Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
1999-07-02
2001-02-20
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
C320S137000
Reexamination Certificate
active
06191560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery charger suited or charging a battery, such as a nickel metal hydride battery, which emits high heat while being charged.
2. Description of the Related 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 a battery by applying high current to the battery is used. Specifically, the battery is quickly charged in about 20 minutes and a power tool can be continuously used by changing a battery to a battery which 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 therefore. Although the nickel metal hydride battery can increase a capacity compared to a nickel cadmium battery, it generates high heat while being charged. If the temperature of the battery becomes high by the generated heat, the electrodes and separator of the cell within the battery deteriorate and battery life is shortened. Due to this, it is impossible to quickly charge the nickel metal hydride battery with high current as done for the nickel cadmium battery stated above.
Considering this, the inventor of the present invention contrived charging a battery while changing charging current based on a map in which the absolute temperatures of the battery and temperature rise values are mapped and detecting completion of battery charge from the map. However, if charging a battery by using this method, the switching of current values occurs frequently even in the earlier and medium periods of battery charge and charging time is disadvantageously lengthened. That is, the states of batteries to be charged vary such as one which capacity is almost zero and one which capacity remains almost full. Here, it is necessary to create the map as the greatest common measure of various states. In case of charging the above-mentioned batteries in various states or, for instance, charging a battery which capacity is almost zero in accordance with the map, current is switched to low current (such as
3
C) based on detected temperature rise values even while the maximum current capacity (such as
4
C) of the battery charger can be applied to the battery, thereby making time longer for completing battery charge. Further, in case of determining charge completion based on the map, it sometimes occurs that charge completion is determined after charging capacity exceeds 100% depending on the conditions.
Moreover, in case of obtaining charging current by retrieving a map from the absolute temperature of the battery and the temperature rise value, it is required that the battery temperature rise value, i.e., the accuracy of a temperature differential value is high so as to obtain an appropriate charging current value. In other words, if the accuracy of detecting the temperature differential value is low, an appropriate temperature value is not selected to thereby cause unnecessary switching of charging current as stated above. In that case, however, as temperature resolution increases, cost increases. It is, therefore, needed that unnecessary switching of current values can be prevented without increasing temperature resolution.
BRIEF SUMMARY OF THE INVENTION
An object of this invention is to provide a battery charger capable of charging a battery in a short time while the temperature rise of the battery is being suppressed in accordance with the state of the battery.
A still further object of this invention is to provide a battery charger capable of 100% charging a battery without overcharge.
A battery charger according to the present invention comprising;
a storage device storing a map, in which an allowable current value, with which a battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value;
temperature detecting means for detecting a present battery temperature;
temperature rise value outputting means for obtaining the temperature rise value from the temperature detected by said temperature detecting means;
charging state determining means for detecting a battery voltage and determining whether a battery state is in a final charging period based on change of the battery voltage;
allowable current value retrieving means for retrieving the map corresponding to the battery charger temperature, based on the temperature detected by said temperature detecting means and the temperature rise value outputted from said temperature rise value outputting means, and for obtaining said allowable current value, the allowable current value retrieving means obtaining a relatively high allowable value if it is determined that the battery state is not in the final charging period by said charging state determining means; and
charging means for charging the battery with the allowable current value retrieved by said allowable current value retrieving means.
A battery charger according to the present invention comprising;
a storage device storing a map, in which an allowable current value, with which a battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value, in accordance with at least a final charging period and a period before the final charging period;
temperature detecting means for detecting a present battery temperature;
temperature rise value outputting means for obtaining the temperature rise value from the temperature detected by said temperature detecting means;
charge state detecting means for detecting a battery voltage and for determining whether a battery state is in the final charging period based on change of the battery voltage;
allowable current value retrieving means for retrieving the map corresponding to the battery state determined by said charge state determining means, based on the temperature detected by said temperature detecting means and the temperature rise value outputted from said temperature rise value outputting means, and for obtaining said allowable current value; and
charging means for charging the battery with the allowable current value retrieved by said allowable current value retrieving means.
In accordance with the more preferred teaching of the present invention, said charge state determining means obtains a change in battery voltage based on voltage values having a same allowable current value switch pattern by said charging means.
In accordance with the more preferred teaching of the present invention, said charge comprises completing means for detecting the battery voltage and for completing battery charge if charge completion is determined based on a battery voltage decrease value.
A battery charger according to the present invention characterized by comprising;
a storage device storing a map, in which an allowable current value, with which a battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value, the allowable current value set at a low value if the battery temperature value is high and set at a low value if the temperature rise value is high;
temperature detecting means for detecting a present battery temperature;
temperature rise value outputting means for obtaining the temperature rise value from the temperature detected by said temperature detecting means;
allowable current value retrieving means for retrieving the map of said storage device based on the temperature detected by said temperature detecting means and the temperature rise value outputted from said temperature rise value outputting means, and for obtaining said allowable current value;
charging means for charging the battery with the allowable current value retrieved by said allowable current value retrieving means;
first count value output
Luk Lawrence
Makita Corporation
Tolpin Thomas W.
Welsh & Katz Ltd.
Wong Peter S.
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