Energy Efficiency Evaluation of a Hybrid Electric Tractor-Semi-Trailer Prototype

The objective of the project was to evaluate the energy efficiency of a hybrid electric tractor-semi-trailer combination prototype. The prototype was developed for log hauling application by integrating an existing tractor with an electric semi-trailer to improve fuel consumption and reduce greenhouse gas emissions. One of the conventional axles of the quad axle semi-trailer was replaced with a drive axle powered by an electric motor. Tests were conducted on a 105 km test route with a maximum difference in elevation of 355 m, including a hilly section with a length of 89 km. The results indicated fuel savings ranging from 10.5% to 14% per test run, with an average fuel savings of 12% when the electric drive axle was engaged. The hybrid electric tractor semi-trailer consumed 17.5% less fuel up-hill and 9.4% less down-hill. Throughout each test run, the battery’s state of charge fluctuated, averaging between 88% at the start and 52% at the end. Prior to each run, the batteries were recharged using the regenerative system’s acceleration-deceleration cycles, lasting approximately one hour. The tests showed an average GHG emission reduction of 23.3 kg/100 km when the electric drive axle was activated on the hybrid electric tractor semi-trailer. Considering an average annual mileage of 100 000 km, the prototype hybrid electric tractor semi-trailer shows a potential to reduce annual GHG emissions of 23 tonnes per vehicle. These reductions will provide the cost-benefits that are of strong interest to the forest sector as they continue the move towards reducing carbon footprint. In addition, operational benefits of having a powered rear-axle on the trailer were confirmed to provide traction benefits, and safety improvements for forestry trailers operating in challenging terrain.