Control strategy for AWD connection and disconnection

1. A computer program product comprising a tangible memory device and a program stored on the tangible memory device, the program being readable and executable by a processor, the program comprising instructions for making connections in a vehicle driveline comprising the steps of:

receiving, at the processor, a request to convert a vehicle from a single drive axle-powered driveline to a two drive axle-powered driveline;

iteratively receiving, at the processor, sensor data from sensors, the sensor data comprising data indicating vehicle dynamics and current engine power;

processing the received sensor data to determine vehicle dynamics and current engine power;

determining an additional amount of engine power required to convert the second drive axle from an idled condition to a powered condition to covert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline;

sending, from the processor, a command to open at least one coupler in the second drive axle;

sending, from the processor, a command to increase engine power by the determined additional amount;

processing sensor data to indicate that the engine power has increased by the determined additional amount;

sending, from the processor, in response to the indication that the engine power has increased by the determined additional amount, a command to engage a power transfer unit to connect the single drive axle to the second drive axle;

receiving, at the processor, a signal that the power transfer unit is engaged; and

sending, from the processor, a command to close the at least one coupler.

2. The computer program product of claim 1 , wherein the tangible memory device further comprises stored predetermined values and stored instructions to:

process the received sensor data to determine at least one of yaw, lateral acceleration, longitudinal acceleration, slip, and vehicle trajectory; and

compare the processed sensor data to the stored predetermined values to determine vehicle readiness to convert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline,

wherein, when the comparison indicates vehicle readiness to convert from the single drive axle-powered driveline to the two drive axle-powered driveline, the processor outputs the command to open the at least one coupler and the command to increase engine power.

3. The computer program product of claim 2 , wherein the stored predetermined values comprise at least a calibration threshold, and the instructions further comprise:

determining a rotation speed of a powered single drive axle;

determining a rotation speed of a drive shaft;

calculating an absolute value of the difference between the rotational speed of the powered single drive axle and the rotational speed of the drive shaft; and

determining if the absolute value is less than the calibration threshold,

wherein, when the determined absolute value is less than the calibration threshold, the processor outputs commands to begin the conversion.

4. The computer program product of claim 1 , further comprising instructions to engage an auxiliary drive unit of the vehicle.

5. The computer program product of claim 1 , further comprising instructions to terminate the increased engine power.

6. The computer program product of claim 1 , further comprising instructions to process sensor data to determine if the coupler has closed, and, if the coupler has closed, to command an auxiliary drive unit of the vehicle to engage.

7. The computer program product of claim 6 , further comprising instructions to process sensor data to determine if the auxiliary drive unit has engaged, and, when the auxiliary drive unit has engaged, to terminate commands to increase engine power by the additional amount.

8. The computer program product of claim 1 , wherein the additional amount of engine power is of sufficient magnitude to avoid transfer of vehicle kinetic energy to an auxiliary drive axle during conversion from the single axle-powered driveline to the two drive axle-powered driveline.

9. A vehicle driveline comprising a plurality of sensors and a plurality of actuators with respective connections to:

an electronic control computer,

a primary drive axle connected to an engine and a power transfer unit, and

an auxiliary drive axle connected to the power transfer unit, the auxiliary drive axle comprising a drive shaft, an all-wheel drive coupling, an auxiliary drive unit, a first auxiliary drive axle on a first side of the auxiliary drive unit, and a second auxiliary drive axle on a second side of the auxiliary drive unit,

wherein the electronic control computer comprises a processor and a tangible memory device, the tangible memory device comprises a stored program, the program being readable and executable by the processor, the program comprises instructions for making connections in the vehicle driveline comprising the steps of:

receiving, at the processor, a request to convert from a single drive axle-powered driveline to a two drive axle-powered driveline;

receiving, at the processor, sensor data from the plurality of sensors;

processing the received sensor data to determine vehicle dynamics and current engine power;

determining an additional amount of engine power required to convert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline;

sending, from the processor, a command to open at least one coupling in one of the all-wheel drive coupling or the auxiliary drive unit;

sending, from the processor, a command to increase engine power by the determined additional amount;

receiving, at the at least one coupling, the command to open the at least one coupling;

receiving, at the engine, the command to increase engine power;

receiving, at the processor, sensor data indicating that the engine power has increased by the determining additional amount; and

sending, from the processor, in response to the received sensor data indicating that the engine power has increased by the determined additional amount, a command to engage at least the power transfer unit,

wherein a first actuator of the plurality of actuators opens the at least one coupling and a second actuator of the plurality of actuators increases the engine power by the determined additional amount.

