Vehicle power supply device and its degradation judgment method

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 electric power to the capacitor unit;

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

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

a controller electrically connected to the temperature sensor, the charge circuit, the capacitor-unit current detector, and the capacitor-unit voltage detector, the controller obtaining an internal resistance value and a capacitance value of the capacitor unit from the voltage value and the current value;

a storage storing a correction calculation formula and a plurality of degradation determination formulas, the correction calculation formula being used to perform the correction calculation of the internal resistance value and the capacitance value in accordance with the temperature in order to obtain a corrected calculated value of internal resistance and a corrected calculated value of capacitance, and the plurality of degradation determination formulas corresponding to numerical ranges of the corrected calculated value of capacitance and being used to calculate an internal resistance standard value from the corrected calculated value of capacitance; and

a determination unit determining a degradation level of the capacitor unit based on at least one of the internal resistance standard value and the corrected calculated value of capacitance.

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

when the capacitor unit is charged at a constant current, the controller makes the capacitor-unit voltage detector detect a change in a charge voltage value of the capacitor unit before and after a charging operation is suspended or before and after the charging operation is resumed;

the controller acquires the internal resistance value of the capacitor unit based on the voltage value detected by the capacitor-unit voltage detector and the current value detected by the capacitor-unit current detector; and

the controller acquires the capacitance value of the capacitor unit based on a charge-voltage-change rate of the capacitor unit during charge and the current value detected by the capacitor-unit current detector.

3. The vehicle power supply device of claim 1 , further comprising:

a discharge circuit discharging the electric power charged in the capacitor unit, wherein

when the capacitor unit is discharged at a constant current, the controller makes the capacitor-unit voltage detector detect a change in a discharge voltage value of the capacitor unit before and after a discharging operation is suspended or before and after the discharging operation is resumed;

the controller acquires the internal resistance value of the capacitor unit based on the voltage value detected by the capacitor-unit voltage detector and the current value detected by the capacitor-unit current detector; and

the controller acquires the capacitance value of the capacitor unit based on a discharge-voltage-change rate of the capacitor unit during discharge and the current value detected by the capacitor-unit current detector.

4. The vehicle power supply device of claim 1 , further comprising:

a switch electrically connected to the controller, the switch being switched to output electric power from the capacitor unit when output of the auxiliary power is requested.

5. The vehicle power supply device of claim 1 , further comprising:

a load connected to the capacitor unit, wherein

the number of the degradation determination formulas used to calculate the internal resistance standard value is equal to the number of times that the capacitor unit supplies electric power intermittently to the load.

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

the controller includes the determination unit.

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

the determination unit determines that the capacitor unit is degraded at least one of when the corrected calculated value of internal resistance is not less than the internal resistance degradation criterion value and when the corrected calculated value of capacitance is not more than a capacitance degradation criterion value previously stored in the storage.

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

the storage stores the plurality of degradation determination formulas corresponding to the temperatures detected by the temperature sensor.

9. A method for determining degradation of a

vehicle power supply device, the method comprising:

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

acquiring an internal resistance value of the capacitor unit;

acquiring a capacitance value of the capacitor unit;

acquiring a corrected calculated value of internal resistance and a corrected calculated value of capacitance by having a microprocessor perform a correction calculation of the internal resistance value and the capacitance value in accordance with the temperature;

acquiring an internal resistance standard value from the corrected calculated value of capacitance using a plurality of different degradation determination formulas corresponding to numerical ranges of the corrected calculated value of capacitance; and

determining a degradation level of the capacitor unit based on at least one of the internal resistance standard value and the corrected calculated value of capacitance.

10. The method for determining degradation of a vehicle power supply device of claim 9 , further comprising:

at least one of charging and discharging the capacitor unit at a constant current;

detecting a current value of the capacitor unit; and

detecting a change, as a voltage value and a voltage change rate, in a voltage change of the capacitor unit before and after a charging or discharging operation is suspended or before and after the charging or discharging operation is resumed in the charge-discharge step when the capacitor unit is charged or discharged, wherein

the internal resistance value is acquired based on the voltage value detected in the voltage value detecting step and the current value detected in the current value detecting step; and

the capacitance value of the capacitor unit is acquired based on the voltage change rate detected in the voltage value detecting step and the current value detected in the current value detecting step.

11. The method for determining degradation of a vehicle power supply device of claim 9 , wherein

the capacitor unit is determined to be degraded based on at least one of when the corrected calculated value of internal resistance is not less than the internal resistance degradation criterion value and when the corrected calculated value of capacitance is not more than a capacitance degradation criterion value previously stored in the storage.