JP4835355B2 - Battery deterioration judgment device - Google Patents

Description

  The present invention relates to a battery deterioration determination device, and more particularly to a battery deterioration determination device that can be mounted on an automobile.

  In recent years, an increasing number of automobiles have an idling stop function that automatically stops the engine operation when the vehicle is stopped, such as when waiting for a signal or when there is a traffic jam, in order to reduce exhaust gas and improve fuel efficiency. The battery of the idling stop vehicle needs to supply power to the load at the time of idling stop as well as engine restart. As described above, the battery of the idling stop vehicle is used more heavily than the battery of the non-idling stop vehicle. If information on battery deterioration can be obtained, the battery life can be extended by performing power management accordingly. In addition, if information regarding the deterioration of the battery can be obtained, the user can know in advance the replacement time of the battery and can avoid a sudden function stop. Therefore, it is an important request to realize a battery deterioration determination mechanism with high accuracy and low cost.

  It is known that the deterioration of the secondary battery appears as a phenomenon in which the internal resistance value of the battery increases with time and the terminal voltage of the battery decreases due to repeated charging / discharging or being left unattended. Therefore, the degree of deterioration of the battery can be estimated by measuring the internal resistance (internal resistance method).

JP 2003-177164 A

  However, according to the inventor's experiment, the amount of increase in internal resistance in the deterioration mode due to repeated idling stops is extremely higher than the amount of increase in internal resistance in normal deterioration modes other than idling stop (for example, neglected deterioration). I know it ’s small. Therefore, it is difficult to determine the deterioration state of the battery due to repeated idling stops based on the internal resistance.

  Further, in an idling stop vehicle, the battery is generally operated so as to be fully charged or close to it before performing idling stop. However, in the state near the full charge of the battery, there is almost no difference between the internal resistance of the battery deteriorated by repeated idling stops and the internal resistance of the new battery. In other words, it can be said that it is more difficult to determine the deterioration state of the battery due to repeated idling stops based on the internal resistance, considering that the normal battery is controlled to be in a fully charged state.

  According to the experiment, when both the battery deteriorated due to repeated idling stop and the new battery decrease the charge amount, the internal resistance of the battery deteriorated due to repeated idling stop becomes the internal resistance of the new battery. It has been found that it increases significantly. Therefore, if the charge amount of the battery is set to a predetermined value (for example, 80%) or less, it is possible to determine the deterioration state of the battery based on the internal resistance. However, if the charge amount of the battery is reduced until the battery deterioration state can be determined based on the internal resistance in this way, there is a possibility that the engine cannot be restarted from the idling stop state. That is, in such battery deterioration determination, engine startability cannot be ensured and cannot be adopted as a determination method performed while the automobile is running.

  Accordingly, there is a need for a battery deterioration determination method that can be performed in a state near full charge so that determination can be performed with higher accuracy than the internal resistance method and can be performed even while the idling stop vehicle is running.

  According to one aspect of the present invention, there is provided a battery deterioration determination device for determining deterioration of a chargeable / dischargeable battery, wherein the battery terminal voltage changes during a predetermined time after the battery is switched from a fully charged state to a discharged state. And calculating means for calculating a parasitic capacity based on a change in discharge current, and a determining means for determining that the battery has a life when the calculated parasitic capacity falls below a predetermined life level. A battery deterioration determination device is provided.

  According to this configuration, it is possible to determine the deterioration of the battery with higher accuracy than in the internal resistance method.

  According to a preferred embodiment of the present invention, the predetermined time is a time for making a substantially linear change in a discharge curve indicating a time change of the terminal voltage of the battery when the battery is discharged from a fully charged state. It is preferable.

  According to this configuration, it is possible to easily detect a time change in the terminal voltage of the battery depending on the parasitic capacity of the battery, so that the battery deterioration determination process can be simplified.

