Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-08-02
2003-12-09
Tibbits, Pia (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C702S063000, C324S428000
Reexamination Certificate
active
06661202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a unit for calculating a degradation degree of a battery to supply an electrical power to a load.
2. Related Art
A battery is an electrical source for starting an engine, operating on-vehicle electrical equipment, etc. so that it is important to know a charged state of the battery.
However, the battery repeats charging and discharging, which increases an inner impedance thereof to gradually decrease a discharging capacity and a full charged capacity.
Thus, to correctly know a charged state of the battery, it is necessary to find its present full charging capacity. Therefore, it is important to find a latest degradation state of the battery which appears with its repeated charging and discharging operations.
For knowing the degradation degree of the battery, an original full charging capacity is measured when the battery is new, and the original full charging capacity is compared with a present full charging capacity of the battery. Conventionally, a battery is completely discharged from its full charged state, while a discharge current value and a discharge time are measured to obtain a discharging current capacity which is considered as a present capacity of the battery.
In a vehicle having an ordinary engine and in a hybrid vehicle having a motor generator which acts at an insufficient torque state of an engine, a battery needs to output a large quantity of power at the initial starting of the engine. After the starting, an alternator or the motor generator provides an electrical power to charge the battery into a full charged state during an operation state of the vehicle.
In this vehicle, to know a present full charge capacity of the battery, it is necessary to remove the battery from the vehicle to completely discharge the battery from its full charged state. This work is unpractical and disadvantageous.
Therefore, to monitor a degradation degree of the battery in a state where the battery has been mounted on the vehicle, factors varying with the degradation degree of the battery are measured. This is important to know a present degradation degree of the battery.
One of the factors varying with the degradation degree of the battery is a concentration polarization impedance (combined resistance). The concentration polarization impedance causes a voltage drop between a pair of terminals of the battery. The voltage drop consists of an IR loss (base resistance, i.e. a voltage drop due to an ohmic resistance) and a voltage drop due to a polarization resistance (activation polarization and concentration polarization) related to a chemical reaction.
Thus, a present degradation degree of the battery can be known by monitoring how the base resistance, the activation polarization, and the concentration polarization resistance vary from their original values to drop the terminal voltage of the battery.
A degradation of such a battery is due to increase of the base resistance, the activation polarization resistance, or the concentration polarization resistance. Therefore, it is insufficient to find only one of the degradations to determine the state of the battery. For example, the base resistance varies little in a charged state (SOC) more than 40%, while the base resistance varies sharply in a SOC less than 40%. In the meantime, the activation polarization resistance and the concentration polarization resistances increase apparently even in a SOC more than 40%.
Thus, the base resistance, the activation polarization resistance, and the concentration polarization resistance do not vary with an apparent regularity in connection to the degradation degree of the battery. However, there are relations among the base resistance, the activation polarization resistance, and the concentration polarization resistance. Therefore, it is necessary for determining a correct degradation state of the battery to monitor all of the base resistance, the activation polarization resistance, and the concentration polarization resistance.
SUMMARY OF THE INVENTION
In view of the aforementioned situation, an object of the invention is to provide a method and a unit for determining a degradation degree of a battery to supply an electrical power to a load. The method considers relations among a base resistance, a activation polarization resistance, and a concentration polarization resistance of the battery. A measurement of the battery is made while the battery is kept at a usage position.
A first aspect of the invention is a degradation degree computing method for a battery for supplying an electrical power to a load, the method comprising the steps of:
a first step for obtaining a base resistance of the battery by cyclically measuring a discharge current and a voltage between a pair of terminals of the battery while a rush current is flowing in an electric load electrically connected to the pair of the terminals, the rush current simply decreasing from a peak to a constant value after the rush current simply increases from zero to the peak,
a second step for obtaining at least one of a concentration polarization resistance and an activation polarization resistance of the battery from the discharge current and the terminal voltage that are measured in the first step,
a third step for obtaining a degradation degree of the base resistance which is a ratio of the base resistance obtained by the first step to an original base resistance of the battery,
a fourth step for obtaining a polarization resistance degradation degree which is a ratio of one of the concentration polarization resistance and the activation polarization resistance to an original polarization resistance, and
a fifth step for obtaining a degradation degree of the battery by multiplying the degradation degrees of the base resistance and the polarization resistance together. Thus, even when there is a relation between the base resistance and the polarization resistance, the degradation degree of the battery is calculated to include the relation.
Preferably, the second step obtains each of a concentration polarization resistance and an activation polarization resistance of the battery, and the fourth step obtains a concentration polarization resistance degradation degree which is a ratio of the concentration polarization resistance obtained in the second step to an original concentration polarization resistance of the battery, the fourth step also obtaining an activation polarization resistance degradation degree which is a ratio of the activation polarization resistance obtained in the second step to an original activation polarization resistance of the battery, wherein the polarization resistance degradation degree of the fifth step is obtained by multiplying the degradation degrees of the concentration polarization resistance and the activation polarization resistance together. Thus, even when there is a relation between the concentration polarization resistance degradation and the activation polarization resistance degradation, the degradation degree of the battery is calculated in consideration of the relation.
A second aspect of the invention is a degradation degree computing unit of a battery for supplying an electrical power to a load. As illustrated in
FIG. 1
, the unit includes:
a measuring means
23
a
-
1
for measuring a discharge current and a voltage between a pair of terminals of the battery while a rush current is flowing in an electric load electrically connected to the pair of the terminals, the rush current simply decreasing from a peak to a constant value after the rush current simply increases from zero to the peak,
a base resistance computing means
23
a
-
2
for obtaining a base resistance of the battery from the discharge current and the voltage that are measured by the measuring means,
a polarization resistance computing means
23
a
-
3
for obtaining at least one of a concentration polarization resistance and an activation polarization resistance of the battery from the discharge current and the terminal voltage that are m
Armstrong Kratz Quintos Hanson & Brooks, LLP
Tibbits Pia
Yazaki -Corporation
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