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978-3-8439-1777-3, Reihe Informationstechnik
Entwicklung und Simulation einer fehlertoleranten mehrkanaligen Aktorstruktur für die Anwendung als Steer-by-Wire-Aktor
182 Seiten, Dissertation Universität Stuttgart (2014), Softcover, B5
In this work a model-based fault-tolerant actuator structure for the steering actuator of a Steerby-Wire system is developed.
The so-called „X-by-Wire-systems” Steer-by-Wire, Brake-by-Wire, Throttle-by-Wire and Shift-by-Wire anticipate advantages on manufacturing and an increase of active and passive safety. The required high safety integrity level of these systems demands that all electronic and electromechanical components, units and subsystems regarding defects in electronic, electrical and mechanical parts should be fault-tolerant.
By directly interfering in the vehicle guidance, the steering actuator subsystem of a Steer-by-Wire system belongs to the safety-relevant systems in automotive vehicles. For the design of the steering actuator the current guidelines and standards on safety and reliability for this application along with space, cost and performance requirements have been considered.
For the safe design of the system deductive (Markov’s models) and inductive (FMEA) methods have been adopted. For the FMEA a model-based analysis of the driving behavior has been carried out. Main focus was the modelling of asymmetries (faults) in the steering actuator, an induction motor.
For the description of the fault effects on the driving performance a single-track model of the vehicle including the steering mechanics was developed and coupled with models of the actuator and drive. With this model a lane-change manoeuvre - known as “elk test” - considering occurrence of faults in the steering actuator were simulated. The criticality of the faults could be determined by the analysis of the vehicle performance during this manoeuvre. The resulting actuator system fulfilling these requirements consists of a three-channel structure with redundant controllers, batteries, sensors and power electronics connected to a dual three phase induction motor. The passivation of the most frequent errors was achieved by a combination of structural and functional redundancy, as it provides a better performance of the faulty system and is cost-effective.
Short circuits within a phase winding or between different phase windings were found to be the critical faults of the system. Their probability of occurrence can be reduced or even neglected by means of proposed design measurements. For handling of those faults within a phase winding or channel intended to be passivated by opening the phase winding an adaptive control strategy has also been proposed.