JP3006293B2 - Battery remaining capacity meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery remaining capacity meter for an electric vehicle, and more particularly to an improvement of a battery remaining capacity meter for detecting the remaining capacity of a battery by utilizing the correlation between the discharge current and voltage and the remaining capacity of the battery. .

[0002]

2. Description of the Related Art In an electric vehicle, it is necessary to explore a battery as an energy source of a driving motor, and a rechargeable secondary battery is used as the battery. Lead batteries are typical of such secondary batteries and have the following configuration.

PbO ₂ | H ₂ SO _4aq | Pb In such a lead battery, the specific gravity of the sulfuric acid aqueous solution is usually 1.28 when charged.

This lead battery is the most widely used storage battery at present, and its basic reaction is as follows.

PbO ₂ + H ₂ SO ₄ + Pb → 2Pb
SO ₄ + 2H ₂ O PbO ₂ + H ₂ SO ₄ + Pb ← 2PbSO ₄ + 2H
₂ O In the above reaction formula, when proceeding to the right is a discharge reaction,
The reaction that proceeds to the left is the charging reaction. As is clear from this equation, both PbO ₂ , which is the positive electrode active material, and Pb, which is the negative electrode active material, become PbSO ₄ (solid) by discharging, and return to their original states by charging. In this lead battery, it is possible to repeat charging and discharging a large number of times (about 1000 times) in order to almost completely return to the original state by charging.

[0006] When a battery is used as an energy source for an electric vehicle, the most important problem is its remaining capacity. That is, if the remaining discharge capacity of the battery, which is the energy source, is not known, the distance that the electric vehicle can travel cannot be determined, and in the worst case, the car may stop where there is no charging facility. Becomes

Therefore, it is necessary to measure the remaining capacity of the battery. As a method of measuring the remaining capacity of a lead battery, there is a method of measuring the specific gravity of an electrolytic solution. That is, as is clear from the above reaction formula, since the lead battery generates water by discharging and generates sulfuric acid by charging, the specific gravity of the electrolytic solution (sulfuric acid aqueous solution) decreases by discharging, and increases by charging. Therefore, the remaining capacity of the battery can be measured by measuring the specific gravity of the electrolytic solution. However, this method of measuring the specific gravity of the electrolytic solution has a disadvantage that a specific gravity sensor must be incorporated in the battery, and the electrolytic cell needs to be improved.

On the other hand, it is known that the residual capacity of a lead battery has a certain relationship with the differential internal resistance (obtained as a gradient of a voltage / current straight line at the time of large current discharge) at the time of large discharge current. Measuring the remaining capacity from the current and the voltage at the time of the discharge current has been proposed, for example, in JP-A-63-157078.

That is, as shown in FIG. 7, when a large current is discharged, when the current value is constant (discharge current 200 A), there is a good correlation between the battery voltage and the remaining capacity. Therefore, if the relationship between the discharge voltage and the remaining capacity of the battery is determined for each discharge current, the remaining capacity of the battery can be determined from the current and voltage of the battery at the time of large current discharge based on the relationship.

According to such a measuring method, there is no change in the battery itself, and the remaining capacity of the battery can be measured by simple measuring means such as current and voltage measurement. For this reason, it is considered to be suitable for measuring the remaining capacity of the battery in the electric vehicle.

[0011]

However, the above-mentioned method is applicable only when the discharge current is large. That is, when the amount of current is small, the relationship between the voltage-current characteristics and the remaining battery capacity varies greatly, and accurate measurement of the remaining battery capacity cannot be performed. This is because the state inside the battery is not the same immediately after charging the battery or after a long time discharge, and when the amount of current is small, the voltage-current characteristics change due to such an internal state of the battery. It is believed that.

Therefore, a voltage and a discharge current at the time of a large discharge current are measured. In order to positively obtain a large discharge current, a new discharger must be newly installed and a large current must be supplied here. Such a discharger is inevitably large, and the battery capacity is reduced due to the discharge. Therefore, there is a problem that the traveling distance per charge is reduced.

On the other hand, Japanese Patent Application Laid-Open No. 1-229986 discloses an apparatus for measuring the remaining capacity of an auxiliary battery in an engine vehicle, which measures the remaining capacity of the battery from the current and voltage when the engine is started. However, such a method can be applied only to an engine-driven vehicle, and cannot be applied to a measurement of a remaining capacity of a battery in an electric vehicle.

