Abstract:
A battery monitor apparatus and method for an automotive battery system including a battery for supplying power to in-vehicle electrical equipment and sensors for detecting battery voltage, the charge/discharge current and the battery temperature are disclosed. The capacitance and the internal actual resistance of the battery are calculated at the time of starting the engine. Further, the theoretical internal resistance of the battery corresponding to the ambient temperature and the battery open-circuit voltage during the stationary engine state are detected in advance. Based on the change in the battery open-circuit voltage, the battery change is provisionally determined. After that, battery change or degeneration can be determined based on battery capacitance, the actual and theoretical internal resistance values of the battery, the battery open-circuit voltage and the provisional battery change determination value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from, and incorporates by reference the entire disclosure of, Japanese Patent Applications No. 2006-055077, filed on Mar. 1, 2006, and No. 2007-045849, filed on Feb. 26, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to an apparatus and method of monitoring the battery of an automotive vehicle, or in particular a battery monitor apparatus and method for automobiles and other vehicles capable of detecting the need of change and the degeneration of the battery with a simple configuration. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventionally, vehicles, or typically, automotive vehicles running on the road have three basic factors of operation to be controlled, “run”, “stop” and “turn”. With the recent development of electronic control operation, however, comfort has become a desire of vehicle users, and the present tendency is toward an increased number of items to be controlled in the vehicle. The manual operation of the seat position and slide door open/close operation, for example, are being electrified, and an electrically-operated curtain and a multispeaker surround system have been added as new parts to be controlled. 
         [0006]    On the other hand, most of the in-vehicle devices to be controlled in seeking comfort are electric devices using an in-vehicle battery, and therefore, the battery for supplying power to these electric devices has come to play an important role in the vehicle. A lead storage battery is mainly used as the in-vehicle battery, and supplies power to electric devices, and is charged by an alternator which generates power by the rotation of the vehicle engine. 
         [0007]    Although the in-vehicle battery is charged and discharged repeatedly, excessive discharge may lead to battery degeneration, and therefore, in order to prevent degeneration, the battery is controlled optimally in accordance with the battery state (battery charging rate). After a vehicle is left parked, for example, the battery may be discharged (exhausted) by the standby current (dark current) of the electric devices. As a means for preventing the battery exhaustion, a control operation to reduce the discharge is carried out in accordance with the battery charging rate. 
         [0008]    If a battery is replaced with another battery of the same size (having the same battery capacitance in a full charged state), then no problems should be encountered. However, in a case where the battery is replaced with a battery of a different size (a battery having a different battery capacity in full charged state), or in the case where the battery is degenerated, the charge control operation or the power cut operation depending on the battery capacitance is required. With regard to the detection of the need for a battery change, Japanese Unexamined Patent Publication No. 2001-297800 discloses a technique comprising a step of detecting when the battery has been changed (hereinafter referred to simply as a battery change), wherein upon detection of a battery change, a new relationship is established between the charge voltage and the current. In this specification, the appended claims and the summary, the battery capacitance is defined as that of a fully charged battery unless otherwise specified. 
         [0009]    Also, in the case where the battery is changed, the following methods are employed to determine the battery capacitance after the change: 
         [0010]    (1) In the case where a vehicle distributor (dealer) has changed the battery, the capacitance of the replacement battery is overwritten by the dealer in a nonvolatile memory for storing battery capacitance. 
         [0011]    (2) Battery capacitance is measured according to battery size using an optical sensor and a battery weight sensor. 
         [0012]    The methods of determining the battery capacitance described above, however, pose the following problems: 
         [0013]    In method (1), no means is available for updating the value of the battery capacitance stored in the nonvolatile memory in the case where another person other than the vehicle dealer changes the battery. If the battery is changed by the user, for example, the battery monitor apparatus may erroneously indicate a battery fault (fault alarm). 
         [0014]    In method (2), on the other hand, a plurality of sensors are required to detect battery size at an increased cost. Also, the battery state such as increased internal resistance cannot be determined from battery size or weight alone. Although the battery change can be recognized, battery degeneration cannot be detected. 
       SUMMARY OF THE INVENTION 
       [0015]    Accordingly, it is an object of this invention to solve the aforementioned problem and provide a vehicle battery monitor apparatus and a method capable of detecting battery change and battery degeneration with a simple configuration. 
         [0016]    In order to achieve the object described above, according to one aspect of the invention, there is provided a vehicle battery monitor apparatus comprising a battery capacitance calculation unit for calculating battery capacitance at the time of starting the engine, a battery internal resistance calculation unit for calculating the actual internal resistance of the battery at the time of starting the engine, a battery theoretical internal resistance calculation unit for calculating the theoretical internal resistance of the battery in accordance with ambient temperature, a battery open-circuit voltage calculation unit for detecting the open-circuit voltage of the battery when the engine is in a stationary state, a battery change provisional determining unit for provisionally determining battery change based on the change in the battery open-circuit voltage, and a battery change determining unit for determining that the battery has been changed based on the provisionally determined values of the battery capacitance, battery internal resistance, battery theoretical internal resistance, battery open-circuit voltage and battery change. 
         [0017]    According to another aspect of the invention, there is provided a vehicle battery monitor method comprising the steps of calculating battery capacitance before starting the engine, calculating the actual internal resistance of the battery at the time of starting the engine, calculating the theoretical internal resistance of the battery corresponding to ambient temperature, detecting the open-circuit voltage of the battery when the engine is in stationary state, provisionally determining battery change based on the change in the battery open-circuit voltage, and determining battery change based on the provisionally determined values of the battery capacitance, battery internal resistance, battery theoretical internal resistance, battery open-circuit voltage and battery change. 
