JP2020119820A - Cell system - Google Patents

Abstract

To determine a failure of a restraint member that restrains a plurality of stacked cells in the stacking direction without adding a component such as a strain gauge, and suppress large deformation of the restraint member.SOLUTION: A cell ECU 60 executes first processing of setting an upper limit SOC of a power storage device 10 on the basis of the degree of deterioration of the power storage device 10, and second processing of determining the fatigue failure of a restraint member 16. The first processing includes processing of setting the upper limit SOC such that the upper limit SOC decreases as the deterioration level increases. The second processing includes processing of estimating a restraint load from the degree of deterioration, the temperature of the power storage device 10, and the SOC, and processing of determining whether or not the restraint member 16 has a fatigue failure on the basis of the cumulative damage amount D calculated from the history of the estimated restraint load.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a battery system including an assembled battery in which a plurality of stacked cells are constrained by a constraining member.

Japanese Unexamined Patent Application Publication No. 2016-100237 (Patent Document 1) discloses a secondary battery module in which a plurality of stacked lithium ion secondary batteries (cells) are fixed by a cell holder. In this secondary battery module, a strain gauge is installed in the cell holder, and a fracture signal is output when the integrated amount of strain measured by the strain gauge exceeds a threshold value. According to this secondary battery module, it is possible to detect the deterioration of the cell holder caused by the strain repeatedly generated by charging and discharging and prevent the damage of the cell holder (see Patent Document 1).

JP, 2016-100237, A JP, 2018-55783, A

The technique described in Patent Document 1 measures strain that is repeatedly generated in the restraining member (cell holder) due to charge and discharge with a strain gauge, and requires additional components such as a strain gauge and a communication line.

Further, when the battery is used for a long period of time, the electrode expands and gas is generated in the cell, so that the internal pressure of the cell rises and the cell expands. Expansion due to such electrode expansion and gas generation (hereinafter, such a condition due to long-term use of the battery is referred to as "deterioration" of the battery) and the state of charge (SOC) of the battery. The constraining member can be largely deformed due to the expansion of the cell due to the expansion of the electrode (negative electrode) at high SOC. Patent Document 1 does not particularly consider a means for suppressing such a large deformation of the restraint member.

The present disclosure has been made to solve such a problem, and an object of the present disclosure is to provide a strain gauge or the like in a battery system including an assembled battery in which a plurality of stacked cells are constrained in a stacking direction by a constraining member. The failure determination of the restraint member is performed and the large deformation of the restraint member is suppressed without adding the parts.

The battery system of the present disclosure includes a battery pack in which a plurality of stacked cells are constrained in the stacking direction by a constraining member, and a processing device. The processing device includes a first process of setting an upper limit of SOC of the battery pack (hereinafter, referred to as “upper limit SOC”) and a second process of determining a fatigue failure of the restraint member based on the degree of deterioration of the battery pack. Configured to perform and. The first process includes a process of setting the upper limit SOC based on the deterioration degree so that the upper limit SOC decreases as the deterioration degree increases. The second process is a process of estimating the restraint load from the deterioration degree, the temperature, and the SOC by using a predetermined relationship between the deterioration degree of the battery pack, the temperature, and the SOC and the restraint load of the restraint member. It includes a process of calculating the cumulative damage amount of the restraint member from the history of the restraint load, and a process of determining that the restraint member has a fatigue failure when the cumulative damage amount exceeds a threshold value.

According to this battery system, the upper limit SOC is set based on the deterioration degree so that the upper limit SOC decreases as the deterioration degree of the assembled battery increases (first processing). Therefore, expansion due to deterioration and high SOC Considering the expansion, it is possible to suppress large deformation of the restraint member. Further, the cumulative damage amount of the restraint member is calculated from the history of the restraint load estimated from the deterioration degree, the temperature, and the SOC, and it is determined whether or not the restraint member has a fatigue failure based on the calculated cumulative damage amount. Therefore (second process), it is possible to determine the fatigue failure of the restraint member without using the strain gauge.

As described above, according to the battery system of the present disclosure, it is possible to determine a failure of the restraint member and suppress large deformation of the restraint member without adding a component such as a strain gauge.

