Publication

Modeling & Simulation, Testing & Validation (MSTV)
2019

THE NEED OF PROPER MODELING OF TRACTION CONTROL SYSTEM IN MOBILITY SIMULATIONS WITH SOFT SOIL

by Jesper Slattengren

Abstract

When building simulation models of military vehicles for mobility analysis over deformable terrain, the powertrain details are often ignored. This is of interest for electric and hybrid-electric vehicles where the maximum torque is produced at low speeds. It is easy to end up with the drive wheels spinning and reducing traction and eventually the vehicle digging itself down in the soil. This paper reveals improvements to mobility results using Traction Control Systems for both wheeled and tracked vehicles. Simulations are performed on hard ground and two types of deformable soil, Lethe sand and snow. For each soft soil, simulations have been performed with a simple terramechanics model (ST) based on Bekker-Wong models and complex terramechanics (CT) using the EDEM discrete element soil model which Pratt & Miller Engineering (PME) has been instrumental in developing. To model the traction control system a PD controller is used that tries to limit the slip velocity at low speed and wheel slip at higher velocity. Controlling the slip velocity, i.e. the relative tangential velocity between the wheel and ground, or track and ground is usually best for low speed. A typical preset value would be in the range of 50 100 mm/s depending on the usage scenario. Using relative slip velocity also avoids a division by zero at low speeds or at wheel lock-up. The lower value is used mainly for crawl mode, when trying to get unstuck after being dug down deep into the soil. Based on the optimal pre-set values for slip or slip velocity, a correction factor is applied to the throttle to limit the slip or slip velocity.