Battery state of charge indicator

• US 6,556,020 B1
• Filed: 04/02/2002
• Issued: 04/29/2003
• Est. Priority Date: 04/02/2002
• Status: Active Grant

• Current Assignee: The Raymond Corporation (Toyota Motor Corporation)
• Original Assignee: The Raymond Corporation (Toyota Motor Corporation)
• Inventors: McCabe, Paul Patrick, Baldini, Augustus R., Harvey, Dean, Driscall, Daniel Robert
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US10/115,107
• Time in Patent Office: 392 Days
• Field of Search: 320/132, 320/149, 324/426, 324/427, 324/430, 324/433, 324/434
• US Class Current: 324/426
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

A state-of-charge indicator system monitors the battery current and voltage during operation of a lift truck. Selected current and voltage samples are used to calculate the internal battery resistance and this is employed to calculate a “dynamic” battery voltage. This dynamic battery voltage is used as input to a stored look-up table which provides a battery state-of-charge value.

Claims

1. A state-of-charge indicator system for a battery which comprises:

a voltage sampling circuit coupled to the battery to measure its voltage;

a current sampling circuit coupled to the battery to measure its current;

battery resistance calculations means coupled to the voltage and current sampling circuits and being operable to calculate a battery resistance value (R_battery) based on a change in measured battery current and the corresponding change in battery voltage;

dynamic voltage calculation means for receiving measured battery current (1) and voltage (V) and calculated battery resistance (R_battery) and calculating a dynamic battery voltage

2. The system as recited in claim 1 in which the battery is a lead-acid battery and the means for converting is a look-up table stored in a memory.

3. The system as recited in claim 1 which includes:

means for detecting a selected change in battery current and in response thereto, enabling the battery resistance calculation means to calculate the battery resistance value.

4. The system as recited in claim 3 in which the battery is a lead-acid battery and the means for converting is a look-up table stored in a memory.

5. The system as recited in claim 1 in which the voltage and current sampling circuits measure battery voltage and battery current periodically while the battery is being used to power a device and the system further includes:

means for detecting a selected change in battery current event which occurs during successive measured current samples I_n and I_n+1 and storing said successive current samples I_n and I_n+1 and the corresponding measured battery voltage samples V_n and V_n+1; and

the battery resistance calculation means calculates the battery resistance value (R_battery) from said stored samples;

6. The system as recited in claim 5 which includes:

a memory for storing battery current and voltage samples from a set of detected battery current events along with the corresponding calculated battery resistance values R_(battery); and

means for averaging the stored battery resistance values for use by the dynamic voltage calculation means.

7. The system as recited in claim 6 which includes:

means for storing in the memory the dynamic battery voltage value calculated for each detected current event; and

the means for converting includes means for calculating an average dynamic battery voltage from dynamic battery voltage values stored in the memory.

8. The system as recited in claim 7 in which the battery is a lead-acid battery and the means for converting includes a look-up table stored in the memory which relates dynamic battery voltages to state-of-charge values.

9. A method for indicating the state-of-charge of a battery connected to a variable load, the steps comprising:

periodically sampling the battery voltage V;

periodically sampling the battery current I;

detecting a battery current change event in which the sampled battery current changes a preselected amount during successive samples I_n and I<sub>n−

1</sub>;

calculating a battery resistance value

10. The method as recited in claim 9 in which the dynamic voltage is converted to a battery state-of-charge value by looking up in a stored table the battery state-of-charge value which corresponds to the dynamic voltage value.

11. The method as recited in claim 9 in which the variable load is a lift truck and the method includes:

displaying the state-of-charge value to a lift truck operator.

12. The method as recited in claim 9 which includes:

storing successively calculated battery resistance values; and

averaging the stored battery resistance values and using the resulting average battery resistance value to calculate the dynamic battery voltage.

13. The method as recited in claim 9 which includes:

storing successively calculated dynamic battery voltage values; and

averaging the stored dynamic battery voltage values and using the resulting average dynamic battery voltage to determine the battery state-of-charge value.