Vehicle battery unit control device

Abstract

To suppress irreversible deterioration of a battery due to high current charging and discharging without making intervention frequency of current limit to be excessively high.SOLUTION: When an increase rate of an internal pressure of a battery cell exceeds a predetermined value during high current charging / discharging of a battery unit 110, the high current charging / discharging are inhibited, and, on the basis of an integral value of duration of the high current charging / discharging until the increase rate of the internal pressure exceeds the predetermined value, a time shorter than the integral value by a predetermined time is set as a time that allows continuation of charging / discharging by high current.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention 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 discloses that when the integrated value of the charge / discharge current of a battery over a specified period of time is equal to or greater than a specified threshold, the battery is judged to be degraded and the charge / discharge current value is limited to a specified value or less, i.e., long-term charging and discharging at a large current is limited. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-69142 Summary of the Invention [Problem to be solved by the invention]

[0005] A simple method for suppressing irreversible deterioration of a battery caused by large current charging and discharging is to set a duration for which large current charging and discharging is permitted, and prohibit large current charging and discharging when the duration is reached. In other words, this method sets the duration for which large current charging and discharging is permitted so that it is stopped just before irreversible deterioration begins.

[0006] However, the timing at which irreversible deterioration of the battery begins due to high-current charging and discharging varies depending on the state of aging of the battery, the current value, temperature, etc. Therefore, in order to avoid irreversible deterioration by controlling the duration of high-current charging and discharging, the permitted duration must be set short with a considerable margin. In that case, the frequency of intervention of current limiting increases depending on the driving conditions of the vehicle, for example, in an electric vehicle, the acceleration of the vehicle is restricted, and in a hybrid vehicle, the engine is forced to be driven, resulting in a deterioration of fuel efficiency.

[0007] Therefore, the present invention suppresses irreversible deterioration of the battery caused by large current charging and discharging without excessively increasing the frequency of current limiting intervention. [Means for solving the problem]

[0008] The inventors have found 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. Based on this finding, the present invention is designed to monitor the internal pressure of the battery cell during large current charging and discharging to determine signs of irreversible deterioration, and to set the permitted continuation time of large current charging and discharging based on this determination.

[0009] The control device for a vehicle battery unit disclosed herein is configured such that the battery unit is configured with a plurality of chargeable and dischargeable battery cells connected in series, a cell internal pressure detector that detects the state of the internal pressure of the battery cell during charging / discharging of the battery unit with a large current equal to or greater than a predetermined current value; a duration integrating unit that integrates a duration during which charging / discharging at the large current is continued while the battery unit is being charged / discharged; an internal pressure determination unit that 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; a current limiting unit that prohibits charging and discharging at the large current when the internal pressure determining unit determines that the rate of increase in the internal pressure has reached a predetermined value or more; The present invention is characterized in that it is provided with a continuation permission time setting unit which, when it is determined by the internal pressure determination unit that the rate of increase of the internal pressure has reached a predetermined value or more, sets, based on the integrated value of the duration of charging / discharging at the high current accumulated by the duration accumulation unit up to the point of this determination, a time that is a predetermined time shorter than the integrated value as the time for which continuation of charging / discharging at the high current is permitted.

[0010] When charging and discharging at a large current are repeated, the internal pressure of the battery cell increases. 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 also increases. When this uneven distribution of the electrolyte is minor, it can be eliminated by suspending charging and discharging. However, when the 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.

[0011] The control device of the vehicle battery unit detects signs of irreversible deterioration of the battery cells by determining that the rate of increase in the internal pressure of the battery cells has reached a predetermined value or higher. When this determination is made, charging and discharging at a large current is prohibited (however, charging and discharging at a small current lower than the predetermined current value is not prohibited), thereby preventing the irreversible deterioration of the battery cells from progressing.

[0012] Then, when the above-mentioned determination is made, a time that is shorter than the integrated value of the duration of the high current charging and discharging up to that point is set as the permitted duration of the high current charging and discharging. Therefore, thereafter, the high current charging and discharging is prohibited just before irreversible deterioration occurs. Thus, irreversible deterioration of the battery cells is efficiently suppressed. In this case, each time the above-mentioned determination is made, the permitted duration of the high current charging and discharging is shortened little by little.