An object of the present invention has been made in view of the above problems, and an object of the present invention is to provide a battery remaining capacity meter suitable for an electric vehicle.

[0015]

A battery state of charge meter for an electric vehicle according to the present invention includes a current detecting means for detecting a discharging current of a battery, and a change state of the discharging current detected by the current detecting means. Change state detecting means, a voltage detecting means for detecting a discharge voltage at the time of discharging of the battery, a discharge current is equal to or more than a predetermined value from the detection results of the current detecting means and the change state detecting means, and the discharge current increases. Condition determination means for determining whether or not the condition that the condition is satisfied is satisfied. When the condition determination means determines that the condition is satisfied, the remaining capacity with respect to a discharge current and a discharge voltage provided in advance is determined. And a remaining capacity detecting means for calculating a remaining battery capacity based on a map indicating the following.

[0016]

In the battery state-of-charge meter of the present invention having the above configuration, the condition judging means determines whether or not the condition that the discharge current is equal to or more than a predetermined value and the discharge current is increasing is satisfied. Is determined. Then, based on the determination result, when the condition is satisfied, the remaining battery capacity is calculated from the detected voltage and the current based on a previously provided map of the discharge voltage and the remaining capacity. This allows
When there is a good correlation between the voltage and the remaining battery capacity, the remaining battery capacity is calculated, and accurate measurement of the remaining capacity can be performed.

In particular, in the present invention, the remaining capacity is measured only when the discharge current is increasing. This is based on a new finding that a good correlation is not maintained between the voltage-current characteristics and the remaining capacity under the condition where the discharge current is decreasing. Under these conditions, the accuracy of the measurement of the remaining capacity is improved.

Further, the above conditions are satisfied when the electric vehicle is accelerated, so that the above conditions frequently occur in ordinary electric vehicle running. Therefore, accurate measurement of the remaining capacity can be frequently performed without the need to newly provide a discharge resistor and without wasting power.

[0019]

FIG. 1 is a block diagram showing the configuration of a battery state of charge meter according to a preferred embodiment of the present invention. As shown in the drawing, the battery state of charge meter according to the present embodiment is configured such that a switch 12 is connected to a vehicle load 11 such as a drive motor of an electric vehicle.
Are connected to a voltmeter 15 that detects a potential difference between both ends of the main battery 13 that supplies power via the power supply, and an ammeter 17 that measures a current flowing from the main battery 13. The battery remaining capacity meter 10 includes a VI characteristic calculating means 19 for taking in data from the voltmeter 15 and the ammeter 17, and a remaining capacity of the battery by taking in data output from the VI characteristic calculating means 19. Calculating means 21 for calculating
The remaining capacity of the battery obtained in step 1 is supplied to the display device 23, and the remaining capacity is displayed here. Further, the temperature of the main battery 13 output from the temperature sensor 24 is taken into the VI characteristic calculating means 19.

Here, the VI characteristic calculating means 19 determines whether or not the value of the current detected by the ammeter 17 is equal to or more than a predetermined value and whether the current flowing from the main battery 13 is increasing. Further, the remaining capacity calculating means 21 includes a map showing a correlation between the voltage and current and the remaining capacity of the battery, and calculates the remaining capacity of the main battery 13 from the discharge voltage of the main battery 13 when discharged at a predetermined discharge current. calculate.

FIG. 2 is a flowchart showing the operation of the SOC meter 10 of the present embodiment shown in FIG. As shown in the figure, first, the VI characteristic calculating means 19
The discharge current I output from the switch 7 is taken in (S101).
Next, it is determined whether the discharge current I is equal to or greater than a predetermined value (S
102). The predetermined value is, for example, 0, 75C (0.75C is 1 / 0.75% of the fully charged main battery 13).
= 1.33 hours), which is a fairly high current value. If the value is equal to or smaller than the predetermined value in S102, this data cannot be used, so the data is cleared (S103) and the process returns to S101.

