Patent Publication Number: US-2018050601-A1

Title: Electrically powered vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2016-160044 filed on Aug. 17, 2016, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Field 
     The present disclosure relates to an electrically powered vehicle and more particularly to an electrically powered vehicle incorporating a secondary battery. 
     Description of the Background Art 
     A secondary battery is mounted on a vehicle as a power supply for driving a motor of an electric car and a hybrid car. A secondary battery has been known to suffer from increase in internal resistance or lowering in full charge capacity due to deterioration over time as it is used. In particular, when the full charge capacity becomes low, decrease in energy which can be recovered in regenerative braking during running and decrease in travel distance with energy stored in the secondary battery are concerned. 
     Japanese Patent No. 5126008 describes a battery diagnosis system for vehicle which determines remaining lifetime of a vehicle-mounted secondary battery by being connected to a vehicle brought to a maintenance and repair service such as a dealer. According to the battery diagnosis system for vehicle in Japanese Patent No. 5126008, diagnosis information on a secondary battery on which drive patterns of a driver and an environment where a vehicle is located is reflected are accumulated, and by using the accumulated diagnosis information, a control plan for extending lifetime of the secondary battery is presented or a control parameter is modified. 
     SUMMARY 
     In estimating remaining lifetime (that is, a deterioration degree) of the secondary battery by using the accumulated diagnosis information as in Japanese Patent No. 5126008, it is important to improve estimation accuracy. If estimation of a deterioration degree is inaccurate, presentation of a control plan for extension of lifetime or modification to a control parameter cannot be sufficient and failure in sufficient suppression of deterioration of the secondary battery is concerned. Alternatively, in contrast, failure in effective use of the secondary battery due to excessive restriction of use is concerned. 
     Japanese Patent No. 5126008, however, fails to mention specific details of or control processing for diagnosis by using the accumulated information in the battery diagnosis system for vehicle. Whereas Japanese Patent No. 5126008 describes measures for extension of remaining lifetime to be taken by a user of a vehicle including a deteriorated secondary battery, it fails to provide advantages to a user of a vehicle including a secondary battery low in deterioration degree. 
     The present disclosure was made to solve such problems, and an object of the present disclosure is to enhance accuracy in estimation of a deterioration degree of a secondary battery mounted on an electrically powered vehicle and to make effective use of the secondary battery in accordance with the estimated deterioration degree. 
     In one aspect of the present disclosure, an electrically powered vehicle includes a secondary battery mounted as a motive power source, a memory, a communicator, and a controller. The memory is configured to accumulate use history data of the secondary battery. The communicator is configured to communicate with a data center outside the electrically powered vehicle. The controller is configured to control charging and discharging of the secondary battery so as to maintain an SOC of the secondary battery within a control range. The data center is configured to receive information on vehicle-mounted secondary batteries from a plurality of vehicles each provided with the vehicle-mounted secondary battery and to calculate a standard deterioration degree over time of the secondary batteries by using the information from the plurality of vehicles. The controller is configured to obtain the standard deterioration degree from the data center at prescribed deterioration diagnosis timing and to increase an upper limit value of the control range of the SOC when a deterioration degree estimated based on the use history data of the electrically powered vehicle is lower than the standard deterioration degree. 
     According to the electrically powered vehicle, whether or not a deterioration degree of a subject battery is lower than the standard can highly accurately be estimated by using actual infatuation on secondary batteries in a plurality of vehicles and a secondary battery of which deterioration degree is estimated to be lower than the standard can effectively be used by broadening an SOC available range by making use of a margin thereof. 
     The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an exemplary configuration of an electrically powered vehicle according to an embodiment of the present disclosure. 
         FIG. 2  is a flowchart for illustrating processing for accumulating battery use history data of the electrically powered vehicle. 
         FIG. 3  is a flowchart illustrating control processing for diagnosing deterioration of a secondary battery in the electrically powered vehicle. 
         FIG. 4  is a scatter diagram of a battery temperature and an SOC based on battery use history data. 
         FIG. 5  is a histogram of a battery temperature in a certain SOC range obtained from the scatter diagram in  FIG. 4 . 
         FIG. 6  shows a table illustrating exemplary definition of a region of use of a secondary battery. 
         FIG. 7  shows a conceptual graph illustrating exemplary estimation of a deterioration curve. 
         FIG. 8  shows a conceptual graph illustrating one example of processing for comparing a deterioration curve of a subject car with a reference deterioration curve. 
         FIG. 9  is a conceptual diagram illustrating SOC control based on a result of diagnosis of deterioration of a secondary battery in the electrically powered vehicle according to the present embodiment. 
         FIG. 10  is a flowchart illustrating a modification of diagnosis of deterioration of the secondary battery in the electrically powered vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present disclosure will be described below in detail with reference to the drawings. The same or corresponding elements in the drawings below have the same reference characters allotted and description thereof will not be repeated in principle. 
       FIG. 1  is a block diagram showing an exemplary configuration of an electrically powered vehicle according to an embodiment of the present disclosure. 
