Cooling methods for battery systems and battery packs

Abstract

The goal is to cool the battery pack with an appropriate cooling capacity based on the amount of heat generated by the battery cells. [Solution] The battery system comprises a battery pack (10) having multiple battery cells (CL1~CLN), voltage sensors (211~21N) for detecting the voltage of each battery cell, current sensors (22) for detecting the current flowing through each battery cell, a fan (50) for cooling the battery pack (10) by blowing air onto it, and a control device (60) for controlling the airflow of the fan (50) to match a target airflow. The control device (60) calculates the internal resistance of each battery cell based on the detected values ​​of the voltage sensors (211~21N) and the current sensors (22). If the internal resistance of any of the multiple battery cells (CL1~CLN) exceeds a threshold, the control device (60) increases the target airflow compared to the case where the internal resistance of all of the multiple battery cells (CL1~CLN) is below the threshold.

Description

Technical Field

[0001] The present disclosure relates to a battery system and a method for cooling a battery pack.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2013-69740 (Patent Document 1) discloses a battery cooling device that cools a battery mounted on an electric vehicle with a fan. In Patent Document 1, in consideration of the reduction in cooling capacity due to the deterioration of the fan over time, for each control cycle, a correction coefficient for making the estimated temperature of the battery calculated from the cooling capacity of the fan and the heat generation amount of the battery coincide with the detected temperature of the battery by the temperature sensor is learned. When the correction coefficient is less than 1.0, it is determined that the actual cooling capacity has decreased, and the target rotational speed of the fan is increased to increase the cooling capacity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An electric vehicle is equipped with a battery pack including a plurality of battery cells connected in series. In order to protect the battery pack from abnormalities (including deterioration and / or failure) caused by the temperature rise of the battery pack, it is desirable to control the air volume of the fan using the internal temperature of each battery cell. The internal temperature of the battery cell depends on the heat generation amount in the battery cell. The heat generation amount in the battery cell is determined by the product of the square of the current flowing through the battery cell and the internal resistance. Therefore, as the internal resistance increases due to the progress of the deterioration of the battery cell, the heat generation amount of the battery cell increases.

[0005] Patent Document 1 describes a method in which a temperature sensor detects the temperature outside the battery case, determines the target fan speed from the detected battery temperature and the current vehicle speed, and corrects this target speed using the correction coefficient described above. However, the temperature detected by the temperature sensor is the external temperature of the battery and is susceptible to the influence of the surrounding environment. Therefore, there is a concern that a discrepancy may arise between the cooling capacity required to cool each battery cell in the battery pack and the cooling capacity of the fan. If the fan's cooling capacity is insufficient to meet the cooling capacity required by the battery cells, the battery cells may overheat. On the other hand, if the fan's cooling capacity exceeds the cooling capacity required by the battery cells, it may unnecessarily generate power consumption and noise from the fan's operation.

[0006] This disclosure is made to solve the above-mentioned problems, and the purpose of this disclosure is to cool the battery pack with an appropriate cooling capacity according to the amount of heat generated by the battery cells. [Means for solving the problem]

[0007] (1) A battery system according to a certain aspect of the present disclosure comprises a battery pack having a plurality of battery cells, a voltage sensor for detecting the voltage of each battery cell, a current sensor for detecting the current flowing through each battery cell, a fan for cooling the battery pack by supplying air to the battery pack, and a control device for controlling the airflow of the fan to match a target airflow. The control device calculates the internal resistance of each battery cell based on the values ​​detected by the voltage sensor and the current sensor. If the internal resistance of any of the plurality of battery cells exceeds a threshold, the control device increases the target airflow compared to the case where the internal resistance of all of the plurality of battery cells is below the threshold.

[0008] According to the configuration described in (1) above, the amount of heat generated by each of the multiple battery cells constituting the battery pack can be estimated by calculating the internal resistance of each cell. This allows the fan's airflow to be controlled to an appropriate level corresponding to the amount of heat generated by each battery cell. Therefore, it is possible to protect the battery pack from overheating while reducing unnecessary noise and power consumption.

[0009] (2) The battery pack is configured to store power for driving an electric vehicle. The battery system further includes a temperature sensor for detecting the external temperature of at least one of the battery cells and a vehicle speed sensor for detecting the vehicle speed of the electric vehicle. The control unit determines a target airflow rate based on the readings of the temperature sensor and the vehicle speed sensor if the internal resistance of all of the battery cells is below a threshold. If the internal resistance of any of the battery cells exceeds the threshold, the control unit increases the target airflow rate compared to the target airflow rate determined based on the readings of the temperature sensor and the vehicle speed sensor.

