Battery capacity calculating method and device therefor

A method for computing a battery capacity comprising the steps of:

• periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;
• calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
• estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic;
• and
• computing a charging capacity of the battery from the estimated voltage,
• wherein whenever the battery is subjected to the constant load discharge by using the predetermined large current value corresponding to a maximum supplying electric power value to the loads, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage Vn of the battery is estimated from the voltage-current characteristic.

An apparatus for computing a battery capacity executing the steps of:

• periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle when the battery is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;
• calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
• estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic;
• and
• computing a charging capacity of the battery from the estimated voltage,
• wherein the apparatus comprises first memory means for memorizing a difference value as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery, said difference value being a difference value between a value of the estimated voltage and a value of an open circuit voltage,
• in which the value of the estimated voltage of the battery in the constant load discharge with a predetermined large current value is estimated from the voltage-current characteristic when the discharge current of the constant load discharging process by the battery that is in an equilibrium state is decreasing from the predetermined large current value, and
• the open circuit voltage estimates the value of the estimated voltage and is a terminal voltage of the battery that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value,
• and wherein the value of the residual voltage drop memorized by the first memory means is added to the value of the estimated voltage of the battery, thereby a present charging capacity of the battery is computed.

An apparatus for computing a battery capacity executing the steps of:

• periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle when the battery is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;
• calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
• estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic;
• and
• computing a charging capacity of the battery from the estimated voltage,
• wherein the apparatus comprises:
• first detecting means for detecting a start of a decrease in the discharge current from the predetermined large current value in the constant load discharge process of the battery by using the predetermined large current value;
• first calculating means for calculating the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery after the first detecting means detects the start of the decrease in the discharge current;
• and
• estimating means for estimating the estimated voltage of the battery in the constant load discharge process of the battery by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means,
• thereby the charging capacity of the battery is computed by using the estimated voltage of the battery estimated by the estimating means.