Performance Enhancement of Road Vehicles Using Active Independent Front Steering (AIFS) 2012-01-2013

Technological developments in road vehicles over the last two decades have received considerable attention towards pushing the safe performance limits to their ultimate levels. Towards this goal, Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) systems have been widely investigated. AFS systems introduce corrective steering angles to conventional system in order to realize target handling response for a given speed and steering input. It is thus expected that such an action under severe maneuvers may cause one tire to reach saturation while the other tire may be capable of developing more force. This study, therefore, proposes an Active Independent Front Steering (AIFS) system capable of controlling a wheel independently. At low speeds, the proposed AIFS system will modify the steer angle with speeds while maintaining pro-ackerman geometry similar to an AFS system. In doing so, it will realize a target response defined as one provided by a neutral steer system. However, in a severe maneuver, as the inner tire approaches the saturation limit, the AIFS system controller will only increase the angle of the outer tire, effectively introducing an anti-ackerman geometry. The study is carried out using a comprehensive 4-wheel handling model with AIFS capability. A PI controller with ability to detect and control the outer wheel independently is incorporated to examine the handling performances of an understeer vehicle under a ramp-step and sinusoidal steering inputs. In general, the results demonstrate that AIFS can perform as well as AFS in realizing target response while AIFS can provide performance enhancement beyond the limits of AFS. The control approach of AIFS is also shown to be effective for split-μ condition.