         [0018]    In the vehicle battery monitor apparatus and method according to this invention, the capacitance of the battery changed can be positively detected with a simple configuration at a decreased cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention is illustrated by way of example, and is not limited thereby, in the figures of the accompanying drawings in which like references indicate similar elements. Note that the following figures are not necessarily drawn to scale. 
           [0020]      FIG. 1A  is a diagram showing a configuration of the battery monitor apparatus according to an embodiment of the invention. 
           [0021]      FIG. 1B  is a block diagram showing an example of the internal configuration of the power supply monitor apparatus shown in  FIG. 1A . 
           [0022]      FIGS. 2A to 2C  are flowcharts showing the steps of the battery capacitance detecting process constituting a part of the battery monitor method executed by the battery monitor apparatus according to the invention. 
           [0023]      FIG. 3A  is a liquid temperature vs. correction value map for correcting the value of the battery capacitance detected by the battery capacitance detecting process of  FIG. 1 , based on the liquid temperature of the battery. 
           [0024]      FIG. 3B  is a liquid temperature vs. correction coefficient map for correcting the value of the discharge electricity amount of the battery based on the battery liquid temperature. 
           [0025]      FIG. 4  is a capacitance vs. voltage value map for correcting the value of the battery capacitance detected by the battery capacitance detecting process of  FIG. 2 , based on the battery voltage. 
           [0026]      FIG. 5  is a characteristic diagram showing the temporal change in battery voltage and the battery current at the time of starting the vehicle engine with the battery monitor apparatus according to the invention mounted thereon. 
           [0027]      FIG. 6  is a flowchart showing the steps of the process for calculating theoretical internal resistance in the battery monitor apparatus according to this invention. 
           [0028]      FIG. 7  is a liquid temperature vs. internal resistance characteristic map used for calculating the internal resistance from the battery liquid temperature and the battery capacitance in the process of calculating the theoretical internal resistance in  FIG. 6 . 
           [0029]      FIG. 8A  is a flowchart showing the steps of calculating the battery open-circuit voltage in the battery monitor apparatus according to the invention when the engine is stationary. 
           [0030]      FIG. 8B  is a flowchart showing the steps of calculating the open-circuit voltage of the battery when connected to the battery monitor apparatus according to the invention. 
           [0031]      FIG. 9  is a flowchart showing the steps of the process for provisionally determining battery change in the battery monitor apparatus according to this invention. 
           [0032]      FIG. 10  is a flowchart showing the steps of the process for determining battery open-circuit voltage change in the battery monitor apparatus according to this invention. 
           [0033]      FIGS. 11A to 11C  are flowcharts showing the steps of the process for detecting battery change in the battery monitor apparatus according to this invention. 
           [0034]      FIG. 12  is a flowchart showing the steps of the process for detecting battery degeneration in the battery monitor apparatus according to this invention. 
           [0035]      FIG. 13  is a flowchart showing the steps of the process for switching control operation in the battery monitor apparatus according to this invention. 
           [0036]      FIGS. 14A to 14C  are flowcharts showing the steps of a modification of the process for detecting battery change in the battery monitor apparatus according to this invention explained with reference to  FIGS. 11A to 11C . 
           [0037]      FIGS. 15A to 15C  are flowcharts showing the steps of a modification of the process for detecting battery change in the battery monitor apparatus according to this invention. 
           [0038]      FIG. 16  is a map showing the relationship between battery internal resistance and battery capacitance, used in the battery change detecting process shown in  FIGS. 15A to 15C . 
           [0039]      FIG. 17  is a flowchart showing the steps of the process executed after the battery capacitance detecting process described with reference to  FIGS. 2A to 2C . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    The embodiments of the invention are explained below with reference to the specific examples shown in the accompanying drawings. 
         [0041]      FIG. 1A  shows a configuration of the battery monitor apparatus  1  according to an embodiment of the invention. The battery monitor apparatus according to this embodiment is mounted in a vehicle such as an automobile supplied with an ignition (IG) signal, a starter drive signal, an engine rotation signal and other monitor signals from the ECU in operation. 
         [0042]    Also, according to this embodiment, a nonvolatile memory  10  is arranged in the body of the power supply monitor apparatus  1 . The nonvolatile memory  10  may alternatively be arranged on the outside of the power supply monitor apparatus  1 . Also, the nonvolatile memory  10  may be a standby RAM. Electric devices  2  mounted on the vehicle are connected to the power supply monitor apparatus  1  through a communication line  22 . Further, the power supply monitor apparatus  1  is connected with an notification means  3  configured as a gauge such as a speed meter driven by an ECU  5 , so that the information described later can be transmitted to the vehicle occupants by the notification means  3 . 
         [0043]    The power supply monitor apparatus  1  and the electric devices  2 , on the other hand, are supplied with power through a power supply line  20  from the battery  6 . The power supply line  20  is connected with a generator (alternator)  4  for charging the battery  6 . A voltage sensor  7  for detecting battery voltage and a current sensor  8  for detecting the of amount current flowing out from or into the battery  6  are arranged in the neighborhood of the positive power supply terminal of the battery  6 . Also, a temperature sensor  9  such as a thermistor for detecting the liquid temperature of the battery  6  is arranged on the housing of the battery  6 . 
         [0044]    Further, the power supply monitor apparatus  1  is supplied with a voltage detection signal from the voltage sensor  7 , a current detection signal from the current sensor. 8  and a battery liquid temperature signal from the temperature sensor  9  through individual signal lines  21 V,  21 A and  21 S, respectively. 