[0010] According to the configuration described in (2) above, even in electric vehicles that are driven using the power of a battery pack, it is possible to reduce unnecessary noise and power consumption while protecting the battery pack from overheating.

[0011] (3) The fan has multiple modes in which the relationship between the vehicle speed of the electric vehicle and the target airflow differs from one another. The fan is configured to be able to switch between the multiple operating modes. If the internal resistance of any of the multiple battery cells exceeds a threshold, the control device increases the target airflow for the same vehicle speed in at least one of the multiple modes compared to the case where the internal resistance of all of the multiple battery cells is below the threshold.

[0012] According to the configuration described in (3) above, the cooling capacity of the fan can be increased to compensate for the heat generated by battery cells whose internal resistance has increased due to degradation, thereby properly protecting the battery pack from overheating.

[0013] (4) The fan has multiple modes in which the relationship between the vehicle speed of the electric vehicle and the target airflow is different from each other. The fan is configured to be able to switch between the multiple operating modes. The control device is configured to switch the operating mode of the fan from the first mode to the second mode, in which the target airflow is greater for the same vehicle speed, when the value detected by the temperature sensor reaches the switching temperature. The control device lowers the switching temperature if the internal resistance of any of the multiple battery cells exceeds a threshold, compared to when the internal resistance of all of the multiple battery cells is below the threshold.

[0014] According to the configuration described in (4) above, the cooling capacity of the fan can be increased to compensate for the heat generated by battery cells whose internal resistance has increased due to degradation, thereby properly protecting the battery pack from overheating.

[0015] (5) A cooling method for a battery pack according to other aspects of the present disclosure is a cooling method for a battery pack having a plurality of battery cells. The battery pack stores power for driving an electric vehicle. The battery pack is provided with a voltage sensor for detecting the voltage of each battery cell, a current sensor for detecting the current flowing through each battery cell, a fan for cooling the battery pack by blowing air onto it, and a temperature sensor for detecting the external temperature of at least one of the plurality of battery cells. The electric vehicle is provided with a vehicle speed sensor for detecting the vehicle speed of the electric vehicle. The cooling method includes the steps of: calculating the internal resistance of each battery cell based on the detected values ​​of the voltage sensor and the current sensor; determining a target airflow for the fan based on the detected values ​​of the temperature sensor and the vehicle speed sensor when the internal resistance of all of the plurality of battery cells is below a threshold; increasing the target airflow compared to the target airflow determined based on the detected values ​​of the temperature sensor and the vehicle speed sensor when the internal resistance of any of the plurality of battery cells exceeds a threshold; and controlling the airflow of the fan to match the target airflow.

[0016] According to the cooling method described in (5) above, the airflow of the fan can be controlled to an appropriate amount according to the heat generated by each battery cell, similar to the configuration described in (1) above.

Advantages of the Invention

[0017] According to the present disclosure, the assembled battery can be cooled with an appropriate cooling capacity according to the heat generation amount of the battery cell.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 schematically shows the overall configuration of an electric vehicle equipped with a battery system according to the present embodiment. [Figure 2] FIG. is a diagram for explaining a method of calculating the internal resistance of a battery cell. [Figure 3] FIG. is a diagram for explaining a method of calculating the internal resistance of a battery cell. [Figure 4] FIG. shows an example of a map. [Figure 5] FIG. is a diagram for explaining the process executed by the ECU. [Figure 6] FIG. is a flowchart showing the processing procedure of the air volume control of the fan according to the present embodiment. [Figure 7] FIG. is a diagram for explaining a modified example of the process executed by the ECU. [Figure 8] FIG. is a flowchart showing the processing procedure of the air volume control of the fan according to a modified example of the present embodiment.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

[0020] <Overall Configuration of Electric Vehicle> FIG. 1 is a diagram schematically showing the overall configuration of an electric vehicle equipped with a battery system according to the present embodiment. In the example of FIG. 1, the electric vehicle 100 is an electric vehicle. The electric vehicle 100 may be a hybrid vehicle, a plug-in hybrid vehicle, a fuel cell vehicle, or the like.

