JP2003331931A - Charged state detecting device for secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charged state detecting device for a secondary cell capable of detecting charged state with high accuracy even in the polarized state for charging. <P>SOLUTION: The charged state detecting device for a secondary cell comprises a voltage detection means 50 detecting the voltage V of the secondary cell B charged and discharged under the regulation of a regulator 30 mounted to a vehicle, regulating an alternating current generator 10 and the output voltage of the same, a current detection means 40 detecting the current I of the secondary cell B, a temperature detection means 60 detecting the temperature T of the secondary cell B; and a charge polarization state detection means 70 detecting the degree of influence P on the current-voltage property of the secondary cell B, caused by the polarization of the secondary cell B. When the degree of influence P exceeds a prescribed value, the degree of influence P is compared with a threshold depending on the voltage V, the current I, and the temperature T of the secondary cell, and the charged state of the secondary cell is determined. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charge state detection device capable of accurately detecting the secondary battery charge state even during charging.

[0002]

2. Description of the Related Art In vehicle battery charging control, a regulated voltage is set to about 13.5V to 14.5V, which is higher than a battery rated voltage of 12V, in order to efficiently charge the battery. In this case, the battery is always overcharged, the load on the internal combustion engine is increased, the fuel efficiency is deteriorated, and the liquid leakage of the battery is promoted. Therefore, we devised a system that adds a current sensor to detect the current flowing in and out of the battery, and controls so that the charge / discharge balance of the detected current becomes zero in the charging state slightly below the over (full) charging state. Has been done.

In these systems, a minimum voltage guard is generally provided in order to prevent deterioration of the state of charge due to self-discharge of the battery, current integration error, and the like. As a conventional technique for detecting the deterioration of the state of charge, current data, voltage data, and battery temperature are measured while the battery is in use, and these data are compared with a discharge current-voltage map stored in advance for each battery temperature. A technique for detecting the state of charge of a battery has been known. This technology is effective as a state-of-charge detecting device for electric vehicles, etc., which is mostly discharged. Also, the current during battery use is detected at a fixed sampling cycle,
As a technique for detecting the polarization state of a battery from a detected current, for example, in Japanese Unexamined Patent Publication No. 2000-258514, an electromotive force measured in advance is used by using a polarization electromotive force calculated in consideration of current charge / discharge history. There is disclosed a technique for correcting the relationship between the battery charge state and the battery charge state. According to this technique, the influence of the polarization electromotive force of the battery is appropriately compensated,
It is possible to accurately detect the charge state of the battery.

[0004]

However, in vehicles other than electric vehicles, the battery may not be discharged by the above-mentioned minimum voltage guard under a low electric load condition such as during daytime running. Therefore, detecting the state of charge (SOC) of the battery at the time of charging, which is performed relatively frequently, can detect the decrease in the state of charge even if the state of charge is reduced by self-discharge or dark current discharge. Therefore, it is effective.

In a hybrid vehicle in which charging is controlled so that the state of charge is maintained at about 60%, the state of charge determined to be low in battery capacity is about 40%, whereas it is more than that at full charge. In a vehicle in which the charging is controlled so as to be maintained at a slightly lower charging state, the state of charge determined to be a decrease in battery capacity is about 50%. A state-of-charge detecting device suitable for detecting a change in state of charge is useful.

Further, in order to detect the state of charge with high accuracy, it is necessary to consider the influence of the polarization of the battery on the current-voltage characteristics, as in the technique described in JP-A-2000-2585142. On the other hand, in the charge polarization state, the influence of polarization is particularly large, and the voltage becomes apparently high due to hydrogen overvoltage, which makes it difficult to handle the detected current-voltage characteristics.

Therefore, the present invention is capable of detecting the state of charge of a battery even during charging, and detecting the state of charge with high accuracy even in the state of charge polarization, and for detecting changes in the state of charge at a relatively high state of charge. An object is to provide a suitable electric state detection device for a secondary battery.