     Referring to  FIG. 1 , a main battery  10  representing a vehicle-mounted secondary battery is mounted on an electrically powered vehicle  100 . Electrically powered vehicle  100  is implemented, for example, as a hybrid car or an electric car including main battery  10  as a vehicle driving power supply (that is, a motive power source). The hybrid car is a vehicle including, in addition to a battery, a fuel cell or an engine which is not shown as a source of motive power for running the vehicle. The electric car is a vehicle including only a battery as a source of motive power of the vehicle. Electrically powered vehicle  100  includes main battery  10 , a boost converter  22 , an inverter  23 , a motor generator  25 , a transmission gear  26 , a drive wheel  27 , and a controller  30 . 
     Main battery  10  is implemented as an assembled battery (a battery pack)  20  including a plurality of battery modules  11 . Each battery module  11  includes a rechargeable secondary battery cell represented by a lithium ion secondary battery. 
     A current sensor  15 , a temperature sensor  16 , a voltage sensor  17 , and a battery monitoring unit  18  are further arranged in battery pack  20 . Battery monitoring unit  18  is implemented, for example, by an electronic control unit (ECU). Battery monitoring unit  18  is also referred to as a monitoring ECU  18  below. 
     Current sensor  15  detects currents IB input to and output from main battery  10  (hereinafter also referred to as a battery current IB). In the following, in connection with battery current IB, a discharging current is expressed as a positive value and a charging current is expressed as a negative value. 
     Temperature sensor  16  detects a temperature of main battery  10  (hereinafter also referred to as a battery temperature TB). A plurality of temperature sensors  16  may be arranged. In this case, a weighted average value, a maximal value, or a minimal value of temperatures detected by the plurality of temperature sensors  16  can be used as battery temperature TB or a temperature detected by specific temperature sensor  16  can be used as battery temperature TB. Voltage sensor  17  detects a voltage output from main battery  10  (hereinafter also referred to as a battery voltage VB). 
     Monitoring ECU  18  receives detection values from current sensor  15 , temperature sensor  16 , and voltage sensor  17 . Monitoring ECU  18  outputs battery voltage VB, battery current IB, and battery temperature TB to controller  30 . Alternatively, monitoring ECU  18  can store also data on battery voltage VB, battery current IB, and battery temperature TB in an embedded memory (not shown). 
     Monitoring ECU  18  is provided with a function to calculate a state of charge (SOC) of main battery  10  by using at least some of battery voltage VB, battery current IB, and battery temperature TB. The SOC is represented by a percentage of a current amount of stored energy to a full charge capacity of main battery  10 . Controller  30  which will be described later can also be provided with a function to calculate an SOC. 
     Main battery  10  is connected to boost converter  22  with system main relays  21   a  and  21   b  being interposed. Boost converter  22  boosts an output voltage from main battery  10 . Boost converter  22  is connected to inverter  23 , which converts direct-current (DC) power from boost converter  22  into alternating-current (AC) power. 
     Motor generator (three-phase AC motor)  25  generates kinetic energy for running a vehicle by receiving AC power from inverter  23 . Kinetic energy generated by motor generator  25  is transmitted to drive wheels  27 . When the vehicle is decelerated or stopped, motor generator  25  converts kinetic energy generated during braking of the vehicle into electric energy. AC power generated in motor generator  25  is converted to DC power by inverter  23 . Boost converter  22  down-converts an output voltage from inverter  23  and supplies the resultant voltage to main battery  10 . Regenerative power can thus be stored in main battery  10 . Motor generator  25  is thus configured to generate driving force or braking force of the vehicle with supply and reception of electric power to and from main battery  10  (that is, charging and discharging of main battery  10 ). 
     Boost converter  22  does not have to be provided. When a DC motor is employed as motor generator  25 , inverter  23  does not have to be provided. 
     When electrically powered vehicle  100  is implemented by a hybrid car in which an engine (not shown) is further mounted as a motive power source, output from the engine in addition to output from motor generator  25  can be used as driving force for running a vehicle. Alternatively, a motor generator (not shown) generating electric power with output from the engine can also further be mounted to generate electric power for charging main battery  10  with output from the engine. 
     Controller  30  is implemented, for example, by an electronic control unit (ECU), and includes a control unit  31  and a memory  32 . Memory  32  stores a program for operating control unit  31  or various types of data. Memory  32  can also be provided outside controller  30  so long as control unit  31  can read data therefrom and write data therein. 
     Controller  30  controls operations of system main relays  21   a  and  21   b,  boost converter  22 , and inverter  23 . When an ignition switch (not shown) is switched from off to on, controller  30  switches system main relays  21   a  and  21   b  from off to on and operates boost converter  22  and inverter  23 . When the ignition switch is switched from on to off, controller  30  switches system main relays  21   a  and  21   b  from on to off and stops an operation of boost converter  22  and inverter  23 . 
     Electrically powered vehicle  100  further includes a communication unit  60 , an operation unit  70 , and an output unit  80 . 
