Abstract:
Methods and apparatus for computing residual battery capacity of a battery pack enable: storing a plurality of correction coefficients for calculating said residual battery capacity for said battery pack at a plurality of pre-set temperatures; detecting a temperature of a battery cell of said battery pack; and at least one of: (i) if a correction coefficient associated with said detected temperature is stored, said residual battery capacity is computed based on said correction coefficient and a voltage of said battery cell; and (ii) if said correction coefficient associated with said detected temperature is not stored, stored correction coefficients associated with preset temperatures above and below said detected temperature are used to compute a correction coefficient associated with said detected temperature and said residual battery capacity is computed based on said computed correction coefficient and said voltage of said battery cell.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a divisional application of U.S. patent application No. 09/517,886, filed Mar. 3, 2000, entitled BATTERY PACK, METHOD FOR CHARGING/DISCHARGING COUNTING AND METHOD FOR SETTING RESIDUAL CAPACITY OF THE BATTERY PACK, the entire disclosure of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a battery pack, a method for charging/discharging counting and a method for setting the residual capacity of the battery pack.  
           [0003]    Up to now, there has been furnished a battery pack having battery cells as secondary batteries, such as lithium ion cells, NiCd cells or nickel hydrogen cells.  
           [0004]    The battery pack usually includes a micro-computer for performing calculations of the residual battery capacity of the battery cells or communication with electronic equipment having the battery cell as a power source, peripherals of the micro-computer and a battery cell status detection circuit necessary in carrying out calculations of the residual battery capacity.  
           [0005]    The number of charging/discharging cycles of the battery pack is not infinite. On the other hand, the maximum number of charging/discharging cycles, capable of maintaining practically tolerable charging/discharging characteristics, is determined to some extent depending on the type of the battery cell.  
           [0006]    In the conventional battery pack, it has been difficult for the user to recognize the maximum number of charging/discharging cycles, capable of maintaining practically tolerable charging/discharging characteristics, that is the service life of the battery cell. The user is only able to recognize the approaching end of service life of the battery cell, as the charging/discharging is repeated, on recognizing that battery capacity is decreasing at a faster rate even though the cell has been charged to its full capacity.  
           [0007]    In order to permit the user to recognize the service life of the battery cell easily, the present Applicant has proposed in Japanese Laying-Open Patent H-9-243718 a battery pack and a method for displaying the state of the battery, referred to below as the first disclosed technique.  
           [0008]    The first disclosed technique, shown in FIG. 1, detects that the voltage of the battery cell has exceeded the first threshold voltage, and further detects that the voltage has become lower than a second threshold voltage. The first disclosed technique counts the number of charging/discharging cycles on the assumption that one cycle of charging or discharging occurs when one of the voltage states is detected after detecting the other voltage state.  
           [0009]    On the other hand, in a battery pack having plural battery cells, the maximum charging voltage differs from one battery cell to another. Thus, the present Assignee proposed in Japanese Laying-Open Patent H-9-285026 a battery charging method and apparatus and a battery pack, referred to below as the second disclosed technique.  
           [0010]    In the second disclosed technique, the residual battery capacity is computed based on the charging of the battery cell and the initial value (e.g., voltage) stored in the battery cell.  
           [0011]    The battery pack is loaded on an electronic equipment, such as a video camera device, to furnish the current to the equipment. If the power source has become depleted, the battery pack is charged. This battery pack has a battery cell, as a chargeable and dischargeable secondary battery, and a micro-computer for detecting the voltage of the battery cell to compute the residual battery capacity.  
           [0012]    Since the residual battery capacity is varied appreciably with temperature, it is computed using a temperature dependent coefficient of the battery cell, as stated for example in Japanese Laying-Open Patent H-9-297166. This temperature dependent residual capacity correction coefficient is referred to below as the correction coefficient. Since this correction coefficient differs in magnitude with temperature, the correction coefficient for each increment of 10° C. is stored in a nonvolatile memory, such as ROM. The micro-computer computes the residual battery capacity using the correction coefficient stored in the non-volatile memory and which corresponds to the current temperature.  
           [0013]    However, in the first disclosed technique, count-up is made only when the battery cell voltage falls below the second threshold value, such that, if the battery cell is charged before the cell voltage falls below the second threshold value, count-up is not made. Thus, there is raised a problem that, even though the battery cell is deteriorated due to charging/discharging, the cycle is not counted correspondingly. Although it may be attempted to set the second threshold to a higher value, count-up then occurs while as yet there is left sufficient battery power, such that count-up cannot be made correctly.  
           [0014]    On the other hand, the conventional battery pack is designed so that, once the charging is made up to 90%, this 90% charging is deemed to be full charging, in order to absorb errors in current detection etc in charging. Thus, in the battery pack, the integrated value of the residual battery capacity on 90% charging is previously stored in the ROM and, if it is verified that charging up to 90% has been made, the battery capacity is set as the integrated residual battery capacity value.  
           [0015]    However, if the charging/discharging is repeated, the battery cell is deteriorated, such that the battery capacity that can be retrieved actually is decreased. With this battery cell deterioration, the integrated residual battery capacity on 90% charging is lowered, thus producing a gap between the integrated residual battery capacity on 90% charging stored in the non-volatile memory and the actual integrated residual battery capacity.  
           [0016]    If the residual battery capacity is computed based on the initial value stored in the battery cell at the time of charging, in accordance with the second disclosed technique, there is presented a problem that the residual battery capacity cannot be computed correctly.  
         SUMMARY OF THE INVENTION  
         [0017]    It is therefore an object of the present invention to provide a battery pack in which, if a battery cell is deteriorated due to charging/discharging, the number of cycles is counted depending on the deterioration, and in which the residual battery capacity can be accurately set depending on the deterioration.  