         [0045]      FIG. 1B  shows an example of the internal configuration of the power supply monitor apparatus  1  shown in  FIG. 1A . The power supply monitor apparatus  1  has therein a sensor output acquisition unit  11  for acquiring an IG signal, a starter drive signal, an engine rotation signal and a monitor signal of the operating conditions of other ECUs. The sensor output acquisition unit  11  is connected to a battery capacitance detector  12 , a battery internal resistance detector  13 , a battery open-circuit voltage detector  14 , a battery change detector  15  and a battery degeneration detector  16 . The battery capacitance detector  12  detects the battery capacitance from the sensor output. The battery internal resistance detector  13  detects the theoretical internal resistance and the actual internal resistance from the sensor output. The battery open-circuit voltage detector  14  detects the battery open-circuit voltage of the engine in a stationary state. The battery change detector  15  detects whether the battery has been replaced or not. The battery degeneration detector  16  detects the degeneration of the battery. 
         [0046]    The output of the battery capacitance detector  12 , the battery internal resistance detector  13 , the battery open-circuit voltage detector  14 , the battery change detector  15  and the battery degeneration detector  16  are input to the battery state announcing unit  17 , which in turn outputs a signal indicating the battery state and thus notifies the vehicle user of the battery conditions using a meter (gauge) mounted in the vehicle. 
         [0047]    The operation of the sensor output acquisition unit  11 , the battery capacitance detector  12 , the battery internal resistance detector  13 , the battery open-circuit voltage detector  14 , the battery change detector  15  and the battery degeneration detector  16  will be explained with reference to the flowcharts and the control maps shown in  FIGS. 2 to 14 . 
         [0048]      FIGS. 2A to 2C  are flowcharts showing the steps of the battery capacitance detection process executed by the battery capacitance detector  12  of the battery monitor apparatus  1  shown in  FIGS. 1A ,  1 B. This process is executed at time intervals of about 10 ms or 8 ms. 
         [0049]    Step  201  determines whether the jump flag JF described later is in the state of  1  or not. The jump flag JF has an initial value (before the engine starter is turned on) of  0 . Therefore, the determination in step  201  before the starter is on is NO, and the process proceeds to step  202 . Step  202  determines whether the starter is turned on or not. First, the process executed with the starter turned on will be explained. 
         [0050]    With the turning on of the starter, the process proceeds from step  202  to step  203 . Step  203  determines whether a predetermined time has elapsed or not after the starter is turned on. In the case where the predetermined time has not elapsed from the time when the starter is turned on, this routine is finished, while in the case where the predetermined time has elapsed from the time when the starter is turned on, the process proceeds to step  204 . This process is intended to prevent the detection process from being executed until the operation is settled after the starter is turned on, and the predetermined time may be set to, for example, about 20 ms. 
         [0051]    In step  204  to which the process proceeds upon lapse of the predetermined time after the starter is turned on, the values (sensor values) detected by the voltage sensor, the current sensor and the temperature sensor are read and stored in a nonvolatile memory. The following step  205  detects, from the value of the flag N, whether the sensor values are stored for the first time upon lapse of the predetermined time. The initial value of the flag N is  0 , and therefore, the process first proceeds to step  206 . 
         [0052]    In step  206 , the voltage value read in step  204  is set to the initial value V 0 , the value of the flag N is set to  1 , and the value of the flag M described later is set to  0 . After the value of the flag N is set to  1 , the determination in step  205  is negative and, the process proceeds from step  205  to  207 , and the voltage value read in step  204  is set to V 5 . Upon completion of the process of step  206  or step  207 , the current value read in step  204  is accumulated in step  208  thereby to calculate the current accumulation value Is 1 . 
         [0053]    The following step  209  determines whether the difference between the voltage value V 0  stored in step  206  and the voltage value V 5  stored in step  207  is larger than a first predetermined voltage V 1  or not. The voltage value V 0  immediately after the starter is turned on is smaller than the subsequent voltage value V 5 , and therefore, the value (V 5 −V 0 ) assumes a positive value. In the case where the value (V 5 −V 0 ) is smaller than the first predetermined voltage V 1 , the process proceeds to step  214  to determine whether the starter is turned on or not. 
         [0054]    In the case where the starter is not turned off, the process proceeds to step  215 , and the jump flag is set to  1  thereby ending the routine. Once the value of the jump flag JF is set to  1 , the process proceeds from step  201  to step  204  and steps  202  and  203  are skipped. In the case where the starter is turned off, the process proceeds to step  216 , and the values of the flag N and the jump flag JF are both set to  0 , thereby ending the routine. 
         [0055]    In the case where the value (V 5 −V 0 ) is larger than the first predetermined voltage V 1  in step  209 , the process proceeds to step  210 . In step  210 , the battery capacitance, as well as the internal resistance of the battery is calculated. 
         [0056]    The actual internal resistance value R 0  at the time of starting the engine is calculated by the following equation: 
         [0000]        R 0=(present detection voltage−preceding detection voltage)/(present detection current−preceding detection current) 
         [0000]    where the present detection voltage and the present detection current are read in step  204 , while the preceding detection voltage and the preceding detection current are read in the preceding process (8 ms before). 
