Vehicle battery unit control device

Abstract

To replenish a battery cell of a vehicle battery unit with an electrolytic solution at appropriate timing.SOLUTION: A vehicle battery unit control device includes a battery unit 110, a cell internal pressure detector (surface pressure sensor 67) that detects an internal pressure of a battery cell 62, and a controller (ECU 70) that controls the battery unit, and the controller determines whether a rate of increase of the internal pressure detected by the cell internal pressure detector is equal to or greater than a predetermined value when a charging / discharging duration is less than a predetermined time during charging / discharging with a large current equal to or greater than a predetermined current value of the battery unit, and urges replenishment of the electrolyte solution to the battery cell when it is determined that the rate of increase of the internal pressure reaches or exceeds the predetermined value.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The technology disclosed herein relates to a vehicle battery unit control device. [Background technology]

[0002] It is known that in rechargeable battery cells used in electric vehicles and hybrid vehicles, continued charging and discharging at a large current causes deterioration (so-called "high-rate deterioration") in which the internal resistance of the battery increases. When the duration of high-current charging and discharging is short, the deterioration is temporary (reversible deterioration) and can be restored by halting charging and discharging. However, when the duration is long, permanent deterioration occurs in which the battery performance does not recover even when charging and discharging are halted, that is, irreversible deterioration occurs.

[0003] Patent Document 1 describes a control method for a lithium-ion battery, which suppresses the progression of high-rate degradation.

[0004] The control method of Patent Document 1 is based on the knowledge that a higher concentration of electrolyte can maintain the internal resistance of the battery cell low at the stage where high-rate degradation has progressed. The battery cell of Patent Document 1 contains microcapsules containing a relatively high concentration of a second electrolyte. The microcapsules dissolve at a predetermined temperature.

[0005] In this control method, a cycle test is performed in advance in which the battery cell is charged and discharged at a high rate to determine the point (i.e., the threshold) at which the resistance value of the battery cell when a low-concentration electrolyte is used is reversed to the resistance value of the battery cell when a high-concentration electrolyte is used. When the resistance value in the battery cell mounted in the vehicle reaches the threshold, the temperature of the battery cell is increased to dissolve the microcapsules, thereby replenishing the electrolyte in the battery cell and increasing the concentration of the electrolyte. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-098064 A Summary of the Invention [Problem to be solved by the invention]

[0007] The amount of electrolyte in a battery cell may decrease with long-term use due to, for example, gasification, etc. If the amount of electrolyte is insufficient, irreversible deterioration is likely to occur during charging and discharging at a large current.

[0008] If the amount of electrolyte is increased by refilling the battery cell, the deterioration of the battery cell can be suppressed. However, the remaining amount of electrolyte in the battery cell is affected by the environment in which the vehicle is used and / or the driving tendency of the driver. Therefore, even if the timing of refilling the electrolyte is set based on a test performed in advance as described in Patent Document 1, if the timing of refilling is too late, the battery cell will deteriorate. On the other hand, in order to inject electrolyte into the battery cell of the vehicle battery unit, the vehicle must be brought into a service center. If the timing of refilling is too early, the frequency of the refilling increases, and usability decreases. So far, no technology has been realized that can optimize the timing of refilling the electrolyte.

[0009] The technology disclosed herein makes it possible to replenish the battery cells of a vehicle battery unit with electrolyte at appropriate times. [Means for solving the problem]

[0010] First, the inventors discovered that there is a correlation between the timing at which irreversible deterioration due to large current charging and discharging begins and the timing at which the internal pressure of the battery cell begins to rise rapidly.

[0011] In other words, when charging and discharging at a large current are repeated, the internal pressure of the battery cell rises. This is because the electrolyte flows out of the negative electrode active material layer due to the expansion and contraction of the negative electrode active material and the volume expansion of the electrolyte caused by the insertion and removal of ions in the electrolyte, causing uneven distribution of the electrolyte in the battery cell. As this uneven distribution occurs, the internal resistance of the battery cell rises. When this uneven distribution of the electrolyte is minor, it can be eliminated by suspending charging and discharging, but when the degree of uneven distribution becomes severe, the internal pressure of the battery cell begins to rise rapidly, and the uneven distribution cannot be eliminated even by suspending charging and discharging. In other words, irreversible deterioration of the battery cell occurs.

[0012] In addition, when the amount of electrolyte in the battery cell is reduced, the state inside the battery cell becomes similar to the state when the electrolyte distribution becomes uneven as described above. Therefore, when the amount of electrolyte in the battery cell is reduced, the internal pressure of the battery cell rises rapidly during high-current charging and discharging. In other words, there is a correlation between the reduction in the amount of electrolyte in the battery cell and the rapid rise in internal pressure of the battery cell due to high-current charging and discharging.

[0013] Based on this knowledge, the inventors have constructed a system that monitors the internal pressure of a battery cell during large current charging and discharging to determine whether there is a shortage of electrolyte, and based on that determination, prompts the user to replenish the electrolyte.

[0014] Specifically, the technology disclosed herein relates to a vehicle battery unit control device. A battery unit that is mounted on a vehicle and has a plurality of chargeable and dischargeable battery cells; a cell internal pressure detector for detecting an internal pressure of the battery cell; A controller for controlling the battery unit, The controller includes: during charging / discharging of the battery unit at a large current equal to or greater than a predetermined current value, when the duration of charging / discharging is less than a predetermined time, determining whether or not a rate of increase in the internal pressure detected by the cell internal pressure detector has reached a predetermined value or greater; When it is determined that the rate of increase in the internal pressure is equal to or greater than the predetermined value, a prompt is given to replenish the electrolyte in the battery cell.