[0008]

According to the first aspect of the present invention, there is provided a voltage detecting means for detecting a voltage value of a secondary battery and a current detecting means for detecting a current value of the secondary battery. A secondary battery charge state detection device including, further comprising a polarization state detection means for detecting the degree of influence of the current-voltage characteristics of the secondary battery by the polarization of the secondary battery, the degree of polarization influence. Achieved by a state-of-charge detecting device for a secondary battery, characterized in that the state of charge of the secondary battery is determined by using the voltage value and current value of the secondary battery in a charge polarization state of a predetermined value or more. To be done.

According to the above-mentioned invention, the state of charge of the secondary battery is judged by using the voltage and current of the secondary battery being charged, so that the state of charge of the battery can be confirmed even if the battery is hardly discharged. A drop can be detected. Therefore, according to the present invention, even when the secondary battery is not discharged in a low electric load state such as during daytime running, it is possible to detect a decrease in the state of charge due to self-discharge or dark current discharge. it can.

Further, as described in claim 2, claim 1
In the charge state detection device for a secondary battery according to the description, the polarization state detection means, when estimating the influence degree of polarization of the secondary battery from the charge and discharge history of the secondary battery, a density meter, a densitometer, The charge polarization state of the battery can be detected without using a complicated polarization state detection means such as a hydrometer.

Further, as described in claim 3, claim 1
In the state-of-charge detecting device for a secondary battery described above, the voltage value of the secondary battery in a charge polarization state in which the degree of influence of polarization is a predetermined value or more, and a predetermined threshold value depending on the current value at this time are compared. By doing so, if the state of charge of the secondary battery is determined, it is possible to accurately detect a decrease in the state of charge of the secondary battery. That is, a secondary battery with a low state of charge can accurately detect a decrease in the state of charge of the secondary battery by utilizing the characteristic that the voltage value does not increase even when the degree of influence of polarization exceeds a predetermined value. it can. Such characteristics are particularly remarkable in a secondary battery with a state of charge of 50% or less. Therefore, a state of charge of 50% or less is determined to be low capacity, and the maximum state of charge that is not determined to be low is about 70%. It is especially effective in control systems. The threshold value that depends on the current value is the voltage value of the secondary battery when the degree of influence of polarization is the above-mentioned predetermined value in the maximum state of charge that is not judged to be capacity reduction, corresponding to the current value. You may Further, this threshold value may be prepared in advance for each current value in consideration of the degree of influence of polarization and the above characteristics in each charge state.

[0012] Further, as described in claim 4, the above object is provided in a vehicle equipped with an AC generator and a regulator for adjusting an output voltage of the AC generator, and is charged and discharged under the adjustment of the regulator. Charging for a secondary battery including voltage detecting means for detecting a voltage value of the secondary battery, current detecting means for detecting a current value of the secondary battery, and temperature detecting means for detecting a temperature of the secondary battery. The state detection device further includes polarization state detection means for detecting a degree of influence on the current-voltage characteristics of the secondary battery due to polarization of the secondary battery, and the degree of influence of the polarization of the secondary battery is a predetermined value. By comparing the voltage value of the secondary battery in the above charge polarization state and a predetermined threshold value depending on the current value and temperature at this time, the state of charge of the secondary battery is determined. Yes, secondary It is achieved by ponds charging state detection device.

According to the above-mentioned invention, since the state of charge of the secondary battery is judged using the voltage and current of the secondary battery being charged, the capacity of the battery is reduced even if the secondary battery is hardly discharged. Can be detected. Further, the secondary battery with a low state of charge uses the characteristic that the voltage value does not increase even if the degree of influence of polarization exceeds a predetermined value.
It is possible to accurately detect a decrease in the state of charge of the secondary battery. Also, since this characteristic appears without depending on the battery temperature, it is necessary to compensate for the change in the battery temperature and detect the decrease in the state of charge of the secondary battery accurately in a general operating environment where the battery temperature changes. You can The threshold depending on the battery temperature and the current value is a secondary value when the degree of influence of polarization is the predetermined value in the maximum charge state that is not judged to be the capacity reduction corresponding to the battery temperature and the current value. It may be the voltage value of the battery. Further, this threshold value may be prepared in advance for each current value and each battery temperature in consideration of the influence degree of polarization and the above characteristics in each charge state.

