Patent ID: 6661231
Filing Date: 2003-12-09
Classification: G01R

Abstract:
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 a 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 corresponding to a maximum supplying electric power value to the loads, a difference value between the value of the estimated voltage and a value of an open circuit voltage, which 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, is calculated in advance as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery, thereafter, whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured during the constant load discharge by using the predetermined large current value, a present estimated voltage of the battery is estimated from the voltage-current characteristic, and the value of the residual voltage drop is added to a value of the present estimated voltage of the battery, thereby a present charging capacity of the battery is computed.