[0015] When the charge / discharge duration becomes long and the rate of increase in the internal pressure of the battery cell exceeds a predetermined value, it can be determined that this is a sign of irreversible high-rate degradation. On the other hand, when the rate of increase in the internal pressure of the battery cell exceeds a predetermined value even though the charge / discharge duration is short, it is estimated that the electrolyte in the battery cell is low. In this case, the controller reminds the user to replenish the electrolyte in the battery cell. When the user brings the car in for service, electrolyte is injected into the battery cell.

[0016] According to the above configuration, the controller can prompt the replenishment of electrolyte at an appropriate timing based on the internal pressure of the battery cell.

[0017] Here, the duration of charging and discharging may be determined by integrating the time for charging and discharging at a large current when charging and discharging at a small current are repeated.

[0018] The controller may also inhibit charging / discharging at the high current while initiating the replenishment of electrolyte in the battery cell.

[0019] If charging and discharging at a large current continues when the electrolyte in the battery cell is low, irreversible deterioration of the battery cell will progress. By prohibiting charging and discharging at a large current, the progression of irreversible deterioration is suppressed. Note that the controller does not prohibit charging and discharging at a small current lower than the predetermined current value.

[0020] The controller may also prompt the battery unit to have its SOC reduced to a predetermined value or lower before the battery cells are replenished with electrolyte.

[0021] When the SOC of the battery unit is high, the electrode windings in the battery cells expand, and when the SOC is low, the expansion of the electrode windings is suppressed. If the SOC is low when injecting electrolyte into the battery cells, the expansion of the electrode windings is suppressed, so the electrolyte is injected quickly. If the SOC of the battery unit is below a specified value before the electrolyte is replenished into the battery cells, the time required to inject the electrolyte can be shortened.

[0022] the battery unit includes a battery module in which the plurality of battery cells are stacked in layers and constrained in an overlapping direction, and a constraint load variable mechanism that changes a constraint load applied to the battery cells; The controller may operate the restraint load variable mechanism so as to reduce the restraint load applied to the battery cell, and then determine whether or not the rate of increase in the internal pressure detected by the cell internal pressure detector has reached or exceeded a predetermined value.

[0023] When the restraining load applied to the battery cell is reduced, it becomes possible to supply the electrolyte to the negative electrode active material, compared to when the restraining load is not reduced, and this slows down the progression of deterioration of the battery cell.

[0024] In the above-described configuration, the rate of increase in the internal pressure of the battery cells is judged in a state in which the restraining load is reduced to slow the progression of deterioration, thereby reducing the progression of irreversible deterioration of the battery cells during this judgment.

[0025] In addition, since the controller performs the determination when the electrolyte is easily supplied to the negative electrode active material due to a decrease in the binding load, the controller can accurately determine a shortage of electrolyte in the battery cell. The controller can accurately determine the timing to replenish the electrolyte.

[0026] The controller may operate the restraint load variable mechanism so as to release a restraint load applied to the battery cell when the battery cell is replenished with electrolyte.

[0027] By releasing the restraining load applied to the battery cell, the injection of the electrolyte into the battery cell can be completed quickly. Effect of the Invention

[0028] The vehicle battery unit control device can prompt the user to replenish the electrolyte at an appropriate time based on the rate of increase in the internal pressure of the battery cell. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a hybrid vehicle equipped with a vehicle battery unit and its control device. [Diagram 2] FIG. 2 is an explanatory diagram showing a battery cell restraint mechanism ((a) shows a state in which the restraint load is released, and (b) shows a state in which the restraint load is applied). [Diagram 3] FIG. 3 is a block diagram of a control device for a vehicle battery unit. [Figure 4] FIG. 4 is a conceptual diagram showing the change in the rate of increase in the internal resistance of a battery due to continued large current charging and discharging. [Diagram 5] FIG. 5 is a graph showing an increase in cell reaction force due to continued large current charging and discharging. [Figure 6] FIG. 6 is a graph showing the change in the rising state of the cell reaction force as the number of cycles of large current charge and discharge increases. [Figure 7] FIG. 7 is a graph showing the difference in the change in the rate of increase in battery resistance depending on whether or not the restraining load control is performed when charging and discharging are suspended after large current charging and discharging. [Figure 8] FIG. 8 is a flow diagram of the control of the battery unit. [Figure 9] FIG. 9 is a flow diagram of the process of injecting an electrolyte into a battery cell. [Figure 10] FIG. 10 is a flow diagram of control of a battery unit according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of a vehicle battery unit control device will be described with reference to the drawings. The vehicle battery unit control device described here is an example. Fig. 1 illustrates a hybrid vehicle (Hybrid Electric Vehicle or Plug-in Hybrid Electric Vehicle) equipped with a vehicle battery unit control device. The vehicle battery unit control device is not limited to application to hybrid vehicles, but can also be applied to electric vehicles (Battery Electric Vehicles) that do not have an engine.