On the other hand, when it is determined in S102 that the discharge current of the main battery 13 is equal to or more than the predetermined value, the voltage of the main battery 13 at that time is taken from the voltmeter 15 (S102).
104). Then, a predetermined period of time (in the illustrated example, two seconds, because normal acceleration is continued for approximately this period, and approximately this time is required for increasing the current above a predetermined value) It is determined whether or not (S105)
If it has not elapsed, the process returns to S101, and this is repeated. Therefore, if the current value falls below 0.75 C during the two seconds, the data is cleared for both I and V.
Then, when the discharge current I does not fall below 0.75C and 2 seconds have elapsed, the current change dI / dt for the 2 seconds is calculated (S106). Then, it is determined whether or not this current change is equal to or more than a predetermined value (for example, whether 0.75C → 1.2C has increased in 2 seconds) (S107). , The fetched data V and I are cleared (S108), and the process returns to S101. As described later, when the relationship between the VI characteristics and the remaining capacity of the main battery 13 in the electric vehicle was examined, not only the discharge current I was large but also a good correlation was found when the discharge current I was increased. It is based on the finding that it can be obtained. The processing in S106 and S107 may be performed by determining whether or not the current amount after 2 seconds exceeds a predetermined value, for example, 1.2C.

If the rate of increase of the discharge current is equal to or greater than a predetermined value, the remaining capacity of the main battery is calculated based on the relationship (VI) between the discharge current I and the battery voltage V (S105).
That is, at the time of high load acceleration where the discharge current I is equal to or more than the predetermined value and the rate of increase dI / dt of the discharge current is equal to or more than the predetermined value, the voltage-current characteristics (VI characteristics) and the remaining capacity of the battery are reduced. Has a good correlation. For this reason, the relationship between the gradient of the straight line indicating the change in the battery voltage with respect to the change in the discharge current and the remaining battery capacity is stored in advance as a map, and the remaining capacity of the battery is obtained by subtracting the map from the gradient obtained from the measurement data. Alternatively, the relationship between the voltage value and the remaining capacity at a specific discharge current value is stored as a map, and the remaining capacity can be calculated by referring to the map from the voltage value obtained from the measurement data. At this time, the temperature of the battery from the temperature sensor 24 is also supplied to the remaining capacity meter 10. The above V-
Since the relationship between the I characteristic and the remaining capacity changes depending on the temperature, the remaining capacity obtained based on the battery temperature may be corrected.

The remaining capacity of the main battery 13 thus determined is displayed on the display panel of the electric vehicle (S110). Thus, the driver can know the remaining capacity of the battery by looking at the display panel.

Here, the maps used in S102 and 107 and the maps used in S105 will be described below. explain.

FIG. 3 is a diagram showing an example of changes in battery voltage and current during acceleration and coasting in a van-type electric vehicle (lead battery, capacity 150 Ah). As is apparent from FIG. 3, the output torque of the driving motor increases during acceleration, so that the current increases with time. Then, as the amount of current increases, the battery voltage decreases. On the other hand, during coasting, as the output torque of the motor decreases, the current decreases with the passage of time, and the battery voltage increases with the passage of time. From this figure, it can be seen that the current values vary considerably during coasting. Note that SO at this time
C (the ratio of the remaining capacity to the full charge) is 80%,
The remaining capacity was 120 Ah.

Next, FIG. 4 shows the relationship between the battery voltage and the current at the same time in FIG. As shown in FIG. 4, when the current from the main battery 13 is 0.75 C or more, it is understood that there is a very good correlation between the battery voltage and the magnitude of the current. On the other hand, when the magnitude of the current from the main battery 13 is 0.75 C or less, the data varies considerably, a sufficient correlation cannot be found, and the course represented by the white mark No correlation could be found between the battery voltage and the current at the time of pitting.

FIG. 4 shows an SOC of the main battery of 50%,
The case of the remaining capacity of 75 Ah is also shown. From this, it can be seen that there is a correlation between the current amount and the voltage when the current amount is 0.75 C or more.

Therefore, when the battery is accelerating and the magnitude of the current flowing out of the main battery 13 is 0.75 C or more, if the remaining capacity of the battery is constant, there is a difference between the battery voltage and the current. There will be a certain correlation. In other words, if the magnitude of the current flowing out of the main battery 13 is 0.75 C or more and it is increasing,
By measuring the values of the battery voltage and current at that time, the remaining capacity of the battery can be obtained.

Therefore, in S102 of FIG. 2 described above,
It is determined whether the current value is equal to or greater than a predetermined value C, and S107
In the above, it is determined whether the rate of increase of the current value is equal to or more than a predetermined value, and the remaining capacity of the battery is measured only when such a condition is satisfied.

