Modelling and validation of steering system response to road and driver induced forces

The driver serves both as a controller for the vehicle direction as well as a sensor for the road induced forces. A vehicle model is developed with both computer simulations as well as driving simulator use in mind. Therefore, the included steering system model was divided into one part below and one part above the steering gear. The presented steering system model focuses on force transmission from the wheels to the steering rack and the rack movements including a friction model. Above the steering gear, the model focuses on servo control through the twist of a torsion bar and includes steering wheel inertia and steering column stiffness and friction. The vehicle model has ten degrees of freedom, includes a Magic Formula 5.1 tyre model and is validated together with the steering system model as well as a geometric road model as a complete vehicle-environment model. The validation is made using data from the KTH experimental vehicle in a number of isolated driving cases performed at the Volvo Hällered test track. The simulations performed with the model are mainly focused on the steering wheel moment sensed by the driver.