When the AWD system operates in the Automatic mode or the Manual mode, the following modes can be automatically initiated by the all wheel drive ECM: Coast mode, Freewheel mode, Diagnostic mode, High temperature mode and Hop stop mode
When the operator places the AWD switch in the OFF position, the AWD system will be deactivated. All of the solenoids for the AWD system will be de-energized.
The AWD system will be active when the AWD switch is placed in the AUTOMATIC position or the MANUAL position and the transmission gear is moved out of the Neutral position.
The AWD lamp will be off.
When the operator places the AWD mode switch in the AUTOMATIC position, the AWD system will be activated. The AWD ECM controls the oil flow of the AWD pump in order to maintain certain hydraulic pressure for the drive motors.
The torque control lever allows the operator to adjust the relationship between the power that is applied to the front wheels and the rear wheel slip.
When the automatic mode is active, the AWD ECM calculates a setpoint value which is used for setting the hydraulic pressure. The setpoint value is a combination of the calculated slip ratio and the position of the torque control lever. The slip ratio is the difference of rear wheel speed and true ground speed divided by rear wheel speed. As the slip ratio increases or the position of the torque control lever increases, the setpoint value will increase. The ECM will then adjust the displacement solenoid valve in order to achieve the new setpoint value for the hydraulic pressure. The ECM continuously repeats the process of calculating the setpoint value and adjusting the hydraulic pressure.
The AWD lamp will be illuminated during the automatic mode.
When the operator places the AWD mode switch in the MANUAL position, the AWD system will be activated. The AWD ECM controls the oil flow of the AWD pump in order to maintain certain hydraulic pressure for the drive motors.
The torque control lever allows the operator to adjust the power that is applied to the front wheels.
Note: Certain operating conditions may cause the operation of the AWD system to become erratic. The ECM recognizes these conditions and the ECM will briefly override the value of the position sensor for the torque control in order to regain control of the AWD system. The override may exist for a few seconds until the operating conditions improve.
When the manual mode is active, the AWD ECM calculates a setpoint value which is used for setting the hydraulic pressure. The setpoint value is calculated from the position of the torque control lever. When the operator adjusts the torque control lever, the setpoint value will be changed accordingly. The ECM will then adjust the displacement solenoid valve in order to achieve the new setpoint value for the hydraulic pressure. The ECM continuously repeats the process of calculating the setpoint value and adjusting the hydraulic pressure.
The AWD lamp will be illuminated during the automatic mode.
When the AWD system operates in the Automatic mode or the Manual mode, the AWD ECM will automatically initiate the coast mode when one of the following conditions are present:
- The inching pedal is depressed.
- Transmission gear is in the Neutral position.
- Transmission gear is in the Park position.
The AWD system will return to the normal operating mode when the previous conditions are no longer present.
The ECM will disable the high pressure oil flow by de-energizing the drive solenoid. The ECM will maintain the charge pressure in order to keep the system in a ready state.
The AWD lamp will remain illuminated during the coast mode.
When the AWD system operates in the Automatic mode or the Manual mode, the AWD ECM will automatically initiate the freewheel mode when one of the following conditions are present:
- Transmission gear is in the eighth gear (forward).
- Transmission gear is in the sixth gear (reverse).
The AWD system will return to the normal operating mode when the previous conditions are no longer present.
The ECM will disable the high pressure oil flow by de-energizing the drive solenoid. The ECM will also disable the charge pressure by de-energizing the charge solenoid.
The AWD lamp will remain illuminated during the freewheel mode.
When the AWD system operates in the Automatic mode or the Manual mode, the AWD ECM will automatically initiate the diagnostic mode when one of the following conditions are present:
- A diagnostic code is active.
Refer to Systems Operation, "Diagnostic Operation" for more information on diagnostic codes.
The AWD system will return to the normal operating mode when the problem is repaired and the AWD switch is cycled from the OFF position.
The ECM will disable the AWD system. All solenoids will be de-energized.
The AWD lamp will be off during the diagnostic mode. The action indicators will be active during the diagnostic mode.
When the AWD system operates in the Automatic mode or the Manual mode, the AWD ECM will automatically initiate the high temperature mode when one of the following conditions are present:
- The temperature of the hydraulic oil becomes high.
The AWD system will return to the normal operating mode when the previous conditions are no longer present.
The ECM will signal the operator of the problem through the Caterpillar Monitoring System. The operator should then reduce the torque control lever. If the operator has not reduced the torque control lever and the temperature remains high for more 30 seconds, the ECM will override the signal of the torque control lever to 66% of the full rating. If the operator has not reduced the torque control lever and the temperature remains high for more 3 minutes, the ECM will override the signal of the torque control lever to 49% of the full rating.
The AWD lamp will remain illuminated during the high temperature mode. The alert indicator for hydraulic temperature will FLASH and the action lamp will FLASH.
When the AWD system operates in the Automatic mode or the Manual mode, the AWD ECM will automatically initiate the freewheel mode when one of the following conditions are present:
- Operating conditions cause the front of the machine to hop.
The AWD system will return to the normal operating mode when the previous conditions are no longer present.
The ECM monitors the pump pressure. When the front wheels are slipping and the wheels suddenly have traction, the pump pressure will fluctuate drastically. The ECM will change the setpoint value to a constant value until the pressure stabilizes. The setpoint value is based on the ground speed only.
The AWD lamp will remain illuminated during the hop stop mode.