Method and apparatus for providing synchronization of low to high shifts in a transfer case

DETAILED DESCRIPTION The present invention overcomes the disadvantages in conventional transfer cases by providing a method to digitally control a transfer case through a digital data bus to provide synchronized low to high shift capabilities in vehicles that employ a controller area network (CAN) system.
More specifically, a method is provided comprising the first step of initiating an actuator to move a clutch from engagement with a gear set to a predetermined neutral synchronization point.
The method also includes the step of sensing the speed of the actuator and routing the signal to the control unit.
The time for the clutch to reach the predetermined neutral synchronization point as a function of the sensed speed of the actuator and the known remaining rotational distance through which the actuator must move for the clutch to reach the predetermined neutral synchronization point is then determined used this method.
The method also includes the step of maintaining the actuation of the clutch until it has reached the predetermined neutral synchronization point.
The actuator is then commanded to stop when the calculated time has elapsed for the clutch to reach the predetermined neutral synchronization point.
The rotational speed of the transfer case input and output shafts is then sensed and compared to determining a difference value.
The method further includes the steps of commanding changes in engine RPM and automatic transmission gear settings through the control area network to bring the difference value within a predetermined range and completing the shift from low to high by commanding further actuation of the clutch from the predetermined neutral synchronization point to a direct torque engagement of the input and output shafts when the calculated difference in the rotational speeds of the input and output shafts is determined to fall within a set predetermined range, indicating synchronization of the shafts.
The present invention also overcomes the disadvantages in conventional transfer cases by providing a transfer case that can be digitally controlled which provides synchronized low to high shifts and is adapted to be integrated into a vehicle with a controller area network (CAN) system