Battery pack deterioration diagnosis device and battery pack deterioration diagnosis method

Abstract

A deterioration diagnosis device of a battery pack includes a discharging section and an estimation section. The discharging section performs discharging on each of a plurality of battery cells included in the battery pack, measures a voltage of each battery cell in the discharging, and ends the discharging if a prescribed discharging end timing is reached. The estimation section estimates a deterioration degree of the battery pack using voltage data indicating a change in voltage of at least one of the plurality of battery cells from a discharging start voltage to a prescribed discharging end voltage. After the voltage of the at least one of the plurality of battery cells reaches the discharging end voltage, the discharging section determines the discharging end timing using the voltage data of the at least one of the plurality of battery cells.

Description

Technical Field

[0001] This disclosure relates to a battery pack degradation diagnosis device and a battery pack degradation diagnosis method. Background Technology

[0002] A battery pack comprises multiple secondary batteries that are electrically connected to each other. A large-capacity battery pack is obtained by combining multiple secondary batteries. However, the full-charge capacity of a secondary battery (the amount of electricity stored in the secondary battery during full charge) decreases as the secondary battery deteriorates. The lifespan of a battery pack is largely determined by the degree of deterioration of the secondary battery (hereinafter also referred to as a "cell") with the smallest full-charge capacity. Therefore, the degree of deterioration of the battery pack can be estimated based on the data of the smallest-capacity cell. For example, Japanese Patent Application Laid-Open No. 2020-38812 discloses a method for diagnosing the degree of deterioration of a battery pack using the voltage change during discharge of the smallest-capacity cell. In this method, each cell constituting the battery pack is discharged, and the cell whose voltage reaches the lower discharge limit voltage (the lower limit voltage indicating that further discharge would result in over-discharge) earliest is considered the smallest-capacity cell. Summary of the Invention

[0003] In the technology described in Japanese Patent Application Publication No. 2020-38812, the battery cell whose voltage reaches the lower discharge limit voltage first during discharge is considered the smallest capacity battery cell, and only the discharge data (voltage change during discharge) of one battery cell is measured. However, the battery cell whose voltage reaches the lower discharge limit voltage first during discharge is not necessarily the smallest capacity battery cell. For example, when there is a voltage difference between battery cells at the start of discharge, the battery cell with the lower voltage at the start of discharge is more likely to reach the lower discharge limit voltage earlier. Therefore, the voltage of battery cells other than the smallest capacity battery cell may reach the lower discharge limit voltage earlier than the smallest capacity battery cell. If the degree of degradation of the battery pack is estimated based on the data of battery cells other than the smallest capacity battery cell, it may not be possible to accurately diagnose the degree of degradation (and lifespan) of the battery pack.

[0004] On the other hand, if discharge continues until the voltage of all the cells in the battery pack reaches the lower discharge limit, at least one cell is likely to be over-discharged. Over-discharge will accelerate the degradation of the cell.

[0005] This disclosure improves the accuracy of battery pack degradation diagnosis while suppressing individual cell degradation during battery pack diagnostics.

[0006] The battery pack degradation diagnostic apparatus according to the first aspect of this disclosure includes at least one processor configured to: discharge a plurality of battery cells included in the battery pack, measure the voltage of each battery cell during discharge, terminate the discharge if a predetermined discharge termination time is reached, and estimate the degree of degradation of the battery pack using voltage data representing the voltage transition of at least one of the battery cells from the discharge start voltage to the predetermined discharge termination voltage. The at least one processor is further configured to determine the discharge termination time using the voltage data of the battery cells whose voltages have reached the discharge termination voltage after the voltage of at least one of the battery cells has reached the discharge termination voltage.

[0007] In the aforementioned battery pack degradation diagnosis device, if the voltage of one of the multiple battery cells reaches the discharge end voltage during the discharge of the battery pack, at least one processor determines the discharge end timing based on the voltage data of that battery cell (the voltage transition from the discharge start voltage to the discharge end voltage). Hereinafter, the battery cell whose voltage reaches the discharge end voltage earliest among the multiple battery cells in the battery pack is referred to as the "target battery cell". According to the above configuration, even if the voltage of the target battery cell reaches the discharge end voltage, the discharge of the battery pack is not stopped; the discharge of the battery pack continues until the discharge end timing determined based on the voltage data of the target battery cell. By using the voltage data of the target battery cell, the discharge end timing can be easily and appropriately determined.

[0008] For example, the lower the voltage at the start of discharge of a target battery cell, the lower the likelihood that the target battery cell is the smallest capacity battery cell (the battery cell with the smallest full-charge capacity in the battery pack). Alternatively, the lower the voltage of the target battery cell at the start of discharge, the later the discharge end timing will be set by at least one processor. This processing makes it easier for at least one processor to obtain the voltage data of the smallest capacity battery cell. However, if discharge is prolonged, the target battery cell may degrade due to over-discharge. Alternatively, at least one processor may determine the discharge end timing within the period from when the voltage of the target battery cell reaches the discharge end voltage until a predetermined time (set as an allowable time to prevent over-discharge) has elapsed, so as not to cause excessive degradation of the target battery cell due to over-discharge. This makes it easier for at least one processor to appropriately determine the discharge end timing using the voltage data of the target battery cell. Thus, it becomes easier to improve the accuracy of battery pack degradation diagnosis while suppressing the degradation of battery cells in battery pack diagnosis. Furthermore, the method of setting the discharge end timing is not limited to the above methods. Other methods will be described later.

[0009] In the first approach described above, the at least one processor may be configured to further determine the discharge end timing using a predetermined voltage of at least one of the plurality of battery cells. The predetermined voltage may be related to the discharge period of the battery pack.

[0010] At least one processor can easily determine whether the voltage of a target battery cell is low at the start of discharge by using the voltage at which each of the multiple battery cells begins discharging. For example, if the voltage of the target battery cell is low at the start of discharge, the target battery cell is unlikely to be a minimum capacity battery cell. Therefore, at least one processor can continue discharging within a range that will not significantly degrade the target battery cell due to over-discharge. This process makes it easier to obtain the voltage data of the minimum capacity battery cell. On the other hand, if the voltage of the target battery cell is high at the start of discharge, the target battery cell is likely to be a minimum capacity battery cell. Therefore, at least one processor can immediately stop discharging once the voltage of the target battery cell reaches the discharge termination voltage. This process makes it easier to suppress the degradation of battery cells during battery pack diagnostics.

[0011] In the first method described above, the at least one processor can be configured to determine whether the voltage at the start of discharge of the target battery cell corresponds to the maximum battery cell voltage, wherein the target battery cell is the battery cell whose voltage reaches the discharge end voltage earliest among a plurality of battery cells during discharge, and the maximum battery cell voltage is the highest voltage among the voltages of each of the plurality of battery cells at the start of discharge. If it is determined that the voltage at the start of discharge of the target battery cell does not correspond to the maximum battery cell voltage, the at least one processor can determine the timing at which the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, as the discharge end timing. If it is determined that the voltage at the start of discharge of the target battery cell corresponds to the maximum battery cell voltage, the at least one processor can immediately terminate the discharge after the voltage of the target battery cell reaches the discharge end voltage.

[0012] If the voltage at the start of discharge of a target battery cell corresponds to the maximum battery cell voltage, the target battery cell can be considered as the minimum capacity battery cell. In this case, by immediately ending the discharge after the voltage of the target battery cell reaches the discharge termination voltage, it is easy to suppress the degradation of battery cells during battery pack diagnosis. If the voltage at the start of discharge of a target battery cell does not correspond to the maximum battery cell voltage, the target battery cell may not be the minimum capacity battery cell. However, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, if the discharge continues until the voltage of the target battery cell reaches the discharge termination voltage, then the voltage of the minimum capacity battery cell reaches the discharge termination voltage. Based on the above configuration, it is possible to use the voltage data of the minimum capacity battery cell to estimate the degree of degradation of the battery pack with high accuracy.

[0013] In the first method described above, the at least one processor can be configured to determine the timing at which the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from a predetermined voltage, as the discharge end voltage, wherein the target battery cell is the battery cell whose voltage reaches the discharge end voltage earliest among a plurality of battery cells during discharge.

[0014] It is possible to predict the voltage corresponding to the maximum cell voltage through experiments or simulations. This predicted voltage can be set in at least one processor. Then, at least one processor can use the set voltage to determine the discharge termination timing, as described above. Even with this configuration, the accuracy of battery pack degradation diagnosis can be improved while suppressing cell degradation during battery pack diagnostics.

[0015] In the first method described above, the discharge end voltage may also be set based on the common discharge lower limit voltage of multiple battery cells.

[0016] As shown above, by setting the discharge termination voltage based on the discharge lower limit voltage (which represents the lower limit voltage at which further discharge would result in over-discharge), it is easier to suppress the degradation of individual cells during battery pack diagnostics. The discharge termination voltage can be set to be the same as the discharge lower limit voltage, or it can be set slightly higher than the discharge lower limit voltage.

[0017] In the first approach described above, all the individual battery cells in the battery pack can also be connected in series. The at least one processor can be configured to maintain a constant current value for each of the multiple battery cells during discharge.

[0018] Based on the above configuration, it becomes easier to ensure that the discharge current values ​​of each individual cell in the battery pack are consistent. Therefore, it becomes easier to estimate the degree of degradation of the battery pack with high accuracy.

[0019] In the first approach described above, the battery pack can be configured to supply power to an electrical load mounted on the vehicle. At least one processor can be configured to perform discharge by controlling the electrical load.

[0020] Based on the above configuration, it is possible to easily and appropriately diagnose the degradation of vehicle battery packs. The aforementioned electrical load, controlled by at least one processor during discharge, may include at least one of an air conditioning unit, a seat heater, and a lighting device.

