Abstract:
An economical running control apparatus is operable to control an economical running in which an engine is automatically stopped when a predetermined engine stopping condition is established and the engine is automatically started when a predetermined engine starting condition is established. The economical running control apparatus is adapted to be mounted on a vehicle including the engine, a first battery operable to supply power to an vehicle mounted electric unit, and a second battery operable to suppress a voltage reduction in the first battery when the engine is started. A judge is operable to judge whether the economical running is permitted or prohibited based on a first quantity of electricity which the first battery is capable of discharging when the engine is started, a second quantity of electricity which the second battery is capable of discharging, and a third quantity of electricity required to completely explode the engine.

Description:
[0001]    The disclosure of Japanese Patent Application No. 2006-042577 filed Feb. 20, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The present invention relates to an economical running control apparatus and more particularly to an economical running control apparatus to perform an economical running in which an engine is automatically stopped when a predetermined engine stopping condition is established and the engine is automatically restarted when a predetermined engine restarting condition is established in a vehicle comprising a primary battery for supplying power to a vehicle mounted electric unit and a secondary battery for suppressing a voltage reduction of the primary battery when the engine is restarted. 
         [0003]    There are some vehicles which are equipped with an economical running system in which the engine is automatically stopped when a predetermined engine stopping condition is established and the engine is automatically restarted when a predetermined engine restarting condition is established. 
         [0004]    In these vehicles, although no power is generated when the engine is stopped while performing the economical running, the vehicle mounted electric unit such as an in-car audio system can be used. Therefore, the voltage reduction of the battery is expected. When the engine is restored from the economical running and restarted, the power supplied to the vehicle mounted electric unit is limited due to the voltage reduction of the battery. Therefore, it is considered that the vehicle mounted electric unit is reset or the engine cannot be restarted. 
         [0005]    In Japanese Patent Publication No. 2002-115578A, in order to prevent the voltage reduction of the battery, a battery voltage value is measured so as to prohibit the engine from being automatically stopped and the economical running is not performed when the voltage reduction is large. 
         [0006]    In addition, in Japanese Patent Publication No. 2004-251234A, a secondary battery (a capacitor) is installed on a vehicle for supplementing the voltage reduction of the primary buttery when the engine is restarted. The engine is prohibited from being automatically stopped and the economical running is not performed until the installed secondary battery restores a predetermined charged state. 
         [0007]    In the above related-art economical running control systems the economical running is not performed when a dischargeable quantity of electricity is insufficient in the secondary battery, even though the dischargeable quantity of electricity of the primary battery is sufficient to perform the economical running. Therefore, opportunities for performing the economical running are decreased. 
       SUMMARY 
       [0008]    It is therefore an object of the invention to provide an economical running control system which can facilitates performing the economical running. 
         [0009]    In order to achieve the above described objects, according to the invention, there is provided an economical running control apparatus operable to control an economical running in which an engine is automatically stopped when a predetermined engine stopping condition is established and the engine is automatically started when a predetermined engine starting condition is established, the economical running control apparatus adapted to be mounted on a vehicle including the engine, a first battery operable to supply power to an vehicle mounted electric unit, and a second battery operable to suppress a voltage reduction in the first battery when the engine is started, the economical running control apparatus comprising: 
         [0010]    a judge operable to judge whether the economical running is permitted or prohibited based on a first quantity of electricity which the first battery is capable of discharging when the engine is started, a second quantity of electricity which the second battery is capable of discharging, and a third quantity of electricity required to completely explode the engine. 
         [0011]    With this configuration, since whether the economical running is permitted or prohibited is judged based on both the first and the second power quantities that the first and second batteries can discharge when the engine started, the economical running can be permitted when the second quantity of electricity is larger than a predetermined value, even though the first quantity of electricity is insufficient to perform the economical running. In addition, the economical running can be permitted when the first quantity of electricity of the primary battery larger than a predetermined value, even though the second quantity of electricity is insufficient to perform the economical running. Thus, the opportunities to perform the economical running are increased, whereby the fuel economy of the vehicle can be increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a hardware block diagram of an economical running control system according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a hardware block diagram of an economical running control apparatus according to the embodiment; 
           [0015]      FIG. 3  is a functional block diagram of the economical running control apparatus; 
           [0016]      FIG. 4  is a flowchart showing a primary battery state detection process according to the embodiment; 
           [0017]      FIG. 5  is a flowchart showing a battery internal resistance value update process according to the embodiment; 
           [0018]      FIG. 6  is a diagram showing battery internal resistance value characteristic relative to battery fluid temperature; 
           [0019]      FIG. 7  is a flowchart showing a primary battery capacity correction process according to the embodiment; 
           [0020]      FIG. 8  is a diagram showing correction coefficient characteristic relative to battery fluid temperature; 
           [0021]      FIG. 9  is a diagram showing correction coefficient characteristics relative to battery internal resistance value; 
           [0022]      FIG. 10  is a flowchart showing a secondary battery state detection process according to the embodiment; 
           [0023]      FIG. 11  is a diagram showing secondary battery capacity characteristics relative to secondary battery voltage value; 
           [0024]      FIG. 12  is a diagram showing correction coefficient characteristics of secondary battery capacity relative to battery ambient temperature; 
           [0025]      FIG. 13  is a flowchart, showing a voltage reduction quantity calculation process according to the embodiment; 
           [0026]      FIG. 14  is a flowchart showing a voltage reduction quantity update process according to the embodiment; 
           [0027]      FIG. 15  is a flowchart showing a primary economical running permission determination process according to the embodiment; 
           [0028]      FIG. 16  is a flowchart showing a secondary economical running permission determination process according to the embodiment; 
           [0029]      FIG. 17  is a flowchart showing an capacity update process according to the embodiment; and 
           [0030]      FIG. 18  is a flowchart showing an automatic engine restarting process according to the embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0031]    Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings. 
         [0032]    As shown in  FIG. 1 , the economical running control system includes an economical running control apparatus  10  for controlling and performing an economical running, and an alternator  11  for generating power when an engine is activated, a vehicle mounted electric unit  12 , a primary battery  13  for supplying power to the vehicle mounted electric unit  12  and a secondary battery  14  (for example, a battery such as a capacitor) for suppressing voltage reduction in the primary battery  13  when the engine is restarted are connected to the economical running control apparatus  10  via a power supply line  15 . 