[0021] The electric vehicle 100 includes a battery pack 10, a monitoring unit 20, a PCU (Power Control Unit) 30, a motor generator 40, a vehicle speed sensor 45, a fan 50, and an ECU (Electronic Control Unit) 60.

[0022] Battery pack 10 contains N battery cells (single cells) CL1 to CLN. N is not particularly limited as long as it is an integer greater than or equal to 2, but it is typically between a dozen and several dozen. Hereafter, battery cells CL1 to CLN may be collectively referred to as "battery cell CL".

[0023] Each battery cell CL is a rechargeable secondary battery such as a lithium-ion battery or a nickel-metal hydride battery. In Figure 1, N battery cells CL1 to CLN are connected in series, but the battery pack 10 may be constructed by combining N battery cells CL1 to CLN in series and / or parallel.

[0024] The battery pack 10 stores power to drive the motor generator 40. The battery pack 10 supplies power to the motor generator 40 through the PCU 30. The battery pack 10 is also charged by receiving the generated power through the PCU 30 when the motor generator 40 is generating power.

[0025] The monitoring unit 20 is a device for monitoring the status of the battery pack 10. The monitoring unit 20 consists of N voltage sensors 211 to 21N, a current sensor 22, and M temperature sensors 231 to 23M.

[0026] N voltage sensors 211 to 21N are provided, each corresponding to one of the N battery cells CL1 to CLN. Hereinafter, voltage sensors 211 to 21N may be collectively referred to as "voltage sensors 21". Each voltage sensor 21 detects the voltage V of the corresponding battery cell CL and outputs a signal indicating the detected value to the ECU 60. Voltage sensor 211 detects the voltage V1 of battery cell CL1. Voltage sensor 212 detects the voltage V2 of battery cell CL2. The same applies to the other voltage sensors 213 to 21N.

[0027] The current sensor 22 detects the current I (i.e., the current I flowing through battery cells CL1 to CLN) input to and output to the battery pack 10, and outputs a signal indicating the detected value to the ECU 60. The current sensor 22 is a sensor for detecting the current I flowing through each battery cell CL. Therefore, if the battery pack 10 is composed of multiple series-connected battery cell groups connected in parallel, the monitoring unit 20 includes a number of current sensors 22 corresponding to the number of parallel-connected battery cell groups.

[0028] The M temperature sensors 231 to 23M are provided, each corresponding to one of the M battery cells CL among the N battery cells CL1 to CLN. M is an integer between 1 and N. In other words, not all battery cells CL are equipped with a temperature sensor. In the example in Figure 1, temperature sensor 231 detects the temperature T1 of battery cell CL1. Temperature sensor 23M detects the temperature TN of battery cell CLN. However, the battery cells CL to which the temperature sensors are installed are not limited to the end cells CL as in this example, but can be set as appropriate.

[0029] The temperature detected by temperature sensors 231-23M is the temperature outside the battery case of at least one of the battery cells CL1-CLN (hereinafter referred to as "external temperature").

[0030] The PCU30 performs bidirectional power conversion between the battery pack 10 and the motor generator 40 according to control commands from the ECU60. The PCU30 includes, for example, a converter that boosts the DC voltage of the battery pack 10 and an inverter (neither of which are shown) that converts the DC power from the converter into AC power to drive the motor generator 40.

[0031] The motor-generator 40 is an AC rotating electric machine, for example, a three-phase AC synchronous motor with permanent magnets embedded in the rotor. The motor-generator 40 is driven by power supplied from the battery pack 10. The driving force of the motor-generator 40 is transmitted to the drive wheels via a drive shaft (not shown). In addition, when the electric vehicle 100 is braking or when acceleration is reduced on a downhill slope, the motor-generator 40 operates as a generator to perform regenerative power generation. The power generated by the motor-generator 40 is stored in the battery pack 10 via the PCU 30.

[0032] The vehicle speed sensor 45 detects the speed S of the electric vehicle 100 (hereinafter referred to as "vehicle speed") and outputs a signal indicating the detected value to the ECU 60. Alternatively, instead of the vehicle speed sensor 45, a signal indicating the detected value of a wheel speed sensor (not shown) that detects the rotational speed of the drive wheels may be output to the ECU 60, and the vehicle speed S may be calculated in the ECU 60 using the wheel speed. Alternatively, a signal indicating the detected value of a rotational speed sensor that detects the rotational speed of the motor generator 40 may be output to the ECU 60, and the vehicle speed S may be calculated in the ECU 60 using the rotational speed.