[0013] Since the above judgment detects signs of irreversible deterioration of the battery cells, it cannot be said that irreversible deterioration of the battery cells will not occur at that time, but even if irreversible deterioration progresses, it will be only slightly. Instead, when the permitted continuous charging and discharging time is set based on the judgment, charging and discharging at a large current is not prohibited until just before irreversible deterioration of the battery cells occurs. Therefore, the frequency of intervention of current limiting by managing the duration of large current charging and discharging is reduced. This makes it possible to suppress deterioration in acceleration of electric vehicles and deterioration in fuel efficiency of hybrid vehicles.

[0014] Here, the accumulation of the duration of charging and discharging at a large current means accumulating the duration of charging and discharging at a large current when charging and discharging at a large current and charging and discharging at a small current are repeated.

[0015] In one embodiment, 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, a restraint load control unit that operates the restraint load variable mechanism so as to reduce the restraint load applied to the battery cell when the internal pressure of the battery cell detected by the cell internal pressure detector during charging / discharging at the large current becomes equal to or higher than a predetermined internal pressure threshold value, The internal pressure determination unit 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 after the restraint load variable mechanism reduces the restraint load.

[0016] As described above, irreversible deterioration of the battery cell (uneven distribution of electrolyte) occurs due to the outflow of electrolyte from the negative electrode active material. In contrast, when the internal pressure of the battery cell reaches or exceeds a predetermined internal pressure threshold, the restraining load applied to the battery cell is reduced, and the amount of electrolyte outflow is reduced compared to when the restraining load is not reduced. In other words, the deterioration of the battery cell progresses more slowly. In this embodiment, the rate of increase in the internal pressure of the battery cell is determined in a state in which the restraining load is reduced to slow the progression of deterioration. Therefore, the progression of irreversible deterioration of the battery cell is reduced each time this determination is made.

[0017] In one embodiment, the internal pressure threshold value, which activates the restraint load variable mechanism so as to reduce the restraint load, is changed to a value higher by a predetermined value each time the internal pressure determination unit determines that the rate of increase of the internal pressure has reached or exceeded a predetermined value.

[0018] The internal pressure of the battery cell increases as the deterioration progresses, and the internal pressure threshold is increased in response to this deterioration. This makes it possible to avoid unnecessarily hastening the reduction of the restraining load before the internal pressure increase rate of the battery cell is determined, and suppresses the reduction of the restraining effect, such as preventing the precipitation of ions in the electrolyte, from decreasing.

[0019] In one embodiment, a battery life prediction unit is provided that predicts whether or not a life of the battery cell will be shorter than expected based on a charge / discharge history of the battery cell, The continued permission time setting unit sets the continued permission time for charging and discharging at a large current to a predetermined minimum time when the battery life prediction unit predicts a short life of the battery cell, and sets the continued permission time for charging and discharging at a large current based on an integrated value of the duration of charging and discharging at the large current when a short life of the battery cell is not predicted.

[0020] As described above, the determination that the rate of increase in the internal pressure of the battery cell has reached a predetermined value or more indicates a sign of irreversible deterioration of the battery cell, and therefore if the determination is repeated frequently, the irreversible deterioration of the battery cell will progress. Therefore, when a short life of the battery cell is predicted, a predetermined minimum permitted continued time is set, rather than setting the permitted continued time based on the determination. This suppresses the progression of the irreversible deterioration associated with the determination, which is advantageous for extending the life of the battery cell. For example, in cases where a vehicle is frequently operated with high current charging and discharging, the battery cell is likely to have a short life, but the determination can be used to prevent the battery life from being further shortened. Effect of the Invention

