JPH09233723A - Charge method of battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge method which can attain full charge without the possibility of overcharge, when a battery voltage does not reach a reference voltage, on account of the discharged state of a battery or the change of battery temperature or some other causes. SOLUTION: When the charge time T1 of a first step until a voltage reaches a reference voltage Vref is shorter than a reference time Tref, the charge time T2 of a second step is changed over to a constant time TS (T2=TS) which is imparted to charge of the second step for attaining the full charged state and shorter than a constant time TC. When the charge time T1 of the first step reaches an upper limit time determined by previously measured discharge current amount, charge of the first step is compulsorily finished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging system for batteries used in electric vehicles and the like, and more particularly to a charging method for preventing overcharging thereof.

[0002]

2. Description of the Related Art In order to charge the battery of an electric vehicle,
The commonly used two-stage charging method is, as shown in FIG. 1, until the battery voltage V _Batt reaches a predetermined reference value V _ref .
After performing the first-stage charging with the constant current I ₁ , the second-stage constant current charging is performed with a small current value I ₂ for a predetermined time T ₂ .

The charging time T ₂ of the second stage is, for example, 1
It is determined by multiplying the charging time T ₁ of the stage by the coefficient A and adding a small constant T _C thereto (T ₂ = A · T ₁ + T _C ).

The proportional term (A ·
T ₁ ) corresponds to the amount of charge required for the second-stage charging, which varies depending on the amount of discharge.

The constant term (T _C ) of the second-stage charging time
Is necessary to achieve the fully charged state obtained from the experimental data, because the charging of the proportional term is not sufficient to achieve the fully charged state such as 100% value, 110% value, 120% value of the rated capacity. It is added as a time. In addition, the charging time T ₂ of the second stage may be a fixed value T _C ′ (> T _C ).

[0006]

In the above-mentioned two-stage charging method, when the discharge amount of the battery is a certain amount or more, charging can be performed without causing overcharging or insufficient charging.

However, when the electric vehicle has a short mileage and a small amount of discharge, and the charging of the first step is completed in, for example, about 5 to 10 minutes, the charging time T ₂ of the second step is set. Has a constant (T _C , T _C ′), it becomes overcharge,
The battery may have worn out.

This is a particular problem in consideration of the fact that charging of an electric vehicle is often performed in a state where the traveling distance is short and the discharge amount is small.

Further, in the above-mentioned two-stage charging, since the charging state changes depending on the battery temperature, there is a problem that the charging becomes excessive or insufficient depending on the temperature at the time of charging.

In the above two-stage charging system, some trouble may occur in the battery or the charger, and the specified reference voltage V _ref may not be reached in the first-stage charging. This trouble occurs, for example, when the cells of the battery are reversed or when the battery fluid is low. In such a case, the first-stage charging is performed for a long time, which adversely affects the battery.

Therefore, according to the present invention, even when the battery voltage does not reach the reference voltage V _ref due to the discharge state of the battery, the fluctuation of the battery temperature, or some reason,
An object of the present invention is to provide a charging method that can be fully charged without fear of overcharging.

[0012]

[Means for Solving the Problems]

 (1) The battery charging method provided by the present invention is
Voltage is reference voltage V_refConstant current charging of the first stage until it rises to
After charging, reduce the current value and set the constant time T _Cincluding
Predetermined time T_Two2 step constant current for only 2 step constant current charging
In the charging method,

The time T ₁ required for charging the first stage is compared with a predetermined reference time T _ref, and when T ₁ is smaller than T _ref , 2
It is characterized in that the charging time T ₂ of the tier is set to a value T _S smaller than T _C.

The charging time T _S of the second stage can be corrected by multiplying it by a coefficient K _TB corresponding to the battery temperature, and the reference time T _ref uses a value T _ref ′ corrected by the battery temperature. be able to.

(2) In addition, charging of the battery provided by the present invention
The battery voltage is the reference value V. _refUntil it rises
After performing the constant current charging of the first step, reduce the current value.
Fixed time T_Two2 step constant current charging that only performs the 2nd step constant current charging
In the electric method,

The upper limit time T _Lim for the first-stage charging is determined from the amount of discharge current measured in advance, and the reference voltage V _ref is set to the reference voltage V _ref even when the upper limit time T _Lim elapses during the first-stage charging. When not reaching, it is characterized by forcibly shifting to the second-stage charging or stopping the charging. The upper limit time T
_Lim can be corrected by multiplying by a coefficient K _TC corresponding to the battery temperature.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, a battery charging method of the present invention for preventing overcharging because charging is performed in a state where the amount of discharge is small will be described.