         [0057]    According to this embodiment, the real internal resistance value R 0  is determined by one calculation session. Nevertheless, the real internal resistance value R 0  may be calculated as an average value Ra of N (integer not larger than 2) calculation sessions of the real internal resistance values (R 01 , R 01 , R 02 , . . . ) as follows: 
         [0000]        R 0− Ra =( R 01+ R 01+ R 02 . . . )/ N    
         [0058]    On the other hand, the battery capacitance calculated at the time of starting the engine according to this embodiment is the battery capacitance BC (ampere hour (AH)/1 V) per reference battery voltage V 7  (V 7 =1, for example, for 1 (V)), and calculated by the equation: 
         [0000]        BC ={[current accumulation value/( V 5− V 0)]/current accumulation time (ms)}× V 7×3600000 
         [0059]    In the case where the reference battery voltage is set to 2 V, battery capacitance BC for 2 V can be determined. 
         [0060]    Assuming that the current accumulation value is determined from the following equation (with the control period of, say, 8 ms): 
         [0000]      Current accumulation value=[(current value×3600000)/control period]+preceding current accumulation value 
         [0061]    Then, the battery capacitance BC per reference battery voltage V 7  can be calculated from: 
         [0000]        BC =[current accumulation value/( V 5− V 0)]× V 7 
         [0062]    In the next step  211 , the battery capacitance calculated in step  210  is corrected by temperature. The correction of the amount of discharge electricity by battery liquid temperature at the time of turning on the starter in step  211  is carried out by the map showing the relationship between the liquid temperature and the correction coefficient in  FIG. 3B . This correction is to convert the battery capacitance calculated in step  210  into the battery capacitance for the battery temperature of 25° C. As shown in  FIG. 3A , assuming that the battery capacitance for the liquid temperature of 25° C. is 1, the battery capacitance for the liquid temperature of 20° C. is known to assume a value corresponding to 0.8 times the battery capacitance for the liquid temperature of 25° C. In the case where the temperature at which the battery capacitance is calculated is 20° C., the particular value is increased to 1.25 times based on the map showing the relationship between the liquid temperature and the correction coefficient in  FIG. 3B . 
         [0063]    In the next step  212 , the battery capacitance is corrected in accordance with battery voltage range, and the values of both the flag N and the jump flag JF are set to  0  in step  213  thereby ending the routine. The battery capacitance is corrected in accordance with the battery voltage range using the map of  FIG. 4  showing the relationship between the capacitance and the voltage value for correcting the battery capacitance by the battery voltage. 
         [0064]    The battery voltage change with respect to battery capacitance is different between the case where the battery capacitance is calculated in the area indicated by A and the case where the battery capacitance is calculated in the area indicated by B in  FIG. 4 . In order to calculate the battery capacitance accurately, the correction is made using the characteristic of  FIG. 4  in such a manner that the battery capacitance against the battery voltage may be identical for the two areas. Usually, the battery capacitance is calculated for the assumed area A, and the correction carried out, only for area B. 
         [0065]    In the case where step  202  determines that the starter is not on, the process proceeds to step  217 . In step  217 , the values (sensor values) detected by the voltage sensor, the current sensor and the temperature sensor are read, and stored in a nonvolatile memory as the present values. In the following step  218 , it is determined whether the jump flag PF described later is  1  or not. The jump flag PF is  0  when the starter is turned off, and therefore, the process proceeds from step  218  to step  219  immediately after the starter is turned on. In step  219 , the present voltage stored in step  217  is subtracted from the preceding voltage, and it is determined whether the difference is larger than a second predetermined voltage V 2  or not. In the case where the difference between the present voltage and the preceding voltage is smaller than the second predetermined voltage, the process proceeds to step  220  where the present value read in step  217  is stored again as the preceding value, thereby ending the routine. In the case where the difference is great, the process proceeds to step  221 . 
         [0066]    Step  221  detects, in accordance with the value of the flag M, whether the sensor value is stored in step  217  for the first time after proceeding from step  202  to step  217 . Since the initial value of the flag M is  0 , the process first proceeds from step  219  to step  222 . 
         [0067]    In step  222 , the voltage value read in step  217  is set to the initial value V 4  and the value of the flag M to  1 . After the value of the flag M is set to  1 , the process proceeds from step  221  to  223 , and the voltage value read in step  217  is set to V 6 . Upon completion of the process of step  222  or step  223 , step  224  calculates the current accumulation value Is 2  by accumulating the current value read in step  217 . 
         [0068]    The following step  225  determines whether the difference between the voltage value V 4  stored in step  222  and the voltage value V 6  stored in step  223  is greater than a third predetermined voltage V 3  or not. As long as the starter is off, the voltage decreases, and if the voltage remains unchanged, V 4  is almost equal to V 6 . Thus, the determination in step  225  is negative. In the case where the voltage changes considerably while the starter is off, V 4  is larger than V 6 . Once this difference equals or exceeds the third predetermined voltage V 3 , the determination in step  225  is positive. 
         [0069]    In the case where the determination in step  225  is negative, the process proceeds to step  230  thereby to determine whether a predetermined time has elapsed from the time when the process proceeds to step  217  from step  202  for the first time. In the case where the predetermined time has not elapsed, the value of the jump flag PF is set to  1  in step  231 , and the routine ends. In the case where the predetermined time has elapsed, the values of the jump flag PF and the flag N are both set to  0  in step  232 , thereby ending this routine. In the case where the value of the jump flag PF is set to  1  in step  231 , the determination in the next step  218  is positive, and therefore, the process of step  219  is subsequently jumped and cut off. 
