Patent Publication Number: US-2020298726-A1

Title: Vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure claims priority to Japanese Patent Application No. 2019-054679 filed Mar. 22, 2019, which is incorporated herein by reference in its entirety including specification, drawings and claims. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle equipped with an internal combustion engine, a storage battery that uses a nickel compound as a positive electrode material, and a control device that performs drive control including charge discharge control of the storage battery. 
     BACKGROUND 
     A proposed vehicle includes an internal combustion engine and a storage battery configured as a nickel metal hydride battery or a nickel cadmium rechargeable battery and is configured to start charging of the storage battery when an SOC (state of charge) of the storage battery reaches a predetermined lower limit value and stop charging of the storage battery when the SOC reaches a predetermined upper limit value (as described in, for example, JP 2004-166350A). The vehicle of this proposed configuration increases and decreases the upper limit value and the lower limit value every time the state of the storage battery is changed over from charging to discharging in the state that the vehicle is not allowed to idle. This aims to eliminate the memory effect caused by repetition of charging and discharging between the upper limit value and the lower limit value of the SOC. 
     SUMMARY 
     When a nickel storage battery that uses a nickel compound as a positive electrode material is used in a low SOC range (low state of charge range) where the state of charge is relatively low, the positive electrode capacity of the storage battery is likely to degrade. Accordingly, in the vehicle of JP 2004-166350A that thoroughly uses from a low SOC range to a high SOC range, degradation of the positive electrode capacity is likely to proceed significantly. Excessive degradation of the positive electrode capacity leads to performance degradation of the storage battery. There is accordingly a demand for improving the degradation of the positive electrode capacity. 
     A main object of a vehicle of the present disclosure provided with a storage battery that uses a nickel compound as a positive electrode material is to more appropriately control the progress of degradation of a positive electrode capacity of the storage battery by long-term use. 
     In order to achieve the above primary object, the vehicle of the present disclosure employs the following configuration. 
     The present disclosure is directed to a vehicle. The vehicle includes an internal combustion engine, a storage battery configured to be charged with electric power that is generated by using power from the internal combustion engine and to use a nickel compound as a positive electrode material and a control device configured to set a state of charge of the storage battery based on a condition of the storage battery and to perform drive control that includes charge and discharge control of the storage battery, based on the set state of charge. The control device integrates an amount of degradation of positive electrode capacity of the storage battery during drive of a first predetermined distance, and when an integrated value of the amount of degradation is equal to or larger than a first predetermined value, the control device performs a degradation suppressing control to suppress charging and discharging of the storage battery in a low state of charge range where the state of charge is lower than a predetermined ratio that accelerates degradation of the positive electrode capacity, compared with charging and discharging of the storage battery in the low state of charge range in an ordinary control. 
     The vehicle according to this aspect of the present disclosure integrates the amount of degradation of the positive electrode capacity of the storage battery during the drive of the first predetermined distance and performs the degradation suppressing control to suppress charging and discharging of the storage battery in the low state of charge range when the integrated value of the amount of degradation is equal to or larger than the first predetermined value, compared with charging and discharging of the storage battery in the low state of charge range in the ordinary control. Degradation of the positive electrode capacity of a nickel storage battery, which uses the nickel compound as the positive electrode material, proceeds when the storage battery is used in the low state of charge range. Performing the degradation suppressing control minimizes the use of the storage battery in the low state of charge range and thereby suppresses degradation of the positive electrode capacity. As a result, this more appropriately controls the progress of degradation of the positive electrode capacity by the long-term use and suppresses the performance degradation of the storage battery. The degradation suppressing control is performed only when the integrated value of the amount of degradation is equal to or larger than the first predetermined value. This configuration ensures the more sufficient performance of the storage battery and reduces the influence on the control of the vehicle, compared with a configuration of continuously performing the degradation suppressing control. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating the schematic configuration of a vehicle according to one embodiment of the present disclosure; 
         FIG. 2  is a block diagram illustrating a procedure of calculating the amount of capacity degradation Q; 
         FIG. 3  is a diagram illustrating one example of a charge discharge required power setting map; 
         FIG. 4  is a diagram illustrating one example of a start reference value setting map; 
         FIG. 5  is a flowchart showing one example of an amount of capacity degradation monitoring process; 
         FIG. 6  is a diagram illustrating a relationship between travel distance and accumulated amount of degradation; 
         FIG. 7  is a diagram illustrating changeover of control mode; 
         FIGS. 8A and 8B  is a diagram illustrating an SOC use range in an ordinary control mode and an SOC use range in a degradation suppressing control mode; 
         FIG. 9  is a flowchart showing one example of a controlling state of charge setting process; 
         FIG. 10  is a diagram illustrating one example of a state of charge adjustment map; and 
         FIG. 11  is a configuration diagram illustrating the schematic configuration of another vehicle according to a modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes some aspects of the disclosure with reference to embodiments. 
       FIG. 1  is a configuration diagram illustrating the schematic configuration of a vehicle  20  according to one embodiment of the present disclosure. As illustrated, the vehicle  20  of the embodiment is configured as a hybrid vehicle including an engine  22 , a planetary gear  30 , motors MG 1  and MG 2 , inverters  41  and  42 , a battery  50 , and a hybrid electronic control unit (hereinafter referred to as “HVECU”)  70 . 
     The engine  22  is configured as an internal combustion engine that outputs power by using, for example, gasoline or light oil as a fuel. This engine  22  is operated and controlled by an engine electronic control unit (hereinafter referred to as “engine ECU”)  24 . 
