Method for measuring capacity of power storage element

Abstract

Provided is a method for measuring the capacity of a power storage element mounted on a vehicle 10 including an OBD port 25 for connecting an OBD scan tool 12 to OBD, wherein a master ECU 21A of the vehicle 10 receives an instruction of capacity measurement for a power storage device 23 for accessories from the OBD scan tool 12 via the OBD port 25, the master ECU 21A, which has received the instruction, controls an electric system 20 of the vehicle 10 to discharge the power storage device 23 for accessories, a BMU 31 of the power storage device 23 for accessories integrates a discharge current of the power storage device 23 for accessories during the discharge and measures the capacity of the power storage device 23 for accessories on the basis of the integrated quantity of electricity.

Description

Method for measuring the capacity of a storage element

[0001] The technology disclosed in this specification relates to a method for measuring the capacitance of an energy storage element.

[0002] Conventionally, a power storage device mounted on a vehicle has been known (see, for example, Patent Document 1). The power storage device described in Patent Document 1 is a rechargeable DC power supply that stores power for running the vehicle, and is made up of a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. Patent Document 1 also describes that the vehicle is equipped with an imbalance monitor that detects an air-fuel ratio imbalance for each cylinder in a multi-cylinder engine, and advanced on-board diagnosis (OBD) for the engine, such as catalyst deterioration in an exhaust purification device.

[0003] Patent No. 5445347

[0004] It is known that energy storage devices such as lithium-ion secondary batteries deteriorate with use, resulting in a decrease in the amount of electricity they can store (fully charged capacity, hereinafter simply referred to as "capacity"). When the capacity decreases, the energy storage device is no longer able to perform as intended, and its reliability decreases. For this reason, the capacity of an energy storage device has traditionally been estimated or measured, and if the capacity has decreased, the energy storage device is replaced.

[0005] Due to the trend toward autonomous driving and the electrification of safety devices, high reliability is required for power storage elements mounted on vehicles. The life cycle of a power storage element is estimated to be 10 to 15 years, and highly accurate estimation or measurement of the capacity during that period is required. One embodiment of the present invention aims to measure the capacity of a power storage element mounted on a vehicle with high accuracy.

[0006] The method for measuring the capacity of a storage element disclosed in this specification is a method for measuring the capacity of a storage element mounted on a vehicle equipped with a diagnostic connector for connecting an external diagnostic device to an on-board fault diagnosis device, in which a control unit of the vehicle receives an instruction to measure the capacity of the storage element from the external diagnostic device via the diagnostic connector, the control unit having received the instruction controls the electrical system of the vehicle to discharge the storage element, and a management device for the storage element accumulates the discharge current of the storage element during the discharge and measures the capacity of the storage element based on the accumulated amount of electricity.

[0007] According to the above configuration, the capacitance of the electric storage element mounted on the vehicle can be measured with high accuracy.

[0008] 1 is a schematic diagram of a measurement system according to a first embodiment; a block diagram showing an electrical configuration of a power storage device; a graph showing a profile of an auxiliary power storage device; a graph showing a change in the capacity of an auxiliary power storage device; a flowchart of measuring the capacity of an auxiliary power storage device; and a schematic diagram of a measurement system according to a second embodiment.

[0009] [Outline of the embodiment] An outline of the embodiment of the present disclosure will be described.

[0010] (1) In one embodiment, a method for measuring the capacity of a storage element is provided in a vehicle equipped with a diagnostic connector for connecting an external diagnostic device to an on-board fault diagnosis device, in which a control unit of the vehicle receives an instruction to measure the capacity of the storage element from the external diagnostic device via the diagnostic connector, the control unit receiving the instruction controls the vehicle's electrical system to discharge the storage element, and a management device for the storage element accumulates the discharge current of the storage element during the discharge and measures the capacity of the storage element based on the accumulated amount of electricity.

[0011] When discharging a storage element, the storage element may be discharged at a constant current until its voltage reaches a specified voltage. By specifying the discharge conditions, the capacity can be measured more accurately. In particular, if the storage element has multiple storage cells connected in series and the cell voltage of each of these storage cells can be measured, the storage cells can be discharged and the cell voltages measured until the total voltage reaches a specified voltage can be compared. This makes it possible to determine the capacity variation (variation in full charge capacity or remaining capacity) of the storage cells.

[0012] A known method for estimating the capacity of a storage element is to estimate it based on a storage element capacity estimation model (model method). However, the model method has issues such as the need to occupy test equipment for long periods of time to acquire data and the need for a large amount of data to achieve high accuracy. A known method for measuring the capacity of a storage element is to discharge the storage element and determine the capacity from the measured discharged amount of electricity and voltage (diagnostic method). The diagnostic method is more accurate than the model method because it actually measures the capacity of the storage element.

[0013] However, the inventors have found that even the diagnostic method may not be able to measure capacity with high accuracy when the vehicle is in use in the market (in other words, when it is not possible to predict when the vehicle will be used). Specifically, in the case of the diagnostic method, in order to measure capacity with high accuracy, it is preferable that the storage element be maintained at a low load (low rate discharge) and a constant current while the storage element is being discharged. Furthermore, it is preferable that changes in environmental temperature are small. However, when the vehicle is in use in the market, there is a possibility that the load and current may fluctuate as the vehicle is used during measurement, or that the environmental temperature may change as the vehicle is moved from a warm region to a cold region.

