Battery capacity calculating method and device therefor

• US 6,661,231 B1
• Filed: 10/09/2001
• Issued: 12/09/2003
• Est. Priority Date: 10/08/1999
• Status: Expired due to Fees

• Current Assignee: Yazaki Corporation
• Original Assignee: Yazaki Corporation
• Inventors: Arai, Youichi, Saigo, Tsutomu, Kamohara, Hideaki
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/856,467
• Time in Patent Office: 791 Days
• Field of Search: 324/426, 324/427, 324/430, 324/433, 320/132, 320/149, 340/635, 340/636, 429/61, 429/90
• US Class Current: 324/426
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

A method and apparatus are provided, by which a state of charge of a battery is accurately computed without being influenced by the polarization effect. An estimated voltage of the battery 13 in a constant load discharge with a predetermined large current value is estimated from a voltage-current characteristic when the discharge current of the constant load discharging process by the battery 13 that is in an equilibrium state is decreasing from the predetermined large current value corresponding to a maximum supplying electric power to the load. A difference between the estimated voltage and an open circuit voltage, which estimates the estimated voltage and is a terminal voltage of the battery 13 that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value, is calculated. Then, the difference is memorized by first memory means 27 for memorizing a residual voltage drop defining as the residual voltage drop due to a residual polarization at the end of the discharging process of the battery 13. The residual voltage drop memorized by the first memory means 27 is added to the estimated voltage of the battery 13, thereby a present charging capacity of the battery 13 is computed.

Claims

1. A method for computing a battery capacity comprising the steps of:

periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;

calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;

estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and

computing a charging capacity of the battery from the estimated voltage,

wherein a value of the estimated voltage of the battery in the constant load discharge with a predetermined large current value is estimated from the voltage-current characteristic when the discharge current of the constant load discharging process by the battery that is in an equilibrium state is decreasing from the predetermined large current value corresponding to a maximum supplying electric power value to the loads,

a difference value between the value of the estimated voltage and a value of an open circuit voltage, which estimates the value of the estimated voltage and is a terminal voltage of the battery that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value, is calculated in advance as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery,

thereafter, whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured during the constant load discharge by using the predetermined large current value,

a present estimated voltage of the battery is estimated from the voltage-current characteristic, and

the value of the residual voltage drop is added to a value of the present estimated voltage of the battery, thereby a present charging capacity of the battery is computed.

2. The method for computing a battery capacity according to claim 1, wherein a value of the terminal voltage of the battery in an equilibrium state is measured in advance so as to set up the measured value as a value of the open circuit voltage,

then, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process is decreasing from the predetermined large current value when the buttery in an equilibrium state is subjected to the constant load discharge by using the predetermined large current value,

then, the estimated voltage of the battery upon the constant load discharge by using the predetermined large current value starting from the equilibrium state is estimated from the voltage-current characteristic, and

then, a value of the estimated voltage of the battery upon the constant load discharge by using the predetermined large current value starting from the equilibrium state is subtracted from the value of the set open circuit voltage, thereby the value of the residual voltage drop is calculated in advance.

3. The method for computing a battery capacity according to claim 2, wherein whenever the battery reaches an equilibrium state, the value of the open circuit voltage is newly replaced by a value of the terminal voltage of the battery, which is measured in the equilibrium state.

4. The method for computing a battery capacity according to claim 1, wherein whenever the battery is subjected to the constant load discharge by using the predetermined large current value, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage of the battery is estimated from the voltage-current characteristic.

5. The method for computing a battery capacity according to claim 1, wherein the predetermined large current value is set to be a current value required upon starting a starter motor of the vehicle, and the voltage-current characteristic is calculated from the terminal voltage and the discharge current, which are periodically measured while the value of the discharge current decreases to a target current value that is smaller than the predetermined large current value and not less than a maximum discharge current value when loads of the vehicle except the starter motor are driven, after the value of the discharge current starts to decrease from the predetermined large current value.

6. The method for computing a battery capacity according to claim 1, wherein whenever the estimated voltage of the battery is estimated upon the constant load discharge by using the predetermined large current value, the value of the residual voltage drop is revised in response to a circumferential temperature of the battery upon the estimation of the estimated voltage and a circumferential temperature of the battery upon the calculation of the open circuit voltage, and the present charging capacity of the battery is computed from the revised value of the residual voltage drop.

7. A method for computing a battery capacity comprising the steps of:

periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;

calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;

estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and

computing a charging capacity of the battery from the estimated voltage,

wherein whenever the battery is subjected to the constant load discharge by using the predetermined large current value corresponding to a maximum supplying electric power value to the loads, the voltage-current characteristic is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the discharge current of the constant load discharging process by using the predetermined large current value is decreasing from the predetermined large current value, thereby the present estimated voltage Vn of the battery is estimated from the voltage-current characteristic.

8. The method for computing a battery capacity according to claim 7, wherein the predetermined large current value is set to be a current value required upon starting a starter motor of the vehicle.

9. The method for computing a battery capacity according to claim 8, wherein the voltage-current characteristic is calculated from the terminal voltage and the discharge current, which are periodically measured while the value of the discharge current decreases to a target current value that is smaller than the predetermined large current value and not less than a maximum discharge current value when loads of the vehicle except the starter motor are driven.

