form. In addition, the process includes applying negative activating material slurry having a negative activating material mainly made of cadmium oxide and adhesive on both sides of a core plate made of a punching metal, after drying, producing a cadmium negative electrode plate by cutting it into a predetermined form. 
     Next, producing a rolled electrode agglomerate  21  by rolling the nickel positive electrode and the cadmium negative electrode with a separator between in a roll shape, then welding a positive collector  21   a  onto the positive core plate exposed at the upper surface of the rolled electrode agglomerate  21 , and welding a negative collector (not shown) onto the negative core plate exposed at the lower surface of the rolled electrode agglomerate  21 . Next, disposing the rolled electrode agglomerate  21  in an outer case  22  formed in a drum shape having a bottom (the outside of the bottom is a negative electrode terminal) made of iron with nickel plating. 
     The process then includes spot-welding a positive collector lead  21   b  extended from the positive collector  21   a  to the bottom of the sealing sheet  15  of the sealing equipment  10  described above. Next, after forming a circular groove portion  22   a  by drawing in the upper outline part of the outer case  22 , attaching the sealing equipment  10  in an opened portion of the outer case  22  by disposing the insulative gasket  17  onto the circular groove portion  22   a . Next, producing the nickel-cadmium storage battery  20  by caulking the opened edge portion  22   b  of the outer case  22  inwardly to seal the battery. 
     3. Connecting with the Charging Circuit. 
     Next, a process of connecting the nickel-cadmium storage battery  20 , produced as described above, with a charging circuit is described in conjunction with FIG. 5 below. 
     The charging circuit has a DC source  29 (also the DC source can be used as a current source commutating an AC source) for providing the charging current to the nickel-cadmium storage battery  20 , a switching circuit  27  for applying or cutting the current source  29  to the nickel-cadmium storage battery  20 , and a control circuit  25  for judging whether the inner pressure of the nickel-cadmium battery  20  is higher than a predetermined threshold or not and outputting a cutting signal to the switching circuit  27  when the inner pressure is higher than the threshold value. The switching circuit  27  may be as a semiconductor switching device such as a transistor or FET or the like. The switching circuit  27  makes contact with AC current or cuts the AC current in accordance with an On or Off signal provided from the control circuit  25 . The switching device applied to the semiconductor switching device can be used for a long period of time stably without breakdown even when used repeatedly with high-current. This is because the semiconductor switching device will not break due to the On and Off switching operation, which differs from a switching device having mechanical contact. 
     When the nickel-cadmium storage battery  20  is connected with the charging circuit described above, the positive side of the DC source is connected with the projection (positive terminal)  16   a  of the electrode cap  16  of the nickel-cadmium storage battery  20  via the switching circuit, and the negative side of the DC source is connected with the bottom (negative terminal) of the outer case  22 . On the other hand, control circuit  25  is connected with one core wire  12   a  of lead wire  12  which connects with the pressure-sensitive conductive rubber  11  and is extended from the pierced hole  16   b  of the electrode cap  16  to outside of the battery. The other core wire  12   b  is connected with connecting portion of the DC source  20  and the negative electrode of the battery  20 . Thereby, the battery  20  is connected with the charging circuit. 
     4. Charge Operation 
     Next, the operation of the charging circuit, connected with the storage battery  20  as mentioned above, is described below. First, switching on a DC source switch (not shown) places the switching circuit  27  in an ON state, then the DC source  29  provides a charging current (constant current) to the battery  20 . By keeping the charging current constant, the charged voltage rises, and when close to the end of the charging period, the inner pressure rises due to gas produced in the battery. When the inner pressure rises, the resisitivity of the pressure-sensitive rubber  11  drops as shown in FIG.  4 . 
     Thereby, the voltage value through the pressure-sensitive rubber  11  decreases. The control circuit  25  does not output the detecting signal when the voltage value is higher than the predetermined threshold so that charging is continued. The detecting signal is output to the switching circuit  27  when the voltage value is lower than the threshold value. Therefore, the switching circuit  27  is in an OFF state so that the charging current is not provided to the battery  20 . Accordingly, overcharge of the battery  20  is prevented. 
     5. Another embodiment 
     Although it is explained that the above-described embodiment has the pressure-sensitive conductive rubber  11  sandwiched between the sealing sheet  15  via the alkali-resisting rubber  14  and the electrode cap  16 , the pressure-sensitive conductive rubber can be disposed on the negative electrode side. In this case, as shown in FIG. 6, an insulative sheet  33  covers one side of a pressure-sensitive conductive rubber  31  joined to a lead  32 , and an alkali-resisting rubber sheet  34  is attached to the other side of the pressure-sensitive rubber which is not joined to the lead  32 , thereby producing a pressure-sensor. Next, the pressure sensor is disposed between a sealing sheet  35  and a electrode cap  36 . In this sealing equipment or assembly  30 , the electrode cap  36  is described as a negative electrode. 