           [0018]    It is another object of the present invention to provide a method for counting the number of charging/discharging cycles in the battery pack, and a method for setting the residual battery capacity of the battery pack.  
           [0019]    In one aspect, the present invention provides a battery pack including voltage detection means for detecting the voltage of a battery cell, storage means for storing a correction coefficient for calculating the residual battery capacity for a pre-set temperature, temperature detection means for detecting the temperature of the battery cell and computing means. This computing means operates so that, if a correction coefficient associated with a temperature detected by the temperature detection means is stored in the storage means, the computer means reads out the correction coefficient to compute the residual battery capacity based on the correction coefficient and the voltage detected by the voltage detection means. The computing means also operates so that, if a correction coefficient associated with a temperature detected by the temperature detection means is not stored in the storage means, the computer means reads out a correction coefficient associated with a pre-set temperature ahead and at back of the detected temperature from the storage means to compute a correction coefficient associated with the detected temperature based on each readout correction coefficient to compute the residual battery capacity based on the computed correction coefficient and the voltage detected by the voltage detection means.  
           [0020]    In another aspect, the present invention provides a method for computing the residual battery capacity of a battery pack associated with a pre-set temperature including storing a correction coefficient for calculating the residual battery capacity for a pre-set temperature, and detecting the temperature of the battery cell, wherein, if a correction coefficient associated with a temperature detected by the temperature detection means is stored in the storage means, the correction coefficient is read out and the residual battery capacity is computed based on the correction coefficient and the voltage detected by the voltage detection means. Also, if a correction coefficient associated with the detected temperature is not stored in the storage means, a correction coefficient associated with a pre-set temperature ahead and at back of the detected temperature is read out from the storage means to compute a correction coefficient associated with the detected temperature based on each read-out correction coefficient to compute the residual battery capacity based on the computed correction coefficient and the voltage detected by the voltage detection means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 illustrates the manner of counting the number of cycles in the related art.  
         [0022]    [0022]FIG. 2 is a graph showing changes in linear characteristics of the integrated residual battery capacity in case the battery cell is deteriorated.  
         [0023]    [0023]FIG. 3 illustrates the state of loading a battery pack embodying the present invention on a video camera device.  
         [0024]    [0024]FIG. 4 is a perspective view of a battery pack.  
         [0025]    [0025]FIG. 5 is a perspective view showing the back side of the battery pack.  
         [0026]    [0026]FIG. 6 is a perspective view of a battery loading unit provided in the video camera device.  
         [0027]    [0027]FIG. 7 illustrates the circuit structure of the battery pack.  
         [0028]    [0028]FIG. 8 illustrates the relation between the voltage level and the battery voltage level.  
         [0029]    [0029]FIG. 9 is a flowchart for illustrating the operating contents of the battery voltage level setting and the cycle counting.  
         [0030]    [0030]FIG. 10 illustrates the counting of the number of cycles.  
         [0031]    [0031]FIG. 11 illustrates an example of changes in the integrated residual battery capacity with respect to the number of cycles.  
         [0032]    [0032]FIG. 12 illustrates another example of changes in the integrated residual battery capacity with respect to the number of cycles.  
         [0033]    [0033]FIG. 13 shows a circuit structure of a battery pack.  
         [0034]    [0034]FIG. 14 is a flowchart for illustrating the main routine in calculating the correction coefficient.  
         [0035]    [0035]FIG. 15 is a flowchart for illustrating the subroutine in calculating the correction coefficient.  
         [0036]    [0036]FIG. 16 illustrates the calculated results of the correction coefficient.  
         [0037]    [0037]FIG. 17 illustrates the state of storage of the correction coefficients for each increment of 2.5° C. in a ROM.  
         [0038]    [0038]FIG. 18 illustrates step widths of correction coefficients in the related art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Referring to the drawings, preferred embodiments of the present invention will be explained in detail.  
         [0040]    The present invention is applicable to, for example, a battery pack  1  shown in FIG. 3. This battery pack  1  is loaded on a battery loading unit  3  of, for example, a video camera device  2 , to supply the power to the video camera device  2 . On the other hand, the battery pack  1  can be loaded on a charging device, not shown, for charging.  
         [0041]    The battery pack  1  includes a casing  19 , as shown in FIG. 4. The casing  19  accommodates therein a battery cell, not shown.  
         [0042]    The casing  19  of the battery pack  1  is formed of, for example, a synthetic resin material. In both width-wise lateral sides of the casing  19  are formed guide grooves  26 ,  26  for guiding the loading relative to the battery loading unit  3 . The guide grooves  26 ,  26  in the respective lateral sides are opened at ends thereof in a bottom surface  24  (FIG. 5) of the casing  19  and are formed side-by-side along the length of the casing  19 .  
         [0043]    On both width-wise lateral sides of the casing  19  on a front surface  20  along the loading direction relative to the battery loading unit  3 , there are provided a first input/output terminal  21  and a second input/output terminal  22 . At a mid portion along the width-wise direction, there is provided a communication terminal  23 .  
         [0044]    The first and second input/output terminals  21 ,  22  furnish the power to a main body portion of the video camera device  1  through the battery loading unit  3 . The communication terminal  23  outputs information signals, such as residual power of the battery cell, to the main body portion of the video camera device  1 . The ends of the input/output terminals  21 ,  22  and the communication terminal  23  facing outwards are positioned in substantially rectangular recesses formed in the front surface  20  of the casing  19  and thereby prevented from being destroyed due to abutting contact on other portions of the battery loading device other than the connection terminals.  
