Electricity: battery or capacitor charging or discharging – Battery or cell discharging – Regulated discharging
Reexamination Certificate
2001-05-18
2002-05-14
Toatley, Gregory (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
Regulated discharging
C320S162000, C320S150000
Reexamination Certificate
active
06388426
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a battery power source device comprising the function of protecting a rechargeable battery from excessive discharge current or a state of excessive discharge, and to an electromotive device using such a battery power source device.
BACKGROUND ART
When a rechargeable battery is allowed to enter a state of excessive discharge, or is used at an excessive discharge current, battery characteristics are degraded and battery lifetime is markedly reduced. Therefore, an excessive discharge prevention circuit and/or excessive current prevention circuit are provided, these circuits being integrated with the rechargeable battery to constitute a battery power source device, such as a battery pack, or the like. The aforementioned excessive discharge prevention circuit provides control whereby discharge is halted when a voltage equal to or lower than a discharge halt voltage at which discharging must be stopped is detected. The aforementioned excessive current prevention circuit detects an excessive current flowing through the discharge circuit based on voltage, and it performs control whereby discharge is halted if a voltage corresponding to an excessive current is detected.
However, in cases where an inrush current arises when the power is switched on in a device connected to the battery power source device, the voltage of the rechargeable battery is reduced as a result of this inrush current, and if the voltage falls to a value equal to or lower than the aforementioned discharge halt voltage, then the excessive discharge prevention circuit will shut off the discharge circuit, and the device will enter a non-operational state. This situation also applies similarly to an excessive current prevention circuit in that discharge will be halted if the inrush current is detected as an excessive current.
Japanese Patent Laid-open No. (Hei)9-266014 discloses the construction of a battery pack which prevents malfunction of an excessive discharge prevention circuit due to the occurrence of inrush current. In this construction, a time-constant circuit is provided on the input side of a battery voltage detection circuit, in such a manner that voltage reductions of short time period caused by inrush current are not detected. Moreover, it is also disclosed that by providing a timer function at the output side of the aforementioned detection circuit, the detection output is halted during voltage reductions of short time period.
Furthermore, Japanese Patent Laid-open No. (Hei)6-303728 discloses a construction for preventing malfunction of an excessive current preventing circuit due to inrush current. In this construction, a capacitor is provided on the input side of a control circuit which halts the discharge circuit when excessive current is detected, and therefore, since the voltage for detecting excessive current is not generated in the control circuit until the capacitor has become charged, any inrush current of short time duration will not be detected.
If a battery power source device is used in a device generating significant load fluctuations, such as an electric power tool, or the like, then the rechargeable battery will be exposed to harsh operating conditions.
Inrush current is generated repeatedly due to frequent ON/OFF switching operations, and the rechargeable battery must also be protected from excess load conditions, or high-temperature conditions, due to motor locking operations, or the like. Such situations cannot be managed satisfactorily simply by means of a control circuit for preventing malfunction due to inrush current according to the prior art constructions described above. In the case where an alkaline rechargeable battery such as a nickel metal hydride battery is used, because of the low output voltage (nominal voltage : 1.2V) of the battery, a battery power source is constituted by connecting a plurality of cells in series. However, if there is variation in battery capacity between the plurality of cells, then when the cell having the smallest capacity has completely discharged, it will start to be charged inversely by the other cells, thereby provoking breakdown of the battery and degradation of battery characteristics.
It is an object of the present invention to provide a battery power source device whereby shortening of battery lifetime is prevented by means of a control structure which prevents a battery from being used in predetermined unfavorable conditions.
DISCLOSURE OF THE INVENTION
In order to achieve the aforementioned object, the present invention according to a first aspect thereof provides a battery power source device comprising:
a rechargeable battery, wherein a discharge circuit is formed; and
discharge control means for controlling discharge of said rechargeable battery, wherein
said discharge control means measures the voltage and discharge current of said rechargeable battery a prescribed number of times at prescribed time intervals,
detects a battery voltage value and a discharge current value for each unit consisting of said prescribed number of measurement operations from running averages for said unit of measurement operations,
detects the battery temperature of said rechargeable battery, and
shuts off the discharge circuit of said rechargeable battery, if said battery voltage value, discharge current value and battery temperature assume any one of the states (1), (2), (3) described below:
(1) if a state where said battery voltage value is less than or equal to a predetermined undercut voltage value is detected consecutively for a prescribed number of measurement operations or more;
(2) if a state where said discharge current value is equal to or greater than a predetermined excessive current value is detected consecutively for a prescribed number of measurement operations or more;
(3) if said battery temperature is equal to or greater than a predetermined temperature.
According to the above described first aspect of the present invention, since the battery voltage and discharge current are measured at prescribed time intervals and are detected by means of the running average for each prescribed number of measurement operations, it is possible to detect the voltage and current in a suitable manner, even when the rechargeable battery is being used in a state where there are severe fluctuations in load and the voltage and current vary significantly, as in an electric power tool. Since an excessive discharge state of the rechargeable battery is identified if a state where the detected battery voltage value is equal to or lower than a predetermined undercut voltage value is detected continuously for a prescribed number of measurement operations or more, it is possible to shut off the discharge circuit, thereby halting battery discharge, in such circumstances. Consequently, the rechargeable battery can be protected from degradation due to excessive discharge. Moreover, if a state where the detected discharge current value is equal to or greater than a predetermined excessive current value is detected continuously for a prescribed number of measurement operations or more, then it is judged that the discharge current is exceeding the rated current of the rechargeable battery, thereby causing degradation of the rechargeable battery, and hence discharge can be halted in such circumstances by shutting off the discharge circuit. Moreover, if the battery temperature is equal to or greater than a predetermined temperature value, then this may cause deterioration of battery characteristics and lead to degradation or damaging of the battery, and hence discharge can be halted in such circumstances by shutting off the discharge circuit.
The rechargeable battery in the battery power source device of the present invention is constituted by a plurality of cells connected in series. According to a second aspect of the present invention, the discharge control means measures the respective unit voltages of each cell or each block of a plurality of cells, in addition to the voltage and discharge current of the rechargeable battery
Kasai Kanako
Tanaka Kenji
Ura Hironori
Yokoo Sadaaki
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Toatley Gregory
LandOfFree
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