Part 2

SHIFT OUT OF NEUTRAL
The following steps describe the process for a shift out of NEUTRAL.
- Extinguish the Neutral LED.
- Engage the shift motor for a maximum of 1 second ±100 msec toward the transfer case 4LOCK mode position while monitoring the mode sensor position.
- Disengage the shift motor when the correct mode sensor position is recognized.
- Extinguish the Neutral LED.
- Transmit a bus message that the transfer case shift is complete.
- If the desired mode sensor position is not received after the shift timer expires (i.e. a blocked or other condition exists), stop driving the motor and wait for 200 msec ± 50 msec. The shift motor is then reversed in the direction back toward the source gear for up to 1.0 seconds 100 msec. The FCM waits for 2.0 seconds ± 50 msec. and repeats the attempt to shift to the desired position.
- When the Neutral button is released, if the 4LOCK position is the desired position, the shift is complete. Illuminate the 4LOCK message icon.
- Otherwise when the Neutral button is released, if all of the shift requirements are being met then engage the shift motor towards the desired position for 1 second ± 100 msec per 'D' channel. (if requirements for shifting are not met, illuminate the 4LOCK message icon and flash the destination message icon as an indication to the driver that all of the driver controllable shift conditions are not being met). If this requires another range or mode shift, begin the range/mode shift process.
- If the desired mode sensor position is not achieved after the shift timer expires (i.e. a blocked or other condition exists), refer to the Blocked Shift Strategy, also known as Phase 2 shifts.

NEUTRAL BLOCKED SHIFT STRATEGY (PHASE 2 SHIFTS)
When a shift is commanded out of neutral, the shift motor will be driven towards its destination position, except in the case of shifting out of NEUTRAL if 4LO was selected (the transfer case will shift to the 4LOCK position first, before proceeding to 4LO). If the shift is blocked on the way to the destination, the FCM may attempt to drive the motor back to the original position. This process will be allowed to occur 5 times. If the transfer case has reached a non-NEUTRAL position during the shift re-attempts, the message icon for the achieved gear position is illuminated and the shift attempts are stopped. To re-attempt the desired shift, the selector switch will need to be rotated to the current position until the switch debounce timer expires then a shift will need to be requested again.

At the end of the 5th blocked attempt, the shift motor is driven towards the last known mode sensor position. If this motor drive allows the transfer case to reach the 2WD or AWD position, the shift is considered complete and the shift attempts are ended.

If the mode sensor is in the NEUTRAL region at the expiration of the shift timer, the FCM will continue to make the shift attempts according to the blocked shift strategy independent of whether or not the driver controlled conditions are met.

For shifts from NEUTRAL, if all 5 attempts fail to reach the desired position (which by default is 4LOCK), the motor will be driven to stall in the direction of 4LOCK or 4LO, depending on the achieved position. Otherwise, the transfer case will be driven in the direction opposite the last attempt with the desired target being 4LOCK or 4LO.

If the transfer case reaches the 2WD or AWD position when being driven in the 4LOCK direction, then one final 1.0 second drive toward 4LOCK is attempted. If the transfer case then reaches the 4LOCK position, the shift is considered complete and the 4LOCK message icon is illuminated. If the transfer case is still the 2WD or AWD position, the shift is considered complete and all message icons are extinguished.

NEUTRAL DRIFT SHIFT STRATEGY (PHASE 3 SHIFTS)

NOTE: If after the 5th blocked shift and reversal attempt, if the transfer case position is in the NEUTRAL or other undesired region, shift attempts will continue until a non-NEUTRAL or a desired position is reached.

Phase 3 is a series of shifts whose intent is to escape from an undesired position that has been reached outside of a shift. A perceived drift of the transfer case into a non-target region without the FCM driving the shift motor will initiate a phase III shift. Phase 3 will be initiated by any non-target region with the exception of a position greater then encoder_4LO_min or less then encoder_4LOCK_max. Whenever these encoder readings have been seen for defined period of time, Phase III shifting will begin.

The shifts in a given Phase 3 shifting event are always in a single-direction, toward the target region from which the drift occurred. These shifts are performed without regard to shift conditions. The timing of each shift should follow the outline of the Phase 1 forward attempts, allowing the shift timer to reach the target. Between each attempt, there is a calibrated delay. After each attempt the shift counter and the Phase 3 max shifts counter will be updated.

SHIFT REVERSAL TARGETS
If the shift timer expires (1.0 seconds per mode sensor position) and the transfer case has not reached the desired position, all shifts will attempt to return to their original position with the exceptions of:
- If the intended shift is going to the High rail from Low and can't make it, but it can make the 2WD or AWD position, the motor stops at that position. The FCM will not attempt to cross back over NEUTRAL if it does not have to. This means that there was a block on the first attempt to go to 4LOCK and the transfer case has made it through NEUTRAL to a known good position, then the motor will go back only to the 2WD or AWD position and execute the remainder of the attempts from there.
- For shifts out of NEUTRAL, any time a shift is commanded out of NEUTRAL, the system needs to get out. The FCM should never go to NEUTRAL unless the driver is commanding it and all required conditions are being met.

ENCODER DRIFT CORRECTION
Whenever a shift is completed, the FCM stores the position in memory as the transfer case's intended position. The FCM continuously monitors the mode sensor and if the mode sensor drifts toward into a NEUTRAL region sensor position for 2.0 seconds, the FCM will perform a motor drive to correct the drift. The transfer case will be driven toward the intended position for 1.0 seconds ± 100 msec. The FCM will wait for 2.0 seconds ± 50 msec. and repeat the attempt to shift to the desired position. This will continue until the intended position is reached.

SHIFT MOTOR CONTROL
The FCM will have the ability to vary the speed of the transfer case motor through pulse width modulation (PWM). It is PWM from 0 to 100% at 100Hz.

The PWM will function as follows:
- Apply an initial duty cycle (APPROXIMATELY 94%) to shift motor control wires.
- Control the acceleration of the shift motor by increasing the applied duty cycle at a specified rate.
- Control the deceleration of the shift motor by updating the applied duty cycle to the shift motor control wires at a specified rate based upon the difference between the desired position and the current position.

SHIFT ATTEMPT LIMIT
To protect the transfer case system, the FCM will impose a limit on the number of shifts that can occur over a calibrated time period. The system will monitor the number of mode sensor position changes that occur in any 25 second time period. If the number of changes is 10 or greater, the system will go into a default mode. The default mode of operation for shifting is that the number of allowed changes permitted to occur will be 3 over each 15 second ± 100 msec calibrated window of time. After 5 minutes ± 100 msec, the motor can be assumed to have cooled down and the system will revert to normal operation. The following rules also apply to the shift limit:
- The attempt limit will not prevent shifts coming out of NEUTRAL, they will be allowed regardless of the counter/timer.
- Any shift that is in progress when the counter reaches a maximum count in time will be allowed to complete before the default mode is entered. Position changes during this period will not be counted towards the default mode limit.
- A block, regardless of the direction, whether towards destination or back towards reversal target (shift timer expiring), will count as a value of 2 position changes towards the 10 position changes to go into default mode as defined above. Current attempt limit values are 10 transitions in 25 seconds and default mode values are 1 transitions every 10 seconds for 5 minutes.