Hall-effect sensor signal offset correction in phase commutation

1. A method of operating a final drive unit clutch, comprising:

providing an electric motor coupled with a clutch, said electric motor including:

a stator;

a first Hall-effect sensor coupled with said stator;

a second Hall-effect sensor coupled with said stator;

a third Hall-effect sensor coupled with said stator; and

a rotor having at least one magnetic pole pair;

providing a controller in electrical communication with said electric motor;

determining a first ideal commutation point;

calculating a first offset of a first Hall-effect sensor state change from said first ideal commutation point; and

calculating a time delay of commutation utilizing said first offset such that a second Hall-effect sensor state change corresponds with a second ideal commutation point; wherein said clutch is transitioning between a non-torque transmitting position and a torque transmitting position.

2. The method of operating said final drive unit clutch according to claim 1 , wherein determining at least one of said first and second ideal commutation points comprises:

calculating a first back-EMF crossing and a consecutive second back-EMF crossing from three measured phase voltages; and

determining a predetermined number of degrees between said first and second back-EMF crossings.

3. The method of operating said final drive unit clutch according to claim 2 , wherein:

at least one of said first and second back-EMF crossings is calculated utilizing three measured phase voltages at an end of said first Hall-effect sensor state change a predetermined number of times.

4. The method of operating said final drive unit clutch according to claim 2 , wherein:

at least one of said first and second back-EMF crossings is calculated utilizing one measured phase voltage and a DC-link voltage at the end of said first Hall-effect sensor state change a predetermined number of times.

5. The method of operating said final drive unit clutch according to claim 2 , wherein:

said predetermined number of degrees between said first and second back-EMF crossings is thirty degrees.

6. The method of operating said final drive unit clutch according to claim 2 , wherein calculating said first offset comprises:

calculating a difference by subtracting a time of said first Hall-effect sensor state change from a time of said second back-EMF crossing;

calculating a product by multiplying said difference by a speed of an output of said electric motor; and

subtracting thirty rotational degrees from said product.

7. The method of operating said final drive unit clutch according to claim 2 , wherein calculating said first offset comprises:

calculating a difference by subtracting a time of said first consecutive back-EMF crossing from said first Hall-effect sensor state change;

calculating a product by multiplying said difference by a speed of an output of said electric motor; and

subtracting said product from thirty rotational degrees.

8. The method of operating said final drive unit clutch according to claim 1 , wherein calculating a time delay of commutation comprises:

determining said first offset has a negative value;

determining a second offset has a negative value;

calculating a difference by subtracting an absolute value of said first offset from sixty rotational degrees;

calculating a quotient by dividing said difference by a speed of an output of said electric motor; and

adding said quotient to said time of said first Hall-effect sensor state change.

9. The method of operating said final drive unit clutch according to claim 1 , wherein calculating a time delay of commutation comprises:

determining said first offset has a positive value;

determining a second offset has a negative value;

calculating a sum by adding said first offset to sixty rotational degrees;

calculating a quotient by dividing said sum by a speed of an output of said electric motor; and

adding said quotient to said time of said first Hall-effect sensor state change.

10. The method of operating said final drive unit clutch according to claim 1 , wherein calculating a time delay of commutation comprises:

determining said first offset has a positive value;

determining a second offset has a positive value;

calculating a quotient by dividing said first offset by a speed of an output of said electric motor; and

adding said quotient to said time of said first Hall-effect sensor state change.

11. A method of operating a final drive unit clutch, comprising:

providing an electric motor coupled with a clutch, said electric motor including:

a stator;

a first Hall-effect sensor coupled with said stator;

a second Hall-effect sensor coupled with said stator;

a third Hall-effect sensor coupled with said stator; and

a rotor having at least one magnetic pole pair;

providing a controller in electrical communication with said electric motor;

determining a first ideal commutation point;

calculating a first offset of a first Hall-effect sensor state change from said first ideal commutation point;

calculating a first time delay of commutation utilizing said first offset such that a second Hall-effect sensor state change corresponds with a second ideal commutation point;

determining said second ideal commutation point;

calculating a second offset of said second Hall-effect sensor state change from said second ideal commutation point;

calculating a second time delay of commutation utilizing said second offset such that a third Hall-effect sensor state change corresponds with a third ideal commutation point;

determining said third ideal commutation point;

calculating a third offset of said third Hall-effect sensor state change from said third ideal commutation point; and

calculating a third time delay of commutation utilizing said third offset such that a fourth Hall-effect sensor state change corresponds with a fourth ideal commutation point;

wherein said clutch is transitioning between a non-torque transmitting position and a torque transmitting position.