JP3432463B2 - Battery capacity measurement device - 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 capacity measuring device for a vehicle battery, and more particularly to improving measurement accuracy.

[0002]

2. Description of the Related Art A battery mounted on a vehicle is used as a power source for a starter of an engine or other auxiliary equipment, and is appropriately charged by a generator operated by the power of an internal combustion engine. The battery capacity measuring device obtains the current capacity of the battery, and the generator is controlled based on the detected battery capacity. Japanese Patent Application Laid-Open No. 6-351166 discloses that when the battery is close to full charge, the adjustment voltage is lowered to prevent overcharging, power can be generated with low fuel consumption, and when the capacity is insufficient, the adjustment voltage is increased. There is disclosed a technique of preventing an over-discharge from occurring and thereby ensuring an appropriate capacity according to the power consumption of a load with low fuel consumption and preventing deterioration of a battery due to over-charging and over-discharging. Here, the battery capacity is calculated based on the integrated value of the charge / discharge current of the battery obtained by the current sensor.

When the battery capacity is calculated from the integrated value of the charging / discharging current of the battery, the detection accuracy of the current sensor is important. In particular, if the detected current value includes an offset error, the offset error is integrated when the current battery capacity is calculated, so that it is difficult to properly control the charging of the battery. This offset error can generally be obtained by detecting the current when the circuit is open, but in vehicles, even when the engine is stopped, auxiliary devices such as watches are in the power supply state, so the circuit is completely open. It is difficult to detect the current. Therefore, there is a method of estimating the dark current when the engine is stopped in advance and removing the dark current to obtain the offset error.

[0004]

However, since the dark current when the engine is stopped varies depending on the usage mode and type of the auxiliary machine, it is not always possible to properly estimate the dark current when the engine is stopped. The detection error may increase.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a battery capacity measuring device with good measurement accuracy.

[0006]

According to a first aspect of the present invention, there is provided a full charge detecting means for detecting that the battery is fully charged, and a current sensor detected during a period from the full charge to the full charge thereafter. The detected current integrating means for integrating the current, the dividing means for dividing the integrated value of the detected current obtained by the detected current integrating means by the length of the period, and the offset correction of the detected current by the divisor value obtained by the dividing means And a correction means.

SOC (Stat) indicating the capacity when fully charged
e Of Charge) 100 same as the previous full charge
%, And the same amount of discharging and charging is performed during the period from the previous full charge to the current full charge.
Therefore, only the offset error component of the current sensor is included in the integrated value of the detected current accumulated during the period from the previous full charge to the current full charge. By dividing the integrated value of the detected current by the length of the period, which is the integration period, an offset error is obtained without being affected by the usage pattern of the battery load such as the engine starter, and accurate battery charging / discharging. You can know the current. Therefore, the battery capacity can be measured with high accuracy.

According to the second aspect of the invention, there is provided a full charge means for controlling the generator to fully charge the battery when a predetermined time has elapsed since the last full charge.

Since the battery is fully charged after the lapse of a predetermined time, the offset error can be reviewed at substantially constant intervals, and the battery capacity can be measured with high accuracy.

[0010]

1 shows the configuration of a battery capacity measuring device of the present invention. A generator 6 is connected to the battery 5 provided with the present battery capacity measuring device 1 and can be charged by the generator 6. The generator 6 operates by engine power (not shown). A load 7 such as an engine starter is connected to the battery 5.

In the battery capacity measuring device 1, a current sensor 2 for monitoring the charging / discharging current of the battery 5 is provided in the middle of a cable from the battery 5 to the generator 6 and the load 7.

A microcomputer 3 is provided with the detection signal of the current sensor 2 as an input, and the present capacity of the battery 5 is calculated based on the charging / discharging current of the battery 5 obtained from the current sensor 2. Microcomputer 3 is CP
A general configuration including U and memory (RAM, ROM) can be used.

The microcomputer 3 also serves to control the generator 6, and outputs a command value of the adjustment voltage to the generator 6 to control the exciting current to control the amount of power generated by the generator 6.