         [0070]    In the case where step  225  determines that the value (V 4 −V 6 ) is not less than the third predetermined voltage V 3 , the process proceeds to step  226 . In step  226 , the actual internal resistance value and battery capacitance are calculated. The methods of calculating the actual internal resistance value and battery capacitance are already explained and will not be explained hereafter. 
         [0071]    In the next step  227 , the battery capacitance calculated in step  226  is corrected by temperature, followed by step  228  in which the battery capacitance is corrected in accordance with the battery voltage range thereby ending the routine. The correction of the battery capacitance by temperature and the battery capacitance correction in accordance with the battery voltage range are already explained and therefore will not be explained hereafter. 
         [0072]      FIG. 5  shows the temporal change of the battery voltage and the battery current when starting the engine of the vehicle having mounted therein the battery monitor apparatus  1  according to the invention. Assuming that the starter is turned on to start the engine at time point t 0 , the battery voltage sharply drops from 12 V and then gradually restores to the original voltage level. Battery current, on the other hand, surges when the starter is first turned on, and then gradually decreases. Actually, the current flows in opposite directions in the current sensor  8  when the battery  6  is charged and discharged.  FIG. 5 , however, fails to take the direction of current flow into consideration, and shows only the magnitude of the current flowing in the current sensor  8 . According to this embodiment, the change in battery voltage and battery current after the starter is turned on at time point t 0  are stored by being sampled at time points t 1 , t 2 , t 3  . . . , for example, with predetermined time intervals (8 ms period) 
         [0073]      FIG. 6  is a flowchart showing the steps of the process for calculating the theoretical internal resistance in the battery monitor apparatus  1  according to this invention. In step  601 , battery liquid temperature is read, and in step  602 , the battery capacitance stored in the nonvolatile memory is read out. In step  603 , theoretical internal resistance is calculated based on the relationship between battery liquid temperature and internal resistance (stored as a map in memory) shown in  FIG. 7 . As understood from  FIG. 7 , the higher the liquid temperature and the larger the battery capacitance, the smaller the theoretical internal resistance value, 
         [0074]      FIG. 8A  is a flowchart showing the steps of calculating the open-circuit voltage of the battery while the engine is stationary in the battery monitor apparatus  1  according to the invention. Step  801  determines whether the engine is running or not, and in the case where the engine is not stationary, the routine is ended. In the case where the engine is stationary, however, the process proceeds to step  802 . Step  802  determines whether the ignition is turned off or not, and in the case where the ignition is not turned off, the routine is finished. In the case where the ignition is turned off, the process proceeds to step  803 . 
         [0075]    Step  803  determines whether the dark current is within a predetermined range while the engine is stationary, and as long as the dark current is not within the predetermined range, the routine is ended. In the case where the dark current is within the predetermined range, the process proceeds to step  504 . Step  804  determines whether the other ECUs are in sleep mode or not, and in the case where the other ECUs are not asleep, the routine is ended, however if other ECUs are asleep, the process proceeds to step  805 . 
         [0076]    Step  805  determines whether a predetermined time has elapsed from the establishment of the condition that all of the determination results of steps  801  to  804  are positive. Before lapse of the predetermined time from the establishment of the condition, the routine is ended, while in the case where the predetermined time has elapsed from the establishment of the condition, the process proceeds to step  806 , and the detection voltage value is stored as an open-circuit voltage value V 8  thereby to end the routine. According to this embodiment, the open-circuit voltage value V 8  is stored in one determining session. As an alternative, the average value of the voltages detected a plurality of times or the value frequently occurring among the voltage values detected a plurality of times may be stored as the open-circuit voltage value V 8 . 
         [0077]      FIG. 8B  is a flowchart showing the steps of calculating the battery open-circuit voltage with the battery connected in the battery monitor apparatus  1  according to this invention. Step  810  determines whether the engine is stationary or not, and while the engine is in operation, the routine is ended, however if the engine stops, the process proceeds to step  811 . Step  811  determines whether the battery is connected or not, and in the case where the battery is not connected, the routine is ended, however if the battery is connected, the process proceeds to step  812 . Step  812  determines whether the ignition is turned off or not, and in the case where the ignition is not off, the routine is ended, however, if the ignition is off, the process proceeds to step  813 . 
         [0078]    Step  813  determines whether the dark current is within a predetermined range while the engine is stationary, and in the case where the dark current is not within the predetermined range, the routine is ended. In the case where the dark current is within the predetermined range, the process proceeds to step  814 . Step  814  determines whether the other ECUs are asleep or not, and in the case where the other ECUs are not asleep, the routine is ended, however if the other ECUs are asleep, the process proceeds to step  815 . 
         [0079]    Step  815  determines whether a predetermined time has elapsed from the establishment of the condition that all the determination results in steps  811  to  814  are positive. In the case where the predetermined time has not passed from the establishment of the condition, the routine is ended, while in the case where the predetermined time has passed, the process proceeds to step  816 , in which the detection voltage value is stored as an open-circuit voltage value V 9  immediately after battery change thereby ending the routine. According to this embodiment, the open-circuit voltage value V 9  is stored at the first determination session. Nevertheless, the average value of the voltages detected a plurality of times or the value frequently occurring among the voltage values detected a plurality of times may be stored as the open-circuit voltage value V 9 . 
         [0080]      FIG. 9  shows the steps of the process for provisionally determining the battery change executed by the battery monitor apparatus  1  according to the invention. Assuming that the battery monitor apparatus  1  has stored therein the open-circuit voltage value V 10  of a brand new battery  6 . This provisional determination is based on the fact that in the case where the battery is changed, the open-circuit voltage value V 9  is near to the open-circuit voltage value V 10  of a brand new battery  6 , and therefore, the difference between V 9  and V 10  is small, while in the case where the battery is removed for maintenance and subsequently mounted again, the open-circuit voltage value V 9  is less than the open-circuit voltage value V 10  of a brand new battery  6 . 
