Four Wheel Drive System Operation - Electronic Shift on the Fly (ESOF)

Principles of Operation 

The ELD system allows the operator to lock the rear differential side gears. When the ELD is engaged both rear wheels turn at the same speed, providing added traction on slippery and/or off road surfaces. The operator can engage the ELD per the charts below:

ELD Engagement/Disengagement Speeds and Availability -- 4WD Vehicles 

ELD Engagement/Disengagement Speeds and Availability -- 2WD Vehicles 

When the operator activates the ELD, the ELD icon displays in the IPC message center. If the vehicle is driven above the disengage speed, the IPC message center no longer displays the ELD icon, alerting the operator that the ELD is disengaged. Once the vehicle speed drops below the re-engage speed, the IPC message center displays the ELD icon again. If there is a malfunction with the ELD system, a CHECK LOCKING DIFFERENTIAL message is displayed in the IPC message center, letting the operator know the ELD is not engaged.

Under certain conditions the ELD system has the ability to modulate powertrain torque output as well as system engagement/disengagement to protect internal ELD hardware.

The ELD feature allows the ABS to override the engage state during special events. When this condition occurs the ELD icon flashes on and off rapidly.

The differential locks when a PWM controlled magnetic field coil located inside the differential energizes. This locks the differential side gears and creates the locked differential.

The ELD system also informs the customer when there is too much wheel slip to safely engage the ELD by displaying TO ENGAGE LOCKING DIFFERENTIAL RELEASE ACCELERATOR PEDAL message in IPC message center. When the ELD is engaged, the TCCM sends PWM voltage to the ELD field coil located in the differential. This voltage is initially 98% duty cycle, and then tapers off after 30 seconds. In order for the TCCM to activate the ELD, certain conditions must be met.

• ELDMSS set to On.
• Wheel speed information via HS-CAN communication from ABS module)
• Operating range (voltage 11.5-16 volts)
• DTC setting range (voltage 10-15 volts)
• Ignition in the ON position
• TP

(2H) OPERATION 

When the ATCM is in 2WD (2H), power is delivered to the rear wheels only. This mode is appropriate for normal on-road driving on dry pavement and provides the best fuel economy. Torque is passed through the transfer case to the rear drive shaft at a 1:1 ratio. In 2WD (2H):

• The ATCM sends a 2WD (2H) mode status to the TCCM via a GWM.

• The IWE are disengaged.

• The TCCM outputs a 0% duty cycle to the synchronization clutch field coil (4WD_CLTCH_OUT # = 0.00%).

• The shift motor is in the full CCW position. Refer to TRANSFER CASE SHIFT MOTOR STATUS In this article for further information.

• (2H) will momentarily be displayed in the message center at key up and after a 4WD (4H) to 2WD (2H) shift.

(4H) OPERATION 

When 4WD (4H) is selected on the ATCM, the 4WD system provides mechanically locked four-wheel drive with power delivered to all four wheels, for increased traction. 4WD (4H) is for use in off-road or winter conditions such as deep snow, sand or mud. This mode is not for use on dry pavement.

Shifts from 2WD (2H) to 4WD (4H) can be made at any speed. When performing this shift, release the accelerator pedal prior to the shift and wait until the Shift in Progress message disappears in the IPC before accelerating. This improves the shift performance as the transfer case and IWEs engage. In 4WD (4H):

• The ATCM sends a 4WD (4H) mode status to the TCCM via GWM.
• The TCCM outputs a 0% to 97% duty cycle to the synchronization clutch field coil (4WD_CLTCH_OUT # = x.xx%).
• The shift motor rotates CW to the 4WD (4H) position. Refer to TRANSFER CASE SHIFT MOTOR STATUS In this article for further information.
• The TCCM outputs a 0% duty cycle to the synchronization clutch field coil (4WD_CLTCH_OUT # = 0.00%).
• The IWE are engaged.
• 4WD (4H) is displayed in the message center.

(4L) OPERATION 

(4L) 4WD provides mechanically locked four-wheel drive power to both the front and rear wheels for use on low traction surfaces, but does so with an additional 2.64 gear reduction for increased torque multiplication. Intended only for off-road applications such as deep sand, steep grades or pulling heavy objects. 4WD (4L) does not engage when your vehicle is moving above 3 mph (5 km/h); this is normal and should be no reason for concern.

Shifts to and from 4WD (4L) can only be made below 3 mph with the transmission in Neutral. When performing this shift, wait until the 4x4 Shift in Progress message disappears in the IPC before moving the selector lever back to Drive. If the vehicle speed or transmission range is not within parameters, the message center will indicate the necessary action needed to complete the shift.

In (4L):

• The ATCM sends a 4WD (4L) mode status to the TCCM via GWM.
• The IWE are engaged.
• The TCCM outputs a 0% duty cycle to the synchronization clutch field coil (4WD_CLTCH_OUT # = 0.00%).
• The shift motor rotates to the full CW position. Refer to TRANSFER CASE SHIFT MOTOR STATUS In this article for further information.
• 4WD (4L) is displayed in the message center.

ESOF Transfer Case Shift Motor 

Vehicles equipped with the Electronic Shift on the Fly (ESOF) system use a shift motor to enter and exit 2WD (2H), 4WD (4H), and 4WD (4L) modes.

The electric shift motor is mounted externally to the transfer case. It drives a rotary cam which moves the mode and range forks within the transfer case. The shift motor moves during shifts between 2WD (2H), 4WD (4H), and 4WD (4L). The TCCM directly controls the electric shift motor and can reverse motor polarity to reverse rotary cam/shift fork direction. The message center may display "Shift in Progress" while the shift motor is operating. The shift motor sense plate, an integral part of the shift motor assembly, informs the TCCM of the transfer case position. The sense plates are a set of 4 contacts that are opened and closed to represent each valid transfer case shift motor position. The mode and range forks are spring loaded so the motor can move to position regardless of the time it takes it takes for the transfer case internal shaft and hub splines to align and engage.

ESOF Transfer Case Shift Motor Status 

Synchronization Clutch 

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 2WD (2H) to 4WD (4H) shifts. The clutch consists of a transfer case field coil, a field coil housing splined to the rear output shaft, and one steel clutch plate splined to the lock-up hub. When the ATCM is switched from 2WD (2H) to 4WD (4H) modes, the TCCM energizes the synchronization clutch. The magnetic field from the field coil pulls the lock-up hub clutch plate against the field coil housing. When the transfer case front and rear output shafts are synchronized, the spring-loaded lockup collar mechanically engages the 4WD drive sprocket to the field coil housing. After the shift to 4WD is completed, the synchronization clutch is deactivated.