10. The vehicle driveline of claim 9 , wherein the tangible memory device further comprises stored predetermined values and stored instructions to:

process the received sensor data to determine at least one of yaw, lateral acceleration, longitudinal acceleration, slip, or vehicle trajectory;

compare the processed sensor data to the stored predetermined values to determine vehicle readiness to convert the vehicle from the single drive axle-powered driveline to the two drive axle-powered driveline,

wherein, when the comparison indicates vehicle readiness to convert from the single drive axle-powered driveline to the two drive axle-powered driveline, the processor outputs control commands to proceed with the conversion.

11. The vehicle driveline of claim 9 , wherein the stored predetermined values comprise at least a calibration threshold, and the instructions further comprise:

determining a rotation speed of a powered single drive axle;

determining a rotation speed of a drive shaft;

calculating an absolute value of the difference between the rotational speed of the powered single drive axle and the rotational speed of the drive shaft; and

determining that the absolute value is less than the calibration threshold,

wherein, when the absolute value is less than the calibration threshold, the processor outputs commands to begin the conversion.

12. The vehicle driveline of claim 9 , further comprising instructions to engage the all-wheel drive coupling and the auxiliary drive unit of the vehicle.

13. The vehicle driveline of claim 12 , further comprising instructions to close the at least one coupling.

14. The vehicle driveline of claim 13 , further comprising instructions to terminate the increased engine power.

15. The vehicle driveline of claim 9 , wherein the additional amount of engine power is of sufficient magnitude to avoid transfer of vehicle kinetic energy to the auxiliary drive axle during conversion from the single axle-powered driveline to the two drive axle-powered driveline.

16. A vehicle driveline comprising a plurality of sensors and a plurality of actuators with respective connections to:

an electronic control computer,

a primary drive axle connected to an engine and to a power transfer unit, and

an auxiliary drive axle connected to the power transfer unit, the auxiliary drive axle comprising a drive shaft, an all-wheel drive coupling, an auxiliary drive unit, a first auxiliary drive axle on a first side of the auxiliary drive unit, and a second auxiliary drive axle on a second side of the auxiliary drive unit,

wherein the electronic control computer comprises a processor and a tangible memory device, the tangible memory device comprises a stored program, the program being readable and executable by the processor, the program comprises instructions for making disconnections in the vehicle driveline comprising the steps of:

receiving, at the processor, a request to convert from a two drive axle-powered driveline to a single drive axle-powered driveline;

receiving, at the processor, sensor data from sensors distributed on the auxiliary drive axle and on the primary drive axle;

processing the received sensor data to determine vehicle dynamics and current engine power;

determining to suspend engine power output during a conversion of the vehicle from the two drive axle-powered driveline to the single drive axle-powered driveline;

sending, from the processor, a command to open at least one coupling in at least one of the power transfer unit, the all-wheel drive coupling, or the auxiliary drive unit;

sending, from the processor, a command to suspend engine power;

receiving, at the at least one coupling, the command to open the at least one coupling; and

receiving, at the engine, the command to suspend engine power,

wherein a first actuator of the plurality of actuators simultaneously opens the at least one coupling while a second actuator of the plurality of actuators suspends the engine power output during the conversion.

17. The vehicle driveline of claim 16 , wherein the program comprises instructions for execution by the processor to:

determine whether to open each of the at least one coupling in the power transfer unit, the all-wheel drive coupling, and the auxiliary drive unit in a stepwise or simultaneous manner with respect to each of the at least one coupling based on the determined engine power; and

send a command to open, simultaneously or stepwise, the at least one coupling in the power transfer unit, the all-wheel drive coupling, and the auxiliary drive unit.

18. The vehicle driveline of claim 9 , further comprising a separate torque source in the auxiliary drive axle, the separate torque source configured to bring one of the drive shaft and the first auxiliary drive axle and the second auxiliary drive axle within a rotational range for coupling with the primary drive axle.

19. The vehicle driveline of claim 16 , further comprising a separate torque source in the auxiliary drive axle, the separate torque source configured to bring one of the drive shaft and the first auxiliary drive axle and the second auxiliary drive axle within a rotational range for coupling with the primary drive axle.