Vehicle drivetrain with interaxle differential and method for drivetrain operation

1. A drivetrain system, comprising:

an interaxle differential (IAD) configured to receive power from a prime mover;

a motor configured to drive a planetary gearset; and

a ball ramp actuator configured to selectively engage a plurality of plates in a clutch pack of a friction clutch in response to receiving rotational input from the planetary gearset;

wherein, in an engaged configuration, the friction clutch prevents speed differentiation between a first IAD output and a second IAD output;

wherein the first IAD output is coupled to a first axle differential and the second IAD output is coupled to a second axle differential; and

wherein the planetary gearset is non-backdrivable.

2. The drivetrain system of claim 1 , wherein the planetary gearset includes a sun gear coupled directly to the motor.

3. The drivetrain system of claim 2 , wherein the planetary gearset includes a ring gear with teeth on an outer surface that mesh with teeth in the ball ramp actuator.

4. The drivetrain system of claim 1 , further comprising a controller including instructions stored in non-transitory memory that when executed by a processor, during a first operating condition, cause the controller to:

automatically energize the motor and rotate the planetary gearset in a first rotational direction, wherein rotating the planetary gearset in the first rotational direction frictionally engages the plurality of plates in the clutch pack; and

de-energize the motor after the plurality of plates frictionally engage and lock the clutch pack.

5. The drivetrain system of claim 4 , wherein the controller includes instructions stored in the non-transitory memory that when executed by the processor, during a second operating condition, cause the controller to:

automatically energize the motor and rotate the planetary gearset in a second rotational direction, wherein rotating the planetary gearset in the second rotational direction frictionally disengages the plurality of plates in the clutch pack; and

de-energize the motor after the plurality of plates frictionally disengage and unlock the clutch pack.

6. The drivetrain system of claim 5 , wherein the first operating condition is a condition when a speed variance between the first and the second axle differentials exceeds a threshold value and the second operating condition is a condition where the speed variance is less than the threshold value.

7. The drivetrain system of claim 1 , wherein the planetary gearset is a two-stage planetary gearset.

8. The drivetrain system of claim 1 , wherein the first and second axle differentials are included in a tandem axle.

9. The drivetrain system of claim 1 , wherein the first and second axle differentials are non-steerable.

10. A method for operation of a drivetrain system, comprising:

automatically locking an interaxle differential (IAD) based on a speed variance between a first axle differential and a second axle differential;

wherein the IAD comprises:

a motor driving a self-locking planetary gearset; and

a ball ramp actuator selectively engaging a plurality of plates in a clutch pack of a friction clutch in response to receiving rotational input from the self-locking planetary gearset;

wherein, in an engaged configuration, the friction clutch prevents speed differentiation between a first output shaft and a second output shaft;

wherein the first output shaft is coupled to the first axle differential and the second output shaft is coupled to the second axle differential; and

wherein automatically locking the IAD includes:

rotating the self-locking planetary gearset in a first rotational direction through energization of the motor until the plurality of plates are frictionally engaged and speed differentiation between the first and second output shaft is prevented; and

after frictional engagement of the plurality of plates, de-energizing the motor.

11. The method of claim 10 , further comprising automatically unlocking the IAD based on a vehicle traction condition.

12. The method of claim 11 , wherein automatically unlocking the IAD includes:

rotating the self-locking planetary gearset in a second rotational direction through energization of the motor until the plurality of plates are frictionally disengaged; and

after frictional disengagement of the plurality of plates, de-energizing the motor.

13. The method of claim 10 , wherein the self-locking planetary gearset is a non-backdrivable planetary gearset.

14. An interaxle differential (IAD), comprising:

an electric motor rotationally coupled to a sun gear in a self-locking planetary gearset; and

a ball ramp actuator configured to selectively engage a plurality of plates in a clutch pack of a friction clutch in response to receiving rotational input from a ring gear in the self-locking planetary gearset;

wherein the ring gear meshes with teeth in the ball ramp actuator;

wherein, in an engaged configuration, the friction clutch prevents speed differentiation between a first output shaft and a second output shaft; and

wherein the first output shaft is rotationally coupled to a first axle differential and the second output shaft is rotationally coupled to a second axle differential.

15. The IAD of claim 14 , further comprising a controller including instructions stored in non-transitory memory that when executed by a processor, during a first operating condition, cause the controller to:

de-energize the electric motor after the plurality of plates become frictionally engaged in a clutch locking sequence.

16. The IAD of claim 15 , wherein the clutch locking sequence is automatically implemented without operator input.

17. The IAD of claim 14 , further comprising a controller including instructions stored in non-transitory memory that when executed by a processor, during a first operating condition, cause the controller to:

energize the electric motor to rotate the electric motor in a direction that frictionally disengages the plurality of plates in the friction clutch.

18. The IAD of claim 14 , wherein the self-locking planetary gearset is a two-stage wolfram planetary gearset.