The NV225 Transfer Box is a full time, permanent four wheel drive, torque splitting transmission with equal torque distribution to the front and rear propeller shafts. The transfer box has the following features:
Permanent four wheel drive with 50/50 torque split
Two speed, fully synchronised 'shift on the move' system with electronic control and operation
High range direct drive and low range via epicyclic gearset
Torsen® Type B torque sensing and torque biasing centre differential
Self lubricating oil pump system.
The transfer box is located under the vehicle in a subframe, behind the transmission. The units used on both the Td6 and V8 variants are identical, with the exception of the large mounting bush. The transfer box is manufactured by New Venture Gear in Roitzsch, Germany.
The transfer box receives an input from the transmission output shaft which is passed through the unit to two outputs for the front and rear propeller shafts.
The transfer box provides full time four wheel drive via a 50:50 torque sensing Torsen® differential. The unit design allows “shift on the move” from high to low range and visa versa. A planetary gearset with helical planetary pinion gears provides low range operation. When in low range, the planetary gearset provides a ratio of 2.69:1 which gives the vehicle an extremely low, low range crawl speed. High range is a direct drive from the transmission output shaft and provides a 1:1 ratio.
The front differential is a conventional design using a hypoid gear layout. This employs a hypoid bevel pinion gear and crown wheel, with the pinion offset below the centre line of the crown wheel. This design allows for a larger pinion gear to be used which has the advantages of increased gear strength and reduced operating noise.
The front differential is available in two ratios. V8 engine vehicles use a differential with a final drive ratio of 3.73:1 and Td6 engine vehicles use a final drive ratio of 4.10:1. The ratio is changed by changing the amount of teeth between the crown wheel drive gear and pinion gear. Therefore for a ratio of 4.10:1, the crown wheel drive gear will have 4.10 times more teeth than the pinion gear. This equates to the crown wheel drive gear having 41 teeth and the pinion gear having 10 teeth.
The rear differential is a conventional design using a hypoid gear layout, similar to the front differential. The rear differential is available in two ratios. V8 engine vehicles use a differential with a final drive ratio of 3.73:1 and Td6 engine vehicles use a final drive ratio of 4.10:1. The ratio is changed by changing the amount of teeth between the crown wheel drive gear and pinion gear. Therefore for a ratio of 4.10:1, the crown wheel drive gear will have 4.10 times more teeth than the pinion gear. This equates to the crown wheel drive gear having 41 teeth and the pinion gear having 10 teeth.