JP2001078365A - Battery capacity measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a capacity of a battery with high accuracy. SOLUTION: A measuring error of battery capacity resulting from an offset error of a current sensor 2 is reduced by obtaining an offset error of the current sensor 2 which does not depend on the application mode of a load 7 of a battery 5 with a detected current accumulating means 31 for substantially obtaining only the accumulated value element of the offset error of the current sensor 2, through accumulation during the period up to the full-charging of this time from the preceding full-charging of the battery 5 by paying attention to the fact that the charging amount is identical to the discharging amount during above period and a divide means 32 for calculating the offset error, by dividing the detected current accumulated value with the length of above period and by also obtaining an accurate charging/discharging current of the battery 5 with a compensation means 33 for reducing the offset of the detected current of the current sensor 2 with such offset error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a battery capacity of a battery for a vehicle, and more particularly to an improvement in 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 and other auxiliary devices, 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. Hei 6-351166 discloses that when the battery is near full charge, the adjustment voltage is lowered to prevent overcharging and to enable power generation with low fuel consumption, and when the capacity is insufficient, the adjustment voltage is increased. A technique has been disclosed in which a proper capacity according to the power consumption of a load is ensured at low fuel consumption by preventing overdischarge by preventing the battery from being deteriorated due to overcharge and overdischarge. Here, the battery capacity is calculated based on the integrated value of the charge / discharge current of the battery obtained by the current sensor.

In calculating battery capacity from the integrated value of battery charge / discharge current, the detection accuracy of the current sensor is important. In particular, if an offset error is included in the detected current value, the offset error is integrated when calculating the current battery capacity, so that it is difficult to properly perform battery charge control. This offset error can generally be obtained by detecting the current when the circuit is open.However, in a vehicle, even when the engine is stopped, auxiliary equipment such as a clock is in a power supply state, so the circuit must be completely open and It is difficult to detect the current. Therefore, there is a method of estimating a dark current when the engine is stopped in advance and obtaining an offset error by excluding the estimated dark current.

[0004]

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

[0005] 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 the first aspect of the present invention, a full charge detecting means for detecting that the battery is fully charged, and a detection of the current sensor during the period from the time of full charge to the time of full charge thereafter. Detection current integration means for integrating current, division means for dividing the detection current integration value obtained by the detection current integration means by the length of the period, and offset correction of the detection current by the divisor value obtained by the division means And a correcting means.

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

According to the second aspect of the present 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 a predetermined period of time, the offset error can be reviewed at substantially constant intervals, and the battery capacity can be measured with higher accuracy.

[0010]

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

The battery capacity measuring device 1 is provided with a current sensor 2 for monitoring the charge / discharge current of the battery 5 in the middle of a cable extending from the battery 5 to the generator 6 and the load 7.

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

The microcomputer 3 is also used for controlling the generator 6, and outputs a command value of an adjustment voltage to the generator 6 to control the amount of power generated by the generator 6 by adjusting the excitation current.

The microcomputer 3 has its CPU
The detected current integrating means 31, dividing means 32 executed above,
A correction means 33 is provided so that the charge / discharge current of the battery 5 is known from the detection current of the current sensor 2. The microcomputer 3 is provided with a full charge means 34 executed on the CPU. When a predetermined condition is satisfied, the regulated voltage is set high to increase the amount of power generation and fully charge the battery 5. To

Further, the battery capacity measuring device 1 includes a full charge determination circuit 4, and when the battery 5 is fully charged, outputs a determination signal to that effect to the microcomputer 3.
The microcomputer 3 determines whether or not the battery is fully charged.
It has become known in. Full charge judgment circuit 4
A battery that detects the voltage between terminals of the battery 5 and determines that the battery is fully charged when the voltage rises significantly; a NiH battery or the like that detects its temperature, for example, the surface temperature, and determines that the battery is fully charged when the temperature rises; Various known techniques can be used, such as a technique of detecting the on / off frequency of the excitation current in No. 6 and determining that the charge is full when the frequency 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, SOC stored in the memory of the microcomputer 3 at the end of the previous control flow.
Is read. Further, I _cor is read.

In step S002, the correcting means 33
In the procedure, the detection current I of the current sensor 2 is _measRead formula
The battery charge / discharge current I is calculated according to (1). Batte
The recharge / discharge current I is, as known from the equation (1),
Style I_measTo the correction value I_corOffset correction by
Is obtained. Correction value I_corIs a step S008 to be described later.
Is calculated and updated. I = I_meas-I_cor... (1)

The following step S003 is a procedure as the detected current integrating means 31, which calculates the integrated value Q of the detected current I _meas by equation (2). In the equation, t is a measurement interval. Q has been initialized to 0 at the time of the previous full charge (see step S007 described later). Q = Q + I _meas × t (2)

In step S004, the SO
Calculate C. In the expression, C is the capacity of the battery 5 at the time of full charge corresponding to SOC 100%. This SOC is used for controlling 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 a determination signal from the full charge determination circuit.

If the battery is not fully charged, a step S00 to be described later is performed.
6, S007 and S008 are skipped and step S00
The program proceeds to 9 to determine whether or not a predetermined time has elapsed from the time of the previous full charge determination based on the count value of the built-in timer.

