Performance Evaluation of Heavy-Duty Vehicles Equipped with Automatic Transmissions and Powertrain Adaptive Systems in Forestry Transportation

The purpose of this study was to evaluate automatic transmissions in a forestry context by comparing their performance with that of standard manual transmissions, and assessing the possibility of improving fuel efficiency by adapting the engine and automatic transmission performances to the vehicle's load. Long-haul test results showed that during the test day, the degradation in driver performance with the manual transmission truck translated into a 2.9% relative increase in fuel consumption when compared with the automatic transmission truck. The fleet data assessment indicated no obvious difference in fuel consumption between the performance of automatic transmissions and manual transmissions.

One system for adapting engine performance to vehicle load uses an onboard weigh scale to determine the load status of the vehicle. Long-haul test results for the engine adaptive system showed a 10.6% improvement when compared with the manual transmission control truck, and 7.9% when compared with the automatic control truck. Computer simulations of the long-haul test showed similar results. In the second system, an electronic control triggers the automatic transmission to convert to an economy shift pattern when the truck is empty. The operational fuel data indicated an overall 4.6% fuel improvement, calculated using baseline and test line ratios between the test and control truck.

The results of this study indicate that automatic transmissions can eliminate driver shifting ability as a factor in fuel efficiency and offer the possibility of adapting a vehicle's performance to meet the changing demands placed on the engine during a trip.