The automated transmission, the Detroit DT12, AMT as Standard is now common across all of the Daimler heavy duty offering, globally, and so will be the main transmission offered in the X Series from Western Star. However, this is a brand which will also be specified with a manual transmission. in the Australian market, the Eaton RoadRanger is available, but the Detroit DT12 AMT should be regarded as the standard offering.
There are two versions of the new AMT available, both are called DT12 and from the same family. The OV is the overdrive version of the box and the HE is designed for high efficiency. With HE being the AMT to be specified to get the most out every litre of fuel on linehaul type operations.
The OV version of the box is specified when the AMT needs to be able to cope with situations like off-highway work. It’s got a whole feature set, which is designed to be useful for things like a rocking mode which helps the truck to get free when it gets stuck in gravel.
In this OV transmission there are two versions available, the OV and the OVX. The difference between the two is essentially that the OV will go up to 62.5 tonnes GCM and OVX doesn’t have a weight limit on it.
According to Detroit the testing in road train has shown the AMT to be very effective, despite only using 12 gears instead of the traditional 18. The take-off feature has worked well when compared to a manual clutch as, it is claimed, the control in the automated manual is much more precise. It knows exactly how much heat it’s putting into the clutch and differential and releases takeoff power at the right rate to minimise risk.
There’s a feature called Powerlaunch, which lets you bring the engine revs up well up above 90 per cent of engine torque. It then brings the clutch in at the right speed to pull away from stationary. To activate it, there’s no switches, the driver simply puts their foot all the way through and the control system does the rest.
In Australia, all the Western Stars that have the AMT use the control stalk to move between different driving modes. These modes are many and varied, but when the end customer orders the truck, they can choose which modes they require and how the AMT will behave.
There will be fleet customers which want a truck to default into economy mode after it is keyed off, but others will prefer the AMT to stay in the chosen mode until next time the truck is fired up.
Other operators may choose the option to make manual gear changing available at relatively low speeds, but remove that option from the driver when the truck is travelling at highway speeds, to enhance fuel economy on long high speed runs, but give the driver flexibility when manoeuvring at slow speeds.