METHOD OF IMPROVING FUEL ECONOMY

• US 20040189254A1
• Filed: 03/11/2003
• Published: 09/30/2004
• Est. Priority Date: 03/11/2003
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Zhao, Yaang, Walters, David W., Kapsokavathis, Nick S.
• Granted Patent: US 6,809,501 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: B60W 10/06 including control of combustion engines
• CPC Class Codes: B60W 10/26 for electrical energy, e.g. batteries or capacitors
• CPC Class Codes: B60W 10/30 including control of auxiliary equipment, e.g. air-conditioning compressors or oil pumps
• CPC Class Codes: B60W 2510/244 Charge state
• CPC Class Codes: B60W 2510/246 Temperature
• CPC Class Codes: B60W 2510/305 Power absorbed by auxiliaries
• CPC Class Codes: B60W 2520/10 Longitudinal speed
• CPC Class Codes: B60W 2555/20 Ambient conditions, e.g. wind or rain
• CPC Class Codes: B60W 2710/244 Charge state
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/371 with remote indication, e.g. on external chargers
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H02J 7/1469 Regulation of the charging current or voltage otherwise than by variation of field

Abstract

A fuel economy control method includes estimating a temperature of a battery, measuring a current of the battery, and measuring a voltage of the battery. A nominal optimum charging voltage is determined as a function of a state of charge (SOC) of the battery and the estimated temperature. The nominal optimum charging voltage is reduced to a fuel economy minimum charging voltage if the SOC is above a predetermined level and the current is within a predetermined range.

Claims

1. A fuel economy control method comprising:

measuring current supplied by a battery;

determining a state of charge (SOC) of said battery;

determining a nominal optimum charging voltage of said battery; and

reducing said nominal optimum charging voltage to a fuel economy minimum charging voltage if said SOC is above a predetermined level and said current is within a predetermined range.

2. The method of claim 1 wherein said predetermined level is approximately 80%.

3. The method of claim 1 wherein said predetermined range is between −

8 A and 15 A.

4. The method of claim 1 wherein said step of reducing is performed if an outside air temperature is within a first temperature range, a vehicle speed is less than a predetermined speed, and an accessory is off.

5. The method of claim 4 wherein said accessory is headlamps.

6. The method of claim 1 wherein said nominal optimum charging voltage is based on said SOC.

7. The method of claim 1 further comprising:

estimating a temperature of said battery; and

measuring a voltage of said battery, wherein said SOC is based upon said temperature, said voltage, and said current.

8. The method of claim 1 further comprising:

converting said fuel economy minimum charging voltage to a % duty cycle; and

charging said battery at said fuel economy minimum charging voltage using a generator based on said % duty cycle.

9. The method of claim 8 further comprising:

determining a difference between said current and a predetermined current value; and

adjusting said % duty cycle until said current is equal to said predetermined current value.

10. The method of claim 8 further comprising:

converting said % duty cycle to a pulse-width modulated (PWM) % duty cycle; and

operating said generator based on said PWM % duty cycle.

11. The method of claim 1 wherein reducing said nominal optimum charging voltage is achieved at a rate of 0.05V/s.

12. The method of claim 1 wherein determining said nominal optimum charging voltage includes:

determining a running SOC of said battery;

interpolating a value of said nominal optimum charging voltage based on said running SOC and said temperature.

13. The method of claim 12 wherein interpolating is based upon a plurality of calibration constants.

14. The method of claim 12 further comprising determining said running SOC as a function of a start-up SOC, an adjusted amp-hours of said battery and battery capacity.

15. The method of claim 14 wherein said start-up SOC is determined using a look-up table that is accessed using an estimated temperature of said battery and a last stored open-circuit voltage.

16. The method of claim 14 wherein said start-up SOC is determined as a function of a plurality of start-up calibration constants, wherein at least one of said start-up calibrations constants is dependent upon an estimated temperature of said battery.

17. A fuel economy control method, comprising:

estimating a temperature of a battery;

measuring current supplied by said battery;

measuring a voltage of said battery;

determining a nominal optimum charging voltage as a function of a state of charge (SOC) of said battery and said estimated temperature; and

reducing said nominal optimum charging voltage to a fuel economy minimum charging voltage if said SOC is above a predetermined level and said current is within a predetermined range.

18. The method of claim 17 further comprising:

converting said nominal optimum charging voltage to a % duty cycle; and

charging said battery using a generator based on said % duty cycle.

19. The method of claim 18 further comprising:

determining a difference between said current and a predetermined current value; and

adjusting said % duty cycle to until said current is equal to said predetermined current value.

20. The method of claim 18 further comprising:

converting said % duty cycle to a pulse-width modulated (PWM) % duty cycle; and

operating said generator based on said PWM % duty cycle.

21. The method of claim 17 wherein said predetermined level is 80%.

22. The method of claim 17 wherein said predetermined range is between −

8 A and 15 A.

23. The method of claim 17 wherein said reducing step is performed if an outside air temperature is within a first temperature range, a vehicle speed is less than a predetermined speed, and an accessory is off.

24. The method of claim 23 wherein said accessory is headlamps.

25. The method of claim 17 wherein said nominal optimum charging voltage is based on said SOC.

26. The method of claim 17 wherein reducing said nominal optimum charging voltage is achieved at a rate of 0.05V/s.

27. The method of claim 17 wherein determining said nominal optimum charging voltage includes:

determining a running SOC of said battery;

interpolating a value of said nominal optimum charging voltage based on said running SOC and said temperature.

28. The method of claim 27 wherein interpolating is based upon a plurality of calibration constants.

29. The method of claim 27 further comprising determining said running SOC as a function of a start-up SOC, an adjusted amp-hours of said battery and a battery capacity.

30. The method of claim 29 wherein said start-up SOC is determined using a look-up table that is accessed based on an estimated temperature of said battery and a last stored open-circuit voltage.

31. The method of claim 29 wherein said start-up SOC is based on a plurality of start-up calibration constants and an estimated temperature of said battery.

32. A method of protecting a battery from sulfation, comprising:

estimating a temperature of a battery;

determining a nominal optimum charging voltage as a function of a state of charge (SOC) of said battery and said estimated temperature;

comparing said nominal optimum charging voltage to a threshold value; and

increasing said nominal optimum charging voltage to above said threshold value if below said threshold value for a first predetermined period of time.

33. The method of claim 32 wherein said threshold value is 13.2V.

34. The method of claim 32 wherein said first predetermined period is 30 minutes.

35. The method of claim 32 further comprising holding said nominal optimum charging voltage above said threshold level for at least a second predetermined period of time.

36. The method of claim 35 wherein said second predetermined period of time is 3 minutes.

37. The method of claim 32 wherein said increasing occurs at a rate of 0.05V/s.