[0021] According to the present invention, when it is determined that the rate of increase in the internal pressure of a battery cell has reached a predetermined value or greater, a time that is shorter than the integrated value of the duration of high current charging and discharging up to that determination is set as the permitted continued high current charging and discharging time.Therefore, from then on, high current charging and discharging is prohibited just before irreversible deterioration occurs, and the frequency of current limitation due to management of the duration of high current charging and discharging is reduced, thereby suppressing deterioration in acceleration in electric vehicles and deterioration in fuel efficiency in hybrid vehicles. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is an overall configuration diagram of a hybrid vehicle equipped with a vehicle battery unit and its control device. [Diagram 2] 1A and 1B are explanatory diagrams showing a battery cell restraint mechanism ((a) shows the state before a restraint load is applied, and (b) shows the state after a restraint load is applied). [Diagram 3] 1 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. [Figure 4] 1 is a graph showing an increase in cell reaction force due to continued large current charging and discharging. [Diagram 5] FIG. 2 is a conceptual diagram showing the movement of an electrolyte solution accompanying the progression of high-rate degradation. [Figure 6] FIG. 11 is a graph showing the change in the state of increase in cell reaction force as the number of large current charge / discharge cycles increases. [Figure 7] 11 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. 4 is a flow diagram of control of the battery unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its application, or its uses.

[0024] This embodiment is an application of the present invention to a hybrid vehicle. <Overall configuration of hybrid vehicle> 1, a hybrid vehicle 100 includes wheels 10, axles 12, an engine 20, a transmission 30, a motor 40, an inverter 50, a battery unit 110, and an electronic control unit (ECU: Electronic Control Unit) 70 that controls the battery unit 110. This hybrid vehicle 100 is of a parallel type, and the engine 20 and the motor 40 function as drive sources that output 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 40, or running using only the motor 40.

[0025] The engine 20 is connected to the axle 12 via the transmission 30. The engine 20 is, for example, a gasoline engine. The motor 40 is connected 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 40. The motor 40 receives the supplied electric power and functions as an electric motor to rotate the axle 12. The motor 40 also functions as a generator by performing a regenerative operation when the hybrid vehicle 100 decelerates, thereby charging the battery module 60.

[0026] <Battery unit> The battery unit 110 includes the battery module 60 and the battery cell restraining mechanism 80. As shown in Fig. 2, 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 on both ends of the stacking direction D and the vertical walls of the casing 61.

[0027] 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.

[0028] 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.

[0029] The restraint load variable mechanism 81 includes a pressure gear 84 coupled 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 restraint load applied to the multiple battery cells 62. The operation of the motor 85 is controlled by a restraint load control unit 82.

[0030] 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.

[0031] The battery cell 62 is constructed 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.

[0032] 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 13 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.

[0033] Although the above-mentioned battery cell 62 is a wound type, it may be 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 it may be in another form; the form of the battery cell 62 is not an issue in the present invention.

[0034] <Battery unit control device> The battery unit 110 is controlled by a control device 70. As shown in Fig. 1, the control device 70 includes a duration integrating unit 71 that integrates the time during which charging / discharging of the battery module 60 at a large current exceeding a predetermined current value Io continues, an internal cell pressure determining unit 72, a current limiting unit 73, a battery life predicting unit 74, an allowed duration setting unit 75, and the aforementioned binding load control unit 82.

[0035] 3 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 the above-mentioned 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, causing 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 when the battery is suspended, causing the internal resistance to remain elevated. When irreversible deterioration begins to occur, the rise in internal resistance becomes rapid.

[0036] In order to prevent irreversible high-rate degradation while continuing high-current charging and discharging as long as possible, the internal resistance of the battery can be monitored and the continuation of high-current charging and discharging can be stopped at the timing when the internal resistance rises sharply. However, this timing varies depending on the operating conditions, etc., and is difficult to grasp. In response to this, a threshold can be set for the duration of high-current charging and discharging, and a current limit can be applied to stop the continuation of high-current charging and discharging before the irreversible degradation occurs, but the timing at which irreversible degradation begins to occur varies depending on the operating conditions and degree of degradation of the battery. Therefore, in order to prevent irreversible degradation, a time threshold must be set so that the continuation of high-current charging and discharging is stopped early, and high-current charging and discharging cannot be continued for a long time.

