Method for estimating a quantity of a state of a battery

There is provided a battery state detecting method that detects states by evaluating depletion caused by reaction processes whose speeds are different. Voltage Vmes, current Imes and temperature Tmes of a battery are measured and inputted in Step S1 and it is judged whether or not an absolute value of the measured current Imes is smaller than a current threshold value Ithre in Step S2. OCV20 hr is estimated from SOCn-1 and SOHn-1 after the previous discharge/charge based on a stable OCV estimating equation in Step S4 and a difference between the voltage measured value Vmes and the OCV20 hr is calculated and stored in Step S5. A relaxation function Fn(t) is updated corresponding to time t in processes in Steps S6 through S19. SOHn is calculated by using the updated Fn (t) in Step S17 and SOCn is calculated in Step S19.

CROSS REFERENCE TO RELATED APPLICATIONS

The application claims priority from a Japanese patent application serial No. 2008-103925, filed on Apr. 11, 2008, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a battery residual capacity detecting method and a battery residual capacity detecting apparatus.

BACKGROUND

Since a vehicle has come to employ many electric devices for travelling lately, an importance of an in-vehicle power source is increasing more and more. Needs on the in-vehicle power source have been limited to perform such functions of starting an engine, operating an air-conditioner and lighting lamps in the past 20 to 30 years. In contrary to that, bi-wiring has spread and even parts of a safety system typified by an electronic parking brake (EPB) have come to be controlled by electricity. Still more, as a measure for improving gas mileage in an effort of saving energy and controlling emission of CO2, it is demanded to provide an idling stop function in stopping for a short period of time at an intersection and the like and to assure its restarting capability. Thus, a variety of functions is demanded on the power source and the battery and corresponding to that, it is desired to improve battery state detecting accuracy.

In such a circumstance, it is an important technology to accurately detect a residual capacity (SOC: state of charge) of the battery in particular for safe and comfortable driving of the vehicle and for realizing an automobile society In which an environment is taken into account, because it is linked with stable operations of the electric devices such as the EPB.

Under a battery stable condition, open circuit voltage (OCV) and the SOC thereof have a relationship of correspondence of one-to-one in general (a reference numeral81inFIG. 12). However, after discharging and charging electricity, the battery is affected respectively by ion generating and annihilating reactions on a surface of a polar plate due to electro-chemical reactions and by moves of ions due to diffusion and convection of electrolytic solution. Therefore, it takes a time, e.g., around 20 hours, to converge to the stable OCV and the OCV does not correspond one-to-one with the SOC when there is such temporal change.FIGS. 13 and 14are graphs showing examples of temporal change of the OCV when the SOC and temperature of the battery are constant.FIG. 13shows that it takes a time until when the OCV (reference numeral82) is stabilized to a constant value even if the SOC is constant. WhileFIG. 14shows changes of the OCVs (reference numerals83,84,85) of batteries whose states of health (SOH) are different, it indicates that the OCVs do not converge to the identical OCV if the SOHs are different even if the SOC and temperature are adjusted so as to fall under the same condition and even if the latest discharge/charge conditions are kept same.

As described above, the influence of the SOH is not reflected in finding the SOC from the OCV by using the state detecting method just by utilizing the latest discharge/charge history. Then, there is a problem that accuracy of state detection drops if the SOC is found from the OVC without reflecting the battery depletion condition.

Patent Document 1 (Japanese Patent Application Laid-open No. Hei.2005-106615 gazette) is known as one exemplary prior art. The Document 1 uses transient response corresponding to discharge/charge history to compensate the OCV as a method for detecting the OCV and SOC of a secondary battery. The Document 1 also refers to the transient response changes corresponding to discharge/charge time and to a resistant component, a polarization component corresponding to internal reaction of the battery and diffusion speed of electrolytic solution.