1 is a block diagram showing a configuration example of a vehicle to which a battery system according to an embodiment of the present disclosure is applied. FIG. 3 is a perspective view showing an example of a configuration of a power storage device. It is a functional block diagram which shows the structure of a battery ECU. It is a figure which shows an example of the relationship of the deterioration degree of an electrical storage apparatus, SOC, and the restraint load by a restraint member. It is a figure which shows an example of the waveform of the restraint load estimated by the restraint load estimation part. It is a figure which shows the relationship between a restraint load and the number of repetitions until it fatigue-fails for every restraint load. It is a flow chart which shows an example of a procedure of processing performed by battery ECU. 9 is a flowchart showing an example of a procedure of cumulative damage amount calculation processing executed in step S55 of FIG. 7.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

<Battery system configuration>
FIG. 1 is a block diagram showing a configuration example of a vehicle to which the battery system according to the embodiment of the present disclosure is applied. Referring to FIG. 1, vehicle 100 includes a power storage device 10, system main relays 15 a and 15 b, a boost converter 20, an inverter 25, a motor generator 30, a transmission gear 35, and drive wheels 40.

Power storage device 10 is mounted on vehicle 100 as a drive power source for vehicle 100. That is, vehicle 100 is an electric vehicle or a hybrid vehicle that uses power storage device 10 as a drive power source. The hybrid vehicle is a vehicle that includes, in addition to the power storage device 10, an engine (not shown) as a power source and further includes a fuel cell as a driving power source. The electric vehicle is a vehicle including only power storage device 10 as a power source of vehicle 100.

Power storage device 10 is a rechargeable power storage element, and is an assembled battery including a plurality of secondary batteries (cells) typified by lithium-ion secondary batteries. The lithium-ion secondary battery is a secondary battery using lithium as a charge carrier, and may include a general lithium-ion secondary battery having a liquid electrolyte, and a so-called all-solid-state battery using a solid electrolyte.

Power storage device 10 is connected to boost converter 20 through system main relays 15a and 15b. Boost converter 20 boosts the output voltage of power storage device 10. Inverter 25 converts the DC power from boost converter 20 into AC power.

Motor generator (three-phase AC motor) 30 receives AC power from inverter 25 and generates kinetic energy for running vehicle 100. The kinetic energy generated by the motor generator 30 is transmitted to the drive wheels 40. On the other hand, when the vehicle 100 is decelerated or stopped, the motor generator 30 converts the kinetic energy of the vehicle 100 into electric energy. AC power generated by motor generator 30 is converted into DC power by inverter 25 and supplied to power storage device 10 through boost converter 20. In this way, motor generator 30 is configured to generate driving force or braking force of vehicle 100 with the exchange of electric power with power storage device 10 (that is, charging/discharging of power storage device 10 ). ..

The boost converter 20 can be omitted. Further, when a DC motor is used as the motor generator 30, the inverter 25 can be omitted.

When vehicle 100 is configured as a hybrid vehicle in which an engine (not shown) is further mounted as a power source, the output of the engine is used as the driving force for running the vehicle in addition to the output of motor generator 30. Can be used. Alternatively, it is also possible to further mount a motor generator (not shown) that generates power by the engine output and generate charging power for the power storage device 10 by the engine output.

Vehicle 100 may be configured to further include a function for charging power storage device 10 with external power supply 90 (hereinafter, charging of power storage device 10 with external power supply 90 is referred to as “external charging”). .. In this case, vehicle 100 further includes charger 45 and charging relays 50a and 50b.

External power supply 90 is a power supply provided outside vehicle 100. As external power supply 90, for example, a commercial AC power supply can be applied. Charger 45 converts electric power from external power supply 90 into electric power for charging power storage device 10. The charger 45 is connected to the power storage device 10 through the charging relays 50a and 50b. When the charging relays 50a and 50b are on, the power storage device 10 can be charged with the electric power from the external power source 90.

The external power source 90 and the charger 45 can be connected by a charging cable 95, for example. That is, when the charging cable 95 is attached, the external power supply 90 and the charger 45 are electrically connected to each other, so that the power storage device 10 can be charged using the external power supply 90. Alternatively, the power may be transferred in a contactless manner between the external power source 90 and the charger 45. For example, power storage device 10 can be charged by external power supply 90 by providing coils in both the external power supply and the vehicle and transmitting electric power through the magnetic fields formed between the coils facing each other.

When AC power is supplied from the external power supply 90, the charger 45 has a function of converting the power supplied from the external power supply 90 (AC power) into charging power (DC power) for the power storage device 10. Composed. Alternatively, when external power supply 90 directly supplies the charging power for power storage device 10, charger 45 only needs to transfer the DC power from external power supply 90 to power storage device 10. The aspect of external charging of vehicle 100 is not particularly limited.