[0031] <Overall configuration of hybrid vehicle> 1, a hybrid vehicle 100 includes wheels 10, axles 12, an engine 20, a transmission 30, a motor / generator 40, an inverter 50, a battery unit 110, and an electronic control unit (ECU) 70. This hybrid vehicle 100 is of a parallel type, and the engine 20 and the motor / generator 40 function as a drive source that outputs driving force for the vehicle, and depending on the driving conditions, the vehicle can run using only the engine 20, using both the engine 20 and the motor / generator 40, or running using only the motor / generator 40. Note that the hybrid vehicle may be of a series type.

[0032] The engine 20 is coupled to the axle 12 via a transmission 30. The engine 20 is, for example, a gasoline engine. The motor / generator 40 is coupled to the axle 12 and is connected to a battery module 60 of the battery unit 110 via an inverter 50. The electric power of the battery module 60 is converted to AC power by the inverter 50 and then supplied to the motor / generator 40. The motor / generator 40 receives the supplied electric power and functions as an electric motor to rotate the axle 12. The motor / generator 40 also functions as a generator by performing a regenerative operation when the hybrid vehicle 100 decelerates, thereby charging the battery module 60.

[0033] <Battery unit> 2 illustrates a battery unit 110. The battery unit 110 includes a battery module 60 and a restraining mechanism 80. The battery module 60 includes a plurality of chargeable and dischargeable battery cells 62, which are stacked in layers. Specifically, the plurality of battery cells 62 are housed in a rectangular parallelepiped casing 61 in a state where they are stacked in a predetermined direction D (the horizontal direction in this embodiment), and a spring 65 is interposed between two adjacent battery cells 62. End plates 66 are provided between the battery cells 62 at both ends in the stacking direction D and the vertical walls of the casing 61.

[0034] Adjacent battery cells 62 are connected in series by bus bars 64. Each bus bar 64 has a pair of connection parts 64a electrically connected to the electrode terminals 63 of the adjacent battery cells 62, and a flexible electric wire 64b extending between the pair of connection parts 64a.

[0035] The restraint mechanism 80 restrains the multiple battery cells 62 in the overlapping direction D by the end plates 66 at both ends of the battery cells 62. The restraint mechanism 80 includes a restraint load variable mechanism 81 that changes the restraint load applied to the battery cells 62 by moving one of the end plates 66 back and forth in the overlapping direction D.

[0036] The variable constraint load mechanism 81 comprises a pressure gear 84 connected to one of the end plates 66, a drive gear 86 that meshes with the pressure gear 84 and rotates to move the pressure gear 84 axially forward and backward, and a motor 85 that rotates the drive gear 86. The advancement and retreat of the pressure gear 84 causes the one of the end plates 66 to advance and retreat, changing the constraint load applied to the multiple battery cells 62. The operation of the motor 85 is controlled by the ECU 70.

[0037] A surface pressure sensor 67 is provided as a cell internal pressure detector between one end plate 66 and the end battery cell 62. The surface pressure sensor 67 detects the cell reaction force acting in the opposite direction to the direction in which the restraining load acts on the battery cell 62. This cell reaction force corresponds to the internal pressure of the battery cell 62. The surface pressure sensor 67 has multiple sensing points on its surface.

[0038] The battery cell 62 is formed by housing an electrode winding body in a flat battery case. An electrode terminal 63 and a gas safety valve (not shown) are provided on the upper surface of the battery case. The electrode winding body is formed by winding a positive electrode sheet and a negative electrode sheet insulated from each other by a sheet-like separator.

[0039] The positive electrode sheet is made by mixing a positive electrode active material such as lithium cobalt oxide, a binder, and a conductive assistant, and applying the mixture to a current collector such as aluminum foil. The negative electrode sheet is made by mixing a negative electrode active material such as a graphite-based carbon material, a binder, and a conductive assistant, and applying the mixture to a current collector such as copper foil. The separator is made of a single-layer or multi-layer microporous film of polyolefin such as polypropylene or polyethylene, and is impregnated with a nonaqueous electrolyte solution mainly composed of an organic compound. The nonaqueous electrolyte solution is made by dissolving a lithium salt (supporting electrolyte) in a nonaqueous solvent, and additives are added as necessary.

[0040] Although the battery cell 62 is of a wound type, it may be of a stacked type in which multiple positive electrode sheets and multiple negative electrode sheets are alternately stacked with a separator sandwiched between the positive electrode sheets and the negative electrode sheets, or of another form; the form of the battery cell 62 is not an issue in the present invention.

[0041] <Battery unit control device> 4 shows a schematic diagram of the rise in internal resistance accompanying the deterioration of the battery cells 62 when the battery module 60 is charged and discharged at a large current. The deterioration of the battery cells 62 includes irreversible normal deterioration in which a thin resin film grows on the surface of the negative electrode, causing an increase in internal resistance, and high-rate deterioration in which the internal resistance rises as a result of continued charging and discharging at a large current due to an imbalance in the Li-ion concentration distribution. High-rate deterioration includes reversible deterioration (temporary deterioration) in which the imbalance in the concentration distribution is eliminated by stopping charging and discharging (suspending the battery), and irreversible deterioration that occurs when the duration of charging and discharging at a large current becomes long, in which the imbalance is not eliminated by suspending the battery, causing the internal resistance to remain elevated. When irreversible deterioration begins to occur, the rise in internal resistance becomes rapid.

[0042] To prevent irreversible high-rate degradation while continuing high-current charging and discharging as long as possible, it is necessary to monitor the internal resistance of the battery and stop the high-current charging and discharging when the internal resistance suddenly increases. However, this timing changes depending on the operating conditions, etc., and it is difficult to grasp this.

