Secondary battery degradation estimation method and secondary battery degradation estimation device

Abstract

The present invention provides a secondary battery degradation estimation method and a secondary battery degradation estimation device that, in estimating a degradation state of a secondary battery, can estimate the degradation state of the secondary battery at low cost while maintaining estimation accuracy by enabling selection of when the degradation estimation is to be performed, taking into account a period during which a vehicle is left unattended and a state of temperature, which exerts significant influence on secondary battery degradation. The secondary battery degradation estimation method comprises: a step for comparing an unattended period of a vehicle equipped with a secondary battery subject to degradation estimation to a prescribed time set in advance (ST1); a step for selecting a timestep interval indicating when to estimate the degradation state within the unattended period (ST2-4); and a step for estimating the degradation state of the secondary battery according to the selected timestep interval (ST5-8).

Description

Method for estimating deterioration of secondary battery and apparatus for estimating deterioration of secondary battery

[0001] Embodiments of the present invention relate to a method for estimating deterioration of a secondary battery and an apparatus for estimating deterioration of a secondary battery.

[0002] Patent Document 1 discloses an invention related to an SOC estimation device that changes the calculation period of SOC using the charge-discharge cycle of a battery mounted on a vehicle in order to improve the estimation accuracy of the state of charge (SOC) of the battery.

[0003] According to the invention, the shorter the charge-discharge cycle of the battery, the shorter the calculation cycle of SOC can be made. Therefore, considering the general characteristics of a battery with high responsiveness in the low-frequency range, SOC calculation can be executed, and it is said that the estimation accuracy of SOC can be improved.

[0004] Japanese Unexamined Patent Application Publication No. 2006-074852

[0005] However, in the invention disclosed in Patent Document 1 described above, the calculation period is determined based on the charge-discharge cycle of the battery. Therefore, for example, when the ignition is turned off and the vehicle is left unattended for a long time, the charge-discharge cycle of the battery mounted on the vehicle becomes long. In such a case, the following problems can be considered.

[0006] First, since there is no charge-discharge, the calculation period is determined to be a long period. And once it is determined to be a long period, the period is fixed. In this case, there is no problem when the storage period is long. On the contrary, when the storage period becomes short, since the calculation period is long, there is a possibility that the calculation accuracy deteriorates.

[0007] Second, if the calculation period is determined to be a short period in order to avoid the above-mentioned disadvantages, although it is good when the storage period is short, when the storage period is long, the calculation process will be frequently executed in a short period. Therefore, the calculation ability will be used more than necessary, and the calculation cost may become enormous.

[0008] The present invention was made to solve the above problems, and the object of the present invention is to provide a secondary battery degradation estimation method and a secondary battery degradation estimation device that can estimate the degradation state of a secondary battery at low cost while maintaining estimation accuracy by making it possible to select the timing of degradation estimation by taking into account the period of time the vehicle has been left unattended and the temperature state which has a major effect on the degradation of the secondary battery when estimating the degradation state of the secondary battery.

[0009] The method for estimating the degradation of a secondary battery in this embodiment includes the steps of: comparing the period of time a vehicle equipped with the secondary battery to be degraded is left idle with a predetermined time; selecting a time step width that indicates the timing for estimating the degradation state within the idle period; and estimating the degradation state of the secondary battery according to the selected time step width.

[0010] Furthermore, the secondary battery degradation estimation device in the embodiment includes an information acquisition unit that acquires information about a vehicle equipped with a secondary battery to be degraded; a determination unit that compares the vehicle's idle period with a predetermined time and selects a time step width indicating the timing for estimating the degradation state within the idle period; and a degradation state determination unit that estimates the degradation state of the secondary battery according to the selected time step width.

[0011] By employing such a secondary battery degradation estimation method and secondary battery degradation estimation device, the present invention makes it possible to select the timing of degradation estimation by considering the period of time the vehicle has been left unused and the temperature conditions that greatly affect secondary battery degradation, thereby enabling the estimation of the secondary battery degradation state at low cost while maintaining estimation accuracy.

[0012] This is a block diagram showing the overall configuration of a degradation estimation system including a secondary battery degradation estimation device according to an embodiment of the present invention. This is a block diagram showing the internal configuration of a secondary battery degradation estimation device according to an embodiment of the present invention. This is an explanatory diagram for explaining the relationship between the temperature of the secondary battery, the vehicle's idle period, and the time step width, which is the timing for executing the degradation estimation process, in the secondary battery degradation estimation process according to an embodiment of the present invention. This is an explanatory diagram for explaining the relationship between the temperature of the secondary battery, the vehicle's idle period, and the time step width, which is the timing for executing the degradation estimation process, in the secondary battery degradation estimation process according to an embodiment of the present invention. This is an explanatory diagram for explaining the relationship between the temperature of the secondary battery, the vehicle's idle period, and the time step width, which is the timing for executing the degradation estimation process, in the secondary battery degradation estimation process according to an embodiment of the present invention. This is a flowchart showing the flow of the secondary battery degradation estimation process according to an embodiment of the present invention.

[0013] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. Furthermore, the embodiments of the present invention shown below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the structure, arrangement, etc., of the components described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0014] Figure 1 is a block diagram showing the overall configuration of a degradation estimation system S, including a secondary battery degradation estimation device 1, according to an embodiment of the present invention. The secondary battery degradation estimation system S is provided with a degradation estimation device 1 connected to a communication network N.