     The engine ECU  24  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. Signals from various sensors required for operation control of the engine  22  are input into the engine ECU  24  via the input port. The signals input into the engine ECU  24  include, for example, a crank angle θcr from a crank position sensor  23  configured to detect a rotational position of a crankshaft  26  of the engine  22  and a throttle position TH from a throttle valve position sensor configured to detect the position of a throttle valve. 
     Various control signals for operation control of the engine  22  are output from the engine ECU  24  via the output port. The control signals output from the engine ECU  24  include, for example, a control signal to a throttle motor configured to regulate the position of the throttle valve, a control signal to a fuel injection valve, a control signal to an ignition coil integrated with an igniter and a variety of other control signals. 
     The engine ECU  24  is connected with the HVECU  70  via the respective communication ports to operate and control the engine  22  in response to the control signals from the HVECU  70  and to output data with regard to the operating conditions of the engine  22  to the HVECU  70  as needed basis. The engine ECU  24  calculates a rotation speed of the crankshaft  26 , i.e., a rotation speed Ne of the engine  22 , based on the crank angle θcr input from the crank position sensor  23 . 
     The planetary gear  30  is configured as a single pinion-type planetary gear mechanism The planetary gear  30  includes a sun gear that is connected with a rotor of the motor MG 1 . The planetary gear  30  also includes a ring gear that is connected with a driveshaft  36  linked with drive wheels  38   a  and  38   b  via a differential gear  37 . The planetary gear  30  further includes a carrier that is connected with the crankshaft  26  of the engine  22 . 
     The motor MG 1  is configured, for example, as a synchronous generator motor and has the rotor that is connected with the sun gear of the planetary gear  30  as described above. The motor MG 2  is configured, for example, as a synchronous generator motor and has a rotor that is connected with the driveshaft  36 . The inverters  41  and  42  are connected with the battery  50  via power lines  54 . A motor electronic control unit (hereinafter referred to as “motor ECU”)  40  performs switching control of a plurality of switching elements (not shown) respectively included in the inverters  41  and  42 , so as to rotate and drive the motors MG 1  and MG 2 . 
     The motor ECU  40  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. Signals from various sensors required for drive control of the motors MG 1  and MG 2  are input into the motor ECU  40  via the input port. The signals input into the motor ECU  40  include, for example, rotational positions θm 1  and θm 2  from rotational position detection sensors  43  and  44  configured to detect the rotational positions of the respective rotors of the motors MG 1  and MG 2 . The input signals also include phase currents from current sensors configured to detect electric currents flowing in the respective phases of the motor MG 1  and MG 2 . 
     The motor ECU  40  outputs via the output port, for example, switching control signals to the plurality of switching elements (not shown) included in the respective inverters  41  and  42 . The motor ECU  40  is connected with the HVECU  70  via the respective communication ports to drive and control the motors MG 1  and MG 2  in response to the control signals from the HVECU  70  and to output data with regard to the driving conditions of the motors MG 1  and MG 2  to the HVECU  70  as needed basis. The motor ECU  40  calculates rotation speeds Nm 1  and Nm 2  of the respective motors MG 1  and MG 2 , based on the rotational positions θm 1  and θm 2  of the respective rotors of the motors MG 1  and MG 2  input from the rotational position detection sensors  43  and  44 . 
     The battery  50  is configured as a nickel storage battery that uses a nickel compound as a positive electrode material, for example, a nickel metal hydride battery or a nickel cadmium rechargeable battery. This battery  50  is connected with the inverters  41  and  42  via the power lines  54  as described above. The battery  50  is under management of a battery electronic control unit (hereinafter referred to as “battery ECU”)  52 . 
     The battery ECU  52  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. Signals from various sensors required for management of the battery  50  are input into the battery ECU  52  via the input port. The signals input into the battery ECU  52  include, for example, a battery voltage Vb from a voltage sensor  51   a  placed between terminals of the battery  50 , a battery current Ib from a current sensor  51   b  mounted to an output terminal of the battery  50 , and a battery temperature Tb from a temperature sensor  51   c  mounted to the battery  50 . 
     The battery ECU  52  is connected with the HVECU  70  via the respective communication ports to output data with regard to the conditions of the battery  50  to the HVECU  70  as needed basis. The battery ECU  52  calculates a base value of a state of charge SOC, based on an integrated value of the battery current Ib of the battery  50  input from the current sensor  51   b  and then calculates the state of charge SOC by correcting the calculated base value according to the battery voltage Vb input from the voltage sensor  51   a  and the battery temperature Tb input from the temperature sensor  51   c . The battery ECU  52  also calculates an input limit Win and an output limit Wout of the battery  50 , based on the calculated state of charge SOC and the battery temperature Tb. The state of charge SOC denotes a ratio of the capacity of electric power dischargeable from the battery  50  to the overall capacity of the battery  50 . The input limit Win and the output limit Wout of the battery  50  respectively denote a maximum chargeable power that is allowed to be charged into the battery  50  and a maximum dischargeable power that is allowed to be discharged from the battery  50 . Furthermore, the battery ECU  52  calculates an amount of capacity degradation Q with a view to monitoring the degradation progress with regard to the positive electrode capacity of the battery  50 . 