[0021] The battery pack degradation diagnostic apparatus according to the second aspect of this disclosure includes at least one processor configured to perform the following processes: charging a plurality of battery cells included in the battery pack respectively; measuring the voltage of each battery cell during charging; ending charging if a predetermined charging end time is reached; and estimating the degree of degradation of the battery pack using voltage data representing the voltage transition of at least one of the battery cells from the charging start voltage to the predetermined charging end voltage. The at least one processor is configured to determine the charging end time using the voltage data of the battery cell whose voltage has reached the charging end voltage after the voltage of one of the battery cells has reached the charging end voltage.

[0022] According to the aforementioned battery pack degradation diagnosis device, the degree of battery pack degradation can be estimated based on voltage changes during charging, using the aforementioned degradation diagnosis method performed through discharge. Therefore, the accuracy of battery pack degradation diagnosis can be improved while suppressing individual cell degradation during battery pack diagnosis.

[0023] However, in degradation diagnosis performed by discharging and degradation diagnosis performed by charging, the direction of the current is opposite. Furthermore, the voltage of each individual battery cell decreases during discharging and increases during charging. In degradation diagnosis performed by charging, the battery cell whose voltage reaches the charging termination voltage first among the multiple battery cells in the battery pack is called the "target battery cell". The charging termination voltage can be set based on the common upper charging limit voltage (the upper limit voltage at which further charging would result in overcharging) of the multiple battery cells in the battery pack. The charging termination voltage can be set to be the same as the upper charging limit voltage or slightly lower.

[0024] The battery pack degradation diagnosis method disclosed in the third aspect includes: performing discharge of each battery cell while measuring the voltage of each of the plurality of battery cells contained in the battery pack; if the voltage of one of the battery cells reaches a predetermined discharge end voltage during discharge, determining a discharge end timing based on voltage data representing the voltage transition of that battery cell from the discharge start voltage to the discharge end voltage; ending the discharge if the discharge end timing is reached; and estimating the degree of degradation of the battery pack using voltage data of at least one of the plurality of battery cells obtained during discharge.

[0025] The battery pack degradation diagnosis method described above, similar to the aforementioned degradation diagnosis device that diagnoses degradation through discharge, can improve the accuracy of battery pack degradation diagnosis while suppressing the degradation of individual battery cells during battery pack diagnosis.

[0026] In the third method described above, the discharge can be performed while the battery pack is mounted in the vehicle. The initial full-charge capacity of the battery pack can be less than 5 kWh.

[0027] When a battery pack is discharged while mounted in a vehicle, it is generally difficult to discharge rapidly. However, if the capacity of the battery pack being diagnosed is appropriate, sufficient throughput diagnosis can be achieved using the discharge-based degradation diagnosis method described above. Specifically, if the capacity of the battery pack, as shown above, is 5 kWh or less, sufficient throughput diagnosis can be achieved using the discharge-based degradation diagnosis method described above. The initial fully charged capacity of the diagnosed battery pack can be 0.1 kWh or more but less than 5 kWh, or 0.3 kWh or more but less than 3 kWh. The battery pack diagnosed using the above method can be a drive battery mounted in a HEV (hybrid electric vehicle).

[0028] The fourth method of this disclosure for diagnosing battery pack degradation includes: simultaneously measuring the voltage of each of the plurality of battery cells contained in the battery pack and charging each battery cell; if the voltage of one of the plurality of battery cells reaches a predetermined charging end voltage during charging, determining a charging end timing based on voltage data representing the voltage transition of that battery cell from the charging start voltage to the charging end voltage; ending charging if the charging end timing is reached; and estimating the degree of degradation of the battery pack using voltage data of at least one of the plurality of battery cells acquired during charging.

[0029] The aforementioned battery pack degradation diagnosis method, similar to the aforementioned battery pack degradation diagnosis device that diagnoses degradation through charging, can improve the accuracy of battery pack degradation diagnosis while suppressing the degradation of individual battery cells during battery pack diagnosis.

[0030] In the fourth method described above, the charging can be performed while the battery pack is mounted in the vehicle. The initial full-charge capacity of the battery pack can be 10 kWh or more.

[0031] When charging of the battery pack is performed while it is installed in a vehicle, it is relatively easy to accelerate the charging speed. For example, rapid charging can be achieved by using a high-output EVSE (Electric Vehicle Supply Equipment). According to the degradation diagnosis method performed by charging described above, large-capacity battery packs (i.e., battery packs with a capacity of 10 kWh or more) can be diagnosed with sufficient throughput. The initial fully charged capacity of the diagnosed battery pack can be 10 kWh or more but less than 500 kWh, or 50 kWh or more but less than 150 kWh. The battery pack diagnosed by the above method can be a drive battery installed in a BEV (Battery Electric Vehicle) or PHEV (Plug-in Hybrid Electric Vehicle).

[0032] According to the various methods disclosed herein, it is possible to improve the accuracy of battery pack degradation diagnosis while suppressing the degradation of individual cells in battery pack diagnosis. Attached Figure Description

[0033] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, in which the same reference numerals denote the same parts, wherein:

[0034] Figure 1 This is a diagram illustrating the configuration of a vehicle according to an embodiment of the present disclosure.

[0035] Figure 2 This diagram illustrates the configuration of a battery pack degradation diagnostic device according to an embodiment of this disclosure.

[0036] Figure 3 This is a flowchart illustrating the discharge control in the battery pack degradation diagnosis method according to the embodiments of this disclosure.

[0037] Figure 4 It is used for explanation Figure 2 The graph shows the discharge characteristics of the battery pack.

[0038] Figure 5 This is a first graph illustrating the method for determining the discharge end timing in the battery pack degradation diagnosis method according to embodiments of this disclosure.

[0039] Figure 6 This is a second graph illustrating the method for determining the discharge end timing in the battery pack degradation diagnosis method according to embodiments of this disclosure.

[0040] Figure 7 This is a flowchart illustrating the process involved in determining battery life in the battery pack degradation diagnosis method according to the embodiments of this disclosure.

[0041] Figure 8 It means Figure 3 The flowchart of the first variation of the process shown.

[0042] Figure 9 It means Figure 2 The diagram shows a modified example of the HVECU.

[0043] Figure 10 It means Figure 2 The diagram shows a variation of the service tool.

[0044] Figure 11 It means Figure 3 The flowchart of the second variation of the process is shown.

[0045] Figure 12 It is a graph used to illustrate the method for determining the charging end timing.

[0046] Figure 13 It means Figure 7 The flowchart shows a variation of the processing.

[0047] Figure 14 It means that it is installed Figure 10 A diagram showing the vehicle control device for the charging section and the estimated section.

[0048] Figure 15 It means Figure 2 A diagram showing a modified example of the battery pack. Detailed Implementation

[0049] The embodiments of this disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same or equivalent parts are labeled with the same reference numerals, and their descriptions will not be repeated. Hereinafter, the Electronic Control Unit (ECU) will also be referred to as "ECU".

[0050] Figure 1 This is a diagram illustrating the configuration of the vehicle involved in this embodiment. (Refer to...) Figure 1Vehicle 100 is a HEV (Hybrid Electric Vehicle). In this embodiment, it is assumed to be a front-wheel drive four-wheel vehicle (more specifically, an HEV), but the number of wheels and the drive method can be changed appropriately. For example, the drive method can be four-wheel drive.

[0051] The vehicle 100 includes a drive battery 11, a voltage sensor 12a, a current sensor 12b, a temperature sensor 12c, an SMR (System Main Relay) 14, a first electric / generator 21a (hereinafter referred to as "MG 21a"), a second electric / generator 21b (hereinafter referred to as "MG21b"), a PCU (Power Control Unit) 24, an engine 31, a transmission mechanism 421, and a hydraulic circuit 422.

[0052] The drive battery 11 includes rechargeable secondary batteries. The drive battery 11 is configured to supply power to the PCU 24 (and the MGs 21a and 21b, which serve as driving motors). In this embodiment, a battery pack comprising multiple secondary batteries with electrical connections is used as the drive battery 11. The initial fully charged capacity of the drive battery 11 is, for example, approximately 1.5 kWh. The secondary batteries included in the drive battery 11 can be modularized in groups of a predetermined number. The battery pack can be constructed by combining multiple modules. The number of secondary batteries included in the drive battery 11 can be 10 or more but less than 100, or it can be 100 or more. In this embodiment, the number of secondary batteries included in the drive battery 11 is set to approximately 50. The drive battery 11 is assembled as a battery pack onto, for example, the floor of a vehicle 100. In this embodiment, the battery pack is formed by mounting auxiliary components (voltage sensor 12a, current sensor 12b, temperature sensor 12c, battery ECU 13, and SMR 14, etc.) on the battery box housing the drive battery 11.

[0053] Each secondary battery contained in a battery pack is referred to as a "cell battery". In this embodiment, all the cells in the battery pack are connected in series (for example, see the description below). Figure 2 In this embodiment, a liquid lithium-ion secondary battery is used as the battery cell. However, it is not limited to this; an all-solid-state secondary battery can also be used as the battery cell. In addition, the battery cell is not limited to a lithium-ion secondary battery; it can also be other secondary batteries (such as nickel-metal hydride batteries). The method of assembling the drive battery 11 on the vehicle 100 is not limited to a battery pack; it can also be a packless method.

[0054] Voltage sensor 12a detects the voltage of each cell in the drive battery 11. Current sensor 12b detects the current flowing through the drive battery 11. Temperature sensor 12c detects the temperature of each cell in the drive battery 11. Each sensor outputs the detection result to the battery ECU 13. Current sensor 12b is located in the current path of the drive battery 11. In this embodiment, one voltage sensor 12a and one temperature sensor 12c are provided for each cell.

