Process for monitoring the residual charge and capacity of a battery

• US 6,329,823 B2
• Filed: 12/15/2000
• Issued: 12/11/2001
• Est. Priority Date: 12/16/1999
• Status: Expired due to Fees

• Current Assignee: Daimler AG (Mercedes-Benz Group AG)
• Original Assignee: Daimler Chrysler Company LLC (Stellantis NV)
• Inventors: Blessing, Alf, Schoner, Hans-Peter
• Primary Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US09/736,376
• Publication Number:
  US 20010020849A1
• Time in Patent Office: 361 Days
• Field of Search: 324/426, 324/427, 320/136, 712/63
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

Process for monitoring the residual charge and the capacity of a battery, where at least two voltage-current measurements have been carried out on the load-carrying battery. The current load of the battery selected here should be greater than 30% of the nominal capacity per hour, e.g. for a 100 Ah battery, at least 30 amperes. The initial voltage-current measurement is taken at an initial time for an initial load condition of the battery. A second voltage-current measurement is carried out at a second time for a second load condition of the battery. It is essential here that the load condition of the battery has changed because of the current that has been drawn. The current-voltage measurements produce an initial measuring point and a second measuring point. The two measuring points set an interpolation line and determine the point of intersection with a limiting voltage level (U_Gr). This point of intersection is marked by a so-called limiting current (I_Gr). The limiting voltage level is decided from the minimum voltage required by the connected consumers in order for them to operate fault-free. The limiting voltage level is therefore stipulated for the technical layout of the battery system and is known. Furthermore, fault-free operation of the connected consumers requires a minimum operating current (I_min), which is also specified and known as a design parameter of the battery system. The difference between the determined limiting current I_Gr and the minimum operating current I_min is determined and recorded. This difference is a dimension for the residual charge of the battery that is still available and in accordance with the invention is here designated as the limiting current reserve.

Claims

1. A process for monitoring the residual charge and the capacity of a load-carrying battery in a battery system with a limiting voltage level (U_Gr) and a minimum current (I_min) where:

at least at an initial time (T₁), at least an initial voltage-current-measurement is carried out for an initial load condition of the battery and at least an initial measuring point (M₁) is determined, at least at a second different time (T₂), at least a second voltage-current measurement is carried out for a second load condition of the battery and at least a second measuring point (M₂) is determined,

the measuring points (M₁ and M₂) are always determined at a load condition of the battery that is greater than 30% of the nominal capacity per hour (K_N/h),

the measuring points (M₁ and M₂) set a mean curve (3), and the point of intersection (S₃) of the mean curve with the limiting voltage level (U_Gr) is determined and the associated limiting current (I_Gr) is determined, and

the differences between the limiting current (I_Gr) and the minimum current (I_min) determines a limiting current reserve as the dimension for the residual charge available in the battery.

2. Process according to claim 1, wherein the mean curve is an interpolation line.

3. Process according to claim 1, wherein the mean curve is obtained by the measuring points (M₁ and M₂) from a large number of measuring points.

4. Process according to claim 3, wherein a mean straight line is set by the large number of measuring points.

5. Process according to claim 1, wherein the mean curve is decided by the continuous observation of the current-voltage characteristic and a mean straight line is decided by use of a state observer.

6. Process according to claim 5, wherein the state observer is a Lü

enberg observer or a Kalman filter.

7. Process according to claim 1, including adding the limiting voltage level (U_Gr) and the limiting current (I_Gr) to determine a dimension for a maximum output that can still be drawn from the battery without falling below the limiting voltage level (U_Gr).

8. Process according to claim 1, wherein a ratio is formed, as a dimension for the residual charge (Q_Rest) of the battery in relation to the nominal charge, from each relevant limiting current reserve and limiting current reserve for a fully-charged battery, at nominal conditions.

9. Process according to claim 1, wherein a ratio is formed, as a dimension for the residual charge (Q_Rest) of the battery, from the limiting current reserve and the maximum limiting current slope.

10. Process according to claim 8, wherein the residual charging time of the battery is determined from the residual charge (Q_Rest) of the battery by dividing it with the relevant load current.

11. Process according to claim 1, wherein it is carried out during the start operation of a vehicle.

12. Process according to claim 1, wherein the battery and battery system are in a vehicle and the load condition of the vehicle electrical system is altered by deliberate load changing, by switching powerful consumers in the vehicle electrical system on and off.

13. Process according to claim 1, wherein the battery and battery system are in a vehicle and the charging condition of the vehicle electrical system is deliberately altered by varying the generator voltage.

14. Process according to claim 1, wherein the battery and battery system are in a vehicle and the load condition of the vehicle electrical system is deliberately altered, both by altering the generator voltage and by switching powerful consumers on and off.