       FIG. 2  is a block diagram illustrating a procedure of calculating the amount of capacity degradation Q. As illustrated, the procedure of calculating the amount of capacity degradation Q sets an amount of capacity degradation q [Ah] per 1 Ah, based on the state of charge SOC and the battery temperature Tb and subsequently multiplies the amount of capacity degradation q per 1 Ah by a quantity of discharged electricity [Ah] that is obtained by multiplying the battery current Ib by a discharge time. An amount of capacity degradation setting map shown in  FIG. 2  is used to set the amount of capacity degradation q per 1 Ah. This amount of capacity degradation setting map sets the amount of capacity degradation q such as to increase with a decrease in the state of charge SOC and to increase with an increase in the battery temperature Tb in a range that the state of charge SOC is lower than a predetermined ratio Sref. 
     The HVECU  70  is configured as a CPU-based microprocessor and includes a ROM configured to store processing programs, a RAM configured to temporarily store data, input/output ports and a communication port, in addition to the CPU, although not being illustrated. Signals from various sensors are input into the HVECU  70  via the input port. The signals input into the HVECU  70  include, for example, an ignition signal from an ignition switch  80 , a shift position SP from a shift position sensor  82  configured to detect an operating position of a shift lever  81 , and a vehicle speed V from a vehicle speed sensor  88 . The input signals also include an accelerator position Acc from an accelerator pedal position sensor  84  configured to detect a depression amount of an accelerator pedal  83  and a brake pedal position BP from a brake pedal position sensor  86  configured to detect a depression amount of a brake pedal  85 . 
     The HVECU  70  is connected with the engine ECU  24 , the motor ECU  40  and the battery ECU  52  via the respective communication ports to send and receive various control signals and data to and from the engine ECU  24 , the motor ECU  40  and the battery ECU  52  as described above. 
     The vehicle  20  of the embodiment having the configuration described above is driven in a hybrid drive (HV drive) mode or is driven in an electric drive (EV drive) mode. In the HV drive mode, the vehicle  20  is driven with operation of the engine  22 . In the EV drive mode, the vehicle  20  is driven with stop of operation of the engine  22 . 
     The HVECU  70  first sets a required torque Td* that is required for driving (i.e., that is to be output to the driveshaft  36 ), based on the accelerator position Acc input from the accelerator pedal position sensor  84  and the vehicle speed V input from the vehicle speed sensor  88 . The HVECU  70  subsequently calculates a driving required power Pdrv* that is required for driving by multiplying the set required torque Td* by a rotation speed Nr of the driveshaft  36 . The rotation speed Nr of the driveshaft  36  used here may be, for example, a rotation speed Nm 2  of the motor MG 2  or a rotation speed obtained by multiplying the vehicle speed V by a conversion factor. The HVECU  70  subsequently sets a charge discharge required power Pb* that is required for the battery  50  (more specifically, that is to be charged into the battery  50  or to be discharged from the battery  50 ), based on the state of charge SOC of the battery  50 . According to the embodiment, a procedure of setting the charge discharge required power Pb* specifies and stores in advance a relationship between the state of charge SOC of the battery  50  and the charge discharge required power Pb* in the form of a charge discharge required power setting map in the ROM and reads a value of the charge discharge required power Pb* corresponding to a given value of the state of charge SOC from the map. One example of the charge discharge required power setting map is shown in  FIG. 3 . As shown in  FIG. 3 , in the charge discharge required power setting map, the charge discharge required power Pb* is set such as to increase the discharging power with an increase in the state of charge SOC in a range that the state of charge SOC is higher than a target state of charge SOC* (for example, 60%) and to increase the charging power with a decrease in the state of charge SOC in a range that the state of charge SOC is lower than the target state of charge SOC*, in order to make the state of charge SOC approach the target state of charge SOC*. The HVECU  70  then sets a vehicle required power Pe* that is required for the vehicle  20  by subtracting the charge discharge required power Pb* of the battery  50  (where the charge discharge required power Pb* takes a positive value when the battery  50  is discharged) from the calculated driving required power Pdrv*. 
     The HVECU  70  subsequently determines whether the current drive mode of the vehicle  20  is the HV drive mode or the EV drive mode. When it is determined that the current drive mode is the EV drive mode, the HVECU  70  performs an engine start determination process to determine whether the engine  22  is to be started. The engine start determination process compares the vehicle required power Pe* with a start reference value Pstart and determines that the engine  22  is to be started when the vehicle required power Pe* is equal to or larger than the start reference value Pstart, while determining that the engine  22  is not to be started when the vehicle required power Pe* is smaller than the start reference value Pstart. According to the embodiment, a procedure of setting the start reference value Pstart specifies and stores in advance a relationship between the state of charge SOC and the start reference value Pstart in the form of a start reference value setting map in the ROM and reads a value of the start reference value Pstart corresponding to a given value of the state of charge SOC from the map. One example of the start reference value setting map is shown in  FIG. 4 . As shown in  FIG. 4 , in the start reference value setting map, the start reference value Pstart is set such as to increase with an increase in the state of charge SOC in a range that the start reference value Pstart is equal to or larger than a predetermined value Sref 1 , which is used as a forced charging start reference value described later. According to a modification, the start reference value Pstart may be set, based on the vehicle speed V in addition to the state of charge SOC. When the HVECU  70  determines that the engine  22  is not to be started by the engine start determination process, the HVECU  70  determines that the vehicle  20  continues driving in the EV drive mode, sets a torque command Tm 1 * of the motor MG 1  equal to a value 0, and sets a torque command Tm 2 * of the motor MG 2 , such that the required torque Td* (i.e., the driving required power Pdrv*) is output to the driveshaft  36  in a range of the input limit Win and the output limit Wout of the battery  50 . The HVECU  70  then sends the torque commands Tm 1 * and Tm 2 * to the motor ECU  40 . The motor ECU  40  performs switching control of the respective transistors included in the inverters  41  and  42 , such that the motors MG 1  and MG 2  are respectively driven with the torque commands Tm 1 * and Tm 2 *. 