         [0033]    A voltage sensor  16  for detecting voltage, a current sensor  17  for detecting current and a temperature sensor  18  for detecting temperature are provided on the primary battery  13 , and although not shown, output terminals of the voltage sensor  16 , current sensor  17  and temperature sensor  18  are connected to the economical running control apparatus  10 . In addition, a voltage sensor  19 , a current sensor  20  and a temperature sensor  21  are provided on the secondary battery  14 , and although not shown, output terminals of the voltage sensor  19 , current sensor  20  and temperature sensor  21  are connected to the economical running control apparatus  10 . 
         [0034]    The vehicle mounted electric unit  12  is an electric unit installed on the vehicle and includes, for example, an electronic control unit for an engine control system and a brake control system and an in-car audio system. 
         [0035]    Based on signals detected by the voltage sensor  16 , the current sensor  17  and the temperature sensor  18  of the primary battery  13 , and signals detected by the voltage sensor  19 , the current sensor  20  and the temperature sensor  21  of the secondary battery  14 , the economical running control apparatus  10  calculates a discharged quantity of electricity which is discharged from the primary battery  13  while the primary battery voltage value of the primary battery  13  changes by a predetermined voltage, a dischargeable quantity of electricity which the secondary battery  14  can discharge and a voltage reduction quantity in voltage value of the primary battery from a start of the engine to a complete explosion of the engine. The economical running control apparatus  10  determines whether the apparatus permits or prohibits an economical running based on results of the calculations. 
         [0036]    As shown in  FIG. 2 , the economical running control apparatus  10  includes a microcomputer  30 , and this microcomputer  30  is connected to a bus  31  within the economical running control apparatus  10  and is then connected to an exterior signal line  33  via an I/F (Interface)  32 . 
         [0037]    The microcomputer  30  has a CPU (Central Processing Unit)  34 , and a ROM (Read Only Memory)  35  and a RAM (Random Access Memory)  36  are connected to the CPU  34  via a bus  37  within the microcomputer  30 . In addition, the bus  31  is connected to the CPU  34  via the bus  37 . 
         [0038]    The CPU  34  controls the whole of the economical running control apparatus  10 . Programs of an OS (Operating System) which is executed by the CPU  34  and at least a part of an application program are temporarily stored in the RAM  36 . In addition, various data which is necessary for processing by the CPU  34  is stored in the RAM  36 . The programs of the OS and the application program are stored in the ROM  35 . 
         [0039]    The application program includes programs for a primary battery state detection process, a secondary battery state detection process, a voltage reduction quantity calculation process and an economical running permission determination process which are executed by the economical running control apparatus  10 . 
         [0040]    As shown in  FIG. 3 , the economical running control apparatus  10  includes a primary battery monitoring unit  41  (first monitor), a secondary battery monitoring unit  42  (second monitor), a primary battery state detection unit  43  (first calculator), a secondary battery state detection unit  44  (second calculator), a voltage reduction quantity calculation unit  45  (third calculator) and an economical running permission determination unit  46  judge). 
         [0041]    The primary battery state monitoring unit  41  samples a primary battery voltage value, a primary battery current value and a battery fluid temperature of the primary battery  13  which are detected by the voltage sensor  16 , the current sensor  17  and the temperature sensor  18 , respectively. In addition, the secondary battery state monitoring unit  42  samples a secondary battery voltage value, a secondary battery current value and a battery ambient temperature of the secondary battery  14  which are detected by the voltage sensor  19 , the current sensor  20  and the temperature sensor  21 , respectively. 
         [0042]    Based on results of the samplings, the primary battery state detection unit  43  calculates a primary battery capacity which indicates a discharged quantity of electricity (first quantity of electricity) that is discharged from the primary battery  13  while the primary battery voltage value changes by a predetermined voltage, the secondary battery state detection unit  44  obtains (or calculates) a secondary battery capacity which indicates a dischargeable quantity of electricity (second quantity of electricity) which the secondary battery  14  can discharge, and the voltage reduction quantity calculation unit  45  calculates a voltage reduction quantity (voltage reduction value) in voltage value of the primary battery from a start of the engine to a complete explosion of the engine. 
         [0043]    Based on results of the calculations, the economical running permission determination unit  46  determines whether it permits or prohibits the economical running by comparing the electric quantities which can be supplied from the primary battery  13  and the secondary battery  14  for starting the engine with an quantity of electricity which is required between the start of the engine to the complete explosion of the engine. 
         [0044]    As shown in  FIG. 4 , the primary battery state detection unit  43  executes a process in accordance with the following steps based on a primary battery state detection process program when the engine is started by driving a starter. 
         [0045]    [Step S 11 ] The CPU  34  determines whether or not the engine has been started by driving the starter. If the engine is determined to have been started through drive of the starter, the process proceeds to a step S 12 , whereas if the engine is determined otherwise, the primary battery state detection process ends. 
         [0046]    [Step S 12 ] The CPU  34  determines whether or not a predetermined period of time has elapsed since the engine was started. This is because a subsequent step needs to be delayed for the predetermined period of time since the start of the engine in order to avoid the sampling of an inrush current, which flows in an initial state of the engine start, as a primary battery current value. If the predetermined period of time is determined to have elapsed, the process proceeds to a step S 14 , whereas if determined otherwise, the process proceeds to a step S 13 . 
         [0047]    [Step S 13 ] The CPU  34  stores the current primary battery voltage value which resulted immediately after the engine was started as a starting voltage value V 0  in order to compare it with a future primary battery voltage and waits for passage of the predetermined period of time. 
         [0048]    [Step S 14 ] The CPU  34  starts sampling primary battery voltage values and primary battery current values which have been detected by the voltage sensor  16  and the current sensor  17 , respectively. 
