Driver Knowledge Tests

What is an automated manual transmission (AMT) on a truck?

Automated manual transmissions are quite common and are fitted to a wide variety of trucks. They include systems such as the Volvo I-Shift, Eaton AutoShift, Renaul Optidriver, Mercedes-Benz PowerShift and UD Trucks ESCOT. They are not the same as ‘automatic’ gearboxes that have a torque converter, they are a modified manual gearbox with electronics controlling the shift instead of the driver.

Automated manual transmissions can produce perfect shifts every time that happen at the optimal rev range, improving fuel economy, reducing driver fatigue, reducing wear and tear on the vehicle and improving driver satisfaction.

All AMT gearboxes work around the same principle: computer-controlled actuators (electric motors, air cylinders or both) to control the selector rods and range/split selectors and clutch application instead of the driver using the gear stick and clutch pedal.

The computer monitors the load on the engine, the road speed and the engine revs and decides which gear is needed. It operates the clutch and matches the revs to make a smooth gear shift in a small amount of time, giving a quick, smooth shift.

The AMT can be overridden, but the result is usually worse fuel economy. The reason you might do this is to keep the truck in a low gear for some reason. However, in the vast majority of cases, it’s best to leave it in A or Auto and let the computer do its work.

Some early models of AMT ‘boxes still use a clutch pedal for getting the vehicle moving, e.g. at traffic lights, however, once you’re moving, the clutch pedal is not required – the AMT takes over.

Even if there’s not a clutch pedal visible in the cab, there will still be a clutch assembly fairly similar to a manual transmission but controlled by electronics.

Automated manual transmissions must not be left in gear when shut down because most use some form of air pressure to shift gears. If the truck has an air leak, you may not be able to get the truck started because it will be in gear, and there’ll be no air to shift it out of gear. A costly callout is required to manually fill the air tanks.

Proper servicing will ensure that the computer system receives the best programming for optimum fuel economy.

Clutch adjustments also need to be made regular intervals so that they don’t slip.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

Posted in Advice