Vehicle power supply device

1. A vehicle power supply device comprising:

a capacitor unit including a plurality of capacitors storing auxiliary power;

a temperature sensor detecting a temperature of the capacitor unit;

a charge circuit charging the capacitor unit;

a capacitor-unit current detector detecting a current of the capacitor unit;

a capacitor-unit voltage detector detecting a voltage of the capacitor unit;

a switch being switched so as to make the capacitor unit output the auxiliary power when necessary; and

a controller electrically connected to the temperature sensor, the charge circuit, the capacitor-unit current detector, the capacitor-unit voltage detector, and the switch, wherein

the controller suspends and resumes a constant current charging or discharging or the capacitor unit so as to make the capacitor-unit voltage detector detect a change in a charge or discharge voltage of the capacitor unit before and after the constant current charging or discharging is resumed, thereby calculating an internal resistance value of the capacitor unit from the change detected by the capacitor-unit voltage detector and from an output of the capacitor-unit current detector;

the controller then calculates a capacitance value of the capacitor unit from a voltage change rate of the capacitor unit during charge or discharge and from the output of the capacitor-unit current detector; and

the controller then calculates a standard value from the capacitance value using a degradation determination formula according to the temperature detected by the temperature sensor, and determines that the capacitor unit is degraded when the standard value is not more than the internal resistance value.

2. The vehicle power supply device of claim 1 , wherein

the voltage change rate during charge or discharge is determined by calculating a time period required to obtain a predetermined voltage difference of the capacitor unit.

3. The vehicle power supply device of claim 1 , wherein the

controller determines that the capacitor unit is degraded when at least a case happens,

wherein the case is that the internal resistance value calculated during charge or discharge of the capacitor unit is bigger than a pre-calculated degradation criterion of the capacitor unit, or that the capacitance value calculated during charge or discharge of the capacitor unit is smaller than the pre-calculated degradation criterion of the capacitor unit.

4. The vehicle power supply device of claim 1 , wherein

the temperature sensor is a thermistor.

5. The vehicle power supply device of claim 1 , wherein

when an output f the temperature sensor exceeds an operating temperature range of the capacitor unit, the determination of degradation of the capacitor unit is not performed.

6. The vehicle power supply device of claim 1 , wherein

when the temperature sensor is disconnected or short-circuited, the determination of degradation of the capacitor unit is performed at a temperature having most severe load conditions in the operating temperature range of the capacitor unit.

7. The vehicle power supply device of claim 1 , wherein the controller corrects the internal resistance value and the capacitance value at a predetermined time interval according to the temperature detected by the temperature sensor so as to calculate a corrected calculated value of internal resistance and a corrected calculated value of capacitance, thereby calculating the standard value from the corrected calculated value of capacitance using the degradation determination formula of the capacitor unit; and

the controller divides and executes at least one of the calculations according to the internal control cycle, thereby determining that the capacitor unit is degraded when the standard value is not more tan the corrected calculated value of internal resistance.