         [0049]    [Step S 15 ] The CPU  34  calculates a variation in primary battery voltage value and a variation in primary battery current value from the primary battery voltage value and the primary battery current value which have been sampled this time and the primary battery voltage value and the primary battery current value which were sampled previously and calculates a battery internal resistance value Rn by diving the variation in primary battery voltage value by the variation in primary battery current value. Namely, , the battery internal resistance value Rn is calculated as below; 
         [0000]        Rn =( V now− V old)/( I now− I old)   (1) 
         [0000]    where, the primary battery voltage value and the primary battery current value which have been sampled this time are Vnow (V) and Inow (A), respectively, and the primary battery voltage value and the primary battery current value which were sampled previously are Vold (V) and Iold (A), respectively. This battery internal resistance value Rn, which is calculated individually for each sampling, is sequentially accumulated, and a value for a sum Rsum of those battery internal resistance values is obtained by the following equation; 
         [0000]        R sum= R 0 +R 1 +R 2 + . . . Rn    (2) 
         [0050]    [Step S 16 ] The CPU  34  calculates a discharged quantity of electricity Isum 0  which has been discharged from the primary battery  13  since the predetermined period of time was determined to have elapsed in the processing in the step S 12  until the current point in time, that is, calculates an accumulated value of primary battery current values. 
         [0051]    [Step S 17 ] The CPU  34  determines whether or not the primary battery voltage value V 1  which was measured in the step S 14  is larger than the starting voltage value V 0  by a predetermined value V 2 . If the primary battery voltage value V 1  is determined to be so larger, the process proceeds to a step S 20 , whereas if smaller, the process proceeds to a step S 18 . 
         [0052]    [Step S 18 ] The CPU  34  determines whether or not there has occurred the complete explosion of the engine. If the complete explosion is determined to have occurred, the process proceeds to the step S 20 , whereas if not, the process proceeds to a step S 19 . 
         [0053]    [Step S 19 ] The CPU  34  determines whether or not a predetermined period of time has elapsed since the sampling was started. This is because when a state continues for the predetermined period of time in which there has occurred no complete explosion since the engine was started, there exists a possibility of occurrence of a problem that the engine has not yet been started and with such a problem, the primary battery state detection process needs to be ended. If the predetermined period of time is determined to have elapsed, the primary battery state detection process ends, whereas the predetermined period of time is determined otherwise, the process returns to the step S 15 . 
         [0054]    In the steps that have been described heretofore, the sampling of the primary battery voltage value and primary battery current value, calculation of each of the battery internal resistance values and the sum thereof and calculation of the discharged quantity of electricity Isum 0  are periodically performed until the difference between the current primary battery voltage value V 1  and the starting voltage value V 0  becomes the predetermined value V 2  or the engine is completely exploded. 
         [0055]    [Step S 20 ] The CPU  34  calculates a primary battery capacity which indicates a discharged quantity of electricity that is discharged from the primary battery  13  while the primary battery voltage value changes by 1V by dividing the discharged quantity of electricity Isum 0  calculated in the processing in the step S 16  by a value which results when subtracting the starting voltage value V 0  from the current primary battery voltage value V 1 . Namely, the primary battery capacity Cm (A sec/V) is calculated as follows; 
         [0000]      Cm= a /(| V 1 −V 0|)× I sum0   (3) 
         [0000]    where, the current primary battery voltage value is V 1  (V), the starting voltage value is V 0  (V), and the discharged power is Isum 0  (A sec),the constant a is a unit variation width of voltage in the primary battery  13 , and here, a=1. 
         [0056]    [Step S 21 ] The CPU  34  determines on a battery internal resistance value. In this embodiment, this battery internal resistance value is made to be a mean value obtained by dividing the value of the sum Rsum of battery internal resistance values which was calculated in the processing in the step S 15  by the number n of samples. Of course, this battery internal resistance value may take a maximum value or a mode value, or the battery internal resistance value may be determined after deleting those of the battery internal resistance values which depart too far. 
         [0057]    [Step S 22 ] The CPU  34  stores the current battery fluid temperature as THB 0  for comparison with a future battery fluid temperature. 
         [0058]    With the processes that have been described heretofore, the primary battery capacity and the battery internal resistance value are obtained based on the primary battery voltage values and the primary battery current values which were measured since the start of the engine until the primary battery voltage value was recovered from the starting voltage value after the passage of the predetermined period of time or the engine is completely exploded, and finally, the battery fluid temperature is obtained, whereby the state of the primary battery  13  is detected. 
         [0059]    Here, since the battery internal resistance value changes at all times to match changes in the primary battery current value and the battery fluid temperature, the battery internal resistance value so calculated needs to be updated by a battery internal resistance value which matches the changes. 
         [0060]    Next, a battery internal resistance value updating process by the primary battery state detection unit  43  will be described. 
         [0061]    As shown in  FIG. 5 , the primary battery state detection unit  43  repeatedly executes a process which follows steps below based on the primary battery state detection process program. 
         [0062]    [Step S 31 ] The CPU  34  determines whether or not an initial calculation of a battery internal resistance value has been completed. If determined to have been completed, the process proceeds to a step S 32 , whereas if determined otherwise, the battery internal resistance value updating process ends here. 
         [0063]    [Step S 32 ] The CPU  34  determines whether or not a difference between the current primary battery current value and the primary battery current value which resulted when the battery internal resistance value was determined is a predetermined value I 0  or more. Note that here, when the primary battery current value has changed by the predetermined value I 0  or more, the battery internal resistance value has been also changed to match the change of the primary battery current value, and therefore, the battery internal resistance value needs to be updated. If the difference is equal to or more than the predetermined value I 0 , the process proceeds to a step S 33 , whereas if the difference is less than the predetermined value I 0 , the process proceeds to a step S 38 . 
         [0064]    [Step S 33 ] The CPU  34  starts sampling primary battery voltage values and primary battery current values which have been detected by the voltage sensor  16  and the current sensor  17 , respectively. 
         [0065]    [Step S 34 ] The CPU  34  calculates a battery internal resistance value Rn. This battery internal resistance value Rn (V/A) is calculated by the previously described equation (1). Following this, a value for a sum Rsum of the battery internal resistance values so calculated is then calculated by the previously described equation (2). 
