Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2000-11-09
2001-08-21
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06278261
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a battery charging device for charging batteries and a charging method thereof, and particularly to a battery charging device for charging batteries and a charging method thereof that may be favorably employed for charging batteries that generate a large amount of heat at the time of charging such as nickel-metal hydride batteries.
Rechargeable batteries that may be repeatedly used are currently being employed as power sources for power tools. Nickel-cadmium batteries are being widely used as batteries in such power tools, and battery charging devices performing rapid charge by supplying a large amount of current to the batteries are being employed. More particularly, by performing rapid charge of batteries in approximately 20 minutes, successive use of power tools is made possible while exchanging run down batteries with charged ones.
The inventors have considered whether it would be possible to improve performance of power tools by using nickel-metal hydride batteries as batteries. However, while nickel-metal hydride batteries enable an increase in capacity compared to nickel-cadmium batteries, they exhibit drawbacks in that the amount of generated heat at the time of charge is large, and in case a high temperature is reached through the heat generation, electrodes of internal cells of batteries or separators would degrade to thereby shorten the life of the batteries. Thus, rapid charge through a large amount of current as it had been performed in the above-described nickel-cadmium batteries could not be performed.
The invention has been made for solving the above-described subjects, and it is an object thereof to provide a battery charging device and a charging method thereof with which batteries may be charged in a short time while restricting rises in temperature of the batteries and without performing excessive charge.
BRIEF SUMMARY OF THE INVENTION
In order to solve the above problems, a battery charging device according to the present invention is characterized by comprising:
a temperature detecting portion for detecting a present temperature of batteries,
a temperature rising value outputting portion for obtaining a temperature rising value from the temperature as detected by the temperature detecting portion,
a current value retrieving portion for retrieving a current value with which the temperature rising value as output from the temperature rising value outputting portion is made constant,
a charge controlling portion for charging the batteries at the current value that has been retrieved by the current value retrieving portion, and
a charge terminating portion for terminating charge when at least one of the following conditions are met:
(a) when the current value has become not more than a specified value indicating completion of charge,
(b) when the temperature keeps on rising beyond the constant temperature rising value even if the current value is decreased, and
(c) when a battery temperature has increased beyond a target temperature value to be reached at the time of completion of charge by not less than a specified value.
In the invention, batteries are charged while adjusting a current value to achieve a constant temperature rising value. With this arrangement, it is possible to perform charge such that a temperature at the time of completion of charge becomes a specified value, and it is thus enabled to perform charge of nickel-metal hydride batteries or the like, which exhibit remarkable increases in temperature, in a short time without increasing the temperature to a high level.
By terminating charge when the current value has become a value that is not more than the specified value indicating that charge has been completed, it is enabled to perform charge up to 100% capacity and further to terminate charge without performing excessive charge. In case the temperature should keep on rising from the above constant temperature rising value also upon decreasing the current value, it is determined that an “overshoot” condition in which the temperature rapidly rises upon completion of charge has occurred. Thus, by terminating charge, it is possible to perform charge up to 100% capacity and further to terminate charge without performing excessive charge. Similarly, in case charge is performed while maintaining the temperature rise constantly, and the battery temperature has increased to beyond a target temperature value to be reached at the time of completion of charge and to be not less than a specified value, it is determined that charge has been already completed. Thus, by terminating charge, it is possible to perform charge up to 100% capacity without causing excessive charge.
A battery charging device according to the present invention is characterized by comprising:
a memory means for storing target temperature values for the batteries to be reached,
a temperature detecting portion for detecting a present temperature of the batteries,
a temperature gradient calculating portion for calculating a temperature rising gradient from a charging time based on a difference between a temperature of batteries at the time charge is started and the target temperature value to be reached as stored in the memory means,
a temperature rising value outputting portion for obtaining a temperature rising value from the temperature as detected by the temperature detecting portion,
a current value retrieving portion for retrieving a current value with which the temperature rising value as output from the temperature rising value outputting portion becomes the temperature rising gradient,
a charge controlling portion for charging the batteries at the current value that has been retrieved by the current value retrieving portion, and
a charge terminating portion for terminating charge when at least one of the following conditions are met:
(a) when the current value has become not more than a specified value indicating completion of charge,
(b) when the temperature keeps on rising beyond the constant temperature rising value even if the current value is decreased, and
(c) when a battery temperature has increased beyond the target temperature value to be reached at the time of completion of charge by not less than a specified value.
In the invention, a temperature rising gradient is calculated from a charging time based on a difference between a battery temperature at the start of charge and the target temperature value to be reached as stored in a memory means. Batteries are thus charged while adjusting current values such that the temperature rising value becomes equal to the temperature rising gradient. With this arrangement, it is enabled to perform charge such that the temperature at the time of completion of charge will be the target temperature value to be reached, and thus to perform charge of nickel-metal hydride batteries or the like, which exhibit remarkable increases in temperature, in a short time without increasing the temperature to a high level.
By terminating charge when the current value has become a value that is not more than the specified value indicating that charge has been completed, it is enabled to perform charge up to 100% capacity and further to terminate charge without performing excessive charge. In case the temperature should keep on rising from the above constant temperature rising value also upon decreasing the current value, it is determined that an “overshoot” condition in which the temperature rapidly rises upon completion of charge has occurred. Thus, by terminating charge, it is possible to perform charge up to 100% capacity and further to terminate charge without performing excessive charge. Similarly, in case charge is performed while maintaining the temperature rise constantly, and the battery temperature has increased to beyond a target temperature value to be reached at the time of completion of charge and to be not less than a specified value, it is determined that charge has been already completed. Thus, by terminating charge, it is possible to perform charge up to 100% capacit
Makita Corporation
Tolpin Thomas W.
Tso Edward H.
Welsh & Katz Ltd.
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