         [0081]    Specifically, the difference between the open-circuit voltage values V 9  and V 10  is large when the battery is removed for maintenance and mounted again, while the difference is small when the battery is replaced with a brand new one. In step  901 , the absolute value of the difference between the open-circuit voltage value V 9  after battery change stored in step  816  and the open-circuit voltage value V 10  of a brand new battery is calculated, and it is determined whether this value is smaller than a threshold voltage V 11 . The threshold voltage value V 11  is about 0.1 V. 
         [0082]    In the case where the determination in step  901  is YES, i.e. the difference of the open-circuit voltage value before and after battery change is small, the process proceeds to step  902  where the battery change is provisionally determined, after which the process proceeds to step  904  where the result of determination is stored in memory and the routine is ended. In the case where the determination in step  901  is NO, i.e. in the case where the difference of the open-circuit voltage value before and after battery change is large, the process proceeds to step  903  where the absence of battery change is provisionally determined, after which the process proceeds to step  904 . Then, the result of determination is stored in memory and the routine is ended. 
         [0083]      FIG. 10  shows the steps of the battery open-circuit voltage change determination process executed by the battery monitor apparatus  1  according to this invention. Assuming that the battery monitor apparatus  1  has stored therein the open-circuit voltage value V 9  immediately after the battery  6  is replaced and the open-circuit voltage value V 8  measured subsequently while the engine is stationary. In step  1001 , the absolute value of the voltage difference between the open-circuit voltage value V 8  and the open-circuit voltage value V 9  immediately after battery change stored in steps  806  and  816 , respectively, are calculated, and it is determined whether this value is greater than the threshold voltage value V 12 . The threshold voltage value V 12  is about 0.05 V. 
         [0084]    In the case where the determination in step  1001  is positive, i.e. when the difference between the open-circuit voltage value V 9  immediately after battery change and the subsequent open-circuit voltage value V 8  is large, the process proceeds to step  1002 , where the change in the open-circuit voltage is provisionally determined, and the process proceeds to step  1004 . This determination result is stored in memory and the routine is ended. In the case where the determination in step  1001  is negative, i.e. when the difference between the open-circuit voltage value V 9  immediately after battery change and the subsequent open-circuit voltage value V 8  is small, the process proceeds to step  1003 , where the absence of an open-circuit voltage change is provisionally determined, followed by proceeding to step  1004 , in which the determination result is stored in memory thereby ending the routine. 
         [0085]      FIGS. 11A to 11C  show the steps of the process for detecting the battery change executed by the battery monitor apparatus  1  according to this invention. In the case where the battery is changed, this detection process determines whether the capacitance is increased, remains unchanged or decreased by battery change. This detection process is executed after the detection of the battery capacitance and the calculation of the internal resistance after the engine starts. 
         [0086]    In step  1101 , the data required to determine the battery change is read from the nonvolatile memory  10 . In the next step  1102 , it is determined whether the battery has ever been cleared. The history of battery indicates the history of battery change, and in the case where the data value (RAM value) in a memory indicating the existence of the battery is destroyed, the battery change can be determined. The nonvolatile memory (RAM) includes standby RAM and normal RAM. The standby RAM has written therein data indicating the existence of the battery, and upon battery change, this data is rewritten to another value. Thus, battery change history can be known from this data. 
         [0087]    Upon determination in step  1102  that the battery has never been cleared, the battery is not changed and therefore the process proceeds to step  1122 . In step  1122 , the process of determining the battery degeneration described later is executed and the routine is ended. 
         [0088]    Upon determination in step  1102  that the battery has never been cleared, the process proceeds to step  1103  to determine whether the difference between the detected battery capacitance and the normal battery capacitance is not smaller than the first capacitance criterion value C 0  or not. An explanation is given regarding each of the cases (1) in which capacitance is increased by battery change, (2) in which the capacitance remains unchanged by battery change, and (3) in which capacitance is decreased by battery change. 
         [0089]    (1) Process Executed in the Case Where the Capacitance is Increased by Battery Change 
         [0090]    In this case, step  1103  determines that the difference between the detected battery capacitance and the normal battery capacitance is not less than the capacitance criterion value C 0 , and the process proceeds to step  1104 . Step  1104  determines whether the battery change is provisionally determined or not, and due to the provisional determination of battery change, the process proceeds to step  1105 . Step  1105  determines whether the open-circuit voltage has ever been changed or not, and due to the open-circuit voltage change, the process proceeds to step  1106 . Step  1106  determines whether or not the theoretical internal resistance value minus the actual internal resistance value is greater than the first resistance value R 1 . In the case where the battery change increases the capacitance, the answer is positive, and the process proceeds to step  1107  to determine the battery change (capacitance increased). In the next step  1108 , the vehicle occupants are informed of the battery change by the announcing means  3  shown in  FIG. 1 , followed by proceeding to step  1109 . In step  1109 , the control switching process described later is executed thereby to end the routine. In the case where the determination Is negative in any one of steps  1104 ,  1105  and  1106 , the battery change is not determined, but the process proceeds to step  1122  to execute the process of determining battery degeneration. 