         [0045]    In the front side of the bottom surface  24  of the casing  19 , that is in the front surface along the lengthwise direction, there are formed a pair of control recesses  28 ,  29 . These control recesses  28 ,  29  are formed line-symmetrically with respect to a mid line, not shown, in the width-wise direction, as shown in FIG. 3. In loading, these control recesses  28 ,  29  are engaged by control projections, not shown, of the battery loading unit  3 , to limit the tilt in the width-wise direction of the bottom surface  24  of the casing  19  relative to the battery loading unit  3 .  
         [0046]    These control recesses  28 ,  29  are each substantially of an L-shape made up of a first portion perpendicular to the bottom surface  24  of the casing  19  and a second portion perpendicular to this first portion, as shown in FIG. 5.  
         [0047]    In a mid portion of the bottom surface  24  of the casing  19  is formed a substantially rectangular discriminating recess  30  for discriminating whether or not the battery loading unit is an appropriate unit.  
         [0048]    The discriminating recess  30  is positioned at a position on a mid line in the width-wise direction of the casing  19  lying closer to the front surface  20  from the mid point of the bottom surface  24  of the casing  19 . In the bottom surface within the discriminating recess  30  is formed a substantially rectangular discriminating groove  32  in continuation to both longitudinal ends of the recess  30  substantially on the centerline along the width-wise direction of the casing  19 . On both sides in the width-wise direction of the bottom surface  24  of the casing  19 , there are formed steps in the discriminating recess  30 . The discriminating recess  30  has a width-wise size of W 0 .  
         [0049]    Adjacent to the communication terminal  23  is formed a first guide groove  34  extending parallel to the longitudinal direction of the casing  19 . This first guide groove  34  has its one end opened in the front surface  20  of the casing  19 , while having its other end formed in continuation to the discriminating recess  30 . Adjacent to the front surface  20  of the casing  19  is formed in the first guide groove  34  a step  35  different in depth in the depth-wise direction corresponding to the direction perpendicular to the bottom surface  24  of the casing  19 . This first guide groove  34  guides the battery pack loading direction relative to the battery loading unit  3 .  
         [0050]    In the bottom surface  24  of the casing  19  is formed a second guide groove  36  facing the first guide groove  34  with the communication terminal  23  in-between. This second guide groove  36  is formed parallel to the longitudinal direction of the bottom surface  24  of the casing  19  so that its one end is opened in the front surface  20  of the casing  19 .  
         [0051]    In both lateral sides in the width-wise direction of the casing  19  are formed control grooves  37 ,  37  adjacent to the first and second input/output terminals  21 ,  22 . The control grooves  37 ,  37  are opened in the front surface  20 , while extending substantially parallel to the bottom surface  24  of the casing  19 , for limiting the tilt in the width-wise direction of the bottom surface  24  relative to the battery loading unit  3 .  
         [0052]    In the bottom surface  24  of the casing  19  are formed a first lock recess  38  and a second lock recess  39  engaged by the battery loading unit  3  on loading the battery pack on the battery loading unit  3 . The first lock recess  38  is substantially rectangular in profile and is positioned neighboring to the discriminating recess  30  on a width-wise mid line of the casing  19 . The second lock recess  39  is substantially rectangular in profile and is slightly larger in size than the first lock recess  38 . The second lock recess  39  is formed close to the back side looking along the loading direction on a width-wise mid line of the casing  19 .  
         [0053]    On the other hand, the battery loading unit  3  (FIG. 6) provided on the camera device  2  is slightly larger in size than the bottom surface  24  of the casing  19 . The battery loading unit  3  is provided on both lateral sides facing both width-wise lateral sides of the battery pack  1  with a pair of guide projections  47  engaging in the guide grooves  26 ,  26  of the battery pack  1 .  
         [0054]    When loading the battery pack on the battery loading unit  3 , the guide projections  47  extend into the guide grooves  26 ,  26  of the casing  19  to guide the extension direction and to hold the battery pack  1  with the bottom surface  24  of the casing  19  substantially parallel to a setting surface  45 .  
         [0055]    On the side of an abutting surface  46  of the battery loading unit  3  facing the front surface  20  of the battery pack  1  is formed a terminal portion  44 . This terminal portion  44  is made up of first to third connection terminals  51  to  53  and a cover member  60 .  
         [0056]    The first and second connection terminals  51 ,  52  are provided on both sides along the width of the battery loading unit  3  for connection to the first and second input/output terminals  21 ,  22 , respectively. The third connection terminal  53  is positioned at a mid point in the width-wise direction of the battery loading unit  3  for connection to the communication terminal  23  of the battery pack  1 . The first to third connection terminals  51  to  53  are provided on the abutting surface  46  of the battery loading unit  3  parallel to the bottom surface  24  and to the longitudinal of the battery pack  1 .  
         [0057]    The cover member  60  is mounted on the battery loading unit  3  for rotation in the direction indicated by arrows a 1 , a 2  to protect the first to third connection terminals  51  to  53  from outside.  
         [0058]    The cover member  60  is formed of, for example, a synthetic resin material, and is made up of a substantially rectangular protection piece  61  and supporting pieces  62 ,  62  for supporting the protection piece  61 . The surface of the protection piece  61  of the cover member  60  facing the setting surface  45  of the battery loading unit  3  is formed with a surface inclined with respect to the thickness direction. When the battery pack  1  is loaded on the battery loading unit  3 , the casing  19  compresses against the protection piece  61  to permit the cover member  60  to be rotated easily in the direction indicated by arrow a 2 . The supporting pieces  62 ,  62  of the cover member  60  are supported by the abutting surface  46  of the battery loading unit  3  for rotation about a pivot shaft, not shown. A torsion coil spring, not shown, is provided on the outer periphery of the pivot shaft of the cover member  60 . This torsion coil spring has its one end retained by the abutting surface  46  of the battery loading unit  3 , while having its other end retained by the supporting pieces  62 ,  62  of the cover member  60 . Thus, the cover member  60  is biased in the direction indicated by arrow a 1  under the elasticity of the torsion coil spring to overlie the first to third connection terminals  51  to  53 .  
