Battery system

Abstract

Battery system, comprising: a battery (200); a battery capacity estimation unit (52) that estimates a capacity of the battery from information regarding a usage history of the battery; a moisture intrusion estimation unit (53) that estimates an amount of moisture that penetrates into the battery; and a battery capacity correction unit (54) which corrects the estimated capacity of the battery based on the estimated amount of moisture entering the battery, wherein the battery capacity correction unit (54) refers to a predetermined ratio between an amount of moisture intruding into the battery and an aged capacity amount to obtain an aged capacity amount corresponding to the amount of moisture intruding into the battery and estimated by the moisture intrusion estimation unit, and the battery capacity correction unit uses the aged capacity amount to correct the battery capacity estimated in the battery capacity estimation unit.

Description

This non-provisional application is based on Japanese Patent Application JP 2015-153 656 A filed with the Japanese Patent Office on Feb. 17, 2014.BACKGROUND OF THE INVENTIONField of the InventionThe following relates to a battery system, and for example, to a battery system mounted in a vehicle.BACKGROUND OF THE INVENTIONJapanese Patent Application Laid-Open No. 2006-250,905 discloses using battery information stored in a database to calculate an aging factor of a battery, which in turn is used to estimate a capacity that the battery can provide to store electric power, i.e., a battery capacity. A method for estimating the capacity and aging for Li-ion cells and Li-ion batteries and a corresponding device are known from DE 101 10 642 A1. DE 10 2012 205 136 A1 also discloses a sensor device for a battery, which has a moisture ingress estimation unit that estimates an amount of moisture ingressing into the battery.SUMMARY OF THE INVENTIONHowever, when the battery has moisture that has penetrated from the atmosphere or the like, the lithium ions of the battery react with the moisture and thus are used up, resulting in reduced battery capacity. Accordingly, the estimated value of the battery capacity calculated as described in Japanese Patent Application Laid-Open No. 2006-250,905 has a deviation from the actual battery capacity, resulting in deterioration of the estimation accuracy.Accordingly, it is an object of the present invention to provide a battery system that makes it possible to estimate the battery capacity thereof without impaired accuracy for a battery having moisture that has penetrated into the battery. This object is achieved with the battery system according to claim 1, advantageous refinements being the subject matter of the dependent claims.The present battery system includes: a battery; a battery capacity estimation unit that estimates a capacity of the battery from information regarding a use history of the battery; a moisture penetration estimation unit that estimates an amount of moisture entering the battery; and a battery capacity correction unit that corrects the estimated capacity of the battery based on the estimated amount of moisture entering the battery. The battery capacity correction unit refers to a predetermined relationship between an amount of moisture entering the battery and an aged capacity amount to obtain an aged capacity amount corresponding to the amount of moisture entering the battery and estimated by the moisture intrusion estimation unit, and the battery capacity correction unit uses the aged capacity amount to correct the battery capacity estimated in the battery capacity estimation unit.Therefore, how large the amount of moisture that has entered the battery is can be considered by obtaining how large its battery capacity is, and when the battery has moisture that has entered it, the battery capacity of the battery can be estimated without deteriorated accuracy.In addition, it can be obtained with high accuracy how large the amount of moisture that has penetrated into the battery is.Preferably, the moisture penetration estimation unit refers to a temperature history of the battery to estimate the moisture amount entering the battery.The temperature data of the battery can be acquired relatively easily, which can help estimate how large the amount of moisture that has penetrated the battery is.Preferably, the battery capacity correction unit refers to a predetermined relationship between an amount of moisture entering the battery and an amount of deteriorated capacity to obtain an aged capacity amount corresponding to the amount of moisture entering the battery estimated by the moisture entry estimation unit, and the battery capacity correction unit uses the aged capacity amount to correct the battery capacity estimated in the battery capacity estimation unit.Therefore, the battery capacity can be obtained with high accuracy when how much battery capacity is present is considered in obtaining how large an amount of moisture that has penetrated into the battery is.Preferably, the battery system further includes a control unit that modifies an input / output limit value of the battery when the corrected capacity of the battery is equal to or less than a threshold value.This can protect the battery from further