         [0091]    (2) Process Executed in the Case Where the Capacitance Remains Unchanged by Battery Change 
         [0092]    In this case, step  1103  determines that the difference between the detected battery capacitance and normal battery capacitance is less than the first capacitance criterion value C 0  (NO), and the process proceeds to step  1110 . Step  1110  determines whether the absolute value of the difference between the detected battery capacitance and the normal battery capacitance is less than a second capacitance criterion value C 1  which is a small value. In the case where the capacitance remains unchanged by battery change, the difference between the detected battery capacitance and normal battery capacitance is very small, and therefore, the determination is positive, followed by proceeding to step  1111 . 
         [0093]    Step  1111  determines whether the battery change has ever been recognized or not, and due to recognition of the battery change, the process proceeds to step  1112 . Step  1112  determines whether the open-circuit voltage has ever been changed, and due to a past change in open-circuit voltage, the process proceeds to step  1113 . Step  1113  determines whether the absolute value of the difference (theoretical internal resistance value−rear internal resistance value) is less than a second resistance value R 2  which is a small value. In the case where the capacitance remains unchanged by battery change, the determination in step  1113  is positive, and the process proceeds to step  1114 . Step  1114  determines the battery change (capacitance remains the same). In this case, the vehicle occupants are informed of the battery change to by the announcing means  3  shown in  FIG. 1  in the next step  1115  thereby ending the routine. In the case where the determination in any of steps  1111 ,  1112  and  1113  is negative, battery change is not determined, and the process proceeds to step  1122  to execute the process of determining battery degeneration. 
         [0094]    (3) Process Executed in the Case Where the Capacitance is Decreased by Battery Change 
         [0095]    In the case where the capacitance is decreased by battery change, the difference, though large between the detected battery capacitance and normal battery capacitance, is opposite in polarity to the case where the capacitance is increased by battery change. This is determined as a case in which the difference between the detected battery capacitance and the normal battery capacitance is not smaller than the first capacitance criterion value C 0  nor the absolute value of the difference between the detected battery capacitance, and the normal battery capacitance is less than the second capacitance criterion value C 1 . In this case, the determination in both steps  1103  and  1110  are negative and the process proceeds to step  1116 . 
         [0096]    Step  1116  determines whether the battery change has ever been recognized or not, and if the battery changed has been recognized, the process proceeds to step  1117 . Step  1117  determines whether the open-circuit voltage has ever been changed or not, and due to the actual open-circuit voltage change, the process proceeds to step  1118 . Step  1118  determines whether the absolute value of the theoretical internal resistance value minus the actual internal resistance value (theoretical internal resistance value−actual internal resistance value) is not smaller than a third resistance value R 3  or not. In the case where the capacitance is decreased by battery change, the determination in step  1118  is positive and the process proceeds to step  1119  to determine battery change (capacitance decreased). In the next step  1120 , the battery change is notified to the vehicle occupants by the announcing means  3  shown in  FIG. 1 , followed by proceeding to step  1121 . In step  1121 , the process of switching the control operation described later is executed thereby to end the routine. In the case where the determination is negative in any of steps  1116 ,  1117  and  1118 , the battery change is not determined, and the process proceeds to step  1122  thereby to execute the process of determining battery degeneration. 
         [0097]      FIG. 12  shows the steps of the process for detecting the battery degeneration executed by the battery monitor apparatus  1  according to this invention. Step  1201  determines whether the value of the normal battery capacitance minus the detected battery capacitance (normal battery capacitance−detected battery capacitance) is not smaller than a third capacitance criterion value C 2  or not, and in the case where the value of the normal battery capacitance minus the detected battery capacitance is not smaller than the third capacitance criterion value C 2 , the process proceeds to step  1202  to determine whether the value of the internal resistance value less the theoretical resistance value is not smaller than a fourth resistance value R 4  or not. Upon determination that the internal resistance value minus the theoretical resistance value is not smaller than the fourth resistance value R 4 , the process proceeds to step  1203  to determine that the battery is degenerated. In this case, the vehicle occupants are notified of the need to change the battery in step  1204 , and the process of switching the control operation is executed thereby to end the routine. 
         [0098]    In the case where step  1201  determines that the value of the normal battery capacitance minus the detected battery capacitance is smaller than C 2  or in the case where step  1202  determines that the value of the internal resistance minus the theoretical resistance is smaller than R 4 , then the battery is not degenerated and therefore the routine is ended. 
         [0099]      FIG. 13  shows the steps of the control switching process executed by the battery monitor apparatus  1  according to the invention. In the case where the battery is changed in capacitance or degenerated, the battery charge characteristic becomes different from the past one. Control switching process, therefore, is executed to prevent the battery from running short of power or from being overcharged while the vehicle is running. Based on the data detected in step  1301 , the battery capacitance is switched, and the battery charging rate calculation method is changed in step  1302  thereby to end-the routine. 
         [0100]    Assuming that the preceding battery capacitance is 50 AH and the present detected battery capacitance is 60 AH, for example, the charging rate is increased by 1.2 times in spite of the same voltage. 
         [0101]      FIGS. 14A to 14C  show the steps of a modification of the battery change detecting process executed by the battery monitor apparatus  1  according to the invention explained with reference to  FIGS. 11A to 11C . The process in this embodiment is different from the process explained with reference to  FIGS. 11A to 11C  only in that the process of rewriting the battery capacitance in the memory is added between steps  1107  and  1108  and between steps  1119  and  1120 . Specifically, in the case where steps  1107  and  1119  determine that the battery is changed to another battery of a different capacitance, the new battery capacitance is stored in memory. The steps representing the same process, therefore, are designated by the same step numbers, respectively, and will not be explained hereafter. 