[0014] The inventors have investigated this issue and found that when a vehicle is in a repair shop for inspection, periodic inspection, or repair, the vehicle is not used unexpectedly, so the storage element is maintained at a low load and constant current for a relatively long period of time (for example, 2 to 3 hours), and changes in environmental temperature due to movement of the vehicle are small. Therefore, it is highly likely that the capacity can be measured with high accuracy when the vehicle is in a repair shop.

[0015] However, in order to measure the capacity when the vehicle is at a repair shop, it is necessary for the vehicle control unit or the storage element management device to determine whether the vehicle is at a repair shop. After studying this issue, the inventors discovered that when an external diagnostic device is connected to the vehicle's diagnostic connector, it is highly likely that the vehicle is at a repair shop. This is because external diagnostic devices are generally installed in repair shops, and it is unlikely that the vehicle user owns an external diagnostic device.

[0016] According to the method for measuring the capacitance of an electric storage element described in (1) above, the capacitance of the electric storage element is measured when an instruction to measure the capacitance of the electric storage element is received from an external diagnostic device via the diagnostic connector, so that it is highly likely that the capacitance can be measured under conditions in which the electric storage element is maintained at a low load and a constant current and there is little change in the environmental temperature. Therefore, according to the method for measuring the capacitance of an electric storage element described in (1) above, the capacitance of the electric storage element mounted on a vehicle can be measured with higher accuracy than when measuring under conditions in which the vehicle is in use in the market.

[0017] (2) In the method for measuring the capacity of a storage element described in (1) above, the control unit that receives the instruction may control the electrical system to charge the storage element, and the discharging may be performed after the charging.

[0018] When charging the energy storage element, constant current constant voltage charging (CCCV charging) may be employed. By specifying the charging conditions, the capacity can be measured more accurately. In particular, when the energy storage element has multiple storage cells connected in series and the cell voltage of each of the storage cells can be measured, the storage cells can be uniformly brought to a fully charged state by CCCV charging. From this state, the storage cells are discharged, and the cell voltages measured until the total voltage reaches a specified voltage are compared, thereby making it possible to grasp the capacity variation among the storage cells.

[0019] In order to discharge a storage element, the storage element must be charged. According to the capacitance measurement method for a storage element described in (2) above, the storage element is charged before discharging, so the storage element can be discharged to measure the capacity. In the charging described above, the storage element only needs to be charged until it stores enough electricity to measure the capacity, and does not necessarily have to be fully charged.

[0020] (3) The method for measuring the capacity of a storage element described in (2) above may include charging the storage element to a voltage range higher than the plateau region in a profile representing the correspondence between the state of charge of the storage element and the open-circuit voltage.

[0021] Some energy storage elements have a plateau region in the profile that represents the correspondence between the state of charge (SOC: State of Charge) and the open circuit voltage (OCV: Open Circuit Voltage) of the energy storage element. Here, in this embodiment, the open circuit voltage is not limited to the voltage when the circuit is completely open, but may also be the voltage when a minute current flows that can be considered to be open circuit. In the following description, when simply referring to voltage, this refers to the open circuit voltage. The plateau region refers to a region in which the amount of change in open circuit voltage relative to the amount of change in the state of charge is small.

[0022] In measuring capacity, a storage element is charged to a certain state of charge (first state of charge) and then discharged from the first state of charge to a lower state of charge (second state of charge), and the capacity is calculated from the amount of electricity discharged during this period. Whether or not the storage element has been charged to the first state of charge is determined from the voltage. Specifically, a voltage corresponding to the first state of charge is identified from the profile, and charging to the identified voltage is determined to have reached the first state of charge. However, in the plateau region, a slight measurement error in voltage significantly changes the corresponding state of charge, making it difficult to accurately determine whether or not the storage element has been charged to the first state of charge. This can result in inaccurate capacity measurement. According to the method for measuring the capacity of a storage element described in (3) above, charging is performed to a voltage range higher than the plateau region, allowing for more accurate measurement of the capacity than when the voltage corresponding to the first state of charge is within the plateau region.

[0023] (4) In the method for measuring the capacity of an electric storage device according to any one of (1) to (3), the electricity stored in the electric storage device may be discharged to a high-voltage electric storage device mounted on the vehicle and having a larger capacity than the electric storage device. The electricity stored in the electric storage device may be discharged to the high-voltage electric storage device via a power conversion device.

[0024] According to the method for measuring the capacity of a storage element described in (4) above, when discharging a storage element, the storage element is discharged into a high-voltage storage element having a larger capacity than the storage element, thereby reducing electrical loss compared to discharging into an electrical resistor, etc.

[0025] (5) In the method for measuring the capacitance of an electric storage element according to any one of (1) to (3) above, the electricity of the electric storage element may be discharged to a discharge destination outside the vehicle.

[0026] According to the method for measuring the capacity of a storage element described in (5) above, the capacity can be measured by discharging the electricity of the storage element to a discharge destination outside the vehicle. In order to reduce the loss of electricity, the discharge destination is preferably a storage device outside the vehicle. Alternatively, the electricity may be discharged to a power grid and sold.

[0027] (6) In the method for measuring the capacity of a storage element described in any one of (1) to (5) above, after receiving the instruction, at least one of the control unit and the management device may determine whether or not conditions for measuring the capacity of the storage element are met, and the control unit may discharge the storage element if it is determined that the conditions are met.

[0028] If the conditions for carrying out the capacitance measurement of the energy storage element are not met, the measured capacitance may be inaccurate or the measurement may have to be stopped midway. According to the method for measuring the capacitance of an energy storage element described in (6) above, the capacitance is measured when it is determined that the conditions for carrying out the capacitance measurement are met, so that the measured capacitance may be inaccurate or the measurement may have to be stopped midway.

