Simulation of the perceptible feed-forward and feed-back properties of hydraulic power-steering systems on the vehicle's handling behavior using simple physical models

Today, often complex component-oriented simulation models are used to study the influences of hydraulic power-steering systems on the vehicle's handling properties. In these simulation models, we have a detailed description of the vehicle suspension components (links, joints, springs, etc.) extended by complex component simulation models of tires, bushings, and of course also by power-steering models. These power-steering models contain a detailed physical description of the complex mechanical and hydraulics properties of the system, like friction in seals, aspects of hydraulic power supply, etc. On the other hand, there is a need for simple model approaches used for basic assessments and system development. These simple models should represent all the essential properties of the vehicle's handling behavior, without the need for the large-scale parameter setup and compute-time requirements of the more complex models. For many applications in handling, we use the class of single-track two-wheel bicycle-type vehicle models. With some nonlinear extensions, these models can represent the complete operating conditions of the vehicle. The parameterization of these models can be achieved online while driving or offline by analysis and identification, on the basis of some standard test maneuvers. In these models, all properties of steering, suspension and tire are condensed to the cornering stiffness or side-force map, a separation e.g. of the steering system influence does not take place. This article shows how modeling of a hydraulic power-steering system can be done to represent the essential feed-forward and feed-back properties, and how this model can be integrated to the complete vehicle's description. This new model approach gives a better insight into the four-pole properties of steering systems and introduces a separation between the steering system and the suspension even in simple model classes.