         [0059]    The battery loading unit  3  is formed with a pair of control projections  65 ,  66  astride the abutting surface  46  and the setting surface  45 , substantially line-symmetrically with respect to the centerline, so as to be engaged in the control recesses  28 ,  29  of the battery pack  1 .  
         [0060]    These control projections  65 ,  66  are each substantially of an L-shape made up of a first portion perpendicular to the setting surface  45  and a second portion perpendicular to this first portion. These control projections  65 ,  66  restrict the bottom surface  24  of the battery pack  1  from being tilted in the width-wise direction with respect to the setting surface  45  of the battery loading unit  3 .  
         [0061]    The battery loading unit  3  is also formed with a first guide projection  68 , near the third connection terminal  53 , astride the abutting surface  46  and the setting surface  45 , for guiding the insertion of the battery pack  1 . This first guide projection  68  is formed parallel to the longitudinal direction of the setting surface  45  for engaging in the first guide groove  34  of the bottom surface  24  of the battery pack  1  being loaded, as shown in FIG. 4.  
         [0062]    The battery loading unit  3  is also formed with a second guide projection  54 , astride the abutting surface  46  and the setting surface  45 , for guiding the loading direction of the battery pack  1 . The second guide projection  54  is formed as one with the setting surface  45  parallel to its longitudinal direction. This second guide projection  54  is engaged in the second guide groove  36  of the battery pack  1  to guide the loading direction.  
         [0063]    Both lateral sides along the width of the battery loading unit  3  are formed as one with control pawls  55 ,  55  engaged in the control grooves  37 ,  37 . The control pawls  55 ,  55  are parallel to the setting surface  45  and to the longitudinal direction of the battery pack  1 .  
         [0064]    At a mid portion of the setting surface  45  of the battery loading unit  3 , there is formed a discriminating projection  56  engaged in the discriminating recess  30  of the battery pack  1 . This discriminating projection  56  is substantially rectangular in profile. The distal end of the discriminating projection  56  is formed as one with a discriminating lug  56  engaged in the discriminating groove  32  of the battery pack  1 . This discriminating projection  56  has a width W 1  parallel to the width of the setting surface  45  smaller than the width W 0  of the discriminating recess  30  of the battery pack  1 , so that the discriminating projection  56  can be inserted into the discriminating recess  30 , as shown in FIG. 6. The discriminating projection  56  is formed at a position spaced a distance L 1  from the abutting surface  46  in the vertical direction.  
         [0065]    With the above-described structure of the battery loading unit  3 , the battery pack  1  can be loaded on the battery loading unit  3 .  
         [0066]    The charging device for charging the battery pack  1  is also provided with a battery loading unit constructed similarly to the battery loading unit  3 .  
         [0067]    The circuit structure of the battery pack  1  is hereinafter explained.  
         [0068]    Referring to FIG. 7, the battery pack  1  is provided with lithium ion batteries  171 ,  172 , as two serially connected battery cells, a first input/output terminal  121  connected to the positive terminal of the lithium ion battery  171  through a resistor R 103  and a second input/output terminal  122  connected to the negative electrode of the lithium ion battery  172 .  
         [0069]    The lithium ion batteries  171 ,  172  are charged or discharged through the first and second input/output terminals  121 ,  122 . The lithium ion batteries  171 ,  172  are connected in parallel with serially connected resistors R 101 , R 102 . That is, the positive electrode of the lithium ion battery  171  is connected to the resistor R 101 , while the negative electrode of the lithium ion battery  172  is connected to the resistor R 102 .  
         [0070]    The battery pack  1  is also provided with a current detection circuit  173  for detecting the current flowing through the resistor R 103 , an A/D converter  174  for digitizing the charging/discharging current value and the battery voltage value and a central processing unit (CPU)  175  for counting the number of charging/discharging cycles, referred to below as the number of cycles, and calculating the residual battery capacity. The battery pack  1  also includes a random access memory (RAM)  176  for transiently storing the current and voltage levels of the lithium ion batteries  171 ,  172  and a read-only memory (ROM)  177  having stored therein the control program for the CPU  175 .  
         [0071]    The current detection circuit  173  detects the current flowing in the resistor R 103  during charging or discharging to route the detected current to an A/D converter  174 .  
         [0072]    The A/D converter  174  digitizes the current value from the current detection circuit  173  to route the digitized current to the CPU  175 . The A/D converter  174  digitizes the voltage value of a connection terminal of resistors R 101 , R 102 , referred to below as a mid point connection terminal, that is the divided voltage value R 102 /(R 101 +R 102 ) of the terminal voltage of the series connected lithium ion batteries  171 ,  172 , to route the digitized voltage to the CPU  175 .  
         [0073]    The CPU  175  is provided with a counter  175   a  for counting the number of cycles. The CPU  175  divides the voltage level of the mid point connection terminal X into four stages of the battery voltage level 0 to the battery voltage level 3 (FIG. 8), with the highest battery voltage level being a battery voltage level 3 and with the lowest battery voltage level being a battery voltage level 0. The CPU  175  counts up one using counter  175   a  each time the battery voltage level is decremented by one.  
         [0074]    Specifically, the CPU  175  sets the battery voltage level in accordance with the flowchart shown in FIG. 9 to count the number of cycles.  
         [0075]    When the current detection circuit  173  detects the charging current of the discharging current, the CPU  175  moves to step ST 1  to capture the battery voltage at the mid point connection terminal X through the A/D converter  174 . The CPU then advances to step ST 2 .  
