Systems Modelling of Steering System using OpenModelica

Steering system is one of the key vehicle-driver interface that impacts driving fatigue and perception of quality by driver. It is also a safety critical system governed by several Homologation requirements. While Homologation rules mandates the steering effort to be within certain limits, for a driver, asymmetric behavior in terms of angle & torque between LH & RH turn is also undesirable. The sub-attributes are affected indirectly by packaging constraints in each vehicle platform and model. For meeting the stringent targets in each variant and to maintain minimal unique parts, several design iterations would be needed. Physical testing involves higher cost and time. Hence development of a steering system simulation model becomes essential. This paper details the development of a steering model to simulate and analyze the steering system performance of commercial vehicles. A single steer model with hydraulic assistance is developed using OpenModelica (OM), an open source system modelling software. The parameters such as steering wheel effort, wheel lock angles, Ackermann error and Turning circle diameter (TCD) are computed along with prediction of dry park effort. Based on iterations, an optimized configuration with reduced asymmetry can be derived.