     In this case, the assembly is formed by inserting one a core wire  32   a  of the lead  32 , which his extended from the pressure-sensitive rubber  31  into the pierced hole  36   b  of the electrode cap  36 , and disposing the pressure-sensitive conductive rubber  31  at an opened hole  35   a  of the sealing sheet  35  after welding the other core wire  32   b  to the bottom of the projection  36   a  of the electrode cap  36 . Subsequently, the pressure-sensitive conductive rubber  31  is sandwiched between sealing sheet  35  via the alkali-resisting rubber  34  and the electrode cap  36  by caulking the periphery  35   b  of the sealing sheet  35  by bending. Next, a sealing equipment  30  is produced by attaching an insulative gasket  37  around the caulked portion of the sealing sheet  35 . 
     Next, welding a negative collector onto a rolled electrode agglomerate produced the same as described above, and welding a positive collector onto the lower surface of the rolled electrode agglomerate, then, disposing the rolled electrode agglomerate in a cylindrical shaped and bottom closed outer case made of iron with nickel plating (in this case, the outer surface of the bottom is a positive electrode terminal). Then, spot-welding a positive collector lead, extended from the negative collector, to the bottom of the sealing sheet  35  of the sealing equipment  30 , after forming a drawn portion by drawing to the upper outline part of the outer case, attaching the sealing equipment in an opened portion of the outer case by disposing the insulative gasket  37  onto the drawn portion. Next, producing the nickel-cadmium storage battery by sealing the battery by caulking the opened edge portion of the outer case toward the inside. 
     In another embodiment of the nickel-cadmium storage battery, the other side of the core wire  32   b  of the lead  32  extended from the pressure-sensitive rubber  31  is welded to the bottom of the projection of the electrode cap  36 , so that the lead connected to the control circuit  25  (See FIG. 5) of the charging circuit is only the one side of core wire  32   a , thus making the connecting work easier. 
     Also, the sealing equipment  30  described above can be disposed in the bottom of the cylindrical outer case and a conventional sealing equipment can be disposed in the top of the outer case. In this case, the conventional sealing equipment has a structure that has a pressure-regulating valve having a valve to shut a hole for exhaust formed in center of a sealing sheet and a spring to bias the valve, between the sealing sheet and an electrode cap which is a positive electrode. Thus disposing the conventional sealing equipment, the pressure-regulating valve can work even if the pressure-sensitive conductive rubber  31  disposed in the sealing equipment  30  is not in operation, so that the safety of the battery is further improved. 
     As described above, according to the prevent invention the seal type storage battery has an alkali-resisting rubber sheet  14 ( 34 ) between a sealing sheet  15 ( 35 ) and an electrode cap  16 ( 36 ), wherein a pressure-sensitive conductive rubber  11  ( 31 ) is disposed in position of an opened hole  15   a ( 35   a ), which is an opened hole portion in the sealing sheet  15 ( 35 ) and sandwiched between the alkali-resisting rubber sheet  14 ( 34 ) and the electrode cap  16 ( 36 ), so that the pressure due to gas produced in the battery can convey to the pressure-sensitive conductive rubber  11 ( 31 ) via the alkali-resisting rubber  14 ( 34 ). Therefore the gas pressure produced in the battery can be conveyed immediately, and then it is instantly output as an electrical signal via a lead wire  12 ( 32 ), which is a lead, connected to the pressure-sensitive conductive rubber  11 ( 31 ). 
     Thereby, connecting the lead  12 ( 32 ) with a control circuit  25  of a charging circuit, so that the control circuit  25  can cut the charging current immediately by operation of a switching circuit  27  when the inner pressure of the battery exceeds a predetermined value input in the control circuit  25 . Therefore, the seal type storage battery  20 , connected with the charging circuit, can prevent overcharge. 
     Furthermore, the sealing equipment of another embodiment according to the present invention which has a pressure-sensitive conductive rubber and a pressure-regulating valve is shown in FIG.  7 . The sealing equipment  50  shown in FIG. 7 has the pressure-regulating valve  60  having a valve  61  and an elastic body  62  between a sealing sheet  55  and an electrode cap  56 . 