Vehicle 100 further includes a current sensor 72, a voltage sensor 74, a temperature sensor 76, a battery ECU (Electronic Control Unit) 60, a display unit 80, and a vehicle ECU 85. The current sensor 72 detects a current Ib input/output to/from the power storage device 10. Voltage sensor 74 detects voltage Vb of power storage device 10. Temperature sensor 76 detects temperature Tb of power storage device 10. The detection value of each sensor is output to the battery ECU 60.

Battery ECU 60 includes a control unit 62, a storage unit 64, and a signal I/F unit (not shown). The control unit 62 is configured to include a CPU (Central Processing Unit), and the storage unit 64 is configured to include a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 64 stores programs and various data for operating the control unit 62. The control unit 62 expands the program stored in the ROM into the RAM and executes the program. The programs stored in the ROM describe the processing executed by the control unit 62. The detection signals of the current sensor 72, the voltage sensor 74, and the temperature sensor 76 are taken into the battery ECU 60 by the signal I/F unit. Specific processing executed by the control unit 62 will be described later in detail.

Display unit 80 is configured to display predetermined information to the user of vehicle 100 in response to a command from battery ECU 60. The information displayed on the display unit 80 will also be described later together with the control unit 62.

The vehicle ECU 85 includes a CPU, a memory (RAM and ROM), and a signal I/F unit (none of which is shown). Vehicle ECU 85 controls the operations of system main relays 15 a and 15 b, boost converter 20, and inverter 25.

FIG. 2 is a perspective view showing an example of the configuration of power storage device 10. Referring to FIG. 2, power storage device 10 includes a plurality of cells 12, two end plates 14, and a restraining member 16. Each cell 12 has a substantially rectangular parallelepiped shape, and the plurality of cells 12 are stacked between each cell via a spacer (not shown). In the following, the plurality of stacked cells 12 will be referred to as a “cell stack”.

The end plates 14 are provided at both ends of the cell stack in the stacking direction, and are arranged so as to sandwich the cell stack from both ends in the stacking direction.

The restraint member 16 is a member for restraining the cell stack in the stacking direction of the cells 12. In this example, the restraint member 16 is composed of four restraint bands extending along the stacking direction of the cells 12, and two restraint bands are provided on the upper surface side and the lower surface side of the cell stack. ..

Although not particularly shown, the cell stack is actually accommodated in a case (not shown) together with the current sensor 72, the voltage sensor 74, the temperature sensor 76, and the battery ECU 60. The power storage device 10 may be configured to include a plurality of cell stacks as described above.

<Protective control of restraint members>
In the cell 12, the electrode repeatedly expands and contracts with charge and discharge, which causes the cell itself to repeatedly expand and contract. Therefore, the restraint member 16 that restrains the plurality of cells 12 is repeatedly loaded, and the restraint member 16 becomes fatigued. In order to detect a fatigue failure (breakage or the like) of the restraint member 16, it is possible to provide a strain gauge on the restraint member 16 and calculate an integrated amount of strain to detect fatigue deterioration. Additional parts are required.

In addition, when the battery is used for a long time, the electrode expands and gas is generated in the cell, which deteriorates the battery. When the battery deteriorates, the internal pressure of the cell rises and the cell expands. The restraint member 16 can be largely deformed due to the expansion due to the deterioration of the battery and the expansion of the cell due to the expansion of the electrode (negative electrode) at high SOC. For this reason, the restraint member 16 needs to suppress not only fatigue deterioration but also large deformation when deterioration progresses.

Therefore, in the battery system according to the present embodiment, battery ECU 60 performs the first process of setting the upper limit SOC of power storage device 10 based on the degree of deterioration of power storage device 10, and the fatigue failure of restraint member 16. Process 2 is executed.

The first process is a process for suppressing large deformation of the restraint member 16. In the first process, the upper limit SOC is set based on the degree of deterioration such that the upper limit SOC decreases as the degree of deterioration of power storage device 10 increases. Accordingly, the large deformation of the restraint member 16 can be suppressed in consideration of the expansion due to deterioration and the expansion at high SOC.