[0029] (7) In the method for measuring the capacity of a storage element described in any one of (1) to (6) above, during the discharging, at least one of the control unit and the management device may determine whether a stop condition is met, and if it is determined that the stop condition is met, the control unit may control the electrical system to stop the discharging, and after the stop, the control unit may control the electrical system to charge the storage element.

[0030] During capacity measurement, a situation may arise in which measurement should be stopped. Continuing measurement in such a case may result in an inaccurate measured capacity. According to the method for measuring the capacity of a storage element described in (7) above, discharging is stopped when a stop condition is met, thereby preventing an inaccurate capacity measurement. However, if charging is not performed after discharging is stopped, there is a possibility that the storage element will be insufficiently charged when the vehicle is handed over to the user. According to the method for measuring the capacity of a storage element described in (7) above, the storage element is charged after discharging is stopped, thereby reducing the possibility that the vehicle will be handed over to the user with the storage element insufficiently charged.

[0031] (8) In the method for measuring the capacity of a storage element described in any one of (1) to (7) above, the management device may estimate the capacity of the storage element based on a capacity estimation model of the storage element, and at least one of the control unit and the management device may compare the measured capacity with the estimated capacity to determine whether or not there is an abnormality in the storage element.

[0032] As mentioned above, the model method does not necessarily have high estimation accuracy, but it does have a certain degree of accuracy. Therefore, if there is a large difference between the capacity measured by discharging the storage element and the capacity estimated based on the capacity estimation model, there is a possibility that some abnormality has occurred in the storage element. According to the method for measuring the capacity of a storage element described in (8) above, the presence or absence of an abnormality in the storage element can be determined by comparing the measured capacity with the estimated capacity.

[0033] (9) In the method for measuring the capacity of an energy storage element according to any one of (1) to (8) above, the control unit may output the measured capacity to the external diagnostic device via the diagnostic connector.

[0034] According to the method for measuring the capacity of a storage element described in (9) above, the measured capacity is output to an external diagnostic device, so that a vehicle mechanic can check the capacity using the external diagnostic device and replace the storage element if the capacity has decreased, thereby preventing the continued use of a storage element with decreased capacity. Furthermore, according to the method for measuring the capacity of a storage element described in (9) above, the capacity can be measured with high accuracy, so that it is possible to prevent a storage element from being replaced due to an error in measuring the capacity even though its capacity has not actually decreased enough to require replacement, or from not being replaced due to an error in measuring the capacity even though its capacity has actually decreased to the point where replacement is required.

[0035] (10) According to an embodiment, a method for measuring the capacity of an energy storage element is provided in a vehicle equipped with a diagnostic connector for connecting an external diagnostic device to an on-board fault diagnosis system. A control unit of the vehicle receives an instruction to measure the capacity of the energy storage element from the external diagnostic device via the diagnostic connector. The control unit, upon receiving the instruction, controls an electrical system of the vehicle to charge the energy storage element. A management device for the energy storage element integrates a charging current of the energy storage element during the charging and measures the capacity of the energy storage element based on the integrated amount of electricity. CCCV charging may be employed when charging the energy storage element. The energy storage element may be discharged (e.g., discharged at a constant current) until its voltage reaches a specified voltage, and then CCCV charging may be performed on the energy storage element.

[0036] According to the method for measuring the capacity of a storage element described in (10) above, the capacity of a storage element mounted on a vehicle can be measured with higher accuracy than when the measurement is performed while the vehicle is in use in the market.

[0037] [Details of the Embodiments] Details of the embodiments of the present disclosure will be described. The present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. The embodiments of the present disclosure can be realized in various forms, such as an apparatus, a method, a computer program for implementing the functions of these apparatuses or methods, and a recording medium on which the computer program is recorded.

[0038] First Embodiment A first embodiment will be described with reference to Figures 1 to 5. In the following description, the reference numerals of the drawings may be omitted for the same components, with some exceptions.

[0039] (1) System Configuration A measurement system 1 that implements the method for measuring the capacitance of an energy storage element according to embodiment 1 will be described with reference to Fig. 1. The measurement system 1 includes a vehicle 10 and an OBD scan tool 12 (an example of an external diagnostic device) that is provided in a maintenance shop 11 for the vehicle 10.

[0040] (1-1) Vehicle The vehicle 10 is a vehicle that runs on an electric motor, and specifically, is an electric vehicle (EV), a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), or the like. Vehicles that run on electric motors are not limited to these. For example, the vehicle 10 may be a forklift, or an automated guided vehicle (AGV) that automatically transports materials in a factory or the like.

[0041] 1, an electrical system 20 of a vehicle 10 will be described in outline. The vehicle 10 includes an electric motor (not shown) that drives the vehicle 10, various auxiliary machinery 21, a drive power storage device 22 (an example of a power storage element and a high-voltage power storage element), an auxiliary machinery power storage device 23 (an example of a power storage element), a bidirectional DC / DC converter 24, and an OBD port 25 (an example of a diagnostic connector).

[0042] The various auxiliary devices 21 include a master ECU 21A (Electronic Control Unit), other ECUs 21B (such as an engine control ECU and a transmission control ECU), headlights (not shown), and an air conditioner (not shown). The master ECU 21A is an example of a vehicle control unit. The master ECU 21A is communicatively connected to various devices, such as other auxiliary devices (such as the other ECUs 21B), a drive power storage device 22, an auxiliary power storage device 23, and a bidirectional DC / DC converter 24.

