The problem of modeling an electro power steering system is dealt with. Although the feed-forward torque control strategy appears as the natural first alternative to the hydraulic-powered systems, it has several drawbacks that limit its use. Among those: (1) the torque model should be adjusted for each individual vehicle characteristics, (2) it does not provide the desired return driving wheel, and the anti-sticking properties (see below for description). The position control strategy consists first, in generate a position desired reference from a mechanical model driven by the driver torque. A second step is to design a suitable driver comfort. Some of the main advantages of the position model approach are: (1) to produce the same steering characteristics regardless the car size and weight, the road conditions, and the tire characteristics. (2) to reject the external disturbances like: road irregularities, and changes in the road conditions. (3) to introduce the 'anti-sticking' strategy (the wheel angle should come to its rest (central) position after the driven has released the driven wheel). (4) to tune only once the reference model using the human expertize. A new position model reference structure composed of two inter-connected models is introduced. The first model is a torque booster stage, modeled by an hydraulic-like power steering unit providing the total desired steering torque. The second model is a mechanical model providing the desired drive wheel angle, and including a desired tire/road stiffness. This model results from physical laws under which the models are derived, but also seems to be necessary for the model has certain passivity properties. Although, some of these properties are well understood, other remain to be clarified. this is the case for the ultimate property of the map. These model are useful for control design. (to be continued)
Control design for an electro power steering system: Part 1. The reference model
Regelungsentwurf für ein elektrisches Fahrzeuglenkungssystem: Teil 1. Das Referenzmodell
ECC, European Control Conference, 2001 ; 3611-3616
2001
6 Seiten, 4 Bilder, 7 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
Control design for an electro power steering system: Part 2. The control design
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