Transfer Case Description and Operation

Transfer Case Description and Operation





The New Venture Gear model NVG 126 RPO NP4 transfer case is a one speed automatic, active, transfer case. The NVG 126 provides only one mode, Auto 4WD, and is transparent to the operator. The active transfer case provides the benefits of on-demand torque biasing, wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features, such as flexible adapt ready position and clutch pre-load torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0 - 7 Nm (0 - 62 inch lbs.) of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 32 km/h (20 mph) and greater. This prevents crow-hop and binding at low speeds, and provides higher torque biases at higher vehicle speeds, to enhance stability. The NVG 126 requires no clutch shimming. The transfer case control module controls the clutch wear and clutch torque levels. The software learns adapt ready positions which are for the correct clutch torque. The learned adapt ready positions vary as the unit wears over its life.

The NVG 126 case halves are high-pressure die-cast aluminum. Ball bearings support the input shaft gear, the front output shaft, and the rear output shaft. A needle bearing is located inside of the input shaft gear to support the front of the rear output shaft. The clutch discs have friction material on one side to prevent warpage. The transfer case requires Auto Trac II Fluid GM P/N 12378508 (Canadian P/N 10953626) which is blue in color. The fluid is designed for smooth clutch application. An oil pump, driven by the rear output shaft, pumps the fluid through the rear output shaft oil gallery to the clutch and bearings.

To drive the rear propshaft (5), the power flows from the transmission to the input shaft gear (1). The input shaft gear (1) is splined to the rear output shaft (2). The power flows from the rear output shaft (2) to the rear propshaft (5).

To drive the front propshaft (8), the clutch hub (3) is splined to the rear output shaft (2). When the transfer case control module commands for more or less clutch torque, the encoder motor (7) turns the control actuator lever shaft (6). The control actuator lever shaft (6) is cam designed, and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the control lever studs and moves toward the clutch apply plate to increase clutch torque. As more pressure is applied to the clutch apply plate, the clutch discs are compressed. Using inner clutch discs, which are engaged with the clutch hub (3), and outer clutch discs, which are engaged with the clutch housing, the power flow is delivered to the clutch housing. The chain drive sprocket is splined to the clutch housing. The power flows from the drive sprocket through the chain (9), to the chain driven sprocket. The driven sprocket is splined to the front output shaft (8). The power flow is delivered to the front propshaft through the front output shaft (8).