Temperature determination for transmission fluid in a vehicle

1. A transmission assembly for use in a vehicle, the assembly comprising:

a transmission configured to receive a transmission fluid;

a controller operatively connected to the transmission, the controller being configured to store a first look-up table defining respective warm-up calibration factors (F W ) for a respective first set of ambient temperatures;

wherein the controller has a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for determining a current temperature (T TF ) of the transmission fluid;

wherein the vehicle is keyed off at an initial time and then keyed on after a key-off time duration (t e ) from the initial time, the controller being deactivated when the vehicle is keyed off and activated when the vehicle is keyed on;

wherein execution of the instructions by the processor causes the controller to:

determine a key-on temperature (T TF key-on ) as a temperature of the transmission fluid when the vehicle was keyed on; and

determine the current temperature (T TF ) of the transmission fluid based at least partially on the first look-up table and the key-on temperature (T TF key-on ).

2. The assembly of claim 1 , wherein said determining the key-on temperature (T TF key-on ) includes:

determining if the key-off time duration (t e ) is greater than or equal to a threshold time;

proceeding to a first set of instructions if the key-off time duration (t e ) is greater than or equal to the threshold time and proceeding to a second set of instructions if the key-off time duration (t e ) is less than the threshold time.

3. The assembly of claim 2 , in combination with first and second electric machines, a main fluid pump and an auxiliary fluid pump each operatively connected to the transmission and defining respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ); and

wherein the second set of instructions includes calculating the key-on temperature (T TF key-on ) of the transmission fluid as a weighted average of the respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ) with respective weighting factors (V 1 , V 2 , V 3 , V 4 ) such that:

T TF key-on =V 1 *T M1 +V 2 *T M2 +V 3 *T MAIN PUMP +V 4 *T AUX PUMP .

4. The assembly of claim 2 , wherein the first set of instructions includes:

obtaining a key-off temperature (T TF key-off ) as a temperature of the transmission fluid when the vehicle was keyed off;

obtaining a current ambient temperature (T amb );

wherein the controller is configured to store a second look-up table defining respective cool-down calibration factors (F C1 , F C2 ) for a respective second set of ambient temperatures;

selecting the respective cool-down calibration factors (F C1 , F C2 ) at the current ambient temperature from the second look-up table;

determining the key-on temperature (T TF key-on ) based at least partially on the key-off temperature (T TF key-off ), the current ambient temperature (T amb ), the second look-up table and the key-off time duration (t e ).

5. The assembly of claim 4 , wherein said determining the key-on temperature (T TF key-on ) includes calculating the key-on temperature (T TF key-on ) as:

T TF key-on =T amb +( F C2 −T amb ) x /( T TF key-off −T amb ) x-1 , such that x=t e /F C1 .

6. The assembly of claim 4 , further comprising:

a transmission fluid temperature sensor operatively connected to the controller; and

wherein said obtaining the key-off temperature (T TF key-off ) includes setting a reading from the transmission fluid temperature sensor as the key-off temperature.

7. The assembly of claim 1 , wherein said determining the current temperature (T TF ) of the transmission fluid based at least partially on the first look-up table and the key-on temperature (T TF key-on ) includes:

obtaining a current ambient temperature (T amb );

obtaining the respective warm-up calibration factor (F W ) at the current ambient temperature from the first look-up table;

obtaining a change (ΔT COMP ) in a weighted average temperature (T COMP ) for a set of vehicle components at a second time (t 2 ) relative to a first time (t 1 ) such that ΔT COMP =T COMP (t 2 )−T COMP (t 1 ); and

calculating the current temperature (T TF ) as: T TF =T TF key-on +F W ΔT COMP .

8. The assembly of claim 7 , wherein the set of vehicle components includes a first and a second motor, a main fluid pump and an auxiliary fluid pump each operatively connected to the transmission and defining respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ); and

wherein the weighted average temperature (T COMP ) for the set of vehicle components includes respective weighting factors (W 1 , W 2 , W 3 , W 4 ) such that:

T COMP =W 1 *T M1 +W 2 *T M2 +W 3 *T MAIN PUMP +W 4 *T AUX PUMP .

9. The assembly of claim 8 , wherein the respective weighting factors (W 1 , W 2 , W 3 , W 4 ) are 30%, 30%, 20% and 20%.

10. A vehicle comprising:

a transmission configured to receive a transmission fluid;

a controller operatively connected to the transmission, the controller being configured to store a first look-up table defining respective warm-up calibration factors (F W ) for a respective first set of ambient temperatures;

wherein the controller has a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for determining a current temperature (T TF ) of the transmission fluid;

wherein the vehicle is keyed off at an initial time and then keyed on after a key-off time duration (t e ) from the initial time, the controller being deactivated when the vehicle is keyed off and activated when the vehicle is keyed on;

wherein execution of the instructions by the processor causes the controller to:

determine a key-on temperature (T TF key-on ) as a temperature of the transmission fluid when the vehicle was keyed on; and

determine the current temperature (T TF ) based at least partially on the first look-up table and the key-on temperature (T TF key-on ).