  According to another aspect of the present invention, an automobile having a battery deterioration determination device having the above characteristics is provided. According to the vehicle having this configuration, it is possible to perform highly accurate battery deterioration processing during driving.

  According to a preferred embodiment of the present invention, the automobile controls the battery to a fully charged state or a state near full charge, and automatically stops idling of the engine when a predetermined condition is satisfied. It is preferable that the battery deterioration determination device further operates when the idling stop unit operates.

  According to this configuration, during the operation of the battery deterioration determination device, it is ensured that the battery is fully charged or in a state near full charge, and high-accuracy deterioration determination can be ensured.

  According to a preferred embodiment of the present invention, it is preferable that the information processing apparatus further includes warning means for giving a warning when the determination means determines that the battery is at the end of its life.

  According to this configuration, the driver of the automobile can easily and timely know the battery replacement time.

  ADVANTAGE OF THE INVENTION According to this invention, the battery degradation determination apparatus which can determine degradation of a battery accurately with the cheap structure which can be mounted in a vehicle is implement | achieved.

(Embodiment 1)
In FIG. 1, the example of the basic circuit model of the battery in this embodiment is shown. In the drawing, E represents an electromotive force, R _A represents a lattice resistance, R _B1 represents a charging resistance, R _B2 represents a discharging resistance, and C represents a parasitic capacitor.

  The grid constituting the battery electrode plate holds the active material and plays a role of electrical conduction between the outside and the active material. As shown in FIG. 2, the active material is subjected to stress due to charging / discharging over time, and the bonding force between the particles is weakened and gradually falls off the electrode plate. When the active material falls off, the remaining capacity is also reduced, which ultimately leads to battery life. The parasitic capacitance C is proportional to the surface area of the active material. From this, it can be considered that the loss of the active material is a reduction of the residual capacitance and a reduction of the parasitic capacitance C. Therefore, it is considered possible to determine the deterioration of the battery by estimating the value of the parasitic capacitance C.

Here, FIG. 3 shows an example of a discharge curve (time change of the battery voltage VBAT) when discharging from the fully charged state. In the section (A), the voltage V _c of the parasitic capacitor C is larger than the electromotive force E, and constant current discharge is caused by the parasitic capacitor C, and VBAT shows a substantially linear characteristic. On the other hand, in the section (B), voltage V _c of the parasitic capacitor C becomes less force E, fell how VBAT by the assist is applied electromotive force E is can be seen that dull.

Now, (A) section, i.e., voltage V _c of the parasitic capacitor C in the case larger than the electromotive force E is the voltage change ΔVBAT the battery is expressed by the following equation.
ΔVBAT = ΔQ / C = (I / C) t
Here, ΔQ is a change in charge amount, I is a battery current, and t is time.
Then
ΔVBAT / ΔI = (1 / C) t
It becomes. From this, the inventor can estimate the value of the parasitic capacitance C by obtaining the slope of the substantially straight section in FIG. 3A corresponding to 1 / C, and obtaining the slope of the substantially straight section in FIG. I thought it was. Moreover, this substantially straight section lasts for several seconds. At present, the sampling time of current sensors and voltage sensors that can actually be mounted on automobiles from the viewpoint of cost is generally the fastest and is on the order of 5 msec. Therefore, it is considered possible to detect the current value at two time points in order to obtain the change ΔI of the battery current in this substantially straight section.

  The inventor verified this hypothesis. FIG. 4 is a new battery and a battery deteriorated by repeated idling stops (hereinafter referred to as “IS deteriorated battery”) obtained by the inventors' experiment. 5) is a discharge curve when discharging from a fully charged state, and FIG. 5 shows that the value of the parasitic capacitance C is obtained a plurality of times from the slope of the substantially straight section (A) in the discharge curve of FIG. The results are shown repeatedly. From the result of FIG. 5, it can be seen that the parasitic capacity of the IS-degraded battery is significantly lower than the parasitic capacity of the new battery. Therefore, it can be said that the battery deterioration can be determined based on the parasitic capacitance value obtained from the slope of the substantially straight section in the discharge curve.

