AMTs offer potential fuel consumption and greenhouse gas emissions reductions by ensuring optimum gear shifting during driving. The result is more efficient use of the engine’s torque more of the time by maintaining optimum engine speeds for the conditions.
A distinction to be made is that this opportunity relates to the automation of a conventional manual gearbox, not the substitution of an automatic (hydrostatic) transmission with torque converter which is inherently less efficient due to its greater energy losses. An AMT converts a three-pedal manual gearbox to a two-pedal version by taking automatic control of the clutch function.
The highly urbanised nature of Australian cities and the stop-start, high gear-shifting drive-cycles suggest a high level of fit for urban applications in the Australian context. However, the technology can also bring benefits in open-road driving.
These systems are typically available as an option on new trucks in particular applications (e.g. I-Shift, powershift, opticruise, etc.). Recent development in the light vehicle sector, particularly in the use of dual-clutch transmissions, may also soon be available in the heavy duty vehicle market, bringing further reductions in fuel use.
The quantum of benefit varies greatly with the skill of the driver, but is largely unverified by independent back-to-back comparisons in Australian conditions. However, benefits are generally optimal where the vehicle is subject to frequent gear changing, such as in urban operation. A range of 1–6% reduction has been seen in overseas tests and manufacturer claims, dependent on duty cycle. Maintenance costs are reduced via reduced clutch wear, and driveline shunt from poor clutch use can also be lessened, resulting in lower risk of component failure.
Key implementation considerations
AMTs entail a price premium over conventional manual gearboxes due to their sophisticated control systems, which can cost anywhere from $2000 to $8500 depending on truck and gearbox specification.
Experience in the US has shown that the fuel savings can deliver an eighteen-month payback on the incremental cost of the AMT (Kilcarr 2008). However, the duty cycle of the vehicle should be considered to ensure the benefits suit the application and that fuel savings will be achieved. Regional and interstate linehaul applications (with reduced gear shifting) are not likely to result in a short payback period.
Examples of implementation
Volvo I-Shift transmission
This Trucking News article (Opens in a new window) PDF 258 KB discusses the benefits, including fuel efficiency, of Volvo’s automated transmission. While the test driver experienced an approximate 5% increase in fuel efficiency, the big advantage of AMT for heavy vehicles is consistency of fuel usage across different drivers in the fleet. Volvo says its I-Shift gearbox decides on the optimal gear based on grade, speed, acceleration, torque demand, loaded weight and air resistance, and with the engine and gearbox in constant communication. Volvo claims its I-Shift transmission, the first to be equipped with this Eco Roll feature, saves 36 hp (27 kW), providing a measurable fuel saving.
This trial sought to conduct an in-field assessment of seven identically configured tipper trucks running like routes in urban and outer urban Sydney. Data was collected for four Allison automatic transmission vehicles and three Eaton AMT vehicles over a two-month period, running like duty cycles.
The results demonstrate that on average vehicles fitted with an Eaton AMT achieved approximately 11% greater fuel econom than vehicles fitted with the Allison automatic transmission.
For the full report, see Fuel for Thought – Identifying potential energy efficiency opportunities in the Australian road and rail sectors (opens in a new window) PDF 1.5 MB.