[0055] SMR 14 is configured to switch the connection / disconnection of the circuit connecting PCU 24 and drive battery 11. For example, an electromagnetic mechanical relay can be used as SMR 14. When SMR 14 is in the closed state (connected state), power can be received / transmitted between drive battery 11 and PCU 24. On the other hand, when SMR 14 is in the open state, the circuit connecting drive battery 11 and PCU 24 is disconnected. SMR 14 is controlled via HVECU 50. SMR 14 is, for example, in the closed state when vehicle 100 is in motion.

[0056] MG 21a and 21b are each an electric motor / generator that functions as both an electric motor and a generator. An electric motor is one that outputs torque by being supplied with driving power, while a generator is one that produces electricity by being supplied with torque. Each MG 21a and 21b uses an AC motor (e.g., a permanent magnet synchronous motor or an induction motor). MG 21a and 21b are electrically connected to the drive battery 11 via PCU 24. MG 21a and MG 21b each have rotor shafts 43a and 43b, respectively. Rotor shafts 43a and 43b correspond to the rotation shafts of MG 21a and MG 21b, respectively.

[0057] The vehicle 100 also features a single-pinion planetary gear 431. The output shaft 41 of the engine 31 is connected to the planetary gear 431 via a transmission mechanism 421. The engine 31 can be any internal combustion engine; in this embodiment, a spark-ignition internal combustion engine with multiple cylinders (e.g., four cylinders) is used. The engine 31 generates power by burning fuel (e.g., gasoline) in each cylinder, and uses this power to rotate a crankshaft (not shown) shared by all cylinders. The crankshaft of the engine 31 is connected to the output shaft 41 via a torsional vibration damper (not shown). The output shaft 41 rotates as the crankshaft rotates. Furthermore, the engine 31 is not limited to a gasoline engine; it can also be a diesel engine or a hydrogen engine.

[0058] The output shaft 41 of the engine 31 corresponds to the input shaft of the transmission mechanism 421. The transmission mechanism 421 is configured to include clutches and brakes (not shown), and the gear ratio (i.e., the ratio of the rotational speed of the input shaft of the transmission mechanism 421 to the rotational speed of the output shaft 42 of the transmission mechanism 421) changes according to the state (engaged / unengaged) of the clutches and brakes included in the transmission mechanism 421. The hydraulic circuit 422 is configured to adjust the hydraulic pressure supplied to the clutches and brakes included in the transmission mechanism 421 according to the instructions of the HVECU 50. The HVECU 50 is configured to switch the respective states (engaged / unengaged) of the clutches and brakes included in the transmission mechanism 421 by controlling the hydraulic circuit 422. Figure 1 In the configuration shown, the transmission mechanism 421 is located upstream of the power splitting mechanism (planetary gear 431), but the transmission mechanism 421 can also be located downstream of the power splitting mechanism (on the side close to the drive wheels 45a, 45b).

[0059] The vehicle 100 also includes a gear shift lever 101 and a P position switch 102. The gear shift lever 101 and the P position switch 102 are each configured to switch between multiple shift zones in response to the user's gear shifting operation. The user can select one of the N (Neutral), R (Reverse), D (Drive), and B (Brake) zones by moving the gear shift lever 101 to a predetermined position. Additionally, the user can select the P (Parking) zone by pressing the P position switch 102 after parking the vehicle 100. The HVECU 50 switches the vehicle 100's shift zone to the zone selected by the user. The HVECU 50, for example, controls the hydraulic circuit 422 corresponding to the shift zone.

[0060] The output shaft 42 of the transmission mechanism 421 and the rotor shaft 43a of MG 21a are respectively connected to the planetary gear 431. The planetary gear 431 has three rotational elements: an input element, an output element, and a reaction force element. More specifically, the planetary gear 431 has a sun gear, a ring gear coaxially arranged with the sun gear, a pinion meshing with the sun gear and the ring gear, and a planet carrier that holds the pinion in order to allow it to rotate on its own axis and revolve around the sun gear. The planet carrier corresponds to the input element, the ring gear corresponds to the output element, and the sun gear corresponds to the reaction force element.

[0061] The output shaft 42 of the transmission mechanism 421 is connected to the planet carrier of the planetary gear 431. The rotor shaft 43a of MG 21a is connected to the sun gear of the planetary gear 431. Torque is input from the output shaft 42 of the transmission mechanism 421 to the planet carrier of the planetary gear 431. The transmission mechanism 421 is configured such that, when it is in a non-neutral state (i.e., a power transmission state), the planetary gear 431 distributes the torque output from the engine 31 to the sun gear (and MG 21a) and the ring gear for transmission. When the torque output from the engine 31 is output to the ring gear, the reaction torque generated by MG 21a acts on the sun gear.

[0062] Planetary gear 431 and MG 21b are configured to combine the power output from planetary gear 431 (i.e., the power output to the ring gear) and the power output from MG 21b (i.e., the power output to the rotor shaft 43b) to transmit the power to drive wheels 45a and 45b. More specifically, an output gear (not shown) that meshes with driven gear 432 is mounted on the ring gear of planetary gear 431. Additionally, the driving gear (not shown) mounted on the rotor shaft 43b of MG 21b also meshes with driven gear 432. Driven gear 432 functions to combine the torque output from MG 21b to rotor shaft 43b with the torque output from the driven ring gear of planetary gear 431. This combined drive torque is transmitted to differential gear 44, and then via drive shafts 44a and 44b extending left and right from differential gear 44 to drive wheels 45a and 45b.

[0063] The vehicle 100 also includes a battery ECU 13, an electric motor ECU 23, an engine ECU 33, and an HVECU 50. In this embodiment, each of the battery ECU 13, electric motor ECU 23, engine ECU 33, and HVECU 50 is equipped with a computer (e.g., a microcomputer). The ECUs are connected via CAN communication.

[0064] The HVECU 50 includes a processor 51, RAM (Random Access Memory) 52, and a storage device 53. The processor 51 may be, for example, a CPU (Central Processing Unit). The RAM 52 functions as a working memory that temporarily stores data processed by the processor 51. The storage device 53 is configured to store stored information. In addition to the program, the storage device 53 also stores information used in the program (e.g., mappings, formulas, and various parameters). The processor 51 executes the program stored in the storage device 53, thereby performing various processes within the HVECU 50.

[0065] Figure 1 Only the detailed structure of HVECU 50 is shown, but other ECUs also have processors, RAM, and storage devices. The number of processors in each ECU is arbitrary, and a single ECU may have multiple processors. Furthermore, the various processes within each ECU are not limited to software execution; they can also be executed through dedicated hardware (circuit).

[0066] MG 21a and 21b are equipped with motor sensors 22a and 22b, respectively, to detect the status of MG 21a and 21b (e.g., current, voltage, temperature, and speed). Motor sensors 22a and 22b output their detection results to the motor ECU 23. Engine 31 is equipped with an engine sensor 32 to detect the status of engine 31 (e.g., intake air volume, intake air pressure, intake air temperature, exhaust pressure, exhaust air temperature, catalyst temperature, engine coolant temperature, and speed). Engine sensor 32 outputs its detection results to the engine ECU 33. HVECU 50 receives the detection values ​​from motor sensors 22a and 22b and engine sensor 32 from motor ECU 23 and engine ECU 33 as needed. Additionally, HVECU 50 receives the status of drive battery 11 (i.e., the detection values ​​from voltage sensor 12a, current sensor 12b, and temperature sensor 12c) from battery ECU 13 as needed.

[0067] Vehicle 100 is equipped with a monitoring unit 80a that detects the state of the auxiliary equipment battery 80 (described later). The monitoring unit 80a includes various sensors that detect the state of the auxiliary equipment battery 80 (e.g., temperature, current, voltage) and outputs the detection results to the HVECU 50. The HVECU 50 can obtain the state of the auxiliary equipment battery 80 (e.g., temperature, current, voltage, and SOC) based on the output of the monitoring unit 80a. Additionally, although not illustrated, other sensors indicating the state of vehicle 100 (e.g., vehicle speed sensor, fuel gauge, odometer, accelerator pedal position sensor, and air pressure sensor) are also mounted on vehicle 100. The HVECU 50 can grasp information about vehicle 100 based on the outputs of the various sensors mounted on vehicle 100 (onboard sensors).

[0068] HVECU 50 is configured to output commands (control commands) for controlling engine 31 to engine ECU 33. Engine ECU 33 is configured to control various actuators of engine 31 (such as throttle valves, ignition devices, and fuel injectors, not shown) according to the commands from HVECU 50. HVECU 50 can control the engine through engine ECU 33.

[0069] The HVECU 50 is configured to output control commands (control commands) for controlling MG 21a and MG 21b respectively to the motor ECU 23. The motor ECU 23 is configured to generate current signals (e.g., signals representing the magnitude and frequency of the current) corresponding to the target torque of each of MG 21a and MG 21b according to the commands from the HVECU 50, and output the generated current signals to the PCU 24. The HVECU 50 can control the motors via the motor ECU 23.

[0070] PCU 24 is configured to include, for example, two converters corresponding to MG 21a and 21b, and a converter (not shown) disposed between each converter and the drive battery 11. PCU 24 is configured to supply power stored in the drive battery 11 to MG 21a and MG 21b respectively, and to supply power generated by MG 21a and MG 21b to the drive battery 11. PCU 24 is configured to control the states of MG 21a and MG 21b respectively, for example, to allow MG 21a to be in a power generation state while MG 21b is in a powered driving state. MG 21a is configured to generate electricity using power output from engine 31 (i.e., engine power generation). HVECU 50 charges the drive battery 11 using power generated by engine power generation in a manner that does not cause excessive reduction in the SOC (State of Charge) of the drive battery 11 during vehicle 100 operation. In addition, the power generated by regenerative braking performed by MG 21b also charges the drive battery 11.