[0043] The master ECU 21A and the other ECUs 21B are equipped with an OBD (an example of an on-board diagnostic device). These ECUs perform optimal control based on signals from sensors to ensure the vehicle's safety and environmental performance, and automatically record information about any malfunctions, such as broken wires or sensor malfunctions.

[0044] The drive power storage device 22 is a vehicle drive power storage device that supplies power to the electric motor that drives the vehicle 10. The drive power storage device 22 has a rated voltage of, for example, 48 V. The drive power storage device 22 has a larger capacity than the auxiliary equipment power storage device 23. The auxiliary equipment power storage device 23 is a power storage device that supplies power to the various auxiliary equipment 21. The auxiliary equipment power storage device 23 has a rated voltage of, for example, 12 V. A positive external terminal 22A of the drive power storage device 22 and a positive external terminal 34 of the auxiliary equipment power storage device 23 are electrically connected via a bidirectional DC / DC converter 24. The OBD port 25 is a connector to which the OBD scan tool 12 is connected. The OBD port 25 is connected to the master ECU 21A via a signal line.

[0045] (1-2) OBD Scan Tool The OBD scan tool 12 is a device that acquires and displays information automatically recorded by the OBD. The OBD scan tool 12 may be a personal computer, a smartphone, a tablet computer, or the like, on which a program that causes the computer to function as the OBD scan tool 12 is installed. The OBD scan tool 12 according to the first embodiment also has a function of instructing the master ECU 21A to measure the capacity of the auxiliary equipment power storage device 23.

[0046] (1-3) Configuration of the Power Storage Device The electrical configuration of the power storage device will be described with reference to Fig. 2. The drive power storage device 22 and the auxiliary power storage device 23 have substantially the same configuration, so the auxiliary power storage device 23 will be described here as an example. The auxiliary power storage device 23 includes a battery pack 30, a BMU (Battery Management Unit) 31, and a communication connector 32. The BMU 31 is an example of a management device.

[0047] The battery pack 30 is connected to a positive electrode external terminal 34 by a power line 33 and to a negative electrode external terminal 36 by a power line 35. The battery pack 30 has 12 storage cells 30A connected in three parallel connections and four in series. In FIG. 2, three storage cells 30A connected in parallel are represented by a single battery symbol. The storage cells 30A are secondary batteries that can be repeatedly charged and discharged, and specifically, are, for example, LFP-Gr type lithium ion secondary batteries. LFP-Gr type lithium ion secondary batteries are lithium ion secondary batteries that use lithium iron phosphate (LFP) as the positive electrode material and graphite (Gr) as the negative electrode material.

[0048] The BMU 31 is a device that manages the auxiliary machinery power storage device 23. The BMU 31 includes a current sensor 40, a voltage sensor 41, a temperature sensor 47, an equalization circuit 42, and a management unit 43. The current sensor 40 is provided on the power line 33. The current sensor 40 measures the charge / discharge current of the assembled battery 30 and outputs the result to the management unit 43. The voltage sensor 41 is connected to both ends of each storage cell 30A. The voltage sensor 41 measures the voltage of each storage cell 30A and outputs the result to the management unit 43. The temperature sensor 47 is a sensor that detects the temperature of the assembled battery 30.

[0049] The equalization circuit 42 is a circuit that equalizes the voltage of each storage cell 30A. The equalization circuit 42 includes a discharge resistor 42A connected in parallel with the storage cell 30A, and a switch 42B connected in series to the discharge resistor 42A. The switch 42B is, for example, a field effect transistor (FET), and is turned on / off by the management unit 43. The equalization circuit 42 is also called a balancer.

[0050] The management unit 43 includes a microcomputer 44 in which a CPU 44A, a RAM 44B, and other components are integrated into a single chip, a storage unit 45 having a rewritable nonvolatile storage medium such as a flash memory, and a communication unit 46. The microcomputer 44 executes a control program stored in the storage unit 45 to manage each component of the auxiliary power storage device 23. The storage unit 45 stores the control program and various data. The various data include information indicating the current capacity of the auxiliary power storage device 23, a profile (described below), a capacity estimation model for the auxiliary power storage device 23, and a usage history (temperature, voltage, current, etc.) of the auxiliary power storage device 23. The communication unit 46 is a communication circuit that enables the microcomputer 44 to communicate with the master ECU 21A.

[0051] The communication connector 32 is a connector to which a signal line is connected for communication between the management unit 43 and the master ECU 21A.

[0052] (2) Capacity Measurement of Auxiliary Electric Storage Device The profile of the auxiliary electric storage device 23 will be described with reference to FIG. 3. The profile is data that represents the correspondence relationship between the SOC and OCV of the auxiliary electric storage device 23. The profile is also referred to as an SOC-OCV characteristic. In the following description, the OCV may also be simply referred to as voltage.

[0053] As shown in Figure 3, the profile of the LFP-Gr auxiliary power storage device 23 is known to have a plateau region. The plateau region is a region in which the change in OCV relative to the change in SOC is small, specifically, for example, a region in which the change in OCV relative to the change in SOC is 2 mV / % or less. Within the plateau region, a slight measurement error in voltage causes a large change in the corresponding SOC, making it difficult to accurately determine whether the battery has been charged to a specific SOC.

[0054] 4, voltage Vc indicates the upper limit voltage of the plateau region, and voltage Vd indicates the lower limit voltage of the plateau region. A solid line 51 indicates the capacity of auxiliary electric storage device 23 when it is new (i.e., when it is unused), and a dotted line 52 indicates the capacity when it is deteriorated. Voltage Va indicates the voltage when auxiliary electric storage device 23 is fully charged (i.e., when the SOC is 100%).

