Modelling and control of active power steering systems for heavy trucks

Abstract

Transportation via trucks constitutes an important part of the logistics chain. Today’s trucks can take a front axle load of approximately 8 tonnes. To be able to maneuver at high front axle loads, the driver needs assistance from additional power sources. The additional power can be provided through different sources in different steering topologies: Hydraulic Power Steering (HPS), Electric Power Steering (EPS) or Electro-Hydraulic Power Steering (EHPS), where HPS and EHPS are more common today. Some benefits of EPS over the other two are reduced energy consumption, improved autonomous drivability, and the absence of hydraulic oils which can contaminate soil, groundwater and seawater. However, hydraulics are faster than electromechanical systems. This thesis aims to see if acceptable steering performance can be achieved with EPS and compare it to EHPS by modelling, designing controllers and simulating the complete vehicle-driver-ground systems. The version of EHPS chosen was a Volvo Dynamic Steering-like (VDS-like) topology. The mechanical systems were mainly modeled using tools in Dymola but also in MATLAB, Simulink, and TruckMaker for Simulink (TM4SL) environment. The Dymola model of the VDS-like model was validated by comparing it to Volvo’s steering black box model at Chalmers. The control was developed in MATLAB and Simulink, where PID controller was selected for the motor and the outer control scheme being H2 for energy optimization. The mechanical system, the motor model, and the controllers were then connected in TM4SL. Evaluation on TruckMaker was conducted by simulating two scenarios namely, path following in a figure of eight and in a wheel lock scenario. The models of the two steering systems developed were found to be acceptable while the designed boost for the EPS system also performed supportively. The controller however did not produce the anticipated behaviour.