FIG. 5 shows the relationship between the battery voltage and the remaining capacity of the battery when the above conditions are satisfied. The discharge current of the main battery 13 at this time is 1.3C. As described above, there is a good correlation between the voltage at the predetermined current and the remaining capacity of the battery. Thus, for example, a current of 1.3 C
If the relationship between the battery voltage and the remaining capacity at the time of is stored in a map, and the voltage at a current of 1.3 C in actual running is obtained, the remaining capacity of the battery can be obtained based on the map. Since the remaining capacity is obtained only when there is a good correlation between the VI characteristics and the remaining capacity as described above, the obtained remaining capacity is highly reliable.

The above conditions frequently occur during normal running such as starting, accelerating at high speed, and climbing a hill, so that the remaining capacity of the battery can be measured at an appropriate frequency.

In particular, when the remaining capacity of the battery decreases,
Battery voltage drops. On the other hand, in driving the motor, it is necessary to set the output torque of the motor to a predetermined value in accordance with the operation of the accelerator, and the output energy W is determined by the product of the voltage and the current (W = VI). As the value decreases, the amount of current increases accordingly. That is, when the remaining capacity decreases, the amount of current increases even during the same traveling, and the probability of satisfying the above-described conditions of large current and large current increase rate increases. When the remaining capacity of the battery is reduced, it is desired to know it more accurately. According to the present apparatus, as the remaining capacity decreases, the frequency of measurement increases, and a suitable measurement of the remaining battery capacity is performed. Can be.

As shown in FIG. 6, the correlation between the battery voltage and the remaining capacity has a temperature dependency. Therefore, when calculating the remaining capacity, such a temperature-dependent characteristic may be used to correct the remaining capacity of the battery based on the temperature detected by the temperature sensor 24.

Further, in this embodiment, the current value and the voltage value during a predetermined time are stored. Therefore, the voltage value at an arbitrary current value can be obtained by estimation (or interpolation) from the stored value. Therefore, even if the voltage value at 1.3 C is not actually measured, the voltage value at 1.3 C can be obtained, and the remaining capacity can be calculated from the obtained value. In addition, the measured voltage,
The correlation between the two may be determined from the current value, and if the correlation is equal to or less than a predetermined value, the calculation of the remaining capacity may be stopped.

[0036]

As described above, in the battery state-of-charge meter according to the present invention, the remaining capacity is measured from the current and voltage of the battery at the time of high load operation, so that there is no additional load such as a discharger. Cut immediately with the enemy. In addition, at the time of high-load operation, since it frequently occurs in normal operation, the timing of detecting the remaining capacity is not significantly limited, so that it is possible to appropriately display the remaining capacity of the battery.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a remaining capacity meter of a battery according to a preferred embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of operation of the battery state of charge meter shown in FIG.

FIG. 3 is a graph showing changes in current and voltage during acceleration and coasting of an electric vehicle.

FIG. 4 is a graph showing that there is a case where there is a correlation between battery voltage and current.

FIG. 5 is a graph showing an example of a map of battery voltage and remaining capacity.

FIG. 6 is a graph showing the temperature dependence of the correlation between the battery voltage and the remaining capacity.

FIG. 7 is a graph showing an example of a correlation between a remaining capacity of a battery and a battery voltage when high-rate discharge is performed.

[Explanation of symbols]

 10 Remaining capacity meter 13 Main battery 15 Voltmeter 17 Ammeter 19V-I characteristic calculating means 21 Remaining capacity calculating means

Continuation of front page (56) References JP-A-4-357467 (JP, A) JP-A-4-186179 (JP, A) JP-A-2-247588 (JP, A) JP-A 1-222986 (JP) JP-A-63-157078 (JP, A) JP-A-62-237370 (JP, A) JP-A-62-298278 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) G01R 31/36

Claims (1)

(57) [Claims] 1. A battery remaining capacity meter for an electric vehicle, comprising: current detection means for detecting a discharge current of a battery; and change state detection means for detecting a change state of the discharge current detected by the current detection means. A voltage detecting means for detecting a discharge voltage when the battery is discharged; and a detection result of the current detecting means and the change state detecting means, the condition that the discharge current is not less than a predetermined value and the discharge current is increasing. Condition determining means for determining whether or not the condition is satisfied; and when the condition determining means determines that the condition is satisfied, the current and voltage at that time and the discharge current and discharge voltage provided in advance are determined. A remaining capacity detecting means for calculating a remaining capacity of the battery based on a map indicating the remaining capacity.