     When the HVECU  70  determines that the engine  22  is to be started by the engine start determination process, on the other hand, the drive mode of the vehicle  20  is shifted from the EV drive mode to the HV drive mode. The HVECU  70  accordingly performs an engine start process that uses the motor MG 1  to motor and start the engine  22 . The engine start process causes a predetermined motoring torque to be output from the motor MG 1 , so as to increase the rotation speed of the engine  22 . The engine start process starts the operation of the engine  22  when the rotation speed Ne of the engine  22  exceeds a starting rotation speed Nestart. When the engine  22  is started and the drive mode is shifted to the HV drive mode, the HVECU  70  sets a target operation point of the engine  22  (i.e., a target rotation speed Ne* and a target torque Te*) and the torque commands Tm 1 * and Tm 2 * of the motors MG 1  and MG 2 , such that the the vehicle required power Pe* is output from the engine  22  and that the required torque Td* is output to the driveshaft  36  in the range of the input limit Win and the output limit Wout of the battery  50 . According to the embodiment, a procedure of setting the target operation point (the target rotation speed Ne* and the target torque Te*) of the engine  22  specifies in advance an optimum operation line that provides an optimal fuel consumption by taking into account the noise, the vibration and the like among operation points of the engine  22  (defined by the rotation speed and the torque) and determines and sets an operation point (defined by the rotation speed and the torque) corresponding to the vehicle required power Pe* on the optimum operation line. The HVECU  70  sends the set target operation point (the target rotation speed Ne* and the target torque Te*) of the engine  22  to the engine ECU  24 , while sending the torque commands Tm 1 * and Tm 2 * of the motors MG 1  and MG 2  to the motor ECU  40 . The engine ECU  24  performs, for example, intake air flow control, fuel injection control and ignition control of the engine  22 , such that the engine  22  is operated on the basis of the target operation point. The motor ECU  40  controls the inverters  41  and  42  as described above. 
     When it is determined that the current drive mode is the HV drive mode, on the other hand, the HVECU  70  performs an engine stop determination process to determine whether the engine  22  is to be stopped. The engine stop determination process compares the vehicle required power Pe* with a stop reference value Pstop and determines that the engine  22  is not to be stopped when the vehicle required power Pe* is equal to or larger than the stop reference value Pstop, while determining that the engine  22  is to be stopped when the vehicle required power Pe* is smaller than the stop reference value Pstop. The stop reference value Pstop is set to a smaller value that is smaller than the start reference value Pstart by a predetermined value according to an engine start and stop reference value setting process. This sets a hysteresis to the start reference value Pstart, in order to prevent frequent repetition of the starts and stops of the engine  22 . When the HVECU  70  determines that the engine  22  is not to be stopped by the engine stop determination process, the HVECU  70  keeps the HV drive mode. When the HVECU  70  determines that the engine  22  is to be stopped by the engine stop determination process, on the other hand, the HVECU  70  performs an engine stop process that causes the motor MG 1  to decrease the rotation speed of the engine  22  and thereby stop the engine  22  and shifts the drive mode from the HV drive mode to the EV drive mode. The series of controls in the HV drive mode and in the EV drive mode are described above. 
     When the state of charge SOC of the battery  50  becomes lower than a predetermined forced charging start reference value Sref 1  (for example, 40%), the HVECU  70  performs forced charging control to forcibly charge the battery  50  until the state of charge SOC of the battery  50  becomes equal to or higher than a forced charging stop reference value Sref 2  (for example, 50%). The forced charging control prohibits the engine  22  from being stopped (i.e., prohibits the drive mode from being shifted to the EV drive mode) irrespective of the determination result of the engine stop determination process described above and sets a predetermined power Pset for charging to the charge discharge required power Pb*, such that the battery  50  is charged with a relatively large electric power in a range of the state of charge SOC from the forced charging start reference value Sref 1  to the forced charging stop reference value Sref 2  as shown in  FIG. 3 . 
     The following describes a series of processing to monitor the degradation of the positive electrode capacity of the battery  50  in the vehicle  20  of the embodiment having the configuration described above.  FIG. 5  is a flowchart showing one example of an amount of capacity degradation monitoring process performed by the CPU of the battery ECU  52 . This routine is performed repeatedly at predetermined time intervals (for example, at every several msec). As shown in  FIG. 6 , it is desirable in design that an accumulated amount of degradation of the positive electrode capacity of the battery  50  reaches an allowable upper limit value when the vehicle is driven by a travel distance guaranteed by an automobile manufacturer (target travel distance). More specifically, it is preferable that the accumulated amount of degradation increases along an ideal line with an increase in the total travel distance as shown by a broken line curve in  FIG. 6 . The allowable upper limit value herein denotes an accumulated amount of degradation of a decrease in capacity in the full charge state (full charge capacity) from an initial value (100%) to a predetermined value (for example, 20%). The full charge capacity has an inflection point where a decrease in the full charge capacity is accelerated with an increase in total discharge capacity. The predetermined value may be a value between the initial value to the inflection point of the full charge capacity. With regard to the battery  50  that uses a nickel compound as the positive electrode material (nickel storage battery), degradation of the positive electrode capacity is more likely to proceed when the battery  50  is used in a low SOC range where the state of charge SOC of the battery  50  is lower than the predetermined ratio Sref. Accordingly, in some cases, the accumulated amount of degradation is likely to increase at a larger increase rate than the increase rate of the ideal line and reach the allowable upper limit value prior to a drive of the vehicle  20  by the target travel distance as shown by a solid line curve in  FIG. 6 . Accordingly, the vehicle  20  of the embodiment performs the amount of capacity degradation monitoring process to monitor whether the accumulated amount of degradation of the positive electrode capacity of the battery  50  increases at the larger increase rate than the increase rate of the ideal line and thereby monitor the degradation progress of the positive electrode capacity. 