[0015] Furthermore, multiple vehicles 2A~ (only vehicles 2A to 2C are shown in Figure 1) are connected to the communication network N, and information about multiple vehicles is transmitted to the deterioration estimation device 1 via the communication network N.

[0016] Furthermore, a vehicle V (hereinafter referred to as "target vehicle V") equipped with a secondary battery whose degradation state is to be estimated is also connected to the communication network N, and information regarding the target vehicle V is transmitted to the degradation estimation device 1 via the communication network N.

[0017] Here, for convenience, the vehicle equipped with the secondary battery whose degradation state is to be estimated is referred to as "Target Vehicle V" to distinguish it from multiple vehicles 2. However, Target Vehicle V is also included in the multiple vehicles 2. That is, for example, if "Vehicle 2B" shown in Figure 1 is designated as "Target Vehicle V," then Target Vehicle V shown in Figure 1 is included in the multiple vehicles 2, and information about these multiple vehicles 2 is used to estimate the degradation state of the secondary battery installed in Vehicle 2B, which is Target Vehicle V.

[0018] Therefore, in the following explanation, when it is necessary to specify vehicle 2, it will be referred to as "Target Vehicle V." On the other hand, when the explanation relates to the entire vehicle, including Target Vehicle V, it will be referred to as "Vehicle 2" as appropriate.

[0019] The degradation estimation device 1 is used to estimate the degradation state of the secondary battery installed in the target vehicle V. While there are various types of "secondary batteries," a lithium-ion battery can be used as an example here.

[0020] Furthermore, the degradation estimation device 1 in the embodiment of the present invention can perform a process to appropriately change the timing of the degradation estimation process, especially when the target vehicle V has been left unattended for a long period of time. By making the timing of the degradation estimation process variable in this way, the degradation state of the secondary battery of the target vehicle V can be estimated at low cost while maintaining the accuracy of the degradation estimation process. The functions of the degradation estimation device 1 will be described below with reference to the drawings as appropriate.

[0021] Figure 2 is a block diagram showing the internal configuration of the secondary battery degradation estimation device 1 according to an embodiment of the present invention. As shown in Figure 2, the degradation estimation device 1 comprises an information acquisition unit 11, a determination unit 12, a degradation state determination unit 13, a calculation unit 14, and a storage unit 15.

[0022] Note that Figure 2 only shows the configuration necessary for the method of estimating the deterioration state in the embodiment of the present invention. Therefore, in addition to the parts shown in Figure 2, configurations for performing functions other than those performed by the parts shown in Figure 2 may also be provided.

[0023] Furthermore, the functions of the degradation estimation device 1 described below are realized by a determination unit 12 and a degradation state determination unit 13, which consist of a processor, executing a computer program stored in a memory unit (not shown). The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

[0024] Furthermore, the degradation estimation device 1 may be formed by dedicated hardware for performing the information processing described below. For example, the degradation estimation device 1 may include functional logic circuits set in a general-purpose semiconductor integrated circuit. The degradation estimation device 1 may also have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0025] The information acquisition unit 11 acquires various information regarding the secondary battery installed in the target vehicle V via the communication network N, indicating the vehicle's usage status or non-use status. This information includes, for example, information indicating the period of time the target vehicle V has been left unused, as well as information used to estimate the deterioration state of the secondary battery installed in the target vehicle V.

[0026] Here, "idle period" refers to the period from when the user of the target vehicle V turns the ignition OFF until they turn the ignition ON again. The target vehicle V has information about the time the ignition was ON and the time it was OFF. Therefore, by acquiring this information, the information acquisition unit 11 can determine the idle period of the target vehicle V.

[0027] The determination unit 12 performs various determinations to determine the timing for the degradation estimation device 1 to estimate the degradation state of the secondary battery installed in the target vehicle V. Specifically, in the degradation estimation process in the embodiment of the present invention, based on two types of information, the period of time the target vehicle V has been left unused and the temperature of the secondary battery, it is selected whether to perform the degradation state estimation process with a long timing interval or with a short timing interval.

[0028] In the following, the timing for estimating the degradation state of the secondary battery described above will be referred to as the "time step." For example, the process of estimating the degradation state of the secondary battery is performed as needed, even while vehicle 2 is in motion. The interval at which this estimation process is performed can be set arbitrarily, but for example, it is every 0.01 seconds. The "time step" refers to the interval (timing) at which the degradation state estimation process is performed.

[0029] As mentioned above, if the target vehicle V has been left unattended for a long period of time, performing estimation processing with short time increments during that period will unnecessarily require computing power for the estimation process. Therefore, the computational cost will be high.

[0030] On the other hand, if we set a long time interval to account for long periods of vehicle abandonment, then the deterioration state estimation process will not be performed at the appropriate time if the abandonment period is short. This could lead to a decrease in the accuracy of the estimation and is therefore inappropriate.

[0031] Therefore, in the embodiment of the present invention, a process is performed to determine the time step size for estimating the degradation state of the secondary battery based on the period of time the target vehicle V has been left unused and the temperature of the secondary battery installed in the target vehicle V. This point will be explained below with reference to Figure 3.

[0032] Figure 3 is an explanatory diagram illustrating the relationship between the temperature of the secondary battery, the period of time the vehicle 2 is left unattended, and the time step width, which is the timing for executing the degradation estimation process, in an embodiment of the present invention.