         [0076]    At step ST 2 , the CPU  175  verifies whether charging is going on or discharging is going on, based on a detection output of the current detection circuit  173 . If the CPU  175  verifies that the charging is going on, the CPU advances to step ST 3 . If the CPU  175  verifies that the discharging is going on, the CPU advances to step ST 9 .  
         [0077]    At step ST 3 , the CPU  175  checks whether or not the voltage level at the mid point connection terminal X is higher than the battery voltage level  3 . If the result is YES, the CPU  175  advances to step ST 4  and, if otherwise, to step ST 5 .  
         [0078]    At step ST 4 , the CPU  175  assumes the current voltage level to be the battery voltage level 3 to write the level in the RAM  176  to terminate the processing.  
         [0079]    At step ST 5 , the CPU  175  checks whether or not the voltage level at the mid point connection terminal X is higher than the battery voltage level 2. If the result is YES, the CPU  175  advances to step ST 6  and, if otherwise, to step ST 7 .  
         [0080]    At step ST 6 , the CPU  175  assumes the current voltage level to be the battery voltage level 2 to write the level in the RAM  176  to terminate the processing.  
         [0081]    At step ST 7 , the CPU  175  checks whether or not the voltage level at the mid point connection terminal X is higher than the battery voltage level 1. If the result is YES, the CPU  175  advances to step ST 8  and, if otherwise, the CPU  175  assumes the current voltage level to be the battery voltage level 0 and writes the level in the RAM  176  to terminate the processing.  
         [0082]    At step ST 8 , the CPU  175  assumes the current voltage level to be the battery voltage level 1 to terminate the processing.  
         [0083]    At step ST 9 , to which the CPU  175  advances when it is verified that discharging is going on at step ST 2 , the CPU  175  verifies whether or not the voltage level at the mid point connection terminal X is lower than the battery voltage level  1 , that is whether or not the battery voltage level has transferred from 1 to 0. If the result of this check is YES, the CPU advances to step ST 10  and, if otherwise, to step ST 11 .  
         [0084]    At step ST 10 , the CPU  175  assumes that the current battery voltage is the battery voltage level 0 to write the level in the RAM  176 . The CPU then advances to step ST 15 .  
         [0085]    At step ST 11 , the CPU  175  verifies whether or not the voltage level at the mid point connection terminal X is smaller than the battery voltage level 2, that is whether or not the battery voltage level has transferred from level 2 to level 1. If the result of this check is YES, the CPU moves to step ST 12  and, if otherwise, to step ST 13 .  
         [0086]    At step ST 12 , the CPU  175  assumes that the current battery voltage is the battery voltage level 1 to write the level in the RAM  176 . The CPU then advances to step ST 15 .  
         [0087]    At step ST 13 , the CPU  175  verifies whether or not the voltage level at the mid point connection terminal X is smaller than the battery voltage level  3 , that is whether or not the battery voltage level has transferred from level  3  to level 2. If the result of this check is YES, the CPU moves to step ST 14  and, if otherwise, it terminates the processing.  
         [0088]    At step ST 14 , the CPU  175  assumes that the current battery voltage is the battery voltage level 0 to write the level in the RAM  176 . The CPU then advances to step ST 15 .  
         [0089]    At step ST 15 , the CPU  75  counts up the number of cycles of the counter  175   a  by ⅓ to terminate the processing.  
         [0090]    That is, the CPU  175  detects to which of the battery voltage levels the voltage level belongs at the time of charging and discharging, and counts up by ⅓ each time the voltage level is lowered due to discharging, such that any one of the three threshold values is exceeded. Thus, if the lithium ion secondary batteries are charged/discharged frequently, the number of cycles can be counted up responsive to the states of actual deterioration of the lithium ion secondary batteries.  
         [0091]    The number of cycles is counted up each time the battery voltage level transfers from 3 to 2, from 2 to 1 and from 1 to 0. If, after the battery voltage level is 3 by charging, discharging occurs again, the number of cycles is counted up each time the battery voltage level transfers from 3 to 2 and from 2 to 1. If, charging takes place again at the battery voltage level equal to 1, so that the battery voltage level transfers to 3, the discharging then taking place again, the number of cycles is counted up each time the battery voltage level number is decremented. Meanwhile, one-third of the number of cycles shown in FIG. 10 represents the actual number of cycles.  
         [0092]    If the number of cycles of the counter  175   a  of the CPU  175  exceeds the maximum number of charging/discharging counts of the lithium ion batteries  171 ,  172 , it may be assumed that the lithium ion batteries  171 ,  172  have been deteriorated and the service life thereof has come to an end.  
         [0093]    In the present embodiment the battery voltage level is divided into four stages. Alternatively, the battery voltage level can be divided into n (&gt;2) stages and the number of cycles can be counted up each time one of the (n−1) thresholds has been exceeded.  
         [0094]    Also, in the present embodiment, the number of cycles is counted up as the voltage level is lowered, that is during discharging. Alternatively, the number of cycles can be counted as the voltage level is increased, that is during charging. Still alternatively, the number of cycles can be counted both during charging and discharging.  
         [0095]    The integrated residual battery voltage value, stored in the ROM  177 , is hereinafter explained. The integrated residual battery voltage [mAh] that can be discharged at the time of 90% charging, referred to below as the 90% integrated residual value, is stored in the ROM  177  for each cycle number, as shown in FIG. 11. Here, the 90% integrated residual value is stored at an interval of 10 cycles, specifically for the numbers of cycles from 0 to 10, from 11 to 20, from 21 to 30,  
         [0096]    For example, the 90% integrated residual value from 11 to 20 cycles is the 90% integrated residual value for 0 to 10 cycles less the deteriorated capacity of the lithium ion batteries  171 ,  172  caused by the 11 to 20 cycles. Similarly, the 90% integrated residual value from 11 to 20 cycles is the 90% integrated residual value for 0 to 10 cycles less the deteriorated capacity of the lithium ion batteries  171 ,  172  caused by the 21 to 30 cycles.  