[0033] The fan 50 cools the battery pack 10 by blowing air onto it. The fan 50 is configured to draw in outside air, circulate the drawn-in outside air through a refrigerant passage provided in the battery case that houses the battery pack 10, and exchange heat with the battery pack 10 to cool the battery pack 10. The airflow of the fan 50 (the rotation speed of the fan 50) is controlled by the ECU 60.

[0034] The ECU 60 includes a processor 62 such as a CPU (Central Processing Unit), memory 64 such as ROM (Read Only Memory) and RAM (Random Access Memory), and input / output ports (not shown) for inputting and outputting various signals. The ECU 60 manages the battery pack 10 based on signals received from the monitoring unit 20 and programs and maps stored in the memory 64. The ECU 60 also estimates the amount of heat generated by each battery cell CL in the battery pack 10 based on signals received from the monitoring unit 20, and controls the airflow of the fan 50 based on the estimation result. The ECU 60 corresponds to one embodiment of the "control device". The ECU 60 may be divided into multiple ECUs for each function.

[0035] <Calculation of internal resistance> The ECU60 calculates the internal resistance of each battery cell CL1 to CLN. The internal resistances of battery cells CL1 to CLN are denoted as R1 to RN, respectively. Since the method for calculating the internal resistance R of each battery cell CL is the same, the method for calculating the internal resistance R1 of battery cell CL1 will be explained here as a representative example.

[0036] Figures 2 and 3 illustrate the calculation method for the internal resistance R1 of the battery cell CL1. Figure 2 shows the time variation of the voltage V1 of the battery cell CL1 and the current I (i.e., the current flowing through the battery cell CL1) input to and output to the battery pack 10. The voltage V1 is the CCV (Closed Circuit Voltage) of the battery cell CL1 detected by the voltage sensor 211. The sign of the current I is positive in the discharge direction from the battery pack 10 and negative in the charging direction to the battery pack 10.

[0037] As shown in Figure 2, the voltage V1 and current I fluctuate as the battery pack 10 is repeatedly discharged and charged. When the current I is positive, the battery pack 10 is discharged, so the voltage V1 decreases. When the current I is negative, the battery pack 10 is charged, so the voltage V1 increases.

[0038] The ECU60 acquires the voltage V1 and current I at the inflection points of the voltage V1 waveform and plots the acquired values ​​on the IV characteristic diagram shown in Figure 3 (IV plot). Figure 3 plots the voltage V1 and current I at the five inflection points A to E shown in Figure 2.

[0039] The ECU60 calculates a regression line L1 that shows the relationship between voltage V1 and current I using regression analysis (DC regression calculation) with the least squares method. The slope of the regression line L1 represents the internal resistance R1 of battery cell CL1. The internal resistances R2 to RN can be calculated for the other battery cells CL2 to CLN in the same way.

[0040] As the degradation of battery cell CL progresses, the internal resistance R of battery cell CL increases. The regression line L2 in Figure 3 is the regression line calculated from the voltage V1 and current I when battery cell CL1 is in a new state. As the degradation of battery cell CL1 progresses, the slope of the regression line becomes steeper, indicating that the internal resistance R1 is increasing.

[0041] <Fan airflow control> As explained in Figure 2, the temperature detected by temperature sensors 231-23M is the external temperature of at least one of the multiple battery cells CL1-CLN. To protect the battery pack 10 from abnormalities (including degradation and / or failure) caused by a rise in temperature, it is desirable to control the airflow of the fan 50 using the internal temperature of each battery cell CL.

[0042] Here, the internal temperature of the battery cell CL depends on the amount of heat generated in the battery cell CL. The amount of heat generated in the battery cell CL (amount of Joule heat generated) is the product of the square of the current I and the internal resistance R (= I 2 This is determined by (×R). In other words, as the internal resistance R increases, the amount of heat generated increases, and the internal temperature of the battery cell CL rises.

[0043] In the example shown in Figure 1, the current I flowing through battery cells CL1 to CLN is common, so the amount of heat generated in battery cell CL, which has a relatively large internal resistance R among the battery cells CL1 to CLN, is relatively large, and as a result, the internal temperature of battery cell CL becomes relatively high. In order to properly protect the battery pack 10 from overheating, it is desirable to control the airflow of fan 50 using the internal temperature of battery cell CL.