The second process is a process for determining a fatigue failure of the restraint member 16. Although the details will be described later, in the second processing, the cumulative damage amount of the restraint member 16 is calculated from the history of the restraint load estimated from the deterioration degree of the power storage device 10, the temperature Tb, and the SOC, and the calculated cumulative damage amount. Based on the above, it is determined whether the restraint member 16 has a fatigue failure. Thereby, the fatigue failure of the restraint member 16 can be determined without using a strain gauge. Hereinafter, the configuration of the battery ECU 60 that executes the first and second processes will be described in detail.

FIG. 3 is a functional block diagram showing the configuration of the battery ECU 60. Referring to FIG. 3, control unit 62 of battery ECU 60 includes SOC calculation unit 112, deterioration degree calculation unit 114, upper limit SOC setting unit 116, restrained load estimation unit 118, fatigue failure determination unit 120, and charging. And a control unit 122.

SOC calculation unit 112 calculates the SOC of power storage device 10 using at least part of current Ib, voltage Vb, and temperature Tb of power storage device 10. Voltage Vb of power storage device 10 is calculated from the voltage of each cell 12-1 to 12-M detected by monitoring unit 66 (not shown in FIG. 1) and transmitted to battery ECU 60. The current Ib and the temperature Tb detected by the current sensor 72 and the temperature sensor 76, respectively, are also taken into the monitoring unit 66 and transmitted to the battery ECU 60.

The SOC is a value indicating the current amount of electricity stored as a percentage with respect to the current full charge capacity of the electricity storage device 10. As the SOC calculation method, various known methods such as a method using an OCV-SOC curve (map or the like) showing a relationship between OCV (Open Circuit Voltage) and SOC, a method using an integrated value of charge/discharge current, and the like. Can be used.

Deterioration degree calculation unit 114 calculates the degree of deterioration indicating the degree of deterioration of power storage device 10. The degree of deterioration indicates the amount of expansion of the electrode that has expanded due to long-term use of the battery and the amount of gas generated in the cell, and the degree of deterioration increases as the period of use of the power storage device 10 increases.

In the first embodiment, the degree of deterioration is calculated by multiplying a correlation coefficient with an amount that correlates with the expansion amount and gas generation amount of the electrode, instead of directly measuring the expansion amount and gas generation amount of the electrode. It As the amount that correlates with the expansion amount of the electrode and the gas generation amount, for example, the capacity retention rate of power storage device 10 can be used. The capacity retention rate is the ratio of the current full charge capacity to the full charge capacity of the power storage device 10 in the initial state (when new). The current full charge capacity can be calculated, for example, by dividing an appropriate current integration amount between two points by the SOC difference between the two points. The correlation coefficient for obtaining the degree of deterioration from the capacity maintenance rate is obtained in advance by an experiment or the like.

It should be noted that an integrated value of the discharge current from the initial state of the power storage device 10 or the like may be used as the amount having a correlation with the expansion amount of the electrode and the gas generation amount. Also in this case, the correlation coefficient for obtaining the degree of deterioration from the integrated value of the discharge current is obtained in advance by an experiment or the like.

Upper limit SOC setting unit 116 sets the upper limit SOC of power storage device 10 based on the deterioration degree calculated by deterioration degree calculation unit 114. The SOC of power storage device 10 is controlled within a range not exceeding the set upper limit SOC. Specifically, upper limit SOC setting unit 116 sets the upper limit SOC based on the deterioration degree so that the upper limit SOC decreases as the deterioration degree increases. Hereinafter, a method of setting the upper limit SOC in the present embodiment will be described.

FIG. 4 is a diagram showing an example of the relationship between the degree of deterioration of power storage device 10, the SOC, and the restraint load applied by restraint member 16. Note that FIG. 4 shows the relationship when the temperature Tb of power storage device 10 is constant at T1.

Referring to FIG. 4, the horizontal axis represents the SOC of power storage device 10, and the vertical axis represents the restraint load by restraint member 16. The restraint load by the restraint member 16 is a load generated between the cell laminate and the restraint member 16 due to the expansion of the cell laminate due to the restraint of the cell laminate by the restraint member 16.

Lines k1 to k3 show an example of the relationship between the SOC and the restraint load with respect to different deterioration degrees, and the deterioration degrees are higher in the order of the lines k3, k2, and k1. Although not shown in FIG. 4, the restraint load also changes depending on the temperature Tb of power storage device 10. For each of lines k1 to k3, the higher the temperature Tb, the greater the restraint load for the same SOC.

The threshold value FU of the restraint load indicates an allowable upper limit of the restraint load, and is a value that is set so that the restraint member 16 may be damaged when a restraint load exceeding this is generated. The threshold value FU is appropriately determined based on the strength of the restraint member 16.