     When the amount of capacity degradation monitoring process is triggered, the CPU of the HVECU  70  first obtains the inputs of the state of charge SOC, the amount of capacity degradation Q and the vehicle speed V (step S 100 ). The state of charge SOC and the amount of capacity degradation Q input here are values calculated as described above. The vehicle speed V input here is a value detected by the vehicle speed sensor  88  and received by the HVECU  70  by communication. 
     The CPU subsequently integrates the input values of the vehicle speed V to calculate a travel distance L (step S 110 ) and integrates the input values of the amount of capacity degradation Q to calculate a capacity degradation judgment value M (step S 120 ). The CPU subsequently determines whether the current control mode is a degradation suppressing control mode or not (step S 130 ). When it is determined that the current control mode is not the degradation suppressing control mode but an ordinary control mode, the CPU subsequently determines whether the travel distance L calculated at step S 110  is equal to or greater than a first predetermined distance Lref 1  (step S 140 ). When it is determined that the travel distance L is less than the predetermined distance Lref 1 , the CPU determines that the current timing is not a timing to determine the degradation progress of the positive electrode capacity and then terminates the amount of capacity degradation monitoring process. When it is determined that the travel distance L is equal to or greater than the predetermined distance Lref 1 , on the other hand, the CPU subsequently determines whether the capacity degradation judgment value M calculated at step S 120  is equal to or larger than a first judgment reference value Mref 1  (step S 150 ). The first judgment reference value Mref 1  is a reference value used to determine whether the slope of an increase in the accumulated amount of degradation (i.e., the degradation progress) is steeper than the slope of the ideal line as shown by a broken line arrow in a traveling section of the first predetermined distance Lref 1  shown in  FIG. 7 . This first judgment reference value Mref 1  is determined to be a larger value by a predetermined value (margin value) than an amount of increase in the integrated value of the amount of capacity degradation Q by the slope of the ideal line relative to traveling of the first predetermined distance Lref 1 . 
     When it is determined at step S 150  that the capacity degradation judgment value M is smaller than the first judgment reference value Mref 1 , the CPU determines that the degradation progress of the positive electrode capacity is appropriate. The CPU accordingly maintains the ordinary control mode, initializes both the travel distance L and the capacity degradation judgment value M to a value 0 (step S 200 ), and then terminates the amount of capacity degradation monitoring process. When it is determined at step S 150  that the capacity degradation judgment value M is equal to or larger than the first judgment reference value Mref 1 , on the other hand, the CPU determines that the degradation progress of the positive electrode capacity is more rapid than the approximate degradation progress. The CPU accordingly shifts the control mode from the ordinary control mode to the degradation suppressing control mode (step S 160 ), initializes both the travel distance L and the capacity degradation judgment value M to the value 0 (step S 200 ), and then terminates the amount of capacity degradation monitoring process. As shown in  FIGS. 8A and 8B , the degradation suppressing control mode is a mode of controlling charge and discharge of the battery  50  such that the use frequency of a low SOC range (filled area in  FIGS. 8A and 8B ) where the state of charge SOC is lower than the predetermined ratio Sref and where the degradation of the positive electrode capacity of the battery  50  is more likely to proceed, is less in the degradation suppressing control mode (shown in  FIG. 8B ) than the use frequency in the ordinary control mode (shown in  FIG. 8A ). The details of the degradation suppressing control mode will be described later. 
     When the control mode is shifted from the ordinary control mode to the degradation suppressing control mode, it is determined at step S 130  that the current control mode is the degradation suppressing control mode in a next cycle of the amount of capacity degradation monitoring process. In this case, the CPU subsequently determines whether the travel distance L is equal to or greater than a second predetermined distance Lref 2  (step S 170 ). According to the embodiment, the second predetermined distance Lref 2  is determined to be a longer distance than the first predetermined distance Lref 1 . This is because the first predetermined distance Lref 1  needs to ensure a travel distance that is required to estimate the degradation progress of the positive electrode capacity, while the second predetermined distance Lref 2  needing to ensure a sufficient execution time of the degradation suppressing control mode with a view to eliminating the state that the degradation progress is more rapid than expected. When it is determined at step S 170  that the travel distance L is less than the second predetermined distance Lref 2 , the CPU terminates the amount of capacity degradation monitoring process. When it is determined at step S 170  that the travel distance L is equal to or greater than the second predetermined distance Lref 2 , on the other hand, the CPU subsequently determines whether the capacity degradation judgment value M calculated at step S 120  is smaller than a second judgment reference value Mref 2  (step S 180 ). The second judgment reference value Mref 2  is a reference value used to determine whether the slope of an increase in the accumulated amount of degradation (i.e., the degradation progress) is gentler than the slope of the ideal line as shown by a broken line arrow in a traveling section of the second predetermined distance Lref 2  shown in  FIG. 7 . This second judgment reference value Mref 2  is determined to be a smaller value by a predetermined value (margin value) than an amount of increase in the integrated value of the amount of capacity degradation Q by the slope of the ideal line relative to traveling of the second predetermined distance Lref 2 . 
