Electricity: battery or capacitor charging or discharging – Battery or cell charging – Gas controlled
Reexamination Certificate
2000-07-03
2001-06-12
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
Gas controlled
C320S137000
Reexamination Certificate
active
06246216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery charge control device which has a “gassing” deciding function to detect an occurrence of the gassing state caused in a battery on a vehicle at the vehicle's traveling, without using a temperature sensor and with ease and accuracy.
2. Description of Related Art
Under general condition that the battery is being charged, if its terminal voltage exceeds a stated voltage, then the battery begins to generate gas (e.g. oxygen gas, hydrogen gas) due to the electrolysis of water contained in the battery. Note that the terminal voltage at the time of beginning to generate such the gas is normally referred to as “gassing voltage”. As the function of temperature of the electrolyte (liquid) in the battery, the gassing voltage Vgs can be obtained by the following formula of:
Vgs=&agr;−&bgr;(T−20° C.) (1)
wherein &agr;, &bgr; are the battery's intrinsic constants; and
T is the temperature of the electrolyte.
Especially in the “hybrid” vehicle equipped with a plurality of power sources, such as an engine and an alternator, a great deal of regenerative energy (electric power) during the vehicle's traveling is charged into the battery one after another. Under the situation, it is remarkably important to detect whether or when the terminal voltage of the battery is reaching the above gassing voltage Vgs in view of preventing the deterioration of battery.
In order to acknowledge the terminal voltage's reaching the gassing voltage Vgs, for example, there is a known system where the battery is equipped with the temperature sensor.
In this system employing the temperature sensor in order to detect the reach for the gassing voltage Vgs, it is executed to calculate it on the basis of a temperature informed by the temperature sensor, in accordance with the above formula (1). Also in the system, when the terminal voltage of the battery reaches the gassing voltage Vgs, it is executed to switch the present charging current into a new charging current prepared for the next stage (i.e. a new current smaller than the current) in view of restricting the generation of gas in the electrolyte.
In the above-mentioned system, however, there exists a problem that the embodied apparatus is high-priced because of the installation of the temperature sensor. Additionally, in order to calculate the gassing voltage Vgs as the function of temperature, the calculation program installed on the apparatus is complicated.
Note that it is desirable to position the temperature sensor in the electrolyte (liquid) in view of detecting the temperature of the electrolyte in the battery precisely. Nevertheless, in the present circumstances, it is impossible to dip the temperature sensor in the electrolyte.
Since, in actuality, the temperature sensor is arranged in the vicinity of the battery or pasted on a sidewall of the battery, there is a difference between the actual temperature of the electrolyte and the temperature information provided by the temperature sensor.
Additionally, it is unavoidable that the temperature of air outside affects the so-positioned temperature sensor.
Thus, the gassing voltage Vgs based on the temperature information provided by the temperature sensor has a reduced reliability in its accuracy due to the above difference between the actual temperature of the electrolyte and the temperature detected by the temperature sensor.
In summary, the conventional system has drawbacks that the gassing cannot be detected despite that the terminal voltage of the battery has already reached the gassing voltage during the vehicle's traveling, and vice versa (erroneous detection of the gassing despite that the battery voltage has not reach the gassing voltage yet). Such the drawbacks cause either surplus or shortage of the charged energy in charging the battery.
SUMMARY OF THE INVENTION
Under the circumstances, it is therefore an object of the present invention to provide a battery charge control device that is capable of easy detection of a time when the battery actually reaches its gassing state, without using the temperature sensor.
The object of the present invention described above can be accomplished by a battery charge control device for controlling to charge a battery electrically connected with a load. The battery charge control device is constructed so as to charge the battery while lowering a charging current brought from the load in a step manner when the battery's residual capacity drops during the load's operation. The battery charge control device comprises a memory unit for collecting and storing a sequential data of terminal voltage of the battery, a temporary-gassing detecting unit connected to the memory unit, a voltage regulation calculating unit connected to the temporary gassing detecting unit and a gassing detecting unit connected to the voltage regulation calculating unit.
In operation, when the so-collected terminal voltage of the battery exceeds a threshold value during charging the battery with a charging current, the temporary-gassing detecting unit generates a signal representing that the battery is in course of reaching its gassing state.
The voltage regulation-calculating unit calculates a changing rate (i.e. voltage regulation) of terminal voltage of the battery while the battery is in course of reaching the gassing state.
When the calculated changing rate exceeds a preset decision value for the changing rate, the gassing detecting unit judges that the battery has just reached the gassing state.
Therefore, without using the temperature sensor, it is possible to judge the gassing state in the battery during the vehicle's traveling, with high accuracy.
The battery charge control device further includes a charging current switching unit which allows the battery to be charged with a designated charging current corresponding to the beginning of charging and a decision value renewing unit. In operation, the charging current switching unit further switches the designated charging current to a next lower charging current as soon as the gassing state of the battery has been detected. Whenever the charging current is switched, the decision value renewing unit changes the preset decision value for the changing rate to a new decision value for the changing rate of the voltage corresponding to the so-switched charging current.
Even after changing the present charging current into a lower one at the battery's reaching the gassing state in order to restrict the occurrence of gassing, the subsequent charging again causes the temperature of the battery to be increased thereby varying the battery voltage abruptly.
According to the invention, since the device is adapted so as to also renew the decision value corresponding to the so-changed charging current, it is possible to detect the gassing state occurring after the charging current has been changed with high accuracy.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompany drawings.
REFERENCES:
patent: 5589757 (1996-12-01), Klang
patent: 5701068 (1997-12-01), Baer et al.
patent: 5808443 (1998-09-01), Lundstrom
patent: 8-278352 (1996-10-01), None
Satake Syuji
Takemoto Hisashi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Luk Lawrence
Wong Peter S.
Yazaki -Corporation
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