13. The apparatus for computing a battery capacity according to claim 9, further comprising:

measuring means for measuring the terminal voltage of the battery, which is judged to be in an equilibrium state by the judging means; and

replacing means for replacing the value of the open circuit voltage memorized by the second memory means with a value of the terminal voltage of the battery measured by the measuring means.

14. The apparatus for computing a battery capacity according to claim 13, further comprising:

second detecting means for detecting a circumferential temperature of the battery; and

revising means for revising the value of the residual voltage drop memorized by the first memory means in response to the circumferential temperature of the battery detected by the second detecting means when the estimating means estimates the estimated voltage of the battery and the circumferential temperature of the battery detected by the second detecting means when the measuring means measures the terminal voltage of the battery,

wherein the revised value of the residual voltage drop revised by the revising means is added to the value of the estimated voltage of the battery estimated by the estimating means, thereby a present charging capacity of the battery is computed.

10. An apparatus for computing a battery capacity executing the steps of:

periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle when the battery is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;

calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;

estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and

computing a charging capacity of the battery from the estimated voltage,

wherein the apparatus comprises first memory means for memorizing a difference value as a value of a residual voltage drop due to a residual polarization at the end of the discharge process of the battery, said difference value being a difference value between a value of the estimated voltage and a value of an open circuit voltage,

in which the value of the estimated voltage of the battery in the constant load discharge with a predetermined large current value is estimated from the voltage-current characteristic when the discharge current of the constant load discharging process by the battery that is in an equilibrium state is decreasing from the predetermined large current value, and

the open circuit voltage estimates the value of the estimated voltage and is a terminal voltage of the battery that is in an equilibrium state before the start of the constant load discharge by using the predetermined large current value,

and wherein the value of the residual voltage drop memorized by the first memory means is added to the value of the estimated voltage of the battery, thereby a present charging capacity of the battery is computed.

11. The apparatus for computing a battery capacity according to claim 10, further comprising:

first detecting means for detecting a start of a decrease in the discharge current from the predetermined large current value in the constant load discharge process of the battery by using the predetermined large current value;

first calculating means for calculating the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery after the first detecting means detects the start of the decrease in the discharge current; and

estimating means for estimating the estimated voltage of the battery in the constant load discharge process of the battery by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means,

wherein the value of the residual voltage drop memorized by the first memory means is added to a value of the estimated voltage of the battery estimated by the estimating means, thereby a present charging capacity of the battery is computed.

12. The apparatus for computing a battery capacity according to claim 11, further comprising:

second memory means for memorizing the value of the open circuit voltage;

judging means for judging whether the battery is in an equilibrium state or not; and

second calculating means for calculating the value of the residual voltage drop by subtracting the estimated voltage estimated by the estimating means from the value of the open circuit voltage memorized by the second memory means in the constant load discharge process of the battery, which is judged to be in an equilibrium state by the judging means, by using the predetermined large current value,

wherein the first memory means memorizes the value of the residual voltage drop calculated by the second calculating means.

15. The apparatus for computing a battery capacity according to claim 11, wherein the predetermined large current value is a current value required upon a start of a starter motor of the vehicle,

the apparatus further comprises third detecting means for detecting that the discharge current of the battery, which is detected by the first detecting means as to start decreasing from the predetermined large current value, decreases to a target current value not less than a maximum discharge current value when loads of the vehicle except a starter motor are driven,

wherein after the first detecting means detects that the discharge current of the battery starts to decrease from the predetermined large current value, the first calculating means calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery until the third detecting means detects that the discharge current of the battery decreases to the target current value.

16. An apparatus for computing a battery capacity executing the steps of:

periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle when the battery is subjected to a constant load discharge by using a predetermined large current value corresponding to a maximum supplying electric power value to the loads;

calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;

estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and

computing a charging capacity of the battery from the estimated voltage,

wherein the apparatus comprises;

first detecting means for detecting a start of a decrease in the discharge current from the predetermined large current value in the constant load discharge process of the battery by using the predetermined large current value;

first calculating means for calculating the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery after the first detecting means detects the start of the decrease in the discharge current; and

estimating means for estimating the estimated voltage of the battery in the constant load discharge process of the battery by using the predetermined large current value, on the basis of the voltage-current characteristic calculated by the first calculating means,

thereby the charging capacity of the battery is computed by using the estimated voltage of the battery estimated by the estimating means.

17. The apparatus for computing a battery capacity according to claim 16, wherein the predetermined large current value is a current value required upon a start of a starter motor of the vehicle.

18. The apparatus for computing a battery capacity according to claim 17, further comprising third detecting means for detecting that the discharge current of the battery, for which the first detecting means detects that the discharge current starts decreasing from the predetermined large current value, decreases to a target current value not less than a maximum discharge current value when loads of the vehicle except a starter motor are driven,

wherein after the first detecting means detects that the discharge current of the battery starts to decrease from the predetermined large current value, the first calculating means calculates the voltage-current characteristic from the periodically measured terminal voltage and the discharge current of the battery until the third detecting means detects that the discharge current of the battery decreases to the target current value.