[0043] Based on the knowledge that the cell reaction force (cell internal pressure) increases as high-rate deterioration of the battery cell 62 progresses, the inventors investigated the change in cell reaction force as the duration of high-current charging and discharging becomes longer. The results are shown in Figure 5. As high-current charging and discharging continues, the cell reaction force increases slowly for a while from the initial point A, but then the cell reaction force increases rapidly from a "cell reaction force rapid rise timing". Investigations revealed that the timing at which this cell reaction force begins to rise rapidly corresponds to the timing at which irreversible high-rate charging begins.

[0044] When the high-current charge and discharge are continued, in the battery cell 62, the entire electrode winding is initially immersed in the electrolyte, so that the battery reaction proceeds in the entire negative electrode. As the high-current discharge proceeds, the electrolyte is pushed out of the negative electrode active material and flows out toward the ends of the battery case as Li ions are inserted into the negative electrode active material. That is, the electrolyte moves to both ends of the electrode winding in the winding axis direction, and the electrolyte becomes less at the center of the electrode (the center of the winding axis direction), and the reaction area of ​​the negative electrode decreases. As the high-current charge and discharge proceeds further, the electrolyte becomes depleted at the center of the electrode, and the reaction area decreases significantly. In this way, the high-rate deterioration proceeds as the high-current charge and discharge proceeds because the reaction area of ​​the negative electrode decreases due to the outflow of the electrolyte. As the electrolyte flows out to the electrode end side, the internal pressure of the battery cell 62, that is, the cell reaction force increases.

[0045] The inventors found that there is a correlation between the timing at which irreversible high-rate degradation begins to occur and the timing at which the internal pressure of the battery cell 62 begins to rise rapidly. The inventors further investigated the cell reaction force as the number of cycles of high-current charging and discharging increases. The number of cycles referred to here is the number of cycles counted as one cycle when the vehicle starts to be driven and then ends after one or more high-current charging and discharging operations. As shown in Fig. 6, as the number of cycles of high-current charging and discharging increases, the cell reaction force becomes higher and the timing at which the cell reaction force rises rapidly becomes earlier.

[0046] In addition, the restraint load applied to the battery cell 62 was reduced at the timing when the cell reaction force indicated by the downward arrow in FIG. 5 begins to rise sharply (the timing when irreversible high-rate degradation begins), and the resistance increase rate of the battery cell 62 was then examined when charging and discharging were suspended. The results are shown in FIG. 7. In the case where the restraint load was not reduced (i.e., without restraint load control), the resistance increase rate increased more significantly as the high-current charging and discharging time became longer. In contrast, in the case where the restraint load was reduced (i.e., with restraint load control), the resistance increase rate did not increase so much even if the high-current charging and discharging time became longer, and the resistance increase rate that finally settled after charging and discharging was suspended was also smaller than in the case where the restraint load was not reduced. In other words, the degree of irreversible degradation was low.

[0047] As described above, the inventor discovered that there is a correlation between the timing at which irreversible high-rate degradation begins and the timing at which the internal pressure of the battery cell 62 begins to rise rapidly, and further discovered that the irreversible degradation can be suppressed by reducing the restraining load applied to the battery cell 62 at the timing at which the internal pressure rises rapidly.

[0048] As described above, when charging and discharging at a large current continues for a long period of time, the electrolyte becomes depleted, the internal pressure of the battery cell 62 increases, and high-rate degradation progresses.

[0049] On the other hand, the amount of electrolyte in the battery cell 62 may decrease due to gasification or the like when the battery cell 62 is used for a long period of time. When the amount of electrolyte in the battery cell 62 is insufficient, the electrolyte is depleted and the reaction area is reduced. Therefore, when charging / discharging at a large current is attempted in a state where the amount of electrolyte is insufficient, the internal pressure of the battery cell 62 increases and irreversible deterioration is likely to progress, as in the case where the duration is long. In this case, as shown by "depletion of electrolyte" in FIG. 6, the internal pressure of the battery cell 62 increases even if the duration of charging / discharging at a large current is not long. In other words, it is possible to determine whether the remaining amount of electrolyte in the battery cell 62 is decreasing based on the duration of charging / discharging at a large current and the internal pressure of the battery cell 62.

[0050] The present invention utilizes the change in the internal pressure of the battery cell 62 to control the battery module 60. That is, based on the internal pressure of the battery cell 62, it is determined whether the remaining amount of electrolyte in the battery cell 62 is reduced, and if the electrolyte is reduced, the user is prompted to replenish the electrolyte. By replenishing the electrolyte in the battery cell 62, the deterioration of the battery unit 110 is suppressed. In addition, by determining the remaining amount of electrolyte based on the internal pressure of the battery cell 62, the timing of the prompting to replenish the electrolyte is appropriate and not too early. Therefore, the frequency of bringing the car into a service center to replenish the electrolyte is not increased. According to the present invention, the usability of the car for the user is improved.