         [0066]    [Step S 35 ] The CPU  34  determines whether or not a predetermined period of time has elapsed since the sampling was started. This determination is made due to the primary battery voltage and the primary battery current value being sampled at a predetermined period over the predetermined period of time. If the predetermined period of time is determined to have elapsed, the process proceeds to a step  536 , whereas if the predetermined period of time is determined not to have elapsed, the process returns to the step S 33 . 
         [0067]    In the steps heretofore, the sampling of the primary battery voltage value and primary battery current value and calculation of the individual battery internal resistance values and the sum thereof are implemented periodically until the predetermined period of time has elapsed since the engine was started. 
         [0068]    [Step S 36 ] The CPU  34  determines a battery internal resistance value. In this embodiment, this battery internal resistance value is made to be a mean value obtained by dividing the value of the sum Rsum of battery internal resistance values which was calculated in the processing in the step S 34  by the number n of samples. Of course, this battery internal resistance value may take a maximum value or a mode value, or the battery internal resistance value may be determined after deleting those of the battery internal resistance values which depart too far. 
         [0069]    [Step S 37 ] The CPU  34  stores the current battery fluid temperature as THB 0  for comparison with a future battery fluid temperature. 
         [0070]    [Step S 38 ] The CPU  34  determines whether or not a difference between the current battery temperature and the battery fluid temperature which resulted when the battery internal resistance value was determined is a predetermined value THB 1  or more. Note that here, when the battery fluid temperature changes by the predetermined value THB 1  or more, the battery internal resistance value has also been changed to match the change of the battery fluid temperature, and therefore, the battery internal resistance value needs to be updated. If the difference is determined to be equal to or more than the predetermined value THB 1 , the process proceeds to a step S 39 , whereas if the difference is determined to be less than the predetermined value THB 1 , the battery internal resistance value updating process ends. 
         [0071]    Here, as is shown in  FIG. 6 , the primary battery  13  has temperature characteristics in which the battery internal resistance value changes to mach the change in the battery fluid temperature. This temperature characteristic data is stored in the ROM  35  in the form of a table in which the battery fluid temperature is related to the battery internal resistance. 
         [0072]    [Step S 39 ] The CPU  34  temporarily updates the battery internal resistance value by obtaining a battery internal resistance value which corresponds to the battery fluid temperature by referring to the temperature characteristic data. 
         [0073]    The processing carried in this step S 39  is such as to temporarily update the battery internal resistance value by a theoretical value in place of an actual value when the battery internal resistance value cannot be updated because the primary battery current value does not change irrespective of the fact that the battery fluid temperature is changing. For example, when a vehicle is driven at constant speeds for hours as when running on a highway, since the engine speed remains constant, the power generation quantity of the alternator  11  changes little, whereby the primary battery current value is made difficult to change, and this makes it difficult for the process to proceed to the step S 36 , the battery internal resistance value being thereby made difficult to be updated. In order to avoid a situation in which the battery internal resistance value is not updated when the battery fluid temperature changes largely in these situations, the battery internal resistance value is temporarily updated in the processing carried out in the step S 39 . Note that when the process can proceed to the step S 36  in any of subsequent cycles to the temporary update after the battery internal resistance value has been temporarily updated, the battery internal resistance value is updated by an actual value which is available then. 
         [0074]    With the processes described above, when the primary battery current value changes, the battery internal resistance value is updated in accordance with the change in the primary battery current value, and when the variation in the battery fluid temperature is large while the variation in the primary battery current value is small, the battery internal resistance value is updated to a battery internal resistance value which corresponds to the battery fluid temperature, so that the battery internal resistance value is designed to be updated to a most updated battery internal resistance value at all times. 
         [0075]    Next, a primary battery capacity correcting process by the primary battery state detection unit  43  will be described. 
         [0076]    As shown in  FIG. 7 , the primary battery state detection unit  43  executes repeatedly a process which follows steps below based on the primary battery state detection process program. 
         [0077]    Here, since the primary battery  13  has the temperature characteristics, the primary battery capacity changes in such a manner as to match a change in the battery fluid temperature. In order to have the primary battery capacity match the change, the primary battery capacity needs to be corrected in accordance with the battery fluid temperature. 
         [0078]    The primary battery  13  has a tendency that ions in the interior of the primary battery  13  get easier to be activated as the battery fluid temperature Tm increases, whereby the primary battery capacity is increased. Because of this, as is shown in  FIG. 8 , a correction coefficient for correction of the primary battery capacity is made to increase as the battery fluid temperature increases. This temperature characteristic data is stored in the ROM  35  in the form of a table in which the battery fluid temperature is related to the correction coefficient. 
         [0079]    [Step S 41 ] The CPU  34  determines whether or not a difference between the current battery fluid temperature and the battery fluid temperature which resulted when the primary battery capacity was calculated is the predetermined value THB 1  or more. Here, if the change in the battery fluid temperature is equal to or more than the predetermined value THB 1 , since the primary battery capacity has changed to match the change in the battery fluid temperature, the process proceeds to a step S 42  to correct the primary battery capacity, whereas if the change is less than the predetermined value THB 1 , the process proceeds to a step S 44 . 
         [0080]    [Step S 42 ] The CPU  34  obtains a correction coefficient of the primary battery capacity which corresponds to the battery fluid temperature by referring to the temperature characteristic data stored in advance in the ROM  35 . Following this, the CPU  34  corrects the primary battery capacity by multiplying the primary battery capacity by the correction coefficient so obtained. 
         [0081]    [Step S 43 ] The CPU  34  stores the current battery fluid temperature as THB 0  for comparison with a future battery fluid temperature. 
         [0082]    Here, since the primary battery  13  has the characteristics in which the primary battery capacity changes with change in the battery internal resistance value, the primary battery capacity has been changed to match the change in the battery internal resistance value. In order to reflect the change in the primary battery capacity thereon, the primary battery capacity needs to be corrected in accordance with the battery internal resistance value. 
         [0083]    The primary battery  13  has a tendency that the primary battery current value decreases as the battery internal resistance value Rm increases, whereby the primary battery capacity decreases. Because of this, as is shown in  FIG. 9 , a correction coefficient for correction of the primary battery capacity is made to decrease as the battery internal resistance value increases. This characteristic data is stored in the ROM  35  in the form of a table in which the battery internal resistance value is related to the correction coefficient. 