[0033] In the explanatory diagram of Figure 3, the vertical axis represents the temperature of the secondary battery and other components installed in vehicle 2 (target vehicle V). Therefore, the temperature of the secondary battery touching the vertical axis represents the temperature when the target vehicle V is stopped. This temperature at the time of stopping can be obtained by various methods. For example, a temperature sensor could store the temperature measured when the vehicle is stopped, or it could be estimated using various information that the target vehicle V can acquire, for example, using a simulation model.

[0034] In the explanatory diagram of Figure 3, the horizontal axis represents time, specifically the period (in hours) that the target vehicle V was left idle. Therefore, in the explanatory diagram of Figure 3, the origin represents the point in time when the user turned the ignition of the target vehicle V OFF, and the point indicated by the vertical dotted line on the far right represents the point in time when the user turned the ignition of the target vehicle V ON.

[0035] In the explanatory diagram of Figure 3, two types of time step sizes are shown: the time step size indicated as "tL" and the time step size indicated as "tS". Of these, the time step size "tL" will be referred to as "the first time step size tL" from now on. Similarly, the time step size "tS" will be referred to as "the second time step size tS" from now on.

[0036] As is clear from the explanatory diagram in Figure 3, the first time step width tL is set to be longer than the second time step width tS. Furthermore, the length of the second time step width tS is set to be longer than the time step width of the deterioration state estimation process performed when the target vehicle V is in use (hereinafter referred to as the "time step width during use" as appropriate). In other words, the relationship between these three types of time step widths is: time step width during use < second time step width tS < first time step width tL.

[0037] In the explanatory diagram in Figure 3, it is shown that, for a period of time immediately after the ignition is turned OFF and the target vehicle V is left idle, the process of estimating the degradation state of the secondary battery is executed multiple times at the second time step interval tS, as indicated by the interval between the two dotted vertical lines labeled "tS". In other words, the process of estimating the degradation state of the secondary battery installed in the target vehicle V is executed at the timings indicated by the dotted vertical lines.

[0038] In contrast, it has been shown that, partway through the process, the estimation of the deterioration state is performed using the first time step width tL instead of the second time step width tS. As mentioned above, the first time step width tL is longer than the second time step width tS.

[0039] In the explanatory diagram shown in Figure 3, in addition to the dotted vertical lines indicating the time intervals, a solid line is shown parallel to the horizontal axis representing time. This represents the ambient temperature at the location where the vehicle V is left unattended. For the sake of explanation, it is assumed that the ambient temperature remains constant throughout the entire period that the vehicle V is left unattended.

[0040] The graph shows a high temperature when the ignition is turned OFF, and a dashed line indicating a gradual decrease in temperature over time. This dashed line represents the temperature change of the secondary battery installed in vehicle 2 (target vehicle V).

[0041] The temperature of the secondary battery has a significant impact on its degradation. In other words, even if the ambient temperature is the same, the higher the temperature of the secondary battery when vehicle 2 starts to come to a stop, the greater the degradation rate (Ah) per unit of time.

[0042] Furthermore, the secondary battery installed in the target vehicle V undergoes frequent charging and discharging during operation, resulting in a high temperature for the battery itself. Consequently, when the target vehicle V is stopped and left idle, the temperature of the secondary battery remains high at the start of this period. However, the high temperature does not persist indefinitely, as charging and discharging do not occur while the target vehicle V is idle, and the temperature gradually decreases over time.

[0043] However, even if the temperature of the secondary battery gradually decreases, this does not mean that the temperature decreases independently of the conditions of the location where the vehicle V is left. In other words, the temperature of the secondary battery will never be lower than the ambient temperature, and will gradually become more even. Ultimately, the temperature of the secondary battery will be equivalent to the ambient temperature.

[0044] Therefore, in the explanatory diagram shown in FIG. 3, the dashed line indicating the temperature of the secondary battery gradually decreases and intersects with the solid line indicating the outside air temperature. However, after that, the temperature of the secondary battery does not continue to decrease and becomes equivalent to the outside air temperature, so the temperature of the secondary battery is shown linearly. The point at which the temperature of the secondary battery becomes the outside air temperature is appropriately referred to as "change point C".

[0045] It is said that the time when the temperature of the secondary battery becomes equivalent to the outside air temperature is approximately 8 to 10 hours after ignition is turned off from experiments or the like. For example, regarding how to set the temperature equivalent to the outside air temperature, it may be set using a simulation model, or may be obtained through experiments.

[0046] More specifically, it is possible to set the temperature of the secondary battery to "outside air temperature + 5°C" or "outside air temperature + 5% of the outside air temperature". The time from when ignition is turned off until the temperature of the secondary battery becomes equivalent to the outside air temperature is hereinafter appropriately referred to as the "predetermined time".

[0047] When the determination unit 12 determines that the temperature of the secondary battery has become equivalent to the outside air temperature, that is, in the explanatory diagram of FIG. 3, at the change point C where the dashed line indicating the temperature of the secondary battery intersects the solid line indicating the outside air temperature, the selected time step width switches from the second time step width tS to the first time step width tL.

[0048] Thus, although the second time step width tS has been selected as the timing for estimating the deterioration state of the secondary battery until now, the first time step width tL is selected because it can be considered that even if there is a temperature difference between the temperature of the secondary battery and the outside air temperature, the influence on the deterioration amount of the secondary battery is small.

