Arrangement for determining an initial internal battery temperature

1. A method of estimating en initial value for an internal temperature of a vehicle battery using a program controlled engine control unit and a program controlled automatic calibration tool, the method comprising:

using the engine control unit to determine which of a predetermined set of time zones correlates with a measured period of time for an engine of the vehicle being in an engine-off condition, wherein the time zones are categorized as four different possible time zones comprising a holding time zone, a model based estimation time zone which is greater in time than the holding time zone, a first self-adjustment time zone which is greater in time than the model based estimation time zone, and a second self-adjustment time zone which is greater in time than the first self-adjustment time zone;

using the automatic calibration tool to generate a set of parameters correlated with the determined time zone; and

using the engine control unit to determine an initial estimated value of the internal temperature of the battery as a function of the set of parameters.

2. The method of claim 1 wherein in the holding time zone, the initial temperature value is determined as a function of an internal battery temperature predicted at the time the engine is placed in the engine-off condition.

3. The method of claim 2 wherein the initial temperature value is equal to the internal battery temperature predicted at the time the engine is placed in the engine-off condition.

4. The method of claim 1 wherein in the model based estimation time zone, the initial temperature value is determined as a function of: battery temperature predicted at engine-off, coolant temperature measured at engine-off, ambient temperature measured at engine-off, coolant temperature measured at engine-on, and ambient temperature measured at engine-on, and time elapsed between engine-off and engine-on.

5. The method of claim 1 wherein in the first self-adjustment time zone, the initial temperature value is determined as a function of ambient temperature measured at engine-on, and charge air temperature measured at engine-on.

6. The method of claim 5 wherein the function comprises a two-dimensional polynomial in charge air temperature measured at engine-on and ambient temperature measured at engine-on.

7. The method of claim 5 wherein the function comprises a linear combination of charge air temperature measured at engine-on and ambient temperature measured at engine-on.

8. The method of claim 1 wherein in the second self-adjustment time zone, the initial temperature value is determined as a function of charge air temperature measured at engine-on.

9. The method of claim 8 wherein the initial temperature value is equal to the charge air temperature measured at engine-on.

10. The method of claim 1 wherein determining an initial estimated value of the internal temperature of the battery further comprises:

calibrating coefficients of an engine-off battery temperature model used during the model-based estimation time zone;

determining a time threshold defining a start of the second self-adjustment time zone using battery temperatures as measured by engine soak data or predicted by a calibrated engine-off battery temperature model; and

calibrating coefficients of a first self-adjustment time zone model used during the first self-adjustment time zone and a time threshold defining a start of the first self-adjustment time zone.

11. The method of claim 10 wherein the coefficients of the engine-off battery temperature model are calibrated by:

forming a model input vector and a model coefficient vector;

selecting a model error function of measured battery temperature and predicted battery temperature; and

choosing the coefficients which minimize the model error function.

12. The method of claim 10 wherein the time threshold defining the start of the second self-adjustment time zone is determined by:

selecting an error function of a difference between battery temperature, as measured from engine soak data or predicted by the calibrated engine-off battery temperature model, and battery temperature predicted by a function of charge air temperature measured at engine-on; and

selecting the time threshold defining the start of the second self-adjustment time zone which minimizes the error function.

13. The method of claim 10 wherein the coefficients of the first self-adjustment time zone model and the time threshold defining a start of the first self-adjustment time zone are determined by:

forming a model input vector and model coefficient vector;

selecting a model error function of a difference between battery temperature, based on engine soak data or predicted by the calibrated engine-off model, and battery temperature predicted by a function of ambient temperature measured at engine-on and charge air temperature measured at engine-on; and

selecting coefficients and the time threshold defining the start of the first self-adjustment time zone which minimize the error function.