Objective: To develop and verify a driver assistance function, working on the electric power steering of passenger cars, to support the driver on handling critical understeer situations. The main objectives of the so-called understeer assistance are reinforcing the driver's awareness of the driving conditions and giving support to handle the situation correctly without inducing irritation by abnormal steering behavior.
Methods: The system was designed in consideration of psychological aspects of human decision making while operating a vehicle in unfamiliar understeer situations. Using a comparison of vehicle dynamics with a reference model computed in the car, the level of understeer is calculated. Depending on the understeer level, the steering wheel restoring torque is increased while a vibration is applied to the steering wheel at the same time. To verify the achievement of the objectives, the standard steering system is compared to the developed understeer assistance in an active driving study on a test track. Not only objective measurement data but also subjective ratings delivered by 63 unbiased participants were used.
Results: The subjects follow the offered steering recommendation by steering less when the assistance function is activated (Δγmax = 44.38°, p = 2.5°·10⁻³%). In the sequel, an enhanced vehicle reaction arises that is validated by analyzing the achieved maximum lateral offset (ΔSy,res = 0.16m, p = 0.07%). In addition, the evaluation of subjective ratings clearly indicates a better awareness of the understeer situation with the assistance function (χ= +0.44, p = 0.89%). Furthermore the subjects rate the understeer assistance better than the standard steering system (χ= +0.43, p = 3.03%).
Conclusions: By measuring vehicle data and eliciting subjective opinions of the participants, the effectiveness regarding an improved handling of an understeering vehicle as well as the acceptance of the understeer assistance by the driver is confirmed. Larger subject groups and more realistic boundary conditions should be considered for additional evaluations. The approach of using standard vehicle hardware to adapt the vehicle to specific driving situations under consideration of psychological aspects of human decision making should be investigated further.
Keywords: active safety; crash avoidance; driver; driver assistance systems; driver behavior; psychology; safety; young drivers.