     Operation unit  70  includes an operation switch for a user of electrically powered vehicle  100  to input various operation commands. Operation unit  70  can be implemented by a hardware mechanism such as a push switch or by software such as a touch switch provided on a touch panel. An instruction from a user which has been input to operation unit  70  is input to controller  30 . 
     Output unit  80  is configured to output a visual and/or auditory message to a user of electrically powered vehicle  100  in response to a control command from controller  30 . For example, output unit  80  can be implemented as a speaker or a display such as a liquid crystal panel. Operation unit  70  and output unit  80  can also be implemented as an integrated device by employing a touch panel. 
     Communication unit  60  functions to establish a communication path  210  with the outside of electrically powered vehicle  100  and to establish wireless communication. For example, communication unit  60  can be implemented by a vehicle-mounted wireless communication module. 
     Electrically powered vehicle  100  can bidirectionally communicate data with data center  250  by connecting to a wide area communication network  240  (representatively the Internet) through communication path  210  by means of communication unit  60 . 
     Data center  250  can also bidirectionally communicate data with a plurality of electrically powered vehicles  100 # through wide area communication network  240 . Each of the plurality of electrically powered vehicles  100 # includes a vehicle-mounted secondary battery, and a deterioration degree of a secondary battery thereof is to be compared with that of electrically powered vehicle  100  (main battery  10 ) as will be described later. For example, electrically powered vehicle  100 # is of the same model as electrically powered vehicle  100  and can be defined as a vehicle incorporating a secondary battery identical in specification to main battery  10  of electrically powered vehicle  100 . For distinction from electrically powered vehicle  100  (a subject car), electrically powered vehicle  100 # is simply also referred to as “other car” below. Main battery  10  mounted on electrically powered vehicle  100  is also simply referred to as a “subject battery” and a secondary battery (a main battery) mounted on electrically powered vehicle  100 # is also simply referred to as an “other battery.” 
     Electrically powered vehicle  100  may be configured to be provided with an external charging function to charge main battery  10  with an external power supply  40 . In this case, electrically powered vehicle  100  further includes a charger  28  and charge relays  29   a  and  29   b.    
     External power supply  40  is a power supply provided outside a vehicle, and for example, a commercial AC power supply can be applied as external power supply  40 . Charger  28  converts electric power from external power supply  40  to charging power for main battery  10 . Charger  28  is connected to main battery  10  with charge relays  29   a  and  29   b  being interposed. When charge relays  29   a  and  29   b  are turned on, main battery  10  can be charged with electric power from external power supply  40 . 
     External power supply  40  and charger  28  can be connected to each other, for example, through a charging cable  45 . As external power supply  40  and charger  28  are electrically connected to each other when charging cable  45  is attached, main battery  10  can be charged with external power supply  40 . Alternatively, electrically powered vehicle  100  may be configured such that electric power is transmitted between external power supply  40  and charger  28  in a contactless manner. For example, main battery  10  can be charged by external power supply  40  by transmitting electric power through a power transmission coil (not shown) on a side of the external power supply and a power reception coil (not shown) on a side of the vehicle. 
     In an example where AC power is thus supplied from external power supply  40 , charger  28  is configured to be provided with a function to convert supply power (AC power) from external power supply  40  to charging power (DC power) for main battery  10 . Alternatively, in an example where external power supply  40  directly supplies charging power for main battery  10 , charger  28  should only transmit DC power from external power supply  40  to main battery  10 . A manner of external charging of electrically powered vehicle  100  is not particularly limited. 
     Electrically powered vehicle  100  runs while main battery  10  is charged and discharging. When the electrically powered vehicle is provided with the external charging function, main battery  10  is charged while electrically powered vehicle  100  is parked. As electrically powered vehicle  100  is thus used, main battery  100  deteriorates over time. Progress of deterioration of main battery  10 , however, has been known to significantly vary depending on a history of patterns of driving by a driver or temperature states of main battery  10 . 
     Therefore, in the electrically powered vehicle according to the present embodiment, deterioration of main battery  10  is diagnosed as below. 
       FIG. 2  is a flowchart for illustrating processing for accumulating battery use history data of the electrically powered vehicle. Processing in accordance with the flowchart shown in  FIG. 2  can be performed by controller  30 . 
     Referring to  FIG. 2 , controller  30  determines in step S 100  whether or not a certain time period has elapsed since previous transmission of battery use history data. For example, a not-shown timer contained in controller  30  can count an elapsed time since previous transmission of battery use history data. For example, the certain time period can be set to approximately 1 hour. 
     Controller  30  has the timer continue counting in step S 110  until the certain time period elapses (determination as NO in S 100 ). As shown in  FIG. 1 , controller  30  can obtain battery current IB, battery voltage VB, and battery temperature TB as well as an SOC of main battery  10  at any timing by means of monitoring ECU  18 . 
     When the certain time period has elapsed (determination as YES in S 100 ), in S 120 , controller  30  has memory  32  accumulate battery use history data of main battery  10 . For example, data on current values of battery temperature TB and an SOC and a battery current square value (IB 2 ) indicating a battery load can be accumulated as battery use history data. In step S 120 , a value of count by the timer is cleared as battery use history data is accumulated. 