Further, as described in claim 5, claim 4
In the secondary battery charge state detection device described, in the case where the comparison result is the same for a predetermined number of times consecutively, if the decrease in the charge state of the secondary battery is to be detected, the decrease in the charge state is high. It can be detected with accuracy.

Other objects, configurations and effects of the present invention will become more apparent from the following description of the embodiments with reference to the drawings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a charge control system 90 for controlling the charging of a vehicle battery using the charge state detecting method according to the present invention. This battery is composed of a secondary battery B such as a lead storage battery.

As shown in FIG. 1, this charging control system 90 includes an AC generator 10 (hereinafter referred to as a generator 10).
And a rectifier 20 and a regulator 30.
The generator 10 is driven by the engine of the vehicle to generate an AC voltage. The rectifier 20 rectifies the AC voltage of the generator 10 to generate a rectified voltage and supplies the rectified voltage to the secondary battery B and the regulator 30. The regulator 30 adjusts the rectified voltage of the rectifier 20 and outputs the rectified voltage to the secondary battery B and the electrical load L under the control of the microcomputer 70 described later.

Further, the charging control system 90 includes a current sensor 40, a voltage sensor 50, a temperature sensor 60,
And a microcomputer 70. The current sensor 40 detects the charging current or the discharging current of the secondary battery B at a predetermined sampling cycle. Similarly, the voltage sensor 50
Detects the terminal voltage of the secondary battery B at a predetermined sampling cycle. The temperature sensor 60 detects the liquid temperature of the secondary battery B or the temperature of the side surface or the bottom surface of a case (not shown) that houses the secondary battery B. Microcomputer 70
Executes the control program according to the flowchart described later. During the execution of this control program, the microcomputer 70 detects the state of charge of the secondary battery B based on the detected values of the current sensor 40, the voltage sensor 50, and the temperature sensor 60, and stores the processing and data required for controlling the regulator 30. Perform processing, etc. The microcomputer 7
0 is always powered from the secondary battery B and is in an operating state,
When a vehicle ignition switch IG is turned on, execution of a control program described later is started. The control program is stored in the ROM of the microcomputer 70 in advance.

<Index Representing Polarization State> In the charge state detecting method according to the present invention, the degree of influence of the polarization of the secondary battery on the current-voltage characteristics of the secondary battery (hereinafter, simply referred to as “polarization state”). ), The index P given by the following equation is used.

[0020]

[Equation 1] This index P (unit: A · sec) expresses the solution concentration in the vicinity of the electrode as an electric quantity, and takes into consideration the change in the solution concentration in the vicinity of the electrode due to charge / discharge and the amount dissolved by diffusion. In this specification, a state where the index P is P <0 is defined as a discharge polarization state, and a state where P ≧ 0 is defined as a charge polarization state.

Here, in the equation 1, I is a detection current (A), and I> 0 is charged and I <0 is discharged. γ
Is a correction term for the fluctuation of the charging efficiency of the secondary battery B (it becomes a value of 0 to 1 when the secondary battery B is charged, but becomes approximately 1 when charging and discharging are repeated). T is time (second). Further, Id is a correction term caused by polarization in the secondary battery B. If P'is the value of the index P one cycle before T1 and a and b are constants, P '> 0
When, Id = a × P ′, and when P ′ = 0, Id = a × P ′
= 0 and P ′ <0, Id = b × P ′.
The reason why the constants a and b are used properly is that the influence time of polarization is different after discharging and after charging. Formula 1 is stored in advance in the ROM of the microcomputer 70.

<Capacity reduction determination method according to the present invention>
The operation of the control program for realizing the capacity decrease determination method according to the present invention will be described with reference to FIG.

When the ignition switch IG of the automobile is turned on to start the execution of the control program, in step 100, the value of the index P representing the polarization state and the integrated value I _sum of the battery charge / discharge capacity are reset to zero.

Next, the processing of steps 110 to 190 is carried out every sampling period ΔT. Step 110
Then, the detection current I of the current sensor 40, the detection voltage V of the voltage sensor 50, and the detection temperature T of the temperature sensor 60 are read. Then, in step 120, the integrated value I _sum of the battery charge / discharge capacity is calculated based on the following equation according to the integrated value I _{sum ′} of the battery charge / discharge capacity one cycle before and the detection current I read in step 110.

