Allison highlights importance of axle ratio settings
Allison Transmission has outlined how fleet operators can improve fuel economy by around three per cent through the lowering of truck axle ratios where appropriate.
The company says it is working with a number of OEMs on rear axle optimisation trials, with positive results reported for refuse vehicles in particular.
Axle ratios play a very important part in a truck’s overall performance, says Allison. Vehicle manufacturers already apply a variety of axle ratios, depending on the type of truck, to ensure they can perform well across wide-ranging road requirements and applications as efficiently and as productively as possible.
However, the trials being undertaken by Allison and its OEM partners are deploying even more application-specific axle ratio settings, in order to help fleets achieve the first EU CO2 regulation reduction of 15 per cent by the 2025 deadline, with the use of current conventional technology.
“To reduce emissions and improve fuel economy to the required level, industry engineers and scientists are going to have to do something fundamentally different, such as looking at drive axle designs, configurations and axle ratios, combined with the use of other technologies,” said Allison’s UK account market development manager, Nathan Wilson.
“In recent years, truck engine capacities have come down, while engine power and peak torque have gone up, to allow for down speeding.
“While the peak torque of Euro 6 trucks has increased thanks to engine improvements, from around 1,000 to 1,400 rpm, not all OEMs have reviewed their associated axle ratios in parallel with engine and transmissions developments.”
The numerically higher (or deeper) an axle ratio, the better the vehicle’s ability to deal with varying topographies, however engine speeds are generally higher. They can also be helpful for vocations where trucks require sufficient torque during the vehicle’s launch, and to maintain continued acceleration on inclines.
Numerically lower (shallower/faster) ratios offer higher average road speeds combined with lower RPM, which generally equals lower fuel consumption.
They work more efficiently for regional haul applications where vehicles are generally used on motorways, dual carriages and A-roads and where there is approximately a 1 in 8 gradient or 12 per cent.
Trucks working around towns and in the countryside – such as those working in refuse, construction and distribution – which face adverse gradients or topography, would especially benefit from a different axle ratio, the company says. The steepest gradients faced by these vehicles can be up to 25 per cent, or a 1 in 4 incline.
“Truck manufacturers are increasingly seeing the benefits to emission values and fuel consumption of providing application-specific trucks – matched to varying axle ratios – to the market,” continued Wilson.
“Our testing of refuse collection vehicles has shown there is an opportunity to improve fuel economy, by around three per cent, through lowering the axle ratio.
“Allison is well-placed to work with OEMs to find an effective alternative ratio that works across a vehicle range and to help them communicate to their customers that an optimised or enhanced ratio can mean better comfort and productivity levels, with no impact on launch gradeability or ride quality.”