aging or impairment.Preferably, the battery system further includes a notification unit that displays information indicating that the battery has a small battery capacity when the corrected capacity of the battery is equal to or less than a threshold value.This allows, for example, a driver to have one dealer replace the battery with another before their life rapidly decreases.The foregoing and other objects, features, aspects and advantages of the present invention will become more fully understood from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a block diagram showing a configuration of a vehicle having a battery system mounted therein according to a first embodiment of the present invention. FIG. 2 is a flowchart of an operation procedure according to the first embodiment. FIG. 3 is an example of information regarding a usage history of the battery stored in a battery information storage unit. FIG. 4 shows a relationship between a temperature TB of a battery 200 and a rate VW of moisture entering the battery 200. FIG. 5 shows a relationship between a temperature TB of the battery 200 and a time of use of the battery ST for each temperature in the battery. FIG. 6 shows how moisture entering a battery 200 varies in amount with time. FIG. 7 shows a relationship between an amount of the permeating moisture IW and an aged capacity amount D. FIG. 8 shows a structure of a control device (or ECU) of a second embodiment. FIG. 9 is a flowchart of an operation of the second embodiment.DESCRIPTION OF THE PREFERRED EMBODIMENTSThe present invention will be described below with reference to the drawings.Hereinafter, reference will be made to the drawings to describe the present invention in more detail by embodiments. In the figures, identical or corresponding components are identically denoted, and descriptions thereof will not be repeated.First EmbodimentFIG. 1 is a block diagram showing a configuration of a vehicle having a battery system mounted therein according to a first embodiment of the present invention.Referring to FIG. 1, a hybrid vehicle includes a battery pack BP, a system main relay SMR, a charging and discharging unit 19, an engine ENG, and a control device 15.A charging and discharging unit 19 charges and discharges a battery 200. A charge and discharge unit 19 includes a power control unit (PCU) 20, motor generators MG 1 and MG 2, and a power split device PG.A battery pack BP includes a battery 200, a voltage monitoring unit DV, a temperature sensor 142, and a current sensor 143. A battery 200 includes a plurality of battery cells connected in series.A battery 200 is a direct current (dc) power supply, and includes, for example, a rechargeable battery such as a nickel-metal hydride battery and a lithium ion battery. A battery 200 supplies a DC voltage to a PCU 20, and is also charged with a DC voltage provided from the PCU 20.A voltage monitoring unit DV detects a DC voltage VB of the battery 200. A temperature sensor 142 measures a temperature TB of the battery 200. A current sensor 143 measures a current IB durchläuft through the battery 200. A temperature TB, a current IB, and a DC voltage VB are output to the control device (or ECU) 15.A controller 15 receives an output 17 from a plurality of sensors indicating a driving state and a vehicle state. A sensor output 17 includes an accelerator pedal position measured by a position sensor disposed on the accelerator pedal, and depends on how far the accelerator pedal is depressed, an output of the vehicle wheel speed sensor, and the like. A control unit 15 operates in response to these outputs of the sensors to generally provide a variety of control applied to the hybrid vehicle.An engine ENG and motor generators MG 1 and MG 2 are mechanically coupled via a power split device PG. Depending on how the hybrid vehicle travels, the power split device serves to associate and couple a driving force between an engine ENG, a motor generator MG 1, and a motor generator MG 2, resulting in driving of a driving wheel.Although the motor generators MG 1 and MG 2 may serve as both an electric power generator and an electric motor, the motor generator MG 1 mainly functions as an electric power generator and the motor generator MG 2 mainly functions as an electric motor.More specifically, the motor generator MG 1 for acceleration is employed as an electric motor for starting the engine. More specifically, the motor generator MG 1 receives an electric power from the battery 200 to be driven as an electric motor to rotate the crankshaft for starting the engine.Further, once the engine has been started, the motor generator MG 1 is rotated by the driving force of the engine transmitted via the power split device PG to generate electric power.The motor generator MG 2 is driven by at least one of the electric power stored in the battery 200 and the electric power generated by the motor generator MG 1. The motor-generator MG 2 provides a driving force, which is in turn transmitted to the drive shaft via a differential gear and / or the like. Motor-generator MG 2 thus assists the engine to drive the vehicle or provides a driving force that drives the vehicle alone.Further, when the vehicle is regeneratively braked, the motor generator MG2 is rotated by the torque of the driving