         [0084]    [Step S 44 ] The CPU  34  determines whether or not a difference between the current battery internal resistance value and the primary battery capacity which resulted when the primary battery capacity was calculated is a predetermined value R 0  or more. Here, if the change in the battery internal resistance value is equal to or more than the predetermined value R 0 , since the primary battery capacity has been also changed to match the change in the battery internal resistance value, the process proceeds to a step S 45  to correct the primary battery capacity, whereas if the change is less than the predetermined value R 0 , the primary battery capacity correction process ends. 
         [0085]    [Step S 45 ] The CPU  34  obtains a correction coefficient of the primary battery capacity which corresponds to the battery internal resistance value by referring to the characteristic data stored in advance in the ROM  35 . Following this, the CPU  34  corrects the primary battery capacity by multiplying the primary battery capacity by the coefficient so obtained. 
         [0086]    With the above processes, when battery fluid temperature changes largely, the primary battery capacity is corrected to a primary battery capacity which corresponds to the battery fluid temperature so changed, and when the battery internal resistance value changes largely with the battery fluid temperature changing little, the primary battery capacity is corrected to a primary battery capacity which corresponds to the battery internal resistance value so changed, whereby the primary battery capacity is designed to be corrected to a most updated primary battery capacity at all times. 
         [0087]    Next, a process by the secondary battery state detection unit  44  will be described. 
         [0088]    As shown in  FIG. 10 , the secondary battery state detection unit  44  executes repeatedly a process which follows steps below based on a secondary battery state detection process program. 
         [0089]    [Step S 51 ] The CPU  34  obtains a secondary battery voltage value detected by the voltage sensor  19 . 
         [0090]    [Step S 52 ] The CPU  34  obtains a secondary battery capacity which indicates a dischargeable quantity of electricity that the secondary battery  14  can discharge. Namely, as is shown in  FIG. 11 , since the secondary battery  14  has a characteristic in which the secondary battery capacity changes with secondary battery voltage value Vs, the CPU  34  obtains (or calculates) a secondary battery capacity which corresponds to the secondary battery voltage obtained thereby by referring to the secondary battery&#39;s characteristic data stored in the ROM  35 . 
         [0091]    [Step S 53 ] The CPU  34  obtains a secondary battery ambient temperature detected by the temperature sensor  21 . This is because since the secondary battery  14  also has inconsiderably temperature characteristics, the secondary battery capacity needs to be corrected to match the secondary battery voltage value in accordance with the secondary battery ambient temperature. In addition, the temperature characteristic data is stored in the ROM  35 . 
         [0092]    [Step S 54 ] The CPU  34  obtains a correction coefficient of the secondary battery capacity relative to the battery ambient temperature by referring to the ROM  35  and corrects the dischargeable quantity of electricity that the secondary battery  14  can discharge, that is, the secondary battery capacity by multiplying the secondary battery capacity obtained in the step S 52  by the correction coefficient so obtained. 
         [0093]    With the above processes, the state of the secondary battery  14  is detected by obtaining the secondary battery capacity which corresponds to the secondary battery voltage value and the battery ambient temperature. 
         [0094]    Next, the voltage reduction quantity calculation unit  45  performs a calculation of a voltage reduction quantity of the primary battery  13  when the starter is driven. A necessary discharged quantity of electricity which is necessary when the starter is driven can be obtained from the voltage reduction quantity so calculated. 
         [0095]    As shown in  FIG. 13 , the voltage reduction quantity calculation unit  45  executes a process in accordance with steps below based on a voltage reduction quantity calculation process program. 
         [0096]    [Step S 61 ] The CPU  34  stores the primary battery voltage value which resulted immediately before the engine was started as V 3  for comparison with a future primary battery voltage value. 
         [0097]    [Step S 62 ] The CPU  34  determines whether or not the engine has been started by driving the starter. If determined to have been so started, the process proceeds to a step S 63 , whereas if determined otherwise, the voltage reduction quantity calculation process ends. 
         [0098]    [Step S 63 ] The CPU  34  starts sampling primary battery voltage values and primary battery current values which have been detected by the voltage sensor  16  and the current sensor  17 , respectively. 
         [0099]    [Step S 64 ] The CPU  34  detects a maximum primary battery current value as Imax from the primary battery current values so sampled. 
         [0100]    [Step S 65 ] The CPU  34  detects a minimum voltage value as Vmin from the primary battery voltage values so sampled. 
         [0101]    [Step S 66 ] The CPU  34  calculates a discharged quantity of electricity Isum 0  that has been discharged from the primary battery  13  since the engine was started until the current point in time. 
         [0102]    [Step S 67 ] The CPU  34  determines whether or not a complete explosion has been produced in the engine. If determined to have been produced, the process proceeds to a step S 70 , whereas if determined otherwise, the process proceeds to a step S 68 . 
         [0103]    [Step S 68 ] The CPU  34  determines whether or not a predetermined period of time has elapsed since the sampling was started. When a state that the engine is not completely exploded since the engine is started, continues for the predetermined period of time, there is a possibility of a problem that the starter is not driven properly. When such a problem really occurs, the voltage reduction quantity calculation process needs to end. Therefore, if the CPU  34  determines that the predetermined period of time has elapsed, the voltage reduction quantity calculation process ends, and if the CPU  34  determines that the predetermined period of time has not elapsed, the process proceeds to a step S 69 . 
         [0104]    [Step S 69 ] The CPU  34  determines whether or not the starter drive has been completed. The starter drive is implemented while the engine is started until the engine is completely exploded. In a case where the starter drive is completed although the engine is not completely exploded, there is a possibility of a problem that the starter is not driven properly. When such a problem really occurs, the voltage reduction quantity calculation process needs to end. When the engine is not completely exploded, if the CPU  34  determines that the starter drive has been completed, the voltage reduction quantity calculation process ends, and if the CPU  34  determines that the starter drive has been determined that the starter drive has not been completed yet, the process returns to the step S 63 . 
