Battery voltage measurement circuit

1. A battery voltage measurement circuit comprising:

a first switch configured to be connected to a positive electrode of a battery;

a second switch configured to be connected to a negative electrode of the battery;

detection resistances that are connected in series between the first switch and the second switch;

capacitors that are connected in parallel to the detection resistances; and

a measurement circuit that measures a voltage applied to the detection resistances, wherein

the battery voltage measurement circuit has a plurality of measurement modes depending upon status of the first and second switches, and further has a failure detection mode for the capacitors based on a change in the voltage measured by the measurement circuit after switching from one to an other of the measurement modes, and

the battery voltage measurement circuit has, of the plurality of measurement modes, at least two measurement modes of

(i) a first measurement mode in which (1) the first switch is turned on and the second switch is turned off to form a first series-connected circuit consisting of the battery, one of the detection resistances, and an insulation member on a negative electrode side of the battery that comes into electrical contact with the negative electrode of the battery, and (2) an insulation resistance of the insulation member on the negative electrode side is calculated based on a first voltage measured by the measurement circuit,

(ii) a second measurement mode in which (1) the first switch is turned off and the second switch is turned on to form a second series-connected circuit consisting of the battery, one of the detection resistances, and an insulation member on a positive electrode side of the battery that comes into electrical contact with the positive electrode of the battery, and (2) an insulation resistance of the insulation member on the positive electrode side is calculated based on a second voltage measured by the measurement circuit, and

(iii) a third measurement mode in which (1) the first switch and the second switch are turned off, and (2) an offset voltage is calculated based on a third voltage measured by the measurement circuit.

2. The battery voltage measurement circuit according to claim 1 , wherein

after switching from the one to the other of the measurement modes, the battery voltage measurement circuit detects the change in the voltage measured by the measurement circuit a plurality of times in a shorter period than a normal period.

3. The battery voltage measurement circuit according to claim 1 , wherein

when a change amount of the voltage measured by the measurement circuit before and after switching from the one to the other of the measurement modes is a predetermined change amount or less, the battery voltage measurement circuit invalidates detection results of failures of the capacitors.

4. The battery voltage measurement circuit according to claim 1 , wherein

when a change amount of the voltage measured by the measurement circuit before and after switching from the one to the other of the measurement modes is a predetermined change amount or less, the battery voltage measurement circuit does not detect failures of the capacitors.

5. The battery voltage measurement circuit according to claim 1 , wherein

when a time until the voltage measured by the measurement circuit stabilizes after switching from the one to the other of the measurement modes is a predetermined time or less, the battery voltage measurement circuit detects failures of the capacitors.

6. The battery voltage measurement circuit according to claim 1 , wherein

the measurement circuit includes a differential amplifier that differentially amplifies the first voltage and the second voltage.

7. The battery voltage measurement circuit according to claim 1 , wherein

the measurement circuit includes a first detector that detects the first voltage and a second detector that detects the second voltage.

8. The battery voltage measurement circuit according to claim 1 , further comprising a controller that controls the first switch and the second switch, wherein

the controller controls the first switch and the second switch to perform a plurality of measurement processes corresponding to the plurality of measurement modes and the controller detects failures of the capacitors based on the change in the voltage measured by the measurement circuit after switching from one to an other of the measurement processes.

9. The battery voltage measurement circuit according to claim 8 , wherein

the controller has at least two measurement processes of

(i) a first measurement process in which (1) the first switch is turned on and the second switch is turned off to form the first series-connected circuit consisting of the battery, one of the detection resistances, and the insulation member on the negative electrode side of the battery that comes into electrical contact with the negative electrode of the battery, and (2) the insulation resistance of the insulation member on the negative electrode side is calculated based on the first voltage measured by the measurement circuit,

(ii) a second measurement process in which (1) the first switch is turned off and the second switch is turned on to form the second series-connected circuit consisting of the battery, one of the detection resistances, and the insulation member on the positive electrode side of the battery that comes into electrical contact with the positive electrode of the battery, and (2) the insulation resistance of the insulation member on the positive electrode side is calculated based on the second voltage measured by the measurement circuit, and

(iii) a third measurement process in which (1) the first switch and the second switch are turned off, and (2) the offset voltage is calculated based on the third voltage measured by the measurement circuit.

10. The battery voltage measurement circuit according to claim 8 , wherein

after switching from the one to the other of the measurement processes, the controller detects the change in the voltage measured by the measurement circuit a plurality of times in a shorter period than a normal period.

11. The battery voltage measurement circuit according to claim 8 , wherein

when a change amount of the voltage measured by the measurement circuit before and after switching from the one to the other of the measurement processes is a predetermined change amount or less, the controller invalidates detection results of the failures of the capacitors.

12. The battery voltage measurement circuit according to claim 8 , wherein

when a change amount of the voltage measured by the measurement circuit before and after switching from the one to the other of the measurement processes is a predetermined change amount or less, the controller does not detect the failures of the capacitors.

13. The battery voltage measurement circuit according to claim 8 , wherein

when a time until the voltage measured by the measurement circuit stabilizes after switching from the one to the other of the measurement processes is a predetermined time or less, the controller detects the failures of the capacitors.

14. The battery voltage measurement circuit according to claim 9 , wherein

the measurement circuit includes a differential amplifier that differentially amplifies the first voltage and the second voltage.

15. The battery voltage measurement circuit according to claim 9 , wherein

the measurement circuit includes a first detector that detects the first voltage and a second detector that detects the second voltage.

16. A failure detection method executed by a battery voltage measurement circuit that includes:

a first switch configured to be connected to a positive electrode of a battery;

a second switch configured to be connected to a negative electrode of the battery;

detection resistances that are connected in series between the first switch and the second switch;

capacitors that are connected in parallel to the detection resistances;

a measurement circuit that measures a voltage applied to the detection resistances; and

a controller that controls the first switch and the second switch, the method comprising the steps of:

(a) performing, by the controller, at least two measurement processes of

(i) a first measurement process in which (1) the first switch is turned on and the second switch is turned off to form a first series-connected circuit consisting of the battery, one of the detection resistances, and an insulation member on a negative electrode side of the battery that comes into electrical contact with the negative electrode of the battery, and (2) an insulation resistance of the insulation member on the negative electrode side is calculated based on a first voltage measured by the measurement circuit,

(ii) a second measurement process in which (1) the first switch is turned off and the second switch is turned on to form a second series-connected circuit consisting of the battery, one of the detection resistances, and an insulation member on a positive electrode side of the battery that comes into electrical contact with the positive electrode of the battery, and (2) an insulation resistance of the insulation member on the positive electrode side is calculated based on a second voltage measured by the measurement circuit, and

(iii) a third measurement process in which (1) the first switch and the second switch are turned off, and (2) an offset voltage is calculated based on a third voltage measured by the measurement circuit; and

(b) detecting, by the controller, failures of the capacitors based on a change in the voltage measured by the measurement circuit after switching from one to an other of the measurement processes.