     When it is determined at step S 180  that the capacity degradation judgment value M is equal to or larger than the second judgment reference value Mref 2 , the CPU determines that rapid progress of degradation of the positive electrode capacity has not yet been overcome. The CPU accordingly maintains the degradation suppressing control mode, initializes both the travel distance L and the capacity degradation judgment value M to the value 0 (step S 200 ), and then terminates the amount of capacity degradation monitoring process. When it is determined at step S 180  that the capacity degradation judgment value M is smaller than the second judgment reference value Mref 2 , on the other hand, the CPU determines that the rapid progress of degradation of the positive electrode capacity has been overcome. The CPU accordingly restores the control mode from the degradation suppressing control mode to the ordinary control mode (step S 190 ), initializes both the travel distance L and the capacity degradation judgment value M to the value 0 (step S 200 ), and then terminates the amount of capacity degradation monitoring process. 
     The following describes a series of operations of the degradation suppressing control.  FIG. 9  is a flowchart showing one example of a controlling state of charge setting process performed by the battery ECU  52 . This routine is performed repeatedly at predetermined time intervals (for example, at every several msec). 
     When the controlling state of charge setting process is triggered, the CPU of the battery ECU  52  first obtains the inputs of the battery voltage Vb from the voltage sensor  51   a,  the battery current Ib from the current sensor  51   b  and the battery temperature Tb from the temperature sensor  51   c  (step S 300 ) and calculates the state of charge SOC of the battery  50 , based on the inputs of the battery voltage Vb, the battery current Ib and the battery temperature Tb (step S 310 ). The CPU subsequently determines whether the current control mode is the degradation suppressing control mode (step S 320 ). When it is determined that the current control mode is not the degradation suppressing control mode but the ordinary control mode, the CPU sets the state of charge SOC calculated at step S 310  to a controlling state of charge SOCc (step S 330 ), sends the set controlling state of charge SOCc to the HVECU  70  (step S 350 ) and then terminates the controlling state of charge setting process. When receiving the controlling state of charge SOCc, the HVECU  70  performs the drive control described above by using the received controlling state of charge SOCc as the state of charge SOC. More specifically, the HVECU  70  sets the charge discharge required power Pb*, based on the controlling state of charge SOCc, sets the start reference value Pstart used for the engine start determination process and the stop reference value Pstop used for the engine stop determination process, based on the controlling state of charge SOCc, and also determines whether the forced charging control is to be performed or not, based on the determination of whether the controlling state of charge SOCc is lower than the forced charging start reference value Sref 1 . 
     When it is determined at step S 320  that the current control mode is the degradation suppressing control mode, on the other hand, the CPU uses a state of charge adjustment map to adjust the state of charge SOC calculated at step S 310  and sets the adjusted state of charge SOC to the controlling state of charge SOCc (step S 340 ), sends the set controlling state of charge SOCc to the HVECU  70  (step S 350 ) and then terminates the controlling state of charge setting process. One example of the state of charge adjustment map is shown in  FIG. 10 . According to the embodiment, as shown in  FIG. 10 , the state of charge adjustment map sets the controlling state of charge SOCc to be lower than the state of charge SOC in a range between the target state of charge SOC* and a lower limit value of a control range. The HVECU  70  sets the charge discharge required power Pb*, based on the controlling state of charge SOCc input from the battery ECU  52 . This enables the battery  50  to be charged with the higher electric power in the degradation suppressing control mode, compared with the charging power provided in the ordinary control mode. The HVECU  70  also sets the start reference value Pstart and the stop reference value Pstop, based on the controlling state of charge SOCc input from the battery ECU  52 . This enables the start timing of the engine  22  to be advanced and enables the stop timing of the engine  22  to be delayed in the degradation suppressing control mode, compared with the start timing and the stop timing in the ordinary control mode. Accordingly, this reduces the frequency in use of the EV drive mode in the degradation suppressing control mode, compared with the frequency in the ordinary control mode. Furthermore, the HVECU  70  determines whether the forced charging control is to be performed or not by determining whether the controlling state of charge SOCc input from the battery ECU  52  is lower than the forced charging start reference value Sref 1 . This accordingly advances the start timing of forced charging control in the degradation suppressing control mode, compared with the start timing in the ordinary control mode. This series of processing minimizes the use of the battery  50  in the low SOC range of lower than the predetermined ratio Sref and thereby suppresses the progress of degradation of the positive electrode capacity. Accordingly, this slows the degradation progress of the positive electrode capacity of the battery  50  as shown by the broken line arrow in the traveling section of the second predetermined distance Lref 2  shown in  FIG. 7  and makes the accumulated amount of degradation relative to the total travel distance closer to the ideal line. 