[0037] Based on the knowledge that the cell reaction force (internal cell 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 increases. The results are shown in Figure 4. As high-current charging and discharging continues, the cell reaction force increases slowly for a while from the initial point A, but then increases rapidly from point B. Investigations revealed that the timing at which this cell reaction force begins to increase rapidly corresponds to the timing at which irreversible high-rate charging begins.

[0038] As shown in FIG. 5, when high-current charging and discharging continues, initially (A) the entire electrode winding 62a is immersed in the electrolyte 62b, so the battery reaction proceeds throughout the entire negative electrode. As high-current discharging progresses, 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 62a in the winding axis direction, and the amount of electrolyte decreases at the center of the electrode (the center of the winding axis direction), and the reaction area of ​​the negative electrode decreases (B). As high-current charging and discharging progresses further, the electrolyte at the center of the electrode seems to have dried up, and the reaction area decreases significantly (C).

[0039] The reason why high-rate deterioration progresses as high-current charging and discharging proceeds is that the reactive 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, i.e., the cell reaction force, increases.

[0040] 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.

[0041] 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. 4 begins to rise sharply (the timing when irreversible high-rate degradation begins), and the resistance rise 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, the resistance rise 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, the resistance rise rate did not increase so much even if the high-current charging and discharging time became longer, and the resistance rise 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.

[0042] As described above, the inventors have found 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 have also found that the irreversible degradation can be suppressed by reducing the binding load applied to the battery cell 62 at the timing at which the internal pressure rises rapidly. The present invention utilizes these phenomena in the control of the battery module 60, making it possible to minimize the frequency of current limiting intervention.

[0043] The battery unit control device 70 will now be described in detail.

[0044] 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.

[0045] The cell internal pressure determination unit 72 determines whether the internal pressure P of the battery cell 62 detected by the surface pressure sensor (cell internal pressure detector) 67 has reached a predetermined internal pressure threshold Po (P≧Po) during charging and discharging at the above-mentioned large current. Furthermore, when the cell internal pressure determination unit 72 determines that the internal pressure P has reached or exceeded the predetermined internal pressure threshold Po and the restraint load control unit 82 has performed the restraint load reduction control described below, it determines whether the increase rate Pr of the internal pressure P has reached or exceeded a predetermined value Pro.

[0046] The current limiting unit 73 limits the current so that the charging / discharging current value I becomes equal to or lower than the predetermined current value Io (prohibition of charging / discharging at the large current) when the integrated value T of the duration of the large current charging / discharging integrated by the duration integrating unit 71 becomes equal to or higher than a threshold value (described later) set by the permitted duration setting unit 74. The current limiting unit 73 also limits the current in the same manner (prohibition of charging / discharging at the large current) when the cell internal pressure determining unit 72 determines that the rate of increase Pr of the internal pressure of the battery cell 62 becomes equal to or higher than a predetermined value Pro.

[0047] The battery life prediction unit 74 predicts whether the battery cells 62 will have a shorter life than expected based on the charge / discharge history (charge / discharge current value and time) of the battery module 60. Specifically, it predicts the SOH (States Of Health) at the EOL (End of Life: end of battery life) from the charge / discharge history, and predicts that the battery cells 62 will have a shorter life when the SOH at the EOL is equal to or lower than the guaranteed SOH (e.g., 30%).

[0048] The continuation permission time setting unit 75 sets a minimum time as the time threshold for permitting continuation of the large current charging and discharging when the battery life prediction unit 74 predicts a short life of the battery cell 62. On the other hand, when a short life of the battery cell 62 is not predicted, the time threshold for permitting continuation of the large current charging and discharging is set based on the integrated value T of the duration of the large current charging and discharging 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 the predetermined value Pro. In this case, a time that is a predetermined time shorter than the integrated value T is set as the time threshold for permitting continuation of the large current charging and discharging.