[0055] As shown in FIG. 4 , the auxiliary equipment power storage device 23 deteriorates with use, and the amount of electricity that can be charged (i.e., capacity) decreases. For this reason, the master ECU 21A of the vehicle 10 measures the capacity of the auxiliary equipment power storage device 23 in cooperation with the management unit 43 of the auxiliary equipment power storage device 23 at a predetermined timing during the life cycle of the auxiliary equipment power storage device 23. Specifically, the master ECU 21A according to the first embodiment measures the capacity when the vehicle 10 is in the maintenance workshop 11. This is because the vehicle 10 is unlikely to be used when the vehicle 10 is in the maintenance workshop 11. If the vehicle 10 is not in use, the auxiliary equipment power storage device 23 is maintained in a low-load discharge / low-load charge state and at a constant current for a certain period of time. Furthermore, changes in the environmental temperature due to vehicle movement are small, so that the capacity can be measured with high accuracy.

[0056] More specifically, when the master ECU 21A is instructed to measure the capacity by the OBD scan tool 12 via the OBD port 25, the master ECU 21A measures the capacity of the auxiliary power storage device 23, assuming that the vehicle 10 is in the maintenance shop 11. Even if the master ECU 21A is not instructed to measure the capacity by the OBD scan tool 12, the master ECU 21A may measure the capacity of the auxiliary power storage device 23, assuming that the vehicle 10 is in the maintenance shop 11, when it detects that the OBD scan tool 12 is connected to the OBD port 25.

[0057] In measuring the capacity of the auxiliary storage device 23, the auxiliary storage device 23 is charged to a certain SOC (referred to as a first SOC) and then discharged to an SOC (referred to as a second SOC) lower than the first SOC, and the capacity is determined from the amount of electricity discharged during this period. The amount of electricity discharged is measured by the BMU 31.

[0058] Whether the auxiliary storage device 23 has been charged to the first SOC or discharged to the second SOC is determined from the voltage. The voltage corresponding to the first SOC and the voltage corresponding to the second SOC are identified from the profile. For example, if the first SOC is 100% and the second SOC is 5%, the voltage corresponding to 100% (voltage Va shown in FIG. 4 ) and the voltage corresponding to 5% (voltage Vb shown in FIG. 4 ) are identified from the profile. Voltage Vb is an example of a discharge stop voltage. If the amount of electricity discharged during this period is, for example, 10,000 Ah, the amount of electricity corresponding to 95% (=100%−5%) of the capacity is 10,000 Ah, and the measured capacity is 10,526 Ah (=10,000 Ah×100 / 95).

[0059] As described above, within the plateau region, even a slight measurement error in voltage significantly changes the corresponding SOC, making it difficult to accurately determine whether the battery has been charged to a specific SOC. In contrast, in voltage ranges higher than the plateau region, the voltage changes rapidly, making it possible to accurately determine whether the battery has been charged to a specific SOC. Therefore, the first SOC is set to a value that places the corresponding voltage (i.e., voltage Va) in a voltage range higher than the plateau region. Specifically, as described above, the first SOC is set to 100%. The voltage Va at an SOC of 100% is assumed to be in a voltage range higher than the plateau region. The first SOC is not limited to 100% as long as the corresponding voltage Va is in a voltage range higher than the plateau region. For example, if the voltage at an SOC of 95% is in a voltage range higher than the plateau region, the first SOC may be 95%.

[0060] Similarly, the second SOC is set to a value that causes the corresponding voltage Vb to be in a voltage range lower than the plateau region. Specifically, for example, as described above, the second SOC is set to 5%. The voltage Vb when the SOC is 5% is assumed to be in a voltage range lower than the plateau region. The second SOC is not limited to 5% as long as the corresponding voltage Vb is in a voltage range lower than the plateau region. However, it is preferable that the voltage Vb be higher than the voltage at which the auxiliary electric storage device 23 is over-discharged.

[0061] (2-1) Discharge Destination of Auxiliary Machinery Storage Device With reference to FIG. 1 , a description will be given of a discharge destination of auxiliary machinery storage device 23 when measuring the capacity of auxiliary machinery storage device 23. The discharge destination can be determined as appropriate, but in the first embodiment, the drive storage device 22 is used for discharging. Specifically, the master ECU 21A charges the drive storage device 22 with electricity from the auxiliary machinery storage device 23 by boosting the voltage of the auxiliary machinery storage device 23 to a voltage higher than the voltage of the drive storage device 22 using the bidirectional DC / DC converter 24. As a result, electricity from the auxiliary machinery storage device 23 is discharged to the drive storage device 22.

[0062] (2-2) Determining the Presence or Absence of Abnormality in the Auxiliary Machinery Power Storage Device As described above, the model method is a method of estimating capacity based on a capacity estimation model of the power storage element. Specifically, the model method is a method of predicting the degree of deterioration from the usage history of the temperature, voltage, current, etc. measured by BMU 31 based on deterioration data of the power storage device acquired in advance, and estimating the capacity by identifying the capacity corresponding to the predicted degree of deterioration from a capacity estimation model that represents the correspondence relationship between the degree of deterioration and the capacity.

