Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-10-03
2004-02-24
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C324S430000
Reexamination Certificate
active
06696818
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a unit for computing a charging efficiency of a battery used for supplying an electrical power to a load at any point between a start and an end of charging of the battery. The charging efficiency is defined as a ratio of an electrical quantity charged in the battery to a total electrical quantity supplied to the battery. The invention also relates to a method and a unit for knowing an electrical quantity charged in the battery based on a plurality of the obtained charging efficiencies.
2. Related Art
For example, in a battery mounted on a motor car, particularly in an electric car having an electric motor as a primary driving unit, it is greatly important to monitor a state of charge (SOC) of the battery to ensure a normal operation condition of the car.
Recently, in a general car having an engine as a driving unit or in a hybrid car having an electric motor for providing an additional driving force to an engine, it has been developed to have an idling function during an engine stop condition, e.g. when the car must temporally stop at an intersection of roads according to a stop signal.
A car having such an idling function requires a battery which can have a discharging capacity enough for restating its engine after the battery has discharged a considerable amount of electrical power for driving a power assisting motor (cell motor) during an idling operation of the car.
Therefore, it is greatly important to correctly know a state and a remaining discharging capacity of a battery concerning a general car and a hybrid car as well as the electric motor car described above.
In a typical electric car, a battery is charged during a non-usage state of the car, e.g. in a garage. In the meantime, a hybrid car has a motor generator which functions a generator to charge a battery when the car is running by a primary engine. The motor generator can also charge the battery at a deceleration period of the car even when the car is running by the driving force of the motor generator. A general car having only a primary engine charges its battery by an alternator driven by the engine.
Accordingly, regardless of the car type such as an electric car, a general car, or a hybrid car, it is important to correctly know a charged state of its battery, because the charged state varies with a charging operation as well as an electrical power supply to a load.
However, a chemical reaction during charging of a battery generates an oxygen gas and a hydrogen gas which are reduced into H
2
O, so that an electrical quantity supplied into the battery is not partially used for charging the battery. Furthermore, this tendency is more apparent when the battery gets nearer to its full charged state. Thus, a mere integration of charging currents with corresponding times can not obtain a correct charged state of the battery at a point during the charging of the battery.
The above-mentioned problem is not limited in an on-vehicle battery but also appears in a general battery supplying an electrical power to a load.
SUMMARY OF THE INVENTION
In view of the above-mentioned situation, an object of the invention is to provide a method and a unit for obtaining a charging efficiency of a battery used for supplying an electrical power to a load at any point between a start and an end of charging of the battery. The charging efficiency is defined as a ratio of an electrical quantity charged in the battery to a total electrical quantity supplied to the battery. The invention also provides a method and a unit for correctly computing an electrical quantity charged in the battery. This can correctly know a charged state of the battery at any point of charging of the battery.
For achieving the object, a first aspect of the invention is a method for computing a charging efficiency, which is a ratio of an electrical quantity charged in a battery as an electromotive force to a total electrical quantity supplied to the battery, at any one point in time between a start and an end of charging of the battery, the method comprising:
measuring an initial resistance of the battery at the start of the charging,
measuring a voltage and a current between a pair of terminals of the battery at the one point to obtain an inner resistance of the battery at the one point,
obtaining a resistance difference which is a difference of the inner resistance at the one point and the initial resistance, and
obtaining a ratio of the resistance difference to a full charged state resistance that is a resistance of the battery at a full charged state of the battery,
whereby, a charging efficiency of the battery at the one point is computed based on the ratio.
Thus, a voltage and a current are measured between the pair of terminals of the battery at a plurality of measuring points between a start and an end of charging of the battery, to obtain an resistance of the battery at each of the measuring points. Then, a resistance difference, which is a difference of a resistance at the charge start point and a resistance at one of the measuring points, is obtained. Furthermore, a full charged state resistance at a full charged state of the battery is obtained, and a ratio of the resistance difference to the full charged state resistance is obtained to know a charging efficiency of the battery at each of the measuring points during charging of the battery. This can correctly know a charged state of the battery, which would be varied with a gas generated in the battery. That is, the charging efficiency includes a charging loss due to the gas generation varying with a charging stage.
In a second aspect of the invention according to the first aspect, the ratio of the resistance difference to the full charged state resistance is deducted from 1 (one) to provide a charging efficiency at the one point.
Thus, a drop of the charging efficiency from an ideal value can be computed at any point during the charging by using the terminal voltage and the discharging current which are measured during the charging.
A third aspect of the invention is a method for computing a charged electrical quantity of the battery according to the first aspect of the invention, wherein a charged electrical quantity stored in the battery at the charging end of the battery is obtained by using a plurality of the charging efficiencies each obtained at each of a plurality of the measuring points in time between the start and the end of charging of the battery.
In the third aspect of the invention, a charged electrical quantity at any point during charge of the battery is obtained based on the charging efficiencies sequentially obtained over the start and the end of charging of the battery according to the first aspect of the invention.
Thus, an electrical quantity actually charged in the battery as compared with an electrical quantity supplied to the battery is correctly computed at each selected point during a time interval. An integration of the charged electrical quantities from the start to the end of the charging correctly provides a final electrical quantity charged in the battery.
A fourth aspect of the invention is a method for computing a charged electrical quantity according to the first aspect of the invention, wherein the battery has poles that are in an active state where no passivating film is formed on the poles, and whether the poles are in the active state is determined based on a pattern of the charging current varying with time during the charging,
the charged electrical quantity charged in the battery being obtained by using a plurality of the charging efficiencies each obtained at each of a plurality of the measuring points in time between the start and the end of charging of the battery when the poles are in the active state,
the charged electrical quantity of the battery being obtained based on an integration of a charging current multiplied by a corresponding charging time during a transition period in which a passivating film remains on the poles of the battery before the charg
Arai Youichi
Satake Shuji
Armstrong Kratz Quintos Hanson & Brooks, LLP
Tso Edward H.
Yazaki -Corporation
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