I _sum = I _{sum '} + I × ΔT Here, the detection current I> 0 is charged, and I <is discharged.

Further, in step 130, the correction amount ΔVm of the adjustment voltage is calculated according to the integrated value I _sum of the battery charge / discharge capacity obtained in step 120, for example, based on the map shown in FIG. In the following step 140, the adjustment voltage Vm is calculated based on the following equation according to the adjustment voltage Vm ′ one cycle before and the adjustment amount ΔVm of the adjustment voltage calculated in step 130.

Vm = Vm '+ ΔVm When the calculated Vm is equal to or higher than a preset upper limit value, it is changed to an upper limit value, and when it is equal to or lower than a preset lower limit value, it is changed to a lower limit value. By these processes, the charge / discharge balance of the secondary battery B is usually controlled to be zero, and the energy loss due to overcharge of the battery can be reduced.

In the following step 150, the index P representing the polarization state is calculated based on the equation (1), and the above step 110 is performed.
It is calculated according to the detected current I read in.

When the index P is calculated in this way, in step 160, the index P is set to a predetermined value, for example, 4
00 (that is, whether the degree of influence of charge polarization is large), and whether the detected current I is larger than zero (that is, whether charging is being performed). If the determination is negative, the process proceeds to step 190, and if the determination is affirmative, the process proceeds to step 170.

In step 170, it is determined whether or not the plot point of the detection voltage V with respect to the detection current I belongs to a region below the boundary line for capacity reduction determination shown in FIG. 4, for example. As shown in FIG. 4, the boundary line for determining the capacity decrease is prepared in advance according to the battery temperature, and the boundary line for determining the capacity decrease corresponds to the detected temperature T read in step 110. To be selected. The method of setting the boundary line for determining the capacity decrease will be described in detail later. If the determination in step 170 is negative, step 190
If the determination is affirmative, the process proceeds to step 180.

In step 180, it is determined that the battery capacity is low, and in order to improve the recovery of the state of charge, the adjustment voltage is set higher and the normal control for charging is performed.
Proceed to step 190. In this step 180,
In order to improve the certainty of the determination, it may be determined that the battery capacity is low when the condition of step 170 is continuously satisfied.

In step 190, it is determined whether or not the ignition switch IG is turned off, and if the determination is affirmative, the process ends. On the other hand, if the determination is negative, the processing from step 110 onward is repeated.

<Method of Determining Boundary Line for Capacity Reduction Judgment> Next, a method of determining a boundary line for capacity reduction determination shown in FIG. 4 will be described with reference to FIG. FIG. 5 is a diagram showing a voltage curve of a secondary battery (battery temperature 30 ° C., rated capacity 48 Ah) when the secondary battery is charged with a constant current, with respect to the index P obtained by the equation (1). FIG. 5A shows the result when the current Ia = 9.6 (A) was charged, and FIG. 5B shows the result when the current Ib = 24 (A) was charged. It should be noted that in each drawing of FIG. 5, the secondary battery (start S
OC: 30%, 50%, 70%, 90%) respective voltage curves are shown.

As shown in FIGS. 5A and 5B,
Charge current is Ia = 9.6 (A) or Ib = 24
In any of the cases (A), it can be seen that the rate of increase of the voltage decreases from the vicinity of the index P exceeding 400 (A · sec) when the SOC is 50% or less. In other words, when charging is continued, as a result, the SOC rises and the voltage rises, but the index P is about 400 (A · se).
Beyond c), in the secondary battery with SOC 50% or less, S
It can be seen that the voltage increase is lower than that of the secondary battery having an OC of 70% or more.

Here, the criterion for determining the battery capacity decrease is SO
Reference will be made to a specific method of determining a boundary line for capacity reduction determination in the case where C50% or less and a maximum SOC of 70% or less is allowed. As shown in FIG. 5A, in the range where the index P exceeds 400 (A · sec), the voltage curve relating to SOC 70% and the voltage curve relating to SOC 50% or less can be separated by the line of voltage Va. Similarly, as shown in FIG. 5B, the index P is 400
In the range exceeding (A · sec), the voltage curve relating to SOC 70% and the voltage curve relating to SOC 50% or less can be partitioned by the line of voltage Vb. These voltages Va and Vb
As shown in FIGS. 5 (A) and 5 (B), SOC7
It may be the respective voltage values at P = 400 in the voltage curve relating to 0%, but in the above step 160, for example, 4
When making a determination in the range of 00 <P <500, P
The voltage value may be lower than the voltage value at 400.