[0071] Vehicle 100 is configured for both HV (High-Voltage) and EV (Electric Vehicle) driving. HV driving is driving via engine 31 and MG 21b while the engine 31 generates driving force. EV driving is driving via MG 21b when the engine 31 is stopped. When the engine 31 is stopped, combustion in the cylinders ceases. If combustion in the cylinders stops, the engine 31 no longer generates combustion energy (and driving force).

[0072] The vehicle 100 also includes an auxiliary battery 80, DC / DC converters 81 and 82, an auxiliary relay 83, a high-voltage load 91, and a low-voltage load 92. The full-charge capacity of the auxiliary battery 80 is less than that of the drive battery 11. The full-charge capacity of a battery is the amount of electricity stored in the battery when it is fully charged, and it decreases as the battery deteriorates. For example, a lead-acid battery can be used as the auxiliary battery 80. Alternatively, a secondary battery other than a lead-acid battery (such as a nickel-metal hydride battery) can also be used as the auxiliary battery 80. The DC / DC converters 81 and 82, the auxiliary relays 83, the high-voltage load 91, and the low-voltage load 92 are controlled by the HVECU 50. The HVECU 50 can also control these elements via the battery ECU 13.

[0073] High-voltage load 91 is a high-voltage auxiliary device type. Low-voltage load 92 is a low-voltage auxiliary device type. The driving voltage of low-voltage load 92 is lower than that of high-voltage load 91. The auxiliary device battery 80 is a low-voltage (e.g., 12V) vehicle battery configured to supply power to low-voltage load 92. In this embodiment, high-voltage load 91 includes an air conditioning unit, and low-voltage load 92 includes a lighting unit. The air conditioning unit is configured to provide heating and cooling for the passenger compartment of vehicle 100. The lighting unit includes lighting devices that illuminate the interior of the vehicle and lighting devices that illuminate the exterior of the vehicle (e.g., headlights). At least one of high-voltage load 91 and low-voltage load 92 may also include a seat heater for heating the seats of vehicle 100.

[0074] DC / DC converter 81 is located between drive battery 11 and high-voltage load 91, and steps down the power supplied from drive battery 11 before outputting it to high-voltage load 91. DC / DC converter 82 steps down the power supplied from drive battery 11 and outputs it to each auxiliary device battery 80 and low-voltage load 92. When SMR 14 is in the off state, no power is supplied from drive battery 11 to each high-voltage load 91, low-voltage load 92, and auxiliary device battery 80. An auxiliary device relay 83 is configured on the circuit connecting DC / DC converter 82 and low-voltage load 92. When auxiliary device relay 83 is in the off state, no power is supplied to low-voltage load 92.

[0075] When SMR 14 is in the ON state, power can be supplied from the drive battery 11 to the auxiliary device battery 80 via the DC / DC converter 82. For example, if the SOC of the auxiliary device battery 80 is less than a specified value, the HVECU 50 uses the power from the drive battery 11 to charge the auxiliary device battery 80. Additionally, the HVECU 50 performs battery pack degradation diagnosis as described later (see...). Figure 3 In S16 and S22), according to the service tool 200 ( Figure 2 As instructed by the drive battery 11, the high-voltage load 91 and the low-voltage load 92 are driven using the power of the drive battery 11. At this time, the HVECU 50 controls the SMR 14, DC / DC converters 81 and 82 and auxiliary equipment relays 83 so that the power of the drive battery 11 is supplied to each of the high-voltage loads 91 and the low-voltage loads 92.

[0076] Vehicle 100 also features a power switch 103. Power switch 103 is used to switch the start / stop of vehicle systems (HVECU 50, etc.). Power switch 103 is operated by the user.

[0077] Vehicle 100 also includes a notification device 104. The notification device 104 is configured to notify the user of vehicle 100 in response to a request from HVECU 50. Examples of notification devices 104 include an instrument panel, head-up display, navigation display, warning lights, or a speaker. The notification device 104 can also function as an input device that receives input from the user. The notification device 104 may include a touch panel display or a smart speaker that receives voice input. The notification device 104 can also be mounted on a portable device (i.e., an electronic instrument that can be carried by the user), such as a tablet computer, smartphone, or wearable device.

[0078] Figure 2 This diagram illustrates the configuration of the battery pack degradation diagnosis device according to this embodiment. Figure 1 Refer to together Figure 2 In this embodiment, the service tool 200 functions as a battery pack degradation diagnosis device. The service tool 200 includes a computer equipped with a processor 201, RAM 202, and a storage device 203. The storage device 203 stores a diagnostic program. The battery pack degradation diagnosis method according to this embodiment (see below) Figure 3 and Figure 7 The diagnostic program stored in the storage device 203 is executed by the processor 201.

[0079] Service tool 200 also includes an HMI (Human Machine Interface) 204. The HMI 204 includes input devices and a display device. The HMI 204 may be a touch panel display. The HMI 204 may include a smart speaker that accepts voice input.

[0080] The HVECU 50 also features a DLC (Data Link Connector) 55a and an interface 55b for the DLC 55a. The DLC 55a is a connector that can connect to the connector 250 of the service tool 200, for example, located around the driver's seat of the vehicle 100. The service tool 200 is, for example, an external diagnostic instrument used by a repair shop operator (e.g., a mechanic) to assess the condition of a vehicle. An example of a service tool 200 is the GST (General Scan Tool). By connecting the connector 250 of the service tool 200 to the DLC 55a, the service tool 200 can read vehicle data stored in the storage device 53.

[0081] In the battery pack degradation diagnosis method according to this embodiment, the service tool 200 acquires a value representing the voltage from the start of discharge to a predetermined end of discharge (hereinafter referred to as "V") for a battery cell that is presumed to be the smallest capacity battery cell (the battery cell with the smallest full-charge capacity in the battery pack). end1 The voltage data of the voltage change up to the present, using the voltage data of the smallest capacity battery cell, are used to estimate the degree of degradation of the drive battery 11 (battery pack).

[0082] However, as a method for estimating the minimum capacity battery cell, it is considered that the voltage of all battery cells included in the drive battery 11 reaches V earliest during discharge. end1 A method for estimating the minimum capacity battery cell (hereinafter referred to as the "objective battery cell") is used. However, this method has low estimation accuracy. On the other hand, if in order to accurately determine the minimum capacity battery cell, it is necessary to continuously discharge until the voltage of all battery cells contained in the battery pack reaches V... end1 This could lead to over-discharge of more than one battery cell. Over-discharge accelerates the degradation of the battery cell.

[0083] Therefore, in the battery pack degradation diagnosis method according to this embodiment, even if the voltage of the target battery cell reaches the discharge end voltage during discharge of all battery cells contained in the drive battery 11, the discharge of the battery pack is not stopped, and the discharge of the battery pack continues until the discharge end timing is determined based on the voltage data of the target battery cell. By using the voltage data of the target battery cell, the discharge end timing can be easily and appropriately determined. As a result, it is easy to improve the accuracy of battery pack degradation diagnosis while suppressing battery cell degradation during battery pack diagnosis.

[0084] The service tool 200 according to this embodiment includes a discharge unit 211 and an estimation unit 212. The discharge unit 211 is configured to discharge all individual cells contained in the drive battery 11, measure the voltage of each individual cell during discharge, and terminate the discharge if a discharge end time is reached. The estimation unit 212 is configured to use a voltage obtained for at least one individual cell contained in the drive battery 11, representing the voltage from the start of discharge to V... end1 The voltage data of the voltage changes up to this point are used to estimate the degree of degradation of the drive battery 11. The discharge section 211 is configured such that if the voltage of a certain battery cell (target battery cell) contained in the drive battery 11 reaches V... end1 Then, the voltage data of the battery cell (the target battery cell) is used to determine the discharge termination timing.

[0085] Figure 3This is a flowchart illustrating the discharge control in the battery pack degradation diagnosis method according to this embodiment. The process shown in this flowchart is performed, for example, after the DLC 55a of the vehicle 100, which is in a parked state, is connected to the connector 250 of the service tool 200, and after a user inputs a prescribed instruction to the HMI 204. However, it is not limited to this. Figure 3 The starting conditions for the process shown can be set arbitrarily. Figure 3 Each step shown is executed by sending control commands to the HVECU 50 via the discharge unit 211 of the service tool 200. Hereinafter, each step in the flowchart will be simply referred to as "S".

[0086] Reference Figure 1 , Figure 2 as well as Figure 3 In S11, the service vehicle 200 drives the engine 31 and uses the electricity generated by the engine to charge the drive battery 11. Through the processing in S11, the MG 21a uses the electricity generated by the power output from the engine 31 to input the drive battery 11 via the PCU 24 and SMR 14.

[0087] In S12, the service tool 200 determines whether all the individual cells contained in the drive battery 11 have reached the specified start voltage (hereinafter referred to as "V"). start The voltage of each individual cell in the drive battery 11 is measured by voltage sensor 12a. start It can be the voltage of a battery cell when it is fully charged, or it can be a voltage slightly lower than the voltage of a fully charged battery cell. V start It can be above 3.7V and below 3.9V.

[0088] Repeat steps S11 and S12 until all the individual cells in the drive battery 11 become V. start That's all (no in S12). If all battery cells become V start If the above is true (in S12), then the service tool 200 stops the engine 31 in S13. Then, in S14, the service tool 200 determines whether the voltage of all the battery cells contained in the drive battery 11 has stabilized. In S14, it waits until the voltage of each battery cell contained in the drive battery 11 stabilizes. If the voltage of each battery cell contained in the drive battery 11 is stable (in S14), then the process proceeds to S15.