wheels to function as an electric power generator. The motor generator MG 2 regenerates electric power, which is in turn charged in the battery 200 via the PCU 20.When the motor generators MG 1 and MG 2 are in a power running operation, the PCU 20 follows a control instruction received from the control device 15 to boost a DC voltage output from the battery 200, and also to convert the boosted DC voltage to an AC (ac) voltage, and thus drive the motor generators MG 1 and MG 2 included in a motive power output device 30.Further, when the motor generators MG 1 and MG 2 are in a regenerative braking operation, the PCU 20 follows a control instruction obtained from the control device 15 to convert the AC voltage generated by the motor generators MG 1 and MG 2 into a DC voltage to charge the battery 200.Thus, the hybrid vehicle includes a battery 200, a PCU 20, and a portion of the control device 15 that controls the PCU 20 to constitute a power supply device for drive-controlling the motor-generators MG 1 and MG 2.The PCU 20 includes a converter 110, a smoothing capacitor 120, motor drivers 131 and 132 associated with the motor generators MG 1 and MG 2, respectively, and a converter / inverter control unit 140. In this embodiment, motor generators MG 1 and MG 2, which are AC motors, are controlled in drive, and thus the motor drivers 131, 132 are configured as inverters. Hereinafter, motor drivers 131, 132 will be referred to as inverters 131 and 132.The control device 15 operates in response to a variety of sensor outputs 17 to take account of allocation and output for an engine ENG and determine a torque to be provided to the motor generators MG 1 and MG 2 accordingly. Further, the control device 15 calculates an optimum engine operating voltage depending on how the motor generators MG1 and MG2 are currently operating.Further, based on the required torque and the optimum motor operation voltage and on a DC voltage VB detected by the voltage monitoring unit DV, the controller 15 generates a voltage control value Vmr for a motor operation voltage Vm and a torque control value Tref for the motor generators MG 1 and MG 2. The voltage control value Vmr and the torque control value Tref are provided to the inverter / converter control unit 140.The control device 15 generates the voltage control value Vmr for the motor operation voltage Vm and the torque control value Tref for the motor generators MG 1 and MG 2 so that an electric power required when the motor generators MG 1 and MG 2 are in the power running operation does not exceed an allowable output electric power WOUT.The control device 15 generates a voltage control value Vmr for the motor operation voltage Vm and a torque control value Tref for the motor generators MG 1 and MG 2, so that an electric power generated when the motor generators MG 1 and MG 2 are regeneratively braked does not exceed an allowable input electric power WIN.The converter / inverter control unit 140 follows a voltage control value Vmr received from the controller 15 to generate a converter control signal Scnv to control an operation of the converter 110. Further, a converter / inverter control unit 140 follows a torque control value Tref received from the controller 15 to generate inverter control signals Spwm 1 and Spwm 2 to control an operation of the inverters 131 and 132, respectively.A control device 15 includes a battery information storage unit 150, a battery capacity estimation unit 52, a moisture penetration estimation unit 53, a battery capacity correction unit 54, and a battery input / output limiting unit 55.The battery information storage unit 51 stores information regarding a use history of the battery 200.The battery capacity estimation unit 52 refers to the information regarding the usage history of the battery 200 to estimate the battery capacity of the battery.The moisture penetration estimation unit 53 estimates an amount of moisture entering the battery 200.The battery capacity correction unit 54 uses the amount of invading moisture estimated in the moisture intrusion estimation unit 53 to correct the battery capacity estimated in the battery capacity estimation unit 52.The battery input / output limiting unit 55 decreases an allowable electric output Wout of the battery 200 and an allowable electric input Win when the corrected battery capacity is equal to or less than a threshold value.FIG. 2 is a flowchart of an operation procedure according to the first embodiment.In step S 101, the battery capacity estimation unit 52 estimates a battery capacity C based on information regarding the use history of the battery stored in the battery information storage unit 51. More specifically, the battery capacity estimation unit 52 estimates the battery capacity C as follows: and where α represents an aging factor determined by what state the battery 200 is used, tu represents a cumulative time of use of the battery 200, y represents a capacity maintenance ratio, and C0 represents an initial capacity of the battery 200.FIG. 3 shows an example of the information stored in the battery information storage unit 51 regarding the usage history of the battery.The cumulative time of use of the battery 200 tu is stored in the battery information storage unit 51. The aging factor α may be