Modeling & Simulation, Testing & Validation (MSTV)


by Paul Ayers; George Bozdech


Determining the required power for the tractive elements of off-road vehicles has always been a critical aspect of the design process for military vehicles. In recent years, military vehicles have been equipped with hybrid, diesel-electric drives to improve stealth capabilities. The electric motors that power the wheel or tracks require an accurate estimation of the power and duty cycle for a vehicle during certain operating conditions. To meet this demand, a GPS-based mobility power model was developed to predict the duty cycle and energy requirements of off-road vehicles. The dynamic vehicle parameters needed to estimate the forces developed during locomotion are determined from the GPS data, and these forces include the following: the gravitational, acceleration, motion resistance, aerodynamic drag, and drawbar forces. Initial application of the mobility power concept began when three U.S. military's Stryker vehicles were equipped with GPS receivers while conducting a proofing mission at the Pohakuloa Training Area (PTA) in Hawaii on a soil with a known rating cone index (RCI). An analysis was conducted on the GPS data which allowed for the variation in the Stryker's mobility power to be estimated as the vehicle traversed the terrain. The subsequent power duty cycle and required energy for the vehicle was determined along with predicted specific energy consumption and production values. Initial validation of the mobility power model began by tracking a hybrid 2006 Toyota Highlander during acceleration tests and on-road maneuvers. The model had an R2 and average absolute percent error of 0.91 and 12.9% respectively during the acceleration tests. The predicted and measured mobility power duty cycles were similar during the on-road maneuvers while an R2 and average absolute error of 0.44 and 7.1 kW was attained.