JP7632149B2 - Vehicle battery unit control device - Google Patents

Description

The present invention relates to a vehicle battery unit control device.

It is known that in rechargeable battery cells used in electric 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 high-current charging and discharging is continued for a short period of time, the deterioration is temporary (reversible deterioration) and can be restored by stopping charging and discharging. However, when the period of time is long, permanent deterioration occurs in which the battery performance does not recover even when charging and discharging are stopped, that is, irreversible deterioration.

Patent document 1 discloses that when the integrated charge/discharge current value of a battery over a specified period of time is equal to or exceeds a specified threshold, the battery is determined to be degraded and the charge/discharge current value is limited to a specified value or less, i.e., charging/discharging at a large current for a long period of time is limited.

JP 2021-69142 A

A simple method for preventing irreversible deterioration of a battery caused by high-current charging and discharging is to set the time that high-current charging and discharging is permitted to continue, and prohibit high-current charging and discharging when that time is reached. In other words, this method sets the time that high-current charging and discharging is permitted to continue so that it stops just before irreversible deterioration begins.

However, the timing at which irreversible deterioration of the battery begins due to high-current charging and discharging varies depending on the state of deterioration of the battery over time, 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 such cases, the frequency of current limit intervention 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 run, resulting in a deterioration of fuel efficiency.

Therefore, the present invention suppresses irreversible deterioration of the battery caused by high current charging and discharging without excessively increasing the frequency of current limiting intervention.

The inventors have found that there is a correlation between the timing at which irreversible deterioration due to high-current charging and discharging begins and the timing at which the internal pressure of the battery cell begins to rise rapidly. Based on this knowledge, the present invention monitors the internal pressure of the battery cell during high-current charging and discharging to determine signs of irreversible deterioration, and sets the permitted continuation time for high-current charging and discharging based on this determination.

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.

When charging and discharging at a large current is 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 volumetric expansion of the electrolyte caused by the insertion and removal of ions in the electrolyte, causing uneven distribution of the electrolyte within the battery cell. As this uneven distribution occurs, the internal resistance of the battery cell also rises. When this uneven distribution of the electrolyte is minor, it can be resolved by pausing charging and discharging, but when the uneven distribution becomes severe, the internal pressure of the battery cell begins to rise rapidly, and the uneven distribution cannot be resolved even by pausing charging and discharging. In other words, irreversible deterioration of the battery cell occurs.

The control device of the vehicle battery unit detects signs of irreversible deterioration of the battery cell by determining that the rate of increase in the internal pressure of the battery cell 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 cell from progressing.

When the above-mentioned judgment is made, the permitted continuous high current charging/discharging time is set to a time that is a predetermined time shorter than the integrated value of the continuous high current charging/discharging time up to that point. Therefore, thereafter, charging/discharging at a high current is prohibited just before irreversible deterioration occurs. This effectively suppresses irreversible deterioration of the battery cells. In this case, each time the above-mentioned judgment is made, the permitted continuous high current charging/discharging time is shortened little by little.

Because the above judgment detects signs of irreversible deterioration of the battery cells, it cannot be said with certainty 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 continued charging and discharging time is set based on this judgment, high-current charging and discharging will not be prohibited until just before irreversible deterioration of the battery cells occurs. This reduces the frequency of current limit intervention due to management of the duration of high-current charging and discharging. This makes it possible to suppress deterioration in acceleration in electric vehicles and deterioration in fuel efficiency in hybrid vehicles.

Here, accumulating 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.

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.

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.

In one embodiment, 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 higher by a predetermined value each time the internal pressure determination unit determines that the rate of increase in the internal pressure has reached or exceeded a predetermined value.

As the battery cell deteriorates, its internal pressure increases, and the purpose of this is to increase the internal pressure threshold in response to this deterioration. This avoids unnecessarily hastening the reduction of the restraining load before determining the rate of increase in the battery cell's internal pressure, and suppresses a decrease in the restraining effect, such as preventing the precipitation of ions in the electrolyte.

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.

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 if this 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 above 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, where the battery cell is likely to have a short life, the above determination can be used to prevent the battery life from being shortened even further.

According to the present invention, when it is determined that the rate of increase in the internal pressure of the battery cell has reached a predetermined value or more, a time that is a predetermined time shorter than the cumulative value of the duration of high-current charging and discharging up to that determination is set as the permitted duration of high-current charging and discharging. Thereafter, high-current charging and discharging is prohibited just before irreversible deterioration occurs, and the frequency of current limitations due to management of the duration of high-current charging and discharging is reduced, thereby suppressing deterioration in the acceleration of electric vehicles and deterioration in fuel efficiency of hybrid vehicles.