  Hereinafter, an embodiment of a battery deterioration determination device based on the above-described knowledge will be described.

  FIG. 6 is a block diagram showing a main part of an automobile on which the battery deterioration determination device of the present invention is mounted.

  In FIG. 6, 1 is an engine, and 2 is a generator (generator) that also serves as a starting motor. The engine 1 feeds power generated by the generator 2 connected to the differential gear 4 provided between the left and right drive wheels 3 and 3 through a drive mechanism (not shown) to the battery 6 through the power line 5. Is done. The battery 6 is a chargeable / dischargeable secondary battery, and is composed of, for example, a lead storage battery, a nickel metal hydride battery, a lithium ion battery, or the like. The discharged power of the battery 6 is supplied to the load 8. The load 8 is an electrical component such as an air conditioner, an audio device, a headlight, or a room light.

  Reference numeral 7 denotes a battery ECU (Electronic Control Unit) that performs a deterioration determination process of the battery 6. The battery ECU 7 is typically realized by a microcomputer having a CPU 71 for controlling, a ROM 72 for storing a control program and fixed data, and a RAM 73 for providing a work area for the CPU 71 as shown in the figure.

  A current sensor 9 is connected in series to the battery 6 and detects a discharge current and a charging current flowing through the battery 6. A voltage sensor 10 is connected in parallel to the battery 6 and detects a terminal voltage of the battery 6. These current sensor 9 and voltage sensor 10 are connected to interfaces (I / F) 74 and 75 of battery ECU 7, respectively. Each of the I / Fs 74 and 75 includes an A / D converter (not shown) that converts the output values of the current sensor 9 and the voltage sensor 10 into digital values.

  FIG. 8 is a flowchart showing the deterioration determination process of the battery 6 in the present embodiment. The program corresponding to this flowchart is included in the control program stored in the ROM 72 and is executed by the CPU 71. This process can be repeatedly performed from when the ignition is turned on until it is turned off.

  In this deterioration determination process, as shown in FIG. 7, a process of detecting the terminal voltage VBAT of the battery 6 at two time points (T1, T2) in a substantially linear section (corresponding to the section (A) in FIG. 3) of the discharge curve. Is included.

  First, in step S1, it waits for the battery 6 to be fully charged. For example, when the charging current value of the battery 6 detected by the current sensor 9 is a predetermined value (for example, 1 A) and the terminal voltage of the battery 6 detected by the voltage sensor 10 is a predetermined value (for example, 14.8 V) The battery 6 is determined to be fully charged.

  When full charge of the battery 6 is detected, it is next determined whether or not the battery 6 is discharged (step S2). Here, when the discharge of the battery 6 is detected, the processing after step S3 is executed. Note that the timing at which steps S1 and S2 are each YES in this manner typically includes an idling stop execution time. On the other hand, when the discharge of the battery 6 is completed, the process proceeds to step S16, and the variables of the time counter T, the battery voltage values V1 and V2, and the discharge current values I1 and I2 are reset to 0, respectively.

  In step S3, the time counter T is incremented. In step S4, it is determined whether or not the time counter T has reached a value corresponding to time T1. When the time counter T reaches a value corresponding to time T1, the process proceeds to step S5, and the terminal voltage VBAT of the battery 6 detected by the voltage sensor 10 at time T1 is set to V1. Thereafter, in step S6, the integral value ∫Idt of the discharge current of the battery 6 detected by the current sensor 9 is reset to zero. Subsequently, in step S7, the discharge current value I of the battery 6 detected by the current sensor 9 at time T1 is set to I1.

  Thereafter, the process returns to step S3 to increment the time counter T, and in step S4, it is determined whether or not the time counter T is a value corresponding to the time T1. Once T1 is detected in the above processing and the processing in steps S5 to S7 is completed, the processing proceeds from step S4 to step S8.

