Patent ID: 8242737

Claim:
In a motor-driven vehicle utilizing power stored in a secondary battery as a source of motive power in which part of vehicle braking is achieved by regenerative braking by generating electrical energy absorbed by charging said secondary the battery, wherein a charging capability of the secondary battery by regenerative power can be guaranteed, a method of regulating a state of charge of the secondary battery while the secondary battery is being charged by an external power source, comprising the steps of: entering a charge mode, and determining a remaining quantity of charge in said secondary battery based at least on a temperature of said battery, calculating a target charge quantity, charging said battery until a state of charge becomes equal to the target charge quantity, when state of charge becomes equal to the target charge quantity, replacing said charge mode by a sleep mode and measuring at least a temperature of said battery periodically as determined by a timer, judging on each occasion whether the temperature has decreased or increased, if the result of judgment corresponds to an increase, returning to the step of target charge quantity calculation, if the judgment finds that the temperature has decreased, shifting said mode to a discharge mode, in said discharge mode, determining a remaining charge quantity as a function of at least the temperature of said battery, and when said remaining charge quantity in said battery is such that a charge quantity corresponding to an amount of regenerative energy for braking of said motor-driven vehicle cannot be received by said battery, calculating a target discharge quantity, and performing discharging of said battery until said target discharge quantity is reached, and then returning to periodically measuring at least a temperature of said battery.