[0089] In S15, the service tool 200 measures the state (voltage, current, and temperature) of each battery cell contained in the drive battery 11 and records the measurement results in the storage device 203. Next, in S16, the service tool 200 discharges the drive battery 11 by controlling the electrical load of the vehicle 100. The drive battery 11 is configured to supply power to the electrical load mounted on the vehicle 100.

[0090] Specifically, in S16, the service tool 200 controls the electrical load of the vehicle 100 (e.g., at least one of the high-voltage load 91 and the low-voltage load 92) to ensure that the discharge current of each battery cell contained in the drive battery 11 is a predetermined value (hereinafter referred to as "Vd"). In this embodiment, the air conditioning unit (high-voltage load 91) and the lighting unit (low-voltage load 92) are driven by the power supplied from the drive battery 11. The service tool 200 adjusts the power supplied from the drive battery 11 to the high-voltage load 91 and the low-voltage load 92 respectively through DC / DC converters 81 and 82. Furthermore, the service tool 200 maintains a constant current value of each battery cell contained in the drive battery 11 during discharge. Vd can be more than 1A and less than 10A, and can be around 5A. In this embodiment, the current value of each battery cell during discharge is maintained at Vd. In this embodiment, Vd is set to a fixed value (e.g., 5A), but Vd can also be variable depending on the situation.

[0091] Figure 4 It is a graph used to illustrate the discharge characteristics of the drive battery 11 (battery pack). Figure 4 Lines L1 to L3 in the diagram show that... Figure 3 This is an example of the changes in current and voltage of the drive battery 11 (battery pack) when steps S11 to S16 are executed. Line L1 shows the change in current of the drive battery 11. Lines L2 and L3 show the discharge characteristics (more specifically, the changes in cell voltage during discharge) of the first and second battery cells contained in the drive battery 11, respectively. Specifically, the full-charge capacity of the first battery cell is greater than that of the second battery cell. (Refer to...) Figure 4 If we compare the voltage transition of the first battery cell (line L2) with the voltage transition of the second battery cell (line L3), the voltage of the second battery cell begins to decrease earlier, reaching a lower voltage. Thus, there is a tendency for battery cells with smaller full-charge capacity to experience a faster voltage drop during discharge. If the voltage of a battery cell becomes too low due to discharge, battery cell degradation is accelerated. The situation where battery cell discharge continues until the battery cell voltage becomes too low is called "over-discharge." In the example shown by line L3, discharge continues until the battery cell is over-discharged. However, in the battery pack degradation diagnosis method of this embodiment, the discharge termination timing is set so that the battery cell does not become over-discharged.

[0092] Refer again Figure 1 , Figure 2 and Figure 3 In S17, the service tool 200 determines whether the voltage of a specific battery cell (the target battery cell) contained in the drive battery 11 reaches the specified V. end1 V end1 The lower discharge limit voltage is set based on the common discharge lower limit voltage of all battery cells contained in the drive battery 11. This discharge lower limit voltage corresponds to a discharge-related lower limit voltage; if the discharge of a battery cell continues below this voltage, it may cause over-discharge. In this embodiment, V end1 It is set to a voltage slightly higher than the lower discharge limit voltage (e.g., the lower discharge limit voltage plus a margin voltage). V end1 It can be above 2.8V and below 3.2V. In this embodiment, V... end1 Set to 3.0V. During the period in S17 where the judgment is "no", repeat the processing of S15 to S17. If the voltage of a single cell in the drive battery 11 reaches V... end1 If S17 is true, then the process proceeds to S18. The voltage of the earliest cell in the drive battery 11 to reach V... end1 The battery cell is equivalent to the object battery cell.

[0093] In S18, the service tool 200 uses the data obtained in S15 to obtain the voltage (hereinafter referred to as "V") of the target battery cell at the start of discharge. A Maximum cell voltage (hereinafter referred to as "V") max The function representing the discharge characteristics of a single battery cell (hereinafter referred to as "Q") A The highest voltage among the individual cell voltages (measured in S15) at the start of discharge of each cell in the drive battery 11 is V. max The voltage of the target battery cell is V. A That is, V A For V max the following.

[0094] Service tool 200 can use the representation of a single battery cell from V A (Discharge start voltage) to V end1 The voltage data of the voltage transition up to (discharge end voltage) (measured in S15) is used to derive Q. A Q can be determined using the least squares method. A Q A It is a function that returns the range discharge capacity (Ah) of a single battery cell within a specified range. For example, if we input Q... A Enter VA and V end1 Then Q A Output from V A To V end1 The discharge amount is the amount of discharge from a single battery cell within a given voltage range. The discharge amount is equivalent to the time integral of the discharge current (A). When the discharge current varies within the range, the discharge amount is obtained by integrating the discharge current over time. When the discharge current is constant within the range, the product of the discharge current (A) and the discharge time (h) represents the discharge amount.

[0095] Next, in S19, service tool 200 determines V. A Does it correspond to V? max Furthermore, in V A Corresponding to V max In the case of (yes in S19), in S24, the service tool 200 terminates the discharge of the drive battery 11. On the other hand, in V A Not corresponding to V max In the case of (no in S19), in S20, service tool 200 uses Q. A V A and V max Determine the discharge termination timing. The following uses... Figure 5 and Figure 6 This describes the method for determining the discharge end timing in the battery pack degradation diagnosis method involved in this embodiment.

[0096] Figure 5 This is a first graph used to illustrate the method for determining the discharge end timing in the battery pack degradation diagnosis method according to this embodiment. Figure 5 Lines L11 and L12 in the diagram illustrate the discharge characteristics of the third and fourth battery cells contained in the drive battery 11, respectively. Specifically, the full-charge capacity of the third battery cell is greater than that of the fourth battery cell. (Refer to...) Figure 5 If we compare the voltage transition of the third cell (line L11) with the voltage transition of the fourth cell (line L12), the voltage of the third cell at the start of discharge is lower than that of the fourth cell, and the voltage of the third cell reaches V earlier than that of the fourth cell. end1 Thus, given the voltage difference between individual battery cells at the start of discharge, the battery cell with the lowest initial voltage will reach its voltage V earlier. end1 During the discharge of the drive battery 11, there is a general trend that the smaller the full charge capacity of a single battery cell, the easier it is for the voltage of that single cell to decrease (see reference). Figure 4 ), but if Figure 5As shown, it is possible that the voltage of a battery cell with a larger full-charge capacity reaches V earlier than the voltage of a battery cell with a smaller full-charge capacity. end1 Therefore, in the battery pack degradation diagnosis method according to this embodiment, even if the voltage of the target battery cell reaches V... end1 The discharge of the drive battery 11 is not stopped, and the discharge of the drive battery 11 continues until the discharge ends at the designated time.

[0097] Figure 6 This is a second graph used to illustrate the method for determining the discharge end timing in the battery pack degradation diagnosis method according to this embodiment. Figure 6 Line L21 in the middle shows the direction from V A To V end1 The change in the discharge amount of the target battery cell within the voltage range. Figure 6 Line L22 in the figure shows the discharge of the assumed object battery cell from V max The voltage change of the target battery cell under the initial conditions.

[0098] Reference Figure 6 Service tool 200 will bring the voltage (line L21) of the target battery cell to V. end1 The discharge capacity of the target battery cell reaches ΔQ A The timing is determined as the discharge end timing.

[0099] Specifically, in Figure 3 In S19, service tool 200 determines V A Does (the voltage at the start of discharge of the target battery cell) correspond to V? max (Maximum cell voltage). Determined to be V. A Corresponding to V max (V A =V max In the case of (yes in S19), line L21 and line L22 are the same, ΔQ A It becomes 0. Therefore, the service tool 200 will bring the voltage of the target battery cell to V. end1 The timing is determined as the discharge end timing. Therefore, when the voltage of the target battery cell reaches V... end1 Then, the discharge of the drive battery 11 immediately ends. Figure 3 (S24).

[0100] On the other hand, when judged as V A Not corresponding to V max In the case of (no in S19), Figure 3 In S20, the service tool 200 will assume the discharge of the target battery cell from V max Initially, the voltage of the target battery cell reaches V. end1The timing is determined as the discharge end timing. Specifically, service tool 200 will send a signal to Q... A Enter V max and V end1 The range discharge capacity of the target battery cell (from V) was obtained. max To V end1 (total discharge) minus Q A Enter V A and V end1 The range discharge capacity of the target battery cell (from V) was obtained. A To V end1 The value obtained after calculating the discharge amount up to this point is denoted as ΔQ. A If the discharge of a single battery cell, assuming the object is to be charged, is from V... max Initially, the discharge of the drive battery 11 continues until the voltage of the target battery cell reaches V. end1 By the time the timing is reached, it is considered that the voltage of the smallest capacity battery cell contained in the drive battery 11 has reached V. end1 .

[0101] Refer again Figure 1 , Figure 2 and Figure 3 If the discharge end timing is determined in S20, then processes S21 and S22 are executed. In S21 and S22, the same processes as those described in S15 and S16 are executed respectively. Through the process in S22, the discharge of the drive battery 11 is continued. In S23, the service tool 200 determines whether the discharge end timing has been reached. Specifically, the service tool 200 determines this when the voltage of the target battery cell reaches V. end1 The discharge quantity begins to accumulate at the set time, and the accumulated discharge quantity reaches ΔQ. A (Refer to Figure 6 When the discharge end time is reached (S21-S23), it is determined that the discharge end time has been reached. During the period when the determination in S23 is negative, the processing of S21-S23 is repeated. If the discharge end time is reached (S23 is positive), then in S24, the service tool 200 terminates the discharge of the drive battery 11.