     The sealing sheet  55  and the electrode cap  56  are produced by pressing metal sheet. The sealing sheet  55  has a projection  55   c  projecting below in center, and has an open hole  55   a  in the center area of the lower surface of the projection  55   c . The electrode cap  56  has a projection  56   a  projecting upward in the center area. Here, the projection  56   a  is a positive electrode in this electrode cap  56 . In addition, the electrode cap  56  has an open pierced hole  56   b  in the side of the projection  56   a . The pierced hole  56   b  serves as a port for exhausting the gas in the battery case to the outside upon operation of the pressure-regulating valve  60 . Note that the lead wire  52 , which is connected with the pressure-sensitive conductive rubber  51  disposed inside of the valve  61  passes to the outside through the pierced hole  56   b . The sealing sheet  55  and the electrode cap  56  are laminated so as to form an interior space, and the valve  61  and the elastic body  62  are disposed in this space. In the sealing equipment  50 , after disposing the valve  61  and the elastic body  62  between the sealing sheet  55  and electrode cap  56 , the sealing sheet  55  and the electrode cap  56  are coupled by bending and then caulking the periphery  55   b  of the sealing sheet  55 . Alternatively the sealing sheet  55  and the electrode cap  56  may be connected by spot-welding at their peripheral portions. 
     The pressure-regulating valve  60  opens when the inner pressure of the battery case is higher than the predetermined pressure to prevent the extremely high pressure from breaking the outer case. The pressure-regulating valve  60  has the valve  61  which seals the opened hole  55   a  of the sealing sheet  55 , and the elastic body  62  which applies a force on the valve  61  in a direction toward the opened hole  55   a.    
     As shown in the enlarged cross sectional view of FIG. 8, the pressure-sensitive conductive rubber  51  is disposed inside of the valve  61 . The valve  61  shown in FIG. 8 has a sheet material  63  coupled to the lower end of the elastic body  62 , a cylindrical body  64  fixed on the lower surface of the periphery of the sheet material  63 , and the alkali-resisting rubber sheet  54  which is fixed on the bottom of the cylindrical body  64  and seals the bottom opening of the cylindrical body  64 . The pressure-sensitive conductive rubber  51  is disposed in the space formed by the sheet material  63 , the cylindrical body  64  and the alkali-resisting rubber sheet  54 . In the valve  61 , the pressure-sensitive conductive rubber  51  is located at a predetermined position by being fixed in the center portion of lower surface of the sheet material  63 . The sheet material  63  is preferably made of hard plastic or metal sheet. This type of sheet material  63  reduces errors caused by the responsiveness of the pressure-sensitive conductive rubber  51  for the gas pressure. In addition, in the valve  61 , the lead wire  52  connected with the pressure-sensitive conductive rubber  51  is extended outside of the valve  61 . The lead wire  52  is pulled out through the pierced hole  56   b  of the electrode cap  56  to outside of the battery. As shown in FIG. 7, the valve  61  is disposed such that it seals the open hole  55   a  of the sealing sheet  55  and the pressure-sensitive conductive rubber  51  faces the opened hole  55   a . Therefore the pressure-sensitive conductive rubber  51  can detect a rise of the inner pressure of the battery. The pressure detecting signal detected by the pressure-sensitive conductive rubber  51  is outputted via the lead wire  52 . 
     In addition, in the valve  61  shown in FIG. 8, the inner shape of the cylindrical body  64  is larger than the outer shape of the pressure-sensitive conductive rubber  51  such that the pressure-sensitive conductive rubber  51  does not contact the cylindrical body  64 . As for the valve  61 , the height of the cylindrical body  64  is higher than the thickness of the alkali-resisting rubber sheet  54  so that a sufficient gap is formed between the pressure-sensitive conductive rubber  51  and the alkali-resisting rubber sheet  54 . The gap between the pressure-sensitive conductive rubber  51  and the alkali-resisting rubber sheet  54  is designed to be 0-2 mm, preferably 0.2-1 mm, most preferably 0.5 mm. In valve  61 , given the inner pressure of the battery rising and the alkali-resisting rubber sheet  54  compressed, as shown in FIG. 9, the alkali-resisting rubber sheet  54  is deformed and the pressure-sensitive conductive rubber  51  is compressed, and thereby the pressure is detected. In a normal battery state, the surface of the pressure-sensitive conductive rubber  51  does not contact the cylindrical body  64  or the alkali-resisting rubber sheet  54 , so that the valve  61  of this structure can reliably prevent erroneous detection of the inner pressure. Also, the pressure-sensitive conductive rubber  51  may be disposed so as to contact the cylindrical body  64  or the alkali-resisting rubber sheet  54 . 
     One end of the elastic body  62  is joined to the valve  61 , the other end is joined to the bottom of the projecting portion of the electrode cap  56 . The elastic body  62  impels the valve toward the opened hole  55   a . The elastic body  62 , shown in the figure, is a coil spring with elastic line-shaped material. The elastic body  62  is fixed to the valve  61  and the electrode cap  56  by welding or adhering. Thus the elastic body  62  disposed between the sealing sheet  55  and the electrode cap  56  holds the valve  61  in a predetermined position, and seals the opened hole  55   a  by pushing and compressing the valve  61  to the bottom of projection potion of the sealing sheet  55 . The elastic body  62  has an optimal elastic force to permit opening of the valve  61  when the inner pressure of the battery is higher than a predetermined pressure. 