[0049] The restraint load control unit 82 operates the restraint load variable mechanism 81 so that a predetermined restraint load is applied to the battery cell 62 in order 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 greater than a predetermined internal pressure threshold Po during the high-current charging / discharging, the restraint load variable mechanism 81 is operated so that the restraint load applied to the battery cell 62 is reduced by a predetermined load. The internal pressure threshold Po for operating the restraint load variable mechanism so as to reduce the restraint load is changed to a value higher by a predetermined value each time the cell internal pressure determination unit 72 determines that the rate of increase Pr of the internal pressure has become equal to or greater than a predetermined value Pro. This is because, as shown in FIG. 6, the cell reaction force increases as the number of cycles of high-current charging / discharging increases.

[0050] (Flow of Control) The flow of control is shown in Fig. 8. In step S1 after starting, the EOL (End of Life: end of battery life) SOH (States Of Health) is predicted from the charge / discharge history of the battery module 60. If this EOL SOH is equal to or lower than the guaranteed SOH (short battery life is predicted), the process proceeds to step S2, where a short minimum time is set as a time threshold for permitting continued charging / discharging at a large current. In the following step S3, the charge / discharge current value I is acquired, and in the following step S4, it is determined whether the charge / discharge current value I exceeds a predetermined value Io (large current charging / discharging). In step S1, if the EOL SOH is greater than the guaranteed SOH (short battery life is not predicted), the process proceeds to step S3 without setting the time threshold.

[0051] If it is determined in step S4 that large current charging / discharging is occurring, the process proceeds to step S5, where the duration of large current charging / discharging is integrated. If it is determined in the following step S6 that the integrated value T is equal to or greater than a threshold value (No), the process proceeds to step S7, where the charging / discharging current value I is limited to a predetermined current value Io or less (large current charging / discharging is prohibited). If it is determined in step S4 that large current charging / discharging is not occurring, the process proceeds to step S8, where it is determined whether or not the vehicle has finished operating (IG-OFF), and if it has finished operating, the control is terminated, and if it has not finished operating, the process returns to step S3, where monitoring of large current charging / discharging is continued.

[0052] If it is determined in step S6 that the integrated value T has not reached the threshold value (Yes), the process proceeds to step S9, 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 S10, where the restraining load applied to the battery cell 62 is reduced by a predetermined value. Then, in the following step S11, it is determined whether the rate of increase Pr of the cell reaction force has reached or exceeded a predetermined value Pro.

[0053] When the rate of increase Pr of the cell reaction force becomes equal to or greater than a predetermined value Pro, it is determined that there is a sign of irreversible high-rate degradation, and the process proceeds to step S12, where the charge / discharge current value I is limited to a predetermined current value Io or less (prohibition of large-current charge / discharge). In the following step S13, based on the integrated value T of the duration of large-current charge / discharge up to the point when the rate of increase Pr of the cell reaction force becomes equal to or greater than the predetermined value Pro, a time period shorter than the integrated value T by a predetermined time (i.e., a slightly shorter time) is set as the threshold for permitting the continuation of large-current charge / discharge. In addition, the internal pressure threshold value Po of the cell reaction force P is set to a pressure higher by a predetermined value than the current threshold value.

[0054] If the cell reaction force P has not reached the internal pressure threshold value Po in step S9, the flow proceeds to step S14 to determine whether the vehicle has ended operation (IG-OFF). If the vehicle has ended operation, the control ends. If the vehicle has not ended operation, the flow returns to step S5 to continue accumulating the duration of large current charging and discharging.

[0055] According to the above control, the time threshold for permitting the continuation of large current charging and discharging is set to a minimum time when a short battery life is predicted (SOH of EOL≦guaranteed SOH), and a time threshold longer than the minimum time is set when a short battery life is not predicted. This long time threshold is set by determining that the rate of increase Pr of the cell internal pressure has reached a predetermined rate of increase Pro or more, and this determination is made based on the signs of irreversible high-rate degradation. Therefore, there is a concern that the setting of the long time threshold may cause the irreversible degradation of the battery to progress, albeit slightly. Therefore, when a short battery life is predicted, the minimum value is set as the permitted continuation time of large current charging and discharging from the viewpoint of extending the battery life, to avoid irreversible high-rate degradation.