         [0097]    Thus, if the residual battery value is computed in discharging, based on the initial value of the integrated residual battery value, the battery pack  1  is able to make calculations using the 90% integrated residual value as set based on the number of cycles. That is, since the 90% integrated residual value, as an initial value for calculating the residual battery value, can be set in keeping with the deterioration due to charging/discharging of the lithium ion batteries  171 ,  172 , the residual battery value can be calculated more accurately than with the conventional method.  
         [0098]    The 90% integrated residual value may also be stored in the ROM  177  every  32  cycles, as shown in FIG. 12. For example, the non-corrected 90% integrated residual value is stored as the reference capacity if the number of cycles is not less than 0 and not more than 32, the reference capacity less the correction data (constant value) is stored if the number of cycles is not less than 32 and not more than 64, the reference capacity less twice the correction data is stored if the number of cycles is not less than 48 and not more than 96 and the reference capacity less thrice the correction data is stored if the number of cycles is not less than 96 and not more than 128. That is, if the deteriorated capacity is linear, the 90% integrated residual value may be stored in accordance with this algorithm.  
         [0099]    With the above-described battery pack and the number of counting the charging/discharging thereof, according to the present invention, in which the voltage is detected from the chargeable/dischargeable battery cell, plural battery voltage levels are set and the number of times the detected voltage has transferred to different voltage levels is counted, the number of cycles can be counted correctly, even if the battery cell is deteriorated due to charging/discharging, depending on the degree of deterioration of the battery cell.  
         [0100]    With the battery pack and the residual battery capacity setting method, according to the present invention, in which the integrated residual battery capacity on charging to a pre-set proportion relative to the full charging of the chargeable/dischargeable battery cell is stored in memory means at an interval of a pre-set number of cycles, the number of times the battery cell has been charged/discharged is counted and the stored integrated residual battery capacity for the pre-set number of cycles in the memory means corresponding to the number of counts by the counter is set as the residual battery capacity on full charging of the battery cell, the value of the integrated residual battery capacity on charging to the pre-set proportion corresponding to the number of cycles can be set. Since this enables the initial value on charging to be set in keeping with deterioration caused by charging/discharging of the battery cell, the residual battery capacity can be calculated more accurately than with the conventional battery pack.  
         [0101]    [0101]FIG. 13 shows a specified circuit structure of the battery pack  1 .  
         [0102]    The battery pack  1  is made up of a battery cell block  70 , having two battery cells, and a battery protection circuit block  80  for protecting the battery cell block  70  against overcharging or overdischarging.  
         [0103]    The battery cell block  70  includes lithium ion batteries  71 ,  72 , as two battery cells, connected in series with each other, and a temperature sensor  76  for detecting the temperature of the lithium ion batteries  71 ,  72 . The positive electrodes and the negative electrodes of the lithium ion batteries  71 ,  72  are connected to a positive terminal  73  and to a negative terminal  74 , respectively. The junction point of the lithium ion batteries  71 ,  72  is connected to a neutral point potential terminal  75 . A temperature sensor  76  detects the temperature of the batteries  71 ,  72  to route the detected results to the battery protection circuit block  80 .  
         [0104]    The battery protection circuit block  80  includes a terminal VH, connected to the positive terminal  73 , a terminal VSS, connected to the negative terminal  74 , a terminal VL, connected to the neutral point potential terminal  75 , resistors R 1  to R 6 , for dividing the voltage across the respective terminals, a resistor R 8  and a first switch S 1 .  
         [0105]    The terminals VH, VL are connected to each other through series connected resistors R 1  to R 3 . The combined resistance of the series connected resistors R 1  to R 3  is the resistance Rb 1  which may, for example, be 20 MΩ.  
         [0106]    The terminals VL, VSS are connected to each other through series connected resistors R 4  to R 6 . The terminals VL, VSS are connected to each other through the resistor R 8  and the first switch S 1 , connected in series with each other. Meanwhile, the combined resistance of the series-connected resistors R 4  to R 6  is Rb 2  which may, for example, be 20 MΩ. That is, the resistance value of the resistor Rb 1  is equal to that of the resistor Rb 2 . The resistance value of the resistor R 8  is 390 kΩ which is appreciably smaller than the combined resistance of the resistors Rb 1  and Rb 2 . The first switch S 1  is usually off and is turned on only during the time a neutral point potential confirming control signal Ts is furnished.  
         [0107]    The battery protection circuit block  80  includes first and second Zener diodes  81 ,  82  for generating reference voltages (where biasing resistors are not shown), first to fourth comparators  83  to  86  for detecting the potential difference between the respective resistors for detecting overcharging or overdischarging, a charging control circuit  89  for turning off a third switch SW C  on overcharging and a discharging control circuit  90  for turning off a second switch SW D  on overdischarging.  
         [0108]    The first comparator  83  has its inverting input terminal connected to a cathode of the first Zener diode  81 , while the anode of diode  81  is connected to the terminal VL. The  
         [0109]    First comparator  83  has its non-inverting input terminal connected to a junction point of the resistors R 1 , R 2 . The first comparator  83  detects whether or not the lithium ion battery  71  has been overcharged. The first comparator  83  outputs a logical H on detecting that the voltage Vb 1  of the lithium ion battery  71  exceeds 4.25V, while outputting a logical L on detecting that the voltage Vb 1  of the lithium ion battery  71  is less than 4.25V.  
         [0110]    The second comparator  84  has its non-inverting input terminal connected to the cathode of the first Zener diode  81 . The second comparator  84  has its inverting input terminal connected to a junction point between the resistors R 2  and R 3 . The second comparator  84  detects whether the lithium ion battery  71  is in the overdischarging state. Thus, the second comparator  84  outputs a logical H if the voltage Vb 1  of the lithium ion battery  71  is less than 2.45 V, while outputting a logical L if the voltage Vb 1  is larger than 2.45 V.  
