Transmissions, Axles Aid in Fuel Conservation for Commercial Vehicles

September 16, 2019

Terry Costlow

Faster axle ratios let engines run at lower rpm levels. (Dana)

Transmissions and axles are evolving rapidly as powertrain design teams push to reduce fuel consumption. Intelligent transmission controls are communicating with engines to improve efficiency, while some of the engine’s workload is being shifted to electrified axles.

Electrified axles augment smaller engines, as in this Dana-Hyliion Class 8 hybrid system. (Dana & Hyliion)

Engines continue to advance. The Detroit Integrated Powertrain Transmission is using sensors and controllers to lighten the load on the engine. Functions such as eCoast, skip shift, descent control, and driveline protection all help engine controls produce power more efficiently.

“eCoast can sense when load and terrain conditions are suited to reduce engine rpm until power is demanded again,” said Brian Daniels, manager of Detroit Powertrain and Components product marketing. “Skip shift can select the correct gear to start in based on the vehicle conditions and to reduce the time it takes to get up to speed. Powertrain down-speeding is allowing the rear axle to have faster ratios, which allow the engine to operate at lower rpm.”

Axle ratios are changing as technology advances. These changes are part of a more holistic approach to vehicle design. When strategic planners and design teams look at all parameters in the powertrain and overall vehicle, they can push specifications to new limits.

“We’ve got an axle that has a 1.59:1 ratio—it’s the fastest axle ratio on the market,” said Steve Mastroianni, senior manager, drive axle product planning, at Dana. “This axle ratio enables engine down-speeding, allowing a slower engine rpm rate at highway speeds.”

Axle suppliers are also following the electrification path, adding motor/generators and inverters to offload engines. Dana’s Spicer electrified e-Axle supplies 139 kW (189 hp) of continuous power and 193 kW (262 hp) at peak power, letting medium-sized mining trucks and large lift trucks reduce engine size or move to alternate fuels.

“Engine downsizing and moving to alternate fuels like compressed natural gas reduce engine performance,” said Harry Trost, senior manager of product planning at Dana. “Adding an electrified axle lets companies regain the performance they lose with downsized diesels.”

Earlier this year, Allison Transmission unveiled the AXE Series electric powertrain, which integrates an electric motor and a multi-speed transmission. A dual-motor axle provides continuous power of 536 hp (400 kW) and peak output power of 738 hp (550 kW).