[0056] The threshold time for permitting the continuation of high-current charging and discharging when the battery is not predicted to have a short life is set based on the integrated value T of the duration of high-current charging and discharging up to the point when the rate of increase Pr of the cell reaction force P becomes equal to or greater than a predetermined value Pro. In other words, a time shorter than the integrated value T by a predetermined time is set as the threshold time for permitting the continuation of high-current charging and discharging. The point when the rate of increase Pr of the cell reaction force P becomes equal to or greater than the predetermined value Pro is the point when signs of irreversible high-rate degradation appear. By setting this threshold, the current is subsequently limited just before signs of irreversible high-rate degradation appear. The purpose is to prevent irreversible high-rate degradation from progressing due to high-current charging and discharging.

[0057] 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.

[0058] In charging and discharging after setting the large current charge / discharge continuation permitted time threshold based on the above-mentioned integrated value T, if the rate of increase Pr of cell reaction force P becomes equal to or exceeds a predetermined value Pro before reaching the threshold, the current is limited at that point, and a new time 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, when the time threshold is set by monitoring the rate of increase Pr of cell reaction force P, the large current charge / discharge continuation permitted time becomes shorter little by little each time the time threshold is set.

[0059] 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. In other words, the progress of irreversible deterioration of the battery cell 62 becomes slower. In this way, the rate of increase of the cell internal pressure is determined in a state in which the progress of irreversible deterioration is slowed down, and the threshold value for the permitted continuation time of large current charging and discharging is set, so that the progress of irreversible deterioration of the battery cell 62 each time the threshold value is set is reduced.

[0060] 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.

[0061] The battery unit control device of the present invention is applicable not only to the hybrid vehicle 100 as described above, but also to electric vehicles (EVs). [Explanation of symbols]

[0062] 60 Battery Module 62 Battery Cell 67 Surface pressure sensor (cell internal pressure detector) 70 Control device 71 Duration accumulation unit 72 Cell internal pressure determination unit 73 Current limiting section 74 Battery Life Prediction Unit 75 Continuation permission time setting section 81 Variable restraint load mechanism 82 Restraint load control unit 100 vehicles 110 Battery unit

Claims

1. A control device for a vehicle battery unit configured by connecting a plurality of chargeable and dischargeable battery cells in series, a cell internal pressure detector that detects the state of the internal pressure of the battery cell during charging / discharging of the battery unit with a large current equal to or greater than a predetermined current value; a duration integrating unit that integrates a duration during which charging / discharging at the large current is continued while the battery unit is being charged / discharged; an internal pressure determination unit that 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; a current limiting unit that prohibits charging and discharging at the large current when the internal pressure determining unit determines that the rate of increase in the internal pressure has reached a predetermined value or more; and a continuation permission time setting unit that, when the internal pressure determination unit determines that the rate of increase in the internal pressure has reached a predetermined value or more, sets a time permitted to continue charging and discharging at the large current that is a predetermined time shorter than the integrated value, based on the integrated value of the continuous charging and discharging time at the large current accumulated by the duration integrating unit up to the point of determination.

2. In claim 1, 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; a restraint load control unit that operates the restraint load variable mechanism so as to reduce the restraint load applied to the battery cell when the internal pressure of the battery cell detected by the cell internal pressure detector during charging / discharging at the large current becomes equal to or higher than a predetermined internal pressure threshold value, The internal pressure determination unit 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 greater after the restraint load variable mechanism reduces the restraint load.

3. In claim 2, A vehicle battery unit control device characterized in that the internal pressure threshold value that activates the restraint load variable mechanism so as to reduce the restraint load is changed to a value that is a predetermined value higher each time the internal pressure determination unit determines that the rate of increase of the internal pressure has reached or exceeded a predetermined value.

4. In any one of claims 1 to 3, a battery life prediction unit that predicts whether a life of the battery cell will be shorter than expected based on a charge / discharge history of the battery cell; the continuous permission time setting unit sets the continuous permission time of the large current charging / discharging to a predetermined minimum time when a short life of the battery cell is predicted by the battery life prediction unit, and sets the continuous permission time of the large current charging / discharging based on an integrated value of the duration of the large current charging / discharging when a short life of the battery cell is not predicted.

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