All Wheel Drive Speed Synchronization and Connection

A method for engaging all-wheel drive operation in a vehicle driveline, comprising:

• using a clutch of a rear-drive-unit to accelerate driveline components toward a speed of secondary wheels;
• using a synchronizer of a power-transfer unit to accelerate the components toward a speed of a transmission output;
• disengaging the clutch;
• engaging the synchronizer to transmit torque between the transmission output and the clutch;
• reengaging the clutch.

A vehicle driveline comprising:

• a power source;
• a transmission connected to the power source and including an output driveably connected to primary road wheels;
• a driveshaft;
• a synchronizer that opens and closes a drive connection between the output and the driveshaft;
• a clutch that alternately opens and closes a drive connection between the driveshaft and secondary road wheels.