In this thesis, Independent Front Wheel Steering (IFWS) is studied. To implement an IFWS system, it is important to understand how dynamics of the front wheel and steering motor work. Furthermore it can be challenging to provide haptic feedback to the driver, especially when an active safety system is constantly adjusting the angle of the front wheel and causing interference. First a model of a front wheel steering system with a variable gear ratio between motor and front wheels is created. At low gear ratios, the simulations show an improvement of the response of the steering system to the tyre forces. A compromise should be made between a small motor and low gear ratio. A low gear ratio is desirable as it improves the accuracy of a direct current measurement (DCM), which is required for providing the driver with haptic feedback with road information. Then a virtual model (VM) based on the bicycle model is created which can estimate the actual tyre forces within a 16 % accuracy. The error in the VM is caused by the approximation of nonlinear vehicle dynamics. The DCM and the VM are compared to their reference tyre forces in a modified double lane change and a steady state corner simulation. A combiner of the DCM and VM (Combiner DCM and VM (CDV)) is proposed which can blend the two feedback sources. At low interference frequencies, the CDV shows good results. At high interference frequencies, presence of the inertia and damping of the steering system become more dominant compared to the tyre forces and causes a phase lead in the DCM. Towards the natural frequency of the steering system, the magnitude of the required motor current decreases. The result is a poor performance of the CDV at high interference frequencies. One of the recommendation for improving the CDV is installing a motor with a high constant torque value. The motor is coupled to the front wheel with a low gear ratio and will lower the inertia and damping of the steering system. This increases the eigenfrequency of the steering system and improves the bandwidth of the DCM. However the space requirements of a bigger motor can cause problems for implementation. (Author/publisher)
Samenvatting