By the action on the steering wheel, the driver has the capability to control the trajectory of its vehicle. Nevertheless, the steering wheel has also the role of information provider to the driver. In particular, the torque level at the steering wheel informs the driver about the interaction between the vehicle and the road. This information flow is natural due to the mechanical chain between the road and the steering wheel. Many studies have shown that steering wheel torque feedback is crucial to ensure the control of the vehicle. In the context of uncoupled steering (steer-by-wire vehicle or driving simulators), the torque rendering on the steering wheel is a major challenge. In addition, of the trajectory control, the quality of this torque is a key for the immersion of drivers in virtual environment such as in driving simulators.
The torque-rendering loop is composed of different steps. At first, a vehicle dynamics model computes the torque level at the steering wheel regarding the vehicle state (steering wheel position, vehicle speed, etc.). The second step is a control strategy, which ensures that the torque-rendering device achieves the torque demand. In this paper, we propose to study the capability of driver to discriminate different torque levels in steady state condition. A specific control strategy was implemented in order to ensure high quality torque rendering. We measured the Just Noticeable Differences for different torque levels: 1, 3 and 5 Nm, in both directions (clockwise and counter-clockwise). This experiment involved 18 subjects. The results of this experiment are compared with the literature and give cues to validate torque rendering control strategies from a driver point of view. It also helps to understand how driver perceives the steering wheel torque.