         [0105]    [Step S 70 ] The CPU  34  calculates an estimated value of a voltage reduction quantity of the primary battery voltage value by dividing the discharged quantity of electricity Isum 0  by the primary battery capacity. Namely, an estimated value Vd 1  (V) of a voltage reduction quantity of the primary battery voltage value is calculated as below; 
         [0000]        Vd 1 =I sum0 /Cm    (4) 
         [0000]    where, the primary battery capacity is Cm. 
         [0106]    [Step S 71 ] The CPU  34  calculates an actual value of the voltage reduction quantity of the primary battery voltage value by subtracting a minimum primary battery voltage value Vmin from the primary battery voltage value V 3  which resulted immediately before the engine was started. Namely, an actual value Vd 2  of the voltage reduction quantity of the primary battery is calculated as bellow; 
         [0000]        Vde=V 3 −V min   (5) 
         [0000]    where, the primary battery voltage value V 3  which resulted immediately before the engine was started is V 3  (V) and the minimum primary battery voltage value is Vmin (V) 
         [0107]    [Step S 72 ] The CPU  34  determines on a voltage reduction quantity of the primary battery voltage value. This voltage reduction quantity is determined based on the estimated value of voltage reduction quantity calculated by the processing in the step S 70  and the actual value of voltage reduction quantity calculated in the step S 71 . Here, a comparison is made between the estimated value of voltage reduction quantity calculated by the processing in the step S 70  and the actual value of voltage reduction quantity calculated in the step S 71 , and a larger value is determined to be the voltage reduction quantity of the primary battery voltage value. Note that the voltage reduction quantity that is determined here may be a mean value of the estimated value of voltage reduction quantity and the actual value of voltage reduction quantity. 
         [0108]    With the above processes, the maximum primary battery current value Imax that had been discharged from the primary battery  13  since the starter was driven until the starter drive was completed when the starter was driven and the voltage reduction quantity of the primary battery voltage value. 
         [0109]    Here, since the voltage reduction quantity changes at all times with changes in the primary battery capacity and the battery internal resistance value, the voltage reduction quantity so calculated needs to be updated by a voltage reduction quantity which matches the changes in the primary battery capacity and the battery internal resistance value. 
         [0110]    Next, a voltage reduction quantity update process by the voltage reduction quantity calculation unit  45  will be described. 
         [0111]    As shown in  FIG. 14 , the voltage reduction quantity calculation unit  45  executes repeatedly a process in accordance with steps below based on the voltage reduction quantity calculation process program. 
         [0112]    [Step S 81 ] The CPU  34  determines whether or not a difference between the current primary battery capacity and the primary battery capacity which resulted when the voltage reduction quantity was calculated is equal to or more than a predetermined Cm 1 . Here, since when the primary battery capacity changes by the predetermined value Cm 1  or more, the voltage reduction quantity of the primary battery voltage value has been also changed to match the change in the primary battery capacity, the voltage reduction quantity of the primary battery voltage value needs to be updated. When the difference is equal to or more than the predetermined value Cm 1 , the process proceeds to a step S 82 , whereas if the difference is less than the predetermined value Cm 1 , the process proceeds to a step S 83 . 
         [0113]    [Step S 82 ] The CPU  34  updates the voltage reduction quantity of the primary battery voltage value by recalculating a voltage reduction quantity of the primary battery voltage value by dividing the discharged current quantity Isum 0  which resulted when the voltage reduction quantity was calculated by the current primary battery capacity. 
         [0114]    [Step S 83 ] The CPU  34  determines whether or not a difference between the current battery internal resistance value and the battery internal resistance value which resulted when the voltage reduction quantity was calculated is equal to or more than a predetermined value R 1 . Here, since when the battery internal resistance value changes by the predetermined value R 1  or more, the voltage reduction quantity of the primary battery voltage value is understood to also have changed to match the change in the battery internal resistance value, the process of updating the voltage reduction quantity of the primary battery voltage value needs to be performed. If the difference is the predetermined value R 1  or more, the process proceeds to a step S 84 , whereas if the difference is less than the predetermined value R 1 , the voltage reduction quantity update process ends. 
         [0115]    [Step S 84 ] The CPU  34  updates the voltage reduction quantity of the primary battery voltage value by multiplying the maximum primary battery current value Imax which resulted when the voltage reduction quantity was calculated by the current battery internal resistance value to thereby recalculate a voltage reduction quantity of the primary battery voltage value. 
         [0116]    With the above processes, when the primary battery capacity has changed by the predetermined value Cm 1  or more after the completion of starter drive or when the battery internal resistance value has changed by the predetermined value R 1  or more while the primary battery capacity has not changed, the voltage reduction quantity of the primary battery voltage value that has already been calculated is updated, so as to be kept updated to the voltage reduction quantity corresponding to the current primary battery voltage value. 
         [0117]    Based on the states of the primary battery and the secondary battery, which are obtained from the processes that have been described heretofore, the economical running permission determination unit  46  executes a determination process of whether an economical running is permitted or prohibited. 
         [0118]    The economical running permission determination unit  46  contains a primary economical running permission determination process and/or a secondary economical running permission determination process program, and these programs are selected as required. 
         [0119]    Firstly, a primary economical running permission determination process by the economical running permission determination unit  46  will be described. 
         [0120]    As shown in  FIG. 15 , the economical running permission determination unit  46  executes repeatedly a process in accordance with steps below based on the economical running permission determination process program. 
         [0121]    [Step S 91 ] The CPU  34  calculates a necessary discharging quantity of electricity Ind 0  which is to be discharged by the primary battery  13  when the starter is driven. This necessary discharging quantity of electricity Ind 0  (A sec) is calculated by multiplying the voltage reduction quantity calculated in the processing in the step S 72  by the primary battery capacity, and the necessary discharging quantity of electricity Ind 0  is expressed as below; 
         [0000]        Ind 0 =Vd×Cm    (6) 
         [0000]    where, the voltage reduction quantity of the primary battery voltage value is Vd (V). 
         [0122]    [Step S 92 ] The CPU  34  determines whether or not the necessary discharging quantity of electricity Ind 0  is equal to or more than the secondary battery capacity (the dischargeable quantity of electricity of the secondary battery  14 ). If determined to be smaller, since the whole of the necessary discharging quantity of electricity that the primary battery  13  is to discharge can completely covered by the dischargeable quantity of electricity of the secondary battery  14 , the process proceeds to a step S 97 , whereas if determined to be larger, the process proceeds to a step S 93 . 