The voltages Va and V thus determined
b is the judgment voltage V for the current values Ia and Ib, respectively.
By connecting a straight line as the _threshold , the boundary line for determining the capacity decrease at the battery temperature of 30 ° C. shown in FIG. 4 is obtained. The determination voltage V _threshold for current values other than the current values Ia and Ib is the voltage value for the current value on the boundary line for determining the capacity decrease. Similarly, by changing the battery temperature, a boundary line for each battery temperature as shown in FIG. 4 is obtained. Therefore, the determination voltage V _threshold is V _threshold = f (I,
T) (see step 170 above).

In this example, the boundary line for capacity decrease determination is obtained based on each determination voltage for two current values Ia and Ib, but the capacity is determined based on each determination voltage for more current values. You may make it determine | determine the boundary line for a fall determination. Further, in the present example, the SOC reduction target is set to 50% or less and the maximum SOC is set to 70% or less, and the boundary line for the capacity determination is determined, but the detection target may be changed as necessary. Good.

Next, the detection result of the capacity decrease of the secondary battery by the above-mentioned control program using the capacity decrease determination boundary line (the boundary line where the detection target is SOC 50% or less) set in this way is used. To mention.

FIG. 6 is a diagram in which the current and voltage during actual vehicle traveling are measured by step 110 (see FIG. 2) of the above-mentioned control program, and the measurement points are plotted for each sampling period ΔT. A) shows the result of using the secondary battery of SOC70%, FIG. 6 (B) shows SOC50%.
2 shows the result of using the secondary battery of FIG.

As shown in FIG. 6A, some of the plot points at SOC 70% (the plot points with small circles) are as follows.
Although it belongs to a region below the boundary line for determining the capacity decrease, the plot points (plot points marked with ▲) where the index P representing the polarization state of the battery exceeds 400 are below the boundary line for determining the capacity decrease. Has never belonged to the area below,
In step 180 above, it was not determined that the capacity had decreased. On the other hand, when the SOC is 50%, even if the plot point has an index of more than 400 (the plot point marked with ▲), FIG.
As shown in (1), since it belongs to the area below the boundary line for capacity reduction determination, it is determined in step 180 that the capacity has decreased. From this result, in the range of P> 400, S is determined by the boundary line for capacity reduction determination set as described above.
It was confirmed that a decrease in the state of charge with an OC of 50% or less can be reliably detected.

When the secondary battery deteriorates, the SOC 70
%, The voltage rise in the charge polarization state decreases in most cases (for example, SOC5 in FIG. 5B).
Since it looks like a 0% voltage curve), the above step 18
It is predicted that the capacity is judged to be reduced when 0. However, in this case, the capacity that can be actually taken out from the SOC 70% secondary battery has decreased, so the capacity remaining in the SOC 70% secondary battery is, for example, a new battery of SOC 50%. It can be considered to be almost the same as the next battery, and the judgment is made on the safe side.

As described above, in the present invention, when the capacity is reduced (the charge state is 50% or less), the voltage rise is suppressed even in the charge polarization state in which the overvoltage occurs, and the predetermined voltage is determined. If the detected charging current-voltage characteristics are lower than the predetermined boundary line for determining the capacity drop, even though the charge polarization state exceeds the value, the secondary battery is judged by the capacity drop. Since the battery is connected in parallel to the generator, it is possible to detect the decrease in the capacity of the secondary battery even when the battery is hardly discharged.

The "polarization state detecting means" described in the claims is realized by the microcomputer 70 executing step 150 of the control program described in the detailed description of the invention.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made to the above-described embodiments without departing from the scope of the present invention. And substitutions can be added. For example, in the above-described embodiment, the index defined by the formula of Formula 1 is used to determine the polarization state, but the formula is not particularly limited to this formula, and the formula is modified. Formulas, formulas derived from the same point of view, or the like, can also be applied to the present invention.