[0049] In the explanatory diagram shown in Figure 3, the example given is that when the ignition is turned OFF, the temperature of the secondary battery is higher than the ambient temperature. However, the opposite is also possible: the temperature of the secondary battery may be lower than the ambient temperature. For example, on a hot day, if vehicle 2 is parked in a place not significantly affected by ambient temperature, such as an underground parking lot, and then driven to a nearby errand and parked there, the temperature of the secondary battery will gradually rise and eventually reach a temperature equivalent to the ambient temperature.

[0050] After a predetermined time has elapsed, it can be estimated that the temperature of the secondary battery will be equivalent to the ambient temperature, regardless of the temperature at the time the ignition was turned off. Therefore, when estimating the degradation state of the secondary battery after change point C, the temperature of the secondary battery is treated as equivalent to the ambient temperature.

[0051] When the determination unit 12 performs the process of estimating the deterioration state of the secondary battery, it compares the period of time the target vehicle V has been left idle with a predetermined time. If it determines that the period of time it has been left idle is longer than the predetermined time, it can determine that the temperature of the secondary battery installed in the target vehicle V, which is the subject of the deterioration state estimation process, has already reached a temperature equivalent to the ambient temperature.

[0052] In this case, since no charging or discharging is occurring, there is no need to frequently perform the degradation state estimation process; it is sufficient to perform the estimation process at a frequency that maintains the accuracy of the estimation. Therefore, in this case, the first time step width tL is selected.

[0053] The degradation state determination unit 13 determines the degradation state of the secondary battery installed in the target vehicle V based on the selected first time step width tL. Here, a known method is used for determining the degradation state of the secondary battery by the degradation state determination unit 13.

[0054] The deterioration state estimation process by the deterioration state determination unit 13 is initiated, for example, after the period of inactivity of the target vehicle V begins. The deterioration state estimation process by the deterioration state determination unit 13 is executed each time the period of inactivity of the target vehicle V occurs.

[0055] On the other hand, if the determination unit 12 determines that the period of inactivity is less than a predetermined time, it can be determined that the temperature of the secondary battery has not yet reached the ambient temperature. In such cases, it is necessary to determine whether to select the first time step width tL or the second time step width tS as the timing for estimating the state of deterioration.

[0056] In order for the final determination unit 12 to perform the determination, the calculation unit 14 calculates one of the pieces of information necessary for that determination. Specifically, the calculation unit 14 calculates the absolute value of the difference between the temperature of the secondary battery and the ambient temperature.

[0057] As mentioned above, if there is a significant temperature difference between the secondary battery temperature and the ambient temperature, it can be determined that the secondary battery temperature does not correspond to the ambient temperature. In this case, when estimating the degradation state of the secondary battery, it is more accurate to consider the temperature of the secondary battery itself rather than the ambient temperature, and to perform the degradation state estimation process at short intervals (time steps).

[0058] Therefore, the calculation unit 14 calculates the temperature difference between the temperature of the secondary battery and the ambient temperature. The reason for calculating the absolute value of the difference here is that, as mentioned above, it is possible that the temperature of the secondary battery may be lower than the ambient temperature.

[0059] The determination unit 12 compares the absolute value of the difference between the secondary battery temperature and the ambient temperature, calculated by the calculation unit 14, with a threshold value. If the determination unit 12 determines that the absolute value of the difference is greater than the threshold value, it can be estimated that the difference between the secondary battery temperature and the ambient temperature is large. In such cases, there is a high possibility that the secondary battery is deteriorating, so it is necessary to perform the deterioration state estimation process at a high frequency. Therefore, in this case, a second time step width tS is selected.

[0060] On the other hand, if the determination unit 12 determines that the absolute value of the difference between the temperature of the secondary battery and the ambient temperature is less than or equal to the threshold, it can be determined that the temperature of the secondary battery is equivalent to the ambient temperature. Therefore, in this case, the first time step width tL is selected as described above. The point at which the selection of the time step width changes from the second time step width tS to the first time step width tL is the change point C described above.

[0061] The threshold value used to compare the absolute difference between the secondary battery temperature and the ambient temperature can be set to any value. However, setting the threshold value too large may result in a discrepancy between the secondary battery temperature and the ambient temperature, potentially causing the secondary battery temperature to not correspond to the ambient temperature. Therefore, the threshold can be set to, for example, "0°C".

[0062] Furthermore, regardless of whether the first time step width tL or the second time step width tS is selected, the determination unit 12 determines whether the deterioration state estimation process has been executed the required number of times. For example, if the first time step width tL, which is set to once a month as the timing for the deterioration state estimation process, is selected, and the period during which the target vehicle V has been left unused is six months, then the deterioration state estimation process needs to be executed six times, once a month.

[0063] The determination unit 12 then determines whether the degradation state estimation process has been executed the required number of times by the degradation state determination unit 13. If it has been executed, the degradation state estimation process for the secondary battery installed in the target vehicle V is terminated. On the other hand, if the determination unit 12 determines that the degradation state estimation process has not been executed the required number of times, the degradation state estimation process continues to be executed until the required number of times is met.

[0064] As explained using the explanatory diagram in Figure 3, before the change point C, the difference between the secondary battery temperature and the ambient temperature is large. However, as the secondary battery temperature gradually adapts to the temperature of the location where the vehicle V is left, the difference between the secondary battery temperature and the ambient temperature gradually decreases, and eventually becomes equivalent to the ambient temperature. In other words, the temperature that affects the estimation process of the degradation state is the secondary battery temperature before the change point C, but after the change point C, it becomes the ambient temperature because the secondary battery temperature becomes equivalent to the ambient temperature.