According to the detection method described in Patent Document 1, it is possible to find depletion corresponding to a fast reaction speed within the battery by measuring a short-period transient response by discharging and charging for a short period of time. However it is unable to measure a long-term transient response, so that it is unable to detect depletion caused by slow reaction speed. Although it is necessary to discharge and charge for a long period of time to measure the long-term transient response, the SOC changes as the discharge/charge time becomes longer and hence the short-term transient response thereafter also changes. Thus, it is unable to detect the depletion corresponding to the different reaction speeds within the battery and to detect the states of the battery such as the residual capacity by the detecting method described in Patent Document 1.

Not only the ion generating and annihilating reactions (fast reaction speed) caused in the vicinity of the polar plate but also ion diffusion speed within the electrolytic solution (slow reaction speed) affects in a series of reaction processes called an electrical-chemical reaction within the battery. The reaction processes whose speeds are different significantly affect the accuracy of the state detection as a factor of error in such reaction system.

SUMMARY

Accordingly, in order to solve those problems, the present invention aims at providing a battery state detecting method for detecting states of a battery by evaluating depletion caused by reaction processes whose speed is different.

According to a first aspect of a battery state detecting method of the invention, the battery state detecting method comprises steps of preparing a relaxation function F(t) for calculating a variation of open circuit voltage (OCV) of the battery after an elapsed time t since the battery has stopped to discharge/charge as a function of predetermined quantity of state of the battery in advance, measuring the OCV variation from OCV during when the battery is stable, optimizing the relaxation function F(t) by the measured OCV variation, estimating the quantity of state from the optimized relaxation function F(t) and detecting the state of the battery based on the estimated quantity of state.

According to another aspect of the battery state detecting method of the invention, the relaxation function F(t) is prepared in advance further as a function of temperature of the battery and the temperature of the battery is measured to use in the relaxation function F(t)

According to a still other aspect of the battery state detecting method of the invention, a stable OCV estimating equation for calculating the OCV during the stable time is prepared in advance and the OCV during the stable time is calculated from the stable OCV estimating equation and a difference from the open circuit voltage measured value of the battery is defined as the OCV variation.

According to a still other aspect of the battery state detecting method of the invention, the OCV during the stable time is OCV when 20 hours has elapsed since the battery has stopped to discharge/charge.

According to a different aspect of the battery state detecting method of the invention, the quantity of state is a residual capacity (SOC) and a level of depletion (SOH) of the battery.

According to a still different aspect of the battery state detecting method of the invention, the relaxation function F(t) is represented by a sum of two or more (m) relaxation functions per reaction speed fi (t) (i=1 through m) prepared in advance corresponding to reaction speeds within the battery and the relaxation function per reaction speed fi (t) (i=1 through m) is optimized by dividing the measured value of the OCV variation into components corresponding to the reaction speeds.

According to another aspect of the battery state detecting method of the invention, the quantity of state is calculated by estimating a quantity of state per reaction speed from the relaxation function per reaction speed fi (t) and by totaling them.

According to another aspect of the battery state detecting method of the invention, the relaxation function per reaction speed fin (t) after the end of the n-th discharge/charge is expressed as: fin(t)firef(t)*{SOCn/SOCref}*{SOHin/SOHiref}*g(T) (Eq. 1) where the relaxation function per reaction speed fi (t) in the standard state, SOC and SOH per reaction speed are denoted respectively as fi ref (T), SOCrefand SOHirefand dependency on the temperature T as G (T) (here, SOHi n is SOH per reaction speed).

According to another aspect of the battery state detecting method of the invention, the battery state detecting method comprises steps of at least measuring voltage and current of the battery, calculating an OCV variation corresponding to an elapsed time since said battery has stopped to discharge/charge from the voltage measured value when it is judged that the battery has stopped to discharge/charge from the current or a predetermined discharge/charge stopping signal, optimizing the relaxation function per react ion speed fi (t) corresponding to the reaction speed whose time constant is shorter than the elapsed time by using the OCV variation and estimating the quantity of state by using immediately preceding one for the relaxation function per reaction speed fi(t) corresponding to the reaction speed which is longer than the time constant together with the optimized relaxation function per reaction speed fi(t).

According to another aspect of the battery state detecting method of the invention, the battery is judged to be stopping to discharge/charge when a current value is what permits to judge a transient change within the battery caused by the discharge/charge to be substantially the same with a transient change in a case of open circuit.

