A Stewart & Stevenson M1084A1 FMTV 5-ton cargo truck was used as the subject of a study to evaluate advanced powertrain thermal management components and subsystems. Funded by the U.S. Army TACOM and the National Automotive Center (NAC) under a Small Business Innovative Research grant (SBIR Phase II), the project focused on improving thermal management of the vehicle while reducing the peak fuel consumption by >10% in a vehicle having limited ram air cooling. The FMTV was used as a surrogate test bed to investigate thermal management technologies that could be applied to vehicles with confined package space, such as light armored vehicles.
The vehicle was equipped with a thermal management system featuring distributed system architecture, electric coolant pumps and fans, electronic control valve, multiple air-cooled heat exchangers, and an electronic control system with PID feedback. The entire thermal management system was mounted in a metal enclosure behind the truck cab. The cab blocked the flow of ram air to the heat exchangers to simulate the confined space requirements.
The production vehicle cooling system was fully instrumented to establish the baseline performance. Steady-state testing was performed in a climatic wind tunnel over a wide range of speed, load, and temperature conditions. The tests were repeated in the same facility under the same conditions after the new thermal management system was installed in the vehicle. Qualitative comparisons were made through road tests as well.
Test results showed that the stability of the fluid temperature of the powertrain systems was significantly improved over the baseline and that the transmission oil temperature warmed to 80°C in nearly half the time required by the base system. The steady-state fuel economy increased by 5-20% over the base vehicle, depending on the speed/load point. A computer model was used to evaluate the performance of the vehicle over a simulated off-road driving cycle. The model results showed fuel economy gains over the base vehicle of 0.57 mpg (15.6%).