set by at least a part of the information stored in the battery information storage unit 51. For example, the aging factor α may be set to have such features as follows:The aging factor α is increased to be larger when a history indicates that the battery per unit time more often reaches a predetermined value of the temperature or higher. The aging factor α is increased to be larger when a history indicates that the battery more often reaches a maximum temperature value equal to or greater than a predetermined value within a unit time. The aging factor α is increased to be larger when a history indicates that the battery is charged / discharged more frequently with a current of a predetermined value or larger within a unit time. The aging factor α is increased to be larger as the battery discharges larger amounts of the total electric power. The aging factor α is increased to be larger when a history indicates that the battery has a larger state of charge (SOC) per unit time. The aging factor α is increased to be larger when a history indicates that the battery has an SOC with maximum and minimum values with a difference therebetween that is more often equal to or larger than a predetermined value within a unit time. The aging factor α is increased to be larger when a course indicates that immediately after the ignition switch is turned on, the battery has an SOC that is equal to or less than a predetermined value more often. The aging factor α is increased to be larger when a course indicates that the ignition switch is less frequently turned off for a period of a predetermined value. The aging factor α is increased to be larger when the battery voltage is more often less than a lower limit value. The aging factor α is increased to be larger when a graph indicates that there are larger differences between an SOC observed when plug-in charging starts and that observed when plug-in charging is ended. The aging factor α is increased to be larger when a history indicates that an EV traveling mode is continuously applied for longer periods of time. The aging factor α is increased to be larger when a history indicates that an HV driving mode is continuously applied for shorter periods of time.In step S 102, the moisture penetration estimation unit 53 refers to a temperature history of the battery 200 to estimate an amount of moisture entering the battery 200. More specifically, the moisture intrusion estimation unit 53 estimates the amount of invading moisture by the following operation:The moisture penetration estimation unit 53 refers to the temperature history of the battery up to a present time t or the battery temperature history per unit time as stored in the battery information storage unit 51 to acquire a moisture penetration rate VW (TB) of the moisture entering the battery 200 from each temperature TB at which the battery 200 was used. FIG. 4 shows a relationship between the temperature TB of the battery 200 and the moisture introduction rate VW of the moisture entering the battery 200. As shown in FIG. 4, 1 / TBand VWare represented by a linear term (Arrheniusplot). The moisture penetration estimation unit 53 acquires, from the relationship of FIG. 4 to each temperature TB, a moisture penetration rate VW (TB) of the moisture entering the battery 200.Moreover, the moisture penetration estimation unit 53 refers to the temperature history of the battery until the present time t to acquire a time of use ST (TB) of the battery 200 for each temperature TB at which the battery 200 was used. FIG. 5 shows a relationship with the use time ST of the battery 200 to the temperature TB of the battery 200.As shown by a term (3), the moisture penetration estimation unit 53 calculates a product of the moisture penetration rate VW (TB) at the temperature TB and a use time ST (TB) of the battery 200 for each temperature at which the battery 200 was used, and the moisture penetration estimation unit 53 adds such calculated products together to obtain, for the current time t, a moisture amount that has penetrated into the battery IW (TB), the sum sign means varying TB, and thus the total sum is obtained.FIG. 6 shows how an amount of the permeated moisture IW(t) varies with time.In step S 103, the battery capacity correction unit 54 uses the amount of the invading humidity IW(t) estimated in the humidity intrusion estimation unit 53 to correct the battery capacity C estimated in the battery capacity estimation unit 52. More specifically, the battery capacity correction unit 54 refers to a predetermined relationship between an amount of the permeated moisture IW and an amount of the aging capacity D indicated in FIG. 7 to obtain an aged capacity amount D corresponding to the amount of the permeated moisture IW estimated in the moisture permeation estimation unit 53. FIG. 7 example determines that the amount of permeated moisture IW multiplied by a gradient k (a constant) is an aged capacity amount D. The battery capacity correction unit 54 subtracts the aged capacity amount D from the battery capacity C estimated in the battery capacity estimation unit 52 to calculate a corrected battery capacity E, i.e., E=C-D.In step S 104, control proceeds to step S 105 when the corrected battery capacity E is equal to or less than a predetermined