In this charging method, as shown in FIG. 1, the time T ₁ required for the first-stage charging, which is performed until the battery voltage V _Batt reaches the reference voltage V _ref at the constant current I ₁ , is measured. The time T ₁ is compared with a predetermined reference time T _ref so that T ₁ is T
_When it is smaller than _ref, the charging time T ₂ of the second stage, which is performed with a small constant current I ₂ (<I ₁ ), is changed to the normal charging time T ₂ (A
The value T _S is smaller than the constant T _{C of} T ₁ + T _C ).

This T_SIs the charging time T of the first stage₁But, for example
For example, if it is finished in a short time of 5 to 10 minutes, overcharge
A battery that is charged at a value that is set so that it does not become a power source.
Types and 1 when charging this by the two-step charging method
Charging current I in the second and second steps ₁, I_TwoRelationship with the size of
Then, based on the experimental data, the reference time T_refCombined with
It is a value determined individually.

[0020] As described above, the charging time T ₁ of the first stage to reach the reference voltage V _ref is compared with the reference time T _ref, when T ₁ <T _ref, small charging time in the second stage Even if the battery is charged by the method of setting the fixed time T _S , the battery voltage varies depending on the battery temperature, so that the charging may be excessive or insufficient. Therefore, according to the battery temperature, by adding a correction to the T _S and T _ref, to be fully in just proportion charged.

T _S is a value corrected by multiplying a correction coefficient K _TB corresponding to the battery temperature θ shown in FIG. 2 T _S ′ = K _TB · T _S
Is used. This correction coefficient K _TB is such that the higher the battery temperature θ, the more difficult it is for the battery voltage to rise for the same charge amount.
This is to correct the increase in the charge amount of the second stage, and the higher the battery temperature, the shorter the charging time T ₂ (= T _S ′) of the second stage. This coefficient value is determined based on experimental data.

As the reference time T _ref , a value T _ref ′ determined by the battery temperature θ is used as shown in FIG.
The higher the battery temperature θ, the more difficult it is for the battery voltage to rise, and the longer it takes to reach the reference voltage V _ref . Therefore, the reference time T increases as the battery temperature θ increases.
_An attempt is made to determine whether or not it is necessary to lengthen _ref ′ and shorten the second-stage charging time to T _S without being affected by the battery temperature. The relationship of FIG. 3 is determined based on experimental data according to a specific charging target.

[0023] Thus, the method of the second stage of the charging time T ₂ shortening the T _S is the second stage of the charging time T ₂ of the normal fixed value T ₂ = T _C 'and (> T _C) If so, the same applies. Also in this case, the time T required for the first charging
T _ref and T _ref ′ to be compared with ₁ and the second-stage charging times T _s and T _s ′ for shortening are also determined in the same manner as in the above case. If the above-mentioned charging method is adopted, even if the amount of discharge is small, full charging is possible without being affected by the battery temperature θ and without fear of overcharging.

Next, a battery charging method of the present invention will be described which prevents the battery voltage from reaching the reference voltage V _ref at the time of the first-stage charging and is overcharged for some reason. The reason why the reference voltage V _ref is not reached even if the battery is charged with the constant current I ₁ is, for example, that the cells of the battery are poled or the battery liquid is low. If it continues, it will be overcharged, and it is expected that the battery will be adversely affected.

Therefore, it is determined by the following means whether or not the first-stage charging is performed within an appropriate time range. The appropriate charging time for the first stage is a value corresponding to the amount of battery discharge. Therefore, the discharge amount of the battery is measured with an ammeter or the like, and the upper limit time T _Lim for charging the first stage is obtained from this discharge current amount. If the reference voltage V _ref is not reached even after the upper limit time T _Lim elapses, the charging is forcibly shifted to the second-stage charging, or the charging is stopped and an abnormal judgment output is made. The relationship between the discharge current amount Ah and the upper limit time T _Lim is determined by experimental data for each battery and its charging environment, and this relationship is determined as shown in FIG. 4, for example.