     The battery use history data can be data on an instantaneous value at each timing every time a certain time period elapses. Alternatively, data resulting from statistical processing of battery temperature TB, an SOC, and a battery load (for example, an average value) within the certain time period may be stored in memory  32  as battery use history data. Consequently, controller  30  can diagnose deterioration of the subject battery using the battery use history data since start of use of main battery  10  (a new battery) stored in memory  32 . The battery use history data is transmitted to data center  250  through communication unit  60 . 
     The processing shown in  FIG. 2  is performed throughout running (an ignition switch being on) and non-running (the ignition switch being off) of the electrically powered vehicle. The processing in  FIG. 2  is performed also while electrically powered vehicle  100  is being parked and let stand and while electrically powered vehicle  100  is externally charged, and a time period of use of the secondary battery (main battery  10 ) includes both of a time period of running and a time period of non-running of electrically powered vehicle  100 . Thus, use history data of main battery  10  can periodically be transmitted to data center  250  as a certain time period elapses. 
     The control processing shown in  FIG. 2  is performed also in each electrically powered vehicle  100 # (other car). Consequently, battery use history data of main batteries of a plurality of vehicles including the subject car (electrically powered vehicle  100 ) is transmitted to data center  250 . 
       FIG. 3  is a flowchart illustrating control processing for diagnosing deterioration of the secondary battery (main battery  10 ) in electrically powered vehicle  100 . The control processing shown in  FIG. 3  can also be performed by controller  30 . 
     Referring to  FIG. 3 , controller  30  determines in step S 200  whether or not prescribed deterioration diagnosis timing has come. When the deterioration diagnosis timing has come (determination as YES in step S 200 ), the process proceeds to step S 210  and deterioration diagnosis processing is started. The control processing shown in  FIG. 3  can be performed in such a manner that processing in step S 210  or later is started as being triggered by sensing of arrival of deterioration diagnosis timing. 
     For example, deterioration diagnosis timing can be set to come in a certain cycle (for example, each time a prescribed number of months or years elapse). For example, determination in step S 200  can be made in such a manner that arrival of deterioration diagnosis timing is sensed each time the control processing shown in  FIG. 2  is performed a prescribed number of times. 
     In general, a secondary battery is often fast in progress of deterioration in an early stage after start of use thereof and a rate of progress of deterioration becomes stable after lapse of approximately one year. Therefore, in step S 200 , determination as NO may be maintained for approximately one year after start of use of main battery  10 . 
     Controller  30  estimates in step S 210  a current deterioration degree of main battery  10  by using battery use history data of the subject car stored in memory  32 . In the present embodiment, by way of example, a deterioration degree of the secondary battery is quantitatively evaluated by using a “ratio of maintained capacity” defined as a percentage of a current full charge capacity (Ah) with respect to a full charge capacity at the time when the battery was new. It is understood from this definition that a higher ratio of maintained capacity means a lower deterioration degree of the secondary battery and a lower ratio of maintained capacity means a higher deterioration degree of the secondary battery. 
     As described above, an SOC of the secondary battery represents in percentage a ratio of a current amount of stored power to a current full charge capacity. Therefore, in an example where the full charge capacity itself has become low due to a ratio of maintained capacity &lt;1.0, an actual amount of stored power (Ah) has become low even though a value for an SOC is the same (for example, SOC=100%). 
     One example of processing for estimating a deterioration degree of main battery  10  will now be described with reference to  FIGS. 4 to 6 . 
       FIG. 4  is a scatter diagram of an SOC (%) and a battery temperature Tb representing battery use history data accumulated in the control processing shown in  FIG. 2 . The abscissa in  FIG. 4  represents an SOC (%) and the ordinate in  FIG. 4  represents a battery temperature (° C.). 
     Referring to  FIG. 4 , combination of battery temperature TB and an SOC (%) in battery use history data obtained at each timing is obtained as each plot in the scatter diagram. The scatter diagram in  FIG. 4  shows tendency of use of main battery  10  in connection with at which temperatures and SOCs they have been used so far. Depending of a condition of use of a vehicle so far, the scatter diagram shown in  FIG. 4  is different for each vehicle. 
       FIG. 5  is a histogram of battery temperatures TB in a certain SOC range obtained from the scatter diagram shown in  FIG. 4 . 
     For example,  FIG. 5  shows a distribution of frequencies for each range set in 10 (° C.) increments of battery temperature TB by using the battery use history data in a range of SOCs from 70 to 80 (%) in  FIG. 4 . A distribution of frequencies similar to that in  FIG. 5  can be found for each SOC (%) range. 
     Since a frequency of appearance of each SOC range can be found, in each SOC range, a probability of occurrence for each region of use defined by a combination of an SOC range and a battery temperature range can be found based on multiplication of the frequency of appearance by the distribution of frequencies for each battery temperature range as in  FIG. 5 . 
       FIG. 6  shows a table illustrating exemplary definition of a region of use of a secondary battery. 