     As described above, the vehicle  20  of the embodiment integrates the amount of capacity degradation Q of the battery  50  during the drive of the first predetermined distance Lref 1 . When the integrated value of the amount of capacity degradation (capacity degradation judgment value M) is equal to or larger than the first judgment reference value Mref 1 , the vehicle  20  shifts the control mode to the degradation suppressing control mode that performs control to suppress charging and discharging of the battery  50  in the low SOC range compared with the ordinary control mode. Degradation of the positive electrode capacity of the battery  50  proceeds when the battery  50  using a nickel compound as the positive electrode material is used in the low state of charge (SOC) range. Accordingly, minimizing the use of the battery  50  in the low SOC range suppresses degradation of the positive electrode capacity. As a result, this more appropriately controls the progress of degradation of the positive electrode capacity by the long-term use and suppresses the performance degradation of the battery  50 . The degradation suppressing control mode is set only when the integrated value of the amount of capacity degradation (capacity degradation judgment value M) is equal to or larger than the first judgment reference value Mref 1 . This configuration ensures the more sufficient performance of the battery  50  and reduces the influence on the drive control of the vehicle  20 , compared with a configuration of continuously setting the degradation suppressing control mode. For example, allowing the use of the battery  50  in the low SOC range in the ordinary control mode ensures the sufficient drivable distance in the EV drive mode. 
     Furthermore, when the control mode is shifted to the degradation suppressing control mode, the vehicle  20  of the embodiment integrates the amount of capacity degradation Q of the battery  50  during the drive of the second predetermined distance Lref 2 . When the integrated value of the amount of capacity degradation (capacity degradation judgment value M) is smaller than the second judgment reference value Mref 2 , the vehicle  20  restores the control mode to the ordinary control mode. Changing over the control mode between the ordinary control mode and the degradation suppressing control mode enables the degradation progress of the positive electrode capacity of the battery  50  to be closer to an appropriate degradation progress, irrespective of the use conditions of the vehicle  20 . Moreover, the second predetermined distance Lref 2  is set to be longer than the first predetermined distance Lref 1 . This ensures the sufficient execution period of the degradation suppressing control and enables the degradation progress of the positive electrode capacity to be easily restored to the appropriate degradation progress. 
     Additionally, in the degradation suppressing control mode, the vehicle  20  of the embodiment adjusts the state of charge SOC that is used in the process of setting the charge discharge required power Pb*, the process of setting the start reference value Pstart and the stop reference value Pstop and the process of determining whether the forced charging control is to be performed, to be lower than the actual state of charge SOC calculated based on the conditions of the battery  50 , for example, the battery current Ib. This configuration provides the degradation suppressing control mode by a simple process of only changing the procedure of setting the state of charge SOC based on the conditions of the battery  50 . 
     In the degradation suppressing control mode, the vehicle  20  of the embodiment adjusts the controlling state of charge SOCc that is used for the series of control of the vehicle  20  (more specifically, the process of setting the charge discharge required power Pb*, the process of setting the start reference value Pstart and the stop reference value Pstop and the process of determining whether the forced charging control is to be performed) to be lower than the actual state of charge SOC calculated based on the conditions of the battery  50 . A modified procedure of setting the charge discharge required power Pb* may use a different charge discharge required power setting map in the degradation suppressing control mode from the charge discharge required power setting map used in the ordinary control mode to set the higher charge discharge required power Pb* on the charging side relative to the state of charge SOC in the degradation suppressing control mode than the charge discharge required power Pb* set in the ordinary control mode. Furthermore, a modified procedure of setting the start reference value Pstart and the stop reference value Pstop may use a different start reference value setting map in the degradation suppressing control mode from the start reference value setting map used in the ordinary control mode to set the smaller start reference value Pstart and the smaller stop reference value Pstop relative to the state of charge SOC in the degradation suppressing control mode than the start reference value Pstart and the stop reference value Pstop set in the ordinary control mode. Moreover, a modified procedure of determining whether the forced charging control is to be performed may heighten the forced charging start reference value Sref 1  that is used to determine whether the forced charging control is to be started, in the degradation suppressing control mode to be higher than the forced charging start reference value Sref 1  used in the ordinary control mode. In this modification, the forced charging stop reference value Sref 2  may similarly be heightened, such that the interval between the forced charging start reference value Sref 1  and the forced charging stop reference value Sref 2  in the degradation suppressing control mode is kept equal to the interval in the ordinary control mode. For example, when the forced charging start reference value Sref 1  is 40% and the forced charging stop reference value Sref 2  is 50% in the ordinary control mode, the forced charging start reference value Sref 1  may be heightened to 45% and the forced charging stop reference value Sref 2  may be heightened to 55% in the degradation suppressing control mode. 
     In the vehicle  20  of the embodiment, the second predetermined distance Lref 2  is set to be longer than the first predetermined distance Lref 1 . According to a modification, however, the second predetermined distance Lref 2  may be set to be equal to the first predetermined distance Lref 1  or may be set to be shorter than the first predetermined distance Lref 1 . 
     The vehicle  20  of the embodiment is configured such that the planetary gear  30  is connected with the engine  22 , the motor MG 1  and the driveshaft  36  that is linked with the drive wheels  38   a  and  38   b  and that the motor MG 2  is connected with the driveshaft  36 . The present disclosure is also applicable to a vehicle  120  according to a modification configured such that a motor MG is connected via a transmission  130  with a driveshaft  36  that is linked with drive wheels  38   a  and  38   b  and that an engine  22  is connected via a clutch  129  with a rotating shaft of the motor MG as shown in  FIG. 11 . 