As described above, the upper limit time T_LimSet
Also depends on the battery temperature θ_BattFluctuates
The upper limit time T_LimIs out of the proper value
There is a case to meet. In this case, the maximum time is
Correction coefficient K corresponding to re-temperature θ _TCValue T corrected by
_Lim'= K_TC・ T_LimCan be used. This corrector
Number K_TCIs longer when the battery temperature is higher,
It is determined individually by experimental data, for example, as shown in Fig. 5.
Swell.

With respect to the upper limit time T _Lim or the corrected upper limit time T _Lim ′, the method for determining whether or not the first-stage charging is performed within an appropriate time range is as follows: When the amount of discharge is small, the charging time for the second step is T
It can be used in combination with the above method of shortening with _S (T _S ′).

In each of the above methods, T _ref , T _S ,
Battery temperature θ used to correct T _Lim
Is obtained by directly measuring the battery temperature every 30 seconds to 2 minutes, for example. As a result, each value is corrected with the temperature at that point in time, and the influence of the fluctuation of the battery temperature θ is eliminated. The method of the present invention can also be used for charging batteries other than those for electric vehicles.

[0029]

According to the present invention, when the battery is charged by the constant current two-step charging method, the charging by the constant time T _C of the second step, which is performed to bring the battery into a fully charged state, is the discharge amount of the battery. When the battery charge is small, the problem of causing overcharge can be solved, and the battery can be fully charged without excess or deficiency without being affected by the battery discharge state and the battery temperature.

When the reference voltage V _ref is not reached by the first charging due to some reason, a predetermined upper limit time T _Lim
As a result, the first-stage charging can be terminated based on the judgment by the above, so that the overcharging of the battery due to this cause can be eliminated.

[Brief description of drawings]

FIG. 1 is a charging characteristic diagram of a two-stage battery charging method.

FIG. 2 is a correction coefficient K _TB for correcting the second-stage charging time T _S
Showing the relationship between battery temperature and

FIG. 3 is a reference voltage V corrected by the battery temperature θ.
Diagram showing an example of the relationship between _ref ′ and battery temperature θ

FIG. 4 is a diagram showing an example of a relationship between an upper limit time T _Lim used for determining whether or not the first-stage charging is within an appropriate time and a battery discharge current amount Ah.

FIG. 5 is a diagram showing an example of the relationship between the correction coefficient K _TC and the battery temperature θ when the upper limit time T _Lim is corrected by the battery temperature θ.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shunichi Miyazaki 2-1-1 Taoyuan, Ikeda City, Osaka Daihatsu Industry Co., Ltd.

Claims (5)

[Claims] 1. The constant current charging of the first stage is performed until the battery voltage rises to the reference voltage V _ref, and then the current value is reduced to the second stage for a predetermined time T ₂ including a constant time T _C. In the two-stage constant current charging method of performing constant current charging, the first-stage charging time T ₁ is compared with a predetermined reference time T _ref, and when T ₁ is smaller than T _ref , the second-stage charging time T 1 ₂
Is a value T _S smaller than T _C. 2. The battery charging method according to claim 1, wherein the second-stage charging time T _S is corrected by multiplying it by a coefficient K _TB corresponding to the battery temperature. 3. A value T _ref ′ corrected by the battery temperature is used as the reference time T _ref used for determining whether to set the second-stage charging time T ₂ to T _S. Item 1. A method of charging a battery according to item 1 or 2. 4. A two-stage constant current charge is performed until the battery voltage rises to a reference value V _ref, and then the current value is reduced and the second constant current charge is performed for a predetermined time T _2. in the constant current charging method, to determine the upper limit time T _Lim pre from the measured discharge current amount of the first stage charging, when the charge of the first stage, the upper limit time T _Lim
When the reference voltage V _ref is not reached even after lapse of, a battery charging method is characterized in that the charging is forcibly shifted to the second-stage charging or the charging is stopped. 5. The method of charging a battery according to claim 4, wherein the upper limit time T _Lim is multiplied by a coefficient K _TC corresponding to the battery temperature for correction.