     Referring to  FIG. 6 , m×n regions of use R11 to Rmn can be defined based on combination between m (m: a natural number not smaller than 2) SOC ranges set in 5 (%) increments and n (n: a natural number not smaller than 2) battery temperature ranges set in 5 (° C.) increments. 
     As described above, a probability of appearance of m SOC ranges can be found and a distribution of frequencies in a battery temperature range set in 5 (° C.) increments can be found in each SOC range. Therefore, frequencies of occurrence P11 to Pmn corresponding to respective regions of use R11 to Rmn can be calculated in accordance with a product of the probability of appearance of each SOC range and the frequency of appearance of each battery temperature range in the SOC range. The total sum of frequencies of occurrence P11 to Pmn is 1.0. 
     In general, a secondary battery has been known to be higher in rate of progress of deterioration over time when a high-temperature and high-SOC condition continues. With such characteristics of the secondary battery being reflected, in each of regions of use R11 to Rmn, a unit degree of progress of deterioration when main battery  10  is used for a unit time period (for example, 1 hour) in each region can be determined in advance. The unit deterioration progress degree is represented by an amount of lowering (%/h) in ratio of maintained capacity per unit time. Thus, memory  32  stores in advance unit deterioration progress degrees C11 to Cmn in correspondence with respective regions of use R11 to Rmn. 
     With the use of a cumulative time period Tt (h) from start of use of main battery  10 , time periods of use in regions of use R11 to Rmn are shown as Tt·P11 to Tt·Pmn. 
     Then, a deterioration degree parameter R of main battery  10  at the current time point can be calculated in accordance with an expression (1) below by totaling the products of unit deterioration progress degrees C11 to Cnm and respective time periods of use in regions of use R11 to Rmn. 
         R= 1.0 −Tt ·( P 11 ·C 11+ . . . +Pmn·Cmn)  (1)
 
     Deterioration degree parameter R corresponds to an estimated value for a ratio of maintained capacity at the current time point. When main battery  10  is new, a condition of R=1.0 (that is, a ratio of maintained capacity being 100 (%)) is satisfied. It is understood that “1.0−R” in connection with deterioration degree parameter R in the expression (1) corresponds to a rate of lowering (that is, a deterioration degree) in full charge capacity from start of use. A deterioration degree of a secondary battery is estimated below by using deterioration degree parameter R, and smaller deterioration degree parameter R means a higher deterioration degree of main battery  10 . 
     The expression (1) above can also be deformed to further combine estimation of a deterioration degree due to charging and discharging cycles, by using history data of a battery load (Ib 2 ). Controller  30  can estimate a deterioration degree of main battery  10  of the subject car at the current time point at each deterioration diagnosis timing by calculating such deterioration degree parameter R (step S 210 ).  FIGS. 4 to 6  merely illustrate one example of processing for estimating a deterioration degree, and the processing in step S 210  can be performed with any technique so long as a deterioration degree parameter for quantitatively estimating a current deterioration degree can be calculated based on past battery use history data. 
     Referring again to  FIG. 3 , controller  30  estimates in step S 220  a deterioration curve of the subject battery by using current deterioration degree parameter R found in step S 210 . 
       FIG. 7  shows a conceptual graph illustrating exemplary estimation of a deterioration curve in step S 220 . The abscissa in  FIG. 7  represents an elapsed time (a time period of use) since start of use of main battery  10  and the ordinate represents a ratio of maintained capacity (%) in accordance with deterioration degree parameter R. 
     Referring to  FIG. 7 , a period until an elapsed time reaches t 0  corresponds to an initial period during which deterioration progresses fast described above. For example, t 0  is approximately one year. Therefore, deterioration is not diagnosed until the elapsed time reaches t 0 . 
     A reference deterioration curve Cr shown with a bold line in  FIG. 7  is determined in advance based on characteristics of main battery  10 . For example, reference deterioration curve Cr can be laid down in advance based on data on deterioration over time in experiments under a standard history of use. For example, information for defining reference deterioration curve Cr can be stored in memory  32 . In  FIG. 7 , a ratio of maintained capacity (deterioration degree parameter R) estimated in step S 210  ( FIG. 3 ) each time deterioration diagnosis timing comes is plotted with a reference  300 . In the example in  FIG. 7 , deterioration is diagnosed seven times until lapse of t 2 . 
     For example, a deterioration curve of the subject battery can be estimated, with prediction after t 2  being included, by correcting a rate of progress of deterioration (reference) along reference deterioration curve Cr with an estimated value for a ratio of maintained capacity obtained in diagnosis of deterioration so far. 
     Referring again to  FIG. 3 , when controller  30  estimates a deterioration curve of the subject battery in step S 220 , it accesses data center  250  in step S 230  to obtain a standard deterioration curve. 
     Here, deterioration degree parameter R (a ratio of maintained capacity) calculated in step S 210  can also be transmitted to data center  250 . In the present embodiment, at least one of battery use history data (S 120  in  FIG. 2 ) and deterioration degree parameter R (S 210  in  FIG. 3 ) is periodically transmitted as “information on secondary batteries” from electrically powered vehicles  100  and  100 # to data center  250 . 