According to another aspect of the battery state detecting method of the invention, the battery is judged to be abnormal when the SOC is less than a first threshold value set in advance or when the SOH is more than a second threshold value.

The invention thus provides the battery state detecting method for detecting the state by evaluating the depletion caused by the reaction processes whose speeds are different, so that it becomes possible to detect the state accurately.

BRIEF DESCRIPTION OF THE REFERENCE NUMERALS

01: BATTERY02: STATE DETECTING APPARATUS03: IN-VEHICLE INFORMATION CONTROLLER20: TEMPERATURE MEASURING MEANS21: VOLTAGE MEASURING MEANS22: CURRENT MEASURING MEANS23: MEMORY AREA (RAM)24: STATIONARY MEMORY AREA (ROM)25: PROCESSOR26: JUDGMENT RESULT OUTPUTTING MEANS27: IN-VEHICLE STATE INPUTTING MEANS28: TIMER50: TRUE VALUE OF ΔV51,52,53,54: RELAXATION FUNCTION PER REACTION SPEED55: RELAXATION FUNCTION61,62,63: RELAXATION FUNCTION PER REACTION SPEED64,65: RATIO OF RELAXATION FUNCTION PER REACTION SPEED70: STABLE OCV ESTIMATING EQUATION81: SOC82,83,84,85: OCV

DETAILED DESCRIPTION

A battery state detecting method of a preferred embodiment of the invention will be explained in detail with reference to the drawings. It is noted that each component having the same function will be denoted by the same reference numeral to simplify the drawings and their explanation.

The battery state detecting method of the invention evaluates SOH (state of health) which is an index of depletion level of the battery corresponding to reaction speed of the battery and evaluates SOC by using the SOH. Because the SOC has the relationship of one-to-one with the open circuit voltage (OCV) as shown inFIG. 12, the SOC can be found by finding the OCV. However, the relationship ofFIG. 12holds when the state of the battery is stable and the OCV after discharge/charge changes as shown inFIG. 13. Due to that, it is necessary to evaluate the SOC by using the OCV when the battery is fully stabilized after discharging/charging electricity.

Still more, because the OCV after discharge/charge changes by the SOH as shown inFIG. 14, the OCV during the stable period also changes by the SOH. Still more, the transient change of the battery after discharge/charge is affected by the reaction processes whose reaction speed is fast such as ion generating and annihilating reaction and whose reaction speed is slow such as those caused by the move of the electrolytic solution.

Then, in order to be able to accurately evaluate the SOC by evaluating the influence of the slow reaction speed even when an elapsed time after discharge/charge is short f the battery state detecting method of the invention evaluates a variation of the SOH per reaction speed and compensates the OCV by using this SOH.

One embodiment of the battery state detecting method of the invention will be explained below.

At first, the OCV during the stable time after fully elapsing a time since discharge/charge will be expressed as OCVs and the relationship of one-to-one of the SOC and the OCVs shown inFIG. 12will be expressed by the following equation:
SOC=FS{OCVs(SOC,SOH,T)}  (Eq. 2)
OCVs(SOC,SOH,T)=lim(Vmes(t)).

Here, lim described above indicates that the elapsed time t is infinitized with respect to a battery voltage (OCV) measured value Vmes(t) after the elapse of time t from the discharge/charge. The OCVs in the above equation also shows that it may be changed by the SOC, SOH and temperature T of the battery. While Vmes(t) is also changed by the SOC, SOH and T of the battery during measurement, the equation (2) is expressed only by the time t when it is measured.

In a case of a liquid-type lead battery, the temporal change of Vmes (t) per hour when 20 hours has elapsed becomes as fully small as 10 mV and an error with respect to magnitude of the OCV (about 12.9V) becomes 0.1% or less. Then, Vmes(t) when 20 hours has elapsed since the battery has stopped to discharge/charge is expressed as OCV20 hrin the following equation and it is used for the OCVs:
OCV20 hr=Vmes(t=20 hr)
OCVs(SOC,SOH,T)=OCV20 hr(Eq. 3)

It is noted that the elapsed time from the stop of the discharge/charge may be a value other than 20 hours depending on types of the battery.