         [0102]      FIGS. 15A to 15C  show the steps of a modification of the battery change detecting process executed by the battery monitor apparatus  1  according to the invention explained with reference to  FIGS. 11A to 11C . The process in this embodiment is different from the process explained with reference to  FIGS. 11A to 11C  only in that steps  1107  to  1108  are replaced with steps  1501  to  1504  and steps  1119 ,  1120  with steps  1505  to  1508 . Therefore, the steps indicating the same processes are designated by the same step numbers, respectively, and will not be explained hereafter. 
         [0103]    According to this modification, upon determination that the theoretical internal resistance minus the real internal resistance is not less than the first resistance value R 1  in step  1106 , i.e. in the case where the battery is required to be changed for capacitance increase, the answer is positive and the process proceeds to step  1501 , in which the battery liquid temperature is acquired, followed by step  1502  in which the battery capacitance is calculated based on the actual internal resistance value. For this calculation, the map of  FIG. 16  showing the relation between the internal resistance and the capacitance of the battery is prepared for each area of, for example, 5° C. of the battery liquid temperature. 
         [0104]    In calculating the battery capacitance in step  1502 , the battery liquid temperature acquired in step  1501  is used and actual internal resistance is corrected to the value for the battery liquid temperature of 25° C. according to the map of  FIG. 3B  showing the relationship between the liquid temperature and the correction coefficient. After that, battery capacitance is calculated from the map of  FIG. 16  showing the relationship between the internal resistance and the capacitance of the battery. In step  1503 , the calculated battery capacitance is stored in memory. In step  1504 , an increase in battery size and battery capacitance stored in the memory are notified to the user, after which the control switching process of step  1109  is executed thereby to end the routine. 
         [0105]    Also, according to this modification, upon determination in step  1118  that the theoretical internal resistance minus the real internal resistance is not less than the third resistance value R 3 , i.e. in the case of battery change for capacitance decrease, the answer is positive and the process proceeds to step  1505 , in which battery liquid temperature is acquired, and the actual internal resistance is corrected to the value for the liquid temperature of 25° C. by the map of  FIG. 3B  showing the relationship between the liquid temperature and the correction coefficient. After that, in step  1506 , the battery capacitance is calculated from the map of  FIG. 16  showing the relationship between the internal resistance and the capacitance of the battery. The battery capacitance thus calculated is stored in memory in step  1507 . In step  1508 , the user is notified of a decrease in the battery capacitance stored in the memory, along with battery size, after which the control switching process is executed in step  1121  to end the routine. 
         [0106]      FIG. 17  is a flowchart showing the steps of the process for detecting the battery capacitance explained with reference to  FIGS. 2A to 2C , which process is executed after steps  213 ,  215 ,  216 ,  229 ,  231 ,  232  shown in  FIGS. 2A to 2C . In step  1701 , the battery change is detected, followed by determination whether the internal resistance value (real internal resistance value) of the battery has been calculated at least N times. In the case where the number of times the internal resistance value of the battery is calculated is less than N, the process is ended as it is, while in the case where the number of times is N or more, the process proceeds to step  1702 . 
         [0107]    In step  1702 , the N internal resistance values R 1  to RN calculated after detection of the battery change are corrected by temperature. In this correction by temperature, as explained above, the actual internal resistance is corrected to the value for the liquid temperature of 25° C. according to the map of  FIG. 3B  showing the relationship between the liquid temperature and the correction coefficient. After complete correction by temperature, the representative internal resistance value R after battery change detection is calculated using the well-known averaging process or the majority rule for the N internal resistance values R 1  to RN. 
         [0108]    After that, in step  1704 , the battery capacitance is calculated from the map of  FIG. 16  showing the relationship between the internal resistance and the capacitance of the battery using the representative internal resistance value R calculated in step  1703 . The battery capacitance may be calculated by a method other than the aforementioned method, and the detection method is not specifically limited. Once the battery capacitance is calculated upon lapse of a predetermined time after battery change detection, step  1705  determines whether the absolute value of the difference between the battery capacitance detected at the time of battery connection (when the old battery is removed and a new battery is connected) and the battery capacitance calculated in step  1704  is larger than a predetermined threshold value or not. 
         [0109]    Upon determination in step  1705  that the absolute value of the difference between the battery capacitance detected at the time of battery connection and the battery capacitance calculated in step  1704  is smaller than the predetermined threshold value, the process is ended as it is. In the case where the difference is larger than the predetermined threshold value, the process proceeds to step  1706 , in which the battery capacitance is corrected to the value calculated from the representative internal resistance value R and the memory contents are rewritten. In step  1707 , the user is notified that the battery has been changed and whether the capacitance of the new battery is the same, larger or smaller than that of the old battery, after which the routine is ended. 
         [0110]    The control operation according to the embodiment described above assumes that the discharge of a large current after battery change at the time of engine starting (turning of the starter), and engine starting is performed first before starting to drive the vehicle after a battery change. By performing this control operation while calculating the internal resistance of the battery based on the discharged state of the large current from the battery after detecting the battery change and then calculating the battery capacitance (capacitance of the full charged battery) based on this internal resistance, i.e. by calculating the battery capacitance according to the discharge state at the time of engine starting, time can be shortened before calculation of the battery capacitance after battery change. 
         [0111]    The aforementioned embodiment represents a case in which a lead battery is used as the in-vehicle battery of which the degeneration or change is to be determined. The determination of battery degeneration and battery change according to the invention is also applicable, to a lithium ion battery or nickel hydrogen battery with equal effect. 
         [0112]    Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.