         [0111]    The third comparator  85  has its inverting input terminal connected to a cathode of the second Zener diode  82 , while the anode of diode  82  is connected to the terminal VSS. The third comparator  85  has its non-inverting input terminal connected to a junction point between the resistors R 4  and R 5 . The third comparator  85  detects whether the lithium ion battery  72  is in the overcharging state. Thus, the third comparator  85  outputs a logical H on detecting that the voltage Vb 2  of the lithium ion battery  72  exceeds 4.25V, while outputting a logical L if the voltage Vb 2  is less than 4.25 V.  
         [0112]    The fourth comparator  86  has its non-inverting input terminal connected to the cathode of the second Zener diode  82 . The fourth comparator  86  has its inverting input terminal connected to a junction point between the resistors R 5  and R 6 . The fourth comparator  86  detects whether the lithium ion battery  72  is in the overdischarging state. Specifically, the fourth comparator  86  outputs a logical H if the voltage Vb 2  of the lithium ion battery  72  is less than 2.45 V, while outputting a logical L if the voltage Vb 2  is larger than 2.45 V.  
         [0113]    A first OR gate  87  takes the logical sum of the outputs of the first and third comparators  83 ,  85  to route the results to the charging control circuit  89 . A second OR gate  88  takes the logical sum of the outputs of the second and fourth comparators  84 ,  86  to route the results to the discharging control circuit  90 .  
         [0114]    The charging control circuit  89  performs control to open and close the second switch Sw C  if fed with the logical H or with the logical L from the first OR gate  87 , respectively. The discharging control circuit  90  performs control to control to open and close the third switch SW D  if fed with the logical H or with the logical L from the second OR gate  88 , respectively.  
         [0115]    It is noted that the second and third switches SW D , SW C  are connected in series with each other. One of the second and third switches SW D , SW C  is connected to the second input/output terminal  22 , while the other switch is connected through resistor R 7  to the terminal VSS.  
         [0116]    The battery pack  1  also includes a charging/discharging current detection circuit  91  for detecting whether the battery pack is charging or discharging, a micro-computer  92  for controlling turning on/off of the first switch S 1  and a communication interface  93  for data transmission/reception with external device.  
         [0117]    The charging/discharging current detection circuit  91  includes first and second operational amplifiers  911 ,  912 , and resistors R 11  to R 16 .  
         [0118]    The first operational amplifier  911  has its non-inverting input terminal connected via resistor R 13  to the terminal VSS, while having its inverting input terminal connected through resistors R 12  and R 7  to the terminal VSS. A resistor R 11  is connected across the inverting input terminal and the output terminal of the first operational amplifier  911 . When the discharging current flows through the resistor R 7 , the first operational amplifier  911  outputs a voltage proportionate to the resistance ratio of resistor R 12  to resistor R 11  to the micro-computer  92  and to a third OR gate  913 . If the charging current flows through the resistor R 7 , the second operational amplifier  912  outputs a voltage proportionate to the resistance ratio of resistor R 15  to resistor R 14  to the micro-computer  92  and to a third OR gate  913 . The third OR gate  913  takes the logical sum to supply the result to the micro-computer  92 . That is, the charging/discharging current detection circuit  91  detects the direction of the current flowing through the resistor R 7  to detect whether charging/discharging is going on and, if the charging or discharging is detected, the charging/discharging current detection circuit  91  routes the result to the micro-computer  92  while also routing the values of the charging current or the discharging current to the micro-computer  92 .  
         [0119]    The micro-computer  92  is programmed to wake up if charging/discharging has been detected by the charging/discharging current detection circuit  91  or if data has been received over a communication interface  93 , and to sleep if otherwise. The micro-computer  92  also is programmed to enter into a sleeping state if no charging/discharging current flows or there is no data communication in two or three seconds after its actuation.  
         [0120]    The micro-computer  92  substantially continuously detects the voltage of the terminal VL and also reads out optimum correction coefficients stored in the ROM  94 , based on the temperature of the lithium ion batteries  71 ,  72  detected by the temperature sensor  76  to calculate the residual battery capacity of the lithium ion batteries  71 ,  72 .  
         [0121]    In the ROM  94  are stored not only the correction coefficients at an interval of 10° C., as discussed above in connection with FIG. 18, but also a control program for completing the correction coefficients or a control program for calculating the residual battery capacity.  
         [0122]    The correction coefficients, at an interval of 10° C., stored in the ROM  94 , are five correction coefficients, namely a correction coefficient 1 (=0.6) for 10° C. or lower, a correction coefficient 2 (=0.8) for 10 to 20° C., a correction coefficient 3 (=1.0) for 20 to 30° C., a correction coefficient 4 (=1.2) for 30 to 40° C. and a correction coefficient 5 (=1.4) for 40° C. or higher.  
         [0123]    For calculating more detailed correction coefficients, based on these correction coefficients, the micro-computer  92  executes the processing as from step ST 1  in the flowchart shown in FIG. 14. Here, the correction coefficient for 20 to 30° C. is taken as an example, the four correction coefficients are computed at an interval of 10° C.  
         [0124]    At step ST 101 , the micro-computer  92  sets the correction coefficients stored in the ROM  94  as correction coefficient  3 - 3  for 25.0 to 27.5° C. That is, the correction coefficient  3 - 3  is set to 1.0. The micro-computer  92  then advances to step ST 102 .  