When a variation of the voltage measured value Vmes(t) after stopping the discharge/charge from the stable OCV, i.e., an OCV variation, is expressed as ΔV(t), it can be expressed as follows:
ΔV(t)=Vmes(t)−OCV20 hr  (Eq. 4)

This change of voltage ΔV(t) has been handled while including all transient changes by using a term “polarization” in the conventional definition of electrical-chemistry. However, because ΔV(t) is a change in voltage caused by a relaxation process until approaching to the stable OCV, it is affected by the following factors of change in voltage. The factors of the change in voltage include a condition of the polar plate, ion concentration in the vicinity of the polar plate, their solid-phase reaction and solid-liquid reaction and moves of ions with deposition, convection and diffusion of the electrolytic solution. ΔV(t) may be considered to be caused by integrating the relaxation processes whose reaction speeds are different.

ΔV(t) may be represented by using a function F(t) composed of m polynomial expressions corresponding to the difference of the reaction speeds.
ΔV(t)=F(t)
=f1(t)+f2(t)+ . . .fm(t)=Σfi(t)  (Eq.5)

In the above F(t) (relaxation function), each term fi (t) (relaxation function per reaction speed) represents a contribution to the change in voltage in each relaxation process intrinsic to the battery and each depends on the state of health SOH, the state of charge (ion concentration) SOC and the temperature T of the battery.

The state detecting system has reference data therein in advance before it is connected with the battery. Initial states corresponding to the battery to be connected will be represented as SOCO=SOCref(0), SOHi 0=SOHiref(0) and OCV20 hr0=OCV20 hrref(O).

Each reference data is used as the initial value in the initial state in which the battery is connected with the state detecting system as n=O-th measurement.

F(t) and each term fi(t) of the equation (5) representing the OCV variation˜V(t) after the end of n-th discharge/charge after connecting the battery with the state detecting system and setting the initial values will be represented as Fn(t) and fin(t), respectively. At this time, fin(t) may be calculated by the following equation from the SOC and SOH corresponding to the i-th reaction speed (represented as SOCnand SOHin, respectively):
fin(t)=firef(t)*{SOCn/SOCref}*{SOHin/SOHiref}*g(T)  (Eq. 6)

Here, firef(t), SOCref, and SOHirefare values in the initial state set in advance (unused state for example) and g(T) is a function indicating temperature dependency.

When the temperature T and the SOC are constant regardless of the time in the equation (6), the SOHincan be calculated from the following equation:
SOHin={fin(t)/firef(t)*SOHiref(Eq. 7)

Accordingly, it is possible to obtain SOHinby using fin(t) obtained from the equation (6).

From the equation (7), the overall SOHnto which SOHincaused by the transient responses whose reaction speeds are different are totaled is composed of respective components as follows:
SOHn=(SOH1n,SOH2n, . . . ,SOHmn)  (Eq. 8)

For instance, when coefficients of m SOHs are A through M, SOHD may be expressed as follows:
SOHn=A*SOH1n+B*SOH2n+ . . . +M*SOHmn=A*f1n(t)/f1ref(t)}SOH1ref+B*{f2n(t)/f2ref(t)}SOH2ref+M*(t)/{fmn(t)/fmref(t)}SOHmref(Eq. 8′)

However, the equation (8′) is one example in which the relationship of SOH1through SOHmshown in the equation (8) is represented in a form of sum. The total of SOHin is not limited to the form of the equation (8′) in which SOH1through SOHm are respectively coupled in that form. It becomes possible to detect the depletion state of the battery by using this SOHn.