[0063] Although the model method does not necessarily have high estimation accuracy, it does have a certain degree of accuracy. Therefore, BMU 31 estimates the capacity of auxiliary power storage device 23 using the model method, and compares the measured capacity with the estimated capacity to determine whether or not there is an abnormality in auxiliary power storage device 23. Specifically, BMU 31 determines that there is an abnormality when the difference between the measured capacity and the estimated capacity is equal to or greater than a predetermined threshold, and determines that there is no abnormality when the difference is less than the threshold.

[0064] (2-3) Capacity Measurement Flow The flow of measuring the capacity of the auxiliary electric storage device 23 will be described with reference to Figure 5. As described above, capacity measurement starts when the master ECU 21A receives an instruction to measure the capacity of the auxiliary electric storage device 23 from the OBD scan tool 12. In the following flow, it is assumed that communication is performed appropriately between the master ECU 21A and the BMU 31.

[0065] In S101, the master ECU 21A determines whether or not conditions (hereinafter referred to as implementation conditions) are met for measuring the capacity of the auxiliary equipment power storage device 23. Specifically, the implementation conditions include, for example, the following two conditions: The temperature of the auxiliary equipment power storage device 23 (more specifically, the battery pack 30) is equal to or higher than a predetermined temperature; and The drive power storage device 22 has available capacity to receive electricity from the auxiliary equipment power storage device 23.

[0066] The reason why the temperature must be equal to or higher than a predetermined temperature is that if the temperature of the auxiliary electric storage device 23 is low, the internal resistance increases and the capacity cannot be measured with high accuracy. The implementation condition is not limited to the above-mentioned condition and can be determined as appropriate. For example, it is assumed that the vehicle 10 may be moved until a certain time has passed since the vehicle 10 was parked. If the vehicle 10 is moved during capacity measurement, the discharge current changes and the measurement accuracy decreases, so the condition may be that a certain time has passed since the vehicle 10 was parked. If the implementation condition is met, the master ECU 21A proceeds to S102, and if not, the master ECU 21A stops the capacity measurement and proceeds to S113.

[0067] In S102, the master ECU 21A controls the bidirectional DC / DC converter 24 to charge the auxiliary storage device 23 to a voltage Va (i.e., fully charge) using electricity from the drive storage device 22. In S103, the BMU 31 controls the equalization circuit 42 to equalize the voltages of the storage cells 30A of the auxiliary storage device 23.

[0068] In S104, the BMU 31 sets an initial value of 0 to a variable for integrating the current value (hereinafter referred to as the integrated value). In S105, the master ECU 21A controls the bidirectional DC / DC converter 24 to start discharging the auxiliary electrical storage device 23. In S106, the BMU 31 measures the discharge current using the current sensor 40, and adds the measured current value to the integrated value.

[0069] In S107, the master ECU 21A determines whether a condition for halting capacity measurement is met. An example of a condition for halting capacity measurement is when a component of the vehicle 10 or the auxiliary storage device 23 fails, making it impossible to continue measurement. The condition for halting capacity measurement is not limited to this. For example, if the vehicle 10 is moved or an on-board device is used during discharge, the discharge current changes and measurement accuracy decreases. Therefore, measurement may be halted if the discharge current falls outside a predetermined range. If the halt condition is not met, the master ECU 21A proceeds to S108; if the halt condition is met, the master ECU 21A halts discharge and proceeds to S113.

[0070] In S108, BMU 31 determines whether the voltage of auxiliary electric storage device 23 has dropped to voltage Vb (discharge stop voltage), and if it has dropped to voltage Vb, proceeds to S109, and if it has not dropped to voltage Vb, returns to S106 and repeats the process. In S109, master ECU 21A controls bidirectional DC / DC converter 24 to stop discharging of auxiliary electric storage device 23. In S110, BMU 31 calculates the capacity of auxiliary electric storage device 23 from the integrated value.

[0071] In S111, BMU 31 estimates the capacity of auxiliary machinery power storage device 23 using a model method, and compares the estimated capacity with the capacity determined in S110 to determine whether or not there is an abnormality in auxiliary machinery power storage device 23. If BMU 31 determines that there is no abnormality, it proceeds to S112, and if it determines that there is an abnormality, it proceeds to S113. In S112, BMU 31 updates the current capacity of auxiliary machinery power storage device 23 stored in memory unit 45 with the capacity determined in S110.

[0072] In S113, the master ECU 21A transmits the capacity calculated in S110 to the OBD scan tool 12 via the OBD port 25. However, if the implementation condition is not met in S101, information indicating that the capacity measurement was not performed is transmitted. If the cancellation condition is met in S107, information indicating that the capacity measurement was canceled is transmitted. If it is determined in S111 that an abnormality exists, information indicating the abnormality exists is transmitted. In S114, the master ECU 21A controls the bidirectional DC / DC converter 24 to fully charge the auxiliary storage device 23 with electricity from the drive storage device 22.

[0073] (3) Effects of the Embodiments According to the method for measuring the capacity of a storage element according to the first embodiment, the capacity of the auxiliary power storage device 23 is measured when an instruction to measure the capacity of the auxiliary power storage device 23 is received from the OBD scan tool 12 via the OBD port 25. This increases the likelihood that the capacity can be measured in a situation where the auxiliary power storage device 23 is maintained at a low load discharge and a constant current and where there is little change in the environmental temperature. Therefore, according to the method for measuring the capacity of a storage element according to the first embodiment, the capacity of the auxiliary power storage device 23 mounted on the vehicle 10 can be measured with higher accuracy than when measuring the capacity while the vehicle 10 is in use in the market.