[0051] FIG. 3 illustrates the configuration of a battery unit control device related to electrolyte replenishment prompting. The above-mentioned ECU 70 is connected to a start switch 51, a current sensor 52, a voltage sensor 53, an electrolyte replenishment switch 54, and the above-mentioned surface pressure sensor 67. The start switch 51 is a switch that the driver operates when starting (turning on) the automobile, and the driver also operates the start switch 51 when the automobile is turned off. The start switch 51 outputs an on / off signal to the ECU 10. The current sensor 52 acquires a charge / discharge current value I of the battery module 60 and outputs it to the ECU 70. The voltage sensor 53 outputs a voltage signal of the battery module 60 to the ECU 70. The ECU 70 grasps the SOC (State of Charge) of the battery module 60 based on the voltage signal from the voltage sensor 53 and the like. The electrolyte replenishment switch 54 is a switch that the service staff operates when replenishing the electrolyte after the automobile is brought into the garage.

[0052] The ECU 70 is also connected to a refill reminder display unit 55, a target SOC display unit 56, an unattended reminder display unit 57, and the motor 85 of the restraining mechanism 80. The refill reminder display unit 55 displays a reminder to the user of the vehicle to refill the electrolyte in the battery module 60. Although details will be described later, when the refill of the electrolyte in the battery module 60 is reminded, the target SOC of the battery module 60 is set to a relatively low SOC. When the target SOC is set low, the target SOC display unit 56 notifies the user of the vehicle. The unattended reminder display unit 57 reminds the user to leave the vehicle without driving it until the electrolyte permeates the electrodes after the electrolyte is injected into the battery module 60 during service. The refill reminder display unit 55, the target SOC display unit 56, and the unattended reminder display unit 57 may be provided, for example, on a meter display at the driver's seat of the vehicle, or may be displayed using a center display of the instrument panel.

[0053] The ECU 70 controls the battery unit 110. The ECU 70 includes a duration integrator 71, a cell internal pressure determiner 72, a current limiter 73, an electrolyte replenishment prompter 74, and a restraining load controller 75 as functional blocks.

[0054] The duration accumulation unit 71 acquires the charge / discharge current value I of the battery module 60 at predetermined sampling periods (e.g., 0.1 to 1 second) while the battery module 60 is being charged or discharged, calculates the duration during which this charge / discharge current value I is equal to or greater than a preset current value Io (high current charging / discharging), and accumulates the duration each time high current charging / discharging is performed.

[0055] The cell internal pressure determination unit 72 determines whether the internal pressure P of the battery cell 62 detected by the surface pressure sensor 67 has reached a predetermined internal pressure threshold Po (P≧Po) during charging / discharging at the large current. The cell internal pressure determination unit 72 also determines whether the internal pressure P has reached or exceeded the predetermined internal pressure threshold Po, and when the restraint load control unit 75 performs the restraint load reduction control described below, determines whether the increase rate Pr of the internal pressure P has reached or exceeded a predetermined value Pro.

[0056] When the integrated value T of the duration of the large current charge / discharge integrated by the duration integration unit 71 becomes equal to or greater than a threshold value described below, the current limiting unit 73 limits the current so that the charge / discharge current value I becomes equal to or less than the predetermined current value Io (prohibition of charging / discharging at the large current). In addition, when the cell internal pressure determination unit 72 determines that the rate of increase Pr of the internal pressure of the battery cell 62 becomes equal to or greater than a predetermined value Pro, the current limiting unit 73 similarly limits the current (prohibition of charging / discharging at the large current).

[0057] When the integrated value T is less than a threshold value, the electrolyte replenishment prompting unit 74 prompts the vehicle user to inject electrolyte into the battery cell 62 when the cell internal pressure determination unit 72 determines that the rate of increase Pr of the internal pressure of the battery cell 62 has reached or exceeded a predetermined value Pro.

[0058] The restraint load control unit 75 operates the restraint load variable mechanism 81 so that a predetermined restraint load is applied to the battery cell 62, for example to prevent ions in the electrolyte from precipitating on the negative electrode. Then, when the cell internal pressure determination unit 72 determines that the internal pressure P of the battery cell 62 has become equal to or higher than a predetermined internal pressure threshold Po during charging or discharging at the high current, it operates the restraint load variable mechanism 81 so that the restraint load applied to the battery cell 62 is reduced by a predetermined load. The restraint load control unit 75 also operates the restraint load variable mechanism 81 so that the restraint load applied to the battery cell 62 is released when electrolyte is injected into the battery cell 62.

[0059] (Flow of Control) The flow of control is shown in Fig. 8. In step S1 after the start, the charge / discharge current value I is acquired, and in the following step S2, it is determined whether the charge / discharge current value I exceeds a predetermined value Io (large current charge / discharge) or not.

[0060] When it is determined in step S2 that a large current charge / discharge is occurring, the process proceeds to step S3, where the duration of the large current charge / discharge is accumulated. When it is determined in the following step S4 that the accumulated value T is equal to or greater than the threshold (No), the process proceeds to step S5, where the charge / discharge current value I is limited to a predetermined current value Io or less (prohibition of large current charge / discharge). The threshold value here is a preset threshold value, and this threshold value is a fixed value. Specifically, as shown by the solid line in FIG. 4 or the dashed line in FIG. 6, it is a "set threshold value" that is set to a time a predetermined time earlier than the time when irreversible high-rate degradation starts. In order to avoid irreversible degradation, the set threshold value is set with a considerable margin with respect to the time when irreversible high-rate degradation starts (ideal threshold value, see FIG. 4).

[0061] If it is determined in step S2 that the charge / discharge is not a large current charge / discharge, the process proceeds to step S6, where it is determined whether the vehicle operation has ended (SW-OFF), and if the operation has ended, the control ends, and if the operation has not ended, the process returns to step S1 to continue acquiring the charge / discharge current value.