     Data center  250  generates a standard deterioration curve based on battery use histories from a plurality of users of secondary batteries identical in type to main battery  10 , by using information on the secondary batteries transmitted from a plurality of electrically powered vehicles  100 # (incorporating the secondary batteries identical in specification to main battery  10 ). The standard deterioration curve can be updated in response to transmission of information from each of electrically powered vehicles  100  and  100 #. For example, the standard deterioration curve corresponds to an aggregate of standard deterioration degrees after time periods of use at each time point in a plurality of electrically powered vehicles which have transmitted information on the secondary batteries to data center  250 . The standard deterioration degree can be set, for example, as an aggregate of average values or median values of deterioration degree parameters R (ratios of maintained capacity) of a plurality of electrically powered vehicles. 
     Data center  250  can calculate deterioration degree parameters R (ratios of maintained capacity) of electrically powered vehicles  100  and  100 # based on battery use history data periodically transmitted from each vehicle as information on the vehicle-mounted secondary battery. Alternatively, as described above, data center  250  may receive transmission of a calculated parameter value each time each vehicle calculates deterioration degree parameter R in the processing (S 210 ) as in  FIG. 3 . 
     Referring again to  FIG. 3 , controller  30  compares in step S 240  a deterioration degree of the subject car in accordance with the deterioration curve (S 220 ) with the standard deterioration degree in accordance with the standard deterioration curve (S 230 ) from data center  250 . 
       FIG. 8  shows a conceptual graph illustrating one example of processing for comparing a deterioration degree in step S 240 . 
     Referring to  FIG. 8 , a determination threshold value Ct at each elapsed time can be set based on a standard deterioration curve CO from data center  250 . 
     For example, determination threshold value Ct can be set by multiplying a value for each deterioration degree parameter R on standard deterioration curve CO by k (k&gt;1.0) or by adding thereto a prescribed margin value. The margin value can also be set, with variation (standard deviation) in deterioration degree parameter R at the same elapsed time among a plurality of vehicles used for setting of standard deterioration curve CO being reflected.  FIG. 8  shows a deterioration determination curve CT corresponding to an aggregate of determination threshold values Ct with a dotted line. 
     Therefore, standard deterioration curve CO and a deterioration curve Cp of the subject car can be compared with each other in step S 240  by comparing deterioration determination curve CT with deterioration curve Cp ( FIG. 7 ) of the subject car. 
     When a ratio of maintained capacity represented by deterioration curve Cp is higher than a ratio of maintained capacity represented by deterioration determination curve CT, a deterioration degree of the subject battery is determined as being lower than the standard deterioration degree. Therefore, on a deterioration curve CA (Cp) for a user A exemplified in  FIG. 8 , the deterioration degree of the subject battery is determined as being lower than the standard. On a deterioration curve CB (Cp) for a user B, the deterioration degree of the subject battery is determined as being higher than the standard deterioration degree. 
     A period during which comparison between deterioration degrees represented by deterioration determination curve CT and the deterioration curve of the subject battery is made can arbitrarily be determined. For example, a period during which comparison of a deterioration degree is made can be set to include both of a period until the current time point (until t 2  in  FIG. 7 ) and a portion after the current time point (after t 2  in  FIG. 7 ), and then determination in step S 240  can be made. Alternatively, a period during which comparison of a deterioration degree is made may be set to include only one of a period until the current time point (until t 2  in  FIG. 7 ) and a period after the current time point (after t 2  in  FIG. 7 ). 
     Alternatively, most simply, determination in step S 240  can also be made based on comparison between deterioration degree parameter R and determination threshold value Ct based on the standard deterioration degree (that is, one point on standard deterioration curve CO) at the present deterioration diagnosis timing. In contrast, determination in step S 240  can more highly accurately be made with prediction of a deterioration degree after the current time point being reflected, based on comparison between deterioration curve Cp and standard deterioration curve CO (deterioration determination curve CT). 
     Referring again to  FIG. 3 , when controller  30  determines that the deterioration degree of the subject battery is lower than the standard (determination as YES in S 240 ), the process proceeds to step S 250  and an upper limit SOC corresponding to an upper limit value for an SOC control range of main battery  10  is increased from a default value (S 1 ) to a prescribed value S 2  (S 2 &gt;S 1 ). 
     When controller  30  does not determine that the deterioration degree of the subject battery is lower than the standard (determination as NO in S 240 ), the process proceeds to step S 260  and the upper limit SOC is maintained at the default value (S 1 ). 
     When a ratio of maintained capacity represented by deterioration curve Cp is higher than the ratio of maintained capacity represented by deterioration determination curve CT throughout the period during which comparison of the deterioration degree is made described above, determination as YES can be made in step S 240 . Alternatively, when a ratio of maintained capacity represented by deterioration curve Cp is higher than a ratio of maintained capacity represented by deterioration determination curve CT in a part of the period in which comparison of the deterioration degree is made under a predetermined condition as well, determination as YES can be made in step S 240 . 