[0065] Thus, as the period of time the target vehicle V is left unused progresses, the temperature of the secondary battery changes, and the degradation state estimation process is performed frequently, i.e., with the second time step width tS, until the point in time when the temperature of the secondary battery of the target vehicle V, which has entered the period of being left unused, becomes equivalent to the ambient temperature (change point C). After the passage of change point C, the timing of the selected degradation state estimation process changes from the second time step width tS to the first time step width tL.

[0066] In the degradation estimation device 1 according to the embodiment of the present invention, the degradation state of the secondary battery can be estimated at low cost while maintaining estimation accuracy by allowing the user to select a time step size while considering the period the vehicle has been left unused and the effect of the secondary battery temperature on the degradation state estimation process.

[0067] As described above, if the absolute value of the difference between the secondary battery temperature and the ambient temperature is greater than the threshold, the second time step size tS is selected, and if the absolute value of the difference is less than or equal to the threshold, the first time step size tL is selected. In the explanatory diagram shown in Figure 3, for the sake of explanation, it was assumed that the ambient temperature was constant, but the ambient temperature can change over time.

[0068] Therefore, taking this point into consideration, the method described below can also be considered for selecting the time step width. Figures 4 and 5 are explanatory diagrams illustrating the relationship between the temperature of the secondary battery, the vehicle's storage period, and the time step width, which is the timing for executing the degradation estimation process, in the secondary battery degradation estimation process according to an embodiment of the present invention.

[0069] First, let's explain using Figure 4. It is basically the same as Figure 3, with the vertical axis representing temperature and the horizontal axis representing time. The origin is the point when the user turns off the ignition of the target vehicle V, and the period of inactivity for the target vehicle V begins from this point.

[0070] Furthermore, the explanatory diagram in Figure 4 shows two types of ambient temperatures. The first ambient temperature T1 is the ambient temperature at the start of the storage period, and represents the temperature from the origin to a point in time after a certain period of time has elapsed (this point in time will be appropriately referred to as "time t0"). From this time t0 onward, the second ambient temperature T2 is shown, and the second ambient temperature T2 is higher than the first ambient temperature T1.

[0071] The reason why the first outside air temperature T1 and the second outside air temperature T2 are shown as being in different stages is that the outside air temperature information used in the degradation estimation device 1 is not real-time measured outside air temperature information, but rather information that represents the temperature averaged over a certain period. Therefore, here, at time t0, the transition from the first outside air temperature T1 to the second outside air temperature T2 is not shown as a gradual increase in outside air temperature, but rather as a stepwise increase in outside air temperature.

[0072] The temperature progression of the secondary battery in the target vehicle V is shown by a dashed curve, as illustrated in the explanatory diagram in Figure 3. The temperature is highest when the ignition is turned OFF, and gradually decreases over time. In Figure 3, assuming that the secondary battery temperature reaches the same temperature as the ambient temperature at the point where it intersects with the ambient temperature (change point C), the selection of the time step width changes from the second time step width tS to the first time step width tL.

[0073] In the explanatory diagram of Figure 4, the dashed line showing the temperature progression of the secondary battery appears to be interrupted midway. The point where it intersects with the first ambient temperature T1 is the change point C shown in Figure 3, which corresponds to time t0 in the explanatory diagram of Figure 4.

[0074] As described above, the ambient temperature information used in the degradation estimation device 1 is temperature information that has been averaged and kept constant over a certain period. However, the actual ambient temperature changes, for example, by gradually rising from early morning to daytime. Therefore, this change in ambient temperature is approximated, for example, by a linear approximation over a certain period.

[0075] The change in ambient temperature shown by the linear approximation is the temperature change T0 in the explanatory diagram of Figure 4. Looking at this temperature change T0, the temperature gradually rises from the moment the ignition is turned OFF, and finally reaches the second ambient temperature T2 at time t0. There is a point in this temperature change T0 where the dashed line showing the temperature progression of the secondary battery intersects. For convenience, this point will be referred to as the "change point C0" below.

[0076] When the ambient temperature and the temperature of the secondary battery match, from this point onward, i.e., from the change point C0 onward, the temperature of the secondary battery can be considered to be equivalent to the ambient temperature. Therefore, when performing the degradation state estimation process from this change point C0 onward, the ambient temperature information is used. However, as explained above, Figure 4 shows two types of ambient temperature information: the first ambient temperature T1 and the second ambient temperature T2.

[0077] In such cases, the degradation estimation device 1 in the embodiment of the present invention uses temperature information of a higher temperature, i.e., information of the second ambient temperature T2. The reason for using the information of the second ambient temperature T2 rather than the information of the first ambient temperature T1, which indicates a relatively lower temperature, is that higher temperatures lead to degradation of the secondary battery.

[0078] In other words, by using information on a second ambient temperature T2, which represents a relatively higher temperature, when estimating the degradation state of a secondary battery, it is possible to estimate the degradation state more strictly without underestimating it.

[0079] Furthermore, at this change point C0, the time step size is also changed; instead of the previously selected second time step size tS, the first time step size tL is selected from the point of change C0 onward. This allows for a reduction in computational cost while maintaining the accuracy of the degradation state estimation.

[0080] In the explanatory diagram shown in Figure 4, the case where the outside air temperature rises is used as an example, but the same approach is used to set the outside air temperature information used in the degradation state estimation process even when the outside air temperature falls. That is, as shown in Figure 5, the first outside air temperature T1 continues for a while from the time the ignition is turned OFF. Specifically, in the explanatory diagram of Figure 5, this is up to time t1.