If the predetermined time has not elapsed since the last full charge determination, step S010 to be described later is skipped and the process proceeds to step S011, where it is determined whether 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 the SOC are updated.

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

During the engine stop period, the computer operates in the sleep mode under the control of the timer, and periodically starts up to execute the above steps S001 to S004 and S01.
2 and the detected current integrated value Q and SOC
Is calculated.

When a predetermined time or more has passed since 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, in which the adjustment voltage is set high and the power generation amount of the generator 6 is increased to a predetermined amount. As a result, the battery 5 is fully charged.
Steps S007 and S008 are executed.

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

The following step S007 is a procedure as the dividing means 32, in which the time T counted 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 equation (4). Note that Q is updated to the initial value of 0 after calculating the offset error I _offset .

I _offset = Q / T (4)

In step S008, the offset value I
The correction value I _cor is updated by the equation (5) based on the _offset . 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, and the SOC is maintained at a predetermined level.

Next, the detection current I _{meas of the} current sensor
_Is corrected by the offset error I _offset to obtain the battery charge / discharge current I. FIG. 3 shows the calculated S in a conventional device using the detection current of the current sensor as it is as the battery charging / discharging current without correction.
This shows how the calculated value of the SOC changes from the initial value of 100% in accordance with the change over time of the OC, according to the integrated value of the detection current of the current sensor 2. Point A is a point in time when the battery is charged and becomes fully charged again. Here, the state of the battery is such that the same amount of discharge and charging is performed during the period from the previous full charge to the current full charge. It has returned to the same state as the previous fully charged state. Therefore, if the current sensor indicates the true value of the battery current, the SOC becomes 100% again as shown in the figure.

[0033] However, if the current sensor has a positive offset error I _offset1, calculated SOC is shifted to the positive side as shown by integrating this offset error I _offset1 (S
OC1). This shift is caused by 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 capacity C of the battery, it can be expressed as in equation (6). _SOC1-100 (%) = T1 * I _offset1 / C * 100 (%) (6)

The current sensor has a negative offset error I
If there is _offset2, calculated SOC is shifted to the negative side as shown by integrating this offset error I _offset2 (SO
C2). This deviation is _{caused by} the offset error I _offset2 during the time T1 from the previous full charge to the current (point A) full charge.
Is the ratio of the integrated value to the capacity C of the battery.
It can be expressed as in equation (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 state of the battery is restored to the same state as in the previous full charge state. Therefore, of the detected current integrated value, the actual discharge component and charge component cancel each other. Therefore, the above T1 ×
I _offset1 and T1 × I _offset2 are equal to the integrated value of the detection current I _meas from the previous full charge to the current full charge. Thus, 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 use form of the load 7 can be determined. The offset error I _offset is obtained without being affected. Then, according to equation (5), the offset error I _offset
, The detection current I _meas is corrected so that the accurate battery charge / discharge current I is known, so that the SOC can be measured with high accuracy.

In this embodiment, the offset correction value I _cor is the offset error I _offset obtained when the battery is fully charged (Equation (5)). Calculating a weighted average of the offset correction value I _cor and the newly calculated offset error I _offset ;
This may be used as the offset correction value I _cor . In the expression, a is a weight (0 <a <1). I _cor = a × I _offset + (1−a) × I _cor (8)

Further, the offset errors I _offset during the last several full charges are averaged and this is used as the offset correction value I.
_It may be _cor . Alternatively, the integration period of the detection current for obtaining the offset error is not from the time of the most recent full charge to the time of this full charge, but from the time of full charge to the time of full charge after passing through one or more full charge states. , The detected current during this period may be integrated.

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

[Brief description of the 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 measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery capacity measuring device 2 Current sensor 3 Microcomputer 31 Detected current integrating means 32 Dividing means 33 Correcting means 34 Full charge means 4 Full charge determination circuit (full charge detection means) 5 Battery 6 Generator 7 Load

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuro Kikuchi 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Prefecture Inside the Japan Automobile Parts Research Institute, Inc. (72) Inventor Shinichi Ito 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 2G016 CA03 CB12 CB13 CB21 CB22 CB31 CB32 CC01 CC03 CC04 CC27 CC28 5G003 AA07 BA01 CA05 DA04 EA05 FA06 5G060 AA04 CA02 DB07 5H030 AA08 AS08 FF42 FF52

Claims (2)

[Claims] 1. A battery capacity measuring device which is attached to a battery which can be charged by a generator and obtains a current capacity of the battery based on an integrated value of the charge / discharge current of the battery obtained by a current sensor. Full charge detection means for detecting that the current is present in the battery, detection current integration means for integrating the detection current of the current sensor during the period from the time of full charge to subsequent full charge, and detection current integration obtained by the detection current integration means Means for dividing the value by the length of the period;
A correction unit for offset-correcting the detected current by the divisor value obtained by the division unit. 2. The battery capacity measurement device according to claim 1, further comprising a full charge means for controlling said generator to fully charge said battery when a predetermined time has elapsed since the last full charge. apparatus.