Operation of modern vehicles is becoming more and more autonomous, i.e., vehicles are becoming more and more able to provide driving control with less driver intervention.
An example of such a system is a so called lane keeping aid system, which aids the driver by reducing the driving burden through attempting to maintain the vehicle near the center of a lane on the road. Such a lane keeping aid system normally applies an overlaying steering torque to the steering system of the vehicle with the objective to prevent unintentional lane change.
It may be possible for a driver to abuse such a lane keeping aid system to stay in lane without touching the steering wheel, i.e. misusing the lane keeping aid system as an autopilot.
A vehicle equipped with such a lane keeping aid system will typically be able to stay in lane for an extended period of time, depending on e.g. road geometry. The vehicle will, however, possibly bounce against lane markings, either repeatedly against lane markings at one side or between left and right hand side lane markings. Although this driving behavior does not necessarily imply an immediate risk, it is likely to lead to an unsuitable vehicle trajectory which stands out as confusing for surrounding vehicles. Potentially, if the lane keeping aid system eventually fails to prevent a lane change, e.g. due to loss of tracking of lane markings, the vehicle might enter an adjacent lane while the driver does not keep his/her hands on the steering wheel causing an undesirable situation.
Thus, it is typically not desirable to reduce the driver's vigilance and attentiveness, even when such systems are providing some or most of the control of the vehicle. It is generally imperative that the driver maintains his/her hands on the steering wheel, and is ready to take over the steering control whenever the situation demands.
Consequently, existing systems of this kind usually comprises functionality for determining if the hands of the driver are on the steering wheel. One such system is previously known through US20100228417, which relates to a system and method for determining whether a vehicle driver is holding a steering wheel of the vehicle while the vehicle is in an autonomous driving mode. The autonomous driving mode may be provided by a system for attempting to maintain the vehicle near the center of a lane on the road.
The vehicle of US20100228417 includes an electric power steering (EPS) system and may include an active front steering (AFS) system, both of which include a motor that can apply a high frequency and low amplitude perturbation signal to the steering wheel of the vehicle. Such a high frequency and low amplitude perturbation signal is not felt by the vehicle driver and does not cause the vehicle to turn, but is able to be detected by a steering angle sensor.
The method proposed by US20100228417 subtracts a steering angle command signal from the steering angle signal and removes road disturbances, and then determines whether the induced perturbation signal is present in the steering angle sensor signal. If the perturbation signal is present, then the system knows that the vehicle driver is not holding the steering wheel.
The system proposed by US20100228417 may cause a warning signal to be issued or provide some type of audible or visual indication that the vehicle driver is not holding onto the steering wheel. The detection is only activated when the vehicle is in the autonomous or semi-autonomous driving mode. Activation thereof is performed through a switch, which will be closed when the system is in the autonomous or semi-autonomous mode.