     In another embodiment, a rubbery elastic body comprises the elastic body as shown in FIG.  10 . The sealing equipment  70  shown in FIG. 10 has a pressure-regulating valve  80 , which includes a valve  81  having a pressure-sensitive conductive rubber  71  disposed inside. The elastic body  82  is disposed between the sealing sheet  75  and the electrode cap  76 . In the valve  81 , the pressure-sensitive conductive rubber  71  is fixed to the lower surface of sheet material  83 , which is joined to the lower end of the elastic body  82 , and disposed in the space formed by the sheet material  83 , the cylindrical body  84  and the alkali-resisting rubber sheet  74 . The valve  81  is positioned to seal the open hole  75   a  of the sealing sheet  75  via the elastic body  82 . For example, the rubbery elastic body, which is the elastic body  82 , can be fixed in a predetermined position by being adhered to the valve  81  and the electrode cap  76 . The lead wire  72 , connected with the pressure-sensitive conductive rubber  71 , is extended through the pierced hole  76   b  of the electrode cap  76  to the outside of the battery, and outputs pressure detecting signal detected in the pressure-sensitive conductive rubber  71 . In the sealing equipment  70 , the sealing sheet  55  and the electrode cap  56  are also coupled by caulking the periphery  75   b  of the sealing sheet  75  by bending. 
     Although it is not shown, the sealing equipment shown in FIG.  7  and FIG. 10 can be attached to the open portion of the outer case after the insulative gasket is attached to the periphery of the caulked portion of the sealing sheet. Then the battery is sealed by caulking the opened edge portion of the outer case inwardly. In addition, as shown in FIG.  7  and FIG. 10, connecting the lead wire  52  ( 72 ) extended from the pierced hole  56   b  ( 76   b ) of the electrode cap  56  ( 76 ) is connected outside of the battery with the charge circuit (not shown). One core wire  52   a  ( 72   a ) of the lead wire  52  ( 72 ) is connected with the control circuit of the charge circuit, and another core wire  52   b  ( 72   b ) is connected to the connector of the power source and the negative electrode of the battery. 
     Although it is not shown, in addition, when the electrode cap be used as a negative electrode, one lead wire can be extended from the pierced hole of the electrode cap to the outside of the battery, and another core wire of the lead wire can be connected electrically in the electrode cap by welding or the like, in the sealing equipment. The seal type storage battery makes connecting work easier, because only one core wire of the lead wire should be connected with the control circuit of the charge battery. 
     The sealing equipment described above outputs a pressure detecting signal to the charge circuit via the lead extended to outside by detecting a rise of the inner pressure of the battery by the pressure-sensitive conductive rubber disposed inside of the valve. The control circuit of the charge circuit then cuts the charge current to prevent overcharge in the seal type storage battery, when the inner pressure of the battery becomes higher than a predetermined pressure. In addition, the sealing equipment prevents the inner pressure of the battery to become extremely high with the pressure-regulating valve opening the valve, even the control circuit does not cut the charge current in some situations when the inner pressure is higher than the predetermined pressure. Therefore, predetermined pressure with the pressure-regulating valve opening is set higher than the predetermined pressure with the control circuit cutting the charge current. 
     States of the battery attached with the sealing equipment described above, in which the charge current is cut by the pressure detecting signal from the pressure-sensitive conductive rubber and the gas is exhausted by the pressure-regulating valve by opening the valve, was experimented below 
     EXAMPLE 1 
     The batteries A-D (500 mAh) having the sealing equipment shown in FIG. 7 were produced. The inner pressures for stopping charging in response to the pressure detecting signal detected by the pressure-sensitive conducting rubber were set at 0.6 MPa, 0.8 MPa, 1.0 MPa and 1.2 MPa respectively. In addition, in the batteries A-D, the inner pressure to operate the pressure-regulating valve was set at 1.5 MPa. These batteries were charged with the charge current 10 A. The charge current of all batteries A-D were cut when the inner pressure of the batteries reached the predetermined pressures, which were 0.6 MPa, 0.8 MPa, 1.0 MPa and 1.2 MPa respectively. 
     EXAMPLE 2 
     Next, in the batteries A-D, the control circuit, which stops charging in response to the pressure detecting signal detected by the pressure-sensitive conducting rubber, was turned off, and these batteries A-D were charged with the charge current 10 A. It was confirmed that the gas was exhausted by the pressure-regulating valve by opening the valve, when the inner pressure became 1.5 MPa or over 1.5 MPa. 
     Here, in the embodiments described above, although the present invention is explained to apply to the nickel-cadmium storage batteries, this invention can also apply to a nickel metal hydride seal type storage battery or the like. 
     As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims, or equivalence of such metes and bounds, are therefore intended to be embraced by the claims.