A modular real-time capable steering torque calculation has been introduced in this paper. The computed steering torque aims to provide the driver of a steer-by-wire (SbW) vehicle with a realistic and simply adjustable steering feel. Unlike former approaches, which are based on a physical steering system model, the proposed steering torque calculation is composed of modular components, which each influence specific steering functions. The adopted modular structure should promise a quick intuitive tuning of the steering feel. The computed steering torque is made up of a main torque which determines the feedback behaviour and therefore defines substantially the steering characteristic. The main torque specifies the transmission of the vehicle's tyre forces to the steering wheel and so determines which information (amplitude and frequency) the driver should perceive through the steering torque. In addition, a damping torque, a friction torque and an inertia torque are introduced to support the driver in his task of controlling the vehicle's direction, and are hence required for the reference behaviour. In order to validate the proposed concept, the steering torque reference model is parameterised to achieve a similar steering feel like a series electric power steering (EPS) system by using parameter identification techniques. For this aim, experiments have been carried out by means of a steering test bench, in which a test EPS system is mounted. The comparison of the steering torques from the EPS and the calculation was made for a weave test executed in the steering test bench coupled with a real-time vehicle model generating realistic rack forces, which are output by a linear actuator at the rack of the test EPS. The hysteresis plot of the steering torque over the steering wheel angle shows a moderate compliance between the test EPS and the steering torque calculation. The latter presents in fact a lower steering stiffness at zero steer, which indicates a more pronounced on-centre steering behaviour of the EPS. The steering torque calculation also notes a larger steering wheel angle deadband, which suggests an insufficient steering returnability and a less precise on-centre handling compared to the EPS system. The differences observed in the hysteresis loops may be explained by the active return module of the test EPS system, which leads to an optimized return-to-centre of the steering wheel as discussed in. Moreover, a frequency response test confirms the moderate matching of the EPS steering torque and the calculated steering torque for steering input frequencies from 0 Hz to 3 Hz. The parameterised steering torque calculation could then serve, thanks to its modular structure, as basis for the generation of another steering feel variants using the tuning parameters, which each would allow the modification of steering properties according to the desired vehicle's or driver's philosophy.
Modular concept for the calculation of the desired steering torque in steer-by-wire systems
2012
26 Seiten, 22 Bilder, 3 Tabellen, 14 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
Personenkraftwagen , automatische Lenkung , Berechnung , Drehmoment , Rückkopplung , Fahrzeugführer , Mensch-Maschine-System , mathematische Modellierung , Referenzmethode , Servolenkung , elektrische Betätigung , Prüfstandsversuch , Lenkmoment , Echtzeitanalyse , Hystereseschleife , Lenkradeinschlag , Rückstellmoment
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