[0081] The dashed line showing the temperature progression of the secondary battery, as shown in the explanatory diagrams in Figures 3 and 4, indicates a gradual decrease in temperature after the ignition is turned OFF. At the change point C (time t0), it intersects with the first ambient temperature T1. Therefore, from time t0 onward, the temperature of the secondary battery becomes equivalent to the first ambient temperature T1. In the explanatory diagram of Figure 5, the solid line shown between time t0 and time t1 illustrates this.

[0082] Then, from time t1, indicated by the dashed line in Figure 5, the ambient temperature drops further to the temperature shown here as the third ambient temperature T3. Once the temperature of the secondary battery reaches a temperature equivalent to the ambient temperature, its temperature changes in accordance with the change in ambient temperature. Therefore, if the ambient temperature drops even further, the temperature of the secondary battery may drop even more.

[0083] However, as mentioned above, the higher the temperature of the secondary battery, the more advanced the degradation. Therefore, if the temperature of the secondary battery, once it reaches a temperature equivalent to the ambient temperature, decreases further as the ambient temperature decreases, it is not appropriate to use the temperature of the secondary battery as equivalent to the ambient temperature and perform the degradation estimation process using, for example, the first ambient temperature T1 shown in the explanatory diagram of Figure 5.

[0084] Therefore, if the temperature of the secondary battery initially reaches a temperature equivalent to the ambient temperature, and then the ambient temperature decreases further, the ambient temperature information used in the degradation state estimation process will be the information indicating a higher ambient temperature. For example, in the explanatory diagram in Figure 5, the temperature of the secondary battery may fall to a temperature equivalent to the third ambient temperature T3 from the time t1 indicated by the dashed line, but the ambient temperature information used in the degradation state estimation process will be the information regarding the first ambient temperature T1.

[0085] In this case, the timing at which the first time step width tL is selected from the previously selected second time step width tS is at time t0 of the change point C. From time t0 onward, the deterioration state determination unit 13 performs the deterioration state estimation process using the first time step width tL.

[0086] The above explains the timing of switching the time step size based on the relationship between the secondary battery temperature and the ambient temperature. However, even if the degradation state estimation process is performed using the first time step size tL, it is possible that the ambient temperature may change significantly during that time.

[0087] In other words, if the vehicle V is left unused for a long period, such as six months (half a year), the seasons will change and the outside temperature will fluctuate significantly. For example, even if the vehicle is left unused in winter, if the period of storage is long, it is conceivable that the storage period may end in summer. Therefore, in such cases, it is not considered appropriate to perform the degradation state estimation process using only one piece of outside temperature information as the temperature of the secondary battery, which has reached a temperature equivalent to the outside temperature.

[0088] Therefore, anticipating such changes in ambient temperature, it is possible to pre-determine, for example, an "allowable ambient temperature change." As mentioned above, the end of the storage period is basically the point when the user turns on the ignition of the target vehicle V. Therefore, if the storage period is, for example, about one month, it is thought that the ambient temperature will not change significantly, and in such cases, the deterioration state estimation process is performed with one first time step width tL.

[0089] However, as mentioned above, if the change in ambient temperature is very large, performing the deterioration state estimation process using a single time step until the end of the storage period may actually decrease its accuracy. Therefore, for example, if the determination unit 12 determines that the change in ambient temperature exceeds the allowable change in ambient temperature, it performs a process to change the first time step tL to a finer time step.

[0090] Specifically, the waiting period, which was originally set to a single first time step width tL, is divided into two parts, for example, by setting the point at which the change in outside air temperature exceeds the allowable change in outside air temperature as the endpoint, and changing the outside air temperature information used in the first part and the outside air temperature information used in the second part.

[0091] By performing this process, it is possible to estimate the degradation state of the secondary battery based on appropriate ambient temperature information corresponding to changes in ambient temperature (seasonal changes). The "allowable ambient temperature change" can be obtained in advance, for example, through simulations or experiments.

[0092] The memory unit 15 stores various information, such as the time step size and threshold values ​​that are compared with the absolute difference between the secondary battery temperature and the ambient temperature. It also stores programs used by the degradation state determination unit 13 when performing estimation processing. Furthermore, it may also store information such as the allowable ambient temperature change and various ambient temperature values ​​mentioned above.

[0093] In the embodiment of the present invention, the degradation estimation device 1 is assumed to have a storage unit 15 inside it, but for example, a server provided in the communication network N may be used as the storage device.

[0094] [Operation] Next, the process of estimating the degradation state of a secondary battery by the degradation estimation device 1 described above will be explained using Figure 6. Figure 6 is a flowchart showing the flow of the secondary battery degradation estimation process according to an embodiment of the present invention.

[0095] The deterioration estimation device 1 first has an information acquisition unit 11 acquire information about the vehicle's storage period from the target vehicle V, and a determination unit 12 compares this with a predetermined time (ST1). Here, the "predetermined time" is the time from when the ignition is turned OFF until the temperature of the secondary battery reaches a temperature equivalent to the ambient temperature, as described above.

[0096] If the determination unit 12 determines that the vehicle has been left unattended for a period of time that is not less than a predetermined time (NO in ST1), a first time step width tL is selected. Then, the deterioration state determination unit 13 performs a deterioration state estimation process using the first time step width tL (ST4).