The microcomputer 3 has its CPU
The detected current integrating means 31, the dividing means 32, which is executed above
The charging / discharging current of the battery 5 is known from the current detected by the current sensor 2. Further, the microcomputer 3 is provided with a full-charging means 34 which is executed on the CPU thereof, and when the predetermined condition is satisfied, the amount of power generation is increased by setting the adjustment voltage high, and the battery 5 is fully charged. To

Further, the present battery capacity measuring device 1 is provided with a full charge determination circuit 4, and when the battery 5 is fully charged, it outputs a determination signal to that effect to the microcomputer 3,
The microcomputer 3 determines whether the battery is fully charged.
Have become known. Full charge determination circuit 4
Is for detecting the voltage across the terminals of the battery 5 and determining that it is fully charged if it rises significantly, for NiH batteries or the like, detecting its temperature, for example, the surface temperature, and determining that it is full charge, or a generator. Various known techniques can be used, such as a method of detecting the on / off frequency of the excitation current of No. 6 and determining that it is fully charged when it increases.

FIG. 2 shows a control flow executed by the microcomputer 3. This control flow starts when the key switch is turned on and the engine is started. In step S001, the Q and SOC stored in the memory of the microcomputer 3 at the end of the control flow of the previous time are stored.
Read out. Also, I _cor is read.

Step S002 serves as the correction means 33.
In the procedure, the detection current I of the current sensor 2 _measLoading formula
The battery charge / discharge current I is calculated according to (1). Batte
The recharging / discharging current I is detected by the detection current as known from the equation (1).
Flow I_measCorrection value I_corOffset correction by
Can be obtained at. Correction value I_corWill be described later in step S008.
Calculated and updated in. I = I_meas-I_cor... (1)

The following step S003 is the procedure as the detection current integration means 31, and calculates the integration value Q of the detection current I _meas by the equation (2). In the formula, t is a measurement interval. Further, Q is initialized to 0 at the last full charge (see step S007 described later). Q = Q + I _{meas xt} (2)

At step S004, SO is calculated by the equation (3).
Calculate C. In the formula, C is the capacity of the battery 5 at full charge corresponding to SOC 100%. This SOC is used to control the generator 6 as in the conventional case. SOC = SOC + I × t × 100 / C (3)

In step S005, it is determined whether the battery 5 is fully charged. This determination is made based on the determination signal from the full charge determination circuit.

If not fully charged, step S00 described later.
6, S007, S008 are skipped and step S00 is performed.
In step 9, it is determined from the count value of the built-in timer whether or not a predetermined time or more has passed since the last full charge determination.

If the predetermined time or more has not elapsed since the last full charge determination, step S010 to be described later is skipped and the process proceeds to step S011 to determine whether or not the key switch is turned off.

If the key switch is on, step S0
Return to 02. That is, steps S002 to S004 are repeated until the engine is in the operating state and it is determined that the engine is fully charged, and the detected current integrated value Q and SOC are updated.

When the key switch is turned off, the process proceeds from step S011 to step S012, and the detected current integrated value Q and SOC calculated in steps S003 and S004 are stored in the memory to prepare for the next start of the control flow.

During the engine stop period, the computer operates in the sleep mode under the control of the timer and is activated at regular intervals to execute the steps S001 to S004 and S01.
Perform the same procedure as in step 2 to integrate the detected current value Q and SOC
Is calculated.

When a predetermined time or more has passed from the last full-charge determination, the process proceeds from step S009 to step S010. Step S010 is a procedure as the full charge means 34, and the regulated voltage is set high to increase the power generation amount of the generator 6 to a predetermined amount. As a result, the battery 5 is fully charged, and following step S005, the above step S006.
Steps S007 and S008 are executed.

In step S006, the SOC is updated to the initial value of 100%. This is because it is fully charged.

The following step S007 is a procedure as the dividing means 32, in which the time T from the previous full charge determination counted by the timer is read and the offset error I _offset of the current sensor 2 is obtained by the equation (4). Note that Q is updated to 0 which is an initial value after the offset error I _{offset is} calculated.

I _offset = Q / T (4)

In step S008, this offset value I
Based on the _offset , the correction value I _cor is updated by the equation (5). I _cor = I _offset (5)

When the battery 5 is fully charged, the regulated voltage is made equal to or slightly lower than the electromotive voltage of the battery 5 to maintain the SOC at a predetermined level.

Next, the detected current I _{meas of the} current sensor
A description will be given of the effect of obtaining the battery charging / discharging current I by compensating for the offset error I _offset . FIG. 3 shows the calculated S in the conventional device in which the current detected by the current sensor is directly used as the battery charge / discharge current without correction.
It shows how the calculated value of SOC changes from the initial value 100% according to the integrated value of the detected current of the current sensor 2 due to the change of OC with time. Point A is the point at which the battery is charged and becomes fully charged again. Here, the state of the battery is the same amount of discharging and charging during the period from the last full charge to the current full charge. It has been restored to the same state as when it was fully charged last time. Therefore, if the current sensor indicates the true value of the battery current, the SOC becomes 100% again as shown in the figure.