         [0125]    At this step ST 102 , the micro-computer  92  calculates the correction coefficient  3 - 1  at 20.0 to 22.5° C. from the correction coefficients  2  and  3  stored in the ROM  94 . The micro-computer  92  transfers to the subroutine processing shown in FIG. 15 to calculate the center of the two correction coefficients (step ST 11 ). Specifically, the micro-computer  92  computes 0.9, as a median value of the correction coefficients  2 ,  3 , to set the correction coefficient  3 - 1  to 0.9. The micro-computer then advances to step ST 3 .  
         [0126]    At step ST 3 , the micro-computer  92  executes the subroutine of step ST 111  shown in FIG. 15 in order to compute the correction coefficient  3 - 2  for 22.5 to 25.0° C. from the correction coefficients  3 - 1  to  3 - 3 . That is, the micro-computer  92  sets a median value 0.95 of the correction coefficient  3 - 1  (=0.9) and the correction coefficient  3 - 3  (=1.0) as the correction coefficient  3 - 2 . The microcomputer  92  then advances to step ST 104 .  
         [0127]    At this step ST 104 , the micro-computer  92  executes the subroutine of step ST 111  of FIG. 15, in order to calculate the correction coefficient  4 - 1  for 30.0 to 32.5° C. from the correction coefficients  3  and  4  stored in the ROM  94 . That is, the micro-computer  92  sets a median value 1.1 of the correction coefficients  3  and  4  as the correction coefficient  4 - 1 . The micro-computer  92  then advances to step ST 105 .  
         [0128]    At step ST 105 , the micro-computer  92  executes the subroutine of step ST 111  of FIG. 15, in order to calculate the correction coefficient  3 - 4  for 27.5 to 30.0° C. from the correction coefficients  3 - 3  and  4 - 1 . That is, the microcomputer  92  sets a median value 1.05 of the correction coefficients  3 - 3  and  4 - 1  as the correction coefficient  3 - 4 . The micro-computer  92  then terminates the processing.  
         [0129]    By the above processing, the micro-computer  92  acquires the correction coefficient  3 - 1  (=0.90) for the temperature of 20.0 to 22.5° C., the correction coefficient  32  (=0.95) for 22.5 to 25.0° C., the correction coefficient  33  (=1.0) for 27.5 to 30.0° C. and the correction coefficient  4 - 1  (=1.1) for 30.0 to 32.5° C., as shown in FIG. 16.  
         [0130]    The micro-computer  92  performs similar processing for the temperature range other than 20.0 to 30.0° C. to calculate the correction coefficient at an interval of 2.5° .C, as shown in FIG. 17.  
         [0131]    Since the micro-computer  92  is able to use these correction coefficients at small step width, it is able to compute the residual battery capacity accurately, based on the voltage at the terminal VL, even if the lithium ion batteries  71 ,  72  undergo temperature changes.  
         [0132]    If the micro-computer  92  has computed the correction coefficients corresponding to the temperature detected by the temperature sensor  76  when it is performing the processing of steps ST 101  ff., shown in FIG. 14, the micro-computer is able to interrupt the processing to use the correction coefficients to calculate the residual battery capacity.  
         [0133]    For example, if the micro-computer  92  has detected the temperature of 26° C., the micro-computer  92  acquires the correction coefficient  3 - 3  (=1.0) for 25.0 to 27.5 at a time point it has performed the processing of step ST 101 . The micro-computer  92  can then halt the processing as from step ST 102  to calculate the residual battery capacity.  
         [0134]    Also, if the micro-computer  92  has detected 23° C., the micro-computer  92  is able to perform the processing of steps ST 101  to ST 103  to make accurate calculations of the residual battery capacity of the lithium ion batteries  71 ,  72  based on the correction coefficient  3 - 2  and the voltage at the terminal VL.  
         [0135]    Meanwhile, the residual battery capacity can be calculated using a technique disclosed in Japanese Laying-Open Patent H-9-297166 without any particular limitations. It is however necessary that the technique used be one that calculates the residual battery capacity using a temperature-dependent correction coefficient or the voltages of the lithium ion batteries  71 ,  72 .  
         [0136]    With the battery pack  1 , in which only necessary minimum correction coefficients are stored in the ROM  94 , and in which, if the temperature of the lithium ion batteries  71 ,  72  is detected, the correction coefficient is calculated only for the range of the detected temperature, correction coefficients can be calculated accurately depending on changes in temperature.  
         [0137]    Also, in the processing of steps ST 102  to ST 105 , the subroutine processing shown in FIG. 15 is performed repeatedly. Thus, the optimum correction coefficient can be computed easily without performing complex processing.  
         [0138]    In the present embodiment, explanation has been made on the assumption that the correction coefficients are stored at an interval of 10 C as shown in FIG. 18. However, the correction coefficients may previously be stored at an interval of 2.5° C., as shown in FIG. 17. Also, in the present embodiment, explanation has been made on the assumption that the range of 10° C. is divided into four stages such that the correction coefficients are calculated at an interval of 2.5 (=10/4)° C. It is, however, possible to divide the temperature range at finer steps to compute more detailed correction coefficients.  
         [0139]    If, with the battery pack and the residual battery capacity computing method, according to the present invention, a correction coefficient associated with a temperature detected by the temperature detection means is stored in the storage means, the correction coefficient is read out and the residual battery capacity is computed based on the correction coefficient and the voltage detected by the voltage detection means. If a correction coefficient associated with the detected temperature is not stored in the storage means, a correction coefficient associated with a pre-set temperature ahead and at back of the detected temperature is read out from the storage means to compute a correction coefficient associated with the detected temperature based on each read-out correction coefficient to compute the residual battery capacity based on the computed correction coefficient and the voltage detected by the voltage detection means. Thus, if there is a temperature change in the battery cell, a correction coefficient can be acquired correctly in keeping with such change to enable the residual battery capacity to be computed accurately at all times.