[0097] The determination unit 12 checks how many times the first time step width tL is included within the vehicle abandonment period and determines whether the deterioration state estimation process has been performed the required number of times (ST5). If the deterioration state determination unit 13 determines that the deterioration state estimation process has not been performed the required number of times (NO in ST5), the process returns to step ST4 and the deterioration state estimation process is performed again.

[0098] On the other hand, if the determination unit 12 determines that the deterioration state estimation process by the deterioration state determination unit 13 has been executed the required number of times (YES in ST5), the deterioration state estimation process is terminated.

[0099] If, when the estimation process is executed in the degradation estimation device 1, the determination unit 12 determines that the vehicle has been left unattended for less than a predetermined time (YES in ST1), the calculation unit 14 calculates the absolute value of the difference between the secondary battery temperature and the ambient temperature (ST2). The determination unit 12 compares the difference (absolute value) calculated by the calculation unit 14 with a threshold value that has been stored in advance in the storage unit 15 (ST3).

[0100] If the determination unit 12 determines, for example, that the difference (absolute value) is greater than the threshold value (NO in ST3), it is considered that there is a discrepancy between the temperature of the secondary battery and the ambient temperature, and that the temperature of the secondary battery is not equivalent to the ambient temperature. Therefore, the determination unit 12 selects a second time step width tS as the time step width. Then, the degradation state determination unit 13 performs a degradation state estimation process using the second time step width tS (ST6).

[0101] The determination unit 12 checks how many times the second time step width tS is included within the vehicle storage period and determines whether the deterioration state estimation process has been performed the required number of times (ST7). If the deterioration state determination unit 13 determines that the deterioration state estimation process has not been performed the required number of times (NO in ST7), the process returns to step ST2 and the calculation unit 14 calculates the absolute value of the difference between the secondary battery temperature and the ambient temperature.

[0102] If the determination unit 12 determines that the deterioration state estimation process by the deterioration state determination unit 13 has been executed the required number of times (YES in ST7), the deterioration state estimation process is terminated.

[0103] On the other hand, if the determination unit 12 determines that the absolute value of the difference between the secondary battery temperature and the ambient temperature is less than or equal to a threshold (YES in ST3), it can be determined that the secondary battery temperature has reached a temperature equivalent to the ambient temperature. In this case, the first time step width tL is selected, and as described above, the deterioration state determination unit 13 performs the necessary number of estimation processes (ST14, ST5).

[0104] [Effects of the embodiment] (1) The method for estimating the degradation of a secondary battery comprises the steps of: comparing the period of time a vehicle equipped with a secondary battery to be degraded is left idle with a predetermined time; selecting a time step width that indicates the timing for estimating the degradation state within the idle period; and estimating the degradation state of the secondary battery according to the selected time step width.

[0105] By adopting this method for estimating the degradation of secondary batteries, it is possible to select the timing of the degradation estimation by considering the period of time the vehicle has been left unused and the temperature conditions that have a significant impact on the degradation of the secondary batteries. This makes it possible to estimate the degradation state of secondary batteries at a low cost while maintaining estimation accuracy.

[0106] (2) In the secondary battery degradation estimation method described in (1) above, if it is determined that the period of inactivity is longer than a predetermined time, a first time step width is selected that is longer than the usage time step width selected when the vehicle is in use, and the degradation state is estimated assuming that the temperature of the secondary battery is equivalent to the ambient temperature.

[0107] When estimating the degradation state of a secondary battery, the longer the vehicle is left unused, the closer the battery temperature becomes to the ambient temperature. Therefore, by adopting a longer time step (time step) for executing the degradation state estimation process, it is possible to reduce computational costs while maintaining the accuracy of the degradation estimation.

[0108] (3) In the method for estimating the degradation of the secondary battery described in (2) above, the endpoint of the first time step is set to the point at which the vehicle has finished being left unused.

[0109] Even if a first time step is selected for estimating the state of deterioration, the estimation process must be performed before the period of inactivity ends. Therefore, by setting the endpoint of the first time step to the point when the vehicle's inactivity period ends, the deterioration state estimation process can be performed even during long periods of inactivity.

[0110] (4) In the method for estimating the degradation of the secondary battery described in (3) above, the first time step is set with the point in time as the endpoint when the amount of change in ambient temperature at the location where the vehicle was left during the period of time the vehicle was left reaches a predetermined allowable change in ambient temperature.

[0111] In particular, when a vehicle is left unattended for a long period, the ambient temperature can change significantly. In such cases, even if the first time step size is selected, using the same ambient temperature information for the entire period makes it difficult to accurately estimate the state of deterioration. Therefore, by appropriately dividing the first time step size based on the allowable ambient temperature change and using suitable ambient temperature information, it is possible to perform an appropriate deterioration state estimation process.

[0112] (5) In the secondary battery degradation estimation method described in (1) above, if it is determined that the period of inactivity is less than a predetermined time, the method includes a step of calculating the absolute difference between the temperature of the secondary battery when the vehicle is parked and the ambient temperature at the location where the vehicle was parked, before the step of selecting the time step size. By performing this process, an appropriate time step size can be selected.

[0113] (6) In the secondary battery degradation estimation method described in (5) above, the absolute value of the calculated difference is compared with a threshold, and if it is determined that the absolute value of the difference is less than or equal to the threshold, the degradation state of the secondary battery is estimated using a first time step that is longer than the usage time step selected when the vehicle is in use.