FIG. 1 is an overall configuration diagram of a hybrid vehicle equipped with a vehicle battery unit and its control device. 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). 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. 1 is a graph showing an increase in cell reaction force due to continued large current charging and discharging. FIG. 2 is a conceptual diagram showing the movement of an electrolyte solution accompanying the progression of high-rate degradation. 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. 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. FIG. 4 is a flow diagram of control of the battery unit.

The following describes the embodiments of the present invention with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

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) 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.

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 the battery module 60 of the battery unit 110 via an inverter 50. The motor 40 receives power from the battery module 60, which is converted to AC power by the inverter 50 and then supplied with the power. The motor 40 receives the power supply and functions as an electric motor to rotate the axle 12. The motor 40 also functions as a generator by performing regenerative operation when the hybrid vehicle 100 decelerates, thereby charging the battery module 60.

<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.

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.

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

The restraint load variable mechanism 81 includes 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 drives the drive gear 86 to rotate. The forward and backward movement 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 the restraint load control unit 82.

A surface pressure sensor 67 is provided between one end plate 66 and the battery cell 62 at the end as a cell internal pressure detector. 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.

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

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 whose main component is 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.

The battery cell 62 is a wound type, but 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 for the present invention.

<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, a cell internal pressure determining unit 72, a current limiting unit 73, a battery life predicting unit 74, a permitted duration setting unit 75, and the above-mentioned binding load control unit 82.

Figure 3 shows a schematic diagram of the rise in internal resistance associated with 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 normal irreversible 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 due to an imbalance in the Li ion concentration distribution caused by continued charging and discharging at a large current. High-rate deterioration includes reversible deterioration (temporary deterioration) in which the above-mentioned 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 above-mentioned 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.

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 when the internal resistance rises sharply. However, this timing varies depending on the operating conditions, etc., and is difficult to grasp. To address 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 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 long.

Based on the knowledge that 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 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. Upon investigation, it was found that the timing at which this cell reaction force begins to increase rapidly corresponds to the timing at which irreversible high-rate charging begins.

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 progresses throughout the entire negative electrode. As high-current discharging progresses, as Li ions are inserted into the negative electrode active material, the electrolyte is pushed out of the negative electrode active material and flows out toward the ends of the battery case. That is, the electrolyte moves to both ends of the electrode winding 62a in the winding axis direction, and there is less electrolyte at the center of the electrode (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).

In this way, high-rate deterioration progresses as high-current charging and discharging proceeds because the reactive area of the negative electrode decreases due to the outflow of electrolyte. As electrolyte flows out to the electrode end side, the internal pressure of the battery cell 62, i.e., the cell reaction force, increases.

The inventors have 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 when the vehicle starts to be driven and then ends after one or more high-current charging and discharging operations. As shown in Figure 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.

In addition, the restraining load applied to the battery cell 62 was reduced at the timing when the cell reaction force indicated by the downward arrow in Figure 4 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 Figure 7. In the case where the restraining load was not reduced, the resistance increase rate increased significantly as the high-current charging and discharging time became longer. In contrast, in the case where the restraining load was reduced, the resistance increase rate did not increase as much even with the high-current charging and discharging time becoming longer, and the resistance increase rate that finally settled after charging and discharging was suspended was also smaller than in the case where the restraining load was not reduced. In other words, the degree of irreversible degradation was low.

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 restraining 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.

The battery unit control device 70 is described in detail below.

The duration integrator 71 acquires the charge/discharge current value I of the battery module 60 at predetermined sampling intervals (e.g., 0.1 to 1 second) while the battery module 60 is being charged or discharged, calculates the duration when this charge/discharge current value I is equal to or greater than a preset current value Io (high current charging/discharging), and integrates the duration each time high current charging/discharging is performed.

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. In addition, 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.

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 set by the permitted duration setting unit 74, which will be described later, the current limiting unit 73 limits the current so that the charge/discharge current value I becomes equal to or less than the above-mentioned predetermined current value Io (prohibiting charging/discharging at the above-mentioned large current). The current limiting unit 73 also limits the current in the same manner 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 (prohibiting charging/discharging at the above-mentioned large current).

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) from the charge/discharge history, and when the SOH at the EOL is equal to or less than the guaranteed SOH (e.g. 30%), it predicts that the battery cells 62 will have a shorter life.

The continuation permission time setting unit 75 sets a minimum time as the time threshold for permitting continuation of charging and discharging at the large current 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 unit 75 sets a time threshold for permitting continuation of charging and discharging at the large current based on the integrated value T of the duration of charging and discharging at the large current 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 a predetermined value Pro or more. 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 large current charging and discharging.

