Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2000-03-20
2001-03-20
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
C320S150000
Reexamination Certificate
active
06204641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery charger and a charging method for charging a battery. The present invention relates, in particular, to a battery charger and a charging method suitable for charging a battery, such as a nickel metal hydride battery, which accumulates a large amount of heat during charging.
2. Description of the Related Art
A charging-type battery which can be repeatedly charged is recently used as a power source for a power tool, for example. A nickel metal hydride battery is widely used as the power tool battery of this type. To charge the battery, a battery charger for rapidly charging the battery with high current is used. That is, while a battery is rapidly charged for about 20 minutes and, a power tool can be continuously used while replacing a currently used battery with another one which has been charged.
The inventor of the present invention studied ways to improve the performance of a power tool by using, as a battery, a nickel metal hydride battery. Although the nickel metal hydride battery can provide higher capacity than a nickel-cadmium battery, a large amount of heat is generated during charging. If the battery temperature becomes high due to the generated heat, the electrodes and separators of cells within the battery deteriorate and battery life is shortened. Due to this, the nickel metal hydride battery cannot be rapidly charged with high current unlike the nickel-cadmium battery.
Furthermore, the nickel metal hydride battery is more sensitive to overcharge than the nickel-cadmium battery and overcharging makes the battery life shorter. For that reason, it is required to avoid overcharging the nickel metal hydride battery. As for equipment which does not require battery replacement, to avoid overcharging the battery, charging current and discharging current are integrated and a battery is charged based on the integrated value. Thus, the battery can be fully charged. In case of charging a battery for equipment such as the above-stated power tool which requires replacing one battery with another, however, it has been difficult to fully charge the battery without overcharging it.
SUMMARY OF THE INVENTION
The invention has been made to solve the above-stated disadvantages and has an object to provide a battery charger and a charging method capable of charging a battery for a short period of time while suppressing battery temperature from rising.
The invention has also been made to solve the above-stated disadvantages and has an object to provide a battery charger and a charging method capable of fully charging a battery without fear of an overcharge.
To attain the above object, the battery charger is technically characterized by comprising:
a memory for storing a map for mapping an allowable value of current, with which a battery can be charged while suppressing battery temperature from rising, based on a battery temperature and a battery temperature rise;
a temperature detection device for detecting a current temperature of the battery;
a temperature rise output device for obtaining the temperature rise from the temperature detected by the temperature detection device;
an allowable current retrieval device for retrieving the map of the memory device from the temperature detected by the temperature detection device and the temperature rise outputted from the temperature rise output device, and for obtaining the allowable value; and
a charging device for charging the battery with the allowable current retrieved by the allowable current retrieval device.
To attain the above object, the battery charger is technically characterized by comprising:
a memory for storing a map for mapping an allowable value of current, with which a battery can be charged while suppressing battery temperature from rising, based on a battery temperature and a battery temperature rise, the map having the allowable current value set low when the battery temperature is high and set low when the temperature rise is large;
a temperature detection device for detecting a current temperature of the battery;
a temperature rise output device for obtaining the temperature rise from the temperature detected by the temperature detection device;
an allowable current retrieval device for retrieving the map of the memory device from the temperature detected by the temperature detection device and the temperature rise outputted from the temperature rise output device, and for obtaining the allowable value;
a charging device for charging the battery with the allowable current retrieved by the allowable current retrieval device;
a charging completion determination device for determining that charging is completed based on whether or not the temperature detected by the temperature detection device and the temperature rise outputted from the temperature rise output device belong to a region indicating a final charging stage (a region in which temperature rise is relatively large and relatively low allowable current is outputted) on the map of the memory device with high frequency; and
a charging completion device for completing charging based on the determination of the charging completion determination device that charging is completed.
To attain the above object, the charging method is technically characterized by comprising:
detecting current temperature of a battery;
obtaining a temperature rise from the detected temperature;
retrieving an allowable current map based on battery temperature and battery temperature rise, from the detected temperature and the obtained temperature rise, and obtaining an allowable value of current, with which the battery can be charged while suppressing the battery temperature from rising; and
charging the battery with the retrieved allowable current.
To attain the above object, the charging method is technically characterized by comprising:
detecting a current temperature of a battery;
obtaining a temperature rise from the detected temperature;
retrieving an allowable current map based on battery temperature and battery temperature rise, from the detected temperature and the obtained temperature rise, and obtaining an allowable value of current with which the battery can be charged while suppressing the battery temperature from rising;
charging the battery with the retrieved allowable current;
determining that charging is completed based on whether the outputted temperature rise is relatively large and whether relatively low allowable current is outputted from the map with a high frequency; and
completing charging based on the determination that charging is completed.
According to the battery charger and charging method, charging current is controlled using a map for mapping an allowable value of current with which a battery can be charged while suppressing battery temperature from rising based on battery temperature and battery temperature rise. That is, the map is retrieved from the battery temperature and temperature rise. The allowable value of current, with which the battery can be charged while suppressing the battery temperature from rising, is obtained. The battery is charged with the allowable current thus obtained. This makes it possible to charge a nickel metal hydride battery, the temperature of which tends to rise during charging, for a short period of time without causing deterioration due to temperature rise. Just before charging is completed, the temperature rise of the nickel metal hydride battery is larger and the battery is charged with relatively low current, therefore it is possible to suppress “overshoot” after the completion of charging.
According to the battery charger and charging method, charging current is controlled using a map for mapping an allowable value of current with which a battery can be charged while suppressing battery temperature from rising based on battery temperature and battery temperature rise. That is, the map is retrieved from the battery temperature and temperature rise. The allowable value of current, with which the battery can be charged while suppr
Makita Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tibbits Pia
Wong Peter S.
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