However, when the elapsed time from the end of the n-th discharge/charge is short, it is unable to obtain fin(t) corresponding to the slow reaction speed and to update the SOCnand SOHin. Then, the equation (6) is used approximately as follows by using the values SOCn-1and SOHin-1at the end of the discharge/charge of the previous time instead of the SOCnand SOHinuntil when fin(t), SOCnand SOHincorresponding to the slow reaction speed can be calculated.
fin(t)=firef(t)*{SOCn-1/SOC iref}*{SOH in-1/SOH iref}*g(T)  (Eq. 6′)

Still more, in the state detecting system to which the equation (6′) is applicable, the measurement of the relaxation speed of Fn(t) can be carried out under the condition in which the discharge/charge of the battery is stopped. It is possible to use SOCn-1for calculation of the relaxation function of Fn(t) when operations are always carried out only with discharge/charge which is less than a threshold value. However, when in-vehicle operation conditions are assumed, discharge/charge is carried out along with an operation of the vehicle in measuring n-th times since the end of the n−1-th times and it becomes necessary to compensate the SOC n−1 by ΔSOC (discharge/charge integrated quantity) as a change of the amount of charge during the operation of the vehicle. In such a case, the following equation (6″) is used by setting as follows:
SOC(n-1)′=SOCn-1+ΔSOC fin(t)=firef(t)*{SOC(n-1)′/SOCref}*{SOH in-1/SOHiref}*g(T)  (Eq. 6″)

fin(t) is updated by the following equation by using the SOHin calculated by the equation (7) to calculate SOCin.
fin(t)=fref(t)*{SOC in-1/SOCref}*{SOHin/SOHiref}*g(T)  (Eq. 6′″)

It is possible to calculate OCV20 hr by the following equation from the equations (4) and (6′″):
OCV20 hr=Vmes(t)−Σ[fref(t)*{SOCn-1/SOCref}*{SOHin-1/SOHiref}]*g(T)  (Eq. 9)

It is possible to calculate the SOCnby substituting this OCV20 hrin the equation (2) and to use to detect the state of the soc.

As described above, it becomes possible to calculate the m relaxation functions per reaction speed fin(t) (i=1 through m) after the n-th discharge/charge based on the m reference values firef(t) (i=1 through m) corresponding to m kinds of reaction speeds, the m reference depletion parameters SOHiref(i=1 through m) and the m reference residual capacity parameters SOCref(i=1 through m). Thereby, it becomes possible to obtain the OCV, SOC and SOH reflecting the level of depletion corresponding to the different reaction speeds and to detect the state accurately.

The battery state detecting method of the present embodiment will be explained below with reference toFIGS. 1 through 7.FIGS. 1 through 7are flowcharts showing flows of processes of the battery state detecting method of the embodiment.

One exemplary procedure of the state detecting method of the battery (01) of the invention will be explained concretely by exemplifying a case of a battery mounted in a vehicle. As shown in a diagram showing the whole system ofFIG. 1, a state detector (02) comprises a means (20) for measuring temperature of the battery (01), a means (21) for measuring voltage of the battery (01), a means (22) for measuring current of the battery (01), a memory area (RAM) (23) for temporarily recording measured values measured by the respective measuring means (20through22), a stationary memory area (24) for storing reference data in advance, a processor (25) for detecting and judging the state based on the data stored in the RAM (23) and the ROM (24), a means (26) for outputting a judgment result to the outside, a means (27) capable of inputting information from an in-vehicle information controller (03) and a timer (28) capable of counting time.

According to the invention, the calculation of the quantity of state is executed when it is judged that the battery (01) has stopped to discharge/charge.FIG. 2shows one exemplary method for judging that the battery (01) has stopped to discharge/charge. This is a case when it is judged that the vehicle is parking or stopping from the information of the in-vehicle information controller (03) or when information on connect and disconnect of the battery (01) and the state detector (02) is inputted for example. Or, this is a case when a current value measured by the current measuring means (22) provided in the state detector (02) becomes a judgment threshold value or less recorded in the stationary memory area (24). The judgment may be made only by the in-vehicle information inputting means (27) or only the judgment of the current threshold value or by freely combining them (the part up to now is referred to as a threshold value judgment means).

When the state detector (02) is connected with the battery (01) is referred to as the initial state, i.e., n=0 (times), and a number of times of judgment when the state is judged that the discharge/charge is stopped by the threshold value judgment means inFIG. 2is referred to as n times. A counter value of the timer is set to be t_count=0.