However, _if there is a positive offset error I _offset1 in the current sensor, the calculated SOC is accumulated with this offset error I _offset1 and shifts to the positive side as shown (S).
OC1). This deviation is the offset error I during the time T1 from the previous full charge to the current (point A) full charge.
_{Since it is the ratio} of the integrated value of _offset1 to the battery capacity C, it can be expressed as in equation (6). _SOC1-100 (%) = T1 * I _offset1 / C * 100 (%) (6)

Further, the current sensor has a negative offset error I
_When there is _offset2 , the calculated SOC is offset by the offset error I _{offset2 and} is shifted to the negative side as shown in the figure (SO
C2). This deviation is the offset error I _offset2 during the time T1 from the previous full charge to the current (point A) full charge.
Since it is the ratio of the integrated value of to the capacity C of the battery,
It can be expressed as in Expression (7). _SOC2-100 (%) = T1 * I _offset2 / C * 100 (%) (7)

As described above, the same amount of charge as the discharge is performed from the time of the previous full charge to the time of the full charge this time, and the battery state is restored to the same state as the previous full charge state. Therefore, the actual discharge component and charge component of the detected current integrated value cancel each other out. Therefore, the above T1 x
I _offset1 and T1 × I _offset2 are equal to the integrated value of the detected current I _meas from the previous full charge to the current full charge. Then, by dividing the detected current integrated value Q by the above expression (4) by the length T of the period from the last full charge to the current full charge, which is the integration period, the usage pattern of the load 7, etc. The offset error I _offset is obtained without being affected. Then, according to equation (5), the offset error I _offset
Since the detected current I _meas is corrected so as to cancel out and the accurate battery charging / discharging current I is known, the SOC can be measured with high accuracy.

In the present embodiment, the offset correction value I _cor is the offset error I _offset obtained at full charge (Equation (5)). However, as shown in Equation (8), until the current full charge, A weighted average of the offset correction value I _cor and the newly calculated offset error I _offset is calculated,
This may be used as the offset correction value I _cor . In the formula, a is a weight (0 <a <1). I _cor = a × I _offset + (1-a) × I _cor ... (8)

Further, the offset error I _offset at the time of full charge of the past several times is averaged and this is averaged to obtain the offset correction value I.
_It may be _cor . Alternatively, the accumulated period of the detected current for obtaining the offset error is not from the last full charge to the current full charge, but from the full charge to the full charge after one or more full charge states. The detected currents during this period may be integrated.

Further, in the present embodiment, when the predetermined time has elapsed from the previous full charge, the power generation amount of the generator 6 is forcibly increased and the battery 5 is fully charged. The configuration is not limited to the configuration of this embodiment as long as the detected current integrated value in the period from charging to the current full charge and the length of the period can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a battery capacity measuring device of the present invention attached to a battery.

FIG. 2 is a flowchart showing control in a microcomputer of the battery capacity measuring device.

FIG. 3 is a graph illustrating the operation of the battery capacity measuring device.

[Explanation of symbols]

1 Battery capacity measuring device 2 Current sensor 3 microcomputer 31 Detection current integrating means 32 division means 33 Correction means 34 Full charge means 4 Full charge determination circuit (full charge detection means) 5 battery 6 generator 7 load

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Kishida 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Shinichi Ito 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation ( 56) References JP-A-5-322998 (JP, A) JP-A-11-133124 (JP, A) JP-A-7-191108 (JP, A) JP-A-10-288654 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) H02J ⁷ /00-7/36 G01R 31/36 H01M 10/48

Claims (2)

(57) [Claims] 1. A battery capacity measuring device, which is attached to a battery which can be charged by a generator, and which calculates the current capacity of the battery based on the integrated value of the charging / discharging current of the battery obtained by a current sensor. The full-charge detection means for detecting that there is a, the detection current integration means for integrating the detection current of the current sensor during the period from the full charge to the subsequent full charge, the detection current integration obtained by the detection current integration means Dividing means for dividing the value by the length of the above period,
A battery capacity measuring device comprising: a correction unit that offset-corrects a detected current based on a divisor value obtained by the division unit. 2. The battery capacity measuring device according to claim 1, further comprising a full charge means for controlling the generator to fully charge the battery when a predetermined time has elapsed since the last full charge. apparatus.