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 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 reached a predetermined internal pressure threshold Po or higher during charging/discharging at the high current, 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 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 reached a predetermined value Pro or higher. This is because, as shown in FIG. 6, the cell reaction force increases as the number of cycles of high current charging/discharging increases.

(Flow of Control)
The flow of control is shown in Fig. 8. In step S1 after the start, the SOH (States Of Health) at the end of life (EOL) is predicted from the charge and discharge history of the battery module 60. If the SOH at the EOL is equal to or less 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 and discharging at a large current. In the following step S3, the charge and discharge current value I is acquired, and in the following step S4, it is determined whether the charge and discharge current value I exceeds a predetermined value Io (large current charging and discharging). In step S1, if the SOH at the EOL is greater than the guaranteed SOH (short battery life is not predicted), the process proceeds to step S3 without setting the time threshold.

If it is determined in step S4 that a large current charge or discharge has occurred, the process proceeds to step S5, where the duration of the large current charge or discharge is accumulated. If it is determined in the following step S6 that the accumulated value T is equal to or greater than the threshold value (No), the process proceeds to step S7, where the charge/discharge current value I is limited to a predetermined current value Io or less (large current charge/discharge is prohibited). If it is determined in step S4 that a large current charge or discharge has not occurred, the process proceeds to step S8, where it is determined whether or not the vehicle has stopped operating (IG-OFF). If it has stopped operating, the control ends, and if it has not stopped operating, the process returns to step S3, where monitoring of the large current charge/discharge continues.

If it is determined in step S6 that the integrated value T has not reached the threshold (Yes), the process proceeds to step S9, where it is determined whether the cell reaction force P has reached the internal pressure threshold Po. If it has reached the threshold 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.

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 (high-current charge/discharge is prohibited). In the following step S13, based on the integrated value T of the duration of high-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 that is a predetermined time shorter than the integrated value T (i.e., a slightly shorter time) is set as the threshold for permitting the continuation of high-current charge/discharge. In addition, the internal pressure threshold value Po of the cell reaction force P is set to a pressure that is a predetermined value higher than the current threshold value.

If the cell reaction force P has not reached the internal pressure threshold value Po in step S9, the process proceeds to step S14 to determine whether the vehicle has stopped operating (IG-OFF). If the vehicle has stopped operating, the control ends. If the vehicle has not stopped operating, the process returns to step S5 to continue accumulating the high current charging/discharging duration.

According to the above control, the time threshold for allowing continued high-current charging and discharging is set to a minimum time when a short battery life is predicted (SOH at 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 higher, and this determination is made when a sign of irreversible high-rate degradation is detected. Therefore, there is a concern that the setting of this long time threshold may cause the battery to deteriorate, even if only slightly. Therefore, when a short battery life is predicted, the minimum value is set as the time for which high-current charging and discharging is allowed to continue, from the perspective of extending the battery life, to avoid irreversible high-rate degradation.

The threshold time for allowing continued 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 where the rate of increase Pr of the cell reaction force P reaches or exceeds 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 allowing continued high-current charging and discharging. The point where the rate of increase Pr of the cell reaction force P reaches or exceeds the predetermined value Pro is the point where 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.

By monitoring the pressure inside the cell, signs of irreversible high-rate degradation are detected and a threshold for the time that high-current charging and discharging is permitted to continue is set, making it possible to continue high-current charging and discharging up to a time close to the limit at which irreversible degradation does not occur. This reduces the frequency of current limit intervention due to management of the duration of high-current charging and discharging. This makes it possible to suppress deterioration in the vehicle's fuel efficiency.

When charging and discharging after setting the allowable continuous time threshold for large current charging and discharging based on the above-mentioned 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 reaching that 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. In this case, the integrated value T 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 the cell reaction force P, the allowable continuous time for large current charging and discharging becomes shorter little by little each time it is set.

In addition, in the above control, the determination of the rate of increase Pr of the cell reaction force P is performed after the restraining 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 restraining load reduces the amount of electrolyte flowing out from the negative electrode active material. In other words, 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 and the threshold value for the permitted continuation time of large current charging and discharging is set in a state in which the progression of irreversible deterioration is slowed down, so that the progression of irreversible deterioration of the battery cell 62 each time this threshold value is set is reduced.

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

The battery unit control device of the present invention can be applied not only to the hybrid vehicle 100 as described above, but also to electric vehicles (EVs).

60 Battery module 62 Battery cell 67 Surface pressure sensor (cell internal pressure detector)
Reference Signs List 70 Control device 71 Duration integrating unit 72 Cell internal pressure determining unit 73 Current limiting unit 74 Battery life predicting unit 75 Permitted duration setting unit 81 Restraint load variable mechanism 82 Restraint load control unit 100 Vehicle 110 Battery unit

Claims (4)

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. 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. 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. 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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