Patent ID: 7586290

Claim:
A battery state of charge detection device for use with an electric circuit that drives a motor by using a current supplied from a battery, the electric circuit comprising an inverter that controls operation of the motor and a controller that outputs a motor control signal to the inverter to supply from the battery to the motor a current corresponding to a requested output to the motor, the battery having a rated discharge range relating to a discharge current, the battery state of charge detection device comprising: a first current sensor that detects a discharge current of the battery, the first current sensor having a measurable current range that slightly exceeds an upper limit value of the rated discharge range; and a microprocessor programmed to: determine whether or not the current detected by the first current sensor exceeds the upper limit value; compute a state of charge of the battery based on the motor control signal when the current detected by the first current sensor exceeds the upper limit value; and compute the state of charge of the battery based on a current value detected by the first current sensor when the current detected by the first current sensor does not exceed the upper limit value.