[0062] If it is determined in step S4 that the integrated value T has not reached the threshold value (Yes), the process proceeds to step S5, where it is determined whether the cell reaction force P has reached the internal pressure threshold value Po. If it has reached the internal pressure threshold value Po, the process proceeds to step S8, where the restraining load applied to the battery cell 62 is reduced by a predetermined value. Then, in the following step S9, it is determined whether the rate of increase Pr of the cell reaction force has reached or exceeded a predetermined value Pro.

[0063] When the rate of increase Pr of the cell reaction force becomes equal to or greater than the predetermined value Pro, as illustrated by "depletion of electrolyte" in FIG. 6, the rate of increase Pr of the cell reaction force becomes equal to or greater than the predetermined value Pro earlier than the set threshold value. That is, when the duration of charging and discharging is less than the predetermined time, the rate of increase Pr of the cell reaction force becomes equal to or greater than the predetermined value Pro. In this case, the remaining amount of electrolyte in the battery module 60 is determined to be reduced, and the process proceeds to step S10, where the charge / discharge current value I is limited to a predetermined current value Io or less (high current charging / discharging is prohibited), and in the following step S11, the refill reminder display unit 55 reminds the user of the vehicle to refill the electrolyte, and in step S12, the target SOC display unit 56 notifies the user that the target SOC is set to a low SOC equal to or less than the predetermined value. The ECU 10 also controls the charging and discharging of the battery module 60 so that the SOC of the battery module 60 becomes relatively low.

[0064] If the cell reaction force P has not reached the internal pressure threshold value Po in step S7, and if the rate of increase Pr of the cell reaction force has not reached or exceeded the predetermined value Pro in step S9, the flow proceeds to step S6 to determine whether the vehicle has ended operation (SW-OFF), and if so, the control ends. If not, the flow returns to step S1 to continue acquiring the charge / discharge current value.

[0065] According to the above control, when the rate of increase Pr of the internal pressure P of the battery cell 62 becomes equal to or greater than the predetermined value Pro even though the duration of charging and discharging at a large current is short, the ECU 70 estimates that the electrolyte in the battery cell 62 is low. The ECU 70 prompts the user through the replenishment prompt display unit 55 to replenish the electrolyte in the battery module 60. It is expected that the user will bring the vehicle in for service and have the electrolyte injected into the battery cell 62. The ECU 70 can prompt the user to replenish the electrolyte at an appropriate time based on the internal pressure P of the battery cell 62.

[0066] In addition, the above control not only encourages the replenishment of electrolyte, but also prohibits charging and discharging at a large current, thereby making it possible to suppress the progression of irreversible deterioration of the battery cells 62.

[0067] In addition, in the above control, the determination of the rate of increase Pr of the cell reaction force P is performed after the binding load applied to the battery cell 62 is reduced based on the cell reaction force P reaching the threshold value Po. This reduction in the binding load reduces the amount of electrolyte flowing out from the negative electrode active material. That is, the irreversible deterioration of the battery cell 62 progresses more slowly. In this way, the rate of increase in the cell internal pressure is determined to determine the remaining amount of electrolyte in the battery cell 62 in a state in which the irreversible deterioration progresses more slowly, so that the irreversible deterioration of the battery cell 62 is prevented from progressing each time this determination is made. In addition, by determining the remaining amount of electrolyte in a state in which the amount of electrolyte flowing out from the negative electrode active material is reduced, the ECU 70 can accurately determine the timing of refilling the electrolyte.

[0068] 9 shows the procedure when a car is brought into a service center and electrolyte is injected into the battery cells 62. In step S21 after starting, it is determined whether the electrolyte replenishment switch 54 has been turned on by the service technician. If the switch has not been turned on, the process repeats step S21. If the switch has been turned on, the process proceeds to step S22, where the ECU 70 releases the restraining force of the battery module 60 via the restraining load variable mechanism 81.

[0069] In the next step S23, the service technician injects the electrolyte into the battery cells 62. As described above, after the electrolyte injection is initiated, the SOC of the battery module 60 is relatively low, and the restraining force on the battery module 60 is also released. Since the SOC of the battery module 60 is low, the expansion of the electrode winding body is suppressed, and the electrolyte can be injected quickly into the battery cells 62. In addition, the release of the restraining force also promotes the injection of the electrolyte. Therefore, the injection of the electrolyte into the battery cells 62 is completed quickly. When the injection of the electrolyte into the battery cells 62 is completed, the service technician turns off the electrolyte refill switch 54.

[0070] In step S24, the ECU 70 determines whether or not the electrolyte replenishment switch 54 has been turned off. If the electrolyte replenishment switch 54 has not been turned off, the process returns to step S23, and if the electrolyte replenishment switch 54 has been turned off, the process proceeds to step S25.

[0071] In step S25, the ECU 70 notifies the service person to leave the vehicle for a predetermined period of time without moving the vehicle through the abandonment notification display unit 57. During this time, the electrolyte permeates the electrodes.

