Principles of Operation - Electronic Shift-on-the-Fly (ESOF) System

The electronic shift-on-the-fly (ESOF) system is an electronic shift system that allows the operator to choose between 2 different 4WD modes as well as two wheel drive (2WD). The operator can switch between 2WD and 4X4 High mode at speeds up to 88 km/h (55 mph). To engage or disengage 4X4 Low, the 4X4 control module requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal pressed and the transmission in NEUTRAL (or clutch pedal applied on manual transmission vehicles). This system contains pulse vacuum hub locks (PVH). The selector on the hub lock, when turned fully counterclockwise to the AUTO position, engages/disengages the hub depending on the driver-selected 4WD mode of operation. The hub locks also contain a manual override. When the selector is rotated fully clockwise to the LOCK position, the 4WD vacuum and electronic system used for coupling the front axle to the wheels is bypassed.

The transfer case is equipped with a dual-cone synchronous clutch. This clutch is used to synchronize the front driveline to the rear. All other internals operate in the same manner as the manual shift system. When the mode select switch (MSS) on the instrument panel is turned, the 4X4 control module powers the transfer case shift motor, which activates a shift fork and engages the clutch. When the shift motor reaches the desired position, as determined by the encoder position inputs to the 4X4 control module, power to the shift motor is removed. When the transfer case front and rear output shafts are synchronized, the lockup collar mechanically engages the mainshaft hub to the drive sprocket. At this point, the front axle PVH are engaged. Instrument cluster (IC) "4X4 High" and "4X4 Low" indicator operation is controlled via the cluster which interprets outputs from the 4X4 control module.