       FIG. 9  is a conceptual diagram illustrating SOC control based on a result of diagnosis of deterioration of the secondary battery in the electrically powered vehicle according to the present embodiment. 
     Referring to  FIG. 9 , an SOC of main battery  10  is controlled to be within a range from a lower limit SOC (Smin) to an upper limit SOC (Smax) between 0 and 100 (%). For example, when the SOC increases to the upper limit SOC during running of the vehicle, controller  30  prohibits charging of main battery  10 . Thus, regeneration by motor generator  25  is prohibited, necessary braking force is ensured by a friction brake (not shown), and energy cannot be recovered during deceleration. When the SOC reaches the upper limit SOC (Smax) also during external charging with charger  28 , controller  30  deactivates charger  28  and quits charging. 
     When the SOC lowers to the lower limit SOC, controller  30  prohibits discharging of main battery  10 . Thus, the vehicle cannot run with electric power stored in main battery  10 . Therefore, it is understood that, as an SOC available range defined as a difference between the upper limit SOC (Smax) and the lower limit SOC (Smin) is greater, a travel distance can be increased by making effective use of main battery  10 . Default value S 1  of the upper limit SOC (Smax) is set within a region where the possibility of progress of deterioration is relatively low even when the main battery is let stand, in consideration of characteristics of main battery  10 . 
     An SOC available range ΔSOC 2  at the time when the upper limit SOC (Smax) is increased from default value S 1  to prescribed value S 2  in step S 250  in  FIG. 10  is greater than an SOC available range ΔSOC 1  at the time when the upper limit SOC (Smax) is set to default value S 1 . Thus, for an electrically powered vehicle in which a deterioration degree of its own battery is lower than the standard, an SOC available range can be broadened by making use of a margin for the standard deterioration degree. Though the possibility of progress of deterioration relatively increases with increase in upper limit SOC (Smax), increase in upper limit SOC is allowed, with the deterioration degree of the own battery being retained within a range not higher than the standard, by making similar determination at each diagnosis timing. The main battery can thus effectively be used. 
     As described above, according to the electrically powered vehicle in the present embodiment, whether or not a deterioration degree of a subject battery is lower than the standard can highly accurately be estimated by using actual information on secondary batteries in a plurality of vehicles. Furthermore, based on such highly accurate estimation, main battery  10  lower in deterioration degree than the standard can be made effective use of by broadening the SOC available range. 
     In particular, by comparing a deterioration degree of a subject secondary battery with the standard deterioration degree with prediction of a deterioration degree after the current time point being reflected by using deterioration curve Cp and standard deterioration curve CO, whether or not the upper limit SOC may be increased can further highly accurately be determined. 
     (Modification) 
       FIG. 10  is a flowchart illustrating a modification of diagnosis of deterioration of the secondary battery (main battery  10 ) in the electrically powered vehicle according to the present embodiment. 
     Referring to  FIG. 10 , when controller  30  senses arrival of timing of deterioration diagnosis in step S 200  as in  FIG. 3 , it performs steps S 210  to S 240  as in  FIG. 3  and determines whether or not the deterioration degree of the subject battery is lower than the standard. Since the control processing up to here is the same as in  FIG. 3 , detailed description will not be repeated. 
     When controller  30  determines that the deterioration degree of the subject battery is lower than the standard (determination as YES in step S 240 ), the process proceeds to step S 242 . Controller  30  notifies that the upper limit SOC may be increased because the deterioration degree of the subject battery is low and outputs a message for checking with a user whether or not to permit increase in upper limit SOC. The message can be provided, for example, by representation on a screen and/or output of sound through output unit  80  shown in  FIG. 1 . 
     Controller  30  determines in step S 244  whether or not an instruction from a user permitting increase in upper limit SOC has been input to operation unit  70  in response to output of the message in step S 242 . For example, in response to the message in step S 242 , a touch switch for input can be shown on a touch panel so that determination in step S 244  can be made based on whether or not the touch switch is operated. 
     When an instruction from a user permitting increase in upper limit SOC has been input to operation unit  70  (determination as YES in S 244 ), the process proceeds to step S 250  as in  FIG. 3  and the upper limit SOC (Smax) is increased from default value S 1  to S 2  as shown in  FIG. 9 . 
     When an instruction from a user permitting increase in upper limit SOC has not been input (determination as NO in S 244 ), controller  30  maintains the upper limit SOC at default value S 1  in step S 260  as in  FIG. 3 . 
     Thus, the user can select which of effective use of main battery  10  (increase in travel distance) and protection against deterioration is to be prioritized, in consideration of the fact that broadening of the SOC available range is disadvantageous to deterioration of main battery  10 . 
     Furthermore, when controller  30  does not determine that the deterioration degree of the subject battery is lower than the standard (determination as NO in S 240 ), it fixes the upper limit SOC at the default value in step S 260  and outputs guidance for suppressing deterioration of main battery  10  in step S 246 . 