The SOC value SU1 indicates the SOC at which the constraint load becomes the threshold value FU in the case of the deterioration degree (high) indicated by the line k3. That is, in the case of the degree of deterioration indicated by the line k3, when the SOC exceeds the value SU1, the constraint load exceeds the threshold value FU.

The SOC value SU2 (SU2>SU1) indicates the SOC at which the restraint load becomes the threshold value FU in the case of the deterioration degree (medium) indicated by the line k2. That is, in the case of the deterioration degree indicated by the line k2, when the SOC exceeds the value SU2, the constraint load exceeds the threshold value FU.

The values SU1 and SU2 correspond to the upper limit SOC set based on the degree of deterioration. The higher the degree of deterioration, the lower the upper limit SOC (SU1<SU2). The relationship between the deterioration degree and the upper limit SOC is obtained in advance by a preliminary experiment or the like, and is stored in the ROM of the storage unit 64 as a map or a relational expression. Then, the upper limit SOC setting unit 116 sets the upper limit SOC using the above map or the relational expression, based on the deterioration degree calculated by the deterioration degree calculation unit 114.

Further, when upper limit SOC falls below predetermined threshold value Sth, upper limit SOC setting unit 116 outputs to display unit 80 a command to display a caution indicating that the upper limit SOC is limited. When the upper limit SOC is limited (decreased), the upper limit of the amount of electricity stored in the power storage device 10 is suppressed, so that the traveling distance (EV traveling distance) by the motor generator 30 becomes shorter than the user's expectation, and the user may be confused. There is. By displaying a caution indicating that the upper limit SOC is limited on display unit 80, it is possible to prevent the user from being confused, and also to prompt the user to replace power storage device 10. Note that threshold value Sth is, for example, 70% of the fully charged state of power storage device 10 in the initial state (when new).

Note that the constraint load also changes depending on the temperature Tb of the power storage device 10. Therefore, if the influence of the temperature Tb on the constraint load is large, the temperature Tb may be included in the parameter. In this case, the relationship between the deterioration degree, the temperature Tb, and the SOC upper limit is obtained in advance by a preliminary experiment or the like, and is stored in the ROM of the storage unit 64 as a map or a relational expression. Then, the upper limit SOC setting unit 116 sets the upper limit SOC using a map or a relational expression based on the deterioration degree calculated by the deterioration degree calculation unit 114 and the temperature Tb detected by the temperature sensor 76. Good.

Referring again to FIG. 3, the restraint load estimation unit 118 estimates the restraint load by the restraint member 16 based on the deterioration degree calculated by the deterioration degree calculation unit 114. Hereinafter, a method for estimating the restraint load according to the present embodiment will be described.

Referring again to FIG. 4, the relationship as shown in the drawing, that is, the relationship between the deterioration degree, the SOC, the temperature Tb, and the restraint load is obtained in advance by a preliminary experiment or the like, and is stored in the storage unit as a map or a relational expression. It is stored in 64 ROMs. Then, the constraint load estimation unit 118 uses the map or the relational expression, and the deterioration degree calculated by the deterioration degree calculation unit 114, the SOC calculated by the SOC calculation unit 112, and the power storage detected by the temperature sensor 76. The restraint load is estimated from the temperature Tb of the device 10.

Note that the restraint load estimation unit 118 repeatedly estimates the restraint load while the SOC is expected to change, for example, during operation of the vehicle system and during charging of the power storage device 10 by the external power supply 90, and the storage unit 64. Accumulated in. That is, the storage unit 64 stores the history of the restraint load estimated by the restraint load estimation unit 118.

Referring again to FIG. 3, fatigue failure determination unit 120 calculates cumulative damage amount D of restraint member 16 from the history of the restraint load estimated by restraint load estimator 118. The cumulative damage amount D is calculated when the vehicle system is started or stopped, when external charging by the external power source 90 is started or stopped, and the like. Then, when the cumulative damage amount D of the restraint member 16 exceeds the threshold value, the fatigue failure determination unit 120 determines that the restraint member 16 has a fatigue failure, and issues a command to display a caution to that effect. Output to the display unit 80.

To calculate the cumulative damage amount D, the so-called rainflow method is used to extract frequency information for each restraint load from the history of the estimated restraint load, and the damage degree of cumulative fatigue is calculated based on the so-called Miner's rule. It is done by that. Hereinafter, a method of calculating the cumulative damage amount D according to the present embodiment will be described.

