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Automatic Gearshift (trucks)


Do not be deceived by the above figure. It does belong to a truck gear box, but, however, one with a conventional clutch. It must be pressed, and then the function button on the side (figure 1) is pressed while moving the gearshift forwards. It is important, at this point, to pay attention to the shift indicator display (figure 2). If the chosen gear is shown, the clutch can be let in and one can pull off as usual. To engage the reverse gear, one must move the lever, while keeping the function button depressed, to the rear, to shift into a higher gear, the shifting operation is repeated. In front there is another rocker switch for shifting quickly through half gears, on the other side there is a similar function button, which allows selecting the neutral position at any time.

In vehicles with an automatic gearbox, instead of the lid in the small gap behind the gearshift, there is a selection area switch. Here one can chose between manual and automatic mode. Apart from letting the clutch in and declutching, in the latter, one is also spared the gear shifting. It is important in this case, that no consumption increase occurs, in fact it should be lower, compared with the previous driving mode. Even in automatic mode, the use of the clutch pedal is also possible for especially difficult shunting manoeuvres.


The basis of the sequential gearbox in the truck is its normal gearbox. Indeed, with roughly the same dimensions, there are a few small changes. The same as the clutch, the gears are selected hydraulically, pneumatically or operated through a servo motor. The relief grinding of the sliding clutch claws is, with only one degree, distinctly lower. Synchronisation is not essential. Therefore, the countershaft has a brake (multi-disk clutch towards the casing). Now the control device is able, e.g., while up-shifting, to slow the countershaft down a little and while down-shifting, couple the clutch to the engine, and by purposely double clutching, to accelerate this shaft. Through suitable sensors exactly the right RPMs are developed to allow a noiseless shifting operation, even without synchro-rings.

Driving with this automated transmission resembles that as with the automatic. One can intervene, but one does not have to. For special cases, several functions are available which can be selected, however, on the quite normal push-button field built into the dash board. Thus the power key allows, for a certain period of time, higher shifting points. The Ecoroll mode allows the truck to roll out instead of braking through the engine or retarder. Because the clutch pedal is absent, slow pulling off is, even for the skilled driver, difficult, e.g., on ramps. In this case, one can somewhat expand the area of clutch slip and spread the accelerator pedal transducer signal. There is a mode which enables one to free oneself by see-sawing back and forth when the wheels are partially dug in. Finally, one can even gradually alter the shifting points upwards and downwards thus changing the shifting hysteresis.


After a clutch replacement, a short-, after a gearbox replacement, a long learning phase isnecessary for the system. In this case, various exactly co-ordinated key strokes on the gearshift are, with full air pressure and chronologically co-ordinated, combined with the turning on and off of the ignition switch, are necessary. 06/10