[0114] In this case, since the temperature of the secondary battery is already considered to be equivalent to the ambient temperature, the degradation state estimation process can be performed using the first time step size, thereby reducing computational costs while maintaining the accuracy of the degradation estimation.

[0115] (7) In the secondary battery degradation estimation method described in (5) or (6) above, if it is determined that the absolute value of the difference is greater than a threshold, the degradation state of the secondary battery is estimated using a second time step that is longer than the usage time step selected when the vehicle is in use, and shorter than a first time step that is longer than the usage time step selected when the vehicle is in use.

[0116] By selecting a second time step size, the degradation state estimation process will be performed more frequently for a while after the idling period begins, which can help maintain its accuracy.

[0117] (8) In the secondary battery degradation estimation method described in (5) to (7) above, the ambient temperature used when calculating the absolute value of the difference is the temperature that shows the highest value within the predetermined period, obtained by linear approximation of the change in ambient temperature within the predetermined period.

[0118] By performing this process, it is possible to change the time step size selection from the second time step size to the first time step size at an early stage, and by selecting a higher temperature for the secondary battery temperature, it is possible to perform a more severe degradation state estimation process.

[0119] (9) A secondary battery degradation estimation device comprises: an information acquisition unit that acquires information of a vehicle equipped with a secondary battery to be degraded; a determination unit that compares the vehicle's idle period with a predetermined time set in advance and selects a time step width that indicates the timing for estimating the degradation state within the idle period; and a degradation state determination unit that estimates the degradation state of the secondary battery in accordance with the selected time step width.

[0120] By employing such a secondary battery degradation estimation device, it is possible to select the timing of degradation estimation by considering the period the vehicle has been left unused and the temperature conditions that greatly affect secondary battery degradation. This allows for the estimation of secondary battery degradation at a low cost while maintaining estimation accuracy.

[0121] (10) The deterioration estimation device described in (9) above is equipped with a calculation unit that calculates the absolute value of the difference between the temperature of the secondary battery when the vehicle is stopped and the ambient temperature at the location where the vehicle was left, which serves as a reference for selecting the time step size. By performing this processing by the calculation unit, an appropriate time step size can be selected.

[0122] 1... Deterioration estimation device, 11... Information acquisition unit, 12... Determination unit, 13... Deterioration state determination unit, 14... Calculation unit, 15... Storage unit, 2... Vehicle, N... Communication network, tL... First time step width, tS... Second time step width, V... Target vehicle

Claims

A step of comparing the period of time a vehicle equipped with a secondary battery subject to degradation estimation is left idle with a predetermined time, The steps include selecting a time step size that indicates the timing for estimating the deterioration state during the aforementioned period of inactivity, A step of estimating the degradation state of the secondary battery according to the selected time step width, A method for estimating the degradation of a secondary battery, characterized by comprising the following: 　 The method for estimating the deterioration state of a secondary battery according to claim 1, characterized in that, if it is determined that the period of inactivity is longer than the predetermined time, a first time step width which is longer than the usage time step width which is selected when the vehicle is in use is selected, and the temperature of the secondary battery is assumed to be equivalent to the ambient temperature when estimating the deterioration state. 　 The method for estimating the degradation of a secondary battery according to claim 2, characterized in that, in the first time step, the endpoint is set to the point at which the vehicle's period of being left unused ends. 　 The method for estimating the deterioration of a secondary battery according to claim 3, characterized in that the first time step width is set with the point in time as the endpoint when the amount of change in ambient temperature at the location where the vehicle was left during the period of being left there reaches a preset allowable change in ambient temperature. 　 The method for estimating the degradation of a secondary battery according to claim 1, characterized in that, if it is determined that the period of inactivity is less than the predetermined time, the method further includes a step of calculating the absolute value of the difference between the temperature of the secondary battery when the vehicle is parked and the ambient temperature at the location where the vehicle was parked, before the step of selecting the time step. 　 The method for estimating the degradation state of a secondary battery according to claim 5, characterized in that the absolute value of the calculated difference is compared with a threshold, and if it is determined that the absolute value of the difference is less than or equal to the threshold, the degradation state of the secondary battery is estimated using a first time step that is longer than the usage time step selected when the vehicle is in use. 　 The method for estimating the degradation state of a secondary battery according to claim 5, characterized in that, if it is determined that the absolute value of the difference is greater than the threshold, the estimation of the degradation state of the secondary battery is performed using a second time step width which is longer than the usage time step width selected when the vehicle is in use, and shorter than a first time step width which is longer than the usage time step width selected when the vehicle is in use. 　 The method for estimating the degradation of a secondary battery according to claim 5, characterized in that the ambient temperature used when calculating the absolute value of the difference is a value obtained by linear approximation of the change in ambient temperature within a predetermined period, and is the temperature that shows the highest value within the predetermined period. 　 An information acquisition unit that acquires information about vehicles equipped with secondary batteries that are subject to degradation estimation, A determination unit compares the period during which the vehicle is left unattended with a predetermined time, and selects a time step width that indicates the timing for estimating the deterioration state within the period of unattended, A degradation state determination unit that estimates the degradation state of the secondary battery according to the selected time step width, A device for estimating the degradation of a secondary battery, characterized by comprising the following: 　 The deterioration estimation device according to claim 9, further comprising a calculation unit that calculates the absolute value of the difference between the temperature of the secondary battery when the vehicle is stopped and the ambient temperature at the location where the vehicle was left, which serves as a reference for selecting the aforementioned time step size.

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