Military Vehicle Off-Road Axle Power Requirements As Related to Soil and Tire Compression.

Slow speed, level military vehicle axle power requirements for mobility are dependent on the tire and soil resistance to rolling.  Inflation pressure (tire deflection) and soil sinkage can significantly influence mobility power.  This study involved exploring the influence of these parameters on the axle power mobility requirements. Mobility power tests were conducted using a 4 wheel-drive HMMWV equipped with 4 wheel torque and RPM sensors.  Multipass, lane change and turning tests were conducted in both fine- and coarse-grain soils at desired speeds ranging from 5 to 10 mph.  Inflation pressure was varied and soil sinkage was measured.  The mobility power, modeled as the power required to compress the soil and tire, is compared to the measured axle power requirements. An average 34% difference between measured power and modeled power was found.  The percentage of the soil compression power increased from 7% to 23% with increasing tire pressure.