     User guidance in step S 246  can be given based on battery use history data accumulated in memory  32 . For example, though a frequency of occurrence of high battery temperature TB becomes higher in main battery  10  high in deterioration degree, which of charging and discharging during running of a vehicle and parking in a high-temperature environment is a main cause for high battery temperature TB can be determined based on combination of a battery load (IB 2 ) and battery temperature TB. Therefore, when influence by parking in a high-temperature environment is greater, guidance for selecting a parking position at which direct sunlight can be avoided can be output. 
     Alternatively, when it can be determined that a period after external charging in which the SOC has attained to the upper limit is long based on a distribution of frequencies of occurrence of the SOC, guidance encouraging timer-controlled charging can be output in order to shorten a time period from end of external charging until start of running of the vehicle. Thus, improvement in environment for use for suppressing deterioration of main battery  10  can be encouraged. 
     In  FIG. 10 , such control processing that any one of output of guidance in step S 246  and checking of an operation by a user in steps S 242  and S 244  is performed can also be performed. Step S 246  may be performed only when a deterioration determination curve is separately prepared under standard deterioration curve CO (on a side of a high deterioration degree) ( FIG. 8 ) and a deterioration degree represented by deterioration curve Cp is higher than the deterioration degree represented by the deterioration determination curve. 
     Thus, according to the modification shown in  FIG. 10 , convenience of a user of electrically powered vehicle  100  can be enhanced by further providing a function for allowing a user to select whether or not to increase the upper limit SOC at the time when the deterioration degree of main battery  10  is lower than the standard and/or a function to output guidance at the time when the deterioration degree of main battery  10  is higher than the standard. 
     The configuration of electrically powered vehicle  100  in  FIG. 1  is merely by way of illustration, and the present disclosure is applicable also to an electrically powered vehicle other than an electric car, such as a hybrid vehicle incorporating an engine or a fuel cell in addition to main battery  10 , without a configuration of a powertrain being particularly limited. Deterioration diagnosis processing according to the present embodiment is applicable to a secondary battery mounted as a motive power source in an electrically powered vehicle. 
       FIGS. 3 and 10  illustrate examples in which controller  30  of electrically powered vehicle  100  estimates a current deterioration degree, that is, calculates a deterioration degree parameter. When battery use history data is periodically transmitted to data center  250  as in  FIG. 2 , however, data center  250  may estimate a deterioration degree of main battery  10  of electrically powered vehicle  100 . In this case, in step S 210  in  FIG. 3 , a deterioration degree parameter is obtained through communication with data center  250 . Furthermore, data center  250  may generate also a deterioration curve in addition to a deterioration degree parameter. In step S 220  in  FIG. 3 , controller  30  may obtain a deterioration curve through communication with data center  250 . Alternatively, controller  30  may generate deterioration curve Cp ( FIG. 7 ) through processing in step S 220  described above by using a deterioration degree parameter obtained through communication with data center  250 . 
     Furthermore, the deterioration degree parameter is not limited to a deterioration degree parameter representing a ratio of maintained capacity exemplified in the present embodiment. So long as a deterioration degree parameter quantitatively represents a deterioration degree of a secondary battery and can be calculated from battery use history data, any parameter value can be used as a deterioration degree parameter in diagnosis of deterioration of a secondary battery in the electrically powered vehicle according to the present embodiment. 
     The present embodiment shows an example that a plurality of electrically powered vehicles  100 # of which deterioration degrees of secondary batteries are to be compared with that of electrically powered vehicle  100  (main battery  10 ) are identical in model to electrically powered vehicle  100  and include vehicle-mounted secondary batteries identical in specification to main battery  10 . Electrically powered vehicle  100 #, however, can also include a vehicle different in model and/or specification of a secondary battery from electrically powered vehicle  100  by introducing normalization for converting a difference in number of cells in a secondary battery or weight of the vehicle in comparison of a deterioration degree parameter. By comparing a normalized deterioration parameter, a deterioration degree of a secondary battery according to the present embodiment can be compared between vehicles different in model and/or specification of the secondary battery. 
     For example, until information on a prescribed number of secondary batteries which are mounted on vehicles identical in model to electrically powered vehicle  100  and are identical in specification to main battery  10  is collected in data center  250 , in order to secure the number of subjects to be compared, a vehicle different in model and/or specification of a secondary battery can be included in a plurality of electrically powered vehicles  100 # so that a deterioration degree can be compared based on a normalized value. Then, after information on at least a prescribed number of secondary batteries identical in specification which are mounted on vehicles identical in model is secured, subjects of which deterioration degree is to be compared (that is, an extent of a plurality of electrically powered vehicles  100 #) can be changed so that a deterioration degree is compared among secondary batteries identical in specification which are mounted on vehicles identical in model. 
     “Information on secondary batteries” transmitted from a plurality of electrically powered vehicles  100 # to data center  250  is not limited to battery use history data and/or a deterioration degree parameter described above, but any information can be employed so long as it is quantitative data which can directly or indirectly be used for comparison of a deterioration degree. 
     Though an embodiment of the present disclosure has been described, it should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.