Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
2001-07-25
2002-08-27
Toatley, Gregory (Department: 2834)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C320S134000
Reexamination Certificate
active
06441619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a remaining charge detection device for a power storage unit, such as a battery. More specifically, the present invention relates to a remaining charge detection device for a power storage unit, which utilizes a technique of calibrating the remaining charge calculated based on a current accumulation method.
2. Description of Related Art
As a method for detecting the remaining charge of a power storage unit (e.g., a battery) which is provided in, for instance, a hybrid car, one is generally known in which the accumulated charge amount and the accumulated discharge amount of the battery are calculated by estimating the charging current and the discharging current of the battery for each given period of time, and adding or subtracting the accumulated charge amount/the accumulated discharge amount to/from the initial charge or the remaining charge of the battery prior to the charging-discharging processes, since the remaining charge of the battery corresponds to the total amount of electric charge retained in the battery.
However, in the above-mentioned method, for instance, measurement errors in the current detector accumulate when the accumulated charge amount and the accumulated discharge amount are calculated, and errors contained in the calculated remaining charge may be increased.
Because of the problems described above, as a remaining charge detection device for a battery, which is capable of calibrating the remaining charge calculated based on the above-mentioned current accumulation method to an accurate value at a suitable timing, Japanese Unexamined Patent Application, First Publication No. 10-132911, for instance, discloses a battery remaining charge detector in which predetermined relational expressions or maps for current values, voltage values, and remaining charges for the battery are stored. The battery remaining charge detector calculates the remaining charge of the battery based on the current value and the voltage value of the charging/discharging current of the battery detected by a current detector and a voltage detector, respectively, and carries out a calibration of the calculated remaining charge based on the stored relational expressions or maps.
However, since the predetermined relational expressions or maps retained in the above-mentioned battery remaining charge detector are prepared based on the voltage characteristic of a battery in its stationary state (i.e., the battery has not deteriorated), there is a difference between the actual remaining charge of the battery and the remaining charge of the battery calculated based on the predetermined maps or relational expressions, and the difference may be increased when the internal resistance of the battery is increased by, for instance, the deterioration of the battery. If a value which contains an error is detected as the remaining charge of a battery, the battery may be used exceeding its limit and the life of the battery may be shortened.
Also, when the remaining charge of a battery is defined as a percentage with respect to a predetermined standard charge of the battery and such a percentage value is used for controlling a motor or an engine, problems may arise in controlling the motor or engine and they may not be properly controlled if the degree of deterioration of the battery is not reflected to the standard charge of the battery.
SUMMARY OF THE INVENTION
The present invention is achieved in consideration of the above situation, and its objectives include the provision of a remaining charge detection device for a power storage unit, which enables calculation, even if the power storage unit has deteriorated, of an accurate remaining charge thereof based on an accumulated charge amount and an accumulated discharge amount obtained by estimating a charging current and a discharging current.
Accordingly, the present invention provides a remaining charge detection device for a power storage unit (for instance, a battery
14
in an embodiment of the invention which will be described later) including: a current detection unit (for instance, a current detector
26
in an embodiment of the invention which will be described later) which detects the current value of a charging current and a discharging current of a power storage unit; a voltage detection unit (for instance, a voltage detector
28
in an embodiment of the invention which will be described later) which detects the voltage value of a terminal voltage of the power storage unit; and a current accumulation remaining charge calculation means (for instance, step S
02
in an embodiment of the invention which will be described later) which accumulates the current value detected by the current detection unit to obtain an accumulated charging current and an accumulated discharging current and, based on the accumulated charging current and the accumulated discharging current, calculates a remaining charge (for instance, a detected remaining charge SOC in an embodiment of the invention which will be described later) of the power storage unit;
wherein the remaining charge detection device further includes: a no-load state detection unit (for instance, a current consumer releasing unit
23
in an embodiment of the invention which will be described later) which detects a no-load state of the power storage unit; and a remaining charge for calibration calculation unit (for instance, a remaining charge for calibration calculation unit
25
in an embodiment of the invention which will be described later) which calculates, according to the voltage value detected in the no-load state of the power storage unit (for instance, OCV in an embodiment of the invention which will be described later), a remaining charge for calibration (for instance, a remaining charge SOC
OCV
in an embodiment of the invention which will be described later) with respect to the remaining charge of the power storage unit.
According to the above remaining charge detection device for a power storage unit, the upper limit and the lower limit of the remaining charge of the power storage unit are determined, for instance, from the viewpoint of protecting the power storage unit, so that the remaining charge calculated by the current accumulation method varies within a predetermined range. Also, predetermined map(s) which show the relationships between the temperature, current, and voltage of the power storage unit corresponding to the upper limit and the lower limit of the remaining charge are provided. The maps are constructed based on a stationary state of the power storage unit having no deterioration, e.g., based on the initial state of the power storage unit.
When an internal resistance of the power storage unit increases due to such factors as the deterioration thereof, it may be erroneously determined that the actual remaining charge of the power storage unit has reached the upper limit, which, in fact, it has not, because the detected terminal voltage of the power storage unit has reached the upper limit voltage corresponding to the map of the upper limit remaining charge. According to the present invention, however, a no-load state of the power storage unit is forcibly created by disconnecting the load, such as a motor, from the power storage unit at this stage, and the terminal voltage at the load-release state is measured after a certain period of time. The characteristics of the remaining charge with respect to the terminal voltage at the load-release state are not related to the deterioration of the power storage unit, i.e., the increase in the internal resistance thereof, and they are almost the same as those in a power storage unit having no deterioration, e.g., at the initial state thereof. For this reason, the remaining charge of the power storage unit may be obtained with high accuracy by providing a predetermined relational expression or map which shows the relationship between the terminal voltage and the remaining charge at the load-release state, and by searching the relational expression
Araki Kazuhiro
Maruno Naoki
Yamada Yasuo
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Toatley Gregory
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