Most of the studies done on lane-tracking control have used the steering angle as the control system input. There are only a few reports of research on methods that use steering torque as the control input. In operating a vehicle, especially at high speed, drivers do not hold the steering wheel with such strong restraining force that there is no deviation of the steering wheel angle. For instance, a person in the front passenger's seat can easily intervene in the steering process while the driver is holding the steering wheel. From this example, it is inferred that drivers control their vehicles mainly on the basis of steering torque, especially in high-speed cruising. In this connection, the development of a lane-tracking control system based on steering torque would also allow the construction of a steering assist system, in addition to enabling automated driving. Since the machine would fulfil the role normally discharged by the driver, the latter would only have to perform intervention steering as needed, in a manner similar to a front-seat passenger. This paper compares two lane-tracking control procedures, one using the steering angle as the control input and the other using steering torque as the input. This comparison will make clear the characteristics of both approaches. While steering angle control provides superior robustness, the control system configuration does not allow the driver to intervene in the steering process. In contrast, steering torque control provides some degree of freedom for allowing the driver to steer even during the control process, thus offering the potential for the provision of a steering assist mechanism.
Samenvatting