Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2001-04-25
2002-11-05
Toatley, Gregory (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06476584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 generates a large amount of heat while being charged.
2. Discussion of the Prior Art
Presently, a chargeable battery which can be repeatedly used for the power supply of, for example, a power tool is used. 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 to a battery that has been charged.
The inventor of the present invention studied improving the performance of a power tool by using a nickel metal hydride battery as a battery therefor. Although the nickel metal hydride battery has an increased charge storage capacity compared to a nickel cadmium battery, it generates high heat while being charged. If the temperature of the battery becomes high due to the generated heat, the electrodes and separators of the cells within the battery will deteriorate and battery life is shortened. Due to this, it has been impossible to quickly charge the nickel metal hydride battery with high current in a manner similar to the nickel cadmium battery stated above.
Further, the nickel metal hydride battery is less resistant against overcharge than the nickel cadmium battery. If overcharged, the battery life is shortened. It is, therefore, necessary to avoid overcharge.
Considering this, the inventor of the present invention contrived a method of controlling charging current and detecting the completion of charge based on a map for determining a current value based on the absolute temperature of the battery and a temperature rise value. With this method, however, if the number of battery cells in a battery pack increases, a battery cell positioned on the end portion of the battery pack tends to be cooled and that on the central portion thereof is difficult to cool, with the result that the completion of charge cannot be detected based on the battery temperature. Furthermore, if the temperatures of the cells in the battery pack become increasingly irregular, the life of a high temperature cell is shortened and the high temperature cell is difficult to charge. Due to this, the capacities become unbalanced among the cells and it may occur that there is a cell charged 100% and one charged 90% (high temperature cell). Here, if the capacity of the battery pack is used up to 90%, some cells have a residual capacity of 10% and the others have a residual capacity of 0% (high temperature cell). The cells of 0% residual capacity are reverse-charged by those of 10% residual capacity and the battery life is considerably shortened.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to solve the above-stated problems and an 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 avoiding overheating the battery during charging.
In one embodiment of the present invention, a battery charger comprises:
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section is constant; and
a charge control section for charging a battery with the current value retrieved by said current value retrieving section.
In another embodiment of the present invention, a battery charger comprises:
a storage device storing a target temperature value which a battery temperature is intended to reach;
a temperature detecting section for detecting a present battery temperature;
a temperature gradient calculating section for calculating a temperature rise gradient from charging time based on a difference between a battery temperature at the beginning of battery charge and said target temperature value held by said storage device;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise gradient; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In another embodiment of the present invention, a battery charger comprises:
a storage device storing a target temperature value which a battery is intended to reach;
a temperature detecting section for detecting a present battery temperature;
a temperature rise pattern retrieving section for retrieving a temperature rise pattern for completing battery charge at said target temperature value based on a difference between a battery temperature at the beginning of the battery charge and said target temperature value held by said storage device;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise pattern; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In accordance with more preferred teaching of the present invention, said temperature rise pattern is such that the temperature rise value is relatively high in a first half of battery charge and is relatively low in a second half of battery charge.
In accordance with more preferred teaching of the present invention, said temperature rise pattern is approximated polygonally.
In accordance with more preferred teaching of the present invention, said target temperature value is a value for completing the battery charge at the lowest temperature.
A battery charging method for making a battery side hold information on a target temperature value, which a battery is intended to reach, corresponding to charging time and charging the battery by means of a battery charger in accordance with the target temperature value, according to the present invention is characterized in that said battery charger comprises:
a storage device storing a temperature rise pattern for completing battery charge at the target temperature value read out from the battery side;
a temperature detecting section for detecting a present battery temperature;
a temperature rise pattern retrieving section for retrieving a temperature rise pattern from said storage device based on a battery temperature at the beginning of the battery charge and charging time;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise pattern; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In accordance with more preferred teaching of the present invention, said target temperature value is a value for completing the battery charge at the lowest temperature.
A battery is charged while adjusting a current value so that a temperature rise value may be constant. This makes it possible to charge the battery so that a battery temperature at the time o
Lyon & Lyon LLP
Makita Corporation
Toatley Gregory
LandOfFree
Battery charger and battery charging method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Battery charger and battery charging method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Battery charger and battery charging method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2932552