According to the battery state detecting method of the present embodiment, the SOC, SOH and OCV20 hr of the battery corresponding to the initial battery state are stored in the stationary memory area (24) in advance by setting the SOC calculation equation of (2) as SOCo=SOCref(0), SOHio=SOHref(O) and OCV20 hro=OCV20 hrref(O).

InFIG. 3, the counter value of the timer is confirmed with predetermined confirmation timing. When the timer count (t count) exceeds its measured timing value at the predetermined measuring timing, the current measuring means (22) measures a voltage value Vmesof the battery (01). A relationship between time and the voltage at this time is expressed as follows:
Vmes(t)=(t,V)=(tcount,Vmes)

Then, Vmes(t)−OCV20 hr—temp is stored as ΔV(t)_temp (see the equation (4), the acquisition of Vmes(t))

FIG. 4shows a flow of a method for calculating OCV20 hr—temp. As the SOC and SOH in starting to calculate the n-th state, the previous calculated values SOCn-1and SOHn-1are used. Measured value T=Tnobtained from the temperature measuring means (20) is used as the temperature of the battery at the present time. When an OCV value after 20 hours presumed from this condition is expressed as OCV20 hr temp, the apparatus (02) has the following relational expression in which OCV20 hrref(h) is correlated with h kinds of conditions combining a plurality of SOC values, SOH values and T values in advance as the reference data:

H(SOC_j, SOH_k, T—1)OCV20 hrref(h) (h, j, k, l are natural numbers) OCV20 hrref(h) at the present is determined by using this equation. This is used to determine OCV20 hrref(h) at present. This is one configuration of stable OCV estimating equations. This is used as the n-th time one (selection of OCV20 hr—temp): OCV20 hr—temp=OCV20 hrref(n)

FIG. 5shows a flow of adding data of ΔV(t)_temp=Vmes(t)−OCV20 hr—temp to the temporary memory area (23) per measurement by using Vmes(t) calculated by using the voltage measured value inFIG. 3and OCV20 hrtemp obtained by using the quantity of states SOC, SOH and T inFIG. 4.

Then, fitting calculation is carried out so as to express ΔV(t) temp calculated inFIG. 5as a sum of two or more (m) relaxation functions per reaction speed fin(t) (I=1 through m) prepared as predetermined functional type. In other words, the relaxation function per reaction speed fin(t) is optimized with respect to the data expressed by ΔV(t) temp.

Although various calculation methods utilizing regression calculation such as a least-squares method are conceivable as for the fitting method, an error becomes large when the regression calculation is carried out by simply using a sum of exponential functions in this method for calculating ΔV(t) temp because it turns out as ΔV(20 hr) temp=O.

Then, it is desirable to deduct an inclination of a tangent around ΔV 20 hr) temp=0, to introduce a function by which ΔV(20 hr) temp>0 always holds and to carry out fitting to the difference by the sum of the exponential functions.

For simplification, the equation (5) is assumed to be composed of the following four terms hereinafter:
F(t)=ffast(t)+fslow(t)={ffast1(t)+ffast2(t)}+{fslow1(t)+fslow2(t)}  (Eq. 10)

It becomes easy to prepare the optimized function with respect to ΔV(t)_temp by expressing the equation (10) as follows for example as one embodiment:

Function 2 of slow relaxation speed:
Fslow2(t)=−a/72000*t+b(10-4)

However, it is possible to use complicated functions or simplified functions depending on conditions such as computing speed of the sensors, an amount of memory and accuracy required to the sensors.

FIGS. 6 and 7illustrate a method for obtaining Fn(t) from 6V(t) temp corresponding to an elapsed time from the timer count. Each coefficient is defined so that the functions shown in the equations (10-1 through 10-4) are dominant respectively to the four reference times (10 s, 1000 s, 36000 s, 72000 s) as a fitting function in that interval. At this time, the exemplified reference times (10 s, 1000 s, 36000 s, 72000 s) can be determined corresponding to a time constant based on the relaxation speed of the reaction speed within the battery. The reference time can be also changed not only by the relaxation speed within the battery but also by the accuracy required to the sensors and timing corresponding to traveling and resting conditions of an actual car.