  In step S8, it is determined whether or not the time counter T has reached a value corresponding to time T2. If the time counter T is not a value corresponding to the time T2, the process proceeds to step S9, and the integrated value ∫Idt is updated by integrating the discharge current value of the battery 6 detected by the current sensor 9.

  On the other hand, when the time counter T reaches a value corresponding to time T2 in step S8, the process proceeds to step S10, and the terminal voltage VBAT of the battery 6 detected by the voltage sensor 10 at time T2 is set to V2. Next, the process proceeds to step S11, and the discharge current integrated value from time T1 to time T2 obtained in step S9 is set as ∫Idt. Subsequently, in step S12, the discharge current value I of the battery 6 detected by the current sensor 9 at time T2 is set to I2.

  In step S13, the parasitic capacitance C is calculated. The parasitic capacitance C is obtained by the following equation based on a known circuit theory. However, here, it is assumed that the discharge by the parasitic capacitance C corresponding to the section (A) in FIG. 3 is not a constant current discharge (that is, I1 ≠ I2).

  Next, it progresses to step S14 and it is judged whether the parasitic capacitance C calculated | required by step S13 has fallen below the predetermined lifetime line. If the parasitic capacitance C is greater than or equal to this life line, the process is exited as it is. On the other hand, if the parasitic capacitance C falls below the life line, it is determined that the battery 6 is at the end of life, and for example, a warning is displayed by an indicator provided on the instrument panel of the automobile (step S15), and then the process is terminated. .

  Thus, according to the present embodiment, it is possible to determine the deterioration of the battery based on the parasitic capacitance value obtained from the slope of the substantially straight section in the battery discharge curve. According to this method, it is possible to determine the deterioration state of the battery with higher accuracy than in the conventional internal resistance method. In addition, as described above, since the substantially straight section in the discharge curve lasts for several seconds, the slope can be obtained using a low-speed current sensor, so this method can be realized at low cost. is there.

(Embodiment 2)
In the first embodiment described above, an example is shown in which the battery life is determined based on the parasitic capacity value obtained from the slope of the substantially straight section in FIG. 3A using the battery basic circuit model shown in FIG. It was. However, as shown in FIG. 3, it can be seen that there is a steep substantially straight section before the section (A). If the slope of this steep substantially straight section can be obtained, it is also possible to determine the battery life.

  Therefore, in this embodiment, a battery basic circuit model as shown in FIG. 9 is used instead of the battery basic circuit model of FIG.

Battery basic circuit model of FIG. 9, the electromotive three resistors connected in series to the power _{E R 0, R 1, R} 2, and a parasitic capacitor _C 1 between _{R 0} and _{R 1, R 1} And a parasitic capacitor C ₂ between R ₂ . In the example of FIG. 9, _{R 0} corresponds to the lattice resistance _{R A} of FIG. 1, it is assumed _{that R 1} and _{R 2} correspond to the charge and discharge resistor _{R B.} Also, C ₁ << C ₂ (for example, C ₁ ≈5F, C ₂ ≈200F).

According to this circuit model, when the voltage of the parasitic capacitor C ₁ + C ₂ is larger than the electromotive force E, a substantially straight section A1 due to the discharge from the parasitic capacitor C ₁ is obtained as shown in the example of the discharge curve of FIG. . The slope of the substantially straight line corresponds to 1 / _{C 1.} Thereafter, a substantially straight section A2 is obtained by discharging from C ₂ (≈C ₁ + C ₂ ). The slope of the substantially straight line corresponds to 1 / _{C 2.}

Therefore, applying the deterioration determination process of the above-mentioned battery in a substantially straight section A1 of inclination corresponding to 1 / C _1. That is, the current and voltage detection time point T1 and T2 mentioned above, by setting in the A1 section, to estimate the value of C _1, do this by lifetime judgment. In this case, it is apparent that the determination result at an earlier timing than the case of the life determination by estimating the value of C ₂ is obtained. That is, a faster deterioration determination process can be realized.

