Transfer Box 2

Function

Transfer gearboxes with gear reduction have become rare. Since the flood of light off-road vehicles (Sport Utility Vehicles) have conquered the market, it has become pretty quiet in the real cross-country vehicles sector. It is doubtful whether many buyers use the four-wheel drive at all. For this reason, the special gear reduction has been saved for maximum traction in rough terrain.

How it works

The series of illustrations above, show the transfer gearbox of a vehicle with front engine and rear-wheel drive. Whereby, this can also apply to a utility vehicle used on the construction site. The mounting is done through shortening the cardan shaft behind the gearbox, which should be found in the above figure on the top left hand side. The upper shaft is made up of two parts . From the left (from the gearbox) it carries on to, and including, the sliding clutch. The upper left pinion is a free running wheel which can only be connected by the sliding clutch to the axle drive shaft. The right shaft with the static gearwheel seen on the right, is inserted into the axle drive shaft, but is not connected with it. With rear-wheel drive the sliding collar, in the right position, connects the two parts of the shafts.

The four-wheel drive is engaged by shifting this sliding clutch to the left. At this point a gear reduction occurs lower down on a somewhat larger gearwheel which is not connected with its shaft, but with the planetary group of the differential gear. From there a part of the torque, through the sun wheel and its static shaft, will be transferred to the front axle. The other part goes via the hollow gear ring to the lower right gearwheel, which in this case, is not connected with its shaft. Without gear reduction it carries on to the upper right pinion and then to the rear axle.

The transfer gearbox in the above illustration always changes, when in four-wheel drive, into the off-road gear, which reduces all the gearbox gears once again. It distributes the torque based on a specific ratio between the front- and the rear axle. This distribution is construction-induced and can be changed, e.g., by using larger planet wheels and a smaller sun wheel in favour of the rear axle. If wheel spin takes place on the whole axle, this can be corrected by locking. To achieve this, the lower sliding clutch is shifted to the left and connects the lower right gearwheel to the shaft. from now on the planetary group works as a block. It is important to remove the locking again when driving on a surface with good grip, reducing the threat of unnecessary tension, difficult steering and high tyre wear. 09/08