Battery state judging method, and battery state judging apparatus
A battery state judging method is provided capable of properly judging a state of a lead-acid battery by measuring voltages without measuring currents. A state of the battery is judged by obtaining, in advance, a DC internal resistance r 0 of a same type battery in a new and fully-charged state; calculating, in advance, a load R [R=r 0 ×Vst 0 /(OCV 0 −Vst 0 )] at an engine starting time (S 112 ) from an open-circuit voltage OCV 0 (S 104 ) and a lowest voltage Vst 0 (S 108 ) at the engine starting time, both measured when the loaded battery is in a new and fully-charged state, and the DC internal resistance r 0 ; calculating a DC internal resistance r [(r=R/(OCV−Vst)/Vst)] of the loaded battery from an open-circuit voltage OCV (S 104 ) and a lowest voltage Vst (S 108 ), both measured when the loaded battery is in a deteriorated/insufficiently-charged state, and the load R; and comparing r and r 0 .
1. A battery state judging method of a lead-acid battery loaded on a vehicle, comprising the steps of:
obtaining, in advance, a DC internal resistance r 0 of a lead-acid battery in a substantially non-deteriorated and fully-charged state;
calculating, in advance, a load R imposed at an engine starting time, using a following Equation (1), from an open-circuit voltage OCV 0 and a lowest voltage Vst 0 at the engine starting time, both measured when the lead-acid battery is in a substantially non-deteriorated and fully-charged state, and the DC internal resistance r 0 ;
calculating a DC internal resistance r of the lead-acid battery, using a following Equation (2), from an open-circuit voltage OCV and a lowest voltage Vst at an engine starting time, both measured when the lead-acid battery is in a deteriorated or insufficiently-charged state, and the calculated load R imposed at the engine starting time; and
judging a state of the lead-acid battery by comparing the DC internal resistance r with the DC internal resistance r 0 ;
R=r 0 ×Vst 0 /( OCV 0 −Vst 0 ) (1)
r=R ×( OCV−Vst )/ Vst (2).
2. The battery state judging method according to claim 1 , wherein, in the step of judging a state of the lead-acid battery, a deteriorated state judging coefficient alpha represented as a value of the DC internal resistance r to that of the DC internal resistance r 0 is calculated, and a state of health (SOH) of the lead-acid battery is calculated from a predetermined correspondence relationship between a deteriorated state judging coefficient alpha and a SOH of the lead-acid battery.
3. The battery state judging method according to claim 2 , wherein, in the step of judging a state of the lead-acid battery, it is judged that replacement of the lead-acid battery is required when the deteriorated state judging coefficient alpha represented as a value of the DC internal resistance r to that of the DC internal resistance r 0 is not less than a predetermined value.
4. A battery state judging apparatus that judges a state of a lead-acid battery loaded on a vehicle, comprising:
a storing means which stores, in advance, a DC internal resistance r 0 of a lead-acid battery obtained in a substantially non-deteriorated and fully-charged state;
an open-circuit voltage measuring means which measures an open-circuit voltage of the lead-acid battery;
a lowest voltage measuring means which measures a lowest voltage at an engine starting time of the lead-acid battery;
a load calculating means which calculates a load R imposed at an engine starting time, using a following Equation (1), from an open-circuit voltage OCV 0 measured by the open-circuit voltage measuring means and a lowest voltage Vst 0 at the engine starting time measured by the lowest voltage measuring means, both measured when the lead-acid battery is in a substantially non-deteriorated and fully-charged state, and the DC internal resistance r 0 stored in the storing means;
a DC internal resistance calculating means which calculates a DC internal resistance r of the lead-acid battery, using a following Equation (2), from an open-circuit voltage OCV measured by the open-circuit voltage measuring means and a lowest voltage Vst at an engine starting time measured by the lowest voltage measuring means, both measured when the lead-acid battery is in a deteriorated or insufficiently-charged state, and the load R imposed at the engine starting time calculated by the load calculating means; and
a state judging means which judges a state of the lead-acid battery by comparing the DC internal resistance r calculated by the DC internal resistance calculating means with the DC internal resistance r 0 stored in the state storing means;
R=r 0 ×Vst 0 /( OCV 0 −Vst 0 ) (1)
r=R ×( OCV−Vst )/ Vst (2).
5. The battery state judging apparatus according to claim 4 , wherein the storing means further stores, in advance, a map or expression showing a correspondence relationship between a deteriorated state judging coefficient alpha represented as a value of the DC internal resistance r to that of the DC internal resistance r 0 and a SOH of the lead-acid battery, and wherein the state judging means calculates the deteriorated state judging coefficient alpha, and calculates the SOH from the correspondence relationship between a deteriorated state judging coefficient alpha and a SOH of the lead-acid battery according to the map or expression stored in the storing unit.
6. The battery state judging apparatus according to claim 5 , wherein the state judging means judges that replacement of the lead-acid battery is required when the deteriorated state judging coefficient alpha represented as a value of the DC internal resistance r to that of the DC internal resistance r 0 is not less than a predetermined value.
7. The battery state judging apparatus according to claim 5 , wherein the load calculating means makes the storing means store the calculated load R imposed at the engine starting time, and wherein the DC internal resistance calculating means calculates the DC internal resistance r of the lead-acid battery, using the Equation (2), from the open-circuit voltage OCV measured by the open-circuit voltage measuring means and the lowest voltage Vst at the engine starting time measured by the lowest voltage measuring means, both measured when the lead-acid battery is in a deteriorated or insufficiently-charged state, and the load R imposed at the engine starting time calculated by the load calculating means.
8. The battery state judging apparatus according to claim 7 , wherein the storing unit is a nonvolatile memory.
9. The battery state judging apparatus according to claim 4 , wherein the DC internal resistance r 0 stored in the storing means is obtained from a relationship equation of V=−r 0 ×I+OCV 0 standing up between a voltage V and a current I, which holds when a lead-acid battery (open-circuit voltage OCV 0 ) in a non-deteriorated and fully-charged state of the same type as the lead-acid battery loaded on the vehicle is discharged at a plurality of current values.
10. The battery state judging apparatus according to claim 4 , wherein the load calculating means judges, when the number of times of the engine starting is less than 5 and the open-circuit voltage OCV 0 exceeds 12.5V, that the lead-acid battery is in the substantially non-deteriorated and fully-charged state and calculates the load R imposed at the engine starting time.