However, the slope corresponding to 1 / C ₁ due to the constant current discharge from the parasitic capacitor C ₁ is steeper than the slope corresponding to 1 / C ₂ due to the constant current discharge from the parasitic capacitor C _2. It is assumed that A1 has a very short period (for example, within 1 second) compared to A2. It is necessary to use a current sensor and a voltage sensor having a sampling time capable of detecting two points within the period A1. However, from the viewpoint of cost, it is conceivable that a sensor with such accuracy may not be mounted on an automobile.

In such a case, by using as a basic circuit model of FIG. 9, by setting the current and voltage detection time point T1 and T2 in the A2 section, estimates the value of C _2, thereby to make the life determination You can do it. In this case, as shown in FIG. 10, R ₀ + R ₁ is regarded as a lattice resistance R _A , and R ₂ is regarded as a charge / discharge resistance R _B. A2 section is strictly a discharge from _{C 1} and _{C 2,} but because it is _C 1 << C ₂ as described above, is a _{C 2} ≒ _C 1 + _{C 2.} Therefore, by setting the current and voltage detection time point T1 and T2 in the A2 section, it is possible to estimate the value of C ₂ with sufficient accuracy.

  Thus, according to the present embodiment, it is possible to use a battery deterioration determination algorithm based on a common basic circuit model, regardless of what sampling time current sensor and voltage sensor are used. That is, in this case, it is only necessary to change T1 and T2 according to the sampling time of the current sensor and voltage sensor to be used, and therefore the battery deterioration determination device according to the present invention can be widely installed in various vehicle types.

It is a figure which shows an example of the basic circuit of a battery. It is a figure explaining omission of the active material of a battery. It is a figure which shows an example of the discharge curve when discharging from the fully charged state of a battery. It is a figure which shows the discharge curve when discharging from a fully charged state of the new battery and the battery deteriorated by repetition of idling stop. It is a figure which shows the result of having repeated the calculation of the value of a parasitic capacitance from the inclination of the substantially linear area of (A) in the discharge curve of FIG. 4 several times. It is a block diagram which shows the principal part of the motor vehicle which has the battery deterioration determination apparatus in embodiment. It is a figure explaining the detection timing of the battery terminal voltage in the battery deterioration determination processing of the embodiment. It is a flowchart which shows the battery deterioration determination process in embodiment. , It is a figure which shows the example of the basic circuit of another battery. It is a figure which shows the example of the discharge curve of the battery based on the basic circuit of FIG. 9, FIG.

Explanation of symbols

1: Engine 2: Generator 3: Drive wheel 4: Differential gear 5: Power line 6: Battery 7: Battery ECU
8: Load (electrical components)
9: Current sensor 10: Voltage sensor 11: Temperature sensor

Claims (5)

A battery deterioration determination device for determining deterioration of a chargeable / dischargeable battery,
Calculation means for calculating a parasitic capacity based on a terminal voltage change and a discharge current change of the battery in a predetermined time after switching from a fully charged state of the battery to a discharged state;
Determining means for determining the battery life when the calculated parasitic capacitance falls below a predetermined life level;
A battery deterioration determination device characterized by comprising:   The said predetermined time is time which makes a substantially linear change in the discharge curve which shows the time change of the terminal voltage of the said battery when discharging from the fully charged state of the said battery. Battery deterioration determination device.   An automobile provided with the battery deterioration determination device according to claim 1. After controlling the battery to a fully charged state or a state near full charge, it further has an idling stop means for automatically stopping idling of the engine when a predetermined condition is satisfied,
4. The automobile according to claim 3, wherein the battery deterioration determining device operates when the idling stop means operates.   5. The automobile according to claim 3, further comprising a warning unit that issues a warning when the battery is determined to have a life by the determination unit.

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