threshold value, whereas control proceeds to step S 106 when the corrected battery capacity E exceeds the threshold value.In step S 105, the battery input / output limiting unit 55 sets the allowable output electric power Wout and the allowable input electric power Win of the battery 200 to a predetermined value.In step S 106, the battery input / output limiting unit 55 does not modify the allowable output electric power Wout and the allowable input electric power Win of the battery 200.Thus, the present embodiment enables a battery having moisture that has entered the same to be nevertheless estimated in its battery capacity without impaired accuracy. Further, when an estimated battery capacity is equal to or less than a threshold, an allowable output electric power and an allowable input electric power of the battery may be decreased to protect the battery from further aging.Second EmbodimentFIG. 8 shows a configuration of a control device (or ECU) 115 of a second embodiment.The control device 115 of FIG. 8 differs from the control device 15 of FIG. 1 in that it excludes a battery input / output limiting unit 55, and instead includes a notifying unit 155.A display device 156 is, for example, a liquid crystal display.When a corrected battery capacity is equal to or less than the threshold, the notification unit 155 provides information indicating that the battery has a small battery capacity, and the display device 156 displays the information.FIG. 9 is a flowchart of an operation procedure according to the second embodiment.The flowchart of FIG. 9 is different from the flowchart of FIG. 2 in that the former step S 105 and the step 106 are excluded, and instead includes the step S 205 and the step S 206.In step S 205, the notification unit 155 provides information that the battery has a small battery capacity, and the display device 156 displays the information. For example, the display device 156 displays such a message by "The battery has a small battery capacity. The battery cannot be used any further. Please contact a dealer to diagnose this battery."In step S 206, the notification unit 155 provides information indicating that the battery has a normal battery capacity, and the display device 156 displays the information. For example, the display device 156 displays such a message by "The battery has a normal battery capacity. The battery may be further used."Thus, the present embodiment, like the first embodiment, enables a battery with moisture that has penetrated thereinto to nevertheless estimate its battery capacity without impaired accuracy. Further, when an estimated battery capacity is equal to or less than a threshold, information indicating that the battery has a small battery capacity is displayed, and this allows the driver to exchange the battery with another, for example, before its lifetime rapidly decreases.Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted with reference to the appended claims.

Claims

A battery system, comprising: a battery (200); a battery capacity estimation unit (52) that estimates a capacity of the battery from information regarding a usage history of the battery; a moisture penetration estimation unit (53) that estimates an amount of moisture entering the battery; and a battery capacity correction unit (54) that corrects the estimated capacity of the battery based on the estimated moisture amount entering the battery, wherein the battery capacity correction unit (54) refers to a predetermined relationship between a moisture amount entering the battery and an aged capacity amount to obtain an aged capacity amount corresponding to the moisture amount entering the battery and estimated by the moisture entry estimation unit, and the battery capacity correction unit uses the aged capacity amount to correct the battery capacity estimated in the battery capacity estimation unit.The battery system according to claim 1, wherein the moisture penetration estimation unit refers to a temperature history of the battery to estimate the amount of moisture entering the battery.The battery system according to claim 2, wherein: the moisture penetration estimation unit refers to information regarding the usage history of the battery to acquire a moisture penetration rate of the moisture entering the battery and a usage time of the battery compared to each temperature at which the battery is used; and the moisture penetration estimation unit calculates a product of the moisture penetration rate and the usage time of the battery for each temperature at which the battery is used, and the moisture penetration estimation unit adds these calculated products together to acquire a total sum of the products to estimate the amount of moisture entering the battery.The battery system according to claim 1, further comprising a control unit (15) that modifies an input / output limit value of the battery when the corrected capacity of the battery is equal to or less than a threshold value.The battery system according to claim 1, further comprising a notification unit (155) that displays information indicating that the battery has a small battery capacity when the corrected capacity of the battery is equal to or less than a threshold value.

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