Assignment

An unloaded truck can manage, without problems and on a level road, with only four speeds using the gear lever positions 2, 4, 6, 8. Even if one considers the lower usable RPM range. However, what happens if trailers, loads and mountain roads come into play? If one then considers the even narrower RPM range for economic engine operation, even a truck which only operates on roads, is wisely equipped with 16 speeds.

Function

There are four change-gates for eight forward gears. What looks the same as for the use in the motor car, is somewhat more technically and more demandingly executed. With the changing from 4th to 5th gear, the 2 speed gearbox of the downstream group transmission is mostly changed through air pressure. Thereby the red gear ratios, seen in the above figure 'group' are usable. At the same time - unnoticeably - the first gear is engaged. Both must harmonise, otherwise the engine overrevs or it causes noises from the gearbox.The pre-change group is normally operated through a small lever on the gear-shift. With this the next half-gear is reached, shown in red in the above figure 'splitting'. Thus one can still drive with a load and a trailer with eight gears the same as in a motor-car with six. However, should an incline be reached, - even on the motorway -, the next lowest half gear is extremely important in preventing the loss of too much momentum. Construction site vehicles exaggerate sometimes by using as many as 32 speeds. 06/09