[0074] According to the method for measuring the capacity of a storage element according to the first embodiment, the auxiliary electric storage device 23 is charged before being discharged, and therefore, in order to measure the capacity, the auxiliary electric storage device 23 can be discharged. The auxiliary electric storage device 23 only needs to be charged until it stores the electricity required for measuring the capacity, and does not necessarily have to be fully charged.

[0075] According to the capacity measurement method for a storage element of embodiment 1, the voltage Va corresponding to the first SOC is a voltage in a voltage range higher than the plateau region, and therefore the capacity can be measured with higher accuracy than when the voltage Va is a voltage within the plateau region.

[0076] According to the capacity measurement method of the storage element of embodiment 1, when the auxiliary storage device 23 is discharged, the discharge is made to the driving storage device 22, which has a larger capacity than the auxiliary storage device 23, and therefore, electrical loss can be reduced compared to when discharging into an electrical resistance, etc.

[0077] According to the method for measuring the capacity of a storage element of embodiment 1, the capacity is measured when the implementation conditions are met, thereby preventing the measured capacity from being inaccurate or the need to stop the measurement midway.

[0078] According to the capacity measurement method of the storage element of embodiment 1, the auxiliary storage device 23 is charged after discharging is stopped, thereby reducing the possibility that the vehicle 10 will be handed over to a user with the auxiliary storage device 23 not being sufficiently charged.

[0079] According to the method for measuring the capacity of a storage element of the first embodiment, the presence or absence of an abnormality in the auxiliary storage device 23 can be determined by comparing the measured capacity with the capacity estimated based on the capacity estimation model.

[0080] According to the method for measuring the capacity of a storage element of the first embodiment, the measured capacity is output to the OBD scan tool 12, so that a mechanic of the vehicle 10 can check the capacity using the OBD scan tool 12 and, if the capacity has decreased, replace the auxiliary storage device 23, thereby preventing the continued use of the auxiliary storage device 23 with decreased capacity. Furthermore, according to the method for measuring the capacity of a storage element of the first embodiment, the capacity can be measured with high accuracy, so that it is possible to prevent the auxiliary storage device 23 from being replaced due to an error in measuring the capacity when the capacity has not actually decreased enough to require replacement, or to prevent the auxiliary storage device 23 from being replaced due to an error in measuring the capacity when the capacity has actually decreased to a level that requires replacement.

[0081] <Second Embodiment> A second embodiment will be described with reference to Fig. 6 . In the first embodiment described above, the capacity of the auxiliary machine power storage device 23 is measured. In contrast, in the second embodiment, the capacity of the drive power storage device 22 is measured. Specifically, a maintenance workshop 211 according to the second embodiment is provided with a charge / discharge device 60 (an example of an external discharge destination) for charging and discharging the drive power storage device 22. The charge / discharge device 60 is connected to the power grid via a power line. Electric power can also be sold to the power grid.

[0082] When measuring the capacity of the drive power storage device 22, a charge / discharge cable provided in the charge / discharge device 60 is connected to the vehicle 10, and the capacity is measured in this state. When the master ECU 21A according to the second embodiment receives an instruction to measure the capacity of the drive power storage device 22 from the OBD scan tool 12 while the charge / discharge cable is connected to the vehicle 10, the master ECU 21A starts measuring the capacity of the drive power storage device 22. When measuring the capacity of the drive power storage device 22, the master ECU 21A discharges electricity from the drive power storage device 22 to the charge / discharge device 60. The electricity discharged to the charge / discharge device 60 is sold from the charge / discharge device 60 to the power grid.

[0083] If the maintenance workshop 211 is equipped with a large-capacity power storage device, the large-capacity power storage device may be discharged by being charged with electricity from the drive power storage device 22. Part of the electricity from the drive power storage device 22 may be used to charge the auxiliary machine power storage device 23.

[0084] According to the method for measuring the capacity of an electric storage element in the second embodiment, the capacity can be measured by discharging electricity from the driving electric storage device 22 to the charging / discharging device 60. According to the method for measuring the capacity of an electric storage element in the second embodiment, the electricity discharged from the driving electric storage device 22 is sold to the power grid from the charging / discharging device 60, so that the loss of electricity can be suppressed.

[0085] <Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0086] (1) In the above-described first embodiment, when measuring the capacity of the auxiliary machinery storage device 23, the auxiliary machinery storage device 23 is charged before starting to discharge the auxiliary machinery storage device 23. However, the auxiliary machinery storage device 23 does not necessarily have to be charged before starting to discharge the auxiliary machinery storage device 23. For example, if the auxiliary machinery storage device 23 is already close to being fully charged, the auxiliary machinery storage device 23 does not necessarily have to be charged.

[0087] (2) In the first embodiment described above, the case where the electricity from the auxiliary electric storage device 23 is discharged to the driving electric storage device 22 is exemplified, but the discharge destination is not limited to the driving electric storage device 22. For example, the electricity may be discharged to an external discharge destination, as in the second embodiment.

[0088] (3) In the first embodiment, it is determined whether the execution conditions are met (S101), but this determination does not have to be made.

[0089] (4) In the first embodiment, it is determined whether the cancellation condition is met (S107), but this determination does not have to be made.

[0090] (5) In the first embodiment, the auxiliary electric storage device 23 is fully charged after the cancellation condition is met and discharging is stopped. However, if the cancellation condition is met, the auxiliary electric storage device 23 may not be fully charged.

[0091] (6) In the above-described first embodiment, the capacity estimated based on the capacity estimation model is compared with the measured capacity to determine whether or not there is an abnormality in the auxiliary storage device 23 (S111). However, this determination does not have to be made.

