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Home >> Ford >> 2012 >> Mustang Base, 2D Coupe, Automatic Trans >> Repair and Diagnosis >> External Pages >> Different car >> Section 714 (Four-Wheel Drive Systems) >> Diagnosis And Testing >> Four-Wheel Drive Systems - Vehicles With: Electronic Shift Transfer Case >> Principles of Operation

Principles of Operation

WARNING: This page is about a different car, the 2015 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.

The Electronic Shift-On-The-Fly (ESOF) system has 3 modes of operation: 2H (4X2), 4H (4X4 HIGH) and 4L (4X4 LOW). When 4H or 4L are selected, TCCM sends a duty cycle command to the synchronization coil which activates the clutch within the transfer case and moves the shift forks. When the 2H mode is selected, IWEs located at each front wheel are disengaged to reduce additional drag from the front driveline.

Engagement and disengagement of the front wheels is done by the IWEs. The IWEs are normally engaged (no vacuum). Vacuum is supplied to the IWEs by actuation of the IWE solenoid when commanded by the TCCM. When actuated, the IWE solenoid allows manifold vacuum to pass through to each IWE. The IWEs disengage and allow the front wheel hubs to be turned freely from the front axle.

NOTE: When shifting to 2H mode in order for the IWEs to completely disengage the vehicle steering wheel must be less than 90 deg and 5 seconds have elapsed since the shift to 2H has been initiated.

The electric shift motor is mounted externally to the transfer case. It drives a rotary cam which moves the 2 shift forks in the transfer case to change between the 2H and 4H modes, neutral and between the 4H and 4L modes. The TCCM directly controls the electric shift motor and can reverse motor polarity to reverse rotary cam/shift fork direction. The shift motor sense plate, an integral part of the shift motor assembly, informs the TCCM of the transfer case position.

The transfer case is equipped with an electronically controlled clutch which is located inside the case. This clutch is used to synchronize the speed of the front driveline with the rear driveline during 2H to 4H shifts. When the MSS is switched between 2H and 4H modes, the TCCM energizes the synchronization clutch. When the transfer case front and rear output shafts are synchronized, the spring-loaded lockup collar mechanically engages (4H) or disengages (2H) the mainshaft hub to the drive sprocket. Finally, the front axle IWEs are engaged (4H) or disengaged (2H) and the synchronization clutch is deactivated.

The TCCM features a cold temperature strategy which is used to warm up the front axle in cold temperatures to improve driveline synchronization. When ambient temperature is below 32 F (0 C). IWEs will engage after initial key cycle and a driven gear is selected. Hubs will stay engaged regardless of 4x4 mode change for proximately 2 miles (3km). Once distance traveled has been achieved IWEs will disengage if vehicle is in 2H. Distance traveled will reset only if the temperature is below calibrated threshold and another key cycle has occurred or customer shifted to park and back to a driven gear within the same key cycle.

Shifts from 2H mode to 4H mode can be made at any speed. The synchronization clutch is applied to equalize output shaft speeds before 4H mode is engaged. The following are the inputs and outputs needed by the TCCM to execute a change between these modes.

Feature inputs: 

Feature outputs: 

When shifting into or out of 4L mode, the TCCM requires the vehicle speed to be less than 5 km/h (3 mph) and the transmission in NEUTRAL.

The following are the inputs and outputs needed by the TCCM to execute a change into or out of 4L mode:

Feature inputs: 

Feature outputs: 

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