[0102] Through the above Figure 3 The process shown involves recording data indicating the state of the drive battery 11 (particularly the degree of degradation) in the storage device 203 of the service tool 200. The service tool 200 uses the recorded data of the drive battery 11 to estimate the degree of degradation of the drive battery 11. Furthermore, the service tool 200 determines whether the lifespan of the drive battery 11 has ended (i.e., whether the drive battery 11 can continue to be used).

[0103] Figure 7This is a flowchart illustrating the processes involved in determining battery life in the battery pack degradation diagnosis method according to this embodiment. The processes shown in this flowchart are executed, for example, after the following conditions: […]. Figure 3 After the processing and service tool 200 obtains data from the drive battery 11, it receives a specified instruction from the user into the HMI 204. However, it is not limited to this. Figure 7 The starting conditions for the process shown can be set arbitrarily. For example, they can also be set in... Figure 3 After the processing shown is completed, it will automatically begin. Figure 7 The processing shown. Figure 7 The steps shown are performed by the estimation unit 212 of the service tool 200. Figure 7 The process shown can be performed when the vehicle 100 and the service tool 200 are connected, or when the service tool 200 has been removed from the vehicle 100.

[0104] Reference Figure 1 , Figure 2 and Figure 7 In S31, the service tool 200 determines the voltage of each individual cell in the drive battery 11 that reaches V at the end of the discharge time. end1 The full charge capacity of each individual battery cell. During the discharge process, except for the voltage of the individual battery cells, none of the values ​​reached V during the discharge cycle. end1 In this case, only the full-charge capacity of the target battery cell is calculated.

[0105] Service tool 200, in order to determine the full charge capacity of a single battery cell in S31, uses... Figure 3 The data obtained from the drive battery 11 during the processing shown (i.e., during the discharge of the drive battery 11) Figure 3 The processing of S15 and S21 is recorded in the storage device 203 (data). In this embodiment, the service tool 200 calculates the range discharge amount of a single battery cell (e.g., from the discharge start voltage to V). end1 The range of discharge (up to the specified discharge range) is transformed into full charge capacity using a prescribed mapping. To determine the full charge capacity of a single battery cell, a mapping representing the relationship between the cell's temperature, discharge range, and full charge capacity can also be used. If the cell's temperature and discharge range are assigned to this mapping, the cell's full charge capacity is output based on the mapping. The cell's temperature can be either the average temperature during discharge or the temperature at the start of discharge. This mapping can be pre-stored in storage device 203. Service tool 200 can obtain this mapping from an external server (e.g., a server that manages various battery-related information) or from vehicle 100.

[0106] Next, in S32, the service tool 200 obtains the full-charge capacity (hereinafter referred to as "Qc1") of the smallest capacity battery cell in the drive battery 11. Specifically, the service tool 200 estimates Qc1 as the smallest full-charge capacity among the full-charge capacities of each battery cell obtained in S31. The discharge of the drive battery 11 continues until... Figure 3 The estimation accuracy of Qc1 in S32 is improved up to the discharge end timing determined by S18 to S20.

[0107] Next, in S33, the service tool 200 determines whether Qc1 is less than a predetermined benchmark value (hereinafter referred to as "Th1"). Th1 is a threshold representing the lifespan of the drive battery 11 in the vehicle 100. If Qc1 is less than Th1, it indicates that the lifespan of the drive battery 11 has ended under current use. Th1 can be pre-stored in the storage device 203. The service tool 200 can obtain Th1 from an external server (e.g., a server that manages various battery-related information) or from the vehicle 100.

[0108] If Qc1 is less than Th1 (yes in S33), in S331, the service tool 200 prompts the replacement of the drive battery 11. For example, the HMI 204 or the notification device 104 displays a message stating that the replacement time for the drive battery 11 has arrived. However, it is not limited to this; the HMI 204 may also prompt the replacement of the drive battery 11 through sound (including audio). In addition, the service tool 200 may also send a pre-defined notification (e.g., a notification informing the user of the vehicle 100 that the drive battery 11 needs to be replaced) to a terminal (e.g., a smartphone or wearable device). After the processing in S331, the drive battery 11 is replaced. In this embodiment, the drive battery 11 is replaced on a battery pack basis. However, it is not limited to this; the battery pack may also be replaced (reassembled) on a cell basis. The drive battery 11 removed from the vehicle 100 can be used for other purposes.

[0109] If Qc1 is Th1 or higher (not in S33), in S332, the service tool 200 notifies that the drive battery 11 does not need to be replaced. For example, the HMI 204 or the notification device 104 displays a message stating that the drive battery 11 can continue to be used. In this case, the drive battery 11 in the vehicle 100 continues to be used.

[0110] After the processing in S331 or S332 is executed, Figure 7 The series of processes shown is now complete. Service tool 200 can also store the diagnostic results of S331 or S332 in vehicle 100 (e.g., storage device 53 of HVECU 50).

[0111] As described above, the battery pack degradation diagnosis method involved in this embodiment includes... Figure 3 The series of processes shown and Figure 7 The series of processes shown. In Figure 3 In the process shown, the service tool 200 performs discharge of each battery cell while measuring the voltage of each individual cell contained in the drive battery 11 (S15 and S16). If the voltage of a certain battery cell reaches a predetermined discharge end voltage during discharge (yes in S17), the service tool 200 determines the discharge end timing based on voltage data representing the voltage transition of that battery cell from the discharge start voltage to the discharge end voltage (S18 to S20). Furthermore, if the discharge end timing is reached (yes in S19 or S23), the service tool 200 terminates the discharge of the drive battery 11 (S24). Figure 7 In the process shown, the degree of degradation of the drive battery 11 (e.g., Qc1) is estimated using voltage data of one or more battery cells acquired during discharge. According to this battery pack degradation diagnosis method, the discharge termination timing is appropriately determined based on the voltage data of the target battery cell. Therefore, the accuracy of battery pack degradation diagnosis can be improved while suppressing the degradation of battery cells during battery pack diagnosis. Furthermore, in the above method, the drive battery 11 is discharged while mounted on the vehicle 100. Since the capacity of the drive battery 11 being diagnosed is less than 5 kWh, a sufficient throughput diagnosis can be performed.

[0112] Figure 3 The processing shown can also be modified appropriately. Figure 8 It means Figure 3 The flowchart of the first variation of the process shown. Figure 8 The treatment shown replaces S18 to S20 ( Figure 3 Besides determining the discharge end timing through S18A and S20A, and with Figure 3 The processing shown is the same.

[0113] Reference Figure 8 In S18A, service tool 200 uses the data obtained in S15 to obtain V. A (Voltage at the start of discharge of the target battery cell) and Q A (A function representing the discharge characteristics of the target battery cell). In this variation, in S18A, the service tool 200 also acquires a predetermined voltage (hereinafter referred to as "Vx"). Vx is related to the discharge period of the drive battery 11. In this variation, Vx is determined in advance through experiments or simulations so that the voltage of the target battery cell reaches Vx. end1 After the discharge termination voltage (Vx) is reached, the discharge of the drive battery 11 continues for an appropriate amount of discharge (or time). Vx is stored, for example, in the storage device 203.

[0114] In S20A, service tool 200 uses Q. A V A And Vx determines the discharge termination timing. For example, service tool 200 will determine the discharge termination timing when the voltage of the target battery cell reaches Vx, assuming that the discharge of the target battery cell starts from Vx. end1 The timing is determined as the discharge end timing. Specifically, service tool 200 will send a signal to Q... A Input Vx and V end1 The range of discharge capacity of the target battery cell (from Vx to V) was obtained. end1 (total discharge) minus Q A Enter V A and V end1 The range discharge capacity of the target battery cell (from V) was obtained. A To V end1 The value obtained after calculating the discharge amount up to this point is denoted as ΔQ. A Furthermore, the service tool 200 will bring the voltage of the target battery cell to V. end1 The discharge capacity of the target battery cell reaches ΔQ A The timing is set to the discharge end timing.

[0115] In the service tool 200 described in the above-described modification, the discharge unit 211 is configured to discharge the target battery cell until the voltage of the target battery cell reaches V, assuming that the discharge of the target battery cell starts from Vx. end1 The timing is determined as the discharge end timing. Vx can be a fixed value or a variable value corresponding to the situation. When Vx is a fixed value, V... A The lower the value, the higher the ΔQ. A The larger it is. This also applies to ΔQ. A An upper limit (safety value) is set to prevent the target battery cell from excessively deteriorating due to over-discharge. Alternatively, the discharge unit 211 can determine Vx using the voltage at the start of discharge of each battery cell in the drive battery 11. For example, the discharge unit 211 can calculate the average value of the voltage at the start of discharge of each battery cell in the drive battery 11 (hereinafter referred to as "Vx"). ave (), based on V ave Determine the threshold. The threshold can be related to V. ave The same value can also be less than V. ave The value. Furthermore, the discharge section 211 can also be at V. A If the value is greater than the above threshold, Vx is set to V. max (Maximum cell voltage) at V A If the value is below the aforementioned threshold, then Vx is set to be less than V. max The value of .

[0116] In the above embodiment, the discharge unit 211 and the estimation unit 212 in the service tool 200 are implemented by the processor 201 and the program executed by the processor 201. However, it is not limited to this, the discharge unit 211 and the estimation unit 212 may also be implemented by dedicated hardware (circuit).

[0117] In addition, the functions of the discharge unit 211 and the estimation unit 212 can also be installed on the vehicle 100. Figure 9 It means Figure 2 A diagram showing a modified example of the HVECU50. (Refer to...) Figure 9 The HVECU 50A installed in the vehicle 100 may also include a discharge unit 211 and a estimation unit 212. The discharge unit 211 and the estimation unit 212 in the HVECU 50A may also be manifested by the processor 51 and the program executed by the processor 51 (e.g., a diagnostic program stored in the storage device 53A).

