DESCRIPTION
The NV244 GENII is an electronically controlled full and part-time transfer case with no two wheel drive operation.
A differential in the transfer case is used to control torque transfer to the front and rear axles. A low range gear reduction system provides increased low speed torque capability for off road operation. The low range provides a 2.72:1 reduction ratio.
The geartrain is mounted in two aluminum case halves attached with bolts. The mainshaft front and rear bearings are mounted in aluminum retainer housings bolted to the case halves.
IDENTIFICATION
A circular ID (1) tag is attached to the rear case of each transfer case. The ID tag provides the transfer case model number, assembly number, serial number, and low range ratio.
The transfer case serial number also represents the date of build.
Scheme 168
OPERATION
The input gear is splined to the transmission output shaft. The input gear drives the mainshaft through the planetary assembly and range sleeve. The front output shaft is operated by a drive chain that connects the shaft to a drive sprocket on the mainshaft. The drive sprocket is splined to a differential assembly. Depending on the position of the mode fork and sleeve, the front output shaft is driven directly by the mainshaft or through the differential. The mode fork operates the mode sleeve and hub. The sleeve and hub are not equipped with a synchronizer mechanism for shifting.
The transfer case mode sensor (1) provides the Front Control Module (FCM) feedback about the position of the transfer case. The sensor consists of a linear analog position sensor that converts the motor output shaft position into a DC signal. The sensor may rotate a full 360 degrees for both the NV144 and the NV244 GENII. The operating envelope or sector rotation is -5 to 180 degrees for the NV144 and -40 to 20 degrees for the NV244 GENII. The FCM must supply 5VDC (+/- 0.5v) to the sensor whenever the FCM is not in sleep mode and monitor the shift motor position. The sensor position is monitored when the ignition is in the RUN position and for 10 seconds after the ignition is shifted to the OFF position. The sensor is mechanically linked to the shaft of the cam which allows the transfer case to shift. The mode sensor will draw less than 20 mA of current during operation.
Scheme 169
During normal vehicle operation, the Front Control Module (FCM) monitors the mode sensor outputs at least every 2 milliseconds when the shift motor is stationary or active.
Refer to SECTOR ANGLES vs. TRANSFER CASE POSITION for the relative angles of the transfer case shift sector versus the interpreted transfer case gear operating mode.
The selector switch assembly is mounted in the right side of the vehicle's Instrument Panel (IP) and consists of a rotary knob connected to a resistive network for the mode and range shift selections. Also located in this assembly is a recessed, normally open momentary switch for making shifts into and out of transfer case NEUTRAL. A pen, or similar instrument, is used to make a NEUTRAL shift selection, thus reducing the likelihood of an inadvertent shift request.
As the position of the selector switch varies, the resistance between the Mode Sensor supply voltage pin and the Mode Sensor output will vary. Hardware, software, and calibrations within the Front Control Module (FCM) are provided that interpret the selector switch resistance as given in the SELECTOR SWITCH INTERPRETATION table.
The shift motor (1) is an electromechanical device consisting of a DC permanent magnet motor, a motor brake, a gear train and an analog position sensor. The shift motors' overall function is to move and lock a gear that moves the mode and range forks found in the transfer case. This allows the transfer case to be shifted electrically to multiple operating positions (4LOCK, AWD, N (neutral), and 4LO). The operating current of the shift motor under stall conditions is 30 amps maximum at 72° F with 13.5 volts, at the motor leads.
The shift motor contains a motor brake, which provides a means of holding the transfer case in a selected position.
Scheme 170
Shifting in the transfer case occurs when the shift motor brake is released and a Pulse Width Modulated (PWM) voltage is supplied to the shift motor by the Front Control Module (FCM). A linear analog position sensor located inside the shift motor, provides the FCM with the motors' angular, rotational position. With this information, the FCM continuously knows the motors' position, and therefore allows it to accurately control the motors' operation, including voltage polarity which is used to control motor direction.
The brake in the shift motor consists of a solenoid that when energized, allows the shift motor to rotate. During normal operation (vehicle ignition ON), pin 6 on the shift motor connector will have a constant positive battery potential with respect to the vehicles ground. The FCM allows a return current path through Pin 7 when the brake needs to be released and allow the transfer case to shift. The operating current should not be greater than 1.2A when 12Vdc is applied. The motor brake functions as follows
- The motor brake must always be released while a shift is taking place.
- The motor brake must always be released for a calibrated amount of time before a shift and after a shift. There is an exception for shifts into a NEUTRAL. The motor brake must always be released for a calibrated amount of time before a shift and after the shift for a period of time greater than 2 but less than 5 seconds.
- The motor brake must always be engaged while a Motor Brake DTC is active.