[0045]

Since the present invention is as described above, it has the following effects. According to the invention of claim 1, it is possible to detect the decrease in the capacity of the battery even in the state where the battery is hardly discharged.

According to the second aspect of the invention, the charge polarization state of the battery can be reliably detected at low cost. Further, according to the invention of claim 3, 4 or 5, the characteristic that the voltage value does not increase in the secondary battery having a low state of charge is utilized even if the degree of influence of polarization exceeds a predetermined value. The deterioration of the state of charge can be accurately detected.

[Brief description of drawings]

FIG. 1 is a diagram showing a charging control system 90 that controls charging of a vehicle battery.

FIG. 2 is a flowchart showing the operation of the microcomputer 70 according to the present invention.

FIG. 3 is a map prepared in advance for calculating a correction amount ΔVm of an adjustment voltage.

FIG. 4 is a diagram showing a boundary line for capacity reduction determination.

5 is a diagram showing a voltage curve of a secondary battery with respect to an index P, and FIG. 5 (A) shows a current Ia = 9.6.
FIG. 5B shows the result of charging with (A), and FIG. 5 (B) shows the result of charging with current Ib = 24 (A).

FIG. 6 is a diagram showing a detection result of a capacity decrease by the control program according to the present invention, and FIG.
The result of 70% is shown, and FIG. 6 (B) shows the result of SOC 50%.

[Explanation of symbols]

10 AC generator 20 rectifier 30 regulator 40 current sensor 50 voltage sensor 60 temperature sensor 70 Microcomputer 90 Charge control system B secondary battery L electrical load

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shoji Sakai             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Jun Hashikawa             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Naohiko Suzuki             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Masayuki Morito             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Hiroshi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Takeshi Sada             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO F term (reference) 2G016 CA03 CB12 CB13 CB21 CB31                       CC01 CC02 CC03 CC04 CC07                       CC12 CC13 CC17 CC20 CC23                       CC27 CC28 CF06                 5H030 AA04 AS08 FF42 FF43 FF44

Claims (5)

[Claims] 1. A state-of-charge detecting device for a secondary battery, comprising a voltage detecting means for detecting a voltage value of a secondary battery and a current detecting means for detecting a current value of the secondary battery, wherein The secondary battery voltage in a charging polarization state further includes polarization state detection means for detecting the degree of influence of the current-voltage characteristics of the secondary battery due to the polarization of the battery, and the degree of influence of the polarization becomes a predetermined value or more. A state-of-charge detecting device for a secondary battery, wherein the state-of-charge of the secondary battery is determined using a value and a current value. 2. The charge state detecting device for a secondary battery according to claim 1, wherein the polarization state detecting means estimates the degree of influence of polarization of the secondary battery from the charge / discharge history of the secondary battery. 3. The secondary battery is obtained by comparing a voltage value of the secondary battery in a charged polarized state in which the degree of influence of polarization is a predetermined value or more with a predetermined threshold value depending on a current value at this time. The charge state detection device for a secondary battery according to claim 1, which determines the charge state of the battery. 4. A voltage detector for detecting a voltage value of a secondary battery which is mounted on a vehicle equipped with an AC generator and a regulator for adjusting an output voltage of the AC generator and which is charged and discharged under the adjustment of the regulator. Means, a current detection means for detecting the current value of the secondary battery, a temperature detection means for detecting the temperature of the secondary battery, a state-of-charge detecting device for a secondary battery, comprising: The secondary battery in a charged polarization state, further comprising polarization state detection means for detecting the degree of influence of the current-voltage characteristics of the secondary battery due to polarization, wherein the degree of influence of the polarization of the secondary battery is a predetermined value or more. 2. The state of charge detecting device for a secondary battery, characterized in that the state of charge of the secondary battery is judged by comparing the voltage value of 1 with a predetermined threshold value depending on the current value and temperature at this time. 5. The state-of-charge detecting device for a secondary battery according to claim 4, wherein a decrease in the state of charge of the secondary battery is detected when the comparison result is the same for a predetermined number of times consecutively.