Connection gearbox and automated transmission (AMT)

The force from the diesel engine in a truck must be converted to propulsion through many different loads — from stationary with full load to high speed on the motorway. This places great demands on the clutch and gearbox, and today most new trucks are controlled by an automated gearbox rather than a traditional gear stick and clutch system.

§The mechanical gearbox

Classically the truck's gearbox is a manual gearbox with many steps — typically 12 or 16 gears divided into a main gearbox combined with a range part (high/low group) and often a splitter that halves the gap between gears. This gives the driver the ability to choose a gear close to the engine's optimal RPM, whether the vehicle is empty or fully loaded, in flat terrain or on a steep slope.

§Automated Manual Transmission (AMT)

In an AMT, the gearbox itself is mechanically identical to a manual gearbox, but the clutch and gear shift are operated by actuators — typically pneumatic or electrically controlled — instead of the driver's foot and hand. A control unit (TCU) calculates the optimal shift time based on load, speed and road gradient, and communicates over the CAN bus with engine control to match torque and revolutions during the shift. The advantage is more consistent shifts, less wear and lower fuel consumption because the system consistently chooses an efficient gear.

§The retarder — braking without wear on the brakes

Many heavy vehicles have a retarder — either hydraulic or electric often integrated into or after the gearbox — that slows the vehicle by converting movement energy into resistance or heat without stressing the service brakes. It is particularly valuable on long downhill slopes with full load where the service brakes would otherwise overheat. The retarder is typically controlled by a handle or automatically together with speed adaptation and is part of the overall brake interaction with air brakes.

§Troubleshooting on transmission

• 01Check oil level and quality in gearbox after manufacturer's service plan — wrong oil can destroy synchronizers and bearings.
• 02Listen for unusual noise during gear changes, which can indicate worn synchroniser rings or bearings.
• 03Read error codes from the TCU if the AMT system switches unexpectedly or goes into emergency mode.
• 04Check actuator air pressure or electrical supply as AMT shift depends on correct actuation pressure.

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