[0044] Since the amount of heat generated by a battery cell CL can be estimated from its internal resistance R, in this embodiment, the ECU 60 controls the airflow rate (rotation speed of the fan 50) of the fan 50 based on the calculated internal resistances R1 to RN of the battery cells CL1 to CLN. Specifically, at predetermined intervals, the ECU 60 calculates the internal resistances R1 to RN of the battery cells CL1 to CLN using the calculation method described above, and compares the calculated internal resistances R1 to RN with a threshold Rth. This threshold Rth corresponds to a determination threshold for determining the deterioration of the battery cell CL. If the internal resistance R of the battery cell CL exceeds the threshold Rth, the ECU 60 determines that the battery cell CL is deteriorated. If the internal resistance R of the battery cell CL is less than the threshold Rth, the ECU 60 determines that the battery cell CL is not deteriorated.

[0045] Furthermore, if the internal resistance R of any of the battery cells CL1 to CLN exceeds the threshold Rth, the ECU60 increases the airflow of the fan 50 compared to when the internal resistance R of all battery cells CL is below the threshold Rth.

[0046] Specifically, the ECU 60 normally determines the target airflow of the fan 50 according to the vehicle speed S detected by the vehicle speed sensor 45. The memory 64 of the ECU 60 stores a map that defines the relationship between the vehicle speed S and the target airflow of the fan 50. Figure 4 shows an example of this map. In Figure 4, the horizontal axis represents the vehicle speed (km / h) of the electric vehicle 100, and the vertical axis represents the target airflow (m³) of the fan 50. 3 This represents / h).

[0047] This map has multiple types (e.g., six types) of graphs showing the relationship between vehicle speed and the target air volume of the fan 50. These six types of graphs respectively correspond to modes 1 to 6, which are the operating modes of the fan 50. As shown in FIG. 4, the relationships between vehicle speed and the target air volume of the fan 50 in modes 1 to 6 are different from each other. Specifically, in modes 1 to 5, the target air volume is set such that as the vehicle speed increases, the air volume increases. On the other hand, in mode 6, regardless of the vehicle speed, the target air volume is fixed at the maximum air volume that the fan 50 can deliver. Also, at the same vehicle speed, the target air volume in mode 1 is the smallest, and the target air volume in mode 6 is the largest. And by switching in order from mode 1 to mode 2, mode 3, ··· mode 6, the target air volume gradually increases.

[0048] The operating mode of the fan 50 is switched based on the external temperature of at least one battery cell CL detected by the temperature sensors 231 to 23M. FIG. 4 shows the switching temperatures for switching the operating mode of the fan 50. For each mode, a switching temperature serving as a determination criterion for determining whether to switch to that mode is set. Among the switching temperatures t0 to t5 for modes 1 to 6, the relationship t0 < t1 < t2 < t3 < t4 < t5 holds.

[0049] When the detected temperatures of the temperature sensors 231 to 23M are at or below the switching temperature t0 °C of mode 1, the ECU 20 switches the operating mode of the fan 50 to mode 1. And during the execution of mode 1, when the detected temperatures of the temperature sensors 231 to 23M reach the switching temperature t1 °C of mode 2, the ECU 60 switches the operating mode of the fan 50 from mode 1 to mode 2. By switching from mode 1 to mode 2, the target air volume of the fan 50 for the same vehicle speed increases.

[0050] During the execution of mode 2, when the detected temperatures of the temperature sensors 231 to 23M reach the switching temperature t2 °C of mode 3, the ECU 60 switches the operating mode of the fan 50 from mode 2 to mode 3. By switching from mode 2 to mode 3, the target air volume of the fan 50 for the same vehicle speed further increases.

[0051] In this way, the ECU 60 switches the operating mode of the fan 50 based on the external temperature of at least one battery cell CL detected by temperature sensors 231-23M. Then, in each operating mode, the ECU 60 refers to the corresponding graph and determines the target airflow of the fan 50 from the current vehicle speed S of the electric vehicle 100. The ECU 60 controls the rotational speed of the fan 50 so that the airflow of the fan 50 matches the target airflow.

[0052] In the airflow control described above, if the internal resistance R of any of the battery cells CL1 to CLN exceeds the threshold Rth, the ECU 60 performs a process to increase the target airflow of the fan 50 relative to the current vehicle speed S. Specifically, the ECU 60 performs a process to change the graph showing the relationship between vehicle speed and the target airflow of the fan 50 in each mode, as shown in the map in Figure 4.