         [0123]    [Step S 93 ] Since when the necessary discharging quantity of electricity Ind 0  is equal to or more than the secondary battery capacity, the secondary battery  14  cannot completely assist the primary battery  13 , the CPU  34  prohibits an economical running by the dischargeable quantity of electricity of the secondary battery  14 . 
         [0124]    [Step S 94 ] The CPU  34  calculates an economical running permitting voltage threshold value V 4  (threshold value) which can permit an economical running by a dischargeable quantity of electricity of the primary battery  13 . This economical running permitting voltage threshold value V 4  is calculated by adding the voltage reduction quantity calculated in the processing in the step S 72  to a lowest voltage determination voltage value. It is determined that the primary battery voltage value cannot become lower than the lowest voltage determination voltage value when the starter is driven. Namely, the lowest voltage determination voltage value means a minimum value of the voltage value of the first battery. 
         [0125]    [Step S 95 ] The CPU  34  determines whether or not the primary battery voltage value is equal to or more than the economical running permitting voltage threshold value V 4 . If determined to be more, it means that the primary battery  13  itself holds the whole of the necessary discharging quantity of electricity that the primary battery  13  is to discharge, and the process proceeds to a step S 96 , whereas if determined to be smaller, the process proceeds to a step S 98 . 
         [0126]    [Step S 96 ] The CPU  34  cancels the prohibition of the economical running by the dischargeable quantity of electricity of the secondary battery  14 . 
         [0127]    [Step S 97 ] The CPU  34  permits the economical running by the discharging quantity of electricity from the primary battery  13  or the economical running by the dischargeable quantity of electricity of the secondary battery  14 . [Step S 98 ] The CPU  34  prohibits the economical running by the discharging quantity of electricity from the primary battery  13 . 
         [0128]    In this way, the economical running permission determination unit  46  firstly determines whether or not the engine can be restarted only by the secondary battery  14 , and although the economical running by the secondary battery  14  is prohibited, when the primary battery voltage value is equal to or more than the economical running permitting voltage threshold value, the economical running permission determination unit  46  cancels the prohibition of the economical running by the secondary battery  14  so as to permit the economical running, whereby even though the economical running is permitted to stop the engine, since the primary battery  13  or the secondary battery  14  holds the necessary discharging quantity of electricity that is to be discharged by the primary battery  13  when the starter is driven, the restart of the engine can be ensured when attempting to restore the normal driving by the engine from the economical running. 
         [0129]    Next, a secondary economical running permission determination process by the economical running permission determination unit  46  will be described. 
         [0130]    As shown in  FIG. 16 , the economical running permission determination unit  46  executes repeatedly a process in accordance with steps below based on the economical running permission determination process program. 
         [0131]    [Step S 101 ] The CPU  34  calculates a necessary discharging quantity of electricity Ind 0  that the primary battery  13  is to discharge when the starter is driven. This necessary discharging quantity of electricity Ind 0  is calculated by multiplying the voltage reduction quantity calculated in the voltage reduction quantity calculation processing in the step  72  by the primary battery capacity. 
         [0132]    [Step S 102 ] The CPU  34  calculates an insufficient quantity of dischargeable power of the secondary battery  14  (fourth quantity of electricity) when the starter is driven. This insufficient quantity of dischargeable power is calculated by subtracting the secondary battery capacity (the dischargeable quantity of electricity of the secondary battery  14 ) which was calculated in the processing in the step  53  from the necessary discharging quantity of electricity Ind 0 . 
         [0133]    [Step S 103 ] The CPU  34  determines whether or not the insufficient quantity of dischargeable power is equal to or more than a predetermined value Ind 1 . If determined to be less, since the whole of the necessary discharging power amount that the primary battery  13  is to discharge can sufficiently be covered by the dischargeable quantity of electricity of the secondary battery  14 , the process proceeds to a step S 108 , whereas if determined to be more, the process proceeds to a step S 104 . 
         [0134]    [Step s 104 ] Since when the insufficient quantity of dischargeable power is equal to or more than the predetermined value Ind 1 , the secondary battery  14  cannot sufficiently assist the primary battery  13 , the CPU  34  prohibits the economical running by the dischargeable quantity of electricity of the secondary battery  14 . 
         [0135]    [Step S 105 ] The CPU  34  calculates an economical running permitting voltage threshold value V 5  (threshold value) which can permit an economical running by the discharging quantity of electricity of the primary battery  13 . This economical running permitting voltage threshold value V 5  is calculated by dividing the insufficient quantity of dischargeable quantity of electricity by the primary battery capacity and adding the lowest voltage determination voltage value to the result of the division. Namely, the economical running permitting voltage threshold value V 5  (V) is calculated as below; 
         [0000]        V 5 =Vt +( If/Cm )   (7) 
         [0000]    where, the insufficient quantity of dischargeable power is If (A sec), the lowest voltage determination voltage value is Vt (V), the primary battery capacity is Cm. 
         [0136]    [Step S 106 ] The CPU  34  determines whether or not the primary battery voltage value is equal to or more than the economical running permitting voltage threshold value V 5 . If determined to be more, it means that the primary battery  13  and the secondary battery  14  hold the whole of the discharging quantity of electricity that the primary battery  13  is to discharge, and the process proceeds to a step s 107 , whereas if determined to be less, the process proceeds to a step S 109 . 
         [0137]    [Step S 107 ] The CPU  34  cancels the prohibition of the economical running by the dischargeable quantity of electricity of the secondary battery  14 . 
         [0138]    [Step S 108 ] The CPU  34  permits the economical running by the discharging quantity of electricity of the primary battery  13  or the economical running by the dischargeable quantity of electricity of the secondary battery  14 . 
         [0139]    [Step S 109 ] The CPU  34  prohibits the economical running by the discharging quantity of electricity of the primary battery  13 . 