     As described above, according to one aspect of the present disclosure, there is provided a vehicle including an internal combustion engine; a storage battery configured to be charged with electric power that is generated by using power from the internal combustion engine and to use a nickel compound as a positive electrode material; and a control device configured to set a state of charge of the storage battery based on a condition of the storage battery and to perform drive control that includes charge and discharge control of the storage battery, based on the set state of charge. The control device integrates an amount of degradation of positive electrode capacity of the storage battery during drive of a first predetermined distance, and when an integrated value of the amount of degradation is equal to or larger than a first predetermined value, the control device performs a degradation suppressing control to suppress charging and discharging of the storage battery in a low state of charge range where the state of charge is lower than a predetermined ratio that accelerates degradation of the positive electrode capacity, compared with charging and discharging of the storage battery in the low state of charge range in an ordinary control. 
     The vehicle according to this aspect of the present disclosure integrates the amount of degradation of the positive electrode capacity of the storage battery during the drive of the first predetermined distance and performs the degradation suppressing control to suppress charging and discharging of the storage battery in the low state of charge range when the integrated value of the amount of degradation is equal to or larger than the first predetermined value, compared with charging and discharging of the storage battery in the low state of charge range in the ordinary control. Degradation of the positive electrode capacity of a nickel storage battery, which uses the nickel compound as the positive electrode material, proceeds when the storage battery is used in the low state of charge range. Performing the degradation suppressing control minimizes the use of the storage battery in the low state of charge range and thereby suppresses degradation of the positive electrode capacity. As a result, this more appropriately controls the progress of degradation of the positive electrode capacity by the long-term use and suppresses the performance degradation of the storage battery. The degradation suppressing control is performed only when the integrated value of the amount of degradation is equal to or larger than the first predetermined value. This configuration ensures the more sufficient performance of the storage battery and reduces the influence on the control of the vehicle, compared with a configuration of continuously performing the degradation suppressing control. The “drive control including charge discharge control of the storage battery” includes, for example, a control process of setting a required charge discharge power that is required for the storage battery, such that the state of charge of the storage battery approaches a target state of charge, and performing control to charge and discharge the storage battery, based on the set required charge discharge power; a control process of performing control to forcibly charge the storage battery with a predetermined charging power when the state of charge of the storage battery is lower than a lower limit value; and a control process of setting a start reference value that is used to determine whether the internal combustion engine is to be started, based on the state of charge of the storage battery, and performing control to start the internal combustion engine when a vehicle required power that is required for the vehicle in response to an accelerator operation amount becomes equal to or greater than the set start reference value. The “amount of degradation of the positive electrode capacity” includes an estimation based on the state of charge of the storage battery and the temperature of the storage battery. 
     In the vehicle according to the above aspect of the present disclosure, when performing the degradation suppressing control, the control device may integrate an amount of degradation of the positive electrode capacity during a drive of a second predetermined distance and may stop execution of the degradation suppressing control when the integrated value of the amount of degradation is smaller than a second predetermined value. The configuration of performing the degradation suppressing control and stopping the degradation suppressing control enables a degradation progress of the positive electrode capacity of the storage battery to become close to an appropriate degradation progress, irrespective of a use condition of the vehicle. In this case, the second predetermined distance may be longer than the first predetermined distance. This configuration ensures the sufficient execution period of the degradation suppressing control and enables the degradation progress of the positive electrode capacity to be readily restored to the appropriate degradation progress. 
     Further, in the vehicle according to the above aspect of the present disclosure, the control device may set the state of charge in the degradation suppressing control to be lower than the state of charge in the ordinary control. This configuration enables the control to be changed over from the ordinary control to the degradation suppressing control by a simple process of only changing the procedure of setting the state of charge based on the condition of the storage battery. 
     Furthermore, in the vehicle according to the above aspect of the present disclosure, when the state of charge is lower than a lower limit value, the control device may perform forced charging control that controls the storage battery to be forcibly charged. In this aspect, the lower limit value in the degradation suppressing control may be set to be larger than the lower limit value in the ordinary control, or the state of charge in the degradation suppressing control may be set to be lower than the state of charge in the ordinary control. The degradation suppressing control of this aspect enables a start timing of the forced charging control to be advanced, thereby suppressing a decrease in state of charge and delaying the degradation progress of the positive electrode capacity. 
     The following describes the correspondence relationship between the primary components of the embodiment and the primary components of the disclosure described in Summary. The engine  22  of the embodiment corresponds to the “internal combustion engine”, the battery  50  corresponds to the “storage battery”, the engine ECU  24 , the motor ECU  40 , the battery ECU  52  and HVECU  70  correspond to the “control device”. 
     The correspondence relationship between the primary components of the embodiment and the primary components of the disclosure, regarding which the problem is described in Summary, should not be considered to limit the components of the disclosure, regarding which the problem is described in Summary, since the embodiment is only illustrative to specifically describes the aspects of the disclosure, regarding which the problem is described in Summary. In other words, the disclosure, regarding which the problem is described in Summary, should be interpreted on the basis of the description in the Summary, and the embodiment is only a specific example of the disclosure, regarding which the problem is described in Summary. 
     The aspect of the disclosure is described above with reference to the embodiment. The disclosure is, however, not limited to the above embodiment but various modifications and variations may be made to the embodiment without departing from the scope of the disclosure. 
     INDUSTRIAL APPLICABILITY 
     The technique of the disclosure is preferably applicable to the manufacturing industries of the vehicle and so on.