[0118] In the above embodiments, the battery pack installed in HEVs (Hybrid Electric Vehicles) without a plug-in connector is considered for degradation diagnosis. However, this is not a limitation; the battery pack installed in PHEVs (Plug-in Hybrid Electric Vehicles) with a plug-in connector can also be considered for degradation diagnosis. Furthermore, the battery packs installed in other xEVs (BEVs, FCEVs, Range-Extended EVs, etc.) can also be considered for degradation diagnosis. xEVs are vehicles that use electricity as a sole or partial power source.

[0119] In the above embodiments, degradation diagnosis by discharge was described. However, it is not limited to this; charging can also be performed instead of discharging, and the degree of degradation of the battery pack can be estimated based on voltage changes during charging. Hereinafter, [the following will be described using...] Figures 10-13 This section will explain degradation diagnosis performed via charging, focusing on the differences between degradation diagnosis performed via discharge and that performed via discharge. In the degradation diagnosis performed via charging described below, the battery pack (drive battery) installed in a BEV (Battery Electric Vehicle) with V2H (Vehicle to Home) functionality will be the subject of the degradation diagnosis. The initial fully charged capacity of the battery pack being diagnosed is, for example, approximately 100 kWh.

[0120] Figure 10 It means Figure 2 A diagram showing a variant of the service tool 200. (Refer to...) Figure 10The service tool 200A includes a charging unit 213 and a estimation unit 214. The charging unit 213 and estimation unit 214 in the service tool 200A are implemented by a processor 201 and a diagnostic program stored in a storage device 203A. The charging unit 213 is configured to charge all individual battery cells in the battery pack, measure the voltage of each individual battery cell during charging, and determine if a predetermined charging end time (hereinafter referred to as "V") is reached. end2 Then charging ends. The estimation unit 214 is configured to use a value indicating the voltage of at least one of the battery cells in the battery pack from the start of charging to V. end2 The voltage data of the voltage changes up to this point are used to estimate the degree of degradation of the battery pack. The charging unit 213 is configured such that if the voltage of a certain battery cell (target battery cell) in the battery pack reaches V... end2 Then, the voltage data of the battery cell (the target battery cell) is used to determine the charging end timing.

[0121] Figure 11 It means Figure 3 The flowchart of the second variation of the process is shown. Figure 11 The steps shown are performed by the charging unit 213 of the service tool 200A. (Refer to...) Figure 11 In S51, the service tool 200A utilizes the V2H function of the BEV to discharge the battery pack. That is, the service tool 200A discharges the power from the battery pack installed in the BEV to the outside of the vehicle. The power of the battery pack can be consumed by electrical loads outside the vehicle or stored in an external energy storage device. However, the discharge method is not limited to V2H; the power of the battery pack can also be consumed by electrical loads installed in the BEV.

[0122] In S52, the service tool 200A determines whether the voltage of all individual battery cells in the battery pack is below the specified charging start voltage. The charging start voltage can be the lower discharge limit voltage or a voltage slightly higher than the lower discharge limit voltage. If the voltage of all individual battery cells is below the charging start voltage after discharging in S51 (yes in S52), then in S53, the service tool 200A stops discharging. Then, the BEV is connected to the EVSE (Electric Vehicle Supply Equipment). Furthermore, in S54, the service tool 200A determines whether the voltage of all individual battery cells in the battery pack has stabilized. If the voltage of each individual battery cell in the battery pack is stable (yes in S54), the process proceeds to S55.

[0123] In S55, the service tool 200A measures the state (voltage, current, and temperature) of each battery cell in the battery pack and records the measurement results in the storage device 203A. Next, in S56, the service tool 200A charges the battery pack using an EVSE (external power source). This allows charging of the battery pack to be performed while it is mounted on the BEV (specifically, external charging via an external power source). The service tool 200A can also use a fast charger as an EVSE to perform fast charging of the battery pack. In S57, the service tool 200A determines whether the voltage of a specific battery cell (the target battery cell) in the battery pack reaches a specified V. end2 V end2 It can be the voltage of a battery cell when it is fully charged, or it can be a voltage slightly lower than the voltage of a battery cell when it is fully charged.

[0124] If the voltage of a single battery cell in the battery pack reaches V end2 (If it is true in S57), then in S58, the service tool 200A uses the data obtained in S55 to obtain the voltage (hereinafter referred to as "V") of the target battery cell at the start of charging. B Minimum cell voltage (hereinafter referred to as "V") min A function representing the charging characteristics of a single battery cell (hereinafter referred to as "Q"). B The lowest voltage among the individual battery cells in the battery pack at the start of charging (measured in S55) is V. min The voltage of the target battery cell is V. B That is, V B For V min That's all. Service tool 200A can use the representation of a single battery cell from V... B To V end2 The voltage data of the voltage transition up to this point (measured in S55) is used to derive Q. B Q can also be determined using the least squares method. B .

[0125] Next, in S59, service tool 200A determines V. B Does it correspond to V? min Furthermore, in V B Corresponding to V min In the case of (yes in S59), in S64, the service tool 200A terminates the charging of the battery pack. On the other hand, in V B Not corresponding to V min In the case of (no in S59), in S60, service tool 200A uses Q. B V B and Vmin Determine the charging end timer.

[0126] Figure 12 It is a graph used to illustrate the method for determining the charging end timing. Figure 12 Line L31 in the middle indicates that from V B To V end2 The change in the charge level of the target battery cell within the voltage range up to that point. Figure 12 The line L32 in the figure represents the charging of a single battery cell, assuming it is from V. min The voltage change of the target battery cell under the initial conditions.

[0127] Reference Figure 12 ,exist Figure 11 In S59, it is determined to be V B Corresponding to V min In this case, line L31 and line L32 are the same, ΔQ B It becomes 0. Therefore, the service tool 200A will bring the voltage of the target battery cell to V. end2 The timing is determined as the charging end timing. Therefore, when the voltage of the target battery cell reaches V... end2 After that, the charging of the battery pack immediately ended. Figure 11 (S64).

[0128] On the other hand, Figure 11 In S59, it is determined to be V B Not corresponding to V min In the following S60, service tool 200A will be directed to Q. B Enter V min and V end2 The range of charge of the target battery cell (from V) is obtained. min To V end2 (To date) minus the amount charged to Q B Enter V B and V end2 The range of charge of the target battery cell (from V) is obtained. B To V end2 The value obtained after charging up to the specified amount is denoted as ΔQ. B .

[0129] Refer again Figure 11 After determining the charging end timer in S60, processes S61 and S62 are executed. S61 and S62 perform the same processes as those described in S55 and S56. Through the process in S62, charging of the battery pack continues. In S63, the service tool 200A determines whether the charging end timer has been reached. If the charging end timer has been reached (yes in S63), then in S64, the service tool 200A terminates the charging of the battery pack.

[0130] Through the above Figure 11 The processing shown indicates that data representing the battery pack's condition (especially the degree of degradation) is recorded in the storage device 203A of the service tool 200A. The service tool 200A is used in… Figure 11 The battery pack data recorded in S55 and S61 are used to estimate the degree of degradation of the battery pack.

[0131] Figure 13 It means Figure 7 The flowchart shows a variation of the processing. Figure 13 Each step shown is performed by the estimation unit 214 of the service tool 200A. Figure 13 The treatment shown is basically based on the aforementioned degradation diagnosis via discharge (see reference). Figure 7 The process of estimating the degree of battery pack degradation is as follows: That is, through processes S71 and S72, the full-charge capacity (Qc2) of the smallest capacity battery cell in the battery pack is obtained. In S73, the service tool 200A determines whether Qc2 is less than a specified reference value (Th2). Th2 is related to Th1 (…). Figure 7 The reference value is as follows: If Qc2 is less than Th2 (yes in S73), the drive battery (battery pack) of the BEV is replaced (S731); if Qc2 is greater than Th2 (no in S73), the battery pack in the BEV continues to be used (S732). Thus, according to the battery pack degradation diagnosis method involved in the modified example, the degree of battery pack degradation can be estimated based on the voltage changes during charging. According to the above-described degradation diagnosis method performed through charging, large-capacity battery packs (e.g., battery packs with a capacity of 10 kWh or more) can be diagnosed with sufficient throughput.

[0132] For various deformations (e.g.) diagnosed through discharge, the degradation diagnosis is performed via discharge. Figure 8 and Figure 9 The variations shown can also be used for degradation diagnosis performed through charging. For example, the charging unit 213 and the estimation unit 214 described above ( Figure 10 The functionality can also be installed on vehicles (such as xEVs). Figure 14 This indicates that it has been installed. Figure 10 The diagram shows the ECU50B of the charging unit 213 and the estimation unit 214. (Refer to...) Figure 14 The ECU 50B, installed in a vehicle (e.g., a BEV or PHEV), includes a processor 51B, RAM 52B, and a storage device 53B. Within the ECU 50B, a charging unit 213 and a estimation unit 214 are implemented via the processor 51B and the program executed by the processor 51B. The ECU of a service tool or vehicle may also be configured to selectively perform degradation diagnostics via discharge (e.g., Figure 3 and Figure 7 The processing shown) and degradation diagnosis performed via charging (e.g. Figure 11 and Figure 13 (The processing shown). For example, if the full charge capacity of the battery pack in its initial state is above a specified value, a degradation diagnosis by charging can be performed; if the full charge capacity of the battery pack in its initial state is below the specified value, a degradation diagnosis by discharging can be performed.