         [0140]    In this way, the economical running permission determination unit  46  firstly determines from the insufficient quantity of dischargeable power whether or not the engine can be restarted only by the secondary battery  14 , and even though the economical running by the secondary battery  14  is prohibited, when primary battery voltage value is equal to or more than the economical running permitting voltage threshold value, the economical running permission determination unit  46  cancels the prohibition of the economical running by the secondary battery  14  so as to permit the economical running, whereby even though the economical running is permitted to stop the engine, since the primary battery  13  or the secondary battery  14  holds the necessary discharging quantity of electricity that the primary battery  13  is to discharge when the starter is driven, the restart of the engine can be ensured when attempting to restore the normal driving by the engine from the economical running. 
         [0141]    Next, an in-economical running capacity update process by the economical running permission determination unit  46  will be described. 
         [0142]    As shown in  FIG. 17 , the economical running permission determination unit  46  executes repeatedly a process which follows steps below while the economical running is in operation based on the economical running permission determination program. 
         [0143]    [Step S 111 ] The CPU  34  determines whether or not the economical running is in operation. If determined to be in operation, the process proceeds to a step S 113 , whereas if determined otherwise, the process proceeds to a process S 112 . 
         [0144]    [Step S 112 ] The CPU  34  stores the primary battery voltage value which resulted before the economical running was put in operation as a starting voltage value V 0  for comparison with a future primary battery value. 
         [0145]    [Step S 113 ] The CPU  34  calculates a battery internal resistance value Rn. This battery internal resistance value Rn (V/A) is calculated by the previously described equation (1). Following this, a value of a sum Rsum of the battery internal resistance values so calculated is then calculated by the previously described equation (2). 
         [0146]    [Step S 114 ] The CPU  34  calculates a battery internal resistance value Rn. This battery internal resistance value Rn (V/A) is calculated in the previously described equation (1). Following this, a value for a sum Rsum of battery internal resistance values is calculated in the previously described equation (2). 
         [0147]    [Step S 115 ] The CPU  34  calculates a discharged quantity of electricity Isum 0  which has been discharged from the primary battery  13  since the sampling was started until the current point in time. 
         [0148]    [Step S 116 ] The CPU  34  determines whether or not a predetermined length of time has elapsed since the start of sampling. This is because the primary battery voltage value and the primary battery current value are sampled at a predetermined period over the predetermined length of time. If determined that the predetermined length of time has elapsed, the process proceeds to a step S 117 , whereas if determined that the predetermined length of time has not elapsed, the process returns to the step s 113 . 
         [0149]    In the steps described heretofore, the sampling of the primary battery voltage value and primary battery current value, calculation of the individual battery internal resistance values and the sum thereof and calculation of the discharged quantity of electricity are designed to be implemented periodically. 
         [0150]    [Step S 117 ] The CPU  34  determines whether or not the primary battery voltage value V 1  is larger than the starting voltage value V 0  by a predetermined value V 2 . If determined to be larger, the necessity occurs of determining whether to permit or prohibit the continuation of economical running due to there being a large change in the primary battery voltage value, and the process proceeds to a step S 118 , whereas if determined to be smaller, the in-economical running capacity update process ends. 
         [0151]    [Step S 118 ] The CPU  34  calculates a primary battery capacity which indicates a discharged quantity of electricity which is discharged from the primary battery while the primary battery voltage value changes by  1 V by dividing the discharged power amount Isum 0  which was calculated in the processing in the step S 115  by a value which results when subtracting the starting voltage value V 0  from the current primary battery voltage value V 1 . This primary battery capacity Cm (A sec/V) is calculated by the previously described equation (3). 
         [0152]    [Step S 119 ] The CPU  34  determines on an battery internal resistance value. In this embodiment, this battery internal resistance value is made to be a mean value obtained by dividing the value of the sum Rsum of battery internal resistance values which was calculated in the processing in the step S 114  by the number n of samples. Of course, this battery internal resistance value may take a maximum value or a mode value, or the battery internal resistance value may be determined after deleting those of the battery internal resistance values which depart too far. 
         [0153]    [Step S 120 ] The CPU  34  stores the current battery fluid temperature as THB 0  for comparison with a future battery fluid temperature. 
         [0154]    In the above processes, in such a situation that a decrease in the primary battery voltage value is expected during the implementation of economical running, when the primary battery voltage value is decreased to less than the predetermined value, the primary battery capacity and the battery internal resistance value are updated. 
         [0155]    Next, an automatic engine restarting process by the economical running permission determination unit  46  will be described. 
         [0156]    As shown in  FIG. 18 , the economical running permission determination unit  46  executes repeatedly a process which follows steps below while the economical running is in operation based on the economical running permission determination process program. 
         [0157]    [Step S 131 ] The CPU  34  determines whether or not the economical running is in operation. If determined that the economical running is in operation, the process proceeds to a step S 132 , whereas if determined otherwise, the automatic engine restarting process ends. 
         [0158]    [Step S 132 ] The CPU  34  determines whether or not the primary battery capacity is equal to or more than the economical running permitting voltage threshold value which was calculated in the processing in the step S 94  or step S 105 . If determined to be more, it means that the primary battery  13  or the secondary battery  14  holds an quantity of electricity that is necessary from start of the engine to occurrence of a complete explosion in the engine, and the process proceeds to a step S 133 , whereas if determined to be less, the process proceeds to a step S 134 . 
         [0159]    [Step S 133 ] The CPU  34  permits the continuation of the economical running. 
         [0160]    [Step S 134 ] The CPU  34  prohibits the continuation of the economical running and forcibly restarts the engine. 
         [0161]    With the above processes, when the primary battery voltage value is equal to or more than the economical running permitting voltage threshold value, the implementation of economical running is allowed to continue, whereas when the primary battery voltage value is less than the economical running permitting voltage threshold value, the engine is forcibly restarted, whereby as long as the primary battery  13  and the secondary battery  14  hold the sufficient quantity of electricity while the economical running is in operation, the economical running can continue. 
         [0162]    Note that while in the description that has been made heretofore, the economical running control apparatus  10  is described as being configured as a single unit, the invention is not limited thereto and hence, a configuration may be adopted in which the economical running control apparatus  10  is integrated with the engine control system for controlling the engine. In addition, another configuration may be adopted in which a power supply management system for controlling the batteries and the alternator  11  is separated from the economical running control apparatus  10 .