[0072] In step S26, the ECU 70 judges whether a predetermined time has elapsed. If the predetermined time has not elapsed, the process proceeds to step S29, where the ECU 70 judges whether the start switch 51 has been turned on. If the start switch 51 has not been turned on, the process returns to step S25 and waits for the predetermined time to elapse. If the start switch 51 has been turned on, the process proceeds to step S28, where the ECU 70 drives the motor 85 of the variable restraining load mechanism 81 so that a restraining force is applied to the battery module 60. In this case, the predetermined time has not elapsed, and if charging or discharging is performed at a large current, there is a risk that irreversible deterioration of the battery module 60 will progress, so the current restriction performed in step S10 of FIG. 8 is not released. The current restriction is released at a predetermined timing thereafter.

[0073] On the other hand, if the predetermined time has elapsed in step S26, the process proceeds to step S27, in which the ECU 70 releases the current limitation performed in step S10 of FIG. 8, and in step S28, the ECU 70 applies a restraining force to the battery module 60 through the restraining load variable mechanism 81.

[0074] (Modification) In the control procedure of FIG. 8, the threshold value of the duration of large-current charging and discharging is set in advance as a fixed value. The timing at which irreversible deterioration of the battery begins due to large-current charging and discharging varies depending on the state of aging deterioration of the battery, the current value, temperature, etc. Therefore, in order to avoid irreversible deterioration by controlling the duration of large-current charging and discharging, the set threshold value, which is a fixed value, must be set with a considerable margin with respect to the ideal threshold value, as shown in FIG. 4. In other words, the permitted duration becomes short. In this case, the intervention of current limitation becomes more frequent depending on the driving conditions of the vehicle, and for example, in an electric vehicle, the acceleration driving of the vehicle is restricted, and in a hybrid vehicle, the engine is forced to be driven, resulting in a deterioration of fuel efficiency.

[0075] As described above, the timing at which irreversible high-rate degradation begins to occur is not constant, and the timing becomes earlier as the number of cycles of high-current charging and discharging increases (see FIG. 6). Since there is a correlation between the timing at which irreversible high-rate degradation begins to occur and the timing at which the internal pressure of the battery cell 62 begins to rise rapidly, the ECU 70 can determine signs of irreversible high-rate degradation by monitoring the internal pressure of the battery cell 62. If the ECU 70 updates the permitted continuation time of high-current charging and discharging based on this determination, it is possible to set a threshold value exemplified as the "ideal threshold value" in FIG. 4. In this case, it is possible to suppress the progression of irreversible high-rate degradation while making the permitted continuation time as long as possible.

[0076] 10 shows a flow of control according to the modified example. In step S31 after the start, the charge / discharge current value I is acquired, and in the following step S32, it is determined whether the charge / discharge current value I exceeds a predetermined value Io (high current charge / discharge).

[0077] If it is determined in step S32 that large current charging / discharging is occurring, the process proceeds to step S33, where the duration of large current charging / discharging is integrated. If it is determined in the following step S34 that the integrated value T is equal to or greater than the first threshold value (No), the process proceeds to step S35, where the charging / discharging current value I is limited to a predetermined current value Io or less (large current charging / discharging is prohibited). Note that the first threshold value here is updated based on changes in the internal pressure of the battery cell 62, as will be described later.

[0078] If it is determined in step S32 that the charge / discharge is not a large current charge / discharge, the process proceeds to step S36, where it is determined whether the vehicle operation has ended (SW-OFF), and if the operation has ended, the control ends, and if the operation has not ended, the process returns to step S31 to continue acquiring the charge / discharge current value I.

[0079] If it is determined in step S34 that the integrated value T has not reached the threshold value (Yes), the process proceeds to step S37, where it is determined whether the cell reaction force P has reached the internal pressure threshold value Po. If it has reached the internal pressure threshold value Po, the process proceeds to step S38, where the restraining load applied to the battery cell 62 is reduced by a predetermined value. Then, in the following step S39, it is determined whether the rate of increase Pr of the cell reaction force has reached or exceeded a predetermined value Pro.

[0080] When the rate of increase Pr of the cell reaction force becomes equal to or greater than the predetermined value Pro, the process proceeds to step S310. In step S310, the ECU 70 determines whether the integrated value T is less than a second threshold value. The second threshold value is a threshold value related to the remaining amount of electrolyte in the battery cell 62, and is a threshold value for determining whether the remaining amount of electrolyte in the battery cell 62 is low. The second threshold value may be, for example, a set threshold value (fixed value) in FIG. 4 or FIG. 6. The second threshold value is smaller than the first threshold value.

[0081] In step S310, if the integrated value T is less than the second threshold, and the charge / discharge duration is less than the predetermined time, the rate of increase Pr of the cell reaction force is equal to or greater than the predetermined value Pro. The process proceeds to step S311, and the ECU 70 limits the charge / discharge current value I to a predetermined current value Io or less (prohibits large current charge / discharge). In the following step S312, the refill reminder display unit 55 reminds the vehicle user to refill the electrolyte, and in step S313, the target SOC display unit 56 notifies the user that the target SOC is set low. The ECU 10 also controls the charge / discharge of the battery module 60 so that the SOC of the battery module 60 becomes relatively low.

[0082] On the other hand, if the integrated value T is equal to or greater than the second threshold in step S310, the process proceeds to step S314. In this case, although refilling of the electrolyte is not necessary, there is a risk of irreversible high-rate deterioration progressing, so the ECU 70 limits the current so that the charge / discharge current value I is equal to or less than a predetermined current value Io, and in the next step S315, based on the integrated value T of the duration of high-current charge / discharge until the rate of increase Pr of the cell reaction force becomes equal to or greater than a predetermined value Pro, a time that is a predetermined time shorter than the integrated value T (i.e., a slightly shorter time) is updated as the first threshold for permitting the continuation of high-current charge / discharge. In addition, the internal pressure threshold Po of the cell reaction force P is set to a pressure that is a predetermined value higher than the current threshold.

