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Final Drive Control Module - Operation






OPERATION

During normal operation of an active transfer case the FDCM control module learns and remembers the Clutch Engagement Point (Kiss Point), the position in the motor actuator's travel where torque begins to be transferred to the front wheels. The position is read out using the encoder as a 0 to 5 volt signal. This information is written into the module's EEPROM area at Ignition OFF. Over time the clutch pack wears and the Kiss Point changes in one direction (going from a lower voltage to a higher value).

POWER UP/DOWN

The Final Drive Control Module (FDCM) will power up with an OFF/ON transition of the hard wired ignition switch input.

The FDCM will power down when the vehicle ignition switch transitions from ON to OFF or there are no system requirements that dictate the controller to remain active

START-UP DIAGNOSTICS

When the FDCM is activated, the internal circuitry will undergo a diagnostic procedure. The controller will examine all inputs and outputs for short circuits to ground, short circuits to battery and open circuits and will also verify proper CPU and memory operation. If a fault is detected, a message will be sent out over the CAN C bus to the Cluster indicating that service is recommended.

After passing all diagnostic tests, the controller will receive and process inputs and produce the appropriate outputs. Proper monitoring of the controller inputs and outputs performance will continue.

INPUTS/OUTPUTS

The following are inputs to the FDCM:

- Transfer Case Mode Sensor Signal
- 1 Direct Battery Feeds
- Ignition RUN Sense
- Sensor Ground
- Module Ground
- CAN C Bus

The following are outputs of the FDCM:

- Transfer Case Motor Brake Control (3022 only)
- 5V Sensor Supply
- Transfer Case Bi-directional Motor Control (A AND B)
- Switched B+ Solenoid Supply
- Transfer Case Motor Brake Control

TRANSFER CASE RANGE SELECT SWITCH INPUT (NEUTRAL, 2WD, 4WD AUTO and 4WD LOW SELECT SWITCH)

The transfer case range select switch is hardwired directly to the Cluster (CCN). The switch position is read by the CCN and is communicated to the TIPM (Gateway) via the CAN-I bus. The TIPM then rebroadcasts this information onto the CAN-C bus where the FDCM is a receiver.

The Cluster (CCN) will support circuitry which interfaces to the system's Transfer Case Range Select Switch, including a Transfer Case Range Select Switch voltage supply and a Transfer Case Range Select Switch input. The purpose of this circuitry is to determine the mode currently being requested by the operator via the resistance ladder network in the shifter assembly, where the Transfer Case Range Select Switch is packaged.

The NEUTRAL Select Switch Input will provide the operator with the ability to place the Transfer Case in Neutral. The Select Switch Input will provide the operator with the ability to place the transfer case in 2WD, 4WD AUTO and 4WD LOW. The NEUTRAL Select Switch is a momentary pushpin switch and the 2WD, 4WD AUTO and 4WD LOW Select Switch is a 3-position toggle or a contact switch and both these switches are provided through a resistor network for diagnostic purposes. The input will have an internal 1.0K +/- 1% pull-up resistor to 5V.

As the selected position in the switch varies and/or the NEUTRAL Switch is depressed or not, the resistance between the Cluster (CCN) voltage supply and Transfer Case Range Select Switches input will vary. Hardware, software, and calibrations within the Cluster will be provided that interpret the external resistance between the module's Transfer Case Range Select Switches voltage supply and Transfer Case Range Select Switches inputs as given in the table below:

NOTE: There is no requirement for the FDCM to distinguish between a neutral request from the 4WD AUTO or the 4WD LOW position. Resistances in these ranges will be represented as a Neutral Switch Activation.

TRANSFER CASE MODE SENSOR SIGNAL

The Transfer Case Mode Sensor Signal Input will provide the FDCM feedback about the position of the transfer case. The mode sensor will be a linear analog position sensor with a 1.4K +/- 20% potentiometer and a 1 K +/- 20% wiper resistor that converts the motor shaft position into a multiplexed voltage. The mode sensor (on the 3022 transfer case) is an active device where the sensor's current changes as the motor shaft position changes

TRANSFER CASE BI-DIRECTIONAL MOTOR CONTROL (A AND B)

This output will control a Bi-directional DC motor that controls a clutch pack in the Transfer Case that varies the torque transfer between the front and rear axles.

MODES OF OPERATION

Normal Operation

This mode is achieved by the ignition being switched in the RUN position, which powers up the 5V regulator and generates the appropriate RESET for the microprocessor. This mode also includes any required power-up system checks.

Shut Down Mode

This mode is activated when the ignition switch turned to the off position. The FDCM will perform any required Shut Down tasks prior to turning off the 5V regulator.

Limp-In Mode

This mode is entered when the FDCM has detected an error condition that prevents the system from performing its' required task. The FDCM operation will vary depending from modified operation to total system shut down based on the failure that has occurred.

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