[0053] Figure 5 is a diagram illustrating the processes performed by the ECU 60. Figure 5 shows a graph extracted from the map shown in Figure 4 that corresponds to Mode 1. In Figure 5, the solid line represents the relationship between vehicle speed and the target airflow of fan 50 under normal conditions (when the internal resistance R of all battery cells CL is less than the threshold Rth). This graph is the same as the graph corresponding to Mode 1 shown in Figure 4. The dashed line represents the relationship between vehicle speed and the target airflow of fan 50 when the internal resistance R of any of the battery cells CL1 to CLN exceeds the threshold Rth.

[0054] As shown in Figure 5, if the internal resistance R of any of the battery cells CL1 to CLN exceeds the threshold Rth, the target airflow is changed so that it is larger than the target airflow for the same vehicle speed compared to normal conditions. The size of the arrows in the figure represents the increase in target airflow at each vehicle speed. The increase in target airflow at each vehicle speed may be the same or may differ for each vehicle speed. For example, the target airflow at each vehicle speed may be increased at a constant rate, as long as the target airflow does not exceed the maximum airflow of the fan 50.

[0055] The ECU60 modifies the target airflow for the graphs corresponding to modes 2 through 5, similar to the graph corresponding to mode 1, so that the airflow for the same vehicle speed increases. Alternatively, the configuration may be such that the target airflow for the graph corresponding to at least one of modes 1 through 6 is modified.

[0056] <Processing Flow> Figure 6 is a flowchart showing the processing procedure for controlling the airflow of the fan 50 according to this embodiment. This flowchart is executed each time a predetermined condition is met (for example, at each control cycle). Each step is implemented by software processing by the ECU 60, but may also be implemented by hardware (electrical circuits) located within the ECU 60. Hereinafter, each step will be abbreviated as S.

[0057] In S01, the ECU 60 acquires voltages V1 to VN from voltage sensors 211 to 211N and current I from current sensor 22 for a predetermined period.

[0058] In S02, the ECU60 calculates the internal resistances R1 to RN based on the voltages V1 to VN and current I obtained in S1. In S2, the calculation methods described in Figures 2 and 3 can be used.

[0059] In S03, the ECU60 compares the internal resistances R1 to RN with the threshold Rth. If all of the internal resistances R1 to RN are greater than or equal to the threshold Rth (resulting in a YES judgment in S03), the ECU60 determines that none of the battery cells CL1 to CLN have deteriorated.

[0060] On the other hand, if any of the internal resistances R1 to RN is less than the threshold Rth (when NO is determined in S03), the ECU 60 determines that any of the battery cells CL1 to CLN are degraded. In this case, in S04, the ECU 60 changes the relationship between vehicle speed and target airflow in at least one of the operating modes of the fan 50. In S04, as shown in Figure 5, the target airflow is changed in the graph corresponding to at least one mode so that it is larger for the same vehicle speed compared to the normal state shown in Figure 4. Note that if it is determined that all of the battery cells CL1 to CLN are not degraded, the process in S04 is not performed.

[0061] In S05, the ECU60 obtains temperatures T1 to TM from temperature sensors 231 to 23M.

[0062] In S06, the ECU60 determines the operating mode of the fan 50 from temperatures T1 to TM by referring to the switching temperatures for each mode shown in the map in Figure 4.

[0063] In S07, the ECU 60 obtains the vehicle speed S of the electric vehicle 100 from the vehicle speed sensor 45.

[0064] In S08, the ECU 60 determines the target airflow for fan 50 from the current vehicle speed S by referring to a graph showing the relationship between vehicle speed and target airflow in the corresponding mode, as shown in the map in Figure 4 or the modified map.

[0065] In S09, the ECU 60 controls the rotational speed of fan 50 so that the airflow of fan 50 matches the target airflow.

[0066] As explained above, if the ECU 60 determines that any of the battery cells CL1 to CLN is degraded based on the internal resistances R1 to RN of the battery cells CL1 to CLN, it increases the target airflow of the fan 50 relative to the current vehicle speed S. This allows the cooling capacity of the fan 50 to be increased in response to the increased heat generation in the degraded battery cell CL. Therefore, it becomes possible to properly protect the battery pack 10 from overheating.