11. The vehicle of claim 10 , wherein said determining the key-on temperature (T TF key-on ) includes:

determining if the key-off time duration (t e ) is greater than or equal to a threshold time;

proceeding to a first set of instructions if the key-off time duration (t e ) is greater than or equal to the threshold time and proceeding to a second set of instructions if the key-off time duration (t e ) is less than the threshold time.

12. The vehicle of claim 11 , in combination with first and second electric machines, a main fluid pump and an auxiliary fluid pump each operatively connected to the transmission and defining respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ); and

wherein the second set of instructions includes calculating the key-on temperature (T TF key-on ) as a weighted average of the respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ) with respective weighting factors (V 1 , V 2 , V 3 , V 4 ) such that:

T TF key-on =V 1 *T M1 +V 2 *T M2 +V 3 *T MAIN PUMP +V 4 *T AUX PUMP .

13. The vehicle of claim 11 , wherein the first set of instructions includes:

obtaining a key-off temperature (T TF key-off ) as a temperature of the transmission fluid when the vehicle was keyed off;

obtaining a current ambient temperature (T amb );

wherein the controller is configured to store a second look-up table defining respective cool-down calibration factors (F C1 , F C2 ) for a respective second set of ambient temperatures;

selecting the respective cool-down calibration factors (F C1 , F C2 ) at the current ambient temperature from the second look-up table;

determining the key-on temperature (T TF key-on ) based at least partially on the key-off temperature (T TF key-off ), the current ambient temperature (T amb ), the second look-up table and the key-off time duration (t e ).

14. The vehicle of claim 10 , wherein said determining the current temperature (T TF ) of the transmission fluid based at least partially on the first look-up table and the key-on temperature (T TF key-on ) includes:

obtaining a current ambient temperature (T amb );

obtaining the respective warm-up calibration factor (F W ) at the current ambient temperature from the first look-up table;

obtaining a change (ΔT COMP ) in a weighted average temperature (T COMP ) for a set of vehicle components at a second time (t 2 ) relative to a first time (t 1 ) such that ΔT COMP =T COMP (t 2 )−T COMP (t 1 ); and

calculating the current temperature (T TF ) as: T TF =T TF key-on +F W ΔT COMP .

15. The vehicle of claim 14 , wherein the set of vehicle components includes a first and a second motor, a main fluid pump and an auxiliary fluid pump each being operatively connected to the transmission; and

wherein the weighted average temperature (T COMP ) for the set of vehicle components includes respective weighting factors (W 1 , W 2 , W 3 , W 4 ) such that:

T COMP =W 1 *T M1 +W 2 *T M2 +W 3 *T MAIN PUMP +W 4 *T AUX PUMP .

16. A method of determining a current temperature (T TF ) of a transmission fluid in a vehicle having a controller, the method comprising:

programming the controller with a first look-up table defining respective warm-up calibration factors (F W ) for a respective first set of ambient temperatures;

wherein the vehicle is keyed off at an initial time and then keyed on after a key-off time duration (t e ) from the initial time, the controller being deactivated when the vehicle is keyed off and activated when the vehicle is keyed on;

determining a key-on temperature (T TF key-on ) as a temperature of the transmission fluid when the vehicle was keyed on; and

determining the current temperature (T TF ) of the transmission fluid based at least partially on the first look-up table and the key-on temperature (T TF key-on ).

17. The method of claim 16 , wherein said determining the current temperature (T TF ) of the transmission fluid based at least partially on the first look-up table and the key-on temperature (T TF key-on ) includes:

obtaining a current ambient temperature (T amb );

obtaining the respective warm-up calibration factor (F W ) at the current ambient temperature from the first look-up table;

obtaining a change (ΔT COMP ) in a weighted average temperature (T COMP ) for a set of vehicle components at a second time (t 2 ) relative to a first time (t 1 ) such that ΔT COMP =T COMP (t 2 )−T COMP (t 1 ); and

calculating the current temperature (T TF ) as: T TF =T TF key-on +F W ΔT COMP .

18. The method of claim 17 , wherein the set of vehicle components includes a first and a second motor, a main fluid pump and an auxiliary fluid pump each operatively connected to the transmission and defining respective temperatures (T M1 , T M2 , T MAIN PUMP , T AUX PUMP ); and

wherein the weighted average temperature (T COMP ) for the set of vehicle components includes respective weighting factors (W 1 , W 2 , W 3 , W 4 ) such that:

T COMP =W 1 *T M1 +W 2 *T M2 +W 3 *T MAIN PUMP +W 4 *T AUX PUMP .