Battery charger and battery charging method

Abstract

A temperature rise pattern is retrieved from charging time based on the difference between a battery temperature at the beginning of battery charge and a target temperature value which a battery is intended to reach (in S116). The battery is charged while adjusting a current value so that a temperature rise value becomes the temperature rise pattern (in S118 and S120). Thus, by optimizing the temperature rise pattern, it is possible to charge the battery so that the temperature at the time of the completion of battery charge becomes the target temperature value (the lowest temperature value).

Description

[0001]This is a reissue of U.S. Pat. No. 6,204,640, issued on Mar. 20, 2001.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a battery charger and a battery charging method for charging a battery and particularly relates to a battery charger and a battery charging method suited for charging a battery, such as a nickel metal hydride battery, which emits high heat while being charged.[0004]2. Discussion of the Prior Art[0005]Presently, a chargeable battery which can be repeatedly used for the power supply of, for example, a power tool is used.[0006]A nickel cadmium battery is popular as a battery for the power tool, and a battery charger for quickly charging the battery by applying high current thereto is used. Specifically, the battery is quickly charged in about 20 minutes and a power tool can be continuously used by switching a battery to that which has been charged.[0007]The present inventor of the present invention studiedhas invest...

AI Technical Summary

Benefits of technology

[0008]TheOne object of the present invention has been made to solveis to overcome the above-stated problems and ananother object of this invention is to provide a battery charger and a battery charging method capable of appropriately charging a battery in a short time while suppressing the temperature rise ofavoiding overheating the battery which is being suppressedduring charging.

[0030]In accordance with the more preferred teaching of the present invention, saidA preferred target temperature value is a value for completingcompletes the battery charge at the lowest temperaturewhile minimizing the increase in battery temperature.

[0039]A battery is charged while adjusting athe charging current value so that athe battery temperature rise valueincrease rate may be substantially constant. This makes it possible to charge the battery so that athe battery temperature at the time of the completion of charge becomeswill be a predetermined value. It is, therefore, possible to charge a nickel metal hydride battery or the like which has large temperature increase in a short time without increasingoverheating the battery temperature .

[0040]A temperature riseincrease pattern is retrieved from charging time based on the difference between athe battery temperature at the beginning of battery charge and athe target temperature value which the battery is intended to reach and which is held bystored in a storage device. The battery is then charged while adjusting athe charging current value so that athe battery temperature rise value may becomeincrease rate follows the temperature riseincrease pattern. Due to this, by optimizing the temperature riseincrease pattern, it is possible to charge the battery so that a battery temperature at the time of the completion of charge may becomebe a predetermined value. It is, therefore, possible to charge a nickel metal hydride battery or the like, which has a large temperature increase, in a short time without increasingoverheating the battery temperature .

[0042]A temperature rise pattern is set such that the difference between a battery temperature and an ambient temperature is small, a battery is difficult to cool, battery capacity is almost empty, temperature rise during battery is relatively small and a temperature rise value is relatively high in the first half of the battery charge, and set conversely such that the difference between the battery temperature and the ambient temperature is large, the battery is easily cooled, temperature rise during battery charge is relatively large and the temperature rise value is relatively low in the second half of the battery charge. That is, by setting the temperature rise pattern so as to optimize them altogether in cooperation with one another, it is possible to charge the battery so that the battery temperature at the time of the completion of charge may become the lowest temperature.

[0043]Since a temperature rise pattern is approximated polygonally, processing such as arithmetic processing can be easily carried out.

Problems solved by technology

If the temperature of the battery becomes high bydue to the generated heat, the electrodes and separators of the cells within the battery will deteriorate and battery life iswill be shortened.

Due to this, it ishas been impossible to quickly charge thea nickel metal hydride battery withusing high current as was previously done for the nickel cadmium battery stated abovebatteries.

Images