[0067] Furthermore, if it is determined that all battery cells CL are not degraded, the ECU 60 does not perform the process of increasing the target airflow as described above, and instead determines the target airflow of the fan 50 according to the external temperature of at least one battery cell CL and the current vehicle speed S. Therefore, it is possible to prevent the cooling capacity of the fan 50 from becoming excessive for the amount of heat generated by each battery cell CL.

[0068] Furthermore, if the rotational speed of the fan 50 is increased to increase the airflow of the fan 50, the generation of noise due to the operation of the fan 50 and the increase in the power consumption of the fan 50 become problems. According to this embodiment, the airflow of the fan 50 can be controlled to an appropriate airflow according to the amount of heat generated by each battery cell CL that makes up the battery pack 10. Therefore, it is possible to prevent overheating of the battery pack 10 while reducing the generation of unnecessary noise and power consumption.

[0069] (modified version) In the embodiment described above, as a process to increase the target airflow of the fan 50 relative to the current vehicle speed S, a process of changing the graph showing the relationship between the vehicle speed and the target airflow of the fan 50 in at least one of modes 1 to 6 was described. The ECU 60 may, instead of this process, or in addition to this process, perform a process to change the switching temperature for switching the operating mode of the fan 50.

[0070] Figure 7 illustrates a modified version of the process performed by the ECU 60. Figure 7 shows the same map as shown in Figure 4. Figure 7 also shows the switching temperature for switching the operating mode of the fan 50.

[0071] In this modification example, when the internal resistance R of any one of the battery cells CL1 to CLN exceeds the threshold value Rth, the ECU 60 executes a process of reducing the switching temperature for at least one of the modes 1 to 6. In the example of FIG. 7, the switching temperature of mode 2 is changed from t1 ° C to t1 - a1 ° C. Also, the switching temperature of mode 3 is changed from t2 ° C to t2 - a2 ° C. Note that the decrease amount a1 ° C of the switching temperature can be appropriately set within a range that satisfies t0 < t1 - a1. The decrease amount a2 ° C of the switching temperature can be appropriately set within a range that satisfies t1 - a1 < t2 - a2.

[0072] According to the process shown in FIG. 7, when the internal resistance R of any one of the battery cells CL1 to CLN exceeds the threshold value Rth, during the execution of mode 1, in response to the detected temperature of the temperature sensors 231 to 23M reaching the switching temperature t1 - a1 ° C of mode 2, the ECU 60 switches the operation mode of the fan 50 from mode 1 to mode 2. That is, the operation mode of the fan 50 is switched from mode 1 to mode 2 at a timing earlier than in the normal state (when the internal resistance R of all the battery cells CL is less than the threshold value Rth). And by being switched from mode 1 to mode 2, the target air volume of the fan 50 for the same vehicle speed increases.

[0073] Also, during the execution of mode 2, in response to the detected temperature of the temperature sensors 231 to 23M reaching the switching temperature t2 - a2 ° C of mode 2, the ECU 60 switches the operation mode of the fan 50 from mode 2 to mode 3. That is, the operation mode of the fan 50 is switched from mode 2 to mode 3 at a timing earlier than in the normal state (when the internal resistance R of all the battery cells CL is less than the threshold value Rth). And by being switched from mode 2 to mode 3, the target air volume of the fan 50 for the same vehicle speed further increases.

[0074] <Processing Flow> Figure 8 is a flowchart showing the processing procedure for controlling the airflow of fan 50 according to this modified example. The flowchart in Figure 8 differs from the flowchart in Figure 6 in that S04 is replaced with S04A.

[0075] In this modified example, if any of the internal resistances R1 to RN is below the threshold Rth (when NO is determined in S03), the ECU 60 lowers the switching temperature in at least one of the operating modes of the fan 50 in S04A. In S04A, as shown in Figure 7, the graph showing the relationship between vehicle speed and the target airflow of the fan 50 in each mode remains unchanged, but the switching temperature for switching modes is changed. Note that if it is determined that all battery cells CL1 to CLN are not degraded, the process in S04A is not performed.

[0076] In this modified example, if any of the battery cells CL1 to CLN is determined to be degraded, the operating mode of the fan 50 is switched at an earlier timing in response to the rise in temperature detected by temperature sensors 231 to 23M, compared to the case where all battery cells CL are determined to be undegraded. This switching of the operating mode increases the airflow of the fan 50 relative to the current vehicle speed S, thereby increasing the cooling capacity of the fan 50 in response to the increased heat generation in the degraded battery cell CL. Therefore, the battery pack 10 can be adequately protected from overheating.