[0092] (7) In the first embodiment described above, the measured capacity is output to the OBD scan tool 12 (S113). However, the measured capacity does not have to be output to the OBD scan tool 12. For example, the measured capacity may be used only to update the current capacity of the auxiliary machinery power storage device 23 stored in the storage unit 45.

[0093] (8) In the above embodiment, the case where the capacity is measured by integrating the discharge current of the auxiliary power storage device 23 and the drive power storage device 22 has been described. However, the capacity may be measured by integrating the charge current of the auxiliary power storage device 23 and the drive power storage device 22. In this case, too, the capacity of the power storage cell 30A mounted on the vehicle 10 can be measured with higher accuracy than when the capacity is measured while the vehicle 10 is being used in the market.

[0094] (9) As described in the first embodiment, the process of measuring the capacity of the auxiliary machinery power storage device 23 is shared between the master ECU 21A and the BMU 31. This sharing of the process is not limited to the sharing described in the first embodiment and can be determined as appropriate. For example, in the first embodiment, the BMU 31 determines whether or not an abnormality exists in the auxiliary machinery power storage device 23 (S111), but the master ECU 21A may also perform this. Alternatively, in the first embodiment, the master ECU 21A determines whether or not the execution condition or the cancellation condition is satisfied (S101, S107), but the BMU 31 may also perform this. The same applies to the second embodiment.

[0095] (10) In the above embodiment, an LFP-Gr lithium ion secondary battery is used as the storage cell 30A, but the storage cell 30A is not limited to this. For example, the storage cell 30A may be a ternary lithium ion secondary battery.

[0096] (11) In the above embodiment, the storage cell 30A has a plateau region. However, the storage cell 30A may not have a plateau region.

[0097] (12) In the above embodiment, a lithium ion secondary battery is used as the storage cell 30A, but the storage cell 30A is not limited to this. For example, the storage cell 30A may be a capacitor that involves an electrochemical reaction.

[0098] 12: OBD scan tool (an example of an external diagnostic device) 20: Electrical system 21A: Master ECU (an example of a vehicle control unit) 22: Drive power storage device (an example of a power storage element and a high-voltage power storage element) 23: Auxiliary power storage device (an example of a power storage element) 25: OBD port (an example of a diagnostic connector) 31: BMU (an example of a management device) 60: Charging / discharging device (an example of an external discharge destination)

Claims

1. A method for measuring the capacity of a storage element mounted on a vehicle equipped with a diagnostic connector for connecting an external diagnostic device to an on-board fault diagnosis system, wherein a control unit of the vehicle receives an instruction to measure the capacity of the storage element from the external diagnostic device via the diagnostic connector, the control unit having received the instruction controls the vehicle's electrical system to discharge the storage element, and a management device for the storage element integrates the discharge current of the storage element during the discharging and measures the capacity of the storage element based on the integrated amount of electricity.

2. A method for measuring the capacity of a storage element according to claim 1, wherein the control unit that receives the instruction controls the electrical system to charge the storage element, and the discharging is performed after the charging.

3. A method for measuring the capacity of an energy storage element according to claim 2, wherein the energy storage element is charged to a voltage range higher than the plateau region in a profile representing the correspondence between the state of charge of the energy storage element and its open-circuit voltage.

4. A method for measuring the capacity of a storage element according to any one of claims 1 to 3, comprising discharging electricity stored in the storage element to a high-voltage storage element mounted on the vehicle and having a larger capacity than the storage element.

5. A method for measuring the capacity of an electric storage element according to any one of claims 1 to 3, wherein the electricity stored in the electric storage element is discharged to a discharge destination outside the vehicle.

6. A method for measuring the capacity of a storage element as set forth in any one of claims 1 to 3, wherein, after receiving the instruction, at least one of the control unit and the management device determines whether or not a condition exists under which the capacity measurement of the storage element can be performed, and the control unit discharges the storage element when it is determined that the condition exists.

7. A method for measuring the capacity of a storage element according to any one of claims 1 to 3, wherein during the discharging, at least one of the control unit and the management device determines whether a stop condition is met, and if it is determined that the stop condition is met, the control unit controls the electrical system to stop the discharging, and after the stop, the control unit controls the electrical system to charge the storage element.

8. A method for measuring the capacity of a storage element according to any one of claims 1 to 3, wherein the management device estimates the capacity of the storage element based on a capacity estimation model of the storage element, and at least one of the control unit and the management device compares the measured capacity with the estimated capacity to determine whether or not there is an abnormality in the storage element.

9. A method for measuring the capacity of a storage element according to any one of claims 1 to 3, wherein the management device updates the capacity of the storage element stored in the management unit of the storage element to the measured capacity.

10. A method for measuring the capacitance of a storage element according to any one of claims 1 to 3, wherein the control unit outputs the measured capacitance to the external diagnostic device via the diagnostic connector.

11. A method for measuring the capacity of an electric storage element according to any one of claims 1 to 3, comprising discharging the electric storage element, and then charging the electric storage element mounted on the vehicle with electricity stored in a high-voltage electric storage element having a capacity larger than that of the electric storage element.

12. A method for measuring the capacity of a storage element mounted on a vehicle equipped with a diagnostic connector for connecting an external diagnostic device to an on-board fault diagnosis system, wherein a control unit of the vehicle receives an instruction to measure the capacity of the storage element from the external diagnostic device via the diagnostic connector, the control unit that has received the instruction controls the vehicle's electrical system to charge the storage element, and a management device for the storage element integrates the charging current of the storage element during the charging and measures the capacity of the storage element based on the integrated amount of electricity.

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