On-Centre Steering Wheel Torque Characteristics during Steady State Cornering 2008-01-0502

The steering wheel torque has an essential influence on the steering feel. In the chassis development process the tuning of the steering wheel torque characteristics is currently done empirically by altering the boost curve of the steering system. This paper shows how the steering assistance has to be chosen in order to achieve a harmonic steady-state steering wheel torque characteristics. It can be achieved by a linear rise of the defined steering assistance ratio versus the vehicle lateral acceleration. To determine the characteristics the gradient factor and the degressivity factor are needed only. The initial rise of the steering wheel torque versus the lateral acceleration is determined by the gradient factor. The degressivity factor describes the subsequent curvature of the characteristics. Based on this steering assistance ratio the required boost pressure of a hydraulic steering system or the required motor current of electro-mechanical steering system can be calculated instantly. The harmonic characteristics of the steering wheel torque are inherent. This analytical method is therefore best suited to determine the required steering assistance map in an efficient way.