As for the determination method of the reference time, it is possible to use a timer within the sensor, to use time of in-vehicle information, typified by car navigation, obtained from the in-vehicle information inputting means or to use their combination.

FIG. 6illustrates a method for obtaining Fn(t) from ΔV(t)_temp when the elapsed time of the timer count is shorter than 20 hours. When the time t is judged to be shorter than a first reference time (10 seconds here), Fn(t) is calculated by the following equation based on the data after finishing the previous discharge/charge Fn-1(t):
Fn(t)=ffast1n-1(t)+ffast2n-1(t)+fslow1n-1(t)+fslow2n-1(t)}  (Eq. 11)

In the same manner, when the time t is judged to be longer than the first reference time and shorter than a second reference time (1,000 seconds here), Fn(t) is calculated by the following equation based on the data after finishing the previous discharge/charge F n−1 (t) and the latest data:
ffast1n(t)+ffast2n-1(t)+fslow1n-1(t)+fslow2n-1(t)}  (Eq. 12)

Still more, when the time t is judged to be longer than the second reference time and shorter than a third reference time (36,000 seconds here), r(t) is calculated by the following equation based on the data after finishing the previous discharge/charge Fn-1(t) and the latest data:
Fn(t)=ffast1n(t)+ffast2n(t)+fslow1n-1(t)+fslow2n-1(t)  (Eq. 13)

Furthermore, when the time t is judged to be longer than the third reference time and shorter than a fourth reference time (72,000 seconds here), Fn(t) is calculated by the following equation based on the data after finishing the previous discharge/charge Fn-1(t) and the latest data:
Fn(t)=ffast1n(t)+ffast2n(t)+fslow1n(t)+fslow2n-1(t)  (Eq. 14)

Then, t=20 hours is substituted to Fn(t) obtained by the equations (11) through (14) to set as follows:
OCV20 hrn=Fn(20 hr)

Thus, fin(t) and OCV20 hrncan be obtained by the equations (11) through (15).

InFIG. 7, when the time t is judged to be more than the fourth reference time, e.g., 20 hours, Fn(t) is calculated by replacing to the following equation (14-2) based on OCV20 hrnobtained the latest Vmes(20 hr) and the data of ΔV(t)_temp: ΔV(t)n=ΔV(t)_temp+OCV20 hr—temp-OCV20 hrn(Eq. 14-2)

Then, Fn(t) is calculated by the following equation by not obtaining ΔV(t)nfrom Fn(20 hr) but by replacing with the equation (14-2):
Fn(t)=ffast1n(t)+ffast2n(t)+fslow1n(t)+fslow2n(t)  (Eq. 15)

InFIG. 8, SOHinis calculated by using fi(t) calculated in the flows inFIGS. 6 and 7and stored in the temporary memory area (23) and reference data firef(t) and SOHirefrecorded in the stationary memory area (24) in advance.

Next, the calculation is made as SOCn=SOCref-nby inputting the respective values to the relational expression of H (OCV20 hrn, SOHn, T_n)=SOCref-nin the stationary memory area (24) by using OCV=OCV20 hrnobtained inFIGS. 6 and 7, SOH and SOHnobtained inFIG. 8and T=t_n obtained inFIG. 4.

It becomes possible to detect the states of charge and depletion of the battery by comparing SOCnand SOHncalculated as described above with predetermined threshold values.

The comparison judging means compares SOCnand SOHnwith the predetermined threshold values set in advance and judges that the battery is in the depletion state when SOCnis less than the threshold value or when SOHnis more than the threshold value. It is noted that the relationship between the magnitudes of SOH and the depletion level of the battery is reversed depending on system design. In such a case, it is needless to say that it is judged that the battery is in the depletion state when SOHnis less than the predetermined threshold value.

FIG. 9shows one example of changes of each term when the relaxation function F(t) is expressed as the equation (10) as one embodiment of optimization of the relaxation function F(t) in the battery state detecting method of the embodiment.