[0133] In battery packs where degradation diagnosis is performed using any of the methods described above, all individual cells do not necessarily need to be connected in series (see [reference]). Figure 2 The construction of the battery pack used for degradation diagnosis is arbitrary. Figure 15 It means Figure 2 A diagram showing a modified example of the battery pack. For example, it can be... Figure 15 The battery pack 500 shown is used as the object of degradation diagnosis. Battery pack 500 contains N parallel battery cell blocks (i.e., parallel battery cell blocks CB-1 to CB-N). Each parallel battery cell block CB-1 to CB-N contains multiple battery cells connected in parallel. The number of battery cells connected in parallel within each parallel battery cell block is arbitrary. Figure 15 The example shown has three cells. The parallel battery cells CB-1 to CB-N are connected in series via power lines.

[0134] It should be understood that all aspects of the embodiments disclosed herein are illustrative and not intended to be limiting. The scope of the invention is not shown by the description of the above embodiments, but by the claims, including all modifications within the meaning and scope equivalent to the claims.

Claims

1. A battery pack degradation diagnosis device, characterized in that, Includes at least one processor, said at least one processor being configured to perform the following processes: Determine whether all the individual battery cells in the battery pack have reached or exceeded the specified starting voltage; When it is determined that multiple battery cells have reached a predetermined starting voltage, it is determined whether the voltage of all battery cells contained in the battery pack has stabilized. The voltage of each of the multiple battery cells contained in the battery pack is measured, and the maximum voltage of each of the multiple battery cells at the start of discharge is obtained as the maximum battery cell voltage. Discharge is performed on each of the multiple battery cells contained in the battery pack; Determine whether the voltage of any single battery cell in the battery pack has reached the discharge end voltage; The battery cell whose voltage reaches the discharge end voltage earliest among all the battery cells contained in the battery pack is identified as the target battery cell; Determine whether the discharge start voltage of the target battery cell corresponds to the maximum battery cell voltage; as well as When it is determined that the discharge start voltage of the target battery cell corresponds to the maximum battery cell voltage, the discharge of the battery pack is terminated after the voltage of the target battery cell reaches the discharge end voltage. When it is determined that the discharge start voltage of the target battery cell does not correspond to the maximum battery cell voltage, the timing at which the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, is determined as the discharge end timing. The determination of the timing when the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, as the discharge end timing includes: The discharge amount of the first interval is obtained by inputting the discharge start voltage and the discharge end voltage of the target battery cell into a function of the discharge characteristics of the target battery cell. The discharge amount in the second interval is obtained by inputting the maximum cell voltage and the discharge end voltage into a function of the discharge characteristics of the target cell. The difference between the discharge amount in the first interval and the discharge amount in the second interval is calculated as the discharge amount in the third interval; as well as If the discharge amount of the target battery cell, starting from the maximum battery cell voltage, exceeds the discharge amount of the third interval, the discharge of the battery pack is terminated.

2. The battery pack degradation diagnosis device according to claim 1, characterized in that, The discharge termination voltage is set based on the common lower discharge limit voltage of the plurality of battery cells.

3. The battery pack degradation diagnosis device according to claim 1 or 2, characterized in that, All the individual battery cells in the battery pack are connected in series. The at least one processor maintains a constant current value for each of the plurality of battery cells during discharge.

4. The battery pack degradation diagnosis device according to claim 1 or 2, characterized in that, The battery pack is configured to supply power to the electrical loads mounted on the vehicle. The at least one processor performs the discharge by controlling the electrical load.

5. A battery pack degradation diagnosis device, characterized in that, Includes at least one processor, said at least one processor being configured to perform the following processes: Determine whether all the individual cells in the battery pack are below the specified starting voltage; When it is determined that multiple battery cells have fallen below a specified starting voltage, it is determined whether the voltage of all battery cells contained in the battery pack has stabilized. The voltage of each of the multiple battery cells contained in the battery pack is measured, and the minimum voltage of each of the multiple battery cells at the start of charging is obtained as the minimum battery cell voltage. Each of the individual battery cells contained in the battery pack is charged. Determine whether the voltage of any single battery cell in the battery pack has reached the charging end voltage; The battery cell whose voltage reaches the charging end voltage earliest among all the battery cells contained in the battery pack is identified as the target battery cell; Determine whether the charging start voltage of the target battery cell corresponds to the minimum battery cell voltage; as well as When it is determined that the charging start voltage of the target battery cell corresponds to the minimum battery cell voltage, the charging of the battery pack is terminated after the voltage of the target battery cell reaches the charging end voltage. When it is determined that the charging start voltage of the target battery cell does not correspond to the minimum battery cell voltage, the timing at which the voltage of the target battery cell reaches the charging end voltage, assuming that the charging of the target battery cell starts from the minimum battery cell voltage, is determined as the charging end timing. The determination of the timing when the voltage of the target battery cell reaches the charging end voltage, assuming that charging of the target battery cell starts from the minimum battery cell voltage, as the charging end timing includes: The charging start voltage and the charging end voltage of the target battery cell are input as a function of the charging characteristics of the target battery cell to obtain the charging amount of the first interval. The minimum battery cell voltage and the charging end voltage are input as a function of the charging characteristics of the target battery cell to obtain the second interval charging amount; The difference between the charging amount in the first interval and the charging amount in the second interval is calculated as the charging amount in the third interval; as well as If the charge amount of a single battery cell, starting from the minimum battery cell voltage, exceeds the charge amount in the third interval, the charging of the battery pack is terminated.

6. A method for diagnosing battery pack degradation, characterized in that, include: Determine whether all the individual battery cells in the battery pack have reached or exceeded the specified starting voltage; When it is determined that multiple battery cells have reached a predetermined starting voltage, it is determined whether the voltage of all battery cells contained in the battery pack has stabilized. The voltage of each of the multiple battery cells contained in the battery pack is measured, and the maximum voltage of each of the multiple battery cells at the start of discharge is obtained as the maximum battery cell voltage. Perform discharge on each of the multiple battery cells contained in the battery pack; Determine whether the voltage of any single battery cell in the battery pack has reached the discharge end voltage; The battery cell whose voltage reaches the discharge end voltage earliest among all the battery cells contained in the battery pack is identified as the target battery cell; Determine whether the discharge start voltage of the target battery cell corresponds to the maximum battery cell voltage; as well as When it is determined that the discharge start voltage of the target battery cell corresponds to the maximum battery cell voltage, the discharge of the battery pack is terminated after the voltage of the target battery cell reaches the discharge end voltage. When it is determined that the discharge start voltage of the target battery cell does not correspond to the maximum battery cell voltage, the timing at which the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, is determined as the discharge end timing. The determination of the timing when the voltage of the target battery cell reaches the discharge end voltage, assuming that the discharge of the target battery cell starts from the maximum battery cell voltage, as the discharge end timing includes: The discharge amount of the first interval is obtained by inputting the discharge start voltage and the discharge end voltage of the target battery cell into a function of the discharge characteristics of the target battery cell. The discharge amount in the second interval is obtained by inputting the maximum cell voltage and the discharge end voltage into a function of the discharge characteristics of the target cell. The difference between the discharge amount in the first interval and the discharge amount in the second interval is calculated as the discharge amount in the third interval; as well as If the discharge amount of the target battery cell, starting from the maximum battery cell voltage, exceeds the discharge amount of the third interval, the discharge of the battery pack is terminated.

7. The battery pack degradation diagnosis method according to claim 6, characterized in that, The discharge is performed while the battery pack is mounted in the vehicle. The initial fully charged capacity of the battery pack is less than 5 kWh.

8. A method for diagnosing the degradation of a battery pack, characterized in that, include: Determine whether all the individual cells in the battery pack are below the specified starting voltage; When it is determined that multiple battery cells have fallen below a specified starting voltage, it is determined whether the voltage of all battery cells contained in the battery pack has stabilized. The voltage of each of the multiple battery cells contained in the battery pack is measured, and the minimum voltage of each of the multiple battery cells at the start of charging is obtained as the minimum battery cell voltage. Perform charging of each of the multiple battery cells contained in the battery pack; Determine whether the voltage of any single battery cell in the battery pack has reached the charging end voltage; The battery cell whose voltage reaches the charging end voltage earliest among all the battery cells contained in the battery pack is identified as the target battery cell; Determine whether the charging start voltage of the target battery cell corresponds to the minimum battery cell voltage; as well as When it is determined that the charging start voltage of the target battery cell corresponds to the minimum battery cell voltage, the charging of the battery pack is terminated after the voltage of the target battery cell reaches the charging end voltage. When it is determined that the charging start voltage of the target battery cell does not correspond to the minimum battery cell voltage, the timing at which the voltage of the target battery cell reaches the charging end voltage, assuming that the charging of the target battery cell starts from the minimum battery cell voltage, is determined as the charging end timing. The determination of the timing when the voltage of the target battery cell reaches the charging end voltage, assuming that charging of the target battery cell starts from the minimum battery cell voltage, as the charging end timing includes: The charging start voltage and the charging end voltage of the target battery cell are input as a function of the charging characteristics of the target battery cell to obtain the charging amount of the first interval. The minimum battery cell voltage and the charging end voltage are input as a function of the charging characteristics of the target battery cell to obtain the second interval charging amount; The difference between the charging amount in the first interval and the charging amount in the second interval is calculated as the charging amount in the third interval; as well as If the charge amount of a single battery cell, starting from the minimum battery cell voltage, exceeds the charge amount in the third interval, the charging of the battery pack is terminated.

9. The battery pack degradation diagnosis method according to claim 8, characterized in that, The charging is performed while the battery pack is mounted in the vehicle. The battery pack has an initial full-charge capacity of 10 kWh or more.

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