Comparison of Dynamic Performance and Fuel Consumption of Direct-drive and Overdrive Transmission Tractors

The main objective of this project was to compare the fuel consumption and dynamic performances of direct-drive and overdrive transmission tractors. Fuel consumption was evaluated at constant high speed and on various road profiles, while the dynamic performance was assessed on various road profiles only. The SAE Fuel Consumption Test Procedure (J1526) was used for constant high speed fuel consumption track test evaluations. The direct-drive transmission tractor consumed less than the overdrive transmission tractor, even though it was heavier. The testing on various road profiles was conducted using a towing dynamometer, for comparing the dynamic capability of the tractors when simulating the same towing load on two hilly road profiles: the Townes Pass path (in the Rocky Mountains) and the Saguenay path (in the Saguenay region of Quebec). Each tractor was to haul the set load along the given path while trying to attain 90 km/h speed. Results from the test showed almost identical dynamic performance for the Saguenay road profile. For the Townes Pass road profile, which has a steeper grade, the overdrive transmission tractor showed, to some extent, better dynamic performance than the direct drive tractor. Direct-drive transmissions are more efficient than overdrive transmissions, if they are geared correctly. The advantage is obvious in top gear, which was the case for the high constant speed test. The overall ratio (transmission plus differential) is higher for the tractors with overdrive transmission, and they provide better startability and gradeability. The tests on the two different road profiles partially confirmed this assumption, especially for the Saguenay route.