[0083] Furthermore, if in step S37 the cell reaction force P has not reached the internal pressure threshold value Po, and if in step S39 the rate of increase Pr of the cell reaction force has not reached or exceeded the predetermined value Pro, the process proceeds to step S36 where it is determined whether or not the vehicle has ended operation (SW-OFF), and if so, the control ends, and if not, the process returns to step S31.

[0084] According to this control, when the integrated value T is equal to or greater than the second threshold value and the rate of increase Pr of the cell reaction force P is equal to or greater than a predetermined value Pro, a time shorter than the integrated value T by a predetermined time is set as a time threshold value (i.e., a first threshold value) that permits the continuation of high-current charging and discharging. The point at which the rate of increase Pr of the cell reaction force P is equal to or greater than the predetermined value Pro is the point at which signs of irreversible high-rate degradation appear. By setting this threshold value, the current is subsequently limited just before signs of irreversible high-rate degradation appear. The purpose is to prevent the progression of irreversible high-rate degradation due to high-current charging and discharging.

[0085] By monitoring the cell internal pressure, signs of irreversible high-rate degradation are detected and a threshold for the permitted duration of large-current charging and discharging is set, so that large-current charging and discharging can be continued until close to the limit at which irreversible degradation does not occur. This reduces the frequency of current restriction intervention due to management of the duration of large-current charging and discharging, thereby suppressing deterioration of the vehicle's fuel efficiency.

[0086] In charging and discharging after setting the large current charge / discharge continuation permitted time threshold based on the integrated value T, if the rate of increase Pr of the cell reaction force P becomes equal to or exceeds a predetermined value Pro before the threshold is reached, the current is limited at that point, and a new first threshold is set based on the integrated value T up to that point. The integrated value T in this case is shorter in time than the integrated value T in the previous time threshold setting. Therefore, in setting the time threshold by monitoring the rate of increase Pr of the cell reaction force P, the large current charge / discharge continuation permitted time becomes shorter little by little each time the time threshold is set.

[0087] In addition, in the above control, the cell internal pressure threshold value Po for reducing the restraining load is changed to a value higher by a predetermined value each time the threshold value for the permitted continuation time of large current charging / discharging is set (determination is made that the rate of increase in the cell internal pressure has reached a predetermined value or more). As shown in Fig. 6, the internal pressure of the battery cells 62 increases as the deterioration progresses, and the purpose of this is to increase the internal pressure threshold value Po in response to this deterioration. This makes it possible to avoid unnecessarily hastening the reduction of the restraining load of the battery cells 62, and suppresses a decrease in the restraining effect, such as preventing the precipitation of ions in the electrolyte.

[0088] Even with the above control, if the accumulated time T until the rate of increase Pr of the internal pressure P of the battery cell 62 becomes equal to or greater than the predetermined value Pro is a short time that is less than the second threshold value, the ECU 70 estimates that the electrolyte in the battery cell 62 is low and prompts the user to replenish the electrolyte, thereby enabling the user to be prompted to replenish the electrolyte at an appropriate time. [Explanation of symbols]

[0089] 100 Hybrid vehicles (vehicles) 110 Battery unit 60 Battery Module 62 Battery Cell 67 Surface pressure sensor (cell internal pressure detector) 70 ECU (Controller) 81 Variable restraint load mechanism

Claims

1. A battery unit that is mounted on a vehicle and has a plurality of chargeable and dischargeable battery cells; a cell internal pressure detector for detecting an internal pressure of the battery cell; A controller for controlling the battery unit, The controller includes: during charging / discharging of the battery unit at a large current equal to or greater than a predetermined current value, when the duration of charging / discharging is less than a predetermined time, determining whether or not a rate of increase in the internal pressure detected by the cell internal pressure detector has reached a predetermined value or greater; When it is determined that the rate of increase in the internal pressure is equal to or greater than the predetermined value, a prompt is given to replenish the electrolyte in the battery cell. Vehicle battery unit control device.

2. 2. The vehicle battery unit control device according to claim 1, The controller prompts the battery cell to be replenished with electrolyte and inhibits charging / discharging at the large current. Vehicle battery unit control device.

3. 3. The vehicle battery unit control device according to claim 1, The controller issues a command to reduce the SOC of the battery unit to a predetermined value or less before the electrolyte is replenished to the battery cells. Vehicle battery unit control device.

4. The vehicle battery unit control device according to any one of claims 1 to 3, the battery unit includes a battery module in which the plurality of battery cells are stacked in layers and constrained in an overlapping direction, and a constraint load variable mechanism that changes a constraint load applied to the battery cells; the controller operates the restraint load variable mechanism so as to reduce the restraint load applied to the battery cell, and then determines whether or not a rate of increase in the internal pressure detected by the cell internal pressure detector has reached a predetermined value or more. Vehicle battery unit control device.

5. 5. The vehicle battery unit control device according to claim 4, the controller activates the restraint load variable mechanism so as to release the restraint load applied to the battery cell when the electrolyte is replenished to the battery cell; Vehicle battery unit control device.

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