FIG. 5 is a diagram showing an example of a waveform of the restraint load estimated by the restraint load estimation unit 118. Referring to FIG. 5, the restraint load is estimated based on the degree of deterioration, SOC and temperature Tb, and largely changes largely in accordance with the fluctuation of SOC. From such a history of restraint loads, the frequency for each restraint load (the number of times a similar restraint load occurs for each restraint load) is counted using the rainflow method. The method of counting the frequency for each restraint load is not limited to the rainflow method, and another method such as the P/V difference method may be used.

FIG. 6 is a diagram showing the relationship between the restraint load and the number of repetitions until fatigue failure occurs for each restraint load. Such a curve is also called a so-called SN curve. This curve can be obtained by a fatigue test on the restraint member 16.

With reference to FIG. 6, N1 indicates the number of repetitions up to fatigue failure with respect to the F1 constraint load, and N2 indicates the number of repetitions up to fatigue failure with respect to the F2 constraint load. FL indicates a fatigue limit, and is assumed to have an infinite life with respect to a constraint load of FL or less.

The fatigue failure determination unit 120 calculates the degree of damage nt/Nt for the frequency nt (t=1 to i) for each restraint load Ft (t=1 to i) counted by using the rainflow method. Then, the fatigue failure determination unit 120 calculates the cumulative damage amount D by calculating the sum of the damage degrees of the respective restraint loads Ft (t=1 to i).

Cumulative damage amount D=n1/N1+n2/N2+...+ni/Ni (1)
When the cumulative damage amount D is smaller than the threshold value Dth (Dth=1), the fatigue failure determination unit 120 determines that the restraint member 16 has no fatigue failure. Then, when the cumulative damage amount D exceeds the threshold value Dth, the fatigue failure determination unit 120 determines that the restraint member 16 has a fatigue failure.

Referring again to FIG. 3, charging control unit 122 controls charger 45 during external charging by external power supply 90. At that time, charging control unit 122 controls charger 45 so that the SOC of power storage device 10 does not exceed the upper limit SOC set by upper limit SOC setting unit 116. Specifically, when the SOC reaches the upper limit SOC, the charger 45 is stopped.

FIG. 7 is a flowchart showing an example of a procedure of processing executed by battery ECU 60. The series of processes shown in this flowchart are repeatedly executed at predetermined intervals, for example, during operation of the vehicle system and during external charging by the external power supply 90.

Referring to FIG. 7, battery ECU 60 acquires current Ib, voltage Vb, and temperature Tb of power storage device 10 from current sensor 72, voltage sensor 74, and temperature sensor 76, respectively (step S10). Next, battery ECU 60 calculates the SOC of power storage device 10 using at least part of acquired current Ib, voltage Vb, and temperature Tb (step S15).

Subsequently, battery ECU 60 calculates the degree of deterioration of power storage device 10 (step S20). In the present embodiment, battery ECU 60 calculates the capacity maintenance rate of power storage device 10 and calculates the degree of deterioration by multiplying the capacity maintenance rate by a correlation coefficient obtained in advance by an experiment or the like.

Next, battery ECU 60 sets the upper limit SOC of power storage device 10 based on the calculated degree of deterioration (step S25). As described above, the relationship between the degree of deterioration and the upper limit SOC, which is obtained in advance by a preliminary experiment or the like, is stored in the storage unit 64 as a map or a relational expression, and the battery ECU 60 uses the map or the relational expression to execute the step. The upper limit SOC is set based on the deterioration degree calculated in S20.

Then, battery ECU 60 determines whether or not the set upper limit SOC is lower than threshold value Sth (step S30). If it is determined that the upper limit SOC is lower than threshold value Sth (YES in step S30), battery ECU 60 controls display unit 80 to display a caution indicating that the upper limit SOC is limited (step S30). ). When the upper limit SOC is equal to or higher than the threshold value Sth (NO in step S30), the process of step S35 is not executed and the process proceeds to step S40.

Next, the battery ECU 60 estimates the restraint load applied by the restraint member 16 (step S40). As described above, the relationship among the deterioration degree, the SOC, the temperature Tb, and the restraint load is obtained in advance by an experiment or the like and stored in the storage unit 64 as a map or a relational expression. Battery ECU 60 uses the map or the relational expression to estimate the constraint load from the deterioration degree calculated in step S20, the SOC calculated in step S15, and the temperature Tb acquired in step S10. Then, the battery ECU 60 stores the estimated restraint load in the storage unit 64 (step S45).