[0077] Furthermore, if it is determined that all battery cells CL are not degraded, the process to lower the switching temperature described above is not performed, and the target airflow of the fan 50 is determined according to the external temperature of at least one battery cell CL and the current vehicle speed S. Therefore, it is possible to prevent the cooling capacity of the fan 50 from becoming excessive relative to the heat generated by each battery cell CL.

[0078] Therefore, in this modified version as well, it is possible to prevent overheating of the battery pack 10 while reducing unnecessary noise and power consumption.

[0079] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0080] 10 battery packs, 20 monitoring units, 211-21N voltage sensors, 22 current sensors, 231-23M temperature sensors, 30 PCUs, 40 motor generators, 45 vehicle speed sensors, 50 fans, 60 ECUs, 62 processors, 64 memory, 100 electric vehicles, CL1-CLN battery cells.

Claims

1. A battery pack having multiple battery cells, A voltage sensor that detects the voltage of each battery cell, A current sensor that detects the current flowing through each of the aforementioned battery cells, A fan that cools the battery pack by blowing air onto it, The system includes a control device that controls the airflow of the fan to match a target airflow, The control device is Based on the detected values ​​of the voltage sensor and the current sensor, the internal resistance of each battery cell is calculated. A battery system that increases the target airflow rate when the internal resistance of any of the plurality of battery cells exceeds a threshold, compared to the case where the internal resistance of all of the plurality of battery cells is below the threshold.

2. The aforementioned battery pack is configured to store power for driving an electric vehicle, A temperature sensor for detecting the external temperature of at least one of the plurality of battery cells, The system further includes a vehicle speed sensor for detecting the vehicle speed of the electric vehicle, The control device is If the internal resistance of all of the aforementioned battery cells is below the threshold, the target airflow is determined based on the detected values ​​of the temperature sensor and the vehicle speed sensor. The battery system according to claim 1, wherein if the internal resistance of any of the plurality of battery cells exceeds the threshold, the target airflow is increased compared to the target airflow determined based on the detection values ​​of the temperature sensor and the vehicle speed sensor.

3. The fan has multiple modes in which the relationship between the vehicle speed of the electric vehicle and the target airflow is different from each other, and is configured to allow switching between the multiple operating modes. The battery system according to claim 2, wherein the control device increases the target airflow for the same vehicle speed in at least one of the multiple modes compared to the case where the internal resistance of any of the multiple battery cells exceeds the threshold, when the internal resistance of any of the multiple battery cells exceeds the threshold.

4. The fan has multiple modes in which the relationship between the vehicle speed of the electric vehicle and the target airflow is different from each other, and is configured to allow switching between the multiple operating modes. The control device is configured to switch the operating mode of the fan from a first mode to a second mode in which the target airflow is greater for the same vehicle speed, in response to the temperature sensor's detection value reaching the switching temperature. The battery system according to claim 2, wherein the control device lowers the switching temperature when the internal resistance of any of the plurality of battery cells exceeds the threshold, compared to when the internal resistance of all of the plurality of battery cells is below the threshold.

5. A cooling method for cooling a battery pack having multiple battery cells, The aforementioned battery pack stores power for driving an electric vehicle, and the aforementioned battery pack contains, A voltage sensor that detects the voltage of each battery cell, A current sensor that detects the current flowing through each of the aforementioned battery cells, A fan that cools the battery pack by blowing air onto it, A temperature sensor is provided to detect the external temperature of at least one of the plurality of battery cells. The electric vehicle is equipped with a vehicle speed sensor for detecting the vehicle speed of the electric vehicle. The steps include calculating the internal resistance of each battery cell based on the detected values ​​of the voltage sensor and the current sensor, The steps include determining the target airflow of the fan based on the detected values ​​of the temperature sensor and the vehicle speed sensor, provided that the internal resistance of all of the plurality of battery cells is below a threshold, If the internal resistance of any of the plurality of battery cells exceeds the threshold, the step of increasing the target airflow compared to the target airflow determined based on the detection values ​​of the temperature sensor and the vehicle speed sensor, A method for cooling a battery pack, comprising the step of controlling the airflow of the fan to match the target airflow.

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