FIG. 9is a graph indicating changes of V(t) (=F(t)) when an axis of abscissa represents the elapsed time from the end of discharge/charge. The reference numerals51through54indicate the changes of each term (Ffast1(t), Ffast2(t) . . . Fslow1(t), Fslow2(t)) in the equation (10), respectively. Still more, the reference numeral50indicates a true value and the reference numeral55indicates a value of F(t) calculated from the equation (10) This indicates that it becomes possible to estimate ΔV(t) in high precision by using F(t) of the embodiment.

SOH1nafter the n-th discharge/charge will be calculated by the following equation by defining a degree of stratification of the slow reaction speed (diffusion of the electrolytic solution and others) as SOH1 in the equation (7):
SOH1n=fslown(t)/fslowref(t)*SOH1ref={fslow1n(t)+fslow2n(t)}/{fslow1ref(t)+fslow2ref(t)}*SOH1ref(Eq. 16)

In the above equation, fin(t), firef(t) in the equation (7) is calculated further from the sums of two terms {fslow1n(t)+fslow2n(t)} and {fslow1ref(t)+fslow2ref(t)}.

As one example, 20 times, 50 times and 100 times of discharge and charge cycles have been carried out from an unused state by using a liquid-type lead battery (model size:55D23) manufactured by Furukawa Battery Co., Ltd. And under conditions of 25° C. of environment temperature and of 10% of DOD (Depth of Discharge). Then, SOH1ncan be calculated by the following equations from the OCV variation fin(5 hr) when 5 hours has passed (t=5 hr) from the stop of discharge/charge based on the measured data after discharge/charge of 20 cycles, after discharge/charge of 50 cycles and after discharge/charge of 100 cycles by using the case of 20 cycles as a measure.
SOH150={fslow150(5 hr)+fslow250(5 hr)}/{fslow120(5 hr)+fslow220(5 hr)}*SOH120(Eq. 17)
SOH1100={fslow1100(5 hr)+fslow2100(5 hr)}/{fslow120(5 hr)+fslow220(5 hr)}*SOH120(Eq. 18)

FIG. 10shows fslown(t)/fslow20(t) calculated from the measured data. The reference numerals61,62and63represent fslow20(t), fslow50(t) and fslow100(t), respectively and the reference numerals64and65represent fslow50(t)/fslow20(t) and fslow100(t)/fslow (t), respectively. This graph permits to obtain a value 1.52 at a point of time t=18,000 seconds for example as follows:
{fslow150(5 hr)+fslow250(5 hr)}/{fslow120(5 hr)+fslow220(5 hr)}=Fslow50(5 hr)/Fslow20(5 hr)=1.52

In the same manner, a value 1.63 is obtained as follows:
fslow100(5 hr)/fslow20(5 hr)=1.63

Thus, it becomes possible to understand the changes of the state of the battery corresponding to the number of discharge/charge cycles from the variation F(t) of OCV.

Still more, the OCV when 20 hours has passed after the end of the discharge/charge turns out as follows as one example with respect to 20, 50 and 100 discharge/charge cycles:

FIG. 11shows a relationship between fslown(t)/fslow20(t) and OCV20 hr20. The result shown inFIG. 11can be used in a stable OCV estimating equation for estimating OCV20 hrof the same type of battery.

As described above, the invention can provide the battery state detecting method for detecting the state by evaluating the depletion caused by the reaction processes whose speeds are different. It becomes possible to accurately detect the residual capacity SOC by detecting the depletion level SOH of the battery. Thereby, it becomes possible to assure stable operation of the electric devices and to promote prediction of risk, thus having an effect of keeping safe operation of the vehicle. The invention also provides an effect of reducing an environmental burden by improving precision of the idling stop function.

It is noted that the descriptions in the embodiment indicate one exemplary battery state detecting method of the invention and the invention is not limited to them. The detailed structures and operations and others of the battery state detecting method of the embodiment can be appropriately modified within a scope not departing from the gist of the invention.