Next, the battery ECU 60 determines whether it is time to calculate the cumulative damage amount D of the restraint member 16 (step S50). This calculation timing is, for example, at least one of starting and stopping the vehicle system and starting and stopping external charging by the external power source 90. When it is determined in step S50 that it is not the timing to calculate the cumulative damage amount D (NO in step S50), battery ECU 60 shifts the process to return without executing the processes of steps S55 to S65.

When it is determined in step S50 that it is the timing for calculating the cumulative damage amount D (YES in step S50), battery ECU 60 executes a process of calculating cumulative damage amount D of restraint member 16 (step S55).

FIG. 8 is a flowchart showing an example of the procedure of the cumulative damage amount calculation processing executed in step S55 of FIG. Referring to FIG. 8, battery ECU 60 obtains the history of the estimated value of the restraint load accumulated in storage unit 64 from storage unit 64 (step S110).

Next, the battery ECU 60 counts the frequency nt (t=1 to i) for each restraint load from the acquired history of the restraint load (step S120). In this example, the rainflow method is used to count the frequency nt for each restraint load, but as described above, the method for counting the frequency nt for each restraint load is not limited to the rainflow method, and P/ Other methods such as the V-difference method may be used.

Then, the battery ECU 60 uses the equation (1) based on the Miner's rule to calculate the restraint member 16 based on the count value of the frequency nt (t=1 to i) for each restraint load calculated in step S120. The cumulative damage amount D is calculated (step S130).

Referring to FIG. 7 again, when cumulative damage amount D is calculated in step S55, battery ECU 60 determines whether the calculated cumulative damage amount D is greater than or equal to threshold value Dth (Dth=1). Yes (step S60).

When it is determined that the cumulative damage amount D is equal to or greater than the threshold value Dth (YES in step S60), the battery ECU 60 determines that the restraint member 16 has a fatigue failure, and displays a caution to that effect. The display unit 80 is controlled so as to do so (step S65). When the cumulative damage amount D has not reached the threshold value Dth (NO in step S60), the process of step S65 is not executed and the process proceeds to return.

As described above, according to the present embodiment, the upper limit SOC is set based on the deterioration degree so that the upper limit SOC decreases as the deterioration degree of power storage device 10 increases. The large deformation of the restraint member 16 can be suppressed in consideration of the expansion of the restraint member 16. Further, the cumulative damage amount D of the restraint member 16 is calculated from the history of the restraint load estimated from the deterioration degree, the temperature Tb, and the SOC, and the restraint member 16 suffers a fatigue failure based on the calculated cumulative damage amount D. Since it is determined whether or not there is a fatigue failure of the restraint member 16 without using a strain gauge.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

10 power storage device, 12 cells, 14 end plate, 15a, 15b system main relay, 16 restraint member, 20 boost converter, 25 inverter, 30 motor generator, 35 transmission gear, 40 drive wheel, 45 charger, 50a, 50b charging relay , 60 battery ECU, 62 control unit, 64 storage unit, 66 monitoring unit, 72 current sensor, 74 voltage sensor, 76 temperature sensor, 80 display unit, 85 vehicle ECU, 90 external power supply, 95 charging cable, 100 vehicle, 112 SOC Calculation unit, 114 Deterioration degree calculation unit, 116 Upper limit SOC setting unit, 118 Restraint load estimation unit, 120 Fatigue failure determination unit, 122 Charging control unit.

Claims (1)

An assembled battery in which a plurality of stacked cells are constrained in the stacking direction by a constraining member,
A processing device configured to execute a first process of setting an upper limit of SOC of the battery pack and a second process of determining a fatigue failure of the restraint member based on the degree of deterioration of the battery pack. With and
The first process includes a process of setting the upper limit based on the deterioration degree so that the upper limit decreases as the deterioration degree increases,
The second processing is
A process of estimating the restraint load from the deterioration degree, the temperature, and the SOC by using a predetermined relationship between the deterioration degree, the temperature of the battery pack, the SOC, and the restraint load by the restraint member. When,
A process of calculating the cumulative damage amount of the restraint member from the restraint load history;
A battery system comprising: a process of determining that a fatigue failure has occurred in the restraint member when the cumulative damage amount exceeds a threshold value.

Images